X-ray image digital substraction system

Claim 2

In a system for subtracting x-ray images including an x-ray source for projecting x-ray beams consecutively through an anatomical region to produce successive x-ray images, means for converting the x-ray images to trains of analog video signals representative of the respective images, means for converting successive samples of the analog video signals to corresponding digital pixel values, means for subtracting digital pixel values representative of at least another image to produce difference digital pixel values corresponding to the differences between said images, means for converting said difference digital pixel values to analog video signals, and television means responsive to input of the last-named analog video signals by displaying a visible difference image, and improved means for converting said digital pixel values to digitally represented values corresponding to their logarithms before subtraction occurs, comprising: memory means having input means for addresses and having output means, said memory means storing digital values representative of the logarithmic values of the digital pixel values at locations whose addresses correspond to the respective digital pixel values provided by said analog-to-digital converter, said memory means responding to a digital pixel value being fed to its address input means by output of the logarithmic value contents of the location which has the address.

Claim 3

A digital fluoroscopy system comprising: means including an x-ray source for producing consecutive x-ray images of an anatomical region, means including video camera means for converting the image to analog video signals which vary in magnitude in correspondence with variations in brightness of the picture elements (pixels) which compose the image and are within a range defined between black and white, analog-to-digital converter means having input and output means, said converter means being operative to convert successive picture element samples of analog video signals fed to its input means to corresponding digital values represented by a predetermined number of bits and appearing on its output means, said digital values constituting digital addresses, memory means having address input means and having output means, said memory means having stored in it digital pixel signals representative of the logarithms, respectively, of the digital values in a range whose minimum value is higher by a predetermined amount than the value that corresponds to black and whose maximum value is substantially equal to a value that corresponds to white in the image and in the analog video signal, said digital pixel signals representative of the respective logarithms of the digital values being located in said memory at addresses corresponding to the value so that when a digital pixel value is fed from said analog-to-digital converter means to the memory input means a digital signal corresponding to the logarithm of the values appears on said output means, means for processing the logarithmic digital pixel signals including means for subtracting the pixel signals representative of different images and means for converting signals resulting from subtraction to analog video signals, and television means responsive to input of the last-named analog signals by displaying a visual image representative of the difference between the x-ray images.

Claim 4

A digital fluoroscopy system comprising: means including an x-ray source for producing consecutive x-ray images of an anatomical region, means including video camera means for converting the image to analog video signals which vary in magnitude in correspondence with variations in brightness of the picture elements (pixels) which compose the image and are within a range defined between black and white, analog-to-digital converter means having input and output means, said converter means being operative to convert successive picture element samples of analog video signals fed to its input means to corresponding digital values represented by a predetermined number of bits and appearing on its output means, said digital values constituting digital addresses, memory means having address input means and having output means, said memory means having stored in it digital pixel signals representative of the logarithms, respectively, of the digital values in a range whose minimum value is higher by a predetermined amount than the value that corresponds to black and whose maximum value is substantially equal to a value that corresponds to white in the image and in the analog video signal, said digital pixel signals representative of the respective logarithms of the digital values being located in said memory at addresses corresponding to the value so that when a digital pixel value is fed from said analog-to-digital converter means to the memory input means a digital signal corresponding to the logarithm of the values appears on said output means, means for processing the logarithmic digital pixel signals including means for subtracting the pixel signals representative of different images and means for converting signals resulting from subtraction to analog video signals, and television means responsive to input of the last-named analog signals by displaying a visual image representative of the difference between the x-ray images.

Claim 5

The system according to claim 2 wherein said memory means is a programmable read-only memory.

Claim 6

The system according to claim 2 wherein said memory means is a random-access memory.

Claim 7

The system according to claim 2 wherein the ratio of said maximum value to said minimum value is between about 10 to about 30.

Claim 8

The system according to claim 2 wherein the ratio of said maximum value to said minimum value is about 20.

Claim 9

The system according to claim 2 wherein said digital pixel signals representative of the logarithms of the digital values are in the range of 8-bit to 10-bit signals to thereby provide for the range of 256 to 1024 brightness levels in the displayed image.