News Column

Patent Issued for Radiation Imaging Device

August 6, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventor Baba, Rika (Kodaira, JP), filed on November 24, 2009, was published online on July 22, 2014.

The patent's assignee for patent number 8787520 is Hitachi Medical Corporation (Tokyo, JP).

News editors obtained the following quote from the background information supplied by the inventors: "A radiation imaging apparatus measures radiation (X-rays) passing through a subject, and obtains a static image or a moving image of the subject. On this occasion, scattered X-rays and beam hardening are considered as factors which reduce image contrast and precision of measured values and deteriorate image quality. The scattered X-rays, which are generated when X-rays pass through the subject, are mixed with direct X-rays being a net transmission amount, and incident on a detector which detects X-rays. The beam hardening, which occurs when X-rays passes through the subject and a part of energy is absorbed by the subject, causing variations in energy distribution, changes an X-ray absorption coefficient of the subject.

"By way of example, there is known a technique for correcting influences of scattered X-rays and beam hardening on measured data in a cone beam CT (e.g., see the patent document 1)."

As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventor's summary information for this patent: "Problem to be Solved by the Invention

"In order to perform highly precise correction on influences of scattered X-rays and beam hardening, it is necessary to favorably separate those influences and obtain highly precise correcting functions respectively. The patent document 1 describes to separate those influences for correction, but it refers to none of the followings; a specific separation method, a correction method, and the functions used for the correction.

"In addition, the patent document 1 describes to perform the correction on the scattered X-rays (hereinafter, referred to as 'scattered X-ray correction') after the correction on the beam hardening is performed (hereinafter, referred to as 'beam hardening correction'). An effect that the beam hardening has on the measured data varies sensitively depending on the thickness of the subject. On the other hand, an effect that the scattered X-rays have on the measured data is slow to respond to a local change of the subject. Therefore, if the corrections are performed sequentially in the order as described above, local variation of the subject have too much influences on the scattered X-ray correction, and this may cause an excessive correction.

"The present invention has been made in view of the situation above, and the object of the invention is to provide a technique of an X-ray imaging apparatus which determines a correcting function for correcting scattered X-rays and a correcting function for correcting beam hardening, easily with high precision, and performs corrections in an appropriate order by using thus determined correction functions with a high degree of correcting precision, thereby improving the precision in correction and enhancing an image quality.

"Means to Solve the Problem

"In the present invention, by using a beam hardening correction function and a scattered X-ray correction function which are calculated from measured data for calculating the correction functions, the scattered X-ray correction and the beam hardening correction are performed sequentially in this order. The scattered X-ray function approximates data items as to each transmission distance, the data items being measured with changes in a transmission distance and with changes in a scattered X-ray amount, and associates a correction value being obtained with transmittance data. On the other hand, the beam hardening correction function converts data items measured with changes in the transmission distance into projection data items, and obtains an ideal value as a beam hardening amount by subjecting the projection data items to linear approximation.

"Specifically, the present invention is directed to providing 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.

"The present invention may be directed to providing the radiation imaging apparatus, 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 the scattered radiation amount is set to be nearly zero, and a second projection data item calculated from a function that returns the beam hardening amount in accordance with the transmission distance, and further the beam hardening correction function returns a beam hardening correction value in response to the corrected detection result after correcting the influence of the scattered radiation; and 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.

"The present invention may be directed to providing the radiation imaging apparatus, 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 further the scattered radiation correction function is a function for returning a correction value of the scattered radiation amount in response to the detection result; and 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.

"Alternatively, the present invention may be directed to providing a radiation imaging apparatus, 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 further the scattered radiation correction function is the function for returning a correction value of the scattered radiation amount according to the detection result, and the correction means converts the first 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.

"Effect of the Invention

"According to the present invention, it is possible to use in the X-ray imaging apparatus, a correction function for the scattered X-ray correction and a correction function for the beam hardening correction, the functions being easily generated and having a high degree of correction precision, and to perform corrections sequentially in appropriate order. Therefore, precision in correction is enhanced, thereby improving the image quality."

For additional information on this patent, see: Baba, Rika. Radiation Imaging Device. U.S. Patent Number 8787520, filed November 24, 2009, and published online on July 22, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8787520.PN.&OS=PN/8787520RS=PN/8787520

Keywords for this news article include: Hitachi Medical Corporation.

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Source: Journal of Engineering


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