Computed tomography (CT) was used to examine 634 solitary pulmonary nodules (SPNs). Each lesion was assessed as benign or indeterminate on the basis of CT criteria. Benign nodules made up 44% of all SPNs and 58% of the 431 that were 2 cm or less in diameter. All malignant SPNs were assessed as indeterminate, and adenocarcinoma (42%) was the most common primary malignancy. A total of 176 (63% of benign SPNs) were correctly assessed as benign by CT. Ninety SPNs assessed as diffusely calcified were not so identified by conventional tomography at outside institutions. An SPN can be reliably assessed by CT as benign if it exhibits high attenuation values, exceeding a critical level and distributed diffusely throughout a CT section through the center of the lesion and a well-defined edge. Although 38 of 283 (13.4%) primary lung cancers contained localized calcification, there was no significant overlap with the diffuse calcification of benign lesions. Central carcinoid tumors may contain focal ossification, but such lesions may be recognized by noting the proximity of larger bronchi. Assessment of SPNs by CT is most effective for lesions 2.0 cm or less in diameter. For larger lesions, the frequency of benign disease was decreased (14.3% of 203), as was the percentage of benign SPNs correctly assessed as benign by CT (37.9%).
Forty-seven patients with a proved (n = 31) or presumed (n = 16) diagnosis of pulmonary hamartoma were studied prospectively by thin-section computed tomography (CT). CT criteria for hamartoma included a diameter of 2.5 cm or less, a smooth edge, and focal collections of fat or fat alternating with areas of calcification. No case of cancer (n = 283) or metastatic disease (n = 72) fulfilled these criteria. Seventeen hamartomas with no detectable calcium or fat were not diagnosed by means of CT. Two other lesions contained diffuse calcium deposits. In 28 lesions, a CT diagnosis of hamartoma was based on the detection of fat (n = 18) or calcium plus fat (n = 10). Twelve such cases were proved histologically by means of thoracotomy or needle biopsy; the remainder, including eight in asymptomatic patients aged 65 years or older, were managed with conservative follow-up.
KEY WORDS ABSTRACTSpecific guidelines for the use of computed tomographic (CT) scanning in analyses of skeletal material are presented and discussed in relation to basic CT principles and empirical observations. Recommendations for scanning procedures, image display parameters, hard copy output, and relating CT numbers to mass densities are given. Experimental verification and standardization of scanning technique are stressed, with examples given from a study of modern (nonfossilized) primate long bones.CT scanning, Imaging techniques, BoneComputed tomography (CT) scanning has been in routine clinical use for more than 10 years (Hounsfield, 1973; Ledley, 1974). However, only relatively recently has its potential applicability to anthropological and paleontological research been fully appreciated (Tate and Cann, 1982;Conroy and Vannier, 1984; Borkan et al., 1985;Sumner et al., 1985;Vannier et al., 1985). Because of the advantages of CT scanning over conventional radiography in two-and three-dimensional imaging, it is likely that this technique will be increasingly used in many areas of skeletal research where nondestructive visualization of internal bone structures is necessary. However, the relatively more sophisticated method of image reconstruction used by CT and the resulting greater "distance" between operator and final image increase the danger of misinterpreting results produced by this technique. In addition, particular problems associated with CT scanning of fossil or modern osteological material may not be familiar to many CT operators working in a normal clinical environment.In the present paper several problems in the application of CT scanning and guidelines for the use of CT in skeletal structural analyses are discussed. While the data reported are specific to the particular scanner we used in the study (AS&E Model 500), the general principles and recommendations are broadly applicable to any CT scanner system currently in operation. BASIC PRINCIPLESDetailed consideration of the physical principles underlying computed tomography has been presented in many reports since Hounsfield's original description of the system in 1973. More recently, Zatz (1981a) and Hendee (1983) have provided comprehensive reviews for the nonspecialist. Only a summary of the basic principles necessary to the following discussion are presented here subsequently.X-ray attenuation As in conventional roentgenography, CT uses the combined absorption and scattering, or attenuation of an x-ray beam as it passes through a medium to reconstruct images. The polyenergetic x-ray source employed by CT scanners is typically operated at a voltage peak near 120 kVp, which corresponds to an effective energy of about 70 keV. ("Effective energy" refers to the energy of a monoenergetic beam of xrays that would undergo an equivalent attenuation when traversing the object scanned.) At this energy level, two interactions dominate the rate of attenuation of 0 1986 Alan R. Liss, Inc.
Computed tomography (CT) with thin sections (2-5 mm) was used to assess tissue density in 91 apparently noncalcified pulmonary nodules in 88 patients. The study included 45 primary lung malignancies and 13 metastases proven by subsequent lung biopsy or thoracotomy. There were 33 benign lesions of which 13 were biopsy proven. The other 20 nodules were presumed benign on the basis of serial radiography showing no growth. A representative CT number based on the 32 most dense voxels was calculated for each lesion. For the primary malignancies, the mean representative CT number was 92 H, with a standard deviation of 18 H. The highest representative CT number for any malignant lesion was 147 H. Of the 33 benign lesions, 20 had a representative CT number of 164 H or greater. It is presumed that nodules with representative CT numbers of 164 H are benign, and that diffuse calcification likely accounts for the higher CT number of some benign lesions. CT has proven to be more objective and more sensitive than standard tomography in assessing the density of pulmonary nodules.
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