Name: Performing 129Xe Spectroscopy and Hyperpolarized 129Xe Imaging for Quality Control at 129Xe MRI Sites
Uploaded: 2024-01-05T14:10:00
Description: Watch this Scientific Journal Video about Performing 129Xe Spectroscopy and Hyperpolarized 129Xe Imaging for Quality Control at 129Xe MRI Sites at JoVE.com

performing 129xe spectroscopy and hyperpolarized 129xe imaging for quality control at 129xe mri sites

Obtaining High-Quality Hyperpolarized Xenon-129 Magnetic Resonance Images

For over a century, lung function assessment has primarily relied on global measurements from spirometry and body plethysmography. However, these traditional pulmonary function tests (PFTs) are limited in their ability to capture early-stage disease&#39;s regional nuances and subtle changes in lung tissue1. Nuclear medicine with inhaled radiotracers has been used widely for the assessment of ventilation/perfusion mismatches commonly associated with pulmonary emboli, but this involves ionizing radiation and yields lower resolution. In contrast, computed tomography (CT) has emerged as the gold standard for lung imaging, offering exceptional spatial and temporal clarity compared to nuclear imaging2. While low-dose CT scans can mitigate radiation exposure, potential radiation risk should still be considered3,4. Proton MRI of the lung is uncommon due to low tissue density of the lung and rapid signal decay from lung tissue, although recent advances offer functional information despite potential low signal. On the other hand, hyperpolarized xenon magnetic resonance imaging (HP 129Xe MRI) is a non-invasive modality that allows for imaging of lung function with regional specificity5,6. It produces a high nonequilibrium nuclear magnetization of the gas in liter quantities. The inert gas is then inhaled by a subject inside the MR scanner for a single breath and is directly imaged by the scanner. Thus, the inhaled gas is directly imaged as opposed to the tissue itself. This technique has been used to assess lung ventilation across many diseases, including asthma, chronic obstructive pulmonary disease (COPD), cystic fibrosis, idiopathic pulmonary fibrosis, coronavirus disease 2019 (COVID-19), and many others3. In December 2022, HP 129Xe MRI was approved by the United States FDA as an MRI ventilation contrast agent to be used in the United States of America (USA) in adults and pediatric patients aged 12 years and older7. Physicians can now use 129Xe MRI to better care for patients with improved/personalized treatment plans.
Historically, clinical MRI focuses exclusively on imaging hydrogen nuclei (protons) which are abundant in nearly all human viscera. The MRI scanners, sequences, and quality control are generally maintained by the scanner manufacturer as part of the site license and warranty. However, 129Xe requires a multinuclear capable MR scanner and has required a dedicated research team to operationalize the hyperpolarizer, custom-built radiofrequency (RF) coils, dedicated pulse sequences, and offline reconstruction/analysis software. Each of these components can be supplied by third-party vendors or developed in-house. Thus, the burden of quality control generally rests on the 129Xe research team as opposed to the scanner manufacturer or individual third party. Consistent acquisition of high-quality 129Xe data is therefore uniquely challenging as each component of the 129Xe MRI process introduces the potential for error, which must be closely monitored by the 129Xe team. Not only can these situations be extremely frustrating as researchers have to troubleshoot and investigate possible causes for any challenges that may have arisen, but they can be very costly as this slows down patient imaging and subject recruitment. Some costs associated with troubleshooting involve MRI time costs, the hyperpolarization of 129Xe, which involves the consumption of different gases, and the use of materials. Additionally, with the recent FDA approval and growth in 129Xe imaging, providing a standardized protocol for quality control is necessary to avoid common issues and setbacks in 129Xe operation8,9.
Here, we present some of the more commonly encountered issues in 129Xe MRI, including RF coil failures, the emergence of various noise profiles that lead to low signal-to-noise ratio (SNR), and poor quality images10. We aim to provide some concise quality control (QC) guidelines and protocols to ensure the acquisition of high-quality image data and troubleshoot some of the more common issues that can arise in 129Xe MRI. The insights provided here are also relevant for hyperpolarized helium-3 troubleshooting.

Author Spotlight: Using Hyperpolarized Xenon-129 MRI to Study Lung Diseases 

Troubleshooting and Quality Assurance in Hyperpolarized Xenon Magnetic Resonance Imaging: Tools for High-Quality Image Acquisition

In hyperpolarized xenon MRI, the actual inhaled gas is directly imaged. The gas uniformly distributes itself in lungs of healthy individuals, but in those with lung disease, such as asthma, COPD or cystic fibrosis, it does not. We aim to understand these diseases better using this technology.X-ray computed tomography, or CT, provides the current clinical standard in pulmonary structural imaging, but involves ionizing radiation and shows only lung tissue, not the inhaled gas. Nuclear medicine, by inhaled or injected radio tracers can also be used to assess pulmonary ventilation and profusion, but is ionizing and relatively low resolution. Xenon MRI, however, provides a high resolution snapshot of an individual's pulmonary ventilation and gas exchange.Implementing xenon MRI is uniquely challenging, requiring specialized hardware, xenon imaging coils, and sequence development. The journey doesn't end there. The acquired data must undergo meticulous reconstruction and analysis.Without proper expertise, these tasks can be daunting, leading to frustrating and expensive outcomes. This protocol offers insight into quality control, troubleshooting, and tools for xenon MRI sites, We explored the setup of hyperpolarizer labs, xenon MRI coils, data acquisition consideration, and image properties. Our goal is to guide the audience through potential errors, challenges, and occurrences that may impact image quality or outcomes.Troubleshooting xenon MRI issues is necessary to mitigate problems in real life. Given the absence of a dedicated hyperpolarized gas infrastructure and limited support from scanner manufacturers, quality control tasks fall solely on individual labs. This video aims to equip viewers with practical tips for addressing challenges and ensuring successful data acquisition.

Watch this Scientific Journal Video about Performing 129Xe Spectroscopy and Hyperpolarized 129Xe Imaging for Quality Control at 129Xe MRI Sites at JoVE.com

Performing 129Xe Spectroscopy and Hyperpolarized 129Xe Imaging for Quality Control at 129Xe MRI Sites  

Performing 129Xe Spectroscopy and Hyperpolarized 129Xe Imaging for Quality Control at 129Xe MRI Sites

Begin by creating a thermally polarized 129 xenon phantom. To do so, connect a glass pressure vessel to a xenon gas filled bag, having an appropriate size and volume aligning with the vessel's capacity. Then submerge the pressure vessel in a small amount of liquid nitrogen to allow xenon diffusion and freezing.Seal the vessel after the xenon has formed frozen snow inside. Allow it to thaw while pressurizing the vessel before calculating the pressure in the vessel. To detect peak frequency, put the phantom inside the xenon 129 coil and place it similar to that of a loaded patient.Perform a scan with proton frequency as some scanners may disallow multinuclear scans without initial proton frequency localizer. Use a broadband transmit pulse if available, high bandwidth and high resolution readout experiment, to accurately detect the xenon frequency peak. Once a well-defined peak is detected, record the frequency to full precision.Repeat the new experiment at the new frequency with a low bandwidth of about 1000 hertz to maximize signal to noise ratio or SNR and peak frequency precision. Once a satisfactory high signal peak is detected, save the protocol for future quality control tests. Use a small amount of hyperpolarized xenon 129, which is well concentrated and free of oxygen for imaging.Measure the xenon 129 dose equivalent or DE accurately immediately prior to imaging. Set the test imaging protocol to reflect desired in vivo parameters as closely as possible. Acquire and save the image of the xenon bag as a baseline measure of scanner performance.Measure and record the SNR of the acquired images alongside all scan parameters and xenon DE.For measuring alpha, the flip angle, perform a full volume spoiled gradient echo scan in which the field of view is imaged twice in succession using identical sequence parameters. Measure the SNR at the DC offset of the two images S0 and S1.Count the number of phase encoding steps n, and calculate the flip angle.

Research

JoVE Journal

Bioengineering

Hyperpolarized (HP) xenon magnetic resonance imaging (129Xe MRI) is a recently federal drug administration (FDA)-approved imaging modality that produces ...