Magnetic susceptibility gradients caused by tissue/air interfaces lead to very short T 2 * times in the human lung. These susceptibility gradients are dependent on the magnetic susceptibility of the respiratory gas and therefore should influence T 2 * relaxation. In this work, a technique for quantitative T 2 * mapping of the human lung during one breath hold is presented. Using this method, the lung T 2 * relaxation time was measured under normoxic (room air, 21% O 2 ) and hyperoxic (100% O 2 ) conditions to verify this assumption. The mean T 2 * difference between room air and 100% O 2 is about 10% and contains ventilation information, since only ventilated regions contribute to signal change due to different susceptibility gradients.

This paper describes imaging of lung function with oxygen-enhanced MRI using dynamically acquired T1 parameter maps, which allows an accurate, quantitative assessment of time constants of T1-enhancement and therefore lung function. Eight healthy volunteers were examined on a 1.5-T whole-body scanner. Lung T1-maps based on an IR Snapshot FLASH technique (TE = 1.4 ms, TR = 3.5 ms, FA = 7 (composite function )) were dynamically acquired from each subject. Without waiting for full relaxation between subsequent acquisition of T1-maps, one T1-map was acquired every 6.7 s. For comparison, all subjects underwent a standard pulmonary function test (PFT). Oxygen wash-in and wash-out time course curves of T1 relaxation rate (R1)-enhancement were obtained and time constants of oxygen wash-in (w(in)) and wash-out (w(out)) were calculated. Averaged over the whole right lung, the mean w(out) was 43.90 +/- 10.47 s and the mean (w(in)) was 51.20 +/- 15.53 s, thus about 17% higher in magnitude. Wash-in time constants correlated strongly with forced expired volume in one second in percentage of the vital capacity (FEV1 % VC) and with maximum expiratory flow at 25% vital capacity (MEF25), whereas wash-out time constants showed only weak correlation. Using oxygen-enhanced rapid dynamic acquisition of T1-maps, time course curves of R1-enhancement can be obtained. With w(in) and w(out) two new parameters for assessing lung function are available. Therefore, the proposed method has the potential to provide regional information of pulmonary function in various lung diseases.

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.

Purpose: To present a single-shot perfusion imaging sequence that does not require contrast agents or a subtraction of a tag and a control image to create the perfusionweighted contrast. The proposed method is based on SEEPAGE. Materials and Methods:Experiments with healthy volunteers were performed to qualitatively and quantitatively obtain pulmonary perfusion values in coronal as well as sagittal orientation. In addition, a first experiment with a lung cancer patient was performed to explore the potentials of SEEPAGE in a clinical application. Results:All experiments clearly showed a perfusionweighted contrast, providing clinical quality images with high spatial resolution. The quantified perfusion rates were consistent in the different imaging orientations and covered the interval of 1.00 -4.00 mL/min/mL. In addition, the gravitational dependence of pulmonary perfusion, the influence of adiabatic pulse duration on signal intensity, and the tracer saturation effect were examined. In the patient examination the presented technique provided additional information of the lung deficiency compared to a conventional anatomical image.Conclusion: SEEPAGE has proved to be a robust and reproducible technique for obtaining perfusion-weighted images in a single measurement and for quantifying pulmonary perfusion using an additional reference scan. Furthermore, the proposed method shows promise for future clinical application.

Purpose:To demonstrate that the use of nonquantitative methods in oxygen-enhanced (OE) lung imaging can be problematic and to present a new approach for quantitative OE lung imaging, which fulfills the requirements for easy application in clinical practice. Materials and Methods:A total of 10 healthy volunteers and three non-small-cell lung cancer (NSCLC) patients were examined using a 1.5T scanner. OE imaging was performed using a snapshot fast low-angle shot (FLASH) T 1 -mapping technique (TE ϭ 1.4 msec, TR ϭ 3.5 msec) as well as a series of T 1 -weighted inversion recovery (IR) halfFourier acquisition single-shot turbo spin-echo (HASTE) (TE effective ϭ 43 msec, TE inter ϭ 4.2 msec, and inversion time [TI] ϭ 1200 msec) images. Semiquantitative relative signal enhancement ratios (RER) of T 1 -weighted images before and after inhalation of oxygen-enriched gas were compared to the quantitative change in T 1 . A hybrid method is proposed that combines the advantages of T 1 -weighted imaging with the quantification provided by T 1 -mapping. To this end, the IR-HASTE images were transformed into quantitative parameter maps. To prevent mismatching and incorrect parameter maps, retrospective image selection was performed using a postprocessing navigator technique. Results:The RER was dependent on the intrinsic values of T 1 in the lung. Quantitative parameters, such as the decrease of T 1 after switching the breathing gas, were more suited to oxygen transfer quantification than to relative signal enhancement. The mean T 1 value during inhalation of room air (T 1,room ) for the volunteers was 1260 msec. This value decreased by about 10% after switching the breathing gas to carbogen. For the patients, the mean T 1,room value was 1182 msec, which decreased by about 7% when breathing carbogen. The parameter maps generated using the proposed hybrid method deviated, on average, only about 1% from the T 1 -maps. Conclusion:For the purpose of intersubject comparison, OE lung imaging should be performed quantitatively. The proposed hybrid technique produced reliable quantitative results in a short amount of time and, therefore, is suited for clinical use.