MR MICROSCOPY OF LUNG AIRWAYS WITH HYPERPOLARIZED HE-3

A technique using hyperpolarized (HP) He-3 to image the small airways of the lung by using moderate flip angles and a short scanning period during early inspiration is demonstrated. Flip angles (alpha) ranging from 10-90 degrees were used in guinea pig experiments with scanning d uring the entire inspiration period. A second series acquired data thr oughout a short window of the ventilatory cycle with alpha = 45 degree s. The success of the animal studies has motivated implementation of s imilar imaging techniques in the clinical arena. Human studies involve d imaging over the total inspiration period with alpha approximate to 10 degrees. The first series of guinea pig experiments demonstrated th at larger flip angles (50-90 degrees) destroy the magnetization before it reaches the smaller airways, At moderate flip angles (20-40 degree s), airway branching down to the fourth generation was apparent. Fifth -order branchings were seen in the images of the second series. The tr achea down to fourth generation pulmonary airway branching, along with some distal air spaces, was seen in the human lung images.