Impact of reduced 18F-MK6240 PET/MR acquisition duration on image quality and tau pathology assessment in patients with cognitive impairment

BACKGROUND: ¹⁸F-MK6240 tau positron emission tomography (PET) is critical in Alzheimer's disease diagnosis and therapeutic monitoring. However, the standard 20-minute static acquisition poses challenges for cognitively impaired patients with limited tolerance for prolonged scans. This study evaluates the feasibility of reducing scan time while maintaining diagnostic accuracy through image quality and quantitative comparisons. METHODS: F-MK6240 PET examinations were retrospectively analyzed. All 20-minutes scans were acquired 90 min post-injection of ~ 3.7 MBq/kg ¹⁸F-MK6240 and reconstructed mainly into 5-, 10-, 15-, and 20-minute datasets. Images were rated on a 5-point scale for overall quality, noise, and diagnostic confidence. Tau status (positive/negative) was the visually defined, and standardized uptake value ratios (SUVr) of Braak regions were calculated using cerebellar gray matter as reference. Agreement across durations was assessed via Bland-Altman analysis. RESULTS: Among the 69 patients, 50 were classified as tau-positive and 19 as tau-negative. Diagnostic efficacy remained consistent across acquisition times compared to the 20-minute reference. The slight reduction in image quality for the 5-minute images relative to the other groups, but none of the images across any of the four durations were rated as poor (score < 3). For 16 predefined regions used for visual assessment of regional tau involvement, both readers showed near-perfect agreement in scoring the extent of involvement (0%, 1-25%, 26-75%, or > 75%) across the four scan durations, as evidenced by Kendall's W coefficients ranging from 0.984 to 1.000 (all p < 0.001). Negative scans showed lower SUVr spread over Braak stages of four different time duration. Bland-Altman analysis demonstrated high agreement in Braak-stage SUVr values between the 20-minute images and the shortened acquisitions with mean differences close to zero across all comparisons. CONCLUSION: Shortening ¹⁸F-MK6240 PET acquisition to 5 min on a modern high-sensitivity PET/MR system results in a small, clinically acceptable decline in image quality. It does not compromise the reliability of visual reads or the stability of semi-quantitative measures compared to the standard 20-minute scan. These findings support the feasibility of 5-minute protocols, which offer practical benefits like reduced motion artifacts and improved patient throughput, as an operationally efficient alternative in clinical tau imaging.