Confusion is caused because some multi-slice CT manufacturers are using the original definition of pitch, and some are using pitch¢. (For quad-slice CT, Pitch¢ = 4 x Pitch.) We agree with McCollough and Zink1 who state that pitch¢ is undesirable because it alters the basic relationship between radiation dose, x-ray beam overlap, and pitch already established in single-slice helical CT.
Definition (1) is preferred because it can be unambiguously applied to both single- and multi-slice scanning (2, 4, 8…channels).
As defined in (1), pitch values less than one alert the user that radiation overlap is occurring, and pitch values greater than two alert the user that image quality may be degraded severely.
Coverage for MSHCT
Longitudinal (z-axis) coverage for MSHCT can be calculated from the equation: