504 Canine Sports Medicine and Rehabilitation
evaluation of the area of interest in slices and
eliminates superimposition of structures that
complicate diagnosis in standard radiography.
The CT scanner is composed of an X‐ray gen-
erator and an X‐ray detector. The X‐ray genera-
tor moves around the patient taking thousands
of X rays at multiple projection angles that are
picked up by the X‐ray detector. In a stop‐step
CT unit, after the projections are acquired, the
patient is advanced to obtain the next “slice”
along the longitudinal (z) axis. Helical or spiral
scanners allow for continuous movement of the
patient through the scanner while the X rays are
being taken. This allows for a more contiguous
scan image and volumetric information for 3‐D
reconstruction. Images are generated through
processing of the attenuation information from
the X‐ray detectors that is filtered and back‐
projected to form the digital image. The digital
image is then converted to a gray‐scale analog
image.
Like a radiograph, CT images provide the
most detail about bony structures, but CT
images are not limited to two planes. This is
a significant diagnostic advantage when evalu-
ating for fracture configuration, osteochondral
fragmentation, or evaluation of joint incongruity.
CT is commonly used in the elbow joint to
detect abnormalities associated with elbow
dysplasia that can be difficult to assess with
standard radiography (Reichle et al., 2000;
Gemmill et al., 2006; Moores et al., 2008; Böttcher
et al., 2009; Cook & Cook, 2009; Shimizu et al.,
2015). In addition to viewing the individual
slices for pathology, 3‐D rendering can be per-
formed on the entirety of the scan images,
reconstructing the area of interest for evalua-
tion (Moores et al., 2008; Dennison et al., 2010)
(Figure 20.3).
Although CT is a modality dependent on
X‐ray attenuation through tissues, making it
particularly valuable for osseous injury, it can
also be used to evaluate soft tissue lesions and
has potential for interventional radiology. CT
has a low‐contrast resolution setting, and
through manipulation of the window and CT
number (Houndsfield units), visualization of
soft tissue structures can be optimized. It is
commonly used for injuries to the spine such as
intervertebral disc disease (Newcomb et al.,
2012). It has also been used clinically in dogs to
evaluate soft tissue abnormalities in the stifle
and iliopsoas (Rossmeisl et al., 2004; Samii et al.,
2009). A comprehensive evaluation of the soft
tissues using CT or computed tomography
angiography (CTA) of the canine shoulder in
cadaver dogs showed that this modality may
have value in evaluation of the shoulder (Reis
Silva et al., 2013). CT may also play a role in
both research and clinical settings to evaluate
response to rehabilitation therapies by evaluat-
ing the CT morphometry of muscle groups in
the regions of interest (Cain et al., 2016). Use of
CT‐guided interventional radiology (IR) proce-
dures for therapeutic purposes in canine
patients may be a future application of this
imaging modality as well. In one experimental
study, CT was used to successfully inject the
canine lumbosacral facet joints with methyl-
prednisolone acetate (Liotta et al., 2016).
CT has value in the evaluation of both osse-
ous and soft tissue injuries and may also have
future roles in therapeutic IR treatment and
outcome measures. Another advantage is that
most exams can be done under sedation ratherFigure 20.3 Three‐dimensional rendering of the radius
and ulna including the humeroradial and radiocarpal
joints. Source: Image courtesy of Dr. Sherman Canapp.