Prepolarized MRI of Hard Tissues and Solid-State Matter

Abstract

Prepolarized Magnetic Resonance Imaging (PMRI) is a long-established technique conceived to counteract the loss in signal-to-noise ratio (SNR) inherent to low-field MRI systems.When it comes to hard biological tissues and solid-state matter, PMRI is severely restricted by their ultra-short characteristic relaxation times. Here we demonstrate that efficient hard tissue prepolarization is within reach with a special-purpose 0.26 T scanner designed for dental MRI and equipped with suitable high-power electronics. We have characterized the performance of a 0.5 T prepolarizer module which can be switched on and off in just 200 µs. To that end, we have used resin, dental and bone samples, all with T 1 times in the order of 20 ms at our field strength. The measured SNR enhancement is in good agreement with a simple theoretical model, and small deviations in extreme regimes can be attributed to mechanical vibrations due to the magnetic interaction between the prepolarization and main magnets. Finally, we argue that these results can be applied to clinical dental imaging, opening the door to replacing hazardous X-ray systems with low-field PMRI scanners.

Benchmarking the performance of a low‐cost magnetic resonance control system at multiple sites in the open MaRCoS community

“…[1][2][3] LF-MRI is developing as a customizable and affordable complement to standard high-field MRI (>1 T), which is an expensive medical imaging modality in terms of purchase cost, maintenance, siting, and training, and consequently is concentrated in large hospitals in the economically developed world. [4][5][6][7][8] In the last few years, LF-MRI has demonstrated its value for point-of-care imaging, [9][10][11][12][13][14][15] home healthcare, 16 quantitative MRI and fingerprinting, 17,18 hard-tissue imaging, [19][20][21] and artifact-free imaging of metallic implants, 16,22 as well as educational purposes, 23 among others. These achievements are enabled by a new generation of scanners combining refined hardware engineering with powerful computational algorithms, including machine learning architectures.…”

MaRCoS, an open-source electronic control system for low-field MRI

“…At the marcos client level, a sequence is specified by supplying pairs of (time, value) arrays for each hardware output and control, such as the TX envelope, gradient waveforms, etc. 15 . The library scales and rounds the arrays to machine units, applies time offsets to cancel out latencies in the gradient serialisers and other hardware, and compiles these values and times into binary instructions.…”

“…This will be used for multi-device synchronization in the future 15. For example, to specify two pulses of 70% full-scale amplitude starting at 20 µs and 100 µs from the beginning of the sequence, each with a duration of 30 µs, one would supply the array pair ([20, 50, 100, 130], [0.7, 0, 0.7, 0]).…”

Low field slice-selective ZTE imaging ofultra-short T2 tissues based on spin-locking

“…Zero Echo Time pulse sequences, otherwise known as Zero TE or ZTE, are designed to capture the weak and short-lived signal emitted by hard biological tissues and solid-state matter in Magnetic Resonance Imaging (MRI) scanners 1,2 . ZTE sequences are particularly suitable for ultra-short (submillisecond) T 2 or T * 2 MRI 3 , and have been successfully used for a wide variety of applications 4 , including imaging of tendons and bones 5,6 , teeth [7][8][9] , myelin 10 or lungs 11 . Two other families of sequences used for MR imaging of short T 2 samples are SWeep Imaging with Fourier Transformation (SWIFT, 12 ) and Ultra-short Echo Time (UTE, 13 ), although the latter is not suitable when the sample T 2 is comparable to or shorter than the time it takes to switch on the encoding magnetic gradient fields.…”