Differentiation between small hepatic hemangiomas and metastases on MR images: importance of size-specific quantitative criteria.

We studied the feasibility of using MR imaging at 0.6 T to differentiate small hepatic hemangiomas from small metastases on the basis of quantitative criteria. Ninety-two liver masses up to 5 cm in diameter, including 51 proved hemangiomas (mean, 1.9 +/- 1.1 cm) and 41 proved metastases (mean, 1.9 +/- 1.2 cm) were analyzed. Lesions were divided into three groups on the basis of size (less than or equal to 1 cm, greater than 1- less than or equal to 2 cm, greater than 2- less than or equal to 5 cm). The ability to distinguish hemangiomas from metastases was examined by using differences in lesion/liver signal-intensity ratio (SIR) and contrast-to-noise ratio (CNR) on T2-weighted images (SE 2350/180). Receiver-operating-characteristic analysis for all lesions grouped together showed that differentiation based on SIR was superior to that based on CNR (p less than .05). The mean SIR of hemangioma and the difference between mean SIRs of hemangioma and metastasis decreased with lesion size (greater than 2- less than or equal to 5 cm: 6.11 +/- 2.61 vs 2.30 +/- 1.22; greater than 1- less than or equal to 2 cm: 4.47 +/- 1.56 vs 2.40 +/- 0.73; less than or equal to 1 cm: 3.59 +/- 0.92 vs 2.01 +/- 0.52). However, in each size group, the difference between the mean SIR of hemangioma and metastasis was statistically significant (p less than .0001). These observations suggest that MR imaging is useful in differentiating small hepatic hemangiomas from small metastases and suggest the need for establishing size-specific quantitative criteria for tissue characterization.