patient preparation and subject training for hyperpolarized xenon mri

Evaluación de la función pulmonar con resonancia magnética hiperpolarizada de xenón-129

Hyperpolarized Xenon-129 (HXe) magnetic resonance imaging (MRI)1 is a technique that offers unique insights into lung structure, function, and gas exchange processes. By dramatically amplifying the magnetization of Xenon gas through spin-exchange optical pumping, HXe MRI achieves an order-of-magnitude improvement in signal-to-noise ratio compared to thermally polarized Xenon MRI2,3,4,5,6. This hyperpolarization enables the direct visualization and quantification of Xenon gas uptake into lung tissue and blood, which would otherwise be undetectable with conventional thermally polarized MRI7.
Chemical shift saturation recovery (CSSR) MR spectroscopy8,9,10,11,12,13 has proven to be one of the most valuable HXe MRI techniques. CSSR involves selectively saturating the magnetization of Xenon dissolved in lung tissue and blood using frequency-specific radiofrequency (RF) pulses. The subsequent recovery of the dissolved-phase (DP) signal as it exchanges with fresh hyperpolarized Xenon gas in the airspaces on a timescale of ms offers important functional information about the lung parenchyma.
Since its development in the early 2000s, the techniques behind CSSR spectroscopy have been progressively refined14,15,16,17,18,19,20,21,22,23. Further, advances in modeling Xenon uptake curves have enabled the extraction of specific physiological parameters, such as alveolar wall thickness and pulmonary transit times10,24,25,26. Studies have shown CSSR&#39;s sensitivity to subtle changes in lung microstructure and gas exchange efficiency in the form of pulmonary abnormalities found in clinically healthy smokers27, as well as in a range of lung diseases, including chronic obstructive pulmonary disease (COPD)18,27,28, fibrosis29, and radiation-induced lung injury30,31. CSSR spectroscopy has also been demonstrated to be sensitive to detect oscillations in the DP signal corresponding to pulsatile blood flow during the cardiac cycle32.
While significant progress has been made, practical challenges remain in implementing CSSR spectroscopy on clinical MRI systems. Scan times requiring single-dose breath holds approaching 10 s may be too long for pediatric subjects33,34 or patients with severe lung disease35,36. Additionally, the technique is susceptible to measurement biases if acquisition parameters such as the order of the saturation delay times or the efficacy of the dissolved-phase saturation are not properly optimized21. To address these limitations and make CSSR more accessible to the broader research community, clear, step-by-step protocols for both conventional breath hold and free-breathing acquisitions, currently under development, are needed.
The objective of this paper is to present a detailed methodology for performing optimized CSSR MR spectroscopy using HXe gas. The protocol will cover polarization and delivery of the Xenon gas, RF pulse calibration, sequence parameter selection, subject preparation, data acquisition, and key steps in data analysis. Examples of experimental results will be provided. It is hoped that this comprehensive guide will serve as a foundation for CSSR implementations across sites and help realize the full potential of this technique for quantifying lung microstructural changes in a range of pulmonary diseases.

Autor destacado: Avance en la investigación de enfermedades pulmonares con resonancia magnética de xenón-129 hiperpolarizado de respiración libre

Medida cuantitativa de la estructura y función pulmonar obtenida de la espectroscopia de xenón hiperpolarizado

Our research focuses on using hyperpolarizing on 129 MRI technology to assess pulmonary function and to investigate lung diseases. The main objective is to see how this imaging technique can lead to better detection, understanding, and tracking of different lung conditions. Most hyperpolarized lung MR imaging is performed during a breath hold.We believe that pulmonary function quantified under such an artificial condition, may not fully reflect gas exchange during regular respiration, and we are testing new free breathing measurements that do not require any breath hold. Current challenges include the optimization of the CSSR acquisition technique for consistency and accuracy in the face of physiological variation and patient compliance. Severely ill or pediatric patients struggle with maintaining lengthy breath holds.The CSSR heart technique appears particularly sensitive to changes in alveolar septal wall thickness. As we and others in the field of demonstrated, alveolar wall thickening can indicate the presence of interstitial edema, inflammation, or pulmonary fibrosis. All metrics derived from CSSR spectroscopy acquisitions are currently based on the temporal dynamics of the signal amplitudes.In the future though, we hope to include changes in peak shape and center frequency in the analysis to obtain a more complete picture of the ongoing gas exchange processes.

Preparación del paciente y entrenamiento del sujeto para la resonancia magnética de xenón hiperpolarizado

Para empezar, configure el sistema de monitorización fisiológica para registrar las curvas de respiración y el análisis de gases en tiempo real durante la toma de imágenes. Conecte y pruebe los auriculares de la sala de resonancia magnética con la señal de audio que guía al sujeto mediante una grabación de audio de inhalación y exhalación. Ajuste la velocidad de reproducción de la pista de audio. Inhala.Exhala.Basado en la frecuencia respiratoria normal de cada sujeto. A continuación, prepare la cama del escáner con un reposacabezas limpio, una almohada de soporte para las piernas y una manta. Coloque la bobina del chaleco pectoral Xenon 129 desabrochada sobre la mesa del escáner de resonancia magnética e inserte el enchufe conector de la bobina.Para un estudio de respiración libre, introduzca al sujeto a la grabación de voz de inhalación-exhalación para sincronizar la respiración durante la toma de imágenes. Lleve al sujeto a la sala de resonancia magnética y colóquelo en la cama del escáner, acostado sobre la bobina abierta del chaleco de xenón. Una vez que el sujeto esté colocado, abrocha las correas de Velcro de modo que la bobina del chaleco esté cerrada, pero no constriña el pecho del sujeto.Para un estudio respiratorio gratuito, coloque una mascarilla con un neumatac sobre la cara del paciente. Apriete las correas para que la mascarilla se ajuste perfectamente sobre la nariz y la boca sin quedar demasiado apretada. Después de la colocación, quítese la mascarilla y déjela a un lado para más tarde, dejando las correas detrás de la cabeza del sujeto.A continuación, coloque dos oxímetros de pulso en ambos dedos índices para controlar continuamente la frecuencia cardíaca y la saturación de oxígeno en sangre durante el estudio. Coloque auriculares compatibles con resonancia magnética sobre las orejas del sujeto. Mueva la mesa del escáner de resonancia magnética en el orificio del imán para que los pulmones del sujeto queden en el centro del campo de visión.

Research

JoVE Journal

Medicine

Patient Preparation and Subject Training for Hyperpolarized Xenon MRI

Quantitative Measure of Lung Structure and Function Obtained from Hyperpolarized Xenon Spectroscopy

Hyperpolarized Xenon-129 (HXe) magnetic resonance imaging (MRI) provides tools for obtaining 2- or 3-dimensional maps of lung ventilation patterns, gas ...

Investigación

Medicina

Polarizing Xenon-129 for Hyperpolarized Xenon Spectroscopy

Xenón-129 polarizador para espectroscopía de xenón hiperpolarizado

Performing Hyperpolarized Xenon-129 Inhalation for Chemical Shift Saturation Recovery (CSSR) Measurement

Realización de inhalación de xenón-129 hiperpolarizado para la medición de la recuperación de la saturación por desplazamiento químico (CSSR)