Due to the convenient half-life of 68Ga, considerable work has been done in the development of 68Ga-labeled myocardial agents. Gallium radiopharmaceuticals that localize in the heart are lipophilic in nature and can be either neutral or cationic.
A series of uncharged lipophilic tripodal tris(salicy-laldimine) ligands (Fig. 11.3) have been investigated with limited success . This work was continued, and analogous species were prepared in which alkoxy sub-stituents were placed on the ethane backbone, resulting in more lipophilic ligands . These ligands provided increased uptake in the heart and higher heart-to-blood ratios, but their increased lipophilicity resulted in higher accumulation in the liver. Along a similar vein, the cationic species [68Ga(4,6-MeO2sal)2BAPEN]+ showed significant myocardial uptake and retention, with a heart-to-blood ratio of 45.6 ± 4.0 achieved two hours post injection . This represents an improvement over the analogous neutral salicylaldimine ligands.
Other ligands examined include the neutral complexes of the type 1-aryl-3-hydroxy-2-methyl-4-pyridones, which were found to have heart uptake in animal models . Unfortunately, these species had a short plasma half-life and were only stable long enough for a first-pass extraction by the heart.
The ligands described so far have the gallium in a hexadentate environment, but four co-ordinate ligands have also been examined. These include ligands of the type N2S2 (BAT-TECH)  and fra(2-mercaptoben-zyl)amine (S3N), which showed both brain and myocardial uptake  (Fig. 11.4).
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