57 research outputs found
Robust GPU-based Virtual Reality Simulation of Radio Frequency Ablations for Various Needle Geometries and Locations
Purpose: Radio-frequency ablations play an important role in the therapy of
malignant liver lesions. The navigation of a needle to the lesion poses a
challenge for both the trainees and intervening physicians. Methods: This
publication presents a new GPU-based, accurate method for the simulation of
radio-frequency ablations for lesions at the needle tip in general and for an
existing visuo-haptic 4D VR simulator. The method is implemented real-time
capable with Nvidia CUDA. Results: It performs better than a literature method
concerning the theoretical characteristic of monotonic convergence of the
bioheat PDE and a in vitro gold standard with significant improvements (p <
0.05) in terms of Pearson correlations. It shows no failure modes or
theoretically inconsistent individual simulation results after the initial
phase of 10 seconds. On the Nvidia 1080 Ti GPU it achieves a very high frame
rendering performance of >480 Hz. Conclusion: Our method provides a more robust
and safer real-time ablation planning and intraoperative guidance technique,
especially avoiding the over-estimation of the ablated tissue death zone, which
is risky for the patient in terms of tumor recurrence. Future in vitro
measurements and optimization shall further improve the conservative estimate.Comment: 18 pages, 14 figures, 1 table, 2 algorithms, 2 movie
An Analysis by Synthesis Approach for Automatic Vertebral Shape Identification in Clinical QCT
Quantitative computed tomography (QCT) is a widely used tool for osteoporosis
diagnosis and monitoring. The assessment of cortical markers like cortical bone
mineral density (BMD) and thickness is a demanding task, mainly because of the
limited spatial resolution of QCT. We propose a direct model based method to
automatically identify the surface through the center of the cortex of human
vertebra. We develop a statistical bone model and analyze its probability
distribution after the imaging process. Using an as-rigid-as-possible
deformation we find the cortical surface that maximizes the likelihood of our
model given the input volume. Using the European Spine Phantom (ESP) and a high
resolution \mu CT scan of a cadaveric vertebra, we show that the proposed
method is able to accurately identify the real center of cortex ex-vivo. To
demonstrate the in-vivo applicability of our method we use manually obtained
surfaces for comparison.Comment: Presented on German Conference on Pattern Recognition (GCPR) 2018 in
Stuttgar
Exploring the effects of replicating shape, weight and recoil effects on VR shooting controllers
Commercial Virtual Reality (VR) controllers with realistic force feedback are becoming available, to increase the realism and immersion of first-person shooting (FPS) games in VR. These controllers attempt to mimic not only the shape and weight of real guns but also their recoil effects (linear force feedback parallel to the barrel, when the gun is shot). As these controllers become more popular and affordable, this paper investigates the actual effects that these properties (shape, weight, and especially directional force feedback) have on performance for general VR users (e.g. users with no marksmanship experience), drawing conclusions for both consumers and device manufacturers. We created a prototype replicating the properties exploited by commercial VR controllers (i.e. shape, weight and adjustable force feedback) and used it to assess the effect of these parameters in user performance, across a series of user studies. We first analysed the benefits on user performance of adding weight and shape vs a conventional controller (e.g. Vive controller). We then explore the implications of adding linear force feedback (LFF), as well as replicating the shape and weight. Our studies show negligible effects on the immediate shooting performance with some improvements in subjective appreciation, which are already present with low levels of LFF. While higher levels of LFF do not increase subjective appreciations any further, they lead users to reach their maximum distance skillset more quickly. This indicates that while adding low levels of LFF can be enough to influence user’s immersion/engagement for gaming contexts, controllers with higher levels of LFF might be better suited for training environments and/or when dealing with particularly demanding aiming tasks
Advanced CT bone imaging in osteoporosis
Non-invasive and/or non-destructive techniques can provide structural information about bone, beyond simple bone densitometry. While the latter provides important information about osteoporotic fracture risk, many studies indicate that BMD only partly explains bone strength. Quantitative assessment of macro- and microstructural features may improve our ability to estimate bone strength. Methods for quantitatively assessing macrostructure include (besides conventional radiographs) DXA and CT, particularly volumetric quantitative CT (vQCT). Methods for assessing microstructure of trabecular bone non-invasively and/or non-destructively include high-resolution CT (hrCT), microCT (μCT), high-resolution magnetic resonance (hrMR) and microMR (μMR). vQCT, hrCT and hrMR are generally applicable in vivo; μCT and μMR are principally applicable in vitro. Despite recent progress made with these advanced imaging techniques, certain issues remain. The important balances between spatial resolution and sampling size, or between signal-to-noise and radiation dose or acquisition time, need further consideration, as do the complexity and expense of the methods vs their availability and accessibility. Clinically, the challenges for bone imaging include balancing the advantages of simple bone densitometry vs the more complex architectural features of bone or the deeper research requirements vs the broader clinical needs. The biological differences between the peripheral appendicular skeleton and the central axial skeleton must be further addressed. Finally, the relative merits of these sophisticated imaging techniques must be weighed with respect to their applications as diagnostic procedures, requiring high accuracy or reliability, compared with their monitoring applications, requiring high precision or reproducibility
Finite element analyses of human vertebral bodies embedded in polymethylmethalcrylate or loaded via the hyperelastic intervertebral disc models provide equivalent predictions of experimental strength
3D Bounding Box Detection in Volumetric Medical Image Data: A Systematic Literature Review
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