Diaphragmatic and cardiac motion during suspended breathing: preliminary experience and implications for breath-hold MR imaging.

Abstract

To investigate and quantify motion of the diaphragm and heart during suspended breathing at end inspiration and end expiration. In 10 healthy adult volunteers, line scanning was performed to monitor the position of the diaphragm during a breath hold at end inspiration and end expiration, with a spatial and temporal resolution of 0.25 mm and 200 msec, respectively. Electrocardiographically gated, turbo fast low-angle shot (FLASH) magnetic resonance (MR) imaging was performed to monitor movement of the diaphragm and heart. During a breath hold, the diaphragm moved upward. At end expiration, the velocity of the diaphragm during suspended breathing was constant (mean, 0.15 mm/sec). At end inspiration, motion of the diaphragm during suspended breathing was more complex (range, 0.1-7.9 mm/sec). During a 20-second breath hold, mean displacement of the diaphragm was 25% of that during normal breathing. FLASH MR imaging revealed variations in the position of the heart during a breath hold. During suspended respiration, the heart did not return to the same position on consecutive heartbeats and, consequently, the margins of the heart typically moved inward. Breath holding does not eliminate motion of the diaphragm. Changes in the motion of the diaphragm and transthoracic pressure during a breath hold result in complex movement of the heart and may cause blurring during breath-hold MR imaging.