Abstract
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 = 1.4 msec, TR = 3.5 msec) as well as a series of T~1~‐weighted inversion recovery (IR) half‐ Fourier acquisition single‐shot turbo spin‐echo (HASTE) (TE~effective~ = 43 msec, TE~inter~ = 4.2 msec, and inversion time [TI] = 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. J. Magn Reson. Imaging 2007. © 2007 Wiley‐Liss, Inc.