Combining Hyperpolarized Xe MR Imaging and Spectroscopy to Non-Invasively Estimate Pulmonary Vascular Resistance.

Hyperpolarized Xe MRI/MRS enables quantitative mapping of function in lung airspaces, membrane tissue, and red blood cells (RBCs) within the pulmonary capillaries. The RBC signal also exhibits cardiogenic oscillations that are reduced in pre-capillary pulmonary hypertension (PH). This effect is obscured in patients with concomitant defects in transfer from airspaces to RBCs, which increase RBC oscillation amplitudes.

Hyperpolarized Xe MRI and spectroscopy of gas exchange abnormalities in chronic hypersensitivity pneumonitis.

Purpose: To evaluate 3D gas-exchange functional imaging characteristics using Xe MRI in a group of study participants with chronic hypersensitivity pneumonitis (CHP) as compared with healthy control participants.

Methods: In this prospective study, 11 participants with clinical and CT findings of CHP (4M 7F, mean age 67 ± 6.1 years) as well as 41 healthy subjects (25M 16F, mean age 44 ± 18 years) were enrolled between 2017 and 2022 and underwent Xe MRI.

Functional gas exchange measures on Xe MRI and spectroscopy are associated with age, sex, and BMI in healthy subjects.

Introduction: Hyperpolarized Xe MRI and spectroscopy is a rapidly growing technique for assessing lung function, with applications in a wide range of obstructive, restrictive, and pulmonary vascular disease. However, normal variations in Xe measures of gas exchange across healthy subjects are not well characterized, presenting an obstacle to differentiating disease processes from the consequences of expected physiological heterogeneity. Here, we use multivariate models to evaluate the role of age, sex, and BMI in a range of commonly used Xe measures of gas exchange.

Quantifying Regional Radiation-Induced Lung Injury in Patients Using Hyperpolarized Xe Gas Exchange Magnetic Resonance Imaging.

Purpose: Radiation-induced lung injury has been shown to alter regional ventilation and perfusion in the lung. However, changes in regional pulmonary gas exchange have not previously been measured.

Methods And Materials: Ten patients receiving conventional radiation therapy (RT) for lung cancer underwent pre-RT and 3-month post-RT magnetic resonance imaging (MRI) using an established hyperpolarized Xe gas exchange technique to map lung function.

Cluster analysis to identify long COVID phenotypes using Xe magnetic resonance imaging: a multicentre evaluation.

Background: Long COVID impacts ∼10% of people diagnosed with coronavirus disease 2019 (COVID-19), yet the pathophysiology driving ongoing symptoms is poorly understood. We hypothesised that Xe magnetic resonance imaging (MRI) could identify unique pulmonary phenotypic subgroups of long COVID. Therefore, we evaluated ventilation and gas exchange measurements with cluster analysis to generate imaging-based phenotypes.

Monitoring and Management of Respiratory Function in Pompe Disease: Current Perspectives.

Pompe disease (PD) is a neuromuscular disorder caused by a deficiency of acid alpha-glucosidase (GAA) - a lysosomal enzyme responsible for hydrolyzing glycogen. GAA deficiency leads to accumulation of glycogen in lysosomes, causing cellular disruption. The severity of PD is directly related to the extent of GAA deficiency - if no or minimal GAA is produced, symptoms are severe and manifest in infancy, known as infantile onset PD (IOPD).

Combining neural networks and image synthesis to enable automatic thoracic cavity segmentation of hyperpolarized Xe MRI without proton scans.

Rationale And Objectives: Quantification of Xe MRI relies on accurate segmentation of the thoracic cavity, typically performed manually using a combination of H and Xe scans. This can be accelerated by using Convolutional Neural Networks (CNNs) that segment only the Xe scan. However, this task is complicated by peripheral ventilation defects, which requires training CNNs with large, diverse datasets.

Establishing a hemoglobin adjustment for Xe gas exchange MRI and MRS.

Purpose: Xe MRI and MRS signals from airspaces, membrane tissues (M), and red blood cells (RBCs) provide measurements of pulmonary gas exchange. However, Xe MRI/MRS studies have yet to account for hemoglobin concentration (Hb), which is expected to affect the uptake of Xe in the membrane and RBC compartments. We propose a framework to adjust the membrane and RBC signals for Hb and use this to assess sex-specific differences in RBC/M and establish a Hb-adjusted healthy reference range for the RBC/M ratio.

Quantitative Imaging Metrics for the Assessment of Pulmonary Pathophysiology: An Official American Thoracic Society and Fleischner Society Joint Workshop Report.

Multiple thoracic imaging modalities have been developed to link structure to function in the diagnosis and monitoring of lung disease. Volumetric computed tomography (CT) renders three-dimensional maps of lung structures and may be combined with positron emission tomography (PET) to obtain dynamic physiological data. Magnetic resonance imaging (MRI) using ultrashort-echo time (UTE) sequences has improved signal detection from lung parenchyma; contrast agents are used to deduce airway function, ventilation-perfusion-diffusion, and mechanics.

View-sharing for 4D magnetic resonance imaging with randomized projection-encoding enables improvements of respiratory motion imaging for treatment planning in abdominothoracic radiotherapy.

Background And Purpose: The accuracy and precision of radiation therapy are dependent on the characterization of organ-at-risk and target motion. This work aims to demonstrate a 4D magnetic resonance imaging (MRI) method for improving spatial and temporal resolution in respiratory motion imaging for treatment planning in abdominothoracic radiotherapy.

Materials And Methods: The spatial and temporal resolution of phase-resolved respiratory imaging is improved by considering a novel sampling function based on quasi-random projection-encoding and peripheral k-space view-sharing.

MR Imaging for the Evaluation of Diffuse Lung Disease: Where Are We?

Patients with diffuse lung diseases require thorough medical and social history and physical examinations, coupled with a multitude of laboratory tests, pulmonary function tests, and radiologic imaging to discern and manage the specific disease. This review summarizes the current state of imaging of various diffuse lung diseases by hyperpolarized MR imaging. The potential of hyperpolarized MR imaging as a clinical tool is outlined as a novel imaging approach that enables further understanding of the cause of diffuse lung diseases, permits earlier detection of disease progression before that found with pulmonary function tests, and can delineate physiologic response to lung therapies.

Persistent Xe MRI Pulmonary and CT Vascular Abnormalities in Symptomatic Individuals with Post-acute COVID-19 Syndrome.

Background: In patients with post-acute COVID-19 syndrome (PACS), abnormal gas-transfer and pulmonary vascular density have been reported, but such findings have not been related to each other or to symptoms and exercise limitation. The pathophysiologic drivers of PACS in patients previously infected with COVID-19 who were admitted to in-patient treatment in hospital (or ever-hospitalized patients) and never-hospitalized patients are not well understood.

Purpose: To determine the relationship of persistent symptoms and exercise limitation with xenon 129 (Xe) MRI and CT pulmonary vascular measurements in individuals with PACS.

Noninvasive diagnosis of pulmonary hypertension with hyperpolarised Xe magnetic resonance imaging and spectroscopy.

Background: The diagnosis of pulmonary hypertension (PH) remains challenging. Pre- and post-capillary PH have different signatures on noninvasive Xe gas-exchange magnetic resonance imaging (MRI) and dynamic MR spectroscopy (MRS). We tested the accuracy of Xe MRI/MRS to diagnose PH status compared to right heart catheterisation (RHC).

Bias field correction in hyperpolarized Xe ventilation MRI using templates derived by RF-depolarization mapping.

Purpose: To correct for RF inhomogeneity for in vivo Xe ventilation MRI using flip-angle mapping enabled by randomized 3D radial acquisitions. To extend this RF-depolarization mapping approach to create a flip-angle map template applicable to arbitrary acquisition strategies, and to compare these approaches to conventional bias field correction.

Methods: RF-depolarization mapping was evaluated first in digital simulations and then in 51 subjects who had undergone radial Xe ventilation MRI in the supine position at 3T (views = 3600; samples/view = 128; TR/TE = 4.

Pediatric Xe Gas-Transfer MRI-Feasibility and Applicability.

Background: Xe gas-transfer MRI provides regional measures of pulmonary gas exchange in adults and separates xenon in interstitial lung tissue/plasma (barrier) from xenon in red blood cells (RBCs). The technique has yet to be demonstrated in pediatric populations or conditions.

Purpose/hypothesis: To perform an exploratory analysis of Xe gas-transfer MRI in children.

Pulmonary functional MRI: Detecting the structure-function pathologies that drive asthma symptoms and quality of life.

Pulmonary functional MRI (PfMRI) using inhaled hyperpolarized, radiation-free gases (such as He and Xe) provides a way to directly visualize inhaled gas distribution and ventilation defects (or ventilation heterogeneity) in real time with high spatial (~mm ) resolution. Both gases enable quantitative measurement of terminal airway morphology, while Xe uniquely enables imaging the transfer of inhaled gas across the alveolar-capillary tissue barrier to the red blood cells. In patients with asthma, PfMRI abnormalities have been shown to reflect airway smooth muscle dysfunction, airway inflammation and remodelling, luminal occlusions and airway pruning.

Utilizing flip angle/TR equivalence to reduce breath hold duration in hyperpolarized Xe 1-point Dixon gas exchange imaging.

Purpose: To reduce scan duration in hyperpolarized Xe 1-point Dixon gas exchange imaging by utilizing flip angle (FA)/TR equivalence.

Methods: Images were acquired in 12 subjects (n = 3 radiation therapy, n = 1 unexplained dyspnea, n = 8 healthy) using both standard (TR = 15 ms, FA = 20°, duration = 15 s, 998 projections) and "fast" (TR = 5.4 ms, FA = 12°, duration = 11.

Protocols for multi-site trials using hyperpolarized Xe MRI for imaging of ventilation, alveolar-airspace size, and gas exchange: A position paper from the Xe MRI clinical trials consortium.

Hyperpolarized (HP) Xe MRI uniquely images pulmonary ventilation, gas exchange, and terminal airway morphology rapidly and safely, providing novel information not possible using conventional imaging modalities or pulmonary function tests. As such, there is mounting interest in expanding the use of biomarkers derived from HP Xe MRI as outcome measures in multi-site clinical trials across a range of pulmonary disorders. Until recently, HP Xe MRI techniques have been developed largely independently at a limited number of academic centers, without harmonizing acquisition strategies.

Hyperpolarized Xe MRI and Spectroscopy of Gas-Exchange Abnormalities in Nonspecific Interstitial Pneumonia.

Background Recent studies demonstrate that antifibrotic drugs previously reserved for idiopathic pulmonary fibrosis (IPF) may slow progression in other interstitial lung diseases (ILDs), creating an urgent need for tools that can sensitively assess disease activity, progression, and therapy response across ILDs. Hyperpolarized xenon 129 (Xe) MRI and spectroscopy have provided noninvasive measurements of regional gas-exchange abnormalities in IPF. Purpose To assess gas exchange function using Xe MRI in a group of study participants with nonspecific interstitial pneumonia (NSIP) compared with healthy control participants.

Hyperpolarized Xe Magnetic Resonance Imaging for Functional Avoidance Treatment Planning in Thoracic Radiation Therapy: A Comparison of Ventilation- and Gas Exchange-Guided Treatment Plans.

Purpose: To present a methodology to use pulmonary gas exchange maps to guide functional avoidance treatment planning in radiation therapy (RT) and evaluate its efficacy compared with ventilation-guided treatment planning.

Methods And Materials: Before receiving conventional RT for non-small cell lung cancer, 11 patients underwent hyperpolarized Xe gas exchange magnetic resonance imaging to map the distribution of xenon in its gas phase (ventilation) and transiently bound to red blood cells in the alveolar capillaries (gas exchange). Both ventilation and gas exchange maps were independently used to guide development of new functional avoidance treatment plans for every patient, while adhering to institutional dose-volume constraints for normal tissues and target coverage.

Regional Gas Exchange Measured by Xe Magnetic Resonance Imaging Before and After Combination Bronchodilators Treatment in Chronic Obstructive Pulmonary Disease.

Background: Hyperpolarized Xe magnetic resonance imaging (MRI) provides a non-invasive assessment of regional pulmonary gas exchange function. This technique has demonstrated that chronic obstructive pulmonary disease (COPD) patients exhibit ventilation defects, reduced interstitial barrier tissue uptake, and poor transfer to capillary red blood cells (RBCs). However, the behavior of these measurements following therapeutic intervention is unknown.

Using hyperpolarized Xe gas-exchange MRI to model the regional airspace, membrane, and capillary contributions to diffusing capacity.

Hyperpolarized Xe MRI has emerged as a novel means to evaluate pulmonary function via 3D mapping of ventilation, interstitial barrier uptake, and RBC transfer. However, the physiological interpretation of these measurements has yet to be firmly established. Here, we propose a model that uses the three components of Xe gas-exchange MRI to estimate accessible alveolar volume (), membrane conductance, and capillary blood volume contributions to DL.

Mapping cardiopulmonary dynamics within the microvasculature of the lungs using dissolved Xe MRI.

Magnetic resonance (MR) imaging and spectroscopy using dissolved hyperpolarized (HP) Xe have expanded the ability to probe lung function regionally and noninvasively. In particular, HP Xe imaging has been used to quantify impaired gas uptake by the pulmonary tissues. Whole-lung spectroscopy has also been used to assess global cardiogenic oscillations in the MR signal intensity originating from Xe dissolved in the red blood cells of pulmonary capillaries.