From Intraoperative Patient Transport to Surgery in the Fringe Field–Intraoperative Application of Magnetic Resonance Imaging Using a 0.2-Tesla Scanner: The Erlangen Experience:

Comparing 0.2 tesla with 1.5 tesla intraoperative magnetic resonance imaging analysis of setup, workflow, and efficiency

RATIONALE AND OBJECTIVES

To compare low-field with high-field intraoperative magnetic resonance imaging (MRI) in respect to setup, workflow, and efficiency.

MATERIALS AND METHODS

A total of 750 patients were investigated either with a 0.2 T (March 1996-July 2001) or a 1.5 T (April 2002-August 2004) MRI system adapted for intraoperative use.

RESULTS

With the low-field setup, 330 patients were examined in 65 months; with the high-field setup, 420 patients were examined in 29 months, which is a 2.8-fold increase in cases per month (14.5 versus 5.1) reflecting improved ease of use. Concerning intraoperative workflow, the time for preparation to start intraoperative imaging decreased fivefold (2 minutes instead of 10 minutes); navigation was applied more often with 57% versus 51% (240/420 versus 167/330), whereas functional data were integrated in 35% versus 39% (84/240 versus 65/167). Application of navigation updates was doubled (22% versus 11%; 53/240 versus 18/167). Image acquisition time was reduced by a factor of two, allowing a more detailed imaging protocol, whereas the image quality is clearly improved in the high-field setup, where there was no difference between the standard preoperative image quality compared with the intraoperative quality. This contributed to an increased detection of tumor remnants and extended resections in pituitary (36% versus 29%; 47/129 versus 17/59) and glioma surgery (41% versus 26%; 38/93 versus 28/106).

CONCLUSION

Compared with the low-field setup, the high-field setup results not only in clearly superior image quality and increased imaging armamentarium, contributing to increased rates of detected tumor remnants, but also in a distinct improvement of intraoperative workflow. Furthermore, intraoperative high-field MRI offers various modalities beyond standard anatomic imaging, such as magnetic resonance spectroscopy, diffusion tensor imaging, and functional MRI.

Volumetric assessment of glioma removal by intraoperative high-field magnetic resonance imaging

OBJECTIVE

To investigate the contribution of high-field intraoperative magnetic resonance imaging (iMRI) for further reduction of tumor volume in glioma surgery.

METHODS

From April 2002 to June 2003, 182 neurosurgical procedures were performed with a 1.5-T magnetic resonance system. Among patients who underwent these procedures, 47 patients with gliomas (14 with World Health Organization Grade I or II glioma, and 33 with World Health Organization Grade III or IV glioma) who underwent craniotomy were investigated retrospectively. Completeness of tumor resection and volumetric analysis were assessed with intraoperative imaging data.

RESULTS

Surgical procedures were influenced by iMRI in 36.2% of operations, and surgery was continued to remove residual tumor. Additional further resection significantly reduced the percentage of final tumor volume compared with first iMRI scan (6.9% +/- 10.3% versus 21.4% +/- 13.8%; P < 0.001). Percentages of final tumor volume also were significantly reduced in both low-grade (10.3% +/- 11.5% versus 25.8% +/- 16.3%; P < 0.05) and high-grade gliomas (5.4% +/- 9.9% versus 19.5% +/- 13.0%; P < 0.001). Complete resection was achieved finally in 36.2% of all patients (low-grade, 57.1%; high-grade, 27.3%). Among the 17 patients in whom complete tumor resection was achieved, 7 complete resections (41.2%) were attributable to further tumor removal after iMRI. We did not encounter unexpected events attributable to high-field iMRI, and standard neurosurgical equipment could be used safely.

CONCLUSION

Despite extended resections, introduction of high-field iMRI in conjunction with functional navigation did not translate into an increased risk of postoperative deficits. The use of high-field iMRI increased radicality in glioma surgery without additional morbidity.

Preliminary experience in glioma surgery with intraoperative high-field MRI

OBJECTIVE

To apply a new setup, combining the benefits of high-field magnetic resonance imaging (MRI) with microscope-based neuronavigation, providing anatomical and functional guidance, in glioma surgery.

MATERIAL AND METHODS

MR imaging was performed using a 1.5 T scanner, located in a radiofrequency-shielded operating theatre. The patient is lying on a rotating operating table, which is locked at the 160 degree position for surgery at the 5 G zone and turned into the scanner for imaging. The microscope, placed in the 5 G zone, in combination with a ceiling mounted navigation system enables microscope-based neuronavigation; integrated data from magnetoencephalography and functional MRI provide functional guidance.

RESULTS

126 patients were investigated with intraoperative high-field MRI, among them were 37 patients with gliomas. In the biopsy/catheter group (n = 8) MRI reliably depicted the needle position or the location of catheter placement. In the group with glioma resection (n = 29) intraoperative MRI revealed that the surgical objective was not achieved in 28%, leading to further tumour removal. We did not observe complications attributable to intraoperative high-field MRI. Image quality was not diminished by the operating room equipment, so that there was nearly no noticeable difference between pre- and intraoperative image quality. Neuronavigational guidance was applied in 31 patients: the integrated use of functional data prevented an increased morbidity despite extended resections.

CONCLUSION

Intraoperative high-field MRI allows a reliable delineation of the extent of resection in glioma surgery. If the surgical objective was not met, a modification of the surgical strategy during the same operation is possible, thus leading to more radical resections. Furthermore, high-field MRI offers increased image quality and a much broader spectrum of different imaging modalities, compared to previous intraoperative low-field systems.

Frameless Stereotactic Surgery Using Intraoperative High-Field Magnetic Resonance Imaging

This study evaluated the clinical validity of frameless stereotaxy using high-field intraoperative magnetic resonance (iMR) imaging combined with an in-room neuronavigation system. A 1.5 Tesla MR scanner in conjunction with a ceiling-mounted neuronavigation system was used during 32 frameless stereotaxy procedures consisting of 19 brain biopsies and 13 catheter placements between April 2002 and mid-October 2003. Evaluation of the procedure was based on either the rate of histological diagnostic yield or the ability to accurately position the catheter in the target region. This technique allowed successful registration with a mean error of 1.2 +/- 0.8 mm and resulted in successful placement of the instrument within the target tissue. Intraoperatively, frozen section analysis showed all biopsy samples contained pathological tissue and locations of sampling points were confirmed by iMR imaging. Specific final diagnosis was made in all 19 brain biopsies. The tip of the catheter was successfully placed into the target in all 13 patients confirmed by iMR imaging. The catheter was repositioned based on iMR imaging in four of 13 patients, increasing the rate of successful placement. There were no procedure-related neurological deficits or mortality, but we encountered two cases of wound infection, one needing surgical revision. Total additional procedure time related to the induction of iMR imaging was 76.7 +/- 23.3 minutes. This initial experience of the combination of conventional frameless stereotaxy and high-field iMR imaging improved the quality of frameless stereotaxy with low morbidity and mortality, but did not translate into a significant reduction of procedure-related time.

Functional neuronavigation and intraoperative MRI

Our concept of computer assisted surgery is based on the combination of intraoperative magnetic resonance (MR) imaging with microscope-based neuronavigation, providing anatomical and functional guidance simultaneously. Intraoperative imaging evaluates the extent of a resection, while the additional use of functional neuronavigation, which displays the position of eloquent brain areas in the operative field, prevents increasing neurological deficits, which would otherwise result from extended resections. Up to mid 2001 we performed intraoperative MR imaging using a low-field 0.2 Tesla scanner in 330 patients. The main indications were the evaluation of the extent of resection in gliomas, pituitary tumours, and in epilepsy surgery. Intraoperative MR imaging proved to serve as intraoperative quality control with the possibility of an immediate modification of the surgical strategy, i.e. extension of the resection. Integrated use of functional neuronavigation prevented increased neurological deficits. Compared to routine pre- or postoperative imaging being performed with high-Tesla machines, intraoperative image quality and sequence spectrum could not compete. This led to the development of the concept to adapt a high-field MR scanner to the operating environment, preserving the benefits of using standard microsurgical equipment and microscope-based neuronavigational guidance with integrated functional data, which was successfully implemented by April 2002. Up to the end of 2002, 95 patients were investigated with the new setup. Improved image quality, intraoperative workflow, as well as enhanced sophisticated intraoperative imaging possibilities are the major benefits of the high-field setup.