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Chapter 2: Ultrasonography: physics and principles
Normal
Incident ray
θ
1
Fig. 2.4. Reflection, transmission, and refraction of sound waves.
Reflected ray
Interface
θ
2
Transmitted (refracted) ray
From sound to image
The creation of an image from sound is achieved in three steps –
producing a sound wave, receiving echoes, and interpreting
those echoes.
Producing a sound wave
The transducer (probe) is a device that converts electrical
signals into ultrasound waves at the desired frequency and
vice versa (Figure 2.5). These sound waves bounce off body
tissues and make echoes. The part of the transducer that
converts electrical impulse to ultrasound and vice versa is
known as the crystal or the active element. Transducers are
made from materials that exhibit the property of piezoelectricity (a Greek word, piezein: to squeeze or press).
Piezoelectricity is the ability of some materials to change
their dimensions when an electric field is applied to them
and conversely to develop electrical charges when they are
deformed. Medical transducers are made from a synthetic
ceramic material (lead zirconate titanate) that is fired in a
kiln and therefore can be model ed into almost any shape.
To establish an electrical connection, thin layers of silver are
evaporated onto the surface to form electrodes. This device
will expand and contract when a voltage is applied to it but
will also create a voltage when subjected to a small pressure
such as a returning echo might exert. Obviously the voltages
generated when receiving echoes are normally much smaller
than those applied to create the ultrasound wave in the first
instance. The material on the face of the transducer is usually
a rubbery coating, a form of impedance matching to enable
the sound to be transmitted efficiently into the body. Thus,
transducers in simple terms are metallic electrodes attached to
a piezoelectric substance that converts electrical energy into
acoustic energy when it is “switched on” and acoustic energy
to electrical energy when it is “listening.”
There are different types of transducers. All types have
advantages and disadvantages and no single transducer can
perform all functions. There are several classification of
transducers. A linear transducer is a rectangular-shaped
probe in which the elements are arranged in a line and
involves a large number of parallel scan lines, whereas a sector
(annular) transducer has the elements in the form of ring
shape and arranged concentrically. This results in a series of
lines that all originate from a single location and travel outward in a pie-shaped wedge. Linear arrays are usually cheaper
than sector scanners but have wider skin contact and therefore make it difficulttofocusonsomeorganssuchasthe
heart. The linear arrays use a firing sequence of alternate
groups of 3–4 elements. A curved array is similar to a linear
array except that the image created is a sector type. A linear
phased array applies voltage pulses to all elements as a group
but with small time differences (phasing). The time difference
is chang ed each time so that the sound pulses will be sent out
in different directions. A phased array results in a sector
image and has several advantages such as being smaller in
size, the fact that the flat face allows better gel coupling, and
the fact that the electronics create high frame rates compared
with annular arrays. The main disadvantage is the poor
superficial visualization because true phased arrays come to
a point in the midline of the probe as the beam is made up of
the whole group of elements. This can be overcome by
exploiting the principles of p hased and linear arrays to form
a hybrid called vector phased array. Some transducers operate
in a burst-excited mode that converts 1–2 cycles of alternating voltage bursts into alternating pressure, resulting in a
sound pulse. It then receives echoes and converts them into
voltage bursts. Others use a shock-excited mode. These create
ultrasound pulses and also receive echoes and convert them
into voltage bursts. The most common mechanical transducers are the oscillating probes and the rotating probes
driven by a motor. These use a combination of single-element
oscillation, multiple-element rotation, or a single element and
set of acoustic mirrors to generate the sweeping beam for 2D
mode. Mechanical probes are subject to wear but produce
excellent images. On the other hand, electrical probes are not
subject to wear but are generally more expensive.
Most transducers are only able to emit one frequency
because the crystals have a certain inherent frequency.
Accordingly, most ultrasonographers use multiple probes.
Multifrequency probes
multiple crystals with different frequencies and a specific frequency is selected by the user. They are convenient because they
save time in not having to switch to different probes.
Nevertheless, they do have slower frame rates and therefore
are useful only for imaging static structures.
do exist, however. These probes have
Receiving the echoes
The return of the sound wave to the transducer results in the
same process that it took to send the sound wave, but in reverse.
The return sound wave vibrates the transducer. The transducer
turns the vibrations into electrical pulses that travel to the
ultrasonic scanner where they are processed and transformed
into a digital image.
Forming the image
The ultrasound scanner must determine two things from
each received echo. First, how l ong did the echo take to be
13
Section 1: Imaging techniques
Acoustic
Transmitting
crystal
Crossed-beam
sound path
barrier
Receiving
crystal
Case
N
Beam from group of elements
compared with single
D
D = diameter of aperture
received from the time the sound was transmitted? From
this the focal length for the phased array is deduced, enabling a sharp image of that echo a t that depth. Second, how
strong was the echo? From these two an swers the scanner
determines which pixel in the image to light up and with
what intensity and at what hue if frequency is processed.
Furthermore, for the ultrasound scan to operate in real
time – i.e., any real movement in tissue is instantly asso-
ciated with a corresponding movement in the displayed
image – it has to avoid judder such as can be seen on
early cinema movies and the object being imaged must not
move excessively between successive views. This can be
maintained by a sufficiently high frame rate,whichisthe
rate at which the image is updated or refreshed. To avoid
judder, the image must be updated at a rate of approximately 25 times per second or higher. Scanners are also
equipped with a facility often labeled frame f reeze whereby
the same image is written onto the screen about 25 times
a second.
The returning echoes from tissues show a steady decline in
amplitude with increasing depth due to attenuation. This is
generally considered to be a nuisance and attempts are made
to correct for it. The amount of amplification or gain given to
the incoming signals is made to increase simultaneously with
the arrival of echoes from the greater depth. This is called the
time gain compensation (TGC) control and is now fitted to
virtually all ultrasound scanners. Of course, the assumption
that all echoes should be made equal is not really valid. The
operator still needs to use the TGC control with care so as not
to produce misleading images; for example, excessive TGC can
turn a normally echo-poor area within a fluid-filled cyst into
one that seems to have small echoes, thereby resembling a
tumor.
The layout of the TGC controls varies from one machine
to another. One of the most popular settings is a set of slider
knobs. Normally each knob in the slider set controls the gain
for a specific depth. It is the task of the operator to set each
level for each patient and often it is necessary to adjust the
TGC during the examination when moving from one anatomic region to another. TGC has also one important clinical
application, to avoid acoustic shadowing and its opposite,
Fig. 2.5. A schematic representation of an
ultrasound transducer and the difference in the
beam shape between a single-element transducer
and an array transducer.
2
N = D
N equals near zone
λ = wavelength
/4λ
flaring or enhancement. Shadowing occurs when the desired
organ to be examined is placed behind another organ that
absorbs too much of the energy of the transmitted and
received pulses. For example, we may see a break in the
posterior uterine wall where it lies posterior to the fetal
head. On the other hand, the posterior wall of an ovarian
cyst may appear to be very bright because the path traveled by
the pulse and its corresponding echoes is largely through cyst
fluid, which absorbs very little of the beam energy. In addition, this can also be used to differentiate between some solid
masses that are quite homogeneous and whose image can be
devoid of internal echoes (i.e. hypoechoic). These can be confused with a cyst, which would also be expected to be hypoechoic. Nonetheless, the solid mass is much more likely to be
absorptive than the cyst and hence the two can normally be
distinguished by the presence or absence of flaring or shadowing posteriorly.
Modes of ultrasonography
Four different modes of ultrasound are used in medical
imaging:
A-mode: This is the simplest type of ultrasound wherein a
single-element transducer scans a line through the body with
the echoes plotted on screen as a function of depth. It is
therefore a one-dimensional view. Therapeutic ultrasound
aimed at a specific tumor is A-mode, to allow for pinpoint
accurate focus of the destructive wave energy.
B-mode: To produce a more useful two-dimensional (2D)
scan, it is necessary to obtain a series of A-mode scans and
assemble them in a convenient format. This is done either
by moving the transducer using a suitable mechanical
device or else by having more than one transducer. This
second option is preferred in modern scanners and the
transducer, which is hand-held by the operator, in fact
contains a row (array) of many transducers (typically
100–200). In this way, a series of A-scans can be obtained
in a closely packed regular format. The amplitude (height)
of each echo is represented by the brightness of a spot
at the position. This display mode, in which the x and
y directions relate to real distance of organs and the use
14
Transducer
(frequency f )
Chapter 2: Ultrasonography: physics and principles
Fig. 2.6. Doppler frequency shift and the
equation for calculating it.
Doppler frequency (f
Beam
θ
Higher doppler frequency obtained if:
– velocity is increased
– beam is aligned more to flow direction
– higher frequency is used
Flow velocity = V
- doppler shift
f
d
c - speed of sound in tissue
- transmited beam
f
t
V - velocity of the blood
θ - angle of incidence between the ultrasound
beam and the direction of the flow
of gray scale to represent echo strength, is known as the
B-mode scan.
M-mode: M-mode is a motion scan wherein a rapid sequence
of B-mode images follow each other in sequence on the screen
to enable physicians to see and measure a range of motion.
This mode can be useful when imaging heart valves, because
the movement of the valves will make distinct patterns.
Doppler mode: This mode produces an image of flow and is
essentially obtained from measurements of movement. In
ultrasound scanners, echoes from stationary tissue are the
same from pulse to pulse. However, echoes from moving
objects exhibit slight differences in the time for the signal to
be returned to the receiver – the Doppler effect. In general,
this refers to a change in the received fr equency compared
with the frequency emitted whenever there is relative motion
between a sound source and the listener. These differences
can be measured as a direct time difference or, more usually,
in terms of a frequency shift from which the Doppler effect is
obtained. This shift falls in the audible range of sound and is
often presented audibly using stereo speakers to produce a
very distinctive, although synthetic, pulsing sound. The
Doppler frequency shift (Figure 2.6) depends on several
factors:
) = 2. ft. V. cos θ
d
c
ABCD
skin
beam
direction
flow
Fig. 2.7. Effect of the Doppler angle on the sonogram. A higher-frequency
Doppler signal is obtained if the beam is aligned more in the direction of flow. In
the diagram, beam A is more aligned than B and produces higher Doppler
signals. The beam/flow angle in C is almost 90° and there is a very poor Doppler
signal. The flow at D is away from the beam and there is a negative signal.
vessel
BA
Sonogram
C
D
1. Blood velocity: As velocity increases, so does the Doppler
frequency.
2. Ultrasound frequency: Higher frequencies give increased
Doppler frequency. However, this is a compromise between
better sensitivity to flow or deeper penetration.
3. The angle of insonation: The Doppler frequency increases as
the beam becomes more aligned to the direction of flow, i.e.,
as the angle between the beam and the direction of flow
becomes smaller (Figure 2.7). Therefore, the maximum
Doppler shift will occur at angles of 0° (maximum positive
Doppler shift) and 180° (maximum negative Doppler shift)
and at an angle of 90° there will be no Doppler shift as the
cosine of 90° is 0.
Types of Doppler ultrasound flow modes
The Doppler frequency shift information can be displayed
graphically in various ways.
*
Color Doppler (directional Doppler) uses a computer to
convert the Doppler measurements into an array of colors.
The transducer elements are switched rapidly between
B-mode and color flow imaging to give an impression of a
combined simultaneous image. Thus, color visualization is
combined with a standard ultrasound picture of a blood
vessel to show the speed and direction of blood flow
(Figure 2.8). The assignment of color to frequency shifts is
usually based on direction and magnitude: red for flow
toward the ultrasound beam and blue for shifts away from it
15
Section 1: Imaging techniques
Fig. 2.8. Color Doppler (directional) showing the flow along the umbilical
vein and arteries.
(a)
(a)
(b)
Fig. 2.9. Color power Doppler, showing its sensitivity to low flow. (a) Color
power angiogram of the circle of Willis in the fetal head. (b) Color power
angiography of a submucosal fibroid; note the small vessels inside the tumor.
and different color hues or lighter saturation for higher
frequency shifts. Color Doppler is very sensitive to low flow
(Figure 2.9) and has the ability to render the directional
information in different colors (color flow maps). However,
it gives limited flow information and poor temporal
resolution/flow dynamics as the frame rate can be low when
scanning deep. The color Doppler image is dependent on
the general Doppler factors , particularly the need for a good
beam/flow angle. In practice, the experienced operator
alters the scanning approach to obtain good insonation
angles so as to get unambiguous flow images.
(b)
Fig. 2.10. Setting the color gain to minimize the signals (artifacts) from
surrounding tissue: (a) color gain = 71; (b) decreasing the color gain to 35.
*
Other factors that control the appearance of the color flow
image include:
1. Power and gain: Color flow uses higher-intensity power
than B-mode. The values are set to obtain good signal
for flow and to minimize the signals from surrounding
tissue (Figure 2.10).
2. Frequency selection: High frequencies give better
sensitivity to low flow and have better spatial resolution.
Nevertheless, low frequencies have better penetration
and are less susceptible to aliasing at high velocities.
3. Velocity scale/pulse repetition frequency: Low pulse
repetition frequencies should be used to examine low
velocities but aliasing may occur if high velocities are
encountered (Figure 2.11).
4. Region of interest: Because more pulses are needed to
look at flow rather than for the B-mode image, reducing
the width and maximum depth of the color flow area
under investigation will usually improve frame rate and
may allow a higher color scan line density with
improved spatial resolution.
16
Chapter 2: Ultrasonography: physics and principles
(a)
(b)
(a)
(b)
Fig. 2.11. Color flow imaging with effects of pulse repetition frequency or scale.
(a) The pulse repetition frequency or scale is set low (yellow arrow). The color
image shows ambiguity within the umbilical artery and vein and there is
extraneous noise. (b) When the scale is set appropriately for the flow velocities,
the color image shows the arteries and vein clearly and unambiguously.
5. Focus: The focus should be at the level of the area of
interest. This can make a significant difference to the
appearance and accuracy of the image.
*
Power Doppler (energy, amplitude flow, nondirectional
Doppler) is a technique that is more sensitive in detecting
blood flow than is color Doppler. It is able to obtain images
that are difficult or impossible to obtain using standard
color Doppler. It also provides greater detail of blood
flow, especially in vessels that are located inside organs.
However, it provides nondirectional information in some
modes and has very poor temporal resolution and is
susceptible to noise.
*
Spectral (pulsed) Doppler, where instead of displaying the
Doppler measurements visually they are displayed
graphically (Figure 2.12). It is used to provide a measure of
the changing velocity in the sample volume “gate.” If an
accurate angle correction is made, then absolute velocities
can be measured. Spectral Doppler has the advantage of
detailed analysis of distribution of flow and good temporal
Fig. 2.12. (a) Spectral Doppler of the common carotid artery and (b) setting up
the sample volume in a sonogram of the descending aorta. With the angle
correction the peak velocities can be measured, where b is the direction of the
Doppler beam, g is the gate or sample volume, and a the angle of correction.
resolution and it can examine flow waveform and allows
calculations of velocity and indices. Spectral Doppler
images are affected by the same factors as color Doppler as
well as the gate size; a large gate may include signals from
adjacent vessels (Figure 2.13).
Since color flow imaging provides a limited amount of
information over a large region, and spectral Doppler provides
more detailed information about a small region, the two modes
are complementary and, in practice, are used as such. Color
flow imaging is used to identify vessels requiring examination,
to identify the presence and direction of flow, to highlig ht gross
circulation anomalies, and to provide beam/vessel angle correction for velocity measurements. Pulsed-wave Doppler is
used to provide analysis of the flow at specific sites in the vessel
under investigation. When using color flow imaging with
pulsed-wave Doppler, the color flow/B-mode image is frozen
while the pulsed wave Doppler is activated. Recently, some
manufacturers have produced concurrent color flow imaging
17
Section 1: Imaging techniques
and pulsed-wave Doppler, sometimes referred to as triplex
scanning. When these modes are used simultaneously, the per-
formance of each is decreased. Because transducer elements are
employed in three modes (B-mode, color flow, and pulsed-wave
Fig. 2.13. Influence of gate size. The spectral Doppler gate insonates an artery
and vein and the sonogram shows flow from both of these vessels. The
calculation of mean velocity (arrow) is meaningless since velocities from one
vessel subtract from those of the other.
Doppler), the frame rate is decreased, the color flow box is
reduced in size, and the available scale is reduced, leading to
increased susceptibility to aliasing.
When pulses are transmitted at a given sampling frequency
(the pulse repetition frequency or the scale), the maximum
Doppler frequency that can be measured unambiguously is
half the scale. Therefore, if the blood velocity and beam/flow
angle being measured combine to give a Doppler frequency
value greater than half of the scale, ambiguity arises in the
Doppler signal. This is aliasing and its bad effect can be corrected by reducing color gain or increasing the scale
(Figure 2.14). The pulse repetition frequency is itself constrained by the range of the sample volume. The time interval
between sampling pulses must be sufficient for a pulse to make
the return journey from the transducer to the reflector and
back. If a second pulse is sent before the first is received, the
receiver cannot distinguish between the reflected signal from
both pulses and ambiguity ensues. As the depth of investigation
increases, the journey time of the pulse to and from the reflector
is increased, reducing the pulse repetition frequency for unambiguous ranging. The result is that the maximum Doppler
frequency measured decreases with depth. Therefore, low
pulse repetition frequencies are employed to examine low
velocities (e.g., venous flow) as the longer interval between
(a) (b)
(c) (d)
18
Fig. 2.14. An example of aliasing and its correction. (a) Abrupt termination of the systolic peak, with the truncated part of the peaks showing below the baseline. (b)
The same case after correction by increasing the pulse repetition frequency and adjusting the baseline (downward). (c) Aliasing of the color flow (yellow arrows) is
corrected by reducing the color gain and increasing the pulse repetition frequency (d).
Chapter 2: Ultrasonography: physics and principles
(a)
(b)
Fig. 2.15. The effects of pulse repetition frequency or scale on aliasing. (a) The
pulse repetition frequency is set low (yellow arrow). The color image shows
ambiguity within the umbilical artery and vein and there is extraneous noise. (b)
The scale is set appropriately for the flow velocities and the color image shows
the arteries and vein clearly and unambiguously.
pulses allows the scanner a better chance of identifying slow
flow. Aliasing will occur if low scale is used and high velocities
are encountered (Figure 2.15). Conversely, if a high scale is
used, low velocities may not be identified.
Modes of Doppler waves
In the sonographic community, the terminology “Doppler” has
been accepted to apply to both the continuous-wave and
pulsed-wave systems despite the different mechanisms by
which velocity is detected.
Continuous-wave Doppler (CW), as the name suggests, uses
continuous transmission and reception of ultrasound by two
separate elements within the transducer, e.g., for listening to
fetal heart rate. Doppler signals are obtained from all vessels in
the path of the beam until it becomes sufficiently attenuated due
to depth. These machines are unable to determine the specific
location or velocities and cannot be used to produce color flow
images.
Pulsed-wave Doppler (PW) machines transmit pulses of
ultrasound, and then switch to receive mode. As such, the
reflected pulse that they receive is not subject to a frequency
shift, as the insonation is not continuous. However, the phase
change in subsequent measurements can be used to obtain the
frequency shift.
Blood flow measurements
*
Calculation of velocity
Theoretically, once the beam/flow angle is know n, velocities
can be calculated from the Doppler equation. Nonetheless,
errors may still occur due to:
(a) Use of multiple elements in array transducers.
(b) Nonuniform insonation of the vessel lumen.
(c) Insonation of more than one vessel.
(d) Use of filters removing low-velocity components.
(e) Use of high angles (>60°) may give rise to error
because of the comparatively large changes in the
cosine of the angle that occur with small changes of
the angle.
(f) The velocity vector may not be in the direction of the
vessel axis.
It is good practice to try to repeat velocity measurements,
using a different beam approach, to gain a feel for the
variability of measurements in a particular application.
*
Calculation of absolute flow
Total flow measurement using color or duplex Doppler
ultrasound is fraught with difficulties, even under ideal
conditions. Errors that may arise include:
(a) Those due to inaccurate measurement of vessel cross-
sectional area
(b) Those originating in the derivation of velocity.
These errors become particularly large when flow
calculations are made in small vessels; errors in
measurement of diameter are magnified when the diameter
is used to derive cross-sectional area.
*
Flow waveform analysis
This has the advantage that derived indices are independent
of the beam/flow angle. Furthermore, changes in flow
waveform shape have been used to investigate both
proximal disease (e.g., peripheral arterial circulation in
adults) and distal changes (fetal circulation and uterine
arteries). Many different indices have been used to describe
the shape of flow waveforms. All are designed to describe
the waveform in a quantitative way. In general, they are a
compromise between simplicity and the amount of
information obtained.
The most commonly used indices available on most
commercial scanners are:
1. Resistance index (RI) (also called resistive index)
2. Systolic/diastolic ratio (S/D) ratio, sometimes called the
A/B ratio
3. Pulsatility index (PI)
19
Section 1: Imaging techniques
Fig. 2.16. Indices of measurement of the flow waveform shape.
These indices are all based on the maximum Doppler shift
waveform and their calculation as described in Figure 2.16.
Although PI takes slightly longer to calculate, it does give a
broader range of values – for instance, in describing a range
of waveform shapes when there is no end-diastolic flow. In
addition to these indices, the flow waveform may be
described or categorized by the presence or absence of a
particular feature, e.g., absent end-diastolic flow in fetal
compromise.
Safety issues
Despite its impressive safety record of ultrasound to date, the
intensity (or acoustic output) level of ultrasound used to scan
the fetus in utero has increased almost eightfold over the level
that was allowed in the early 1990s. Therefore, the comfort
obtained from the absence of any harm based on epidemiological evidence must be tempered by the fact that there are not
enough studies appropriate and adequate for guiding current
clinical practice.
On the basis of some concerns about the theoretical effects of
ultrasound on the developing fetus, researchers have conducted
epidemiological studies looking for associations between ultrasound exposure and various traits, particularly brain development (dyslexia, non-right-handedness, and delayed speech
development), reduced birth weight, and childhood cancers.
Meta-analyses of randomized controlled trials of adverse effects
show only that there is a just-significant increased tendency to
non-right-handedness in the offspring of women who have had
scans; however, the complexity of the study makes the observation difficult to interpret [1]. Nevertheless, continual vigilance is
necessary particularly in areas of concern such as the use of
pulsed Doppler in the first trimester.
Ultrasound causes heating, referred to as thermal and non-
thermal effects. The main areas of concern among nonthermal
effects are cavitation and microstreaming, but effects due to
movement of cells in liquids, electrical changes in cell membranes, and pressure changes also exist.
Thermal heating is a consequence of the absorption of the
ultrasound wave by tissue. Absorption increases with increasing frequency, and the temperature rise caused by an ultrasound beam depends on many factors such as beam intensity
and output power, focusing, beam size and depth, tissue
absorption coefficient, tissue-specific heat and thermal conductivity, time, and blood supply. The Consensus Rep ort on
Potential Bioeffects of Diagnostic Ultrasound in 2007 [2] stated
that “Due to the movement of the transducer and of the structures being imaged during clinical examination, the acoustic
field remains fixed over a given structure or volume of tissue for
brief periods of time, typically measured in seconds or fractions
of a second. Under these conditions, the probability of local
tissue or organ heating is small and unlikely to be of clinical
significance.”
Cavitation (bubble formation) is the growth, oscillation,
and decay of small gas bubbles under the influence of an
ultrasound wave. These bubbles often grow to some limiting
size and continue to vibrat e at the ultrasound frequency. The
growth and collapse of these microbubbles focuses and transfers energy and produces extremely high localized pressures
and temperatures that add further stress to cell boundaries.
When bubbles expand and contract without growing to critical size, the activity is termed stable cavitation. Unstable
cavitation does not occur in the therapeutic range in normal
tissues except in air- filled cavities, most notably adult lung
and intestine. Luckily, the fetal lung and intestine do not
contain obvious air bubbles. Cavitation is limited by lowintensity and pulsed Doppler because there will be enough
time for bubbles to regain their initial size during the “off ”
period.
Microstreaming when ultrasound passes through liquid
causes a sort of stirring action termed acoustic streaming. As
the acoustic pressure of the ultrasound increases, the flow of
liquid speeds up. Cavitation sets up eddy currents in the fluid
surrounding the vibrating bubbles and the eddy currents in
turn exert a twisting and rotational motion on nearby cells. In
the vicinity of vibrating gas bubbles, intracellular organelles are
also subjected to rotational forces and stresses. This stirring
action, in theory, could occur in fluid-filled parts of a patient’s
body, such as blood vessels, the bladder, or the amniotic sac. In
experimental animals shearing can occur when streaming
liquid comes near a solid object, and this can damage platelets
and lead to abnormal blood clotting (thrombosis). It is not clear
to what extent this effect occurs in humans exposed to diagnostic ultrasound.
Accordingly, the conclusion should always be that the diagnostic procedure
valid medical indication, with the lowest possible ultrasonic
exposure setting to gain the necessary diagnostic information.
This requires self-regulation on the part of the manufacturer
and in part of the operator to keep the time limit as short and
informative as possible.
should be performed only when there is a
20
References
1. Miller DL. Safety assurance in obstetrical ultrasound. Semin
Ultrasound CT MR. 2008; 29(2): 156–64.
2. Barnett SB, Duck F, Ziskin M. WFUMB symposium on safety of
ultrasound in medicine: conclusions on recommendations on
biological effects and safety of ultrasound contrast agents.
Ultrasound Med Biol 2007; 33(2): 233–4.
Suggested reading
Elvy M. Physics of medical ultrasound. http://www.qmseminars.co.nz/
PDF/ElvyPhysicsMedicalUltrasound.pdf (Accessed May 10, 2008).
Kremkau FW. (2005). Diagnostic Ultrasound Principles and
Instruments, 7th edn. Philadelphia, WB Saunders, 2005.
Deane C. Doppler ultrasound: Principles and practice. http://www.
centrus.com.br/DiplomaFMF/SeriesFMF/doppler/capitulos-html/
chapter_02.htm (Accessed April 20, 2008).
Evans T. Physics and instrumentation. In: Chudleigh T, Thilaganathan
B, eds. Obstetric Ultrasound: How, Why and When. 3rd edn.
Edinburgh, Churchill Livingstone, 2004; 1–15.
Chapter 2: Ultrasonography: physics and principles
21
Chapter
Hysterosalpingography
3
Shawky Z. A. Badawy, Stuart J. Singer and Amr Etman
Introduction
The evaluation of the pelvic organs and pathology related to
them has always been dependent on proper pelvic examination,
rectal examination, and external palpation of the abdomen and
pelvic areas. That there were marked limitations to such methods of evaluation was long realized by physicians. About a
century ago various investigators developed technologies to
visualize the pelvic organs. One of the earliest technologies
was the introduction of air into the abdominal cavity using a
needle, and there was discussion about what type of air medium
should be introduced. Investigators started by using oxygen,
but they real ized that this gas takes many hours to be absorbed,
thus subjecting the patient to unnecessary pain and discomfort
after the procedure. They replaced the oxygen medium by
carbon dioxide and found that within 15–20 minutes carbon
dioxide is very easily absorbed into the circulation; patients
therefore will not have any lasting discomfort and may go
home comfortably after the procedure. The practice of introducing carbon dioxide into the abdominal cavity, producing
pneumoperitoneum, developed in association with radiological
science. After the production of pneumoperitoneum, radiography is used to visualize many organs in the abdominal cavity,
including tumors and adhesions. Contraindications to the use
of transabdominal pneumoperitoneum are, of course, the presence of large masses or the suspicion of massive adhesions; the
technique is also contraindicated in patients who are suspected
of having heart prob lems. This technique was useful for limited
evaluation of the pelvic cavity and for outlining the pelvic
organs.
Isodor Clinton Rubin introduced the technology of transcervical carbon dioxide insufflation for diagnosis of tubal pathology [1]. He used an apparatus that allowed him to monitor
the flow of carbon dioxide as well as the pressure during the
procedure. Carbon dioxide was introduced through the cervix
into the uterus using a cannula with a rubber end that fitted
onto the cervix and produced a seal with the external os. The
carbon dioxide was then allowed to flow and Rubin noted that
the pressure usually rose to 60–100 mmHg and then began to
drop, indicating that carbon dioxide had easy access through
the tubes into the peritoneal cavity and that at least one tube was
patent. If the pressure continued to rise, reaching almost
200 mmHg without any drop, the patient started to suffer
pain; this suggested that tubes were blocked and the procedure
was then terminated. This was an elegant procedure to make a
diagnosis of tubal factors in infertility. However, the limitations
at that time involved whether one tube or both were patent,
which could not be ascertained with this technique, depending
on reading the intrauterine pressure with a special manometer.
The procedure was supplemented by using a stethoscope to
listen suprapubically to the sound of air passing through the
tube if it was patent.
Limitations on the use of Rubin’s insufflation test include
acute or subacute pelvic infections and also the presence of
cervical infection as diagnosed by purulent fluid discharging
from the cervix.
The principle of transuterine insufflation appealed to other
investigators, who introduced modification of the technique for
producing pneumoperitoneum, which, associated with radiography of the pelvis, proved more useful in outlining pelvic
pathology. Essentially, the patient was placed in the knee–chest
position or Simm’s position, the cannula was introduced into
the cervix in that position, and transuterine insufflation was
performed to produce pneumoperitoneum. Certainly if the
tubes are open then pneumoperitoneum will be sufficient to
show on the radiographs, thus outlining the uterus and ovaries
and any pathology in the pelvis. Some uterine anomalies might
even be diagnosed by this technology.
Clearly, transuterine insufflation was an important technology that laid the foundation for evaluation of the uterus, tubes,
and pelvic organs and was an advance that preceded the use of
dyes to outline the uterine cavity and the fallopian tube.
Hysterosalpingography
Hysterosalpingography is a technique introduced by Rubin
used to visualize the uterine cavity and fallopian tubes. Many
investigators have attempted to bypass this method in the
evaluation of the infertile couple, going on to laparoscopic
and hysteroscopic procedures instead. However, hysterosalpingography has withstood the test of time as a noninvasive procedure that is used without any anesthesia, and much of the
Ultrasonography in Reproductive Medicine and Infertility, ed. Botros R. M. B. Rizk. Published by Cambridge University Press. © Cambridge
University Press 2010.