Gain calibration and correction in radiation system
Among other things, one or more techniques and/or systems for calibration of a radiation system to compute a gain correction(s) are provided. A calibration procedure is performed during which a portion of the detector array is shadowed by an object, causing the detector array to be non-uniformly exposed to radiation. A portion of a projection generated from the calibration procedure and indicative of radiation that did not traverse the object is separated from a portion of the projection indicative of radiation that did traverse the object, and a gain correction(s) is computed from the portion of the projection indicative of radiation that did not traverse the object (e.g., and is thus indicative of radiation that merely traversed air).
1. A method of calibrating a computed tomography (CT) system when a field of view is partially obstructed by an object, comprising:
acquiring a projection, corresponding to a first view angle of a CT scan, from a calibration procedure performed while the field of view was partially obstructed by the object, the projection comprising object projection data indicative of radiation that traversed the object and calibration projection data indicative of radiation that did not traverse the object;
separating the calibration projection data from the object projection data, the separating comprising:
averaging measurements of the projection acquired from a plurality of detector cells to determine an average measurement for the projection; and
comparing the average measurement for the projection to a measurement acquired from each detector cell of the plurality of detector cells to identify the calibration projection data; and
computing one or more gain corrections as a function of the calibration projection data, the one or more gain corrections utilized during an examination procedure to correct measurements yielded from a detector array of the CT system.
2. The method of claim 1 , the comparing comprising:
identifying measurements, acquired from detector cells of the plurality of detector cells, that are within a specified threshold of the average measurement as the calibration projection data.
3. The method of claim 1 , comprising:
acquiring a second projection, corresponding to a second view angle of the CT scan, from the calibration procedure, the second projection comprising second object projection data indicative of radiation that traversed the object and second calibration projection data indicative of radiation that did not traverse the object;
separating the second calibration projection data from the second object projection data; and
compiling the calibration projection data of the projection with the second calibration projection data of the second projection to generate compiled calibration projection data.
4. The method of claim 3 , the computing comprising:
computing the one or more gain corrections as a function of the compiled calibration projection data.
5. The method of claim 3 , the projection representative of measurements acquired during a first rotation of at least one of the detector array or a radiation source of the CT system relative to the object and the second projection representative of measurements acquired during a second rotation.
6. The method of claim 5 , the first view angle and the second view angle being a same view, and the object located at a first position relative to an axis of rotation for at least one of the detector array or the radiation source during the first rotation and located at a second position relative to the axis of rotation during the second rotation.
7. The method of claim 1 , comprising:
rotating at least one of a radiation source of the CT system or the detector array relative the object during the calibration procedure to view the object at multiple view angles.
8. The method of claim 1 , comprising:
storing the one or more gain corrections in an air table.
9. A computed tomography (CT) system, comprising:
a radiation source configured to emit radiation;
a detector array comprising a plurality of detector cells configured to detect at least some of the radiation;
a projection separation component configured to:
acquire a projection, corresponding to a first view angle of a CT scan, from a calibration procedure performed while a field of view between the radiation source and the detector array was partially obstructed by an object;
average measurements of the projection acquired from a plurality of detector cells to determine an average measurement for the projection; and
compare the average measurement for the projection to a measurement acquired from each detector cell of the plurality of detector cells to identify calibration projection data, indicative of radiation that did not traverse the object, comprised within the projection; and
a gain computation component configured to compute one or more gain corrections using the calibration projection data to apply to measurements yielded from an examination of a subject.
10. The system of claim 9 , the projection separation component configured to:
identifying measurements, acquired from detector cells of the plurality of detector cells, that are within a specified threshold of the average measurement as the calibration projection data.
11. The system of claim 9 , comprising a compilation component configured to compile the calibration projection data of the projection with second calibration projection data of a second projection to generate compiled calibration projection data.
12. The system of claim 11 , the projection representative of measurements acquired during a first rotation of at least one of the detector array or the radiation source relative to the object and the second projection representative of measurements acquired during a second rotation.
13. The system of claim 9 , comprising an object translation component configured to move the object relative to an axis of rotation for at least one of the detector array or the radiation source during the calibration procedure.
14. The system of claim 13 , the object translation component configured to locate the object in a first position relative to the axis of rotation during a first rotation from which measurements represented in the projection are acquired and to locate the object in a second position relative to the axis of rotation during a second rotation from which measurements represented in a second projection, corresponding to a first view angle of the CT scan, are acquired.
15. The system of claim 9 , comprising:
a compilation component configured to compile the calibration projection data of the projection with second calibration projection data of a second projection to generate compiled calibration projection data, and
the gain computation component configured to compute the one or more gain corrections as a function of the compiled calibration projection data.