Image fusion of fluid-attenuated inversion recovery magnetic resonance imaging sequences for surgical image guidance

Nonenhancing brain lesions can be relatively poorly defined on volumetric data sets routinely used for surgical guidance. Fluid-attenuated inversion recovery MRI sequences can provide better margin visualization of nonenhancing or poorly enhancing lesions.

Using image fusion programs, we combined data sets of SPGR imaging pulse sequence or volumetric CT with volumetrically acquired FLAIR sequences and subsequently used the fused data set for image-guided surgery. This technique was used in 50 surgical cases. Of these, 9 were nonenhancing intrinsic brain tumors, 13 were partially enhancing tumors, and 11 were enhancing tumors. In addition, FLAIR fusion was selectively used for 6 nontumoral lesions and in 11 nonlesional epilepsy surgery cases.

Image guidance using the fused data set was accurate in all 50 cases. Despite the lack of enhancement, 3 of the 9 nonenhancing tumors were found to be high grade. One of the low-grade tumors was associated with considerable areas of gliotic change not considered to represent tumor on permanent histology. In all other cases, the FLAIR-bright resected margins were consistent with tumor, not gliosis. Radical resection (>95% volume) was achieved in 21 of 23 tumor cases in which this had been the preoperative intent.

Nonenhancing lesions are often poorly demarcated not only on imaging studies, but also during surgery. Fluid-attenuated inversion recovery fusion allows resection of such lesions using intraoperative computer image guidance. Complementary FLAIR information can also occasionally be useful during surgical approaches to enhancing lesions or in nontumor cases. It must be kept in mind that FLAIR has high sensitivity but low specificity. Fluid-attenuated inversion recovery abnormalities do not obviate the need for mapping in potentially functional areas.