Radiation imaging device

• US 8,787,520 B2
• Filed: 11/24/2009
• Issued: 07/22/2014
• Est. Priority Date: 11/27/2008
• Status: Expired due to Fees

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi Medical Corporation (Hitachi, Ltd.)
• Inventors: Baba, Rika
• Primary Examiner(s): Ton, Toan
• Assistant Examiner(s): CORBETT, JOHN M
• Application Number:
  US13/131,604
• Publication Number:
  US 20110235773A1
• Time in Patent Office: 1,701 Days
• Field of Search: 378/7, 382/131
• US Class Current: 378/7
• CPC Class Codes: A61B 6/032 Transmission computed tomography [CT]
• CPC Class Codes: A61B 6/4441 the rigid structure being a C-arm or U-arm
• CPC Class Codes: A61B 6/4464 the source unit or the detector unit being mounted to ceiling
• CPC Class Codes: A61B 6/585 Calibration of detector units
• CPC Class Codes: G01T 1/00 Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation G01T3/00, G01T5/00 take precedence
• CPC Class Codes: G06T 11/005 Specific pre-processing for tomographic reconstruction, e.g. calibration, source positioning, rebinning, scatter correction, retrospective gating

Abstract

Disclosed is an X-ray imaging apparatus in which a correction function used to correct scattered X-rays and a correction function used to correct beam hardening can be simply and precisely determined so that the correcting operations are performed in an appropriate sequence using the correction functions thus determined to enhance the precision in the correction and improve the image quality. The scattered X-rays and the beam hardening are corrected sequentially in this order, using the scattered X-ray correction function and the beam hardening correction function, both calculated using measured data for calculating the correction functions. The scattered X-ray correction function approximates as to each transmission distance, the data measured with changes in the transmission distance and with changes in the scattered X-ray amount, and associates the correction value thus obtained with transmittance data. Upon calculation of the beam hardening correction function, data measured with changes in the transmission distance is converted into projection data and is linearly approximated to obtain an ideal amount of beam hardening.

Claims

1. A radiation imaging apparatus, comprising:

a radiation source for irradiating a subject with radiation;

a detector having multiple pixels for detecting the radiation;

a storage means for storing a scattered radiation correction function for correcting influence of scattered radiation on a detection result obtained from the detector, and a beam hardening correction function for correcting influence of beam hardening on the corrected detection result; and

a correction means for correcting the detection result by the scattered radiation correction function, and for correcting the corrected detection result by the beam hardening correction function,

wherein the scattered radiation correction function is calculated by using data measured with changes in a transmission distance and with changes in a scattered radiation amount, and returns a correction value of the scattered radiation amount in response to the detection result,

wherein the scattered radiation correction function is obtained by approximating a relation between a first transmittance data item corresponding to a first scattered radiation amount obtained from a first function that approximates a relation between the transmittance data and the scattered radiation amount with respect to each transmission distance, and a difference value obtained by subtracting the transmittance data when the scattered radiation amount obtained from the first function is nearly zero, from the first transmittance data item, and

wherein the correction means converts the detection result detected by the detector using the first scattered radiation amount, into the transmittance data, and corrects the influence of the scattered radiation by subtracting the correction value calculated from the transmittance data from the transmittance data.

2. The radiation imaging apparatus according to claim 1, wherein the beam hardening correction function is calculated by using data measured with changes in a transmission distance, and returns a beam hardening correction value in response to the corrected detection result after correcting the influence of the scattered radiation.

3. The radiation imaging apparatus according to claim 2,

wherein the beam hardening correction function is a linear function passing through an original point, obtained by approximating a relation between a first projection data item obtained by converting the detection result measured with changes in the transmission distance when a scattered radiation amount is set to be nearly zero, and a second projection data item calculated from a function that returns a beam hardening amount in accordance with the transmission distance, and

wherein the correction means corrects transmittance data obtained from the detection result from the detector using the scattered radiation correction function, then converts the corrected transmittance data into a third projection data item, and replaces the third projection data item by the beam hardening correction value associated with the third projection data item, thereby correcting the influence of the beam hardening.

4. The radiation imaging apparatus according to claim 1,

wherein the scattered radiation correction function is expressed by:

5. The radiation imaging apparatus according to claim 1, further comprising;

a collimator for adjusting an amount of radiation on the subject,

wherein the collimator is adjusted to have a collimator condition of a fan beam computed tomography (CT), so as to establish a state that the scattered radiation amount is nearly zero.

6. The radiation imaging apparatus according to claim 1, further comprising;

a correction function calculation means for calculating at least one of the scattered radiation correction function and the beam hardening correction function, respectively from the detection result.

7. The radiation imaging apparatus according to claim 1, further comprising

a controller for moving the radiation source and the detector relative to the subject;

and

a reconstruction processor for reconstructing an image from the corrected detection result,

wherein the controller rotates the radiation source and the detector relative to the subject, and

wherein the reconstruction processor performs a reconstructing operation by using the corrected detection result to acquire a three-dimensional image.

8. The radiation imaging apparatus according to claim 1,further comprising;

a collimator for adjusting an amount of radiation on the subject,

wherein the scattered X-ray radiation amount is changed by changing a width between shielding plates forming the collimator.

9. A radiation imaging apparatus, comprising:

a radiation source for irradiating a subject with radiation;

a detector having multiple pixels for detecting the radiation;

a storage means for storing a scattered radiation correction function for correcting influence of scattered radiation on a detection result obtained from the detector, and a beam hardening correction function for correcting influence of beam hardening on the corrected detection result; and

a correction means for correcting the detection result by the scattered radiation correction function, and for correcting the corrected detection result by the beam hardening correction function,

wherein the scattered radiation correction function is calculated by using data measured with changes in a transmission distance and with changes in a scattered radiation amount, and returns a correction value of the scattered radiation amount in response to the detection result,

wherein the scattered radiation correction function is obtained by approximating a relation between a first transmittance data item corresponding to a first scattered radiation amount obtained from a first function that approximates a relation between the transmittance data and the scattered radiation amount with respect to each transmission distance, and a second transmittance data when the scattered radiation amount obtained from the first function is nearly zero, and

wherein the correction means converts the detection result detected by the detector using the first scattered radiation amount, into the transmittance data, and corrects the influence of the scattered radiation by replacing the transmittance data with the correction value calculated from the transmittance data.

10. The radiation imaging apparatus according to claim 9, wherein the beam hardening correction function is calculated by using data measured with changes in a transmission distance, and returns a beam hardening correction value in response to the corrected detection result after correcting the influence of the scattered radiation.

11. The radiation imaging apparatus according to claim 10,

wherein the beam hardening correction function is a linear function passing through an original point, obtained by approximating a relation between a first projection data item obtained by converting the detection result measured with changes in the transmission distance when a scattered radiation amount is set to be nearly zero, and a second projection data item calculated from a function that returns a beam hardening amount in accordance with the transmission distance, and

wherein the correction means corrects transmittance data obtained from the detection result from the detector using the scattered radiation correction function, then converts the corrected transmittance data into a third projection data item, and replaces the third projection data item by the beam hardening correction value associated with the third projection data item, thereby correcting the influence of the beam hardening.

12. The radiation imaging apparatus according to claim 9, further comprising:

a collimator for adjusting an amount of radiation on the subject,

wherein the collimator is adjusted to have a collimator condition of a fan beam computed tomography (CT), so as to establish a state that the scattered radiation amount is nearly zero.

13. The radiation imaging apparatus according to claim 9, further comprising:

a correction function calculation means for calculating at least one of the scattered radiation correction function and the beam hardening correction function respectively from the detection result.

14. The radiation imaging apparatus according to claim 9, further comprising:

a controller for moving the radiation source and the detector relative to the subject; and

a reconstruction processor for reconstructing an image from the corrected detection result,

wherein the controller rotates the radiation source and the detector relative to the subject, and

wherein the reconstruction processor performs a reconstructing operation by using the corrected detection result to acquire a three-dimensional image.

15. The radiation imaging apparatus according to claim 9, further comprising:

a collimator for adjusting an amount of radiation on the subject,

wherein the scattered X-ray radiation amount is changed by changing a width between shielding plates forming the collimator.

16. A radiation imaging apparatus, comprising:

a radiation source for irradiating a subject with radiation;

a detector having multiple pixels for detecting the radiation;

a storage means for storing a scattered radiation correction function for correcting influence of scattered radiation on a detection result obtained from the detector, and a beam hardening correction function for correcting influence of beam hardening on the corrected detection result;

a correction means for correcting the detection result by the scattered radiation correction function, and for correcting the corrected detection result by the beam hardening correction; and

a correction function calculation means for calculating the beam hardening correction function from the detection result,

wherein the correction function calculation means comprises;

a beam hardening function determination means for determining a beam hardening function for specifying an ideal value of the beam hardening amount in accordance with a transmission distance; and

a beam hardening correction function generation means for calculating and plotting on a graph, the ideal value at an identical transmission distance by using the beam hardening function, with respect to each first projection data obtained by converting the transmittance data being obtained by minimizing the scattered radiation amount, approximating the values by an approximate curve, thereby determining the beam hardening correction function for returning projection data after the beam hardening correction, associated with the projection data calculated from the detection result.

17. The radiation imaging apparatus according to claim 16, further comprising;

a correction function calculation measuring means for performing correction function calculation measurement to obtain the first projection data by converting the transmittance data obtained by minimizing the scattered radiation amount at multiple transmission distances,

wherein beam hardening function determination means plots on a graph the first projection data with respect to each transmission distance, approximates the data by a linear function passing through an original point, using the transmission distance as a variable, thereby determining the beam hardening function.

18. The radiation imaging apparatus according to claim 16, wherein the beam hardening correction function is calculated by using data measured with changes in a transmission distance, and returns a beam hardening correction value in response to the corrected detection result after correcting the influence of the scattered radiation.

19. The radiation imaging apparatus according to claim 16, further comprising:

a collimator for adjusting an amount of radiation on the subject,

wherein the collimator is adjusted to have a collimator condition of a fan beam computed tomography (CT), so as to establish a state that the scattered radiation amount is nearly zero.

20. The radiation imaging apparatus according to claim 16, further comprising:

a correction function calculation means for calculating at least one of the scattered radiation correction function and the beam hardening correction function, respectively from the detection result.