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Technologist AbstractsTechnologist Papers II |
1 Department of Nuclear Medicine, TU München, Munich, Germany
2013
Objectives: The SUV in FDG-PET showed to be a good parameter especially for cancer therapy monitoring. For its reliable estimation the total injected activity must be known precisely. However, (partial) paravenous injected activity can induce errors in the SUV calculation. We investigated the amount of paravenous injected activity and its influence on the SUV.
Methods: Within 10 months, 15 patients with an activity deposit at the injection site were registered by the responsible PET/CT technologists. This activity was estimated for each patient by a semiautomatic isocontour algorithm, and physiological tissue activity was subtracted. The method was validated with a cylindrical shaped foam phantom simulating the arm in which various amounts of activity were injected and measured in the PET with a patient like protocol.
Results: In phantom studies injected activity was reproduced with an error <14%. In 12 patients the activity at the injection site was lower then 2 MBq (<1% of inj. act.) hence the influence on the SUV was lower than 1%. In 3 patients the activity was 21, 79 and 72 MBq, leading to a SUV change of 4, 21 and 23%. These amounts are – particularly as they arrive from quite conservative estimations - relevant and can alter therapy monitoring results and hence therapy schemes.
Conclusions: If activity deposits at the injection site become obvious, the amount should be measured: More than 1% of the injected activity should lead to corrections for appropriate SUV values. A corrected data set can be created by entering the injected activity subtracted by the measured paravenous activity into the data header. All these steps can be done by an experienced technologist.
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