PD is one of the most common neurodegenerative diseases, characterized by the loss of dopamine neurons in the substantia nigra and striatum [2, 19, 20]. 11C-CFT PET brain imaging, with its specific binding to DAT, plays a vital role in visualizing and assessing the density of presynaptic dopaminergic neurons in the striatum [4]. A notable reduction in 11C-CFT uptake in regions like the caudate nucleus and putamen has been observed in PD patients, underscoring its diagnostic significance [7, 8]. Recent consensus and guidelines suggest obtaining 11C-CFT PET brain images at least 60 min post-injection for a 15–20 min duration [10]. However, such prolonged scan durations can compromise patient comfort and increase the likelihood of movement-induced artifacts. Conversely, excessively short PET scan times might not allow for optimal tracer detection that is essential for accurate dopaminergic function assessment.

According to previous simulation research, the total-body PET/CT scanner (uEXPLORER) could provide gains of 40-fold sensitivity for total-body imaging compared with the conventional PET/CT with short axial extent. Moreover, the detection performance can still be improved by approximately 4–5 fold for single-organ imaging benefiting from its excellent detector efficiency and timing resolution [11, 13, 21, 22]. Previous studies have demonstrated that the acquisition time can be effectively reduced, and high diagnostic efficacy can be achieved in oncological patients using total-body PET/CT. Notably, recent research utilizing total-body PET/CT for 11C-CFT dynamic imaging has provided insights into the real-time internal biodistribution in PD patients [23]. However, there have been few studies about rapid acquisition of 11C-CFT PET brain imaging for PD assessment using a total-body PET/CT scanner. Therefore, this study sought to identify the shortest viable PET scan duration that still preserves adequate image quality using 11C-CFT, addressing this critical need in PD imaging.

Our findings showed that for the G900, G720, and G600 images, the overall image quality, image noise, and lesion conspicuity scores were consistently high. The scan duration of 600 s sufficiently preserved image quality necessary for accurate assessment of key brain regions like the caudate nucleus and putamen, which are crucial for early detection and disease progression monitoring. Subjective image quality assessments indicated that the G600 image maintained a relatively high overall image quality score (4.9 ± 0.3), with minimal compromise in image noise and lesion conspicuity. Semi-quantitative measurements further corroborated that SUVmean and DAT binding values at G600 of various regions of interest only exhibit minor reductions compared to longer durations, suggesting that the quantitative integrity of the PET images was still preserved at this duration. As shown in Fig. 3, when the scan durations were below 600 s, image noise was significantly enhanced and the boundaries of the basal ganglia structures were gradually blurred, especially the posterior putamen, where CFT uptake showed the most paramount reduction, leading to poor lesion conspicuity. Therefore, this study indicated that the scan duration of 600 s appeared to be a reasonable balance between the need for high-quality imaging and ensuring patient comfort in a clinical setting for PD assessment using 11C-CFT total-body PET/CT.

A 54-year-old man with PD underwent 11C-CFT PET/CT brain scan. The axial images showed decreased CFT uptake in bilateral putamen. The serial PET brain images were generated by shortening the length of frame duration used for reconstruction. The overall image quality scores of the G900 to G30 images were 5, 5, 5, 4, 4, 3, 3, 2, and 1, respectively

Although previous studies such as those utilizing total-body PET/CT in oncology have explored similar concepts [14,15,16, 24], our study focusing on 11C-CFT in PD fills a specific niche. Differing from the primary concern of lesion detectability in oncological PET imaging, the uniformity and consistency of tracer uptake are crucial in PD assessment. Notably, we observed in this study that although noise affected lesion visualization in areas with reduced CFT uptake, qualitative diagnoses remained largely unaffected due to the inherent “negative imaging” characteristics of CFT PET scans, except in images with excessive noise at lower photon counts (G120-G30). The lesion detectability remained high (100%) until a scan duration of 180 s, but significantly dropped at shorter durations. In particular, the image quality scores of all G300 images were acceptable (≥ 3 points), which was considered to meet the needs of clinical diagnosis.

Moreover, in previous studies investigating low dose of 18F-FDG PET, the objective analyses showed pronounced increase in background SUVmax and SD as the acquisition time reduced [14,15,16]. This increase was explained by noise amplification with reduced scan duration, therefore resulting in a higher maximum pixel value in the background measurement. Our findings demonstrated stability in SUVmean values of the reference region (occipital cortex) across various scan durations in CFT PET, highlighting that SUVmean is a stable parameter for PET assessment and provides a reliable metric in low-count images. Besides, our study demonstrated a trend of decrease in SUVmean and DAT binding of caudate nucleus and putamen as the scan time reduced, which can be attributed to reduced photon detection with shorter scan duration. Besides, a notable observation from our study was the increased change in lesion DAT binding with reduced scan time. This pattern aligned with findings from previous studies and was likely attributable to amplified noise in shorter-duration scans [15]. However, an interesting aspect of our data was the relatively low variability in the DAT binding of the posterior putamen. This observation can be explained by the inherently low DAT binding in this region, a consequence of the pathological characteristics of PD.

The limitations of this study include its small sample size and retrospective design, which may affect the generalizability of the findings. Furthermore, the study’s applicability is primarily limited to the total-body scanner, posing restrictions in broader extrapolation. While reducing PET scan durations in PD assessments could significantly enhance patient comfort and improve the efficiency of medical systems, it is imperative to cautiously evaluate the potential implications on image quality and diagnostic accuracy. A notable concern is that diminished image quality due to shortened scan times might adversely affect the effectiveness of semi-quantitative analysis in assessing the efficacy of therapeutic interventions. Besides, more 11C-CFT brain PET data using total-body PET/CT scanner need to be further collected to establish normal reference database for more accurate quantification. These considerations necessitate further investigation in subsequent studies. Advancements in PET imaging technology and the integration of innovative algorithms may provide solutions to these challenges, potentially reducing the required scan time while maintaining high-quality images.