| Popis: |
Purpose The most challenging aspect of imaging dynamically changing objects by MRI is achieving the desired temporal resolution without sacrificing the required spacial resolution. The present authors have developed a new MRI sequence termed Radial Echo Planer Imaging with a Central High-Resolution Area (REPI with CHRA), in which high temporal resolution is balanced with high spatial resolution in the center of the field of view (FOV). \nMethod Using a 1.5T Sigma Horizon LX MRI system (GE Medical Systems, Milwaukee, WI, U.S.A.) and EPIC (Environment for Programming in C), we developed the REPI with CHRA technique, in which radii of a sector area of k-space are scanned in one excitation, with the first radius being twice the width of the subsequent radii. The entire k-space is scanned in multiple excitations. After all radii other than the first in a sector area are zero-filled, the image is reconstructed by back projection. A MRI fluoroscopy of the heart and a contrast enhanced MR angiography (CEMRA) of the head were taken by applying REPI with CHRA continuously. \nResults Using 16-shot REPI with CHRA, with a FOV of 24 cm, we achieved a TR of 320 ms for the acquisition of a 128 ´ 128 image with a resolution of 1 mm in the center of the FOV and a resolution of 2 mm in the peripheral area. As REPI with CHRA is basically a radial sampling method, the image suffered less from the phase error artifacts characteristic of multi-shot EPI. Using 16-shot REPI with CHRA, we took images of the heart and CEMRA of the head both with a FOV of 24 cm, for 32 s. Using the view-sharing technique, we obtained images with a temporal resolution of 20 ms and a spatial resolution of 1 mm in the center area. The images exhibited fewer density discontinuities than by ordinary EPI. The motion artifact manifested as a star-like shadow, which offers greater clarity than the blurring characteristic of ordinary EPI. \nConclusion We proved that REPI with CHRA can be used successfully to balance high temporal resolution with high spatial resolution, which is necessary for imaging dynamically changing objects. The images produced using the technique exhibit minimal density discontinuity, and less obtrusive motion artifacts. These characteristics render this technique suitable for imaging moving objects or for CEMRA. |
