Abstract
The design and development of a new dual-frequency RF probe-head are presented. This probe was initially dedicated for the MRI of both proton (1H) and hyperpolarized Xenon-129 (HP 129Xe) in the rat brain at 2.35 Tesla. It consists of a double-tuned (100 MHz- 27.7 MHz) volume coil, which could be used for both transmitting and receiving, and of a receive-only single-tuned (27.7 MHz) coil. The double-tuned coil consists of two concentric birdcage resonators. The inner one is a low-pass design and it is tuned to 27.7 MHz, while the outer one, tuned to 100 MHz, is high-pass. The receive-only coil is a surface coil which is decoupled from the double-tuned volume coil by an active decoupling circuitry based on the use of PIN diodes. A home-built Transmit/Receive (T/R) driver ensures biasing of the PIN diodes in both volume and surface coils. The original concepts of the design are addressed, and practical details of realization are presented. One of the underlying ideas behind this work is to proceed well beyond the application to the MRI of HP 129Xe. Actually, this design could be easily adapted for a large palette of other MRI applications. Indeed, we tried to make the design versatile, simple and easy to replicate by other research groups, with a low-cost, minimum development time and accepted performances. The prototype was validated at 100 MHz and at 26.4 MHz (sodium-23 resonance frequency at 2.35 T). MRI experiments were performed using phantoms. In vivo 1H images and 23Na spectra of the rat brain are also presented.
Highlights
Nuclear Magnetic Resonance (NMR) and MagneticResonance Imaging (MRI) are important diagnostic and analytical tools for biomedical studies
The receive-only coil is a surface coil which is decoupled from the double-tuned volume coil by an active decoupling circuitry based on the use of PIN diodes
The measurement of changes in both global cerebral blood flow2 and regional cerebral blood flow3 is of great value for functional brain studies as well as for the diagnosis of a large number of brain diseases (Alzheimer, epilepsy, Parkinson, ischemia...)
Summary
Nuclear Magnetic Resonance (NMR) and MagneticResonance Imaging (MRI) are important diagnostic and analytical tools for biomedical studies. Several studies carried out in our laboratory and by some research groups in the world, have already demonstrated that the MRI of HP 129Xe may allow quantitative measurement of the cerebral blood flow (CBF) with a high spatial resolution [2,3,4,5] This physiological parameter, which is defined as the blood supply to the brain in a given time and per mass unit of brain tissue, is tightly regulated to meet the brain’s metabolic demands. The measurement of changes in both global cerebral blood flow (gCBF) and regional cerebral blood flow (rCBF) is of great value for functional brain studies as well as for the diagnosis of a large number of brain diseases (Alzheimer, epilepsy, Parkinson, ischemia...) For such measurements, especially those of the rCBF, to become quantitatively reliable by the MRI of HP 129Xe, one must first overcome several experimental and instrumental challenges
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