X-RAY EXAMINATION DEVICE AND METHOD

• US 20120121063A1
• Filed: 07/20/2010
• Published: 05/17/2012
• Est. Priority Date: 07/29/2009
• Status: Active Grant

• Current Assignee: Koninklijke Philips N.V.
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Proksa, Roland
• Granted Patent: US 8,842,805 B2
• Time in Patent Office: Days
• US Class Current: 378/16
• CPC Class Codes: A61B 6/032 Transmission computed tomography [CT]
• CPC Class Codes: A61B 6/4021 involving movement of the focal spot
• CPC Class Codes: A61B 6/405 Source units specially adapted to modify characteristics of the beam during the data acquisition process A61B6/4021, A61B6/4035 take precedence
• CPC Class Codes: A61B 6/4233 using matrix detectors
• CPC Class Codes: A61B 6/4241 using energy resolving detectors, e.g. photon counting
• CPC Class Codes: A61B 6/482 involving multiple energy imaging
• CPC Class Codes: A61B 6/508 for non-human patients
• CPC Class Codes: A61B 6/542 involving control of exposure
• CPC Class Codes: A61B 6/585 Calibration of detector units
• CPC Class Codes: G01T 1/171 Compensation of dead-time counting losses see provisionally also G01T1/17

Abstract

The present invention relates to an X-ray examination device and a corresponding method. A fast and periodical modulation of the X-ray flux within each detection interval is performed having a low X-ray flux at the beginning of the detection interval to ensure that no detection channel is overloaded. With increasing the X-ray flux particularly the peripheral detection channels will nm into saturation, which is detected. A saturated detector channel is stopped from further detecting radiation, and the time of effective radiation detection without saturation is measured for correcting those detection signals. From all detection signals, after any correction of detection signals from saturated detection channels, an X-ray image can be reconstructed.

Claims

1. An X-ray examination device comprising:

an X-ray source for emitting an X-ray beam of X-ray radiation while rotating around an imaging region,

an X-ray detector (6) having a plurality of detector cells for detecting X-ray radiation emitted by said X-ray source and having passed through said imaging region and for outputting detection signals,

a source control unit for modulating an X-ray flux during detection intervals, starting at a beginning of a detection interval with an X-ray flux level that avoids saturation of the X-ray detector in the direct X-ray beam and thereafter increasing the X-ray flux,

a detection control unit for evaluating said detection signals, the detection control unit comprising

i) a saturation detection unit for detecting, during a detection interval, saturation at predetermined detector cells and/or groups of detector cells,

ii) a detection stopping unit for stopping detection of X-ray radiation at saturated detector cells or groups of detector cells for a remaining time of the detection interval and

iii) a time measuring unit for obtaining a time information indicating an effective time portion of the detection interval during which X-ray radiation has been detected without saturation, and

a signal processing device for reconstructing an X-ray image based on the detection signals, wherein detections signals of detector cells and/or groups of detector cells at which detection of X-ray radiation has been stopped during a detection interval due to saturation are corrected using the time information.

2. The X-ray examination device as claimed in claim 1, wherein said source control unit is adapted for modulating the X-ray flux in such a manner that the X-ray flux continuously increases over time during a detection interval.

3. The X-ray examination device as claimed in claim 1, wherein said source control unit is adapted for modulating the X-ray flux of said X-ray source according to a saw-tooth like function.

4. The X-ray examination device as claimed in claim 1, wherein said X-ray detector is a photon-counting X-ray detector.

5. The X-ray examination device as claimed in claim 1, wherein said detection control unit comprises a plurality of detection control sub-units for a plurality of individual detector cells and/or groups of detector cells, in particular for individual detector cells and/or groups of detector cells at the peripheries of the X-ray detector.

6. The X-ray examination device as claimed in claim 1, wherein said detection control unit comprises a detection control sub-unit for each detector cell.

7. The X-ray examination device as claimed in claim 1, wherein said saturation detection unit comprise a current measuring unit for measuring the detector current, in particular the mean detector current, at the output of a detector cell or a group of detector cells, and a comparator for comparing the detector current to a reference current indicating saturation.

8. The X-ray examination device as claimed in claim 1, wherein said detection stopping unit is adapted for registering and/or evaluating a detection signal from a saturated detector cell or group of detector cells.

9. The X-ray examination device as claimed in claim 1, wherein said signal processing device is adapted for correcting a detection signal of a detector cell and/or a group of detector cells, at which detection of X-ray radiation has been stopped during a detection interval, by estimating the missing detection signal portion of the detection signal for the remaining time interval of the detection interval, during which the X-ray radiation has not been detected, based on a known flux modulation function, the measured detection signal portion and the time information obtained for this detection signal.

10. An X-ray examination method comprising the steps of:

emitting an X-ray beam of X-ray radiation while rotating around an imaging region,

detecting X-ray radiation having passed through said imaging region and outputting detection signals by an X-ray detector having a plurality of detector cells,

modulating the X-ray flux during detection intervals, starting at a beginning of a detection interval with an X-ray flux level that avoids saturation of the X-ray detector in the direct X-ray beam and thereafter increasing the X-ray flux,

evaluating said detection signals, the evaluating step comprising

i) detecting, during a detection interval, saturation at predetermined detector cells and/or groups of detector cells,

ii) stopping detection of X-ray radiation at saturated detector cells or groups of detector cells for a remaining time of the detection interval, and

iii) obtaining a time information indicating an effective time portion of the detection interval during which X-ray radiation has been detected without saturation, and

reconstructing an X-ray image based on the detection signals, wherein detections signals of detector cells and/or groups of detector cells at which detection of X-ray radiation has been stopped during a detection interval due to saturation are corrected using the time information.

11. A computer program comprising program code means for causing a computer to control an X-ray examination device comprising an X-ray source for emitting an X-ray beam of X-ray radiation while rotating around an imaging region, and an X-ray detector having a plurality of detector cells for detecting X-ray radiation emitted by said X-ray source and having passed through said imaging region and for outputting detection signals, said computer program comprising program code means to control the X-ray examination device to

modulate the X-ray flux during detection intervals, starting at a beginning of a detection interval with an X-ray flux level that avoids saturation of the X-ray detector in the direct X-ray beam and thereafter increasing the X-ray flux,

evaluate said detection signals, the evaluation comprising the steps of

i) detecting, during a detection interval, saturation at predetermined detector cells and/or groups of detector cells,

ii) stopping detection of X-ray radiation at saturated detector cells or groups of detector cells for a remaining time of the detection interval and

iii) obtaining a time information indicating an effective time portion of the detection interval during which X-ray radiation has been detected without saturation, and

reconstruct an X-ray image based on the detection signals, wherein detections signals of detector cells and/or groups of detector cells at which detection of X-ray radiation has been stopped during a detection interval due to saturation are corrected using the time information.