New Frontiers in Asthma Chest Imaging.

Modern pulmonary imaging can reveal underlying pathological and pathophysiological changes in the lungs of people with asthma, with important clinical implications. A multitude of imaging modalities are now used to examine underlying structure/function relationships including computed tomography, magnetic resonance imaging, optical coherence tomography, and endobronchial ultrasound. Imaging-based biomarkers from these techniques, including airway dimensions, blood vessel volumes, mucus scores, ventilation defect extent and air trapping extent, often have increased sensitivity compared to traditional lung function measurements, and are increasingly used as endpoints in clinical trials.

Pulmonary Structural MRI using Free-Breathing, Self-Gated Ultra-short Echo Time Imaging.

High quality MRI of the lungs is challenged by low tissue density, fast MRI signal relaxation, and respiratory and cardiac motion. For these reasons, structural imaging of the lungs is performed almost exclusively using Computed Tomography (CT). However, CT imaging delivers ionizing radiation, and thus is less well suited for certain vulnerable populations (e.

A decay-modeled compressed sensing reconstruction approach for non-Cartesian hyperpolarized Xe MRI.

Purpose: Hyperpolarized Xe MRI benefits from non-Cartesian acquisitions that sample k-space efficiently and rapidly. However, their reconstructions are complex and burdened by decay processes unique to hyperpolarized gas. Currently used gridded reconstructions are prone to artifacts caused by magnetization decay and are ill-suited for undersampling.

Cluster Analysis to Identify Long COVID Phenotypes Using Xe Magnetic Resonance Imaging: A Multi-centre Evaluation.

Background: Long COVID impacts ∼10% of people diagnosed with 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.

Methods: COVID-negative controls and participants who previously tested positive for COVID-19 underwent XeMRI ∼14-months post-acute infection across three centres.

A single-breath-hold protocol for hyperpolarized Xe ventilation and gas exchange imaging.

Hyperpolarized Xe MRI (Xe-MRI) is increasingly used to image the structure and function of the lungs. Because Xe imaging can provide multiple contrasts (ventilation, alveolar airspace size, and gas exchange), imaging often occurs over several breath-holds, which increases the time, expense, and patient burden of scans. We propose an imaging sequence that can be used to acquire Xe-MRI gas exchange and high-quality ventilation images within a single, approximately 10 s, breath-hold.

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.

Imaging in Asthma Management.

Asthma is a heterogeneous disease characterized by chronic airway inflammation that affects more than 300 million people worldwide. Clinically, asthma has a widely variable presentation and is defined based on a history of respiratory symptoms alongside airflow limitation. Imaging is not needed to confirm a diagnosis of asthma, and thus the use of imaging in asthma has historically been limited to excluding alternative diagnoses.

Improving hyperpolarized Xe ADC mapping in pediatric and adult lungs with uncertainty propagation.

Rationale: Hyperpolarized (HP) Xe-MRI provides non-invasive methods to quantify lung function and structure, with the Xe apparent diffusion coefficient (ADC) being a well validated measure of alveolar airspace size. However, the experimental factors that impact the precision and accuracy of HP Xe ADC measurements have not been rigorously investigated. Here, we introduce an analytical model to predict the experimental uncertainty of Xe ADC estimates.

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.

Preclinical MRI to Quantify Pulmonary Disease Severity and Trajectories in Poorly Characterized Mouse Models: A Pedagogical Example Using Data from Novel Transgenic Models of Lung Fibrosis.

Structural remodeling in lung disease is progressive and heterogeneous, making temporally and spatially explicit information necessary to understand disease initiation and progression. While mouse models are essential to elucidate mechanistic pathways underlying disease, the experimental tools commonly available to quantify lung disease burden are typically invasive (, histology). This necessitates large cross-sectional studies with terminal endpoints, which increases experimental complexity and expense.

Improved preclinical hyperpolarized Xe ventilation imaging with constant flip angle 3D radial golden means acquisition and keyhole reconstruction.

Hyperpolarized (HP) Xe MRI is increasingly used to noninvasively probe regional lung structure and function in the preclinical setting. As in human imaging, the primary barrier to quantitative imaging with HP gases is nonequilibrium magnetization, which is depleted by T relaxation and radio frequency excitation. Preclinical HP gas imaging commonly involves mechanically ventilating small animals and encoding k-space over tens or hundreds of breaths, with small subsets of k-space data collected within each breath.

Validating in vivo hyperpolarized Xe diffusion MRI and diffusion morphometry in the mouse lung.

Purpose: Diffusion and lung morphometry imaging using hyperpolarized gases are promising tools to quantify pulmonary microstructure noninvasively in humans and in animal models. These techniques assume the motion encoded is exclusively diffusive gas displacement, but the impact of cardiac motion on measurements has never been explored. Furthermore, although diffusion morphometry has been validated against histology in humans and mice using He, it has never been validated in mice for Xe.

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.

Preclinical hyperpolarized Xe MRI: ventilation and T * mapping in mouse lungs at 7 T using multi-echo flyback UTE.

Fast apparent transverse relaxation (short T *) is a common obstacle when attempting to perform quantitative H MRI of the lungs. While T * times are longer for pulmonary hyperpolarized (HP) gas functional imaging (in particular for gaseous Xe), T * can still lead to quantitative inaccuracies for sequences requiring longer echo times (such as diffusion weighted images) or longer readout duration (such as spiral sequences). This is especially true in preclinical studies, where high magnetic fields lead to shorter relaxation times than are typically seen in human studies.

Improved pulmonary Xe ventilation imaging via 3D-spiral UTE MRI.

Purpose: Hyperpolarized Xe MRI characterizes regional lung ventilation in a variety of disease populations, with high sensitivity to airway obstruction in early disease. However, ventilation images are usually limited to a single breath-hold and most-often acquired using gradient-recalled echo sequences with thick slices (~10-15 mm), which increases partial-volume effects, limits ability to observe small defects, and suffers from imperfect slice selection. We demonstrate higher-resolution ventilation images, in shorter breath-holds, using FLORET (Fermat Looped ORthogonally Encoded Trajectories), a center-out 3D-spiral UTE sequence.

Mapping and correcting hyperpolarized magnetization decay with radial keyhole imaging.

Purpose: Hyperpolarized (HP) media enable biomedical imaging applications that cannot be achieved with conventional MRI contrast agents. Unfortunately, quantifying HP images is challenging, because relaxation and radio-frequency pulsing generate spatially varying signal decay during acquisition. We demonstrate that, by combining center-out k-space sampling with postacquisition keyhole reconstruction, voxel-by-voxel maps of regional HP magnetization decay can be generated with no additional data collection.