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US 5,396,531 AGranted
Method of achieving reduced dose X-ray fluoroscopy by employing statistical estimation of poisson noise
AssigneeGeneral Electric Company
InventorRichard I. Hartley
Life of this patent
Estimating the term…
Abstract
An interactive system for producing X-ray fluoroscopic images determines X-ray tube photon count and voltage for producing acceptable quality images while minimizing X-ray radiation dosage to a subject. An image is created and a signal to noise (S/N) ratio is estimated from the image, assuming a Poisson model is assumed for the X-ray image. The S/N ratio is determined by solving several simultaneous equations and the photon count is estimated to produce an image with a desired S/N ratio. Subsequent X-ray fluoroscopy images are produced with the optimum photon count Q, thereby reducing X-ray dosage. The optimization is repeated periodically to readjust the system.
Claims3
A method of reduced dose X-ray imaging of a subject comprises the steps of:
- a) selecting a minimum signal-to-noise (P.sub.S /P.sub.Nmin) ratio;
- b) creating an X-ray image with an initial photon count Q.sub.init and X-ray tube voltage U;
- c) determining an average image intensity I from the image according to the equation:
- ##EQU24## where C is the total number of pixels in the image and i.sub.x,y is the pixels with coordinates (x,y);
- d) determining a variance .sigma..sup.2 from the image according to the equation:
- ##EQU25## e) determining P.sub.S /P.sub.N from the image according to the following equation:
- ##EQU26## f) determining the value of I.sub.opt required to produce an image with a signal-to-noise ratio at least as great as P.sub.S /P.sub.Nmin assuming that P.sub.S /P.sub.N is proportional to I according to:
- ##EQU27## h ) determining an optimal photon count Q.sub.opt required to produce an image with intensity I.sub.opt ;
- and
- i) creating subsequent images with the same X-ray voltage U and the optimal photon count Q.sub.opt having a signal-to-noise ratio at least as great as P.sub.S /P.sub.Nmin and with a reduced X-ray dose.
7 more elements
A method of reduced dose X-ray imaging of a subject comprises the steps of:
- a) selecting a minimum signal-to-noise ratio (P.sub.S /P.sub.Nmin);
- b) setting a photon count Q to a value Q.sub.init ;
- c) creating an x-ray image with a photon count Q and X-ray tube voltage U;
- d) determining an average image intensity I from the image according to:
- ##EQU28## where C is the total number of pixels in the image and i.sub.x,y is the pixels with coordinates (x,y);
- e) determining a variance .sigma..sup.2 of the image according to:
- ##EQU29## f) creating an equation proportionality constants for k.sub.1 and k.sub.2 of the form:
- k.sub.1 I.sup.1/2 +k.sub.2 I.sup.-1/2 =.sigma..sup.2 I.sup.-3/2 ;
- g) repeating steps "c"-"f" for several images of differing intensity;
- h) solving the equations of step f by simultaneous methods to acquire k.sub.1 and k.sub.2 ;
- i) determining P.sub.S /P.sub.N according to the following equation:
- ##EQU30## j) determining an optimum image intensity I.sub.opt required to form an image with a signal-to-noise ratio greater than P.sub.S /P.sub.Nmin according to the following equation:
- ##EQU31## k) determining an optimal photon count, Q.sub.opt necessary to produce an image with image intensity I.sub.opt, based upon the observed relationship between image intensity Y and photon count Q, equal to Q.sub.init ;
- and
- l) creating subsequent images with the same X-ray voltage and the optimal photon count Q.sub.opt having a S/N ratio at least as great as the P.sub.S /P.sub.Nmin and with a reduced X-ray dose.
12 more elements
A method of reduced dose X-ray imaging of a subject comprises the steps of:
- a) selecting a minimum signal-to-noise (P.sub.S /P.sub.Nmin) ratio;
- b) creating a first X-ray image with an initial photon count Q.sub.init and X-ray tube voltage U;
- c) determining an initial average image intensity I=I.sub.init of the first image according to the equation:
- ##EQU32## where C is a number of pixels in the image,and i.sub.x,y is a pixel intensity at an image location x,y, with the summation covering all pixel locations;
- d) determining a variance .sigma..sup.2 from the image according to the equation:
- ##EQU33## e) determining P.sub.S /P.sub.N from the image according to the following equation:
- ##EQU34## f) determining an initial estimated value of I.sub.opt required to produce an image with a signal-to-noise ratio at least as great as P.sub.S /P.sub.Nmin assuming that P.sub.S /P.sub.N is proportional to I according to:
- ##EQU35## g) determining an optimal photon count Q.sub.opt based upon the optimal image intensity I.sub.opt ;
- h) creating a second image with the same X-ray voltage U and the optimal photon count Q.sub.opt ;
- i) determining an average image intensity i of the second image according to:
- ##EQU36## j) determining a variance of the second image according to:
- ##EQU37## k) creating an equation for proportionality constants k.sub.1 and k.sub.2 for each of the first and second images according to the equation:
- k.sub.1 I.sup.1/2 +k.sub.2 I.sup.-1/2 =.sigma..sup.2 I.sup.31 3/2 ;
- l) solving the equations of step k by simultaneous methods to acquire k.sub.1 and K.sub.2 ;
- m) solving, to obtain a second estimate of the optimum image intensity I.sub.opt required to form an image with a signal-to-noise ratio greater than P.sub.S /P.sub.Nmin, the equation:
- ##EQU38## n) determining an optimal photon count, Q.sub.opt required to produce an image with intensity I.sub.opt ;
- and
- o) creating subsequent images with the same X-ray voltage and the optimal photon count Q.sub.opt having a S/N ratio at least as great as P.sub.S /P.sub.Nmin and with a reduced X-ray dose.
15 more elements
Dependencies are inferred from the claim text.