Purpose: To compare radiologists' subjective size estimation to computerise
d volume quantification of tumour-like phantoms in spiral CT.
Material and Methods. Eight tubular phantoms with the inside irregularly co
vered with silicone (8.7-31.6 ml) were imaged. The phantoms were pairwise c
ompared to analyse the differences in silicone volumes. The observers, 2 ra
diologists and 2 residents, used both subjective image analysis (2 sessions
) and computerised volume quantification (1 session). Accuracy and observer
agreement of both methods were calculated.
Results: Subjective size estimation was correct in 51% (mean weighted kappa
, kappa (qw)=0.73). Using four observers mean value (kappa (qw)=0.81) or me
dian value (kappa (qw)=0.77) slightly improved the results. Average intra-o
bserver agreement was better than average interobserver agreement. In compu
terised volume quantification 70% of all classifications were correct (mean
kappa (qw)=0.85). The results were moderate even when every second or four
th slice were measured.
Conclusion: Subjective size estimation of irregular rumours should be repea
tedly performed by the same observer, or by using the mean or median estima
te of several observers. Computer-based methods are even more reliable and
their use is especially recommended for film readers with limited radiologi
cal experience. Only every fourth slice may be measured without a major los
s of measurement accuracy.