Compensation for geometric changes during monitoring of 133Xe washout from subcutaneous adipose tissue

A method is described for automatic compensation of changes in geometry during monitoring of 133Xe-washout curves from subcutaneous depots. A 99mTc source is placed on the skin over the 133Xe depot, and both isotopes are counted simultaneously. Variations in the 99mTc activity (corrected for radioactive decay) reflects changes in counting geometry and efficiency and are used for correction of the 133Xe elimination curve. The method permits accurate elimination curves to be obtained from subjects exercising on a bicycle ergometer or running a treadmill.