The influence of filtered back-projection and iterative reconstruction on partial volume correction in PET

Summary

Aim: We assess the influence of the reconstruction algorithms [OS-EM for the iterative one vs. a filtered back-projection in Fourier space (DiFT)] on partial volume correction in PET employing a fully 3D 3-compartment MR based PVcorrection algorithm. The gray matter voxels in the PET image – after removal of the white matter and cerebrospinal fluid contribution – are corrected voxel-by-voxel using the image resolution. Material, methods: Phantom measurements and one healthy human brain FDG study were carried out. For the OSEM reconstruction, a combination of iteration steps and subset numbers (It/Sub) was used, whereby in case of no-convergence the image resolution had to be fitted. The results from the DiFT reconstruction were equivalent to those obtained from the OSEM reconstruction with 10/32 combination for objects with widespread activity concentration. For the sphere phantom, the mean recovery based on the actual values achieved 99.2% ± 1.8 for all spheres and all reconstruction modes and It/ sub combinations (except for 2/8). In case of the Hoffman 3D brain phantom the mean recovery of the cortical regions was 101% ± 1.2 (the increase based on the uncorrected values: 35.5% ± 1.5), while the subcortical regions reached a mean recovery of 80% with an increase of 43.9% ± 2.5. For the human data, an increase of the metabolized values of several cortical regions ranged between 42% and 48% independent from the reconstruction mode. Conclusions: Our data show that the 3-compartment fully 3-D MR based PV-correction is sensitive to the choice of reconstruction algorithms and to the parameter choice. They indicate that despite improved spatial resolution, the use of the iterative reconstruction algorithm for PV-correction results in similar recovery factors when compared to a correction using DiFT reconstruction, insofar the image resolution values are fitted at the It/Sub combinations.

Zusammenfassung

Ziel: Der Einfluss verschiedener Rekonstruktionsalgorithmen auf die Partialvolumen(PV)-Korrektur von PET-Daten wird untersucht. Material, Methoden: Ein auf MR-Daten basierender dreidimensionaler 3-Kompartment-PV-Korrekturalgorithmus; Phantom-Messungen und eine FDGStudie. Im PET-Bild wurden die Voxel der grauen Substanz mit Hilfe der Bildauflösung nach Entfernung des Beitrages der weißen Substanz und des Liquors korrigiert. Für die OSEM-Rekonstruktion wurde eine Kombination von Iterationsschritten und Anzahl von Subsets (It/Sub) benutzt. Bei zur Konvergenz unzureichenden Gesamtiterationsschritten wurde die Bildauflösung angepasst. Ergebnisse: Die FBPRekonstruktion war äquivalent zu der OSEM-Rekonstruktion mit der 10/32 Kombination für Objekte mit ausgedehnter Aktivitätsverteilung. Für das Kugelphantom erreichte die mittlere Wiedergewinnung bezogen auf die Sollwerte 99,2% ± 1,8 für alle Kugeln und It/Sub Kombinationen (außer für 2/8). Beim Hirnphantom war die mittlere Wiedergewinnung der kortikalen Regionen 101% ± 1,2 (Anstieg bezogen auf die unkorrigierten Werte: 35,5% ± 1,5), wogegen die subkortikalen Regionen eine mittlere Wiedergewinnung von 80% mit einem Anstieg von 43,9% ± 2,5 erreichten. Für die ¹⁸F-FDG-Daten eines menschlichen Gehirns bewegte sich der Anstieg der metabolischen Werte in den kortikalen Regionen zwischen 42% und 48%, unabhängig vom Rekonstruktionsmodus. Schlussfolgerung: Unsere Daten belegen, dass der auf MR-Daten basierende dreidimensionale 3-Kompartment-PV-Korrekturalgorithmus empfindlich gegenüber der Wahl des Rekonstruktionsalgorithmus und seiner Parameter ist. Die iterative Rekonstruktion liefert ähnliche Wiedergewinnungsfaktoren im Vergleich zu einer Korrektur nach einer FBP-Rekonstruktion, wenn die Bildauflösungswerte an die It/Sub Kombination angepasst werden.

Keywords

PET - MR imaging - 3-dimensional partial volume correction - reconstruction - filtered back-projection - OSEM - phantom experiments

Schlüsselwörter

Positronenemissionstomographie - Kernspintomographie - dreidimensionale Partialvolumen-Korrektur - Rekonstruktion - gefilterte Rückprojektion - OSEM - Phantommessungen

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