Considerations for Positioning Arthritic Patients on the uExplorer Total-Body PET/CT System
2020
3125 Objectives: The uEXPLORER total-body PET/CT scanner, with its 194cm field-of-view(FOV), provides a unique opportunity to examine systemic inflammatory burden of arthritic conditions, such as Rheumatoid or Psoriatic Arthritis. However, due to functional constraints and joint symptoms in patients, immobilization of extremities and patient comfort during scanning are of key importance for reducing image artifacts resulting from intrascan motion. We assessed immobilization schemes for the arms, hands, fingers and feet in an arthritic population with the additional consideration of patient position within the scanner’s units (detector rings). Methods: Fourteen participants with arthritis from a prospective IRB-approved study were injected with 75.5 (+4.4) MBq of [18F]FDG. A 20-minute PET/CT scan was acquired after a 40-minute uptake. Two different arm positions and three hand/finger immobilization schemes were considered. The study participants were positioned supine on the scan table; arms down and hands on top of the pelvis/thighs over fluidized positioners, or with elbows bent and hands on fluidized positioners over the chest. Both positions utilized support straps to provide stability at the elbows. Method 1 of hand/finger immobilization utilized a flat hand-shaped plastic mold with flexible Velcro straps to stabilize the fingers and wrist. Method 2 used gauze pads positioned at the metacarpophalangeal joints to separate the fingers and a strap to immobilize the hands on the fluidized positioners. Method 3 utilized foam finger spacers at the metacarpophalangeal and distal interphalangeal joints with hands strapped to fluidized positioners. Velcro straps were used to ensure immobility of the feet. The PET/CT images were reconstructed in 1-min frames and participant motion was evaluated visually over the 20 frames. Motion was then classified into three categories: no motion, minimal motion and gross motion. Results: Positioning the arms down on top of pelvis/thighs allowed the upper extremities to be placed within the most sensitive area of the scanner and was found to be the most comfortable position across all 14 participants. However, in participants with a larger abdominal girth (n=2), the hands in this position were outside the scanner’s transaxial FOV; therefore, elbows bent and hands over the chest allow for visualization of fingers and wrist, but sub-optimal imaging of the elbows. Imaging with participants’ arms up and outstretched above the head was considered, but it would place the anatomy of interest outside of the most sensitive units of the scanner and was reported to be uncomfortable or unachievable in majority of the participants (n=13). Method 1 for hand/finger positioning, while ideal for image analysis due to finger extension(n=1), was unable to provide comfort in participants with wrist and finger manifestations (n=13), commonly presented by arthritic patients. Method 2 was not successful at immobilization of the fingers because of the malleability of the gauze (n=3). Method 3 allowed for a reasonable separation between the fingers (n=10), however major finger or hand movement was still noted in several participants. Patient comfort for Methods 2 and 3 was high. No movement was found in 3 participants, gross motion was found in 3 participants, while minimal movement was found in 8 participants. Placing Velcro straps around the participant9s feet was essential to immobilize the feet, although intrascan motion >1 cm was noted in 2 out of the 14 participants. Conclusion: Amongst the immobilization schemes evaluated, imaging with the arms down; hands either on top of the pelvis/thighs or over the chest (when abdominal girth was large), using foam finger separators and hands strapped to fluidized positioners, allowed for the greatest participant comfort and the highest level of immobilization. We found that these techniques while valuable did not ensure complete immobilization in every participant evaluated.
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