Chronic exertional compartment syndrome of the lower extremities: Improved screening using a novel dual birdcage coil and in-scanner exercise protocol

Objective: The purpose of this study was to design and evaluate an MRI screening protocol for chronic exertional compartment syndrome (CECS) of the lower legs using an in-scanner exercise protocol and novel dual birdcage coil design for improved imaging. Materials and methods: Coil and phantom studies: a custom-made dual birdcage coil designed for this protocol was evaluated for uniformity and signal-to-noise ratio (SNR) compared with a conventional phased-array receive-only torso coil and the body coil. Phantom and normal subject studies were performed to confirm coil performance. In-vivo studies: eight unaffected subjects and 42 patients with lower extremity symptoms suggestive of CECS were imaged with the dual birdcage coil and an in-scanner exercise protocol which included imaging at rest, during isometric resisted dorsi flexion, at rest (recovery), during isometric resisted plantar flexion and, again, at rest. Of 42 patients, 14 had confirmed CECS and 28 had lower extremity anomalies attributable to other causes. Ratios of relative T2-weighted signal intensities were calculated for exercise and recovery images compared to baseline after processing of images, including re-registration for motion, smoothing and segmentation to remove bone and pulsation artifacts from blood vessels. Results: Receiver operating characteristic (ROC) analysis showed a threshold for the ratio of relative T2-weighted signal intensity of 1.54 to have a sensitivity of 96%, specificity of 90% and accuracy of 96% for CECS. Patients with CECS had their peak ratio of signal intensity compared with baseline during the first recovery period after isometric dorsi flexion, whereas unaffected subjects and patients with other causes of exercise-induced lower extremity pain reached their peak values during exercise (P < 0.001). Conclusion: We have developed the first in-scanner MRI exercise protocol for the assessment of patients with suspected CECS. The technique shows high accuracy, sensitivity and specificity for diagnosis in this small cohort of patients with CECS. Further study may allow this non-invasive test to be used as a triage tool for invasive intracompartmental pressure measurements in patients with suspected CECS.