VOLUMETRIC HIGH-RESOLUTION CT IN THE DIAGNOSIS OF INTERSTITIAL LUNG-DISEASE AND BRONCHIECTASIS - DIAGNOSTIC-ACCURACY AND RADIATION-DOSE

OBJECTIVE. The purpose of this study was to evaluate the diagnostic ac curacy and radiation dose of volumetric high-resolution CT in the diag nosis of interstitial lung disease and bronchiectasis when four contig uous sections were acquired at each of three levels. The potential ben efits were weighed against the increased radiation dose of multiple sc ans. SUBJECTS AND METHODS. High-resolution CT scans of four contiguous sections were obtained at each of three locations (the aortic arch, t he carina, and 2 cm above the diaphragm) in 50 consecutive patients (m ean age, 44 years old) with known or suspected interstitial lung disea se or bronchiectasis who were referred for evaluation with high-resolu tion CT. Each individual scan was analyzed for the presence of motion- induced streaking, blurring, or doubling. The diagnostic information c ontained in each set of four scans was compared with that contained in the first of the four scans in the set. RESULTS. Motion degraded at l east one of the four images in each set in 69 (46%) of 150 volumetric acquisitions. When the full set of four images was considered instead of just the first scan from the set, the number of motion-free studies in patients with suboptimal respiratory suspension was increased by 4 0% (from 99 to 139). Diagnostic accuracy was improved as more features were identified on contiguous scans: the sensitivity of the first sca n compared with that of the complete set of four scans was 84% for the detection of bronchiectasis, 97% for ground-glass opacity, 88% for ho neycombing, 88% for septal thickening, and 86% for nodular opacities. Although the integral radiation exposure for a set of four CT scans wa s 2.8 times that of a single scan obtained with standard technique, pe ak skin exposure was unchanged. Slightly increased image noise with th e reduced technique compromised diagnostic ability in 6% of studies. C ONCLUSION. The use of volumetric high-resolution CT increased diagnost ic accuracy, particularly for bronchiectasis at the lung bases, withou t increasing peak skin radiation exposure. With the availability of fo ur contiguous scans per anatomic level, the subjective confidence in i nterpretation and number of motion-free studies also increased.