EP0002540A2 — Radiation imaging system

Claim 1

Independent Claim 61 words

A radiation imaging system, comprising: a radiation transducer producing signals proportional to apparent orthogonal spatial coordinates of detected radiation events; means for storing true spatial coordinates corresponding to a plurality of predetermined apparent spatial coordinates relative to selected detected radiation events; and means for interpolating the true spatial coordinates of the detected radiation events located intermediate the stored true spatial coordinates.

Claim 2

Dependent Claim 61 words

A radiation imaging system, comprising: a radiation transducer producing signals proportional to apparent orthogonal spatial coordinates of detected radiation events; means for storing true spatial coordinates corresponding to a plurality of predetermined apparent spatial coordinates relative to selected detected radiation events; and means for interpolating the true spatial coordinates of the detected radiation events located intermediate the stored true spatial coordinates.

Claim 3

Dependent Claim 22 words

The system of Claim 1 having means for converting each of the spatial coordinates to digital equivalents having a plural bit precision.

Claim 4

Dependent Claim 55 words

The system of Claim 2 wherein the plurality of predetermined apparent coordinates define a regularly- spaced matrix array and the corresponding true spatial coordinates are stored in the matrix in accordance therewith, and wherein the true spatial coordinates of the detected radiation events having apparent spatial coordinates intermediate the stored true spatial coordinates are interpolated.

Claim 5

Dependent Claim 36 words

The system of Claim 3 wherein the matrix array comprises: two square matrices in which each orthogonal coordinate of the true spatial coordinates are stored respectively in accordance with the predetermined apparent spatial coordinate corresponding thereto.

Claim 6

Dependent Claim 55 words

The system of Claim 4 wherein the means for in- erpolating performs a linear interpolation to determine each ortheconal coordinate of the true spatial coordinate intermediate the stored apparent coordinates of each of the matrix arrays, thereby presiding a precision of location for the detected radiation events greater than that stored in the matrix arrays.

Claim 7

Dependent Claim 71 words

The system of Claim 5 wherein most significant bit contents of the apparent coordinates of detected radiation events correspond to the precision of the matrix arrays and are used to address the matrix, and wherein the true coordinates of the addressed position and three next higher selected coordinates of the matrix arrays are used to interpolate the true spatial coordinates corresponding to least significant bit contents of the detected radiation events.

Claim 8

Dependent Claim 61 words

The system of Claim 6 wherein each of the spatial coordinates has a 12 bit content, the true spatial coordinates relative to the predetermined apparent spatial coordinates are stored in 64 x 64 matrices and interpolation in accordance with the six least significant bit content provides the true coordinates for the radiation events located intermediate the selected coordinates of the matrices.

Claim 9

Dependent Claim 37 words

The system of Claim 7 wherein the transducer is a gamma ray camera having a scintillation crystal sensitive to received energy quanta, and the coordinate signals are generated by photomultiplier tubes in optical communication with the crystal.

Claim 10

Dependent Claim 27 words

The system of Claim 1 including means for generating the true spatial coordinates corresponding to the plurality of predetermined apparent spatial coordinates relative to the selected events.

Claim 11

Dependent Claim 23 words

The system of Claim 9 including calibration means forming a radiation image precisely located in space for providing the selected detected radiation events.

Claim 12

Dependent Claim 45 words

The system of Claim 10 wherein the calibration plate is a radiation shield mounted in close proximity to the transducer face having a plurality of parallel gaps formed therein, thereby providing a plurality of corresponding line images of radiation when irradiated by a uniform field.

Claim 13

Dependent Claim 19 words

The system of Claim 11 wherein the calibration plate is irradiated by a point source effectively focused at infinity.

Claim 14

Dependent Claim 90 words

The system of Claim 11 wherein the lines of radiation are three millimeters in width, and wherein orthogonal coordinates of the selected radiation events are determined by profiles taken across the image in accordance with a predetermined number of coordinates normal to the lines of the image, and wherein the radiation image is first formed with the lines parallel to a first axis and subsequently parallel to a second axis normal to the first, thereby establishing the plurality of predetermined apparent spatial coordinates relative to the selected detects radiation events.

Claim 15

Dependent Claim 58 words

The system of Claim 13 wherein a non-linear polynomial expression is fitted to the apparent coordinates of the selected radiation events for each profile as a function of the true spatial coordinates of the events, thereby describing intervals between the detected events from which the true spatial coordinates corresponding to the predetermined apparent spatial coordinates may be derived.

Claim 16

Dependent Claim 55 words

A radiation imaging system comprising: a radiation transducer producing signals proportional to the energy content of detected radiation events; means for storing selected threshold values as a function of event spatial coordinates; and means for comparing the energy content signals of the detected radiation events to the threshold value corresponding to the event spatial coordinates.

Claim 17

Dependent Claim 55 words

A radiation imaging system comprising: a radiation transducer producing signals proportional to the energy content of detected radiation events; means for storing selected threshold values as a function of event spatial coordinates; and means for comparing the energy content signals of the detected radiation events to the threshold value corresponding to the event spatial coordinates.

Claim 18

Dependent Claim 68 words

The system of Claim 15 wherein the radiation transducer is a scintillation crystal camera sensitive to radiation event quanta; the threshold values are stored in a matrix array in accordance with regularly spaced spatial coordinates relative to the crystal face; and the spatial coordinates of each of the detected events addresses an appropriate one of the stored threshold values for comparison with the energy content signal associated therewith.

Claim 19

Dependent Claim 44 words

The system of Claim 16 including means for generating signals proportional to the spatial coordinates of the detected events and the energy content signals, the threshold values and the spatial coordinate signals are digitized to plural bit equivalents in analog to digital converter means.

Claim 20

Dependent Claim 36 words

The system of Claim 17 wherein the threshold value matrix array is a square 64 x 64 matrix addressed by a corresponding six most significant bit content of the spatial coordinates of the detected radiation events.

Claim 21

Dependent Claim 65 words

The system of Claim 18 including means for producing a field irradiating the camera crystal, means for accumulating histograms of detected radiation events as a function of the energy content signal, and the spatial coordinates thereof for each coordinate element of the camera associated with the 64 x 64 matrix; and means for entering in the matrix the desired threshold values relative to matrix elements.

Claim 22

Dependent Claim 65 words

The system of Claim 16 wherein the system further comprises: means producing signals proportional to apparent orthogonal spatial coordinates of the detected radiation events; means for storing true spatial coordinates corresponding to a plurality of predetermined apparent spatial coordinates relative to selected detected radiation events; and means for interpolating the true spatial coordinates of the detected radiation events located intermediate the stored true spatial coordinates.

Claim 23

Dependent Claim 36 words

The system of Claim 20 wherein each orthogonal coordinate of the stored true spatial coordinates corresponds to the spatial coordinates of the threshold matrix array and are each stored in second and third matrix arrays respectively.

Claim 24

Independent Claim 170 words

A method for calibrating a scintillation crystal energy quanta sensitive camera to provide true spatial coordinates for detecting radiation events, comprising the steps of: exposing the camera to a uniform field image having a plurality of parallel radiation lines; accumulating energy events for each given row of the image corresponding to a selected plurality of coordinate axes normal to the image lines thereby representing a one-dimensional profile with radiation event peaks coinciding with the line locations; determining a centroid coordinate value associated with the peaks associated with each of the profiles, thereby providing apparent spatial coordinates associated with the true spatial coordinates of each of the line profiles; fitting the profile data to a non-linear polynomial expression describing the true spatial coordinates as a function of the apparent spatial coordinates for each of the profiles and accumulate the true values in accordance with predetermined apparent coordinates; and rotating the image 90° repeat the method steps for a selected plurality of coordinate axes normal to the lines of the rotated image.

Claim 25

Independent Claim 170 words

A method for calibrating a scintillation crystal energy quanta sensitive camera to provide true spatial coordinates for detecting radiation events, comprising the steps of: exposing the camera to a uniform field image having a plurality of parallel radiation lines; accumulating energy events for each given row of the image corresponding to a selected plurality of coordinate axes normal to the image lines thereby representing a one-dimensional profile with radiation event peaks coinciding with the line locations; determining a centroid coordinate value associated with the peaks associated with each of the profiles, thereby providing apparent spatial coordinates associated with the true spatial coordinates of each of the line profiles; fitting the profile data to a non-linear polynomial expression describing the true spatial coordinates as a function of the apparent spatial coordinates for each of the profiles and accumulate the true values in accordance with predetermined apparent coordinates; and rotating the image 90° repeat the method steps for a selected plurality of coordinate axes normal to the lines of the rotated image.

Claim 26

Dependent Claim 38 words

The method of Claim 22 including expressing the coordinate signals as digital plural bit equivalents, and storing each orthogonal true spatial coordinate as a function of the same selected apparent spatial coordinates in regularly spaced matrix arrays respectively.

Claim 27

Dependent Claim 44 words

The method of Claim 22 wherein the selected apparent spatial coordinates established a square 64 x 64 array; and further including the step of interpolating the true spatial coordinates of the detected radiation events spatially located intermediate the selected coordinates of the matrix arrays.

Claim 28

Independent Claim 82 words

A method for normalizing a scintillation crystal camera response signal to energy content of detected radiation events, comprising the steps of: irradiating the entire camera crystal; accumulating the histograms of the detected radiation events as a function of predetermined apparent spatial coordinate position and magnitude; selecting desired threshold values for recognizing the detected events as a function of the histograms for each of the apparent spatial coordinates; and storing the selected threshold values in accordance with the apparent spatial coordinates associated therewith.

Claim 29

Independent Claim 82 words

A method for normalizing a scintillation crystal camera response signal to energy content of detected radiation events, comprising the steps of: irradiating the entire camera crystal; accumulating the histograms of the detected radiation events as a function of predetermined apparent spatial coordinate position and magnitude; selecting desired threshold values for recognizing the detected events as a function of the histograms for each of the apparent spatial coordinates; and storing the selected threshold values in accordance with the apparent spatial coordinates associated therewith.

Claim 30

Dependent Claim 21 words

The method of Claim 25 wherein the predetermined spatial coordinates form a regular rectangular matrix array relative to the camera crystal.

Claim 31

Dependent Claim 25 words

The method of Claim 26 wherein the signals are expressed as plural bit digital equivalents and the matrix is a 64 x 64 square array.

Claim 32

Dependent Claim 44 words

The method of Claim 26 further including comparing the response signal associated with each of the detected events with the threshold value associated with the apparent spatial coordinate of the event as stored in the matrix, and recognizing the response signal if comparatively appropriate.

Claim 33

Dependent Claim 155 words

The method of Claim 25 further including the steps of: exposing the camera to a uniform field image having a plurality of parallel, radiation lines; accumulating energy events for each given row of the image corresponding to a selected plurality of coordinate axes normal to the image lines, thereby representing a one-dimensional profile with radiation event peak coinciding with the line; determining a centroid coordinate value associated with the peaks associated with each of the profiles, thereby providing apparent spatial coordinates associated. with the true spatial coordinates of each of the line profiles; fitting the profile data to a non-linear polynomial expression describing the true spatial coordinates as a function of the apparent spatial coordinates for each of the profiles and accumulate the true values in accordance with predetermined apparent coordinates; and rotating the image 90° repeat the method steps for a selected plurality of coordinate axes normal to the lines of the rotated image.

Claim 34

Dependent Claim 89 words

The method of Claim 20 further including the steps of: producing a new image of the calibration image in accordance with the true coordinates accumulated in the steps of Claim 20; repeating the steps of Claim 20 on the new image establishing new true coordinates relative to new apparent coordinates of the new image; and using the predetermined apparent coordinates of the calibration image of Claim 20 developing a regular matrix array interpolating the new true coordinates corresponding thereto from the new true coordinates established from the new image.

Radiation imaging system

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