DD259692A1 - METHOD FOR LASER-ASSESSED DETERMINATION OF THE MODULATION TRANSFER FUNCTION FROM ROOM RADIATION DISTRIBUTIONS - Google Patents

Abstract

The method is used in the technical quality assurance in Roentgendiagnostikeinrichtungen. The object of the invention is to determine the modulation transfer function of X-ray diagnostic devices as quality-determining parameters with high accuracy, relatively little time expenditure with realization of physically-technically reproducible method steps using the X-ray radiation distribution after a phantom. According to the invention, the object is achieved by quantitatively evaluating the representation of a gap "washed out" during the roentgenographic imaging process (X-ray radiation distribution) quantitatively by means of the relative maxima of the integral sine and compressing it to the modulation transfer function (MUeF) in a optically coherent processor (laser-driven).

Description

- si (-ψ>)

withX (h) = amplitude density function of the spectral representation, χ = path coordinate, A = helicity amplitude, d = slit width, Ω = spatial frequency, si = integral sine. The evaluation of the relative maxima of the integral sinus can thus be used as exact support values for the fast MTF determination. The overall process is therefore within the technical quality assurance in physical-metrologically clear process steps timely comprehensible.

embodiment

In a first method step, a geometrically defined gap cut in lead is brought into the central beam path of the X-ray diagnostic device and the X-ray radiation distribution is recorded on an X-ray film image in the image plane. In the second method step, the X-ray image of the gap is suitably clamped in the image plane of an optically coherent processor adjusted for the task. The third process step. includes the optical Fourier transformation and the densitometric evaluation of the Fourier transform of the X-ray image of the gap by quantizing the amplitude values of the intensity distribution in the Fourier plane of the optically coherent processor.

In a fourth method step, the MTF of the tested X-ray diagnostic device is graphically interpolated from the relative maxima of the densitometric amplitude spectrum of the Fourier transform. For this purpose, the relative maxima of the intensity sine of the abovementioned amplitude spectrum running according to the integral sinus (si) are normalized with the direct light value (amplitude value at the spatial frequency = 0 Lp / mm). The spatial frequency support values directly readable from the calibrated output image on the optically coherent processor are plotted against the prepared spatial frequency axis of the MTF to be created and graphically connected to the MTF curve.

Claims (3)

Invention claim: 1. A method for laser-based determination of the modulation transfer function of X-ray distributions, characterized in that the relative maxima of the integral sine of the splitting function obtained from a radiographic mapping are used exactly as local frequency discrete nodes in the graphic interpolation to determine the modulation transfer function (MTF). 2. A method for laser-based determination of the modulation transfer function of X-ray distributors, characterized in that task-appropriate (attention to the law of radiation and the γ-curves involved) the optical Fourier transform and signal amplitude quantization in the Fourier level in a process step can be realized in a timely manner. 3. A method for laser-based determination of the modulation transfer function of X-ray distributions, characterized in that the use of the X-rayly particularly suitable and easily realizable Spaltphantoms error-minimizing in coordination with the physical-technical properties of the laser-driven optical coherent processor in the MTF determination. Field of application of the invention The invention relates to a method that is used in the technical quality assurance of X-ray diagnostic equipment. Characteristic of the known technical solution The previous methods and devices have two essential characteristics in the technical solutions. Common to both solution groups is the introduction of phantoms into the central beam path of the X-ray diagnostic device to be tested in terms of its technical quality. A group uses point and edge phantoms and evaluates the X-ray distribution by means of further process steps at the output of the X-ray imaging system. The lack consist both in the inevitable in practical realizations erroneous assumed for the mathematical approach (Fourier or Laplace transformation using the exact Diracstoßes or error-free jump function at the system input) ideal phantoms in the central beam and in the relatively high computational time spent in the Receipt of the modulation transfer function (MTF) evaluations to be performed. The second group uses as phantom in the central beam the well-known lead line bars grid. Thus, a spatially frequent discrete densitometric recording of the MTF by appropriately structured detector systems is possible. The disadvantage is that the lead bar rasters do not produce a sinusoidal signal function at the system input and corresponding detector structures distort the measurement result. Therefore, the MUF of the radiological imaging device can not be determined exactly with these devices and methods and can only be used to a limited extent as a technical quality parameter. Object of the invention The invention has for its object to determine the modulation transfer function of X-ray diagnostic equipment (as a quality-determining parameter) with high accuracy, relatively little time with the realization of clearly physico-technically reproducible process steps using the X-ray distribution for a phantom. Essence of the invention According to the invention, the object is achieved in that the fast Fourier-transformed in an optically coherent processor representation of a "scrambled" during X-ray imaging "gap" (X-ray distribution) following basic relationship follows: