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Control/Tracking Number : 04-237-SCMR
Activity :Abstract
Current Date/Time : 9/12/2003 3:59:30 PM

Low Dose Dobutamine Stress 3D Tagged and First-Pass Contrast-enhanced Magnetic Resonance Imaging for Regional Detection of Stunned Myocardium

Izlem Izbudak, MD1, Walter G. O'Dell, PhD2, Luciano Amado, MD1, Raymond C. Boston, PhD3, Dara L. Kraitchman, VMD, PhD1.
1Radiology, Johns Hopkins University, Baltimore, MD, USA, 2Radiology, University of Rochester, Rochester, NY, USA, 3University of Pennsylvania, Kennett Square, PA, USA.

Introduction: The differentiation of reversibly injured, i.e., stunned, myocardium from irreversibly injured myocardium is important for driving clinical therapy.

Purpose: A canine model of transient ischemia was used to investigate the role of low dose dobutamine stress (LDDS) tagged and perfusion MRI for the detection of stunned myocardium and recovery at 1 week.

Methods: Five mongrel dogs underwent a 20 minute coronary artery balloon occlusion followed by reperfusion to create myocardial stunning. Three-dimensional tagged MRI (fast, breath-hold, segmented k-space, ECG-gated gradient echo acquisition) was performed at rest and during 5 ug/kg/min dobutamine stress at one week before (baseline), ~1hr after, and one week after transient ischemia (recovery) on a 1.5T MR scanner. Short-axis and rotating long-axis tagged images were obtained spanning the left ventricle. The tag lines detection and tracking and 3D circumferential strain in the midwall were calculated in 12 circumferential segments at 8 anatomic levels using custom software. Myocardial tissue at risk of stunning (S) was identified based on <0.1 ml/g/min microsphere blood flow during occlusion and compared to remote (R) tissue. Early after reperfusion, 248 S segments and 424 R segments were identified for statistical analysis. A linear regression analysis of strain versus time yielded systolic strain rate (SSR) comparing the same S and R segments at baseline and recovery. First-pass CE MRI (saturation recovery fast gradient echo EPI hybrid sequence) was performed in the 4-6 short-axis planes after a 0.05 mmol/kg iv bolus of Gd-DTPA. TTC staining was performed post-mortem.

Results: TTC staining demonstrated 100% viable myocardium at euthanasia. Signal intensity time curves of CE MRI were similar between stunned (S) and non-stunned remote (R) tissue (P=NS). SSR was reduced in stunned tissue in the first hours after ischemia relative to remote at rest (-0.15 0.12 S vs. -0.32 0.10 R, P<0.05). LDDS in the first hours of reperfusion showed improved function in stunned tissue (-0.30 0.16 LDDS vs -0.15 0.12 rest, P<0.05) as well as remote ( -0.45 0.23 LLDS vs 0.32 0.10 rest, P<0.05 ). Moreover, S regions showed complete recovery of function at 1 week at rest (-0.53 0.23 S vs -0.44 0.20 R, P=NS ). There was no significant change in SSR at rest in R regions from baseline to reperfusion and recovery. LDDS caused significant increase in SSR in all regions at each time point of MR imaging.

Conclusion: LDDS MRI with 3D myocardial tagging can non-invasively identify dysfunctional myocardium that can be recruited, which is the hallmark of stunned tissue. CE-MRI did not demonstrate any differences between stunned and non-stunned tissue. Thus, tagged serial MRI exams may be sufficient to demonstrate stunned tissue and recovery at 1 week.

Category (Complete):  Experimental MRI
Additional Information (Complete):
      : Oral or Poster Presentation
      : Yes
      : Yes

Status: Complete
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