OBJECTIVE: 3D volume reconstruction of CT images can be used to measure temporal bone aeration. This study evaluates the technique with respect to reproducibility and acquisition parameters. MATERIAL AND METHODS: Helical CT images acquired from patients with radiographically normal temporal bones using standard clinical protocols were retrospectively analyzed. 3D image reconstruction was performed to measure the volume of air within the temporal bone. The appropriate threshold values for air were determined from reconstruction of a phantom with a known air volume imaged using the same clinical protocols. The appropriate air threshold values were applied to the clinical material. RESULTS: Air volume was measured according to an acquisition algorithm. The average volume in the temporal bone CT group was 5.56 ml, compared to 5.19 ml in the head CT group (p = 0.59). The correlation coefficient between examiners was > 0.92. There was a wide range of aeration volumes among individual ears (0.76-18.84 ml); however, paired temporal bones differed by an average of just 1.11 ml. CONCLUSIONS: The method of volume measurement from 3D reconstruction reported here is widely available, easy to perform and produces consistent results among examiners. Application of the technique to archival CT data is possible using corrections for air segmentation thresholds according to acquisition parameters.
OBJECTIVE: 3D volume reconstruction of CT images can be used to measure temporal bone aeration. This study evaluates the technique with respect to reproducibility and acquisition parameters. MATERIAL AND METHODS: Helical CT images acquired from patients with radiographically normal temporal bones using standard clinical protocols were retrospectively analyzed. 3D image reconstruction was performed to measure the volume of air within the temporal bone. The appropriate threshold values for air were determined from reconstruction of a phantom with a known air volume imaged using the same clinical protocols. The appropriate air threshold values were applied to the clinical material. RESULTS: Air volume was measured according to an acquisition algorithm. The average volume in the temporal bone CT group was 5.56 ml, compared to 5.19 ml in the head CT group (p = 0.59). The correlation coefficient between examiners was > 0.92. There was a wide range of aeration volumes among individual ears (0.76-18.84 ml); however, paired temporal bones differed by an average of just 1.11 ml. CONCLUSIONS: The method of volume measurement from 3D reconstruction reported here is widely available, easy to perform and produces consistent results among examiners. Application of the technique to archival CT data is possible using corrections for air segmentation thresholds according to acquisition parameters.