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Technical Briefs

Left Ventricular Pressure Gating in Ovine Cardiac Studies: A Software-Based Method

[+] Author and Article Information
Gabriel Acevedo-Bolton

Department of Radiology,
University of California,
San Francisco, CA 94143

Zhihong Zhang

Department of Surgery,
Department of Veterans Affairs Medical Center,
San Francisco, CA 94121

Arthur W. Wallace

Department of Anesthesia,
University of California,
San Francisco, CA 94143;
Department of Veterans Affairs Medical Center,
San Francisco, CA 94121

Julius M. Guccione

Department of Surgery,
University of California,
San Francisco, CA 94143;
Department of Veterans Affairs Medical Center,
San Francisco, CA 94121

David A. Saloner

Departments of Radiology,
University of California,
San Francisco, CA 94143;
Department of Veterans Affairs Medical Center,
San Francisco, CA 94121

Mark B. Ratcliffe

Department of Surgery,
University of California,
San Francisco, CA 94143;
Department of Veterans Affairs Medical Center,
San Francisco, CA 94121
e-mail: mark.ratcliffe@med.va.gov

1Corresponding author.

Contributed by the Bioengineering Division of ASME for publication in the Journal of Biomechanical Engineering. Manuscript received July 3, 2012; final manuscript received December 14, 2012; accepted manuscript posted January 10, 2013; published online February 11, 2013. Assoc. Editor: Ender A. Finol.

J Biomech Eng 135(3), 034502 (Feb 11, 2013) (5 pages) Paper No: BIO-12-1261; doi: 10.1115/1.4023370 History: Received July 03, 2012; Revised December 14, 2012; Accepted January 10, 2013

Cardiac imaging using magnetic resonance requires a gating signal in order to compensate for motion. Human patients are routinely scanned using an electrocardiogram (ECG) as a gating signal during imaging. However, we found that in sheep the ECG is not a reliable method for gating. We developed a software based method that allowed us to use the left ventricular pressure (LVP) as a reliable gating signal. By taking the time derivative of the LVP (dP/dt), we were able to start imaging at both end-diastole for systolic phase images, and end-systole for diastolic phase images. We also used MR tissue tagging to calculate 3D strain information during diastole. Using the LVP in combination with our digital circuit provided a reliable and time efficient method for ovine cardiac imaging. Unlike the ECG signal the left ventricular pressure was a clean signal and allowed for accurate, nondelay based triggering during systole and diastole.

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Figures

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Fig. 1

Schematic of experimental setup. Note that cables pass through RF filters.

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Fig. 2

Comparison of optimal ECG and trigger pulse from software-based timing circuit. Figure 2(a) shows the ECG trace on the top panel and systolic triggering from the dP/dt trigger in the bottom. Arrows, indicating where the scanner is detecting the trigger point, coincide at the R-wave as seen on the ECG. Figure 2(b) shows the ECG trace on the top panel and diastolic triggering from the dP/dt trigger in the bottom. In this case, the trigger point is offset from the R-wave peak shown on the ECG. These plots also show that the dP/dt signal triggers on every other heartbeat.

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Fig. 3

The same image acquired with three different cabling methods. (a) Transducer cables passed through physical ports in wall, (b) Transducer cables disconnected from computer, and (c) Transducer signals passed through low-pass RF filters.

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Fig. 4

Sequence of short axis slice which has been tagged, going through the first eight time frames of diastole (TR = 40 ms). The papillary muscles are seen inside the white contour.

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Fig. 5

(a) Map of segment locations in the Left Ventricle. (b), (c) and (d) show the circumferential, longitudinal and radial strain components, respectively.

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