Page 141 - Basic Monitoring in Canine and Feline Emergency Patients

Table 7.1. Continued.

VetBooks.ir Artifact Causes of artifact How the artifact appears
Mirror image
DH view during AFAST , air-soft tissue interference
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Created by altered paths of reflected sound
between interfaces
Create the illusion of anatomic structures in between liver, diaphragm, and lungs creates
mirror image
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areas where they are not actually located SR view during AFAST in very small dogs and
Example: highly reflective surface of the cats:
diaphragm → makes liver appear to be Possible to image both kidneys in same US
on both sides of the diaphragm (could be image
mistaken as a diaphragmatic hernia) Can be misinterpreted as a false mirror image
artifact
Slice thickness US beam plane is near the edge of a Simulates debris in normally anechoic structures
cystic structure (e.g. gall bladder or Misrepresents a cystic structure as a solid structure
urinary bladder), echoes are received Example: false mass or sludge effects within the
from outside the structure due to beam's urinary bladder
thickness. Recognized by scanning in more than one plane,
‘Filling-in’ of the structure may occur → allowing resolution of the artifact
falsely simulates debris or causes a
smaller cystic structure to appear solid
Side lobe Stray echoes displaced laterally, outside Side lobe artifact similar in appearance to slice
the main beam, from US transducer thickness
Transducer is positioned over a fluid- Creates the appearance of echogenic material
filled structure and ‘side beams’ may within a fluid-filled structure:
encounter soft tissue structure outside Example: bowel gas near the gall bladder or
the fluid structure: urinary bladder creating a strong reflection
US machine assumes side lobes confused with echogenic debris or calculi
originated from the main US beam DH view during AFAST predisposed to side lobe
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within the fluid-filled structure and edge shadowing artifacts:
US machine places the echogenic Causes decreased clarity along luminal borders
signal within the fluid Gives false appearance of sediment
AFAST , abdominal focal assessment sonographically for trauma/triage/tracking; CC, cystocolic; DH, diaphragmaticohepatic; HR,
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hepatorenal; SR, splenorenal; TFAST , thoracic focal assessment sonographically for trauma/triage/tracking; US, ultrasound.
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probe with a minimum frequency of 7.5 MHz nearly every examination. Right lateral is also a
should be utilized as it has superior detail for standard recumbency during triage for electrocar-
superficial structures. However, a curvilinear probe diogram assessment (see Chapter 3). Additionally,
with a frequency range of 5–8 MHz with an adjust- when performing abdominocentesis, right lateral
able depth to less than 4 cm may also allow for recumbency minimizes the chance of mistakenly
sufficient imaging for vascular access. In contrast sampling the spleen by keeping it elevated and
to other bedside imaging, when using an ultrasound- away from the more gravity-dependent free abdom-
guided technique (UST) for vascular access, the inal fluid.
patient needs to have fur clipped, the site should In patients that are hemodynamically unstable or
be aseptically prepared, and the US probe should extremely stressed in lateral recumbency a modi-
be aseptically housed in a sterile cover such as a fied sternal approach (Fig. 7.4) has been described
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sterile glove filled with coupling gel. Alcohol can be for AFAST and TFAST (albeit not validated in
applied to the skin to allow for contact between the veterinary medicine). In this approach, the cranial
skin and sterile US probe cover. aspect of the patient is kept sternal while the caudal
When completing the AFAST and TFAST aspect of the patient is rotated to the desired right
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examinations, a veterinary patient is typically lateral recumbency. An AFAST examination is not
placed in right lateral recumbency (Figs 7.2 and recommended to be performed in dorsal recumbency,
7.3). This position is ideal because it allows for full primarily due to risks of exacerbating potential
assessment of the left kidney and gallbladder in hemodynamic instability and respiratory compromise
Applications of Serial Focal Ultrasound Techniques in the Hospitalized Small Animal Patient 133