Novel magnetic technology for intraoperative intracranial frameless navigation: in vivo and in vitro results

OBJECTIVE

To characterize the accuracy of the Magellan electromagnetic navigation system (Biosense Webster, Tirat HaCarmel, Israel) and to demonstrate the feasibility of its use in image-guided neurosurgical applications.

DESCRIPTION OF INSTRUMENTATION

The Magellan system was developed to provide real-time tracking of the distal tips of flexible catheters, steerable endoscopes, and other surgical instruments, using ultra-low electromagnetic fields and a novel miniature position sensor for image-correlated intraoperative navigation and mapping applications.

METHODS

An image registration procedure was performed, and static and qualitative accuracies were assessed in a series of phantom, animal, and human neurosurgical studies.

EXPERIENCE AND RESULTS

During the human study phase, an accuracy error of up to 5 mm was deemed acceptable. Results demonstrated that this degree of accuracy was maintained throughout all procedures. All anatomic landmarks were reached with precision and were accurately viewed on the display screen. Navigation that relied on the system was also successful. No interference with operating room equipment was noted. The accuracy of the system was maintained during regular surgical procedures, using standard surgical tools.

CONCLUSION

The system provides precise lesion localization without limiting the line of vision, the mobility of the surgeon, or the flexibility of instruments. Electromagnetic navigation promises new advances in neuronavigation and frameless stereotactic surgery.

High-energy (511-keV) imaging with the scintillation camera

A dual-head scintillation camera has been adapted for high-energy (511-keV) imaging by extending the useful energy range and linearity maps to 560 keV, implementing high-energy sensitivity maps, and developing high-energy collimators. High-energy parallel-hole collimators have inferior spatial resolution and sensitivity relative to the low-energy, high-resolution collimators commonly in use. With high-energy parallel-hole collimators, phantom studies show that the limit for detectability of "hot" lesions is 1.5 cm and 1.3 cm in diameter or larger for 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) uptake ratios of 5:1 and 10:1, respectively, if one assumes adequate counting statistics. Dual-isotope, single-acquisition techniques for using technetium-99m methoxy isobutyl isonitrile and FDG have been developed and proved useful in identification of ischemic but viable myocardium. High-energy fan-beam collimators have superior spatial resolution but inferior sensitivity relative to low-energy, high-resolution collimators. Metabolic images of the brain obtained with FDG demonstrate spatial resolution comparable with that of positron emission tomography, but such studies are often limited by inadequate counting statistics.

FDG-SPECT: correlation with FDG-PET

The clinical utility of FDG-PET imaging in the evaluation of patients with cardiac, oncologic and neurologic diseases is well documented. The major disadvantages of PET continue to be its high cost and limited availability.

METHODS

With the goal of providing equivalent diagnostic information using a widely available, less expensive modality, we evaluated the clinical utility of FDG-SPECT imaging with a conventional dual-headed camera as compared to PET in 21 patients.

RESULTS

To compare the image quality of the two modalities, major physical parameters and phantom determinations were obtained. By using the 511-keV collimators, we achieved resolution and system volume sensitivity that were less than those for PET by factors of 2.6 and 8, respectively. The SPECT system, on the other hand, could easily resolve 2 x 0.5-cm cold defects in the heart phantom and 2-cm hot lesions in a 22-cm cylindrical phantom with a target-to-background ratio of 5:1. FDG-SPECT imaging of nine patients with heart disease yielded similar diagnostic information of the amount of viable myocardium present when compared to PET. In seven of eight patients, malignant tissue visualized with FDG-PET was seen equally well with SPECT. The lesions not visualized with FDG-SPECT were either small (< or = 1.5 cm) or benign. SPECT imaging of four patients with cerebral lesions was inconclusive due to the small sample size but seemed promising.

CONCLUSION

FDG-SPECT with 511-keV collimation is less expensive, more available and technically simpler than PET. We believe that FDG-SPECT has achieved sufficient sensitivity and resolution to detect myocardial viability and diagnose malignant tumors > or = 2 cm in diameter.