Details about (most of) the methods used and implemented in gVirtualXRay can be found in our paper published in Computerized Medical Imaging and Graphics in 2016 and our paper presented at the Theory and Practice of Computer Graphics conference in 2009. Other publications demonstrate the use of the earlier implementation of the X-ray simulation code in real-time medical training simulators.

Scientific Journals (peer reviewed articles)

[1] Vidal2016CMIG illustration F. P. Vidal, and P.-F. Villard. Development and validation of real-time simulation of X-ray imaging with respiratory motion. Computerized Medical Imaging and Graphics, 49:1-15, April 2016.  BibTeX  DOI  PMID  .pdf 

We present a framework that combines evolutionary optimisation, soft tissue modelling and ray tracing on GPU to simultaneously compute the respiratory motion and X-ray imaging in real-time. Our aim is to provide validated building blocks with high fidelity to closely match both the human physiology and the physics of X-rays. A CPU-based set of algorithms is presented to model organ behaviours during respiration. Soft tissue deformation is computed with an extension of the Chain Mail method. Rigid elements move according to kinematic laws. A GPU-based surface rendering method is proposed to compute the X-ray image using the Beer-Lambert law. It is provided as an open-source library. A quantitative validation study is provided to objectively assess the accuracy of both components: (i) the respiration against anatomical data, and (ii) the X-ray against the Beer-Lambert law and the results of Monte Carlo simulations. Our implementation can be used in various applications, such as interactive medical virtual environment to train percutaneous transhepatic cholangiography in interventional radiology, 2D/3D registration, computation of digitally reconstructed radiograph, simulation of 4D sinograms to test tomography reconstruction tools.

Keywords: Deterministic simulation (ray-tracing); Digitally reconstructed radiograph; Imaging guidance; Interventional radiology training; Medical virtual environment; Respiration simulation; X-ray simulation

[1] Villard2009IntJComputAssistRadiolSurg illustration P.-F. Villard, F. P. Vidal, C. Hunt, F. Bello, N. W. John, S. Johnson, and D. A. Gould. Simulation of percutaneous transhepatic cholangiography training simulator with real-time breathing motion. International Journal of Computer Assisted Radiology and Surgery, 4(9):571-578, November 2009.  BibTeX  DOI  PMID  .pdf 

Purpose: We present here a simulator for interventional radiology focusing on percutaneous transhepatic cholangiography (PTC). This procedure consists of inserting a needle into the biliary tree using fluoroscopy for guidance. Methods: The requirements of the simulator have been driven by a task analysis. The three main components have been identified: the respiration, the real-time X-ray display (fluoroscopy) and the haptic rendering (sense of touch). The framework for modelling the respiratory motion is based on kinematics laws and on the Chainmail algorithm. The fluoroscopic simulation is performed on the graphic card and makes use of the Beer-Lambert law to compute the X-ray attenuation. Finally, the haptic rendering is integrated to the virtual environment and takes into account the soft-tissue reaction force feedback and maintenance of the initial direction of the needle during the insertion. Results: Five training scenarios have been created using patient-specific data. Each of these provides the user with variable breathing behaviour, fluoroscopic display tuneable to any device parameters and needle force feedback. Conclusions A detailed task analysis has been used to design and build the PTC simulator described in this paper. The simulator includes real-time respiratory motion with two independent parameters (rib kinematics and diaphragm action), on-line fluoroscopy implemented on the Graphics Processing Unit and haptic feedback to feel the soft-tissue behaviour of the organs during the needle insertion.

Keywords: Interventional radiology; Virtual environments; Respiration simulation; X-ray simulation; Needle puncture; Haptics; Task analysis

International Conferences (peer reviewed articles)

[1] Vidal2015VCBM-PosterXRay illustration F. P. Vidal, and P.-F. Villard. Simulated Motion Artefact in Computed Tomography. In Eurographics Workshop on Visual Computing for Biology and Medicine, Chester, United Kingdom, September 2015. Eurographics Association.  BibTeX  DOI  .pdf 

We propose a simulation framework to simulate the computed tomography acquisition process. It includes five components: anatomic data, respiration modelling, automatic parametrisation, X-ray simulation, and tomography reconstruction. It is used to generate motion artefacts in reconstructed CT volumes. Our framework can be used to evaluate CT reconstruction algorithm with motion artefact correction in a controlled environment.

[1] Vidal2010EGPoster illustration F. P. Vidal, M. Garnier, N. Freud, J. M. Létang, and N. W. John. Accelerated deterministic simulation of x-ray attenuation using graphics hardware. In Eurographics 2010 - Poster, page Poster 5011, Norrköping, Sweden, May 2010. Eurographics Association.  BibTeX  .pdf 

In this paper, we propose a deterministic simulation of X-ray transmission imaging on graphics hardware. Only the directly transmitted photons are simulated, using the Beer-Lambert law. Our previous attempt to simulate Xray attenuation from polygon meshes utilising the GPU showed significant increase of performance, with respect to a validated software implementation, without loss of accuracy. However, the simulations were restricted to monochromatic X-rays and finite point sources. We present here an extension to our method to perform physically more realistic simulations by taking into account polychromatic X-rays and focal spots causing blur.

Keywords: Three-Dimensional Graphics and Realism; Raytracing; Physical Sciences and Engineering; Physics

[2] Bello2009EGMedPrize illustration F. Bello, A. Bulpitt, D. A. Gould, R. Holbrey, C. Hunt, N. W. John, S. Johnson, R. Phillips, A. Sinha, F. P. Vidal, P.-F. Villard, and H. Woolnough. ImaGiNe-S: Imaging guided needle simulation. In Eurographics 2009 - Medical Prize, pages 5-8, Munich, Germany, March 2009. Eurographics Association. Second prize and winner of €300.  BibTeX   PDF 

We present an integrated system for training visceral needle puncture procedures. Our aim is to provide a cost effective and validated training tool that uses actual patient data to enable interventional radiology trainees to learn how to carry out image-guided needle puncture. The input data required is a computed tomography scan of the patient that is used to create the patient specific models. Force measurements have been made on real tissue and the resulting data is incorporated into the simulator. Respiration and soft tissue deformations are also carried out to further improve the fidelity of the simulator.

Keywords: Physically based modelling, Virtual reality

International Conferences (abstracts)

[1] Vidal2010MedPhys-B illustration F. P. Vidal, P. F. Villard, M. Garnier, N. Freud, J. M. Létang, N. W. John, and F. Bello. Joint simulation of transmission x-ray imaging on GPU and patient's respiration on CPU. Medical Physics, 37(6):3129, July 2010.  BibTeX  DOI  .pdf 

Purpose: We previously proposed to compute the X‐ray attenuation from polygons directly on the GPU, using OpenGL, to significantly increase performance without loss of accuracy. The method has been deployed into a training simulator for percutaneous transhepatic cholangiography. The simulations were however restricted to monochromatic X‐rays using a point source. They now take into account both the geometrical blur and polychromatic X‐rays.
Method and Materials: To implement the Beer‐Lambert law with a polychromatic beam, additional loops have been included in the simulation pipeline. It is split into rendering passes and uses frame buffer objects to store intermediate results. The source shape is modeled using a variable number of point sources and the incident beam is split into discrete energy channels. The respiration model is composed of ribs, spine, lungs, liver, diaphragm and the external skin. The organ motion simulation is based on anatomical and physiological studies: the model is monitored by two independent active components: the ribs with a kinematics law and the diaphragm tendon with an up and down translation. Other soft‐tissue components are passively deformed using a 3D extension of the ChainMail algorithm. The respiration rate is also tunable to modify the respiratory profile.
Results: We have extended the simulation pipeline to take into account focal spots that cause geometric unsharpness and polychromatic X‐rays, and dynamic polygon meshes of a breathing patient can be used as input data.
Conclusions: X‐ray transmission images can be fully simulated on the GPU, by using the Beer‐Lambert law with polychromatism and taking into account the shape of the source. The respiration of the patient can be modeled to produce dynamic meshes. This is a useful development to improve the level of realism in simulations, when it is needed to retain both speed and accuracy.

[2] Villard2009CARS illustration P.-F. Villard, F. P. Vidal, C. Hunt, F. Bello, N. W. John, S. Johnson, and D. A. Gould. Percutaneous transhepatic cholangiography training simulator with real-time breathing motion. In Proceeding of the 23rd International Congress of Computer Assisted Radiology and Surgery, volume 4 (Suppl 1) of International Journal of Computer Assisted Radiology and Surgery, pages S66-S67, Berlin, Germany, June 2009. Springer.  BibTeX  DOI 

Keywords: Interventional radiology, Virtual environments, Respiration simulation, X-ray simulation, Needle puncture, Haptics, Task analysis

National Conferences (peer reviewed articles)

[1] Vidal2009TPCG illustration F. P. Vidal, M. Garnier, N. Freud, J. M. Létang, and N. W. John. Simulation of X-ray attenuation on the GPU. In Proceedings of Theory and Practice of Computer Graphics 2009, pages 25-32, Cardiff, UK, June 2009. Eurographics Association. Winner of Ken Brodlie Prize for Best Paper.  BibTeX   DOI   PDF 

In this paper, we propose to take advantage of computer graphics hardware to achieve an accelerated simulation of X-ray transmission imaging, and we compare results with a fast and robust software-only implementation. The running times of the GPU and CPU implementations are compared in different test cases. The results show that the GPU implementation with full floating point precision is faster by a factor of about 60 to 65 than the CPU implementation, without any significant loss of accuracy. The increase in performance achieved with GPU calculations opens up new perspectives. Notably, it paves the way for physically-realistic simulation of X-ray imaging in interactive time.

Keywords: Physically based modeling, Raytracing, Physics

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