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Value of T1 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 echoplanar imaging in characterizing focal hepatic lesions on the basis of image-derived T1 and T2 relaxation times.


SUBJECTS AND METHODS
Forty-six proven hepatic lesions were analyzed: 24 solid (21 metastases, three primary liver tumors) and 22 nonsolid (11 hemangiomas and 11 cysts). 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 echoplanar-equipped MR scanner was used to obtain fat-suppressed, single-excitation (TR essentially infinite) axial images with a slice thickness of 10 mm. T1-weighted inversion recovery images (TE = 25 msec; TI = 100, 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 acquired for 45 of 46 lesions. For each acquisition (i.e., each different TI or TE), the entire liver was imaged in a single breath-hold of 12 sec or less.


RESULTS
The mean T1 was 1004 (+/- 234) msec for solid lesions, 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. Mean T2 times were 80 (+/- 18) msec for solid lesions, 178 (+/- 40) msec for hemangiomas, and 517 (+/- 429) msec for cysts. The mean T2 for hemangiomas is the longest reported to date. A T2 cutoff of 116 msec was 100% accurate for classifying lesions as solid or nonsolid and 93% accurate for characterizing them as benign or malignant.


CONCLUSION
Our study suggests that echoplanar-derived T2 times (but not T1 times) are useful for characterizing focal hepatic lesions. An important use may be to characterize small lesions measuring less than 2.0 cm. The main 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 relaxation times.