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 perfor med to optimize gadolinium-enhanced 3D MR angiography (MRA) of the tho racic aorta and arch vessels. Method: Thirty patients referred for gad olinium-enhanced 3D MRA of the thoracic aorta and branch vessels under went two timing examinations: one performed during free breathing and one during apnea at end-inspiration to replicate more closely the resp iratory pattern used to obtain 3D MRA. For each, axial images at the l evel of the proximal neck were acquired every 2 s for 40 s, during whi ch time 1 mi of gadolinium contrast agent followed by 20 ml of saline was infused at 2 ml/s. The time to peak arterial enhancement (T-a), ti me to first jugular venous enhancement (T-j), and arteriovenous window (time from peak arterial enhancement to first jugular venous enhancem ent; AV) were compared for the two examinations in each patient. Resul ts: Overall there was no statistically significant difference in T-a, T-j, or AV between examinations performed during free breathing and ap nea in end-inspiration, although a trend to delayed circulation times was observed with apnea (p = 0.2-0.3). In five patients (17%), the dif ference in T-a between free breathing and apnea was 4 s; in three pati ents (10%), the difference was 6 s.Conclusion: Circulation times deter mined during apnea at end-inspiration may differ from those obtained d uring free breathing by as much as 6 s in an individual patient. This difference may account for inappropriately timed gadolinium-enhanced M R angiograms performed with timing examinations, especially when very short acquisition times and low doses of gadolinium (20 mi) are used.