A method of spatially filtering the primary x-ray beam to emphasize the middle and upper frequency structure within a patient is under investigation. In a feasibility study, a copper filter is constructed which complements the low frequency structure of a scout film. The filter is placed in the x-ray beam and a new radiograph is taken. The result is a final x-ray in which the low frequency structures are suppressed, i.e., the middle and upper frequency structures are emphasized. This provides nearly constant detection probabilities for small, low contrast structures, regardless of their location in the patient. The results obtained from several such filters are very encouraging.
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