In order to determine the modulation transfer functions (MTF's) for x-ray computed tomography (CT) scanners, a measurement must be performed to obtain either the point spread function (PSF) or the line spread function (LSF). Thereafter, the usual procedure is to interpolate between the measured points and to determine the Fourier transforms numerically in order to obtain the MTF. Since this must usually be done many times to evaluate various reconstruction kernels and scan modalities, the process is tedious. Fortunately, it can be greatly simplified by utilizing a mathematical function to describe the PSF or LSF. Measured data for five CT scanners indicates that the PSF can usually be described by a Gaussian function. Hence, the MTF can be written in a generalized form eliminating the necessity of performing Fourier transformations each time. The MTF is determined directly from a single performance characteristic related to the full width at half maximum. The accuracy of the approach is compared with detailed MTF calculations for five CT scanners and it is shown to agree favorably with this data.

Fourier Analysis↗

PubMedDate not supplied

Mandibular advancement and obstructive sleep apnea syndrome.

A surgical procedure performed to advance the mandible in patients with retrognathia and obstructive sleep apnea is described. The case history of an obese patient with severe sleep apnea problems who underwent a number of treatments, responding only to mandibular advancement, is presented.

Adult↗

PubMedDate not supplied

Federal/Provincial Task Force on alcohol statistics.

Explore the source record for details and available documents.

Alcoholism↗