Step by Step® Ultrasound in Obstetrics Jaideep Malhotra, Nidhi Gupta, Narendra Malhotra, Neharika Malhotra, Kuldeep Singh
INDEX
Page numbers followed by f refer to figure and t refer to table
A
Abdomen 53, 58, 65, 68, 73, 91, 150, 179, 222f
pain in 128
Abdominal circumference 288, 305
Abdominal perimeter 82, 450
Abdominal wall
and umbilicus 68
defect, anterior 150, 150f, 248f
Abnormal pregnancy 51, 57
ectopic 57
multiple 57
Abortion
complete 100, 104f
diagnosis of
inevitable 460t
threatened 55, 460t
incomplete 105
kinds of 462t
missed 92f, 106f, 107f
predict 464t
threatened 84
ultrasound diagnosis of 463t
Abruptio placenta, failure to diagnose 45
Accommodation facilities 76
Acoustic gel 2
Acoustic impedance, changes of 378
Acrania 123, 126f
anencephaly sequence 147
Adjunct to cervical cerclage 84
Adjunct to chorionic villus sampling 84
Adnexa 81
Adnexal mass 80, 99f, 100
left 98f
Adverse pregnancy 143
Aliasing 30, 35
American Congress of Obstetricians and Gynecologists 43
American Institute of Ultrasound in Medicine 43
Amniocentesis 172f
Amniodecidual separation 90
Amniotic fluid 479t
amount of 306
and placenta, assessment of 68
assessment 50, 56, 286
cells 172f
evaluation 55
index assessment 283f, 449
volume 479t
volume assessment 306
Amniotic index 479t
Amniotic sac, irregular 96f
Anencephalic fetus 187f
Anencephaly with toad sign 186f
Anomaly scanning 55
Anophthalmia 116f
Anorectal malformation 244f
Antenatal Diagnostic Center 63
Antenatal fetal monitoring 63
Antepartum fetal surveillance 480t
Antepartum obstetric ultrasound examination 43
Anterior fontanelle, 16 weeks 422
Aorta, descending 82, 231f, 297f
Aortic arch 232f
Aortic isthmus 328, 329
Doppler 323, 327
Artefacts 67
Arterial flow 235f
Arterial spectral wave form 26f, 27f
Atrial septal defect 236f
Atrioventricular valves 234f
Audible signal 37
Audible sound waves 1
Audio volume 34
B
Back sprain 364
Basic physics 1
Battery injury 43
Bedside examinations 370
Binocular distance 450
Biomechanical factors 361
Biometery 55
normal 51, 57
Biophysical profile
evaluation by 290
interpretation of 291
scoring of 478t
Biophysical scoring systems 70
Biparietal diameter 304, 450
Bladder 250
outlet obstruction 257f
Blood cells 31
concentrations of 33
Body
proportionality 307
stalk anomaly 145
Bowel herniation 121
Brain 52, 58, 68, 72
Brain sparing 314f
effect 300, 310
Brain tissue 185f, 188f
herniation of 189f
Brain vascularity
13 weeks 410
20 weeks 439
Brain-sparing process 304
Breast
cancer 46
diagnose 46
ultrasound 46
cyst 46
Breathing movements 53
Bulging membrane covering vertebral lesion 216f
C
Calvarium, calcification of 121
Cardiac abnormalities 200f
Cardiac activity 92, 94f
Cardiac configuration 121
Cardiac defects 133, 164
Cardiac pulsations 121, 160f
Cardiac rhabdomyoma 237f
Cardiac tumor 238f
Carpal tunnel syndrome 363
Cavum septum pellucidum 180, 180f, 193f
Central nervous system malformations 147
Cerebellar defects 147
Cerebellar hemispheres 112f, 182f
Cerebellar transverse diameter 81, 183f, 448, 449
Cerebellar vermis 182f, 183f, 195f
Cerebellum 201f, 305, 449
Cerebral artery, middle 82, 296f, 297f, 310, 320, 328, 329
Cerebral ventricles 68
Cerebro-placental ratio 320, 328, 329
Cervical 101f
insufficiency, ultrasonographic diagnosis of 464t
length 64, 100
vertebrae, 20 weeks 423
waist 101f
Cervix 81, 278f, 279
measurement 50, 56
Chest 64
Chirping sound 28
Chorioangioma 268f
Choriodecidual separation 90
multiple foci of 92f
Chorionic villous 170f
Chorionic villous sampling 169, 170f
Chorionicity 69
determination of 468t
Choroid plexus 121, 181f, 182f, 449
cyst 68, 197f
Chromosomal abnormality
amniocentesis for 48
chemical markers with 137
Chromosomal anomalies 131
ultrasound for 132, 132f
Chromosomal disorders 130
Chronic renal disease 289
Cisterna magna 68, 201f, 448, 449
depth 81
Cleft lip 150, 270f
bilateral 210f, 211f
unilateral 208f, 209f
Cleft palate 270f
bilateral 211f
Cleft upper lip 210f
Clinical polyhydramnios, evaluation of 471t
Club foot 263f
deformity 264f
diagnosis of 259f
Color Doppler 55
studies obstetric 51, 57
Color flash 33
Color flow
baseline 32
display 30
imaging 30
Color inversion 32
Color misregistration artifact 38
Common carotid artery, origin of 34
Comparative power output 41
Complete abortion, diagnosis of 461t
Compression elastography 19
Computer equipment 370
Computer processor technology, development of 152
Conception, retained products of 159
Congenital anomalies 164
Congenital diaphragmatic hernia 227f
Congenital heart 145
defects 163
disease 145, 146
Continuous wave Doppler 24
Corpus luteum 80, 102f, 103f
cyst 159
flow 99
in left ovary 98f
site of 100
vascularity of 100, 103f
Cranial biometry 180f, 280f, 450
Cranium 91, 179, 180
Crown-rump lengths 474t
Cubital tunnel syndrome 363
Current equipment, ergonomic adaptations of 369
Cursor movement control 34
Cutaneous thickness 448
Cyanotic heart disease 289
Cyst 58, 71
hydrosalpinx 52
midline 194f
multiple 257f
Cystic adenomatoid malformation 225f, 226f, 287
Cystic area, detection of 416
Cystic hygroma 119f, 133, 200f, 202f, 203f
extensive 97f, 115f
Cystic sacrococcygeal teratoma 219f
D
Damping material 8
Dandy-Walker malformation 195f, 196f
De Quervain disease 364
Deformed cranium 184f
Delivery
indications of 301
mode of 301
Dense hyperechoic foci 246f
Deoxyribonucleic acid 139
Department of Labor 361
Department of Obstetrics and Gynecology 63
Diabetes mellitus, maternal 289
Diagnose ovarian torsion 45
Diaphragm 65
Diaphragmatic hernia 150
right sided 228f
Diastolic flow increases 309
Distal femoral epiphysis 82, 280f
Distended stomach 241f
District Advisory Committee 335
Doppler and color flow 31
principles 22
Doppler effect 22, 23
Doppler equation, components of 23f
Doppler in obstetrics, indications for 478t
Doppler indices, explanation of 311
Doppler pencil probes 24
Doppler signal 33
Doppler ultrasound 308
Doppler waveform analysis 313
Double bubble sign 241f
Down syndrome 131
signs 46
Ductus venosus 82, 135, 160, 328
Doppler 322
flow reflects acidosis 298f
flow velocity 132
Duodenal atresia 242f, 287
Duodenal bulb 242f
Duodenum 243f
Duties of Registered Center 337
Dysplastic kidney 256f
E
Ear, external 208f
Early amniocentesis 171
Early diagnosis, advantages of 131, 165
Early fetal echocardiography 163
Early gestation sac, diagnosing 156
Early pregnancy 52, 58, 72
discriminatory levels for 463t
failed 463t
failure 72, 116t
impending 95
investigation of 68
loss, classification of 96
Echocardiography transducer 14f
Echogenic bowel 244f
Echogenic choroid plexii 112f
Echogenic kidneys
bilateral 256f
enlarged 258f
Ectopic and corpus luteum 158
Ectopic gestation 97
Ectopic pregnancy 55, 61, 72, 99f, 157
diagnostic pathway for 467t
failure to recognize 45
management of 172
signs of 465t
suspected 84
Edward's syndrome 131
Elastography 19
Electrical pulse strikes crystal 3f
Electronic cable 8
Electronically steered systems 9
Electrophysiology applications 15
Embryo 92, 94f, 97f
attenuated 94f
with cardiac activity 98f
Embryonic bradycardia 116
Embryonic cardiac activity 87
Embryonic pole 121
Emergency studies 45
Encephalocele 147, 149f
End diastolic velocity, absent 328
End-diastolic frequencies, loss of 300
Endocavity ultrasound systems 13
Endometrial thickness 52
Enterocolitis 298
lateral 364
medial 364
Equipment care and quality control 39
Ergonomic equipment 367
Ergonomic principles 367
Esophageal atresia 241f, 287
Evidence, collection of 343
Extra-fetal evaluation 100, 454
Extremities 65, 179
Eye
movements 53
vascularity, 19 weeks 435
Eyeball 434, 437
and lens, 19 weeks 435
F
Face 179
Facial anatomy 203f
False positive rate 146
Faulty work organization 361
Fetal abdomen 240f, 253f
Fetal abdominal viscera 300
Fetal abnormalities
gross 72
in trisomy 13 456
in trisomy 18 456
in trisomy 21 456
Fetal acrania 184f
Fetal adrenal glands 254f
Fetal age estimation 476t
Fetal anatomy
development of 68
normal 68
survey 179
Fetal anemia 133
ultrasonographic signs of 471t
Fetal aneuploidies, diagnosis of 139
Fetal anomalies
detection of 142
failure to diagnose 45
schematic analysis for 454
Fetal behavior 66
Fetal biometry 50, 53, 56, 59, 69, 73
Fetal biophysical profiling 51
Fetal blood flow 480t
evaluation of 70
Fetal brain sparing 321f
Fetal breathing 290
Fetal cerebral circulation 310
Fetal cytomegalovirus infection 473t
Fetal death 48
misdiagnosis of 45
unexplained 289
Fetal ductus venosus 160
Fetal echocardiography 61
Fetal evaluation 84, 454
Fetal face 187f
Fetal facial angle 134
Fetal feet 259f
Fetal growth
assessment of 69
restriction 470t
role of ultrasound in 469t
Fetal head, retroflexion deformity of 190f
Fetal heart 146f, 160
anterior thoracic wall with 222f
enveloping 239f
rate 132, 138, 140
Fetal hepatomegaly 250f-252f
Fetal hydrops, severe 251f, 252f
Fetal hypoxemia, stage of 310
Fetal hypoxia 321f
Fetal kidney 114f
Fetal lens 205f
Fetal lungs 220f, 226f
Fetal macrosomia 144
Fetal medicine unit 49, 54
Fetal movement 53, 121, 290
decreased 289
Fetal nasal bone 134
Fetal node 118f
Fetal nuchal translucency 140
Fetal orbits and face 181
Fetal reactivity 290
Fetal scan, detailed 476t
Fetal spine 113f, 114f, 150, 153f
Fetal stomach 226f, 227f, 242f
bubble 114f
Fetal surveillance 289
Fetal thorax 222f, 261f
narrow 222f
Fetal tone 290
Fetal urinary bladder 115f
Fetal venous Doppler 310
Fetal weight, estimated 308
Fetal wellbeing 289
Fetus 433
abnormal 123
first 444
normal 244f
Fibroids 5, 51, 52, 57, 58
First trimester 83, 141
abdomen 150
biochemical markers 136, 137
cervicometry 167
color Doppler in 155
decision-making in 130
detection 142
embryonic, normal 84
invasive procedures in 169
non-chromosomal abnormalities 144
normal parameter evaluation in 92
scan checklist 128
screening for preeclampsia in 175
transvaginal abnormal 61
ultrasound
indications for 474t
of chromosomal anomalies in 130
Flaccid gestational sac 118f
Floating brain 184f
Flow direction 25
Flow distortion 28
Flow velocity 25
Flow volume 29, 290
Fluid-filled organ 2
Follicular development, monitoring of 71
Fossa and cerebellum, posterior 68
Frequency compounding 19
Frontomaxillary facial angle 132, 134
Fundamental frequency 17
G
Gallbladder 4
Gastrointestinal tract 110
Gastroschisis 145, 150, 150f, 248f
with bowel
loops 247f
segments 247f
Genetic amniocentesis 171
Genetic counseling center 332
Genetic laboratory 332
Genitourinary 110
Gestational age, estimation of 69, 84
Gestational diabetes 144
Gestational sac 68, 85f, 86f, 90f, 92, 93, 93f, 117f, 121, 158, 474t
live ectopic with 98f
seven weeks 95f
thin-walled irregular 95f
transvaginal scan of 93f
two 86f
wall of 91f
Gestations, determine number of 50, 56
Growth restriction 51, 57
assessment of 50
Gynecological complications 70
Gynecological disorders 51, 57
Gynecology 49, 51, 57, 70
Doppler in 71
ultrasound 54
H
Hanafy lens technology 11
Hand-eye coordinations 55
Harmonic frequencies 18
Harmonic imaging 17
Harmonic signals 18
HDlive silhouette 378, 381, 399, 416, 427
Head perimeter 450
Heart 179, 250
beats, absence of 157
rate 89f, 90f
Hematological disorders 133
Hemorrhage 102f, 298
Hepatic calcification, multiple foci of 250f
Hepatofugal 25
Hepatopetal 25
Herniated sac 150
High-pitched systolic component 23
Holoprosencephaly 147
Homogeneous fetal lung 221f
Human chorionic gonadotropin 138
Hyaloid artery 433
Hydatidiform mole 72
suspected 84
Hydranencephaly 147
Hydrocephalus 46
Hydronephrosis, missing 44
Hydrops fetalis 472t
Hydrosalpinx 58
Hypochondrium 278
Hypogastric arteries 272f, 273f
Hypoplastic cerebellar vermis 189f, 194f
Hypoplastic left heart syndrome 46
Hypotelorism, severe 127
Hypoxia 318
I
Iliac fossae, cranium in 278
Illegal advertisement 343
Immunological disorders 289
In vitro fertilization 333
Inadequate trophoblastic invasion 157
Incomplete abortion, diagnosis of 460t
Infertility 71
diagnostic unit 49
Inhomogeneous
adnexal mass 98f
cavity echoes 105
echoes 105f
Injury management 361
Instrumentation 7
Internet revolution 374
Interocular distance 450
Interval sac growth poor 116
Interventional ultrasound 49
Intra-abdominal organ 305
Intra-amniotic blood 244f
Intracardiac transducers 14
Intraesophageal cardiac probe 15f
Intraluminal transducers 14
Intrauterine contraceptive device 52, 58
extraction of 71
Intrauterine death, diagnosis of 467t
Intrauterine gestation sac, normal 156
Intrauterine growth restriction 47, 302
color Doppler in 315
diagnosis of 304
Doppler in 308
sonographic diagnosis of 302
Intrauterine growth retardation 289
Intrauterine infection 133, 250f
Intrauterine peritrophoblastic flow 99, 105f
Intrauterine pregnancy 45, 107f, 157
abnormal 92, 100
confirm 50, 56
Intrauterine venous flow 104
Ipsilateral corpus luteum, visualization of 159
K
Kidney 4, 68, 121, 148
normal 253f, 254f
Knobology 20, 31
calipers 22
depth gain compensation 20
dynamic contrast 20
dynamic range 20
edge enhancement 20
frequency selection 20
gain 20
log compression 20
maps 21
persistence 21
postprocessing 21
preprocessing 20
speckle reduction imaging 21
transducer selection 21
write zoom 21
zoom 21
Kyphoscoliosis 150
L
Laminar flow 28
Large bowel loops 245f
Lateral occipital meningocele 188f
Laws of ultrasound, medicolegal aspects 50
Lead zirconate titanate 7
Left ventricular outflow tract 230, 232f
Legally hazardous situations 45
Lemon sign 218f
Lethal skeletal dysplasias 145
Limb 53, 69, 73
absent 46
buds 121
Linear sequenced arrays 10, 10f
Lips 206f
Liquor amnii 81, 279
Liver 4, 68
lntraoperative transducers 13f
Lobar holoprosencephaly 192f
Locate corpus luteum 102
Long bones 306
bowed 262f
Low vs high resistance flow 26
Lower limb 111f
Lower segment scar, thinned 286f
Low-pitched diastolic component 23
Lumbosacral meningomyelocele 217f, 218f
Lumbosacral region 64
Lung, right 225f
M
Malfunction 42
Malpractice
and ultrasound 42
causes of 42
insurance 48
Manning's biophysical profile 291
Matching layers 8
Maternal age 136
Maternal bloodstream 140f
Maternal infections, fetal abnormalities in 459
Matrix array transducers 11
Measurement methodology 449
Mechanical sector 13
Mechanical transducers 8
Meconium peritonitis 245f, 246f
Meconium pseudocyst 246f
Medical ultrasound, basic principles of 66
Medullary veins slice cine mode, 29 weeks 440
Megacystis 145
Metabolic disorders 133
Methodology 50
Methotrexate 45
Mid trimester amniocentesis trial 171
Middle cerebral artery, normal 314f
Miscarried last time 128
Missed abortion, diagnosis of 461t
Mobile genetic clinic 332
Mobile medical unit 331
Modem ultrasound systems 42
Modern technology 376
Modified biophysical profile
interpretation of 480t
rationale for 479t
Molar change 106
Molar pregnancy 61, 108f, 109f
Molecular genetical technology 442
Multicystic dysplastic kidney 243f, 257f
Multiembryonic reduction 173
Multifetal pregnancy reduction 173
Multiple gestation, suspected 84
Multiple pregnancy 53, 59, 69, 73
Multiple transducer elements 10
Muscle physiology 364
Musculoskeletal disorder 361, 365
causes of 361
risk factors of 361
symptoms of 363
types of 363
work-related 361
Musculoskeletal injury
diagnosis of 365
symptoms of 363
Musculoskeletal system 110
Myocardial function 295f, 299f
Myometrium 81, 100, 237f
masses in 101f
N
Nasal abnormalities 270f
Nasal bone 132
absence of 127
ossification 127, 127f
presence of 127
Neck 64, 179
sprain 364
Neighboring soft-tissue 2
Non-chromosomal abnormalities 143
Non-chromosomal anomalies, detection of 141
Noninvasive direct-viewing all-inclusive technology 443
Noninvasive prenatal diagnosis and testing 139
Non-stress test 290f
Nonviable gestational sac 108f
Nonviable pregnancies 51, 57
Normal heart
12 weeks 413
13 weeks 415
18 weeks 431
Nostril 206f
single 213f
Nuchal edema 133
Nuchal skin 181, 450
fold 69, 447
thickness 201f
thickness 81
Nuchal thickness, measurement of 475t
Nuchal translucency 120, 122f, 123f, 132, 132f, 133, 143, 145, 164, 200f, 447, 449
thickness 120, 125f, 127, 164
increased 124f
O
Obstetric care unit 49, 54
Obstetric complication, greatest 167
Obstetric imaging 374
Obstetrics gynecology ultrasonography 60
Obstruction, severe 29
Occipital bone 188f, 189f
Occipital encephalocele, large 189f
Ocular diameter 450
Offences and penalties 335
Oligoamniotic sac 95, 116, 119f
Oligohydramnios 289
causes of 287
evaluation of 471t
severe 258f, 269f
Omphalocele 150, 248f, 249f
Oocyte retrieval 71
Operative probes 16f
Orbit deformity, single 116f
Orbital measurements 450
Organization of Ultrasound Unit 57, 71
Oscillating transducer (volume) 9, 9f
Osseous deformity 214f
Ovarian cysts 51, 57
aspiration of 71
injection of 71
Ovarian masses 33, 159
Ovaries 70, 71
measurement of 52
P
Panchnamah 345
Patau's syndrome 131
Pelvic
abscess, drainage of 71
anatomy, normal 52, 70
hematocele 99f
mass 44
tumors 52, 72, 58
Pelviureteric junction obstruction 256f
Penile arterial flow 30
Pericardial effusion 239f
Pericardial fluid 448
Periendometrial venous flow 106
Perigestational hemorrhage 157, 158f
Perilesional fluid collection 98f
Perinatal complications, incidence of 309
Peristalsis, active 38
Peritoneal fluid 52
Peritrophoblastic arterial flow 106
Peritrophoblastic vascularity 100f
Persistent corpus luteum 275f
Physiological herniation 113f
Picture-archiving and communication system 370
Placenta 81, 91f, 139, 279, 282f
accreta 473t
rules out 286
Placenta previa 47
classification of 472t
ultrasonography in 472t
unrecognized 46
Placental assessment 50, 56
Placental evaluation 55
Placental growth 307
Placental impedance, increased 320
Placental mass 306
Planar mode 153
Planoconcave fashion 11
Plastic freezer bags 40
Pleural effusion 224f
bilateral 224f, 225f
large 223f
unilateral 223f
Polycystic kidney disease, infantile 258f
Polyethylene catheter 170
Polyhydramnios 289
causes of 287
classification of 470t
moderate 270f
Ponderal index 303
Posterior cranial fossa 194f
abnormalities 182f
Posterior wall subserous fibroid 101f
Postsacral mass 219f
Potential cerebral damage, risk of 327
Pouch of Douglas 99f
Power Doppler 33
Preconceptional Prenatal Diagnostic Techniques Act 331
Preeclampsia 144, 175, 176, 289
prediction of 162
Pregnancy
complications stillbirths 144
confirmation of 84
failure, incidence of 157
high risk 63
induced hypertension 316f
losses, risk of 172
progresses 309
stage of 317f
vaginal bleeding in 84
weeks of 476t
Pregnant women, blood of 139
Premature babies 433
Prenatal diagnosis, first modality of 443
Prenatal diagnostic techniques 347
Prenatal test 169
Preterm delivery 144, 167
high risk of 167
Preventive maintenance 39
Prune-Belly syndrome 149, 400
Pseudoascites 239f
Pseudohydronephrosis 44
Pulmonary artery 231f
and vein 409
20 weeks 432
Pulmonary malformations 133
Pulsatility index 27, 157, 328, 329
Pulse
inversion 17
techniques 18
repetition frequency 325f
Pulsed Doppler 24
transducer 22f
Pulse-ECHO principle 2, 3f
Pulseless embryo 95f, 96f
Q
Quality assurance 40
Quality control tests 41
R
Rail track appearance 271f
Region of interest 31
Registration, suspension of 336
Regulation and Prevention of Misuse Act 347
Regulation of Portable Machines 333
Regulation of Prenatal Diagnostic Techniques 331
Renal malformations 148
Renal parenchyma, normal 257f
Renal pelvis 255f, 256f, 447
Renewal of certificate of registration, application for 334
Renewal of registration 334
Reporting 80
Residual placental tissue 159f
Reverse end diastolic velocity 328
Rhabdomyoma 238f
Right atrium 233f
Right ventricular outflow tract 231f
S
Sac
location of 84
number of 84
size of 84
Sacral meningocele 216f
Sacrococcygeal mass 220f
Scatter 3
echogenic foci 245f
Sealing 342
Search and witnesses 340
Second trimester
3D and 4D scan 276
abnormal 276
color Doppler in 276
dilemmas 276
extra-fetal evaluation 265
fetal abdomen 228
fetal biometry 265
fetal evaluation 179
fetal heart 228
fetal skeleton 258
fetal spine 211
fetal thorax 219
fetus 178, 249f
indications 179
malformations 179
ultrasound, indications for 475t
Semilobar holoprosencephaly 192f
Semilunar valves 235f
Seminar presentations, check-list for evaluation of 74
Septum pellucidum 192f
Sex
chromosome disorders 131
communication of 343
Shear-wave elastography 19
Signature vessel 318
Skeletal dysplasia 133, 150, 426
Skeletal system diseases, investigation of 427
Skin
and soft tissue 121f
problem 40
Skull, shape of 52, 58
Small bowel 448
atresia 287
obstruction 243f
Soft plaque 31
Soft tissue 65
swelling 64
Software errors 42
Sole of foot 264f
Sonoembryology chart 109
Sonography, reducing injury risk in 361
Sound beam 6, 7f
Sound wave propagation 1
Special transducers 13
Speckle reduction imaging 19
Spectral broadening 28, 37
Specular reflectors 3
Spina bifida 147, 148
missed 46
Spinal cord
delineate 214f
dividing 217f
Spinal degeneration 364
Spine 53, 58, 64, 73, 91, 179
Spiral arteries 157
Stomach 68, 240f, 243f
bubble 121
Subchorionic hematoma 80
Subcutaneous thickness 65
T
Tardus et parvus 29
Tendonitis 363
Tenosynovitis 363
Termination of pregnancy 166
Thalamus 180, 180f
Thanatophoric dysplasia 262f
Theoretical course 55
Third trimester 277
abnormal 301
biophysical profile 289
color Doppler 292
dilemmas 302
extra-fetal evaluation 279
fetal evaluation 278
fetal growth 287
indication 278
for color Doppler 292
obstetric study in 46
placental checklist 285
serial evaluation 291
ultrasound examination, indications for 477t
Thoracic outlet syndrome 364
Thoracic region 64
Thoraco-omphalopagus conjoined twins 154
Thorax 179
Three dimensional sonoembryology 152
Tissue
acoustic impedance 4
harmonic imaging 17
vibration 38
Tortuous ureter 243f
Total intrauterine volume 306
Trained ultrasonologist 52
Training 49
parameters 50
Transabdominal ultrasound 52, 57
Transcerebellar diameter 69
Transducer 7, 40
care 40
case 8
construction 8f
crystal 7
elements, types of 8
focal zone 6
formats 15
frequency 6
variety of 12f
Transesophageal echocardiography transducer 12f
Transesophageal transducers 14
Transluminal transducers 14
Transmitted frequency 17
Transmitted pulsation 38
Transvaginal color Doppler 156, 156f-158f
Transvaginal decision flowchart 129
Transvaginal scan 51, 57
Transvaginal sonography 53
Transvaginal transducer 12f
Transvaginal ultrasound 52, 57, 168f
Transverse cerebellar diameter 305
Traversing uterine cavity 270f
Tricuspid regurgitation 132, 135, 147
Trigger finger 364
Triphasic inferior vena cava, normal 299f
Triploidy 131
Trophoblastic reaction 89
Tubes 71
Turner's syndrome 131, 458
Twin 46
dizygotic 468t
monozygotic 468t
Twin pregnancy 379, 475t
role of ultrasonography in 468t
Twin to twin transfusion syndrome 59
diagnosis of 469t
Quintero staging systems for 469t
U
Ultrasonic scanning, suggested scheme for 64
Ultrasonography, basics in 1
Ultrasound
combined, types of 45
machines, advances in 130
practice of 49, 54
Umbilical artery 82, 271f, 294f, 309, 313f, 327, 328
aneurysm, 21 weeks 430
Doppler 318
normal 313f
significance of single 473t
Umbilical cord 81, 113f, 279
insertion 427
Umbilical vein 82, 295f, 323
abnormal 296f
single 271f
Undue color gain 38
Unhealthy pregnancy, diagnosis of 117f
Upper limb 111f
Ureter
left 255f
right 255f
Urethra, proximal 257f
Urinary bladder 68, 121, 240f, 255f, 258f, 273f
wall 257f
Urinary tract, obstruction of 255f
Urine test negative 128
Uterine 101f
circulation 309
fundus 85f, 86f, 95f
mass 80
size 52
vascularity 104f
Uterine arteries 162, 175f, 293f, 315, 328, 329
abnormal 312f
maternal 82
normal 312f
right 162f, 176f, 316f, 317f
Uterine cavity 86f, 105f, 108f
irregular 159f
Uteroplacental blood flow, evaluation of 70
Uteroplacental circulation, development of 315
Uterus 70, 283f
normal 60
V
Velamentous cord insertion, 12 weeks 412
Velocity range 32, 36
Velocity scale 32
Vena cava, inferior 82, 310
Ventricular atrium 447
Ventricular end-diastolic pressure 310
Ventricular septal defect, large 236f
Vertebrae
18 weeks 425427
and ribs
18 weeks 425
20 weeks 422
Viable pregnancies 51, 57
W
Wall filter (Doppler) 33
Water-soluble coupling gel 40
Wedged-shaped field 11f
Worsening hypoxia 480t
Wound, open 40
Y
Y chromosome 139
Yolk sac 68, 92, 94f, 95f, 98f, 117f, 118f, 121
abnormal
shape of 116
size of 116
hyperechoic shrunken 119f
large 97f, 120f
shrunken 97f
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Chapter Notes

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Basics in UltrasonographyCHAPTER 1

 
1.1 BASIC PHYSICS
In order to obtain the best image possible, basic fundamentals of ultrasound wave physics must be understood and applied.
 
Audible Sound Waves
Audible sound waves lie between 20 and 20,000 Hz: Ultrasound uses sound waves between l and 30 MHz.
 
Sound Wave Propagation
Sound waves need a media to travel and do not exist in a vacuum, and propagation in gases is poor because the molecules are widely separated.2
The closer the molecules are, the faster the sound wave moves through a medium, so bone and metals conduct sound exceedingly well.
 
Effect on Image
Air-filled lungs and gut containing air conduct sound so poorly that they cannot be imaged with ultrasound instruments. Structures behind them cannot be seen.
A neighboring soft-tissue or fluid-filled organ must be used as a window through which to image a structure that is obscured by air.
An acoustic gel must fill the space between the transducer and the patient, otherwise sound will not be transmitted across the air-filled gap.
Bone conducts sound at a much faster speed than soft tissue.
Because ultrasound instruments cannot accommodate the difference in speed between soft tissue and bone, current systems do not image bone or structures covered by bone.
 
Pulse-Echo Principle (Figs.1.1A and B)
Because the crystal in the transducer is electrically pulsed, it changes shape and vibrates, thus producing sound waves that propagates through the tissues.
The crystal emits sound for a brief moment and then waits for the returning echo reflected from the structures in the plane of the sound beam.
When the echo is received the crystal again vibrates, generating an electrical voltage comparable to the strength of the returning echo.
 
Effect on Image
Greyscale imaging shows echoes in varying levels of grayness, depending on the strength of the interface.3
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Figs. 1.1A and B: The pulse-echo principle. (A) The electrical pulse strikes the crystal and produces a sound beam, which propagates through the tissues. (B) Echoes arising from structures are reflected back to the crystal, which in turn vibrates, generating an electrical impulse comparable to the strength of the returning echo.
 
Beam Angle to Interface (Fig. 1.2)
The strength of the returning echo is related to the angle at which the beam strikes the acoustic interface. The more nearly perpendicular the beam is, the stronger the returning echo will be smooth. Interfaces at right angles to the beam are known as specular reflectors.
Echoes reflected at other angles are known as scatter.4
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Fig. 1.2: Beam angle to interface.
 
Effect on Image
To demonstrate the borders of a body structure, the transducer must be placed so that the beam strikes the borders more or less at a right angle.
It is worthwhile to attempt to image a structure from different angles to produce the best representation (Fig. 1.3).
 
Tissue Acoustic Impedance
The returning echo's strength also depends on the differences in acoustic impedance between the various tissues in the body.
Acoustic impedance relates to tissue density; the greater the difference in density between two structures, the stronger the returning interface echoes defining the boundaries between those two structures on the ultrasound image will be.
 
Effect on Image
Structures of differing acoustic impedance (such as the gallbladder and the liver) are much easier to distinguish from one another than are structures of similar acoustic texture (e.g. kidney and liver).5
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Fig. 1.3: When visualizing a structure, it is important to scan at several different angles to find the best possible interface (thick arrows). Only a few echoes return from the interfaces at an oblique angle to the beam—specular reflections (thin arrows). Most of the echoes are scattered.
 
Absorption and Scatter
Because much of the sound beam is absorbed or scattered as it travels through the body, it undergoes progressive weakening (attenuation).
 
Effect on Image
Increased absorption and scatter prevent one from seeing the distal portions of a structure. In obese patients, the diaphragm is often not visible beyond the partially fat filled liver.
Fibroids may absorb so much sound that their posterior borders may be difficult to define.6
 
Transducer Frequency
Transducers come in many different frequencies—typically 2.5, 3.5, 5, 7, and 10 MHz.
Increasing the frequency improves resolution but decreases penetration.
Decreasing the frequency increases penetration but diminishes resolution.
 
Effect on Image
Transducers are chosen according to the structure being examined and the size of the patient. The highest possible frequency should be used because it will result in superior resolution. Pediatric patients can be examined at 5–10 MHz.
Lower frequencies (e.g. 2.5 MHz) permit greater penetration and may be needed to scan larger patients.
 
Beam Profile (Fig.1.4)
The sound beam varies in shape and resolution.
Close to the skin, it suffers from the effect of turbulence, and resolution here is poor. Beyond the focal zone, the beam widens.
 
Effect on Image
Information that appears to be present in the near field may actually be an artifact. Structures beyond the focal zone are distorted and difficult to see. A structure as small as a pinhead may appear to be half a centimeter wide.
 
Transducer Focal Zone
Sound beams can be focused in a similar fashion to light. Most systems use electronic focusing which permits the transducer to be focused at one or more variable depths. The sonographer can alter the focus level electronically.7
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Fig. 1.4: Diagram of the waveforms in a sound beam. Unequal waveforms in the near field (Fresnel zone). Widening of focal beam (Fraunhofer zone) beyond the focal zone.
 
Effect on Image
To achieve high resolution choose an transducer with a proper focal zone or use a electronically focusing set at the right depth.
 
1.2 INSTRUMENTATION
 
Transducers
The transducer assembly consists of five main components (Fig. 1.5).
  1. The transducer crystal is composed of a piezoelectric material, most commonly lead zirconate titanate. It converts the electrical voltage into acoustic energy upon transmission and acoustic energy to electrical energy upon reception.8
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    Fig. 1.5: Diagram showing transducer construction. Matching layers of material decrease the size of the main bang acoustic interface that occurs between the crystal and the skin. Backing material acts as a damping tool to stop secondary reverberations of the crystal. The crystal is constructed of piezoelectric material, which can convert electrical impulses into sound waves and vice versa.
  2. The matching layers lie in front of the transducer element and provide an acoustic connection between the transducer element and the skin.
  3. Damping material is attached to the back of the transducer element to decrease secondary reverberations of the crystal with returning signals.
  4. The transducer case provides a housing for the crystal and damping layer and insulation from interference by electrical noise.
  5. The electronic cable contains the bundle of electrical wires used to excite the transducer elements and receive the returned electrical impulses.
There are several types of transducer elements:
  1. Mechanical transducers
    • The transducer crystal is physically moved to provide steering for the beam
    • Less commonly used in modern equipment than phased-array transducers9
    • Often used in volume transducers for 3D or 4D applications.
  2. Oscillating transducer (volume)
    • The drive motor and transducer array are housed in the transducer case
    • The motor drives the transducer array back and forth to generate an image (Fig. 1.6).
  3. Electronically steered systems
    • In this type of transducer, multiple piezoelectric elements are used and a separate electrical signal is provided for each element
    • Steering and focusing occur by sequentially exciting individual elements across the face of the transducer
    • Focusing is controlled electronically by the operator through placement of the focal zone or focus caret
    • The images are displayed in a sector, vector, linear, or curved linear format.
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Fig. 1.6: Oscillating transducer (volume).
10
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Fig. 1.7: Linear sequenced arrays.
  1. Linear sequenced arrays
    • Multiple transducer elements are mounted on a straight or curved bar.
    • Groups of elements are electronically pulsed at once to act as a single larger element
    • Pulsing occurs sequentially down the length of the transducer face, moving the sound beam from end to end (Fig. 1.7)
    • Linear arrays produce a rectangular shaped image which is used in breast, small parts, vascular, and musculoskeletal imaging
    • Curved arrays provide a large fan-shaped image with a curved apex. These transducers are most commonly used in obstetric, gynecologic, abdominal, and endocavity imaging.
  2. Phased array
    • The phased array consists of multiple transducer elements mounted compactly in a line
    • All elements are pulsed as a group with small time delays to provide beam steering and focusing
    • The resulting image is in a sector or vector format and is particularly useful in cardiac and intercostal imaging (Fig.1.8).11
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Fig. 1.8: Wedged-shaped field.
Matrix Array (Multi-O Array, 1.5D Array, 2D Array) Transducers:
  • This type of transducer utilizes multiple rows of elements to form a matrix of crystals (Fig. 1.9)
  • Through the use of multiple pulses, these crystals may be pulsed in sequence to create a very thin elevation plane (slice thickness), which yields increased resolution.
 
Hanafy Lens Technology
  • This is another technique used to create a very thin slice thickness that is uniform throughout the field of view
  • With this technology, the transducer crystals are cut in a planoconcave fashion (Figs. 1.10 and 1.11), which creates crystals that are thin in the center and thicker at the edges12
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    Fig. 1.9: A variety of transducers are available for specific purposes.
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    Figs. 1.10A and B: Transvaginal transducer. Transesophageal echocardiography transducer.
    13
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    Fig. 1.11: lntraoperative transducers are designed to allow easy access to anatomy.
  • The thinner center will ring at a higher frequency (focusing in the near field), and the thicker edges will ring at a lower frequency (focusing in the far field), automatically creating a uniform elevation plane (slice thickness) throughout the field of view.
 
Special Transducers
Special transducers (Fig. 1.11) have been produced to help view specific areas:
  • Small parts (7.5–15MHz) transducer
  • Rectal transducers in longitudinal (linear) and transverse (radial) configurations (biplane)
  • Biopsy transducer
  • Doppler probes.
 
Endocavity Ultrasound Systems
The transducer array, which can be a linear, curved, or phased array (or mechanical sector) scanner, is placed at the end of 14the transducer shaft. This transducer shaft is inserted into the rectum or vagina to produce high-resolution images of the male or female pelvic organs (see Figs. 1.10A and B).
 
Transesophageal Transducers
A transesophageal transducer may be introduced into the esophagus to visualize the heart and provides a higher resolution image than does transthoracic echocardiography (Fig. 1.12).
 
Intraluminal and Intracardiac Transducers
  • Smaller transducers at the ends of catheters can be introduced into vessels, the biliary duct, or the ureter (transluminal transducers)
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    Fig. 1.12: Echocardiography transducer.
    15
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    Fig. 1.13: Intraesophageal cardiac probe.
  • These transducers allow close visualization of the anatomy that is being examined, but are not commonly used
  • Intracardiac catheters have been developed more recently. A small catheter (IOF or BF), which may be introduced into the right heart (Fig. 1.13), provides very high-resolution imaging and may be used for interventional and electrophysiology applications.
 
Operative Systems
Standard ultrasound systems are modified so they can be used in a sterile fashion in the operating room. Special high-frequency ultrasound probes are used for this purpose (Fig. 1.14). Intraoperative transducers are designed with a size and shape to allow easy handling and positioning during intraoperative procedures.
 
Transducer Formats
There are a variety of transducer formats available in modern equipment, each suited to particular scanning applications.16
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Fig. 1.14: Operative probes.
Linear array: The linear format provides a rectangular image. This transducer is most useful in “small parts” and vascular imaging.
Vector: A vector format provides a trapezoidal image. This small foot-print transducer is often used in abdominal, gynecologic, and obstetric applications.
Sector: The sector image is wedge-shaped and is commonly used in cardiac, abdominal, gynecologic, obstetric, and transcranial imaging.
Curved array: A curved array transducer will provide a large field of view with a convex near field. This transducer is most commonly used in obstetrics; however, other applications include abdominal and gynecologic imaging.
 
NEW TECHNIQUES FOR IMPROVING THE IMAGE
 
3D Imaging Systems
  • 3D imaging capabilities have been increasing in popularity’ over recent years17
  • It is most commonly used in obstetric and cardiac imaging to evaluate the surface of structures or to evaluate orthogonal planes
  • It utilizes specialized transducers which relate the transducers position to the ultrasound system allowing for a very accurate display of the acoustic echoes.
 
4D Imaging Systems
  • 4D imaging systems use specialized transducers to display the realtime motion of a 3D image
  • These are most commonly used for obstetric and cardiac applications
  • The transducers are commonly mechanical transducers, which are held in place while the ultrasound system controls the acquisition of the images by “rocking” the transducer crystals and displaying the 4D images.
 
Harmonic Imaging
  • Images are obtained from returning signals, which are a multiple of the transmitted (fundamental) frequency
  • The harmonic signal is created from the compression and relaxation of tissues during sound propagation
  • It is helpful to reduce noise and clutter in an image, especially in technically difficult patients; however, harmonic imaging may suffer from decreased penetration due to the higher receive frequency.
 
Tissue Harmonic Imaging, Pulse Inversion
  • With traditional ultrasound techniques, the ultrasound system transmits a pulse of a specific frequency and receives a pulse of the same frequency. This frequency is known as the fundamental frequency18
  • As this fundamental frequency travels through tissues, the tissues compress and expand with the variations in acoustic pressure, resulting in the generation of additional ultrasound frequencies, known as harmonics
  • The harmonic frequencies are multiples of the transmitted fundamental frequency
  • The challenge for the ultrasound system is to separate the clean harmonic signals from the fundamental signals. Tissue harmonic imaging removes noise from images, especially in patients who are difficult to image
  • The simplest separation method is to lengthen the transmitted pulse
  • Pulse inversion techniques utilize multiple pulses on transmit which vary in phase, which is maintained on transmit and receive
  • The harmonic signals generated by the tissue have a different shape and phase than that of the transmitted pulse
  • By summing the received pulses, the ultrasound system cancels the fundamental frequencies (destructive interference) and adds the harmonic signals (constructive interference)
  • This technique often results in reduction in frame rate.
 
Image Compounding
Multiple ultrasound frames are averaged together to produce an image with increased contrast resolution.
 
Compound Imaging/Sie Clear Multiview Spatial Compounding/Sona CT Cross Beam Imaging
Image compounding averages multiple ultrasound frames to produce an image with increased contrast resolution.
Image compounding may use image frames of varying frequency (transmit or frequency compounding) or by utilizing 19image frames from varying angles (spatial compounding). They are of the following types:
Frequency Compounding
  • Frequency compounding uses multiple transmit pulses to obtain images of the same area with different frequencies
  • It provides an increase in contrast resolution and penetration.
Spatial Compounding
  • This technique interrogates the same area of interest from various locations
  • By averaging these ultrasound frames, the speckle pattern is reduced and will provide an image with increased contrast resolution
  • Spatial compounding may occur by varying the transmitted beam's location, varying the transducer position, or by varying the location of the receive beam.
Speckle Reduction Imaging
Speckle reduction imaging is processing algorithm that reduces image speckle. The resultant images appear smoother and have increased contrast resolution as compared to the image without speckle reduction.
Elastography
  • Elastography is an ultrasound technique used to evaluate the relative stiffness of tissue as compared to the surrounding area
  • Results may be qualitative or quantitative in nature.
Compression elastography: It is a qualitative imaging technique that utilizes manual compression to present the relative stiffness of tissue through a color or black/white overlay of the image. It is most commonly used in breast imaging .
Shear-Wave Elastography: It is a technique that utilizes an electronic push pulse to provide compression of tissues. The speed of the shear wave generated by the tissue compression may then be measured. It is most commonly used in the evaluation of the liver.20
 
1.3 KNOBOLOGY
Learning to use the knobs effortlessly is an important part of the art of ultrasound imaging.
 
Gain
The system gain controls the degree of echo amplification or brightness of the image. Care must be taken with the use of gain. Too much overall gain can fill fluid-filled structures with artifactual echoes, whereas too little gain can negate real echo information.
 
Depth Gain Compensation
The depth gain compensation (DGC) attempts to compensate for acoustic loss of sound waves by absorption, scatter, and reflection and to show structures of the same acoustic strength with the same brightness, no matter what the depth is.
 
Dynamic Range (Dynamic Contrast/Log Compression)
The dynamic range (log compression) is the range of intensities from the largest to the smallest echo that a system can display. Changing the log compression does not affect the number of gray shades in the image; instead, it varies the display of the gray shades.
 
Edge Enhancement (Preprocessing)
The preprocessing control alters the edges of the image pixels to accentuate the transition between areas of different echogenicities, making the borders sharper.
 
Frequency Selection (MultiHertz)
Frequency selection allows the user to optimize the imaging for the best resolution or penetration. Increasing the frequency will improve resolution but sacrifice penetration.21
 
Maps (Postprocessing)
Maps alter image aesthetics by placing more or less emphasis on specific echo intensities. Changing the map may aid the user in evaluating pathology.
 
Persistence
It is a frame-averaging function that allows echo information to be accumulated over a longer period of time. By increasing the persistence subtle tissue texture differences will be enhanced and by decreasing it the moving structures are evaluated more easily.
 
Speckle Reduction Imaging
Speckle reduction imaging (SRI) is an image processing algorithm that reduces image speckle for enhanced contrast resolution. Higher SRI settings result in images with a smoother appearance and increased contrast resolution, as compared to the image without speckle reduction.
 
Zoom
The zoom function allows image magnification by increasing the pixel size, although this change results in image degradation.
 
Write Zoom (Res)
With write zoom, a box is placed on the screen, and the area seen within the box can be expanded to fill the screen.
 
Transducer Selection
The transducer selection feature allows the user to activate the transducer of choice.22
 
Calipers
Caliper markers are available to measure distances. The ellipsoid measurement is an added feature in most units. A dotted line can be created around the outline of a structure to calculate either the circumference or the area.
 
1.4 DOPPLER AND COLOR FLOW PRINCIPLES
Doppler physics as it relates to diagnostic ultrasonography concerns the behavior of high-frequency sound waves as they are reflected off moving fluid (usually blood) (Fig.1.15).
 
Doppler Effect
When a high-frequency sound beam meets a moving structure, such as blood flow in a vessel, the reflected sound returns at a different frequency.
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Fig. 1.15: Diagram of a pulsed Doppler transducer demonstrating the direction of the transmitted sound beam toward the flow of blood and the receiving sound beam back to the transducer.
23
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Fig. 1.16: Diagram showing the components of the Doppler equation. φ, angle of insonation of the vessel; C, speed of sound in tissue (–1,540 m/sec); Fr, return frequency; Ft, sending frequency; V, blood flow velocity.
The speed (velocity) of the moving structure can be calculated from this frequency shift (Fig. 1.16). The returning frequency will be increased if flow is toward the sound source (transducer) and will be decreased if flow is away from the sound source.
 
Clinical Correlation
The Doppler effect is helpful in localizing blood vessels and determining optimal sites for velocity measurements. Veins typically have a low-pitched hum, whereas arteries have an alternating pattern with a high-pitched systolic component and a low-pitched diastolic component.24
 
Continuous Wave Doppler
The sound beam is continuously emitted from one transducer crystal and is received by the second. Both transducers are encased in one housing.
  • Dedicated continues wave (CVV) Doppler pencil probes.
  • Imaging CW Doppler.
 
Clinical Correlation
Vascular surgeons use CW Doppler to check for the presence or absence of flow in superficial arteries. CW Doppler is also sometimes used to monitor umbilical artery flow. Because the cord lies in the amniotic fluid, no other confusing vessels are within the ultrasonic beam.
 
Pulsed Doppler
A Doppler sound beam is sent and received (pulsed) over a short period of time. Because the time that the Doppler signal takes to reach the target can be converted to distance, the depth of the site sampled is known.
The pulsed sound beam is “gated.” Only those signals from a vessel at a known depth are displayed and analyzed.
 
Clinical Correlation
Pulsed Doppler is used to detect the presence of blood flow in a select vessel at a given depth when there are several vessels within the ultrasonic beam. Clots can appear echo-free, so a real time image may erroneously appear to show a normal vessel even if it is occluded. Doppler will detect no flow. Flow from other vessels outside the region of the gate is not analyzed because only the gated area is examined.25
 
Flow Direction
The direction of blood flow can be discovered by assessing whether the frequency of the returning signal is above or below the baseline in a suspect vessel. Flow toward the transducer is traditionally displayed above the baseline, and flow’ away from the transducer is shown below the baseline.
 
Clinical Correlation
Flow in the portal vein is sometimes reversed when pressure in the liver increases in portal hypertension; flow away from the liver is known as hepatofugal and indicates that the portal pressure is so high that flow has been reversed. A memory aid that some sonographers find useful to remember this often confusing terminology, is “fugitives flee.” Flow toward the liver is known as hepatopetal. Flow direction analysis allows the diagnosis of the abnormal hepatofugal flow.
 
Flow Pattern
The pattern of flow can be assessed with Doppler ultrasound. Typically, a vein shows a continuous rhythmic flow in diastole and systole and emits a lower pitched signal than does arterial flow. Arterial flow has an alternating high-pitched systolic peak and a much lower diastolic level.
 
Clinical Correlation
Veins may be confused with arteries in realtime.
 
Flow Velocity
The velocity of blood flow can be deduced from the arterial waveform. If the peak systolic flow frequency and the angle 26at which the beam intersects the vessel are known, a simple formula allows the calculation of velocity (see Fig. 1.16). The velocity calculation formula is only accurate if the angle of the Doppler beam to the interrogated vessel is less than 60 degrees.
 
Clinical Correlation
Velocity is an important factor in calculating the severity of carotid stenosis. Generally, the more severe the stenosis is, the greater the velocity through the narrowed vessel will be. As the vessel becomes critically occluded, however, flow velocity will diminish.
 
Low-versus High-resistance Flow
Doppler flow analysis allows the detection of two types of arterial flow: a high- resistance (Fig. 1.17) and a low-resistance (Fig. 1.18) pattern.
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Fig. 1.17: Diagram of an arterial spectral wave form in a high resistance bed.
27
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Fig. 1.18: Diagram of an arterial spectral wave form in a low resistance bed.
The high-resistance pattern has a high systolic peak and a low diastolic flow.
Low-resistance arterial systems demonstrate a biphasic systolic peak and a relatively high level of flow in diastole.
Resistance index (RI) is commonly calculated by the following formula:
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An alternative technique, known as the pulsatility index (PI), evaluates the diastolic flow in a different fashion. A cursor is run along the superior aspect of the systolic and diastolic flow envelope, and the mean is calculated by the system.
PI = (Systolic velocity – Mean flow)/(Systolic velocity)
In obstetrics, the A/B or systolic-diastolic (SID) ratio is commonly used:
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All three of these parameters (RI, PI, and SID ratio) are just different mathematical constructs that attempt to estimate the relative difference in flow velocity between systole and diastole.28
 
Clinical Correlation
If a high-resistance pattern is seen where there is normally a low-resistance appearance, such as in the common carotid or renal artery, vessel narrowing is present. Quantifying the severity of the resistance may help in clinical management.
A high-resistance pattern is usually seen in the vessel supplying the ovaries in the proliferative phase of the cycle.
If a low resistance pattern (RI <0.4) is seen within an ovarian mass, carcinoma is more likely.
 
Flow Pattern within a Vessel (Laminar Flow)
In a normal vessel, the velocity of blood is highest in the center of a vessel and is lowest closer to the wall. This condition is termed laminar flow. When there is a wall irregularity or if the artery is angled, the flow is distorted and may be greatest when it is closest to the vessel wall. Stenosis markedly increases the flow velocity—through an area of narrowing, whereas vessel dilatation decreases the speed of flow.
 
Clinical Correlation
To accurately measure the flow velocity in a tortuous carotid artery, place the sample volume (the area that is gated) at the center of the highest flow. Listening to the audible signal is useful in determining the site for optimal measurement. A high-grade stenosis will have a shrill, chirping sound.
 
Flow Distortion
Normal laminar flow at and immediately beyond an area of wall irregularity or stenosis is disturbed, resulting in abnormal spectral waveforms. Flow distortion (non-laminar) is characterized by high velocities in both systole and diastole. The presence of many echoes within the sonic window is termed spectral broadening and may indicate considerable flow disturbance.29
 
Clinical Correlation
Flow disturbance in an artery such as the carotid may indicate pathologic atheromatous changes.
 
Flow Changes beyond a Narrowed Area (Poststenotic Changes)
Poststenotic changes in arterial flow may be seen in the next few centimeters beyond a narrowed area. When there is severe stenosis, the systolic peak in the poststenotic area will be lower (more rounded) with lower velocities throughout diastole. The acceleration slope of the systolic peaks (peak systole) will be diminished. This pattern is known as the tardus et parvus abnormality. In less severe obstruction, the spectral waveform may resume the normal high- or low-resistance flow appropriate for that artery.
 
Clinical Correlation
Detecting a poststenotic pattern is particularly valuable in evaluating the renal arteries because the usual site of stenosis, adjacent to the aorta, is rarely seen owing to the presence of bowel gas. Poststenotic changes may also be seen in the common carotid artery when the stenosis involves the origin of the common carotid. The waveform of the other common carotid should be evaluated for comparison. Large calcified plaques may obscure the area of stenosis, so one may be dependent on poststenotic changes to determine the severity of narrowing.
 
Flow Volume
The flow volume through a given vessel can be roughly estimated if the velocity of flow (using the formula shown in Figure 1.16) and the vessel diameter are known.30
 
Clinical Correlation
The calculation of flow volume is important in situations in which a low level of flow is associated with inadequate function, e.g. penile arterial flow.
 
Aliasing
If there is a marked frequency shift with a high measured velocity, the signal may return after the next pulse has started. This condition is called aliasing.
To compensate for aliasing, increase the velocity range (PRF). Lowering the baseline may also prevent aliasing.
 
Clinical Correlation
If aliasing is present, the peak signal will be inaccurately measured as lower than it really is, and the severity of the stenosis will be incorrectly measured.
 
Color Flow Imaging
Color flow assigns different hues to the red blood cells in a vessel depending on their velocities and the direction of the blood flow relative to the transducer. This allocation is based on the Doppler principle.
 
Clinical Correlation
The site of maximum flow can be visualized quickly so that the pulsed Doppler gate can be inserted where the flow is highest.
 
Color Flow Display and Direction within a Vessel
In most systems, flow toward the transducer is allocated red, and flow away from the transducer is allocated blue. The flow velocity is displayed with faster velocities in brighter colors and 31slower velocities in darker colors. The fastest velocity may be displayed in yellow or white. Turbulent flow will demonstrate a mixture of colors.
As with pulsed Doppler, optimal images are only obtained at an oblique angle. If a vessel runs a straight course, flow at 90 degrees to the color box will not be displayed. The angle of the color box region of interest (ROI) can be adjusted to the left or right when linear steering is available; otherwise, the probe can be manually angled to provide the angle needed to receive the returning signals.
 
Clinical Correlation
Soft plaque may be missed on gray scale but a flow void will be seen using color flow. Sometimes, soft plaques may show no changes on grayscale. Once correct color allocation has been made, normal vessels will fill with color.
 
Knobology: Doppler and Color Flow
 
Range Gate Cursor (Sample Volume)
The Doppler sample volume is displayed on the B-scan image. This cursor, which may be presented as a box or two parallel bars, indicates the depth and area from which the Doppler signal is obtained.
 
Region of Interest
This box is used to restrict the color display of a blood flow image and to eliminate an unnecessary display of color.
 
Inversion and Direction of Flow and its Relation to Baseline (Doppler)
When blood flow is moving toward the transducer, sound waves of high frequency are reflected, and positive signals are seen above the baseline. Blood cells that are moving away from the 32transducer appear as negative signals below the baseline. Both veins and arteries can show flow in either direction because interpreting flow direction depends on the angle of the vessel to the transducer.
 
Color Inversion
As in spectral Doppler, the display of color is dependent on the angle of the flow to the transducer.
 
Color Flow Baseline
Blood flow toward the transducer will be shown within the measurable range of colors above the color bar baseline. Blood flow away from the probe will be displayed in the range of colors below the baseline.
 
Velocity Scale/Velocity Range/PRF (Doppler)
The range of velocities that can be seen in the spectral display is determined by the PRF value. Higher velocity vessels (e.g. carotid) requires a high PRF; therefore, the velocity range should be increased.
 
PRF (Color Flow)
The range of velocities used in color flow is lower compared to the spectral waveform because the average Doppler shift frequency is displayed rather than the peak velocity. Depending on the color map used, lower PRF values may present a shift to a different color, representing a slightly higher velocity flow (i.e. white or yellow).
 
Sweep Speed (Doppler Only)
The rate at which the spectral information is displayed can be adjusted using the sweep speed controls. A slow speed (e.g. 25 mm/sec), a moderate speed (e.g. 50 mm/sec), or a fast speed (e.g. 100 mm/sec) can be selected.33
 
Wall Filter (Doppler)
Blood flow signals that are not wanted can be eliminated by using the wall filter.
 
Filter (Color Flow)
A phenomenon called color flash, caused by cardiac or peristaltic motion or by transducer movement, produces a flash of spurious color in an area where there is no real flow. The area of interest can be concealed by the flash artifact.
 
Gain (Doppler and Color Flow)
The gain controls alter the spectral waveform and the color flow image. Inadequate gain results in an image in which the vessel is incompletely filled with color or in which no spectral Doppler signal can be obtained in areas of slow flow.
 
Angle Correct Bar (Flow Vector)
An angle correct bar is situated within the range gate cursor. This bar should be aligned with the direction of blood flow. The angle created by the insonating ultrasound beam and this bar must be known if the flow velocity is to be deduced from the frequency of the returning Doppler signal. The angle should be less than 60 degrees.
 
Power Doppler
Power Doppler utilizes the amplitude of the Doppler signal to generate the ultrasound image. Areas with high concentrations of blood cells will appear in brighter colors while lower concentrations of blood cells will appear in darker colors. This technique is more sensitive for subtle flow than is conventional color flow Doppler. Power Doppler typically does not provide any directional information and is particularly useful for evaluating the presence of flow or low flow in small or subtle vessels (e.g., ovarian masses).34
 
Audio Volume
The Doppler sound will be heard from the built-in speakers. Usually, there are independent speakers for both forward and reverse flow. The control varies the volume of the Doppler sound.
 
Cursor Movement Control
The cursor (range gate cursor and ROI) movement can be manipulated by means of a trackball or a joystick.
 
Measurements
The standard measurement unit used in displaying the spectral waveform is velocity (m/sec or cm/sec). When dealing with a high grade stenosis, obtain maximum velocities at and just beyond the area of lumen narrowing.
 
Pitfalls
 
Incorrect Angle
A waveform that appears to indicate a distal obstruction is displayed in a vessel; however, no plaque is seen in the vessel.
Correction Technique
Check the position of the ultrasound beam relation to the direction of flow. If the angle greater than 60 degrees, then the velocity is not being accurately calculated, and an abnormal waveform is created (see Fig. 17).
 
Little or No Doppler Signal in an Artery
The spectral waveform shows apparent low systolic flow and minimal diastolic flow. This may be because of:
  • There may be a severe obstruction proximal to this area and in an area too difficult to evaluate with the ultrasound beam (e.g., origin of the common carotid artery)
  • This patient may have diminished cardiac output35
  • The sample volume (gate) may not be placed where maximum flow is present
  • The sample volume is too large for the small amount of flow
  • The wall filters level is set too high.
Correction Technique
  • Do not depend solely on the visualization of the vessel
  • Color flow highlights the higher velocities in the artery and helps in gate placement, but a keen ear is more sensitive
  • A higher velocity may be evident as the sound beam is angled slightly off the center of the stream
  • A larger sample size may be needed when scanning to locate the site of flow, but to obtain a more precise flow measurement within an artery, decrease the gate size
  • The wall filter should be set at the lowest setting that does not introduce artifacts, especially when scanning a vein (a low-flow state)
Try the following maneuvers before giving up:
  • Change to another acoustic window or different incident angle
  • Open up the gate setting
  • Lower the velocity’ range
  • Use a lower frequency transducer. The patient may be too obese for a higher frequency transducer.
 
A High-resistance Waveform in a Low- resistance Bed
 
Explanation
There may be soft plaque distal to this area. If the B-scan gain is too low, soft plaque may be missed. Use color flow to outline the true patent lumen.
 
Aliasing
A tight stenosis causes such high velocities at the site of flow and immediately distal to the narrowed area that flow is seen above the baseline and at the lower edge of the spectral display. 36When color is used, there may be peaks of color from the other end of the spectrum. A chirping sound may be heard as you angle through the stenotic area.
This may be due to the fact that, the velocity is so high that the signal wraps around itself, and peak velocities are displayed below the baseline. This problem arises because the selected PRF is too low to accurately pick up the high velocities that are occurring.
 
Correction Techniques
  • Place the baseline at its lowest site to allow the systolic peaks to be displayed
  • Increase the PRF (velocity range)
  • Some units allow the B-scan image to be frozen while the Doppler signal is obtained. This will also widen the measurable velocity range
  • Increase the Doppler angle, but do not exceed 60 degrees
  • Decrease the insonating frequency. Most units offer a choice of several Doppler frequencies for each transducer. Otherwise, change to a lower frequency transducer
  • Change to CW (not widely available on most current machines).
 
Inadequate Venous Signal
Venous flow is difficult to detect even when the vessel is clearly demonstrated. This may be due to:
  • There may be little venous flow at rest
  • The vein may be compressed by patient position
  • The B-scan gain may be too low to demonstrate the clot within the vein.
 
Correction Technique
  • Respiration affects venous flow. With inspiration and the descent of the diaphragm, pressure increases in the 37abdomen. Ask the patient to perform a Valsalva maneuver. As the breath is released, venous flow increases, and the venous signal will become more pronounced
  • Ask the patient to flex the leg slightly and re-evaluate. Use color flow’ in these instances to accentuate subtle flow
  • Increase the gain and apply gentle compression to see if the vein collapses.
 
Audible Signal but Vessel not Seen
A venous signal can be heard, but a patent vessel cannot be visualized.
The vein may be subtotally occluded, or the presence of adjacent collaterals may cause the audible signal.
 
Correction Technique
Color flow will demonstrate the smaller collateral vessels as well as a small amount of residual flow in an almost occluded vessel.
 
Spectral Broadening
Apparent spectral broadening may be caused by too much gain or by scanning too close to the vessel wall, picking up lower velocities.
 
Correction Technique
Make sure the supposed spectral broadening reflects true pathology and is not just noise by comparing it to an area known to be normal.
 
A Flickering Image
Sometimes, it is difficult to evaluate color flow when obtaining a pulsed Doppler signal because the image flickers.38
A large amount of data is being processed to generate the image for each frame of information when obtaining the Doppler signal or color flow. Therefore, the frame rate is lowered, and a flicker may occur.
 
Correction Technique
To reduce this flicker, evaluate one mode at a time (e.g. use color flow only) or reduce the width of the color flow box.
 
Color Misregistration Artifact (Color Flash)
If the transducer is rapidly moved, a flash of color related to transducer movement and not to vascular flow may develop.
 
Correction Technique
Use the filter to reduce noise and move the transducer slowly, using caution not to remove real vascular flow from the image.
 
Tissue Vibration or Transmitted Pulsation
In the region of a highly pulsatile structure such as an artery, neighboring structures may move, causing some color artifact in the surrounding tissues.
 
Correction Technique
Scan from a different axis if possible.
 
Active Peristalsis
Active peristalsis may induce a color flow artifact.
 
Undue Color Gain
The outline of vessels may be misregistered owing to excessive gain, so the flow appears to fill in some of the surrounding tissues (color bleed).39
 
Correction Technique
Decrease gain so the color image corresponds to the vessel outline.
 
1.5 EQUIPMENT CARE AND QUALITY CONTROL
Ultrasound systems are precision instruments that require careful handling and regular maintenance to ensure optimum performance.
 
Preventive Maintenance
  • Liquids other than contact gel should not be stored on the equipment
  • The hand used to adjust control settings should be kept clean to ensure that contact gel does not affect the trackball or other functions
  • Cables and transducers should be visually inspected for worn areas or cracks
  • Careless placement of the transducer and cable on the machine can cause cable damage
  • Transducers should be placed in proper holders to avoid stress on cables
  • When taking ultrasound equipment to wards, it should be moved carefully to avoid sudden impact, which may dislodge printed circuit boards from their connectors, resulting in failure of operation
  • Many ultrasound systems have cooling fans with overlying air filters to prevent deposition of dust and particles on circuit boards within the unit. These should be cleaned periodically (weekly), especially if used in carpeted areas
  • Error messages should be noted and recorded for referral to service personnel.40
 
Transducer Care
Transducers are delicate instruments and require careful handling. Transducers that have been dropped or treated roughly may have “dead” elements that no longer transmit or receive signals (due to debonding of electrodes from crystal elements).
Each time a transducer is removed from its cradle, ensure that the transducer cable is not snagged on part of the ultrasound system (such as the wheel support). The compromised length of cable may result in the transducer being pulled out of the hand as it is moved toward the patient.
Transducers should be cleaned after each patient with an alcohol sponge or transducer disinfectant, particularly if the patient has an open wound or a skin problem. Plastic freezer bags are an inexpensive means of covering the transducer to avoid contact with open wounds and to avoid contamination. Some transducers can be immersed in Cidex up to the handle for sterilization. Approximately 10 minutes of immersion is required for adequate sterilization.
Use a commercial water-soluble coupling gel to ensure good acoustic contact between the transducer and patient. Thick, high-viscosity gels are desirable when scanning the patient in an erect position because they do not slide off easily. Thicker gels are also helpful for obstetric patients with large abdomens.
Use disposable gloves when scanning a patient to avoid the risk of infection. Spread the gel around the abdomen with the transducer rather than by hand. Do not handle the controls with gel on your hand or glove.
 
Quality Assurance
Quality assurance tests may be tedious to perform but are worthwhile because it may be difficult or even impossible to detect calibration and measurement distortions from 41examination of the images alone. Clearly, major clinical problems may result if erroneous measurement data are produced. Quality assurance checks should be performed on a quarterly basis with most systems or more often if a problem a suspected e.g., if a transducer has been dropped or measurements are consistently higher or lower than expected.
 
Quality Control Tests
The standard tests performed to ensure that the system is working satisfactorily are:
  • Aspect ratio and calibration tests
  • Resolution tests (both axial and lateral)
  • A comparative power output test that equates to a depth of penetration measurement.
All these tests are performed on a tissue-equivalent phantom.
 
Aspect Ratio and Calibration Test
The aspect ratio and calibration test measures whether distances are accurate in both directions—horizontal and vertical directions and whether these measurements are displayed accurately on a hard-copy device transducer.
 
Resolution
Axial and lateral resolution capability can be determined using closely spaced pins in a phantom.
 
Comparative Power Output
The test for comparative power output determines whether the sound beam emitted by the transducer can reach a depth adequate to see deep structures. The test is performed at full power output, and the time gain compensation is set at 42maximum at the area of depth visualization. The comparative power output can be calculated as follows:
Attenuation factor (0.7) × Depth (7.35) ×
Transducer frequency (5) = 25.725 dB
This number is recorded in the quality control logbook as the output for this transducer using this phantom. Repeat tests should give the same result. For the comparison of results to be valid, all settings must be the same each time the test is undertaken. This is a useful test to see whether transmitter and/or receiver characteristics are changing over time.
 
Malfunction
Modem ultrasound systems are very reliable but occasionally can malfunction, resulting in disruption of images.
This is rare in modern systems, but when it occurs, it is usually obvious with clear disruption of the images.
The disruption may relate to circuitry for a specific transducer, so the equipment may still be usable with different transducers until the problem can be rectified. Occasionally, a transducer that has been selected may not initialize correctly, or its connection to the ultrasound system may be fault, but can be corrected by disconnecting and reconnecting the transducer so that it re-initializes.
Software errors occasionally occur and can often be rectified by switching the ultrasound unit off and on again, allowing the system to reboot. It may be necessary to wait 30 seconds before switching the system on again to allow time for correction of the software error.
 
1.6 MALPRACTICE AND ULTRASOUND
 
Causes of Malpractice
Legally malpractice as it relates to ultrasound comes in two forms:43
  1. Battery Injury: The patient is injured during the examination by assault or inadequate care (e.g., falls off the table). Failure to obtain informed consent is another type of “battery” injury.
  2. Negligence: The examination is performed in a fashion that is “below the standard of care.”
Standard of care is defined as the way in which a “reasonable and prudent” physician or sonographer would act under the same circumstances. In our court system, the standard of care is established in several inherent ways:
  • Expert witnesses testify as to the standard of care
  • Guidelines such as the American Institute of Ultrasound in Medicine (AIUM) “Practice Guidelines for the Performance of an Antepartum Obstetric Ultrasound Examination” or American Congress of Obstetricians and Gynecologists technical bulletins set national standards. There are no such laid down in our country
  • Local hospital, radiology, or obstetric department policy statements also set the standard of care.
 
Responsibilities of the Physician or Sonographer Reporting the Study
  • The physician or sonographer reporting the study is required to accurately describe the findings on the examination, including pertinent negative findings with a clinical conclusion about the presence or absence of an abnormality
  • Suggestions about additional procedures or follow-up studies may be required
  • Problems in the performance of the study, such as obesity or suboptimal patient position, should be covered in the narrative portion of the report
  • A preliminary report is not considered legally hazardous as long as the sonographer does not attempt to make a diagnosis44
  • If a sonographer is working for a sonologist, the sonographer is not responsible for errors in the study, provided that the study is performed according to standards set by the sonologist, even if the study is of poor quality
  • The sonographer is not liable if he or she uses a technique that creates an image that looks like pathology but is not
  • Some examples of misleading findings or wrong techniques that are not the sonographers legal responsibility if uncorrected by the sonologist are the following:
    • Pseudohydronephrosis as the result of a full urinary bladder
    • Sludge-filled gallbladder due to an overgained image
    • Not following up on a pathologic finding, such as missing hydronephrosis with a pelvic mass
    • Missing a pancreatic mass by not trying different scanning techniques, such as erect scanning or having the patient drink to fill the stomach to create an acoustic window
    • Missing stones in the gallbladder or kidneys due to a failure to use a high-frequency transducer.
Although the sonographer is not held legally responsible for these errors, there is still the moral and ethical element to consider.
 
Responsibilities of the Physician or Sonographer Performing the Examination
  • The primary responsibility is to perform a comprehensive examination that conforms to the national standards
  • One should care for the patient and make sure that the patient comes to no harm by rough treatment or carelessness
  • Confidentiality must be observed.
Some examples of situations in which a sonographer is liable are:45
  • Physically molesting the patient
  • Letting a patient fall, causing injury
  • Giving the patient or accompanying doctor a wrong diagnosis
  • Revealing confidential information about the contents of the sonogram or disclosing any information that has adverse effects on the patient
 
Legally Hazardous Situations
 
Emergency Studies
Emergency ultrasound studies often modify clinical management from conservative to aggressive, and because any management changes hinge on the sonographic findings, the examination may be legally hazardous.
Litigation is common when a wrong diagnosis leads to immediate consequences.
Some examples of emergency situations often followed by litigation are as follows:
  • Failure to recognize ectopic pregnancy: Few ectopic pregnancies now require immediate surgery because many are now treated with methotrexate. This has created a new risk: misdiagnosis of a normal pregnancy as an ectopic pregnancy with subsequent methotrexate treatment with survival of a deformed but viable intrauterine pregnancy
  • Failure to diagnose ovarian torsion
  • Misdiagnosis of fetal death: Wrongly diagnosing fetal death with the subsequent delivery of a live but damaged infant can occur
  • Failure to diagnose abruptio placenta
  • Failure to diagnose a fetal anomaly: Fetal abnormalities are a common cause of litigation because the monetary award for a missed anomaly is so large. Litigation related to obstetric ultrasound is many times more frequent than for all other types of ultrasound combined46
  • The common missed fetal abnormalities resulting in litigation are as follows:
    • Missed spina bifida
    • Hypoplastic left heart syndrome
    • Absent limb or limbs
    • Down syndrome signs
    • Hydrocephalus.
Often, the litigation concerns a basic level obstetric study in which there is a possibility of an abnormality and no recommendation is made for referral for a targeted or referral study to be performed at a specialized center.
 
Failure to Diagnose Major Obstetric Findings
Some obstetric ultrasound findings that have been overlooked and that have serious consequences to pregnancy management are as follows:
  • Twins or triplets: Failure to diagnose twins or triplets can lead to severe long-term disability if the presence of twins is first discovered at delivery.
  • Unrecognized placenta previa during a sonographic examination may lead to a major bleed at delivery.
  • Breast cancer that is misdiagnosed as merely a breast cyst:
    Failure to diagnose breast cancer is the most common cause of imaging litigation. Most suits relate to mammography, but breast cancer ultrasound cases are occurring increasingly.
 
Substandard Reporting of the Ultrasound Study
  • Dating an obstetric study in the third trimester: The range of possible dates for a series of obstetric measurements such as the biparietal diameter, head circumference, femur length, and abdominal circumference in the third trimester is ± three to four weeks, so accurate dating if the patient presents in the third trimester is not possible. This error is 47so well known that the obstetrician and radiologist share responsibility if delivery is performed before fetal viability under these circumstances
  • Dating or weight estimation with unsatisfactory measurement data: It is not always possible to obtain a quality abdominal circumference or fetal head measurements with an unusual fetal position. Problems of this type should be noted in the report. Not reporting these problems may result in wrong clinical decisions about delivery or the presence of intrauterine growth restriction (IUGR)
  • Failure to compare the dates or weight on the current examination with earlier sonographic studies may mean a failure to diagnose IUGR. Data from earlier sonograms should be obtained if later examinations are performed at another facility.
 
Tardy Reporting
  • Delayed reporting of an ultrasound study or delayed transmission of an ultrasound report to the referring doctor can lead to litigation.
  • Findings that change management, such as the discovery of an ectopic pregnancy or a low biophysical profile score of 0 to 2, require immediate notification to the managing physician.
  • Some examples of serious consequences of a delayed report are as follows:
    • Failure to relay a report of a placenta previa resulted in the loss of the pregnancy in a patient with heavy vaginal bleeding
    • Two week delay in transmitting a report of IUGR resulting in the loss of that pregnancy.
Failure to Perform an Appropriate Ultrasound Study when a Patient Presents with a Family History of a Malformation Or a Drug History predisposing to a Malformation.48
A common indication of an ultrasound study is a family history of fetal malformations or when the patient is taking drugs like valproic acid, that causes the fetal malformations. Specific views of potential malformations such as the lumbar spine with valproic acid or the face with a family history of cleft lip and palate, need to be obtained and reported.
 
Interventional Guidance Problems
Amniocentesis for chromosomal abnormality or to establish fetal lung maturity is still commonly performed and is standardly performed under ultrasound guidance. Suits related to fetal damage or fetal death due to the procedure still occur. Documentation of the amniocentesis site and of fetal viability after the procedure and a written report of the way in which the procedure was performed are helpful in avoiding litigation and defending complaints. By convention, only two passes are made if aspiration of amniotic fluid is unsuccessful.
 
MALPRACTICE INSURANCE: WHO NEEDS IT?
Any sonographer performing freelance work should invest in malpractice insurance. Sonographers employed by a hospital. or other institution do not generally need to purchase insurance because they are covered by the hospital's or clinic's policy.