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Quantitative Assessment of the Influence of Location, Internal Temperature, Idle Time, and Normalization on the Sensitivity of a Mobile PET/CT Scanner

Phoebe Putney Memorial Hospital, Albany, Georgia

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

The superiority of PET/CT and ¹⁸F-FDG imaging in cancer assessment has created the need in rural community hospitals to acquire this technology. However, high cost and lack of patient volume have prohibited these institutions from attaining in-house scanners. By using mobile PET/CT scanners, small rural hospitals are able to deliver this valuable clinical tool to their patients. As mobile PET/CT scanners are shifted from one site to another, however, they are exposed to harsher and frequently varying ecologic conditions that can alter their performance. Because of the importance of the standardized uptake value in cancer evaluation and its linear relationship to the sensitivity of the scanner, we investigated conditions affecting the sensitivity of the mobile PET/CT scanner. Methods: We used a ⁶⁸Ge cylindric phantom with 2 bed frames scanned for 3 min each to simulate a patient to assess quantitatively the influence of location, increase in scanner internal temperature, idle time, and normalization on the sensitivity of the mobile PET/CT scanner. The raw phantom data were acquired and reconstructed with the parameters used for oncology patients. The scanner sensitivity values (Bq/mL) were obtained from circular regions of interest drawn on the phantom images. These values were compared with the true phantom activity concentration after it was decay-corrected to the specific scanning day. Results: The average sensitivity errors (mean ± SD) of this mobile PET/CT scanner at sites 1–4 were 1.84% ± 0.98%, 2.43% ± 2.05%, 2.08% ± 0.91%, and 4.34% ± 1.93%, respectively. A 41.17% increase in the scanner internal temperature decreased its sensitivity by an average of 16.09% ± 3.58%. After day 1 and day 2, its average sensitivity errors were 3.27% ± 0.01% and 2.65% ± 0.02%, respectively. Before and after normalization, the average sensitivity errors were 3.06% ± 1.37% and 2.69% ± 1.69%, respectively. Conclusion: Temperature and normalization affected the sensitivity of the scanner the most and should be monitored closely, with normalization performed as recommended by the manufacturer.

Key Words: instrumentation; molecular imaging; PET/CT; quality assurance; mobile PET/CT sensitivity; parameters affecting sensitivity