A new J-shape antenna array for simultaneous MR-PET or MR-SPECT imaging
3rd December 2021
Chang-Hoon Choi, Suk-Min Hong, Jörg Felder, Lutz Tellmann, Jürgen Scheins, Elena Rota Kops, Christoph Lerche and N. Jon Shah
Magnetic resonance imaging (MRI), positron emission tomography (PET) and single-photon emission computed tomography (SPECT) are well-established medical imaging modalities used in hospitals around the world. While PET/SPECT imaging uses a variety of radioactive tracers to obtain valuable insights into physiological and metabolic processes, MRI provides high quality structural/anatomical imaging, with both outstanding soft tissue contrasts and functional information. The advantages of combining these modalities in one scan in terms of efficiency and breadth of information obtained are clear and is currently an active area of research and development.
Concurrent acquisitions often require the MRI antenna located inside the PET/SPECT field-of-view. However, to really optimise the capabilities of each modality, this needs to be operated without compromising any aspects of system performance or image quality compared to the stand-alone instrumentation. Researchers in INM-4 have sought to overcome this problem by developing a novel gamma- radiation-transparent antenna concept.
The construction of the developed antenna is an end-fed J-shape, making it particularly adept for hybrid ultra-high field MR- PET/-SPECT applications as it enables all highly attenuating materials to be placed outside the imaging field-of-view. Furthermore, this unique configuration also provides advantages in stand-alone MR applications by reducing coupling between the cables and the antenna elements and lowering the potential specific absorption rate burden.
The use of this new design was experimentally verified according to the important features for both ultra-high field MRI and the 511 keV transmission scan. The results demonstrated reconstructed attenuation maps showed much lower attenuation (~15%) for the proposed array when compared to the conventional dipole antenna array since there were no high-density components. In MR, it was observed that the signal-to-noise ratio from the whole volume obtained using the proposed array was comparable to that acquired by the conventional array, which was also in agreement with the simulation results.
The figure below shows the construction of the J-shaped array and a conventional array alongside their associated attenuation maps and sinograms. It can be seen that the attenuation for the conventional antenna array was significantly higher (~ 18%) in the planes with the inserted components compared to the attenuation observed with the proposed array.
It is strongly anticipated that the unique features of this J-shape array will enable simultaneous MR-PET/-SPECT experiments to be conducted without unduly compromising any aspects of system performance and image quality compared to the stand-alone instrumentation. Furthermore, the nature of the system means that this new concept is not limited only to 7 T hybrid multi-modal imaging applications as it can be optimised for stand-alone MRI systems operating even higher field strengths, such as 9.4 T, 10.5 T and 11.7 T. In addition, the concept can also be implemented in certain applications at clinically relevant field strengths, e.g., 3 T body 1H MR-PET imaging and total-body PET systems.
Future work will look at how the proposed antenna design could be applied to investigate X-nuclei (non-proton nuclei that have comparatively lower gyromagnetic ratio and MR sensitivity and are closely connected to the biochemical and metabolic processes in the human body) if it is used as a body X-nucleus coil at ultra-high field.
Origional publication: A novel J-shape antenna array for simultaneous MR-PET or MR-SPECT imaging