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Original Articles

Intrinsic Gating for Small-Animal Computed Tomography

A Robust ECG-Less Paradigm for Deriving Cardiac Phase Information and Functional Imaging

Julien Dinkel, MD; Soenke H. Bartling, MD; Jan Kuntz; Michael Grasruck, PhD; Annette Kopp-Schneider, PhD; Masayoshi Iwasaki, MD; Stefanie Dimmeler, MD; Rajiv Gupta, PhD, MD; Wolfhard Semmler, PhD, MD; Hans-Ulrich Kauczor, MD and Fabian Kiessling, MD

From the Departments of Radiology (J.D., H.-U.K.), Medical Physics in Radiology (S.H.B., J.K., W.S., F.K.), Statistics (A.K.-S.), German Cancer Research Center (DKFZ), Heidelberg, Germany; Siemens Medical Solutions, Forchheim, Germany (M.G.); Department of Molecular Cardiology, University of Frankfurt, Germany (M.I., S.D.); Department of Radiology, Massachusetts General Hospital, Boston, Mass (R.G.); Department of Radiology, University Hospital Heidelberg, Germany (H.-U.K.); Department of Experimental Molecular Imaging, RWTH-Aachen University, Germany (F.K.).

Correspondence to Julien Dinkel, Department of Radiology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany. E-mail j.dinkel{at}dkfz-heidelberg.de

Received April 8, 2008; accepted September 24, 2008.

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.

Key Words: flat-panel detector • imaging • intrinsic gating • small-animal imaging • tomography

Drs Dinkel and Bartling contributed equally to this work.

The online Data Supplement is available at http://circimaging.ahajournals.org/cgi/content/full/1/3/235/DC1.