Patent Number: 
Section: description

The apparatus according to FIG. 1 comprises a support part 2, beneath which is connected a panoramic imaging apparatus 4, which turns in a pivoting manner around the rotation centre 13, the imaging apparatus comprising a C arm 7, on one vertical branch 7a of which is arranged an X-ray source 5 and the primary collimator 6 in its vicinity. To the support part 2 is connected a supporting arm 3, at the other end of which is the cephalometric imaging apparatus 10, which comprises a line detector camera 8 to be placed behind the object being imaged, and a secondary collimator 9 to be placed in front of the object being imaged. FIG. 2 shows diagrammatically one implementation of a line detector camera 8, wherein on one side of the camera is formed a slot 14, behind which, inside the camera 8, is a digital detector 15, for example, a CCD sensor comprising several pixels. The active imaging area of the detector 15 consists of areas 15A and 15B, of which 15A represents the area which the ray beam must meet in a normal situation. In cephalometric imaging, the patient""s head is scanned by means of a vertically positioned ray beam 11 from right to left or vice versa by turning the X-ray source 5 about the rotation centre 13, whereby the ray beam 11 is directed at the detector 15 behind the substantially vertical slot 14 of the line detector camera 8, from which detector 15 the image data is transmitted further, for example, to a microprocessor. According to the FI application no. 20000369, the rotation centre 13 is arranged to be transferred by means of a linear movement, transversely with respect to the ray beam 11, as shown by reference marking A in FIG. 1. In the embodiment shown in FIG. 1, the apparatus is further provided with three identifying detectors 20-22 on that surface of the secondary collimator 9, which is on the X-ray source 5 side, of which the middlemost identifying detector 21 is located preferably at the slot 19 of the secondary collimator 9. In the embodiment shown, the identifying detectors are located according to FIG. 3 in the upper part of the secondary collimator, but they may also be located elsewhere on the said surface or outside it. There may obviously also be only one or two or more than three identifying means, depending on the amount of information desired. FIG. 3 depicts a situation at stage I, where the middlemost identifying detector 21 is in the ray beam and the outer identifying detectors are outside it. In such a case, the ray beam 11 moves synchronically with the secondary collimator, and the radiation is directed correctly at the imaging detector, which means that no corrective movements are required. Stage II depicts a situation, where the ray beam 11 meets partly both the middlemost identifying detector 21 and the outer detector 22, whereby the ray beam 11 and the secondary collimator 9 move at different speeds and a corrective movement is required to bring them back to the synchronised movement according to stage I. For this purpose, the identifying detectors transmit signals by means of which the movements are guided in a desired direction, for example, a fast movement is slowed down. Stage III depicts a situation, where the corrective movement has not given the desired end result, but the middlemost identifying detector 21 has moved completely outside the ray beam 11, whereby the radiation is no longer directed at the imaging area of the imaging detector 15 at all. In such a case, the signals transmitted by the identifying detectors are preferably used to discontinue exposure to avoid unnecessary irradiation. The identifying detectors are preferably located in conjunction with the secondary collimator, but they may also be located elsewhere, for example, in connection with the imaging detector 15, or the imaging detector itself can be used as an identifying detector, for example, by using, as the pixels forming the identifying detector, the pixels in such an area (area 15B in FIG. 2) of the active imaging area of the imaging detector, which are not irradiated in a normal situation, and which give out an identifying signal if radiation is directed at them. Alternatively, can also be used such pixels (in area 15A in FIG. 2) located inside the active imaging area, which are normally arranged to be in the field of rays and to give information on the radiation meeting the detector. The necessary corrective movements are made or the exposure is discontinued on the basis of the information received from the detector. Using the imaging detector as an identifying detector or locating identifying detectors in connection with it is more disadvantageous than using identifying detectors located in front of the secondary collimator in the respect that any corrective movements or discontinuance of exposure are based on radiation that has passed through the patient, whereby radiation scattered from the patient may cause unclear situations and unnecessary corrective movements or discontinuance of exposure. Furthermore, in a situation where exposure is discontinued, the patient is exposed to more radiation than in a situation where the identifying detectors are located in conjunction with the secondary collimator or in another part of the imaging apparatus in front of them.