Intraoperative magnetic resonance imaging: considerations for the operating room of the future

How to objectively evaluate the impact of image-guided surgery technologies

PURPOSE

This manuscript aims to provide a better understanding of methods and techniques with which one can better quantify the impact of image-guided surgical technologies.

METHODS

A literature review was conducted with regard to economic and technical methods of medical device evaluation in various countries. Attention was focused on applications related to image-guided interventions that have enabled procedures to be performed in a minimally invasive manner, produced superior clinical outcomes, or have become standard of care.

RESULTS

The review provides examples of successful implementations and adoption of image-guided surgical techniques, mostly in the field of neurosurgery. Failures as well as newly developed technologies still undergoing cost-efficacy analysis are discussed.

CONCLUSION

The field of image-guided surgery has evolved from solely using preoperative images to utilizing highly specific tools and software to provide more information to the interventionalist in real time. While deformations in soft tissue often preclude the use of such instruments outside of neurosurgery, recent developments in optical and radioactive guidance have enabled surgeons to better account for organ motion and provide feedback to the surgeon as tissue is cut. These technologies are currently undergoing value assessments in many countries and hold promise to improve outcomes for patients, surgeons, care teams, payors, and society in general.

Feasibility of intraoperative MRI for endovascular coiling of intracranial aneurysms: A single centre experience

BACKGROUND

Intraoperative magnetic resonance imaging system (iMRIS) surgical theatre is a highly integrated operating room with an intraoperative magnetic resonance imaging (iMRI) designed originally for brain tumour surgery. Its use in neurointerventional procedures, particularly in the setting of endovascular coiling of intracranial aneurysms, has not been discussed in the literature to date. We present our initial experience about the safety and feasibility of iMRI to assess post operative complications and provide baseline imaging post coiling of intracranial aneurysms.

METHODS

Consecutive patients who underwent iMRI between 2015 and 2018 were included in the study. Demographic, clinical details, endovascular technique and surgical outcomes were collected. Details of anesthesia during the procedure were also collected.

RESULTS

Fifteen patients underwent iMRI with MRA to assess post coiling status of their elective endovascular coiling of intracranial aneurysms. The mean age in this cohort was 61 years and 46.7% were male. No immediate complications were seen either from the endovascular procedures or from the iMRI. All iMRI scans were performed as planned with no aborted or truncated scans. The image quality of the iMRI/MRA was adequate to detect the residual aneurysm, if present. There was no residual aneurysm on the angiogram that were not detected on the iMRIs. Of the 15 patients, 10 were safely discharged the following day and other 5 were discharged 2 days after their surgery.

CONCLUSIONS

The iMRI is an advantageous tool which can be integrated into neurointerventional workflow resulting in early post peri-procedural feedback and potentially reduced post-operative hospital stay.

The use of intraoperative computed tomography navigation in pituitary surgery promises a better intraoperative orientation in special cases

OBJECTIVE

The safety of endoscopic skull base surgery can be enhanced by accurate navigation in preoperative computed tomography (CT) and magnetic resonance imaging (MRI). Here, we report our initial experience of real-time intraoperative CT-guided navigation surgery for pituitary tumors in childhood.

MATERIALS AND METHODS

We report the case of a 15-year-old girl with a huge growth hormone-secreting pituitary adenoma with supra- and perisellar extension. Furthermore, the skull base was infiltrated. In this case, we performed an endonasal transsphenoidal approach for debulking the adenoma and for chiasma decompression. We used an MRI neuronavigation (Medtronic Stealth Air System) which was registered via intraoperative CT scan (Siemens CT Somatom). Preexisting MRI studies (navigation protocol) were fused with the intraoperative CT scans to enable three-dimensional navigation based on MR and CT imaging data. Intraoperatively, we did a further CT scan for resection control.

RESULTS

The intraoperative accuracy of the neuronavigation was excellent. There was an adjustment of <1 mm. The navigation was very helpful for orientation on the destroyed skull base in the sphenoid sinus. After opening the sellar region and tumor debulking, we did a CT scan for resection control because the extent of resection was not credible evaluable in this huge infiltrating adenoma. Thereby, we were able to demonstrate a sufficient decompression of the chiasma and complete resection of the medial part of the adenoma in the intraoperative CT images.

CONCLUSIONS

The use of intraoperative CT/MRI-guided neuronavigation for transsphenoidal surgery is a time-effective, safe, and technically beneficial technique for special cases.

A systematic evaluation of intraoperative white matter tract shift in pediatric epilepsy surgery using high-field MRI and probabilistic high angular resolution diffusion imaging tractography

OBJECTIVE Characterization of intraoperative white matter tract (WMT) shift has the potential to compensate for neuronavigation inaccuracies using preoperative brain imaging. This study aimed to quantify and characterize intraoperative WMT shift from the global hemispheric to the regional tract-based scale and to investigate the impact of intraoperative factors (IOFs). METHODS High angular resolution diffusion imaging (HARDI) diffusion-weighted data were acquired over 5 consecutive perioperative time points (MR₁ to MR₅) in 16 epilepsy patients (8 male; mean age 9.8 years, range 3.8-15.8 years) using diagnostic and intraoperative 3-T MRI scanners. MR₁ was the preoperative planning scan. MR₂ was the first intraoperative scan acquired with the patient's head fixed in the surgical position. MR₃ was the second intraoperative scan acquired following craniotomy and durotomy, prior to lesion resection. MR₄ was the last intraoperative scan acquired following lesion resection, prior to wound closure. MR₅ was a postoperative scan acquired at the 3-month follow-up visit. Ten association WMT/WMT segments and 1 projection WMT were generated via a probabilistic tractography algorithm from each MRI scan. Image registration was performed through pairwise MRI alignments using the skull segmentation. The MR₁ and MR₂ pairing represented the first surgical stage. The MR₂ and MR₃ pairing represented the second surgical stage. The MR₃ and MR₄ (or MR₅) pairing represented the third surgical stage. The WMT shift was quantified by measuring displacements between a pair of WMT centerlines. Linear mixed-effects regression analyses were carried out for 6 IOFs: head rotation, craniotomy size, durotomy size, resected lesion volume, presence of brain edema, and CSF loss via ventricular penetration. RESULTS The average WMT shift in the operative hemisphere was 2.37 mm (range 1.92-3.03 mm) during the first surgical stage, 2.19 mm (range 1.90-3.65 mm) during the second surgical stage, and 2.92 mm (range 2.19-4.32 mm) during the third surgical stage. Greater WMT shift occurred in the operative than the nonoperative hemisphere, in the WMTs adjacent to the surgical lesion rather than those remote to it, and in the superficial rather than the deep segment of the pyramidal tract. Durotomy size and resection size were significant, independent IOFs affecting WMT shift. The presence of brain edema was a marginally significant IOF. Craniotomy size, degree of head rotation, and ventricular penetration were not significant IOFs affecting WMT shift. CONCLUSIONS WMT shift occurs noticeably in tracts adjacent to the surgical lesions, and those motor tracts superficially placed in the operative hemisphere. Intraoperative probabilistic HARDI tractography following craniotomy, durotomy, and lesion resection may compensate for intraoperative WMT shift and improve neuronavigation accuracy.

Automated alignment of perioperative MRI scans: A technical note and application in pediatric epilepsy surgery

Conventional image registration utilizing brain voxel information may be erroneous in a neurosurgical setting due to pathology and surgery-related anatomical distortions. We report a novel application of an automated image registration procedure based on skull segmentation for magnetic resonance imaging (MRI) scans acquired before, during and after surgery (i.e., perioperative). The procedure was implemented to assist analysis of intraoperative brain shift in 11 pediatric epilepsy surgery cases, each of whom had up to five consecutive perioperative MRI scans. The procedure consisted of the following steps: (1) Skull segmentation using tissue classification tools. (2) Estimation of rigid body transformation between image pairs using registration driven by the skull segmentation. (3) Composition of transformations to provide transformations between each scan and a common space. The procedure was validated using locations of three types of reference structural landmarks: the skull pin sites, the eye positions, and the scalp skin surface, detected using the peak intensity gradient. The mean target registration error (TRE) scores by skull pin sites and scalp skin rendering were around 1 mm and <1 mm, respectively. Validation by eye position demonstrated >1 mm TRE scores, suggesting it is not a reliable reference landmark in surgical scenarios. Comparable registration accuracy was achieved between opened and closed skull scan pairs and closed and closed skull scan pairs. Our procedure offers a reliable registration framework for processing intrasubject time series perioperative MRI data, with potential of improving intraoperative MRI-based image guidance in neurosurgical practice. Hum Brain Mapp 37:3530-3543, 2016. © 2016 Wiley Periodicals, Inc.

Three-dimensional brain surface visualization for epilepsy surgery of focal cortical dysplasia

Focal cortical dysplasia (FCD) causes medically intractable seizures in 5-10% of adult epilepsy patients, but patients can become seizure free through surgical resection. The authors present the utility of three-dimensional surface visualization (3DSV) that expands on existing imaging datasets to highlight surface vasculature as a tool for achieving more successful resections in patients with FCD. In this prospective series of six patients, preoperative 3DSV was performed for planning the surgical approach to the lesion and for intraoperative guidance. Reconstructions involved volume rendering of a contrast-enhanced dataset to visualize surface venous vasculature. Postoperatively, five of the six patients had complete resections, with one patient having a subtotal resection due to proximity to crucial vasculature. We report that 3DSV is a useful tool for surgical planning, since topographical relationships between lesion location and surface vasculature landmarks are less likely to change with surgical progress.

Clinical and economic outcomes of low-field intraoperative MRI-guided tumor resection neurosurgery

PURPOSE

To compare low-field (0.15 T) intraoperative magnetic resonance imaging (iMRI)-guided tumor resection with both conventional magnetic resonance imaging (cMRI)-guided tumor resection and high-field (1.5 T) iMRI-guided resection from the clinical and economic point of view.

MATERIALS AND METHODS

We retrospectively compared 65 iMRI patients with 65 cMRI patients in terms of hospital length of stay, repeat resection rate, repeat resection interval, complication rate, cost to the patient, cost to the hospital, and cost effectiveness. In addition, we compared our low-field results with previously published high-field results.

RESULTS

The complication rate was lower for iMRI vs. cMRI in patients presenting for their initial tumor resection (45 vs. 57 complications, P = 0.048). The iMRI repeat resection interval was longer for this cohort (20.1 vs. 6.7 months, P = 0.020). iMRI was more cost-effective than cMRI for patients who had repeat resections ($10,690/RFY vs. $76,874/RFY, P < 0.001). We found no other clinical or economic differences between iMRI- and cMRI-guided tumor resection surgeries. Overall, we did not find the advantages to low-field iMRI that have been reported for high-field iMRI.

CONCLUSION

There is no adequate justification for the widespread installation of low-field iMRI in its current development state.

Origins of intraoperative MRI

Neurosurgical diagnosis and intervention has evolved through improved neuroimaging, allowing better visualization of anatomy and pathology. This article discusses the various systems that have been designed over the last decade to meet the requirements of neurosurgical patients and opines on the potential future developments in the technology and application of intraoperative MRI. Because the greatest amount of experience with intraoperative MRI comes from its use in brain tumor resection, this article focuses on the origins of intraoperative MRI in relation to this field.

Origins of intraoperative MRI

Neurosurgical diagnosis and intervention has evolved through improved neuroimaging, allowing better visualization of anatomy and pathology. This article discusses the various systems that have been designed over the last decade to meet the requirements of neurosurgical patients and opines on the potential future developments in the technology and application of intraoperative MRI. Because the greatest amount of experience with intraoperative MRI comes from its use in brain tumor resection, this article focuses on the origins of intraoperative MRI in relation to this field.

Advances in brain tumor surgery

Advances in the fields of molecular and translational research, oncology, and surgery have emboldened the medical community to believe that intrinsic brain tumors may be treatable. Intraoperative imaging and brain mapping allow operations adjacent to eloquent cortex and more radical resection of tumors with increased confidence and safety. Despite these advances, the infiltrating edge of a neoplasm and distant microscopic satellite lesions will never be amendable to a surgical cure. Indeed, it is continued research into the delivery of an efficacious chemobiologic agent that will eventually allows us to manage this primary cause of treatment failure.

Functional imaging in a low-field, mobile intraoperative magnetic resonance scanner: expanded paradigms

OBJECTIVE

We previously demonstrated the capability to obtain functional magnetic resonance imaging (MRI) scans of the motor cortex in healthy volunteers using a low-field mobile operating room-based MRI scanner with 0.12-T field strength. Using an expanded (0.15-T), but still mobile, version of this system, our goal was to acquire data showing activation of other areas of functionally important cortex.

METHODS

Five healthy volunteers were scanned with the low-field scanner using finger tapping, hand touch, silent word generation, text listening, and visual stimulation paradigms. The data was analyzed offline using publicly available software. For comparison, the volunteers were then scanned with a 3-T diagnostic MRI scanner.

RESULTS

Significant cortical activation was demonstrated on 16 out of 22 images obtained on the operating room-based scanner. Motor activation was most robust, followed by silent word generation, text listening, and hand touch paradigms. The correlation coefficients compared favorably with the images obtained on the 3-T scanner. The signal changes were higher for images obtained with the low-field, mobile scanner compared with those performed with the 3-T diagnostic MRI scanner.

CONCLUSION

Functional MRI scans of multiple cortical areas can be acquired with a low-field strength magnet designed for intraoperative imaging. Further refinement of this technique may allow for the acquisition of true intraoperative functional MRI scans immediately, before, and even during cranial surgery in select patients.

Survival rates and patterns of care for patients diagnosed with supratentorial low-grade gliomas: data from the SEER program, 1973-2001

BACKGROUND

Detailed population-based estimates of long-term survival as well as patterns of care for patients with low-grade gliomas examined by age at diagnosis, gender, and race have not been widely available.

METHODS

Time to death was examined among 2009 individuals diagnosed with a supratentorial low-grade glioma and reported to the Surveillance, Epidemiology, and End Results (SEER) program of the National Cancer Institute from 1973-2001 using Kaplan-Meier estimation. A Cox proportional hazards model was used to assess the effect of age at diagnosis, race, gender, histology, anatomic location within the brain, first course of treatment, and year of diagnosis upon this risk.

RESULTS

The cumulative 5-, 10-, 15- and 20-year survival rates among all individuals initially diagnosed with a supratentorial low-grade glioma were 59.9% (95% confidence interval [95% CI], 57.6-62.2); 42.6% (95% CI, 39.9-45.2); 31.9% (95% CI, 29.0-34.8); and 26.0% (95% CI, 22.7-29.2), respectively. Improved survival was significantly associated with female gender (hazard ratio [HR], 0.84; 95% CI, 0.74-0.95), younger age, white race (HR, 0.70; 95% CI, 0.54-0.93), histology, and later year of diagnosis. Surgical treatment was associated with increased survival. The use of radiation therapy as a first course of treatment for these lesions has significantly decreased over time with the majority of patients receiving only surgery as a first course of treatment.

CONCLUSIONS

Data for patients diagnosed with low-grade gliomas revealed increasing survival times over the past 25 years with a subset of patients surviving for decades. Differences in survival by race, gender, histology, and first course of treatment were appreciated. These data suggested that the clinical course of low-grade glioma for some patients may be more encouraging than previously perceived and that the identification of this group of patients may allow refinement of current treatment protocols.

Intraoperative MR imaging: preliminary results with 3 tesla MR system

Aim of this study is to present the initial clinical experience with 3 tesla intraoperative MR (ioMR).

MATERIAL AND METHODS

The 3T MRI suite is built adjacent to the neurosurgical operation theatre. The magnet room and the operation theatre are interconnected by a door and both RF-shielded. Before the operation, the magnet (3T Trio, Siemens) and the console rooms are disinfected. Whenever imaging is needed during the operation, the door is opened and the patient is transferred from the operation table to the magnet cradle. Axial, sagittal and/or coronal TSE T2, SE T1 and 3D Flash T1 weighted images (4-6 mm section thickness, 1 mm interslice gap) are obtained according to the lesion. Total examination time is approximately 10 minutes.

RESULTS

Twenty-six patients were examined with ioMR. There were ten female and seven male patients. Lesions were pituitary adenoma in 10, low grade glial tumor in 9, meningioma and high grade glial tumor in 2 each and metastasis, haemangioblastoma and chordoma in one each. Follow-up time was 1 to 9 months. In 16 patients the first intraoperative examination revealed gross total tumor excision. However, in 10 patients due to tumor remnants surgical intervention was continued and a second examination revealed gross total tumor excision in all. Postoperative routine MR examinations confirmed total tumor excision in all patients. No complication occurred in this series.

CONCLUSION

This small group of patients examined with ioMR demonstrated that the procedure is simple, helpful in achieving gross total tumor excision without complications.

Correlation of factors predicting intraoperative brain shift with successful resection of malignant brain tumors using image-guided techniques

BACKGROUND

Intraoperative brain shift may cause inaccuracy of stereotactic image guidance on the basis of preoperatively acquired imaging data. The purpose of our study was to determine whether factors predicting brain shift affect the success of image-guided resection of malignant brain tumors.

METHODS

We retrospectively studied 54 patients who underwent image-guided resections of histopathologically confirmed malignant brain tumors (9 metastases, 45 high-grade gliomas). Precautions were taken during surgery to minimize brain shift, but intraoperative imaging was not performed. The following factors predictive of intraoperative brain shift were assessed: tumor size, periventricular location, patient age, prior surgery or radiation therapy, patient positioning, use of mannitol, and length of operative time. Postoperative magnetic resonance imaging was obtained in all cases within 48 hours of surgery to assess extent of resection.

RESULTS

Perioperative mortality was 0% in our series; perioperative morbidity was 3 of 54 patients (5.5%); 1 patient required reoperation for a hematoma, and 2 had transient neurological deficits. Successful resection was accomplished in 93% of tumors less than 30 cm(3) compared with 63.6% of tumors greater than 30 cm(3) (P = .026, Fisher exact test). This difference was more pronounced for patients with malignant gliomas. However, other factors predictive of intraoperative brain shift were not associated with unsuccessful resection.

CONCLUSIONS

Intraoperative brain shift does not significantly affect the likelihood of successful resection of malignant brain tumors smaller than 30 cm(3). Larger tumors are less likely to be successfully resected, although factors other than brain shift can contribute to unsuccessful resection.

A low-field intraoperative MRI system for glioma surgery: is it worthwhile?

As intraoperative MRI expands its presence, its use will undoubtedly increase in glioma surgery. The foregoing discussion makes it clear that its benefits are unsurpassed by any other existing system. Because of their radiographic characteristics and gross appearance, gliomas are particularly suited for intraoperative MRI-guided surgery. It enables us to localize gliomas and define tumor margins precisely when, during surgery, the difference between tumor and brain is not easy to discern. The images generated during surgery serve as a detailed and updated map within which navigation is performed with utmost precision. Its significance is further highlighted when dealing with tumors in eloquent areas of the brain, where uncertainties over the location of tumor in relation to important brain structures can hinder the removal of tumor. By providing accurate positional information and in conjunction with cortical mapping techniques, intraoperative MRI enhances the confidence of the surgeon to go forward with resection or to stop when reaching important cortex. It allows us to perform the resection to the desired limit without causing injury to nearby important structures, thereby preventing postoperative neurologic deficits. The tracking system guides us in targeting each minute part of the tumor with unprecedented accuracy, and the ability to update images makes possible the constant evaluation of the progress of surgery. This near-real-time imaging can eliminate the errors brought about by the brain shifting that occurs throughout surgery. It also serves the important purpose of verifying the presence and position of any remaining tumor in the operative field. By means of sequential imaging, additional resection can be performed on any remaining tumor until imaging shows completion. The unwanted occurrence of finding residual tumor on a postoperative scan is thus practically eliminated. As a result, the surgical goal of complete or optimal resection can be achieved without any guesswork. Ultimately, what this means for the glioma patient is increased likelihood of longer survival brought about by a more thorough tumor resection. Intraoperative MRI addresses many of the surgical challenges posed by gliomas. As it becomes more available, there will come a point when the prevailing persuasion will be that some poorly defined tumors near eloquent cortex should not be operated on without intraoperative MRI. In the final analysis, not only is intraoperative MRI worthwhile but it will, in all likelihood, become a standard of care for many glioma cases.

Survival rates in patients with low-grade glioma after intraoperative magnetic resonance image guidance

BACKGROUND

No age-adjusted or histologic-adjusted assessments of the association between extent of resection and risk of either recurrence or death exist for neurosurgical patients who undergo resection of low-grade glioma using intraoperative magnetic resonance image (MRI) guidance.

METHODS

The current data included 156 patients who underwent surgical resection of a unifocal, supratentorial, low-grade glioma in the MRI suite at Brigham and Women's Hospital between January 1, 1997, and January 31, 2003. Estimates of disease-free and overall survival probabilities were calculated using Kaplan-Meier methodology. The association between extent of resection and these probabilities was measured using a Cox proportional hazards model. Observed death rates were compared with the expected death rate using age-specific and histologic-specific survival rates obtained from the Surveillance, Epidemiology, and End Results Registry.

RESULTS

Patients who underwent subtotal resection were at 1.4 times the risk of disease recurrence (95% confidence interval [95% CI], 0.7-3.1) and at 4.9 times the risk of death (95% CI, 0.61-40.0) relative to patients who underwent gross total resection. The 1-year, 2-year, and 5-year age-adjusted and histologic-adjusted death rates for patients who underwent surgical resection using intraoperative MRI guidance were 1.9% (95% CI, 0.3-4.2%), 3.6% (95% CI, 0.4-6.7%), and 17.6% (95% CI, 5.9-29.3%), respectively: significantly lower than the rates reported using national data bases.

CONCLUSIONS

The data from the current study suggested a possible association between surgical resection and survival for neurosurgical patients who underwent surgery for low-grade glioma under intraoperative MRI guidance. Further study within the context of a large, prospective, population-based project will be needed to confirm these findings.

Shim design using a linear programming algorithm

The advent of open magnetic resonance imaging (MRI) scanners and dedicated MRI scanners tailored to specific body parts has led to an increasing number of noncylindrical MRI scanner geometries, for which noncylindrical gradients and shims are needed. These new scanner geometries are driving the need for fast, flexible shim design methods that can design shim coils for any geometry. A linear programming (LP) algorithm was developed to design minimum-power resistive shim coils on an arbitrary surface. These coils can be designed to produce any order shim field over an arbitrarily shaped target region, which can be placed anywhere within the coil. The resulting designs are relatively sparse and can be readily constructed. This algorithm was used to design and construct a seven-coil cylindrical shim set for a knee imaging magnet with a cylindrical homogeneous region. The algorithm was then used to design shim coils for a biradial head imager with an asymmetrically located spherical target region for brain imaging.

Intraoperative imaging in glioblastoma resection

The use of intraoperative imaging (IOI) in neurosurgical practice is proving to be yet another important advance in the evolution of brain tumor resection, particularly for the most common adult primary brain tumor--glioblastoma (GBM). The number of surgeons using IOI continues to increase, and the experience to date affords an opportunity to assess the value of the various techniques used for IOI.

Evaluation of factors predicting accurate resection of high-grade gliomas by using frameless image-guided stereotactic guidance

Object

Frameless image-guided stereotaxy is often used in the resection of high-grade gliomas. The authors of several studies, however, have suggested that brain shift may occur intraoperatively and result in inaccurate resection. To determine the usefulness of frameless stereotactic image-guided surgery of high-grade gliomas, the authors correlated factors predictive of brain shift, such as tumor size, periventricular location, and patient age (as an indicator of brain atrophy) with the extent of resection.

Methods

Inclusion criteria included the following: 1) stereotactic volumetric craniotomy for resection of tumor; 2) histologically proven high-grade glioma; 3) preoperative magnetic resonance (MR) imaging demonstration of an enhancing portion of tumor; 4) postoperative MR imaging within 48 hours to assess the extent of resection; and 5) preoperative intention to perform gross-total resection of the enhancing tumor. Fifty-four patients met these criteria between September 1997 and November 2002. Accurate resection was considered to be indicated by a lack of nodular enhancement on postoperative Gd-enhanced MR images obtained within 48 hours of surgery.

Frameless stereotactic image-guided surgery resulted in the successful resection of 46 (85%) of 54 high-grade gliomas. Accurate resection was significantly more likely with tumors less than 30 ml in volume than with those greater than 30 ml (93 and 58%, respectively [p < 0.05]). In addition, small periventricular tumors were associated with significant less successful resection compared with nonperiventricular tumor (77 and 96%, respectively [p = 0.5]). Patient age did not affect the likelihood of successful resection.

Conclusions

Frameless image-guided stereotactic techniques can be reliably used for accurate resection of high-grade gliomas when the tumor is less than 30 ml in volume and not adjacent to the ventricular system. In cases involving tumors larger in volume or located near the ventricles, intraoperative ultrasonography or MR imaging updates should be considered.

Vision of the future: initial experience with intraoperative real-time high-resolution dynamic infrared imaging. Technical note

High-resolution dynamic infrared (DIR) imaging provides intraoperative real-time physiological, anatomical, and pathological information; however, DIR imaging has rarely been used in neurosurgical patients. The authors report on their initial experience with intraoperative DIR imaging in 30 such patients. A novel, long-wave (8-10 microm), narrow-band, focal-plane-array infrared photodetector was incorporated into a camera system with a temperature resolution of 0.006 degrees C, providing 65,000 pixels/frame at a data acquisition rate of 200 frames/second. Intraoperative imaging of patients was performed before and after surgery. Infrared data were subsequently analyzed by examining absolute differences in cortical temperatures, changes in temperature over time, and infrared intensities at varying physiological frequencies. Dynamic infrared imaging was applied in a variety of neurosurgical cases. After resection of an arteriovenous malformation, there was postoperative hyperperfusion of the surrounding brain parenchyma, which was consistent with a loss of autoregulation. Bypass patency and increased perfusion of adjacent brain were documented during two of three extracranial-intracranial bypasses. In seven of nine patients with epilepsy the results of DIR imaging corresponded to seizure foci that had been electrocorticographically mapped preoperatively. Dynamic infrared imaging demonstrated the functional cortex in four of nine patients undergoing awake resection and cortical stimulation. Finally, DIR imaging exhibited the distinct thermal footprints of 14 of 16 brain tumors. Dynamic infrared imaging may prove to be a powerful adjunctive intraoperative diagnostic tool in the neurosurgical imaging armamentarium. Real-time assessment of cerebral vessel patency and cerebral perfusion are the most direct applications of this technology. Uses of this imaging modality in the localization of epileptic foci, identification of functional cortex during awake craniotomy, and determination of tumor border and intraoperative brain shift are avenues of inquiry that require further investigation.