Role of high resolution in magnetic resonance (MR) imaging: Applications to MR angiography, intracranialT1-weighted imaging, and image interpolation

Abstract

The role of high-resolution imaging has generally been limited because of the associated loss of signal-to-noise ratio (SNR) as voxel size decreases and imaging time increases. Despite these truths, we show that high-resolution imaging methods can be used to perform better magnetic resonance angiography (MRA), enhance visibility of small structures, and allow better image interpolation. Specifically, we show that very small vessels can be seen with conventional MRA methods, and small lesions on the order of a few cubic millimeters can be seen with a single dose of gadolinium diethyltriaminepentaacetic acid, and structures such as the hippocampal formation are best depicted when a high-resolution three-dimensional (3D) imaging method is used. We also show that image interpolation for the 3D visualization of structures with complicated geometry is best accomplished with a fractional voxel evaluation using the Fourier transform shift theorem on high-resolution images. We demonstrate that the expression for visibility, CNR √p, can be used to establish the optimal resolution to see a given structure. CNR refers to the contrast-to-noise ratio and p is the number of voxels occupied by the object in the image. The optimal resolution is determined from theoretical curves of visibility as a function of voxel size relative to object size. We also demonstrate the enhancement of small vessel visibility on individual images and maximum-intensity projection images with voxel sizes as small as 0.29 mm using 1024 sampled points in the readout direction. Using 3D visibility arguments, it is predicted that under the right conditions, objects of interest much smaller than the voxel size can be seen on conventional MR images. © 1997 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 8, 529–543, 1997