X-ray impingement event detection system and method for a digital radiography detector
View Patent ↗A wireless, independent digital imaging sensor utilizes an external charge balance capacitor to establish a sense voltage at a common node between the charge capacitor and the pixel intrinsic capacitors in the sensor panel. A variable width pulse train responds to the sense voltage to control injection of charge to the external capacitor to maintain a constant voltage at the common equal to a reference voltage. An increase in pulse width above a threshold level representative of the onset of X-ray exposure is detected to generate an output control signal used to control subsequent image acquisition functions of the imaging sensor.
1. A digital radiography X-ray imaging sensor adapted for independent detection of the existence of impinging X-rays from a remote X-ray source, comprising:
an imaging panel including a two-dimensional array of imaging pixels, each of the pixels having an intrinsic capacitor which is charged, directly or indirectly, by the impinging X-rays to establish an image of an object being X-rayed;
a source of a reference voltage;
a charge balance capacitor connected at a common node to the pixel intrinsic capacitors;
a control unit for varying a level of charge injection to the charge balance capacitor in response to changes in charge balance between the pixel capacitors and the charge balance capacitor for maintaining a constant charge voltage on the common node as determined by the reference voltage; and
a control signal generator responsive to the control unit for generating an output control signal indicating presence of impinging X-rays on the imaging panel when the level of charge injection exceeds a predetermined threshold value.
2. The imaging sensor of claim 1 wherein individual nodes of the pixel capacitors opposite to the common node are connected to a virtual ground prior to detection of X-ray impingement on the imaging panel and all but one segment of individual pixel nodes are disconnected from the virtual ground after detection of X-ray impingement;
whereby retention of connection of virtual ground to the one segment enables detection of the cessation of impingement of X-rays on the imaging panel.
3. The imaging sensor of claim 2 wherein the control signal generator indicates termination of X-ray impingement when the charge injections with respect to the one segment of pixels remaining connected to virtual ground falls below the predetermined threshold value.
4. The imaging sensor of claim 2 wherein the segment comprises at least one row of pixels.
5. The imaging sensor of claim 3 wherein the control unit comprises a programmable constant current source which outputs a first level of input current to the charge balance capacitor prior to the detection of X-ray impingement and outputs a second, lower level of input current to the charge balance capacitor after the detection of X-ray impingement.
6. The imaging sensor of claim 1 wherein the control unit comprises a programmable constant current source.
7. A digital radiography X-ray imaging sensor adapted for independent detection of the existence of impinging X-rays from a remote X-ray source, comprising:
an imaging panel including a two-dimensional array of imaging pixels, each of the pixels having an intrinsic capacitor which is charged, directly or indirectly, by the impinging X-rays to establish an image of an object being X-rayed;
an external capacitor connected at a common node to the pixel intrinsic capacitors; and
an impinging X-ray detection unit including:
(a) a reference voltage source,
(b) a charge source to establish a charge voltage at the common node,
(c) a source of a pulse-width-modulated train of pulses switchably connected to the charge voltage source and the common node to vary injection of charge to the external capacitor to establish a voltage on the common node representative of charge balance between the external capacitor and the pixel capacitors,
(d) a controller operative while awaiting onset of impinging X-rays to set the pulse width of the pulse train at a first duration necessary to maintain the common node voltage at a predetermined value determined by the reference voltage and for adjusting the pulse width to a second duration necessary to maintain the common node voltage at the predetermined value during impingement of the X-rays on the panel, and
(e) a pulse width detection circuit responsive to the second pulse width duration for outputting an X-ray detection signal indicative of impingement of X-rays from the remote source.
8. The imaging sensor of claim 7 wherein individual nodes of the pixel capacitors opposite to the common node are connected to a virtual ground while awaiting detection of the onset of X-ray impingement on the imaging panel and all but one segment of individual pixel nodes are disconnected from the virtual ground after detection the onset of X-ray impingement;
whereby retention of connection of virtual ground to the one segment enables detection of the cessation of impingement of X-rays on the imaging panel.
9. The imaging sensor of claim 8 wherein the control signal generator indicates termination of X-ray impingement when the charge injections with respect to the one segment of pixels remaining connected to virtual ground falls below the predetermined threshold value.
10. The imaging sensor of claim 8 wherein the segment comprises at least one row of pixels.
11. The imaging sensor of claim 8 wherein the charge balance capacitor is a variable capacitor and the control unit includes means for varying the capacitor value after the control signal generator indicates presence of X-ray impingement on the imaging panel.
12. The imaging sensor of claim 8 wherein the charge source is a programmable constant current source which outputs a first level of charge current to the charge balance capacitor prior to the detection of X-ray impingement and outputs a second, lower level of charge current to the charge balance capacitor after the detection of X-ray impingement.
13. The imaging sensor of claim 7 wherein the pulse width is increased to a longer duration during impingement of X-rays on the imaging panel to increase charge on the external capacitor to correspond to increased charge on the array of pixel capacitors.
14. A digital radiography X-ray imaging sensor adapted for independent detection of the existence of impinging X-rays from a remote X-ray source, comprising:
an imaging panel including a two-dimensional array of imaging pixels, each of the pixels having an intrinsic capacitor which is charged, directly or indirectly, by the impinging X-rays to establish an image of an object being X-rayed;
a source of a reference voltage;
a charge balance capacitor connected at a common node to the pixel intrinsic capacitors;
a charge injection source;
a source of a train of pulses switchably connected to the common node and the charge injection source, the pulses being width modulated in response to changes in charge balance between the charge balance capacitor and the imaging pixel capacitors to maintain a constant charge voltage at the common node as determined by the reference voltage, the pulse width durations increasing above a threshold value during onset of impingement of X-rays on the imaging pixels; and
a pulse width modulation detector responsive to pulse width durations above the threshold value for generating an output control signal indicating presence of the impinging X-rays on the imaging panel.
15. The imaging sensor of claim 14 wherein individual nodes of the pixel capacitors opposite to the common node are connected to a virtual ground while awaiting detection of the onset of X-ray impingement on the imaging panel and all but one segment of individual pixel nodes are disconnected from the virtual ground after detection the onset of X-ray impingement;
whereby retention of connection of virtual ground to the one segment enables detection of the cessation of impingement of X-rays on the imaging panel.
16. The imaging sensor of claim 15 wherein the control signal generator indicates termination of X-ray impingement when the charge injections with respect to the one segment of pixels remaining connected to virtual ground falls below the predetermined threshold value.
17. The imaging sensor of claim 15 wherein the segment comprises at least one row of pixels.
18. The imaging sensor of claim 15 wherein the charge balance capacitor is a variable capacitor and the control unit includes means for varying the capacitor value after the control signal generator indicates presence of X-ray impingement on the imaging panel.
19. The imaging sensor of claim 15 wherein the charge source is a programmable constant current source which outputs a first level of charge current to the charge balance capacitor prior to the detection of X-ray impingement and outputs a second, lower level of charge current to the charge balance capacitor after the detection of X-ray impingement.
20. An imaging sensor according to claim 14 , wherein the output control signal indicates the start of X-ray impingement when the pulse width durations increase above the threshold value and indicates the stop of X-ray impingement when the pulse width durations fall below the threshold value.
21. A method of detecting impingement of X-rays on a digital radiography imaging panel having a two-dimensional array of imaging pixels, each of the pixels having an intrinsic capacitor which is charged, directly or indirectly by the impinging X-rays to establish an image of an object being X-rayed, comprising:
providing an external capacitor connected at a common node to the capacitors of the imaging pixels:
establishing a predetermined bias voltage on the pixel capacitors during a period prior to onset of impingement of the X-rays on the imaging panel by injecting pulses of charge into the external capacitor under control of a pulse train that is pulse width modulated in response to charge voltage sensed at the common node; and
detecting the width modulation of the pulse train and generating a output control signal indicative of the onset of impingement of X-rays onto the imaging panel when the detected pulse width exceeds a predetermined threshold value.
22. The method of claim 21 wherein during the prior period, individual nodes of the imaging pixels opposite the common node are connected to a virtual ground potential, the method further including the steps of:
in response to the output signal signifying onset of impingement of X-rays, disconnecting all but one segment of imaging pixels from the virtual ground potential;
continuing to monitor charge balance at the common node between the external capacitor and the one segment of imaging pixels; and
generating a second output signal indicative of cessation of the impingement of X-rays when the pulse width falls below the predetermined threshold.
23. The method of claim 22 wherein the one segment comprises at least one row of the pixels.
24. The method of claim 22 further including the step of:
after generating the control signal indicative of the onset of impingement of X-rays, varying the value of the external capacitor so as to enhance detection of the cessation of the impingement of X-rays.
25. The method of claim 22 further including the steps of inputting programmable levels of charge current to the charge balance capacitor;
setting a first level of charge current to the charge balance capacitor prior to detection of X-ray impingement; and
setting a second, lower level of charge current to the charge balance capacitor after detection of X-ray impingement.
26. The method of claim 21 further including the steps of:
providing a reference voltage;
controlling the pulse width modulation to maintain charge voltage on the common node at a constant value in relation to the reference voltage;
wherein at onset of X-ray impingement on the imaging panel, the pulse width is increased to maintain charge balance between the external capacitor and the pixel capacitors thereby to maintain the charge value on the common node at the constant value.
27. A digital radiography X-ray imaging sensor adapted for independent detection of the existence of impinging X-rays from a remote X-ray source, comprising:
an imaging panel including a two-dimensional array of imaging pixels, each of the pixels having an intrinsic capacitor which is charged, directly or indirectly, by the impinging X-rays to establish an image of an object being X-rayed;
a source of a reference voltage;
a charge balance capacitor connected at a common node to the pixel intrinsic capacitors;
a control unit for varying a level of charge injection to the charge balance capacitor in response to changes in charge balance between the pixel capacitors and the charge balance capacitor for maintaining a constant charge voltage on the common node as determined by the reference voltage, wherein the control unit includes generator of a pulse width modulated train of pulses for varying the charge injection; and
a control signal generator responsive to the control unit for generating an output control signal indicating presence of impinging X-rays on the imaging panel when the level of charge injection exceeds a predetermined threshold value.
28. A digital radiography X-ray imaging sensor adapted for independent detection of the existence of impinging X-rays from a remote X-ray source, comprising:
an imaging panel including a two-dimensional array of imaging pixels, each of the pixels having an intrinsic capacitor which is charged, directly or indirectly, by the impinging X-rays to establish an image of an object being X-rayed;
a source of a reference voltage;
a charge balance capacitor connected at a common node to the pixel intrinsic capacitors;
a control unit for varying a level of charge injection to the charge balance capacitor in response to changes in charge balance between the pixel capacitors and the charge balance capacitor for maintaining a constant charge voltage on the common node as determined by the reference voltage; and
a control signal generator responsive to the control unit for generating an output control signal indicating presence of impinging X-rays on the imaging panel when the level of charge injection exceeds a predetermined threshold value;
wherein individual nodes of the pixel capacitors opposite to the common node are connected to a virtual ground prior to detection of X-ray impingement on the imaging panel and all but one segment of individual pixel nodes are disconnected from the virtual ground after detection of X-ray impingement;
whereby retention of connection of virtual ground to the one segment enables detection of the cessation of impingement of X-rays on the imaging panel;
wherein the charge balance capacitor is a variable capacitor and the control unit includes means for varying the capacitor value after the control signal generator indicates presence of X-ray impingement on the imaging panel.