Correction of off-focal radiation

Claim 2

In a CT scanner which includes a radiation source which generates a beam of radiation, a cantry on which the radiation source is mounted for rotation around an examination region, a multiplicity of radiation detectors which receive radiation from the source that has traversed the examination region and convert the received radiation into electronic data, the improvement comprising: an off-focal radiation filter which corrects the electronic data for off-focal radiation with a filter function that is dependent on a relative position of the radiation source and each radiation detector as each radiation detector converts the received radiation into a datum element of the electronic data, the off-focal radiation filter including: a deconvolution memory for storing deconvolution functions, the deconvolution function memory being addressed in accordance with relative positions of the radiation source and the detectors to retrieve corresponding deconvolution functions; and a convolver for convolving the electronic data with the retrieved deconvolution functions.

Claim 3

In the CT scanner of claim 1, the improvement further comprising: the convolver includes an iterative loop.

Claim 4

A CT scanner comprising: an x-ray source for generating a fan beam of radiation which is directed across an examination region; a rotatable gantry upon which the x-ray source is mounted for rotational movement; an angular position encoder connected to the gantry for measuring a position of the x-ray source around the examination region; detectors disposed across the examination region from the x-ray source for converting rays of the fan beam of radiation which has traversed the examination region into electronic data; a first memory for storing the electronic data in fans, each fan having a plurality of logarithmic data values with each data value corresponding to a fan beam ray; an off-focal radiation filter for filtering with a linear mathematic operation the data value corresponding to each ray of the electronic data with a filter function; a means for changing the filter function in accordance with a relative angular position of each ray within the fan; a first convolver for convolving the filtered electronic data fans; a backprojector for backprojecting the convolved electronic data fans into an image memory; and a video processor for converting image data from the image memory into appropriate format for display.

Claim 5

A CT scanner comprising: an x-ray source for generating a fan beam of radiation which is directed across an examination region; a rotatable gantry upon which the x-ray source is mounted for rotational movement; an angular position encoder connected to the gantry for measuring a position of the x-ray source around the examination region; detectors disposed across the examination region from the x-ray source for converting rays of the fan beam of radiation which has traversed the examination region into electronic data; a first memory for storing the electronic data in fans, each fan having a plurality of logarithmic data values with each data value corresponding to a fan beam ray; an off-focal radiation filter for filtering with a linear mathematic operation the data value corresponding to each ray of the electronic data with a filter function; a means for changing the filter function in accordance with a relative angular position of each ray within the fan; a first convolver for convolving the filtered electronic data fans; a backprojector for backprojecting the convolved electronic data fans into an image memory; and a video processor for converting image data from the image memory into appropriate format for display.

Claim 6

The CT scanner of claim 3 wherein the off focal radiation filter filters electronic data corresponding to a plurality of rays in parallel.

Claim 7

A CT scanner comprising: an x-ray source for generating a fan beam of radiation which is directed across an examination region; a rotatable gantry upon which the x-ray source is mounted for rotational movement; an angular Position encoder connected to the gantry for measuring a position of the x-ray source around the examination region; detectors disposed across the examination region from the x-ray source for converting rays of the fan beam of radiation which has traversed the examination region into electronic data; a first memory for storing the electronic data in fans, each fan having a plurality of data values with each data value corresponding to a fan beam ray; an off-focal radiation filter including a first convolver for convolving each data fan stored in the first memory with deconvolution functions in accordance with a relative angular position of the x-ray source and a one of the detectors corresponding to each data value; a means for changing the deconvolution function in accordance with a relative angular position of each ray within the fan; a second convolver for convolving the filtered electronic data fans; a backprojector for backprojecting the convolved electronic data fans into an image memory; and a video processor for converting image data from the image memory into appropriate format for display.

Claim 8

A CT scanner comprising: an x-ray source for generating a fan beam of radiation which is directed across an examination region; a rotatable gantry upon which the x-ray source is mounted for rotational movement; an angular Position encoder connected to the gantry for measuring a position of the x-ray source around the examination region; detectors disposed across the examination region from the x-ray source for converting rays of the fan beam of radiation which has traversed the examination region into electronic data; a first memory for storing the electronic data in fans, each fan having a plurality of data values with each data value corresponding to a fan beam ray; an off-focal radiation filter including a first convolver for convolving each data fan stored in the first memory with deconvolution functions in accordance with a relative angular position of the x-ray source and a one of the detectors corresponding to each data value; a means for changing the deconvolution function in accordance with a relative angular position of each ray within the fan; a second convolver for convolving the filtered electronic data fans; a backprojector for backprojecting the convolved electronic data fans into an image memory; and a video processor for converting image data from the image memory into appropriate format for display.

Claim 9

The CT scanner of claim 5 wherein the off-focal radiation filter further includes a third memory for storing a plurality of deconvolution functions.

Claim 10

A CT scanner comprising: an x-ray source for generating a fan beam of radiation which is directed across an examination region; a rotatable gantry upon which the x-ray source is mounted for rotational movement; an angular position encoder connected to the gantry for measuring a Dosition of the x-ray source around the examination region; detectors disposed across the examination region from the x-ray source for converting rays of the fan beam of radiation which has traversed the examination region into electronic data; a first memory for storing the electronic data in fans, each fan having a plurality of data values with each data value corresponding to a fan beam ray; an off-focal radiation filter for filtering the data value corresponding to each ray of the electronic data with a filter function, the off-focal radiation filter including a recursive loop in which the data value corresponding to each ray is filtered using a data value of a corresponding preceding ray; a means for changing the filter function in accordance with a relative angular position of each ray within the fan; a first convolver of convolving the filtered electronic data fans; a backprojector for backprojecting the convolved electronic data fans into an image memory; and a video processor for converting image data from the image memory into appropriate format for display.

Claim 11

A CT scanner comprising: an x-ray source for generating a fan beam of radiation which is directed across an examination region; a rotatable gantry upon which the x-ray source is mounted for rotational movement; an angular position encoder connected to the gantry for measuring a Dosition of the x-ray source around the examination region; detectors disposed across the examination region from the x-ray source for converting rays of the fan beam of radiation which has traversed the examination region into electronic data; a first memory for storing the electronic data in fans, each fan having a plurality of data values with each data value corresponding to a fan beam ray; an off-focal radiation filter for filtering the data value corresponding to each ray of the electronic data with a filter function, the off-focal radiation filter including a recursive loop in which the data value corresponding to each ray is filtered using a data value of a corresponding preceding ray; a means for changing the filter function in accordance with a relative angular position of each ray within the fan; a first convolver of convolving the filtered electronic data fans; a backprojector for backprojecting the convolved electronic data fans into an image memory; and a video processor for converting image data from the image memory into appropriate format for display.

Claim 12

A CT scanner comprising: an x-ray source; a rotatable gantry upon which the x-ray source is mounted for rotational movement around an examination region; a ring of detectors encircling the examination region to detect radiation from the x-ray source which has traversed a portion of a subject in the examination region; a first convolver for convolving lines of data; a backprojector for backprojecting convolved data lines into an image memory; a video processor for converting image data from the image memory into a human-readable display on a monitor; and a means for reducing image artifacts in the human-readable display relating to radiation source position dependent off-focal radiation.

Claim 13

A CT scanner comprising: an x-ray source; a rotatable gantry upon which the x-ray source is mounted for rotational movement around an examination region; a ring of detectors encircling the examination region to detect radiation from the x-ray source which has traversed a portion of a subject in the examination region; a first convolver for convolving lines of data; a backprojector for backprojecting convolved data lines into an image memory; a video processor for converting image data from the image memory into a human-readable display on a monitor; and a means for reducing image artifacts in the human-readable display relating to radiation source position dependent off-focal radiation.

Claim 14

The CT scanner of claim 8 wherein the means for reducing images artifacts further includes an off-focal radiation filter for removing radiation position dependent off focal radiation components from the data lines.

Claim 15

A CT scanner comprising: an x-ray source; a rotatable gantry upon which the x-rav source is mounted for rotational movement; a plurality of detectors positioned to detect radiation from the x-ray source which has traversed a portion of a subject in an examination region; a first convolver for convolving lines of data; a backprolector for backprojecting convolved data lines into an image memory; a video processor for converting image data from the image memory into a human-readable display on a monitor; and an off-focal radiation filter for removing radiation position dependent off-focal radiation components from the data lines, the off-focal radiation filter including a second convolver for convolving data lines with a radiation ray position dependent deconvolution function.

Claim 16

A CT scanner comprising: an x-ray source; a rotatable gantry upon which the x-rav source is mounted for rotational movement; a plurality of detectors positioned to detect radiation from the x-ray source which has traversed a portion of a subject in an examination region; a first convolver for convolving lines of data; a backprolector for backprojecting convolved data lines into an image memory; a video processor for converting image data from the image memory into a human-readable display on a monitor; and an off-focal radiation filter for removing radiation position dependent off-focal radiation components from the data lines, the off-focal radiation filter including a second convolver for convolving data lines with a radiation ray position dependent deconvolution function.

Claim 17

A CT scanner comprising: an x-ray source for generating a fan of radiation; an array of detectors, each detector receiving radiation from the x-ray source which has traversed an examination region along a corresponding ray, each detector being sampled at intervals to generate corresponding data values; a data filter for deconvolvinq the data values in accordance with relative angular positions of each corresponding ray within the radiation fan when the detector was sampled; a first convolver for convolving the deconvolved data; a backprojector connected to the convolver which backprojects the convolved data; and an image memory connected with the backprojector to receive and store the backprojected data.

Claim 18

A CT scanner comprising: an x-ray source for generating a fan of radiation; an array of detectors, each detector receiving radiation from the x-ray source which has traversed an examination region along a corresponding ray, each detector being sampled at intervals to generate corresponding data values; a data filter for deconvolvinq the data values in accordance with relative angular positions of each corresponding ray within the radiation fan when the detector was sampled; a first convolver for convolving the deconvolved data; a backprojector connected to the convolver which backprojects the convolved data; and an image memory connected with the backprojector to receive and store the backprojected data.

Claim 19

The CT scanner of claim 11 wherein the data filter includes a second convolver for convolving data with a first deconvolution function.

Claim 20

The CT scanner of claim 12 wherein the data filter includes a third convolver for convolving data with a second deconvolution function concurrently with convolution of the second convolver.

Claim 21

The CT scanner of claim 13 wherein the data filter further includes a means for generating the first and second deconvolution functions in accordance with relative x-ray source and detector positions.

Claim 22

The CT scanner of claim 12 wherein the data filter further includes a recursive loop in which the data value is filtered as a function of a preceding data value.