Intraoperative 3D quantitative magnetic resonance imaging in paediatric brain tumour surgery

• To investigate if R1 and R2 can reliably be measured using 3D quantitative MRI in an intraoperative setting when paediatric brain tumour surgery is performed. • To determine whether B1+ inhomogeneities affect R1 and R2 measurements in normal-appearing white matter and the thalamus, respectively, and how R1 and R2 measurements are affected by different coils. • To assess how the relaxation parameters of brain tissue are affected by the intraoperative setting.

The accuracy of R1 and R2, the effect of B1+-field inhomogeneity and how the flex coil position affected R1 and R2 were evaluated, both pre- and intraoperatively during surgery. Ten patients were recruited, six girls and four boys aged 2-15 years, with varying tumour entities, all referred to surgery with intraoperative MR. The patients were scanned using a head coil preoperatively and flex coils intraoperatively. Control experiments were performed on phantoms in various positions, equivalent to the patient positions. ROIs (Regions of Interest) were positioned in areas representing normal-appearing matter. Relaxation rates R1 and R2 were calculated from 3D-quantification using an interleaved Look-Locker acquisition sequence with T2 preparation pulse (3D-QALAS) data.

There was a significant increase of R2 in the intraoperative setting compared to the preoperative 3D-QALAS measurements. In contrast to the patient examinations, control experiments using relaxation phantoms did not demonstrate similar differences.

Relaxometry is feasible in the intraoperative setting. The detected differences between the quantitative R2 values in tissue pre- and intraoperatively seem to be explained by the physiological conditions characterising the surgical situation.