Method and structure for optimizing radiographic quality by controlling X-ray tube voltage, current focal spot size and exposure time

A method for optimizing an X-ray image from an X-ray apparatus comprising

• an X-ray tube having a cathode which emits electrons and an anode on which said electrons impinge and which is a source of X-rays, said tube having an operating voltage which is the voltage drop between said anode and said cathode, a tube current which is the current between said anode and said cathode, and a focal spot size which is the area of said anode on which said electrons impinge, and in which said voltage, said current and said focal spot size have initial settings;
• a collimator having an opening through which said X-rays leaving said source in the direction of said opening may pass;
• means for holding tissue to be examined in position for being irradiated;
• means for showing an image of X-rays which have passed through said tissue;
• at least one sensor which generates sensor signals for detecting radiation passed through said tissue and through said means for showing an image, and for calibrating said X-ray apparatus;
• and
• means for receiving said sensor signals from said at least one sensor and based on said sensor signals sending control signals which control said operating voltage, said tube current, and said focal spot size;
• comprising the steps of:
• positioning said tissue;
• determining thickness of said tissue and providing said tissue thickness to said microprocssor;
• operating said X-ray apparatus at said initial settings;
• in a sampling time small in comparison to an expected total exposure time calculating optimum voltage, current and focal spot size settings for the tissue being exposed;
• at the end of said small sampling time changing voltage, current and focal spot size settings to said optimum voltage, current and focal spot size settings for the tissue being exposed;
• and
• continuing to operate said X-ray apparatus at said optimal settings until an optimum visualization of said means for showing an image is achieved.

A method for optimizing an X-ray image from an X-ray apparatus as in claim [22] 24 wherein said at least one sensor is two sensors, a first sensor located in the path of X-rays which have passed through said tissue and through said means for showing an image, and a second sensor located in the path of X-rays which have not passed through said tissue, and said step of calculating optimum voltage, current and focal spot size settings for the tissue being exposed comprises:

• before positioning said tissue but after locating said means for producing an image, said first sensor, and said second sensor[.] ;
• determining a normalization factor N between said first and second sensors by operating said X-ray apparatus and measuring current through said first sensor iN.sub.1, current through said second sensor iN.sub.2, distance from said X-ray source to said first sensor DN.sub.1, and distance from said X-ray source to said second sensor DN.sub.2, and calculating N=iN.sub.1 DN.sub.1.sup.2 /iN.sub.2 DN.sub.2.sup.2 ;
• then before a particular exposure of said tissue,
• determining distance D.sub.1 from said source of X-rays to said first sensor;
• determining distance D.sub.2 from said source of X-rays to said second sensor;
• after said positioning said tissue, said determining said thickness x, and said operating said X-ray apparatus at said initial settings in said sampling time small compared to said expected total exposure time, determining current through said first sensor i.sub.1, and current through said second sensor i.sub.2 ;
• calculating a tissue absorption coefficient as ##EQU10## and determining said optimum voltage, current, and focal spot size as a function of said absorption coefficient and said initial settings of voltage, current, and focal spot size.

An X-ray apparatus comprising

• an X-ray tube having a cathode which emits electrons and an anode on which said electrons impinge and which is a source of X-rays, said tube having an operating voltage which is the voltage drop between said anode and said cathode, a tube current which is the current between said anode and said cathode, and a focal spot size which is the area of said anode on which said electrons impinge, and in which said voltage, said current and said focal spot size having initial settings;
• a collimator having an opening through which said X-rays leaving said source in the direction of said opening may pass;
• means for holding an object to be examined in position for being irradiated;
• means for showing an image of X-rays which have passed through said object;
• at least one sensor which generates sensor signals for detecting radiation passed through said object and through said means for showing an image, and for calibrating said X-ray apparatus;
• and
• means for receiving said sensor signals from said at least one sensor and based on said sensor signals sending control signals which control said operating voltage, said tube current, and said focal spot size.

An x-ray apparatus comprising:

• means for generating x-rays, said means for generating having an operating anode to cathode voltage;
• means for showing an image of x-rays which have passed through an object being examined;
• means for determining thickness of said object;
• at least one sensor for detecting radiation passed through said object and through said means for showing an image, said at least one sensor generating sensor signals in response to said radiation;
• and
• means for receiving said sensor signals from said at least one sensor and receiving said thickness from said means for determining thickness, and based on said sensor signals and said thickness sending control signals which control said operating anode to cathode voltage.

A method for optimizing an x-ray image as in claim 56 further comprising the steps of:

• operating said x-ray apparatus at an initial current;
• after said sampling time determining an optimum current;
• and
• changing said initial current to said optimum current.

A method for optimizing an x-ray image as in claim 56, further comprising the steps of:

• operating said x-ray apparatus at an initial focal spot size;
• after said sampling time determining an optimum focal spot size;
• and
• changing said initial focal spot size to said optimum focal spot size.

A method for optimizing an x-ray image from an x-ray apparatus as in claim 56 in which said step of making a determination related to an optimum anode to cathode voltage comprises:

• determining the integral of voltage provided by a first sensor which detects radiation from said x-ray apparatus passing through said object;
• determining the integral of voltage provided by a second sensor which detects radiation from said x-ray apparatus not passing through said object;
• determining the ratio of said integrals;
• and
• determining from a table an attenuation factor corresponding to said ratio.

A method for optimizing an x-ray image from an x-ray apparatus as in claim 56 in which said object comprises tissue and said step of making a determination related to an optimum anode to cathode voltage comprises:

• determining the integral of voltage provided by a first sensor which detects radiation passing through said tissue from said x-ray apparatus being operated at said initial anode to cathode voltage;
• determining the integral of voltage provided by a second sensor which detects radiation from said x-ray apparatus not passing through said tissue;
• determining the ratio of said integrals;
• and
• determining a tissue density corresponding to said ratio. . An x-ray apparatus comprising:
• means for generating x-rays, said means for generating having an operating anode to cathode voltage;
• means for compressing tissue;
• means for showing an image of x-rays which have passed through said tissue;
• at least one sensor for detecting radiation passed through said tissue and through said means for showing an image, said at least one sensor generating sensor signals in response to said radiation;
• and
• means for receiving said sensor signals from said at least one sensor and based on said sensor signals sending control signals which control said
• operating anode to cathode voltage.

A method for optimizing an x-ray image from an x-ray apparatus comprising the steps of:

• positioning and compressing tissue to be exposed;
• operating said x-ray apparatus at an initial anode to cathode voltage;
• after a sampling time small in comparison to an expected total exposure time, making a determination related to an optimum anode to cathode voltage for said tissue based on radiation passed through said tissue at said initial anode to cathode voltage, and changing said initial anode to cathode voltage to said optimum anode to cathode voltage;
• and
• continuing to operate said x-ray apparatus at said optimum anode to cathode voltage until an optimum visualization of means for showing an image is achieved.

An x-ray apparatus comprising:

• means for generating x-rays, said means for generating having an operating anode to cathode voltage;
• means for showing an image of x-rays which have passed through an object being examined;
• a first sensor for detecting radiation passed through said object and through said means for showing an image, and a second sensor for detecting radiation not passed through said object, said sensors generating sensor signals in response to said radiation;
• and
• means for receiving said sensor signals from said sensors and based on said sensor signals sending control signals which control said operating anode to cathode voltage.

A method for optimizing an x-ray image from an x-ray apparatus comprising the steps of:

• positioning an object to be exposed;
• operating said x-ray apparatus at an initial anode to cathode voltage;
• after a sampling time small in comparison to an expected total exposure time, making a determination related to an optimum anode to cathode voltage for said object based on radiation passed to a first sensor through said object and on radiation passed to a second sensor not through said object at said initial anode to cathode voltage, and changing said initial anode to cathode voltage to said optimum anode to cathode voltage;
• and
• continuing to operate said x-ray apparatus at said optimum anode to cathode voltage until an optimum visualization of means for showing an image is
• achieved.

A method for optimizing an x-ray image from an x-ray apparatus comprising the steps of:

• positioning an object to be exposed;
• operating said x-ray apparatus at an initial anode to cathode voltage;
• after a sampling time small in comparison to an expected total exposure time making a determination related to an optimum anode to cathode voltage for said object, comprising:
• determining the integral of voltage provided by a sensor which detects radiation from said x-ray apparatus passing through said object, and
• determining from a table a value related to attenuation factor corresponding to said integral;
• changing said initial anode to cathode voltage to said optimum anode to cathode voltage;
• and
• continuing to operate said x-ray apparatus at said optimum anode to cathode voltage until an optimum visualization of said means for showing an image is achieved.