Tc-99m for heart disease

Excuse me. i would like to ask some questions. 1. Why does Tc99m sestamibi would reach and stay in hearts, or will Tc99m still goes to another organ? 2. Is the half life of sestamibi making a difference to the heart testing?
                                                  Thanks  

[Jack54]

Technetium Tc99m Sestamibi is a cationic Tc99m complex which has been found to accumulate in
viable myocardial tissue.

Technetium Tc99m decays by isomeric transition with a physical half-life of 6.02 hours.

The myocardial biological half-life is approximately six hours after a rest or exercise injection.
The biological half-life for the liver is approximately 30 minutes after a rest or exercise injection. The
effective half-life of clearance (which includes both the biological half-life and radionuclide decay) for
the heart is approximately 3 hours, and for the liver is approximately 30 minutes, after a rest or exercise injection. The ideal imaging time reflects the best compromise between heart count rate and surrounding organ uptake.



http://www.cardiolite.com/pdfs/cardiolite.pdf