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FIGURE 7. z-Spacing in helical CT. (A) Minimum z-spacing equal to d/2 (d = slice thickness) is achieved in SSCT with pitch of 1 and interpolation between interleaved parallel opposed rays. (B) With pitch of 1 in MSCT, parallel opposed rays overlap rather than interleave, giving z-spacing equal to d. (C) z-Spacing equivalent to that in SSCT is achieved with pitch that overlaps one slice thickness but results in double irradiation of some tissue. Reduced z-spacing can also be achieved with other pitches. det = detector; rot = rotation.
