Improved depiction of small anatomic structures in magnetic resonance images using a Gaussian-weighted spiral acquisition

Partial-volume artifacts reduce the contrast and continuity of small structures in magnetic resonance images. Zero-filled (band-limited) interpolation can be used to reduce partial-volume artifacts and improve the appearance of small structures and edges. However, zero-filling exacerbates Gibbs ringing, also known as the truncation artifact, which manifests itself as spurious ringing around sharp edges. The ripples caused by Gibbs ringing are problematical in magnetic resonance imaging (MRI) because they can obscure or mimic diagnostically important features. The degree of ringing present in the image is determined by the sampling technique used during data acquisition.; Most MRI techniques sample along a grid or in an otherwise uniform manner, resulting in a sharp truncation of the Fourier series model due to insufficient sampling of higher frequencies. This truncation causes severe ringing, which is most commonly diminished by filtering the data before the Fourier transform to reduce the abruptness of the truncation. Unfortunately, the application of a post-acquisition filter also reduces the spatial resolution of the reconstructed image.; This dissertation presents an effective alternative approach that can reduce ringing without an associated loss of spatial resolution. A Gaussian-weighted spiral acquisition, designed to reduce ringing, is proposed. This sampling method is compared with conventional spiral sampling both with and without the application of a filter used to reduce ringing. The two spiral sampling techniques are compared by using simulations, phantom images, and in vivo brain images.; The Gaussian-weighted spiral demonstrates reduced ringing without the loss of spatial resolution commonly associated with post-acquisition filtering. Additionally, this acquisition technique is shown to work well in conjunction with zero-filling. Together, they reduce partial-volume artifacts without the apparent increase in Gibbs ringing usually associated with zero-filled reconstruction. This improved visualization has important implications for high-resolution diagnostic MRI.