Overranging

To reconstruct the first and last sections of a helical computed tomographic (CT) scan, the scan length is automatically extended beyond the planned image boundaries, a phenomenon known as overranging.

Overranging allows a DVM to measure voltage values above the normal decade transfer points without the necessity of having to change ranges.

Overranging was instituted to take full advantage of the upper limits of a range . It also provides better accuracy at the top of a range .

In helical scanning, exposure is needed before the start and after the end of the planned scan range in order to reconstruct images at these positions [46]. This overranging requires at least one extra gantry rotation, even though only a small portion of this data is utilised for image reconstruction.