Digital radiography detector image readout process
A radiographic detector acquires a first partial exposed image signal during an image readout of each of the rows of photosensors, one row at a time. A first scan of each row includes measuring the charge delivered to each cell of the rows, including some rows having partial charge and other rows having full charge, and obtaining a first null image signal during the scan. A second scan includes measuring remaining charge delivered to those rows having partial charge. The null image signal data is subtracted from a sum of the first two scans.
1. An area x-ray detector, comprising:
a plurality of electrically-chargeable photosensitive cells arranged in rows and columns;
controllable row selecting switches;
electric circuits connected to the plurality of electrically-chargeable photosensitive cells of each column and to the controllable row selecting switches to provide a reading of charge stored in the plurality of electrically-chargeable photosensitive cells of each column;
an acquisition control and image processing circuit programmed to:
acquire a first partial exposed image signal during a readout of each of the rows of electrically-chargeable photosensitive cells one row at a time, a first scan of a current row including measuring the total charge stored in each electrically-chargeable photosensitive cell of the current row, using the electric circuits, and resetting the electric circuits;
restore the charge of said each electrically-chargeable photosensitive cell of the current row by means of the electric circuits; and
acquire a first null image signal during the readout of said each of the rows of electrically-chargeable photosensitive cells one row at a time; and
acquire a second scan of the current row including measuring the total charge stored in each electrically-chargeable photosensitive cell of the current row by means of the electric circuits, and resetting the electric circuits.
2. The area x-ray detector of claim 1 , wherein the acquisition control and image processing circuit is programmed to detect an x-ray exposure by testing each row for increased image signal intensity.
3. The area x-ray detector of claim 1 , further comprising a first buffer and a second buffer, wherein the first buffer stores the first partial exposed image signal and the second buffer stores the first null image signal.
4. The area x-ray detector of claim 1 , further comprising buffers for storing image frames, wherein the buffers store an x-ray beam exposure of an object as at least two partial image frames and at least two null image frames.
5. The area x-ray detector of claim 4 , wherein the buffers are configured to correct the x-ray beam exposure of the object by combining at least one of the partial image frames and at least one of the null image frames in the buffers.
6. The area x-ray detector of claim 1 , further comprising a first buffer and a second buffer, wherein the electric circuits are configured to perform the first scan and the second scan of row N of the plurality of electrically-chargeable photosensitive cells and to store data from the first scan in the first buffer and data from the second scan in the second buffer, and wherein the electric circuits are configured to perform the first scan and the second scan of row N+1 of the plurality of electrically-chargeable photosensitive cells and to store data from the first scan of row N+1 in the first buffer and data from the second scan of row N+1 in the second buffer.
7. The area x-ray detector of claim 1 , further comprising a first buffer and a second buffer to combine the first partial image signal with the first null image signal.
8. The area x-ray detector of claim 1 , wherein the acquisition control and image processing circuit is programmed to determine if an extraneous signal is present by comparing the first null image signal to a threshold.
9. A method of operating an area x-ray detector producing repeated image signals at a frame rate, the area x-ray detector including a plurality of electrically-chargeable photosensitive cells arranged in rows and columns with readout electronics connected to the electrically chargeable photosensitive cells of each column to provide a reading of charge of the electrically chargeable photosensitive cells of each column, the method comprising:
acquiring a pair of signals during a dual scan of each of the rows of a portion of the electrically chargeable photosensitive cells, one row at a time, the dual scan of each of the rows of electrically chargeable photosensitive cells comprising:
a first scanning of each row including (i) enabling the electrically chargeable photosensitive cells of a current row for a first predetermined time period, (ii) measuring the total charge of each electrically chargeable photosensitive cell of the row by means of the readout electronics, (iii) outputting the total charge to form a row of a first partial image signal, and (iv) resetting the readout electronics and the electrically chargeable photosensitive cells of the current row; and
a second scanning of each row including (i) disabling the electrically chargeable photosensitive cells of the current row, (ii) measuring the charge of each column of said each electrically chargeable photosensitive cell of the current row by means of the readout electronics, (iii) outputting the charge of each column of said each electrically chargeable photosensitive cell to form a null image signal, and (iii) resetting the readout electronics.
10. The method of claim 9 , where the null image signal is row-correlated to the first partial image signal.
11. A computer implemented method comprising:
scanning an image charge level in a two dimensional array of pixels and recording in a first portion of an electronic memory the image charge level of the scanned two-dimensional array of pixels;
exposing the two dimensional array of pixels to radiographic radiation during the step of scanning, the step of exposing generating charges in the two-dimensional array of pixels such that the step of scanning results in at least one of:
(i) a first subset of the scanned two-dimensional array of pixels having a partial image charge level recorded therefor; and
(ii) a second subset of the scanned two-dimensional array of pixels having a full image charge level recorded therefor;
rescanning the image charge level of the two dimensional array of pixels and recording in a second portion of the electronic memory the image charge level of the rescanned two-dimensional array of pixels; and
summing, for each corresponding pixel, the image charge level recorded in the first portion of the electronic memory during the step of scanning and the image charge level recorded in the second portion of the electronic memory during the step of rescanning.
12. The computer implemented method of claim 11 , further comprising:
storing the summed image charge level in a third portion of the electronic memory;
scanning a null sample of charges in the two dimensional array of pixels and recording the null sample of charges in a fourth portion of the electronic memory; and
subtracting the null sample of charges recorded in the fourth portion of the electronic memory from the summed image charge level in the third portion of the electronic memory.
13. The computer implemented method of claim 12 , wherein the step of scanning the image charge level in the two dimensional array of pixels comprises sequentially scanning rows of pixels individually in the two dimensional array of pixels.
14. The computer implemented method of claim 13 , wherein the step of scanning the null sample of charges in the two dimensional array of pixels comprises sequentially scanning rows of pixels individually, and wherein scanning each row of pixels for the null sample of charges occurs immediately after scanning each row of pixels for the image charge level.
15. The computer implemented method of claim 14 , further comprising scanning at least a third time the image charge level of the two dimensional array of pixels and recording in at least a fifth portion of the electronic memory the charge level of the two-dimensional array of pixels rescanned for said at least the third time.
16. The computer implemented method of claim 11 , wherein the step of exposing occurs in a fraction of the time used for the step of scanning the image charge level in the two dimensional array of pixels.
17. The computer implemented method of claim 16 , wherein the step of exposing further generates charges in the two-dimensional array of pixels such that the step of scanning results in a third subset of the of the scanned two-dimensional array of pixels having no charge recorded therefor.
18. The computer implemented method of claim 11 , further comprising:
storing the summed image charge level in a third portion of the electronic memory;
scanning a null sample of charges in the two dimensional array of pixels and recording the null sample of charges it in a fourth portion of the electronic memory; and
rescanning the null sample of charges in the two dimensional array of pixels and recording the null sample of charges it in a fifth portion of the electronic memory.
19. The computer implemented method of claim 11 , further comprising scanning a null sample of charges in the two dimensional array of pixels, before the step of scanning the image charge level, to determine whether a source of magnetic flux is affecting the two dimensional array of pixels.