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Biomedical subjects

D L Kirch

Publications and source records attributed to D L Kirch.

17 recordsLinked to original sources

Abdominal organ segmentation using texture transforms and a Hopfield neural network.

Abdominal organ segmentation is highly desirable but difficult, due to large differences between patients and to overlapping grey-scale values of the various tissue types. The first step in automating this process is to cluster together the pixels within each organ or tissue type. We propose to form images based on second-order statistical texture transforms (Haralick transforms) of a CT or MRI scan. The original scan plus the suite of texture transforms are then input into a Hopfield neural network (HNN). The network is constructed to solve an optimization problem, where the best solution is the minima of a Lyapunov energy function. On a sample abdominal CT scan, this process successfully clustered 79-100% of the pixels of seven abdominal organs. It is envisioned that this is the first step to automate segmentation. Active contouring (e.g., SNAKE's) or a back-propagation neural network can then be used to assign names to the clusters and fill in the incorrectly clustered pixels.

Algorithms↗

A new method for the correction of gamma camera nonuniformity due to spatial distortion.

A methodology for correcting scintillation camera nonuniformity resulting from spatial linearity distortion is described. The method simultaneously corrects for both variations in count density and distortions in spatial linearity without altering the intrinsic sensitivity or resolution of the imaging system. This approach to linearity correction requires only a single flood image from which the spatial shift vectors are derived. The algorithm has been implemented on a PC-based, EISA bus microcomputer, and reduces the measurement of integral uniformity for 201Tl from 25% to 5%. Combined with regional correction for photopeak pulse-heights shifts (i.e. energy correction), the algorithm represents a novel technique for implementing uniformity correction completely within software.

Algorithms↗

Augmentation of mortality risk discriminating power of left ventricular ejection fraction by measures of nonuniformity in systolic emptying on radionuclide ventriculography.

Employing equilibrium-gated radionuclide ventriculography in the left anterior oblique view, six geometric models and five mathematic coefficients of nonuniformity in regional left ventricular emptying were tested for their relative mortality risk-stratifying power and capacity to augment the risk-discriminating potency of the continuous and dichotomized global ejection fraction. Radionuclide ventriculography was performed an average of 7.6 days after acute myocardial infarction. All geometric models significantly separated 20 normal subjects from 137 patients with recent infarction (p less than 0.001). Cumulative mortality data demonstrated that significant independent univariate dichotomizing potency and augmentation of the mortality risk-discriminating power of the global ejection fraction were provided by models of regional emptying that 1) conformed to coronary artery perfusion areas, 2) encompassed total ventricular counts, 3) expressed variability in regional relative to global ejection fraction, and 4) simulated a pattern of emptying directed toward the center of geometry of the left ventricle. The combination of a four quadrant geometric model with axes drawn 45 degrees above the horizontal and a coefficient of variation calculated as square root of sigma(GEF - REF)2/4 x 100/GEF (where GEF = global ejection fraction and REF = regional ejection fraction) proved to be optimal. This coefficient averaged 12.2% in normal subjects and 32.2% in patients with recent acute myocardial infarction (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗

Left ventricular platelet deposition after acute myocardial infarction. An attempt at quantification using blood pool subtracted indium-111 platelet scintigraphy.

Since indium-111 platelet scintigraphy for the detection of left ventricular thrombosis often shows considerable non-specific blood pool activity a subtraction method using simultaneous technetium-99m blood pool scintigraphy was undertaken in 11 subjects with well documented remote myocardial infarction, who served as positive or negative controls, and in 18 consecutive patients with acute myocardial infarction. The results were compared with those of cross sectional echocardiography. Thirteen patients had transmural myocardial infarction and the calculated count per pixel in the left ventricle of the subtracted indium-111 platelet scintigram was (mean (SD)) 0.28(0.35), but five patients with subendocardial myocardial infarction had a mean count of 0.04(0.06). In seven patients with transmural myocardial infarction (two anterior and five inferior) left ventricular thrombosis was detected by indium-111 platelet scintigraphy but in only one of these by cross sectional echocardiography. None of the patients with subendocardial myocardial infarction had left ventricular thrombosis. Subtracted left ventricular counts correlated well with the visual results. It is concluded that left ventricular platelet sequestration after acute myocardial infarction may be quantified and precisely located and that quantitative longitudinal studies of the natural history and drug intervention are now possible.

Adult↗

Seven-pinhole tomography--a technical description.

A single-photon emission tomography system was developed and studied. Based upon a seven-pinhile-collimated Anger camera, interfaced to a digital minicomputer, this imaging configuration yielded seven independent, nonoverlapping projection images of the radioactivity in a commonly viewed volume. The computer was used to implement an iterative algorithm that processed these projections to yield a three-dimensional reconstruction of the soruce distribution. The algorithm provudes a nonlinear first approximation to the reconstruction, then use a single iteration technique to reduce errors resulting from that approximation. Point spread functions (PSF) at various distances from the collimator face, and point-source sensitivity (PSS) at a location in the middle of the reconstruction volume were determined. The system was used for thallium-201 imaging, where it was shown to reduce imaging time and increase sensitivity without loss in specificity when compared with standard parallel-hole-collimated imaging. Seven-pinhole tomography is a practical three-dimensional imaging system that has been demonstrated to be useful in the emission cardiology setting.

Heart↗

Quality control of scintillation cameras using a minicomputer.

A minicomputer-based technique compiles objective indicators of scintigraphic system performance. The evaluation begins with the acquisition of a single image of an orthogonal hole pattern from which quantitative and regional measurements of point-source sensitivity, spatial resolution, and spatial linearity are derived. Two computer programs offer the user different but complementary features. The first program is the basis of an evaluation performed by a technologist for purposes of quality control. Operator intervention is minimal, and the entire protocol, including data acquisition and processing, can be completed in 20 min. The results are automatically compiled and displayed as graphs showing 100 consecutive sets of daily performance measurements. A second computer program is designed as an interactive diagnostic and research tool to display measurements as histograms and functional images. The operator can use the program to determine the quantitative and spatial characteristics of the system's intrinsic performance measurements made during the quality-control evaluations.

Computers↗

A mathematical model for the determination of cardiac regurgitant and ejection fractions from radioisotope angiocardiograms.

A mathematical model taking into account the pulsatile pumping action of the heart has been developed which describes, in terms of a set of four recursive equations, the activity in the atrium and in the ventricle of the left or right heart at successive end-systoles and end-diastoles after bolus injection. The resulting closed form solutions permit calculations of chamber forward ejection fractions and valvular regurgitant fractions from computerized radioisotope angiocardiogram data. The method has been applied to a series of over thirty clinical studies with encouraging results.

Angiocardiography↗

Cross-sectional anatomic images by gamma ray transmission scanning.

60Co gamma-ray transmission data were measured along linear scan paths at a number of angular orientations with respect to the patient and submitted to a computer software program. Reconstructed images are displayed as digital density printouts and as isodensity contours on an x-y plotter or oscilloscope screen. Image resolution is limited primarily by factors such as collimation and the amount of transmission data collected; with the rather rudimentary apparatus at disposal, a spatial resolution better than 5 mm has been achieved.

Computers↗

Nuclear medicine computing. Where we have been, where we are and where we are going.

Demand for the newest and most elaborate Nuclear Medicine equipment is at an all time high. Never has there been more to offer than now with such improvements as large field of view, high resolution, whole-body capability and so on. The dedicated minicomputer systems that are available to go with these latest imaging devices are equally impressive. Still, the headaches associated with putting together a full capability camera/computer system are numerous. Things just do not seem to go together the way they ought to. If we are to truly get the most value out of our new equipment, we must put tremendous work loads on our clinical staff by expecting them to use very awkward and poorly configured systems in which several complicated steps are required to to produce the finished product ready for the reading room. The relatively low usage factor which most clinical Nuclear Medicine computer systems experience is not surprising when we consider the ridiculous way in which these systems are configured. It is time for a little human engineering to be introduced into the design process. Unfortunately, this proliferation of equipment is wasteful of money as well as the operator's time. It would make more sense to consolidate the multitude of displays and controlling elements into a single console which would allow a single operator to perform all necessary data processing operations quickly and interactively.

Computers↗