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Sensitivity and Daily Quality Control of a Mobile PET/CT Scanner Operating in 3-Dimensional Mode

Radiology Department, Phoebe Putney Memorial Hospital, Albany, Georgia

Correspondence: For correspondence or reprints contact: Abdelfatihe Belakhlef, PhD, Radiology Department, Phoebe Putney Memorial Hospital, 417 Third Ave., P.O. Box 1828, Albany, GA 31702-1828. E-mail: abelakhl{at}ppmh.org

This study investigated the stability of the sensitivity of a mobile PET/CT scanner and tested a phantom experiment to improve on the daily quality control recommendations of the manufacturer. Unlike in-house scanners, mobile PET/CT devices are subjected to a harsher, continuously changing environment that can alter their performance. The parameter of sensitivity was investigated because it reflects directly on standardized uptake value, a key factor in cancer evaluation. Methods: A ⁶⁸Ge phantom of known activity concentration was scanned 6 times a month for 11 consecutive months using a mobile PET/CT scanner that operates in 3-dimensional mode only. The scans were acquired as 2 contiguous bed positions, with raw data obtained and reconstructed using parameters identical to those used for oncology patients, including CT-extracted attenuation coefficients and decay, scatter, geometry, and randoms corrections. After visual inspection of all reconstructed images, identical regions of interest were drawn on each image to obtain the activity concentration of individual slices. The original activity concentration was then decay-corrected to the scanning day, and the percentage sensitivity of the slice was calculated and graphed. The daily average sensitivity of the scanner, over 11 consecutive months, was also obtained and used to evaluate the stability of sensitivity. Results: Our particular scanner showed a daily average sensitivity ranging from –8.6% to 6.5% except for one instance, when the sensitivity dropped by an unacceptable degree, 34.8%. Conclusion: Our 11-mo follow-up of a mobile PET/CT scanner demonstrated that its sensitivity remained within acceptable clinical limits except for one instance, when the scanner had to be serviced before patients could be imaged. To enhance our confidence in the uniformity of sensitivity across slices, we added a phantom scan to the daily quality control recommendations of the manufacturer.

Key Words: instrumentation; PET/CT; quality assurance; daily QC; mobile PET/CT; sensitivity

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