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S Loncaric

Publications and source records attributed to S Loncaric.

9 recordsLinked to original sources
PubMed2000

Web-based virtual endoscopy.

A web-based application for computed tomography (CT) image analysis and visualization of the bronchial airways is presented in the paper. The technique used in this application provides a noninvasive way to examine the interior of the bronchial tubes. Many different properties of the tubes such as presence of the foreign objects or structure abnormalities of the tubes can be detected this way. This method can also be used for other similar structures, such as blood vessels. The application uses the CT images obtained by spiral computed tomography as input. Amplitude thresholding is used for segmentation of the airways. The medial axis of the airways has been used as the path for animation. The procedure produces a fly-through animation in the MPEG format, which is obtained by volume rendering of the original CT images along the extracted path. The user can choose the appropriate path using the Virtual Reality Modeling Language (VRML) model, which is sufficient for visualization of basic structures. The algorithms and the software have been developed on the SUN Ultra 1 workstation.

Bronchoscopy↗
PubMed2000

3-D image analysis of abdominal aortic aneurysm.

In this paper we propose a technique for 3-D segmentation of abdominal aortic aneurysm (AAA) from computed tomography (CT) angiography images. Output data form the proposed method can be used for measurement of aortic shape and dimensions. Knowledge of aortic shape and size is very important for selection of appropriate stent graft device for treatment of AAA. The technique is based on a 3-D deformable model and utilizes the level-set algorithm for implementation of the method. The method performs 3-D segmentation of CT images and extracts a 3-D model of aortic wall. Once the 3-D model of aortic wall is available it is easy to perform all required measurements for appropriate stent graft selection. The method proposed in this paper uses the level-set algorithm instead of the classical active contour algorithm developed by Kass et al. The main advantage of the level set algorithm is that it enables easy segmentation surpassing most of the drawbacks of the classical approach. In the level-set approach for shape modeling, a 3-D surface is represented by a real 3-D function or equivalent 4-D surface. The 4-D surface is then evolved through an iterative process of solving the differential equation of surface motion. Surface motion is defined by velocity at each point. The velocity is a sum of constant velocity and curvature-dependent velocity. The stopping criterion is calculated based on image gradient. The algorithm has been implemented in MATLAB and C languages. Experiments have been performed using real patient CT angiography images and have shown good results.

Algorithms↗
PubMed1998

Using fast sequential asymmetric fanbeam transmission CT for attenuation correction of cardiac SPECT imaging.

UNLABELLED: The objective of this study was to determine the feasibility of using a fast (short-duration) transmission computed tomogram (TCT), acquired immediately before or after the emission CT, to correct for photon attenuation in cardiac SPECT. METHODS: The asymmetric fanbeam geometry with a 99mTc line source was used to acquire TCTs after conventional cardiac emission CT imaging on a triple-head SPECT system. The TCTs were reconstructed to generate patient-specific attenuation maps, which were used with an iterative maximum likelihood algorithm to reconstruct attenuation-corrected cardiac SPECT studies. The results of attenuation correction based on TCTs as short as 1 min were compared with long-duration transmission imaging for a phantom and several human studies. RESULTS: Attenuation correction based on asymmetric fanbeam TCT significantly improves the uniformity of images of a uniform tracer distribution in a cardiac-thorax phantom configured to simulate a large patient. By using a high-activity line source and a rapid camera rotation, a suitable attenuation map for this phantom can be obtained from a 4-min TCT. A similar result is obtained for patients with thorax widths of <40 cm. CONCLUSION: A sequential imaging protocol for acquiring a fast TCT can be used for attenuation correction of cardiac SPECT imaging. The sequential TCT can be acquired without significantly extending the duration of the imaging study. This method provides a way to perform attenuation correction on existing triple-head SPECT systems without extensively modifying the system.

Adult↗
PubMed1995

3-D image analysis of intra-cerebral brain hemorrhage from digitized CT films.

A new 3-D technique for the segmentation and quantification of human spontaneous intra-cerebral brain hemorrhage (ICH) is presented in this paper. The algorithm for ICH primary region segmentation uses the spatially weighted K-means histogram-based clustering algorithm. The ICH edema region segmentation algorithm employs an iterative morphological processing of the ICH brain data. A volume rendering technique is used for the effective 3-D visualization of ICH segmented regions. A computer program is developed for use in the human spontaneous ICH study involving a large number of patients. Experimental measurements and visualization results are presented which were computed on real ICH patient brain data.

Algorithms↗
PubMed1995

Asymmetric fan transmission CT on SPECT systems.

For proper attenuation correction of SPECT images, a set of 3D attenuation maps specific to the imaging slices is needed. Among the many different approaches for deriving the attenuation maps, fan beam transmission CT (FBTCT), performed on the same SPECT system as emission imaging, has many promising and clinically practical features. The major problem of FBTCT is that the current SPECT systems do not have a large enough field of view (FOV) to cover the typical cross-sectional size of patients. To address this problem, we have developed a novel asymmetric fan (AsF) sampling scheme to extend the FOV to practical sizes for clinical TCT imaging on existing SPECT systems. This AsF scheme samples only half of the intended FOV in each projection; the other half would be sampled in an opposing projection after detector rotation. We have implemented the AsF sampling on a three-head SPECT system through a specially designed source-collimator assembly. We have modified the conventional convolution backprojection algorithm to facilitate simple and fast image reconstruction. The feasibility of the approach is confirmed by the quality of the derived TCT images of various phantoms and human subjects. The AsF sampling scheme could also have applications in other general transmission CT systems.

Biophysical Phenomena↗
PubMed1994

Feasibility of dual radionuclide brain imaging with I-123 and Tc-99m.

A study was conducted to evaluate the feasibility of simultaneous dual radionuclide brain imaging with 123I and 99mTc using photopeak image subtraction techniques or offset photopeak image acquisition. The contribution of the photons from one radionuclide to a second radionuclide's photopeak energy window (crosstalk) was evaluated for SPECT and planar imaging of a brain phantom containing 123I and 99mTc for a range of activity levels and distribution properties approximating those in rCBF images of the adult human brain. Crosstalk was evaluated for 10% symmetrical energy windows centered on the 123I and 99mTc photopeaks and for 10% energy windows asymmetrically placed to the left and right of the center of the respective photopeaks. Major observations include: (1) in the centered photopeak windows, 99mTc crosstalk in the 123I window is 8.9% of the 99mTc seen in the 99mTc window and ranges from 37.5% to 75.0% of the 123I in the 123I window. 123I crosstalk is 37.8% of the 123I seen in the 123I window and ranges from 4.4% to 8.9% of the 99mTc seen in the 99mTc window; (2) the spatial distribution of a radionuclide's crosstalk photons differs from that observed in the radionuclide's photopeak window; (3) a 99mTc photopeak window offset to the left does not decrease 123I crosstalk, and the percentage of 99mTc scattered photons is significantly increased in the window.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Short-axis circumferential profiles of the heart in healthy subjects: comparison of T1-201 SPECT and two-dimensional echocardiography.

To correlate the findings at thallium-201 single photon emission computed tomography (SPECT) with left ventricular anatomy, circumferential wall thickness was measured in 12 healthy subjects with two-dimensional echocardiography. At the midpapillary level, eight anatomic structures were identified with echocardiography, as were four maxima (papillary muscles and junctions of the left ventricular myocardium with the right ventricle, both anteriorly and posteriorly) and the intervening minima (including the septum). Tl-201 SPECT was performed in the same subjects. The normalized circumferential count profiles of the short-axis sections that included the papillary muscles showed the same basic pattern as that on echocardiograms. In most cases, the posterior papillary muscle and the posterior junction with the right ventricle were not distinguishable from each other, which produced three circumferential profile maxima instead of four. When values from all subjects were averaged, left ventricular anatomy was less evident in the circumferential profile. Left ventricular anatomic structures were reflected to a similar degree with either 180 degrees or 360 degrees data sampling.

Adult↗
PubMed1987

Comparison of transaxial resolution in 180 degrees and 360 degrees SPECT with a rotating scintillation camera.

Using circular 180 degrees and 360 degrees SPECT acquisition modes the transaxial resolution of line sources in air and water were measured at different positions in the field of view. With the 180 degrees acquisition mode, all line sources in air located off the axis of camera rotation (AoR) showed an oval distortion. This distortion was systematically related to the starting point of the rotating detector. On axis line sources in air were undistorted, regardless of the 180 degrees acquisition starting angle. The 360 degrees acquisition images of the line sources in air showed a similar effect but in a very mild form. In water, transaxial reconstructions of line sources (off axis) showed an enhancement of the oval distortion for both the 180 degrees and 360 degrees acquisitions. Computer simulations of the line source measurements were performed and correlated well with the experimental data. The line source results are explainable by the inherent depth dependent response of the scintillation camera. In clinical SPECT studies, distortions of this nature will be most appreciable with 180 degrees imaging of small organs that are located off the AoR.

Air↗