Towards fast whole-body PET/MR: Investigation of PET image quality versus reduced PET acquisition times
Purpose The trend towards faster acquisition protocols in whole-body positron emission tomography/ magnetic resonance (PET/MR) arises the question of whether short PET data acquisition protocols in a whole-body multi-station context allow for reduced PET acquisition times while providing adequate PET image quality and accurate quantification parameters. The study goal is to investigate how reducing PET acquisition times affects PET image quality and quantification in whole-body PET/MR in
... dy PET/MR in patients with oncologic findings. Conclusions Reconstruction of PET data with different time intervals has shown that 2 minutes acquisition time per bed position instead of 4 minutes is sufficient to provide accurate lesion detection and adequate image quality in a clinical setting, despite the trends to lower image quality with shorter PET acquisition times. This provides latitude for potential reduction of PET acquisition times in fast PET/MR whole-body examinations. (MR) imaging into one whole-body PET/MR system combines the excellent soft-tissue contrast and several functional imaging parameters provided by MR with the high sensitivity and quantification of radiotracer metabolism supplied by PET   . From the clinical introduction of the new hybrid method   , PET/MR imaging has shown great potential in various applications over the recent years. An inherent advantage of PET/MR over PET/CT is that MR provides a wide range of soft tissue contrasts and potentially adds diagnostic information complementary to the PET data. However, in most PET/MR imaging protocols this comes at the at the cost of considerably increased PET/MR acquisition times when compared to PET/CT. This is because MR requires the acquisition of multiple different imaging sequences (e.g. T1, T2, diffusion weighted imaging) to generate a choice of soft tissue contrasts per bed position. The repeated acquisition of multiple sequences adds to the PET/MR acquisition times per bed position    . In conventional PET/CT imaging, the data acquisition approximately lasts 2 minutes per bed position with PET being the time limiting factor. Standard clinical whole-body MR protocols today may last between 5-10 minutes per bed position or even longer depending on the clinical indication. A clinical routine whole-body PET/MR protocol including 4-5 bed positions with a duration of 5-10 minutes per bed position mainly consists of five MR sequences (T1-weighted Dixon-VIBE, diffusion weighted EPI, T2-weighted TIRM, T2-weighted HASTE and T1-weighted VIBE post contrast). This prolonged whole-body MR protocol ensures different soft tissue for diagnostic assessment in a variety of oncologic indications. Thus, in such rather lengthy protocols, MR is currently the time limiting factor in PET/MR imaging. Long acquisition times for whole-body PET/MR have been identified as a main limitation of PET/MR vs. PET/CT, reducing patient comfort and patient throughput . Since the clinical introduction of PET/MR, investigators have worked on the optimization of the wholebody PET/MR imaging workflow and on shortening of the overall exam duration   . Recent efforts have now demonstrated that defined hybrid imaging protocols allow for further reduced MR imaging protocols       . In these studies, sequences and contrast weightings providing only redundant diagnostic information have been eliminated from the list of MR protocols while maintaining diagnostic PET/MR information in specific clinical settings. Thus, PET/MR imaging workflow was streamlined and a fast, but still diagnostic imaging protocol was realized in these studies    . Updated whole-body ultra-fast MR protocols in clinical routine have recently been shortened to 3 to 5 minutes per bed position and might fall within the scope of PET being the time limiting factor in PET/MR. In these ultra-fast MR protocols only three MR sequences are used for reading: a T1-weighted Dixon-VIBE for attenuation correction, and a T2-weighted HASTE and T1-weighted VIBE post contrast for high-resolution diagnostic MR imaging.