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


METHODS
NEMA 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.


RESULTS
Using 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.


CONCLUSIONS
This 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.
Institute of Medical Physics, University of Erlangen-Nuremberg, Henkestraße 91, 91052, Erlangen, Germany. susanne.ziegler@imp.uni-erlangen.de.
Susanne
S
Ziegler
Siemens Healthcare, Erlangen, Germany.|University of Surrey, Guildford, Surrey, UK.
Bjoern W
BW
Jakoby
Institute of Medical Physics, University of Erlangen-Nuremberg, Henkestraße 91, 91052, Erlangen, Germany.
Harald
H
Braun
Institute of Medical Physics, University of Erlangen-Nuremberg, Henkestraße 91, 91052, Erlangen, Germany.
Daniel H
DH
Paulus
Institute of Medical Physics, University of Erlangen-Nuremberg, Henkestraße 91, 91052, Erlangen, Germany.|Erwin L. Hahn Institute for Magnetic Resonance Imaging, University of Duisburg-Essen, Essen, Germany.|High Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany.
Harald H
HH
Quick
CT-based attenuation correction; Integrated PET/MR hybrid imaging; MR-based attenuation correction; NEMA image quality measurements; PET/MR phantom measurements