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

Ziegler S, Jakoby BW, Braun H, Paulus DH, Quick HH - EJNMMI Phys (2015)

Bottom Line: The PET image quality parameters contrast recovery, background variability, and signal-to-noise ratio (SNR) were determined and compared for both phantom AC methods.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.

View Article: PubMed Central - PubMed

Affiliation: Institute of Medical Physics, University of Erlangen-Nuremberg, Henkestraße 91, 91052, Erlangen, Germany. susanne.ziegler@imp.uni-erlangen.de.

ABSTRACT

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.

Conclusion: 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.

No MeSH data available.


a The NEMA IQ phantom. b MR imaging (in-phase image) of the NEMA IQ phantom using the MR AC Dixon VIBE sequence showing only fluid phantom filling (water). The phantom housing (Plexiglas) is not visible in MR imaging and thus, also not considered in the MR-based μ-map of the phantom (c). Note that the glass spheres are displayed as signal voids (dark rims in b) that are segmented as water in the MR-based μ-map (c)
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Fig1: a The NEMA IQ phantom. b MR imaging (in-phase image) of the NEMA IQ phantom using the MR AC Dixon VIBE sequence showing only fluid phantom filling (water). The phantom housing (Plexiglas) is not visible in MR imaging and thus, also not considered in the MR-based μ-map of the phantom (c). Note that the glass spheres are displayed as signal voids (dark rims in b) that are segmented as water in the MR-based μ-map (c)

Mentions: To obtain quantitative PET images that can be used to determine the scanner performance parameters, the acquired PET data need to be corrected for attenuation of the photons caused by the scanned object as well as by the attenuating hardware components of the system [10]. In PET/CT imaging, information about the attenuating characteristics of the scanned object is derived from the CT scan itself. In PET/MR patient imaging, MR-based attenuation correction (AC) methods are applied to correct for attenuation caused by human tissue [11], however, the applicability in phantom imaging has not yet been quantified. Current MR-based AC only considers the fluid phantom filling as it provides sufficient MR signal, but it does not correct for plastic or glass materials commonly used in PET phantom housings, as these cannot be reliably detected in standard MR imaging (Fig. 1).Fig. 1


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

Ziegler S, Jakoby BW, Braun H, Paulus DH, Quick HH - EJNMMI Phys (2015)

a The NEMA IQ phantom. b MR imaging (in-phase image) of the NEMA IQ phantom using the MR AC Dixon VIBE sequence showing only fluid phantom filling (water). The phantom housing (Plexiglas) is not visible in MR imaging and thus, also not considered in the MR-based μ-map of the phantom (c). Note that the glass spheres are displayed as signal voids (dark rims in b) that are segmented as water in the MR-based μ-map (c)
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4542864&req=5

Fig1: a The NEMA IQ phantom. b MR imaging (in-phase image) of the NEMA IQ phantom using the MR AC Dixon VIBE sequence showing only fluid phantom filling (water). The phantom housing (Plexiglas) is not visible in MR imaging and thus, also not considered in the MR-based μ-map of the phantom (c). Note that the glass spheres are displayed as signal voids (dark rims in b) that are segmented as water in the MR-based μ-map (c)
Mentions: To obtain quantitative PET images that can be used to determine the scanner performance parameters, the acquired PET data need to be corrected for attenuation of the photons caused by the scanned object as well as by the attenuating hardware components of the system [10]. In PET/CT imaging, information about the attenuating characteristics of the scanned object is derived from the CT scan itself. In PET/MR patient imaging, MR-based attenuation correction (AC) methods are applied to correct for attenuation caused by human tissue [11], however, the applicability in phantom imaging has not yet been quantified. Current MR-based AC only considers the fluid phantom filling as it provides sufficient MR signal, but it does not correct for plastic or glass materials commonly used in PET phantom housings, as these cannot be reliably detected in standard MR imaging (Fig. 1).Fig. 1

Bottom Line: The PET image quality parameters contrast recovery, background variability, and signal-to-noise ratio (SNR) were determined and compared for both phantom AC methods.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.

View Article: PubMed Central - PubMed

Affiliation: Institute of Medical Physics, University of Erlangen-Nuremberg, Henkestraße 91, 91052, Erlangen, Germany. susanne.ziegler@imp.uni-erlangen.de.

ABSTRACT

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.

Conclusion: 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.

No MeSH data available.