Method for controlling X-ray exposure
Inventors
Assignees
Publication Number
US-9784696-B2
Publication Date
2017-10-10
Expiration Date
2033-05-16
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Abstract
The present invention pertains to a system and method for X-ray imaging wherein a targeted fluence at the detector for projection images can be achieved at a plurality of projection angles around the imaging subject by control of exposure times implemented during image acquisition. Exposure time for a second projection image may be determined by the fluence in a first projection image, and in a third projection image by the fluence in a second projection image, where projection images are acquired within two degrees of one another. An acquisition parameter calculation can be configured to calculate acquisition parameters, such as said exposure times, to achieve the targeted fluence in projection images and can be coupled to a rotation controller that implements the acquisition parameters by controlling a relative angle between the imaging subject and X-ray image acquisition device.
Core Innovation
The invention addresses X-ray imaging, particularly in computed tomography (CT), by introducing a system and method that enables achieving a targeted fluence at the detector for each projection image at multiple projection angles around the imaging subject. This is accomplished by dynamically controlling and modulating exposure times during image acquisition, where exposure times for subsequent projections are based on fluence measurements from preceding projections taken at close angular proximity, within two degrees. An acquisition parameter calculation can determine these exposure parameters and interact with a rotation controller to achieve the desired relative angles and exposure conditions.
The background explains that in current CT applications, microfocus X-ray sources are often used due to their high resolution, but their limited power and the high attenuation properties of materials can lead to significantly longer scan times, which decreases throughput. Furthermore, existing tube current modulation techniques are constrained by maximum allowable current and are not optimal for ensuring consistently high image quality across all projections, resulting in possible noise and artifacts in the final reconstructed images.
This invention overcomes those limitations by actively determining and applying tailored exposure times for each projection angle based on measured or predicted attenuation characteristics. It allows either continuous or stepwise rotation of the imaging subject or image acquisition device, with real-time adjustment of exposure and acquisition parameters to ensure the desired quality (fluence) at the detector for each image. The result is consistent image quality and improved utility for industrial metrology, dental imaging, and other CT applications, even within constraints on scan time and X-ray tube power.
Claims Coverage
There is one independent claim that defines several inventive features for X-ray imaging acquisition and reconstruction methodologies.
Acquiring X-ray images at multiple projection angles with targeted exposure for each angle
- The method requires positioning the object in the field of view of an X-ray image acquisition device. - A set of unique projection angles is selected, spanning at least 45 degrees around the object. - For each projection angle, a targeted X-ray exposure at a detector region is chosen. - The method includes determining a total exposure duration time for each projection angle corresponding to the targeted exposure. - The set of targeted total exposure duration times is implemented in the image acquisition device to acquire an image data set. - An X-ray image is reconstructed from the obtained image data set.
The main inventive feature involves selectively determining and controlling exposure duration times for each projection angle during X-ray imaging, ensuring a targeted exposure at the detector for every projection angle, and reconstructing an X-ray image from the collected data set.
Stated Advantages
Provides high image quality within the scan time and tube power constraints of computed tomography applications.
Reduces the occurrence of noise and artifacts in reconstructed images by achieving targeted detector fluence at each projection angle.
Allows for modulation of exposure without necessarily increasing total scan time, compensating increased exposure at high-attenuation angles with decreased exposure at transparent angles.
Enables reduced occurrences of detector saturation by decreasing exposure times at more transparent projection angles.
Particularly useful for applications where long scan times are acceptable, such as industrial metrology and dental CT, ensuring high-quality imaging of complex or dense objects.
Documented Applications
Computed tomography systems in industrial metrology, facilitating non-destructive measurement or validation of work pieces and components.
Dental computed tomography imaging, including assessment of teeth, jaw bone structure, nerve positioning, and surgical planning.
Cone beam computed tomography and flat panel detector systems for both metrology and dental fields.
Tomosynthesis applications, including digital tomosynthesis and mammography, using controlled exposure at various projection angles.
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