Page 328 - Biomedical Engineering and Design Handbook Volume 2, Applications

306 DIAGNOSTIC EQUIPMENT DESIGN

FIGURE 10.43 Raster scan imaging with small-area detector.

FIGURE 10.44 Direct magnification imaging with large-area detector.

composition. Also, scattering may compromise the image quality, though at the higher magnifica-
tions the effect would be reduced because of the larger source to detector distance D .
SD
The relative separation of the source, specimen and detector provides direct magnification
according to Eq. (10.89). Here, the magnification can be chosen so that the resolution limit of the
detector does not compromise the resolution of the x-ray source. For a given detector pixel size d
p
at the input plane, the corresponding voxel element size d = d p /M. This also determines the size of
v
the specimen to be imaged, since the frame size (height H = d N , width W = d N ) relates to the size
F
F
p W
p H
of the reconstruction volume (height H = H /M, width W = W /M, depth D = W /M), where N ×
V F V F V F H
N is the number of frame pixels.
W
If a wide range of specimen sizes is to be accommodated, the detector/camera input plane needs be
of adequate extent, >50 mm. However, the charged coupled device (CCD) that is the actual detector is