CROSS-REFERENCE TO RELATED APPLICATION

This application is based on and claims the benefit of priority from earlier Japanese Patent Application No. 2017-120433 filed on Jun. 20, 2017, the description of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an X-ray device, an X-ray inspection method, and a data processing apparatus which scan an object with X-rays to acquire X-ray transmission data and inspect the object based on the acquired data, and in particular, to the X-ray device, the X-ray inspection method, and the data processing apparatus which focus on differences in respective X-ray transmission characteristics provided by a plurality of energy ranges (i.e., energy bins) set on the X-ray energy spectrum.

BACKGROUND ART

In recent years, inspection using X-ray beams to check the internal state of an object has been widely used in various fields, such as foreign matter inspection of food, baggage inspection, and medical X-ray mammography.

For example, airports, public facilities, or the like use a content inspection that is an inspection of the types and shapes of baggage or mail contents, which is carried out without opening the baggage or mail. It is desired that such a content inspection should find out the presence of foreign matters (for example, metal pieces), if mingled into known types of objects (for example, food such as bread), and specify the types of the foreign matters. In other words, there is a potentially higher need for determining the types and/or shapes of objects (materials) by using X-rays.

For such needs, for example, there is proposed a technique as set forth in a patent publication 1 (JP-A-2010-091483, title of the invention is a “method and apparatus for inspecting foreign matters”). This patent publication 1 is based on an inspection technique called a dual energy technique (or a subtraction technique). This inspection technique uses the fact that two types of X-rays of energy (that is, two types of X-rays having different wavelengths) penetrating a substance arises a difference therebetween in X-ray transmission information. Practically, this inspection technique uses the following processing. First, two types of X-ray images based on lower X-ray energy and higher X-ray energy are made simultaneously, and a difference between the images is calculated. Then, from the resultant image difference, image components of a mingled foreign matter are extracted. The image components are then subjected to threshold processing to detect the foreign matter.

In the patent publication 1, optimum parameters for the difference calculation are set automatically, in addition to performing the foregoing basic process, to detect foreign maters at higher sensitivity. The patent publication 1 suggests use of a detector capable of detecting incidence of X-ray photons, with X-ray photon energy being discriminated. In other words, as a measure to simultaneously obtain two types of X-rays having lower energy and higher energy, the patent publication 1 suggests use of a well-known photon-counting X-ray radiation and detection system.

There is known another inspection method based on the foregoing dual energy technique as described in a non-patent publication 1. This non-patent publication 1 provides a detecting system using a basic configuration for the dual energy technique. With this configuration, an overlap of objects on the conveyance belt is ensured not to be mistakenly taken as foreign matters, so that foreign matters are detected with higher sensitivity.

When using the dual energy technique described in the patent publication 1 and the non-patent publication 1, an object or foreign matters mingled into the object may be detected with sensitivity that is improved to some extent. The term “improved to some extent” means that the detection sensitivity is improved if imaging conditions and/or image processing conditions are narrowed to specific conditions. Thus, detection conducted under such specific conditions limits imaging objects or imaging conditions to which the technique is applied, that is, narrows the conditions for detecting foreign matters.

Specifically, the dual energy technique described in these publications offers accuracy that is so low as not to reflect the difference in attenuation degree of the X-ray photon energy and materials, and gives little consideration to the electric noise or nonlinear characteristics of X-ray detection circuits, which may be unignorable problems.

CITATION LIST

Patent References

[Patent Publication 1] JP-A-2010-091483
[Non-Patent Publication 1]“Development of dual-energy X-ray foreign matter detector”, No. 87, March 2012, Anritsu Technical

SUMMARY OF THE INVENTION

Technical Problem

By the way, in X-ray dental applications such as an X-ray panoramic imaging device, the X-ray beams pass through hard tissues such as teeth and/or jaws. The X-ray beams which have entered such objects are subjected to beam hardening (beam hardening phenomenon), whereby a detected X-ray spectrum is shifted relatively to a higher energy side thereof. In other words, due to the beam hardening, the quantity of X-rays (the number of X-ray photons) in a lower energy side is reduced, thereby being influenced more hardly by noise.

In addition, influence of the beam hardening will also appear such that the effective (average) energy amounts of the respective X-ray energy ranges depend on object thicknesses. Particularly, as the X-ray energy range shifts toward its lower energy side in the X-ray spectrum, fluctuations occurring due to differences among object thickness become prominent, thereby reducing quantitative quality of reconstructed images.

With consideration of such drawbacks, an object of the present invention is to reduce the influence of the beam hardening on the attenuation of the X-ray beams, obtain a reduction of image noise and improved image contrast, and secure more quantitative inspection performance as to differences of object thicknesses in the X-ray paths when an X-ray inspection of objects is performed.

Solution to the Problems

With consideration of the forgoing situation, one mode of the present invention provides an X-ray device which inspects an object, wherein beam-shaped X-rays are radiated to the object and the object is inspected based on amounts of the X-rays transmitted through the object. This device is characterized in that the device includes:

X-ray generating means that generates the X-rays;

X-ray detecting means that detects transmitted amounts of the X-rays generated by the X-ray generating means and transmitted through the object in each of n-number X-ray energy bins (n is a positive integer of 2 or more) which are set in advance to the X-rays, and outputs detection signals corresponding to the transmitted amounts;

information acquiring means that acquires, based on the detection signals detected by X-ray detecting means, information showing a thickness t of the object and an average linear attenuation coefficient μ in a transmission direction of fluxes of the X-rays, in each of the energy bins; and

pixel data calculating means that calculates pixel data composed of pixel values each obtained by multiplying addition information by the thickness t, based on the information acquired by the information acquiring means, the addition information being obtained by mutual addition of the average linear attenuation coefficients μ in the respective energy bins.

Practically, the X-ray device is for example an in-line X-ray foreign matter inspection apparatus, a substance identifying apparatus for identifying (estimating or evaluating) the type and/or property of an object (or compositions thereof) using X-rays, a medical apparatus for X-ray mammography, or a dental X-ray diagnostic apparatus for diagnosing states of tooth rows and/or gums. The “object” is, for example, an object itself to be X-ray inspected or foreign matter which is present in an object. For medial X-ray devices, the “object” is the breast, oral cavity, or limb, which is parts of a human or animal body.

Further, the energy ranges of the X-rays are defined as partial energy ranges which are set to a continuous energy spectrum of the X-rays (i.e., polychromatic X-rays). In the present invention, the energy ranges are previously set as n-number energy ranges (n is a positive integer of two or more). For example, in a case where the X-rays are detected in photon-counting measurement under the “n”=3, the energy ranges are set as a lower energy range of 18 to 23 key, an intermediate energy range of 23 to 38 keV, and a higher energy range of 38 to 50 keV. When the X-ray detection is carried out under the dual energy method (normally n=2), the energy ranges are set as a lower energy range of 18 to 23 keV and a higher energy range of 38 to 50 keV. The energy range is also referred to as energy bins.

Incidentally the foregoing information acquisition and image data calculation can be performed every energy range (bin) and every pixel or every pixel area consisting of two or more pixels. In addition, the acquisition of characteristics and calculation of correcting data can be applied to a detection signal outputted from a detector (or sensor) having a single pixel or outputted form an X-ray spectrometer.

Effect of the Invention

In the present invention, the image data calculating means calculates image data composed of pixel values which are multiplied values of addition information by a thickness t taken along an X-ray path in an object. The addition information is obtained by mutual addition of the average linear attenuation coefficients μ in the respective energy ranges (bins). The beam hardening will cause an X-ray amount (i.e., the number of X-ray photons) in the lower energy ranges to decrease, thereby relatively increasing noise component. However, the image data calculated in the present invention suppress the noise components from increasing relatively to signals, compared to a method of calculating the image data based on the square of the linear attenuation coefficient μ. In addition, an effective energy amount in the lower energy ranges increase relatively, so that the liner attenuation coefficient μ becomes smaller. However, since there can be provided larger contribution of a relative noise reduction, a CNR (contrast to noise ratio) can be improved without lowering the image contrast, so that the conventional image contrast is maintained.

Moreover, the pixel values are calculated by being multiplied by the thickness t, thereby representing a quantitative performance to the thickness t. From these points of view, the X-ray inspection can be conducted such that influence of the beam hardening on the X-ray attenuation is reduced, nose in the images is suppressed from increasing and a higher image contrast is provided, thus securing a quantitate analysis based on an object thickness in an X-ray path direction.

