Jonathan D. Thiessen^1,2, Ehsan Shams^3,4, Greg Stortz⁵, Graham Schellenberg⁴, Daryl Bishop⁶, Muhammad Salman Khan⁷, Piotr Kozlowski⁸, Fabrice Retière⁶, Vesna Sossi⁵, Christopher J. Thompson⁹, and Andrew L. Goertzen^4,10
1Imaging Program, Lawson Health Research Institute, London, Ontario, Canada, ²Medical Biophysics, Western University, London, Ontario, Canada, ³Graduate Program in Biomedical Engineering, University of Manitoba, Winnipeg, Manitoba, Canada, ⁴Physics & Astronomy, University of Manitoba, Winnipeg, Manitoba, Canada, ⁵Physics & Astronomy, University of British Columbia, Vancouver, British Columbia, Canada, ⁶Detector Development Group, TRIUMF, Vancouver, British Columbia, Canada, ⁷Electrical & Computer Engineering, University of Manitoba, Winnipeg, Manitoba, Canada, ⁸Radiology, University of British Columbia, Vancouver, British Columbia, Canada, ⁹McConnell Brain Imaging Centre, Montreal Neurological Institute, Montréal, Québec, Canada, ¹⁰Radiology, University of Manitoba, Winnipeg, Manitoba, Canada

We are building an MRI compatible, high-resolution small animal positron emission tomography (PET) insert. The PET insert is designed to achieve 1 mm spatial resolution in the center of its field-of-view and fit within the 114 mm inner diameter of a BGA-12S gradient system installed in a Bruker 7T MRI. Good PET detector and MRI performance was demonstrated with the PET insert operating inside the MRI. A data acquisition system capable of acquiring energy data from all 16 detector modules is currently being developed on the OpenPET firmware platform, with the first PET/MR images anticipated in early 2015.

Meher Juttukonda^1,2, Bryant Mersereau^1,2, Yasheng Chen^2,3, Yi Su⁴, Brian Rubin⁴, Tammie Benzinger⁴, David Lalush^1,2, and Hongyu An^2,3
1Joint Department of Biomedical Engineering, University of North Carolina - Chapel Hill & North Carolina State University, Chapel Hill, North Carolina, United States, ²Biomedical Research Imaging Center, University of North Carolina - Chapel Hill, Chapel Hill, North Carolina, United States, ³Radiology, University of North Carolina - Chapel Hill, Chapel Hill, North Carolina, United States, ⁴Mallinckrodt Institute of Radiology, Washington University, St. Louis, Missouri, United States

In this study, we have developed a method for UTE-based bone/air segmentation and a model to predict CT values of bone tissue directly from R2* values obtained from UTE images. We subsequently used this model to produce continuous-valued PET attenuation coefficients in bone tissue employing a straight-forward conversion from R2* to CT Hounsfield units, followed by a piece-wise linear scaling of the predicted CT values to PET attenuation coefficients. Our results show that the proposed method produces more accurate PET reconstructions than the vendor-provided UTE method.

Jochen Franke^1,2, Ulrich Heinen¹, Heinrich Lehr¹, Alexander Weber¹, Frederic Jaspard³, Wolfgang Ruhm¹, Michael Heidenreich¹, and Volkmar Schulz^2
1R&D Magnetgic Particle Imaging, Bruker BioSpin MRI GmbH, Ettlingen, Germany, ²Physics of Molecular Imaging Systems, University RWTH Aachen, Aachen, Germany, ³R&D Gradient Systems, Bruker BioSpin, Wissembourg, France

Hybrid imaging systems become more and more important in modern medicine to improve the diagnostic value. Combining data acquired with the novel tracer-based imaging modality Magnetic Particle Imaging (MPI) with Magnetic Resonance Imaging (MRI) data has been shown to be a promising approach. This work presents a fully integrated 12 channel hybrid magnet system design as well as first MPI-MRI images using this preclinical demonstrator. This hybrid system offers sequentially MPI and MRI imaging without any movement of the object.

Daniel H Paulus¹, Mark Oehmigen², and Harald H Quick^1,2
1Institute of Medical Physics, University of Erlangen-Nürnberg, Erlangen, Germany, ²High Field and Hybrid MR Imaging, University Hospital Essen, Essen, Germany

PET and MR imaging have become an important part in radiation therapy (RT) treatment planning for accurate target volume delineation. A novel concept for hybrid PET/MR systems is presented that allows for whole-body imaging with dedicated RT equipment including a flat RT table overlay and RF body coil holders. Height adjustable body bridges fix a body RF coil above the patient’s body without touching it and can be mounted at different positions. Attenuation correction maps can be automatically generated for each patient setup. MR and PET compatibility has been systematically evaluated using phantom scans and a first patient study.

Frederik Testud¹, Elmar Fischer¹, Katharina Göbel¹, Nils Spengler², Ulrike Wallrabe², Maxim Zaitsev¹, and Matthias Wapler^2
1Medical Physics, University Medical Center Freiburg, Freiburg, Germany, ²Department for Microsystems Engineering – IMTEK, University of Freiburg, Freiburg, Germany

Magnetic resonance microscopy allows resolving structures smaller than 100 m. It is used to image for example organotypic slice cultures. However, the identification of specific microstructural elements is performed by light-microscopy based correlative histology techniques. MR image artefacts because of susceptibility effects, motion or sample preparation during staining can lead to discrepancies, impairing the comparison between images from both modalities. In this work an optical microscope was built to fit in an ultra-high field small animal scanner for simultaneous optical microscopy and magnetic resonance experiments. First successful concurrent and mutually unaffected optical microscopy and magnetic resonance experiments are presented.

Mingyan Li¹, Thimo Hugger², Ewald Weber¹, Jin Jin¹, Feng Liu¹, Peter Ullmann², Simon Stark², Yasvir Tesiram³, Yang Yang¹, Sven Junge², and Stuart Crozier^1
1The School of Information Technology and Electrical Engineering, The University of Queensland, Brisbane, QLD, Australia, ²Bruker BioSpin MRI GmbH, Ettlingen, Baden-Württemberg, Germany, ³Centre for Advanced Imaging, The University of Queensland, Brisbane, QLD, Australia

This work presents a novel, practical imaging scheme for the rotating coil by using radial trajectories. A single channel pneumatically-driven rotating coil is built for 9.4 T preclinical system. We show in theory that with proper combination of rotation speed and sequence TR, the averaging effect of radial trajectories can be employed to minimise the effects of the rotation-dependent sensitivity on image formation. Preliminary experiments show that when radial ultra-short TE (UTE) sequence is combined with the rotating scheme, the single element rotating coil is capable of reconstructing images free of artefacts and intensity variation without using sensitivity calibration.

Yicheng Chen¹, Di Cui^1,2, Yingmao Chen³, Jinsong Ouyang⁴, Georges El Fakhri⁴, and Kui Ying^1
1Key Laboratory of Particle and Radiation Imaging, Ministry of Education, Department of Engineering Physics, Tsinghua University, Beijing, Beijing, China,²Department of Diagnostic Radiology, The University of Hong Kong, Hong Kong, China, ³Department of Nuclear Medicine, The general hospital of Chinese People's Liberation, Beijing, China, ⁴Department of Radiology, Division of Nuclear Medicine and Molecular Imaging, Harvard Medical School and Massachusetts General Hospital, Boston, Massachusetts, United States

In this study, a novel method using support vector machine (SVM) regression to predict continuous pseudo-CT from MR T2 and UTE information for PET attenuation correction is proposed. The SVM regression model is trained and tested with patient data. Compared to Gaussian mixture regression (GMR) model method, a pseudo-CT attenuation correction approach, the proposed method provides higher fidelity to the gold standard CT with our limited data set.

Chuan Huang^1,2, Jinsong Ouyang¹, Timothy Reese³, Yaotang Wu⁴, Georges El Fakhri¹, and Jerome Ackerman^3
1Center for Advanced Medical Imaging Sciences, Radiology, Massachusetts General Hospital, Boston, MA, United States, ²Research Radiology, Psychiatry, Stony Brook Medicine, Stony Brook, NY, United States, ³Martinos Center for Biomedical Imaging, Radiology, Massachusetts General Hospital, Boston, MA, United States, ⁴Radiology, Children's Hospital Boston, Boston, MA, United States

Simultaneous MR-PET is an emerging hybrid modality that is attracting substantial interest. Currently, one of the hurdles for MR-PET is its quantitative accuracy due to challenges in obtaining accurate attenuation correction. For MR-PET, the PET attenuation map typically needs to be derived from the MR images. The standard approach is to segment an MR image volume into different tissue classes and then assign the corresponding attenuation coefficients to them. Accurate attenuation correction in regions within or near bone is still an open problem due to lack of signal from solid bone in most MR sequences. Investigators have proposed to use atlas-based maps and the ultrashort echo time (UTE) pulse sequence to identify bones. These approaches do not take into account the intra- and inter-patient bone density variations and may lead to bias in the quantitation. In this work, we investigated the possibility of using the Water- And fat-Suppressed Proton projection Imaging (WASPI) sequence to measure bone density.

Christoph Kolbitsch¹, Mark Ahlman², Michael Hansen³, Javier Royuela del Val^1,4, Peter Kellman³, David A. Bluemke², and Tobias Schaeffter^1
1Division of Imaging Sciences and Biomedical Engineering, King's College London, London, London, United Kingdom, ²Clinical Center, Radiology and Imaging Sciences, National Institute of Health, Bethesda, MD, United States, ³National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, United States, ⁴Laboratorio de Procesado de Imagen, Universidad de Valladolid, Valladolid, Valladolid, Spain

Positron emission tomography (PET) is commonly used to diagnose and assess ischemic heart disease. Respiratory and cardiac motion during data acquisition can severely impair the obtained cardiac perfusion information. Here we present a simultaneous PET-MR acquisition technique, which yields 3D high-resolution anatomical MR images and non-rigid motion information of both respiratory and cardiac movement. Both types of motion information can be used to compensate for artefacts in PET and MR images. The feasibility of the motion compensated PET-MR approach is demonstrated.

Jakob Wehner¹, Bjoern Weissler^2,3, David Schug¹, Peter Dueppenbecker⁴, Pierre Gebhardt⁴, Benjamin Goldschmidt¹, Andre Salomon⁵, Rene Botnar⁴, Fabian Kiessling¹, and Volkmar Schulz^1,3
1Institute for Experimental Molecular Imaging, RWTH Aachen University, Aachen, NRW, Germany, ²Institute of High Frequency Technology, RWTH Aachen University, NRW, Germany, ³Philips Research Europe, Aachen, NRW, Germany, ⁴King's College London, London, United Kingdom, ⁵Philips Research Europe, Eindhoven, Netherlands

Our group has built the world’s first preclinical, digital PET insert which is designed to be installed inside a clinical 3T MRI system and makes use of digital Silicon Photomultipliers. In this work, we investigate the MR-compatibility of our PET detector in combination with a 3T MRI system and performed a first animal studies to demonstrate the imaging performance. This comprehensive interaction investigation includes interference studies between the PET detector and all sub-systems of the MRI scanner. We found acceptable level of MRI performance degradation with the PET system operated and no relevant PET performance degradation during normal imaging conditions.