Clinical Utility of CT Imaging Techniques for Tracheobronchial Diseases scores was obtained in 40 cases (98%) (Fig. 6). Thus, SSD was significantly superior to other techniques (Fig. 7). SSD provided information about airways, but none with which to evaluate the relationship between abnormalities and adjacent structures (Fig. 8A). For this modality, a score of 2 was assigned in 37 cases (90%), while for RCT and MPR, a score of 3 or 4 was deemed appropriate in 40 cases (98 %) (Fig. 8). For TCT, the score in all 41 cases was 3 or 4, and in assessing relationship of a lesion with adjacent structures, this technique was thus significantly superior to the others. There was no significant difference between RCT and MPR. As regards characterization of a lesion, TCT and MPR were assigned a score of 3 or 4 in 39 cases (95%). TCT had the highest mean score, and was significantly superior to RCT and SSD. In terms of overall information, SSD was regarded as sig- Fig. 6. Tracheal tumor in a 54-year-old man. The histology of this tumor was not confirmed because its hypervascularity, as re- vealed by bronchoscopy, precluded biopsy. Coronal MPR image demonstrates the extent of concentric wall thickening of the tra- chea (arrows). nificantly more informative than other modalities. In 40 cases (98 %), the score for TCT, MPR and SSD was 3 or 4. DISCUSSION High voltage chest radiography is cheap but still not sen- sitive enough to accurately evaluate airway stenoses (8). Although chest radiography remains in use for initial imag- ing of diseases of the chest, our study showed that the re- sults obtained provided poor information with which to evaluate the tracheobronchial tree. When a lesion is locat- ed in the extrathoracic or proximal trachea, the modality may, however, provide certain valuable information, and it is also useful in excluding pulmonary disease or providing additional important lung-related data with which to evalu- ate tracheobronchial diseases. As previously emphasized in the literature, an endo- bronchial tumor located in the central airway can be missed on conventional CT, particularly on 10-mm thick- section CT scans (6, 7). A spiral CT scanner can acquire a set of volumetric data during a single breath hold, and ef- fectively obviates misregistration caused by varying depths of respiration between scans. In our study, all RCT in- volved the use of spiral CT, but even so, a small endotra- cheal lesion was missed. This was, however, clearly demonstrated by TCT, MPR, and SSD, the last of which was found to be most informative with regard to lesion de- tection. Lee et al. emphasized that the acquisition of SSD images led to no significant improvement in lesion detec- tion (9). Transverse imaging, however, has an inherent lim- itation, and mild airway changes, especially those without A B Fig. 7. Endobronchial tuberculosis in a 55-year-old woman. SSD image (A) (score for extent = 4) and coronal MPR image (B) (score for extent =2) show irregular narrowing of the left main bronchus (arrow) and complete obstruction of the left upper lobar bronchus (arrow- heads). Korean J Radiol 1(3), September 2000 139