X-ray or gamma ray systems or devices – Photographic detector support – Sheet film cassette
Reexamination Certificate
2002-03-01
2003-07-29
Dunn, Drew A. (Department: 2882)
X-ray or gamma ray systems or devices
Photographic detector support
Sheet film cassette
C250S584000, C250S585000, C250S586000, C250S588000
Reexamination Certificate
active
06599014
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a device for reading flexible storage foils.
2. Background Art
Recently, flexible storage foils are being used instead of X-ray films. When ionizing radiation or X-rays impinge on such foils, metastable storage centers will be produced, which are lattice defects or color centers (or generally trap centers), which have trapped a charge carrier (electron or hole) produced by the ionizing radiation. Such storage centers are stable over long times. If the storage centers are illuminated with a very narrow laser beam of corresponding wave length, the storage centers will be moved into a higher excited state, from which the charge carriers can recombine under emission of light called photo-stimulated luminescence (PSL). The latter process is also shortly referred to as recombination of storage centers.
At such points of the storage foil, whereon a larger amount of X-rays has impinged, one obtains by reading this point using a reading light beam, a higher amount of light quanta than at such points, which have received only a few X-rays. If the storage foil is scanned in two dimensions, the output signals of a light detector receiving the PSL corresponds to the optical density of a conventional X-film.
In known reading devices, two dimensional scanning of the storage foil is obtained by arranging the storage foil on the outer surface of a drum, by rotating the drum and by moving a reading unit along a generating line of the drum. The reading unit includes a laser source and a light detector.
Such drum type scanners, which are also known for scanning images, are disadvantageous in that they have larger moving masses and in that the scanning velocity which can be achieved is only small due to this fact so that the scanning process takes a long time. It is thus an object of the present invention provide a reading device, wherein the moving masses are smaller and which allows high scanning velocities and short scanning times.
In a reading device in accordance with the present invention the storage foil support has the form of a part cylinder or of a cylinder, and a light deflecting element is arranged on the axis of this cylinder's surface. This deflecting element produces a fine rotating reading light beam, which scans the interior surface of the storage foil. This light deflecting element requires only very small dimensions and is of small mass, only. Due to this construction, the reading device in accordance with the present invention can work well with higher speed or rpm.
These and other objects of the present invention will become apparent in light of the present specification, claims and drawings.
SUMMARY OF THE INVENTION
If in accordance with the present invention, a pentaprism is used as the deflecting element for the reading light beam, one obtains a particularly precise deflection. The reflection of the reading light beam is exactly at 90° with respect to the axial direction of irradiation and into a radial measuring direction not withstanding whether the prism is exactly aligned or not. Also play of a bearing journaling a prism carrying shaft has no influence on the deflection of the reading light beam. Thus motors of simple construction showing some play of the shaft can be used for rotating the light deflecting element without impairing the precision of the deflection of the light.
The improvement of the present invention allows the use of the light deflecting element also for focusing the reading light beam onto the interior surface of the storage foil. In one preferred embodiment, there is a reading light source which already per se provides a reading light beam of very small cross section and small divergence. This makes it possible to construct the light deflecting element as a very small component.
A further improvement of the invention is advantageous in view of a compact structure of the reading device and makes it possible to arrange the reading light source also at a distance from the axis of the cylindrical surface.
In a preferred embodiment of the invention, both mirrors of the reading device, which deflect the light, which is provided by the laser on an axis being parallel to the axis of the support surface, exactly onto the axis of the support surface, are in fixed relative position since the two deflecting mirrors are part of a single rigid optical element. This is advantageous in view of reducing the adjusting steps.
A further improvement is advantageous in that only a single deflecting mirror is necessary to provide an incoming laser beam on the axis of the foil support.
In another preferred embodiment, the reading light beam of a semiconductor laser diode has a circular cross section which results in pixels of the scanned image which have equal dimension in the two scanning directions.
The present invention is advantageous in view of utilizing as much of the fluorescence light as possible. A further advantage resides in the fact that the efficiency in detecting fluorescence light, which is emitted along the scanning circle by the storage foil, is constant. Thus no subsequent corrections of the detected fluorescence signals are necessary.
The light detector of the present invention may have a smaller radius so that the costs for the detector are smaller. In spite of this advantage, the light generated at a larger radius can still be used due to the annular mirror reflecting this light onto an opposing mirror which will then reflect the light into the light detector.
The improvement of the present invention is also useful in view of using as much of the fluorescence light as possible, which light is emitted by the storage foil after illumination with laser light.
In a preferred embodiment of the invention, the light deflecting element can be driven directly without an intermediate direction changing gear by a motor that is arranged behind or in the mirror opposing the light detector.
In this respect, the improvement of the invention is advantageous in that such light is guided to the light detector, which impinges onto the mirror under large angles (grazing impingement). Thus the detection efficiency for fluorescence light is increased. Since the measured intensity of the fluorescence light is proportional to the intensity of the laser light as well as proportional to the detection efficiency, one can reduce the intensity of the laser light and still obtain the same sensitivity of demeasuring system. This is advantageous in that low cost laser light sources can be used.
In accordance with the present invention, the mirror opposing the light detector can also serve as an absorbing layer for reading light. Thus, undesired reflections of the laser light can be avoided, which could result in storage centers lying in regions of the foil, which are not yet to be scanned, being already caused to fluoresce. This would result in poorer resolution of the image. Also the contrast of the storage foil would be noticeably impaired.
The geometry of the mirror can have a large radial extension without having large axial extension and without requiring thin wall sections in the radial outward portion thereof. Also, transport means provided to feed the storage foils across a reading gap defined by the foil support, can be arranged close to the axial end of the mirror which is advantageous in view of precisely advancing the storage foil in axial direction at the location of the reading gap.
In such a preferred embodiment, reflected light will not travel in circumferential direction for a longer time but will be diffusely reflected to the light detector.
If the mirror is a cast component, the optical surfaces of the mirror can be already provided in the casting process. These surfaces need none or very little final treatment.
The present invention is likewise advantageous in still further reducing the amount of reading light which reaches the light detector.
In another preferred embodiment of the invention, as much of the fluorescence light as possible is detected by increasing the overall detect
Durr Dental GmbH & Co. KG
Factor & Partners, LLC.
Thomas Courtney
LandOfFree
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