Anatomic, differential diagnosis key to MRI success - DVM
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Anatomic, differential diagnosis key to MRI success


DVM360 MAGAZINE


Electromyography is better than MRI for muscle disease evaluation, and a muscle biopsy is the only manner in which a definitive diagnosis can be made. However, MRI has proven a useful adjunctive diagnostic procedure for cases of polymyositis where diagnosis is elusive, particularly if a specific anatomic localization cannot be reached by other means. The MRI signal intensity of normal muscle is intermediate between that of fat and cortical bone. MRI studies in dogs have shown a good correlation between uniform hyper-intensity on T1-W and T2-W images showing enhancement after contrast medium administration and muscle inflammation identified histopathologically.

Vascular-related neurological disorder

In addition to stroke, vascular-related neurological disorders include aortic thromboembolism (ischemic neuro-myopathy), congenital portosystemic shunt (hepatic encephalopathy) and other vascular malformations (such as caudal vena cava malformation) as a possible cause of exercise-induced weakness and collapse. In addition to its use for tissue evaluation, MRI (i.e., magnetic resonance angiography or MRA) can non-invasively assess the vascular system. Two techniques can be used: 1. time of flight (TOF) MRA and 2. contrast MRA. The TOF MRA can be implemented on every MR system, is easy to use, and do not need contrast medium injection. TOF may be used in either a 2-D (sensitive to slow-flowing blood) or a 3-D sequence (high spatial resolution and sensitive to fast-flowing blood). Contrast MRA is based on the use of paramagnetic contrast agents in combination with gradient-echo sequences. Paramagnetic contrast media strongly enhance the MR signal due to T1 shortening. Image data can be collected during the whole measurement cycle, demonstrating arterial and venous contrast passage. In all MRA techniques, image contrast is the result of blood motion. Although less invasive, one of the main limitations of MRA is its lower resolution compared with conventional angiography that becomes progressively worse as the vessel luminal size decreases.


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