Extend your conventional animal MRI to a microimaging system

Introduction MR microscopy offers great potential to apply anatomical, functional and spectroscopic MRI techniques to small objects or small regions of interest with high SNR. With the Bruker Coil-on-a-Chip technology (Bruker BioSpin AG, Switzerland), highly sensitive microcoils are available on the market for high resolution imaging in NMR spectrometers [1]. In this work, we show that these microcoils can be implanted and used also in a conventional animal MRI system without expensive changes in hardware architecture. Material and Methods Implementation and MRI experiments were performed on a 9.4T Bruker BioSpec 94/20 system (Bruker BioSpin, Ettlingen, Germany) equipped with a B-GA12S1 gradient system (max. gradient amplitude: 675 mT/m, slew rate: 4673 T/m/s). The tailor-made probehead is mounted on the standard animal bed sliding system. This allows one to position the inlet containing the microcoil and sample (Fig. 1b) inside the magnet without contact to the vibrating gradient tube. Thus the transfer of vibrations during the experiment to the probe head is avoided. In addition, it includes a complete tune & match network, which can be easily adjusted from outside the magnet (Fig. 1c). As the typical power consumption of a micro coil is in the order of μW, high transmitter attenuation would be necessary, resulting in very noisy pulse signals. To overcome this problem, microcoils were directly connected to and operated using the Signal Generation Unit (SGU). Hence, no additional amplifier or attenuator was needed within the transmit path. Standard adjustment routines (such as pulse power estimation) have been extended to provide a semiautomatic and quick adjustment of all MRI system settings. Basic imaging sequences (GE and SE) have been modified to improve spatial resolution To demonstrate the successful extension of the conventional MRI system to a microimaging system, GE images of different resolution phantoms were acquired using a planar micro surface coil with a multi-turn spiral (ID 1000 μm, OD 1300 μm, see Fig. 1 a) [2]. In addition, SNR has been compared to results from a conventional mouse quadrate birdcage coil (ID 35 mm).