Xe Image Processing Pipeline: An open-source, graphical user interface application for the analysis of hyperpolarized Xe MRI.

Purpose: Hyperpolarized Xe MRI presents opportunities to assess regional pulmonary microstructure and function. Ongoing advancements in hardware, sequences, and image processing have helped it become increasingly adopted for both research and clinical use. As the number of applications and users increase, standardization becomes crucial.

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.

Finite element simulations of hyperpolarized gas DWI in micro-CT meshes of acinar airways: validating the cylinder and stretched exponential models of lung microstructural length scales.

Purpose: This work assesses the accuracy of the stretched exponential (SEM) and cylinder models of lung microstructural length scales that can be derived from hyperpolarized gas DWI. This was achieved by simulating He and Xe DWI signals within two micro-CT-derived realistic acinar airspace meshes that represent healthy and idiopathic pulmonary fibrosis lungs.

Methods: The healthy and idiopathic pulmonary fibrosis acinar airway meshes were derived from segmentations of 3D micro-CT images of excised human lungs and meshed for finite element simulations of the Bloch-Torrey equations.

Incorporation of Prior Knowledge of Signal Behavior Into the Reconstruction to Accelerate the Acquisition of Diffusion MRI Data.

Diffusion MRI data are generally acquired using hyperpolarized gases during patient breath-hold, which yields a compromise between achievable image resolution, lung coverage, and number of -values. In this paper, we propose a novel method that accelerates the acquisition of diffusion MRI data by undersampling in both the spatial and -value dimensions and incorporating knowledge about signal decay into the reconstruction (SIDER). SIDER is compared with total variation (TV) reconstruction by assessing its effect on both the recovery of ventilation images and the estimated mean alveolar dimensions (MADs).

Regional Ventilation Changes in the Lung: Treatment Response Mapping by Using Hyperpolarized Gas MR Imaging as a Quantitative Biomarker.

Purpose To assess the magnitude of regional response to respiratory therapeutic agents in the lungs by using treatment response mapping (TRM) with hyperpolarized gas magnetic resonance (MR) imaging. TRM was used to quantify regional physiologic response in adults with asthma who underwent a bronchodilator challenge. Materials and Methods This study was approved by the national research ethics committee and was performed with informed consent.

Detection of early subclinical lung disease in children with cystic fibrosis by lung ventilation imaging with hyperpolarised gas MRI.

Hyperpolarised He ventilation-MRI, anatomical lung MRI, lung clearance index (LCI), low-dose CT and spirometry were performed on 19 children (6-16 years) with clinically stable mild cystic fibrosis (CF) (FEV>-1.96), and 10 controls. All controls had normal spirometry, MRI and LCI.

Finite element modeling of (129)Xe diffusive gas exchange NMR in the human alveoli.

Existing models of (129)Xe diffusive exchange for lung microstructural modeling with time-resolved MR spectroscopy data have considered analytical solutions to one-dimensional, homogeneous models of the lungs with specific assumptions about the alveolar geometry. In order to establish a model system for simulating the effects of physiologically-realistic changes in physical and microstructural parameters on (129)Xe exchange NMR, we have developed a 3D alveolar capillary model for finite element analysis. To account for the heterogeneity of the alveolar geometry across the lungs, we have derived realistic geometries for finite element analysis based on 2D histological samples and 3D micro-CT image volumes obtained from ex vivo biopsies of lung tissue from normal subjects and patients with interstitial lung disease.

Whole lung morphometry with 3D multiple b-value hyperpolarized gas MRI and compressed sensing.

Purpose: To demonstrate three-dimensional (3D) multiple b-value diffusion-weighted (DW) MRI of hyperpolarized He gas for whole lung morphometry with compressed sensing (CS).

Methods: A fully-sampled, two b-value, 3D hyperpolarized He DW-MRI dataset was acquired from the lungs of a healthy volunteer and retrospectively undersampled in the k and k phase-encoding directions for CS simulations. Optimal k-space undersampling patterns were determined by minimizing the mean absolute error between reconstructed and fully-sampled He apparent diffusion coefficient (ADC) maps.

Pulmonary ventilation and micro-structural findings in congenital diaphragmatic hernia.

Background: With increasing survival of patients with more severe forms of congenital diaphragmatic hernia (CDH) and risk of long-term respiratory morbidity, studies on lung morphology are needed. We used hyperpolarised (3) He MRI and anatomical (1) H MRI in a cohort of young adult CDH patients to image regional lung ventilation and microstructure, focusing on morphological and micro-structural (alveolar) abnormalities.

Methods: Nine patients with left-sided CDH, born 1975-1993, were studied.

Comparison of CT-based Lobar Ventilation with 3He MR Imaging Ventilation Measurements.

Purpose: To compare lobar lung ventilation computed from expiratory and inspiratory computed tomographic (CT) data with direct measurements of ventilation at hyperpolarized helium 3 ((3)He) magnetic resonance (MR) imaging by using same-breath hydrogen 1 ((1)H) MR imaging examinations to coregister the multimodality images.

Materials And Methods: The study was approved by the national research ethics committee, and written patient consent was obtained. Thirty patients with asthma underwent breath-hold CT at total lung capacity and functional residual capacity.

A method for quantitative analysis of regional lung ventilation using deformable image registration of CT and hybrid hyperpolarized gas/1H MRI.

Hyperpolarized gas magnetic resonance imaging (MRI) generates highly detailed maps of lung ventilation and physiological function while CT provides corresponding anatomical and structural information. Fusion of such complementary images enables quantitative analysis of pulmonary structure-function. However, direct image registration of hyperpolarized gas MRI to CT is problematic, particularly in lungs whose boundaries are difficult to delineate due to ventilation heterogeneity.

Experimental validation of the hyperpolarized Xe chemical shift saturation recovery technique in healthy volunteers and subjects with interstitial lung disease.

Purpose: To assess the sensitivity of the hyperpolarized Xe chemical shift saturation recovery (CSSR) technique for noninvasive quantification of changes to lung microstructure and function in idiopathic pulmonary fibrosis (IPF) and systemic sclerosis (SSc).

Methods: Ten healthy volunteers, four subjects with SSc and four with IPF were scanned at 1.5 T.

Response to Commentary on "The influence of lung airways branching structure and diffusion time on measurements and models of short-range 3He gas MR diffusion".

Our extensive investigation of the cylinder model theory through numerical modelling and purpose-designed experiments has demonstrated that it does produce inaccurate estimates of airway dimensions at all diffusion times currently used. This is due to a variety of effects: incomplete treatment of non-Gaussian effects, finite airway size, branching geometry, background susceptibility gradients and diffusion time dependence of the (3)He MR diffusion behaviour in acinar airways. The cylinder model is a good starting point for the development of a lung morphometry technique from (3)He diffusion MR but its limitations need to be understood and documented in the interest of reliable clinical interpretation.

Quantification of regional fractional ventilation in human subjects by measurement of hyperpolarized 3He washout with 2D and 3D MRI.

Multiple-breath washout hyperpolarized (3)He MRI was used to calculate regional parametric images of fractional ventilation (r) as the ratio of fresh gas entering a volume unit to the total end inspiratory volume of the unit. Using a single dose of inhaled hyperpolarized gas and a total acquisition time of under 1 min, gas washout was measured by dynamic acquisitions during successive breaths with a fixed delay. A two-dimensional (2D) imaging protocol was investigated in four healthy subjects in the supine position, and in a second protocol the capability of extending the washout imaging to a three-dimensional (3D) acquisition covering the whole lungs was tested.

(3)He pO2 mapping is limited by delayed-ventilation and diffusion in chronic obstructive pulmonary disease.

Purpose: Lung pO2 mapping with (3)He MRI assumes that the sources of signal decay with time during a breath-hold are radiofrequency depolarization and oxygen-dependent T1 relaxation, but the method is sensitive to other sources of spatio-temporal signal change such as diffusion. The purpose of this work was to assess the use of (3)He pO2 mapping in patients with chronic obstructive pulmonary disease.

Methods: Ten patients with moderate to severe chronic obstructive pulmonary disease were scanned with a 3D single breath-hold pO2 mapping sequence.

Simultaneous imaging of lung structure and function with triple-nuclear hybrid MR imaging.

Purpose: To re-engineer a standard clinical magnetic resonance (MR) imaging system to enable the acquisition, in the same breath hold, of lung images from two hyperpolarized gases (helium 3 [(3)He] and xenon 129 [(129)Xe]) with simultaneous registered anatomic proton (hydrogen 1 [(1)H]) MR images of lung structure.

Materials And Methods: Studies with (3)He and (129)Xe were performed with National Research Ethics Committee approval, with informed consent from the volunteer. (1)H-(3)He-(129)Xe MR imaging was achieved in the same breath by using mutually decoupled nested radiofrequency coil hardware capable of transmit and receive on each respective nucleus without power cross talk.

The influence of lung airways branching structure and diffusion time on measurements and models of short-range 3He gas MR diffusion.

Hyperpolarized (3)He diffusion experiments have been shown to be sensitive to changes in acinar structure due to emphysematous lung disease. Extracting quantitative information about lung microstructure from the diffusion signal is complicated due its dependence on a number of factors including diffusion time and the complex branching acinar geometry. A theoretical model (cylinder model) has been proposed as a means of estimating acinar airway dimensions from measured diffusivities.

Hyperpolarized 129Xe gas lung MRI-SNR and T2* comparisons at 1.5 T and 3 T.

In this study, the signal-to-noise ratio of hyperpolarized (129)Xe human lung magnetic resonance imaging was compared at 1.5 T and 3 T. Experiments were performed at both B(0) fields with quadrature double Helmholtz transmit-receive chest coils of the same geometry with the same subject loads.

Direct visualisation of collateral ventilation in COPD with hyperpolarised gas MRI.

Background: Collateral ventilation has been proposed as a mechanism of compensation of respiratory function in obstructive lung diseases but observations of it in vivo are limited. The assessment of collateral ventilation with an imaging technique might help to gain insight into lung physiology and assist the planning of new bronchoscopic techniques for treating emphysema.

Objective: To obtain images of delayed ventilation that might be related to collateral ventilation over the period of a single breath-hold in patients with chronic obstructive pulmonary disease (COPD).

K-space filter deconvolution and flip angle self-calibration in 2D radial hyperpolarised 3He lung MRI.

In hyperpolarised (3)He lung MRI with constant flip angles, the transverse magnetisation decays with each RF excitation imposing a k-space filter on the acquired data. For radial data acquired in an angularly-sequential order, this filter causes streaking, angular shading and loss of spatial resolution in the images. The main aim of this work was to reduce the effects of the RF depletion k-space filter in radial acquisitions.

A flexible 32-channel receive array combined with a homogeneous transmit coil for human lung imaging with hyperpolarized 3He at 1.5 T.

Parallel imaging presents a promising approach for MRI of hyperpolarized nuclei, as the penalty in signal-to-noise ratio typically encountered with (1)H MRI due to a reduction in acquisition time can be offset by an increase in flip angle. The signal-to-noise ratio of hyperpolarized MRI generally exhibits a strong dependence on flip angle, which makes a homogeneous B(1)(+) transmit field desirable. This paper presents a flexible 32-channel receive array for (3) He human lung imaging at 1.

Combined measurement of pulmonary inert gas washout and regional ventilation heterogeneity by MR of a single dose of hyperpolarized 3He.

Washout of inert gases is a measure of pulmonary function well-known in lung physiology. This work presents a method combining inert gas washout and spatially resolved imaging using hyperpolarized (3) He, thus providing complementary information on lung function and physiology. The nuclear magnetic resonance signal of intrapulmonary hyperpolarized (3) He is used to track the total amount of gas present within the lungs during multiple-breath washout via tidal breathing.

Synchronous acquisition of hyperpolarised 3He and 1H MR images of the lungs - maximising mutual anatomical and functional information.

The development of hybrid medical imaging scanners has allowed imaging with different detection modalities at the same time, providing different anatomical and functional information within the same physiological time course with the patient in the same position. Until now, the acquisition of proton MRI of lung anatomy and hyperpolarised gas MRI of lung function required separate breath-hold examinations, meaning that the images were not spatially registered or temporally synchronised. We demonstrate the spatially registered concurrent acquisition of lung images from two different nuclei in vivo.