X-ray imaging apparatus dose calibration method

Claim 1

A method of calibrating the dose of an X-ray imaging system having an X-ray tube with an anode, a cathode and a filament which tube is excited to emit X-rays; and having an image intensifier with a photocathode, said method comprising the steps of: selecting a desired dose rate for an X-ray exposure; producing an X-ray exposure from the system; sensing the magnitude of an electrical current flowing through the photocathode; deriving the actual X-ray exposure dose rate from the sensed magnitude of the photocathode current; comparing the actual exposure dose rate to the selected desired dose rate; and altering the excitation of the X-ray tube in response to the comparing step until the actual exposure dose rate substantially equals the selected desired dose rate.

Claim 2

A method of calibrating the dose of an X-ray imaging system having an X-ray tube with an anode, a cathode and a filament which tube is excited to emit X-rays; and having an image intensifier with a photocathode, said method comprising the steps of: selecting a desired dose rate for an X-ray exposure; producing an X-ray exposure from the system; sensing the magnitude of an electrical current flowing through the photocathode; deriving the actual X-ray exposure dose rate from the sensed magnitude of the photocathode current; comparing the actual exposure dose rate to the selected desired dose rate; and altering the excitation of the X-ray tube in response to the comparing step until the actual exposure dose rate substantially equals the selected desired dose rate.

Claim 6

A method of calibrating the dose of an X-ray imaging system having an X-ray tube, an image intensifier with a photocathode; a video camera which converts an image from the image intensifier to a video signal, and a control circuit which regulates the electrical excitation of the X-ray tube in response to a characteristic of the video signal, said method comprising the steps of: producing an X-ray exposure from the system; sensing the magnitude of an electrical current flowing through the photocathode; deriving the actual X-ray dose rate from the sensed magnitude of the photocathode current; comparing the actual dose rate to a desired dose rate; and altering the excitation of the X-ray tube in response to the comparing step until the actual dose rate substantially equals the desired dose rate.

Claim 7

A method of calibrating the dose of an X-ray imaging system having an X-ray tube, an image intensifier with a photocathode; a video camera which converts an image from the image intensifier to a video signal, and a control circuit which regulates the electrical excitation of the X-ray tube in response to a characteristic of the video signal, said method comprising the steps of: producing an X-ray exposure from the system; sensing the magnitude of an electrical current flowing through the photocathode; deriving the actual X-ray dose rate from the sensed magnitude of the photocathode current; comparing the actual dose rate to a desired dose rate; and altering the excitation of the X-ray tube in response to the comparing step until the actual dose rate substantially equals the desired dose rate.

Claim 12

A method of calibrating the dose of an X-ray imaging system having an X-ray tube, an image intensifier with a photocathode, a video camera which converts an image from the image intensifier to a video signal, a film camera for recording an image from the image intensifier, a photodetector which produces an output signal indicative of the brightness of the image from the image intensifier, means for integrating the photodetector output signal including a variable gain amplifying means, and a control circuit which regulates the electrical excitation of the X-ray tube; the X-ray imaging system being operable in either a fluoroscopic mode or a film camera mode; said method comprising the steps of: (a) calibrating a first dose rate for the fluoroscopic mode by: (1) producing a first X-ray exposure from the system; (2) sensing the magnitude of an electrical current flowing through the photocathode; (3) deriving the actual X-ray dose rate from the sensed magnitude of the photocathode current; (4) comparing the actual dose rate to a desired dose rate; (5) altering the excitation of the X-ray tube in response to the comparing step until the actual dose rate substantially equals the desired dose rate; and (6)storing system data which define the excitation of the X-ray tube when the actual dose rate substantially equals the selected dose rate; and (b) then calibrating the system for the film camera mode by: (1) producing a second X-ray exposure in the fluoroscopic mode at a given dose rate derived from the previously calibrated first dose rate; (2) when the system stabilizes at the given dose rate, maintaining the emission from the X-ray tube at a substantially constant level, and (3) adjusting the gain of the means for amplifying until the means for integrating produces a predefined output in a given interval of time.

Claim 13

A method of calibrating the dose of an X-ray imaging system having an X-ray tube, an image intensifier with a photocathode, a video camera which converts an image from the image intensifier to a video signal, a film camera for recording an image from the image intensifier, a photodetector which produces an output signal indicative of the brightness of the image from the image intensifier, means for integrating the photodetector output signal including a variable gain amplifying means, and a control circuit which regulates the electrical excitation of the X-ray tube; the X-ray imaging system being operable in either a fluoroscopic mode or a film camera mode; said method comprising the steps of: (a) calibrating a first dose rate for the fluoroscopic mode by: (1) producing a first X-ray exposure from the system; (2) sensing the magnitude of an electrical current flowing through the photocathode; (3) deriving the actual X-ray dose rate from the sensed magnitude of the photocathode current; (4) comparing the actual dose rate to a desired dose rate; (5) altering the excitation of the X-ray tube in response to the comparing step until the actual dose rate substantially equals the desired dose rate; and (6)storing system data which define the excitation of the X-ray tube when the actual dose rate substantially equals the selected dose rate; and (b) then calibrating the system for the film camera mode by: (1) producing a second X-ray exposure in the fluoroscopic mode at a given dose rate derived from the previously calibrated first dose rate; (2) when the system stabilizes at the given dose rate, maintaining the emission from the X-ray tube at a substantially constant level, and (3) adjusting the gain of the means for amplifying until the means for integrating produces a predefined output in a given interval of time.

Claim 20

A method of calibrating the dose of an X-ray imaging system having an X-ray tube, an image intensifier with a photocathode, a video camera which converts an image from the image intensifier to a video signal, a film camera for recording an image from the image intensifier, a photodetector which produces an output signal indicative of the brightness of the image from the image intensifier, means for integrating the photodetector output signal, and a control circuit which regulates the electrical excitation of the X-ray tube, the X-ray imaging system being operable in either a fluoroscopic mode or a film camera mode; said method comprising the steps of: (a) calibrating the system for a first dose level in the fluoroscopic mode by: (1) producing a first X-ray exposure from the system, (2) detecting the actual X-ray dose level generated by the X-ray tube, (3) comparing the actual dose level to a desired dose level, (4) altering the excitation of the X-ray tube in response to the comparing step until the actual dose level substantially equals the desired dose level, and (5) storing system data which define the excitation of the X-ray tube when the actual dose level substantially equals the selected dose level; and (b) thereafter calibrating the system for the film camera mode by: (1) producing a second X-ray exposure in the fluorscopic mode at a given dose level derived from a previously calibrated dose level, (2) when the system stabilizes at the given dose level, maintaining the emission from the X-ray tube at a substantially constant level, (3) adjusting the means for integrating to produce a predefined output indicative of the given dose level, and (4) storing data representing the adjustment of the means for integrating which produced the predefined output indicative of the given dose level.

Claim 21

A method of calibrating the dose of an X-ray imaging system having an X-ray tube, an image intensifier with a photocathode, a video camera which converts an image from the image intensifier to a video signal, a film camera for recording an image from the image intensifier, a photodetector which produces an output signal indicative of the brightness of the image from the image intensifier, means for integrating the photodetector output signal, and a control circuit which regulates the electrical excitation of the X-ray tube, the X-ray imaging system being operable in either a fluoroscopic mode or a film camera mode; said method comprising the steps of: (a) calibrating the system for a first dose level in the fluoroscopic mode by: (1) producing a first X-ray exposure from the system, (2) detecting the actual X-ray dose level generated by the X-ray tube, (3) comparing the actual dose level to a desired dose level, (4) altering the excitation of the X-ray tube in response to the comparing step until the actual dose level substantially equals the desired dose level, and (5) storing system data which define the excitation of the X-ray tube when the actual dose level substantially equals the selected dose level; and (b) thereafter calibrating the system for the film camera mode by: (1) producing a second X-ray exposure in the fluorscopic mode at a given dose level derived from a previously calibrated dose level, (2) when the system stabilizes at the given dose level, maintaining the emission from the X-ray tube at a substantially constant level, (3) adjusting the means for integrating to produce a predefined output indicative of the given dose level, and (4) storing data representing the adjustment of the means for integrating which produced the predefined output indicative of the given dose level.