R. Martin

Universidad Nacional Autónoma de México

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F. Vázquez

Universidad Nacional Autónoma de México

O. Marrufo

Instituto Nacional de Neurología y Neurocirugía

Sergio Solís-Nájera

Universidad Nacional Autónoma de México

A. O. Rodríguez

Universidad Autónoma Metropolitana

A. O. Rodrı́guez

Universidad Nacional Autónoma de México

Jelena Lazović

Univerzitetski Klinički Centar Srbije

Luis A. Medina

Universidad Nacional Autónoma de México

Lydia M. Zopf

Ludwig Boltzmann Institute for Experimental and Clinical Traumatology

Alejandro Villareal

Universidad Nacional Autónoma de México

Sergio Solis

Cooperative Institutions

Universidad Nacional Autónoma de México

Universidad Autónoma Metropolitana

Brookhaven National Laboratory

Universidade de Santiago de Compostela

University of Illinois Chicago

The University of Texas System

Anderson Hospital

Chevron (United States)

Google (United States)

University of Oxford

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Functional Magnetic Resonance Study of Non-conventional Morphological Brains: malnourished rats

Measurement Science Review (2015)

R. Martin F. Vázquez Sergio Solís-Nájera O. Marrufo R. Godı́nez

Abstract Malnutrition during brain development can cause serious problems that can be irreversible. Dysfunctional patterns of brain activity can be detected with functional MRI. We used BOLD functional Magnetic Resonance Imaging (fMRI) to investigate region differences of brain activity between control and malnourished rats. The food-competition method was applied to a rat model to induce malnutrition during lactation. A 7T magnet was used to detect changes of the BOLD signal associated with changes in brain activity caused by the trigeminal nerve stimulation in malnourished and control rats. Major neuronal activation was observed in malnourished rats in several brain regions, including cerebellum, somatosensory cortex, hippocampus, and hypothalamus. Statistical analysis of the BOLD signals from various brain areas revealed significant differences in somatosensory cortex between the control and experimental groups, as well as a significant difference between the cerebellum and other structures in the experimental group. This study, particularly in malnourished rats, demonstrates increased BOLD activation in the cerebellum.

Neocortex

10.1515/msr-2015-0025

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Citations (1)

SAR of a birdcage coil with variable number of rungs at 300 MHz

Measurement (2016)

R. Martin J.F. Vazquez O. Marrufo S. Solís Alexander Osorio

Specific absorption rate

Absorption rate

Quadrature (astronomy)

10.1016/j.measurement.2016.01.013

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Citations (9)

Origin of lanthanide nuclear magnetic resonance shifts and their uses

Journal of the Chemical Society Chemical Communications (1972)

B. Bleaney Christopher M. Dobson Barry A. Levine R. Martin Robert J. P. Williams

Series of experimental data on the n.m.r. line shifts of nuclei in ligands bound to lanthanide cations are presented; the agreement between the observed shifts and those predicted by a new theoretical treatment is excellent, and a procedure for the use of the lanthanides in structural studies, as aqueous cations or in shift reagents is outlined.

Chemical shift

Line (geometry)

10.1039/c3972000791b

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Citations (151)

Travelling-wave transmitted with a simple waveguide for rodents Magnetic Resonance Imaging at 9.4 T

arXiv (Cornell University) (2015)

Richard Baeza F. Vázquez O. Marrufo R. Martin Sergio Solis

Waveguide

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RF shield parallel-plate waveguide for travelling-wave MRI experiments at 3 T

Journal of Physics Conference Series (2019)

O. Marrufo F. Vázquez R. Martin Sergio Solís-Nájera A. O. Rodríguez

Abstract Ultra high field magnetic resonance imaging systems suffer from the standing wave problems produced by conventional radiofrequency coils. This causes inhomogeneous fields degrading the image quality. To overcome this problems, propagation of RF waves by antennas inside a waveguide is suggested. We assessed the feasibility of using the magnet RF shield with aluminium strips to form a parallel-plate waveguide for travelling-wave magnetic resonance imaging at 3 T. Imaging results showed that a number of constraints must be solved before good image quality can be obtained. A brief discussion is presented on the possible sources or error and interference. Despite these limitations, results are really encouraging to continue investigating the implementation of this approach.

Waveguide

STRIPS

10.1088/1742-6596/1221/1/012067

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Field focusing and focal heating patterns using a hybrid radiofrequency hyperthermia system.

PubMed (1983)

Boddie Aw Yamanashi Ws James W. Frazer McBride Cm R. Martin

A novel three-element radiofrequency hyperthermia system, consisting of paired multiple-feed inductors positioned between two large capacitor plates and a moveable grounding point, was designed and constructed. The spatial orientation of these elements and the phase of the current flowing through them can be varied to produce asymmetric magnetic field patterns resulting in development of asymmetric eddy current patterns orthogonal to the magnetic lines of force. These patterns could be further focused by manipulation of the capacitor plates and grounding point. Field and eddy current patterns were subsequently correlated with two-dimensional heating patterns at midplane depth in solid phantoms.

Focal point

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Citations (6)

Electric Field Sensing with a Modified SRR for Wireless Telecommunications Dosimetry

Electronics (2021)

F. Vázquez Alejandro Villareal A. O. Rodríguez R. Martin Sergio Solís-Nájera

Split ring resonators (SRRs) have been used extensively in metamaterials, showing a strong localization and enhancement of fields, which significantly improves the sensitivity and resolution of the electromagnetic field sensors. We propose the development of an electric field sensor for 2.4 GHz industrial, scientific, and medical (ISM) band applications, by modifying the renowned SRR to contain three concentric pairs of rings. The reduced size makes the sensor affordable for experiments by inserting it in phantoms in order to measure the specific absorption rate (SAR). Power was transmitted from a patch antenna to SRR, with a varying set of distances 1λ, 2λ, 3λ, or 5λ. Experimental measurements of power were conducted with and without a cylindrical distilled-water phantom with agar (4.54%) and NaCl (0.95%). We then computed the electric and magnetic fields and the SAR using these experimental readings of power for different distances. Our sensor was able to measure power values from 20 nW to 0.3 µW with no phantom, and 1 nW to 10 nW with a phantom, in accordance with the values reported for radiofrequency (RF) dosimetry. The sensitivity as a function of the distance determined for the specific case of a phantom was 0.3 µW/cm.

Specific absorption rate

10.3390/electronics10030295

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A theoretical and experimental investigation on a volume coil with slotted end-rings for rat MRI at 7 T

Magnetic Resonance Materials in Physics Biology and Medicine (2023)

Sergio Solís-Nájera Rodrigo Ruiz R. Martin F. Vázquez O. Marrufo

Abstract Objective A volume coil with squared slots-end ring was developed to attain improved sensitivity for imaging of rat’s brain at 7 T. Material and Methods The principles of the high cavity resonator for the low-pass case and the law of Biot-Savart were used to derive a theoretical expression of $$B_1/i$$ B 1 / i . The slotted-end ring resonator showed a theoretical 2.22-fold sensitivity improvement over the standard birdcage coil with similar dimensions. Numerical studies were carried out for the electromagnetic fields and specific absorption rates for our coil and a birdcage coil loaded with a saline-filled spherical phantom and a digital brain of a rat. Results An improvement of the signal-to-noise ratio (SNR) can be observed for the slotted volume coil over the birdcage regardless of the load used in the electromagnetic simulations. The specific absorption rate simulations show a decrement for the digital brain and quite similar values with the saline solution phantom. Phantom and rat’s brain images were acquired at 7 T to prove the viability of the coil design. The experimental noise figure of our coil design was four times less than the standard birdcage with similar dimensions, which showed a 44.5% increase in experimental SNR. Discussion There is remarkable agreement among the theoretical, numerical and experimental sensitivity values, which all demonstrate that the coil performance for MR imaging of small rodents can be improved using slotted end-rings.

10.1007/s10334-023-01096-w

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External Waveguide Magnetic Resonance Imaging for lower limbs at 3 T

Medical Physics (2021)

F. Vázquez O. Marrufo Sergio Solís-Nájera R. Martin A. O. Rodríguez

We report a method based on the traveling-wave MRI approach, in order to acquire images of human lower limbs with an external waveguide at 3 T.We use a parallel-plate waveguide and an RF surface coil for reception, while a whole-body birdcage is used for transmission. The waveguide and the surface coil are located right outside the magnet, in the magnetic resonance (MR) conditional devices zone. We ran numerical simulations to investigate the B1 field generated by the surface coil located at one of the waveguides, as well as a saline-solution phantom positioned on the opposite side (150 cm away) inside the magnet.We obtained phantom images by varying the distance between the coil and the phantom, in order to investigate the signal-to-noise ratio and to validate our numerical simulations. Lower limb images of a healthy volunteer were also acquired, demonstrating the viability of this approach. Standard pulse sequences were used and no physical modifications were made to the MR imager.These numerical and experimental results show that traveling-wave MRI can produce high-quality images with only a simple waveguide and an RF coil located outside the magnet. This can be particularly favorable when acquiring images of lower limbs requiring a larger field of view.

Waveguide

Radiofrequency coil

10.1002/mp.15281

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Unmonitored Cardiac Magnetic Resonance Imaging of rats at 7 T

Journal of Physics Conference Series (2022)

O. Marrufo S E Solis Najera F. Vázquez R. Martin A. O. Rodrı́guez

Abstract Unmonitored cardiac images of a rat were acquired using a standard gradient echo sequences to study the artefact ghosting mainly caused by heart and respiration motion. All imaging experiments were performed using a transceiver circular-shaped coil and a preclinical magnetic resonance imager at 7 T. Heart images showed the ghosting artefact along the frequency encoding direction. However the image quality was not drastically affected by this type of ghosting. These results showed that standard acquisition parameters may serve to establish a reference to study this unwanted artefact without ECG and respiratory gating and using a single-channel transceiver coil.

Ghosting

Transceiver

10.1088/1742-6596/2307/1/012036

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