Clinical aspects of the apparent diffusion coefficient in 3He MRI:: Results in healthy volunteers and patients after lung transplantation

Purpose: To measure the apparent diffusion coefficient (ADC) after inhalation of hyperpolarized 3 He in healthy volunteers and lung transplant recipients, and demonstrate the gravity dependence of ADC values. Materials and Methods: Six healthy volunteers, 10 patients after single-lung transplantation, and six patients after double-lung transplantation were examined at 1.5T during inspiration and expiration. The inhalation of 300 mL of hyperpolarized 3 He was performed with a computer-controlled delivery device. A two-dimensional fast low-angle shot (FLASH) sequence measured the 3 He diffusive gas movement. From these data the ADC was calculated. Results: The mean ADC was 0.143 cm(2) /second in healthy individuals, 0.162 cm(2) /second in transplanted healthy lungs, and 0.173 cm(2) /second in rejected transplanted lungs, whereas it was 0.216 cm(2) /second in native fibrotic lungs and 0.239 cm(2)/ second in emphysematous lungs. The difference in mean ADC values among healthy lungs, healthy transplanted lungs, and native diseased lungs was significant (P < 0.001). In inspiration the healthy volunteers showed higher ADC values in the anterior than in the posterior parts of the lungs. In expiration this gradient doubled. Conclusion: An anterior-posterior (A/P) gradient was found in inspiration and expiration in healthy lungs. Healthy, transplanted, and native diseased lungs had significantly different mean ADC values. From our preliminary results, 3 He MRI appears to be sensitive for detecting areas of abnormal ventilation in transplanted lungs.