Lucia Zamorano

Image-guided insertion of transpedicular screws. A laboratory set-up.

Study design A computer-assisted system allowing precise preoperative planning and real-time intraoperative image localization of surgical instruments is tested in a laboratory setup. Objectives The purpose of this study is to assess the applicability, functionality, and accuracy of this transpedicular spinal fixation technique. Summary of background data Most techniques in transpedicular spinal fixation rely on the identification of predefined targets with the help of anatomic landmarks and on the intraoperative use of image intensifiers. Various studies report considerable screw misplacement rates which may lead to serious clinical sequelae such as permanent nerve damage. Methods The proposed system was tested in an in vitro setup drilling 20 pedicle pilot holes in lumbar vertebrae. The accuracy was assessed using precision cuts through the pedicles and simulation of a 6-mm pedicle screw insertion. Results An ideal screw position was found in 70 of 77 cuts, and in no case was an injury to the pedicular cortex observed. Conclusions The presented technique provides a safe, accurate, and flexible basis for transpedicular screw placement in the spine. This approach should be further evaluated in clinical applications.

Computer-Aided Fixation of Spinal Implants

Medical imaging provides an important basis for modern diagnosis as well as for preoperative planning of surgical procedures. However, information gained cannot be transferred directly into the operating room. Furthermore, the safety and accuracy of the surgical intervention would be improved by interactive navigation of surgical instruments. These features are provided by the system for computer-aided fixation of spinal implants described in this paper.

Interactive intraoperative localization using an infrared-based system.

We discuss new methods of localizing and treating brain lesions for both the conventional method of a base-ring fixed to the patients skull (referred to as frame-based procedures) and the new method of frameless procedures (no base ring). Frame-based procedures are used for finding a precise instrument position during neurosurgical procedures, such as stereotactic biopsy of deep-seated lesions, placing electrodes for functional stereotaxis or catheters with radioactive seeds for brachytherapy, or even the placement of a stereotactic retractor or endoscope for removal or internal decompression of lesions. In such procedures, the intraoperative image localization of instruments becomes useful as it tracks instruments as they travel through the preplanned trajectory. Additional intraoperative digitization of surgical instruments, e.g., bipolar suction, biopsy forceps, microscope, ultrasound probe, etc, can be achieved during the stereotactic resection of eloquent areas or deep intracranial lesions by adding an infrared-based system. Frameless procedures broaden the range of surgical approaches, image guidance planning, and operative procedures, since no ring is attached to the patients head which might interfere with the surgical approach, and offers logistic advantages in scheduling diagnostic studies. Frameless diagnostic studies employ anatomical markers and/or surface matching techniques for data registration in the computer software surgical preplanning program. This simplifies scheduling of the procedures since the image study does not need to be acquired the same day as surgery. Frameless diagnostic studies allow for the use of more than one type of imaging data for planning and optimization of surgical procedures, and greatly improve patient tolerance and comfort during these procedures and during surgery, as compared with frame-based procedures.(ABSTRACT TRUNCATED AT 250 WORDS)

Permanent 125iodine implants for recurrent malignant gliomas

PURPOSE To determine the efficacy and toxicity of permanent 125iodine implants for recurrent malignant gliomas. METHODS AND MATERIALS Between January 1989 and January:, 59 patients with histologically confirmed recurrent malignant gliomas (22 nonglioblastoma malignant gliomas, 37 glioblastoma multiforme at the time of implant) received a permanent 125iodine implant. Patients ranged in age from 13-74 years. The median ages for the overall group, nonglioblastoma (nonGBM), and glioblastoma (GBM) groups was 47 years, 39 years, and 53 years, respectively. RESULTS With a median follow-up of 40 months, the median survival for the 59 total patients is 1.34 years; nonGBM 2.04 years, GBM 0.9 years. Factors predictive for poor prognosis were GBM histology, age 60 years or more, target volume 17 cc or more, and/or tumor location within the corpus callosum or thalamus. Reoperations have been performed in 24 (40%) patients; 15 (25%) for tumor progression; 3 (5%) for radiation necrosis; 2 (3%) for skull necrosis/infection, and 4 (7%) for other reasons (Ommaya reservoir insertion, catheter removal, hematoma evacuation). CONCLUSION Permanent 125iodine implants in selected patients with recurrent malignant gliomas are associated with reasonable long-term survival and a low risk of complications. Given the low incidence of radiation necrosis, future plans are to increase dose rate and/or total dose delivered with the permanent implant.

In vivo and in vitro Study of the Lesions Produced with a Computerized Radiofrequency System

For many years, radiofrequency-generated lesions have been used for the treatment of pain and abnormal movements. However, the reliability of this method has been questioned because of the variation in the size of lesions produced by the electrode at different times and temperatures. A 500-kHz radiofrequency generator with different electrodes was used to determine the size of lesions, using different time and temperature exposures. A computerized feedback mechanism kept the tip temperature constant during the production of the lesion, regardless of varying tissue impedance. Eight electrodes of different size and tip characteristics were evaluated at different temperatures and time settings, both in vitro and in vivo. Graphic display of the curves in time were obtained at 65, 70, 75, 80, 85 and 90 degrees C. The effects of thermo-coagulation were studied in vitro in fresh egg whites, using time intervals of 20, 40, 60, 80 and 100 s, and in vivo, in the subcortical white matter of 20 adult New Zealand white rabbits. Animals were sacrificed after 7 days. Lesions were photographed and measured under magnification. In all cases, the coagulated masses were ellipsoid, with regular, well-demarcated borders. A two-way statistical analysis of variance was done. The coagulum size increased with higher temperatures and with larger probes. The increase was significant in both diameter and length (p = 0.001). In contrast, the use of different times at the same level of temperature showed no significant increase in most of the electrodes. There were two statistical significant time effects, for both diameter and length, with the monopolar 2-mm electrode. The use of real-time monitoring with graphic display and the feedback information provided for the computerized control of power and current allows high precision of the temperature at the electrode tip during the production of the lesion.

Image-Guided Computer-Assisted Spine Surgery: A Pilot Study on Pedicle Screw Fixation

As the pedicle offers a strong point of attachment to the spine, several instrumentation systems using screws that go through the pedicle into the vertebral body have been developed to provide internal stability. All pedicle screw systems share the risk of damage to adjacent neural structures as a result of improper screw placement. A computer-assisted system allowing precise preoperative planning and real-time intraoperative interactive image localization has been implemented for spine instrumentation to optimize transpedicular spine fixation. A validation study was performed in an in vitro set-up drilling 20 pedicle pilot holes in lumbar vertebrae. An analysis in 77 histological cuts showed an ideal location in 70 with no case of injury to the pedicle cortex. We discuss initial clinical experience on cases of posterior lumbar stabilization. Interactive computer-assisted spine surgery provides an accurate and safe approach for transpedicular screw fixation and may provide a useful tool for optimization of spine surgery.

Computer-assisted neurosurgery system: Wayne state university hardware and software configuration

Computer-assisted neurosurgery uses the latest technological advancements in imaging, computers, mechanics, and electronics to improve the accuracy and reduce the invasiveness and risk of neurosurgical procedures. We describe the Wayne State University, Detroit, Michigan, computer-assisted neurosurgical system with the emphasis on software and discuss the theory guiding the development of this system and its application in real-time position tracking systems. Our system consists of the Neurological Surgery Planning System (NSPS) software which we developed at our medical center and three types of position tracking systems: the Zamorano-Dujovny (Z-D) are digitizer for frame-based procedures, an articulated arm, and an infrared-based digitizer for frameless procedures. The NSPS software is designed to offer neurosurgeons a safe and accurate method to approach intracranial lesions by preoperatively planning a surgical trajectory. Software consisting of the most advanced technologies in computer vision, computer imaging/graphics, and stereotactic numeric analysis forms the core of the system. Capabilities for correlating data from imaging studies to facilitate image reconstruction, image mapping, and three-dimensional (3D) visualization of target volumes enable the neurosurgeon to simulate surgical procedures into a preoperative protocol to be used during surgery, both to follow the preplanned trajectory and to track the position of surgical instruments in real-time on the computer monitor. The tracking systems position and orient the surgical instruments relative to the patients head. With these devices, the display of the surgical instruments together with the virtual images create an excellent intraoperative tool.

Permanent iodine-125 implants in the up-front treatment of malignant gliomas.

Between July 1989 and July 1992, 58 patients with newly diagnosed, histologically confirmed malignant gliomas (40 anaplastic astrocytomas, 18 glioblastoma multiforme) underwent implantation with low-activity iodine-125 sources. Patients were considered appropriate candidates for brachytherapy if their Karnofsky scores were > or = 70 and their contrast-enhancing tumors were < 6 cm in maximum diameter. Tumor volumes ranged from 0.1 to 90 ml. Ten patients had implants only. The other 48 patients received additional external beam radiation; 38 patients received radiation 1 to 2 weeks after the implant, and 10 patients received radiation preceding the implant. Median survival has not been reached but is currently greater than 31 months for patients with anaplastic astrocytoma and greater than 23 months for patients with glioblastoma. The rate of second operation for this group of patients was 45% (26 patients). Brain necrosis requiring resection occurred in 11 patients (19%). Although further follow-up is required, we conclude that low-activity permanent iodine-125 implants provide patients who have newly diagnosed malignant gliomas long-term survival with an acceptable risk of late complications.

Application Accuracy Study of a Semipermanent Fiducial System for Frameless Stereotaxis

The accuracy of a semipermanent fiducial marker system developed at Wayne State University in collaboration with Fisher-Leibinger (Freiburg, Germany) was compared with reference to a standard stereotactic frame (Zamorano-Dujovny Localizing Unit; Fisher-Leibinger). For each patient in our study, 10 semipermanent markers were placed on the skull through a small incision and a pilot hole drilled for the marker; five markers were used for registration, and five were used for comparison. Gadolinium-enhanced magnetic resonance imaging was performed, and, upon registration using both ring and fiducial markers, 184 random points were collected by infrared digitization. All three-dimensional measurements (x, y, z) were converted into distance values correlating each value to the origin by the formula dij = SQRT (xij2 + yij2 + zij2). The mean difference of fiducial coordinates vs. absolute image coordinates was 1.72 +/- 0.42 mm (P = .0001), implying no significant difference. The mean difference in dij of the stereotactic ring coordinates vs. the absolute image coordinates was 3.35 +/- 0.59 mm (P = .00011). The mean difference in the fiducial markers vs. the stereotactic ring coordinates was 2.95 +/- 0.45 mm (P = .0001). All tests were declared significant at alpha = .016. The combination of interactive guidance with semipermanent fiducial markers allows for accurate localization of intracranial targets (as accurate or even more accurate than the stereotactic frame). Semipermanent fiducial markers facilitate the procedure logistically, allow for staged procedures (i.e., at the skull base or in epilepsy), and provide access for combined supra- and infratentorial approaches. We believe that the semipermanent fiducial markers system might represent an important development leading toward widespread use of interactive image guidance in conventional neurosurgery.

Radiosurgery for Cerebral Arteriovenous Malformations

From September 1991 to May 1997, a total of 59 patients diagnosed with cerebral arteriovenous malformations were treated using radiosurgery. There were 29 men and 30 women, with an age range of 5 to 75 years (mean 36). Of these patients, 39 patients were treated using a LINAC-based system (group 1) and 20 using the Leksell γ-knife unit (group 2). Tumor volume ranged from 0.38 to 35 cc, and the number of isocenters varied from 1 to 3 in group 1 and from 2 to 15 in group 2. Lesion location was as follows: 14 temporal, 8 basal ganglionic, 8 frontal, 6 parietal, 6 thalamic, 5 intraventricular, 5 cerebellar, 3 brain stem, 3 occipital, and 1 corpus callosal. Seven patients underwent prior embolization and three patients had prior surgery with incomplete resection of their lesions. The marginal radiation dose ranged between 1500 and 2000 cGy with a mean of 1800 cGy. Twelve patients had concomitant embolization done on the morning of radiosurgery. Follow-up ranged from 1 month to 4 years. Thirty-six patients have been followed for more than 1 year. Thirty had an angiography during the follow-up period that showed complete obliteration of the lesion in 28 patients. The rate of obliteration was estimated to be 47.1% at 1 year, 82.3% at 2 years and 88.2% at 3 years.