Performance of a 200-MHz cryogenic RF probe designed for MRI and MRS of the murine brain

A cryogenic 200-MHz RF transmit/receive probe (CryoProbe) made of copper and designed for murine brain studies is described. The probe operates at 30K and its performance was compared to a home-made surface coil of equal dimensions and a mouse head volume resonator, both operating at room temperature (RT). Since for small volumes of tissue interrogated (< 5 mL) sample noise and thermal noise of the receiver are of comparable magnitude, considerable noise reduction can be achieved by cooling of the receiver system, e.g., using cold helium gas. The effect of temperature lowering on the signal-to-noise ratio (SNR) was assessed in phantom and in vivo murine brain studies using conventional MRI sequences (spin and gradient echo) and single voxel MR spectroscopy. Consistent sensitivity increases were observed for the CryoProbe. SNR increases by a factor >= 2 for the phantom experiments and by factors of 1.8 to 1.9 for in vivo experiments when compared to the RT surface coil for both MRI and MRS experiments. These results are in good agreement with estimated SNR gains for a circular surface coil probe cooled to 30K. The use of a cryogenic probe represents an economically attractive option to enhance the sensitivity in small animal MRI/MRS.