The region of partial illumination or radiation caused by light or x-rays not originating from a point source; also called geometric unsharpness. [Mod. L., fr. L. paene, almost, + umbra, shadow]
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pe·num·bra pə-'nəm-brə n, pl -brae -(.)brē, -.brī or -bras a blurred area in a radiograph at the edge of an anatomical structure
pe·num·bral -brəl adj
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pen·um·bra (pə-numґbrə) [L. pēne almost + umbra] 1. the area of a shadow where there is partial illumination; it surrounds the umbra. 2. in radiography, an area of blurring around the edges of a structure.Medical dictionary. 2011.