3D/4D Ultrasound in Obstetrics, Gynecology and Infertility Narendra Malhotra, Kuldeep Singh
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Instruments and Scanning Techniqueschapter 1

 
HISTORY
  • A 3D machine uses different probes
  • The probe captures images in the 3 planes simultaneously
  • Scanning may be done by free hand technique
  • Automatic 3 plane scan by most machines
  • 1980's first 3D rendering pictures of fetus
  • 1990's section reconstruction as the orthogonal planes
  • 1991 volume rendering as translucent display
  • Computers to obtain images
  • 1993 3D with defocusing lens without computer
  • 1994 first surface rendered fetal images
  • 1996 real time ultrasound beam tracing without a computer.
 
BASICS OF 3D ULTRASOUND
  • 3D is volume visualization
  • Aim is to represent morphology of organ of interest in 3D space.
 
DEFOCUSING LENS METHOD (Flow chart 1.1)
  • Volume imaging or thick slice 3D imaging
  • Simple and lens expensive
  • Convex or linear probe with a defocusing lens on its surface
  • The lens diverges the beam
  • Resolution is poorer
  • All echoes within the diverged ultrasound beam are displayed
  • Hence a volume image is obtained
  • With probe solution a good visual perception of 3D structure is possible
    zoom view
    Flow chart 1.1: 3D imaging
    2
  • Sometimes high quality surface rendered images can also be possible
  • Real time observation of fetus possible
  • Difficult in obese patients and with less liquor
  • This is also sometimes referred as “Pseudo 3D” and alsmost all 2D machines can have this feature with joint one defocused lens mounted on a 2D probe.
 
VOLUME VISUALIZATION AND COMPUTER PROCESSING
  • Presently this is the method of choice for 3D and 4D imaging
  • It involves:
    • 3D data acquisition
    • 3D data sets construction
    • 3D data display on a 2D screen.
 
Acquisition of 3D Data
  • Movement of ultrasound probe
  • Large number of consecutive tomograms
  • Parallel fan like scanning
  • Free surface scanning and rotation
  • Automatic 3 D probes having a built in convex/sector probe which brings in a fan like manner
  • Tomogram is digitized
  • Fed into computer.
 
Construction of 3D Data Sets
  • Data as many tomograms
  • These data are reconstructed into 3D data sets
  • 3D data sets are fed into computer
  • Interpolation and filtering to improve data quality
  • Now data is as volume elements or voxels
  • Each voxel is assigned a gray value or brightness value.
 
Display of 3D Data on a 2D Plane (Fig. 1.1)
  • Presented on a 2D display (Monitor)
  • Section reconstruction
  • Surface rendering
  • Volume rendering.
 
Section
  • Normally a 3D set is multiplanar representation
  • Information from all three planes that cut the voxel
  • Orthogonal to each other
  • These planes can be shifted and rotated
  • Like anatomic cross section pictures
  • Does not produce a 3D impression of that object.
 
Surface Rendering
  • Objects are extracted from voxel
  • Projected on a 2D plane3
    zoom view
    Fig. 1.1: Basics of a 2D probe with image as compared to a 3D probe with image
  • Surface rendered display
  • 3D data set can be rotated to view or change direction
  • Image is shaded to give a 3D appearance (done by dept cueing) (near components bright distant image components darker).
 
Volume Rendering
  • 3D data projected in 2D plane directly
  • Volume ray tracing method
  • A variety of images may be obtained
  • A still image may not have a 3D appearance
  • 3D appearance is seen by rotation.
 
REAL TIME 3D OR 4D IMAGING
  • Real time 3D is now possible with good frame rate
  • 3D volume can be imaged live with visualization of fetal movements and expressing (Yawning, etc.)
  • Also helpful in fetal echocardiography
  • 3D data acquisition and calculation and projection is done simultaneously
  • With real time 3D (4D) the viewing direction limited to that of the probe.
 
KRETZ (VOLUSON) TECHNIQUE (FIGS 1.2 TO 1.4)
  • Kretz technique Austria were the first to make available of the voluson 3D systems
  • Voluson 530D commercially available systems in late 1990's4
    zoom view
    Fig. 1.2A and B: 3D machine with probes
    zoom view
    Fig. 1.3: Transabdominal 3D probe
    5
    zoom view
    Fig. 1.4: Transvaginal 3D probe
  • Rapid developments have occurred in the last few years in hardware and software
  • Voluson 730 Pro with harmonics, stic, inversion, etc. features are new available commercially as state of the art ultrasound machine.
 
HOW TO DO 3D STEP BY STEP?
  • Proper equipment
  • Adequate training
  • Patience and sound knowledge
  • Select transducer for organ of interest (transabdominal, transvaginal, transrectal)
  • Liberal use of gel
  • Get a proper window by a 2D scan with the 3D probe. Ask patient to hold breath for 3D volume acquisition
  • If mechanical probe hold at area of interest 4 to 10 second
  • Free hand scanning with defocusing lens probe
  • Move probe slowly with small step size
  • Use smooth sweep with uniform velocity without tilling or twisting
  • Automatic probe to be hold with the target in view till the machine completes all three planes sweep
  • View planar slices (orthogonal planes)
  • Reorient anatomy by rotation (x, y or z)
  • Identify area of interest, review volume data
  • View the rendered image, free from artefacts
  • Ray costing, acquire nest volume if desired
  • Maximum or minimum projection6
  • Surface rendering
  • Threshold settings, use inversion, stic or whatever needed
  • Adjust view, use electronic scalpel, vocal if needed
  • Save and store
  • Save in rotation mode
  • Save as volume or surface rendered image
  • Print hard copy and archive images with volume
  • Save as AVI file on hard disk or as CD Rom or on attached VCR
  • View as 4D for fetal and same AVI 4D.