@misc{BeyerWeigertPalmetal., author = {Beyer, Thomas and Weigert, Markus and Palm, Christoph and Quick, Harald H. and M{\"u}ller, Stefan P. and Pietrzyk, Uwe and Vogt, Florian and Martinez, M.J. and Bockisch, Andreas}, title = {Towards MR-based attenuation correction for whole-body PET/MR imaging}, series = {The Journal of Nuclear Medicine}, volume = {47}, journal = {The Journal of Nuclear Medicine}, number = {Suppl. 1}, pages = {384P}, subject = {Kernspintomografie}, language = {en} } @article{WeigertPietrzykMuelleretal., author = {Weigert, Markus and Pietrzyk, Uwe and M{\"u}ller, Stefan P. and Palm, Christoph and Beyer, Thomas}, title = {Whole-body PET/CT imaging}, series = {Zeitschrift f{\"u}r Medizinische Physik}, volume = {18}, journal = {Zeitschrift f{\"u}r Medizinische Physik}, number = {1}, doi = {10.1016/j.zemedi.2007.07.004}, pages = {59 -- 66}, abstract = {Aim Combined whole-body (WB) PET/CT imaging provides better overall co-registration compared to separate CT and PET. However, in clinical routine local PET-CT mis-registration cannot be avoided. Thus, the reconstructed PET tracer distribution may be biased when using the misaligned CT transmission data for CT-based attenuation correction (CT-AC). We investigate the feasibility of retrospective co-registration techniques to align CT and PET images prior to CT-AC, thus improving potentially the quality of combined PET/CT imaging in clinical routine. Methods First, using a commercial software registration package CT images were aligned to the uncorrected PET data by rigid and non-rigid registration methods. Co-registration accuracy of both alignment approaches was assessed by reviewing the PET tracer uptake patterns (visual, linked cursor display) following attenuation correction based on the original and co-registered CT. Second, we investigated non-rigid registration based on a prototype ITK implementation of the B-spline algorithm on a similar targeted MR-CT registration task, there showing promising results. Results Manual rigid, landmark-based co-registration introduced unacceptable misalignment, in particular in peripheral areas of the whole-body images. Manual, non-rigid landmark-based co-registration prior to CT-AC was successful with minor loco-regional distortions. Nevertheless, neither rigid nor non-rigid automatic co-registration based on the Mutual Information image to image metric succeeded in co-registering the CT and noAC-PET images. In contrast to widely available commercial software registration our implementation of an alternative automated, non-rigid B-spline co-registration technique yielded promising results in this setting with MR-CT data. Conclusion In clinical PET/CT imaging, retrospective registration of CT and uncorrected PET images may improve the quality of the AC-PET images. As of today no validated and clinically viable commercial registration software is in routine use. This has triggered our efforts in pursuing new approaches to a validated, non-rigid co-registration algorithm applicable to whole-body PET/CT imaging of which first results are presented here. This approach appears suitable for applications in retrospective WB-PET/CT alignment. Ziel Kombinierte PET/CT-Bildgebung erm{\"o}glicht verbesserte Koregistrierung von PET- und CT-Daten gegen{\"u}ber separat akquirierten Bildern. Trotzdem entstehen in der klinischen Anwendung lokale Fehlregistrierungen, die zu Fehlern in der rekonstruierten PET- Tracerverteilung f{\"u}hren k{\"o}nnen, falls die unregistrierten CT-Daten zur Schw{\"a}chungskorrektur (AC) der Emissionsdaten verwendet werden. Wir untersuchen daher die Anwendung von Bildregistrierungsalgorithmen vor der CT-basierten AC zur Verbesserung der PET-Aufnahmen. Methoden Mittels einer kommerziellen Registrierungssoftware wurden die CT-Daten eines PET/CT- Tomographen durch landmarken- und intensit{\"a}tsbasierte rigide (starre) und nicht-rigide Registrierungsverfahren r{\"a}umlich an die unkorrigierten PET-Emissionsdaten angepasst und zur AC verwendet. Zur Bewertung wurden die Tracerverteilungen in den PET-Bildern (vor AC, CT-AC, CT-AC nach Koregistrierung) visuell und mit Hilfe korrelierter Fadenkreuze verglichen. Zus{\"a}tzlich untersuchten wir die ITK-Implementierung der bekannten B-spline basierten, nicht-rigiden Registrierungsans{\"a}tze im Hinblick auf ihre Verwendbarkeit f{\"u}r die multimodale PET/CT-Ganzk{\"o}rperregistrierung. Ergebnisse Mittels landmarkenbasierter, nicht-rigider Registrierung konnte die Tracerverteilung in den PET-Daten lokal verbessert werden. Landmarkenbasierte rigide Registrierung f{\"u}hrte zu starker Fehlregistrierung in entfernten K{\"o}rperregionen. Automatische rigide und nicht-rigide Registrierung unter Verwendung der Mutual-Information-{\"A}hnlichkeitsmetrik versagte auf allen verwendeten Datens{\"a}tzen. Die automatische Registrierung mit B-spline-Funktionen zeigte vielversprechende Resultate in der Anwendung auf einem {\"a}hnlich gelagerten CT-MR-Registrierungsproblem. Fazit Retrospektive, nicht-rigide Registrierung unkorrigierter PET- und CT-Aufnahmen aus kombinierten Aufnahmensystemen vor der AC kann die Qualit{\"a}t von PET-Aufnahmen im klinischen Einsatz verbessern. Trotzdem steht bis heute im klinischen Alltag keine validierte, automatische Registrierungssoftware zur Verf{\"u}gung. Wir verfolgen dazu Ans{\"a}tze f{\"u}r validierte, nicht-rigide Bildregistrierung f{\"u}r den klinischen Einsatz und pr{\"a}sentieren erste Ergebnisse.}, subject = {Positronen-Emissions-Tomografie}, language = {en} } @misc{WeigertBeyerQuicketal., author = {Weigert, Markus and Beyer, Thomas and Quick, Harald H. and Pietrzyk, Uwe and Palm, Christoph and M{\"u}ller, Stefan P.}, title = {Generation of a MRI reference data set for the validation of automatic, non-rigid image co-registration algorithms}, series = {Nuklearmedizin}, volume = {46}, journal = {Nuklearmedizin}, number = {2}, pages = {A116}, subject = {Kernspintomografie}, language = {en} } @misc{WeigertPalmQuicketal., author = {Weigert, Markus and Palm, Christoph and Quick, Harald H. and M{\"u}ller, Stefan P. and Pietrzyk, Uwe and Beyer, Thomas}, title = {Template for MR-based attenuation correction for whole-body PET/MR imaging}, series = {Nuklearmedizin}, volume = {46}, journal = {Nuklearmedizin}, number = {2}, pages = {A115}, subject = {Kernspintomografie}, language = {en} } @article{BeyerWeigertQuicketal., author = {Beyer, Thomas and Weigert, Markus and Quick, Harald H. and Pietrzyk, Uwe and Vogt, Florian and Palm, Christoph and Antoch, Gerald and M{\"u}ller, Stefan P. and Bockisch, Andreas}, title = {MR-based attenuation correction for torso-PET/MR imaging}, series = {European Journal of Nuclear Medicine and Molecular Imaging}, volume = {35}, journal = {European Journal of Nuclear Medicine and Molecular Imaging}, number = {6}, doi = {10.1007/s00259-008-0734-0}, pages = {1142 -- 1146}, abstract = {Purpose MR-based attenuation correction (AC) will become an integral part of combined PET/MR systems. Here, we propose a toolbox to validate MR-AC of clinical PET/MRI data sets. Methods Torso scans of ten patients were acquired on a combined PET/CT and on a 1.5-T MRI system. MR-based attenuation data were derived from the CT following MR-CT image co-registration and subsequent histogram matching. PET images were reconstructed after CT- (PET/CT) and MR-based AC (PET/MRI). Lesion-to-background (L/B) ratios were estimated on PET/CT and PET/MRI. Results MR-CT histogram matching leads to a mean voxel intensity difference in the CT- and MR-based attenuation images of 12\% (max). Mean differences between PET/MRI and PET/CT were 19\% (max). L/B ratios were similar except for the lung where local misregistration and intensity transformation leads to a biased PET/MRI. Conclusion Our toolbox can be used to study pitfalls in MR-AC. We found that co-registration accuracy and pixel value transformation determine the accuracy of PET/MRI.}, subject = {Kernspintomografie}, language = {en} }