Ventilation Magnetic Resonance Research Articles

Current Advances in COPD Imaging

To review the recent advances in available technologies for imaging COPD and present the novel optical coherence tomography (OCT) airway imaging technology. This is an unstructured review of published evidence of available pulmonary imaging technologies along with a demonstration of state-of-the-art OCT imaging technology of in vivo human and animal airways. Advanced imaging techniques such as Magnetic Resonance (MR) imaging using hyperoloarized noble gases, micro-Computed Tomography (micro-CT), and OCT aim to further our understanding of COPD. Lung densitometry can aid in identifying an exacerbation prone phenotype which may have implications for targeting specific therapies to these individuals. MR ventilation scans have the ability to provide a functional and regional distribution of airflow obstruction offering insight into the airway and parenchymal changes induced by COPD. Micro-CT gives a near microscopic view of the terminal bronchioles and alveoli permitting study of the microarchitecture of the lung ex vivo. Optical coherence tomography can visualize the microstructure of the airway walls (epithelium, smooth muscle, blood vessels, cartilage) permitting real time in vivo as well as longitudinal evaluation of airway changes in patients with COPD. Advanced imaging techniques play a vital role in expanding our current understanding of COPD.

Chronic Obstructive Pulmonary Disease: Lobar Analysis with Hyperpolarized 129Xe MR Imaging.

Purpose To compare lobar ventilation and apparent diffusion coefficient (ADC) values obtained with hyperpolarized xenon 129 (129Xe) magnetic resonance (MR) imaging to quantitative computed tomography (CT) metrics on a lobar basis and pulmonary function test (PFT) results on a whole-lung basis in patients with chronic obstructive pulmonary disease (COPD). Materials and Methods The study was approved by the National Research Ethics Service Committee; written informed consent was obtained from all patients. Twenty-two patients with COPD (Global Initiative for Chronic Obstructive Lung Disease stage II-IV) underwent hyperpolarized 129Xe MR imaging at 1.5 T, quantitative CT, and PFTs. Whole-lung and lobar 129Xe MR imaging parameters were obtained by using automated segmentation of multisection hyperpolarized 129Xe MR ventilation images and hyperpolarized 129Xe MR diffusion-weighted images after coregistration to CT scans. Whole-lung and lobar quantitative CT-derived metrics for emphysema and bronchial wall thickness were calculated. Pearson correlation coefficients were used to evaluate the relationship between imaging measures and PFT results. Results Percentage ventilated volume and average ADC at lobar 129Xe MR imaging showed correlation with percentage emphysema at lobar quantitative CT (r = -0.32, P < .001 and r = 0.75, P < .0001, respectively). The average ADC at whole-lung 129Xe MR imaging showed moderate correlation with PFT results (percentage predicted transfer factor of the lung for carbon monoxide [Tlco]: r = -0.61, P < .005) and percentage predicted functional residual capacity (r = 0.47, P < .05). Whole-lung quantitative CT percentage emphysema also showed statistically significant correlation with percentage predicted Tlco (r = -0.65, P < .005). Conclusion Lobar ventilation and ADC values obtained from hyperpolarized 129Xe MR imaging demonstrated correlation with quantitative CT percentage emphysema on a lobar basis and with PFT results on a whole-lung basis. © RSNA, 2016.

Effect of supplemental oxygen on native blood and myocardial MOLLI T1 relaxation times

Background Magnetic resonance (MR) T1 relaxation time measurements are increasingly used for myocardial tissue characterization. Significant differences in native and gadolinium-enhanced measurements have been associated with ischemic and non-ischemic cardiomyopathies, myocardial fat deposition, fibrosis and edema as well as regional and global ventricular functional parameters. Supplemental oxygen is often given to cardiac MR patients for improved breatholding. High flow supplemental oxygen with a non-rebreather mask is reported to reduce both myocardial and blood T1 relaxation times and has been studied with HASTE and FLASH T1 relaxation measurements for the optimization of MR ventilation scanning. The primary mechanism is dissolved oxygen acting as a paramagetic contrast agent. Conversely other reports show an increase of blood T1 times with increasing oxygen saturation. We studied the effect of supplemental oxygen on myocardial and blood T1 relaxation times using a well-documented T1 MOdified Look-Locker Imaging (MOLLI) protocol. Methods Twelve healthy subject without respiratory or cardiac disease (age: 47.4±5.3 years; 6 male) were studied at 1.5T using MOLLI T1 mapping (TE/TE= 2.8/1.2 ms; 3(3)-5; 2 inversions, 3 heartbeat rest period; TI start=120 ms; TI increment=120ms; 3 parameter curve fitting). Images were acquired in the four chamber view. Five measurements spaced by 10 minutes were performed with supplemental oxygen supplied by nasal cannula and a non-reberather mask alternating with room air (M1: Room air, M2: nasal oxygen (2 l/m), M3: Room air, M4: non-rebreather mask (15 l/m), M5: room air). Regions-of-interest were drawn for T1 measurements in the boodpool of each ventricle and atria as well as septal myocardium. The effects of supplemental oxygen were investigated statistically using a mixed model analysis of variance.

Hyperpolarized HHe 3 MRI of the Lung in Cystic Fibrosis: Assessment at Baseline and After Bronchodilator and Airway Clearance Treatment 1

The purpose of this study is to determine hyperpolarized helium 3 (HHe) magnetic resonance (MR) findings of the lung in patients with cystic fibrosis (CF) compared with healthy subjects and determine whether HHe MR can detect changes after bronchodilator therapy or mechanical airway mucus clearance treatment. Thirty-one subjects, 16 healthy volunteers and 15 patients with CF, underwent HHe lung ventilation MR imaging and spirometry at baseline. Eight patients with CF then were treated with nebulized albuterol, after which a follow-up HHe MR scan was obtained. Subsequently, recombinant human deoxyribonuclease (DNase) treatment and chest physical therapy were performed in these eight subjects, followed by a third HHe MR scan. For each MR study, the number of ventilation defects was scored by a human reader. Patients with CF had significantly more HHe MR ventilation defects per image than healthy subjects (mean, 8.2 defects in patients with CF vs 1.6 defects in healthy subjects; P < .05). Even the four subjects with CF with a normal forced expiratory volume in 1 second had significantly more ventilation defects than healthy subjects (mean, 6.5 defects in these patients with CF; P = .0002). After treatment with albuterol, there was a small, but statistically significant, decrease in number of ventilation defects (mean, 9.6-8.0 defects; P = .025). After DNase and chest physical therapy, there was a trend toward increasing ventilation defects (mean, 8.3 defects; P = .096), but with a residual net improvement relative to baseline. In patients with CF, HHe MR ventilation defects correlate with spirometry, change with treatment, and are elevated in number in patients with CF with normal spirometry results. Thus, HHe MR appears to possess many of the characteristics required of a biomarker for pulmonary CF and may be useful in the evaluation of CF pulmonary disease severity or progression.

Pulmonary Embolism: Comprehensive Evaluation with MR Ventilation and Perfusion Scanning with Hyperpolarized Helium-3, Arterial Spin Tagging, and Contrast-enhanced MRA

Development of a comprehensive magnetic resonance (MR) examination consisting of MR angiography (MRA) and MR ventilation and perfusion (MR V/Q) scan for the detection of pulmonary emboli (PE) and assessment of the technique in a rabbit model. Reversible PE was induced by inflating a non-detachable silicon balloon in the left pulmonary artery of five New Zealand White rabbits. MR V/Q scans were obtained prior to, during, and after balloon deflation. MRA was performed during balloon inflation. MR ventilation imaging was performed after the inhalation of hyperpolarized helium-3. MR perfusion imaging was performed with Flow-sensitive Alternating Inversion Recovery with an Extra Radiofrequency pulse technique (FAIRER). High-resolution contrast-enhanced MR pulmonary angiography was used to confirm the occlusion of the pulmonary artery. All imaging was performed on a 1.5-T whole body scanner with broadband capabilities. High-resolution ventilation images of the lungs were obtained. No ventilation defects were detected before, during, or after resolution of simulated PE. FAIRER imaging allowed visualization of pulmonary perfusion. No perfusion defects were detected prior to balloon inflation. During balloon inflation (PE), there was decreased perfusion in the left lower lobe. After reversal of the PE, there was improved perfusion to the left lower lobe. In analogy to nuclear medicine techniques, acute PE produced a mismatched defect in the MR V/Q scan. MRA verified the occlusive filling defect in the left pulmonary artery. High-resolution MRA and MR V/Q imaging of the lung is feasible and allows comprehensive assessment of pulmonary embolism in one imaging session.

Clinical oxygen-enhanced magnetic resonance imaging of the lung.

Oxygen-enhanced magnetic resonance (MR) ventilation imaging is a new technique, and the full extent of its physiologic significance has not been elucidated. This review article includes (1) theory of oxygen enhancement; (2) respiratory physiology; (3) oxygen-enhanced MR imaging (MRI) sequence design; (4) basic study of oxygen-enhanced MRI in animal models and humans; (5) clinical study of oxygen-enhanced MRI; and (6) merits and demerits of the technique in comparison with hyperpolarized noble gas MR ventilation imaging. Oxygen-enhanced MRI provides not only ventilation-related information but also respiration-related information. Although application of oxygen-enhanced MR ventilation imaging to patients with pulmonary diseases has been limited, oxygen-enhanced MRI offers the possibility of demonstrating regional pulmonary function and substituting for nuclear medicine ventilation-perfusion study, when combined with MR perfusion imaging. We believe that further basic studies and clinical applications of this new technique will define the real significance of oxygen-enhanced MR ventilation imaging in the future of pulmonary functional imaging and its usefulness for diagnostic radiology.

Oxygen-enhanced magnetic resonance ventilation imaging of lung

The oxygen-enhanced magnetic resonance (MR) ventilation imaging is a new technique, and the full extent of its physiological significance has not been elucidated. This review article includes background on (1) respiratory physiology; (2) mechanism and optimization of oxygen-enhanced MR imaging technique; (3) recent applications in animal and human models; and (4) merits and demerits of the technique in comparison with hyperpolarized noble gas MR ventilation imaging. Application of oxygen-enhanced MR ventilation imaging to patients with pulmonary diseases has been very limited. However, we believe that further basic studies, as well as clinical applications of this new technique will define the real significance of oxygen-enhanced MR ventilation imaging in the future of pulmonary functional imaging and its usefulness for diagnostic radiology.

The Stripe Sign

PURPOSE: The aim of this study was to correlate regional ventilation and perfusion images and perfusion SPECT with images made using a newly developed magnetic resonance ventilation (MRV) method. MATERIALS AND METHODS: The investigation included a single patient with chronic obstructive pulmonary disease and a healthy control participant. Ventilation and perfusion images using Xe-133 and Tc-99m MAA, including perfusion SPECT, were compared with single-breath MRV with hyperpolarized He-3. RESULTS: Ventilation and perfusion defects correspond to areas of poor ventilation on MRV. High-resolution MRV images show preservation of bronchi and acinus units in areas of the "stripe sign" on the V/Q study. CONCLUSIONS: MRV imaging confirms that the stripe sign seen on nuclear perfusion imaging correlates with subsegmental preserved lung. MRV imaging has the potential for high-resolution innovative studies of subsegmental lung function, using either He-3 or Xe-129 hyperpolarized gases.

Magnetic Resonance Imaging of Pulmonary Ventilation

The authors investigate whether a modified gadolinium (Gd)-DTPA formulation can be aerosolized and used as a contrast agent for magnetic resonance (MR) ventilation imaging of the lungs. Gadolinium-DTPA (gadopentetate dimeglumine, Schering AG, Berlin, Germany, 100 mmol Gd/L) was modified by addition of mannitol (Sigma, Deisenhofen, Germany, 10 mg/mL) and the surface active detergent Lutrol F68 (BASF, Mannheim, Germany, 2 mg/mL). The imaging was performed in an anesthetized rat model after inhalation of the contrast agent aerosol (PulmoSonic, De Vilbiss, Germany, 10-minute nebulization). T1-weighted spin echo images (repetitive time [TR]/echo time [TE] = 40/3 mseconds) were acquired at 2 T (SIS 85; Sisco, Fremont, CA) before and as long as 120 minutes after administration of the contrast agent. The modified Gd-DTPA aerosol elicited high and relatively homogeneous enhancement of the lung directly after nebulization. The enhancement was more pronounced than that obtained with a Gd-DTPA formulation without additives. Gadolinium-DTPA-based aerosol appears to be a suitable contrast agent for MR ventilation imaging in an experimental animal model. Modification by mannitol (to increase proton density through a slight additional osmotic effect) and a detergent (to reduce droplet size by decreasing surface tension) is suitable and effective in increasing signal intensity compared with Gd-DTPA without modification.