Quantitative and O₂ Enhanced MRI of the Pathologic Lung: Findings in Emphysema, Fibrosis, and Cystic Fibrosis

Abstract

Purpose: beyond the pure morphological visual representation, MR imaging offers the possibility to quantify parameters in the healthy, as well as, in pathologic lung parenchyma. Gas exchange is the primary function of the lung and the transport of oxygen plays a key role in pulmonary physiology and pathophysiology. The purpose of this review is to present a short overview of the relaxation mechanisms of the lung and the current technical concepts of T1 mapping and methods of oxygen enhanced MR imaging. Material and Methods: molecular oxygen has weak paramagnetic properties so that an increase in oxygen concentration results in shortening of the T1 relaxation time and thus to an increase of the signal intensity in T1 weighted images. A possible way to gain deeper insights into the relaxation mechanisms of the lung is the calculation of parameter Maps. T1 Maps based on a snapshot FLASH sequence obtained during the inhalation of various oxygen concentrations provide data for the creation of the so-called oxygen transfer function (OTF), assigning a measurement for local oxygen transfer. T1 weighted single shot TSE sequences also permit expression of the signal changing effects associated with the inhalation of pure oxygen. Results: the average of the mean T1 values over the entire lung in inspiration amounts to 1199 +/− 117 milliseconds, the average of the mean T1 values in expiration was 1333 +/− 167 milliseconds. T1 Maps of patients with emphysema and lung fibrosis show fundamentally different behavior patterns. Oxygen enhanced MRT is able to demonstrate reduced diffusion capacity and diminished oxygen transport in patients with emphysema and cystic fibrosis. Discussion: results published in literature indicate that T1 mapping and oxygen enhanced MR imaging are promising new methods in functional imaging of the lung and when evaluated in conjunction with the pure morphological images can provide additional valuable information.

Dynamic oxygen-enhanced magnetic resonance imaging of the lung in asthma—Initial experience

“…The entire-lung median PO 2max l showed slightly better correlations with PFT parameters than the enhancing-region median PO 2max l . Similar correlations of OE-MRI readouts with FEV 1 %predicted, FVC%predicted, FEV 1 /FVC ratio and MMEF%predicted have been demonstrated in asthmatics and patients with other lung diseases [13,15,[19][20][21], while the correlations with the airway resistance indices of sR tot and sR eff are to our knowledge the first reported. In a previous asthma OE-MRI study, Ohno et al reported significant but much weaker correlations between the mean signal enhancement ratio and FEV 1 (r = 0.55, P < 0.05) and the average forced expiratory flow between 25% point and 75% point of FVC (FEF 25%-75% , r = 0.55, P < 0.05) [21].…”

“…Dynamic oxygen-enhanced (OE-) MRI can provide spatial and temporal information on regional delivery and uptake of O 2 in the lung by using 16 O 2 as a contrast agent [10][11][12][13]. The paramagnetic O 2 molecules dissolve in the tissue water and blood plasma within the lung and increase the lung spin-lattice relaxation rate (R 1 ) in proportion to dissolved O 2 concentration [11] and thus the local O 2 partial pressure (PO 2 ) [14].…”

“…Although OE-MRI has been used to investigate lung function changes in many pulmonary disorders [13,15,[18][19][20], there is little data regarding its utility in asthma. Ohno et al demonstrated an equivalent efficacy of OE-MRI to quantitative CT in the classification of asthma severity [21].…”

Ventilation/perfusion imaging of the lung using ultra‐short echo time (UTE) MRI in an animal model of pulmonary embolism

“…In addition, modulation of T1 values seen in parenchymal lesions may complicate the variation. For example, it was reported that the T1 values of the lung were shorter in pulmonary emphysema (33) and fibrosis (34) than in normal lungs. Moreover, inversion-recovery HASTE is time consuming, and difficult to assess oxygen-enhancement within whole lung.…”

UTE‐SENCEFUL: first results for 3D high‐resolution lung ventilation imaging

“…Moreover, hyperpolarized gases such as helium or xenon are used for ventilation imaging with high resolution and SNR at a few specialized centers . Oxygen‐enhanced MRI is a cheaper alternative, but low SNR and long acquisition times limit its broader utilization …”