Abstract
Background and purposeThe restricted bore diameter of current simultaneous positron emission tomography/magnetic resonance imaging (PET/MRI) systems can be an impediment to achieving similar patient positioning during PET/MRI planning and radiotherapy. Our goal was to evaluate the B1 transmit (B1+) uniformity, B1+ efficiency, and specific absorption rate (SAR) of a novel radiofrequency (RF) body coil design, in which RF shielded PET detectors were integrated with the specific aim of enabling a wide-bore PET/MRI system.Materials and methodsWe designed and constructed a wide-bore PET/MRI RF body coil to be integrated with a clinical MRI system. To increase its inner bore diameter, the PET detectors were positioned between the conductors and the RF shield of the RF body coil. Simulations and experiments with phantoms and human volunteers were performed to compare the B1+ uniformity, B1+ efficiency, and SAR between our design and the clinical body coil.ResultsIn the simulations, our design achieved nearly the same B1+ field uniformity as the clinical body coil and an almost identical SAR distribution. The uniformity findings were confirmed by the physical experiments. The B1+ efficiency was 38% lower compared to the clinical body coil.ConclusionsTo achieve wide-bore PET/MRI, it is possible to integrate shielding for PET detectors between the body coil conductors and the RF shield without compromising MRI performance. Reduced B1+ efficiency may be compensated by adding a second RF amplifier. This finding may facilitate the application of simultaneous whole-body PET/MRI in radiotherapy planning.
Highlights
The development of clinical whole-body positron emission tomog raphy/magnetic resonance imaging (PET/MRI) systems has stimulated research on possibilities to apply positron emission tomography/ magnetic resonance imaging (PET/MRI) for treatment planning and diagnostic workup of image-guided radiotherapy [1,2,3,4,5]
We introduced a new strategy to increase the inner bore diameter of whole-body simultaneous PET/MRI systems: positioning the PET detectors in the gap between the body coil conductors and the RF shield
Simulations of a prototype body coil based on this strategy showed that it can achieve nearly the same B1+ field uniformity as the body coil of a clinical wide-bore MRI system (Fig. 2) and a similar specific absorption rate (SAR) distribution with the peak value well within the safe range (Fig. 3)
Summary
The development of clinical whole-body positron emission tomog raphy/magnetic resonance imaging (PET/MRI) systems has stimulated research on possibilities to apply PET/MRI for treatment planning and diagnostic workup of image-guided radiotherapy [1,2,3,4,5]. Scan the patient in the same position as during therapy (e.g. with the arms upwards, or using large immobilization and positioning aids) To address this limitation, we investigated the possibility of increasing the inner bore diameter by integrating the PET detectors into the confined space between the RF shield and the conductors of the RF body coil. The restricted bore diameter of current simultaneous positron emission tomography/ magnetic resonance imaging (PET/MRI) systems can be an impediment to achieving similar patient positioning during PET/MRI planning and radiotherapy. Reduced B1+ efficiency may be compensated by adding a second RF amplifier This finding may facilitate the application of simultaneous wholebody PET/MRI in radiotherapy planning
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