Quantitative Regional Oxygen Transfer Imaging of the Human Lung

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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) T1-mapping technique (TE = 1.4 msec, TR = 3.5 msec) as well as a series of T1-weighted inversion recovery (IR) half- Fourier acquisition single-shot turbo spin-echo (HASTE) (TEeffective = 43 msec, TEinter = 4.2 msec, and inversion time [TI] = 1200 msec) images. Semiquantitative relative signal enhancement ratios (RER) of T1-weighted images before and after inhalation of oxygen-enriched gas were compared to the quantitative change in T1. A hybrid method is proposed that combines the advantages of T1-weighted imaging with the quantification provided by T1-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 T1 in the lung. Quantitative parameters, such as the decrease of T1 after switching the breathing gas, were more suited to oxygen transfer quantification than to relative signal enhancement. The mean T1 value during inhalation of room air (T1,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 T1,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 T1-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.

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