A phantom study to evaluate variations in the quantization derived from a new 3D reconstruction algorithm.

Objectives Clinical review of PET-CT patient data reconstructed with a new 3D-OSEM technique (TrueX) have demonstrated improved contrast, resolution and subjective image quality compared to 2D-OSEM. Variations have been noted in the quantitative results derived from reconstructions performed with TrueX versus 2D-OSEM. The aim of this investigation is to evaluate TrueX in a phantom model.

Methods A PET-CT Phantom was imaged with a Siemens Biograph40 PET-CT system. The data was reconstructed using 2D-OSEM (2D) and 2 TrueX reconstructions (HD1 and HD2) with HD2 producing a “smoother” image set. Volumes of interest (VOIs) were created from the attenuation correction CT volume and copied to each PET reconstruction. Standard Uptake Values (SUV) and specific activity measurements were collected for the lesions and background regions.

Results For all lesions, SUV mean and max were increased for both TrueX reconstructions. The largest increase was seen with the SUVs of a 17mm lesion with HD1; SUV mean and SUV max increased 29% and 51% compared to 2D. For the same lesion, HD2 SUV mean and max were 8% and 20% higher. The impact was decreased for lesions <17mm. HD1 and HD2 produced higher lesion:background activity ratios for the smallest lesions. For larger lesions and background, measured SUVs tended toward equality, particularly with HD2. HD1 produced measured specific activity values more accurately.

Conclusions TrueX reconstructions produced higher SUV values than 2D-OSEM. Although TrueX reconstructions produce images of subjectively improved quality, care must be taken when comparing SUV values derived from different reconstruction techniques.