John C. Magill

Image stabilization for scanning laser ophthalmoscopy

A scanning laser ophthalmoscope with an integrated retinal tracker (TSLO) was designed, constructed, and tested in human subjects without mydriasis. The TSLO collected infrared images at a wavelength of780 nm while compensating for all transverse eye movements. An active, high-speed, hardware-based tracker was able to lock onto many common features in the fundus, including the optic nerve head, blood vessel junctions, hypopigmentation, and the foveal pit. The TSLO has a system bandwidth of ~1 kHz and robustly tracked rapid and large saccades of approximately 500 deg/sec with an accuracy of 0.05 deg. Image stabilization with retinal tracking greatly improves the clinical potential of the scanning laser ophthalmoscope for imaging where fixation is difficult or impossible and for diagnostic applications that require long duration exposures to collect meaningful information.

Active retinal tracker for clinical optical coherence tomography systems

An active, hardware-based retinal tracker is integrated with a clinical optical coherence tomography (OCT) system to investigate the effects of stabilization on acquisition of high-resolution retinal sections. The prototype retinal tracker locks onto common fundus features, detects transverse eye motion via changes in feature reflectance, and positions the OCT diagnostic beam to fixed coordinates on the retina with mirrors driven by a feedback control loop. The system is tested in a full clinical protocol on subjects with normal and glaucomatous eyes. Experimental analysis software is developed to coalign and coadd multiple fundus and OCT images and to extract quantitative information on the location of structures in the images. Tracking is highly accurate and reproducible on all but one subject, resulting in the ability to scan the same retinal location continually over long periods of time. The results show qualitative improvement in 97% of coadded OCT scans and a reduction in the variance of the position of the optic disc cup edge to less than 1 pixel (< 60 microm). The tracking system can be easily configured for use in research on ultra-high-resolution OCT systems for advanced image modalities. For example, tracking will enable very high density 3-D scans of the retina, which are susceptible to eye motion artifacts even for new high-speed systems.

Compact scanning laser ophthalmoscope with high-speed retinal tracker

The effectiveness of image stabilization with a retinal tracker in a multifunction, compact scanning laser ophthalmoscope (TSLO) was demonstrated in initial human subject tests. The retinal tracking system uses a co confocal reflectometer with a closed-loop optical servo system to lock onto features in the fundus. The system is multifarious and modular to allow configuration for many research a clinical applications. Adult volunteers were tested without mydriasis to optimize the tracking instrumentation and to characterize imaging performance. The retinal tracking system achieves a bandwidth of greater than 1 kHz, which permits tracking at rates that greatly exceed the maximum rate of motion of the human eye. The TSLO system stabilized images to an accuracy of 0.05 deg in all test subjects during ordinary saccades with a velocity up to approximately 500 deg/s. Feature lock was maintained for minutes despite subject eye blinking. Even when nearly 1000 frames were coadded, image blur was minimal. Successful frame coaddition allowed image acquisition with decreased noise in low-light applications. The retinal tracking system significantly enhances the imaging capabilities of the scanning laser ophthalmoscope.

Osteomark: A surgical navigation system for oral and maxillofacial surgery

The purpose of this project was to test a surgical navigation tool designed to help execute a surgical treatment plan. It consists of an electromagnetically tracked pencil that is used to mark bone intraoperatively. The device was tested on a precision block, an ex vivo pig mandible and during performance of six endoscopic vertical ramus osteotomies on pig cadavers. The difference between actual pencil position and that displayed by the computer was measured three times each at ten 2mm holes on the block (n=30 observations) and on the ex vivo mandible (n=11 measurements). Errors between planned and actual osteotomy locations for the cadaver procedures were measured. The mean distance between known and displayed locations was 1.55 ± 0.72 mm on the precision block and 2.10 ± 0.88 mm on the pig mandible. The error measured marking the same point on the block multiple (n=5) times was 0.58 ± 0.37 mm. The mean error on the simulated osteotomies was 2.35 ± 1.35 mm. Osteomark was simple to use and permitted localisation of holes and osteotomies with acceptable accuracy. In the future, the device and algorithms will be revised to further decrease error and the system will be tested on live animals.

Dual OCT-SLO imager with 3D tracker

We have designed, developed, and tested a three-dimensional tracking and imaging system that uses a novel optical layout to acquire both en-face confocal images by scanning laser imaging (e.g. scanning laser ophthalmoscopy, SLO) and high-resolution depth sections by optical coherence tomography (OCT). The present application for this system is retinal imaging. The instrument is capable of sequentially collecting OCT and SLO images with the simple articulation of an optic affixed to a flip-mount. In addition, we have extended our mature transverse tracking system for full three-dimensional motion stabilization. The tracking component employs an innovative optical and electronic design that encodes transverse and depth tracking information on a single beam. We have demonstrated en face SLO imaging with a resolution of ~25 μm and depth-resolved OCT imaging with a resolution of ~10 μm. On artificial targets, transverse tracking was robust up to 1 m/s with a bandwidth of ~1 kHz and depth tracking was robust up to a velocity of ~15 cm/sec, a range of ~1 mm, and a bandwidth of a few hundred Hz. The details of the instrument, including optical and electronic design, are discussed. The system has the potential to provide clinicians and researchers with a wide variety of diagnostic information for the early detection and treatment of retinal diseases.

A novel actuator for simulation of epidural anesthesia and other needle insertion procedures.

Introduction: When navigating a needle from skin to epidural space, a skilled clinician maintains a mental model of the anatomy and uses the various forms of haptic and visual feedback to track the location of the needle tip. Simulating the procedure requires an actuator that can produce the feel of tissue layers even as the needle direction changes from the ideal path. Methods: A new actuator and algorithm architecture simulate forces associated with passing a needle through varying tissue layers. The actuator uses a set of cables to suspend a needle holder. The cables are wound onto spools controlled by brushless motors. An electromagnetic tracker is used to monitor the position of the needle tip. Results: Novice and expert clinicians simulated epidural insertion with the simulator. Preliminary depth-time curves show that the user responds to changes in tissue properties as the needle is advanced. Some discrepancy in clinician response indicates that the feel of the simulator is sensitive to technique, thus perfect tissue property simulation has not been achieved. Conclusions: The new simulator is able to approximately reproduce properties of complex multilayer tissue structures, including fine-scale texture. Methods for improving fidelity of the simulation are identified.

Tracking scanning laser ophthalmoscope (TSLO)

The effectiveness of image stabilization with a retinal tracker in a multi-function, compact scanning laser ophthalmoscope (TSLO) was demonstrated in initial human subject tests. The retinal tracking system uses a confocal reflectometer with a closed loop optical servo system to lock onto features in the fundus. The system is modular to allow configuration for many research and clinical applications, including hyperspectral imaging, multifocal electroretinography (MFERG), perimetry, quantification of macular and photo-pigmentation, imaging of neovascularization and other subretinal structures (drusen, hyper-, and hypo-pigmentation), and endogenous fluorescence imaging. Optical hardware features include dual wavelength imaging and detection, integrated monochromator, higher-order motion control, and a stimulus source. The system software consists of a real-time feedback control algorithm and a user interface. Software enhancements include automatic bias correction, asymmetric feature tracking, image averaging, automatic track re-lock, and acquisition and logging of uncompressed images and video files. Normal adult subjects were tested without mydriasis to optimize the tracking instrumentation and to characterize imaging performance. The retinal tracking system achieves a bandwidth of greater than 1 kHz, which permits tracking at rates that greatly exceed the maximum rate of motion of the human eye. The TSLO stabilized images in all test subjects during ordinary saccades up to 500 °/sec with an inter-frame accuracy better than 0.05 °. Feature lock was maintained for minutes despite subject eye blinking. Successful frame averaging allowed image acquisition with decreased noise in low-light applications. The retinal tracking system significantly enhances the imaging capabilities of the scanning laser ophthalmoscope.

Continuous Mandibular Distraction Osteogenesis: Novel Device and Preliminary Results in Minipigs

PURPOSEnTo develop and test a novel, hydraulic, continuous, automated distraction device capable of 3D movements for treatment of mandibular deformities.nnnMATERIALS AND METHODSnWe used 2 cadaveric and 5 live female Yucatan minipigs to test the distractor. The 3 components (miniature buried distractor, external power and control box, and user interface on handheld computer) operate on a closed loop in which the hydraulic pulse strength correlates with the resistance of the bone and soft tissue. The system auto-adjusts to correct any discrepancy between the actual and desired position of mandibular fragments. The distraction protocol included 0-day latency, 1 mm (divided into 94 increments) per day, and 24 days fixation. Clinical examination was performed and lateral and anteroposterior cephalometric radiographs were obtained preoperatively and postoperatively, at mid distraction osteogenesis (DO), end DO, and end fixation. Position information was obtained through the user interface.nnnRESULTSnBoth cadaveric trials resulted in the desired distraction gap (11 to 12 mm), with all components functioning as designed. In 4 of the 5 live animals, distraction averaged 7.29 mm (range, 5 to 11 mm) over 12 days of activation. In 3 of the 5 live animals, the osteotomy gap filled in with bone by 24 days of fixation. Two animals were sacrificed prematurely (1 at mid DO and 1 at end DO) because vital components malfunctioned.nnnCONCLUSIONSnThe device is capable of automated, continuous, hydraulically powered DO at a rate of 1 mm/d. Future work will be directed at fortifying the device components and testing it in larger numbers of animals at varying distraction rates.

Automated Continuous Distraction Osteogenesis May Allow Faster Distraction Rates: A Preliminary Study

PURPOSEnTo determine if automated continuous distraction osteogenesis (DO) at rates faster than 1xa0mm/day results in bone formation by clinical and radiographic criteria, in a minipig model.nnnMATERIALS AND METHODSnAn automated, continuous, curvilinear distraction device was placed across a mandibular osteotomy in 10 minipigs. After 12 mm of distraction and 24 days of fixation, the animals were sacrificed and bone healing was evaluated. The continuous distraction rates were 1.5 mm/day (nxa0= 5) and 3 mm/day (nxa0= 5). A semiquantitative scale was used to assess the exxa0vivo clinical appearance of the distraction gap (3xa0= osteotomy not visible; 2xa0= <50% visible; 1xa0= >50% visible; 0xa0= 100% visible), stability (3xa0= no mobility; 2 and 1xa0= mobility in 1 plane or 2 planes, respectively; 0xa0= mobility in 3 planes), and radiographic density (4xa0= 100% of gap opaque; 3xa0= >75%; 2xa0= 50% to 75%; 1xa0= <50%; 0xa0= radiolucent). Groups of 4 minipigs distracted discontinuously at 1, 2, and 4 mm/day served as controls.nnnRESULTSnAutomated, continuous DO at 1.5-mm/day and 3-mm/day had similar bone formation compared to discontinuous DO at 1-mm/day. The continuous DO 1.5-mm/day group had significantly higher scores for appearance and radiographic density compared with the discontinuous 4-mm/day group. The continuous DO 3-mm/day group had significantly higher scores for appearance and radiographic density compared with the discontinuous 4-mm/day group and greater stability compared with the discontinuous 2- and 4-mm/day groups.nnnCONCLUSIONSnResults of this preliminary study indicate that continuous DO at rates of 1.5 and 3.0xa0mm/day produces better bone formation compared with discontinuous DO at rates faster than 1 mm/day.

Demonstration of a Wire Suspension for Wind-Tunnel Virtual Flight Testing

This paper describes the development of a wire suspension system for dynamic testing of missiles in a wind tunnel. The system restrains the missile, permits motion in 3 rotational degrees of freedom, and measures forces on the model. The apparatus allows testing of missile control systems in the wind tunnel, reducing the cost and risk of a flight-test program. Hydraulic actuators control cable tension and model position. Bearings provide free roll and pitch, whereas yaw motion is created by the cable actuation system and a repetitive-learning controller. The paper describes the cable arrangement, force balance, bearings, closed-loop hydraulic control, and the repetitive-learning controller. Two sets of tests were conducted with the broad ocean area missile (a sidewinder variant) in the HighVelocity Air Stream facility at the China Lake Naval Weapons Center. The tests, conducted at M 0:4–0:6, demonstrate functionality of the system in a series of missile pitch and yaw maneuvers. The learning controller is shown to learn an s maneuver in the yaw plane.