X-ray or gamma ray systems or devices – Specific application – Tomography
Reexamination Certificate
1999-06-28
2001-05-15
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Tomography
C378S010000, C378S011000, C378S022000
Reexamination Certificate
active
06233305
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a method, apparatus and their use for tomographic imaging and, more particularly, to a method and apparatus for producing complex motion or spiral tomography images in medical x-ray imaging.
BACKGROUND OF THE INVENTION
Imaging methods utilizing electromagnetic radiation can be divided into two groups: radioscopic methods and tomographic methods. In traditional radioscopy, the radiation source, the object to be imaged and the radiation detector, e.g., an x-ray film, are stationary with respect to one another during the imaging session. Imaging methods in which a narrow beam is moved over the object to be imaged are also known.
Tomographic methods can be divided into linear (i.e. planar) tomographic methods and complex motion or spiral tomographic methods. In linear tomographic imaging, the radiation source and the radiation detector are moved with respect to one another in a controlled manner. That is, the radiation source and the radiation detector are rotated around a vertical axis passing through the object to be imaged so that the radiation beam from the radiation source passes through the object to be imaged and is received by the detector, the radiation beam remaining in a single plane. In complex motion tomography, in addition to rotating around the vertical axis passing through the object to be imaged, the radiation source and radiation detector move vertically in opposite directions from one another thereby varying the angle of the radiation beam passing through the object to be imaged. Both methods preferably use a beam which is of the same size as the object to be imaged. Therefore, in complex tomography, the object to be imaged is usually held in place as the radiation source and radiation detector move dependently on one another on opposite sides of the object to be imaged in opposite vertical directions so that the beam penetrates the object at different angles. However, the location at which the beam penetrates the object does not change. These methods provide accurate images of the imaging area in the center of rotation of the beam, whereas the other parts of the object are blurred partially or totally.
There also exist “narrow beam tomography” methods in which a beam considerably narrower than the object to be imaged sweeps across the area to be imaged and the beam is turned with respect to the object to be imaged. In that case, the imaging means (i.e., the radiation source and the radiation detector) must be moved in a controlled manner so that the detector moves in relation to the beam at a lateral velocity which corresponds to the perpendicular sweeping speed of the beam in the area to be imaged multiplied by the ratio of magnification, i.e., by a coefficient which is the ratio of the distance of the beam focus (radiation source) and the distance of the focus from the area to be imaged. Here, the term “detector” refers to a film or the like. In digital imaging, for example, the movement of the detector with respect to the area to be imaged may be replaced with a suitable electrical function, such as a charge transfer on the surface of a semiconductor sensor.
Thus, it is known to move the radiation source and the radiation detector both horizontally and vertically for producing a tomographic effect. Many prior art devices that enable complex motion paths have very massive structures, and thus it may not be possible to move the imaging means rapidly and change its direction due to the limits set by the general physical principles of moving heavy masses and mechanical solutions of the devices. Against this background, it is not easy to develop commercially feasible devices. The present trend is to develop devices which enable the use of the same device for various purposes, i.e., the goal is to be able to use the same device in different tomographic methods and for imaging different projections. When the same device has different imaging modes, investment in imaging sensors based on modem digital technology becomes more profitable, which lowers the threshold of introducing them. Digital technology facilitates a doctors' work since, for example, it not only allows doctors to produce better images than earlier thereby enabling them to make more accurate diagnoses, but it also enables doctors to store the images and manage them in electronic form, together with all of the other documents related to the patient.
OBJECTS AND SUMMARY OF THE INVENTION
An object of the present invention is to provide a new device for complex tomographic imaging which uses prior devices intended for linear tomographic imaging. For example, several prior art devices used for linear x-ray photography of the cranial area already include structures which can be utilized as such or with minor structural or programmatical changes for complex motion tomographic imaging.
Prior art tomographic imaging devices include a device such as that disclosed in Finnish Patent 88671, in which the radiation source and radiation detector (sometimes referred to herein collectively as “imaging means”) of the device are attached to respective ends of a suspension arm that can be rotated in the horizontal plane, the arm being provided with a degree of freedom for moving in the direction of the axis between the imaging means. Furthermore, the arm can be tilted with respect to the horizontal plane. The imaging means can also be arranged so that they can be moved vertically with respect to the object to be imaged by forming the suspension arm in the shape of an arc and by moving the arm in the direction of its longitudinal axis along a supporting structure in which the imaging means move upwards along a curved path of the arm and correspondingly downwards on the opposite sides of the object to be imaged. The publication does not disclose use of these features (which is known per se from other contexts) for actual complex motion or spiral tomography imaging, i.e., the use of the upward movements enables the production of a tomographic effect with respect to two directions during radiation. The device according to the Finnish publication utilizes a narrow beam, and the imaging means are moved vertically with respect to the object to be imaged in order to obtain a perpendicular cross-sectional image of the patient's teeth which are diagonal to the vertical plane.
In tomographic imaging, it is particularly important that the object to be imaged and the imaging means are in a controlled position with respect to each other during the entire imaging session. There are several prior art patents wherein the object is to position the object to be imaged and/or the imaging means accurately before imaging. Examples of mechanical and motorized positioning are disclosed in U.S. Pat. Nos. 5,666,392 and 5,642,392. However, these solutions are related to controlled and reproducible positioning of the object to be imaged and/or the imaging means before the actual imaging or between separate radiation sessions, such as in tomosynthesis imaging. The patents do not disclose devices for controlling the movement of the imaging means during radiation when the tomographic movement is performed in complex motion tomographic imaging. The tomographic movement is usually implemented so that it is continuous, but in some cases it may be necessary to stop the movement and/or radiation momentarily for purely technical reasons.
The present invention combines the ideas of utilizing structures that already exist in imaging devices for producing a tomographic effect by means of a vertical movement and producing a vertical movement without having to move large masses which imposes limitations on tomographic imaging. The method of implementing the tomographic movement includes the feature of synchronizing, by means other than conventional mechanical synchronization, the vertical movement of the imaging means with respect to the object to be imaged. For example, according to one preferred embodiment of the invention, the imaging means, i.e., the radiation source and the radiati
Bruce David V.
Hobden Pamela R.
Planmeca Oy
Steinberg & Raskin, P.C.
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