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1. (US20060018430) Active dose reduction device and method
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Claims

1. An x-ray imaging system comprising:
an x-ray tube which generates x-rays for x-ray imaging when a pre-selected voltage is supplied thereto;
a power supply for supplying power to the x-ray tube at the pre-selected voltage;
a cable set comprising an anode cable and a cathode cable for operatively connecting the power supply to the x-ray tube;
a plurality of electronic cells, each cell having a first state which prevents flow of current upto a threshold voltage and a second state which permits flow of current, said cells operatively connected to at least one component of the x-ray imaging system, said component selected from the group comprising the x-ray tube, the power supply and the cable set, such that said plurality of cells prevent current flow to ground when in the first state and permit current flow from the at least one component when in the first state and permit current flow from the at least one component when in the second state;
an overvoltage circuit to cause at least a first cell of the plurality of electronic cells to exceed the threshold voltage and change from the first state to the second state; and
wherein while the power supply supplies power to the x-ray tube at the pre-selected voltage, the cells in the first state prevent current flow from the at least one component, and, upon termination of the power supply supplying power to the x-ray tube at the pre-selected voltage, the overvoltage circuit causes at least the first cell of the plurality of cells to change from the first state to the second state which causes successive cells to change from the first state to the second state to permit current to flow from the at least one component thereby reducing the x-rays generated by the x-ray tube.
2. The x-ray imaging system as defined in claim 1, wherein each cell in the plurality of cells changes from the second state to the first state once the current passing through the plurality of cells decreases below a threshold current; and
wherein after sufficient stored energy in the x-ray imaging system is discharged, the current passing through the plurality of cells decreases below the threshold current to cause the plurality of cells to change from the second state to the first state such that the plurality of cells prevent current flow from the at least one component to ground.
3. The x-ray imaging system as defined in claim 1, wherein the at least one component of the x-ray system is the cable set only; and
wherein said plurality of cells operatively connect the cable set to ground by operatively connecting either the anode cable to ground, or, the cathode cable to ground, or both the anode cable to ground and the cathode cable to ground.
4. The x-ray imaging system as defined in claim 3, wherein said plurality of cells are arranged in series between either the anode cable and ground or the cathode cable and ground but not both the anode cable to ground and cathode cable to ground.
5. The x-ray imaging system as defined in claim 1, wherein the first cell changing from the first state to the second state causes a cascading effect which successively changes each of the cells of the plurality of cells to the second state.
6. The x-ray imaging system as defined in claim 1, wherein the overvoltage circuit causes at least the first cell to exceed the threshold voltage and change from the first state to the second state in response to a command signal from the power supply indicating termination of the pre-selected voltage.
7. The x-ray imaging system as defined in claim 1, wherein the threshold voltage for each cell is approximately equal.
8. The x-ray imaging system as defined in claim 2, wherein the threshold voltage for each cell is approximately equal and the threshold current for each cell is approximately equal.
9. The x-ray imaging system as defined in claim 1, wherein when the cells are in the first state, the pre-selected voltage creates a voltage potential across corresponding cells, and, the number of cells in the plurality of cells and the threshold voltage of the cells is selected such that the threshold voltage of each of the cells in the plurality of cells is in excess of the voltage potential across the corresponding cell created by the pre-selected voltage; and
wherein the overvoltage circuit comprises a voltage pulse source for selectively supplying a voltage pulse to the first cell which is summed with the voltage across the first cell created by the pre-selected voltage, the voltage pulse being of sufficient magnitude that the voltage sum across the first cell exceeds the threshold voltage for the first cell causing the first cell to move from the first state to the second state thereby permitting the flow of current through the first cell.
10. The x-ray imaging system as defined in claim 9, wherein after the first cell moves from the first state to the second state, the voltage potential across corresponding cells created by the pre-selected voltage increases; and
wherein the voltage pulse is of sufficient magnitude that the voltage sum across a cell immediately adjacent the first cell exceeds its threshold voltage causing the cell immediately adjacent the first cell to move from the first state to the second state.
11. The x-ray imaging system as defined in claim 10 wherein as each cell in the plurality of cells moves from the first state to the second state, the voltage potential created by the pre-selected voltage across corresponding cells remaining in the first state increases until the voltage potential across the corresponding cells in the first state created by the pre-selected voltage exceeds the threshold voltage of the cells remaining in the first state and current is permitted to flow through the cells in the second state from the at least one component to ground.
12. The x-ray imaging system as defined in claim 1, further comprising a fault current detection device for detecting presence of an x-ray reduction current from the at least one component through at least one cell of the plurality of cells;
wherein the fault current detection device sends a fault signal to stop the power supply from supplying power to the x-ray tube if the x-ray reduction current is present before the command signal is sent or the x-ray reduction current is not present after the command signal is sent.
13. The x-ray imaging system as defined in claim 1, wherein each cell of the plurality of cells comprises at least one overvoltage device, said overvoltage device having a first state which is substantially non-conductive and a second state which is highly conductive, wherein the overvoltage devices electronically change from the first state to the second state when overvoltaged beyond a pre-determined threshold voltage.
14. The x-ray imaging system as defined in claim 13, wherein each overvoltage device has only two terminals and wherein each cell comprises one or more overvoltage devices.
15. The x-ray imaging system as defined in claim 13, wherein the two terminal overvoltage devices comprises silicon control rectifiers.
16. A device for reducing x-ray dosage from an x-ray imaging system, said device comprising:
a plurality of electronic cells, each cell having a first state which prevents flow of current upto a threshold voltage and a second state which permits flow of current, said plurality of electronic cells operatively connected to at least one component of the x-ray imaging system such that, when each of the plurality of cells is in the first state, the voltage differential between across the plurality of cells is insufficient to surpass the threshold voltage of any one cell of the plurality of cells;
a voltage pulse source for generating a voltage pulse of sufficient magnitude to cause at least a first cell of the plurality of electronic cells to exceed the threshold voltage;
wherein substantially simultaneously with the termination of an x-ray imaging exposure, the voltage pulse source causes a first cell of the plurality of cells to exceed its threshold voltage changing the first cell from the first state to the second state; and
wherein the first cell changing from the first state to the second state causes the plurality of cells to change from the first state to the second state permitting discharge of stored energy in the at least one component of the imaging system to ground to reduce the x-ray dosage from the imaging system.
17. A device for reducing x-ray dosage from an imaging system as defined in claim 16, wherein the first cell changing from the first state to the second state causes a cascading effect which successively changes each of the cells of the plurality of cells to the second state.
18. A device for reducing x-ray dosage from an imaging system as defined in claim 16 wherein each cell in the plurality of cells changes from the second state to the first state once the current passing through the plurality of cells decreases below a threshold current; and
wherein after sufficient stored energy in the x-ray imaging system is discharged, the current passing through the plurality of cells decreases below the threshold current to cause the plurality of cells to change from the second state to the first state such that the plurality of cells prevent current flow from the at least one component to ground.
19. A device for reducing x-ray dosage from an imaging system as defined in claim 16, wherein the x-ray system has an anode side, which has a positive voltage with respect to ground, and, a cathode side, which has a negative voltage with respect to ground; and
wherein said plurality of cells operatively connect only the cathode side to ground or the anode side to ground, or the cathode side to the anode side.
20. The x-ray imaging system as defined in claim 1 wherein the x-ray system has an anode side, which has a positive voltage with respect to ground, and, a cathode side, which has a negative voltage with respect to ground; and
wherein said plurality of cells operatively connect only the cathode side to ground or the anode side to ground, or the cathode side to the anode side.
21. The x-ray imaging system as defined in claim 1 wherein the plurality of cells operatively connect an anode side of the at least one component of the x-ray imaging system to a cathode side of the at least one component of the x-ray imaging system; and
wherein while the power supply supplies power to the x-ray tube at the pre-selected voltage, the cells in the first state prevent current flow from the cathode side of the at least one component to the anode side of the at least one component, and, upon termination of the power supply supplying power to the x-ray tube at the pre-selected voltage, the overvoltage circuit causes at least the first cell of the plurality of cells to change from the first state to the second state which causes successive cells to change from the first state to the second state to permit current to flow from the cathode side of the at least one component to the anode side of the at least one component thereby reducing the x-rays generated by the x-ray tube.
22. A method for reducing an active dose of x-rays during x-ray imaging, said method comprising:
applying a pre-selected voltage through a cable set, said cable set including an anode cable and a cathode cable operatively connecting a power supply to an x-ray tube, said pre-selected voltage being sufficient to cause the x-ray tube to generate x-rays for x-ray imaging;
upon termination of the pre-selected voltage, over voltaging a first cell of a purality of cells operatively connecting at least one of the cable set or the x-ray tube to ground, each cell in said plurality of cells having a first state which prevents flow of current until overvoltaged and a second state which permits flow of current;
wherein over voltaging the first cell of the plurality of cells causes each of the remaining plurality of cells to become overvoltaged whereby stored energy in at least one of the x-ray tube, the anode cable and the cathode cable are discharged to ground thereby decreasing the x-rays generated by the x-ray tube upon termination of the pre-selected voltage.