Myocardial imaging

Technetium-99m teboroxime is a myocardial imaging agent and is excreted primarily by the hepatobiliary system. It is rapidly taken up by the myocardium and mosdy washes out within 30 minutes. Imaging protocols are performed immediately after injection. The product is a lyopbili ed mixture of boronic acid, dioxine, and other excipients, and the agent is formed with a beating step. 

Despite a common perception that organometallic chemistry essentially belongs in the province of catalysis rather than in vivo applications because of high reactivity of metal carbon bonds, certain organometallic species have very high kinetic stability. Indeed, this point is highlighted by the present wide application of the isonitrile complex Tc(ses-tamibi), [Tc(2-methoxyisobutylisonitrile)6]+, in myocardial imaging. Rhenium tricarbonyl and cyclopentadienyl complexes offer further ex-... 

The search for other myocardial imaging agents goes on, and it remains a challenge for coordination chemists to synthesize new complexes based on the known mechanisms of heart uptake and heart retention. As is obvious from the described compounds, a cationic charge is not a necessity, but the mechanism related to the retention of such compotmds has been the most thoroughly studied and rationalized (Scheme 78). 

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... 

T. Takahashi, S. Nishimura, T. Ido, K. Ishiwata, R. Iwata, Biological evaluation of 5-methyl-branched-chain omega-[ F]-fluorofatty acid A potential myocardial imaging tracer for positron emission tomography, Nucl. Med. Biol. 23 (1996) 303-308. 

I[Pg.967]

Myocardial imaging under II Cation uptake in myocardium Chelating ditertiary phosphine or 20, 613, 614... 

As fatty acids are taken up into the myocardium, Karesh et al.134) incorporated similar structures into polyaminopolycarboxylic acids, radiolabelled them with "mTc and 57Co and examined them for myocardial imaging. These chelators, which possessed chelating moieties similar to DTPA, had a low uptake into the heart (<0.94%) but showed an uptake into the liver of 16%. 

Fig. 3 Novel complexes for myocardial imaging based on the [99mTc(CO)3]+ core...

Fig. 5 Novel fatly acid-based complexes for myocardial imaging...

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