Background/Purpose: The uEXPLORER system enables the unique, simultaneous acquisition of PET data over the entire adult human body with a high-sensitivity, alongside concurrent CT data. We hypothesized that these unique characteristics of the uEXPLORER system will yield shorter scan time and reduction in radiation dose, both crucial to an arthritic population. We aimed to prospectively (1) document the glucose uptake patterns – using the radiotracer ¹⁸F-FDG – in arthritic lesions across the entire body of participants with established rheumatoid arthritis (RA), psoriatic arthritis (PsA) and osteoarthritis (OA); and (2) evaluate the influence of shortening the scan time or dose reduction on image quality.

Methods: An ultra-low-dose 18F-FDG scanning protocol was employed in 14 patients (all males, 59±13 yrs) with RA (n=3), PsA (n=8) or OA (n=3) (injected radiotracer dose 75.5±4.4 MBq (1/5th of standard clinical dose)). PET/CT scans were acquired for 20-min starting at 40-min after the injection of 18F-FDG; data were then reconstructed as a single frame (20-min long), four 5-min frames, and twenty 1-min frames, using the same standard protocol. A single volume of interest (VOI) >3cm3 was drawn on the ascending aorta as a background blood pool [BP], and on arthritic lesions to calculate target-to-background ratio (TBR). Coefficient of variation (COV%) was used to estimate image noise and was calculated from the VOIs in the BP.

Results: uEXPLORER scans were successfully conducted for the 14 participants. The entire body was in the field-of-view in all participants. The effective dose from the PET radiotracer and ultra-low-dose CT was approximately 2.7 mSv compared to typically ~14-15 mSv for clinical PET/CT scans on standard scanners. When evaluating the most active lesion, the average TBR was 1.3±0.4. The COV for the 20-min, 5-min, and 1-min scans were (median [range]): 8 [6,13], 15 [8,25], 31 [16, 57]. Qualitatively, all lesions detected on 20-min images could also be seen on 5-min images. Although lesions were still visualized on 1-min frames (TBR=1.4±0.5), the surrounding tissue background was elevated, and the image quality was sub-optimal.

Conclusion: All joints of the body could be visualized simultaneously and assessed in the same phase of radiotracer uptake on uEXPLORER PET/CT scans. Scan times as short as 5-min, with 1/5th of the standard 18F-FDG dose, appeared to be feasible and provide image quality not inferior to the full 20-min PET/CT scan. Further work is warranted to evaluate the methods on more participants, and further develop software-based methods to enhance the image quality of shorter duration scans.

Maximum intensity projection total body images of a 72-year-old male (172 cm, 85 kg) with established diagnosis of psoriatic arthritis. Images were acquired for 20-min duration starting at 40-min after IV injection of 77.6 MBq of 18F-FDG. Images were further subsampled in software into 5-min and 1-min frames. Note that changes in tracer intensity in the left shoulder (arrow) and wrist (arrowhead) are preserved over the different frames.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/feasibility-of-ultra-low-dose-short-duration-total-body-evaluation-of-inflammatory-arthritis-using-uexplorer-18f-fdg-pet-ct/