Biomedical subjects

Ali Khamene

Publications and source records attributed to Ali Khamene.

7 recordsLinked to original sources

PubMed2006

Augmented reality visualization for CT-guided interventions: system description, feasibility, and initial evaluation in an abdominal phantom.

UNLABELLED: The purpose of this study was to evaluate the feasibility and performance of an augmented reality (AR) visualization prototype for virtual computed tomography (CT)-guided interventional procedures in a multimodality abdominal phantom. With the aid of AR guidance, three radiologists performed 30 attempts at targeting simulated liver lesions of different sizes (range, 5-15 mm) with a biopsy needle. The position of the needle tip relative to the lesion was verified by using ultrasonography and CT. With AR guidance, lesions were successfully targeted with the first needle pass in all cases. On the basis of these results, AR visualization for CT-guided intervention appears feasible and allows intuitive and accurate lesion targeting in a phantom. SUPPLEMENTAL MATERIAL: radiology.rsnajnls.org/cgi/content/full/2401040018/DC1

Abdomen↗

PubMed2006

An augmented reality system for MR image-guided needle biopsy: initial results in a swine model.

PURPOSE: To evaluate an augmented reality (AR) system in combination with a 1.5-T closed-bore magnetic resonance (MR) imager as a navigation tool for needle biopsies. MATERIALS AND METHODS: The experimental protocol had institutional animal care and use committee approval. Seventy biopsies were performed in phantoms by using 20 tube targets, each with a diameter of 6 mm, and 50 virtual targets. The position of the needle tip in AR and MR space was compared in multiple imaging planes, and virtual and real needle tip localization errors were calculated. Ten AR-guided biopsies were performed in three pigs, and the duration of each procedure was determined. After successful puncture, the distance to the target was measured on MR images. The confidence limits for the achieved in-plane hit rate and for lateral deviation were calculated. A repeated measures analysis of variance was used to determine whether the placement error in a particular dimension (x, y, or z) differed from the others. RESULTS: For the 50 virtual targets, a mean error of 1.1 mm +/- 0.5 (standard deviation) was calculated. A repeated measures analysis of variance indicated no statistically significant difference (P > .99) in the errors in any particular orientation. For the real targets, all punctures were inside the 6-mm-diameter tube in the transverse plane. The needle depth was within the target plane in 11 biopsy procedures; the mean distance to the center of the target was 2.55 mm (95% confidence interval: 1.77 mm, 3.34 mm). For nine biopsy procedures, the needle tip was outside the target plane, with a mean distance to the edge of the target plane of 1.5 mm (range, 0.07-3.46 mm). In the animal experiments, the puncture was successful in all 10 cases, with a mean target-needle distance of 9.6 mm +/- 4.85. The average procedure time was 18 minutes per puncture. CONCLUSION: Biopsy procedures performed with a combination of a closed-bore MR system and an AR system are feasible and accurate.

Animals↗

PubMed2005

Automatic registration of portal images and volumetric CT for patient positioning in radiation therapy.

The efficacy of radiation therapy treatment depends on the patient setup accuracy at each daily fraction. A significant problem is reproducing the patient position during treatment planning for every fraction of the treatment process. We propose and evaluate an intensity based automatic registration method using multiple portal images and the pre-treatment CT volume. We perform both geometric and radiometric calibrations to generate high quality digitally reconstructed radiographs (DRRs) that can be compared against portal images acquired right before treatment dose delivery. We use a graphics processing unit (GPU) to generate the DRRs in order to gain computational efficiency. We also perform a comparative study on various similarity measures and optimization procedures. Simple similarity measure such as local normalized correlation (LNC) performs best as long as the radiometric calibration is carefully done. Using the proposed method, we achieved better than 1mm average error in repositioning accuracy for a series of phantom studies using two open field (i.e., 41 cm2) portal images with 90 degrees vergence angle.

Algorithms↗

PubMed2005

A novel phantom-less spatial and temporal ultrasound calibration method.

This paper introduces a novel method for ultrasound calibration for both spatial and temporal parameters. The main advantage of this method is that it does not require a phantom, which is usually expensive to fabricate. Furthermore, the method does not require extensive image processing. For spatial calibration, we solve an optimization problem established by a set of equations that relate the orientations of a line (i.e., calibration pointer) to the intersection points appearing in the ultrasound image. The line orientation is provided through calibration of both ends of the calibration pointer. Temporal calibration is achieved by processing of the captured pointer orientations and the corresponding image positions of intersection along with the timing information. The effectiveness of the unified method for both spatial and temporal calibration is apparent from the quality of the 3D reconstructions of a known object.

Algorithms↗

PubMed2004

An AR system with intuitive user interface for manipulation and visualization of 3D medical data.

We report on a stereoscopic video-see-through augmented reality system which we developed for medical applications. Our system allows interactive in-situ visualization of 3D medical imaging data. For high-quality rendering of the augmented scene we utilize the capabilities of the latest graphics card generations. Fast high-precision MPR generation ("multiplanar reconstruction") and volume rendering is realized with OpenGL 3D textures. We provide a tracked hand-held tool to interact with the medical imaging data in its actual location. This tool is represented as a virtual tool in the space of the medical data. The user can assign different functionality to it: select arbitrary MPR cross-sections, guide a local volume rendered cube through the medical data, change the transfer function, etc. Tracking works in conjunction with retroreflective markers, which frame the workspace for head tracking respectively are attached to instruments for tool tracking. We use a single head-mounted tracking camera, which is rigidly fixed to the stereo pair of cameras that provide the live video view of the real scene. The user's spatial perception is based on stereo depth cues as well as on the kinetic depth cues that he receives with the viewpoint variations and the interactive data visualization. The AR system has a compelling real-time performance with 30 stereo-frames/second and exhibits no time lag between the video images and the augmenting graphics. Thus, the physician can interactively explore the medical imaging information in-situ.

Diagnostic Imaging↗

PubMed2003

An Augmented Reality system for MRI-guided needle biopsies.

A navigation system can increase the speed and accuracy of MR guided interventions that make use of scanners with high-field closed magnets. We report on first needle placement experiments performed with an Augmented Reality (AR) navigation system. AR visualization provides very intuitive guidance, resulting in a faster procedure. The accuracy of the needle placement depends on the registration accuracy of the system. In the present trials, the needle was placed as good as 1mm close to the target center, however in a small number of cases substantially larger errors occurred and were most likely caused by needle bending.

Biopsy, Needle↗

PubMed2002

An augmented reality system for ultrasound guided needle biopsies.

We have developed an augmented reality visualization system that helps the physician perform ultrasound guided needle biopsies. For a needle biopsy, the needle has to be inserted into an anatomical target to remove a tissue sample. Ultrasound guidance is routinely used e.g. for breast needle biopsies. The real-time ultrasound images allow the physician to locate the target and to monitor the needle position. Our system uses a combination of an optical laser guide and a virtual guide in the augmented image to provide intuitive guidance for the needle placement. There is no need to track the needle, i.e. there is no need to instrument the needle for tracking. In phantom tests, users have performed well with the system without prior training. This paper describes special features of our system and the workflow for the needle placement procedure.

Biopsy, Needle↗