Optimization of patient dose and image quality for positron emission tomography-computed tomography

The present study focuses on optimizing radiation dose for whole-body PET/CT in patients while minimizing impacts on image quality.

Whole-body PET/CT scans were conducted on two cohorts of consecutive adults. A pre-optimization dose study involving 100 patients was conducted to establish the baseline dose for whole-body PET/CT examinations. A sample of 100 patients was evaluated to assess the reduction in radiation dose following optimization. The effective radiation dose of FDG PET was determined using a conversion coefficient (k) of 0.019 mSv/MBq based on ICRP Publication 106. Absorbed dose coefficients (mGy/MBq) for the bladder, heart, brain, liver, and lungs were obtained from ICRP 106 and multiplied by injected activity to derive organ equivalent doses (mSv). The effective dose (E) from the CT component of the examination was calculated as the product of the dose-length product (DLP) and the relevant conversion coefficient. Image quality was evaluated by measuring the SUV_max of the largest lesion and SUV_mean of the liver. The SUV is defined as the activity concentration (Bq/mL) divided by the injected activity (Bq), normalized to body weight (kg).

A total of 100 adult PET/CT scans were assessed before protocol optimization, including 53 men and 47 women. The average patient-specific E from a mean injected activity of ¹⁸F-FDG at 281.4 MBq was 10.7 ± 3.1 mSv. The five organs that received the highest organ doses were the bladder, heart, brain, liver, and lungs. Following protocol optimization, an additional 100 adult PET/CT scans were evaluated. The average injected ¹⁸F-FDG activity decreased to 200.8 MBq. The average E for PET was 4.1 mSv (range: 2.4-14.9 mSv), the average E for CT was 15.3 mSv (range: 7.2-27.8 mSv), and the average total E was 19.7 mSv (range: 10.0-42.5 mSv). Blinded analysis of image quality indicated no clinically significant degradation in the lower-dose studies. Statistical analysis demonstrated that the higher-dose CT scans provided improved visualization of only the carotid arteries and the posterior triangle region.

Optimizing FDG injection doses based on body weight resulted in a significant reduction in E without compromising image quality in patients weighing 50-115 kg.