Method and system for acquiring full spine and full leg images using flat panel digital radiography

Apparatus for acquiring an elongated radiographic image. The apparatus includes a flat panel electronic detector of radiographic images, the detector having a known length; and a transport mechanism for mounting the detector for movement in a direction parallel to the known length so that the detector can be positioned in sequential contiguous partially-overlapping positions to acquire a radiation image greater in length than the detector length. At least one marker is disposed in a region corresponding with each partially-overlapping position of the detector.

FIELD OF THE INVENTION

This invention relates in general to digital radiographic imaging, and in particular to the acquisition of multiple, standard sized radiographs for purposes of constructing a larger composite radiographic image.

BACKGROUND OF THE INVENTION

Full spine and full leg radiographic examinations require images that are longer than the length of normal-sized radiographic films. The problem is circumvented by two approaches. The first approach uses an extra long, non-standard film. This approach is expensive and inconvenient. The second approach uses several normal-size films for exposure and then tape the sub-images together (see U.S. Pat. Nos. 3,725,703 and 3,774,703). Computed Radiography (CR) has the same problem. The problem is circumvented by either using an elongated CR plate (U.S. Pat. No. 5,130,542) or by using several CR plates for imaging, and then using digital image processing to stitch the sub-images together (U.S. Pat. Nos. 5,111,045, 5,986,279 and EPO 919856A1).

With the advent of flat panel digital radiography (DR), it is natural to apply the technology to full spine/leg imaging. Various patents teach the assembly of smaller sensor arrays to form a large sensor (U.S. Pat. Nos. 5,105,087, 4,467,342, and 4,755,686). However, DR sensors are expensive. Thus the DR assembly approach is economically prohibitive. One patent teaches the use of a moving sensor to detect fan beam X-ray in CT scan (U.S. Pat. No. 4,873,708). The approach takes the scanned signals and constructs a sliced image of the body. U.S. Pat. Nos. 4,613,983 and 5,123,056 disclosure systems for imaging a human subject on a table including an X-ray source, a table and an image intensifier tube. Either the table or X-ray source and table are moved to produce a series of overlapping electronic images which are combined into an elongated image for display or printing. Another patent teaches a moveable X-ray cassette holder design.

The field of DR is expanding rapidly. Physicians order full spine and full leg imaging routinely for scoliosis patients and for leg length, angulation and deformity measurements. It is therefore necessary to provide an economically feasible capability for acquiring images using flat panel digital radiography that can be used for subsequent construction of full spine and long bone images.

SUMMARY OF THE INVENTION

According to one feature of the invention, it focuses on the sequential acquisition of multiple radiographic images using a moveable DR plate for purposes of digitally constructing a composite larger spine or long bone image.

According to another feature of the present invention, a standard DR plate is mounted on a moving plate holder. Two or more radiographic images are acquired sequentially. The spatial position of each subsequent image is acquired with a small amount of overlap of the spatial position of the previous image to aid in the construction of the composite image.

Individual images are acquired in the presence of a reference grid or some other fiducial markers to aid in performing geometric corrections for distortion introduced by the image acquisition process as the DR plate is moved.

ADVANTAGEOUS EFFECT OF THE INVENTION

The invention has the following advantages.

1. Composing sub-images acquired by DR is useful for full spine and full leg radiographic examinations. This approach combines the convenience of DR with the flexibility of digital image processing.

2. Only one DR plate is used for image acquisition. The first sub-image can be processed while the second one is being taken. Both cost saving and the convenience of DR imaging can be achieved.

DETAILED DESCRIPTION OF THE INVENTION

The present invention enables the sequential acquisition of multiple flat panel digital radiographs using a standard sized flat panel detector in such a way as to facilitate the subsequent construction of a larger composite image. As shown inFIG. 1, the flat panel detector10is mounted to a transport mechanism12that enables the detector to be moved in the vertical (up or down) direction14between each image acquisition. Mechanism12is mounted on a frame16. Detector10can be moved manually or be motor driven (not shown). The images are acquired such that there is a small amount of overlap between the previous and next acquisition.FIG. 2shows the acquisition of 3 overlapped images20,22,24. Fiducial markers are superimposed on the image of the patient so that the distortion introduced by the change in position of the detector relative to the direction of the primary radiation for sequential acquisitions can be corrected.FIG. 3shows an elongated guide30of radiation opaque material, such as lead. As shown inFIG. 4, grid30is placed in front of DR plate10.

Referring now toFIG. 4, there is shown a radiographic imaging system40incorporating the present invention. As shown, system40includes a source42of penetrating radiation, such as X-rays41. A patient44is placed between source42and detector10. Detector10is mounted for movement in the vertical direction14on transport assembly12on frame16. Radiation attenuating grid30is positioned between detector10and patient44.

FIGS. 5 and 6illustrate the use of fiducial markers50disposed proximate an edge of frame16. At least one fiducial marker50is stationarily disposed on frame16so as to be located in the region of the overlapping images.

Fiducial marker50is comprised of a radiation attenuating material or radiation opaque material, for example, lead. Fiducial marker50can be comprised of any shape, for example, a circle, square, triangle, and the like. Fiducial marker50can also be of any size, however, it should be of a size readily detectable in the acquired image, but not of a size that would interfere/obstruct/obscure the image content of the acquired image.

So as to not to interfere/obstruct/obscure the image content of the acquired image, fiducial marker50is disposed proximate an edge of frame16which is parallel to the direction of motion of transport system12, at a location corresponding to a region of the overlapping images. (More than one marker can be disposed within the region, for example, one marker50along each edge of frame16.) As such, when detector10is positioned and an image is acquired, at least one fiducial marker50will be imaged within each acquired image. The fiducial marker is superimposed on the image of the patient so that the distortion introduced by the change in position of the detector relative to the direction of the primary radiation for sequential acquisitions can be corrected.

Fiducial marker50provides an advantage over guide30in that there is no need to reconstruct the entire guide30. Only marker50needs to be reconstructed.

In addition, marker50is simple in its shape and size. Further, marker50can be sufficiently large in size for detection since it is located along the edge and is not obstructing or obscuring the image content of the acquired image. Because of its size, marker50are not subject to tensional deformation.