A Prototype Wireless Digital MR Spectrometer on a Single Integrated Circuit

Stanford University, Stanford CA

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Abstract

DESCRIPTION (provided by applicant): The final deliverable of this project is a powerful microchip, or system-on-a-chip (SOC), that contains the functionality of a complete digital MR spectrometer and wireless transmitter. The three specific aims present an iterative, three stage strategy for chipset development. With the completion of each specific aim, the deliverables will be fully functional chipsets with decreasing footprint until we reach the dimensions of the final SOC. We begin with a 50x50x20mm prototype on a printed circuit board that will eventually be reduced to a miniature 2x2x1mm complete SOC blueprint. This microchip technology will be the centerpiece of a wireless, digital RF chain that is superior in performance to the traditional wired, analog RF chain, and is a paradigm shift for the entire field of MRI. Integration of this microchip into an RF coil will enable digital processing of the MR signal to be performed directly on the coil, followed by digital wireless signal transmission, thereby improving SNR and removing all mechanical connections between the RF coil and MR scanner. Specifically, we will develop the microchip technology for integration into a miniature RF coil-based wireless marker, whose position can be tracked inside the MR scanner bore. Motion tracking of the head is performed using three wireless markers that are easily placed on the forehead, which will provide pose information for real-time motion correction of brain MRI. This application fittingly highlights the strengths of the microchip approach (miniature, wireless device), as well as our significant in-house expertise in motion correction. Head motion is still a fundamental problem for brain MRI, which adds to healthcare costs while also reducing diagnostic confidence. A wireless marker based motion correction solution will significantly benefit healthcare by reducing prep/scan time, costs, and stress to patient that are caused by a dependence on anesthesia and repeat scans due to motion. The diagnostic quality of MRI will also be improved, particularly in patient populations who have difficulty keeping still (e.g. pediatrics, elderly). Wireless markers also possess several advantages over alternative techniques, including: (1) improved patient safety by eliminating electrically conducting wires that can cause tissue heating; (2) no additional load is placed on the existing MR receiver hardware since communication occurs within its own wireless network; (3) compatibility with a wide range of clinical scans, as only a short navigator pulse-sequence is needed for position measurement; (4) does not require any cross-calibration routines (e.g. optical camera tracking), since tracking and imaging are performed in the same MR coordinate system; and (5) importantly, a miniature, wireless-marker tracking-device will be easy to use, thereby facilitating their portability to the high-throughput clinic. Looking beyond motion correction (and the scope of this R21), the powerful chipsets are an enabling technology for wireless, digital communication between ALL RF coils and the MR scanner. The chipset digitizes the MR signal directly on the RF coil, digitally modulates, and wirelessly transmits the digital MR signal. SNR i therefore increased by avoiding resistive losses and coupling due to long coaxial cables. In the case of a multi-channel imaging RF coil, each channel would have a matching set of on-coil microchips that perform all MR spectrometer operations. By performing these operations directly on the RF coil, the MR scanner becomes channel independent, and RF channel upgrades a thing of the past. An array of microchips may be deployed in a massively multi-channel coil, thereby facilitating the trend in MRI towards parallel imaging. Finally, the elimination of cables and large oncoil electronics will result in lighter and easier to handle RF coils. Digital wireless links in MRI may also benefit from similar technology that is being rapidly advanced in the field of modern mobile telephony. In summary, the powerful chipsets developed here will not only influence motion correction, but also innovate a fully digital and fully wireless MR scanner in the future. In the current R21, we expect to produce a high-impact motion correction strategy that is, overall, the most comprehensive, robust, and patient friendly solution to date. The technology and preliminary results garnered will then be used for two future R01 proposals. The first R01 will be for clinical validation of an even more refined wireless marker. The second R01 will be to refine and validate a high-fidelity wireless spectrometer IC for imaging RF coils. Another future application would be MR-PET where a small footprint IC spectrometer would eliminate a lot of the current x-ray dense RF electronics, which interacts with 511keV photons and thus perturbs the PET imaging process.