Radiant energy – Source with recording detector – Using a stimulable phosphor
Reexamination Certificate
1999-09-17
2002-04-23
Hannaher, Constantine (Department: 2878)
Radiant energy
Source with recording detector
Using a stimulable phosphor
C250S585000
Reexamination Certificate
active
06376856
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of reading the radiation image recorded two-dimensionally in an imaging plate that uses a stimulable phosphor as a radiation detecting medium. The invention relates particularly to a method characterized by rapid reading of the radiation image in the imaging plate and its continuous reading as the plate is illuminated with radiation. Because of these features, the invention is useful in understanding dynamic events based on rapid processing and real-time radiation image detection as in medical X-ray diagnosis, X-ray structural analysis and research, neutral structural analysis and research, and autoradiography using X-rays and neutrons.
FIG. 1
shows a conventional method of reading the radiation image recorded two-dimensionally in an imaging plate that uses a stimulable phosphor as a radiation detecting medium. An irradiated imaging plate
201
on a transport belt
202
is moved as it is scanned over the surface with a spot beam of exciting light
204
from a light source
203
that has been reflected by a galvano-mirror
205
. The exciting light is typically laser light. The exciting light
204
generates photostimulated fluorescence
206
that is directed by a condensing guide
207
typically made of an optical fiber bundle and passed through a bandpass optical filter
208
having the wavelength of the photostimulated fluorescence as a center wavelength before it is detected with a photomultiplier tube
209
. The detected light is then supplied to a signal processor
210
, where it is converted to digital signals in accordance with intensity and reconstructed as a radiation image; this is the process of reading the radiation image recorded two-dimensionally in the imaging plate
201
[Nucl. Instr. and Meth., A246, p. 572-578 (1986); Gendai Kagaku, No. 223, p. 29-36 (1989)].
Another method currently used to transport the imaging plate is by rotating it on a drum [Nucl. Instr. and Meth., A310, p. 366-368 (1991); Hoshasen, Vol. 23, No. 2, p. 43-51 (1995)].
In the conventional method of reading radiation images, an imaging plate mounted on a belt or a drum is moved as its surface is scanned two-dimensionally pixel by pixel with a spot beam of laser light. Reading the radiation image from the entire surface of the imaging plate by this method is a time-consuming job. In addition, the imaging plate is moved mechanically in order to read one of the two axes in two-dimensional scanning and this not only limits the moving speed but also increases the chance of mechanical troubles. As a result, it has been difficult to perform real-time detection of the radiation image at high speed as the imaging plate is illuminated with radiation.
As a further problem, detecting the photostimulated fluorescence from the same side of the imaging plate as where the exciting light is incident makes the system highly sensitive to the intense scattering of the exciting light which can be background noise to the radiation image. In order to avoid the undesired effects of the scattered light, improvements have been made on the technique of processing the surface of the imaging plate and the method of condensing the photostimulated fluorescence by the condensing guide.
SUMMARY OF THE INVENTION
The principal object of the invention is to provide a method of reading the radiation image in an imaging plate that is capable of rapid reading of the radiation image with high sensitivity and reduced background noise from the scattering of exciting light, that minimizes the mechanically moving parts to reduce the causes of trouble, and that enables the radiation image to be read continuously in real time and stored as a digital image while the imaging plate is illuminated with radiation.
In order to attain this object, the exciting light for reading the photostimulated fluorescence from color centers created by radiation in the bulk of the stimulable phosphor used as a detecting medium in the imaging plate is applied in a rectangular shape to the front side of the imaging plate whereas the photostimulated fluorescence from the back side of the imaging plate is detected with a planar array of wavelength shifters that is positioned at right angles to the rectangular shape of exciting light, thereby reading the two-dimensionally recorded radiation image. This enables the radiation image to be read from the imaging plate at high speed since the whole image can be read by scanning with the moving rectangular shape of exciting light. As a further advantage, the imaging plate fixed on the scan table is scanned by illumination with the rectangular shape of exciting light and this reduces the causes of trouble since the only mechanical part of the system is found in the mechanism for performing one-directional scan.
The imaging plate used in the method of the invention which relies upon a stimulable phosphor as a detection medium is capable of transmitting light through both front and back sides and exciting light is incident on the front side whereas the photostimulated fluorescence emitted from the back side is detected. Therefore, almost all of the scattered exciting light that is emitted simultaneously with the photostimulated fluorescence is rejected by the bandpass optical filter that is placed behind the imaging plate and which has the wavelength of the photostimulated fluorescence as a center wavelength. Any leakage of the scattered exciting light from the optical filter is incident on the wavelength shifters in fiber form at right angles and only a very portion of it propagates through the shifters. The fluorescence shifted in wavelength by the wavelength shifters is passed through a bandpass optical filter having the wavelength of the fluorescence as a central wavelength and this ensures that the scattered exciting light will not be launched into a photodetector to become background noise to the radiation image.
The imaging plate used in the invention may be so modified as to comprise a planar array of fibers made of a transparent glass capable of emitting photostimulated fluorescence. Since this type of glass itself is in fiber form, the imaging plate allows for efficient reading of photostimulated fluorescence from the color centers created by radiation. The already described method of reading can be employed without any change and the radiation image in the imaging plate can be read at high speed and with high sensitivity by scanning with the moving rectangular shape of exciting light.
In the conventional method, a photomultiplier tube has been used as a photodetector. In the invention, a multi-channel photodetector is substituted that consists of optics, a streak tube and a CCD camera. The streak tube consists of a photocathode, electrodes with a slit, a deflector, a micro-plate channel and a fluorescent screen. The fluorescence emitted from the array of wavelength shifters is passed through the optics and allowed to be incident on the horizontal axis of the streak tube. Since the streak tube sweeps the deflector by time, its vertical axis is swept in correspondence with the reading position in the longitudinal direction of the imaging plate, whereby a streak image is produced on the fluorescent screen. The streak image is cumulatively detected with the CCD camera capable of two-dimensional recording and the accumulated signals are digitized with a signal processor, thereby reading the radiation image recorded two-dimensionally in the imaging plate. Using this multi-channel photodetector, one can detect photostimulated fluorescence, integrate the amount of fluorescence and store a large volume of data within very short times. On the other hand, if photomultiplier tubes are to be used, their number must be equal to that of the wavelength shifters used and the same numbers of signal amplifiers, integrators and analog/digital converters must also be used at subsequent stages; this raises the need to use a huge volume of modules but offers the advantage of enabling real-time processing. It should also be noted that the time requir
Banner & Witcoff , Ltd.
Gabor Otilia
Hannaher Constantine
Japan Atomic Energy Research Institute
LandOfFree
Apparatus for reading radiation image recorded in an imaging... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for reading radiation image recorded in an imaging..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for reading radiation image recorded in an imaging... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2860441