Patent Number: 
Section: description

In accordance with the invention, an X-ray system with symmetric collimation as described above may be readily modified for chest imaging, while minimizing the impact of the modification on the overall system architecture, and without losing important benefits and advantages of the system. Such modification is usefully understood by first referring to FIG. 1, which shows an X-ray tube 10 disposed to project a beam of X-rays through a collimator 12 adjacent thereto. The projected beam is incident upon the detector plane 14a of a digital solid-state X-ray detector 14, within an active imaging area or AIA. Collimator 12 is provided with internal collimator blades 16 and 18, which are movable toward or away from each other to respectively decrease or increase the vertical dimension of the AIA. FIG. 1 shows collimator blades 16 and 18 adjusted to provide an X-ray beam 20 bounded by an upper ray 20a and a lower ray 20b, which are directed to the upper and lower edges, respectively, of detector 14. Thus, collimator 12 in FIG. 1 provides a full field view, that is, the vertical dimension of beam 20 and the vertical dimension of detector plane 14a of detector 14 coincide at their intersection. In FIG. 1, internal collimator blades 16 and 18 provide symmetric collimation in that for any adjustment thereof, the X-ray beam projected therethrough will be symmetric about the focal point center line 22 of the beam. Referring to FIG. 2, there is shown the arrangement depicted in FIG. 1, modified in accordance with the invention by joining a fixed collimator blade 24 to the collimator 12. More specifically, collimator blade 24 is fixably joined to collimator 12 so that it lies in the path of the upper portion of an X-ray beam projected out from collimator 12. Thus, upper ray 20a of beam 20 is blocked by collimator blade 24. As shown by FIG. 2, the uppermost portion of any beam which may be projected by collimator 12 is bounded by ray 26a.  As described hereinafter in connection with FIG. 4, detector 14 is vertically adjustable with respect to X-ray tube 10 and collimator 12. Accordingly, FIG. 2 further shows detector 14 vertically adjusted so that ray 26a of a projected beam intersects the upper edge of detector 14. To provide a full field of view on the detector plane 14a, so that the entire area of the detector plane may be used to acquire an image, collimator blades 16 and 18 are selectively moved apart, with respect to their positions as shown in FIG. 1, to provide an X-ray beam 28. Beam 28, which is wider than beam 20, has a lower ray 28b which intersects the lower edge of detector 14. However, upper ray 28a of beam 28 is blocked by the fixed collimator blade 24. Referring to FIG. 3, there is shown collimator blades 16 and 18 moved toward one another, with respect to their positions shown in FIG. 2, to project an X-ray beam 30 having an upper ray 30a and a lower ray 30b. Upper ray 30a is blocked by fixed collimator blade 24, and ray 26a continues to intersect the upper edge of detector 14. However, ray 30b intersects the detector plane 14a at a distance Xclose above the lower edge thereof. Thus, a lower region 14b of detector 14 does not receive X-rays of beam 30. Moreover, the dimension xclose of lower region 14b may be readily changed by adjustment of collimator blades 16 and 18, up to a limit described hereinafter, while the remainder of the detector continues to receive X-radiation. Accordingly, the collimator arrangement shown in FIGS. 2 and 3 is operable to asymmetrically collimate an X-ray beam projected therethrough. Such arrangement may be readily employed for chest imaging as described above. A patient would be positioned directly in front of detector 14, with his or her chin near the top of the detector. Collimator blades 16 and 18 would then be adjusted to bring lower region 14b of detector 14 and the lower abdominal region of the patient, which is to be excluded from X-ray exposure, into coincident relationship. Thus, the arrangement of FIGS. 2 and 3 allows symmetric X-ray collimator 12 to be used in an application requiring asymmetric collimation, while at the same time maintaining image quality. In addition, the effective radiation received by a patient can be reduced without the use of cumbersome shields or aprons of the type described above. Moreover, in products such as the Revolution XQ/i, referred to above, a user will be able to position the patient in a customary manner utilizing the auto tracking tube designed for overall customer productivity. Collimator 12 is also provided with a pair of internal collimator blades (not shown) which are used to adjust the horizontal dimension of the AIA. Though available, such collimator blades are generally not used in connection with the present embodiment of the invention. Referring to FIG. 4, there is shown tube 10 and collimator 12 mounted for selected vertical positioning along a support column 32. Detector 14 is likewise shown to be mounted for vertical positioning along a support column 34. There is further shown collimator 12 adjusted as previously described in connection with FIG. 2, so that the X-ray system of FIG. 4 is set up for full field of view operation. That is, the AIA coincides with the entire detector plane 14a of detector 14. This is illustrated by FIG. 5. which also depicts a region 24a directly above detector 14. Region 24a represents an area from which X-rays projected by tube 10 are blocked by the action of fixed blade 24. Referring further to FIG. 4, there is shown the center line 36 of detector 14 offset from focal spot center line 22 of the X-ray tube 10 by an amount Xoffset, due to the effect of fixed collimator blade 24. Referring to FIG. 6, there is shown collimator 12 adjusted as previously described in connection with FIG. 3. Thus, the AIA on detector 14 is reduced by lower region 14b of length Xclose, as described above and as illustrated by FIG. 7. As collimator blades 16 and 18 are moved closer together, the X-ray field of view on detector 14 will continue to close from the bottom of the detector upward, until Xclose=2xoffset. At this point the field of view will converge together from the top and bottom of detector 14 at an equal rate, until the collimator blades 16 and 18 close together at focal spot center line 22. Obviously, many other modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the disclosed concept, the invention may be practiced otherwise than as has been specifically described.