Temporal bone: Comparison of isotropic helical CT and conventional direct axial and coronal CT

OBJECTIVE. The objective of the study was to compare helical CT (with refor mation of coronal images from the axial data set) with conventional direct axial and coronal CT of the temporal bones. SUBJECTS AND METHODS. Nineteen patients underwent both conventional 1-mm di rect axial and coronal CT and helical 0.5-mm axial CT. The helical data set was reconstructed at 0.2-mm increments, and axial and coronal images were reconstructed in a plane similar to that of the conventional study, with a slice width of 0.5 mm and 0.5-mm increments. Forty small structures were ev aluated independently by three observers, who were unaware of the method of imaging. Observers graded the 40 structures using a modified Likert scale. The graded differences between the two techniques were evaluated using a p aired t test. Correlation between observers' gradings was evaluated using a nalysis of variance. RESULTS. The helical CT technique scored significantly higher than the conv entional technique for many individual structures and groups of structures (scutum [p = .041], stapes footplate [p = .006], stapes crura [p = .004], o val window [p = .026], crista falciformis [p = .006], whole temporal bone [ p =.012], middle ear [p = .033], inner ear [p = .021], ossicles [p.044], an d stapes [p =.010]). The correlation coefficient among observers was .91 fo r the whole temporal bone. CONCLUSION. Helical CT using 0.5-mm technique and reconstruction produces d iagnostic images comparable with or superior to conventional I-mm technique because helical CT can obtain thinner slices.