gms | German Medical Science

Objective: Intraoperative magnetic resonance imaging (MRI) is a unique tool visualizing structures for resection control during brain surgery. Not only structural imaging, but also functional information (e.g. perfusion imaging) can become important in both preoperative imaging as well as during the procedure and for evaluating the success of tumor removal. Commonly used method to enhance certain structures and visualize perfusion includes contrast agent application and is therefore limited in their application. A remedy might be Arterial Spin Labeling (ASL) as this method allows for visualizing cerebral perfusion without any external contrast injection. The goal of this study is to present and to evaluate the use of ASL in an intraoperative setting and also to compare the results to routinely performed (contrast-enhanced) structural imaging.

Methods: In a previous study, ten volunteers were scanned on different MRI machines (3T and 1.5T) in radiology and neurosurgery to ensure comparability of the obtained results. In this study the same scanners were used (all from Philips Healthcare, Best, Netherlands). Pseudo-continuous ASL (pCASL) was used and CBF quantified as ml blood/min/100g brain tissue. Data was obtained on currently six patients (3 male, 3 female, mean age = 59.2 years) suffering from glioblastoma multiforme who underwent pre-, intra- and postoperative imaging according to the local standard of care with ASL performed additionally. The results from ASL regarding the possibility to visualize residual tumor mass during and after surgery were directly compared to contrast enhanced structural imaging.

Results: In four out of six patients the same results could be obtained (two had total removal, two residual tumor mass). In one patient structural imaging data was first false-positively misinterpreted. Here, a partial-volume effect of an artery was interpreted as residual tumor mass, but the result was later changed without taking the information from ASL into consideration. On the ASL data no uncertainties occurred in this case. In a second patient no residual tumor was identified on the structural images, but ASL showed an area of elevated perfusion. The results from structural imaging were then amended and concluded that there is in fact residual tumor mass.

Conclusion: The currently obtained data appears promising to use ASL routinely for intraoperative perfusion imaging. As ASL data allows to be quantified in absolute values, a comparison between different scanners and equipment can be performed straight-forward. The presented data obtained on patients shows that ASL allows for delineation of tumors in concordance with contrast-enhanced structural imaging sequences. In one case, ASL was even superior to structural imaging alone, changing the final diagnosis of the patient.