Ultrasound Physics Garringer and Aliison Dr. Muhammad Bin Zulfiqar

1. 3Ultrasound
DR. Muhammad Bin Zulfiqar
PGR-FCPS III SIMS/SHL
GRAINGER & ALLISON’S DIAGNOSTIC RADIOLOGY

2. • FIGURE 3-1 ■ Harmonic
imaging. (A)
Conventional grey-
scale imaging through
the liver at the porta
hepatis. (B) In harmonic
mode (note the diff
logo on the left) the
image has much higher
contrast and the portal
vein is more clearly
delineated. PV = portal
vein.

3. • FIGURE 3-2 ■ The A-scan. The A-scan is a trace
indicating echo intensity of tissue with depth. In this
example, there is a fluid space from 6 to 10 cm, from
which no echoes arise. Tissues superficial and deep to
this produce echoes of varying intensities and there is a
particularly strong echo from the skin (0–5 cm). The
time gain compensation (TGC) curve is also shown.

4. • FIGURE 3-3 ■ M-mode trace. The echo intensity is displayed as
brightness and the trace is swept across the screen so that the x-
axis represents time. This is an M-mode echocardiogram showing
the rapid movement of the valve apparatus with thicker proximal
and distal moving bands representing the ventricular walls. There is
a small pericardial effusion separating the epicardium of the right
ventricle from the chest wall.

5. • FIGURE 3-4 ■ Mechanical transducer. (A) Diagram of a
mechanical endoprobe transducer. A motor rotates the
transducer assembly to sweep out a circular path. (B) An
intravascular image of a coronary artery showing the
endothelium as a bright inner layer interrupted by an
atheromatous plaque (arrowhead). T = transducer. (Figure
B courtesy of Professor Ton van der Steen, Erasmus Medical
College, Rotterdam, the Netherlands.)

6. • FIGURE 3-5 ■ Phased array. (A) Diagram illustrating steering an
ultrasound beam with a phased array transducer. The delay lines
introduce small timing differences in the pulses driving the
elements so that those at one end are fired earlier than those
further along the array. This has the effect of steering the beam
away from the centre line, rather as if the transducer face had been
tilted. (B) Right lobe of liver taken with a phased array showing the
advantage of the small footprint in accessing the portions that lie
high under the diaphragm, especially segment 8. 7 and 8 =
segments 7 and 8, D = diaphragm.

7. • FIGURE 3-5 ■ Phased array. (A) Diagram illustrating steering an
ultrasound beam with a phased array transducer. The delay lines
introduce small timing differences in the pulses driving the
elements so that those at one end are fired earlier than those
further along the array. This has the effect of steering the beam
away from the centre line, rather as if the transducer face had been
tilted. (B) Right lobe of liver taken with a phased array showing the
advantage of the small footprint in accessing the portions that lie
high under the diaphragm, especially segment 8. 7 and 8 =
segments 7 and 8, D = diaphragm.

8. • FIGURE 3-6 ■ Linear array. Diagram of a linear array
showing the formation of one ultrasound beam by
triggering a set of elements at one end of the probe. The
next beam would be formed by the adjacent or partially
overlapping set of elements so that the beam is swept
along the transducer face to give a rectangular image.

9. • FIGURE 3-7 ■ Breast carcinoma. A
heterogeneous mass (arrowheads) with irregular
margins and distal shadowing are characteristics
of a breast cancer. This image was taken with an
18-MHz linear array probe. The rectangular
format is particularly suitable for superficial
structures.

10. • FIGURE 3-8 ■ Convex array.
(A) Sagittal image of a
normal upper abdomen
taken with a 6-MHz curved
array. (B) Transvaginal
image of a uterus with a
fibroid (arrowheads) taken
with a tightly curved 9-MHz
array. The convex format is
a compromise between the
footprint requirements of
sector and linear probes
and has the advantage of
giving a wide field of view
for deeper structures. E =
endometrium, GB =
gallbladder, IVC = inferior
vena cava, L = liver, PV =
portal vein.

11. • FIGURE 3-9 ■ Ultrasound beam shapes. The shapes of the ultrasound
beam from four transducers are indicated. All are of the same frequency
(3.5 MHz). The beam from the 10-mm probe in (A) has a complex region
close to the transducer face, then a mid-portion with near parallel sides,
before the beam spreads out in the far field. The white lines indicate the
half-power limits. Increasing the probe diameter (B) improves the overall
beam width. In (C), weak focusing has been added by concave shaping of
the crystal. This further improves the beam shape in the focal zone but
causes it to spread more severely further out. This
would be a useful compromise for general abdominal imaging Stronger
focusing (D) exaggerates these effects, producing a fine beam but only
over a short distance. This would be useful for imaging superficial
structures.

12. • FIGURE 3-10 ■ Electronic
focusing. Diagram to
illustrate the principle of
electronic focusing. The
delay lines are set to send
the pulses from the outer
elements fractionally ahead
of those from more central
elements. The resulting
interference patterns
accentuate the central part
of the beam and cancel the
off-axis portions. The effect
is greatest at the focal zone.

13. • FIGURE 3-11 ■ Ultrasound beam plot. The complexity and marked
deviation from the ideal of a practical diagnostic ultrasound beam
is shown in this intensity plot. The beam is very complex for the first
few millimetres from the transducer face (on the left of the figure)
but improves towards the focal zone where it reaches an effective
diameter of a few millimetres before spreading out again in the far
field. Unfortunately, some ultrasound energy is also sent out as side
lobes at angles to the main beam, further complicating the effective
beam shape. These divergences from the ideal narrow shape limit
both the spatial and contrast resolution of ultrasound images.
(Beam plot kindly supplied by Dr Adam Shaw of the National
Physical Laboratory, Teddington.)

14. • FIGURE 3-12 ■ Beam width artefact. In this
ultrasound examination of the bladder, the
intense echoes from gas in a loop of bowel
(arrow) have spread across into the urine
(arrowhead). This artefact results from the
finite width of the ultrasound beam.

15. • FIGURE 3-13 ■ Velocity artefact from a silicone prosthesis.
This unfortunate young man developed a second teratoma
having had an orchiectomy on the right with insertion of a
prosthesis. The depth of the prosthesis is depicted as being
greater than that of the tumour-bearing testis, in conflict
with the clinical impression, which was the reverse; this
geometric distortion is the result of the lower speed of
sound in the prosthetic material that delays the echoes so
that they are plotted as lying deeper than they really are. P
= prosthesis, T = teratoma.

16. • FIGURE 3-14 ■ Beam dispersion by fat. Deep
to this fatty renalhilum, the retroperitoneal
tissue layers (arrowheads) are less clear than
adjacent tissue planes because the hilar fat
has defocused the beam. S = renal sinus.

17. • FIGURE 3-15 ■
Reverberation artefacts. (A)
Multiple internal reflections
within tissue layers give rise
to false repeated signals,
which are most obvious
where they fall over echo-
free fluid spaces such as the
gallbladder (arrowhead). (B)
Whereas the intima–media
layer is well delineated at
the deeper surface of this
normal common carotid
artery (arrow), the
superficial laye is partly
obscured by reverberation
artefact (arrowheads). C =
common carotid artery.

18. • FIGURE 3-16 ■ Mirror image artefact. One of the
structures in the liver such as this cyst is mirrored
at the air–pleura surface and appears in the
position of the lower lobe of the lung, producing
the ‘percentage sign’ artefact (arrowhead). When
this surface is absent, for example when a pleural
effusion is present, the effect does not occur. C =
cyst.

19. • FIGURE 3-17 ■ Acoustic shadowing. The dark
band (arrowheads) deep to the gallstones
(arrow) is an example of shadowing produced
by a combination of high absorption and
reflection. GB = gallbladder, K = kidney.

20. • FIGURE 3-18 ■ Increased sound transmission.
The echoes (arrowheads) deep to this liver cyst
(arrow) appear brighter than those from the rest
of the liver; this is because the cyst fluid
attenuates less than the solid liver and so signals
from beyond it are relatively overamplified.

21. • FIGURE 3-19 ■ Congested liver. In heart failure,
the liver may become congested with extra fluid.
The separation of the reflectors reduces the liver
echoes so that it becomes less echogenic than
the kidney. In addition, the vascular markings are
accentuated because they are not affected. GB =
gallbladder, K = kidney.

22. • FIGURE 3-20 ■ Fatty liver. The multiple
interfaces between fatladen liver lobules and the
surrounding watery tissues give these fatty liver
high-intensity echoes which can be seen as
increased contrast with the adjacent renal cortex
(compare Fig 3-19). K = kidney, L = liver.

23. • FIGURE 3-21 ■ Laminar flow. Diagrammatic
representation of the concentric layers of
blood flowing at different velocities, with the
highest velocity in the centre of the vessel.

24. • FIGURE 3-22 ■ Parabolic velocity profile. The
fastest flow is in the centre of the vessel, with
a progressive reduction in velocity towards the
vessel wall.

25. • FIGURE 3-23 ■ Plug flow. The flow velocities
are almost equal across the whole vessel
diameter.

26. • FIGURE 3-24 ■ Normal common femoral
artery flow. There is triphasic flow with early
diastolic flow reversal.

27. • FIGURE 3-25 ■ Low-resistance flow. The flow is
continuously forward throughout the cardiac
cycle, with moderately high flow throughout
diastole. There is very little low-velocity flow
throughout most of the cardiac cycle (compare
with Figs 3-26 and 3-27).

28. • FIGURE 3-26 ■ Moderate spectral
broadening. The spectrum throughout late
systole and most of diastole has been filled in
by an increased range of blood flow velocities.

29. • FIGURE 3-27 ■ Complete spectral broadening.
There is now complete filling of the spectrum
throughout the cardiac cycle, with brief
periods of simultaneous reverse flow during
systole.

30. • FIGURE 3-28 ■ Turbulence beyond a stenosis.
There is highvelocity flow beyond this carotid
artery stenosis, with simultaneous forward and
reverse velocities. The internal : common carotid
peak systolic velocity ratio is 2.14, indicating a
haemodynamically significant stenosis.

31. • FIGURE 3-29 ■ Close-up view of the spectral trace. The
spectral trace is composed of increments on both the
vertical and horizontal axes. The horizontal increments
indicate the individual time intervals during which Doppler
sampling occurs, 20 ms in this example. The vertical
increments indicate increasing frequency. The brightness of
the trace within each pixel indicates the number of blood
cells moving with that velocity at that time.

32. • FIGURE 3-30 ■ Dependence of RI on heart
rate. The value of enddiastole is relatively
high if the heart rate is rapid (1). A slower
heart rate allows a greater time for diastolic
deceleration, leading to a lower end-diastolic
velocity (2) and a higher resistance index. V =
velocity, T = time.

33. • FIGURE 3-31 ■ (A) Spectral
distribution in plug flow. A
very narrow band of
velocities is present
throughout the cardiac
cycle in this artery. (B)
Spectral distribution in
parabolic flow. The slower
flow in this wide portal
vein gives rise to a wide
range of velocities during
each time interval.

34. • FIGURE 3-32 ■ Colour Doppler. Fetal circle of Willis. The
flow in the right middle cerebral artery, the left anterior
communicating artery, the left posterior communicating
artery and the right posterior cerebral artery is displayed in
red as the flow is towards the transducer. The flow in the
other vessels is passing away from the transducer and is
therefore represented by blue.

35. • FIGURE 3-33 ■ Power Doppler display of a right
kidney. This extended field of view shows the
flow in the inferior vena cava, main renal vessels
and the intrarenal vessels right out to the
capsule. The loss of directional information
prevents the differentiation of arteries from
veins.

36. • FIGURE 3-34 ■ Vessel wall definition. Normal
carotid artery. The power Doppler display colour
intensity decreases near the vessel wall owing to
the volume elements lying partly outside the
vessel. This gives an apparent improvement in
the definition of the intimal surface.

37. • FIGURE 3-35 ■ (A) Colour
Doppler with 90° beam-
to-vessel angle. There is
poor flow detection and
direction ambiguity
throughout the vessel. (B)
Power Doppler display
with 90° beam-tovessel
angle. As direction
information is not used in
the display, uniform flow
detection is achieved
throughout the vessel
segment.

38. • FIGURE 3-36 ■ Calculation of time-averaged
mean velocity. The weighted mean velocity
during each time interval has been calculated.
The average of these throughout the trace is a
close estimate of the true mean velocity.

39. • FIGURE 3-37 ■ Superior
mesenteric arterial trace.
(A) Normal: the vessel
has remained within the
range gate throughout
the cardiac cycle, giving a
satisfactory Doppler
trace. (B) Artefactually
abnormal SMA trace: the
gate is too small and is
misplaced so that the
vessel moves out of the
range gate during
diastole, giving rise to the
false appearance of
increased vascular
resistance.

40. • FIGURE 3-38 ■ Dependence of velocity error on
beam-to-vessel angle. The error in velocity
calculation is less than 10% for angles of less
than 50°. There is a rapid and unacceptable rise in
the error rate for angles greater than 70°.

41. • FIGURE 3-39 ■ Mean peak velocity
calculation. Automatic software has
calculated the peak instantaneous velocity for
each time interval throughout the cardiac
cycle. The mean of these values is the mean
peak velocity.

42. • FIGURE 3-40 ■ Aliasing.
(A) The frequencies
above the Nyquist limit
have appeared on the
wrong side of the
baseline. (Note that no
beam-to-vessel angle has
been set so the velocity
values are uncorrected
and therefore
meaningless.) (B) The
aliased peaks have been
electronically transposed
to their correct locations.

43. • FIGURE 3-41 ■ Inappropriately high wall
filter. The wall filter has been set at 200 Hz
and has removed all the low-velocity
information in this venous study.

44. • FIGURE 3-42 ■ Artefactual flow reversal on colour flow
imaging. Flow within the splenic vein (arrowheads) is from
left to right. In this transverse epigastric image, on the left
side of the image the flow is towards the curvilinear array
probe and is therefore displayed as red. On the right side,
the flow is away from the probe and is therefore displayed
as blue. There is a thin black area at the point where the
colour changes, indicating a true flow direction reversal,
rather than aliasing, as the cause of the colour change. A =
aorta, I = inferior vena cava.

45. • FIGURE 3-43 ■ True and artefactual colour flow reversal. The high-
velocity jet through this portal vein stenosis has given rise to
aliasing. The aliased green signal passes through yellow to red in a
continuous gradation (in the vertical limb of the vessel in this
display). The coarse vortex within the poststenotic dilatation gives
rise to a true area of flow reversal, colour-coded blue, which is
separated from the forward flow red component by a black margin.

46. • FIGURE 3-44 ■ Contrast-enhanced ultrasound (CEUS) of a
haemangioma. The baseline transverse section through the right
lobe of the liver (A) shows a subtle lesion (arrowheads). The system
was then reset to display the contrast image on the left (using
contrast pulse sequences) and the B-mode image on the right, both
with low mechanical indices. SonoVue (2.4 mL) was given IV and the
haemodynamics of the flow through the lesion observed in real
time. At 11 s after injection (B), the lesion showed peripheral
nodular enhancement (arrowhead). By 22 s (C), the lesion shows
centripetal filling and by 41 s (D) it had almost completely filled, a
pattern characteristic of a haemangioma. The liver and the kidney
also show enhancement. The ability to provide a firm diagnosis of a
benign mass as soon as it was detected is a benefit of CEUS. K =
kidney.

47. • FIGURE 3-44 ■ Contrast-enhanced ultrasound (CEUS) of a
haemangioma. The baseline transverse section through the right
lobe of the liver (A) shows a subtle lesion (arrowheads). The system
was then reset to display the contrast image on the left (using
contrast pulse sequences) and the B-mode image on the right, both
with low mechanical indices. SonoVue (2.4 mL) was given IV and the
haemodynamics of the flow through the lesion observed in real
time. At 11 s after injection (B), the lesion showed peripheral
nodular enhancement (arrowhead). By 22 s (C), the lesion shows
centripetal filling and by 41 s (D) it had almost completely filled, a
pattern characteristic of a haemangioma. The liver and the kidney
also show enhancement. The ability to provide a firm diagnosis of a
benign mass as soon as it was detected is a benefit of CEUS. K =
kidney.

48. • FIGURE 3-45 ■ Elastography. The echogenic
lesion in the left pane has the appearances of a
haemangioma (arrowhead). In the elastogram in
the right pane, it is seen as a blue region against
the liver’s mainly green coloration; this indicates
that the lesion is stiffer than the liver.