Brigham and Women's Hospital, Harvard Medical School, Boston, U.S.A.

• Introduction
• Methods
• Cases
• Case1: Young woman with right frontal glioma
• Case2: Young woman with left superior temporal arteriovenous malformation
• Case3: Middle-aged woman with right fronto-parietal AVM
• Conclusion
• Figures
• Figure1: 3D model of Case 1
• Figure2: Surface rendering of Case 2
• Figure3: 3D model of Case 3
• Figure4: Intraoperative imaging techniques
• References

Introduction

Functional MRI is increasingly used as an adjunct to neurosurgical planning. Our laboratory has developed techniques for 3D reconstruction of morphologic and angiographic MR images. The 3D model may be registered with functional information derived from multiple modalities (fMRI, SPECT, TMS, and intraoperative cortical mapping). We present three illustrative cases in which preoperative fMRI data were integrated with real-time intraoperative imaging techniques for surgical guidance.

Methods

fMRI

• 1.5 T (GE Signa), HORIZON EPIBOLD sequence
• 21 contiguous 7mm coronal slices
• TE=50msec, TR=3sec, FOV=24cm, 64x64 image matrix
• 6 alternating 30 second epochs of stimulus and control tasks (Total experimen t time=180sec)
• MATLAB data analysis

Anatomic

• 124 contiguous 1.5mm sagittal slices, 256x256 image matrix
• Phase contrast MR Angiography
• Threshold based segmentation and reconstruction of 3D model [1]

Surgical Navigation System

• LED based frameless stereotatic system [2]
• LED probe (Image Guided Technologies, Inc.) tracked with optical digitizer
• Precise localization simultaneously in operative space and 3D model

Intraoperative MR System [3]

• Mid field open-configuration MR scanner (GE 0.5T Signa SP)

Cases

Case 1

A 36 year old right handed woman presented with generalized tonic-clonic seizure and mild right hemiparesis. Structural MRI revealed a 4cm posterior right frontal lobe lesion, c/w a low grade glioma. fMRI showed increased signal with left hand movements in the precentral gyrus directly adjacent and posterior to the tumor. The functional data was merged with the 3D reconstruction and was projected into the surgical field. Electrophysiological phase reversal using subdural grid electrodes determined the boundaries of motor and sensory cortices. The motor cortex was mapped using a LED-based frameless navigational system [2] and showed excellent correspondence to the preoperative fMRI localization (Figure 1).

Case 2

A 29 year old right handed woman presented with generalized tonic-clonic seizures and a normal neurological examination. MRI revealed a left superior temporal arteriovenous malformation. fMRI during a verb generation task [4] revealed focal areas of activation in inferior left frontal and prefrontal cortices (Figure 2). The patient underwent resection of the vascular malformation in the intraoperative MR system [3]. 2D images acquired during the surgery were integrated with the 3D multi-modal reconstruction allowing the surgeon to visualize the resection in relation to the functional data.

Case 3

A 46 year old right handed woman with a history of seizures and left lower extremity weakness was known to have a large right fronto-parietal AVM. She had undergone multiple embolizations, and was being considered for surgical resection. fMRI during left hand and foot movements revealed several areas of activation widely distributed in the posterior right frontal lobe, as well as some contralateral activation. Transcranial magnetic stimulation was also used to map motor cortex and showed a distributed area which partially overlapped the areas of fMRI activation. She underwent resection in a conventional surgical suite with intraoperative cortical mapping and the LED navigational system (Figure 3).

Conclusion

The combination of preoperative functional imaging with intraoperative real-time imaging methods may prove extremely valuable in surgical guidance. The 3D model allows integration of functional and structural data into a single reference frame, which may be updated during the surgical procedure. These techniques allow validation of the functional localization and may be particularly useful for cases in which major anatomic distortion occurs during the surgical procedure.

Figures

Figure 1: 3D model of Case 1: Young woman with right frontal glioma (green). fMRI activation (red) corresponded exactly with intraoperative cortical mapping of motor cortex (white pointer)

Figure 2: Surface rendering of Case 2: Young woman with left superior temporal arteriovenous malformation (green). fMRI activation (red) in left frontal areas during verb generation task

Figure 3: 3D model of Case 3: Middle-aged woman with right fronto-parietal AVM (blue). fMRI (red), TMS (green) and intraoperative cortical mapping (purple) showed diffuse distribution of motor cortex

 a:   b:   c:

Figure 4: Intraoperative imaging techniques
a. The navigational interface displayed on a monitor during surgery
b. The LED navigational probe
c. The intraoperative MR suite

References

1. Cline HE et al. J Comput Assist Tomogr 14:1037-1045 (1990)

2. Jolesz FA et al. Radiology 204:601-612 (1997)

3. Nakajima S et al. Neurosurgery 41(2):403-409 (1997)

4. Petersen SE et al. J Cog Neurosci 1:153-170 (1989)