Comparison of intraobserver and interobserver variability for CT perfusion values and CT perfusion ratios
| Variability | SDDrel (Range of Relative Differences) | ||
|---|---|---|---|
| CBV | CBF | MTT | |
| Intraobserver | |||
| CT perfusion values | 16% (−62%, 54%) | 18% (−59%, 63%) | 5% (−35%, 21%) |
| CT perfusion ratios | 11% (−51%, 37%) | 10% (−42%, 33%) | 6% (−30%, 23%) |
| P* | .000 | .000 | .048 |
| Interobserver | |||
| CT perfusion values | 17% (−78%, 63%) | 18% (−67%, 55%) | 9% (−30%, 34%) |
| CT perfusion ratios | 16% (−44%, 71%) | 13% (−49%, 51%) | 9% (−36%, 30%) |
| P* | .135 | .000 | .295 |
Note:—SDDrel indicates SDs of relative differences; CBV, cerebral blood volume; CBF, cerebral blood flow; MTT, mean transit time. Pooled data from all flow territories. Variability is expressed as the SD of the relative differences for each pair of observations (SDDrel) and is thus expressed as a percentage. The range of relative differences is given in parentheses. Note that both intraobserver and interobserver variability are significantly lower for CBF ratios than for absolute CBF values, whereas for CBV, this effect was seen only in intraobserver variability. For MTT, the difference was small and significant for intraobserver variability only.
* F test.