Introduction to Ultrasonography 
Richard Davis 
OPEN MANUAL OF SURGERY IN RESOURCE-LIMITED SETTINGS 
www.vumc.org/global-surgical-atlas 
This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License  
 
Background:  
 
Proficiency in ultrasound can be an 
advantage to a surgeon practicing in a resource-
limited setting. Ultrasound performed by the surgeon 
can give tremendous insight into the patient’s 
disease, especially if more advanced imaging such as 
CT or MRI aren’t immediately available. In this 
Chapter 
we 
explain 
the 
principles 
of 
Ultrasonography as they relate to you, and we give 
some basic guidelines for performing ultrasound and 
interpreting the images. In other chapters, we will 
discuss Focused Abdominal Sonography for Trauma 
(FAST) and Ultrasound-Guided Interventions.  
 
Physics: 
The Piezoelectric Effect:  
Quartz is a solid made of Silicone and 
Oxygen molecules in a highly ordered structure. 
Ultrasound transducers contain a quartz crystal. 
According to the Piezoelectric effect, when 
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. 
 
A 
piece 
of 
Quartz 
crystal. 
Source: 
JJ 
Harrison 
(https://www.jjharrison.com.au/) - Own work, CC BY-SA 2.5, 
https://commons.wikimedia.org/w/index.php?curid=6023737 
 
 Inside the transducer, both forms of the 
Piezoelectric effect occur. First, the ultrasound 
waves are generated: electrical energy is applied to 
the crystal and converted to high frequency 
soundwaves, which  enter enter the tissue below the 
transducer. These soundwaves interact with the 
tissue, and then are reflected back towards the 
transducer at different frequencies, based on the 
characteristics of the tissue. When these sound waves 
return, they interact with the same crystal. Here 
again, mechanical energy is converted to electrical 
energy, this time containing information about the 
tissue it has been reflected from. This energy is then 
converted to an image. 
The sound waves emitted by the crystal are in 
the range of 2-10 Megahertz (mHz, millions of 
cycles per second.) By comparison, human hearing 
occurs at 20Hz to 20kHz. 
The tissue below the probe reflects the sound 
waves differently based on its characteristics. The 
more dense a tissue is, the more “bright” it appears 
on the screen. Therefore, the image on the screen is 
a reflection of the amount of time a sound wave takes 
to return to the transducer (depth of the structure) and 
the strength of the sound wave (brightness of the 
image.)  
 
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 
(depth and width) image. 
 
Anatomy: 
Acoustic Shadowing: 
Some tissue does not allow sound to pass 
through it at all. This causes an “acoustic shadow” 
deep to the tissue, as no sound waves return from 
below that area. The simplest example of this is when 
the gel between the probe and the skin is inadequate, 
literally all of the image will be an acoustic shadow.  
Introduction to Ultrasonography 
Richard Davis 
OPEN MANUAL OF SURGERY IN RESOURCE-LIMITED SETTINGS 
www.vumc.org/global-surgical-atlas 
This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License  
 
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.  
 
Location and orientation of the ultrasound transducer for 
echocardiography, over the anterior intercostal spaces. 
 
 
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.  
 
 
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 
that it aligned better with the intercostal space. Case courtesy 
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.  
 
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 
Introduction to Ultrasonography 
Richard Davis 
OPEN MANUAL OF SURGERY IN RESOURCE-LIMITED SETTINGS 
www.vumc.org/global-surgical-atlas 
This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License  
 
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.  
 
If possible, position yourself on the other side of the patient 
from  the monitor, so that you can see it without turning to one 
side.  
 
 
Every transducer has external markings that 
can be seen (or felt, when it is inside a sterile probe 
cover.) These allow you to align the transducer with 
the image on the screen, which also has a marker. 
The screen marker is usually a blue dot. When the 
transducer’s marker and screen’s marker are aligned, 
the image on the screen correlates with the anatomy 
being examined, and the images move in the same 
direction as you move the transducer.  
 
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 
all, it is helpful to understand the different types and 
their intended use.  
 
The shape and frequency of the transducer 
will determine its best use. The two shapes of 
transducers are linear and curved.  
Linear array transducers will be better for 
shallow work such as breast assessment and biopsy, 
vascular studies and vascular access. These will have 
a higher frequency of 5-7.5mHz which can show 
greater detail but will not penetrate tissue as deeply.  
 
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.  
Introduction to Ultrasonography 
Richard Davis 
OPEN MANUAL OF SURGERY IN RESOURCE-LIMITED SETTINGS 
www.vumc.org/global-surgical-atlas 
This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License  
 
 
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 
not go, depending on its intended function. A 
vascular transducer (linear array) can usually see up 
to about 6cm. If you are trying to examine a vessel 
that is 2cm deep, set the depth to 3cm to see 
maximum detail. Similarly, when using a curved 
transducer to examine all of the liver, set the depth 
around 13cm. Once you have settled on a tumor that 
is 6cm deep and decide to biopsy it, change the depth 
on the probe to around 8cm. This allows you to see 
the tumor in greater detail.  
 
The depth setting on the ultrasound console.  
 
 
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 
interest in greater detail. Once you know their scale, the dots 
also allow you to estimate the size of a structure on the screen. 
In this case, the depth is set to 16cm (Red circle.)  
 
 
The gain allows the surgeon to manipulate 
the image by amplifying it. If the image is not 
amplified enough, it will be too dark. If amplified too 
much, it will be too light. The appropriate setting will 
vary, even according to the depth of the image. 
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.  
 
On this portable ultrasound machine, the dial immediately 
below the Red box controls the gain for the whole image. The 
Introduction to Ultrasonography 
Richard Davis 
OPEN MANUAL OF SURGERY IN RESOURCE-LIMITED SETTINGS 
www.vumc.org/global-surgical-atlas 
This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License  
 
two dials inside the Red box separately control the gain for the 
upper and lower portions of the screen.  
 
 
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 
waves so it is good to have a lot of it, especially over 
an uneven surface such as the chest in a cachectic 
person. If you are using a sterile transducer cover (or 
a sterile glove), there should be adequate gel inside 
the cover, between the transducer and the cover. Run 
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, 
and the gain set properly, you should be able to see 
the hepatic tissue in one of the right lower intercostal 
spaces. Once that is accomplished, try to find the 
kidney, deep and inferior to the liver. Move caudally 
and medially towards the abdomen and continue to 
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.  
 
When performing ultrasound of the abdomen, start in the right 
intercostal spaces over the liver. Orient the probe so that it is 
parallel to the intercostal spaces. Adjust the gain and depth. 
Then slide anteriorly or posteriorly within the interspace, move 
to a lower interspace, or go below the costal margin and push 
the probe towards the dorsum to see more of the liver.  
 
 
View of the liver from one of the right intercostal spaces.  
 
In the neck, start with the linear probe 
oriented transversely over the lower 1/3 of the 
Introduction to Ultrasonography 
Richard Davis 
OPEN MANUAL OF SURGERY IN RESOURCE-LIMITED SETTINGS 
www.vumc.org/global-surgical-atlas 
This work is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License  
 
sternocleidomastoid muscle. You will see the 
common carotid artery, which is smaller and 
pulsatile, and the jugular vein, which is larger and 
collapses with inspiration. Move medially and you 
will find the thyroid gland and, in the center, the 
trachea, a round structure that creates a shadow, as 
ultrasound waves can not pass through air. Move in 
a cranial direction to follow the vessels upwards to 
the submandibular gland.  
 
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 
operator technique, so the more time you spend with 
it, the more useful it will be to you.  
 
Richard Davis MD, FACS, FCS(ECSA) 
AIC Kijabe Hospital 
Kenya 
 
Reviewed by: 
Geoffrey Mashiya, Dip (Rad) HND (Ultrasound) 
AIC Kijabe Hospital  
Kenya 
 
 
 
 
 
