PubMed Health⌕ Search

Biomedical subjects

S Aharon

Publications and source records attributed to S Aharon.

7 recordsLinked to original sources
PubMed1999

Quantitative and clinical analysis of SPECT image registration for epilepsy studies.

UNLABELLED: This study reports quantitative measurements of the accuracy of two popular voxel-based registration algorithms--Woods' automated image registration algorithm and mutual information correlation--and compares these with conventional surface matching (SM) registration. METHODS: The registration algorithms were compared (15 different matches each) for (a) three-dimensional brain phantom images, (b) an ictal SPECT image from a patient with partial epilepsy matched to itself after modification to simulate changes in the cerebral blood flow pattern and (c) ictal/interictal SPECT images from 15 patients with partial epilepsy. Blinded visual ranking and localization of the subtraction images derived from the patient images were also performed. RESULTS: Both voxel-based registration methods were more accurate than SM registration (P < 0.0005). Automated image registration algorithm was more accurate than mutual information correlation for the computer-simulated ictal/interictal images and the patient ictal/interictal studies (P < 0.05). The subtraction SPECTs from SM were poorer in visual ranking more often than the voxel-based methods (P < 0.05). CONCLUSION: Voxel intensity-based registration algorithms provide significant improvement in ictal/interictal SPECT registration accuracy and result in a clinically detectable improvement in the subtraction SPECT images.

Algorithms↗
PubMed1997

Patient-specific anatomic models from three dimensional medical image data for clinical applications in surgery and endoscopy.

Virtual surgery and endoscopy use computer-generated volume renderings and/or models created from 3D medical image scans (CT or MRI) of individual patients. The patient's anatomy, including organs and other internal structures of interest, are then traversed in a virtual "fly-through," giving nearly the same visual impression as if the corresponding real organ was being examined intraoperatively, or as if an actual video or fiberoptic endoscopic procedure was being performed. Such virtual examinations may provide capabilities and information not possible or available in physical examinations. The potential is to provide a noninvasive computer-aided treatment plan or diagnostic screening procedure to augment or replace conventional invasive procedures. With sophisticated image processing and computational analysis, it is possible to perform realistic and useful simulations of surgical and endoscopic procedures, including "virtual dissection and resection" and "virtual biopsy." Surgical margins can be accurately assessed and differential tissue diagnoses made based upon spectral or other information contained in the patient-specific images and models.

Algorithms↗
PubMed1997

3-D surface reconstruction of patient specific anatomic data using a pre-specified number of polygons.

Virtual reality environments provide highly interactive, natural control of the visualization process, significantly enhancing the scientific value of the data produced by medical imaging systems. Due to the computational and real time display update requirements of virtual reality interfaces, however, the complexity of organ and tissue surfaces which can be displayed is limited. In this paper, we present a new algorithm for the production of a polygonal surface containing a pre-specified number of polygons from patient or subject specific volumetric image data. The advantage of this new algorithm is that it effectively tiles complex structures with a specified number of polygons selected to optimize the trade-off between surface detail and real-time display rates.

Algorithms↗
PubMed1996

Parallel computation enables precise description of Ca2+ distribution in nerve terminals.

Parallel computation employing a domain decomposition method was used to calculate precisely without approximations the spatio-temporal distribution of Ca2+ in nerve terminals. The results showed, contrary to expectations, that for equal admitted Ca2+ currents at low (one channel open) and high (four channels open) depolarization, the average Ca2+ concentration at the release area is higher at the low depolarization. These calculations provide additional support for the Ca(2+)-voltage hypothesis for neurotransmitter release.

Animals↗
PubMed1994

The magnitude and significance of Ca2+ domains for release of neurotransmitter.

It is now widely accepted that localized high concentrations of Ca2+ (Ca2+ domains) play a major role in controlling the time course of neurotransmitter release. In the present work we calculate the magnitude and the time course of Ca2+ domains that evolve in the vicinity of a Ca2+ channel and an adjacent release site. In the calculations we consider a accurately dimensioned Ca2+ channel. Moreover, the Ca2+ current is continuously adjusted with regard to the accumulated intracellular Ca2+ and, in addition, endogenous buffers are considered. The calculations, carried out by the software FIDAP, based on finite element method, show that the Ca2+ concentrations achieved near the release sites are significantly lower than claimed by other investigators. Furthermore, we present arguments indicating that the Ca2+ domains, regardless of their magnitude, do not play a role in controlling the time course of release of neurotransmitter.

Animals↗
PubMed1993

Semi-automatic computer construction of three-dimensional shapes for the finite element method.

Precise estimation of spatio-temporal distribution of ions (or other constitutives) in three-dimensional geometrical configuration plays a major role in biology. Since a direct experimental information regarding the free intracellular Ca2+ spatio-temporal distribution is not available to date, mathematical models have been developed. Most of the existing models are based on the classical numerical method of finite-difference (FD). Using this method one is limited when dealing with complicated geometry, general boundary conditions and variable or non-linear material properties. These difficulties are easily solved when the finite-element-method (FEM) is employed. The first step in the implementation of the FEM procedure is the mesh generation which is the single most tedious, time consuming task and vulnerable to mistake. In order to overcome these limitations we developed a new interface called AUTOMESH. This tool is used as a preprocessor program which generates two- and three-dimensional meshes for some known and often-used shapes in neurobiology. AUTOMESH creates an appropriate mesh by using the mesh generator commercial tool of FIDAP.

Calcium↗