Motion study on upright patient positioning in walk-through PET: evaluation in a clinical setting

The novel upright walk-through PET (WT-PET) scanner enhances patient throughput compared to the conventional cylindrical PET systems but introduces unique challenges related to patient motion. This study evaluates the rigid body motion of the head, shoulders, chest, and abdomen of patients standing in a WT-PET mock-up scanner, focusing on ergonomic features, including a headrest and hand supports, designed to minimize motion during upright imaging. To contextualize these findings, a patient study using a conventional PET scanner was conducted, along with a control healthy volunteer study involving both WT-PET and conventional PET systems.

Motion data were collected from 30 patients positioned on the WT-PET, 13 patients scanned with a conventional cylindrical PET, and 12 healthy volunteers scanned with both systems. Infrared markers placed at anatomical positions tracked three-dimensional marker positions during 30-s periods of normal breathing and breath-hold instructions in the WT-PET mock-up. Conventional PET scans for patients and healthy volunteers involved 8-min acquisitions. Motion was quantified by calculating the Euclidean distance (ED) of the markers' 3D centroids.

In WT-PET patients, breath-holding significantly reduced mean abdominal motion by 24%, with mean ED decreasing from 2.31 ± 1.32 mm during normal breathing to 1.76 ± 0.81 mm during breath-holding. While only 30% of patients completed a full 30-s breath hold, 80% maintained breath holds longer than 20 s. Age was significantly correlated with increased head motion during normal breathing, whereas body mass index and gender showed no significant effects. Compared with WT-PET healthy volunteers, patient motion on the WT-PET was over three times higher for the head (0.47 ± 0.13 mm vs. 1.51 ± 2.32 mm) and 36% higher for the abdomen (1.70 ± 0.63 mm vs. 2.31 ± 1.32 mm). Relative to patients in conventional PET, WT-PET patients showed slightly lower head motion (1.55 ± 1.05 mm vs. 1.51 ± 2.32 mm), but abdominal motion was 44% lower in WT-PET (2.31 ± 1.32 mm vs. 4.12 ± 3.00 mm), underscoring both the distinct motion patterns and the specific challenges of upright imaging.

The upright WT-PET scanner presents distinct motion control challenges in clinical practice. This study demonstrates that combining ergonomic supports with breath-holding protocols can effectively reduce patient motion during upright PET imaging; however, a full 30-s breath-hold is not feasible for 70% of patients. Since 50% of patients were able to perform a moderate breath-hold, a two-step acquisition can be performed, each comprising 15 s. Moreover, including a healthy volunteer control group and comparisons with conventional PET confirm both the feasibility and the current limitations of the WT-PET.