6
46TH
ANNUAL
CONGRESS
OF
THE
SAEVA
SKUKUZA
16-‐20
FEBRUARY
2014
Diagnostic Imaging – Computed Tomography
CT has recently gained attention as a useful alternative to MRI as a cross sectional
imaging modality with the potential to identify clinically significant lesions when they
occur within the foot. CT maps x-ray attenuation in cross-sectional images, similar
to routine radiography. Because of the method of image acquisition, CT is very
useful for the evaluation of osseous structures12,25 and has more recently been
advocated for complete evaluation of the foot in horses with foot lameness10,11,26,27.
In general, CT has high spatial resolution, thin slices and rapid acquisition. CT image
generation is dependent on the detection of alteration in tissue density. Historically,
this dependence has made it less optimal for the identification of soft tissue lesions.
Improved hardware (multi-slice CT scanning, better detectors) and improved
software (image processing, 3-dimensional rendering) have ameliorated many of
these concerns. Furthermore, the use of contrast media can aid in the detection of
pathology through the addition of a physiological assessment of the underlying tissue
(vascular studies) or the addition of improved delineation of structures similar in
density (arthrography).
Contrast enhanced CT (CECT) is a relatively new addition to the foot lameness
diagnostic armamentarium. Contrast media can be administered by a variety of
different routes, most commonly intra-vascular. In the horse, intra-arterial delivery
of contrast media during scanning provides an assessment of the vasculature,
highlights areas of increased flow or permeability as expected in tissues with active
inflammation, and the direct delivery allows for the administration of a relatively
small amount of contrast media relative to a horses’ total dose. This technique can
be used to evaluate the vascular supply to the foot but also aids in the identification
and characterisation of soft tissue lesions within the hoof capsule.
Diagnostic Imaging – Magnetic Resonance Imaging
Magnetic resonance imaging is invaluable in equine lameness diagnosis and has acted
as a catalyst to propel our collective understanding of foot lameness to new and ever
increasing levels. The use of MRI has identified soft tissue injuries or soft tissue
pathology previously under diagnosed via conventional techniques. Structures with
pathology include but are not limited to the deep digital flexor tendon, navicular
suspensory and impar ligament, navicular bursa and bone7,9,24-29. Further, injury or
pathology of structures of the distal interphalangeal joint such as the phalanges, the
collateral ligaments and the synovial structures can also be identified7,30. Newer MRI
sequences in high field strength magnets have better ability to define and identify
lesions of the cartilage. Some authors advocate for the use of MRI for pastern level
soft tissue injuries traditionally diagnosed with ultrasound such as distal sesamoidean
ligament injury31.
MRI acquisition is not easily understood and many of the advantages of the technique
are afforded by its complexity and ability to display tissues variably, depending their
composition. MRI is considered to have fair spatial resolution with excellent
contrast resolution, meaning that adjacent structures can be easily discerned based
on imaging characteristics such as proton density and proton mobility. The corollary
to this statement is that MRI can also clearly identify pathologic tissue when it is
immediately adjacent to normal tissue. Many different MRI sequences exist and
sequence development generally occurs to ameliorate a traditional problem or to
improve imaging of a tissue or pathology of a specific tissue type. In general, with all
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