The small beads in the ramps may also be used as impulse sources to estimate the point source response function of the Tomosynthesis system. Use the pixel values of the area surrounding the impulse source to determine the two-dimensional array of the image values arising from the impulse source. The full width at half maximum (FWHM) of the point spread function is determined from the best-fit curve of the point-spread function numerical data following subtractions of any background intensity. The average of several different arrays of impulse response (beads) functions is calculated to obtain the average point spread function of the system. These numerical values are used in conjunction with a Fourier Transform Program to provide an estimate of the two-dimensional spatial frequency response characteristics (MTF) of the Digital Breast Tomosynthesis (DBT) system. This is illustrated on the next page. The tungsten carbide bead has a diameter of 0.18m. Compensation may be made for the near pixel size of the bead and some MTF programs are designed to do this. Note from examination of profiles from several beads as shown on the next page, the general Gaussian-like nature of the profiles can be used for either the point source response function or the corresponding Fourier Transform (FT) to obtain the frequency response estimation for the system.

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