Monte Carlo scatter correction method for computed tomography of general object geometries

• US 6,163,589 A
• Filed: 06/13/1998
• Issued: 12/19/2000
• Est. Priority Date: 06/13/1998
• Status: Expired due to Fees

• Current Assignee: Michael H. Vartanian & Co., Inc.
• Original Assignee: General Electric Company
• Inventors: Vartanian, Michael H.
• Primary Examiner(s): Bruce, David Vernon
• Application Number:
  US09/097,047
• Time in Patent Office: 920 Days
• Field of Search: 378/4, 378/7, 378/8, 378/15, 378/901, 382/131
• US Class Current: 378/7
• CPC Class Codes: G01N 2223/419 computed tomograph
• CPC Class Codes: G01N 23/046 using tomography, e.g. computed tomography [CT]
• CPC Class Codes: Y10S 378/901 Computer tomography program or processor

Abstract

A method of correcting aberrations caused by target x-ray scatter in three-dimensional images generated by a volumetric computed tomographic system is disclosed. The method uses a Monte Carlo simulation to determine the distribution of scattered radiation reaching the detector plane. The geometry for the scatter calculation is determined using the uncorrected three-dimensional tomographic image. The calculated scatter is used to correct the primary projection data which is then processed routinely to provide the corrected image.

Claims

1. A method for correcting errors in the three-dimensional image of an object as measured by a volumetric computed tomographic device wherein said errors are induced by the scattering of x-rays by the object, comprising:

(a) configuring the EGS4 Monte Carlo Code System to simulate the overall geometry of the volumetric computed tomographic system, in particular the position and characteristics of the x-ray source and those of the planar projection view detector,

(b) importing the uncorrected three-dimensional image array as provided by said computed tomographic system into the Monte Carlo process,

(c) transforming the spatial coordinates of the image array from those of the computed tomographic system to those of said EGS4 Code System,

(d) finding the maximum value of the image array and subtracting one-half this value from all elements of the array,

(e) importing an uncorrected projection view as provided by the computed tomographic device into the Monte Carlo process,

(f) translating and rotating as required the spatial coordinates of the three-dimensional image array so as to correspond to the particular projection view,

(g) running the EGS4 Monte Carlo Code System and computing in the subroutine HOWFAR the distance from a given point along a given direction to the point where the image array values change sign by using the bisection or equivalent method,

(h) counting the total number of simulated x-rays at the end of the Monte Carlo run reaching each pixel in the simulated projection plane and the number of these scattered by the target,

(i) transforming the x-ray counts into energy units and calculating the fraction of energy induced by scattered x-rays at every pixel in the simulated projection view,

(j) subtracting the calculated fraction of scattered energy from the measured signal at every pixel in the uncorrected projection view,

(k) returning the corrected projection view to the computed tomographic system,

(l) repeating steps (e) through (k) for every uncorrected projection view as measured by the computed tomographic system,

whereby said volumetric computed tomographic system will provide a corrected three-dimensional image of the object.