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Comparison of Radiography, Scintigraphy, and Magnetic Resonance Imaging Techniques: How Does One Image Compare to Another?
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Each imaging modality has its own strengths and weaknesses. Knowing the caveats of each will help determine what modalities to use and how to interpret the findings. Author’s address: Alamo Pintado Equine Medical Center, 2501 Santa Barbara Ave., Los Olivos, CA 93441; e-mail: carter@alamopintado.com.
1. Introduction
Advanced imaging techniques such as magnetic resonance imaging (MRI) and scintigraphy have helped to improve the diagnostic capabilities in the horse. They have allowed a unique perspective into many problems that previously may have been difficult to determine otherwise. With the proliferation of these different imaging modalities, they are being performed much more commonly and, often, in conjunction with each other. The purpose of this presentation is to discuss how MRI, scintigraphy, and radiographic imaging techniques relate to each other and to discuss some of the benefits and pitfalls of each and how over- and under-interpretation of various imaging modalities occur.
2. Scintigraphy and MRI
Nuclear scintigraphy has been used in equine orthopedic imaging to identify physiologic changes in bone and soft tissue metabolism and has been used to identify regions of lameness for decades. While it requires a regulatory license and involves the use of radioactive labeled isotopes, it is still a simple relatively non-invasive diagnostic technique that is performed standing under light sedation. The entire horse can be screened using this technique.
Magnetic resonance imaging (MRI) is the gold standard in imaging human orthopedic conditions and is quickly becoming more commonly available to equine veterinarians. It can be performed in the standing patient using a low field system or in the anesthetized patient using either a low or high field imaging system. The high field systems provide very detailed information about both physiology and anatomy.
Both of these techniques have traditionally been considered in isolation when considering imaging a patient. Scintigraphy is often used when the region of lameness is unknown or indeterminate using routine techniques such as nerve blocks to localize the area of pain. Magnetic resonance imaging is used when the area of pain is known but the cause has not been well established using other techniques.

Fig. 1. Plantar scintigraphic projection of the hock region with focal increased uptake of the right hind proximal metatarsus. Transverse T1 image of the proximal metatarsus of the right hind limb in the same region as the scintigraphic uptake showing only suspensory ligament pathology.

Fig. 2. MRI images of the region of increased uptake on the scintigraphy examination. A, Proton density axial, B, T2 short tau inversion recovery (STIR) axial, C, T1 VIBE FS axial, D, proton density FS axial, E, T2 STIR sagittal, and F, T2 STIR dorsal. Note the increased signal (white area in the palmar aspect of MC3) on images B–F and decreased signal on A. This is consistent with bone “edema.” Note the normal appearance to the suspensory ligament, which contains fat and muscle, creating a region of light gray and white within the black ligament fibers.
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