Transmission scanning for accurate magnetic resonance / positron emission tomography
In this project, we have integrated a transmission scan mechanism into a wide-bore 1.5T PET-MRI system. Whereas transmission images for PET are currently obtained from a CT or transmission scan obtained sequentially, prior to the PET-MRI scan, our system is designed to acquire truly simultaneously obtained PET-MRI-transmission images.
Simultaneous PET-MRI is expected to enable dramatic improvements in medical research and patient management in several clinical domains such as neurology, cardiology and oncology. Also, PET-MRI can significantly increase the precision of new image-guided cancer therapies such as MR-guided radiotherapy (MR-LINAC). A limitation of current PET-MRI systems is that achieving quantitative accuracy of the PET scan (determining the exact amount of radioactive tracer) is difficult because (CT) transmission data are not available. Clinical validation of methods for converting MRI to CT data have until now only been successful for brain scans and has been difficult for other body parts.
To prepare the PET-MRI system developed in our hospital for integration of the simultaneous transmission scan mechanism, we have adapted and extended its PET detector technology and 3-D image reconstruction pipeline. We then adopted an approach for implementing an annulus-shaped transmission source that was proven in literature previously, and have taken it several steps further towards practical implementation. Most notably, our prototype demonstrator is the first of its kind that is tightly integrated into a PET-MRI system, and we developed a mechanism to fill and empty the transmission source using a peristaltic pump. With this system, we were able to perform MRI experiments showing for the first time that it is possible to integrate an annulus-shaped transmission source into the body coil of a wide-bore PET-MRI system, without affecting MRI performance and without sacrificing bore size. These results are an important step towards enabling a flexible and robust one-stop pipeline for PET-MRI-guided radiotherapy.
