Page 158 - Canine Lameness

130 10 Diagnostic Imaging Techniques in Lameness Evaluation

multi‐planar reconstructions (using a commercially available software imaging tool), thus
permitting complete visualization of all anatomic structures.
CT terminology uses the term “attenuation” to describe tissue characteristics in relation to each
other: tissues presenting as bright are described as hyperattenuating, dark tissues are described as
hypoattenuating, and tissues of similar brightness are described as isoattenuating. Fluids are typi-
cally hypoattenuating.

10.5 Magnetic Resonance Imaging

MR (Figure 10.5) is a newer modality in veterinary medicine for evaluation of musculoskeletal
conditions. Soft tissue injuries of the shoulder are often diagnosed with MR imaging (Agnello et al.
2008; Murphy et al. 2008; Schaefer et al. 2010). It provides excellent contrast resolution of the soft
tissues and multiple anatomic planes to visualize the region of interest. Although CT and MR both
offer excellent contrast resolution, MR is considered the gold‐standard imaging modality for evalu-
ation of soft tissue injuries. CT uses X‐rays and attenuation differences in tissues, whereas MR uses
electromagnetic radiation to evaluate the hydrogen nuclei (protons) composition in tissues.
Because different tissues have different amounts of protons, MR imaging can characterize tissues
more sensitively than CT.
However, MR is not without its limitations. Detection of subtle bone changes is more difficult
with MR imaging, and in contrast to CT imaging, MR is usually limited to one region and is often
more time‐consuming due to the multiple sequences in different planes that need to be acquired
for a complete study. Other disadvantages to MR imaging include the need for general anesthe -
sia, added expense, and decreased availability compared to radiography, ultrasonography, and
CT imaging.

(A) (B) (C)

Figure 10.5 MR images of the shoulder showing proton density fat‐saturated images: (A) sagittal plane at
the level of the biceps tendon. Note the hyperintensity of the tendon and surrounding bursa (arrow); (B)
dorsal plane at the level of the biceps tendon within the intertubercular groove of the humerus. Note the
hyperintensity within the tendon and surrounding bursa (small arrow) and the hyperintensity within the
muscle belly distally (large arrow); (C) transverse plane at the level of the biceps tendon within the
intertubercular groove of the humerus. Note the hyperintensity within the biceps tendon and adjacent
bursa (arrow). Diagnosis was biceps tenosynovitis and with possible biceps tendon tear.