The effects of apnea on timing examinations for optimization of gadolinium-enhanced MRA of the thoracic aorta and arch vessels

Purpose: Our purpose was to determine the effects of apnea during end- inspiration compared with free breathing on timing examinations performed to optimize gadolinium-enhanced 3D MR angiography (MRA) of the thoracic aorta and arch vessels. Method: Thirty patients referred for gadolinium-enhanced 3D MRA of the thoracic aorta and branch vessels underwent two timing examinations: one performed during free breathing and one during apnea at end-inspiration to replicate more closely the respiratory pattern used to obtain 3D MRA. For each, axial images at the level of the proximal neck were acquired every 2 s for 40 s, during which time 1 ml of gadolinium contrast agent followed by 20 ml of saline was infused at 2 ml/s. The time to peak arterial enhancement (T(a)), time to first jugular venous enhancement (T(j)), and arteriovenous window (time from peak arterial enhancement to first jugular venous enhancement; AV) were compared for the two examinations in each patient. Results: Overall there was no statistically significant difference in T(a), T(j), or AV between examinations performed during free breathing and apnea in end-inspiration, although a trend to delayed circulation times was observed with apnea (p = 0.2-0.3). In five patients (17%), the difference in T(a) between free breathing and apnea was 4 s; in three patients (10%), the difference was 6 s. Conclusion: Circulation times determined during apnea at end-inspiration may differ from those obtained during free breathing by as much as 6 s in an individual patient. This difference may account for inappropriately timed gadolinium-enhanced MR angiograms performed with timing examinations, especially when very short acquisition times and low doses of gadolinium (20 ml) are used.