Magrwic RcsononcP Imaging, Vol. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 1 I, pp. 27-33, 1993 0730-725X/93 $6.00 + .&l Printed in the USA. All rights reserved. Copyright 0 1992 Pergamon Press Lrd. l zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Original Contribution zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA LOW RESOLUTION SPIN ECHO: A SIMPLE TIMESAVING TECHNIQUE FOR MRI LIVER EXAMS RENEE J. BUTLER-LEWIS, WILLIAM A. ERDMAN, HAL T. JAYSON, BRUCE A. BARKER, BRANCH T. ARCHER, AND RONALD M. PESHOCK Department of Radiology, The University of Texas Southwestern Medical Center, Dallas, TX 75235-9058, USA MR evaluation of the liver at mid-field strength requires relatively lengthy T,-weighted sequences (T2W) for dif- ferentiation 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 x 1.7 mm pixel) T2W sequence (matrix 64 x 256, FOV 21.7 cm phase x 43.5 cm fre- quency) were compared to the 17 min standard resolution (1.7 mm x 1.7 mm) T2W sequence (256 x 256 matrix, FOV 43 x 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% (31131) 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 (IV = 1). Thus in many situations low resolution zyxwvutsrqponmlkjihgfed T2 may provide a substantial timesaving alternative to standard T2W particularly where T2W is used primarily for lesion classification in normal sized patients. Keywords: MRI; Liver neoplasm; Pulse sequence; Abdominal MRI; Rapid image MRI. INTRODUCTION Magnetic resonance imaging (MRI) is an effective non- invasive technique for detection and characterization of liver tumors’-’ because of its high tissue contrast. A variety of pulse sequences have been evaluated, 1,5*6,8,9 with sensitivity and specificity ranging between 85 to 100% and 74 to 93070, respectively.3~5~7,9-11 At mid- field strength (0.35 T) the standard liver screening examination includes T2W sequences which are im- portant for their ability to help characterize lesions (es- pecially benign cavernous hemangiomas), and Tl W images which are used for both good anatomical res- olution and high lesion-to-liver contrast. T2W sequences generally have lower signal-to-noise ratios (SN) and take longer than TlW sequences be- cause of their inherently longer TR and TE values. As a result, the T2W sequence is the single longest acqui- sition in the MRI liver examination. More recently, rapid acquisition techniques have been introduced which may significantly reduce study time.“-‘4 De- spite the promise of quicker studies, many of the new rapid acquisition techniques are difficult to implement on current MRI systems or provide tissue contrast which are non-conventional. The standard T2W at mid-field (0.35 T) employs a TR of 2000 msec, a TE of 40, 80, 120 msec, 1.7 x 1.7 pixel, 256 x 256 mm matrix, and a 43.5 x 43.5 cm field-of-view (FOV). This acquisition takes 17 min when two excitations are used. The average size patient usually requires only a 21 cm FOV in the phase-encod- ing direction to prevent wrap around. However, we have found at 0.35 T that any attempts to reduce ac- quisition time by decreasing the matrix size (and thus the FOV) result in unacceptable decreases in SN. A simple and easily implementable approach to re- ducing acquisition time without decreasing SN or FOV is to employ rectangular pixels which are longer in RECEIVED 12/20/91; ACCEPTED 7/3/92. Address correspondence to William A. Erdman, MD, Department of Radiology, The University of Texas South- western Medical Center, 5323 Harry Hines Boulevard, Dal- las, TX 75235-9058. 27