1175 Magnetic Resonance Imaging with Respiratory Gatung: Techniques and Advantages Richard L. Ehrnan1 Michael 1. McNamara1 Michael Pallack2 Hedvig Hricak1 Charles B. Higgins1 Received July 2, 1984; accepted after revision September 5, 1984. ‘Department of Radiology, University of Califor- nia School of Medicine, San Francisco, CA 94143. Address reprint requests to C. B. Higgins. 2Diasonica MRI Division, South San Francisco, CA 94080. AJR 143:1175-1182, December 1984 0361 -803x/84/1 436-1175 © American Roentgen Ray Society Respiratory motion is an important problem in magnetic resonance imaging (MRI) of the thorax and upper abdomen. This study assessed several approaches for practical respiratory gating. Methods of acquiring respiratory signals, gated sequencing methods, duration of examination, strategies for reducing examination time, diagnostic quality of gated images, and the influence of respiratory gating on relaxation time measurements were evaluated. Of three different devices for acquiring the respiratory signal, a belt containing a displacement transducer placed around the upper abdomen was found to be most effective and practical. Two pulse-gating modes were implemented, as well as a method for combining cardiac and respiratory gating. Gating methods were tested using phantoms and human volunteers. A spin-conditioned mode of respiratory gating was found to be superior to a more simply implemented triggered mode in which spin-echo (SE) sequencing was inter- rupted. The time penalty for respiratory gating is technique-dependent. Gated studies with uncontrolled tidal breathing took two to four times longer than nongated studies. When the time between respirations was voluntarily prolonged, gated studies could be only 30%-50% longer than nongated. The standard deviation of relaxation-time meas- urements for organs that are displaced during respirations was substantially reduced by respiratory gating. Gating acquisition without spin-conditioning caused systematic errors in Ti relaxation times that were not present with spin-conditioned gating. Respi- ratory gating is a practical and useful technique for improving the contrast and spatial resolution of SE images of the upper abdomen and chest. SE images produced with short repetition times were particularly improved by respiratory gating. The time required for acquisition of magnetic resonance (MR) images with high spatial and contrast resolution is long in comparison with the time scale of physiologic motions, such as cardiac contraction with the time scale of physiologic motions, such as cardiac contraction, respiratory motion, and even gastrointestinal peristalsis. Even though multislice and multiecho acquisition techniques improve clinical throughput, these do not reduce the total time of data collection for the individual anatomic sections [1 , 2]. Physiologic motion still degrades the images by causing a variety of artifacts [3-5]. One of the major obstacles to further improve- ment of the diagnostic quality of MR images of the chest and upper abdomen is respiratory motion. Gated data acquisition has been used with great success for imaging the heart [6, 7]. Similarly gated acquisition techniques have been demon- strated for reduction of the effect of respiratory motion on MR images [8, 9]. However, questions remain regarding the ideal technique for acquiring the respiratory pulse, the method for synchronizing radiofrequency pulses to the respiratory cycle, and the possible effect of respiratory gating on the relaxation times calculated from MR images. We evaluated several methods for obtaining respiratory signals suitable for use in respiratory gating, determined the best time in the respiratory cycle for data acquisition, and evaluated different approaches to regulating imager sequencing and data collection. In addition, the effect of respiratory gating on measurement of Downloaded from www.ajronline.org by 52.73.204.196 on 05/13/22 from IP address 52.73.204.196. Copyright ARRS. For personal use only; all rights reserved