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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.


Images of the first five iterations reconstructed with 3D OP-OSEM for different matrix and Gaussian filter sizes and using CT-based AC. Note: increasing the number of iterations is associated with increasing lesion sharpness while also increasing background noise. This also applies when increasing the image matrix size from 172 x 172 to 344 x 344
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Fig6: Images of the first five iterations reconstructed with 3D OP-OSEM for different matrix and Gaussian filter sizes and using CT-based AC. Note: increasing the number of iterations is associated with increasing lesion sharpness while also increasing background noise. This also applies when increasing the image matrix size from 172 x 172 to 344 x 344

Mentions: When comparing two different matrix sizes (344 x 344 and 172 x 172), it can be observed that with higher image matrix the contrast increases but at the same time it causes an increase in noise. These effects can also be perceived in the phantom images in Fig. 6.Fig. 6


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)

Images of the first five iterations reconstructed with 3D OP-OSEM for different matrix and Gaussian filter sizes and using CT-based AC. Note: increasing the number of iterations is associated with increasing lesion sharpness while also increasing background noise. This also applies when increasing the image matrix size from 172 x 172 to 344 x 344
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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

Fig6: Images of the first five iterations reconstructed with 3D OP-OSEM for different matrix and Gaussian filter sizes and using CT-based AC. Note: increasing the number of iterations is associated with increasing lesion sharpness while also increasing background noise. This also applies when increasing the image matrix size from 172 x 172 to 344 x 344
Mentions: When comparing two different matrix sizes (344 x 344 and 172 x 172), it can be observed that with higher image matrix the contrast increases but at the same time it causes an increase in noise. These effects can also be perceived in the phantom images in Fig. 6.Fig. 6

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.