Intraoperative high-field-strength MR imaging: implementation and experience in 200 patients

AN INTEGRATED RADIO FREQUENCY PROBE AND CRANIAL CLAMP FOR INTRAOPERATIVE MAGNETIC RESONANCE IMAGING

OBJECTIVE

To design an integrated radio frequency (RF) head probe and cranial clamp for intraoperative magnetic resonance imaging (MRI) that do not interfere with the operating procedures.

METHODS

A concept based on four inductively coupled rings was developed and applied for an intraoperative RF probe. The probe was integrated with a specially designed cranial clamp and incorporated into the intraoperative MRI system.

RESULTS

The design of the RF probe allows splitting the probe into two separate parts; the lower two rings and matching ring are permanently incorporated into the patient table, and the two upper rings can be removed to expose the patient's head during neurosurgery. The probe produces a homogeneous B1 field over the entire region of interest with sufficient sensitivity to obtain high quality images. The cranial clamp, made of MRI compatible materials, is asymmetrical to allow variable head positioning.

CONCLUSION

The described RF head probe and cranial clamp have been used successfully in more than 400 brain surgeries without compromising sterility of the operating area. Pre-, intra-, and postsurgical MRI scans have been obtained without a need to move a patient or reposition the head for imaging sessions. The images were of high quality and free of susceptibility or eddy currents artifacts. With minor modifications, the integrated RF probe and cranial clamp can be used successfully in other intraoperative MRI systems.

Periventricular nodular heterotopia: A challenge for epilepsy surgery

Pharmacoresistant focal epilepsies due to periventricular nodular heterotopia are a diagnostic and therapeutic challenge because of the need of invasive presurgical diagnostics and the selection of an optimal surgical approach. Invasive investigations in previous studies showed that focal epileptic activity can be correlated predominantly either with one of the nodular heterotopia or with neocortical epileptogenic zones distant to the periventricular nodules. Up to now, invasive recordings were required for localization of epileptic activity and its correlation to heterotopia. The following case presentation reports on a non-invasive approach using magnetic source imaging (MSI) combined with intraoperative ECoG. MSI combines preoperative data from magnetic resonance imaging (MRI) with magnetoencephalography (MEG). The MSI data for definition of the localization of the epileptic activity and functional important areas were coregistered with the intraoperative high-field-MRI and diffusion tensor imaging-based fiber tracking (DTI) of the visual pathway using a neuronavigational system. A neuronavigation-guided surgical resection of the epileptogenic area was performed leaving the heterotopia and the visual tract fibers intact. Postoperatively preservation of the visual fields was documented and the frequency of seizures was markedly reduced.

Presurgical planning for tumor resectioning

Since the birth of functional magnetic resonance imaging (fMRI)-a noninvasive tool able to visualize brain function-now 15 years ago, several clinical applications have emerged. fMRI follows from the neurovascular coupling between neuronal electrical activity and cerebrovascular physiology that leads to three effects that can contribute to the fMRI signal: an increase in the blood flow velocity, in the blood volume and in the blood oxygenation level. The latter effect, gave the technique the name blood oxygenation level dependent (BOLD) fMRI. One of the major clinical uses is presurgical fMRI in patients with brain abnormalities. The goals of presurgical fMRI are threefold: 1) assessing the risk of neurological deficit that follows a surgical procedure, 2) selecting patients for invasive intraoperative mapping, and 3) guiding of the surgical procedure itself. These are reviewed here. Unfortunately, randomized trials or outcome studies that definitively show benefits to the final outcome of the patient when applying fMRI presurgically have not been performed. Therefore, fMRI has not yet reached the status of clinical acceptance. The final purpose of this article is to define a roadmap of future research and developments in order to tilt pre-surgical fMRI to the status of clinical validity and acceptance.

Gliomas: histopathologic evaluation of changes in directionality and magnitude of water diffusion at diffusion-tensor MR imaging

PURPOSE

To retrospectively correlate changes in fractional anisotropy (FA) and mean diffusivity in gliomas at diffusion-tensor magnetic resonance (MR) imaging with the degree of tumor cell infiltration determined histologically.

MATERIALS AND METHODS

The institutional review board required neither ethics committee approval nor patient informed consent for this study. Twenty patients (eight women, 12 men; age range, 18-53 years) with glioma (seven World Health Organization grade II and 13 grade III tumors) underwent diffusion-tensor MR imaging at 1.5 T. Diffusion-tensor data were obtained with an echo-planar imaging sequence with six diffusion directions (b = 1000 sec/mm(2)), isotropic 1.9-mm voxels, and five averages. FA and mean diffusivity values were calculated from diffusion-tensor data. Coregistration with a three-dimensional MR imaging data set (used for stereotactic brain biopsies) enabled correlation of FA and mean diffusivity values with the histopathologic findings total cell number (CN), tumor CN, and percentage tumor infiltration (TI) by using linear, exponential, and logarithmic models. Student t and Mann-Whitney U tests were performed.

RESULTS

Histopathologic findings of 77 MR image-guided stereotactic biopsies in all 20 patients were correlated with FA and mean diffusivity values at the biopsy locus. For FA and mean diffusivity, a logarithmic model showed strongest correlation with tumor CN and total CN; a linear model showed strongest correlation with percentage TI. For FA there were negative logarithmic (R = -0.802, P < .001) and linear (R = -0.796, P < .001) correlations with tumor CN and percentage TI, respectively. For mean diffusivity there were positive logarithmic (R = 0.557, P < .001) and linear correlations (R = 0.521, P < .001) with tumor CN and percentage TI, respectively. Differences between correlations for FA and mean diffusivity versus tumor CN (P < .001) and percentage TI (P < .001) were significant.

CONCLUSION

FA is better than mean diffusivity for assessment and delineation of different degrees of pathologic changes (ie, TI) in glioma.

Fluorescent nanoparticle uptake for brain tumor visualization

Accurate delineation of tumor margins is vital to the successful surgical resection of brain tumors. We have previously developed a multimodal nanoparticle CLIO-Cy5.5, which is detectable by both magnetic resonance imaging and fluorescence, to assist in intraoperatively visualizing tumor boundaries. Here we examined the accuracy of tumor margin determination of orthotopic tumors implanted in hosts with differing immune responses to the tumor. Using a nonuser-based signal intensity method applied to fluorescent micrographs of 9L gliosarcoma green fluorescent protein (GFP) tumors, mean overestimations of 2 and 24 microm were obtained using Cy5.5 fluorescence, compared to the true tumor margin determined by GFP fluorescence, in nude mice and rats, respectively. To resolve which cells internalized the nanoparticle and to quantitate degree of uptake, tumors were disaggregated and cells were analyzed by flow cytometry and fluorescence microscopy. Nanoparticle uptake was seen in both CD11b+ cells (representing activated microglia and macrophages) and tumor cells in both animal models by both methods. CD11b+ cells were predominantly found at the tumor margin in both hosts, but were more pronounced at the margin in the rat model. Additional metastatic (CT26 colon) and primary (Gli36 glioma) brain tumor models likewise demonstrated that the nanoparticle was internalized both by tumor cells and by host cells. Together, these observations suggest that fluorescent nanoparticles provide an accurate method of tumor margin estimation based on a combination of tumor cell and host cell uptake for primary and metastatic tumors in animal model systems and offer potential for clinical translation.

Bibliography. Current world literature. Nose and paranasal sinuses

PURPOSE OF REVIEW

Patients with advanced head and neck cancer are being treated with chemo-radiotherapy, and life is being prolonged, with or without persistent disease, for longer than was previously. Hypercalcaemia may present in patients with advanced or disseminated head and neck cancer, and, as such, these patients may present to a larger variety of clinicians for advice concerning their symptoms and illness. Modes of presentation of hypercalcaemia and treatment strategies are reviewed.

RECENT FINDINGS

There were previously few large series of head and neck cancer patients diagnosed with hypercalcaemia, which may or may not have been related to their cancer being treated. Investigations, by way of blood/serum calcium level, may identify such patients. Patients with cancer-related hypercalcaemia have a poor prognosis, but many may respond temporarily to treatment when offered, with an improvement of their quality of life and death.

SUMMARY

Hypercalcaemia should and must be considered in all patients who have or possibly have a diagnosis of a head and neck cancer and who present unwell with symptoms of fatigue, lethargy and somnolence. Investigation must include serum calcium (corrected for serum albumin binding) and parathyroid hormone level. Patients may be treated by a combination of rehydration and bisulphonate therapy until the serum calcium is reduced to a level below 3 mmol/l. The majority of patients diagnosed with hypercalcaemia due to head and neck malignancy die of their diseases in the short term, but some may enjoy a prolongation of life with reasonable quality if diagnosed and treated aggressively.

A review of the endoscopic approach to the pituitary through the sphenoid sinus

PURPOSE OF REVIEW

The refinement of minimally invasive endoscopic techniques has resulted in 'pure' endoscopic endonasal trans-sphenoidal surgery, which is a new approach for the removal of pituitary tumors.

RECENT DEVELOPMENTS

This procedure is performed via a wide anterior sphenoidotomy with detachment of the septum from the sphenoid face, and avoids the use of a trans-sphenoidal retractor and any intraoral or nasal incisions. Straight and angled endoscopes are used throughout the procedure to provide a wide view of the sella and are manipulated by a co-surgeon. This technique represents an improvement over pituitary microsurgery, with decreased post-operative morbidities and a shortened postoperative stay, and it eliminates the need for packing while providing an opportunity to monitor the sella after surgery. The technique has been established as being efficacious and safe. It incorporates image-guided surgery, with the fusion of computer tomography and magnetic resonance imaging, and employs new and dedicated instrumentation. Training in endoscopic techniques is required.

SUMMARY

Future advancements in intraoperative imaging, cranial base reconstruction, and robotics will make this technique even more successful.

Application Accuracy of Automatic Registration in Frameless Stereotaxy

OBJECTIVE

We compared the application accuracy of an infrared-based neuronavigation system when used with a novel automatic registration with its application accuracy when standard fiducial-based registration is performed.

METHODS

The automatic referencing tool is based on markers that are integrated in the headrest holder we routinely use in our intraoperative magnetic resonance imaging (MRI) setting and can be detected by the navigation software automatically. For navigation targeting we used a Plexiglas phantom with 32 notched rods of different heights. The phantom was fixed in the head holder and multiple optimized gradient echo slices containing the clamp-integrated markers were acquired. After that we measured a T1 MPRAGE sequence with a slice thickness of 1.0 mm for navigation. The deepest points of the surface of the rods were defined as target points in image space. In three measurement series we referenced the phantom once with 4, once with 7 fiducials and twice automatically. In one series we performed only one automatic registration. The localization error was measured 3 times per rod and registration.

RESULTS

The median localization errors for standard registration with 7 fiducials were between 1.2 and 3.05 mm. With 4 fiducials, medians were in the range from 1.87 to 2.21 mm. For the automatic registration we obtained median localization errors between 0.88 and 2.13 mm. In 6 of the 8 samples that were compared the automatic registration showed an application accuracy that was highly significantly better (p < 0.001 in most cases) than that of fiducial-based standard registration.

CONCLUSION

The application accuracy found for automatic referencing is at least not worse than that for standard registration no matter whether 4 or 7 fiducial markers were used. Therefore, its use in the operating room is feasible. In combination with intraoperative MRI it may become a favorable alternative to standard fiducial-based registration especially when an intraoperative update of navigation data is necessary.

Intraoperative High-Field Magnetic Resonance Imaging in Transsphenoidal Surgery of Hormonally Inactivepituitary Macroadenomas

OBJECTIVE

The aim of the study was to evaluate the effect of intraoperative, high-field (1.5 T) magnetic resonance imaging (MRI) on the results of transsphenoidal surgery of hormonally inactive pituitary macroadenomas.

METHODS

One hundred six patients (tumor size, 29.9 +/- 10.1 mm; minimum, 11.3 mm; maximum, 57.2 mm) with hormonally inactive pituitary macroadenoma were investigated by intraoperative high-field MRI during transsphenoidal surgery. If intraoperative imaging depicted an accessible tumor remnant, resection was continued.

RESULTS

Among the 85 patients in whom complete tumor removal was intended preoperatively, intraoperative imaging revealed definite tumor remnants or suspicious findings in 36 (42%) patients. Imaging led to an extended resection in 29 (34%) patients of this group. Among them, resection could be completed in 21. This increased the rate of complete tumor removal from 58% (49 out of 85) to 82% (70 out of 85). In the group of patients with intended partial removal (n = 21), resection was extended in 38% (eight out of 21) because of intraoperative imaging. Comparison with scanning 3 months after surgery did not reveal any false-negative findings of intraoperative MRI; in six cases, intraoperative MRI was suspicious for some minor remnant that could not be reproduced in the postoperative control.

CONCLUSION

The extent of resection in transsphenoidal surgery can be reliably assessed using intraoperative high-field MRI. In addition to the suprasellar compartment, intra- and parasellar structures are also visualized in great detail. Intraoperative imaging acts as an immediate intraoperative quality control, allowing one to not only increase the extent of resection, but to also increase the percentage of complete removals.

Enhancement of brain tumors in 0.23-T low-field MRI: comparison of edema attenuated inversion recovery (EDAIR) sequences with T1-weighted sequence

RATIONALE AND OBJECTIVES

The aim of this study is to explore whether edema attenuated inversion recovery (EDAIR) sequences could be used to improve tumor contrast in contrast-enhanced low-field 0.23-Tesla magnetic resonance imaging (MRI) using 0.1 mmol/kg of gadolinium-based contrast agent.

MATERIALS AND METHODS

Ten patients with brain tumors were examined by using the following contrast-enhanced sequences: T1-weighted spin echo, EDAIR with inversion time (TI) of 600 milliseconds, and EDAIR with TI of 800 milliseconds. Images were assessed both quantitatively and qualitatively.

RESULTS

Results suggest that tumor contrast enhancement in low-field MRI can be improved without increasing contrast agent dose. EDAIR 600 appears to be optimal in most cases.

CONCLUSIONS

This inversion recovery sequence could be applicable as an additional sequence in the imaging of metastases in low-field MRI, as well as imaging of any other enhancing brain tumors or lesions in low-field MRI.

Intraoperative magnetic resonance imaging-guided neurosurgery at 3-T

OBJECTIVE

Between 1997 and 2004, more than 700 neurosurgical procedures were performed in a 1.5-T magnetic resonance-guided therapy suite. During this period, the concept of high-field intraoperative magnetic resonance imaging (MRI) was validated, as was a new surgical guidance tool, the Navigus (Image-guided Neurologics, Melbourne, FL), and its methodology, prospective stereotaxy. Clinical protocols were refined to optimize surgical techniques. That implementation, the "Minnesota suite," has recently been revised, and a new suite with a 3-T MRI scanner has been developed.

METHODS

On the basis of experience at the initial 1.5-T suite, a new suite was designed to house a 3-T MRI scanner with wide surgical access at the rear of the scanner (opposite the patient couch). Use of electrocautery, a fiberoptic headlamp, a power drill, and MRI-compatible neurosurgical cutlery was anticipated by inclusion of waveguides and radiofrequency filter panels that penetrate the MRI suite's radiofrequency shield. An MRI-compatible head holder was adapted for use on the scanner table. A few items exhibiting limited ferromagnetism were used within the magnetic field, taking strict precautions.

RESULTS

During the initial procedures (all magnetic resonance-guided neurobiopsies), the new suite functioned as anticipated. Although metallic artifact related to titanium needles is more challenging at 3 T than at 1.5 T, it can be contained even at 3 T. Similar to 1.5 T, such artifact is best contained when the device is oriented along B0, the main magnetic field. Surgical needles, disposable scalpels, and disposable razors, despite being minimally ferromagnetic, were easily controlled by the surgeon.

CONCLUSION

An intraoperative magnetic resonance-guided neurosurgical theater has been developed with a 3-T MRI scanner. Intraoperative imaging is feasible at this field strength, and concerns regarding specific absorption rate can be allayed. Infection control procedures can be designed to permit neurosurgery within this environment. Despite the increase in magnetic field strength, safety can be maintained.

Craniopharyngiomas

Craniopharyngiomas are rare, mainly sellar/parasellar, epithelial tumors diagnosed during childhood or adult life. Histologically, two primary subtypes have been recognized (adamantinomatous and papillary) with an as yet, unclarified pathogenesis. They may present with a variety of manifestations (neurological, visual, and hypothalamo-pituitary). Despite their benign histological appearance, they often show an unpredictable growth pattern, which, combined with the lack of randomized studies, poses significant difficulties in the establishment of an optimal therapeutic protocol. This should focus on the prevention of recurrence(s), improvement of survival, reduction of the significant disease and treatment-related morbidity (endocrine, visual, hypothalamic, neurobehavioral, and cognitive), and preservation of the quality of life. Currently, surgical excision followed by external beam irradiation, in cases of residual tumor, is the main treatment option. Intracystic irradiation or bleomycin, stereotactic radiosurgery, or radiotherapy and systemic chemotherapy are alternative approaches; their place in the management plan remains to be assessed in adequately powered long-term trials. Apart from the type of treatment, the identification of clinical and imaging parameters that will predict patients with a better prognosis is difficult. The central registration of patients with these challenging tumors may provide correlates between treatments and outcomes and establish prognostic factors at the pathological or molecular level that may further guide us in the future.

A Novel Platform for Image-guided Ultrasound

OBJECTIVE:

The combination of classic neuronavigation and intraoperative ultrasound is a recent innovation in image guidance technology. However, this technique requires two hardware components (neuronavigation and an ultrasound system). It was the aim of the study to describe a new simplified technology of a so-called one-platform navigation system developed by our institution in collaboration with the industry and to demonstrate its range of various applications.

METHODS:

An ultrasound device (IGSonic; BrainLAB, Munich, Germany) is integrated into the VectorVision2 navigation system (BrainLAB, Munich, Germany). The IGSonic Probe 10V5 is connected to the VectorVision Navigation station via an IGSonic Device Box. Once the ultrasound probe is calibrated, the navigated ultrasound displays the sonographic image of the intracranial anatomy on the navigation screen in a composed overlay fashion. It might depict vascular structures within the ultrasound plane by a duplex mode. Ultrasound can also be operated independently from navigation.

RESULTS:

The VectorVision2 system combines intraoperative ultrasound data sets with preoperatively acquired neuronavigation data sets in plug and play fashion. The system provides a cost-effective intraoperative imaging modality that offers a good anatomic orientation by various composite images, including the display of the amount of brain shift. In our institution, the comprehensible interface led to a routine use of the technology by several neurosurgeons who had not been familiar with the ultrasound technology before.

CONCLUSION:

The integration of an ultrasound device into an existing navigation system has been successfully developed. The system offers a friendly user interface and cost-effective intraoperative imaging feedback. Although brain shift can be visualized by an image overlay technology as demonstrated by the present system, future developments should aim at fusion techniques of both intra- and preoperative image data sets.

Intra-operative 3D ultrasound in neurosurgery

In recent years there has been a considerable improvement in the quality of ultrasound (US) imaging. The integration of 3D US with neuronavigation technology has created an efficient and inexpensive tool for intra-operative imaging in neurosurgery. In this review we present the technological background and an overview of the wide range of different applications. The technology has so far mostly been applied to improve surgery of tumours in brain tissue, but it has also been found to be useful in other procedures such as operations for cavernous haemangiomas, skull base tumours, syringomyelia, medulla tumours, aneurysms, AVMs and endoscopy guidance.

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.

Intraoperative high-field MRI: anatomical and functional imaging

Intraoperative high-field magnetic resonance (MR) imaging with integrated microscope-based navigation is at present one of the most sophisticated technical methods providing a reliable immediate intraoperative quality control. It enables intraoperative imaging at high quality that is up to the standard of up to date pre- and postoperative neuroradiological routine diagnostics. The major indications are pituitary tumor surgery and glioma surgery. In pituitary tumor surgery intraoperative MRI helps to localize hidden tumor remnants that would be otherwise overlooked. The same is true for glioma surgery, where the optimal extent of resection by simultaneous preservation of functional integrity can be achieved. This is possible since high-field MR imaging offers various modalities beyond standard anatomical imaging, such as MR spectroscopy, diffusion tensor imaging, and functional MR imaging which may also be applied intraoperatively, providing not only data on the extent of resection and localization of tumor remnants but also on metabolic changes, tumor invasion, and localization of functional eloquent cortical and deep-seated brain areas.

Intraoperative visualization of the pyramidal tract by diffusion-tensor-imaging-based fiber tracking

Functional neuronavigation allows intraoperative visualization of cortical eloquent brain areas. Major white matter tracts, such as the pyramidal tract, can be delineated by diffusion-tensor-imaging based fiber tracking. These tractography data were integrated into 3-D datasets applied for neuronavigation by rigid registration of the diffusion images with standard anatomical image data so that their course could be superimposed onto the surgical field during resection of gliomas. Intraoperative high-field magnetic resonance imaging was used to compensate for the effects of brain shift, which amounted up to 8 mm. Despite image distortion of echo planar images, which was identified by non-linear registration techniques, navigation was reliable. In none of the 19 patients new postoperative neurological deficits were encountered. Intraoperative visualization of major white matter tracts allows save resection of gliomas near eloquent brain areas. A possible shifting of the pyramidal tract has to be taken into account after major tumor parts are resected.

3-Tesla intraoperative MR imaging for neurosurgery

Intraoperative magnetic resonance (MR) image-guided neurosurgery has been performed since 1994. Using a 1.5-Tesla (T) intraoperative MR imaging system, we have performed more than 750 interventional procedures. Having validated the safety and efficacy of this surgical technique that is relatively amenable to nearly all new in-hospital MR suites, we sought to adapt this approach at our sister hospital where a new short-bore 3-T MR suite was being installed. Using many of the lessons learned from our initial experience at 1.5-T, we designed a new interventional suite that would enable surgery to be performed entirely within a 3-T MR environment. All surgical instrumentation including electrocautery, fiberoptic headlamp, power drill, and ultrasonic aspirator was entirely MR-compatible. A few items with limited ferromagnetism were utilized within the magnetic field under strict precaution. From 2/04 to 7/05, those cases initially performed within the 3-T surgical suite included one drainage and reservoir placement for a cystic craniopharyngioma, five brain biopsies and two craniotomies; one for open brain biopsy and another for lesion resection. The craniopharyngioma was successfully aspirated and had the reservoir catheter placed within the cyst. All five brain biopsies yielded diagnostic tissue. The craniotomy for mass resection demonstrated radiation necrosis. Although the metallic artifact from the biopsy needle was more prominent than at 1.5-T, accurate image interpretation was possible. Surgical needles, disposable scalpel, disposable razor, and surgical stapler were minimally ferromagnetic and safely controlled by the surgeon. There were no adverse events associated with any procedure. MR-guided neurosurgery can be safely and effectively performed at 3-T. The surgical environment at 3-T is comparable to that present at 1.5-T.

Treatment of pituitary tumors: surgery

Following a century of technical developments and refinements, a variety of standard operation techniques to date are available for the surgical treatment of pituitary tumors. The vast majority of the lesions can be dealt with satisfactorily utilizing transsphenoidal approaches. The goal of surgical treatment is rapid eradication of the tumor mass, decompression of visual pathways, and elimination of hormonal oversecretion while preserving the normal gland and avoiding potential surgical complications. The tumor's size, extension, and configuration and the magnitude of hormonal oversecretion, are the essential factors that decide whether all the goals can be reached. Another important factor is the individual skill and experience of the surgeon. Still, several lesions that are mainly developed outside of the sella require transcranial approaches, of which the pterional and subfrontal routes are the most widely used. With microsurgical techniques and standard approaches, mortality is far below 1% and morbidity is remarkably low. The most favorable surgical results are obtained with microadenomas, which in the MR image are depicted as distinct low intensity lesions. Only recently has the recovery of pituitary function following surgery been convincingly demonstrated. With the extended transsphenoidal approaches, lesions become accessible that previously have been considered contraindications for transsphenoidal surgery. The introduction of new technical gadgets such as neuronavigation, endoscopy, and intraoperative imaging open new avenues and, even more, widen the spectrum of accessible lesions. Indications for surgery, the preoperative workup, surgical techniques, results, limitations, and new technical developments are briefly reviewed in this article.

The history of the treatment of pituitary adenomas

The immense history leading to our current understanding and treatment of pituitary pathology is inextricably linked to the evolution of the understanding of the numerous functions of the hypophysis cerebri as the "master gland" of the endocrine system. When the anatomists of old encountered this small organ sequestered "like a nugget in the innermost of Chinese boxes" at the base of the brain, they had no inkling of its importance in the control of multiple target organs in the human body. It would ultimately take two millennia and a vast amount of clinical and laboratory research for its role in the body to eventually become more completely appreciated.

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.

MR Imaging-guided percutaneous tumor ablation

RATIONALE AND OBJECTIVES

The purpose of this study is to compare the feasibility and precision of renal artery angioplasty and stent placement using two different MR scanners.

MATERIALS AND METHODS

MR imaging-guided angioplasty and stent placements were performed on seven pigs using 0.2 and 1.5 T scanners (Magnetom Open and Magnetom Sonata, Siemens Medical Solutions, Erlangen, Germany). For guidance of catheters, guide wires and stents susceptibility artifact-based tracking was used. The end point of each intervention was to position a stent in the renal artery with its proximal end at the level of the aortic wall. Procedure time and stent position were evaluated.

RESULTS

Catheterization, angioplasty, and stent placement were feasible using MRI guidance at both 0.2 and 1,5 Tesla. At 1.5 T all catheter manipulations and interventions were performed in less than 30 minutes. At 0.2 T the interventions took up to 90 minutes. No significant difference in the stent deviation was noted between the two scanners.

CONCLUSION

The use of a high-performance 1.5 T scanner helped to reduce the procedure time to half of that of a low-field system. Since no difference in stent placement precision was noted, a dedicated MR-stent might be mandatory for more precise stent placement.

Imaging in neurooncology

Imaging in patients with brain tumors aims toward the determination of the localization, extend, type, and malignancy of the tumor. Imaging is being used for primary diagnosis, planning of treatment including placement of stereotaxic biopsy, resection, radiation, guided application of experimental therapeutics, and delineation of tumor from functionally important neuronal tissue. After treatment, imaging is being used to quantify the treatment response and the extent of residual tumor. At follow-up, imaging helps to determine tumor progression and to differentiate recurrent tumor growth from treatment-induced tissue changes, such as radiation necrosis. A variety of complementary imaging methods are currently being used to obtain all the information necessary to achieve the above mentioned goals. Computed tomography and magnetic resonance imaging (MRI) reveal mostly anatomical information on the tumor, whereas magnetic resonance spectroscopy and positron emission tomography (PET) give important information on the metabolic state and molecular events within the tumor. Functional MRI and functional PET, in combination with electrophysiological methods like transcranial magnetic stimulation, are being used to delineate functionally important neuronal tissue, which has to be preserved from treatment-induced damage, as well as to gather information on tumor-induced brain plasticity. In addition, optical imaging devices have been implemented in the past few years for the development of new therapeutics, especially in experimental glioma models. In summary, imaging in patients with brain tumors plays a central role in the management of the disease and in the development of improved imaging-guided therapies.

Intraoperative MR Imaging

With the rapid evolution of technologic advances in neurosurgery, it is no surprise that the use of MR imaging to guide the performance of safe and effective surgical procedures is at the forefront of development. This article highlights the current capabilities of intraoperative MR-guided surgery for a variety of neurosurgical procedures and traces the evolution of the field to its present level of technical sophistication. The costs of intraoperative MR imaging and its future directions are discussed.

The Interventional MR Imaging Suite: Magnet Designs and Equipment Requirements

Soon after the introduction of MR imaging as an imaging tool, researchers began to investigate its capabilities to guide interventional minimally invasive procedures, such as biopsies. These early efforts have encouraged vendors and numerous research groups worldwide to identify clinical problems in the field of image-guided intervention, for which MR imaging is beneficial as an imaging modality, and to develop and refine soft-ware and hardware components to meet the specific requirements of interventional MR imaging. Over nearly 20 years, continuous advances in magnet and system design have accelerated the progress of MR-guided intervention.

Transsphenoidal surgery in acromegaly investigated by intraoperative high-field magnetic resonance imaging

OBJECTIVE

The aim of the study was to evaluate the effect of intraoperative high-field (1.5 Tesla) magnetic resonance imaging (MRI) on the results of transsphenoidal surgery of GH-secreting pituitary macroadenomas.

METHODS

Twenty-three acromegalic patients (mean tumor size, 25 +/- 12 mm; untreated preoperative GH, 4.2-159 microg/l; IGF-I, 349-1111 microg/l) were investigated by intraoperative high-field MRI. If intraoperative imaging depicted an accessible tumor remnant, resection was continued.

RESULTS

In five patients intraoperative MRI led to further tumor removal, two of these met the consensus criteria for endocrine remission after 3 months. In two patients basal GH and oral glucose tolerance test (OGTT) were <2 microg/l, only IGF-I was slightly elevated, and in one patient GH was <5 microg/l and OGTT was 2 microg/l, with elevated IGF-I. Final intraoperative MRI showed no tumor remnants in 14 patients; eight of them met the consensus criteria for remission of acromegaly. In the patients with MRI showing incomplete removal (four suspect findings and five patients with intended partial removal) none was normalized.

CONCLUSION

With regard to the patients with a tumor configuration in whom complete tumor removal was considered (n = 18), intraoperative MRI increased the rate of endocrine normalization from 33 to 44% applying the consensus criteria, and improved endocrine outcome to 'nearly normalization' in another 17%. With regard to preoperative GH levels and tumor size, intraoperative MRI can help to achieve endocrine remission in patients who are normally considered not to be curable. However, taking GH as the tumor marker, even intraoperative high-field MRI was not able to detect tumor remnants in every case.

Evaluation of intra-operative ultrasound imaging in brain tumor resection: a prospective study

AIMS

The purpose of our study was to evaluate intra-operative ultrasound (IOUS) as a tool of resection control after brain tumor surgery. In addition, we looked for tumor species suitable for ultrasound representation.

METHODS

Using a Siemens Omnia Sonoline Ultrasound, 36 tumors were examined, high-grade gliomas (62%), metastases (22%) and others (16%). We focused on tumor imaging by ultrasound with regard to its reliability of tumor expansion and margins. Evaluation of the images was carried out by correlating the ultrasound-based intra-operative measured tumor volume before and after resection with a pre- and post-operative (within 48 hours) measured volume by MRI. The IOUS measurements were performed by the neurosurgeon and the MRI measurements by the neuroradiologist. Thus, the measurement procedures were blinded. Corresponding to a deviation of the ultrasound volume by 10, 20 and > 20% from the MRI volume, the correlation was ranked good, moderate and poor. For assessing the agreement between these two methods of imaging, the statistical analysis was conducted using a method described by Bland and Altman.

RESULTS

High-grade gliomas mostly showed a moderate or poor correlation in comparing IOUS- and MRI-tumor volumetry resulting in incomplete resection. Metastases resulted in a good to moderate correlation with a satisfactory extent of resection. The other tumors had poor images with larger tumor residues. The MRI measured volumes tended to be larger on average; the deviation grew with tumor size .

CONCLUSION

The reliability of IOUS depends on tumor type. It is beneficial to use IOUS for the resection of metastases and a few high-grade gliomas. Concerning the volumetric accuracy, the value of IOUS is worse than its value of navigation and resection control.

Intraoperative functional MRI: Implementation and preliminary experience

For a non-invasive identification of eloquent brain areas in neurosurgical procedures up to now only preoperative functional brain mapping techniques are available. These are based, e.g., on preoperative functional magnetic resonance imaging (fMRI) investigations in awake patients. The aim of this study was to investigate the feasibility to perform fMRI during neurosurgical procedures in anesthetized patients. For that purpose, a passive stimulation paradigm with peripheral nerve stimulation was applied. A 1.5-T MR scanner placed in a radiofrequency-shielded operating room with an adapted operating table was used for intraoperative fMRI. The fMRI data were analyzed during acquisition by an online statistical evaluation package installed on the MR scanner console. In addition, phase reversal of somatosensory evoked potentials was used for verification of intraoperative fMRI. In four anesthetized patients with lesions in the vicinity of the central region a total of 11 fMRI measurements were successfully acquired and analyzed online. Activation was found in the somatosensory cortex, which could be confirmed by intraoperative phase reversal for each measurement. Furthermore, statistical parametric mapping (SPM) was employed for an extensive offline data analysis. We did not observe any neurological deterioration or complications due to the stimulation technique. Intraoperative fMRI is technically feasible allowing a real-time identification of eloquent brain areas despite brain shift.

Intelligent Operating Theater Using Intraoperative Open-MRI

Malignant brain tumors vary among patients and are characterized by their irregular shapes and infiltration. Localization of functional areas in the brain also differs among patients, and excess removal of tumor near eloquent areas may increase the risk of damage of function, such as motor paresis and speech disturbance. Recent progress in magnetic resonance (MR) imaging technology has enabled acquisition of intraoperative images and totally changed the neurosurgery of malignant brain tumors. Before, surgeons could merely speculate about the results of surgical manipulation and have no certainty about procedure outcomes until postoperative examination. Because intraoperative MR images allow visualization of the size of residual tumor(s) and the positional relationship between the tumor(s) and eloquent areas, surgeons are now able to achieve safe and reliable surgery. As an example, positional error on preoperative MR images caused by shifting of the brain (brain shift), a long-standing annoyance for surgeons, has been resolved using intraoperative MR images for surgical navigation, allowing precise resection. Two types of open-MR imaging scanner, a 0.2- or 0.3-tesla hamburger-type scanner with a horizontal gap and a 0.12- or 0.5-tesla double doughnut-type scanner with a vertical gap, are now available in the operating theater, and 1.5-tesla bore-type scanners are available. A 3.0-tesla bore-type scanner is planned. Intraoperative MR imaging includes diffusion-tensor and diffusion-weighted imaging, which allows visualization of nerve fibers in the white matter, especially the pyramidal tract. Such images are valuable aids in the precise resection of residual lesions of malignant brain tumors near eloquent areas without injuring motor function.