4.3 ULTRASONOGRAPHY Flashcards
DESCRIBE the basic terminology associated with ultrasonography
a. Basic Physics behind Ultrasound
(1) Ultrasound is a mechanical wave propagated through a medium at a
high frequency.
(2) Diagnostic US uses frequencies of 2.5 to 10.5 MHz.
(3) The ultrasound waves are generated by the application of electrical
current to piezoelectric crystals in the US transducer (probe).
(4) The wave propagates through tissue, reflecting a portion of the energy
back to the probe at each change in tissue density.
(5) The reflected waves again contact the piezoelectric crystals that
generate a small electrical current that is analyzed by a computer
processor.
(6) The data is then translated onto the display screen.
(7) The best images are those that are directly below the probe, as the
waves are directed away from the probe the waves scatter and less come
back to the piezoelectric crystals to be able to display an image.
(8) Any images on the edges of the probe will have a less clear image as
less ultrasound waves are reflected back.
b. Depth vs Frequency
(1) The depth to which ultrasound will penetrate depends on the frequency
of the sound wave.
(2) The higher the frequency, the better the resolution but the distance from
the skin you can image is reduced.
(3) The lower frequency probes are used for deep abdominal imaging while
higher- frequency probes are used to give high resolution images of
shallow structures.
c. Tissue Density and Ultrasound
(1) Various tissues conduct sound differently.
(2) Fluid always reflects BLACK images on US.
(3) Tissue is always a shade of GRAY on the image.
(4) The denser the tissue, the brighter white it will appear with brightest
white being bone.
d. Acoustic Enhancement
(1) An ultrasound wave loses energy or attenuates as it passes through
tissue; this is due mostly to reflection as interfaces between tissues of
different density are encountered.
(2) When there are no differences in density, such as when imaging through
collections of urine, blood, or other homogenous fluid, no energy is
reflected.
(3) This allows more energy to arrive at the structures beneath the fluid and
to reflect back to the probe.
(4) Structures underlying fluid collections will appear to be brighter (more
echogenic) than other structures at the same depth.
e. US Terminology
(1) Attenuation: Reduction in amplitude and intensity with increasing
distance traveled due to scatter, reflection, and absorption. Dependent
on frequency; higher frequencies give less penetration.
(2) Color Flow Doppler: Operating mode in which a two-dimensional
image is generated that portrays moving reflectors in color
simultaneously with images.
(3) Cystic: a sac or pouch with a definite wall that contains fluid or
semisolid material.
(4) Density: Concentration of matter (mass per unit volume).
(5) Echogenic: capable of producing echoes. Correlate with the terms
hyperechoic, hypoechoic and anechoic which refer to the quality of
echoes produced.
(6) Gain: regulates the amplification (brightness) of returning echoes to
compensatefor loss of transmitted sound caused by absorption and
reflection.
(7) Hyperechoic: a relative term that refers to the echoes returned from a
structure. Hyperechoic refers to a lesion or tumor which produces a
stronger echo thanthe surrounding structures or tissues.
(8) Hypoechoic: refers to structures that contain fewer or weaker echoes
than surrounding tissues.
(9) Resolution: ability to distinguish between two adjacent structures
(interfaces).
(10) Transducer: an electromechanical device that is part of an ultrasound
system. The device that contacts the patient and converts electrical
energy into mechanical energy and vice versa.
f. Knobology
(1) On/Off button: turns the machine on/off.
(2) Depth: depth controls the depth of field on your screen, the depth is
usually measured in centimeters to the right of the monitor screen.
(3) Gain: this adjust the gain (brightness) at various depths while compact
machines often have automatic adjustments.
(4) Dynamic Range: Dynamic range determines how many shades of gray
will be displayed between black and white. In practice, lower numbers increase contrast while higher numbers visualize subtle differences in
tissue.
(5) Freeze: the freeze button “freezes” the image on the screen to allow
saving, printing, or measurements.
(6) Color Doppler: Color doppler assigns two colors to represent flow
toward or away FROM THE PROBE. Often used to determine blood
flow in a vessel or structure. Typically, most machines utilize red color
to indicate flow going TOWARD the probe, and blue color to indicate
flow going AWAY from the probe.
(7) Calipers: this control places one or more icons on the screen that can be
moved to measure objects or select points in tracings for calculations.
(8) M-mode: “Motion” mode. A line is positioned vertically across the
display; when activated, the image within the line is scrolled across the
screen. Useful for calculation of fetal heart rate and measuring cardiac
structures.
g. Probes
(1) US probes have a marker, either a printed dot or a raised ridge, on one
side of the probe to establish probe direction.
(2) The marker will correspond to an icon on the display screen that is
usually found at the top left corner (but can be reversed or inverted).
(3) By convention, the probe marker is positioned generally to the patient’s
right or cephalad while imaging.
(4) Three main types of ultrasound probes or transducers:
(a) Curved probes: are used for abdominal and obstetric imaging.
(b) Linear probes: are used for soft tissue and small parts imaging.
(c) Phased array probes: use computer control to “bend” the US beam from flat,
small footprint to a wider pie-shaped wedge distally.
h. Conducting Gel
(1) US requires the use of a conducting gel to eliminate air between the
probe and skin.
(2) Ultrasonic medium gel is preferred but, in a pinch, any clear gel (KY
gel or lubricant) or water or blood can be used.
DESCRIBE the heart structures visible on ultrasound.
a. Two different views to visualize cardiac structures.
(1) Sub-xyphoid View:
(a) The probe is placed under the xyphoid process almost horizontal with the floor
and aimed directly under or slightly left of the sternum.
(b) The probe marker should face the patient’s right side.
(c) The probe should be positioned so that the pericardium, right and left ventricle
are visualized in long axis.
(d) The structures to the top of the screen are closest to the probe and the
structures on the bottom of the screen are the furthest (deepest) from the probe
for orientation purposes.
(e) The display screen should show a portion of the liver at the top, followed in
order the right ventricle, intraventricular septum, and the left ventricle.
(2) Left Parasternal View:
(a) The probe is placed just to the left of sternum at about the 5th Intercostal space
with the probe marker to the patient’s right.
(b) The probe can be rotated cephalad, aiming toward the right shoulder to obtain
the long-axis view.
(c) You should be able to visualize the pericardium, right ventricle,
interventricular septum, and left ventricle.
(d) You can then rotate the probe marker to point to the patient’s left shoulder to
obtain the short-axis view to see the same structures in a different view.
b. Pericardial Effusion
(1) Will reveal a hypoechoic rim of fluid around the heart.
c. All 4 cardiac Valves can be seen on US and evaluated for stenosis or regurgitation
(but those views are beyond this lecture).
d. Can visualize the right and left atrium in the 4 chamber view and in short axis.
IDENTIFY the difference between veins and arteries on ultrasound.
a. Most larger veins in the extremities run with or alongside the major arteries of the
upper and lower extremities.
b. You can tell the difference between arteries and veins by two different maneuvers.
(1) First and the most used maneuver is that since veins have less of a
muscular wall than arteries, veins are collapsible under pressure.
(a) You can put pressure on the probe and attempt to totally collapse the vessels.
The vessel that collapses will be the vein.
(2) Secondly, you can put a doppler over the vessels. If you have the probe
angled proximally on the extremity, then the artery will pulse a red
color and the vein will be blue.
DESCRIBE the steps to place an IV catheter with Ultrasound.
Setup
(1) Select linear probe.
(2) Use patient’s right arm for right-handers.
(3) Preset screen depth to 2-2.5 cm.
(4) Apply tourniquet.
(5) Pre-scan to find a suitable vein with non-sterile gel.
(a) Compressible and non-pulsatile.
(b) Avoid nearby muscle and nerves.
(c) Depth less than 2 cm.
(d) Width more than 0.4 cm.
(e) Length at least ¾ screen.
(6) Mark transverse and longitudinal plan course with skin marker.
(7) Remove excess non-sterile gel.
(8) Clean skin with Chloraprep (Chlorhexadine).
(9) Apply small bead of non-sterile gel to probe and cover with a large
Tegaderm.
b. Needle Insertion
(1) Re-scan selected vessel.
(2) Once midpoint of the vessel is identified, insert needle ½ c back from
probe at a 30- degree angle.
(3) Slowly watch the needle tip advance toward the anterior vessel wall
(move needle and probe up the arm a few mm at a time).
(4) Tent anterior vessel wall and enter with a quick “jab” (identify blood
return).
(5) Ensure you didn’t go through the posterior vessel wall by “waving” the
needle side to side and/or checking long axis view.
(6) Advance Angiocath
