![]() ![]() Such an endeavor would require specialized software, a streamlined patient selection protocol, and close coordination between the radiologist and technologist however, with the proper equipment, the idea is imaginable. Ultimately, one could conceive of an abbreviated ACS protocol that uses isotopic 3D volume acquisition combined with P31-MRS and MRE to yield anatomic and biochemical information. It remains to be seen whether the muscle compartment tension associated with myositis and ACS coincides with measurable tissue stiffness afforded by MRE. The inherent tissue stiffness affects the speed of the wave propagation, with stiffer tissue inducing faster wave speed. MRE “measures tissue stiffness by encoding displacements due to the propagation of externally induced acoustic waves into the MR phase signal”. Another emerging technology is MR elastography (MRE). reported a scan time of 4 min using a 3T system. MRS uses the relative chemical shift of inorganic phosphate (Pi) and phosphocreatine (PCr) to calculate pH using the Henderson-Hasselbalch equation. Efforts are in progress to measure muscle compartment pH by using an indwelling catheter or needle however, P31 magnetic resonance spectroscopy (MRS) has proven to accurately measure intracellular pH in a noninvasive manner. ![]() Conversely, lactate concentration has been shown to increase, leading to decreased tissue pH. Pyruvate and phosphocreatine levels have been shown to decrease in the setting of muscle glycolysis (anaerobic respiration). The inconsistent performance of intracompartmental pressure measurements has spawned research into the biochemical markers of impending irreversible muscle ischemia. However, with the ever-increasing accessibility, more efficient image acquisition, and the clinical use of techniques formerly reserved for research or less acute entities, emergent MRI could be useful in the diagnosis of myositis and even cases complicated by acute compartment syndrome (ACS). In general, MRI has been criticized for long scan times, difficulty of access, and lack of specificity. Occasionally, paraspinal muscles and shoulders are imaged when clinically indicated. The use of composed MR post-processing technique helps to seamlessly link upper and lower components of the arms or legs. The brevity of the protocol reflects the inherent sensitivity of MR in the detection of abnormal muscle signal over specificity. Currently, MR myositis protocols are characteristically brief, using a fluid-sensitive sequence such as short TI inversion recovery (STIR) or proton density with fat saturation in the axial and coronal planes as well as an axial T1 sequence. ![]()
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