X-ray or gamma ray systems or devices – Beam control – Scanner
Patent
1991-08-28
1993-05-11
Porta, David P.
X-ray or gamma ray systems or devices
Beam control
Scanner
378145, 378151, G21K 510
Patent
active
052107825
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for slit radiography, in which, with the aid of an X-ray source and a slit-type diaphragm placed in front of the X-ray source, a fan-type X-ray beam is formed, with which beam a body under examination is scanned at least partially in a direction transverse to the longitudinal direction of the slit of the slit-type diaphragm in order to form an X-ray shadow image on an X-ray detector placed behind the body, which fan-type X-ray beam is formed by a multiplicity of sectors situated adjacently to one another, the transmitted X-ray radiation being influenced instantaneously during the scanning movement per sector of the fan-type beam, while in operation, by means of controllable beam sector modulators interacting with the slit diaphragm, the quantity of radiation transmitted through the body being measured with the aid of detection means instantaneously per sector of the X-ray beam during the scanning movement and the measurement result being used to control the beam sector modulators. The invention furthermore relates to an apparatus for applying the method.
Such a method and such an apparatus are known from the Dutch Patent Application 84.00845. According to the technique known from the Dutch Patent Application 84.00845, to regulate the quantity of x-ray radiation transmitted through the slit diaphragm at any instant in time, use is made of attenuating devices which are placed near or in the slit of the slit diaphragm and act as beam sector modulators, which can each influence a sector of the fan-type X-ray beam and which, depending on the attenuation occurring in the associated sector and caused by the body under examination, are controlled in a manner such that the attenuating devices extend to a greater or lesser degree into the X-ray beam. If the attenuation due to the transradiated body is large in a particular sector at a particular instant, the attenuation device. associated with the sector is moved completely or largely out of the X-ray beam. On the other hand, if the attenuation due to the body is low in a particular sector at a particular instant, the associated attenuation device is brought further into the X-ray beam.
The advantage of this technique is that equalized radiographs can thereby be obtained, that is to say, radiographs which have a good contrast both in the light parts and in the dark parts. Therefore if, for example, a radiograph is made in this manner of the upper part of the body of a patient, the radiologist is able to find, in one and the same radiograph, adequate information for both the chest and the abdominal cavity of the patient, whereas two different radiographs were hitherto necessary to obtain the same information.
One problem in the known method is that the beam sector modulators may exhibit hysteresis phenomena. These phenomena occur, in particular, if piezoelectric tongues are used as (carriers of) absorption devices, but also, for example, in the case of beam sector modulators which comprise spring devices or are linked thereto.
As a consequence of such hysteresis phenomena, for example, the position of a beam sector modulator with respect to the beam sector to be influenced may deviate from the position which corresponds to the signals provided by the detection means. Undesirable artefacts may consequently be produced in the final X-ray shadow image.
The object of the invention is to eliminate, or at least to reduce, the problem outlined.
For this purpose, according to the invention, a method of the type described is characterized in that, during operation, the instantaneous position of each beam sector modulator is continuously detected, in that an electrical signal representing the instantaneous position is generated for each beam sector modulator, in that the electrical signal representing the instantaneous position is compared with the measurement result provided by the detection means and associated with the respective beam sector, and in that a control signal for the respective beam sector modulator is formed from the measuremen
REFERENCES:
patent: 4677652 (1987-06-01), Duinker et al.
patent: 4785471 (1988-11-01), Boersma
patent: 4996701 (1991-02-01), Geluk
Geluk Ronald J.
Vlasbloem Hugo
B.V. Optische Industrie "De Oude Delft"
Marn Louis E.
Porta David P.
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