title: Intrinsic gating for small-animal computed tomography: a robust ECG-less paradigm for deriving cardiac phase information and functional imaging.
abstract: BACKGROUND
  A projection-based method of intrinsic cardiac gating in small-animal computed tomography imaging is presented.
  
  
  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.
authors.affiliation: Department of Radiology, German Cancer Research Center, Heidelberg, Germany. j.dinkel@dkfz-heidelberg.de
authors.forename: Julien
authors.initials: J
authors.lastname: Dinkel
authors.forename: Soenke H
authors.initials: SH
authors.lastname: Bartling
authors.forename: Jan
authors.initials: J
authors.lastname: Kuntz
authors.forename: Michael
authors.initials: M
authors.lastname: Grasruck
authors.forename: Annette
authors.initials: A
authors.lastname: Kopp-Schneider
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Iwasaki
authors.forename: Stefanie
authors.initials: S
authors.lastname: Dimmeler
authors.forename: Rajiv
authors.initials: R
authors.lastname: Gupta
authors.forename: Wolfhard
authors.initials: W
authors.lastname: Semmler
authors.forename: Hans-Ulrich
authors.initials: HU
authors.lastname: Kauczor
authors.forename: Fabian
authors.initials: F
authors.lastname: Kiessling
mesh_terms: D000818:Animals; D002306:Cardiac Volume; D055424:Cardiac-Gated Imaging Techniques; D004562:Electrocardiography; D006439:Hemodynamics; D007091:Image Processing, Computer-Assisted; D051379:Mice; D008807:Mice, Inbred BALB C; D008809:Mice, Inbred C3H; D023421:Models, Animal; D009203:Myocardial Infarction / Q000000981:diagnostic imaging; D051381:Rats; D055425:Respiratory-Gated Imaging Techniques; D013318:Stroke Volume; D015898:Tomography Scanners, X-Ray Computed; D014057:Tomography, X-Ray Computed / Q000379:methods*