Comparison of cadaveric and isomorphic virtual haptic simulation in temporal bone training

Background

Virtual surgery may improve learning and provides an opportunity for pre-operative surgical rehearsal. We describe a novel haptic temporal bone simulator specifically developed for multicore processing and improved visual realism. A position locking algorithm for enhanced drill-bone interaction and haptic fidelity is further employed. The simulation construct is evaluated against cadaveric education.

Methods

A voxel-based simulator was designed for multicore architecture employing Marching Cubes and Laplacian smoothing to perform real-time haptic and graphic rendering of virtual bone.

Ten Otolaryngology trainees dissected a cadaveric temporal bone (CTB) followed by a virtual isomorphic haptic model (VM) based on derivative microCT data. Participants rated 1) physical characteristics, 2) specific anatomic constructs, 3) usefulness in skill development and 4) perceived educational value. The survey instrument employed a Likert scale (1-7).

Results

Residents were equivocal about the physical properties of the VM, as cortical (3.2 ± 2.0) and trabecular (2.8 ± 1.6) bone drilling character was appraised as dissimilar to CTB. Overall similarity to cadaveric training was moderate (3.5 ± 1.8). Residents generally felt the VM was beneficial in skill development, rating it highest for translabyrinthine skull-base approaches (5.2 ± 1.3). The VM was considered an effective (5.4 ± 1.5) and accurate (5.7 ± 1.4) training tool which should be integrated into resident education (5.5 ± 1.4). The VM was thought to improve performance (5.3 ± 1.8) and confidence (5.3 ± 1.9) and was highly rated for anatomic learning (6.1 ± 1.9).

Conclusion

Study participants found the VM to be a beneficial and effective platform for learning temporal bone anatomy and surgical techniques. They identify some concern with limited physical realism likely owing to the haptic device interface. This study is the first to compare isomorphic simulation in education. This significantly removes possible confounding features as the haptic simulation was based on derivative imaging.

Gesture-controlled interactive three dimensional anatomy: a novel teaching tool in head and neck surgery

Background

There is a need for innovative anatomic teaching tools. This paper describes a three dimensional (3D) tool employing the Microsoft Kinect™. Using this instrument, 3D temporal bone anatomy can be manipulated with the use of hand gestures, in the absence of mouse or keyboard.

Methods

CT Temporal bone data is imported into an image processing program and segmented. This information is then exported in polygonal mesh format to an in-house designed 3D graphics engine with an integrated Microsoft Kinect™. Motion in the virtual environment is controlled by tracking hand position relative to the user’s left shoulder.

Results

The tool successfully tracked scene depth and user joint locations. This permitted gesture-based control over the entire 3D environment. Stereoscopy was deemed appropriate with significant object projection, while still maintaining the operator’s ability to resolve image details. Specific anatomical structures can be selected from within the larger virtual environment. These structures can be extracted and rotated at the discretion of the user. Voice command employing the Kinect’s™ intrinsic speech library was also implemented, but is easily confounded by environmental noise.

Conclusion

There is a need for the development of virtual anatomy models to complement traditional education. Initial development is time intensive. Nonetheless, our novel gesture-controlled interactive 3D model of the temporal bone represents a promising interactive teaching tool utilizing a novel interface.

Mixed reality temporal bone surgical dissector: mechanical design

Objective

The Development of a Novel Mixed Reality (MR) Simulation.

An evolving training environment emphasizes the importance of simulation. Current haptic temporal bone simulators have difficulty representing realistic contact forces and while 3D printed models convincingly represent vibrational properties of bone, they cannot reproduce soft tissue. This paper introduces a mixed reality model, where the effective elements of both simulations are combined; haptic rendering of soft tissue directly interacts with a printed bone model.

This paper addresses one aspect in a series of challenges, specifically the mechanical merger of a haptic device with an otic drill. This further necessitates gravity cancelation of the work assembly gripper mechanism. In this system, the haptic end-effector is replaced by a high-speed drill and the virtual contact forces need to be repositioned to the drill tip from the mid wand.

Previous publications detail generation of both the requisite printed and haptic simulations.

Method

Custom software was developed to reposition the haptic interaction point to the drill tip. A custom fitting, to hold the otic drill, was developed and its weight was offset using the haptic device. The robustness of the system to disturbances and its stable performance during drilling were tested. The experiments were performed on a mixed reality model consisting of two drillable rapid-prototyped layers separated by a free-space. Within the free-space, a linear virtual force model is applied to simulate drill contact with soft tissue.

Results

Testing illustrated the effectiveness of gravity cancellation. Additionally, the system exhibited excellent performance given random inputs and during the drill’s passage between real and virtual components of the model. No issues with registration at model boundaries were encountered.

Conclusion

These tests provide a proof of concept for the initial stages in the development of a novel mixed-reality temporal bone simulator.

The physical basis of perceived roughness in virtual sinusoidal textures

Using a high-fidelity haptic interface based on magnetic levitation, subjects explored virtual sinusoidal textures with a frictionless probe and reported the subjective magnitude of perceived roughness. A psychophysical function was obtained spanning 33 levels of spatial periods from 0.025 to 6.00 mm. Kinematic and dynamic variables were recorded at 1,000 Hz and used to derive a set of variables to correlate with the psychophysical outcome. These included position, velocity, kinetic energy, instantaneous force (based on acceleration), mean force, and variability of the z-axis force signal from the power spectral density. The analysis implicates power of the force signal as the physical correlate of perceived roughness of sinusoidal textures. The relationship between power and roughness held across the range of spatial periods examined.

A Novel Rapid-Prototyped Temporal Bone Model for Surgical Dissection

Objectives:

Temporal bone surgery requires knowledge of complex 3D anatomical features and significant technical skill. An adjunctive training methodology is needed, as educational experiences are limited while public expectations regarding outcome are understandably high. Models employed in training must accurately duplicate the surgical experience, simulating bone structure and procedural drilling qualities. This study describes a novel rapid-prototyped model made of 3D printed rigid, bone-like material and includes both face and content validation. In contrast to previous iterations, the model represents requisite subcortical density, and air spaces are void of printing material.

Methods:

Model aeration was assessed. Different harden-ing agents/resins were compared to sheep femur in accelerometer-based vibrational properties, penetration depth, and tensile and compressive strength analysis. Two subjective trials provided face validation. Surgeons compared disparate resin agents to sheep femur, while residents compared the model to cadaveric bone. The residents evaluated appearance, mechanical properties, surgical approaches, and educational value.

Results:

The model illustrates comparable aeration to the template images. Hardening resins all compared favorably to sheep bone in mechanical properties and subjective ratings. Face validation found the Rapid Prototyped Model to have realism in appearance, drill character, and surgical approach and significant perceived educational benefit.

Conclusions:

The model performs well in subjective and objective analysis, with representative mechanical properties, and provides a platform for adjunctive training.

Roughness Perception in Virtual Textures

Haptic devices allow the production of virtual textured surfaces for psychophysical experiments. Some studies have shown inconsistencies between virtual and real textures with respect to their psychophysical functions for roughness, leading to speculation that virtual textures differ in some way from real ones. We have determined the psychophysical function for roughness using textures rendered with a high-fidelity magnetic levitation haptic device. A constraint surface algorithm was used to simulate the motion of a spherical probe over trapezoidal gratings and randomly dithered cones. The shape of the psychophysical functions for roughness is consistent between subjects but varies with changes in texture and probe geometry. For dithered cones, inverted "U"-shaped functions were found nearly identical, in maxima and curvature, to those in the literature for real textures with similar geometry.

Diagnostic accuracy of 3D time-of-flight MR angiography compared with digital subtraction angiography for follow-up of coiled intracranial aneurysms: influence of aneurysm size

BACKGROUND AND PURPOSE

3D time-of-flight MR angiography (3D TOF MRA) may be used as noninvasive alternative to digital subtraction angiography (DSA) for the follow-up of patients with intracranial aneurysms treated with Guglielmi detachable coils (GDCs). We aimed to determine the influence of aneurysm size and location on diagnostic accuracy of 3D TOF MRA for follow-up of intracranial aneurysms treated with GDCs.

MATERIALS AND METHODS

Two hundred and one 3D TOF MRAs in 127 consecutive patients with 136 aneurysms were compared with DSA as standard of reference. Sensitivity and specificity of 3D TOF MRA for detection of residual or reperfusion of the aneurysms was calculated with regard to aneurysm size and location.

RESULTS

Overall sensitivity and specificity of MRA was 88.5% and 92.9%, respectively. Sensitivity was lower for aneurysms <or=5 mm (72.2%) and <or=3 mm (63.6%). In addition to the small aneurysm size, interpretation of MR angiograms was compromised by susceptibility artifacts at the air-bone interface, arterial overlap, and pulsation-induced artifacts. The small number of disagreements between MRA and DSA hampered reliable interpretation of the possible influence of aneurysm location on MRA accuracy.

CONCLUSION

The sensitivity of 3D TOF MRA for detection of reperfusion or residual perfusion of coiled intracranial aneurysms varies considerably depending on the size of the aneurysms. No conclusions can be drawn regarding a possible influence of aneurysm location on diagnostic accuracy of 3D TOF MRA. These findings may influence the decision about whether to replace DSA by 3D TOF MRA for the follow-up of patients with intracranial aneurysms treated with GDCs.