In 1997, Azuma published a survey on augmented reality (AR). Our goal is to complement, rather than replace, the original survey by presenting representative examples of the new advances. We refer one to the original survey for descriptions of potential applications (such as medical visualization, maintenance and repair of complex equipment, annotation, and path planning); summaries of AR system characteristics (such as the advantages and disadvantages of optical and video approaches to blending virtual and real, problems in display focus and contrast, and system portability); and an introduction to the crucial problem of registration, including sources of registration error and error-reduction strategies.

https://www.cc.gatech.edu/~blair/papers/ARsurveyCGA.pdf

Recent advances in augmented reality

Task Group 101 of the AAPM has prepared this report for medical physicists, clinicians, and therapists in order to outline the best practice guidelines for the external-beam radiation therapy technique referred to as stereotactic body radiation therapy (SBRT). The task group report includes a review of the literature to identify reported clinical findings and expected outcomes for this treatment modality. Information is provided for establishing a SBRT program, including protocols, equipment, resources, and QA procedures. Additionally, suggestions for developing consistent documentation for prescribing, reporting, and recording SBRT treatment delivery is provided.

https://aapm.onlinelibrary.wiley.com/doi/pdf/10.1118/1.3438081

Stereotactic body radiation therapy: The report of AAPM Task Group 101

We are on the verge of ubiquitously adopting Augmented Reality (AR) technologies to enhance our percep- tion and help us see, hear, and feel our environments in new and enriched ways. AR will support us in fields such as education, maintenance, design and reconnaissance, to name but a few. This paper describes the field of AR, including a brief definition and development history, the enabling technologies and their characteristics. It surveys the state of the art by reviewing some recent applications of AR technology as well as some known limitations regarding human factors in the use of AR systems that developers will need to overcome.

/pdf/a-survey-of-augmented-reality-technologies-applications-and-3d9hf1tnc4.pdf

A Survey of Augmented Reality Technologies, Applications and Limitations

The task group (TG) for quality assurance of medical accelerators was constituted by the American Association of Physicists in Medicine's Science Council under the direction of the Radiation Therapy Committee and the Quality Assurance and Outcome Improvement Subcommittee. The task group (TG-142) had two main charges. First to update, as needed, recommendations of Table II of the AAPM TG-40 report on quality assurance and second, to add recommendations for asymmetric jaws, multileaf collimation (MLC), and dynamic/virtual wedges. The TG accomplished the update to TG-40, specifying new test and tolerances, and has added recommendations for not only the new ancillary delivery technologies but also for imaging devices that are part of the linear accelerator. The imaging devices include x-ray imaging, photon portal imaging, and cone-beam CT. The TG report was designed to account for the types of treatments delivered with the particular machine. For example, machines that are used for radiosurgery treatments or intensity-modulated radiotherapy (IMRT) require different tests and/or tolerances. There are specific recommendations for MLC quality assurance for machines performing IMRT. The report also gives recommendations as to action levels for the physicists to implement particular actions, whether they are inspection, scheduled action, or immediate and corrective action. The report is geared to be flexible for the physicist to customize the QA program depending on clinical utility. There are specific tables according to daily, monthly, and annual reviews, along with unique tables for wedge systems, MLC, and imaging checks. The report also gives specific recommendations regarding setup of a QA program by the physicist in regards to building a QA team, establishing procedures, training of personnel, documentation, and end-to-end system checks. The tabulated items of this report have been considerably expanded as compared with the original TG-40 report and the recommended tolerances accommodate differences in the intended use of the machine functionality (non-IMRT, IMRT, and stereotactic delivery).

/pdf/task-group-142-report-quality-assurance-of-medical-o6ba8j4qls.pdf

Task Group 142 report: quality assurance of medical accelerators.

A review of 3D/2D registration methods for image-guided interventions

Purpose: The objective of this work was to demonstrate the feasibility of acquiring low-exposure megavoltage cone-beam CT (MV CBCT) three-dimensional (3D) image data of sufficient quality to register the CBCT images to kilovoltage planning CT images for patient alignment and dose verification purposes. Methods and Materials: A standard clinical 6-MV Primus linear accelerator, operating in arc therapy mode, and an amorphous-silicon (a-Si) flat-panel electronic portal-imaging device (EPID) were employed. The dose-pulse rate of a 6-MV Primus accelerator beam was windowed to expose an a-Si flat panel by using only 0.02 to 0.08 monitor units (MUs) per image. A triggered image-acquisition mode was designed to produce a high signal-tonoise ratio without pulsing artifacts. Several data sets were acquired for an anthropomorphic head phantom and frozen sheep and pig cadaver heads, as well as for a head-and-neck cancer patient on intensity-modulated radiotherapy (IMRT). For each CBCT image, a set of 90 to 180 projection images incremented by 1° to 2° was acquired. The two-dimensional (2D) projection images were then synthesized into a 3D image by use of cone-beam CT reconstruction. The resulting MV CBCT image set was used to visualize the 3D bony anatomy and some soft-tissue details. The 3D image registration with the kV planning CT was performed either automatically by application of a maximization of mutual information (MMI) algorithm or manually by aligning multiple 2D slices. Results: Low-noise 3D MV CBCT images without pulsing artifacts were acquired with a total delivered dose that ranged from 5 to 15 cGy. Acquisition times, including image readout, were on the order of 90 seconds for 180 projection images taken through a continuous gantry rotation of 180°. The processing time of the data required an additional 90 seconds for the reconstruction of a 256 3 cube with 1.0-mm voxel size. Implanted gold markers (1 mm 3 mm) were easily visible for all exposure levels without artifacts. In general, the presence of high Z materials such as tooth fillings or implanted markers did not result in visible streak artifacts. The registration of structures such as the spinal canal and the nasopharynx in the MV CBCT and kV CT data sets was possible with millimeter and degree accuracy as assessed by displacement simulations and subsequent visual evaluation. Conclusions: We believe that the quality of these images, along with the rapid acquisition and reconstruction times, demonstrates that MV CBCT performed by use of a standard linear accelerator equipped with a flat-panel imager can be applied clinically for patient alignment. © 2005 Elsevier Inc. Cone-beam CT, Electronic portal-imaging device, Image-guided radiotherapy.

Low-dose megavoltage cone-beam CT for radiation therapy.

Recently there has been increasing interest in obtaining three-dimensional reconstructions of arterial vessels from multiple planar radiographs (obtained at angles around the object). Interventional angiography is the motivating application behind this research. Different methods have been proposed to acquire the planar data such as a gantry mounted x-ray image intensifier (XRII) or a C-arm mounted XRII. In order to obtain a three-dimensional reconstruction from a C-arm mounted XRII the trajectory of the source and detector system must be characterized. We have designed a calibration system that provides the necessary trajectory information using uniquely identifiable markers positioned on a cylinder. This calibration ring is to be placed around the patient's head, and consists of steel balls positioned in a predefined arrangement on a cylindrical acrylic support. The balls are arranged such that calibration can be done from almost any partial view, allowing reconstruction of a region of interest (ROI). Steel balls are placed around an acrylic cylinder, restricted to a band approximately 8.5 mm wide, thereby obscuring only a small fraction of the image. In this case the radiograph includes the region of interest (ROI) as well as a partial view of the calibration ring. This enables us to recover the geometry of X-ray imaging system from each individual frame. We call this process 'dynamic calibration' as opposed to 'off-line' calibration procedures which try to characterize the motion of C-arm before introducing the patient.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

/pdf/dynamic-geometrical-calibration-for-3d-cerebral-angiography-14av6zujuq.pdf

Dynamic geometrical calibration for 3D cerebral angiography

This paper presents the basic concept of CAMC and some of its applications. A CCD camera is attached to a mobile C-arm fluoroscopy X-ray system. Both optical and X-ray imaging systems are calibrated in the same coordinate system in an off-line process. The new system is able to provide X-ray and optical images simultaneously. The CAMC framework has great potential for medical augmented reality. We briefly introduce two new CAMC applications to the augmented reality research community. The first application aims at merging video images with a pre-computed tomographic reconstruction of the 3D volume of interest. This is a logical continuation of our work on 3D reconstruction using a CAMC (1999). The second approach is a totally new CAMC design where using a double mirror system and an appropriate calibration procedure the X-ray and optical images are merged in real-time. This new system enables the user to see an optical image, an X-ray image, or an augmented image where both visible and invisible are combined in real-time. The paper is organized in two independent sections describing each of the above. Experimental results are provided at the same time as the methods and apparatus are described for each section.

Merging visible and invisible: two Camera-Augmented Mobile C-arm (CAMC) applications

An X-ray apparatus has an X-ray examination system with an X-ray source and an X-ray detector which can be displaced relative to a subject for the pickup of 2D projections, an arrangement for determining extrinsic imaging parameters and an arrangement for determining intrinsic imaging parameters, for determining the projection geometry in the examination system for each 2D projection, and having a control and computing stage for reconstructing 3D images from the 2D projections using the extrinsic and intrinsic imaging parameters. The arrangement for determining the intrinsic imaging parameters includes X-ray-positive marks which are allocated to the X-ray source and which are in the path of an X-ray beam emanating from the X-ray source, these marks following displacement of the X-ray system.

X-ray apparatus for producing a 3D image from a set of 2D projections

C-arm volume reconstruction has become increasingly popular over the last years. These imaging systems generate 3D data sets for various interventional procedures such as endovascular treatment of aneurysms or orthopedic applications. Due to their open design and mechanical instability, C-arm imaging systems acquire projections along non-ideal scan trajectories. Volume reconstruction from filtered 2D X-ray projections requires a very precise knowledge of the imaging geometry. We show that the 3D image quality of C-arm cone beam imaging devices can be improved by proper design of the calibration phantom.

Improving 3D image quality of x-ray C-arm imaging systems by using properly designed pose determination systems for calibrating the projection geometry

Matthias Mitschke

Papers

Low-dose megavoltage cone-beam CT for radiation therapy.

Dynamic geometrical calibration for 3D cerebral angiography

Merging visible and invisible: two Camera-Augmented Mobile C-arm (CAMC) applications

X-ray apparatus for producing a 3D image from a set of 2D projections

Improving 3D image quality of x-ray C-arm imaging systems by using properly designed pose determination systems for calibrating the projection geometry