performing hyperpolarized xenon-129 inhalation for chemical shift saturation recovery (cssr) measurement

使用超极化氙 129 MRI 评估肺功能

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.

作者聚焦：利用自由呼吸超极化氙 129 MRI 推进肺病研究

通过超偏振氙光谱法获得的肺结构和功能的定量测量

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.

执行超极化氙 129 吸入以测量化学位移饱和恢复 （CSSR）

要使用屏气方法进行氙气吸入，请将鼻夹放在受试者的鼻子上，以方便通过嘴呼吸。在正常呼气至功能性残余容量结束时，将氙气袋的吹嘴插入受试者的口中。让受试者从氙气袋中吸入 500 毫升氙气。然后取下吹嘴并指示受试者继续吸入室内空气，直到肺部充满。在吸气结束时，要求受试者举起拇指。要求护士协调员将此信息口头传达给扫描仪操作员，以开始脉冲序列。数据采集期结束后，指示受试者恢复正常呼吸。将受试者从MRI扫描仪中移出。将口罩盖在他们的鼻子和嘴巴上。将软管连接到面罩上，然后将预装的带子从头后连接到面罩并将其固定到位。将受试者移动到 MRI 扫描仪内的原始位置。一旦受试者遵循呼吸方案，请护士协调员通知 MRI 操作员开始数据采集。然后，护士协调员打开气体输送系统上的阀门，受试者吸入 50 毫升超极化氙 1-29，这些氙气与呼吸面罩内的气流混合在一起。指示受试者继续呼吸约 10 次呼吸，直到氙气的体积用于成像协议。加载 CSSR 脉冲序列以进行自由呼吸。根据校准扫描期间确定的超极化氙气相频率设置采集频率。调整基准电压以匹配从校准扫描中获得的值。按照系统供应商的操作说明，选择“等待用户”选项或其等效选项以执行序列。开始 MRI 扫描仪序列。在数据采集之前，扫描仪将暂停以供用户输入。一旦护士协调员切换超极化氙气或空气混合物，就开始数据采集。确保在受试者吸入第一剂氙气之前，序列已经在运行。在三分钟的数据采集或超极化氙气耗尽后，将受试者从 MRI 扫描仪中取出。在年轻、健康的女性中，由于薄壁的快速填充，膜信号迅速增加。在年龄较大的肺移植受者中，膜信号逐渐上升，反映了填充较厚的室间隔壁所需的时间更长。

performing-hyperpolarized-xenon-129-inhalation-for-chemical-shift

Research

JoVE Journal

Medicine

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

39 次观看.  University of Pennsylvania. 要使用屏气方法进行氙气吸入，请将鼻夹放在受试者的鼻子上，以方便通过嘴呼吸。在正常呼气至功能性残余容量结束时，将氙气袋的吹嘴插入受试者的口中。让受试者从氙气袋中吸入 500 毫升氙气。然后取下吹嘴并指示受试者继续吸入室内空气，直到肺部充满。在吸气结束时，要求受试者举起拇指。要求护士协调员将此信息口头传达给扫描仪操作员，以开始脉冲序列?...

视频: 执行超极化氙 129 吸入以测量化学位移饱和恢复 （CSSR）

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 diffusion, Xenon uptake by lung parenchyma, and other lung function metrics. However, by trading spatial for temporal resolution, it also enables tracing of pulmonary Xenon gas exchange on a ms timescale. This article describes one such technique, chemical shift saturation recovery (CSSR) MR spectroscopy. It illustrates how it can be used to assess capillary blood volume, septal wall thickness, and the surface-to-volume ratio in the alveoli. The flip angle of the applied radiofrequency pulses (RF) was carefully calibrated. Single-dose breath-hold and multi-dose free-breathing protocols were employed for administering the gas to the subject. Once the inhaled Xenon gas reached the alveoli, a series of 90&#176; RF pulses was applied to ensure maximum saturation of the accumulated Xenon magnetization in the lung parenchyma. Following a variable delay time, spectra were acquired to quantify the regrowth of the Xenon signal due to gas exchange between the alveolar gas volume and the tissue compartments of the lung. These spectra were then analyzed by fitting complex pseudo-Voigt functions to the three dominant peaks. Finally, the delay time-dependent peak amplitudes were fitted to a one-dimensional analytical gas-exchange model to extract physiological parameters.

The manuscript presents a detailed protocol for using hyperpolarized Xenon-129 chemical shift saturation recovery (CSSR) to trace pulmonary gas exchange, assess the apparent alveolar septal wall thickness, and measure the surface-to-volume ratio. The method has the potential to diagnose and monitor lung diseases.

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

科研

医学

Patient Preparation and Subject Training for Hyperpolarized Xenon MRI

To begin, set up the physiological monitoring system to record breathing curves and real-time gas analysis during imaging. Connect and test the MRI room headphones with the audio signal that guides the subject using an inhale-exhale audio recording. Adjust the playback speed of the audio track.Inhale.Exhale.Based on the normal breathing rate of each subject.Inhale.Exhale. Next, prepare the scanner bed with a clean headrest, leg support pillow and blanket. Place the unfastened Xenon 129 chest vest coil on the table of the MRI scanner and insert the connector plug of the coil.For a free breathing study, introduce the subject to the inhale-exhale voice recording for synchronized breathing during imaging. Lead the subject into the MRI room and position them on the scanner bed, lying on top of the open xenon vest coil. Once the subject is positioned, fasten the Velcro straps so that the vest coil is closed, but does not constrict the subject's chest.For a free breathing study, place a face mask with a pneumatac over the patient's face. Tighten the straps so the mask fits snugly over the nose and mouth without being too tight. After fitting, remove the mask and set it aside for later, leaving the straps behind the subject's head.Then place two pulse oximeters on both index fingers to continuously monitor heart rate and blood oxygen saturation during the study. Place MRI compatible headphones over the subject's ears. Move the MRI scanner table into the magnet bore so the subject's lungs are positioned in the center of the field of view.

超极化氙气 MRI 的患者准备和受试者培训

Polarizing Xenon-129 for Hyperpolarized Xenon Spectroscopy

To begin, heat up the xenon polarizer approximately 2.5 hours before the study starts. Thread the connector two of a 250 milliliter specialized polyvinyl fluoride or PVF bag through a ceiling clip. Attach the bag to one of the four available polarizer dispense ports.On the polarizer touchscreen, select the enriched xenon tank. Set the flow rate to medium and the polarization volume to 250 milliliters. Then press the start button to initiate the polarization process.Once the polarized xenon gas has been dispensed, the polarizer's touchscreen will display a message to remove the bag. Pinch the connector tube of the specialized PVF bag shut with the ceiling clip, and then disconnect the bag to place it inside the bore of the MRI scanner.

偏振氙-129用于超偏振氙光谱

To perform xenon inhalation using the breath hold method, place a nose clip on the nose of the subject to facilitate breathing through the mouth. At the end of a normal exhalation to functional residual capacity, insert the mouthpiece of the xenon bag into the subject's mouth. Allow the subject to inhale 500 milliliters of xenon gas from the xenon bag.Then remove the mouthpiece and instruct the subject to continue inhaling room air until the lungs are full. At the end of inhalation, ask the subject to raise their thumb. Request the nurse coordinator to verbally convey this information to the scanner operator to start the pulse sequence.After the data acquisition period, instruct the subject to return to normal breathing. Move the subject out of the MRI scanner. Place a face mask over their nose and mouth.Connect the hoses to the mask, and then connect the pre-fitted straps from behind the head to the mask and secure it in place. Move the subject to its original position inside the MRI scanner. Once the subject follows the breathing protocol, ask the nurse coordinator to inform the MRI operator to initiate data acquisition.The nurse coordinator then opens the valves on the gas delivery system and the subject inhales 50 milliliters of hyperpolarized xenon 1-29 mixed with the airflow inside the breathing mask. Instruct the subject to continue breathing for approximately 10 breaths until the volume of xenon gas has been used up for the imaging protocol. Load the CSSR pulse sequence for free breathing.Set the acquisition frequency according to the hyperpolarized xenon gas phase frequency determined during the calibration scan. Adjust the reference voltage to match the value obtained from the calibration scan. Select the wait for user option, or its equivalent, for sequence execution, following the system vendor's operating instructions.Start the MRI scanner sequence. The scanner will pause for user input before data acquisition. Once the nurse coordinator switches the hyperpolarized xenon gas or air mixture, start data acquisition.Ensure the sequence is already running before the subject inhales the first dose of xenon gas. After the three minute data acquisition, or exhaustion of hyperpolarized xenon gas, remove the subject from the MRI scanner. In the young, healthy female, the membrane signal increases rapidly due to the quick filling of thin walls.In the older, lung transplant recipient, the membrane signal rises more gradually reflecting the longer time required to fill the thicker septal walls.

执行超极化氙 129 吸入以测量化学位移饱和恢复 （CSSR）

执行超极化氙 129 吸入以测量化学位移饱和恢复（CSSR）