Cranial surgery with an expanded compact intraoperative magnetic resonance imager

Abstract

In this article the authors report the implementation of an expanded compact intraoperative magnetic resonance (iMR) imager that is designed to overcome significant limitations of an earlier unit. The PoleStar N20 iMR imager has a stronger magnetic field than its predecessor (0.15 tesla compared with 0.12 tesla), a wider gap between magnet poles, and an ergonomically improved gantry design. The additional time needed in the operating room (OR) for use of iMR imaging and the number of sessions per patient were recorded. Stereotactic accuracy of the integrated navigational tool was assessed using a water-covered phantom. Of the 55 patients who have undergone surgery in the PoleStar N20 device, diagnoses included glioma in 13, meningioma in 12, pituitary adenoma in nine, other skull base lesions in seven, and miscellaneous other diagnoses. The extra time required for use of the system averaged 1.1 hours (range 0.5-2 hours). Imaging sessions averaged 2.3 per surgery (range one-six sessions). Measurement of stereotactic accuracy revealed that T1-weighted images were the most accurate. Thinner slices yielded measurably greater accuracy, although this was of questionable clinical significance (all sequences < or =4 mm had a mean error of < or = 1.8 mm). The position of the phantom in the center compared with the periphery of the magnetic field did not affect accuracy (mean error 0.9 mm for each). The PoleStar N20 appears to make intraoperative neuroimaging with a low-field-strength magnet much more practical than it was with the first-generation device. Greater ease of positioning resulted in a decrease in added time in the OR and encouraged a larger number of imaging sessions.

Recent advances in pituitary tumor management

“…Low-field MRI leads to a diminution of image quality, with a limitation of specific sequences, which may impact the interpretation of disorder [76,77,81,82]. Many authors, however, feel that despite these shortcomings, the ability of iMRI to detect occult residual tumor affords it a significant advantage over other forms of navigation during TSS [58,79 ].…”

Compact Intraoperative MRI: Stereotactic Accuracy and Future Directions

“…The use of the N30 during surgical procedures is similar to that of the N20, as previously described [17]. In brief, both systems require that anesthesia machines and monitors be compatible with the imager.…”

“…However, these advantages did not come without cost. The 0.15-T magnet significantly increased the size and weight of the system, detracting from the versatility of the device [17]. Our experience with the N20 raised an important question regarding the future of intraoperative imager design: can the enhancements in image quality and stereotactic accuracy achieved with the integration of higher magnetic field strength be accomplished without compromise to the surgical workspace?…”

Development and Design of Low Field Compact Intraoperative MRI for Standard Operating Room

“…The design goals of the PoleStar compact system were met [3][4][5]. Its intraoperative images serve as the data for navigation and for resection control.…”