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 technology companies have demonstrated the first decisive steps towards portability within medical facilities and vehicles. However, these scanners’ weight and dimensions are 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, small footprint, 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 and tissue contrast suffice for 2D and 3D reconstructions with diagnostic value. 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.

Prepolarized MRI (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 ex vivo 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 200 μs. To this end, we have used resin, dental and bone samples, all with T1 times of the order of 20 ms at our field strength. The measured SNR enhancement is in good agreement with a simple theoretical model, and deviations in extreme regimes can be attributed to mechanical vibrations due to the magnetic interaction between the prepolarization and main magnets.

Laser–plasma proton sources and their applications to preclinical research has become a very active field of research in recent years. In addition to their small dimensions as compared to classical ion accelerators, they offer the possibility to study the biological effects of ultra-short particle bunches and the correspondingly high dose rates. We report on the design of an experimental setup for the irradiation of cell cultures at the L2A2 laboratory at the University of Santiago de Compostela, making use of a 1.2 J Ti: Sapphire laser with a 10 Hz repetition rate. Our setup comprises a proton energy separator consisting of two antiparallel magnetic fields realized by a set of permanent magnets. It allows for selecting a narrow energy window around an adaptable design value of 5 MeV out of the initially broad spectrum typical for Target Normal Sheath Acceleration (TNSA). At the same time, unwanted electrons and X-rays are segregated from the protons. This part of the setup is located inside the target vessel of the L2A2 laser. A subsequent vacuum flange sealed with a thin kapton window allows for particle passage to external sample irradiation. A combination of passive detector materials and real-time monitors is applied for measurement of the deposited radiation dose. A critical point of this interdisciplinary project is the manipulation of biological samples under well-controlled, sterile conditions. Cell cultures are prepared in sealed flasks with an ultra-thin entrance window and analysed at the nearby Fundación Pública Galega Medicina Xenómica and IDIS. The first trials will be centred at the quantification of DNA double-strand breaks as a function of radiation dose.

Objective. The goal of this work is to extend previous peripheral nerve stimulation (PNS) studies to scenarios relevant to magnetic particle imaging (MPI) and low-field magnetic resonance imaging (MRI), where field dynamics can evolve at kilo-hertz frequencies. Approach. We have constructed an apparatus for PNS threshold determination on a subject’s limb, capable of narrow and broad-band magnetic stimulation with pulse characteristic times down to 40 μ s. Main result. From a first set of measurements on 51 volunteers, we conclude that the PNS dependence on pulse frequency/rise-time is compatible with traditional stimulation models where nervous responses are characterized by a rheobase and a chronaxie. Additionally, we have extended pulse length studies to these fast timescales and confirm thresholds increase significantly as trains transition from tens to a few pulses. We also look at the influence of field spatial distribution on PNS effects, and find that thresholds are higher in an approximately linearly inhomogeneous field (relevant to MRI) than in a rather homogeneous distribution (as in MPI). Significance. PNS constrains the clinical performance of MRI and MPI systems. Extensive magneto-stimulation studies have been carried out recently in the field of MPI, where typical operation frequencies range from single to tens of kilo-hertz. However, PNS literature is scarce for MRI in this fast regime, relevant to small (low inductance) dedicated MRI setups, and where the resonant character of MPI coils prevents studies of broad-band stimulation pulses. This work advances in this direction.

We present a magnet and high-power electronics for prepolarized magnetic resonance imaging (PMRI) in a homemade, special-purpose preclinical system designed for simultaneous visualization of hard and soft biological tissues. The sensitivity of magnetic resonance imaging (MRI) systems grows with field strength, but so do their costs. PMRI can boost the signal-to-noise ratio (SNR) in affordable low-field scanners by means of a long and strong magnetic pulse. However, this must be rapidly switched off prior to the imaging pulse sequence, in timescales shorter than the spin relaxation (or $T_{1}$ ) time of the sample. We have operated our prepolarizer at up to 0.5 T and demonstrated enhanced magnetization, image SNR, and tissue contrast with PMRI of tap water and an ex vivo mouse brain and food samples. These have $T_{1}$ times ranging from hundreds of milli-seconds to single seconds, while the preliminary high-power electronics setup employed in this work can switch off the prepolarization field in tens of milli-seconds. In order to make this system suitable for solid-state matter and hard tissues, which feature $T_{1}$ times as short as 10 ms, we are developing new electronics, which can cut switching times to $\sim {300} {\mu{\mathrm {s}}}$ . This does not require changes in the prepolarizer module, opening the door to the first experimental demonstration of PMRI on hard biological tissues.

This article presents the design and experimental characterization of an electromagnet rampable up to 1 T and tailored to meet the demands of a magnetic resonance imaging (MRI) system conceived for spatial resolutions at the level of tens of microns. For high image quality, MRI requires a homogeneous magnetic field over the field of view (FoV) where the sample is imaged. We have opted for passive shimming based on optimal pole profiling and measure a relative field inhomogeneity of 71 parts per million over a spherical FoV of 20 mm diameter. Fringe-field lines are strongly confined to avoid interference with other devices. The magnet performance closely follows our expectations from numerical simulations in all of the experimental tests carried out. In addition, we present the solutions adopted for thermal management and the design of a mechanical structure to distribute the weight and integrate the platform to move the sample in and out of the magnet.

Magnetic Resonance Imaging (MRI) of hard biological tissues is challenging due to the fleeting lifetime and low strength of their response to resonant stimuli, especially at low magnetic fields. Consequently, the impact of MRI on some medical applications, such as dentistry, continues to be limited. Here, we present three-dimensional reconstructions of ex-vivo human teeth, as well as a rabbit head and part of a cow femur, all obtained at a field strength of 260 mT. These images are the first featuring soft and hard tissues simultaneously at sub-Tesla fields, and they have been acquired in a home-made, special-purpose, pre-medical MRI scanner designed with the goal of demonstrating dental imaging at low field settings. We encode spatial information with two pulse sequences: Pointwise-Encoding Time reduction with Radial Acquisition and a new sequence we have called Double Radial Non-Stop Spin Echo, which we find to perform better than the former. For image reconstruction we employ Algebraic Reconstruction Techniques (ART) as well as standard Fourier methods. An analysis of the resulting images shows that ART reconstructions exhibit a higher signal-to-noise ratio with a more homogeneous noise distribution.

RESULTS A multichannel system based on an array of 10 planar coils has been chosen to design the shimming system. This system is composed by two PCBs each containing 5 Planar Coils (see Fig.1b) placed each around the FoV. For the coil design a fingerprint pattern was chosen. Each coil has an outer diameter of 50mm (16 turns) and there is composed of 8 layers and connected in series. For the power supply and control of the shimming system, an in-house system was built (see Figs.1c-d) with each coil can be powered up to 40 W and independently controlled. A driver board controls up to 20 channels independently and is powered by LCM600 power supply [3]. The communication with the PC is performed with a USB-i 2 C adapter. A more detailed description of the control system can be found in [4]. Before manufacturing the shimming array, a system formed by two coils was built and characterized with a magnetic test bench available in the i3M (Fig.1e). Fig.1f shows the MF profile for this proof system using a current I=7A.

Gradient coils are a main part of a Magnetic Resonance Imaging (MRI) system. The aim of gradient coils in a MRI system is to encode spatially the Field of View (FoV). Different gradient coil design methods have been presented in the last years. Some factors such as linearity, inductance and resistance must be taken in account to obtain an optimized design for the gradient coils. A combinatorial method to design the MRI gradient coils is presented. The method developed uses very simple shapes to obtain the coil path patternand it allows finding the best coil design in a time less than 2 minutes. Path combination which generates the highest gradient field is chosen for the X/Y gradient coil, and also the most homogeneous magnetic field is considered to select the Z-gradient path combination. Efficiencies values of 93 and 19.4 mT/m/A are obtained for X/Y and Z gradient coil, respectively. The gradient system has been tested in a biplanar permanent magnet (PM) system. Experimental gradient coil evaluation shows the ability to generate a strong gradient field (0.56 and 0.75 T/m for X/Y and Z gradient coil, respectively). A preliminary 2D MRI image with 1mm accuracy is obtained.

We report on benchmark tests of a 3 TW/50 fs, table-top laser system specifically developed for proton acceleration with an intrinsic pump rate up to 100 Hz. In two series of single-shot measurements differing in pulse energy and contrast the successful operation of the diode pumped laser is demonstrated. Protons have been accelerated up to 1.6 MeV in interactions of laser pulses focused on aluminium and mylar foils between 0.8 and 25 μm thickness. Their spectral distributions and maximum energies are consistent with former experiments under similar conditions. These results show the suitability of our system and provide a reference for studies of laser targets at high repetition rate and possible applications.

Purpose/Introduction MRI has been traditionally used to study soft tissue. Currently, the most used technique to obtain teeth images is projection radiography or cone beam computer tomography (CBCT) [1]. The main disadvantage of these methods is that they involve ionizing radiation. Typical MRI pulse sequences are not appropriate to catch signal from short T2* tissues, such as bones or teeth, because their relaxation times are of the order of the gradient rise time. However, there are pulse sequences, such as UTE, ZTE [2] or SPRITE [3], which seem more suitable for these kinds of tissues. In this work, we have implemented SPRITE pulse sequences in order to study the advantages they can provide for obtaining teeth images compared to typical pulse sequences, such as Gradient Echo [4].

In PET systems with a geometry different from a closed ring, the Time of Flight (TOF) of the annihilation photons appears to be relevant. Such a system capability helps to compensate the missing angular information that generates artifacts on the reconstructed images. In this work, two ASIC designs are evaluated for their use in PET systems having accurate coincidence resolving times (CRT) while preserving both energy and spatial resolutions. One of the ASIC options is the TOFPET1 from PETsys and the other the so-called PETIROC2 from Weeroc. Detection blocks based on scintillation LYSO crystal arrays have been used to first optimize the experiments. Parameters such as spatial, energy and time resolution have been obtained. Promising CRT results were found nearing 350 ps FWHM for a pair of photosensor channels (PETsys) and roughly 800 ps for all 16 against 16 channels (Weeroc). In terms of spatial resolution, 2 mm pixels size are well resolved with energy values approaching 15% have preliminary been measured for both ASICs. With the TOFPET1 ASIC, also tests with monolithic crystals were carried out. Those showed the system to provide depth of interaction (DOI) information. A DOI resolution (FWHM) of about 3 mm was preliminary estimated in a 25×25×10 mm 3 LYSO scintillator. A calibration process for time alignment of the signal paths was carried out to provide accurate CRT results. The time walk error between channels was also compensated. Several methods for the timestamp averaging have been tried, resulting on preliminary CRT values in the 1 ns FWHM range.

Magnetic Resonance Imaging (MRI) is a widely used technique to obtain images in different applications based on the nuclear magnetic renonance (NMR) phenomenon. Gradient coils are the responsible components for encoding the volume of interest (VOI). Linearity, inductance and resistance are taken in account to perform the gradient coil design. In this work, EM and thermal gradient coil properties are studied and two cooling system are presented to cool them. Finally, the gradient coils are tested in a biplanar permanent magnet system and a 2D phantom image is obtained.

A histological intraoperative analysis of tissue specimen is usually required for evaluation of sentinel lymph node (SLN) and determination of margins of surgical resection. Currently, this analysis is performed by Touch Imprint Cytology (TIC), Frozen Section (FS) analysis, scrape cytology or a combination of these methods. We propose an alternative approach based on Magnetic Resonance Imaging (MRI). In particular, in this contribution we present the development, components, characterization as well as the first images obtained with our tabletop and transportable MRI system. Experiments with our MRI system shown that we can get images with high image spatial resolution (about 100 urn) and good signal-to-noise ratio in only few seconds using fast pulse sequences (fast and spin gradient echo).

In this work, a direct image reconstruction algorithm for PET is proposed. This method follows naturally from the concept of LOR, and easily admits depth of interaction and time of flight information. In addition, this algorithm does not require the computation of sinograms or a system matrix. Thus, it is not restricted in the formation of high pixel density images and allows the image formation in real-time (simultaneously to the data acquisition process). One of the key advantages of this algorithm is the preservation of high frequencies, producing accurate images that can be generated in high resolution, because of the lack of space restrictions imposed by the intermediate generation of sinograms, aside of the native support of real-time image reconstruction. In this work, a C++ implementation of the described algorithm has been developed. Image reconstructions of simulated PET events according to the MindView (a brain dedicated PET insert) scanner geometry and real data measured with the first one ring prototype system have been performed. Results show capability of correct image formation, either with simulated and real data.

In PET detectors based in monolithic scintillators the interaction coordinates of each photon impact, in particular the 511 keV energy, can be determined from the light distribution sampled at the photosensors pixels. However, some of these distributions can be produced by pure dark noise from the SiPM photosensor, multi-interaction events with long travelled distance, pile-up, etc. Early rejection of these events can improve the SNR of the detector block and, as a result, in the also in reconstructed PET image. Moreover, this early rejection can reduce the statistics necessary to reconstruct those images preserving the SNR. To perform the rejection of noisy distributions, a comparison between a theoretical light distribution and the measured one is made by means of the Pearson product-moment correlation coefficient. This coefficient provides a metric, with range [-1, 1], suitable for assessing the similarity between the two distributions and, thus, allowing the rejection of uncorrelated events. The theoretical model of the light distribution has been obtained using a model based on Montecarlo simulations of a detector block formed by a thick LYSO scintillator crystals (50×50×20 mm 3 ). We carried out an experiment based on two detector blocks with the described monolithic LYSO scintillators coupled to a custom photosensor SiPM array. After analyzing the FWHM of small size 22 Na sources, an improvement of the SNR from 2.2 to 4.1 was observed when the filter was applied. In another test with reconstructed images using data belonging to the one ring prototype of the MindView brain PET insert also showed an improvement in the SNR. Moreover, the filter reduced the data used for reconstruction in about 20% but obtaining, as mentioned above, an improved image quality.

A series of small size 22 Na point sources have been simulated using GATE, following the NEMA protocol, and applied to the geometry of a brain dedicated PET so-called MindView. The simulated scanner geometry is currently composed by one ring of 20 detector blocks with a distance of about 330 mm between opposite detectors. Each detector module includes a monolithic LYSO crystal of 50 × 50 × 20 mm 3 and a custom 12 × 12 SiPM array (TSV-type, SensL). The system defines an axial and trans-axial fields of view (FoV) of about 46 mm and 240 mm, respectively. The scintillation light inside the monolithic block was simulated in GEANT4 and is sampled following the readout scheme providing information on each SiPM array row and column (12 + 12). Out of this, three different approaches for the determination of the impact coordinates within the monolithic crystals have been considered. A first approach makes use of the center of gravity (CoG) calculation for the planar XY coordinates but the photon impact depth of interaction (DoI) is not considered. The other methods obtain the XY coordinates using the Raise to Power algorithm (RTP) before CoG calculation, with both discrete (second method) and continuous (third one) DoI information. The data is introduced on the STIR platform for reconstruction using a filtered back projection 3D re-projected algorithm (FBP3DRP). Spatial resolutions ranging in the intervals [2 mm, 3.4 mm], [2.3 mm, 3.3mm] and [2.2 mm, 2.3 mm] have been obtained for the radial, tangential and axial directions, respectively. The points sources were positioned at a radial offset of 100 mm radially out of the center.

Background: The interaction of highly intense laser pulses with solid targets covers a wide range of phenomena over several orders of magnitude in laser intensity. Time-of-flight measurements provide an accurate reconstruction of the ion energy spectra. We report on the observation of aluminium ions from a laser-plasma interaction by a scintillator-based detector with adjustable dynamic range. Methods: Data have been taken at a 30 fs, 200 TW pulsed Ti:Sapphire laser focused on aluminium foils with 1.8 and 12.5 μm thickness. A time-of-flight detector consisting in a plastic scintillator with fibre-optic coupling to a PMT has been mounted 50 cm behind the target. The PMT output pulses have been recorded on a fast oscilloscope. Results: After an initial peak caused by prompt X-rays and relativistic electrons, a second peak has been observed in the time-of-flight spectra after several microseconds. It corresponds to Al ions with energies of the order 1 keV. Quantitative spectra have been reconstructed. A PIC simulation of the plasma expansion gives an explanation for the acceleration of initially thermal ions to the observed energies. Discussion: At the given ion energies the detection mechanism, based on electrostatic charge transfer, is different to the usual ionisation process in scintillators. Additional tests have been performed to corroborate its working principle. At the nominal, focused laser intensity with femtosecond pulses, proton acceleration to MeV energies would be expected, but is excluded by our observations. This detailed study of the interaction kinematics indicates the formation of a cold plasma by a prepulse several picoseconds ahead of the peak intensity.

In Positron Emission Tomography (PET) detectors based on monolithic scintillators, the photon interaction position needs to be estimated from the light distribution (LD) on the photodetector pixels. Due to the finite size of the scintillator volume, the symmetry of the LD is truncated everywhere except for the crystal center. This effect produces a poor estimation of the interaction positions towards the edges, an especially critical situation when linear algorithms, such as Center of Gravity (CoG), are used. When all the crystal faces are painted black, except the one in contact with the photodetector, the LD can be assumed to behave as the inverse square law, providing a simple theoretical model. Using this LD model, the interaction coordinates can be determined by means of fitting each event to a theoretical distribution. In that sense, the use of neural networks (NNs) has been shown to be an effective alternative to more traditional fitting techniques as nonlinear least squares (LS). The multilayer perceptron is one type of NN which can model non-linear functions well and can be trained to accurately generalize when presented with new data. In this work we have shown the capability of NNs to approximate the LD and provide the interaction coordinates of γ-photons with two different photodetector setups. One experimental setup was based on analog Silicon Photomultipliers (SiPMs) and a charge division diode network, whereas the second setup was based on digital SiPMs (dSiPMs). In both experiments NNs minimized border effects. Average spatial resolutions of 1.9 ±0.2 mm and 1.7 ±0.2 mm for the entire crystal surface were obtained for the analog and dSiPMs approaches, respectively.