Micro MRI of the mouse brain using a novel 400 MHz cryogenic quadrature RF probe

Abstract

The increasing number of mouse models of human disease used in biomedical research applications has led to an enhanced interest in non-invasive imaging of mice, e.g. using MRI for phenotyping. However, MRI of small rodents puts high demands on the sensitivity of data acquisition. This requirement can be addressed by using cryogenic radio-frequency (RF) detection devices. The aim of this work was to investigate the in vivo performance of a 400 MHz cryogenic transmit/receive RF probe (CryoProbe) designed for MRI of the mouse brain. To characterize this novel probe, MR data sets were acquired with both the CryoProbe and a matched conventional receive-only surface coil operating at room temperature (RT) using conventional acquisition protocols (gradient and spin echo) with identical parameter settings. Quantitative comparisons in phantom and in vivo experiments revealed gains in the signal-to-noise ratio (SNR) of 2.4 and 2.5, respectively. The increased sensitivity of the CryoProbe was invested to enhance the image quality of high resolution structural images acquired in scan times compatible with routine operation (< 45 min). In high resolution (30 x 30 x 300 microm(3)) structural images of the mouse cerebellum, anatomical details such as Purkinje cell and molecular layers could be identified. Similarly, isotropic (60 x 60 x 60 microm(3)) imaging of mouse cortical and subcortical areas revealed anatomical structures smaller than 100 microm. Finally, 3D MR angiography (52 x 80 x 80 microm(3)) of the brain vasculature enabled the detailed reconstruction of intracranial vessels (anterior and middle cerebral artery). In conclusion, this low temperature detection device represents an attractive option to increase the performance of small animal MR systems operating at 9.4 Tesla.

<i>In Vivo</i> Brain MR Imaging at Subnanoliter Resolution: Contrast and Histology

“…2 In GM, nerve cell bodies are often tightly assembled as layers or nuclei that play specific roles as functional units. Based on the shorter relaxation times of water in intracellular spaces compared to free water, 59 cell assemblies can be delineated by T 1 W, 17,29 T 2 W, 19,60 T 2 *-weighted, 61 and MT-weighted MR imaging. 29 Comparisons of T 1 , T 2 , and MT contrast at sufficient resolution indicate that the relaxation enhancement predominantly reflects the presence of paramagnetic ions and does not primarily result from interactions with diamagnetic macromolecules.…”

Current Developments In Mri For Assessing Rodent Models of Multiple Sclerosis

“…At 9.4T, cryogenic coils boost Signal to Noise Ratio (SNR) by a factor of up to 2.9, which can be exploited for in--vivo imaging to significantly shorten experiment time [111,112]. For example, a volumetric T 2 WI at (60 μm) 3 --isotropic resolution could be acquired within 45 min.…”

“…For example, a volumetric T 2 WI at (60 μm) 3 --isotropic resolution could be acquired within 45 min. The cryocoil has a maximum signal penetration of approximately 3 mm from the brain surface and can reveal intricate cortical and subcortical details of the mouse brain [112]. Despite its high sensitivity, the cryocoil has some disadvantages in terms of its inhomogeneous RF excitation profile.…”

“…Gradual loss of signal--to--noise ratio for deeper (ventral) brain structures were also observed due to the positioning of the surface array coil on the cortex. However, such artifacts can be minimized with careful adjustment of the RF power and image post--processing [111,112].…”

In Vivo X-Ray Digital Subtraction and CT Angiography of the Murine Cerebrovasculature Using an Intra-Arterial Route of Contrast Injection

“…While micro-CTA of the cerebral vasculature in live mice is feasible at high resolutions (16 m)-at the expense of relatively high contrast doses (tail vein injection of 350 L contrast agent over a 40-second scan time) and high radiation doses 9,11 -due to insufficient temporal resolution, micro-CTA and small-animal MRA [12][13][14][15][16] do not yet allow monitoring of the murine cerebrovascular blood flow.…”