Dhakal, B., Hardy, B. M., Anderson, A. W., Does, M. D., Xu, J., & Gore, J. C. (2025). A practical prescription for magnetic resonance microscopy in a horizontal bore magnet. NPJ Imaging, 3(1), 64. https://www.nature.com/articles/s44303-025-00129-4
Magnetic resonance microscopy (MRM) allows researchers to create extremely detailed proton images of biological tissues, plants, and porous materials, revealing microstructures that other imaging methods cannot capture. A key challenge in MRM is that achieving such high spatial resolution reduces the signal strength, making it harder to get clear images. To overcome this, specialized equipment like highly sensitive microcoils, powerful gradient systems, and strong magnetic fields is required. In this work, we provide a step-by-step guide for building a cost-effective and flexible microimaging probe system that works with horizontal bore high-field MRI machines. We demonstrate its capabilities at 15.2 T by acquiring ultra-high-resolution images (15 μm isotropic voxels) of ex vivo mouse spinal cord and hippocampus, clearly showing microstructural details, with signal-to-noise ratios of 38 and 67, respectively, over scans lasting 45–46 hours. Faster imaging is possible using compressed sampling techniques. The flexible design allows solenoid coils from less than 1 mm to 10 mm in diameter, making it adaptable for imaging a wide range of biological samples at very high resolution.
Fig. 1: SNR optimization of the micro-solenoid imaging coil.
a Simulated SNR as a function of the wire diameter-to-pitch ratio (dwire/s) for solenoids with wire diameters ranging 150–440 μm. The solenoid length was fixed to the arithmetic mean length of solenoids used for experimental SNR measurements (shown in b–e). For example, for dwire = 150 µm (red plot), the solenoid length was set to the average length of the four solenoids (red hollow triangles) used for SNR measurements in (b). A similar approach was applied to other wire diameters. b–e Comparison of simulated and experimentally measured SNR versus dwire/s for wire diameters of (b) 150 µm, (c) 230 µm, (d) 280 µm, and (e) 440 µm. Measured SNR values are shown as hollow triangles, with error bars indicating mean ± standard deviation across three adjacent slices. Hollow circles represent simulated SNR values accounting for the actual solenoid lengths, while the dotted curves represent the same simulation plots from subplot (a). To allow direct comparison across coil geometries, all simulated and experimental SNR values (in all subplots) were normalized by dividing by the minimum SNR of the 150 µm dataset for that data type (hollow red circle for simulated and hollow red triangle for experimental in subplot (b)). As a result, the 150 µm dataset has a baseline of 1, while the other datasets are scaled relative to this same reference, allowing direct comparison of relative SNR across wire diameters. f Summary table showing measured and simulated peak dwire/s values (see Supplementary Fig. 1 for details of peak calculation), absolute and percentage differences (), root-mean-square error (RMSE), and correlation coefficients (R) between simulated and measured SNR curves for each wire diameter. g Simulated maximum deviation of RF field strength at the sample’s edges versus length of coil to diameter of the coil ratio (lcoil/dcoil) given the length of sample to diameter of coil ratio (lsample/dcoil) of 2. h Simulated SNR versus wire diameter (dwire) for various numbers of solenoid turns, considering the following coil geometry: coil diameter (dcoil) = 3.7 mm, coil length (lcoil) = 8.4 mm, sample diameter = 3 mm, and sample length = 6 mm. All the SNR values in (h) were normalized by the minimum SNR across all cases, occurring at dwire = 4.2 mm.