systemic noise detection and characterization during 129xe mri troubleshooting

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 Systemic Noise Detection and Characterization During 129Xe MRI Troubleshooting at JoVE.com

Systemic Noise Detection and Characterization During 129Xe MRI Troubleshooting  

Systemic Noise Detection and Characterization During 129Xe MRI Troubleshooting

Begin by creating a control noise profile for quality control, or QC purposes. Use a specific customized 2D GRE sequence, including a high field of view, to capture the maximum signal from the area, a high bandwidth per pixel to identify nearby noise resonances and the lowest possible repetition time, or TR, and echo time, or TE.Acquire the QC for noise profile using a xenon vest or a loop coil. Obtain an image with no hyperpolarized xenon 129 sample in the coil.This image will characterize the noise profile. Examine the acquired noise data, particularly the K-space for non-Gaussian elements, such as spikes, patterns, or discretized or binned values. Create a quantile-quantile, or QQ plot, by plotting the acquired real or imaginary data against a synthesized Gaussian dataset with identical mean, standard deviation, and vector length, both ordered from the smallest to largest.Deviations from the line Y is equal to X in the QQ plot, indicate the presence of non-Gaussian components within the acquired data, requiring further investigation. Proceed to identify the noise distribution pattern and potential outliers with a suitable plot of choice. To rule out the scanner as a noise source, acquire images using the standard site protocol with various pulse sequence parameters disabled, and electronic components powered off.Refer to the list on the screen for possible noise sources. To eliminate noise sources from the room, use a simple surface loop coil tuned to the xenon 129 frequency to sniff around the magnet room for noise sources. Physically place the xenon coil element near potential problematic devices and run a test sequence to detect amplified noise.Examine K-space and image data to pinpoint the exact source of coherence noise. If a specified source is identified, attempt to disable it or cover it with aluminum foil, flashing or a copper mesh to reduce noise. Rerun the scan after disabling or covering noise sources to see if the noise resolves.Continue this process until all noise sources are eliminated, leaving only low root mean square Gaussian noise. Identify irregular noise as high signal spikes in individual K-space pixels with abnormally high or low signals in the real or imaginary channels. Perform imaging in different phase encoding orientations, including anterior to posterior, head to foot, and left to right.Eliminate potential issues with X-Y-or Z-gradients, by enabling or disabling individual gradients selectively. Systematically examine the resulting images to identify which specific gradient direction is contributing to the noise. The results of the noise characterization analysis performed on the noise scan demonstrated the impact of both regular and irregular noise on the K-space.Regular noise led to a continuous pattern in the K-space, while irregular noise resulted in high value outliers in the QQ plot. A series of lung images acquired using HPG MRI showed that a distinct bright spot centered in the K-space indicated a clear lung signal with low noise. Conversely, the presence of regular noise was spread throughout the images.Irregular noise evidently caused high value spikes in the K-space, and resulted in a striped pattern in image space. A scenario where both regular and irregular noises were present simultaneously also affected the lung image.

systemic-noise-detection-characterization-during-129xe-mri

Research

JoVE Journal

Bioengineering

74 ビュー.  University of Missouri. まず、品質管理(QC)の目的で制御ノイズプロファイルを作成します。高視野を含む特定のカスタマイズされた2D GREシーケンスを使用して、エリアから最大信号をキャプチャし、ピクセルあたりの帯域幅を広くして近くのノイズ共振を特定し、可能な限り短い繰り返し時間(TR)とエコー時間(TE)を特定します。キセノンベストまたはループコイルを使用してノイズプロファイ?...