Method for determining the function representing the effect of non-reciprocity of a radiographic film
AssigneeGeneral Electric CGR S.A.
InventorRobert Heidsieck
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Abstract
The invention relates to radiology systems and, more particularly in such systems, to a method that enables the effect of non-reciprocity of the radiographic film to be determined. This effect of non-reciprocity is expressed by coefficients CNRD(d.sub.i) which are a function of the photon dose rate (d.sub.i) on the film, the coefficients CNRD(d.sub.i) being obtained from the coefficients CNRT(t.sub.i) and the determination of the reference lumination L.sub.ref received by the film.
Claims11
A method for determining the function representing the effect of non-reciprocity of a radiographic film in a system of radiology designed to examine an object that includes an X-ray tube, the supply voltage V of which may assume various values V.sub.m, with continuous or discrete variation, said X-ray tube emitting an X-ray beam in the form of pulses of variable duration t.sub.i towards the object to be examined, a receiver of the X-radiation that has crossed the object to form an image of said object, a cell for the detection of the X-rays that have crossed the object to be examined, that enables the conversion of a physical variable, characterizing the X-ray beam, into a measurement signal L, an integrator circuit that integrates the measurement signal L for the duration t.sub.i and gives a signal M, and a device to compute the yield D given by the ratio of M to the product I.times.t.sub.i (or mA.s) of the anode current I of the tube by the duration ti of the exposure, wherein said method includes the following steps:
- (a) determining the coefficients of non-reciprocity CNRT (t.sub.i) of the film expressed in exposure time t.sub.i for an optical density DO.sub.refo of said film;
- (b) determining the reference lumination L.sub.ref received by said film;
- (c) calculating the photon dose rates d.sub.i on said film by the formula:
- ##EQU13## (d) determining the coefficients of non-reciprocity CNRD (d.sub.i) expressed in photon dose rate d.sub.i by the application of the formula:
- CNRD (d.sub.i)=CNRT (t.sub.i)
- wherein the step (a) comprises the following steps:
- (a1) modifying the tube heating current so as to obtain different values of said current,
- (a2) reading the values M (t.sub.i) given by the integrator circuit for different exposure times (t.sub.i) so as to obtain an optical density DO.sub.1 of the film,
- (a3) calculating the ratio ##EQU14## which gives the coefficient CNRT (t.sub.i) with M (t.sub.ref) the value M (t.sub.i) for t.sub.i =t.sub.ref.
A method for determining the function representing the effect of non-reciprocity of a radiographic film in a system of radiology designed to examine an object that includes an X-ray tube, the supply voltage V of which may assume various values V.sub.m, with continuous or discrete variation, said X-ray tube emitting an X-ray beam in the form of pulses of variable duration t.sub.i towards the object to be examined, a receiver of the X-radiation that has crossed the object form an image of said object, a cell for the detection of the X-rays that have crossed the object to be examined, that enables the conversion of a physical variable, characterizing the X-ray beam, into a measurement signal L, an integrator circuit that integrates the measurement signal L for the duration t.sub.i and gives a signal M, and a device to compute the yield D given by the ratio of M to the product I.times.t.sub.i (or mA.s) of the anode current I of the tube by the duration t.sub.i of the exposure, wherein said method includes the following steps:
- (a) determining the coefficients of non-reciprocity CNRT (t.sub.i) of the film expression in exposure time t.sub.i for an optical density DO.sub.refo of said film;
- (b) determining the reference lumination L.sub.ref received by said film;
- (c) calculating the photon dose rates d.sub.i on said film by the formula:
- ##EQU15## (d) determining the coefficients of non-reciprocity CNRD (d.sub.i) expressed in photon dose rate d.sub.i by the application of the formula:
- CNRD (d.sub.i)=CNRT (t.sub.i)
- wherein the step (a) includes the following operations:
- (a1) making, by means of a variable time sensitograph, a first sensitogram S.sub.refo when the exposure time is set for a reference time t.sub.refo ;
- (a2) making, by means of the same variable time sensitograph, q sensitograms S.sub.1 to S.sub.q for q different exposure times t.sub.i ;
- (a3) choosing a reference optical density DO.sub.refo ;
- (a4) measuring, on each sensitogram, the illumination step Ech.sub.refo ;
- Ech.sub.1 . . . Ech.sub.i . . . Ech.sub.q corresponding to the optical density DO.sub.refo ;
- (a5) calculating the coefficient CNRT (t.sub.i) by the equation:
- ##EQU16##
A method for determining the function representing the effect of non-reciprocity of a radiographic film in a system of radiology designed to examine an object that includes an X-ray tube, comprising the steps of:
- supplying voltage to the tube at various values, V.sub.m ;
- exposing an object to X-ray beams in the form of pulses of variable duration, t.sub.i ;
- exposing film to X-ray beams after passage through the object;
- subjecting an X-ray radiation detector cell to tile beams for converting beam energy, passed through the object, into a measurement signal L;
- integrating the signal L for tile duration ti and generating a resulting signal M;
- measuring the current I supplied to an anode of the X-ray tube;
- calculating the yield D from the ratio of tile signal M to the product of I.times.t.sub.i during an interval of exposure;
- determining the coefficient of non-reciprocity CNRT (t.sub.i) of the film as a function of exposure time t.sub.i for an optical density DO.sub.refo of the film;
- calculating the photon dose rates d.sub.i, as a function of a reference illumination on the film (L.sub.ref) by the formula:
- ##EQU19## and determining the coefficients of non-reciprocity CNRD (d.sub.i) as a function photon dose rate d.sub.i by the formula:
- CNRD (d.sub.i)=CNRT (t.sub.i).
Dependencies are inferred from the claim text.