WO1989007322A1 - Filtre de reduction de rayonnement utilise dans le diagnostic medical - Google Patents

Filtre de reduction de rayonnement utilise dans le diagnostic medical Download PDF

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Publication number
WO1989007322A1
WO1989007322A1 PCT/US1989/000265 US8900265W WO8907322A1 WO 1989007322 A1 WO1989007322 A1 WO 1989007322A1 US 8900265 W US8900265 W US 8900265W WO 8907322 A1 WO8907322 A1 WO 8907322A1
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WO
WIPO (PCT)
Prior art keywords
filter
ray
radiation
kev
examination object
Prior art date
Application number
PCT/US1989/000265
Other languages
English (en)
Inventor
Kenneth E. Demone
Earl J. Mccutcheon
Original Assignee
Tech-Enomed Imaging Corp. U.S.A.
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 Tech-Enomed Imaging Corp. U.S.A. filed Critical Tech-Enomed Imaging Corp. U.S.A.
Publication of WO1989007322A1 publication Critical patent/WO1989007322A1/fr

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Classifications

    • 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 X-ray radiography and fluoroscopy and particularly to filters for limiting the radiation dosage to a patient exposed to X-rays during medical and dental diagnosis.
  • X-rays are produced in an X-ray tube as a result of high speed electrons striking a target material.
  • the electrons strike and penetrate the surface layers of the target material and through interaction or collision with the atoms of the target- the energy of the electron is imparted to the electrons in the target.
  • the energy of the electron is dissipated through a series of collisions with the outer electrons of the target atoms, then the energy is released either in the form of heat or as visible light.
  • An electron may, after a series of collisions, also emerge from the target as a back- scattered electron. These collisions result in most of the energy losses contributing to target heating and hence reduced X-ray tube life.
  • the electron may also have radiative collisions, giving up part or sometimes all of its energy to photons.
  • the photons produced as a result of these collisions have an energy less than or equal to the energy given up by the electron.
  • the excited target atom when the electrons in the outer shells drop into the vacant inner shell, will return to its ground state and a photon will be emitted-
  • the energies of these transitions are dependent upon the atoms comprising the target material and hence the energies of the photons emitted are characteristic of the target atom.
  • This radiation is known in the art as the characteristic X- ray radiation and is produced by the X-ray tube only when the energy of the electron striking the target is above the level required to dislodge the K-electron of the target atom.
  • the energy of the photon comprising the X-ray is directly related to the energy given up by the electron in the collision with the target molecules.
  • the relationship between the wavelength ( ⁇ ) of a photon and its energy is expressed by the Duane-Hunt equation:
  • the ability of the X-rays to penetrate an examination object depends on the wavelength or energy of the X-ray photons as well as the composition of the examination object - i,e. its chemical elements, thickness and density.
  • the penetration ability is inversely proportional to wavelength or directly proportional to energy.
  • short wavelength (high energy) X-rays have a greater penetrating ability than long wavelength (low energy) X-rays.
  • the chemical elements making up the examination object generally, the higher the atomic number of the element, the less the penetration of the X-ray beam.
  • I is the intensity of the radiation transmitted
  • I 0 is the intensity of the incident radiation
  • e is the base of natural logarithm
  • ⁇ is the mass attenuation co ⁇ efficient for the chemical element comprising the filter material
  • p is the density of the filter material
  • x is the thickness of the filter material.
  • the attenuation co-efficient ⁇ are independent of the frequency or energy of the incident radiation.
  • the attenuation co-efficient varies with the energy of the incident radiation and is related to the atomic number of the chemical element of the filter material.
  • U.S. Patent 2,225,940 discloses a wedge which is brought into the path of the X-ray beam.
  • U.S. Patent 3,976,889 discloses the use of variable thicknesses of aluminum filters in dental x- rays to vary exposure levels. Almost all commercial x- ray units have some inherent filtration equivalent to about 1.0 to 1.5 mm of aluminum and those designed for medical and/or dental applications, utilize additional aluminum filtration.
  • U.S. Patent 3,515,874 discloses the use of molybdenum for both a target and filter, particularly for mammography where it has been found that the energy level of the K ⁇ line emitted from a molybdenum target is ideal for resolution of tumors in mammography applications.
  • an X-ray filter which significantly reduces low energy radiation normally absorbed by the examination object without significantly affecting the desired high energy radiation.
  • the filter is comprised of one or more materials containing as the major component elements selected from the group consisting of aluminum and elements having atomic numbers between 26 and 50 with the filter being selected to have X-ray filtering characteristics such that the intensity of X- rays having energies of 50 keV are reduced by about 8% to about 35% of the normal radiation levels.
  • the filter is encased in a thin plastic sheet which provides for protection of the filter during handling as well as some absorption of the secondary radiation emitted from the filter when it is contacted by the X-ray beam.
  • the filter is comprised of a metal foil constructed of a single elemental material, the elemental material being selected from the group consisting of niobium, copper, silver, tin, iron, nickel, zinc, zirconium, aluminum or molybdenum.
  • the filter is comprised of a niobium metal foil having a maximum thickness of about 75 microns or a niobium metal foil in combination with additional filtering foils.
  • the filter of the present invention filters energy from the X-ray beam which is usually absorbed by the examination object and does not contribute to the radiographic image of the examination object. This is achieved with little, if any, increased loading of the X-ray tube which would otherwise reduce its effective life.
  • Figure 1 shows a perspective view of a filter constructed in accordance with the present invention
  • Figure 2 is a sectional view of the filter of figure 1;
  • Figure 3 is an elevational view of an X-ray diagnostic apparatus with the filter of the present invention in place;
  • Figure 4 is an x-ray wavelength spectrum of the typical apparatus of figure 3, showing both filtered and unfiltered spectrum;
  • Figure 5 is an X-ray wavelength spectrum of the apparatus of figure 3, showing the unfiltered and the filtered spectrum wherein a filter of a second embodiment of the present invention has been utilized.
  • Figures 1 and 2 show a preferred embodiment of a filter of the present invention generally indicated at 10 comprising a metal foil 12 preferably constructed of an elemental material selected from the group consisting of niobium, copper, silver, tin, iron, nickel, zinc, zirconium or molybdenum.
  • a particularly suitable construction is niobium in a thickness of up to about 75 microns, preferably about 40 to 60 microns, the most preferable thickness of the niobium metal foil being about 50 microns.
  • This metal foil is encased in a coloured cardboard 14 wherein the colour can be used as an identifying means for the filter material and its thickness or the application in which the filter is to be utilized.
  • a plastic covering 16 which serves as a protective covering to the filter. Additionally the combination of the cardboard 14 and the plastic covering 16 serves to absorb some of the secondary radiation emitted from the metal foil 12 when an X-ray beam contacts the metal foil and also reduces or eliminates the exposure of the metal foil to air, thereby reducing oxidation.
  • Attached to one side of the filter 10 is a means for attaching the filter to the X- ray unit shown in the figures as a strip of double sided tape 18. The method of attaching the filter to an X-ray apparatus is discussed below.
  • Figure 2 shows a cross-section of the filter 10 of figure 1 illustrating clearly the relationship between the metal foil 12, the cardboard envelope 14 and the plastic encasing material 16.
  • FIG. 3 illustrates an X-ray generating apparatus 20 of typical lead based construction.
  • the apparatus comprises an X-ray tube 30 with a cathode 22 and a rotating anode 24.
  • a filament Located within the cathode is a filament (not shown) which when heated by an electric current produces a cloud of electrons around the cathode.
  • high voltage from a generator also not shown
  • the electrons in the cloud surrounding the cathode are accelerated as a beam towards the anode 24 which is comprised of a metallic material suitable as a target.
  • the target is constructed of tungsten.
  • the energy of the electron beam is absorbed by the target material and results in the production of X-rays as explained hereinabove.
  • the X-ray beam is, to a large degree, focused and emitted from the X-ray apparatus 20 through a port 26.
  • Port 26 usually comprises a window made of glass or plastic with an inherent filtration equivalent to about 0.5 mm of aluminum.
  • the X-ray beam emitted from the tube is focused through the use of a collimator 28.
  • the purpose of collimator 28 is to direct the X-ray beam to cover only the area required in exposure of the examination object. This is achieved through adjustment of diaphrams 32 and 36, setting the collimator opening 34.
  • the X-ray apparatus also has inherent and added filtration (not shown), usually equivalent to 2.5 to 3.5 mm aluminum to remove, from the beam, very low energy X- rays which would be generally absorbed within the first few millimetres of the examination object. These very low energy X-rays do not contribute at all to the resolution of the radiograph, but rather merely contribute to increase the exposure dose of the examination object 42.
  • the X-ray beams, once they pass through the examination object 42, are detected by a radiation detecting device as for example, an image intensifier 38 or directly on a radiographic film 40.
  • Filter 10 is shown attached in the apparatus between the port 26 of the tube 30 and the collimator 28.
  • the filter is attached to the apparatus using the double sided tape 18, by sticking it onto either the port 26 of the tube 30 or the additional aluminum filtration.
  • Figure 4 shows generally the X-ray wavelength spectrum emitted from an X-ray apparatus of figure 3.
  • the apparatus with a tungsten target and 3.5 mm of aluminum equivalent filtration was operated at an accelerating voltage of 80 kVP thereby resulting in production of a continuous spectrum with a minimum wavelength of about 0.15 A° and the characteristic K ⁇ and K ⁇ radiations of tungsten of about 0.21 A° and 0.18 A° respectively.
  • the solid line shows the wavelength spectrum of the the normal radiation X-ray beam emitted from the apparatus prior to filtration by a 50 micron niobium filter.
  • the long dash line is the attenuation properties of the 50 micron niobium filter.
  • Niobium with an atomic number of 41 has a K absorption edge at about 0.65 A° and an i absorption edge at about 4.58 A° (not shown on the figure) .
  • the short dash line shows the wavelength spectrum of X-ray beam after passing through the niobium filter. There is a marked decrease in the X-ray wavelengths from about 0.25 A° to just before the K absorption edge at 0.65 A° wherein only about 3% of the incident normal radiation is not absorbed by the filter. Thereafter the normal radiation of the X-ray beam is attenuated such that effectively all of the radiation is absorbed.
  • filter materials for the filters are dependent upon the requirements of the diagnostic technique as different techniques may require differing X-ray wavelength spectrums. For most medical and dental diagnostic techniques wherein the X-ray apparatus is operated at a peak voltage of between 55 keV and 110 keV, then any material whose major component is an element having an atomic number between 26 and 50 will be suitable for attenuating the X-rays beam.
  • the elements having atomic numbers between 26 and 50 have K absorption edges between about 7 keV and 30 keV and hence in these kVP ranges will not exhibit appreciable K-edge phenomenon and hence will generally act as non ⁇ specific filters.
  • the choice of the filter materials is also dependent upon availability of the material in a form suitable for filter construction, preferably in a metal foil of a suitable thickness.
  • Filters constructed in accordance with the present invention are easily adaptable to existing X-ray installations, thus resulting in reduced radiation exposure to the patient without significant increased cost.
  • the filters also have the added benefit of reducing incident scattered radiation from the X-ray source, thereby reducing the levels of radiation to which operators of such equipment may be exposed.
  • a combination filter can be utilized.
  • the combination filter will contain one or more materials containing more than one element selected from the group consisting of aluminum and elements having atomic numbers between 26 and 50.
  • the combination filter can be constructed by layering individual metal foils or by alloying the materials into a single foil. The selection of the materials and the elements comprising the materials will be dependent upon the desired spectrum of the X-ray beam which in turn will be dependent upon the particular application.
  • a combination filter of 25 microns of niobium and 50 microns of selenium is utilized.
  • the keys to the curves are the same as in figure 4 where the solid line is the unfiltered spectrum, the long dash line is the attenuation profile of the combination filter and the short dash line is the filtered spectrum.
  • selenium with a K absorption edge of about 0.98 A 0 in combination with niobium, substantially all of the X- rays with wavelengths greater than about 0.6 A° are removed from the X-ray beam by the combination filter.
  • the combination of niobium and selenium is particularly useful for applications where it is desirous to have an X-ray beam with wavelengths less than about 0.4 A°.
  • a harder beam i.e. one where the wavelengths are less than 0.3 A° or 0.2 A 0
  • the filter material would be chosen to remove X-rays with wavelengths longer than this.
  • tin with a K absorption edge at about 0.42 A° or indium with a K absorption edge at about 0.44 A° or silver with K absorption edge at about 0.48 A° would be useful.
  • the above or other materials similar in attenuation properties would be used in combination with one or more materials having K absorption edges in the region of about 0.6 A 0 to 1.0 A 0 as for example materials from technetium to germanium in the periodic table.
  • the preferred thickness of the selected materials is dependent upon the density and attenuation co-efficients as discussed above.
  • the total thickness of the filter should be chosen such that the product obtained by multiplying together the thickness, the density and the attenuation coefficient at 50 keV is in the range of about 0.15 to about 0.45, most preferably from about 0.25 to 0.35.
  • the sum of the products for each of the individual elements should be in the above ranges.
  • each of the individual elements should be in the range of about 0.075 to about 0.225 and most preferably from about 0.125 to about 0.175.
  • a 50 micron niobium filter encased in plastic was placed at the face of the collimator of a 3 phase 6
  • This experiment was carried out using a General Electric Three Phase Generator and an automatic beam limiting device with an inherent filtration of 1.5 mm equivalent of aluminum at 150 kVP.
  • the radiation detection device used was a Rad Check Plus, Model No. 06-526.
  • the added filtration was 2.0 mm of aluminum, making a total filtration of 3.5 mm of aluminum equivalent. Since the majority of X-ray examinations are carried out between 75 to 100 kVP, the generator was used at the following settings; mA - 200; Time - .35 Seconds; kVP - 80.
  • a half value layer experiment was carried out, as well as a comparison of radiation dose obtained under; a) Normal operation - with only the 3.5 mm aluminum/equivalent between source and the detector b) exactly as in item a) , but with 100 microns of Yttrium added at the source in the field. c) Exactly as in item a) , but with 50 microns of Niobium added at the source in the field. d) Exactly as in item a) , but with 25 microns of Niobium added at the source in the field.
  • Tests were conducted utilizing water phantoms of 5 cm, 10 cm, 15 cm, and 20 cm in depth. A step wedge was placed in the water to provide a measurable optical density (O.D) .
  • a Siemens Tridoros Optimatic 800 generator was used for testing using the 0.6 focal spot size. Testing was done using a Keithly 35055 digital dosimeter at 115 cm FFD. The HVL measured before testing was 3.8 mm Al at 80 kV. A 50 micron niobium filter added to the 3.8 mm Al outside the collimator window. The results are as follows:
  • the films taken with the niobium filter were judged by an experienced radiologist and determined to have greater detail than the unfiltered films.
  • the 50 micron Nb filter results in 30 to 50% dose reductions to the patient.

Abstract

Un filtre à rayons X réduit sensiblement le rayonnement de faible puissance normalement absorbé par l'objet de l'examen, sans affecter de manière significative le rayonnement de forte puissance voulu. Le filtre se compose d'un ou de plusieurs matériaux (12) comprenant à titre de constituant principal des éléments choisis dans le groupe composé d'aluminium, et d'éléments dont le nombre atomique est compris entre 26 et 50. On choisit le filtre pour que ses caractéristiques de filtration des rayons X réduisent d'environ 8 à 35 % les niveaux de rayonnement normaux de l'intensité des rayons X ayant des puissances de 50 KeV. Le résultat de cet agencement est que le filtre de cette invention filtre la puissance du faisceau de rayons X normalement absorbée par l'objet de l'examen, et n'a aucun effet sur l'image radiographique dudit objet. On parvient à ce but en augmentant peu ou pas la charge du tube de rayons X, autrement la durée de vie de ce dernier serait réduite.
PCT/US1989/000265 1988-01-29 1989-01-27 Filtre de reduction de rayonnement utilise dans le diagnostic medical WO1989007322A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
CA000557752A CA1250062A (fr) 1988-01-29 1988-01-29 Filtre pour l'attenuation des radiations emises par les appareils de diagnostic medical
CA557,752 1988-01-29

Publications (1)

Publication Number Publication Date
WO1989007322A1 true WO1989007322A1 (fr) 1989-08-10

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Application Number Title Priority Date Filing Date
PCT/US1989/000265 WO1989007322A1 (fr) 1988-01-29 1989-01-27 Filtre de reduction de rayonnement utilise dans le diagnostic medical

Country Status (10)

Country Link
EP (1) EP0356488A4 (fr)
JP (1) JPH03503213A (fr)
CN (1) CN1023849C (fr)
AU (1) AU3056689A (fr)
CA (1) CA1250062A (fr)
DD (1) DD294119A5 (fr)
DE (1) DE8912419U1 (fr)
ES (1) ES2011731A6 (fr)
IN (1) IN172608B (fr)
WO (1) WO1989007322A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3834731A1 (fr) * 2019-12-12 2021-06-16 Koninklijke Philips N.V. Filtres k-edge combinés pour la réduction de dose dans l'imagerie par rayons x

Families Citing this family (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GR890100445A (el) * 1989-07-12 1991-12-10 Rad Red Lab Inc Φιλτρο μειωσης της ακτινοβολιας για χρηση σε ιατρικες διαγνωσεις
DE9402609U1 (de) * 1994-02-17 1994-08-11 Thiess Axel Dipl Holzw Mehrschichtiges, flexibles Röntgenschutzmaterial nach DIN - 6813
JP3741613B2 (ja) 2001-01-29 2006-02-01 株式会社光子発生技術研究所 高エネルギーｘ線イメージング装置およびその方法
DE102006059143A1 (de) * 2006-12-14 2008-06-26 Siemens Ag Filteranordnung zur Ausfilterung von Röntgenstrahlen, insbesondere bei einem Mammographiegerät, und Röntgenfilter
WO2009122317A2 (fr) * 2008-04-01 2009-10-08 Koninklijke Philips Electronics N.V. Étalonnage de détecteur spectral
DE102011083845A1 (de) * 2011-09-30 2012-08-23 Siemens Aktiengesellschaft Filtereinrichtung zur Strahlaufhärtung bei einer Röntgeneinrichtung
CN104535592A (zh) * 2014-12-31 2015-04-22 同方威视技术股份有限公司 一种滤波装置和方法及一种物质探测装置和方法
CN105181723B (zh) * 2015-09-28 2019-02-12 同方威视技术股份有限公司 双能射线扫描系统、扫描方法以及检查系统
CN107731332A (zh) * 2017-08-31 2018-02-23 深圳市斯玛仪器有限公司 一种x射线防护器及放射性装置

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US3674687A (en) * 1969-09-19 1972-07-04 Underwater Storage Inc Storm sewage treatment
DE3022997A1 (de) * 1980-06-20 1982-05-19 Adolf Dipl.-Ing. 5788 Winterberg Voß Regenueberlauf-bauwerk fuer eine mischkanalisation
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DE3514726A1 (de) * 1984-06-07 1985-12-12 Ingenieur-Gemeinschaft Meerestechnik Und Seebau (Ims) Gmbh, 2000 Hamburg Vorrichtung fuer die zeitweise speicherung von mischwasser
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DE3022997A1 (de) * 1980-06-20 1982-05-19 Adolf Dipl.-Ing. 5788 Winterberg Voß Regenueberlauf-bauwerk fuer eine mischkanalisation
DE3514726A1 (de) * 1984-06-07 1985-12-12 Ingenieur-Gemeinschaft Meerestechnik Und Seebau (Ims) Gmbh, 2000 Hamburg Vorrichtung fuer die zeitweise speicherung von mischwasser
DE3435477A1 (de) * 1984-09-27 1986-03-27 Hansjörg Dr.-Ing. 6990 Bad Mergentheim Brombach Abwasserdrossel
DE8502827U1 (de) * 1985-02-02 1985-07-18 Giehl, Klaus-Ulrich, Dipl.-Ing. (FH), 5239 Heimborn Flüssigkeitsspeicherraum mit einer Spüleinrichtung

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See also references of EP0356488A4 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3834731A1 (fr) * 2019-12-12 2021-06-16 Koninklijke Philips N.V. Filtres k-edge combinés pour la réduction de dose dans l'imagerie par rayons x
WO2021116003A1 (fr) 2019-12-12 2021-06-17 Koninklijke Philips N.V. Filtres combinés de bord k pour réduction de dose en imagerie aux rayons x

Also Published As

Publication number Publication date
IN172608B (fr) 1993-10-23
EP0356488A1 (fr) 1990-03-07
DE8912419U1 (fr) 1990-02-01
JPH03503213A (ja) 1991-07-18
AU3056689A (en) 1989-08-25
DD294119A5 (de) 1991-09-19
EP0356488A4 (en) 1991-09-25
ES2011731A6 (es) 1990-02-01
CN1023849C (zh) 1994-02-16
CN1036285A (zh) 1989-10-11
CA1250062A (fr) 1989-02-14

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