Computed Tomography of the Pulmonary Parenchyma: Conclusion
There is no doubt that HRCT, with its resolution in the order of 200 μ and its freedom from tissue superimposition, could offer significant advantages over plain radiography. For instance, unlike plain films, HRCT does not require summation of nonresolvable small lesions for effective detection. However, even at 200 p., the resolution of HRCT is still one to two orders of magnitude below what would be needed to match histologic resolution. Likewise, whether HRCT could provide more observer-independent and quantifiable data remains to be seen.
Assessment of Disease Extent, Activity and Response: An exciting prospect for pulmonary CT would be a role in monitoring known disease to precisely quantify extent of damage, measure response to therapy, and evaluate disease activity. The feasibility of quantifying lung damage secondary to bleomycin toxicity has already been demonstrated.
The CT changes in desquamative interstitial pneumonia can be monitored before and after corticosteroid therapy and used as an index of response. Ill-defined patches of increased CT density by CT have been correlated with regions of disease activity in idiopathic fibrosing alveolitis. Such a finding, if further confirmed, would indicate a potentially major role for HRCT monitoring of disease progression and guidance of pulmonary tissue sampling toward such areas and away from reticulated cystic regions of so-called honeycombed lung, where end-stage nondiagnostic fibrosis is more likely to be found. Similar findings can also be made in pulmonary sarcoidosis and usual interstitial pneumonia. More info
The chest roentgenogram is and should remain for the foreseeable future the primary method of imaging the pulmonary parenchyma. CT is playing an increasingly important role in the characterization of focal pulmonary pathology using densitometric as well as specific morphologic information demonstrable only by CT. Although in its infancy, HRCT shows great promise in the investigation of diffuse parenchymal pathology. The richness of the HRCT semiology provides an opportunity to test whether this technique could offer: (1) more powerful classification of disease states; (2) possible quantification of disease extent; (3) less observer-dependent detection and characterization of pathology as in pneumoconioses for instance; (4) means of monitoring disease activity and therapeutic response; and (5) more sensitive means than plain films to detect occult pulmonary disease in relevant clinical settings. As the real cost of CT has decreased and as this technology has become the mainstay of radiologic imaging, it is not unreasonable to expect a greater awareness of its potential in defined clinical contexts. This should lead to more formal prospective studies and more definitive answers in the near future.