Introduction to Ultrasonography

Richard Davis
Background: tissue, and then are reflected back towards the
Proficiency in ultrasound can be an transducer at different frequencies, based on the
advantage to a surgeon practicing in a resource- characteristics of the tissue. When these sound waves
limited setting. Ultrasound performed by the surgeon return, they interact with the same crystal. Here
can give tremendous insight into the patient’s again, mechanical energy is converted to electrical
disease, especially if more advanced imaging such as energy, this time containing information about the
CT or MRI aren’t immediately available. In this tissue it has been reflected from. This energy is then
Chapter we explain the principles of converted to an image.
Ultrasonography as they relate to you, and we give The sound waves emitted by the crystal are in
some basic guidelines for performing ultrasound and the range of 2-10 Megahertz (mHz, millions of
interpreting the images. In other chapters, we will cycles per second.) By comparison, human hearing
discuss Focused Abdominal Sonography for Trauma occurs at 20Hz to 20kHz.
(FAST) and Ultrasound-Guided Interventions. The tissue below the probe reflects the sound
waves differently based on its characteristics. The
Physics: more dense a tissue is, the more “bright” it appears
The Piezoelectric Effect: on the screen. Therefore, the image on the screen is
Quartz is a solid made of Silicone and a reflection of the amount of time a sound wave takes
Oxygen molecules in a highly ordered structure. to return to the transducer (depth of the structure) and
Ultrasound transducers contain a quartz crystal. the strength of the sound wave (brightness of the
According to the Piezoelectric effect, when image.)
electricity passes through a crystal it causes the
crystal to vibrate. And conversely, if a crystal is
made to vibrate, it emits electricity. The properties of
the crystal determine the frequency of the vibration.

The distance the wave travels, and its strength on return, cause
the crystal to vibrate differently than when the signal was
generated. The vibrations are transformed into electrical
signals, which are reconstructed to make a two dimensional
A piece of Quartz crystal. Source: JJ Harrison (depth and width) image.
(https://www.jjharrison.com.au/) - Own work, CC BY-SA 2.5,
https://commons.wikimedia.org/w/index.php?curid=6023737 Anatomy:
Acoustic Shadowing:
Inside the transducer, both forms of the Some tissue does not allow sound to pass
Piezoelectric effect occur. First, the ultrasound
through it at all. This causes an “acoustic shadow”
waves are generated: electrical energy is applied to deep to the tissue, as no sound waves return from
the crystal and converted to high frequency below that area. The simplest example of this is when
soundwaves, which enter enter the tissue below the the gel between the probe and the skin is inadequate,
transducer. These soundwaves interact with the literally all of the image will be an acoustic shadow.
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 Introduction to Ultrasonography
Richard Davis
When attempting to scan the chest cavity, the
ribs cause acoustic shadows. The best way to
overcome this effect is to rotate the transducer so that
it lies entirely within the space between the ribs. The
operator must therefore keep in mind the orientation
of the ribs wherever the transducer is being used.

The liver, right kidney and hepatorenal recess are seen in this
ultrasound view taken with the transducer in between the ribs
on the right. The diaphragm is also seen (Red arrow.) By sliding
the transducer posteriorly within the intercostal space, more of
the diaphragm and lower right hemithorax could be seen. A rib
shadow (Red dot and below) obscures the view of the liver; this
view could be improved if the transducer was rotated a bit, so
Location and orientation of the ultrasound transducer for that it aligned better with the intercostal space. Case courtesy
echocardiography, over the anterior intercostal spaces. of Dr David Carroll, from the case
https://radiopaedia.org/cases/64279?lang=us

Another effect of acoustic shadowing is the

detection of gallstones and other calculi. Although
calculi of the kidney, bladder or gallbladder can often
not be directly seen by ultrasound, their acoustic
shadows can be seen. An exception is any stone that
is not sufficiently calcified; these will reflect some
sound waves and may be seen as “masses” or
“sludge” in the gallbladder.

Location and orientation for liver ultrasound, including

assessment of the hepatorenal space for FAST scan to detect
intra-abdominal fluid. By sliding the transducer posteriorly
along the intercostal space, the diaphragm and any fluid in the
thoracic cavity can be seen.

Ultrasound image of the gallbladder with stones and acoustic

shadowing. There is no data available from below the stones,
as no ultrasound waves are reflected back towards the

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 Introduction to Ultrasonography
Richard Davis
transducer. Case courtesy of Dr Hani Makky Al Salam, From
the case https://radiopaedia.org/cases/14461?lang=us

Setup and Orientation

If you have a portable machine, try to place it
opposite the patient from you. Then, as you are
performing the study or doing any interventions, the
images are right in front of you. Having the machine
on the same side as you forces you to turn your neck
or torso in an awkward manner to see the images as
you obtain them.

The transducer is held so that its marker aligns with the one on
the screen (Red arrows.) If you do not do this, the image you
see on the screen may be a “mirror image” of what you would
expect, and it will not correspond with your movements if you
attempt to maneuver the probe.

Transducers and Settings

Assuming you have a choice of transducers at
If possible, position yourself on the other side of the patient all, it is helpful to understand the different types and
from the monitor, so that you can see it without turning to one
side. their intended use.
The shape and frequency of the transducer
Every transducer has external markings that will determine its best use. The two shapes of
can be seen (or felt, when it is inside a sterile probe transducers are linear and curved.
cover.) These allow you to align the transducer with Linear array transducers will be better for
the image on the screen, which also has a marker. shallow work such as breast assessment and biopsy,
The screen marker is usually a blue dot. When the vascular studies and vascular access. These will have
transducer’s marker and screen’s marker are aligned, a higher frequency of 5-7.5mHz which can show
the image on the screen correlates with the anatomy greater detail but will not penetrate tissue as deeply.
being examined, and the images move in the same
direction as you move the transducer.

A linear array transducer. Note the arrow in the center of the

head improves accuracy during venous cannulation.

Curved array transducers are better suited for

abdominal or pelvic work. These have a lower
frequency, in the range of 2-3mHz, so they penetrate
tissue more deeply.
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 Introduction to Ultrasonography
Richard Davis

A curved array transducer.

The depth at which each transducer sees can

be set by the user. This will be visible as a column of
numbers on the right side of the screen. Each
transducer has a preset depth beyond which it will The vertical column on the right of the screen shows the depth
setting. This can be adjusted to allow you to see the area of
not go, depending on its intended function. A interest in greater detail. Once you know their scale, the dots
vascular transducer (linear array) can usually see up also allow you to estimate the size of a structure on the screen.
to about 6cm. If you are trying to examine a vessel In this case, the depth is set to 16cm (Red circle.)
that is 2cm deep, set the depth to 3cm to see
maximum detail. Similarly, when using a curved The gain allows the surgeon to manipulate
transducer to examine all of the liver, set the depth the image by amplifying it. If the image is not
around 13cm. Once you have settled on a tumor that amplified enough, it will be too dark. If amplified too
is 6cm deep and decide to biopsy it, change the depth much, it will be too light. The appropriate setting will
on the probe to around 8cm. This allows you to see vary, even according to the depth of the image.
the tumor in greater detail. Therefore, most ultrasound machines allow the
operator to adjust the gain at various depths. On
portable machines there may be two dials, but on
console machines there typically 8 or more sliding
dials corresponding to the gain at 8 or more different
depths for the image.

The depth setting on the ultrasound console.

On this portable ultrasound machine, the dial immediately

below the Red box controls the gain for the whole image. The

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 Introduction to Ultrasonography
Richard Davis
two dials inside the Red box separately control the gain for the and medially towards the abdomen and continue to
upper and lower portions of the screen. examine the liver, pushing the probe into the
abdomen under the costal margin and pushing
upwards. Move medially to find the vena cava with
its vein branches entering the liver. The aorta, a
pulsatile vascular structure that is farther to the left,
is also easy to locate relative to the liver. When
examining the pelvis, start by finding the bladder and
examine the surrounding structures. Pushing
downwards with the probe into the abdomen will
move the bowels out of the way and allow you to find
the uterus and the ovaries in a woman.

On this console (less portable) ultrasound machine, these

sliding controls allow the operator to adjust the gain on the
image at 8 different levels.

If you are not seeing a useful image, it is

important to decide whether you are using the right
probe, one that is designed to see at the depth you are
trying to see, as explained above. Then assess the
amount of gel. Gel facilitates the passage of sound
When performing ultrasound of the abdomen, start in the right
waves so it is good to have a lot of it, especially over intercostal spaces over the liver. Orient the probe so that it is
an uneven surface such as the chest in a cachectic parallel to the intercostal spaces. Adjust the gain and depth.
person. If you are using a sterile transducer cover (or Then slide anteriorly or posteriorly within the interspace, move
a sterile glove), there should be adequate gel inside to a lower interspace, or go below the costal margin and push
the cover, between the transducer and the cover. Run the probe towards the dorsum to see more of the liver.
your finger over the transducer surface to remove any
bubbles between it and the sterile cover. We discuss
an easy way to make a sterile ultrasound transducer
cover in “Ultrasound-Guided Interventions.”
Once you have enough gel and no bubbles, if
you are still not happy with the image try adjusting
the gain.

Principles:
Using the ultrasound machine alone to
evaluate a patient is difficult. The images are hard to
comprehend, even if you use the right transducer and
apply all the principles we have explained so far.
In the abdomen, begin with the liver. With the
appropriate probe set to the right depth, enough gel, View of the liver from one of the right intercostal spaces.
and the gain set properly, you should be able to see
the hepatic tissue in one of the right lower intercostal In the neck, start with the linear probe
spaces. Once that is accomplished, try to find the oriented transversely over the lower 1/3 of the
kidney, deep and inferior to the liver. Move caudally
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 Introduction to Ultrasonography
Richard Davis
sternocleidomastoid muscle. You will see the operator technique, so the more time you spend with
common carotid artery, which is smaller and it, the more useful it will be to you.
pulsatile, and the jugular vein, which is larger and
collapses with inspiration. Move medially and you Richard Davis MD, FACS, FCS(ECSA)
will find the thyroid gland and, in the center, the AIC Kijabe Hospital
trachea, a round structure that creates a shadow, as Kenya
ultrasound waves can not pass through air. Move in
a cranial direction to follow the vessels upwards to Reviewed by:
the submandibular gland. Geoffrey Mashiya, Dip (Rad) HND (Ultrasound)
AIC Kijabe Hospital
Kenya

In the neck, start with a linear array probe held transversely

and find the carotid artery, jugular vein, trachea and thyroid
gland. These familiar structures allow you to orient yourself
and then move upwards or to either side.

Looking transversely over the lower right neck just off midline,
you are rapidly oriented by finding the sternocleidomastoid
muscle (Purple dot,) the internal jugular vein (Blue dot,) the
common carotid artery (Red dot,) the right lobe of the thyroid
gland (Green dot,) and the trachea (White dot.) Case courtesy
of Dr. Derek Smith, From the case
https://radiopaedia.org/cases/65792?lang=us

Above all, take every opportunity you have

to practice your ultrasound technique. Ultrasound
can be used to diagnose many conditions and is very
useful in settings like ours. Its accuracy depends on
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