Prepolarized MRI of hard tissues and solid-state matter.

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.

Coinfections and In-Hospital Mortality in a Group of Patients With HIV/AIDS: A Longitudinal Study.

Human immunodeficiency virus (HIV) is a global public health problem. Coinfections in HIV patients are frequent complications that increase their mortality. The aim of this study was to assess coinfections and in-hospital mortality in a group of patients infected with HIV in Colombia. A retrospective longitudinal study was carried out. Patients treated in 4 highly complex clinics in Colombia between 2015 and 2023 were included. The cases were identified from International Classification of Diseases codes related to HIV. Sociodemographic, clinical, laboratory and pharmacological variables were collected. Descriptive, bivariate, and multivariable analyses were performed. Of the 249 patients identified, 79.1% were men, and the median age was 38.0 years. Approximately 81.1% had a diagnosis of acquired immune deficiency syndrome (AIDS). Coinfections caused by Mycobacterium tuberculosis (24.1%) and Treponema pallidum (20.5%) were the most frequent. A total of 20.5% of the patients had sepsis, 12.4% had septic shock, and the fatality rate was 15.7%. Antibiotics and antifungals were used in 88.8% and 53.8%, respectively, of the patients. Patients with a diagnosis of HIV before admission, those infected with M. tuberculosis, and those who presented with sepsis were more likely to die, whereas patients who received antiretroviral agent treatment before admission presented a lower risk. In this study, most HIV patients were in an advanced stage of the disease. Coinfection with M. tuberculosis was common and was associated with an increased risk of death. Previous HIV diagnosis and sepsis also increased the risk. Approximately half of the patients with a previous HIV diagnosis were receiving antiretroviral therapy and had a better prognosis.

Magneto-stimulation limits in medical imaging applications with rapid field dynamics.

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 40µs.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.

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 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.

Population trends of seabirds in Mexican Islands at the California Current System.

The Baja California Pacific Islands (BCPI) is a seabird hotspot in the southern California Current System supporting 129 seabird breeding populations of 23 species and over one million birds annually. These islands had a history of environmental degradation because of invasive alien species, human disturbance, and contaminants that caused the extirpation of 27 seabird populations. Most of the invasive mammals have been eradicated and colonies have been restored with social attraction techniques. We have recorded the number of breeding pairs annually for most of the colonies since 2008. To assess population trends, we analyzed these data and show results for 19 seabird species on ten island groups. The maximum number of breeding pairs for each nesting season was used to estimate the population growth rate (λ) for each species at every island colony. We performed a moving block bootstrap analysis to assess whether seabird breeding populations are increasing or decreasing. San Benito, Natividad, and San Jerónimo are the top three islands in terms of abundance of breeding pairs. The most widespread species is Cassin's Auklet (Ptychoramphus aleuticus) with 14 colonies. Thirty-one populations of 14 species are significantly increasing while eleven populations of seven species are decreasing. We did not find statistical significance for 19 populations, however, 15 have λ>1 which suggest they are growing. Twelve of the 18 species for which we estimated a regional population trend are significantly increasing, including seven surface-nesting species: Brandt's Cormorant (Phalacrocorax penicillatus), Brown Pelican (Pelecanus occidentalis), Caspian Tern (Hydroprogne caspia), Double-crested Cormorant (P. auritus), Elegant Tern (Thalasseus elegans), Laysan Albatross (Phoebastria immutabilis) and Western Gull (Larus occidentalis), and five burrow-nesting species: Ainley's (Hydrobates cheimomnestes), Ashy (H. homochroa) and Townsend's (H. socorroensis) Storm-Petrels, and Craveri's (Synthliboramphus craveri) and Guadalupe (S. hypoleucus) Murrelets. The BCPI support between 400,000 and 1.4 million breeding individuals annually. Our results suggest that these islands support healthy and growing populations of seabirds that have shown to be resilient to extreme environmental conditions such as the "Blob", and that such resilience has been strengthen from conservation and restoration actions such as the eradication of invasive mammals, social attraction techniques and island biosecurity.

Simultaneous imaging of hard and soft biological tissues in a low-field dental MRI scanner.

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.

Principios filosóficos de la homeopatía / Philosophical principles of homeopathy

De una manera clara, directa y muy didáctica, los autores de este trabajo realizan un recorrido por los principios que configuran la estructura de la filosofía homeopática, rescatando muchos de los conceptos inscritos en algunas de las obras literarias del célebre Higinio G. Pérez, fundador de la Escuela Libre de Homeopatía, y del fisiólogo norteamericano Walter Bradford Cannon, los cuales, por supuesto, son coincidentes con muchos de los preceptos hipocráticos y hahnemaniannos. Para complementar su análisis, los investigadores refieren las opiniones de algunos otros científicos (fisiólogos y biólogos) y citan de manera textual diversos parágrafos del doctor Samuel Hahnemann, al tiempo que expresan su opinión sobre la vigencia de dichas premisas en la época moderna...

In a clear direct and very didactic manner the authors of this paper perform a journey by the principles that configure the philosophical structure of homeopathy, recovering many of the concepts written in various of the literary works of the notorious physician Higinio G. Pérez, founder of the Homeopathic Free Scholl and from the north American physiologist Walter Bradford Cannon, which of course, are coincidental with most of the Hippocratic an Hanemanniann precepts. In order to complete their analysis, these researchers refer the opinions of some other scientists (Physiologist and Biologists) and quoted verbatim various paragraphs of Dr. Samuel Hahnemann, at the same time, that they state their personal opinion on the validity of these assumptions in modern times...

Principios filosóficos de la homeopatía / Philosophical principles of homeopathy

De una manera clara, directa y muy didáctica, los autores de este trabajo realizan un recorrido por los principios que configuran la estructura de la filosofía homeopática, rescatando muchos de los conceptos inscritos en algunas de las obras literarias del célebre Higinio G. Pérez, fundador de la Escuela Libre de Homeopatía, y del fisiólogo norteamericano Walter Bradford Cannon, los cuales, por supuesto, son coincidentes con muchos de los preceptos hipocráticos y hahnemaniannos. Para complementar su análisis, los investigadores refieren las opiniones de algunos otros científicos (fisiólogos y biólogos) y citan de manera textual diversos parágrafos del doctor Samuel Hahnemann, al tiempo que expresan su opinión sobre la vigencia de dichas premisas en la época moderna. (AU)

In a clear direct and very didactic manner the authors of this paper perform a journey by the principles that configure the philosophical structure of homeopathy, recovering many of the concepts written in various of the literary works of the notorious physician Higinio G. Pérez, founder of the Homeopathic Free Scholl and from the north American physiologist Walter Bradford Cannon, which of course, are coincidental with most of the Hippocratic an Hanemanniann precepts. In order to complete their analysis, these researchers refer the opinions of some other scientists (Physiologist and Biologists) and quoted verbatim various paragraphs of Dr. Samuel Hahnemann, at the same time, that they state their personal opinion on the validity of these assumptions in modern times. (AU)