Myocardial blood flow tracers

A.R. Studenov, M.S. Berridge, Synthesis and properties of F-labeled potential myocardial blood flow tracers, Nucl. Med. Biol. 28 (2001) 683-693. 

PET offers the possibility to quantitatively measure the myocardial blood flow (MBF). MBF tracers can be divided into two groups. The first group is freely diffusible and represented by [ 0]H20. These tracers do not show any specific absorption and their distribution is completely determined by diffusion. Consequently, the measurement of the MBF is based on the first-pass extraction and clearance data. Because of the low heart-to-blood radioactivity ratio, the freely diffusible tracers provide myocardial images with low signal-to-background ratios. The second class is composed of highly extractable heart tracers. The tracer p NjNHs belongs to this family. These radiolabeled compounds are characterized by a selective extraction and retention in the myocardium. The... 

Generator-produced (equation 165) [ Cu]copper(ll) bis (iV -methylthiosemicarbazo-ne)CuPTSM and CuPTSMj have been suggested as a Cu-62 radiopharmaceutical for evaluation of cerebral and myocardial blood flow by PET Complexes 282-387 of copper-67, a convenient radiolabel which has a half-life of 2.58 days (equation 166), have been prepared in >95% radiochemical yield by addition of NaOH solution of the ligand to an acetate-buffered ethanol solution of the ionic radiocopper [Cu(II) in 2N HCl, specific activity 5 x 10 Ci mol ). The biodistribution of each [ Cu] bis(thio-semicarbazone) complex has been determined. Methylation of the terminal amino groups was found to be essential for good cerebral uptake of tracer . ... 

Since fatty acids are the primary substrate for aerobic metabolism within the heart, they are also of interest as potentially useful tracers of myocardial perfusion (12-18). This class of compounds labeled with the positron emitter is being used with specially designed positron imaging (ECT) systems to quantitatively measure the regional distribution of myocardial blood flow in three dimensions (12,13,14). Carbon-11 labeled palmitic acid is also being evaluated as a tracer for studies of myocardial metabolism. Likewise, the o-iodofatty acids, which are structural analogs of the physiologic substrates, have been shown to be taken up by myocardial tissue in proportion to blood flow (15). Iodine-123 labeled 16-iodo-9-hexadecenoic acid (18,17) and 17-iodo-heptadeca-noic acid (18) have been used in conjunction with conventional scintillation cameras for in vivo studies in humans. In all cases with this class of compounds, turnover of the label within the tissue is related to some aspect of metabolism (17,18). 

The biological behavior of myocardial imaging agents has excellently been reviewed in particular in respect of the mechanism of myocardial uptake, the relationship between myocardial blood flow and radiotracer uptake, and redistribution of the tracers (Jain 1999). 

The Rb-82 generator permits serial studies in the same patient as often as every 10 minutes with 20-60 mCi of Rb-82 for rapid bolus intravenous infusion. Inherent in the administration of high levels of Rb-82 activity is the need for precise flow control from an automated system to deliver the desired amount of radioactivity. The development of the alumina column parameters and the elution protocol as well as the automated microprocessor system controller are presented here. Some of the details of this system have been discussed in earlier publications (15,21). Generator produced Rb-82 is used as a diffusible flow tracer in myocardial perfusion studies and as a nondiffusible tracer in brain studies to assess blood brain barrier permeability changes in patients with brain tumors or Alzheimer s type dementia. 

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