NEMA image quality phantom measurements and attenuation correction in integrated PET/MR hybrid imaging

Abstract

BackgroundIn integrated PET/MR hybrid imaging the evaluation of PET performance characteristics according to the NEMA standard NU 2–2007 is challenging because of incomplete MR-based attenuation correction (AC) for phantom imaging. In this study, a strategy for CT-based AC of the NEMA image quality (IQ) phantom is assessed. The method is systematically evaluated in NEMA IQ phantom measurements on an integrated PET/MR system.MethodsNEMA IQ measurements were performed on the integrated 3.0 Tesla PET/MR hybrid system (Biograph mMR, Siemens Healthcare). AC of the NEMA IQ phantom was realized by an MR-based and by a CT-based method. The suggested CT-based AC uses a template μ-map of the NEMA IQ phantom and a phantom holder for exact repositioning of the phantom on the systems patient table. The PET image quality parameters contrast recovery, background variability, and signal-to-noise ratio (SNR) were determined and compared for both phantom AC methods. Reconstruction parameters of an iterative 3D OP-OSEM reconstruction were optimized for highest lesion SNR in NEMA IQ phantom imaging.ResultsUsing a CT-based NEMA IQ phantom μ-map on the PET/MR system is straightforward and allowed performing accurate NEMA IQ measurements on the hybrid system. MR-based AC was determined to be insufficient for PET quantification in the tested NEMA IQ phantom because only photon attenuation caused by the MR-visible phantom filling but not the phantom housing is considered. Using the suggested CT-based AC, the highest SNR in this phantom experiment for small lesions (<= 13 mm) was obtained with 3 iterations, 21 subsets and 4 mm Gaussian filtering.ConclusionThis study suggests CT-based AC for the NEMA IQ phantom when performing PET NEMA IQ measurements on an integrated PET/MR hybrid system. The superiority of CT-based AC for this phantom is demonstrated by comparison to measurements using MR-based AC. Furthermore, optimized PET image reconstruction parameters are provided for the highest lesion SNR in NEMA IQ phantom measurements.

MR‐based truncation and attenuation correction in integrated PET/MR hybrid imaging using HUGE with continuous table motion

“…Large fluid filled phantoms provide MR artifacts that may lead to fat/water swaps and signal drop‐outs in the Dixon‐based AC maps . For all these reasons, NEMA phantom measurements on the Siemens PET/MR system are today performed by using 3D CT‐based templates of the NEMA phantom for attenuation correction . The same holds true for the other available PET/MR systems from GE and Philips .…”

“…For converting CT data with an energy level of 140 keV to the PET energy level of 511 keV, a bilinear function was used . Both, MR‐based AC techniques, Dixon‐VIBE and HUGE, do not display and consider the PET signal attenuating phantom housing as the CT‐based AC‐map does . For that reason, the housing in the CT‐based AC‐map was retrospectively eliminated by using a segmentation algorithm to ensure better comparability between MR and CT‐based attenuation correction methods.…”

A dual‐tuned13C/1H head coil forPET/MRhybrid neuroimaging: Development, attenuation correction, and first evaluation

“…Thus, the Dixon MR data was only used for position detection; the CT data was used for attenuation correction of the phantom as described below. The MR‐based data was not directly used for attenuation correction of the phantom since the phantom casing and other attenuating parts of the phantom do not provide MR signal and, thus, cannot be accurately corrected …”

Recent Developments in Combined PET/MRI

“…Another challenge is to establish a method of quality control to verify adequate PET quantification and calibration. Two recent studies looked at NEMA phantoms studies on PET/MR machines and suggest that PET/MR QC is feasible, but only when specific, dedicated phantom protocols are used [13,14].…”

“…For a more comprehensive overview, including early advances in the field, the reader is referred to several outstanding prior reviews [2][3][4][5][6][7]. In particular, we highlight recent technical developments, including new methods of attenuation correction, and integration with advanced MR imaging including arterial spin labeling (ASL) and hyperpolarized 13 C spectroscopy, and innovative clinical applications in oncology, cardiology, and neurology.…”