Intrinsic Gating for Small-Animal Computed Tomography

Abstract

Background-A projection-based method of intrinsic cardiac gating in small-animal computed tomography imaging is presented. Methods and Results-In this method, which operates without external ECG monitoring, the gating reference signal is derived from the raw data of the computed tomography projections. After filtering, the derived gating reference signal is used to rearrange the projection images retrospectively into data sets representing different time points in the cardiac cycle during expiration. These time-stamped projection images are then used for tomographic reconstruction of different phases of the cardiac cycle. Intrinsic gating was evaluated in mice and rats and compared with extrinsic retrospective gating. An excellent agreement was achieved between ECG-derived gating signal and self-gating signal (coverage probability for a difference between the 2 measurements to be less than 5 ms was 89.2% in mice and 85.9% in rats). Functional parameters (ventricular volumes and ejection fraction) obtained from the intrinsic and the extrinsic data sets were not significantly different. The ease of use and reliability of intrinsic gating were demonstrated via a chemical stress test on 2 mice, in which the system performed flawlessly despite an increased heart rate. Because of intrinsic gating, the image quality was improved to the extent that even the coronary arteries of mice could be visualized in vivo despite a heart rate approaching 430 bpm. Feasibility of intrinsic gating for functional imaging and assessment of cardiac wall motion abnormalities was successfully tested in a mouse model of myocardial infarction. Conclusions-Our results demonstrate that self-gating using advanced software postprocessing of projection data promises to be a valuable tool for rodent computed tomography imaging and renders ECG gating with external electrodes superfluous. (Circ Cardiovasc Imaging. 2008;1:235-243.)

<em>In Vivo</em> Quantitative Assessment of Myocardial Structure, Function, Perfusion and Viability Using Cardiac Micro-computed Tomography

“…Earlier MicroCT studies confirmed that quantitative evaluation of global cardiac function is feasible in murine cardiovascular disease models and that pronounced decrease in global heart function takes place soon after LAD artery occlusion. These findings are in agreement with previous reports in that marked reduction in LVSV, LVEF, and CO occurred already on day 1 after occlusion 29,[40][41][42][43] . It is noteworthy to mention that cardiac functional performance is dependent on the type and degree of anesthesia, thus for accurate measurements the heart rate during image acquisition should be kept as physiological as possible 44 .…”

“…Over the past several years MicroCT has become the modality many researches considered for characterization of cardiac structure and function in small animals [26][27][28][29]30 . However, the instrumentation used in the prior work was either custom built or no longer commercially available.…”

“…Intrinsic retrospective gating utilizes proprietary image-based software to reconstruct end-diastolic and end-systolic cardiac phases without need for dedicated respiratory and cardiac monitoring devices 29,31,32 . An excellent agreement of intrinsic retrospective and extrinsic ECG-dependent retrospective gating for studying cardiac function in mice and rats was demonstrated by Dinkel et al 29 .…”

Micro-CT of rodents: State-of-the-art and future perspectives

“…In addition to these extrinsic gating techniques, an intrinsic image-based gating approach without any external devices was developed, initially for a clinical, spiral cone-beam CT scanner [49]. In intrinsic gating, a post-processing algorithm evaluates the center of mass of certain regions of interest (ROIs) within each projection to detect respiratory and cardiac motion [50–52]. …”

High-Resolution CT for Small-Animal Imaging Research

“…In addition to these extrinsic gating techniques, an intrinsic image-based gating approach without any external devices has been developed initially for a clinical cone beam spiral CT scanner (Kachelriess et al, 2002). In intrinsic gating, a postprocessing algorithm evaluates the center of mass of certain regions of interest within each projection to detect the respiratory and cardiac motion Dinkel et al, 2008;Sawall et al, 2011).…”