Speaker
S. Majewski
Description
Abstract. Brain is the most interesting organ to image and there is lately a high level of fascination in the society about imaging brain, due to the increasing hope that many severe debilitating disease conditions such as dementia (Alzheimer’s, other), mental diseases and severe depression can be diagnosed early and treated under imaging guidance. The very recently introduced hybrid PET/MRI scanners are already demonstrating the power of this hybrid dual-modality system in diagnosing and staging the abnormal brain biology. In this tandem PET plays the role of a molecular imaging modality. However, these formidable PET/MRI imagers, starting with the Siemens mMR machine, are very expensive and one can predict that their availability to millions of people who are concerned about the deteriorating conditions of their brains (memory loss, loss of cognitive function, deteriorating mental disease conditions) will be limited for quite a long time, and many medical centers will not be even able to acquire these systems. Nevertheless, one can have a vision that high performance and economical dedicated imaging instruments presently under development around the world can provide sufficient dual-modality functionality and can be available much sooner to much larger populations of patients. In this presentation we will review the development efforts primarily in dedicated sequential and simultaneous PET/MRI imagers. This latest relevant technical “revolution” in nuclear medicine imaging is spearheaded by the enabling Silicon Photomultiplier technology. This very compact and robust solid state technology with high intrinsic signal gain is highly immune to strong multi-Tesla magnetic fields and is making possible construction of compact insert-type PET (and single gamma) imagers that can be used in conjunction with MRI scans. In principle “any” MRI scanner could be converted into a PET/MRI brain imager. The efforts in making the two modalities, PET and MRI, compatible with each other are mostly focused on preventing that the insertion of the PET imager deteriorates the signal to noise (S/N) in the MRI scans. Majority of the on-going projects focus on development of special MRI coils that are inside the PET (or gamma) insert, and/or on combining these inserts with the RF coils. There are also development projects that are assuming minimal modification to the MRI modality and application of the standard RF coils. While this solution presents the main challenge of high potential interference on the MRI performance, it also offers maximum potential benefit of practically “converting” any standard MRI scanner into a PET/MRI machine to image a particular organ, such as brain, (but also breast, head/neck, extremities, etc). A next level combination of PET/MRI/EEG was already proposed to study epileptic and mental patients. PET/CT is still the most available hybrid imager and there are new developments in mobile PET/CT imagers, also benefiting from the SiPM technology, with applications to imaging of brains of stroke patients or monitoring radiation treatment in case of brain cancer. An important feature of these dedicated PET brain imagers is that they can be made highly efficient and therefore can permit low-dose PET scans. In principle, this will open possibility to longitudinal studies requiring multiple PET scans and multiple injections, for example in short and long term monitoring of the disease treatment effects.