Implementation of a stereotactic microscope using an optically coupled tracking system

Image-to-patient registration techniques in head surgery

Frame-based stereotaxy was developed in neurosurgery at the beginning of the last century, evolving from atlas-based stereotaxy to stereotaxy based on the individual patient's image data. This established method is still in use in neurosurgery and radiotherapy. There have since been two main developments based on this concept: frameless stereotaxy and markerless registration. Frameless stereotactic systems ('navigation systems') replaced the cumbersome stereotactic frame by mechanically and later also optically or magnetically tracked instruments. Stereotaxy based on the individual patient's image data introduced the problem of patient-to-image data registration. The development of navigation systems based on frameless stereotaxy has dramatically increased its use in surgical disciplines other than neurosurgery, but image-guided surgery based on fiducial marker registration needs dedicated imaging for registration purposes, in addition to the diagnostic imaging that might have been performed. Markerless registration techniques can overcome the resulting additional cost and effort, and result in more widespread use of image-guided surgery techniques. In this review paper, the developments that led to today's navigation systems are outlined, and the applications and possibilities of these methods in the field of maxillofacial surgery are presented.

Image-guided craniotomy for cerebral metastases: techniques and outcomes

OBJECTIVE

The purpose of the present study was to analyze the outcomes after craniotomies for brain metastases in a modern series using image-guided technologies either in the regular operating room or in the intraoperative magnetic resonance imaging unit.

METHODS

Neurosurgical outcomes were analyzed for 49 patients who underwent 55 image-guided craniotomies for excision of brain metastases during a 5-year period. Tumors were located in critical and noncritical function regions of the brain. A total of 23 craniotomies for tumors in critical brain were performed using intravenous sedation anesthesia; craniotomies for noncritical function brain regions were completed under general anesthesia. The patients were also divided into Radiation Therapy Oncology Group recursive partitioning analysis (RPA) classes on the basis of age, Karnofsky Performance Scale scores, state of primary disease, and presence or absence of extracranial metastases.

RESULTS

There was no perioperative mortality. Gross total resection, as verified by postoperative contrast-enhanced computed tomography or magnetic resonance imaging, was achieved in 96% of patients. The median anesthesia time was 4.25 hours, and the median length of hospital stay was 3 days. In 51 symptomatic cases, there was complete resolution of symptoms in 70% (n = 36), improvement in 14% (n = 7), and no change in 12% (n = 6) postoperatively. No patient who was neurologically intact preoperatively deteriorated after surgery, and 93% of patients maintained or improved their functional status. Only two patients (3.6%) with significant preoperative deficits had increased long-term deficits postoperatively. The mean follow-up was 1 year, and the local recurrence rate was 16%. The median survival of the entire group was 16.23 months (17.5 mo in RPA Class I, 22.9 mo in RPA Class II, and 9.8 mo in RPA Class III).

CONCLUSION

Gross total resection of brain metastases, including those involving critical function areas, can be safely achieved with a low morbidity rate using contemporary image-guided systems. RPA Class I and II patients with controlled primary disease benefit from aggressive treatment by surgery and radiation.

Visualization, tracking, and navigation of instruments for magnetic resonance imaging-guided endovascular procedures

Interventional procedures using magnetic resonance imaging (MRI) guidance have increased in interest during the last few years. Central to the success and safety of MRI-guided procedures is the accurate visualization of the interventional instruments relative to the surrounding anatomy. A variety of methodologies for visualizing and automatically tracking instruments, including needles, radiofrequency and laser ablation devices, endoscopes, catheters, and guidewires have been developed and introduced to help the interventionalist to safely guide the device toward the target region. This article describes and compares characteristics of the four most commonly used localization and tracking systems used for MRI-guided interventional procedures: those based on the susceptibility artifact of the device, those that intentionally create field inhomogeneity along the device, those that rely on an optical tracking system, and active tracking systems using micro receive coils.

Incorporation of ultrasonic imaging in an optically coupled frameless stereotactic system

Frameless stereotactic interactive tracking systems relate a point in the surgical field to a corresponding point on the patients MR or CT scans in multiple planes. A basic weakness with these systems is that they cannot compensate for movement of target points due to brain shift caused by CSF drainage or lesion removal. Real time images can be obtained using ultrasonic techniques but the poor quality and definition and the ill-defined scan plane make interpretation difficult and reduce the usefulness of this modality. The authors have combined these two modalities by mounting light emitting diodes (LEDs) on the ultrasonic probe, thus allowing a "virtual tip" to be developed in the centre of the ultrasonic beam, and tracked via an optically coupled frameless stereotactic system (Radionics, OTS). This has allowed a direct correlation between pre-operative MR and the per-operative ultrasonic images using reformatted MR images. Ultrasound images are obtained through a separate skull opening and the image plane is determined by the position of the virtual tip. The ultrasonic and MR images are presented side by side for visual comparison. Minimally invasive tumour resection or haematoma removal could be carried out under ultrasonic guidance with direct interactive relation to the preoperative MR scans. Alternatively interactive image directed surgical procedures can be up-dated in real time by dynamic ultrasonic images taken in clearly defined scan planes.