Clinical assessment of lesion detection in time-of-flight FDG-PET imaging

Objectives The aim of this study was to evaluate the clinical utility of time-of-flight (TOF) technology for the detection of lesions in FDG-PET images.

Methods 72 lesions were evaluated in 50 patients (BMI range 16-48) with documented metastatic or primary malignancy. Images were acquired on a Philips Gemini TF PET/CT scanner and reconstructed both with the TOF kernel and without TOF (line of response) using the manufacturer’s software. ROIs were drawn around each lesion and a standardized liver area, serving as uniform background, in both TOF and non-TOF images. Lesions were classified as superficial or deep based on their 3D anatomical position within the body. Lesion detectability was evaluated quantitatively by calculating the difference in lesion to background SUV ratios (L/B) in TOF versus non-TOF. The L/B ratios were statistically analyzed to assess the influence of TOF on detecting lesions with respect to their location and patient BMI.

Results There is an overall improvement in lesion detectability in TOF imaging with increasing BMI. TOF is most advantageous in detecting deep lesions and these gains are potentiated as BMI increases. However, there does not appear to be a significant difference in detection of lesions in individuals with BMI less than 30. Furthermore, superficial lesions demonstrated higher SUV values in non-TOF images by up to 50% (mean 17.1%) in the 43 superficial lesions assessed.

Conclusions Lesion detectability in TOF imaging improves with increasing BMI and the gains are greatest for deep lesions. Further investigation is warranted to validate the accuracy of SUV values in superficial lesions with TOF imaging.