EP0224726A2 - Abschwächungsplatte für Röntgengeräte - Google Patents

Abschwächungsplatte für Röntgengeräte Download PDF

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Publication number
EP0224726A2
EP0224726A2 EP86115149A EP86115149A EP0224726A2 EP 0224726 A2 EP0224726 A2 EP 0224726A2 EP 86115149 A EP86115149 A EP 86115149A EP 86115149 A EP86115149 A EP 86115149A EP 0224726 A2 EP0224726 A2 EP 0224726A2
Authority
EP
European Patent Office
Prior art keywords
plate
ray
rays
transmission factor
patient
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP86115149A
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English (en)
French (fr)
Other versions
EP0224726A3 (de
Inventor
Michael Leslie Cocklin
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
International Business Machines Corp
Original Assignee
International Business Machines Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by International Business Machines Corp filed Critical International Business Machines Corp
Publication of EP0224726A2 publication Critical patent/EP0224726A2/de
Publication of EP0224726A3 publication Critical patent/EP0224726A3/de
Withdrawn legal-status Critical Current

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    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21K—TECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
    • G21K1/00—Arrangements for handling particles or ionising radiation, e.g. focusing or moderating
    • G21K1/10—Scattering devices; Absorbing devices; Ionising radiation filters

Definitions

  • This invention relates to an X-ray attenuator plate and X-ray apparatus incorporating such a plate.
  • X-rays are the most common means of non-invasively investigating the internal human anatomy in medical diagnosis.
  • the X-ray tube produces X-rays that pass through the patient and typically produce a shadow on film. This shadow is due to the differential attenuation of the X-rays by the different structures in the body. Attenuation of the X-rays is either by complete absorption or by scattering of the X-rays.
  • the former process gives rise to the PRIMARY radiation exiting the patient and the most useful image information.
  • the latter process results in SCATTERED radiation which produces a general fog on the radiograph, essentially unrelated to the true image information.
  • an anti-scatter grid see above reference, pp 89-91.
  • This consists of a grid of lead bars with the spaces between the bars filled with some radiolucent material.
  • the lead bars have an X-ray transmission factor that is effectively zero, while that of the radiolucent material is close to one (ie most X-rays are allowed to pass).
  • the X-ray trans­mission factor of an object is defined as the fraction, between 0 and 1, of incident X-ray flux which passes through the object.
  • the grid is placed between the patient and the X-ray detector. X-rays that are scattered by the patient usually impinge on the grid at an angle to their original direction and are absorbed by the lead bars. Unscattered (primary) X-rays, however, have the same direction as they had when entering the patient, and so can pass freely between the lead bars.
  • an object of the invention to provide an attenuator plate useful in X-ray imaging which permits the reduction of the effect of scattered radiation without requiring significantly higher patient dosages.
  • the present invention provides an attenuator plate for insertion between a source of X-rays and a patient under examination, the plate having an X-ray transmission factor which varies across the surface of the plate in at least one of two orthogonal directions to provide a large number of alternate local maxima and minima, the X-ray transmission factor at the minima being sufficiently greater than zero that primary X-rays are transmitted to a substantial extent through the entire area of the plate.
  • the invention further comprises an X-ray apparatus comprising a source of X-rays of given peak energy, a plate having a transmission factor for the X-rays which varies across the surface of the plate in at least one of two orthogonal directions to provide a large number of alternate local maxima and minima, the X-ray transmission factor at the minima being sufficiently greater than zero that primary X-rays are transmitted to a substantial extent through the entire area of the plate, and means for recording an image of the X-rays from the source after passage through the plate and a patient in that order.
  • the invention comprises a special plate of non-uniform X-ray transmission factor which 'codes' the X-ray beam before it enters the patient.
  • Knowledge of the coded X-ray input may be used to calcu­late and remove the scattered radiation contribution from the recorded image, after the X-ray image has been converted directly or indirectly into digital form for processing.
  • Such conversions are currently done in Computed Tomography (brain and body) Scanners.
  • the maxima and minima in the X-ray transmission factor preferably occur with a fixed period across the plate in one or both directions, and the transitions from one to the other may take place in distinct steps or smoothly such as sinusoidally.
  • the average X-ray transmission factor of the plate as a whole is typically in the region of 0.7 to 0.9, with the X-ray transmission factor at the minima about 0.5 to 0.6 and that at the maxima close to 1.
  • the distance, ie the fixed period, between adjacent maxima (and minima) is typically from 0.4 mm up to about 2.0 mm depending upon the processing techniques used. Placing this plate between the X-ray tube and the patient results in an X-ray field of non-uniform intensity entering the patient. This is the coded X-ray beam.
  • the plate must cover the full area of the recorded X-ray field. If it is placed close to the X-ray tube, its size may be as small as a few centimetres on a side. However, the rate of variation of X-ray transmission factor across the plate would then have to be very high, leading to manufacturing problems. At the other extreme, the plate may be placed close to the patient so the required size is effectively the size of the X-ray detector (eg films for chest radiography are about the largest generally available and are typically 43 cm ⁇ 35 cm). Putting the plate close to the patient relaxes the manufacturing constraints, but means that spurious X-rays produced by the non-unifor­mity of the plate itself may not be dissipated before the X-ray beam enters the patient.
  • Plate position would therefore have to be some compromise between the above requirements.
  • a reasonable choice for chest radiography, for example, is about 50 cm in front of the patient, giving a plate about 30 cm on each side.
  • the required rate of variation of the X-ray transmission factor edge-to-edge across the plate is determined by the position of the plate. If the plate is in the above position, it will be about 100 cm from the film or other image recording means. If the distance between the X-ray tube and the film is about 300 cm, this gives a plate magni­fication at the film of about 1.5. Given that the radiographic image is to be digitised, the upper limit on the rate of variation is deter­mined by the elemental size of the digital array (the pixel size). At the film plane this may be expected to be in the region of 0.2 to 0.4 mm.
  • the varying X-ray transmission of the plate may be achieved by using one material and varying its thickness or density across the surface of the plate, by using a combination of materials of the same thickness with different X-ray attenuation characteristics, or by a combination of these two techniques.
  • An example of the first technique is an aluminium plate 10 (Figure 1) provided with closely spaced parallel ridges 11 on one side so that its thickness fluctuates smoothly and periodically (preferably sinusoi­dally) between about 2 mm to 7 mm from one edge to the opposite edge (see Figure 2).
  • Such a plate will have a smoothly varying X-ray transmission factor.
  • An example of the second technique is a plate 12 (Figure 3) of uniform thickness of about 5 mm consisting, across the surface of the plate, of alternate thin parallel strips of aluminium 13 and perspex 14 separated by thin strips of magnesium 15, aluminium being a material that attenuates X-rays quite a lot, perspex one that only attenuates a little, and magnesium one that has an attenuation in between.
  • a plate 12 will have a stepped X-ray transmission factor.
  • the lead strips in conventional grids are about 0.05 mm wide, with the radiolucent material between them about 0.4 mm wide.
  • the peak X-ray energies used in medical diagnosis typically lie in the range from 50 to 150 KeV, and the invention is useful throughout that range.
  • the plate accord­ing to the invention has the following advantages:
  • an X-ray appa­ratus may comprise a standard X-ray source 16 ( Figure 4) emitting X-rays 17 of a given peak energy lying within the above range, an image recording means 18, and a plate 10 or 12 as described above mounted in any convenient manner between the two such that X-rays can pass through a patient 19 after passing through the plate.
  • the plate is so constructed that there are areas (occurring periodically, and aligned with the pixels of the digital array) having an X-ray transmission close to the average of the plate as a whole.
  • This assumption can be made valid for the case of the layered plate construction, and is sufficiently valid for a plate of smoothly varying X-ray transmission.
  • a smoothly varying plate more closely follows the constant scattering assumption used in the theory below, but small steps (in space and X-ray transmission) do not violate this to any significant extent.
  • Range of k will typically be from about 0.6 to about 1, with an average value K of about 0.8. This means that the X-ray tube exposure will be some 25% higher than normal, but there is no change to the exposure to the patient.

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  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Apparatus For Radiation Diagnosis (AREA)
  • Radiation-Therapy Devices (AREA)
  • Analysing Materials By The Use Of Radiation (AREA)
EP86115149A 1985-12-02 1986-10-31 Abschwächungsplatte für Röntgengeräte Withdrawn EP0224726A3 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB858529615A GB8529615D0 (en) 1985-12-02 1985-12-02 Attenuator plate
GB8529615 1985-12-02

Publications (2)

Publication Number Publication Date
EP0224726A2 true EP0224726A2 (de) 1987-06-10
EP0224726A3 EP0224726A3 (de) 1988-10-19

Family

ID=10589113

Family Applications (1)

Application Number Title Priority Date Filing Date
EP86115149A Withdrawn EP0224726A3 (de) 1985-12-02 1986-10-31 Abschwächungsplatte für Röntgengeräte

Country Status (3)

Country Link
EP (1) EP0224726A3 (de)
JP (1) JPS62133398A (de)
GB (1) GB8529615D0 (de)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0333276A1 (de) * 1988-03-18 1989-09-20 Koninklijke Philips Electronics N.V. Röntgenuntersuchungsapparat mit einem Streustrahlengitter mit Vignettierung unterdrückender Wirkung
CN103063686A (zh) * 2012-12-18 2013-04-24 中国科学院近代物理研究所 切片式高能离子束辐射成像系统
GB2611545A (en) * 2021-10-07 2023-04-12 Mbda Uk Ltd Shielded apparatus

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3678637A (en) * 1970-02-17 1972-07-25 Arthur Klipfel Building construction system

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3867637A (en) * 1973-09-04 1975-02-18 Raytheon Co Extended monochromatic x-ray source

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3678637A (en) * 1970-02-17 1972-07-25 Arthur Klipfel Building construction system

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
APPLIED OPTICS, vol. 13, no. 10, October 1974, pages 2202-2208, New York, US; A. MACOVSKI et al.: "Selective material X-ray imaging using spatial frequency multiplexing" *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0333276A1 (de) * 1988-03-18 1989-09-20 Koninklijke Philips Electronics N.V. Röntgenuntersuchungsapparat mit einem Streustrahlengitter mit Vignettierung unterdrückender Wirkung
CN103063686A (zh) * 2012-12-18 2013-04-24 中国科学院近代物理研究所 切片式高能离子束辐射成像系统
GB2611545A (en) * 2021-10-07 2023-04-12 Mbda Uk Ltd Shielded apparatus
WO2023057768A1 (en) * 2021-10-07 2023-04-13 Mbda Uk Limited Shielded apparatus

Also Published As

Publication number Publication date
JPS62133398A (ja) 1987-06-16
GB8529615D0 (en) 1986-01-08
EP0224726A3 (de) 1988-10-19

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Inventor name: COCKLIN, MICHAEL LESLIE