WO2000057788A1

WO2000057788A1 - Method and apparatus for x-ray tomosynthesis

Info

Publication number: WO2000057788A1
Application number: PCT/FI2000/000216
Authority: WO
Inventors: Jyrki OJANPERÄ; Douglas Woods
Original assignee: Instrumentarium Corporation
Priority date: 1999-03-18
Filing date: 2000-03-17
Publication date: 2000-10-05
Also published as: FI990608A0; FI105448B

Abstract

The invention relates to a method for X-ray photography of the head and neck area, especially for producing three-dimensional X-ray photographs of the object to be imaged. In the method is used an imaging apparatus (1) equipped with an X-ray source and a digital image sensor which is positioned in the radiation field of the X-ray source of the imaging apparatus (1), behind the object to be imaged each time, as viewed from the X-ray source. In the method relating to the invention, the radiation source of the apparatus (1) is positioned on an irradiation plane located at a desired distance from the image sensor and the radiation source is moved on th said irradiation plane along an essentially circular path (20) in such a way that the central ray (21) of the X-ray source is directed at the same point (23) during the movement. The sensor is positioned at this point (23) or in its vicinity. In order to image the object from different directions, the X-ray source is optionally stopped at the desired points (22) of the circular path (20) for the duration of exposure in each desired direction of imaging. The invention also relates to an apparatus for X-ray photography of the head and neck area.

Description

Method and apparatus for X-ray to osynt esis

The present invention relates to a method for X-ray photography of the head and neck area, especially for producing three-dimensional X-ray images of the object to be imaged, in which method is used an imaging apparatus equipped with an X- ray source and a digital image sensor which is immobile at least during exposure, the image sensor being positioned in the radiation field of the X-ray source of the imaging apparatus, behind the object to be imaged each time, as viewed from the X-ray source. The invention further relates to an apparatus for X-ray photography of the head and neck area, especially for producing three-dimensional X-ray images of the object to be imaged, the apparatus comprising an imaging apparatus equipped with an X-ray source and a digital image sensor which is positioned in the radiation field of the X-ray source of the imaging apparatus so as to be immobile at least during exposure, behind the object to be imaged each time, as viewed from the X-ray source.

Three-dimensional imaging methods, for example, those disclosed in US patents 5668 844 and 5 359637, require that several images are taken of the object from different directions. This type of images taken from different directions can be taken automatically by applying, for example, the method disclosed in the Applicant's FI application 980146, which uses a panoramic X-ray apparatus for the imaging. This type of panoramic X-ray apparatus is not, however, a functional solution in cases where it is desirable to take a three-dimensional X-ray image without moving the patient from the dentist's chair. In addition, with a view to three-dimensional imaging, the panoramic X-ray apparatus also provides a limited path for the X-ray source, which means that the quality of the image is not the best possible. It is, therefore, an important aim of the invention to provide an improved method and apparatus for producing three-dimensional X-ray images of a part of the head or neck area, for example, a tooth, which method is in addition preferably automated.

In order to achieve the aims of the invention, it is characteristic of the method relating to the invention that in the method, the X-ray source of the apparatus is positioned on an irradiation plane located at a desired distance from the image sensor, and the X-ray source is moved on the said irradiation plane along an essentially circular path in such a way that the central ray of the X-ray source is directed at the same point during the movement; that in the method, the sensor is positioned at this point or in its vicinity; and that in order to image the object from different directions, the X-ray source is optionally stopped at different points of the circular path for the duration of exposure in each desired direction of imaging, or the exposure is carried out while the X-ray source is moving.

Preferred embodiments of the method relating to the invention are described in dependent claims 2 to 7.

The apparatus relating to the invention is, on the other hand, characterised in that the apparatus comprises means for placing the X-ray source on an irradiation plane located at a desired distance from the image sensor, and means for moving the radiation source on the said irradiation plane along an essentially circular path in such a way that the central ray of the X-ray source is directed at the same point during the movement, at which point or in its vicinity the sensor is positioned; and that in order to image the object from different directions, the apparatus comprises means for optionally stopping the X-ray source at desired points of the circular path for the duration of exposure in each desired direction of imaging, or for carrying out the exposure while the X-ray source is moving.

Preferred embodiments of the apparatus relating to the invention are described in dependent claims 10 to 12.

The invention is described in greater detail in the following, with reference to the appended drawings in which:

Figures 1 and 2 show diagrammatically the travel of the X-rays when applying the method relating to the invention, Figures 3 to 6 show diagrammatically an example of an embodiment of the apparatus used in the method relating to the invention as seen from the side, from above and from the front, and as a perspective view in corresponding order, and

Figures 7 and 8 show a detail of the apparatus relating to Figures 3 to 6 on an enlarged scale.

In accordance with Figures 1 and 2, in the method relating to the invention, the X- ray source is positioned to move on the irradiation plane, along a circular path 20, in such a way that the central rays 21 of the X-ray fields emitted from different points 22 of the path 20 intersect at the same point 23, to which point 23 or in its vicinity is positioned a digital image sensor, for example, a radiation sensitive semiconductor sensor, such as a CCD sensor or other sensor system producing digital image information, which sensor is immobile at least during exposure. The sensor is positioned behind the object to be imaged, for example, in the mouth or outside the mouth. The surface of this sensor which receives radiation information is preferably located on a parallel plane with respect to the irradiation plane comprising the circular path 20. The angle 24 between the central axis 25 of the circular path 20 and the central rays 21 of the X-rays can be adjusted according to the desired image quality, that is, the thickness of the layer and this angle determine also the distance of the irradiation plane from the image sensor located at point 23 or in its vicinity. The determination of this angle is also affected by whether the image sensor is in the patient's mouth or outside the mouth.

When implementing the method, the movement of the X-ray source can optionally be stopped for the duration of exposure in each desired direction of imaging; points 22 on the circular path 20. When the operator presses the switch, the X- ray apparatus exposes the first image and moves automatically to the next point of imaging. When the digital image sensor has recorded and transmitted the image information for further processing, for example, to a computer, and is again ready for recording the next image, the X-ray apparatus exposes the next image and continues in this manner until it has moved around the whole circumference of the circle 20. The imaging can also be carried out while the X-ray source is moving if the movement is sufficiently slow. The number of images taken is typically 8 to 20, but there may also be more or fewer of them.

In the case of the embodiment shown in Figures 3 to 8, the apparatus used in the method relating to the invention comprises a connecting piece 5 to be fixed to a supporting structure, for example, a wall or pillar, to which connecting piece 5 is articulated an articulated arm 2 permitting movement in different directions. At the end of the articulated arm is installed a supporting arch 10 which can be turned, for example, by means of a motor (not shown) arranged on the arm 2, around a first pivoted axle A. To the free outer end of the supporting arch 10 is attached a fork bracket 6 which can be turned about a second pivoted axle B, for example, by means of a motor 13, which motor is covered by a protective casing 14. In the fork bracket 6 is articulated a casing 3 by means of a joint pin 7, the casing housing the X-ray source (not shown), the X-ray beam emitted from which travels through the tubular part 4 limiting the field of rays. The casing 3 can be turned about a third pivoted axle C, for example, by means of a motor (not shown) placed inside the casing. The first and second pivoted axles A and B are preferably positioned at an angle of essentially 90° with respect to each other, and in the embodiment shown in Figures 3 to 6, are located essentially on the horizontal plane, while axle C, on the other hand, is located on the vertical plane. This type of apparatus which permits a turning movement about three axles makes it possible to position the X-ray source in the desired direction of exposure with respect to the object to be imaged, and the travel of the X-ray source along the circular path 20.

In the fork bracket 6 is in addition arranged an aperture 9 provided with a scale and in it a moving indicator 8 by means of which the direction of the casing 3 and thus of the X-rays can easily be set as desired. The casing 3 containing the X-ray source is preferably balanced to avoid problems relating to vibration during the rotary movement. Alternatively, or in addition, the different articulated points on the articulated arm may be locked to eliminate vibration.

When the X-ray source is being positioned on the desired irradiation plane, its distance from the sensor can be measured and it can be directed at the sensor, for example, mechanically, by means of a ray of light, or by means of ultrasound. For mechanical measurement can be used, for example, a measuring rod having an adjustable length, which rod is located in the casing 3 and positioned against, for example, a stopper outside the mouth which is connected to the image sensor. The determination of this distance can also be automated, if necessary.

The X-ray apparatus relating to the invention, which is similar to an intra-oral X- ray apparatus, can be brought to the patient while the patient is sitting in the treatment chair, thus avoiding moving the patient. The apparatus is intended especially for producing three-dimensional X-ray images but, if necessary, it can also be used for ordinary two-dimensional X-ray imaging.

The invention is not limited to the foregoing embodiments but may be modified within the scope of protection determined by the appended claims. For example, the means for placing the X-ray source on the irradiation plane located at the desired distance from the image sensor may comprise, in accordance with Figure 9, an articulated arm 2 attached to the supporting structure, at the end of which arm is arranged, in an articulated manner, a casing 3 housing the X-ray source, and which X-ray source is arranged to move by rotary movement inside the casing. In this way is obtained a mechanically slightly simpler solution by means of which is avoided, for example, the use of the supporting arch 10 and the fork bracket 6 shown in Figure 8.

Claims

1 . A method for X-ray photography of the head and neck area, especially for producing three-dimensional X-ray images of the object to be imaged, in which method is used an imaging apparatus (1 ) equipped with an X-ray source and a digital image sensor which is immobile at least during exposure, the image sensor being positioned in the X-ray field of the radiation source of the imaging apparatus (1 ), behind the object to be imaged each time as viewed from the X-ray source, characterised in that in the method, the radiation source of the apparatus (1 ) is positioned on an irradiation plane located at a desired distance from the image sensor and the radiation source is moved on the said irradiation plane along an essentially circular path (20) in such a way that the central ray (21 ) of the X-ray source is directed at the same point (23) during the movement; that in the method, the sensor is positioned at this point (23) or in its vicinity; and that in order to image the object from different directions, the X-ray source is optionally stopped at different points (22) of the circular path (20) for the duration of exposure in each desired direction of imaging, or the exposure is carried out while the X-ray source is moving.

2. A method as claimed in claim 1 , characterised in that the movement of the X- ray source on the circular path (20), the optional stopping of the X-ray source at different points (22) of the path (20), and each exposure, respectively, are carried out automatically.

3. A method as claimed in claim 1 or 2, characterised in that the sensor is placed in the patient's mouth or outside the patient's mouth, at the object being imaged.

4. A method as claimed in any of the claims 1 to 3, characterised in that when the X-ray source is being positioned on the desired irradiation plane, the distance of the X-ray source from the sensor is measured and the X-ray is directed at the sensor mechanically.

5. A method as claimed in any of the claims 1 to 3, characterised in that when the X-ray source is being positioned on the desired irradiation plane, the distance of the X-ray source from the sensor is measured and the X-ray is directed at the sensor by means of a ray of light.

6. A method as claimed in any of the claims 1 to 3, characterised in that when the X-ray source is being positioned on the desired irradiation plane, the distance of the X-ray source from the sensor is measured and the X-ray is directed at the sensor by means of ultrasound.

7. A method as claimed in any of the above claims, characterised in that the distance of the X-ray source from the sensor and at the same time the thickness of the layer being imaged are adjusted by changing the angle (24) between the central ray (21 ) of the X-ray source and the normal (25) of the irradiation plane running through the intersection (23) of the central rays (21 ).

8. An apparatus for X-ray photography of the head and neck area, especially for producing three-dimensional X-ray images of the object to be imaged, the apparatus comprising an imaging apparatus (1 ) equipped with an X-ray source and a digital image sensor which is positioned in the radiation field of the radiation source of the imaging apparatus (1 ), so as to be immobile at least during exposure, behind the object to be imaged each time, as viewed from the X- ray source, characterised in that the apparatus (1 ) comprises means for placing the radiation source on an irradiation plane located at a desired distance from the image sensor and means for moving the radiation source on the said irradiation plane, along an essentially circular path (20), in such a way that the central ray (21 ) of the X-ray source is directed at the same point (23) during the movement, at which point (23) or in its vicinity the sensor is positioned; and that in order to image the object from different directions, the apparatus comprises means for optionally stopping the X-ray source at desired points (22) of the circular path (20) for the duration of exposure in each desired direction of imaging, or for carrying out the exposure while the X-ray source is moving.

9. An apparatus as claimed in claim 8, characterised in that the means for placing the X-ray source on the irradiation plane located at a desired distance from the image sensor comprise an articulated arm (2) fixed to a supporting structure, at the end of which articulated arm is arranged a supporting arch (10) which can be turned about a first pivoted axle (A), on which supporting arch is arranged a fork bracket (6) which can be turned about a second pivoted axle (B), to which fork bracket is articulated a casing (3) which can be turned about a third pivoted axle (C), inside which casing the X-ray source is housed.

10. An apparatus as claimed in claim 9, characterised in that the said first and second pivoted axles (A and B) are at an essentially 90° angle with respect to each other.

11. An apparatus as claimed in any of the claims 8 to 10, characterised in that it further comprises means for measuring the distance between the X-ray source and the sensor and means for directing the X-ray at the sensor.

12. An apparatus as claimed in claim 8, characterised in that the means for placing the X-ray source on the irradiation plane located at the desired distance from the image sensor comprise an articulated arm attached to the supporting structure, at the end of which arm is arranged, in an articulated manner, a casing housing the X-ray source, which X-ray source is arranged to move by rotary movement inside the casing.