Method and apparatus for automatically correcting subtraction image desity

Claim 1

In a temporal subtraction processing for radiation images including the steps of exposing two or more stimulable phosphor sheets respectively to radiations passing through an object injected with contrast media into a specific structure and said object without injection of contrast media to have radiation images of said object stored in said stimulable phosphor sheets, the image information on said specific structure being different between said radiation images, scanning said stimulable phosphor sheets by stimulating rays which cause said stimulable phosphor sheets to emit light in proportion to the stored radiation energy, photoelectrically detecting and converting the amounts of the emitted light into digital image signals, obtaining a difference signal for forming an image of said specific structure by carrying out a subtraction processing of said digital image signals between corresponding picture elements of said radiation images, and conducting a gradation processing of said difference signal on the basis of a predetermined gradation conversion table, a method of automatically correcting the density of a subtraction image, which comprises the steps of: calculating maximum transmitting radiation amounts of said digital image signals, calculating the difference 4x between said maximum transmitting radiation amounts, and carrying out (i) correction by adding said difference Ax to said difference signal prior to said gradation processing, or (ii) correction by shifting said gradation conversion table by said difference nx towards the high density side along the input signal coordinate axis.

Claim 8

An apparatus for automatically correcting the density of a subtraction image, which comprises: (a) an image read-out means for scanning stimulable phosphor sheets carrying radiation images stored therein by stimulating rays which cause said stimulable phosphor sheets to emit light in proportion to the stored radiation energy, and photoelectrically detecting and converting the emitted light into digital image signals, (b) a subtraction operation means for obtaining a difference signal for forming an image of a specific structure by conducting a subtraction processing of the digital image signal of an object injected with contrast media into said specific structure and the digital image signal of the same object without injection of contrast media, said digital image signals being detected by said image read-out means, between the corresponding picture elements of said radiation images, (c) an image processing means for conducting a gradation processing on said difference signal on the. basis of a gradation conversion table, (d) an operation means for calculating maximum transmitting radiation amounts of said digital image signals, and (e) a signal correcting circuit for calculating the difference 8x between said maximum transmitting radiation amounts and adding said difference Δx to said difference signal prior to said gradation processing.

Claim 9

An apparatus for automatically correcting the density of a subtraction image, which comprises: (a) an image read-out means for scanning stimulable phosphor sheets carrying radiation images stored therein by stimulating rays which cause said stimulable phosphor sheets to emit light in proportion to the stored radiation energy, and photoelectrically detecting and converting the emitted light into digital image signals, (b) a subtraction operation means for obtaining a difference signal for forming an image of a specific structure by conducting a subtraction processing of the digital image signal of an object injected with contrast media into said specific structure and the digital image signal of the same object without injection of contrast media, said digital image signals being detected by said image read-out means, between the corresponding picture elements of said radiation images, (c) an image processing means for conducting a gradation processing on said difference signal on the. basis of a gradation conversion table, (d) an operation means for calculating maximum transmitting radiation amounts of said digital image signals, and (e) a signal correcting circuit for calculating the difference 8x between said maximum transmitting radiation amounts and adding said difference Δx to said difference signal prior to said gradation processing.

Claim 10

An apparatus for automatically correcting the density of a subtraction image, which comprises: (a) an image read-out means for scanning stimulable phosphor sheets carrying radiation images stored therein by stimulating rays which cause said stimulable phosphor sheets to emit light in proportion to the stored radiation energy, and photoelectrically detecting and converting the emitted light into digital image signals, (b) a subtraction operation means for obtaining a difference signal for forming an image of a specific structure by conducting a subtraction processing of the digital image signal of an object injected with contrast media into said specific structure and the digital image signal of the same object without injection of contrast media, said digital image signals being detected by said image read-out means, between the corresponding picture elements of said radiation images, (c) an image processing means for conducting a gradation processing on said difference signal on the basis of a gradation conversion table, (d) an operation means for calculating maximum transmitting radiation amounts of said digital image signals, and (e) a gradation conversion table correcting circuit for calculating the difference Ax between said maximum transmitting radiation amounts and shifting said gradation conversion table by said difference dx towards the high density side along the input signal coordinate axis.

Claim 11

An apparatus for automatically correcting the density of a subtraction image, which comprises: (a) an image read-out means for scanning stimulable phosphor sheets carrying radiation images stored therein by stimulating rays which cause said stimulable phosphor sheets to emit light in proportion to the stored radiation energy, and photoelectrically detecting and converting the emitted light into digital image signals, (b) a subtraction operation means for obtaining a difference signal for forming an image of a specific structure by conducting a subtraction processing of the digital image signal of an object injected with contrast media into said specific structure and the digital image signal of the same object without injection of contrast media, said digital image signals being detected by said image read-out means, between the corresponding picture elements of said radiation images, (c) an image processing means for conducting a gradation processing on said difference signal on the basis of a gradation conversion table, (d) an operation means for calculating maximum transmitting radiation amounts of said digital image signals, and (e) a gradation conversion table correcting circuit for calculating the difference Ax between said maximum transmitting radiation amounts and shifting said gradation conversion table by said difference dx towards the high density side along the input signal coordinate axis.

Claim 12

An apparatus for automatically correcting the density of a subtraction image, which comprises: (a) an image read-out means for scanning stimulable phosphor sheets carrying radiation images stored therein by stimulating rays which cause said stimulable phosphor sheets to emit light in proportion to the stored radiation energy, and photoelectrically detecting and converting the emitted light into digital image signals, (b) a preliminary read-out means for, prior to final read-out conducted by said image read-out means, scanning said stimulable phosphor sheets by stimulating rays of a level lower than the level of the stimulating rays used in said image read-out means, and photoelectrically detecting and converting the light emitted by said stimulable phosphor sheets into preliminary read-out digital image signals, (c) a subtraction operation means for obtaining a difference signal for forming an image of a specific structure by conducting a subtraction processing of the" digital image signal of an object injected with contrast media into said specific structure and the digital image signal of the same object without injection of contrast media, said digital image signals being detected by said image read-out means, between the corresponding picture elements of said radiation images, (d) an image processing means for conducting a gradation processing on said difference signal on the basis of a gradation conversion table, (e) an operation means for calculating maximum transmitting radiation amounts of the preliminary read-out digital image signal of said object injected with contrast media into said specific structure and the preliminary read-out digital image signal of said object without injection of contrast media, which are detected by said preliminary read-out means, and (f) a signal correcting circuit for calculating the difference Ax between said maximum transmitting radiation amounts and adding said difference Ä X to said difference signal prior to said gradation processing.

Claim 13

An apparatus for automatically correcting the density of a subtraction image, which comprises: (a) an image read-out means for scanning stimulable phosphor sheets carrying radiation images stored therein by stimulating rays which cause said stimulable phosphor sheets to emit light in proportion to the stored radiation energy, and photoelectrically detecting and converting the emitted light into digital image signals, (b) a preliminary read-out means for, prior to final read-out conducted by said image read-out means, scanning said stimulable phosphor sheets by stimulating rays of a level lower than the level of the stimulating rays used in said image read-out means, and photoelectrically detecting and converting the light emitted by said stimulable phosphor sheets into preliminary read-out digital image signals, (c) a subtraction operation means for obtaining a difference signal for forming an image of a specific structure by conducting a subtraction processing of the" digital image signal of an object injected with contrast media into said specific structure and the digital image signal of the same object without injection of contrast media, said digital image signals being detected by said image read-out means, between the corresponding picture elements of said radiation images, (d) an image processing means for conducting a gradation processing on said difference signal on the basis of a gradation conversion table, (e) an operation means for calculating maximum transmitting radiation amounts of the preliminary read-out digital image signal of said object injected with contrast media into said specific structure and the preliminary read-out digital image signal of said object without injection of contrast media, which are detected by said preliminary read-out means, and (f) a signal correcting circuit for calculating the difference Ax between said maximum transmitting radiation amounts and adding said difference Ä X to said difference signal prior to said gradation processing.

Claim 14

An apparatus for automatically correcting the density of a subtraction image, which comprises: (a) an image read-out means for scanning stimulable phosphor sheets carrying radiation images stored therein by stimulating rays which cause said stimulable phosphor sheets to emit light in proportion to the stored radiation energy, and photoelectrically detecting and converting the emitted light into digital image signals, (b) a preliminary read-out means for, prior to final read-out conducted by said image read-out means, scanning said stimulable phosphor sheets by stimulating rays of a level lower than the level of the stimulating rays used in said image read-out means, and photoelectrically detecting and converting the light emitted by said stimulable phosphor sheets into preliminary read-out digital image signals, (c) a subtraction operation means for obtaining a difference signal for forming an image of a specific structure by conducting a subtraction processing of the digital image signal of an object injected with contrast media into said specific structure and the digital image signal of the same object without injection of contrast media, said digital image signals being detected by said image read-out means, between the corresponding picture elements of said radiation images, (d) an image processing means for conducting a gradation processing on said difference signal on the basis of a gradation conversion table, (e) an operation means for calculating maximum transmitting radiation amounts of the preliminary read-out digital image signal of said object injected with contrast media into said specific structure and the preliminary read-out digital image signal of said object without injection of contrast media, which are detected.by said preliminary read-out means, and (f) a gradation conversion table correcting circuit for calculating the difference αx between said maximum transmitting radiation amounts and shifting said gradation conversion table by said difference &x towards the high density side along the input signal coordinate axis.

Claim 15

An apparatus for automatically correcting the density of a subtraction image, which comprises: (a) an image read-out means for scanning stimulable phosphor sheets carrying radiation images stored therein by stimulating rays which cause said stimulable phosphor sheets to emit light in proportion to the stored radiation energy, and photoelectrically detecting and converting the emitted light into digital image signals, (b) a preliminary read-out means for, prior to final read-out conducted by said image read-out means, scanning said stimulable phosphor sheets by stimulating rays of a level lower than the level of the stimulating rays used in said image read-out means, and photoelectrically detecting and converting the light emitted by said stimulable phosphor sheets into preliminary read-out digital image signals, (c) a subtraction operation means for obtaining a difference signal for forming an image of a specific structure by conducting a subtraction processing of the digital image signal of an object injected with contrast media into said specific structure and the digital image signal of the same object without injection of contrast media, said digital image signals being detected by said image read-out means, between the corresponding picture elements of said radiation images, (d) an image processing means for conducting a gradation processing on said difference signal on the basis of a gradation conversion table, (e) an operation means for calculating maximum transmitting radiation amounts of the preliminary read-out digital image signal of said object injected with contrast media into said specific structure and the preliminary read-out digital image signal of said object without injection of contrast media, which are detected.by said preliminary read-out means, and (f) a gradation conversion table correcting circuit for calculating the difference αx between said maximum transmitting radiation amounts and shifting said gradation conversion table by said difference &x towards the high density side along the input signal coordinate axis.

Claim 16

An apparatus for automatically correcting the density of a subtraction image, which comprises: (a) an image read-out means for scanning stimulable phosphor sheets carrying radiation images stored therein by stimulating rays which cause said stimulable phosphor sheets to emit light in proportion to the stored radiation energy, and photoelectrically detecting and converting the emitted light into digital image signals, (b) a subtraction operation means for obtaining a difference signal for forming an image of a specific structure by conducting a subtraction processing of the digital image signal of an object injected with contrast media into said specific structure and the digital image signal of the same object without injection of contrast media, said digital image signals being detected by said image read-out means, between the corresponding picture elements of said radiation images, (c) an image processing means for conducting a gradation processing on said difference signal on the basis of a gradation conversion table, (d) a histogram operation means for obtaining a histogram of said difference signal and determining a maximum frequency point signal from said histogram, (e) a storage means for storing a standard background density of a subtraction image formed by said difference signal, and (f) a signal correcting circuit for calculating the difference dx between a standard background density signal representing said standard background density read from said storage means and said maximum frequency point signal, and adding said difference Ax to said difference signal prior to said gradation processing.

Claim 17

An apparatus for automatically correcting the density of a subtraction image, which comprises: (a) an image read-out means for scanning stimulable phosphor sheets carrying radiation images stored therein by stimulating rays which cause said stimulable phosphor sheets to emit light in proportion to the stored radiation energy, and photoelectrically detecting and converting the emitted light into digital image signals, (b) a subtraction operation means for obtaining a difference signal for forming an image of a specific structure by conducting a subtraction processing of the digital image signal of an object injected with contrast media into said specific structure and the digital image signal of the same object without injection of contrast media, said digital image signals being detected by said image read-out means, between the corresponding picture elements of said radiation images, (c) an image processing means for conducting a gradation processing on said difference signal on the basis of a gradation conversion table, (d) a histogram operation means for obtaining a histogram of said difference signal and determining a maximum frequency point signal from said histogram, (e) a storage means for storing a standard background density of a subtraction image formed by said difference signal, and (f) a signal correcting circuit for calculating the difference dx between a standard background density signal representing said standard background density read from said storage means and said maximum frequency point signal, and adding said difference Ax to said difference signal prior to said gradation processing.

Claim 18

An apparatus for automatically correcting the density of a subtraction image, which comprises: (a) an image read-out means for scanning stimulable phosphor sheets carrying radiation images stored therein by stimulating rays which cause said stimulable phosphor sheets to emit light in proportion to the stored radiation energy, and photoelectrically detecting and converting the emitted light into digital image signals, (b) a subtraction operation means for obtaining a difference signal for forming an image of a specific structure by conducting a subtraction processing of the digital image signal of an object injected with contrast media into said specific structure and the digital image signal of the same object without injection of contrast media, said digital image signals being detected by said image read-out means, between the corresponding picture elements of said radiation images, (c) an image processing means for conducting a gradation processing on said difference signal on the basis of a gradation conversion table, (d) a histogram operation means for obtaining a histogram of said difference signal and determining a maximum frequency point signal from said histogram, (e) a storage means for storing a standard background density of a subtraction image formed by said difference signal, and (f) a gradation conversion table correcting circuit for calculating the difference dx between a standard background density signal representing said standard background density read from said storage means and said maximum frequency point signal, and shifting said gradation conversion table by -âx, which has the same absolute value as that of said difference Δx and the sign reverse to the sign thereof, along the input signal coordinate axis.

Claim 19

An apparatus for automatically correcting the density of a subtraction image, which comprises: (a) an image read-out means for scanning stimulable phosphor sheets carrying radiation images stored therein by stimulating rays which cause said stimulable phosphor sheets to emit light in proportion to the stored radiation energy, and photoelectrically detecting and converting the emitted light into digital image signals, (b) a subtraction operation means for obtaining a difference signal for forming an image of a specific structure by conducting a subtraction processing of the digital image signal of an object injected with contrast media into said specific structure and the digital image signal of the same object without injection of contrast media, said digital image signals being detected by said image read-out means, between the corresponding picture elements of said radiation images, (c) an image processing means for conducting a gradation processing on said difference signal on the basis of a gradation conversion table, (d) a histogram operation means for obtaining a histogram of said difference signal and determining a maximum frequency point signal from said histogram, (e) a storage means for storing a standard background density of a subtraction image formed by said difference signal, and (f) a gradation conversion table correcting circuit for calculating the difference dx between a standard background density signal representing said standard background density read from said storage means and said maximum frequency point signal, and shifting said gradation conversion table by -âx, which has the same absolute value as that of said difference Δx and the sign reverse to the sign thereof, along the input signal coordinate axis.