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Technetium-99m methoxyisobutyl isonitrile (RP30) for quantification of myocardial ischemia and reperfusion in dogs
Q S Li1, T L Frank, D Franceschi
1Department of Medicine, Johns Hopkins Medical Institutions, Baltimore, Maryland 21205.
Abstract:
This study was done to determine whether [99mTc]methoxyisobutyl isonitrile (RP30), a nonredistributing myocardial perfusion agent, could be used to quantify regional myocardial blood flow distribution during ischemia and reperfusion, employing sequential injections of tracer, tomographic imaging, and appropriate image subtraction. Dogs underwent transient (6 min) coronary artery occlusion, followed by two paired injections of RP30 and radioactive microspheres combined with tomographic imaging, the first during coronary occlusion and the second after 60 min of reperfusion. To obtain a true image representative of reperfusion, the first set of images was corrected for 99mTc decay and subtracted from the second. During occlusion, tissue microsphere content and scintigraphic RP30 activity in the center of the ischemic region (both expressed as a fraction of the nonischemic region) were closely correlated, although RP30 consistently exceeded microsphere content (0.43 +/- 0.03 vs. 0.24 +/- 0.04, p less than 0.01). Direct tissue counting of RP30 confirmed its relative excess in ischemic myocardium. Reperfusion was successful in 7/8 dogs, with an increase in RP30 activity to 0.98 +/- 0.04 compared to 0.89 +/- 0.03 for microspheres (p = N.S.). In one dog with microsphere-documented persistent ischemia, the RP30 defect was still present after reflow. Our results indicate that because of the lack of myocardial clearance and redistribution, repeat injections of RP30 can be used to quantify serial changes in regional myocardial blood flow.
Insights
Technetium-99m-methoxyisobutyl isonitrile (RP30) can quantify myocardial blood flow during ischemia and reperfusion. Its nonredistributing properties allow for serial assessments of regional blood flow changes.
Area of Science:
- Cardiovascular Imaging
- Nuclear Cardiology
- Myocardial Perfusion Imaging
Background:
- Assessing regional myocardial blood flow (MBF) during ischemia and reperfusion is crucial for understanding heart function.
- Nonredistributing myocardial perfusion agents are needed for accurate serial assessments of MBF.
Purpose of the Study:
- To evaluate the utility of [99mTc]methoxyisobutyl isonitrile (RP30) for quantifying regional MBF distribution during transient ischemia and reperfusion.
- To determine if sequential RP30 injections combined with tomographic imaging can accurately reflect changes in MBF.
Main Methods:
- Transient coronary artery occlusion was induced in dogs, followed by paired injections of RP30 and radioactive microspheres during occlusion and after 60 minutes of reperfusion.
- Tomographic imaging and image subtraction techniques were employed to assess RP30 distribution.
- Direct tissue counting of RP30 was performed to confirm its myocardial uptake.
Main Results:
- RP30 activity in the ischemic region strongly correlated with microsphere content during occlusion, though RP30 levels were higher.
- Successful reperfusion (7/8 dogs) showed RP30 activity returning to near-normal levels, comparable to microsphere data.
- One dog with persistent ischemia showed a persistent RP30 defect post-reperfusion, consistent with microsphere findings.
Conclusions:
- [99mTc]methoxyisobutyl isonitrile (RP30) is a reliable nonredistributing agent for quantifying regional myocardial blood flow.
- Sequential RP30 injections and tomographic imaging enable accurate assessment of serial changes in MBF during ischemic events and recovery.
- RP30's lack of myocardial clearance and redistribution makes it suitable for dynamic perfusion studies.