Showing papers presented at "Computer Assisted Radiology and Surgery in 2005"

Developing a needle guidance virtual environment with patient-specific data and force feedback

Abstract: We present a simulator for guided needle puncture procedures. Our aim is to provide an effective training tool for students in interventional radiology (IR) using actual patient data and force feedback within an immersive virtual environment (VE). Training of the visual and motor skills required in IR is an apprenticeship which still consists of close supervision using the model: (i) see one, (ii) do one, and (iii) teach one. Training in patients not only has discomfort associated with it, but provides limited access to training scenarios, and makes it difficult to train in a time efficient manner. Currently, the majority of commercial products implementing a medical VE still focus on laparoscopy where eye–hand coordination and sensation are key issues. IR procedures, however, are far more reliant on the sense of touch. Needle guidance using ultrasound or computed tomography (CT) images is also widely used. Both of these are areas that have not been fully addressed by other medical VEs. This paper provides details of how we are developing an effective needle guidance simulator. The project is a multi-disciplinary collaboration involving practising interventional radiologists and computer scientists.

Hip joint anatomy virtual and stereolithographic reconstruction for preoperative planning of total hip replacement

Abstract: The purpose of the present work was to develop a tool for preoperatively planning the Total Hip Replacement (THR). Starting from the MR images, the 3D surface model of both the pelvis and the femur was built and the surgical operation was virtually performed. Data coming from gait analysis were added to visualize the physiologic movement of the hip joint. The resulting triangular mesh was sufficiently accurate to allow the building of the stereolithographic model of the joint by means of rapid prototyping technique. The plastic bones allow the user to have an enhanced vision of the surgical procedure to be performed.

Real-time analysis of ultrasound images using GPU

Abstract: Analysing the increasing number of medical images stemming from various imaging modalities is a time-consuming task for the clinicians. Presently, medical images are mainly hand-segmented and manually analysed. Automatic tools are needed to make medical image analysis easier, and to create better presentations of information needed prior to and during surgery. In this article, we focus on real-time analysis of ultrasound images, and on how inexpensive graphics hardware can be utilised to accelerate current image processing techniques. Algorithms evaluated on the GPU were mathematical morphology, gradient vector flow, and the snake model. The results are promising and show that a large number of iterations can be run in 1/24 of a second.

PACS storage requirements - influence of changes in imaging modalities

Abstract: In current radiology departments, imaging modalities are changing rapidly. One reason for these changes is the continuous technical development providing new imaging modalities with higher spatial and temporal resolution and increased capabilities. Another important reason for change is the replacement of non-digital modalities by digital DICOM modalities to ensure easy storage into the Picture Archiving and Communication System (PACS). Besides the impact on working procedures for both radiologists and technologists, these changes in imaging modalities also influence the storage requirements of the PACS. In the University Hospital Groningen, digital archiving of imaging data started late 1999. From this time on, monthly production figures were collected from different modality types and the dates of changes in imaging modalities were recorded. Our results show that increase in data production is not limited to the recent advancement of multi-detector computed tomography (MDCT), but also new ultrasound (US) devices, magnetic resonance imaging (MRI), and X-ray angiography (XA) could have major impact on the storage capacity requirements. Our measurements show that PACS storage capacity planning should take into account a large margin for growth because of image modality replacement.

Ground truth for evaluation of ischemic stroke hybrid segmentation in a rat model of temporary middle cerebral artery occlusion

Abstract: In vivo rodent models of focal cerebral ischemia have been developed to investigate stroke therapy. Typically these models require rapid quantification of cerebral infarct volumes using vital stains with tetrazolium salts to delineate the extent of neuronal death. To avoid animal sacrifice, we sought a study with MR acquired volumetric rat data where surrogate of ground truth is obtained by repeated manual delineation by experts, and an automated hybrid segmentation is evaluated for accuracy. We propose a rating system for the expert delineations that captures intra- and inter-expert discrepancy. Our preliminary results show that surrogate ground truth derived from MR data is at least as good as the one derived from histologic stained slices. Hence animal sacrifice is not necessary to evaluate ischemic stroke automated segmentation in a rat model of temporary middle cerebral artery occlusion.

A computer-assisted curved-bladed Tuke Saw for spherical osteotomy

Abstract: In order to perform spherical osteotomy precisely, quickly and safely, we have developed a novel computer-assisted surgical tool utilizing an oscillating bone saw, “Tuke Saw,” with a curved-blade in combination with a CT-based optical navigation system. In this study, the accuracy and feasibility of this curved-bladed Tuke Saw in spherical osteotomy were examined in comparison with the conventional curved chisel. Hemispherical osteotomy on rectangular parallelepiped blocks of Sawbones and rotational acetabular osteotomy on cadaveric pelves were performed with these surgical tools. With both the tools, the distance error of the actual osteotomy surface from the sphere of the plan got larger when the position got deeper, however, the extent was smaller with the curved-bladed Tuke Saw. The procedure time with the curved-bladed Tuke Saw was about half of that with the curved chisel. Therefore, it can be said that the curved-bladed Tuke Saw is more accurate and feasible than the conventional curved chisel.

Automatic subthalamic nucleus targeting for deep brain stimulation. A validation study

Abstract: In functional stereotactic neurosurgery, one of the cornerstones upon which the success and the operating time depends is an accurate targeting. The subthalamic nucleus (STN) is the usual target involved when applying Deep Brain Stimulation (DBS) for the Parkinson's disease (PD). Unfortunately, STN is usually not clearly visible in common medical imaging modalities, which justifies the use of atlas-based segmentation techniques to infer the STN location. We propose a scheme that allows both, to perform a comparison between different non-rigid atlas registration algorithms and to evaluate their usability to locate the STN automatically. Using our validation–evaluation scheme and accurate registration algorithms, we demonstrate that automatic STN localization is possible and accurate.

Integration of a surgical robot and intraoperative imaging

Abstract: The operating room installation at the department of cranio-maxillofacial surgery at the University Clinic Heidelberg consists of an operating table moving on rails in the floor (AWIGS, MAQUET GmbH and Co. KG, Rastatt), together with a sliding gantry computer tomograph (CT Emotion, SIEMENS, Erlangen, both Germany). With this setup of intraoperative imaging, we want to overcome the limits of marker screw registration that acts as the golden standard for robotic registration. The first robotic intervention performing a complex trajectory at the human skull was fulfilled by a modified Staeubli RX90 robot on a mobile platform. We adopted this robot for the setup with the intraoperative CT by using a gripper-change system with force-torque sensor measurement and an automatic registration algorithm.

DICOM storage into PACS of out-hospital CD-ROMs - a half year experience report

Abstract: With the advance of digitalization of radiology departments, the interchange of data between institutions is shifting towards shipment of CD-ROMs instead of physical film. Although this is a positive change in terms of costs, it also has its downsides. One of the main problems is how to integrate these CD-ROMs in the normal workflow. Although most CD-ROMs are equipped with a dedicated viewer, these viewers are different per vendor and thus users have to learn to operate many different software packages. Some of the software packages also require installation on the local workstation, which is not always allowed. To solve these problems, we have to include the data from the CD-ROMs into the normal hospital workflow. To achieve this, a beta-version of a software packages was evaluated (DICOM Litebox; ETIAM, France). This software package reads all DICOM files from the CD-ROM, reconciliates the DICOM header and stores the DICOM files into the PACS. A pilot in 77 CD-ROMs clearly showed the advantage of the procedure, all CD-ROMs were Successfully stored into the PACS and thus available using the normal viewers within the hospital, During the first half year after implementing procedure, changes were made only to store second opinion cases into the PACS, all other data was only stored on the web-server and will be removed after 2 years. (c) 2005 CARS & Elsevier B.V.. All rights reserved.

Virtual microphones in the operating theatre

Abstract: With a linear array of microphones, 'virtual microphones' can be created with good results on isolating, tracking and separating sources of sound. This technique could be used for command control and speech recognition purposes in an operating theatre.

Model-based segmentation of short-axis MR cardiac images

Abstract: Reliable automatic segmentation of MR cardiac images is still an important problem in medical image processing. Although image data quality has improved considerably during the last years, this segmentation is still considered a difficult problem. Manual segmentation is hardly an option as this is extremely labour intensive. This paper describes a combined bottom-up and top-down approach to the problem of automatic segmentation of short-axis MR cardiac images, i.e. extract the boundaries of the left and right ventricle and the myocardium. The method is evaluated using 69 datasets for which manual segmentations were available.

Experiences in moving from CRT to flat panel LCD monitors for diagnostic PACS workstations

Abstract: PAH and RBWH implemented PACS as part of the Queensland Health QPACS project that commenced in 1999. These implementations are based around the AGFA Impax® PACS, AGFA Web1000 for enterprise delivery and AGFA CR. Towards the end of year 2004 it was evident from QA measurements and increasing failure rates, that the original CRT monitors (see Figure 1) were rapidly approaching their end of life. This represented an obvious problem for the hospitals in terms of maintaining a soft copy based radiology service. It also represented a problem for the product vendor (Agfa) in terms of an ability to continue to service superceded technology, plus the cost of providing that service. PACS Support had previously undertaken studies[1] to define the requirements of a “diagnostic” monitor. As a consequence of these studies and the aging of the original CRT monitors, a decision was taken to move to high brightness, high resolution, monochrome LCD panels. In collaboration with the vendor a plan was developed to deal with this problem. The vendor proposed to replace the CRT display monitors with Planar C3i and Planar PX212 LCD monitors, under the existing service contract terms in return for a continuing commitment on the part of the hospitals to the workstation service contracts. PAH and RBWH were able to completely replace their inventory of CRT “diagnostic” monitors with Planar C3i monochrome flat panels (see Figure 2). This monitor was known from previous evaluations [2] to be a high quality image viewing monitor suitable for radiological diagnosis. The monitor replacement project was completed in December 2004 to the benefit of all parties involved.

Analysis of image viewing by clinicians in a hospital wide PACS

Abstract: We present statistics on about clinicians' use of our hospital-wide PACS, in terms of the number of studies retrieved from clinical departments, timing of such retrieval, and how often specific functions of the viewer are used.