Ultrasonography Flashcards
ultrasonography
imaging method that uses sound waves to produce images of structures in the body
what can you use an ultrasound to evaluate?
texture of organs and real-time visualization of functional ability of organs
principles of ultrasound
they’re based on the conversion of electrical energy into mechanical energy
electrical energy applied in pulses to a probe and converted to sound waves by crystals in the probe
how do ultrasounds convert sound waves into images?
sound waves are directed to patient —> waves can be absorbed, scattered, or reflected back as an echo to the transducer —> transducer receives echoes, converts them back into electrical impulses and then they are translated and read by computer
what is the most important component for converting the energy in an ultrasound?
the transducer
made of piezoelectric ceramics which have unique properties that allow them to change shape in the presence of an electrical current
the electrical impulses make the ceramic vibrate and causes crystals within the ceramic to emit a mechanical vibration at a preset frequency
sound waves
made by areas of high pressure alternated by an area of low pressure
high pressure areas are represented as peaks
low pressure areas are represented as troughs
wavelength
physical distance between 2 consecutive peaks in a sound wave
amplitude
distance of maximum vertical displacement of wave from its mean position
high amplitude = loud sounds
low amplitude = quieter sounds
frequency
rate of vibration of the sound travelling through the air and is calculated in cycles per second
measured in Hertz (Hz)
1 wave cycle/sec = 1 Hz
1000 cycles = 1 kilohertz (KHz)
1 million cycles = 1 mega-Hertz (MHz)
most procedures use frequencies that range from 2-15 MHz
how are frequency and wavelength related?
inversely related
high frequencies have shorter wavelengths which yields greater resolution but decreased penetrating power
low frequencies have longer wavelengths which yields lower resolution and increased penetrating power
what is the enemy of ultrasound?
air
ultrasound waves tend to reflect strongly wherever air meets biological tissue but waves travel very easily through liquids which is why we use lube
echogenicity
appearance of tissues on ultrasound based on ability of tissues to reflect sound waves
refers to the brightness of tissues that are being projected on a B-mode plane
anechoic
structure that is lacking in internal echoes or is echo free
appears dark to black
hyperechoic
tissue of interest reflects back more intense sound waves and appears brighter than tissues surrounding it
hypoechoic
tissue of interest reflects fewer sound waves and with less intensity making it appear darker than surrounding tissues
isoechoic
2 structures have relatively similar echogenicity toward each other
attenuation
loss of sound wave energy as it traverses the tissue of the medium due to absorption, reflection, or scattering
reverberation
sound wave is repeatedly reflected between 2 highly reflective surfaces
near field
area of a structure of interest that is closest to probe
far field
area of a structure of interest that is farthest from probe
ultrasound machine models
cart, laptop, handheld portable
ultrasound machine
wider range of tissue densities than radiographs
at least 256 shades of gray
what are the basic components of an ultrasound machine?
power source, transducer, control panel
transducer
can generate single or multiple (used more often) frequency ranges
frequency is generated based on size of crystals in the probe (frequencies can reach up to 22 MHz)
why do transducers have a marker?
can be in the form of an indentation, raised surface, or illuminated light
matches up with the marker in one of the corners on the ultrasound screen to tell you which side you are viewing
footprint
area where transducer makes contact with the patient
types of transducers
linear, convex/curvilinear, microconvex, phased array
linear transducer
most common
rectangle/trapezoid footprint
high resolution, used in fine detail imaging for imaging vessels, skin, M/S, testicles, eyes, or breasts
convex/curvilinear transducer
curved/wide footprint
lower resolution
used for organs in the abdomen
microconvex transducer
smaller convex footprint
used for smaller dogs, cats, or exotics
phased array transducer
have piezoelectric crystals aligned linearly that are evaluated in sequence
used for cardiac studies, lungs, pleura space
what are the other less common transducers?
matrix: 2D matrix that produces a 3D image
volume: 4 and 5D reconstructions
transducer care
wipe after each use with dry or water moistened soft cloth
if the probe gets contaminated use 10% bleach solution, glutaraldehyde based disinfectant, or 70% isopropyl alcohol but don’t go past 2cm from the tip of the probe
each probe is $3,000-16,000
control panel/knobology of ultrasound machine
common controls are gain, depth, time gain compensation, presets, frequency selection, and optimization
gain
affects brightness by modifying strength of returning echo
affects range of greyscale used
depth
every type and size of transducer has a set minimum and maximum
rule of thumb: limit depth of scan so that the area of interest fills full monitor screen
time gain compensation (TGC)
allows operator to selectively adjust gain at various depths to obtain a smooth greyscale image which is done through manipulating a series of sliding tabs that affect the level of brightness at various depths
presets on ultrasound machine
facilitate and maximize performance of the transducer
frequency selection
allows operator to change frequency within the range allowed by the probe, affects maximum penetration depth of sound waves in tissues
optimization control on ultrasound machine
automatically optimizes settings in order to get the best image
image display modes
A-mode, B-mode, M-mode, doppler
A-mode
amplitude mode
least common
measures distance and only has 1D information
used for ophthalmic evaluations and measurement of SQ fat
B-mode
brightness mode
most common
returning echoes in this mode are displayed as bright dots on the monitor with varying degrees of brightness corresponding to the intensity of the returning signal
M-mode
motion mode
creates B-mode image in motion
cursor line is set over an area of interest as imaged in B-mode which creates a B-mode image while displaying motion of tissues over a 2D scale
used in echocardiography
doppler image display mode
used to image flow of blood and other liquids while measuring velocity
color doppler: information collected is presented as a color overlay over a B-mode image
uses 2 colors: blue shows blood flow away from transducer and red shows blood flow towards transducer
power color doppler: assess blood flow but doesn’t identify direction, used to detect lower velocities of blood flow in tissues like a neoplastic mass
continuous wave doppler display mode
2 types of crystals in transducer: 1 sends out signals and the other receives signals
allows for accurate measurements during cardiac studies of very high velocity blood flow
patient prep for an ultrasound
dorsal recumbency in trough for abdominal, right/left lateral recumbency for echocardiogram,
fur clipped away and 70% isopropyl alcohol followed by large amount of lube
abdominals should be done with food withheld for 12-24 hours before
AFAST scan
abdominal focused assessment with sonography for trauma
identifies free fluid within the peritoneal space
lateral recumbency
what type of examination technique is used for an AFAST scan?
divide abdomen into 4 quadrants
1. diaphragmatic hepatic (DH): 12 o’clock position located caudal to the xiphoid process, evals diaphragm and liver
2. splenorenal (SR): 3 o’clock position over left flank for patient in right lateral recumbency, evals spleen and left kidney
3. cysto-colic (CC): 6 o’clock position caudal to abdomen, evaluates bladder and colon
4. hepatorenal (HR): 9 o’clock position on right flank area for patient in right lateral recumbency, evals right kidney and liver
views of each area for an AFAST scan
2 views of each area: longitudinal (transducer notch pointed cranially) and transversal plane (rotating transducer 90 degrees so notch is pointing to patient’s right side)
TFAST
thoracic focused assessment with sonography for trauma
identifies free fluid within pleural or pericardial spaces
where should the probe be positioned for looking at the pleural space in a TFAST ultrasound?
on dorsolateral region of thoracic wall with transducer notch pointing cranially
what regions of the lung are visualized in a pleural space effusion assessment?
caudodorsal lung lobe, middle lobe, perihelia lung lobe, cranial lung lobe
