arXiv subjects

P. Martínez

Publications and source records attributed to P. Martínez.

5 recordsLinked to original sources

arXiv2026

The SPHERE infrared survey for exoplanets (SHINE) V. Full sample characterization

Unbiased surveys of large stellar samples are the prime means through which the prevalence of exoplanets can be derived, and crucial constraints to planet formation models can be set. Direct imaging (DI) is ideally positioned to probe the outer regions (5-300au) of planetary systems, providing complementary information to techniques such as transits and radial velocities. We present the full sample of the SpHere INfrared survey for Exoplanets (SHINE), the second largest DI campaign to date. SHINE observed 460 stars between 2015 and 2023 thanks to the guaranteed time observations (GTO) allocated by ESO to the SPHERE consortium at VLT. The goal of this paper is to homogeneously derive the stellar properties of the targets and to define a subsample of young single hosts to be used as a starting point for the final statistical analysis of the survey. Stellar ages were determined based on kinematic indicators (such as the membership to young moving groups), age diagnostics (lithium abundance, rotation, activity), and isochrone fitting. A thorough vetting for binarity was undertaken combining astrometric, spectroscopic, and imaging data. A subsample of 333 stars, covering a large extent of stellar ages and masses, was constructed. Selection criteria, global features, as well as the properties of individual stars are reported and discussed.

astro-ph.EP↗

arXiv2023

Portable MRI for major sporting events -- a case study on the MotoGP World Championship

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.

physics.med-ph↗

arXiv2023

Portable magnetic resonance imaging of patients indoors, outdoors and at home

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.

physics.med-ph↗

arXiv2021

Proton radiographs using position-sensitive silicon detectors and high-resolution scintillators

Proton therapy is a cancer treatment technique currently in growth worldwide. It offers advantages with respect to conventional X-ray and $γ$-ray radiotherapy, in particular, a better control of the dose deposition allowing to reach a higher conformity in the treatments. Therefore, it causes less damage to the surrounding healthy tissue and less secondary effects. However, in order to take full advantage of its potential, improvements in treatment planning and dose verification are required. A new prototype of proton Computed Tomography scanner is proposed to design more accurate and precise treatment plans for proton therapy. Here, results obtained from an experiment performed using a 100-MeV proton beam at the CCB facility in Krakow (Poland) are presented. Proton radiographs of PMMA samples of 50-mm thickness with spatial patterns in aluminum were taken. Their properties were studied, including reproduction of the dimensions, spatial resolution and sensitivity to different materials. They demonstrate the capabilities of the system to produce images with protons. Structures of up to 2 mm are nicely resolved and the sensitivity of the system was enough to distinguish thicknesses of 10 mm of aluminum or PMMA. This constitutes a first step to validate the device as a proton radiography scanner previous to the future tests as a proton CT scanner.

physics.med-ph↗

arXiv2016

CMOS based image cytometry for detection of phytoplankton in ballast water

We introduce an image cytometer (I-CYT) for the analysis of phytoplankton in fresh and marine water environments. A linear quantification of cell numbers was observed covering several orders of magnitude using cultures of Tetraselmis and Nannochloropsis measured by autofluorescence in a laboratory environment. We assessed the functionality of the system outside the laboratory by phytoplankton quantification of samples taken from a marine water environment (Dutch Wadden Sea, The Netherlands) and a fresh water environment (Lake Ijssel, The Netherlands). The I-CYT was also employed to study the effects of two ballast water treatment systems (BWTS), based on chlorine electrolysis and UV sterilization, with the analysis including the vitality of the phytoplankton. For comparative study and benchmarking of the I-CYT, a standard flow cytometer was used. Our results prove a limit of detection (LOD) of 10 cells/ml with an accuracy between 0.7 and 0.5 log, and a correlation of 88.29% in quantification and 96.21% in vitality, with respect to the flow cytometry results.

q-bio.QM↗