Cardiac Imaging Using a Radioisotope As part of her nuclear stress test, Simone s...

Cardiac Imaging Using a Radioisotope

As part of her nuclear stress test, Simone starts to walk on the treadmill. When she reaches the maximum level, Dr. Paul injects a radioactive dye with Tl-201 with an activity of 74 MBq. The radiation emitted from areas of heart is detected by a scanner and produces images of her heart muscle. A thallium stress test can determine how effectively coronary arteries provide blood to the heart. If Simone has any damage to her coronary arteries, reduced blood flow during stress would show a narrowing of an artery or a blockage. After Simone rests for 3 h, Dr. Paul injects more dye with Tl-201 and she is placed under the scanner again. A second set of images of her heart muscle at rest are taken. When Simone’s doctor reviews her scans, he assures her that she had normal blood flow to her heart muscle, both at rest and under stress.

How many days will it take until the activity of the Tl-201 in Simone’s body is one-eighth of the initial activity?