No abstract

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.

Spatial resolution in single‐shot imaging is limited by signal attenuation due to relaxation of transverse magnetization. This effect can be reduced by minimizing acquisition times through the use of short interecho spacings. However, the minimum interecho spacing is constrained by limits on gradient switching rates, radiofrequency (RF) power deposition and RF pulse length. Recently, simultaneous acquisition of spatial harmonics (SMASH) has been introduced as a method to acquire magnetic resonance images at increased speeds using a reduced number of phase‐encoding gradient steps by extracting spatial information contained in an RF coil array. In this study, it is shown that SMASH can be used to reduce the effects of relaxation, resulting in single‐shot images with increased spatial resolution without increasing imaging time. After a brief theoretical discussion, two strategies to reduce signal attenuation and increase spatial resolution in single‐shot imaging are introduced and their performance is evaluated in phantom studies. In vivo single‐shot echoplanar imaging (EPI), BURST, and half‐Fourier single‐shot turbo spin‐echo (HASTE) images are then presented demonstrating the practical implementation of these resolution enhancement strategies. Images acquired with SMASH show increased spatial resolution and improved image quality when compared with images obtained with the conventional acquisitions. The general principles presented for imaging with SMASH can also be applied to other partially parallel imaging techniques. Magn Reson Med 41:1236–1245, 1999. © 1999 Wiley‐Liss, Inc.

The feasibility of three-dimensional (3D), single breath-hold, gadolinium-enhanced magnetic resonance (MR) coronary angiography was investigated. A 3D spoiled gradient-echo imaging technique was used to image the passage of intravenously injected paramagnetic contrast agent through the coronary vasculature in four healthy subjects. Image contrast depended solely on the injected contrast agent. 3D acquisition allowed retrospective reformation and display with maximum intensity projection and rendering algorithms.

Ventilation and perfusion MR imaging are able to provide regional pulmonary functional information with high spatial and temporal resolution. The ability of MR imaging to assess both the magnitude and regional distribution of pulmonary functional impairment could have an important effect on the evaluation of lung disease.