Radiant energy – Source with recording detector – Using a stimulable phosphor
Reexamination Certificate
1999-11-24
2002-03-12
Hannaher, Constantine (Department: 2878)
Radiant energy
Source with recording detector
Using a stimulable phosphor
C250S234000, C250S235000, C250S585000
Reexamination Certificate
active
06355938
ABSTRACT:
TECHNICAL FIELD
The present invention relates to methods and systems for reading images stored on photo-stimulable media, and in particular to reading images stored on phosphor radiation screens.
BACKGROUND OF THE INVENTION
The use of photostimulable phosphor image storage screens as a replacement for an x-ray film and other sensors is well known. Phosphor image screens work by trapping individual x-ray photons in a storage layer. The latent image trapped in the screen can then be read by scanning the storage layer using a suitable wavelength excitation beam, preferably from a focussed laser. The laser excitation beam causes the screen to release the latent image in the form of emitted stimulable phosphor light that is proportional to the x-ray energy applied to the screen during exposure. The emitted light is collected by an optical system and is converted into an electronic signal proportional to the emitted light. The electrical signal is then converted into a digital value and passed to a computer which generates and stores an image file. The image file can then be displayed as a representation of the original radiograph, with image enhancement software applied to augment the radiographic information.
Various known systems for moving a scanning head or directing a scanning beam across image or data storage screens are known. In one family of systems, an X-Y raster scan is taken as follows. The scanning head or beam first scans in a straight line across the screen in an X direction. The screen is then moved a short incremental distance in the Y direction. (Alternatively, the scanning head or the optics directing the beam can be moved incrementally in the Y direction). Thereafter, an X directional scan is repeated. Accordingly, by scanning back and forth in one direction, while intermittently advancing the screen, (or re-directing the scanning beam), in a perpendicular direction, an X-Y raster scan is generated. In a second family of systems, the image or data storage screen is rotated in the plane of the screen about a center point in the screen while a scanning head is moved radially across the screen.
A problem common to both families of scanning systems is the problem of precisely controlling the movement of the scanning head, (or the movement of the optical system directing the scanning beam, which may comprise a galvanometric mirror). This is partially due to the fact that the scanning head or scanning beam optics must be rapidly moved back and forth in at least one direction with the speed of such movement constantly and quickly changing. Accordingly, such scanning heads or scanning beam optical systems which rapidly move back and forth are typically subject to accelerations which cause problems including mechanical wear and failure and reduce read efficiency (i.e.: duty cycle) time to less than 100%. Moreover, problems exist when attempting to accurately position such a moving scanning head or beam direction system to direct an incident beam at a desired location on the phosphor screen.
A second problem common to existing imaging systems is that such systems are configured such that the response radiation emitted by the screen is not directed back to a light detector through the same optical train that was used to direct incident laser light at the screen. Accordingly, a first optical train is required to direct and focus the incident light on the screen, and a second optical train is required to detect and measure the response radiation emitted by the screen.
It would instead be desirable to provide a system for high speed scanning of a phosphor screen, (or any other photostimulable media), which moves a scanning beam head in a path across the surface of the phosphor screen to generate a raster scan, yet avoids the problems of controlling the back and forth movement of the scanning head across the screen. It would also be desirable to avoid potential inaccuracies, control and wear and tear problems caused by acceleration forces moving such a scanning head back and forth in one or two directions, at the same time achieving near 100% duty cycle read efficiency.
Moreover, it would be desirable to create a high speed scanning system which has minimal dead time during its operation such that a near continuous data stream can be generated as the phosphor screen is scanned.
Additionally, it would be desirable to create a high speed scanning system which does not require a transport mechanism which either moves the phosphor screen in two perpendicular directions (such as would be accomplished with an X-Y transport mechanism), or rotates the phosphor screen.
Additionally, it would be desirable to create a high speed scanning system which uses the same optical train for phosphor screen stimulation and data collection.
SUMMARY OF THE INVENTION
The present invention provides systems and methods for scanning a photostimulable imaging plate, (which may preferably comprise phosphor storage screen), with a scanning system comprising a continuous belt drive having at least two scanning heads mounted thereon. In one preferred aspect, a dual-head scanning device is provided, but the present invention also encompasses more than two scanning heads being used.
In accordance with the present invention, the two (or more) scanning heads are moved across the surface of a phosphor screen by a rotating belt drive, and are preferably attached to the continuous belt drive at equidistant locations around the belt drive.
A laser is positioned to direct a laser beam in a beam path which passes above, and fully across, the imaging plate. Preferably, the laser beam path is parallel to the surface of the imaging plate, however, the laser beam path can also be angled to the surface of the imaging plate as long as it passes fully across the surface of the imaging plate.
The continuous belt drive is dimensioned and positioned to sequentially move each of the first and second scanning heads across the surface of the imaging plate in a path which is collinear with the laser beam, with only one of the scanning heads being disposed in the laser beam path at a time.
Each scanning head operates to reflect the incident laser beam onto the surface of the imaging plate. In addition, each of the scanning heads directs response radiation emitted by the imaging plate towards a photodetector. The signal output of the photodetector is used to create an image corresponding to the image stored on the phosphor screen.
The present invention also provides methods for scanning an imaging plate, comprising, directing a laser beam in a beam path across the surface of the imaging plate; and alternatingly moving first and second scanning heads across the surface of the imaging plate in a path collinear with the beam path wherein only one of the first and second scanning heads is positioned collinear with the beam path at a time.
Each of the plurality of scanning heads scans one after another in repeating sequence across the surface of the phosphor screen in the path of the laser beam such that only one scanning head is actively scanning over the phosphor screen at a time. Accordingly, two scanning heads are used in conjunction with a single laser light source and a single photodetector.
The present invention operates with only a minimal amount of dead time during which scanning is not performed. Specifically, dead time only occurs when the system is switching between scanning heads, (i.e., when the first scanning head has just completed its scan across the screen and the second scanning head is just about to commence its scan across the screen). As such, dead time will only occur during the interval when the first scanning head has passed beyond the edge of the screen and immediately prior to the second scanning head moving into position above the screen. The data gap which occurs during this dead time can advantageously be used to distinguish between data gathered by the successive scanning heads such that a raster scan image can easily be generated of the phosphor screen.
An advantage of the present invention is that scannin
Cantu Gary
Evans Wayne
Lewis Todd
Barrish, Esq. Mark D.
Hannaher Constantine
Israel Andrew
PhorMax Corporation
Townsend & Townsend & Crew LLP
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