Toshihiko Sasama

Surface-based registration accuracy of CT-based image-guided spine surgery

Registration is a critical and important process in maintaining the accuracy of CT-based image-guided surgery. The aim of this study was to evaluate the effects of the area of intraoperative data sampling and number of sampling points on the accuracy of surface-based registration in a CT-based spinal-navigation system, using an optical three-dimensional localizer. A cadaveric dry-bone phantom of the lumbar spine was used. To evaluate registration accuracy, three alumina ceramic balls were attached to the anterior and lateral aspects of the vertebral body. CT images of the phantom were obtained (1-mm slice thickness, at1-mm intervals) using a helical CT scanner. Twenty surface points were digitized from five zones defined on the basis of anatomical classification on the posterior aspects of the target vertebra. A total of 20 sets of sampling data were obtained. Evaluation of registration accuracy accounted for positional and rotational errors. Of the five zones, the area that was the largest and easiest to expose surgically and to digitize surface points was the lamina. The lamina was defined as standard zone. On this zone, the effect of the number of sampling points on the positional and rotational accuracy of registration was evaluated. And the effects of the additional area selected for intraoperative data sampling on the registration accuracy were evaluated. Using 20 surface points on the posterior side of the lamina, positional error was 0.96xa0mm±0.24xa0mm root-mean-square (RMS) and rotational error was 0.91°±0.38°RMS. The use of 20 surface points on the lamina usually allows surgeons to carry out sufficiently accurate registration to conduct computer-aided spine surgery. In the case of severe spondylosis, however, it might be difficult to digitize the surface points from the lamina, due to a hypertrophic facet joint or the deformity of the lamina and noisy sampling data. In such cases, registration accuracy can be improved by combining use of the 20 surface points on the lamina with surface points on other zones, such as on the both sides of the spinous process.

A Novel Laser Guidance System for Alignment of Linear Surgical Tools: Its Principles and Performance Evaluation as a Man-Machine System

A novel laser guidance system that uses dual laser beam shooters for the alignment of linear surgical tools is presented. In the proposed system, the intersection of two laser planes generated by dual laser shooters placed at two fixed locations defines the straight insertion path of a surgical tool. The guidance information is directly projected onto the patient and the surgical tool. Our assumption is that a linear surgical tool has cylindrical shape or that a cylindrical sleeve is attached to the tool so that the sleeve and tool axes are aligned. The guidance procedure is formulated mainly using the property that the two laser planes are projected as two parallel straight lines onto the cylindrical tool surface if and only if the cylinder axis direction is the same as the direction of the intersection of the two laser planes. Unlike conventional augmented reality systems, the proposed system does not require the wearing of glasses or mirrors to be placed between the surgeon and patient. In our experiments, a surgeon used the system to align wires according to the alignment procedure, and the overall accuracy and alignment time were evaluated. The evaluations were considered not to be simply of a mechanical system but of a man-machine system, since the performance depends on both the system accuracy and the surgeons perceptual ability. The evaluations showed the system to be highly effective in providing linear alignment assistance.

Optical High-Precision Three-Dimensional Position Measurement System Suitable for Head Motion Tracking in Frameless Stereotactic Radiosurgery

Head motion is a significant source of therapy-effect degradation in frameless stereotactic radiosurgery (SRS). In this study, a three-dimensional (3-D) optical head motion measurement system and a coordinate transformation algorithm were used to track patient head motion. With this system, head motion in frameless SRS was carefully investigated with a precision of < 0.1 mm. Head motions without any restraint (three cases) and with a Laitinen adapter (four cases) were measured with a data sampling rate of once per second for 30 min. Positions of IR light emission diode markers attached to the head were analyzed by two statistical methods. From these data, mathematically simulated head motions were obtained in each of the three coordinate directions for nonrestraint and Laitinen-adapter SRS. The results show that segmenting a frameless SRS procedure into a sequence of short intervals and repeating registration of the target position for each interval is a good strategy for better therapy precision. This optical 3-D position measurement system is suitable for high-precision head motion tracking in frameless SRS.

Magneto-Optic Hybrid 3-D Sensor for Surgical Navigation

The objective of the work described in this paper was to develop an accurate three dimensional (3-D) sensory system without a line-of-sight requirement for surgical navigation inside the body. Although magnetic sensors seem to be particularly suitable for this purpose, their accuracy is affected by metallic objects, which can hardly be avoided in a surgical environment. We propose a new magneto-optic hybrid 3-D sensor configuration that overcomes this limitation. Unlike previous hybrid systems, both the receiver and transmitter of the magnetic sensor are mobile, thereby permitting them to be positioned flexibly and adaptively so as to minimize inaccuracies arising from the presence of peripheral metallic objects. The 3-D position and orientation of the transmitter are measured by an optical sensor in order to accurately track the transformation between the coordinate systems of the magnetic and optical sensors. The effects of the distance between the receiver and the transmitter and their respective distances from metallic objects on the accuracy of the system were evaluated by experiments both in the laboratory and in the operating room.

Intraoperative Simulation and Planning Using a Combined Acetabular and Femoral (CAF) Navigation System for Total Hip Replacement

This paper describes intraoperative simulations for the limb length and the range of motion (ROM) adjustment in total hip relacement (THR) surgery, and their utility in intraoperative planning. After implantation of the cup and stem, final adjustments can be made to the limb length and ROM by selecting the optimal combination of femoral neck and head components from the range available in a changeable modular system. The aim of this work is to provide intraoperative assistance to the surgeon in selecting the optimal component combination as well as in planning additional osteotomy to remove unwanted bone impingements and widen the safe ROM. Using the positions and orientations of the cup and stem intraoperatively measured by a combined acetabular and femur (CAF) navigation system, limb length and ROM simulations are carried out for neck and head components of various lengths and angles. These simulations provide information on limb length, the ROM, and where in a 3D model impingements will occur for each combination of components. The accuracy of the simulations was evaluated by comparison with postoperative CT data for the limb length and actually measured motions for the ROM.

Automated CT-based 3D surgical planning for total hip replacement: a pilot study

Abstract At the preoperative planning stage of CT-based computer-assisted total hip replacement, a surgeon determines the parameters such as size, position, and orientations of the implants based on interactive visualization of 3D models of the implants and hip joint bone. However, the parameters depend on surgeons visual assessment of spatial relationship between the hip joint bone and implants. Our objective is to investigate objective criteria for determination of the optimal parameters and formulate an automated determination procedure based on the criteria. We objectified expertise in the preoperative planning of an experienced surgeon into quantitative evaluations and geometrical constraints, then formulated the automated procedure as an optimization problem. The automated planning system was applied to three cases of patient data sets and compared with an experienced surgeon. In the preliminary results, the planning parameters determined by the system were generally acceptable as a pilot experiment.

Clinical applications of a laser guidance system with dual laser beam rays as augmented reality of surgical navigation

We have developed a novel laser guidance system that uses 2 or more laser beam emitters. Two or more fan-shaped beam tracts intersect in a line that can be controlled in any direction by changing the angle and direction of beam oscillation. The laser guidance system draws cross hairs on a target, and the intersection of the cross hairs is the entry point for a drill or wire. After stabilization of this entry point, the system draws 2 or more lines along the guide sleeve. We have used this laser guidance system in 10 total hip arthroplasty (THA) procedures and 1 open-wedge-type high tibial osteotomy (HTO) procedure. In our clinical experience, this laser guidance system has worked well in the operating room. It effectively draws laser cross hairs on the patient to indicate the entry point of straight surgical tools. The direction of the tools was indicated by parallel laser beams projected onto the guide sleeves. The system assisted surgeons with acetabular cup placement and femoral reaming and rasping in THA. It was also useful for screw insertion and drilling of the osteotomy plane in HTO.

Effects of CT threshold value to make a surface bone model on accuracy of shape-based registration in a CT-based navigation system for hip surgery

Abstract To clarify the effects of different CT threshold values used to make computer models on the accuracy of surface registration in a CT-based navigation system, a simulation study was performed using CT data of 30 patients who underwent total hip arthroplasty with navigation guidance. Surface models of the pelvis for use in clinical applications were made by contouring the periosteal boundary at threshold ranging from 140 to 260 Hounsfield units (HU) (mean, 200 HU). In each case, the threshold was determined to be approximately 200 HU, based on the balance between soft tissue noise and surface defects. Ten pelvic surface models were made from each set of CT data, using 10 different CT threshold values ranging from 50 to 320 HU with an increment of 30 HU. The center of the acetabulum was defined as the target point in each set of CT data, so that each set of 10 surface models should have the same reference point for measuring the positional and rotational differences among the models after registration. The average residue of registration reached its nadir was minimum with the 200 HU models, and there were no significant differences in residue of registration among the models made at thresholds ranging from 110 to 320 HU. The target registration errors for position and rotation both showed strong correlation with the residue of registration (R=0.879 and 0.880, respectively). We thus conclude that accurate surface registration can be obtained with computer models made at thresholds ranging from 110 to 320 HU by assessing the balance between soft tissue noise and bone surface defects.

Surgical Tool Alignment Guidance by Drawing Two Cross-Sectional Laser-Beam Planes

Conventional surgical navigation requires for surgeons to move their sight and conscious off the surgical field when checking surgical tools positions shown on the display panel. Since that takes high risks of surgical exposure possibilities to the patients body, we propose a novel method for guiding surgical tool position and orientation directly in the surgical field by a laser beam. In our navigation procedure, two cross-sectional planar laser beams are emitted from the two laser devices attached onto both sides of an optical localizer, and show surgical tools entry position on the patients body surface and its orientation on the side face of the surgical tool. In the experiments, our method gave the surgeons precise and accurate surgical tool adjusting and showed the feasibility to apply to both of open and percutaneous surgeries.

Measurement of Pelvic Tilting Angle During Total Hip Arthroplasty Using A Computer Navigation System

The purpose of this study was to measure pelvic orientation during total hip arthroplasty (THA) in a lateral decubitus position using a computer navigation system with an optical localizer (OPTOTRAK). THA was performed in 17 hips. Much attention was paid to set the patients in neutral axial rotation with the anatomical plane of the pelvis perpendicular to the operating table. After shape-based registration, pelvic orientation was tracked with light emitting diode markers fixed to the pelvis. Measurements were based on the anatomical plane. Mean movement of the pelvis from the supine position to the dislocated lateral decubitus position was 8 degrees posterior (26 posterior to 6 anterior), 3 degrees abducted (6 adduction to 20 abduction), and 4 degrees internally rotated (24 internal to 5 external). This study showed that the pelvis was not always placed in neutral axial rotation, despite the surgical plan. It was further tilted posteriorly and rotated internally when the socket was inserted. This tilt can lead to decreased socket anteversion with conventional alignment guide systems, while unknown pelvic orientation in general can cause socket malposition with such systems. Therefore, intraoperative three-dimensional measurements of pelvic orientation seems to be useful to avoid socket malposition.