Extending the range of diffusion times for regional measurement of the ³He ADC in human lungs

A stimulated-echo-based technique was developed to measure the regional apparent diffusion coefficient (ADC) of hyperpolarized ³He during a single breathhold for diffusion times of 25 ms or greater. Compared to previous methods, a substantially shorter minimum diffusion time was achieved by decoupling diffusion sensitization from image acquisition. A hyperpolarized-gas phantom was used to validate the method, which was then tested in four healthy subjects in whom regional ADC maps were acquired with diffusion times of 50, 200, and 1500 ms and a tag wavelength of 5 or 10 mm. ADC values from healthy subjects were in good agreement with reported literature values and decreased with increasing diffusion time. Mean ADC values were 0.07, 0.03, and 0.015 cm²/s for diffusion times of 50, 200, and 1500 ms, respectively. ADC maps were generally homogeneous, with similar mean values when measured with the same parameters in different subjects.