Left ventricular volume estimation from radionuclide images using an ellipsoidal model

Au, Colin L. (1997) Left ventricular volume estimation from radionuclide images using an ellipsoidal model. Masters thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (10MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

This thesis presents a method of left ventricular (LV) volume estimation that is an improvement over existing methods. The author has developed a method of left ventricular volume estimation using an ellipsoidal model. It is shown, in this thesis, that the volume of an ellipsoid can be estimated from three planar projections (radionuclide images). Thus, this method can be applied to estimate the volume of the left ventricle from three radionuclide images, taken at different angles. Left ventricular radionuclide images are formed when a radioactive source is injected into a patient. Generally, a patient's red blood cells are labelled with technetium ⁹⁹mTc which will emit gamma (γ) rays during radioactive decay. -- Two methods have been developed to estimate left ventricular volumes from these radionuclide images. Count based methods use the principle that the number of γ rays detected over a surface is proportional to the volume of the source located under that surface. Geometric methods rely on the outline of the left ventricle and the accuracy heavily depends upon how well the geometric model fits the left ventricle. -- To test the accuracy of using this geometric method, hollow ellipsoidal models were constructed. A total of 20 trials were performed in which the models were arbitrarily located relative to a fixed reference frame. Each image from the γ camera (elliptic in shape) was then analyzed to determine the axes lengths and angle of rotation. The estimated volumes were compared with the theoretical volume and the percentage discrepancies ranged in magnitude from 0.7% to 13.9%. -- One problem is that it may be difficult to determine the exact location of the left ventricular projection border because of scattering, interference of radiation from other organs, and pixel size (resolution of 6.13 mm/pixel). This problem can be minimized by selecting a certain count threshold to help determine where the left ventricular border is located. Another problem of using a geometric method of volume estimation is how well the geometric model fits the actual organ. For most cases, an ellipsoidal model does seem to be a relatively accurate model but abnormalities in the left ventricle will affect the accuracy. -- It was discovered that self attenuation caused the observed counts to differ by as much as 33.7% for images within the same trial. If a count based left ventricular volume estimation method was performed on this same set of images, then there would be a relatively large discrepancy among the volume estimates. Because of so many factors such as attenuation, self attenuation, radioactive decay, scattering, and interference from other organs, it would appear as though count based methods would not be able to estimate accurately the volume of the left ventricle.

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