Light stimulating and collecting methods and apparatus for storage-phosphor image plates

Abstract

Methods and apparatus are described for retrieving information from a storage medium. A first portion of the surface of the storage medium is exposed to stimulating light which diffuses in the storage medium under a second portion of the surface adjacent the first portion. The second portion of the surface is shielded from exposure to the stimulating light. Stimulated light corresponding to the information is received with at least one detector positioned to receive the stimulated light via the second portion of the surface of the storage medium. The stimulated light is released from the storage medium in response to the stimulating light diffused under the second portion of the surface.

Description

RELATED APPLICATION DATA [0001] The present application claims priority from and is a continuation of U.S. patent application Ser. No. 10 / 789,547 filed Feb. 26, 2004 (Attorney Docket No. SAY1P004D1), which claims priority from U.S. patent application Ser. No. 09 / 887,543 filed Jun. 21, 2001 (Attorney Docket No. SAY1P004), which claims priority from U.S. Provisional Application No. 60 / 257,622 filed Dec. 20, 2000 (Attorney Docket No. SAY1P004P), the entire disclosures of both of which are incorporated herein by reference for all purposes.BACKGROUND OF THE INVENTION [0002] The present invention relates to the field of digital radiography and more specifically to methods and apparatus for obtaining an electrical representation of a radiation image using a storage-phosphor image plate. [0003] In the field of digital radiography a variety of methods have emerged. One such method is based on capturing the prompt-emitting light of a conventional phosphor screen with an image intensifier, a f...

AI Technical Summary

Benefits of technology

[0019] By controlling the intensity of the stimulating light on one region of a storage-phosphor plate a well-defined diffusion distribution (and therefore stimulation) under an adjacent region can be achieved. Efficient collection of the stimulated light released from this indirectly stimulated region of the storage medium may then be effected by one or more detectors in direct contact with (or at some very small distance from) the surface of the plate.

Problems solved by technology

Unfortunately, because only one pixel is read at a time, the readout time for a typical storage-phosphor plate is unacceptably long.

In addition, the laser scanning mechanism necessary to stimulate one pixel at a time on a 14″×17″ phosphor plate is very large and complex.

Another problem relates to interplay between the dimension of the stimulating laser pencil beam on the plate (which dictates the spatial resolution of the overall reading apparatus) and the efficiency with which light released from the storage medium is collected.

However, it is very difficult to achieve high collection efficiency since the stimulating light path gets in the way of the stimulated light collection device.

In addition, the stimulated light emits in all directions due to the turbid nature of the storage phosphor plate, which makes it even more difficult to collect.

Unfortunately, because of a variety of tradeoffs, none of the previous techniques addressing the spatial resolution issues of storage-phosphor based systems has been universally effective.

These clear plates can potentially achieve higher spatial resolution since no light diffusion occurs in them, but they are very difficult to manufacture and extremely sensitive to scratches and mishandling.

On the other hand, with conventional powder phosphor plates, laser-based scanning systems require complex and sub-optimal tradeoffs between spatial resolution, bleaching ratio (i.e., readout efficiency), and readout speed.

The required spatial resolution limits the stimulating laser power (too strong of a laser beam creates too large of a spot) and, as a result, only a fraction of the available stimulated light is read out (i.e., partial bleaching).

These tradeoffs result in a degradation of image quality (lower Detective Quantum Efficiency, i.e., DQE) since not all the information is read out of the plate.

Whereas the storage-phosphor plates themselves are ideal replacements to film-screen combinations, currently available laser-based scanning systems are far from ideal.

The theoretical advantages of linescanning over pixel-by-pixel scanning are clear, but the practical implementation of the stimulating fan beam and the associated collecting optics is extremely challenging.

These two requirements are very difficult to achieve with conventional techniques as evidenced by the fact that no linescanning plate reader is yet commercially available.

Numerous designs have been proposed, some relying on traditional optics (e.g., U.S. Pat. No. 5,747,825 the entire disclosure of which is incorporated herein by reference), but most assuming that traditional optics are not practical to efficiently image the surface of a plate onto a photodetector line array.

This constraint creates a serious challenge as far as stimulating the area right underneath the linear array.

A small gap can be placed between the plate and the linear array to let the stimulating light pass through, but since the plate has a Lambertian emission, this has a catastrophic effect on the collection efficiency and spatial resolution of the system.

However, as discussed above, the cost of producing and handling this type of phosphor plate can be prohibitively expensive.

This design has the limitations mentioned earlier relating to the gap between the plate and the receiving optical fibers.

Unfortunately, in all these proposed designs, the confinement of the stimulating light to the imaging area is a great engineering challenge.

Images