Intraoperative diffusion-weighted imaging for visualization of the pyramidal tracts. Part I: pre-clinical validation of the scanning protocol.

Integration of intraoperative diffusion-weighted imaging (iDWI) into neuronavigation can be potentially useful for identification of the pyramidal tract during surgery for parenchymal brain lesions. The technique of iDWI using an intraoperative MR scanner of low magnetic field strength (0.3 Tesla) has been developed. For image acquisition, a specially designed solenoid radiofrequency receiver coil integrated with a modified Sugita head holder (head-holder coil) was used. While the sensitivity characteristics of the head-holder coil were found to be 29% lower compared to a diagnostic quadrature head coil, they were sufficient to obtain iDWI images of good quality. The relationship between the angle of the motion probe gradient (MPG) pulse to the vertical axis and pyramidal tract contrasting were examined in 4 healthy men with a mean age of 30+/-5.7 years. The contrast ratio reached a maximum when the MPG pulse was applied exactly in the anteroposterior direction. The difference of the contrast ratio between right and left sides was not statistically significant. Pyramidal tract visualization became worse and the contrast ratio was reduced when the MPG pulse was applied at different angles to the vertical axis; the reduction rate varied from 20.1 to 27.9% for each 15 degrees of rotation irrespective of its side. In conclusion, the developed scanning protocol for iDWI using an originally designed head-holder coil allowed effective visualization of the pyramidal tracts using an intraoperative MR scanner of low magnetic field strength.

Intraoperative diffusion-weighted imaging for visualization of the pyramidal tracts. Part II: clinical study of usefulness and efficacy.

Precise identification and preservation of the pyramidal tract during surgery for parenchymal brain tumors is of crucial importance for the avoidance of postoperative deterioration of the motor function. The technique of intraoperative diffusion-weighted imaging (iDWI) using an intraoperative MR scanner of low magnetic field strength (0.3 Tesla) has been developed. Its clinical usefulness and efficacy were evaluated in 10 surgically treated patients with gliomas (5 men and 5 women, mean age: 41.2+/-13.9 years). iDWI permitted visualization of the pyramidal tract on the non-affected side in all 10 cases, and on the affected side in 8 cases. Motion artifacts were observed in four patients, but were not an obstacle to identification of the pyramidal tract. Good correspondence of the anatomical landmarks localization on iDWI and T (1)-weighted imaging was found. All participating neurosurgeons agreed that, in the majority of cases, iDWI was very useful for localization of the pyramidal tract and for clarification of its spatial relationships with the tumor. In conclusion, image quality and accuracy of the iDWI obtained with an MR scanner of low magnetic field strength (0.3 Tesla) are sufficient for possible incorporation into an intraoperative neuronavigation system. The use of iDWI in addition to structural iMRl and subcortical functional mapping with electrical stimulation can potentially result in a reduction of the postoperative morbidity after aggressive surgical removal of lesions located in the vicinity to the motor white matter tracts.