GPU accelerated viscous-fluid deformable registration for radiotherapy.

Repeated acquisitions of computed tomography and magnetic resonance imaging are increasingly used during radiotherapy treatment to accurately deliver radiation while limiting side effects. This is only feasible however after all acquisitions have been correlated to a single reference scan using a deformable registration method. This paper presents a parallel implementation of one such method, the viscous-fluid registration method, on modern graphics hardware. A significant speedup close to two orders of magnitudes was observed when comparing to a CPU based implementation. As a consequence of the reduced registration time it is now feasible to perform larger scale clinical evaluation of the method. An example of registration results obtained during a treatment course is included in the paper.

A framework for shape matching in deformable image registration.

Many existing image registration methods have difficulties in accurately describing significant rotation and bending of entities (e.g. organs) between two datasets. A common problem in this case is to ensure that the resulting registration is physically plausible, i.e. that the registration describes the actual bending/rotation occurring rather than just introducing expansion in some areas and shrinkage in others. In this work we developed a general framework for deformable image registration of two 3D datasets that alleviates this problem. To ensure that only physically feasible and plausible solutions to the registration problem are found, a soft tissue deformable model is used to constrain the search space for the desired correspondence map while minimizing a similarity metric between the source and reference datasets. Results from a deformable phantom experiment were used to verify and evaluate the framework.

The visible ear surgery simulator.

This paper presents a real-time computer simulation of surgical procedures in the ear, in which a surgeon drills into the temporal bone to gain access to the middle or inner ear. The purpose of this simulator is to support development of anatomical insight and training of drilling skills for both medical students and experienced otologists. The key contributions in this application are the visualization and interaction models in the context of ear surgical simulation. The visualization is based on an existing data set, "The Visible Ear", containing a unique volume depicting the inner ear in natural colours. The applied visualization is based on GPU ray casting, allowing high quality and flexible volume rendering using modern graphics card. In connection with the visualization model, different methods for optimizing the GPU ray casting procedure are presented, along with a method for combining polygon based graphics with volume rendering. In addition, different light models are presented that contribute to a realistic rendering of the different parts of the inner ear. To achieve a physically plausible drilling experience, a Phantom Omni force feedback device is utilized. The applied interaction model facilitates a realistic user experience of the response forces from the drilling tool.

[Good experiences with interactive temporal bone surgical simulator].

The Visible Ear Simulator (VES) is a freeware temporal bone surgical simulator utilizing a high-fidelity haptic and graphical voxel model compiled from segmented digital images of fresh frozen sections. A haptic device provides the 3-dimensional handling and drilling with force-feedback in real time. In a multilingual user interface the integrated tutor function provides stepwise instructions during drilling through an intuitive, volumetric approach. A censor function draws on metrics derived from the simulator to provide instant and summary feedback for the user. The VES can be downloaded from http://ves.cg.alexandra.dk.

Simple DVH parameter addition as compared to deformable registration for bladder dose accumulation in cervix cancer brachytherapy.

BACKGROUND AND PURPOSE: Variations in organ position, shape, and volume cause uncertainties in dose assessment for brachytherapy (BT) in cervix cancer. The purpose of this study was to evaluate uncertainties associated with bladder dose accumulation based on DVH parameter addition (previously called "the worst case assumption") in fractionated BT. MATERIALS AND METHODS: Forty-seven patients treated for locally advanced cervical cancer were included. All patients received EBRT combined with two individually planned 3D image-guided adaptive BT fractions. D(2cm(3)) and D(0.1cm(3)) were estimated by DVH parameter addition and compared to dose accumulations based on an in-house developed biomechanical deformable image registration (DIR) algorithm. RESULTS: DIR-based DVH analysis was possible in 42/47 patients. DVH parameter addition resulted in mean dose deviations relative to DIR of 0.4±0.3 Gy(αß3) (1.5±1.8%) and 1.9±1.6 Gy(αß3) (5.2±4.2%) for D(2cm(3)) and D(0.1cm(3)), respectively. Dose deviations greater than 5% occurred in 2% and 38% of the patients for D(2cm(3)) and D(0.1cm(3)), respectively. Visual inspection of the dose distributions showed that hotspots were located in the same region of the bladder during both BT fractions for the majority of patients. CONCLUSION: DVH parameter addition provides a good estimate for D(2cm(3)), whereas D(0.1cm(3)) is less robust to this approximation.