Bush__The_Essential_Physics_for_Medical_Imaging - Biomedical ...

for digital stereotactic biopsy. Breast biopsy systems using digital detectors are typically5 X 5 cm and make use of either fiberoptic tapers or mirrors coupled to CCDcameras (Fig. 11-11). X-ray energy absorbed in the intensifYing screen releases light,which is conducted through light pipes that focus the image onto the surface of aCCD chip. A secondary quantum sink is avoided because the fiberoptic lens is quiteefficient and the demagnification factor is small.Full-field digital mammography systems based on CCD cameras make use of amosaic of CCD systems. The use of several CCD chips is necessary to increase thearea of the light sensor and thereby keep the demagnification factor low (similar tothat of digital biopsy) in order to avoid a secondary quantum sink. A mosaic CCDsystem based on fiberoptic tapers is shown in Fig. 11-11, and lens-coupled systems(still with low demagnification factors) exist as well. With mosaic CCD systems, theFIGURE 11-11. A: A digital biopsy system is illustrated. The systemuses a fiberoptic taper to couple a small intensifying screen to thechip of a Charged-coupled device (CCD). B: By combining several digitalbreast biopsy modules into a mosaic, a full-field digital mammographydetector can be assembled. C: Image acquisition using aslot-scan system for digital mammography is illustrated. A narrow slotbeam of x-rays scans across the breast, striking a CCOdetector system.The detector system moves inside a plastic detector housing.