Patent Number: 056174659
Section: description

DESCRIPTION OF THE INVENTION As illustrated in FIG. 1 in conjunction with FIG. 2, X-ray source 7 provides an X-ray output, or beam, 8 that is directed to a positioning unit 10 positioning an object, or a body portion, 11 at a scan area 12. X-rays passing through the object, or body portion, 11 are received at fixed, or stationary, X-ray converter screen 14, preferably a standard high efficiency phosphor converter screen having the size of the field of view (FOV) to be scanned, with the converter screen being mounted in holder 15 so that the converter screen is a curved membrane, as indicated in FIG. 2. Light signals are generated at converter screen 14 in response, and proportional to, received X-rays, as is well known, and the light signals are provided to sensor/coupling unit 16. Sensor/coupling unit 16 includes a coupler 18, preferably a fiber optic (FO) coupler such as a fiber optic window (FO-window) or a fiber optic reducer (FO-reducer) with an input face, or portion, 19 engaging the side of converter plate 14 opposite to the side of the converter plate facing the X-ray source. Sensor/coupling unit 16 also includes a sensor 20, preferably a single stage (or multiple stage) charge coupled device (CCD) or, preferably, a time delay integrated (TDI) CCD. X-ray source 7 is mounted at the pivot end 22 of mounting, or swing, arm 23, and sensor/coupling unit 16 is mounted at the free end 24 of the swing arm. When so mounted, X-ray source 7 is essentially pivoted to effect field of view (FOV) motion, while sensor/coupling unit 16 is moved in an arc below converter screen 14 to effect full FOV coverage (the curvature of the converter screen is the same as the arcuate path of travel of the sensor/coupling unit). In such swing arm systems, the sensor is maintained in register with the X-ray beam and the coupler remains closely adjacent to the converter screen (with the input face of the coupler engaging the converter screen) since the curvature of the converter screen is the same as the arcuate path followed by the sensor/coupling unit. As indicated in FIG. 1, movement of mounting arm 23 is controlled by actuator unit 26, implemented, for example, by a conventional mechanical and/or motor arrangement. Actuator unit 26 is controlled by control unit 28, which unit also controls sensor 20. Sensor 20 provides an electrical output signal indicative of the object, or body portion of a patient, then being subjected to X-rays, and the analog output signal is normally converted to a digital signal at digital conversion unit 30, and the digital signal is then typically coupled to an electronic unit, preferably an electronic readout and/or storage unit 32, which unit normally includes a computer 34 having data storage 36 and monitor 38 connected therewith. An air gap between X-ray converter screen 14 and input face 19 of coupler 18 cannot be tolerated since the presence of such an air gap would result in an unacceptable loss of resolution. It is therefore necessary that positive contact, or engagement, between converter screen 14 and input face 19 be maintained throughout the scan. To assure and/or establish positive contact between converter screen 14 and input face 19, a force is provided: to urge the converter screen in a direction toward the input face of the coupler (such as by introducing a cushion, preferably an air cushion, 40 between positioning unit 10 and converter screen 14, as indicated in FIG. 3); to pull the converter screen and the input face toward one another (such as by introducing a vacuum between the converter screen and the input face of the coupler using a vacuum source 42 and tube 43, as indicated in FIG. 4); and/or to bias the sensor/coupling unit toward the converter screen (such as by introducing springs 45 between a reference, plate 46 and the sensor of the sensor/coupling unit, as indicated in FIG. 5). In some types of systems, such as, for example, in gantry type systems, the X-ray source and sensor/coupler follow a straight line path. In this type of system, the converter screen is also flat, rather than having a curvature as shown in FIG. 2, with the system operating in the same manner with respect to maintaining positive engagement between the fixed converter screen and the input face of the movable coupler. This invention is not meant to be limited to use in the medical field, but has been found to be useful in medical applications and/or procedures to X-ray predetermined body portions (such as, for example, to X-ray breasts when used in a mammogram system). In addition, this invention is also not meant to be limited to a single, or multiple, CCD or TDI-CCD arrangement, and can be used, for example, with multiple ones of such sensors to obtain stereo or volumetric imaging information. For stereo imaging, two such sensors are utilized, and, for volumetric imaging, three such sensors are utilized. As can be appreciated from the foregoing, this invention provides a system and method for X-ray imaging wherein signals from a fixed converter screen are coupled to a movable sensor through a movable coupler having an input face maintained in engagement with the converter screen.