A data compression method for image time series

Image time series for functional studies frequently vary relatively little from one time point to the next. We describe here a method of lossless file compression that calculates the change in signal intensity as a char (one byte), as opposed to a short or long integer (usually two or four bytes), thus resulting in a compressed file size just over half the size of the original (a 2:1 compression ratio). The calculations and format are exceedingly simple; the compression time is comparable to the time required for a file copy, and is thus transparent to most users. The approach works equally well on any integer-based scanning modality, such as PET, CT, or DSA. Our purpose in this communication is to advocate it as a potential standard, to promote free interchange of scan data.