Impact of section doubling on lesion contrast.

Misregistration between section position and a feature of interest, such as a lesion, can result in loss of contrast on magnetic resonance images. Because the section direction typically has the poorest resolution, reduction of section misregistration can improve lesion contrast. Lesions occur at random sites; hence, to reduce misregistration, it is necessary to repeat imaging with a small amount of offset. This is impractical. Therefore, a reconstruction algorithm that yields offset sections was implemented, in which sections were produced with a zero- and a half-section shift. This algorithm was tested in 14 patients with multiple sclerosis. As expected, because of randomness associated with section placement relative to lesions, the half-shifted sections provided greater contrast as often as the zero-shifted sections. The combined set improved contrast significantly in 39% of lesions; improvement was greatest in lesions with lesser contrast. Signal-to-noise ratios were not affected by this process, whi...