VALUE OF T1-RELAXATION AND T2-RELAXATION TIMES FROM ECHOPLANAR MR IMAGING IN THE CHARACTERIZATION OF FOCAL HEPATIC-LESIONS

OBJECTIVE. The purpose of this study was to determine the value of ech oplanar imaging in characterizing focal hepatic lesions on the basis o f image-derived T1 and T2 relaxation times. SUBJECTS AND METHODS. Fort y-six proven hepatic lesions were analyzed: 24 solid (21 metastases, t hree primary liver tumors) and 22 nonsolid (11 hemangiomas and 11 cyst s). Mean lesion size (maximal length) was 4.0 (+/- 3.2) cm, and 16 of 46 lesions were less than 2.0 cm. A commercially available 1.5-T echop lanar-equipped MR scanner was used to obtain fat-suppressed, single-ex citation (TR essentially infinite) axial images with a slice thickness of 10 mm. T1-weighted inversion recovery images (TE = 25 msec; TI = 1 00, 380, 600, or 800 msec) were acquired for 28 of 46 lesions, and T2- weighted spin-echo images (TE = 25, 50,100, 75 or 150 msec) were acqui red for 45 of 46 lesions. For each acquisition (i.e., each different T I or TE), the entire liver was imaged in a single breath-hold of 12 se c or less. RESULTS. The mean T1 was 1004 (+/- 234) msec for solid lesi ons, 1337 (+/- 216) msec for hemangiomas, and 3143 (+/- 1392) msec for cysts. Although the mean T1 of solid and nonsolid lesions differed (p < .004), overlap precluded the use of T1 as a discriminatory index. M ean T2 times were 80 (+/- 18) msec for solid lesions, 178 (+/- 40) mse c for hemangiomas, and 517 (+/- 429) msec for cysts. The mean T2 for h emangiomas is the longest reported to date. A T2 cutoff of 116 msec wa s 100% accurate for classifying lesions as solid or nonsolid and 93% a ccurate for characterizing them as benign or malignant. CONCLUSION. Ou r study suggests that echoplanar-derived T2 times (but not T1 times) a re useful for characterizing focal hepatic lesions. An important use m ay be to characterize small lesions measuring less than 2.0 cm. The ma in advantages of echoplanar imaging are the absence of motion-induced volume averaging and phase artifacts, the ability to acquire purely T2 -weighted images, and the use of multiple data points to calculate rel axation times.