Final Report Summary - MREXCITE (Unlocking the potential of ultra-high-field MRI through manipulation of radiofrequency excitation fields in human tissue)
In the past three and a half decades, magnetic resonance imaging (MRI) has emerged as a vital tool for clinical diagnosis and research. A major trend is the introduction of magnets with more powerful static magnetic fields, including magnets at 7 Tesla and higher. Currently, only magnets up to 3 Tesla are available for routine clinical use. Advantages of higher magnetic fields include enhanced sensitivity as well as enhanced soft-tissue contrasts, which enable improved spatial and temporal resolution and ultimately more detailed insight into pathological processes.
Unfortunately, the radiofrequency (RF) fields used to excite tissue in MRI are subject to interference and penetration effects at higher magnetic fields, leading to signal dropouts that vary from subject to subject depending on body size and composition. Thus, the inherent advantages of 7 Tesla often cannot be leveraged to realize practical imaging benefits, and the diagnostic potential of 7 Tesla cannot be achieved. Particularly in the torso, 7 Tesla MRI cannot be considered for routine clinical use or even effectively evaluated for such use until these hurdles have been overcome.
In this project, we developed a highly optimized 32-channel transmit/receive RF coil for body MRI at 7 Tesla. On each of the 32 channels, a different RF pulse form can be applied, making each transmit channel fully independent. This coil was used to exploit and manipulate the complex RF field patterns at 7 Tesla using parallel transmission techniques. In contrast to previous approaches at 7 Tesla, which utilize transmission coils placed directly on the subject being imaged, this body coil was fully integrated under the covers of the 7 Tesla magnet, allowing a workflow very similar to clinical MRI systems at lower field strengths like 1.5 and 3 Tesla. Whereas most previous parallel transmit systems have provided 8 independently controllable channels and in some cases 16, this is the first system worldwide to provide fully independent control on all 32 transmit channels.
The flexibility provided by a 32-channel coil has demonstrated that it is possible to perform high-quality MRI throughout the entire body at 7 Tesla. This technology will allow us to vastly improve imaging quality in torso MRI at 7 Tesla and open up completely new applications. Our expectation is that the MRexcite system will pave the way for exploiting the benefits of ultra-high-field MRI for clinical use and allow us to explore the true potential of high magnetic fields for the diagnosis and characterization of numerous disease processes.
Unfortunately, the radiofrequency (RF) fields used to excite tissue in MRI are subject to interference and penetration effects at higher magnetic fields, leading to signal dropouts that vary from subject to subject depending on body size and composition. Thus, the inherent advantages of 7 Tesla often cannot be leveraged to realize practical imaging benefits, and the diagnostic potential of 7 Tesla cannot be achieved. Particularly in the torso, 7 Tesla MRI cannot be considered for routine clinical use or even effectively evaluated for such use until these hurdles have been overcome.
In this project, we developed a highly optimized 32-channel transmit/receive RF coil for body MRI at 7 Tesla. On each of the 32 channels, a different RF pulse form can be applied, making each transmit channel fully independent. This coil was used to exploit and manipulate the complex RF field patterns at 7 Tesla using parallel transmission techniques. In contrast to previous approaches at 7 Tesla, which utilize transmission coils placed directly on the subject being imaged, this body coil was fully integrated under the covers of the 7 Tesla magnet, allowing a workflow very similar to clinical MRI systems at lower field strengths like 1.5 and 3 Tesla. Whereas most previous parallel transmit systems have provided 8 independently controllable channels and in some cases 16, this is the first system worldwide to provide fully independent control on all 32 transmit channels.
The flexibility provided by a 32-channel coil has demonstrated that it is possible to perform high-quality MRI throughout the entire body at 7 Tesla. This technology will allow us to vastly improve imaging quality in torso MRI at 7 Tesla and open up completely new applications. Our expectation is that the MRexcite system will pave the way for exploiting the benefits of ultra-high-field MRI for clinical use and allow us to explore the true potential of high magnetic fields for the diagnosis and characterization of numerous disease processes.