A comparison of detectability and image quality in Iodine-124 PET across different PET system generations to optimize the protocol for recurrent thyroid cancer patients

Ziel/Aim In recurrent differentiated thyroid cancer patients, the detectability in I-124 PET can be limited for lesions with low radioiodine uptake. The aim of this study was to evaluate the improvements in detectability and image quality across three generations of PET scanners using different detector technologies. The results are used to suggest protocol optimizations.

Methodik/Methods PET data sets of 10 patients, all with low increasing thyroglobulin or thyroglobulin antibody levels after total thyroidectomy and radioiodine therapies, were included. The data were acquired and reconstructed on three PET systems: A Biograph mCT PET/CT (whole-body, 4-min acquisition time per bed position; OSEM, OSEM+TOF, OSEM-TOF+PSF), a non-TOF Biograph mMR PET/MR (neck region, 4-min and 20-min; OSEM), and a new generation “digital” Biograph Vision PET/CT (whole-body, 4-min; OSEM, OSEM+TOF, OSEM-TOF+PSF). The detection efficacy was calculated for the neck region using the 20-min image on the mMR as reference. Moreover, the image quality was rated on a five-point-scale. The maximum administered I-124 activity to avoid thyroid stunning was estimated using a simple absorbed dose threshold model.

Ergebnisse/Results All detected lesions were in the neck region. Detection efficacy was 8/9 for the Vision (OSEM-TOF and OSEM-TOF+PSF), 4/9 for the Vision (OSEM), 3/9 for the mMR (OSEM) and the mCT (OSEM-TOF+PSF), and 2/9 for the mCT (OSEM and OSEM-TOF). Median image quality was 4 for the Vision (OSEM-TOF and OSEM-TOF+PSF), 3 for the Vision (OSEM), mCT (OSEM-TOF+PSF) as well as mMR (20-min OSEM), 2 for the mCT (OSEM-TOF), 1.5 for the mCT (OSEM), and 1 for the mMR (4-min OSEM). A threshold activity of 100 MBq of I-124 was estimated to avoid stunning.

Schlussfolgerungen/Conclusions The highest detectability and image quality was reached on the new generation digital Biograph Vision using TOF-based image reconstruction algorithms. If available, a digital PET system should preferably be used for imaging of low-uptake lesions. Up to 100 MBq of I-124 activity could be administered. The mostly affected neck region could be emphasized by a selectively prolonged acquisition time.

Publikationsverlauf

Artikel online veröffentlicht:
08. April 2021