Is dedicated extremity 1.5-T MRI equivalent to standard large-bore 1.5-T MRI for foot and knee examinations?

Objective: The purpose of this study was to prospectively compare dedicated extremity MRI and standard large-bore MRI of the lower extremities in the same patients.

Subjects And Methods: Sixty-nine patients (27 feet and 42 knees) were examined both with extremity 1.5-T MRI and standard 1.5-T MRI. Scanning duration was measured, and patients completed a detailed questionnaire after each examination (4-point scale). Two readers assessed image quality parameters. Data were analyzed with the paired Student t test, Wilcoxon signed rank test, and chi-square test.

Results: Scanning duration was significantly longer for extremity MRI (foot, 29.9±5.5 minutes; knee, 30.4±5.6 minutes) than for standard MRI (foot, 21.9±5.0 minutes; knee, 20.5±3.9 minutes) (p<0.001 for all comparisons). Acoustic noise reported by the patient was significantly lower on extremity MRI (foot, 1.9±0.9; knee, 2.1±0.7) compared with standard MRI (foot, 2.9±1.0; knee, 2.9±0.8) (p<0.001 for all). Patient satisfaction for both systems was high (1.4-1.6 for all, p=0.2-1.0). Image quality and fat suppression were equally good for both scanners for foot examinations (p≥0.48). Knee examinations generally featured good image quality on both systems, but standard MRI had superior image quality (p≤0.01) and fat suppression (p≤0.001) compared with extremity MRI. More motion artifacts were present on extremity MRI than on standard MRI, which was significant for the knee (p≤0.04) but not for the foot (p≥0.32).

Conclusion: Extremity MRI featured less acoustic noise than standard MRI, but examination duration was longer on extremity MRI. Patient satisfaction was high for both scanners. For foot examinations, image quality on extremity MRI was equivalent to standard MRI. Image quality for knee examinations was better on standard MRI compared with extremity MRI, but overall it was good on both systems.