Page 140 - Basic Monitoring in Canine and Feline Emergency Patients

coupling gel ± alcohol. In patients that are hemody- When performing bedside US-guided vascular
namically unstable and could imminently arrest, access, the US setting should be changed to vascu-
VetBooks.ir the use of alcohol is discouraged as it is a fire haz- lar imaging with the ability to adjust depth. Some
machines may have a needle enhancement setting
ard if a patient needs electrical defibrillation.
Additionally, alcohol has the potential to damage
cannulation of vessels. Ideally a linear phase array
some piezoelectric US transducers. which may be helpful in seeing the needle during
Table 7.1. Common ultrasound artifacts.
Artifact Causes of artifact How the artifact appears

Reverberation Occurs when the ultrasound beam bounces Appear as regularly spaced echo signals NOT
back and forth between two highly representative of anatomic structures:
reflective interfaces Distance between each signal corresponds to
Occur within the tissue or between the distance between the two interfaces
tissue-transducer interface and another Each reverberation signal weaker than the one
structure within the tissues preceding it
Seen when imaging irregular lung surfaces, the
gastrointestinal tract, and abscesses containing
gas producing bacteria
B-lines are an example in TFAST 3
3
Air artifacts during SR, HR, and CC views on AFAST :
Air within the colon creates an air interface
which US cannot pass through well
Results in dirty shadow within the far field
Acoustic An absence or significant reduction of echo Mineralized structures present a black shadow
shadowing signal (reduced amplitude) occurring seen distal to the structure:
deep to a strongly reflective (i.e. gas), or Example: rib shadows during lung ultrasound
absorptive (i.e. bone) interface Gas produces a ‘dirty’ or white shadow distally:
3
Shadowing most pronounced when the Example: gas within the colon during AFAST
structure is located within the focal (CC examination)
zone of the transducer, high-frequency Bowel gas shadow may move with peristalsis
transducer is utilized
Shadowing useful to diagnose renal
and cystic calculi, other mineralized
abdominal structures
Refraction Bending of the sound beam occurring on Same effect as shadowing (seen as black areas
the margins of rounded organ structures. distal to structure creating the artifact):
US beam strikes an object at angle other Example: hypoechoic shadowing on cranial and
than 90° and the beam returns in a caudal poles of a rounded mass or kidney
different position mistaken as fluid
Sound wave deflected from its true path Avoid artifact by moving US probe so beam is
more perpendicular to the structure
Acoustic Sound beam travels through tissue with no Beam attenuated to lesser extent as it passes
enhancement interfaces through structure with no interfaces → louder/
Attenuation occurs as beam passes increased intensity echoes in tissue interfaces
through tissue → increases intensity of through which the beam passes
images distal to structure, creating falsely Structures distal to things such as urinary bladder,
hyperechoic structure gall bladder, cysts, and ascites are falsely
Example: fluid-filled structure (gall bladder, hyperechoic; can be mistaken as hyperechoic
urinary bladder) lesion within surrounding tissues
3
CC view during AFAST predisposed to acoustic
enhancement of the tissues deep to the urinary
bladder
Continued

132 D.M. Hundley