Integrated Transmission Source System in PET/MR Imaging

The combination of tomographic imaging methods provides additional benefit for diagnostic imaging. Classical examples are SPECT/CT and PET/CT, where an image of metabolic processes is taken side to side with a three- dimensional high-resolution anatomical image of the patient. CT, aside from providing an anatomical map for the low resolution image data from nuclear medicine modalities (SPECT and PET), also allows for the quantification of self-absorption of the emitted photons. Therefore, acquisition time and imaging artifacts are reduced, and the corrected image data allows for a precise quantification of metabolic processes. Around 2006 clinical PET/MR systems were introduced. They also provide fused images but cannot directly provide data for correction of absorption and scatter artifacts. This research project proposes the usage of radioactive point sources, which are moved hydraulically in a helical hose inside the PET/MR gantry around the patient. Such systems were introduced as prototypes in conventional PET-scanners here, this approach is to be pursued further in a sense that the point source for measuring the attenuation is to be integrated in the receiver coil of the MR system. The novelty in this case is a full-fledged attenuation correction approach that also takes bone into account (as opposed to other MR-based techniques), allowing for a classical reconstruction of transmission images. A special difficulty lies in the fact that the mechanism also has to be MR-compliant. Finally, our research aims at improving the diagnostic value of PET/MR imaging systems. Abbreviations: CT Computed Tomography MR Magnetic Resonance Tomography PETPositron Emission Tomography SPECTSingle Photon Emission Computed Tomography

In nuclear medicine a small dose of a radioactive substance is applied to the patient. Its distribution in the human body depends on the substance and can be measured and used for diagnosis. From x-ray imaging we know that such rays are attenuated by different parts of the human body differently. This attenuation has to be corrected in nuclear medicine imaging systems. The more recent imaging systems in nuclear medicine combine two different imaging techniques in one device, which is called hybrid imaging. Popular combinations include the combination of PET, a nuclear medicine procedure with computed tomography (CT) of magnetic resonance imaging (MRI). Attenuation correction is then provided using the other procedure (CT or MRI, respectively). While CT based attenuation correction gives good results, using MR in the head region can lead to typical artefacts. In this research project we developed a Head Coil System for MRI that is connected with an attenuation correction device to be used in PET/MRI. Attenuation is gained from a transmission image that is produced by a small radioactive source which is moved around the patient in a water filled hose. The coil was evaluated using phantoms and piglets. The correction was slightly superior to the corrections done by present day commercial PET/MRI systems but with the additional complexity of using this coil. In a next step we will simplify the handling of the coil and the perform a patient study.