Qinghang Li

Tracking Methods for Medical Augmented Reality

Recently, the capabilities of real-time PC-based video image processing and computer graphic systems converged to make possible the display of a virtual graphical image correctly registered with a view of the 3D environment of the user’s object of interest. The generation of an Augment Reality scene can now be done with a PC computer graphics system. An Augmented Reality (AR) system generates a composite view for the user. It is a combination of the real scene viewed by the user and a virtual scene generated by the computer (a 3D model) that augments the scene with additional information. Fig. 1 displays one possible AR scene where a phantom is overlaid with graphics models of tumors. One of the most important issues to consider for a very accurate AR application is the method for tracking the various elements of the environment such as the video camera.

The Application Accuracy of the Frameless Implantable Marker System and Analysis of Related Affecting Factors

The purpose of this study was to determine the application accuracy of a new frameless marker system for interactive intraoperative localization of intracranial lesions. The influence of image quality, registration error, repeatability, and marker distribution on the application accuracy were analyzed and compared. A phantom was mounted with the standard Z-D ring and also implanted with frameless marker system, which randomly distributed on the surface. The phantom was scanned as routine with 1 mm and 2 mm sections. The pixel sizes were used 1.18×1.18 and 0.59×0.59. The two systems were tested under different image quality and registration. The target point was digitized and the coordinates were recorded and compared with reference points. The difference between two systems were tested with paired t-test. Image data were loaded into a SUN Workstation and registered with NSPS.4.0 software. The coordinate of each fiducial marker was recorded into a file as the reference. The tip of each semi-invasive fiducial marker was digitized to achieve a frameless transformation matrix, and the special points on the Z-D ring were digitized to achieve a frame-based transformation matrix. The differences from the reference points were used as the deviation from “true point”. The mean square root (RMS) was calculated to show the sum of vectors. The results of 2 mm section group showed that the registration error of frame-based system is 3.42±0.22 mm and the error of the frameless system is 1.01±0.63 mm (P<0.001). The RMS are 2.57±0.54 mm and 1.53±0.65 mm respectively (P<0.001). The RMS of error registration (one point off 5 mm) are 5.01±0.26 mm and 2.23±0.13 mm respective (P=0.003). The results of 1mm section group showed that the RMS are 1.20±0.42 mm and 0.90±0.47 mm respectively (P=0.121). The higher the quality (the thinner scan thickness) of image it is, the better the application accuracy will be (P=0.001 and 0.032 respectively). These preliminary results showed that the frameless semi-invasive fiducial marker system can provide clinical acceptable accurate localization as the frame based surgical localization system did. There is no significant difference between the experimental and clinical results. The higher the quality of image it is, the better the application accuracy will be. But there is no significant difference between 1mm sections and 3 mm sections of MRI images.

Permanent Iodine-125 Interstitial Radiation Therapy in the Treatment of Non-Glioblastoma multiforme High-Grade Gliomas

Background: This study evaluates prognostic factors influencing survival outcomes for 60 patients with permanent iodine-125 implants in the primary treatment of non-glioblastoma multiforme (GBM) high-grade gliomas. Methods: Stereotactic treatment planning aimed to encompass the contrast-enhancing rim of the tumor visualized by CT, with an initial dose rate of 0.05 Gy/h with 125I, delivering 100 Gy at 1 year and 103.68 Gy at infinity. Survival was evaluated using the Kaplan-Meier method for univariate analysis and the Cox regressional method for multivariate analysis. In addition to the implant, 34 patients received external radiation therapy (5,000–6,000 cGy) before the implant; 13 patients were implanted without additional external beam radiation, and 13 patients underwent external radiation therapy before implant placement. Results: With a mean follow-up of 77.6 months (range 3.5–164 months), 1-, 3-, 5- and 10-year survival were 86.7% (±0.05%), 60% (±0.07%), 50% (±0.07%) and 45.7% (±0.7%), respectively. The median survival time was 57 months. Second surgery was performed following the implant in 19 patients. Findings were tumor recurrence in 11 patients (22.5%), radiation necrosis in 7 patients (14.3%) and brain abscess in 1 patient (2%). Age, sex, tumor location, side of brain, tumor volume, Karnofsky score and neurological status were correlated with survival outcome. Favorable prognostic factors were age younger than 45 years, superficial tumor location and preoperative Karnofsky score greater than 70. RPA classification was used to define this group of patients. In RPA classes I and II (n = 43), 1-year survival was 93%, while 3-, 5- and 10-year survival was 67.4, 60.5 and 55.5%, respectively, and median survival time was 91 months. In RPA class III (n = 7), 1-year survival was 71.4%, while 3- and 5-year survival was 42.9 and 28.6%, respectively, and median survival time was 47 months. In RPA class IV (n = 10), 1-year survival was 60%, while 3-, 5- and 10-year survival was 50, 22.2 and 11.1%, respectively, and median survival time was 37 months. Conclusion: Brachytherapy with permanent implant of 125I appears promising in the treatment of primary non-GBM malignant gliomas. It improved survival time and reduced the incidence of complications and provided good quality of life. In order to further confirm these results, multicenter randomized prospective studies are needed. RPA analysis is a valid tool to define prognostically distinct survival groups. In this study, 2-year survival and median survival time were improved in all prognostic classes. This would suggest that selection bias alone does not account for the survival benefit seen with 125I implants. Further randomized studies with effective stratification are needed.

Computer-Assisted Insertion of Pedicle Screws

The possible complications of a pedicle screw fixation system include injury to neurologic and vascular structures resulting from inaccurate placement of the instrumentation. In a review of 617 surgical cases in which pedicle screw implants were used, Esses and co-authors reported a overall complication rate of 27.4%. The most common intraoperative problem was unrecognized screw misplacement (5.2%). Fracturing the pedicle during screw insertion and iatrogenic cerebrospinal fluid leak occurred in 4.2% of cases. Such a complication rate is not acceptable in clinical practice. In this paper, we discuss a computer-assisted spine surgery system designed for real-time intraoperative localization of surgical instruments on precaptured images used during surgery. Localization was achieved by combining image-guided stereotaxis with advanced opto-electronic position sensing techniques. The insertion of pedicle screws can be directly monitored by interactive navigation using specially equipped surgical tools. Our preliminary results showed no misplacement of pedicle screw, which have further confirmed the clinical potential of this system.

Influence of different medical images on the application accuracy during image-guided surgery

Application accuracy is a crucial factor for stereotactic surgical localization systems. The different qualities of medical images can produce different influences on the application accuracy. However there are a lot of factors that can have an effect on the application accuracy. In this study, we compared the influences of different section thickness of MRI and CT images on the application accuracy during image-guided surgery. An implantable frameless marker system was used. CT scans were taken using 2 kinds of thickness, 1 and 2 mm, and with 2 resolution 256 X 256, 512 X 512. T1 weighted MRI images were used with 3 kinds of thickness, 1 and 3 and 10mm. The IR tracking systems and the Neurosurgery Planning System software were used to do image registration and intraoperative digitization. The differences among the mechanical measurements, image digitization from the computer and the measurement through the tracking systems were compared. The mechanical measurement was used as the most accurate measurement. A statistical study was used to analyze the results. In the CT group, there was a significant difference between 1mm and 2mm sections. There was also a difference found between the 256 X 256 and 512 X 512 image quality groups. In the MRI group, there was a significant difference between 10mm and 1mm or 3mm sections, but no difference between 1mm and 3mm sections. When compares CT and MRI with 1mm thickness, there was no significant difference. For the evaluation of the application accuracy during image-guided surgery, the quality of the medical image is an important factor to be dealt with. The thickness of section is usually used factor to analyze the influence. It is commonly accepted that the thinner the thickness, the better the application accuracy. However there is a limitation. Our results showed that for CT images the thickness when reduced from 2mm to 1mm can still significantly improve the application accuracy. But in MRI image when the thickness were reduced from 3mm to 1mm, the application accuracy remained the same. These results may reflect the difference of machines producing these medical images. The quality of medical images do have influences on the application accuracy during image guided surgery.

Information control for image-guided surgery: method and implementation

Computer-assisted surgery technology relies heavily on multi-modality medical image and multimedia information. To systematically manage this information is a challenging task due to fast information growth and geographical expansion of the computer-assisted surgery (CAS) field. After many years developing image-guided surgery techniques, types and media of information are rapidly growing. CAS can grow from a traditional single suite containing only one operating room with a workstation, to a distributed CAS center that can include multiple operating rooms and a control room in order to distribute CAS service throughout a large medical center or an entire metropolitan area. This expansion increases the sophistication of information management or CAS significantly. This paper first identifies different types of multi-modality information and multimedia information involved in the CAS field, and then presents strategies and methods of managing this information. We discuss our CAS system developed at Wayne State University. Detroit Medical Center as a typical example.