Measurement of longitudinal (T1) relaxation in the human lung at 3.0 Tesla with tissue-based and regional gradient analyses

Purpose: The purpose of this study is to measure the longitudinal (T1) relaxation time of human lung parenchyma at 3.0 Tesla M, independent of large vessel signal, and to examine T1 as a function of position in gravitational, iso-gravitational, and radial planes. Materials and Methods: Sixteen subjects were imaged. A series of 16-20 turbo field echo images was acquired over a 6-s period after the application of a single nonselective inversion (180 degrees) pulse. Tissue-based segmentation was used to separate parenchymal tissue from large pulmonary vascular tissue in the resulting images. Time-intensity curves for each tissue type were constructed and spin-lattice relaxation time was determined by line-fitting the time-intensity curves. The lung slice was divided into 10 regions of interest in the gravitational, iso-gravitational, and radial directions and regional T1 versus position gradient analyses were performed. Results: The T1 relaxation time of human lung parenchyma at 3.0T was determined to be 1374 226 ms, while the T1 of blood in large pulmonary vessels was 1623 +/- 236 ms. Whole lung T1 was found to be 1397 +/- 214 ms. T1 of lung parenchyma was found to be significantly shorter than the T1 of blood in large pulmonary vessels and whole lung TI. No regional gradient was seen in the gravitational or isogravitational directions, but a significant gradient was seen in the radial direction.