DIAPHRAGMATIC AND CARDIAC MOTION DURING SUSPENDED BREATHING - PRELIMINARY EXPERIENCE AND IMPLICATIONS FOR BREATH-HOLD MR-IMAGING

Purpose: To investigate and quantify motion of the diaphragm and heart during suspended breathing at end inspiration and end expiration. Mat erials and methods: In 10 healthy adult volunteers, line scanning was performed to monitor the position of the diaphragm during a breath hol d at end inspiration and end expiration, with a spatial and temporal r esolution of 0.25 mm and 200 msec, respectively. Electrocardiographica lly gated, turbo fast low-angle shot (FLASH) magnetic resonance (MR) i maging was performed to monitor movement of the diaphragm and heart. R esults: During a breath hold, the diaphragm moved upward. At end expir ation, the velocity of the diaphragm during suspended breathing was co nstant (mean, 0.15 mm/sec). At end inspiration, motion of the diaphrag m during suspended breathing was more complex (range, 0.1-7.9 mm/sec). During a 20-second breath hold, mean displacement of the diaphragm wa s 25% of that during normal breathing. FLASH MR imaging revealed varia tions in the position of the heart during a breath hold. During suspen ded respiration, the heart did not return to the same position on cons ecutive heartbeats and, consequently, the margins of the heart typical ly moved inward. Conclusion: Breath holding does not eliminate motion of the diaphragm. Changes in the motion of the diaphragm and transthor acic pressure during a breath hold result in complex movement of the h eart and may cause blurring during breath-hold MR imaging.