L'invention concerne les tubes intensificateurs d'image radiologique comportant un tube électronique à vide et un écran d'observation luminescent (20) comportant des moyens d'amélioration du contraste de l'image. Ces moyens consistant en une couche d'aluminium d'une épaisseur d'au moins 1 micromètre, partiellement absorbante pour les électrons incidents (Ei), placée dans le trajet des électrons générés par le tube et à proximité de la couche des luminophores (28), la couche déposée ayant pour effet de réduire la quantité d'électrons réémis de l'écran d'observation vers le tube et d'autre part la proportion de ces électrons qui reviennent frapper la couche de luminophores.

Application aux tubes intensificateurs d'image de type radiologique.

A high resolution radiographic element is described to comprise an ultraviolet emitting X-ray intensifying screen. The screen comprises a phosphor and an acutance dye defined by

wherein R¹ and R² are independently chosen from the set consisting of hydrogen, alkyl, and aryl;

R³, R⁴, R⁵ and R⁶ are independently chosen from the set consisting of H, alkyl, halogen, alkoxy, hydroxy;

R⁷ represents alkyl, aryl, -OR⁹, -NR¹⁰R¹¹ wherein R⁹, R¹⁰ and R¹¹ independently represent hydrogen, alkyl, and aryl;

R⁸ is alkyl, aryl, -CN, -COR¹² wherein R¹² is alkyl, aryl, -COOR¹³ wherein R¹³ is alkyl, and aryl;

R⁷ and R⁸ can be taken together to form a five or six member ring or a substituted five or six member ring.

The present invention relates to an X-ray intensifying screen comprising a support, a reflective layer, and a phosphor layer, wherein said phosphor is selected in the group of UV-blue emitting phosphors having their emission maximum at a wavelength shorter than 450 nm, and wherein a fluorescent dye is dispersed into the reflective layer or into a fluorescent dye layer interposed between said reflective layer and said phosphor layer, said fluorescent dye having its spectral absorption maximum at a wavelength shorter than 400 nm and its spectral emission maximum at a wavelength longer than 400 nm.

X-ray intensifying screens of different speed classes are disclosed, showing a synergistic effect between screen speed or sensitivity and image quality, especially sharpness, if for each speed class the right combination is applied for the amount of dye in the screens and the weight amount and weight coverage of selected mixtures of yttrium tantalate or niobate phosphor and rare earth activated alkaline earth metal fluorohalide phosphors coated onto selected supports showing well-determined reflectance characteristics.

An x-ray examination apparatus in accordance with the invention comprises an imaging arrangement devised for performing fluoroscopy. To that end image sensors are efficiently optically coupled with an x-ray sensitive radiation conversion screen. Consequently, the image sensors produce an electrical signal having a high signal-to-noise ration when low doses of x-radiation are administered. An x-ray conversion screen is provided with a multilayer interference filter so as to concentrate light in the forward direction. Furthermore, the x-ray conversion screen is preferably fitted with a light reflecting layer for reflecting light that has been reflected by the multilayer interference filter, said light reflecting layer being transparent for x-radiation. Further concentration of light in the forward direction is achieved by placing a light-transparent material having a suitable refractive index between the radiation conversion screen and lenses that concentrate the light onto the image sensors.

Semiconductor image sensors in the form of charge-coupled devices are provided for converting a visible image into an electronic video signal. In order to improve the effectiveness of the CCDs, weak avalanching is applied so as to increase both sensitivity and signal-to-noise ration of the sensors.

An improvement of a radiographic intensifying screen comprises a support, a phosphor layer and a protective layer in order resides in the protective layer which is formed on the phosphor layer by coating a fluoro-resin on the phosphor layer to give a coated layer having a thickness of less than 5 µm.

An improved combination for forming a radiographic image comprises an intensifying screen which is high-sensitive and shows high contrast transfer function values and a silver halide photographic material having a specifically defined sensitivity: that is, 0.010-0.035 lux·second of exposure dose is required to obtain an image having a density of 0.5 more than the minimum density on its photosensitive layer: the density is determined by the steps of exposing the photosensitive layer to monochromatic light of which wavelength is the same as the main emission wavelength of the above intensifying screen and of which half width is 15±5 nm, developing at 35°C for 25 seconds in the specified developing solution, removing the photosensitive layer on the side reverse to the exposed side and then measuring the density of the remaining photosensitive layer. Another combination based on the analogous concept is also disclosed.

An X-ray phosphor mixture consisting of :

• (1) a monoclinic M' structure yttrium or yttrium/gadolinium strontium tantalate or niobate phosphor, and
• (2) a phosphor with empirical formula : (Ba_1-x,Sr_x)F_yX_z:Eu²⁺⁽³⁺⁾, wherein :
  
  X is halogen other than fluorine, but represents at least 80 atom % of Br,
  
  x is a value in the range 0 ≦ x ≦ 0.75, but is prefereably zero,
  
  y is in the range 0.8 ≦ y ≦ 1.2 and y + z = 2; and
  
  wherein (1) to (2) are present in a weight ratio range of 5/95 to 95/5.

An improved intensifying lead screen for use with photographic, industrial X-ray films, having a low propensity to produce electrostatic changes, is described. This screen comprises a lead foil adhesively applied to a polyester support with an overcoat or protective layer applied over the lead layer and coated thereon, a layer of a fluorosurfactant.