Development and Validation of a combined PET/MRI Scanner for Biomedical Research
Final Report Abstract
We could successfully build and test a large field of view small animal PET-insert enabling simultaneous PET/MRI data acquisition. Our performance evaluation showed that neither PET nor MR image quality are in general impacted by installing the PET insert into a 7 T small animal MR system. Signal to noise ratio (SNR) as well as image homogeneity has been assessed for five different MR sequences, commonly used in small animal imaging. Four imaging sequences showed no significant differences between the configuration without or with the PET insert installed and operating. The differences in the SNR ratio and image homogeneity for the turbo spin echo (TSE) sequence are probably caused by small differences in phantom positioning between the measurements, as well as changes in the tune-up and shimming situation between these measurements. However, the effects observed in the TSE sequence are small compared to the variability observed in in-vivo animal imaging studies. Therefore, it is a safe conclusion that these slight changes will not impair the MR image quality per se. The modified sequences showed a good image quality and the temporal stability of the MR system is not influenced by the presence of the PET insert. To make these sequences as similar as possible with clinical protocols, no alterations to more fundamental parameters such as gradient polarity patterns were implemented. No obvious artefacts such as from eddy currents were noticeable. We successfully conducted in-vivo imaging studies. In-vivo imaging quality showed high resolution spectra of the rat brain, obtained with the PET insert installed. It can be concluded, that MR spectroscopy studies can be performed without negative influence of the PET insert. We did not perform extensive phantom studies using the PET insert, since our experiences with the in-vivo imaging (rat brain) as well as the line width of the natural water peak allowed us to go directly into an animal model. The use of PET/MR in oncology clearly gains from the use of multimodality information. The treatment study showed a good agreement between MR measured tumor size reduction and reductions in cell proliferation visualized with [18F]FLT in the treatment group. The [18F]FLT results correlated well with Ki67 immunohistochemistry. It can be concluded that PET/MR is a valuable tool in monitoring disease progression as well as treatment effectively in brain tumors. Comparison between brain activation in small animals using [18F]FDG and fMRI BOLD showed similarities in the somatosensory stimulation network (e.g. primary somatosensory cortex barrel field). Additionally activated areas were found in the PET data. Partially this can be explained by the different stimulus durations between PET and MR paradigm, involving also pain processing networks for the [18F]FDG acquisition. Therefore multiple metabolic networks and stages of brain activation can be revealed by simultaneous PET/MR imaging. The results of this study were successfully published. Within this grant we conducted further small animals studies comparing MR spectroscopy with [11C]choline PET and also BOLD-fMRI with [15O]H2O-PET.
Publications
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Combined PET/MRI: one step further in multimodality imaging,
Trends in Molecular Medicine, Vol. 16. 2010, Issue 11, pp. 508-515.
Alexander W. Sauter, Hans F. Wehrl, Armin Kolb, Martin S. Judenhofer, Bernd J. Pichler
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Assessment of MR compatibility of a PET insert developed for simultaneous multiparametric PET/MR imaging on an animal system operating at 7 T. Magnetic Resonance in Medicine, Vol. 65. 2011 , Issue1, pp. 269-279.
Hans F. Wehrl, Martin S. Judenhofer, Axel Thielscher, Petros Martirosian, Fritz Schick, Bernd J. Pichler
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Development of a Second Generation MRI Compatible PET Insert for Preclinical in Vivo Studies, IEEE 2011, Valencia
M. Hossain et al.
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Multimodal Elucidation of Choline Metabolism in a Murine Glioma Model using Magnetic Resonance Spectroscopy and 11C-choline Positron Emission Tomography. Cancer Research, Vol. 73. 2013, Issue 5, pp. 1470-1480.
Hans F. Wehrl, Julian Schwab, Kathy Hasenbach; Gerald Reischl, Ghazaleh Tabatabai, Leticia Quintanilla-Martinez, Filip Jiru, Kamila Chughtai, Andras Kiss, Funda Cay, Daniel Bukala, Ron M. A. Heeren, Bernd J. Pichler, Alexander W. Sauter
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Simultaneous PET/MR reveals Brain Function in Activated and Resting State on Metabolic, Hemodynamic and Multiple Temporal Scales.
Nature Medicine, Vol. 19.2013, pp. 1184–1189.
Hans F. Wehrl, Mosaddek Hossain, Konrad Lankes, Chih-Chieh Liu, Ilja Bezrukov, Petros Martirosian, Fritz Schick, Gerald Reischl, Bernd J. Pichler
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Assessment of rodent brain activity using combined [15O]H2O-PET and BOLD-fMRI. NeuroImage, Vol. 89. 2014, pp. 271-279.
Hans F. Wehrl, Petros Martirosian, Fritz Schick, Gerald Reischl, Bernd J. Pichler
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Preclinical and Translational PET/MR Imaging. Journal of Nuclear Medicine, vol. 55. 2014, no. Supplement 2, pp. 11S-18S.
Hans F. Wehrl, Stefan Wiehr, Matthew R. Divine, Sergios Gatidis, Grant T, Gullberg, Florian C. Maier, Anna-Maria Rolle, Johannes Schwenck, Wolfgang M. Thaiss, Bernd J. Pichler
