Low resolution spin echo: A simple timesaving technique for MRI liver exams

MR evaluation of the liver at mid-field strength requires relatively lengthy T₂-weighted sequences (T2W) for differentiation of benign cavernous hemangiomas from malignant lesions. A short duration T2W, which maintains standard signal-to-noise ratio and also contrast relationships, can be easily implemented by increasing the pixel size in the phase-encoding direction (thus reducing spatial resolution) and proportionally decreasing the number of phase-encoding steps in the matrix (thus reducing acquisition time). Blinded interpretations of a quick (4 min), low resolution (3.4 mm × 1.7 mm pixel) T2W sequence (matrix 64 × 256, FOV 21.7 cm phase × 43.5 cm frequency) were compared to the 17 min standard resolution (1.7 mm × 1.7 mm) T2W sequence (256 × 256 matrix, FOV 43 × 43 cm) in 25 patients suspected of having liver metastasis. Lesions felt to be cavernous hemangiomas showed a 100% ( 24 24) agreement for interpreter "A" and 96% ( 22 23) agreement for interpreter "B" when 4 min low resolution T2W was compared to the standard 17 min sequence. Sensitivity (for all types of lesions) of the low resolution T2W sequence ranged from 100% ( 31 31) for interpreter "A" to 80% ( 28 35) for interpreter "B". Missed lesions (interpreter "B") were either partially obscured by excessive fat (wrap around) (N = 4), less than 1 cm in size (N = 2), or degraded by motion artifact (N = 1). Thus in many situations low resolution T₂ may provide a substantial timesaving alternative to standard T2W particularly where T2W is used primarily for lesion classification in normal sized patients.