Date of Award
2010
Degree Type
Thesis
Degree Name
Master of Engineering Science
Program
Biomedical Engineering
Supervisor
Dr. Maria Drangova
Second Advisor
Dr. Aaron Fenster
Third Advisor
Dr. David W. Holdsworth
Abstract
Objective: To identify and quantify all sources of time delay affecting prospectively gated cardiac micro-CT imaging in order to select an optimum trigger delay for prospectively gated cardiac imaging. The physiological motion of the heart is a challenge in cardio-thoracic small animal imaging. Prospective and retrospective gating techniques have been developed to freeze cardiac motion and to enable imaging of the heart at different phases of the cardiac cycle. In prospectively gated cardiac micro-CT, there exist several time delays that are inherent in the different processes of prospective gating. Specifically, delays due to the recording of the ECG signal, processing of the ECG signal and generating the control signal to be sent to the scanner, and the physical delay of the scanner in starting image acquisition can all affect the time at which a cardiac image is acquired. Quantification of cardiac function based on prospective gating techniques, requires that all sources of time latencies be determined to accurately perform image acquisition at a desired time point of the cardiac cycle. In the current study, it was shown that without considering the effective delays, image acquisition by prospectively gated cardiac micro-CT happens with a lag from the desired time point of the cardiac cycle. This lag results in inaccurate left ventricular (LV) volume extraction from the prospectively gated images, potentially leading to erroneous quantification of cardiac function. It was found that the prospective gating method has 14 % to 30 % error (22 % ± 7 %) in LV volume estimation at end-systole. The error at enddiastole is 3 % to 13 % (8 % ± 5 %). Consequently it was shown that stroke volume when 111 obtained by prospectively gated images have 18 % to 47 % (35% ± 12 %) inaccuracy compared with the actual values. This error for ejection fraction is 16 % to 9 % (29% ± 9 %). By taking the inherent delays into account in a prospectively gated cardiac scan, it is possible to establish an optimum trigger delay to send the trigger pulses to the scanner; hence to compensate for the inherent delays and to acquire images accurately at the key time points of the cardiac cycle, i.e. end-systole, and end-diastole. For the equipment used in this study, the optimum trigger delay for imaging at end-systole and end-diastole was respectively 36.2 ms and 86.2 ms with the condition that for imaging at end-diastole, for any view angle, the first cycle should be skipped. In conclusion, for any prospectively gated cardiac scanning, all sources of time latencies should be determined beforehand to set an optimum trigger delay for imaging at any desired time point of the cardiac cycle.
Recommended Citation
Shirmohammad, Maryam, "Evaluating Delays in Prospectively Gated Cardiac Micro-Computed Tomography" (2010). Digitized Theses. 4463.
https://ir.lib.uwo.ca/digitizedtheses/4463