Objectives: This study was designed to evaluate the biodistribution and blood clearance characteristics of 99mTcN-15C5 and its potential as a myocardial perfusion radiotracer.
Methods: Five normal mongrel dogs were injected with 99mTcN-15C5 intravenously. Blood samples were collected at 0.5, 1, 2, 3, 4, 5, 10, 15, and 30 min postinjection (p.i.). Anterior planar images were acquired at 5, 15, 30, 60, 90, and 120 min p.i. Regions of interest (ROIs) were drawn around heart, liver, and lungs. The raw activity in each ROI was expressed as counts/pixel/min. Heart/liver and heart/lung ratios were calculated by dividing the mean counts in heart ROI by the mean counts in liver and lung ROI, respectively. For comparison, 99mTc-sestamibi was also evaluated in the same five dogs. In dogs with coronary stenoses, single photon emission computed tomography images were acquired at 30, 60, and 120 min after administration of 99mTcN-15C5 with/without adenosine.
Results: 99mTcN-15C5 and 99mTc-sestamibi had very similar blood clearance characteristics during the first 30 min p.i. The heart/liver ratio of 99mTcN-15C5 increased from 0.48±0.05 at 5 min p.i. to 1.85±0.11 at 120 min p.i., whereas the heart/liver ratio of 99mTc-sestamibi was improved only slightly from 0.45±0.04 at 5 min p.i. to 0.74±0.15 at 120 min p.i. SPECT imaging studies in canines with coronary stenoses indicated that good visualization of the perfusion defect could be achieved at 30 min after administration of 99mTcN-15C5 with the adenosine stress.
Conclusion: The combination of high heart uptake and rapid liver clearance makes 99mTcN-15C5 a promising new radiotracer for myocardial perfusion imaging.