Patent Number: 042648246
Section: summary

BACKGROUND OF THE INVENTION This invention relates to obtaining information about radiation sources, and is particularly useful for locating astronomical bodies. My U.S. Pat. No. 4,090,080 (hereby incorporated by reference) described a device useful for mapping a nearby source ("near field") of radiation, e.g., a gamma ray emittig radioisotope located in a patient undergoing a medical procedure. Each slit of the collimator is defined by a pair of parallel, radiation absorbing sheets. The collimator is rotated about its axis, and detectors are arranged to measure the radiation passing through each slit in each of many angular positions of the collimator. Simultaneous equations are then solved, applying known computer techniques, to generate the desired map. As is mentioned in said patent, honeycomb-like channel collimators have also been used for such mapping; a single picture is taken with the collimator stationary, each channel viewing a different portion of the source. Channel collimators have also been used in x-ray astronomy, where the source is so distant ("far field") that all channels receive the same radiation flux; the collimator is mounted to pivot about orthogonal axes in a raster scan pattern. As in the near field case, a major problem in far field imaging with channel collimators is that when the channels are made narrower or longer to improve resolution, sensitivity is reduced and a long time is required for the collimator to transmit enough radiation to assemble an image. In my pending U.S. patent application Ser. No. 921,200, filed July 8, 1978, now U.S. Pat. No. 4,205,228, (hereby incorporated byreference) there is described a far field imaging device. A collimator is rotated about its own axis while that axis moves about a fixed axis pointing toward the overall field of view of the collimator. Radiation from the source is transmitted through the collimator during each of its revolutions about its axis. The position of the collimator relative to its axis, and the angular position of the collimator axis relative to the fixed axis, at the time of each such transmission, define a response plane. Computerized data reduction is used to find the intersection of the response planes, which will be a line pointing precisely at the source. For multiple sources, there are a corresponding number of intersections. SUMMARY OF THE INVENTION My invention provides excellent sensitivity and resolution, with a device of simple construction that requires motion only about a single axis. In general, the collimator has a multiplicity of portions, the transmissivities of the portions to radiation reaching the collimator from a given source being different from portion-to-portion for a given orientation of the collimator; these transmissivities are varied over time, and radiation passing through each portion is detected for successive values of its transmissivity. In preferred embodiments the collimator has slits defined by radiation absorbing sheets which lie along planes intersecting in a common focal line, and the transmissivities of the slits are varied over time by rotating the collimator about an axis pointing toward its field of view and perpendicular to the focal line. Other advantages and features of the invention will appear from the following description of a preferred embodiment thereof. DESCRIPTION OF PREFERRED EMBODIMENT I turn now to the structure and operation of a preferred embodiment of the invention, after first briefly describing the drawing.