Curt Salisbury

Reconstruction and exploration of virtual middle-ear models derived from micro-CT datasets

BACKGROUND Middle-ear anatomy is integrally linked to both its normal function and its response to disease processes. Micro-CT imaging provides an opportunity to capture high-resolution anatomical data in a relatively quick and non-destructive manner. However, to optimally extract functionally relevant details, an intuitive means of reconstructing and interacting with these data is needed. MATERIALS AND METHODS A micro-CT scanner was used to obtain high-resolution scans of freshly explanted human temporal bones. An advanced volume renderer was adapted to enable real-time reconstruction, display, and manipulation of these volumetric datasets. A custom-designed user interface provided for semi-automated threshold segmentation. A 6-degrees-of-freedom navigation device was designed and fabricated to enable exploration of the 3D space in a manner intuitive to those comfortable with the use of a surgical microscope. Standard haptic devices were also incorporated to assist in navigation and exploration. RESULTS Our visualization workstation could be adapted to allow for the effective exploration of middle-ear micro-CT datasets. Functionally significant anatomical details could be recognized and objective data could be extracted. CONCLUSIONS We have developed an intuitive, rapid, and effective means of exploring otological micro-CT datasets. This system may provide a foundation for additional work based on middle-ear anatomical data.

Integration of patient-specific paranasal sinus computed tomographic data into a virtual surgical environment.

Background The advent of both high-resolution computed tomographic (CT) imaging and minimally invasive endoscopic techniques has led to revolutionary advances in sinus surgery. However, the rhinologist is left to make the conceptual jump between static cross-sectional images and the anatomy encountered intraoperatively. A three-dimensional (3D) visuo-haptic representation of the patients anatomy may allow for enhanced preoperative planning and rehearsal, with the goal of improving outcomes, decreasing complications, and enhancing technical skills. Methods We developed a novel method of automatically constructing 3D visuo-haptic models of patients’ anatomy from preoperative CT scans for placement in a virtual surgical environment (VSE). State-of-the-art techniques were used to create a high-fidelity representation of salient bone and soft tissue anatomy and to enable manipulation of the virtual patient in a surgically meaningful manner. A modified haptic interface device drives a virtual endoscope that mimics the surgical configuration. Results The creation and manipulation of sinus anatomy from CT data appeared to provide a relevant means of exploring patient-specific anatomy. Unlike more traditional methods of interacting with multiplanar imaging data, our VSE provides the potential for a more intuitive experience that can replicate the views and access expected at surgery. The inclusion of tactile (haptic) feedback provides an additional dimension of realism. Conclusion The incorporation of patient-specific clinical CT data into a virtual surgical environment holds the potential to offer the surgeon a novel means to prepare for rhinologic procedures and offer training to residents. An automated pathway for segmentation, reconstruction, and an intuitive interface for manipulation may enable rehearsal of planned procedures.

Effects of haptic device attributes on vibration detection thresholds

Human vibrotactile detection experiments were used to compare temporal sinusoids displayed on three commercial haptic devices to a high-fidelity linear voice-coil actuator. The three commercial haptic devices we used span the cost spectrum, supposing that cost of a device is correlated with the fidelity of its virtual textures. This turned out not to be the case. The results indicated that none of the three haptic devices we tested were able to render perceptually distortion-free, periodically regular vibrations at detection threshold levels. Further investigation into the electrical and mechanical device properties that limited the performance of these devices revealed that D/A resolution, amplifier non-linearity and stiction were the primary sources of signal corruption.

What you can't feel won't hurt you: Evaluating haptic hardware using a haptic contrast sensitivity function

In this paper, we extend the concept of the contrast sensitivity function - used to evaluate video projectors - to the evaluation of haptic devices. We propose using human observers to determine if vibrations rendered using a given haptic device are accompanied by artifacts detectable to humans. This determination produces a performance measure that carries particular relevance to applications involving texture rendering. For cases in which a device produces detectable artifacts, we have developed a protocol that localizes deficiencies in device design and/or hardware implementation. In this paper, we present results from human vibration detection experiments carried out using three commercial haptic devices and one high performance voice coil motor. We found that all three commercial devices produced perceptible artifacts when rendering vibrations near human detection thresholds. Our protocol allowed us to pinpoint the deficiencies, however, and we were able to show that minor modifications to the haptic hardware were sufficient to make these devices well suited for rendering vibrations, and by extension, the vibratory components of textures. We generalize our findings to provide quantitative design guidelines that ensure the ability of haptic devices to proficiently render the vibratory components of textures.

A high bandwidth low inertia motor for haptic rendering based on clutched eddy current effects

The capacity of a conventional haptic device to render a mechanical impedance that approximates free space requires actuators with exceptionally low rotor inertia. Reducing rotor inertia in a DC motor design invariably means reducing the peak torque output, which in turn compromises the devices ability to render stiff, massive objects. To meet the large dynamic range requirement in haptic device applications without compromise, we present the design of an actuator that produces high torque on a low inertia rotor through the use of the eddy current braking effect. Eddy currents couple the rotor to a spinning, motorized stator through the action of a torque proportional to relative speed. In our design, permanent magnets are fixed to a two-part stator such that magnetic fields with alternating polarity transect a thin, aluminum disk-shaped rotor. By shifting the relative angular position of the two opposing stator parts under motor control, the magnetic fields traversing the rotor can be modulated between near zero and full intensity. Thus the torque output is effectively clutched under computer control. In this paper we analyze the limits to the speed of response of this design and present characterization results obtained using a prototype device.