Ultrasound in Subfertility: Routine Applications and Diagnostic Challenges K Jayaprakasan, Sonal Panchal
INDEX
Page numbers followed by b refer to box, f refer to figure and t refer to table.
A
Acquired immunodeficiency syndrome 181
Acquired urogenital abnormalities 162
Addison's disease 173
Adenomyosis 29, 35, 36, 36f
areas of 37
management of 37
sonographic features of 36b
uterus 50f
Adnexal
cyst 16f
mass 65f
pathologies 27, 105, 112
signs 65
torsion 148
Adrenal hyperplasia, congenital 173
Adrenogenital syndrome 173
Alara principle 14
Allis forceps 136
Amenorrhea 49
Ammonia, anhydrous 13
Anal canal 20f
Androgen Excess Society Criteria 96
Anechoic lacunae 36
Anesthesia 132
general 133
Anteverted uterus 30f
Antimicrobial solution, type of 18
Anti-Müllerian hormone 40, 80, 96
Antral follicles 5f, 25f, 85f
count 80, 82, 84, 85, 119
multiple 97f
Arcuate uterus 19f, 198f
Artery, diameter of 10f
Ascites, continuous autotransfusion system of 141
Ascitic fluid, aspiration of 132, 141
Asherman's syndrome 50, 50f, 54
Assisted reproduction
role of ultrasound in 188
treatment 79, 147
complications of 147
Assisted reproductive technology 123
Atrophic seminal vesicles 186
Automatic volume calculation 123
B
Bacterial contamination 13
Beam, depth penetration of 2
Benzyl or methyl alcohol 13
Bicornuate 40
uterus 39f, 51f, 55f, 67f
Biopsy guides 13
Bird's nest appearance 109f
Bladder 21f
endometriosis 110, 110f
Bleeding 153
Blood flow
high-resistance 126
subendometrial 57
Blood vessels 6
Borderline ovarian tumors 92, 102
Bowel
endometriosis 110, 111f
muscular layer of 22f
normal 22f
C
Calmette-Guerin therapy 183
Cannula, removal of 137f
Carcinoma in situ, development of 49
Caseous necrosis 184
Cervical canals, separate 51
Cervical ectopic pregnancy 159f
Cervix 22, 30f, 68
canal 29
longitudinal of 19f
Cesarean scar
pregnancy 160f
previous 160f
Chlamydia trachomatis 62, 157
Chromopertubation 66, 70
Clomiphene citrate 119
Color Doppler ultrasound examination 26
Conception
chances of 37
cycles 57
Congenital uterine anomalies
classification of 40t
management of 40
Contralateral pelvic wall 22
Contrast hysterography 56
Corpora lutea, ultrasound images of 26
Corpus luteum 25, 25f, 92, 93, 116, 116f, 117f, 157, 158f
hemorrhagic 94f
Corpus uteri 19, 22
Count antral follicles 86b, 86f
Cross-beam focusing 105
Crown-rump length 156
Cryptorchidism 168
Cumulus oophorus 122f
Cyclical maximum appropriate 46
Cyst
aspiration 132, 140, 164
technique 140b
hemorrhagic 95f
wall 95f
Cystadenoma 92, 99
borderline serous 102f
Cystic corpus luteum 25f 94f
Cystic structure 157f
Cystic teratoma 92, 100
Cytoreductive laparoscopic 37
D
Decidualized endometrium, thick 48f
Deep endometriosis 110f
Dermoid cyst, benign 100f
Diamniotic twin gestation 154f
Digital versatile disk 196
Distal hydrosalpinx 75f
Distal vasal obstruction 179f
Dominant ovary 25
Doppler angle 10, 11f
Doppler beam 10
Doppler gain 7
Doppler image, normal spectral 7f
Doppler sample volume 10f
Doppler spectrum 6
Doppler studies 5
Doppler ultrasound 57, 70
Double endometrial echo complex 38
Dysfunctional uterine 49
Dystrophic calcifications 183f
E
Echogenic polyp 2f
Ectopic pregnancy 147, 157
Ectopic trophoblast 159f
Ejaculatory duct 162, 164, 179, 182
cyst 179
obstruction 179
Ejaculatory volume, low 163
Electronic array transducers cost 13
Electronic transducers 2
Embryo
reduction 144f
transfer 50, 56, 132, 136, 136f, 137f, 197
abandon 50
day of 140
technique 136b, 138
Endocrine factors 162
Endogenous hormones, high levels of 51
Endometrial adhesions 49
Endometrial appearances 48
Endometrial assessment 50
Endometrial blood flow, analysis of 58
Endometrial cavity 43, 52, 54, 73f, 125
shape of 44f
Endometrial columnar epithelium 124
Endometrial complexes 38f
Endometrial cycle 44
Endometrial evaluation 123
Endometrial hyperplasia 49f
resulting 48
Endometrial interface 49
Endometrial intramural fibroids, large 52
Endometrial malignancy 50f
Endometrial myometrial
border 21
interface 123
junction 124f, 125
Endometrial pattern 129
Endometrial polyp 52, 53f, 54f, 56f, 58, 199
assessment of 55
Endometrial proliferation 50
Endometrial receptivity 203
Endometrial stripe 29
Endometrial synechiae 68f
Endometrial texture 55
Endometrial thickness 19f, 21f, 23f, 45, 49, 55, 126, 128, 129
assessment of 43
measuring 21, 47
Endometrial ultrasound
morphology 23
reporting on 55b
Endometrial vascularity
pulse Doppler of 126f
zones 125f
Endometrioma 92, 99, 108f, 109f
ground glass appearance of 108f
small 99f
three-dimensional power Doppler of 109f
ultrasound features of 109
Endometriosis 105, 106f
deep infiltrating 20
deep retroperitoneal 110
superficial 106, 107f
Endometriotic lesions, types of 105, 106
Endometriotic nodule 100f, 111f
signs of 20
Endometrium 4f, 6f, 19f, 49f, 55, 57, 116, 124, 125f
abnormalities of 48
B-mode features of 123
grade B, multilayered 124f
histogram of 127f
morphology of 124
protrusions of 36f
thin 45f
ultrasound examination of 44b
Endomyometrial junction 50f
zone 36
Enlarged heterogeneously hypoechoic epididymis 184f
Enterobacteriaceae 13
Epididymal calcification 174, 178f
Epididymal cysts 182
Epididymal tail, tapering of 174
Epididymis 162, 163, 184
absence of 174
dilated tubules in 180, 182
ectasia of 179
enlarged 163
tail of 185f
tuberculosis of 183
tubular ectasia of 174
Epididymitis 173
chronic 173
Epididymo-orchitis 173
Epithelial ovarian tumors 102
Escherichia coli 62
European Association of Urology on Male Infertility 168
European Society for Gynaecological Endoscopy 198
European Society for Human Reproduction and Embryology 39
Excision, method of 37
F
Fallopian tube 44, 56, 61, 62f, 71f
anatomy of 61
inflammatory lesions of 62
Femoral region 170
Fertility
practitioners 51
treatment 30
background 147
Fertilization 122
Fetal intrathoracic position of needle tip 143f
Fetal reduction 132, 141
Fibroid 40f, 52, 198
affects pregnancy rates 35
degenerated 33
in subfertile patient, management of 35
mapping 32f
multiple 32f
subserosal 34f
uterus 37f, 56f
Doppler of 34f
Fibrosis 184
Fimbrial cyst 64, 64f
Fire, ring of 158
Flow index 122f
Focal nodular heterogeneous lesion 185f
Focal zones, multiple 4
Follicle
and endometrium
Global vascularity of 128, 129
maturation of 119
aspiration equipment 134f
in normal ovary, mature 46f
increasingly produce estrogen 45
peripheral distribution of 96f
stimulating hormone 80, 93, 115, 164, 201
higher 35
Follicular cysts 148
Follicular diameter 119
Follicular monitoring 204
Follicular volume 123
Food endometrial receptivity 126
Frank bicornuate uterus 51
Frozen embryo cycle 50
Fundal endometrial polyp 57f
Fundus uteri 23f
G
Gain amplifies returning waves 3
Gardnerella vaginalis 62
Gel infusion sonography 71
Genital tract
infection 162
tuberculosis 180
Gestational sac 49f, 65, 160f
Gestations, multiple 155
Gland margin, lateral 164
Gonadotropin
normal 164
releasing hormone 35, 84, 93, 147
stimulated cycle 119
Granuloma
formation 184
healing of 183f
Ground glass appearance 99f
H
Haemophilus influenzae 62
Halo sign 94f
Hemiuterus, noncommunicating horns of 52
Hemodynamic parameter 116
High frequency probes 29
High-resistance flow 117f
High-resolution ultrasound systems 26
High-velocity blood flow 7
Hormonal preparations 44
Hormone, adrenocorticotropic 173
Human chorionic gonadotropin 47, 89, 120, 203
Hycosy 72, 77
over, advantage of 56
Hydrosalpinx 63, 63f, 64, 64f, 67
aspiration of 132, 141
diagnostic of 63f
Hyperechogenic endometrial edge 125
Hyperechoic lesion 31
Hypoechogenic simple cyst 95f
Hypoechoic mass 186f
multiple 186
single 186
Hypoechoic nodules 185
multiple small 185f
Hypoechoic ovary, heterogenously 149f
Hypopituitary disorders 172
Hypothalamo-pituitary ovarian 43
Hystero-contrast-salpingography 70
Hystero-contrast-sonography 56
Hystero-contrast-sonosalpingography 64, 72b, 72f, 73, 76
Hysterosalpingography 66, 67
I
Implantation potential maximum 127, 138
In vitro fertilization 35, 50, 79, 119, 132, 147, 202
Infertility tests, armamentarium of 43
Inguinal canal 169f
Inguinal pouch, superficial 170
Inner myometrium 36f
International ovarian tumor analysis 100
Intra-abdominal testis 173f
Intracavitary fibroid 52, 53f
multiplanar of 199f
Intracytoplasmic sperm injection 162
Intramural extension, degree of 35
Intramural fibroids 31f
Intraovarian lesion, beak sign of 63f
Intrauterine
adhesions 54, 54f
device 54
in situ 55f
insemination 118
population 53
pregnancy 54, 65f
Invasive investigative procedures, replace routine 29
Invasive procedures 29
Iodine 13
compounds 13
Ischemia 172
J
Junctional zone alteration 37
K
Kidney
left 177
right 177
L
Laparoscopy 29
Leiomyosarcoma 33
Lesion, malignant nature of 33
Liver cirrhosis 172
Lower-pregnancy rates 51
Low-frequency sound 2
Low-velocity blood flow 7
Luteinizing hormone 83, 93, 115, 164, 201
Lymph node, abdominal 2
M
Male infertility
evaluation of 162
nonobstructive causes of 164
obstructive causes of 174
Malignant lesions, typical vascular morphology of 66f
Mass, heterogenous 158f
Mature follicle, B-mode features of 119
Mechanical transducers 2
Mediastinum testis 163
Menstrual cycle 21, 24f, 25f, 44
different phases of 25f
secretory phase of 27
Menstrual period, last 43
Methanol 13
Miscarriage, second trimester 37
Mock transfer 139
Monochorionic 154
diamniotic 154, 155
Monozygotic 154
Mucinous cystadenocarcinoma 101, 101f
Mullerian duct cysts 179
Multifetal pregnancy reduction 132
Multifrequency probes 29
Multiple pregnancy 141, 147, 153
Mycoplasma hominis 62
Myomas 31
Myometrial cysts 36
Myometrium
amount of 37
heterogeneous 36
N
National Institute for Health and Clinical Excellence 76
National Institute of Clinical Excellence 167
National Institutes of Health 95
Natural cycle, monitoring 115
Neisseria gonorrhoeae 62
Neurovascular bundle 164
Nonobstructive azoospermia 174
Nonpalpable testes 162, 168
Numerous cystic spaces 163
O
Obstructive azoospermia, cause of 163
Oligozoospermia, severe 163
Oocyte retrieval 56
complications of 147, 151
technique 135b
Oral contraceptive pill, combined 95
Orchitis and epididymo-orchitis 173
Ovarian blood flow 86
Ovarian cysts 147, 201
functional 92, 95
simple 201f
Ovarian dysfunction, premature 26
Ovarian endometrioma 107, 202f
Ovarian follicle 121f
tracking 115
Ovarian hyperstimulation syndrome 79, 95, 119, 132, 149, 151
Ovarian pathology 92
malignant 92, 100
Ovarian reserve 202
assessment of 79
tests 79, 80
Ovarian stroma 151
blood flow 119
Ovarian tissue, rim sign of 63f
Ovarian torsion 92, 98
Ovarian vascularity, three-dimensional power Doppler assessment of 88f
Ovarian volume 80, 119
Ovary 17f, 25f, 26f, 27, 199
benign cystadenoma of 99f
hyperstimulated 92, 97
inversion mode of 202f
three-dimensional multiplanar display of 85f
tomographic ultrasound images of 194f
transvaginal ultrasound images of 25f
two-dimensional pulse wave Doppler of 87f
P
Pampiniform plexus, dilatation of 165
Paracervical block 133
Paraovarian cyst 102, 194f
Paratubal cyst 64
Peak systolic velocity 11, 87, 117
Pedicle sign 54f
Pedunculated intracavitary fibroids protrude 52
Pelvic
assessment 15f
endometriosis 105
enhance delineation of 12
floor 18f
inflammatory disease 62, 112
organs, normal appearances of 27
Perifollicular vascularity of dominant follicle 120
Perifollicular vessel 121f
Perineal region 170
Perineal testis 170f
Periprostatic region 181
Peritoneal implants 20
Persistent noncyclical hormonal stimulation 48
Pie, apex of 17, 18f
Polycystic ovarian syndrome 82, 92, 95, 96, 124, 199
Polycystic ovary 97f, 98f
Polyethylene glycol 13
Polyp 53, 200f
Polypectomy
controlled study of 53
simple 53
Postmenopausal 44
bleeding, history of 21
ovaries 26f
uterus 26
Postmenses thin endometrium 48f
Postmenstrual appearance 48
Postmenstrual uterus 45f
with thinned endometrium 45f
Postoocyte collection ovary 151
Potassium chloride injection 142
Pouch of Douglas 4f, 20, 21f, 27, 98, 152f, 158
Power Doppler studies 12
Pregnancy
extrauterine 65f
heterotopic 160
Premature rupture of membranes 143
Premenopausal 44
Preovarian block 133
Preovulatory follicle 116f, 120f-122f
measurement of 120f
Preovulatory scan 119
Preovulatory uterine artery waveform 126f
Prevotella bivia 62
Progesterone 115
Proliferative endometrium 30f, 45f
Prostate
apex of 164
gland 164
normal 165f
systematic survey of 164
Prostatic utricle, cyst of 179
Pseudogestational sac 66f
Pseudosac 65, 157
Pulsatility index 87, 117
Pulse repetition frequency 7, 121, 166
Pyosalpinx 64, 64f
R
Randomized controlled trials 168
Rectal endometriosis 111f
Rectovaginal endometriosis 111f
Rectum 20
Renal tract anomalies 52
Residual uterine septum 40, 41f
Resistance index 87, 109, 117
Rete testis 181, 182
Retrograde ejaculation 162
Royal College of Obstetricians and Gynaecologists 150
Rudimentary horn
unicornuate with 40
unicornuate without 40
S
Saline 68
Saline infusion
salpingography 69f
procedure 68f
sonography 31, 40f, 54, 54f, 56, 57f, 66
sonohysterography 38
sonohysteroscopy 31
sonosalpingography 67
Salpingitis 62
acute 62, 63
chronic 64
Scanning technique 106
Scrotum, perineum posterolateral to 170f
Secretory endometrial integrity 47
Secretory endometrium 116f
Seminal vesicle 164, 179f, 186f
left 186f
normal 165f
right 186
sections of 187f
tuberculosis of 186
Septate uterus 67f
complete 198f
Septated mucinous cystadenoma 99f
Serosal surface 31
Serous cystadenocarcinoma 101
lying behind uterus 101f
Shallow internal fundal indentation 38
Sildenafil citrate 51
Sim's speculum 136
Singleton intrauterine pregnancy 153f
Smooth multilocular solid tumor 101
Solid component 16f
Sonographic anatomy, normal 163, 164
Sonographic features 166
Sonographic technique 166
Sonography-based automatic volume count 85
Sonohysterosalpingography 67
Sonosalpingography 68
Sophisticated ultrasound 115
Speckle reduction imaging 105
Spectral Doppler measurements 10
Sperm
abnormal 162
parameters, abnormal 162
Spermatic cord 168, 186
Spermatozoa 162
Spontaneous conception, chance of 35
Staphylococcus aureus 13
Stimulated cycles, monitoring of 118
Stimulated ovary, automated evaluation of 196f
Stimulates regeneration 45
Stimulation complication 147
Strictly speaking 52
Stromal arteries 7
Subendometrial blood flow 125
Submucosal fibroid 31, 32f- 34f, 41, 52f
presence of 33, 40
Submucosal type, suspicion of 40f
Subseptate uterus, partial 198f
Subserous fibroids, removal of 35
Supraphysiological levels 124
Surgery, role of 37
Symmetrical endometrial thickness 65f
Systematic examination technique 27
Systematic scanning technique 18
T
Testicular artery 173f
Testicular atrophy 172
Testicular dysfunction 162
Testicular ectopia, transverse 170f
Testicular sperm aspiration 188
ultrasound-guided 188
Testicular tuberculosis 183
Testicular tumor 174, 177f
Testis 166, 170f
adrenal rest in 173, 177f
enlarged 185, 185f
left 164f
normal 163f, 164f
posterolateral aspect of 163f
transverse scan of both 182f
undescended 162, 168
Thin endometrium, heterogenous 50f
Three-dimensional ultrasound imaging 123f, 191
Time-gain compensation 3
Tissue
harmonic imaging 3
heterogeneous 36f
Tomographic ultrasound imaging 106, 193
Torsion 172
Total intravenous anesthesia 133
Transvaginal ultrasound scan image 134f
Transabdominal gynecological ultrasound examination 22
Transabdominal scan 30f
Transabdominal sonography 29
Transabdominal transducers 2
Transabdominal ultrasound examination 22
Transrectal examination 22
Transrectal ultrasonography 162, 163, 187f
reveals 186
Transvaginal color flow Doppler ultrasonography 29
Transvaginal oocyte retrieval 147
Transvaginal probe 15
Transvaginal scan 2, 29, 30f
Transvaginal sonography 29, 106
Transvaginal three-dimensional 30
Transvaginal ultrasound 92, 115
examination 18, 27
image 23f, 134f
Trauma 172
Trilaminar endometrium 30f
Triple-layered proliferative phase morphology 4f
True perifollicular vessel 121f
Tubal assessment 204
Tubal ectopic pregnancy 159
Tubal evaluation 62
Tubal neoplasms 66
Tubal patency assessment, tests of 61, 66
Tubal pathologies, diagnosis of 61, 62
Tubal pregnancy 64
direct signs of 65
indirect signs of 65
Tuberculosis, extrapulmonary 186
Tuberculous abscess 185f
Tuberculous epididymitis 184, 184f
Tuberculous orchitis 185
Tubo-ovarian mass 64f
Tunica vaginalis 184
Twin growth discrepancy 156
Typical corpus luteum 47f
U
Ultrasound, safety of 12
Ultrasound-guided procedures 132, 204
Uniform ultrasound morphology 26
Unruptured follicle, luteinized 117f
Unstimulated endometrial echo 45
Unstimulated endometrium comparable 48
Ureaplasma urealyticum 62
Ureteral endometriosis 110
Urethra 21f, 164, 188f
observe 21
stricture 187
Urinary bladder 5f, 20, 21f, 27, 187f
normal 21f
Urinary tuberculosis 180
Urogenital abnormalities, congenital 162
Uropathy, obstructive 110
Uterine anomalies, congenital 29, 30, 37, 41, 197
Uterine artery 7, 7f, 118, 126
Doppler of 58f
embolization 35
flow 118
pulse Doppler analysis of 126
Uterine cavity
assessment of 43
distortion of 39f
normal 30f, 67f
Uterine contractions 128
Uterine cornu 139f
Uterine fibroids 29, 31
Uterine monitoring 117
Uterine septum, presence of 40
Uterine signs 65
Uterocervical junction 44f
Uterosacral ligament endometriosis 112
Uterus 21f, 23f, 30f, 38f, 41f, 45f
abdominal ultrasound images of 23f
adenomyomatous 37f
anterior posterior diameter of 23f
congenital abnormalities of 51
coronal view of 36f
demonstrates periodic contractile activity 128
detailed evaluation of 29
fundus of 160f
multiplanar of 192f
normal 27, 197, 198f
ultrasound morphology of 23f, 26f
retroverted 30f, 159f
structural abnormalities of 51
subseptate 39f
three-dimensional multiplanar of 7f
transverse section of 44f, 52
ultrasound 29
scanning of 55
unicornuate 38f
with linear echo 44f
V
Vagina, introitus of 18f
Vaginal canal 29
Vaginal progesterone 128
Vaginal septum 52
Vaginal stripe 29
Vaginal wall, insertion of 19f
Vanishing twin syndrome 156
Varicocele 164
classification of 167
ultrasound classification of 168t
Vas deferens 162
obstruction 178
Vasa deferentia, tuberculosis of 186
Vascular flow index 122f
Vascular index 122f
Vascular morphology, evaluation of 12
Veins of varicocele 167f
Viagra 51
Virtual organ computer-aided analysis 80, 88, 119, 193, 194f, 195
Vocal-imaging program 96
Volume contrast imaging 106
Volume sonography 191
W
Wall motion filter 9, 9f
Whirlpool sign on color Doppler 149f
Wolffian duct 102
×
Chapter Notes

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Ultrasound: Principles and ApplicationsChapter 1

Ashok Khurana
Chapter Outline
  • • Introduction
  • • Getting Started
  • • Physics of Transducer Choice
  • • Resolution
  • • How and Why Knobs That Should Be Used Often, Should Be Used
  • • Doppler Studies
  • • 3D and 4D Ultrasound
  • • Safety of Ultrasound
  • • Cleaning and Disinfecting the Probes
  • • Cleaning and Maintaining the Probe
  • • Disinfecting the Probe
  • • Conclusion
  • • Key Points
 
INTRODUCTION
While a basic knowledge of the principles of physics of ultrasound for the everyday practice of ultrasound is essential, a deep understanding may not be necessary. This is equally relevant to ultrasound in subfertility as well. What is more pertinent is a working knowledge of how the machine acquires, processes, and displays an image, and how the knobs and software improve the image. The aim is to obtain an image that quickly and reliably helps to answer the questions that are sought from the examination.
 
GETTING STARTED
In order to rapidly obtain optimal images on a daily basis, a three-step training strategy is what is often useful. This requires no knowledge or understanding of physics or the principles of ultrasound, and is an empirical approach to a quick start. The first step is an all-important and efficient shortcut of a hands-on demonstration of each knob and menu of the unit by an applications expert from the manufacturer. This should be followed by a hands-on routine on the patient with the applications expert standing by for a few days. The third step is working with the unit independently. As a final follow-up, it is wise, efficient, and inexpensive to recall the applications expert for 1 day on every 3 weeks or so for a few months, so that the technology in the unit is then optimally utilized. Follow-up exposure at workshops that demonstrate newer equipment and techniques by experts is useful for refining technique on an ongoing basis and learning newer applications. At this stage, a working knowledge of applied physics and applied mathematics becomes indispensable.
This chapter is a practical treatise of applied physics in the perspective of obtaining an optimal image. Pure physics has been dispensed with, since it would occupy unnecessary space in this book!
 
PHYSICS OF TRANSDUCER CHOICE
The choice of transducers in evaluating subfertile and indeed, all gynecological patients is based on the understanding of two equations in physics. The first is the relationship of frequency (f) and wavelength (l). Velocity (n) is a product of wavelength and frequency (n = lf). The second equation relates to ultrasound beam geometry. The depth (d) at which the transition of the beam takes place from the near field to the far field is given by the equation d = r 2/l, where r is the diameter of the circular transducer. 2Information from these relationships yields guidelines for tailoring transducer use.
zoom view
Figs. 1.1A and B: Images from the same patient using a (A) 5 MHz and a (B) 12 MHz transducer frequency. The inhomogeneous endometrium translates into an echogenic polyp. The indistinct posterior uterine wall on a higher frequency reveals an intramural fibroid. Thick-walled fluid loculi are evident posterior to the uterus on a high-frequency study.
The velocity with which a sound wave makes its way through any material is dependent on the density of the medium and is 330 m/s in air, 1,480 m/s in water, 1,589 m/s in muscle, and 3,500 m/s in bone.1 Ultrasound machines are now standardized and calibrated to use 1,540 m/s as the speed of sound in human tissue. Since the velocity is a product of wavelength and frequency (n = lf), the higher the frequency the shorter the wavelength. Frequency refers to the degree of highness or lowness of a tone. The loudness of a tone is referred to as intensity.
Low-frequency sound, such as the human voice, spread all over a room. High-frequency sound behaves like light and moves like a beam along a straight line. High-frequency ultrasound moves through tissue as a narrow beam and can be focused by acoustic lenses. This is possible in the nearer relatively narrow part of the beam. The depth equation (d = r 2l) implies that the wider the transducer face and the longer the wavelength (i.e. low frequency) the greater the depth. Resolution, however, depends on frequency; therefore, the higher the frequency the better the resolution.
The vast majority of scans in fertility patients are transvaginal scans. Since the transducer is closer to the region of interest than with transabdominal scans, a higher transducer frequency can be used. This greatly enhances resolution. Currently available transducers employ frequencies of up to 12 MHz, and the difference in resolution is remarkable (Figs. 1.1A and B). The trade-off with higher frequencies is of course, depth penetration of the beam, and these higherfrequency transducers have a limited resolution beyond a certain distance from the transducer. This limitation can be overcome by using a multifrequency transducer. Console keys permit a choice of low, middle, and high frequencies with the same transducer, enabling a great combination of resolution and depth. Transabdominal transducers have an advantage of a more panoramic field of view and a greater depth of penetration. These are therefore useful for identifying extraovarian adnexal structures and ovaries located at the pelvic brim. They are also indispensable for the assessment of associated abdominal lymph node disease, the suprarenal glands, kidneys, liver, abdominal peritoneal disease, and the pleura.
Transvaginal transducers are either mechanical or electronic array transducers. Mechanical transducers have one or more crystals that rotate or oscillate. Electronic transducers either have an array of crystals that are fired sequentially (phased array) or a set of crystals shaped to produce the sector image.2 A large number of variations on these three types are commercially available and the user is warned to sift through the hyperbole and mystique of pseudophysics in making a choice! In general, mechanical transducers are less expensive. They have a wide field of view but have poorer resolution in the near field. Focal zones are fixed. Electronic array transducers cost more but have the advantage of good near-field resolution and multiple focal zones.
 
RESOLUTION
Technically, resolution refers to the ability of the ultrasound unit to differentiate two different adjacent structures as two discrete different structures and not fuse them into a single structure. High resolution refers to a very short distance between these two structures, and low resolution refers to a larger distance between these structures.
3Axial resolution refers to the resolution along the path of the beam and is the most discerning resolution. This is also termed as the radial resolution or the range resolution. The shorter the pulse, i.e. the higher the frequency, the better the axial resolution.
Lateral resolution refers to resolution in the plane perpendicular to the plane of the beam. This is also called the azimuth plane. Beam quality and the size of side lobes determine lateral resolution. Side lobes are like skirts around the main lobe. “Main lobe” refers to the thin, round, and useful portion of the ultrasound beam. When such a beam passes through tissue and is reflected back, structures in the side-lobe zone are wrongly assigned to the main beam. These falsify and degrade the image. Lateral resolution can be improved by focusing the ultrasound beam. This is achieved by complex technology. From a practical viewpoint, arrows along the margin of the image indicate focused areas and these can be manually set to enhance the axial resolution at the depth of interest. This is a simple and extremely useful step in imaging but is largely neglected by most operators.
Axial resolution has a direct bearing on measurements. Since axial resolution is superior to lateral resolution, measurements are more accurate in the axial direction.
Elevation plane resolution refers to resolution in the slice thickness perpendicular to the axial plane. Good elevation plane resolution prevents superimposition of solid echoes over cystic areas in the slice thickness. This aspect of resolution is not electronically enhanceable and is achieved by a fixed acoustic lens. Limitations in this plane can be overcome only by operator's knowledge, skill, and vigilance.
 
HOW AND WHY KNOBS THAT SHOULD BE USED OFTEN, SHOULD BE USED
 
Depth, Magnification, and Zoom
Depth refers to the depth of tissues on display. It is wise to commence with a deeper region of interest to ensure that deeply located lesions are not missed. The depth is then reduced to a level that includes the region of interest. Typically, the depth should be adjusted so that the main area of interest ultimately occupies two-thirds of the screen.3 Reducing depth increases magnification in the near field and this improves resolution. All available pixels are used to form the image, and the image therefore improves.4 When the depth is too large it takes much longer for the transducer to receive echoes that return from deeper structures. This reduces the frame rate adversely. The zoom function allows magnification of one area on the monitor.3 The image appears larger. The resolution of the magnified area does not change. Zoom allows a better study of small areas of interest. Beyond a point in zoom mode, the pixels become too few and the image becomes grainy. The structure to be assessed in detail should, therefore, be imaged at as shallow a depth as possible.
Zoom selects a square area that is sized in real time before it is activated. Depth should be adjusted before zoom is selected.
 
Gain
Adjusting gain alters how the transducer perceives returning echoes. Increasing the gain brightens the display of the returning echo information. Gain may be adjusted for the entire image (overall gain), or at depth, known as time-gain compensation (TGC).3 Excessive gain makes the image too bright, and too little gain makes it dark (Figs. 1.2A and B). Excessive gain can make the picture bright with noise. This can obscure fluid echoes (Figs. 1.3A and B). Too little gain may create fluid echoes where no fluid exists (Figs. 1.4A and B). Many currently available medium- and high-end units now have a one-touch image optimization button that works automatically to fix the gain in an image.
 
Power Level
Power and gain are not the same. Power level refers to the amount of energy produced by the transducer.4 Gain amplifies returning waves. Increasing the power helps to image deeper structures. It may, however, produce secondary vibrations in tissues. This can produce ring-down artifacts (Fig. 1.5). Some sound energy may bounce back and forth within a cyst, resulting in reverberation artifacts (Fig. 1.6). Power that is too low produces a faint image.4 A weak signal gets mixed up with inherent noise in any equipment, and the result is a degraded image called snow4 (Figs. 1.7A and B). Power should, therefore, be adjusted to ensure a balance between snow and artifacts.
 
Tissue Harmonic Imaging
While conventional ultrasound uses the same frequency bandwidth for both the transmitted and received signals, tissue harmonic imaging (THI) uses a low frequency for transmitted signal and a high frequency for the received signal. When echoes return after being reflected, they do so not only at the basic frequency but also at multiples of the basic frequency. These higher frequency waves experience less attenuation, less scatter, and less side-lobe artifact and may generate clearer images, particularly at the interface between fluid and tissue. The trade-off is a slightly longer processing time. This is now routinely available on most ultrasound machines.
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Figs. 1.2A and B: Excessive gain obscures textural detail. There is excessive gain in the image (A) and the texture and margins of the endometrium are indistinct. The image (B) has optimal gain. The triple-layered proliferative phase morphology is distinct and no focal lesion is evident.
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Figs. 1.3A and B: Excessive gain can obscure fluid echoes. The image (B) was obtained at optimal gain settings and shows a small quantity of free fluid (<<<<) in the pouch of Douglas. The image (A) was obtained at high-gain settings and the fluid (<<<<) is largely obscured.
 
Dynamic Range
A clear cyst is best assessed with a minimum of gray levels. A wider range of grays better assesses solid lesions. Dynamic range permits this variation of gray scale (Figs. 1.8A and B). Dynamic range is the range in acoustic power between the faintest and strongest signals. Dynamic range controls the image contrast with increasing the dynamic range produces a grayer image.
 
Focal Zones
While doing ultrasound scan, one should constantly check the position of focal zone/s to ensure that they are at the depth of interest. Multiple focal zones, which create a long narrow beam, can be used to maximize lateral resolution over depth with the overall image quality will be improved throughout a static image. However, it is best to minimize the number of focal zones, when assessing moving structures as it may take more time to form a scan line and result in frame rate being reduced making the images disjointed.
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Figs. 1.4A and B: Inadequate gain can “create” fluid where none exists. In the image (A), a large fluid collection is evident in the right adnexa. Increasing the gain [image (B)] reveals an ovary with three antral follicles.
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Fig. 1.5: Increasing the power in order to image deeper structures may produce secondary vibrations in tissues. This can produce ringdown artifacts.
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Fig. 1.6: Reverberation artifact. High-level echoes are seen in the anterior extent of the urinary bladder. These may obscure solid lesions and also render an entirely fluid lesion echogenic.
 
Presets
Most current machines have settings that will adjust an image based on the anatomy being scanned. These presets are programmed to optimize images based on certain gain and power settings, focal zones, frame rates, and other settings.3 It is imperative that the applications expert checks factory set presets.
 
DOPPLER STUDIES
The term “Doppler” is loosely used to indicate blood-flow information. It is based on the Doppler effect wherein the returning frequency of waves is altered by the movement of a target. The moving target is red blood cells in 6the blood vessels in the region of interest. The returning signal is mapped in two ways.5 A map of the vessels can be obtained which can be superimposed on the gray-scale image. This is known as color flow mapping. This indicates direction and velocity of flow. The other method of mapping is known as the Doppler spectrum. This consists of a graph showing flow characteristics as a waveform (Fig. 1.9). These can then be quantified as velocities, ratios, and indices. The Doppler spectrum has an equivalent simultaneous audio signal as well which one learns to assess and analyze with increasing experience.6
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Figs. 1.7A and B: Inadequate power and excessive gain combine to create noise called snow (B). This creates medium-sized high-level echoes which obscure margins and fluid densities in the region of interest when comparing with the image obtained with optimum power and gain (A).
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Figs. 1.8A and B: Solid organs and lesions are best studied by a wide dynamic range setting. The image (A) was done at fluid-level settings and failed to reveal an 8 mm echogenic polyp in the endometrium. The image (B) was optimized with a wide dynamic range and clearly (<<<<<<<) shows an echogenic endometrial polyp.
Power Doppler is a newer form of flow imaging. It uses amplitude of scatter rather than a frequency shift to make a map of tissue flow. It is by its inherent nature far more sensitive to slow flow and therefore extremely useful in evaluating cyclical and pathologic changes in the female pelvis. Recent technical advances have made power Doppler directionality available as well. Doppler requires fine-tuning of sets as much as does gray scale.
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Fig. 1.9: Normal spectral Doppler image of a uterine artery with velocity-wave form.
 
Pulse Repetition Frequency or Scale
Adjusting the pulse repetition frequency (PRF) alters the sensitivity of Doppler for flow velocity (Figs. 1.10A to C). A lower PRF will result in a lower scale, more sensitive for slower flows, but may cause aliasing artifacts.3 Pulse repetition frequency should be ideally kept low when assessing vessels with low-velocity blood flow (e.g. ovarian stromal arteries) and be kept high when assessing vessels with high-velocity blood flow (e.g. uterine arteries).
 
Doppler Gain
Similar to the basic B-mode or two-dimensional (2D) image, gain may be adjusted for Doppler. Increasing Doppler gain will amplify returning signals, resulting in more color or a stronger spectral signal (Figs. 1.11A to C and 1.12A to C). As in B-mode imaging, too much gain will 8result in noise and artifact.7 Doppler gain should be set so that the vessel lumen is filled with color but there is no spill outside.
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Figs. 1.10A to C: Doppler pulse repetition frequency (PRF) settings: PRF settings should be kept low for vessels with low-velocity blood flow and high for vessels with high-velocity blood flow. This figure demonstrates the effect of PRF on velocity-wave form on an ovarian stromal vessel. Pulse repetition frequency is kept low (A), optimum (B), and high (C).
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Figs. 1.11A to C: Doppler gain (Power Doppler): Increasing gain will amplify the returning signal resulting stronger Doppler signal. The gain is kept low (A), optimum (B), and high (C). Too much gain in (C) results in artifact signals.
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Figs. 1.12A to C: Doppler gain (Pulse Wave): Increasing gain will amplify the returning signal resulting stronger Doppler signal. The gain is kept low (A), optimum (B), and high (C).
 
Baseline
Doppler can display flow either toward or away from the probe. Typically for color or spectral Doppler, the “zero” is in the center of the scale (or Y-axis). If you want to look only at the positive or negative flow, you can adjust the baseline up or down.
 
Wall Motion Filter
Filter allows adjustment of the signal so that lower velocities up to a certain number will not be displayed. A higher filter will reduce artifact but may limit visualization of lower flow (Figs. 1.13 and 1.14).3
 
Probe Angle
When red blood cells move perpendicular to the ultrasound beam, the transducer fails to detect them.4 Most machines, fortunately, will detect signals with even a minimal change beyond the perpendicular plane. When a vessel is anticipated to have slow flow, it should be imaged more vertically to the transducer.
 
Color Box Size
Large box sizes result in large amounts of data for processing. This slows the rate at which images are generated. Even if the frame rate is increased, this delay in generating an image is not easily overcome. Until large computers get incorporated into machines, and this will happen only if computers get cheaper, small color boxes should be used.4
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Figs. 1.13A and B: Wall motion filter (Power Doppler): A higher filter setting (A) limits artifacts, but limits visualization of lower flows, when compared with optimal setting (B).
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Figs. 1.14A and B: Wall motion filter (Pulse Wave Doppler): A higher filter setting (A) can affect pulse wave forms in comparison with optimal setting (B).
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Figs. 1.15A and B: Doppler sample volume (Doppler gate) as well as size and location: The width of the Doppler gate is kept 2 mm (A) and 3 mm (B). In figure (B), the Doppler gate is wider than the diameter of the artery and is placed partly over an adjacent vein and therefore picking up both arterial and venous flow.
 
Sample Volume Size and Position
The precise location of sample volume may affect the appearance of the Doppler spectrum and therefore may affect the results of spectral Doppler measurements. The relationship between the size of the sampling box applied with pulsed-wave Doppler and the size of the vessel is another important consideration (Figs. 1.15A and B). The average flow velocity within the center of a small vessel may be double to that of the average velocity across its full width due to turbulence near the vessel wall. It follows therefore that too small a sample box placed centrally over a vessel may overestimate the true flow. Whilst the diameter of the ascending uterine artery ranges from 2 to 5 mm in the nonpregnant patient, the spiral arteries at the level of the endometrium measure 1–2 mm in diameter. The diameter of the ovarian stromal vessels is also around 1–2 mm. This leaves little room for placement error considering the smallest volume box usually starting at 1 mm. The width of the volume box (Doppler gate) should be adjusted to the inner diameter of the vessels to be evaluated.
 
Doppler Angle (Angle of Insonation)
The angle of insonation between the Doppler beam and the direction of vessel is generally calculated by the observer who rotates a line so that it lies parallel to the direction of blood flow (Figs. 1.16A to C). A 5° error in the orientation of this line leads to an error in the velocity measurement of less than 2%, but this increases to 5.4% if the real angle is 30° and 12% when it is 60°. In this respect, the most accurate velocity measurements are made when the angle of insonation is as close to zero as possible but this is not always possible as it is dependent on the position and direction of the blood vessel being studied.
 
3D AND 4D ULTRASOUND
In this era of rapidly evolving technology, threedimensional (3D) and real-time three-dimensional (4D) ultrasound are emerging as necessary tools in the assessment of the pelvic viscera. As for other anatomical regions, freehand or automated devices may be used to acquire volume data for 3D evaluation of pelvic organs. In the freehand method, the transducer is manually moved through the region of interest and a position sensor registers the slice in space and time, or alternatively, image-based software may be built into the 3D package. The freehand method may be used on-line where the ultrasound unit manages all functions, or off-line where the analog video output is fed into a workstation. The transducer and attachments in the free-hand system are bulky and awkward to use particularly in the vagina. Most units currently in vogue are automated 3D probes. These are unit specific, more accurate, and easy to use. When these units are employed, an area of interest is chosen in the real-time 2D image, and the size and depth are outlined. A speed of acquisition is then selected and the acquisition activated. The transducer 11elements automatically sweep through the volume box chosen. The slower the speed of acquisition the higher the resolution. Resolution is highest in the plane of acquisition. The closer the plane of acquisition to the plane of study the better the resolution. The machine automatically receives and stores data from the region of interest and displays it in an orthogonal format. Images may then be rendered by various algorithms which rely on the difference between acoustic impedances at tissue interfaces and have been variably named by various manufacturers. In conventional ultrasound, the endometrium is visualized as a variably thick, linear, or ovoid structure in longitudinal, transverse, and oblique plane. The shape of the cavity is difficult to assess, as in the coronal plane. With 3D, the entire extent of the endometrium can be shown, including the corpus, fundus, cervix, and cornual areas.8 Coronal, sagittal, and transverse planes can be simultaneously displayed to permit more exhaustive viewing (Fig. 1.17).
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Figs. 1.16A to C: Doppler angle (angle of insonation): The angle of insonaton between the Doppler beam and the direction of vessel can affect the velocity measurements. At angles of insonation of 22° (A), 30° (B), and 68° (C), respectively, peak systolic velocity (PS) measurements from the same vessel were 21.33 cm/s, 27.11 cm/s, and 56.87 cm/s.
The images may be automatically zoomed in or out. Once acquired, the volume data can be reviewed by first rotating the planes to obtain standard anatomic orientations and then scrolling through the entire data to locate and characterize lesions, both focal and diffuse. Multiplanar orthogonal viewing offers virtually unlimited numbers of planes, and time constraints should not impede the endeavor to obtain information. In fact, the additional time spent on a 3D gynecologic scan is far less than on 3D obstetric scan because this time is spent not so much on data acquisition but in exploring the data obtained. The time factor would, of course, depend on the complexity of a case and on operator expertise. In experienced hands, the exercise takes no more than 3–10 minutes. Once identified in any one plane, the lesion can be marked by a center point, and this center point is automatically displayed in all three orthogonal planes. All or part of the studied volume can be automatically rendered and displayed as a single image or along with the orthogonal planes. The evaluation is enhanced by using volume measurements, niche mode studies, power Doppler studies, and a retrospective review of stored data. Unlike obstetric 3D, surface rendering is infrequently required in gynecologic 3D studies except in saline infusion sonohysterography where it often adds diagnostic information. The entire acquired data can be transmitted electronically to obtain second opinions, facilitate remote conferencing with experts, and can be efficiently stored for review and recall.
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Fig. 1.17: Three-dimensional multiplanar view of a uterus showing longitudinal plane (upper left), transverse plane (upper right), coronal plane (lower left), and rendered view of transverse plane (lower right).
The sagittal plane is selected for volume measurements and the other two planes for ensuring that the entire pathology is included in the measured area. Surface rendering permits contoural evaluation. Niche mode studies permit a virtual tour of the entire lesion and surrounding tissue along with evaluation of vascular morphology. Three-dimensional power Doppler permits an unsurpassed view of vascularity and permits quantification of neovascularization. Three-dimensional saline infusion sonohysterography enhances the sensitivity in select situations. Real-time 3D (4D) is useful in saline infusion sonohysterography for storing data sets, excluding the need for reinstillation, permitting multiplanar analysis, and allowing magnification of stored data during re-evaluation.
In patients who have not been sexually active, 3D data acquisition via the rectum, using an intracavitary transducer, can greatly enhance delineation of pelvic lesions and developmental abnormalities when compared to transabdominal 3D studies.
Three-dimensional data are basically a sum total of 2D data sets, and, as a logical consequence, a 3D study does not replace a 2D study. It, in fact, extends the wealth of information obtainable from an ultrasound scan. Principles of 3D ultrasound and its application in subfertility are further detailed in Chapter 13.
 
SAFETY OF ULTRASOUND
The Bioeffects Committee of the American Institute of Ultrasound in Medicine has repeatedly established based on the available evidence that there are no confirmed biological effects on patients and their fetuses from the use of diagnostic ultrasound evaluation and that the benefits to patients exposed to the prudent use of this modality outweigh the risks if any.1 It is wise, however, as for any medical test, to perform the examination only when clearly indicated. The operator performing the examination should exercise due care to use appropriate energies and 13keep a track of the duration of the study in order to comply with the “as low as reasonably achievable” (ALARA) principle. This principle simply states that the use of technicalities should be optimized to obtain quality images with frequencies, power, and duration.
 
CLEANING AND DISINFECTING THE PROBES
 
Why is It Required?
Bacterial contamination was observed on 98.8% of transvaginal probes. Microbial analysis revealed 36 different species of bacteria, including skin and environmental bacteria as well as pathogenic bacteria such as Staphylococcus aureus, enterobacteriaceae, and Pseudomonas spp.
 
CLEANING AND MAINTAINING THE PROBE
Cleaning means removing the visible contaminants from the probe. The probe must be cleaned, each time it is used. After every examination, ensure the acoustic coupling gel is completely wiped off the transducer. Transducers should not be left soaking in gel. Remove any transducer cover, biopsy guides, or protective devices from the transducer. When not in use it should be stowed in the relevant probe slot and should be covered to avoid its exposure to dust. Do not kink, tightly coil, or apply excessive force on the probe cable. Do not apply excessive bending or pulling force to the transducer cable. Do not let transducer cables dangle loosely from the ultrasound system where they might be caught in the casters while moving. Do not drop transducers into holders or disinfectant containers with lens face down.
Use a moistened soft cloth or wipe to remove any remaining contaminants that remain on the transducer or cable. Do not reuse cloths or wipes. Soap, detergents, or enzymatic cleaners should be used in accordance with the manufacturer's instructions. Use a lint-free soft and clean dry cloth or wipe to thoroughly dry the transducer and cable. Cleaning products should be as close to neutral pH as possible. Any gel, cleaning or disinfectant products containing surfactants, methanol, ethanol, benzyl or methyl alcohol, bleach, methyl or ethyl paraben, polyethylene glycol, mineral oil, lubricant oil, oil-based lotions, acetone, ammonia, anhydrous ammonia, iodine, iodine compounds, and acids with 5 pH or greater may damage or discolor your transducer. Though thus cleaning with the damp cloth or readily available wipes do not clean the probes actually. Not only the probe head, even the handle is a potential source of bacterial contamination.
Automated disinfection had a statistically significantly higher success rate of 91.4% (106/116) compared with 78.8% (89/113) for manual disinfection (P = 0.009).
The risk of contamination was increased by 2.9-fold when disinfection was performed manually [odds ratio, 2.9 (95%CI, 1.3–6.3)].9
 
DISINFECTING THE PROBE
When performing high-level disinfection of ultrasound probes with the (trophon® EPR) dedicated disinfectants supplied by the manufacturer, it is not necessary to disconnect the probe from the ultrasound system. However, the probe should be inactive (not selected) during the disinfection cycle. If rinsing is required, use caution not to expose the system connector to moisture or liquids. If the possibility of cross-contamination or exposure to unhealthy or nonintact skin exists, then high-level disinfection should be performed. Good hand-hygiene practice is highly recommended to help further reduce the risk of cross-contamination. A validated high-level disinfection process combined with the use of a sterile gel and a transducer cover is an accepted method of infection control for ultrasound transducers. Where possible, use of an automated system for disinfection of ultrasound transducers that is FDA-cleared and provides a consistent disinfection process and minimizes the risk of exposure to disinfectants is recommended. Do not immerse transducers deeper than permissible levels. Never immerse the connector or adapter into any liquid. The disinfection of the probe is essential when probe is used for any ultrasound-guided invasive procedures and also when the patients with vaginal infections have been examined.
 
CONCLUSION
A basic knowledge of ultrasound principles makes it simple to obtain optimal images in patients who have infertility.
 
KEY POINTS
  • Electronic array transducers cost more but have the advantage of good near-field resolution and multiple focal zones
  • 14Low frequency is good for penetration, and high frequency is good for resolution
  • Resolution is ability to separate and define two different adjacent structures
  • Axial resolution is superior to lateral resolution; measurements are more accurate in the axial direction
  • Depth, magnification, and zoom should be often used to optimize images
  • Power defines the energy produced by the transducer
  • Gain refers to the amplitude of returning beam
  • Dynamic range defines the number of gray shades and should be higher for examination of solid tissues
  • Tissue harmonics improves resolution but reduces frame rate
  • Power Doppler is more sensitive to low-velocity flows
    • For Doppler studies, low PRF for low-velocity vessels and high PRF for high-velocity vessels
    • Doppler gains should be so set that the vessel lumen is filled with color but there is no spill outside
    • Wall filter should be set not to cut down diastolic (low velocity) flows
    • When a vessel is anticipated to have slow flow, it should be imaged more vertically to the transducer
    • Small color boxes should be used
  • 3D ultrasound: Coronal, sagittal, and transverse planes can be simultaneously displayed to permit more exhaustive viewing
    • Three-dimensional study does not replace a 2D study
    • Exercise due care to use appropriate energies and keep a track of the duration of the study in order to comply with the ALARA principle
REFERENCES
  1. Eik-Nes SH. Physics and instrumentation. In: Wladimiroff JW, Eik-Nes SH (Eds). Ultrasound in Obstetris and Gynecology: European Practice in Gynaecology and Obstetrics, 1st edition. Elsevier Limited;  Philadelphia: 2009. pp. 1-20.
  1. Kennedy A, Peterson CM. Transvaginal sonography in reproductive endocrinology and infertility. In: Carrell DT, Peterson CM (Eds). Reproductive Endocrinology and Infertility: Integrating Modern Clinical and Laboratory Practice, 1st edition. Springer;  New York: 2010. pp. 545-65.
  1. Markowitz J. Probe selection, machine controls and equipment. In: Carmody KA, Moore CL, Feller-Kopman D (Eds). Handbook of Critical Care & Emergency Ultrasound, 1st edition. McGraw Hill;  New York: 2011. pp. 25-38.
  1. Peisner DB. Applied physics: selecting and adjusting the equipment. In: Timor-Tritsch IE, Goldstein SR (Eds). Ultrasound in Gynecology, 2nd edition. Elsevier Limited;  Philadelphia: 2007. pp. 9-32.
  1. Khurana A. Ultrasound in obstetrics. In: Misra R (Ed). Ian Donald's Practical Obstetric Problems, 6th edition. BI Publications Pvt. Ltd.;  New Delhi: 2007. pp. 62-88.
  1. Khurana A. Female genital system. In: Mani S (Ed). Textbook of Abdominal Ultrasound, 1st edition. Jaypee Brothers Medical Publishers;  New Delhi: 2009. pp. 217-98.
  1. Martin K. Properties, limitations and artefacts of B-mode images. In: Hoskins P, Martin K, Thrush A (Eds). Diagnostic Ultrasound: Physics and Equipment, 2nd edition. Cambridge University Press;  New York: 2010. pp. 64-74.
  1. Khurana A. The endometrium. In: Khurana A, Dahiya N (Eds). 3D and 4D Ultrasound: A Text and Atlas, 1st edition. Jaypee Brothers Medical Publishers;  New Delhi: 2004. pp. 166-98.
  1. Buescher DL, Möllers M, Falkenberg MK, Amler S, Kipp F, Burdach, Klockenbusch W, Schmitz R. Disinfection of transvaginal ultrasound probes in a clinical setting: comparative performance of automated and manual reprocessing methods. Ultrasound Obstet Gynecol. 2016;47:646-51.