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The goal of this work is to showcase the clinical value that portable MRI can provide in crowded events and major sports competitions. We temporarily installed a low-field and low-cost portable MRI system for extremity imaging in the medical facilities of the Ricardo Tormo Motor Racing Circuit during the four days of the Motorcycle Grand Prix held in Valencia (Spain), which closed the 2022 season of the MotoGP. During this time, we scanned 14 subjects, running a total of 21 protocols for wrist, knee and ankle imaging. Each protocol included a minimum of one T1-weighted 3D-RARE sequence for general anatomical information, and one 3D-STIR sequence to highlight fluid accumulation and inflammation. The circuit medical staff were able to visualize a number of lesions and conditions in the low-field reconstructions, including gonarthrosis, effusion, or Haglund's syndrome, as well as metallic implants and tissue changes due to surgical interventions. Out of eight low-field acquisitions on previously diagnosed lesions, only two (a meniscus tear and a Baker cyst) were not detected by the experts that evaluated our images. The main highlight was that a low-field MRI scan on a subject reporting pain in a wrist revealed a traumatic arthritis which an X-ray radiograph and visual inspection had missed. We have operated in a scenario where high-field MRI is unlikely to play a role but where a low-field system can lead to improved medical attention. In the case reported here, system transport, installation in the circuit facilities and calibration were all uncomplicated. The images presented to the medical staff were mostly unprocessed and there is thus room for improvement. In conclusion, this work supports the claim that low-field MRI can likely provide added value whenever concepts such as accessibility, portability and low-cost outweigh exquisite detail in images.

Mobile medical imaging devices are invaluable for clinical diagnostic purposes both in and outside healthcare institutions. Among the various imaging modalities, only a few are readily portable. Magnetic resonance imaging (MRI), the gold standard for numerous healthcare conditions, does not traditionally belong to this group. Recently, low-field MRI start-up companies have demonstrated the first decisive steps towards portability within medical facilities, but these are so far incompatible with more demanding use cases such as in remote and developing regions, sports facilities and events, medical and military camps, or home healthcare. Here we present in vivo images taken with a light, home-made, low-field extremity MRI scanner outside the controlled environment provided by medical facilities. To demonstrate the true portability of the system and benchmark its performance in various relevant scenarios, we have acquired images of a volunteer's knee in: i) an MRI physics laboratory; ii) an office room; iii) outside a campus building, connected to a nearby power outlet; iv) in open air, powered from a small fuel-based generator; and v) at the volunteer's home. All images have been acquired within clinically viable times, and signal-to-noise ratios (SNR) and tissue contrast suffice for 2D and 3D reconstructions with diagnostic value, with comparable overall image quality across all five situations. Furthermore, the volunteer carries a fixation metallic implant screwed to the femur, which leads to strong artifacts in standard clinical systems but appears sharp in our low-field acquisitions. Altogether, this work opens a path towards highly accessible MRI under circumstances previously unrealistic., Comment: 17 pages, 4 figures, comments welcome

Purpose: To expand the capabilities of Zero Echo Time (ZTE) pulse sequences with a slice selection method suitable for the shortest-lived tissues in the body. Methods: We introduce two new sequences that integrate spin-locking pulses into standard ZTE imaging to achieve slice selection: one for moderately short $T_2$ (DiSLoP), the other for ultra-short $T_2$ samples (PreSLoP). These methods exploit the slower signal decay (at $T_{1\rho}\gg T_2$) to retain the magnetization in the slices during the selection process, which is otherwise comparable to or even much longer than $T_2$. Results: We demonstrate control over the slice profiles and positions for 2D imaging. We measure magnetization decay times during spin-locking ($T_{1\rho}$) as a function of pulse amplitude, showing significant lifetime enhancement for amplitudes as low as 10 uT. We show imaging of slice-selected samples with $T_2$ characteristic times in the range of single milliseconds with DiSLoP and PreSLoP, and with the latter for sub-millisecond $T_2$ tissues. As compared to standard 3D ZTE sequences, PreSLoP achieves the same signal-to-noise ratio (SNR) in 2-5 times shorter scan times, and we argue that this is due to the filling scheme of the finite gap at the center of $k$-space unavoidable with ZTE sequences. Finally, we discuss a combination of DiSLoP with a dynamical decoupling sequence to avoid this central gap, leading to further scan time accelerations. Conclusions: The proposed sequences are capable of slice-selected 2D imaging of tissues with $T_2$ as low as 275 us with good SNR within clinically acceptable scan times., Comment: 12 pages, 14 figures, commments welcome