Limits...
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 MR-based μ-map in transversal and coronal orientation only contains discrete attenuation values for water and air, and therefore only corrects for photon attenuation caused by the water content of the phantom and not by the phantom housing materials, as these materials cannot be detected with standard MR imaging. b, c CT-based μ-map contains continuous attenuation values including μ-values for the phantom housing, glass spheres, and styrofoam block used as phantom holder (displayed in c). b and c visualize the same content, however windowing properties were adjusted individually in order to visualize either the phantom content (b) or the styrofoam holder, on which the phantom is placed (c)
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4542864&req=5

Fig4: a MR-based μ-map in transversal and coronal orientation only contains discrete attenuation values for water and air, and therefore only corrects for photon attenuation caused by the water content of the phantom and not by the phantom housing materials, as these materials cannot be detected with standard MR imaging. b, c CT-based μ-map contains continuous attenuation values including μ-values for the phantom housing, glass spheres, and styrofoam block used as phantom holder (displayed in c). b and c visualize the same content, however windowing properties were adjusted individually in order to visualize either the phantom content (b) or the styrofoam holder, on which the phantom is placed (c)

Mentions: The assigned μ-values were restricted to two μ-values for water and air for the performed phantom measurements. Attenuation caused by the styrofoam material in the lung insert was not accounted for. In general, imaging the NEMA IQ phantom filled with pure water on a 3.0 Tesla MR system leads to artifacts and signal inhomogeneities due to standing-RF-wave phenomena and T1 effects, thus affecting MR-based AC of the NEMA phantom in PET/MR hybrid imaging (as shown in [17]). Manually reducing the initial voltage of the RF transmitter adjustment algorithm led to a lower adjusted transmitter voltage of 92.7 Volts, instead of the default value for patient imaging (~300 V), and resulted in fairly homogeneous μ-maps of the NEMA IQ phantom filling (Fig. 1c, Fig. 4a) [17]. Alternatively the addition of substances (e.g. NiSO4) could be considered that decrease the T1 relaxation time of water and as a consequence decrease the mentioned image artefacts, as discussed in [17]. However, this was not further evaluated in the present study.Fig. 4


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 MR-based μ-map in transversal and coronal orientation only contains discrete attenuation values for water and air, and therefore only corrects for photon attenuation caused by the water content of the phantom and not by the phantom housing materials, as these materials cannot be detected with standard MR imaging. b, c CT-based μ-map contains continuous attenuation values including μ-values for the phantom housing, glass spheres, and styrofoam block used as phantom holder (displayed in c). b and c visualize the same content, however windowing properties were adjusted individually in order to visualize either the phantom content (b) or the styrofoam holder, on which the phantom is placed (c)
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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

Fig4: a MR-based μ-map in transversal and coronal orientation only contains discrete attenuation values for water and air, and therefore only corrects for photon attenuation caused by the water content of the phantom and not by the phantom housing materials, as these materials cannot be detected with standard MR imaging. b, c CT-based μ-map contains continuous attenuation values including μ-values for the phantom housing, glass spheres, and styrofoam block used as phantom holder (displayed in c). b and c visualize the same content, however windowing properties were adjusted individually in order to visualize either the phantom content (b) or the styrofoam holder, on which the phantom is placed (c)
Mentions: The assigned μ-values were restricted to two μ-values for water and air for the performed phantom measurements. Attenuation caused by the styrofoam material in the lung insert was not accounted for. In general, imaging the NEMA IQ phantom filled with pure water on a 3.0 Tesla MR system leads to artifacts and signal inhomogeneities due to standing-RF-wave phenomena and T1 effects, thus affecting MR-based AC of the NEMA phantom in PET/MR hybrid imaging (as shown in [17]). Manually reducing the initial voltage of the RF transmitter adjustment algorithm led to a lower adjusted transmitter voltage of 92.7 Volts, instead of the default value for patient imaging (~300 V), and resulted in fairly homogeneous μ-maps of the NEMA IQ phantom filling (Fig. 1c, Fig. 4a) [17]. Alternatively the addition of substances (e.g. NiSO4) could be considered that decrease the T1 relaxation time of water and as a consequence decrease the mentioned image artefacts, as discussed in [17]. However, this was not further evaluated in the present study.Fig. 4

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.