A technique utilizing an incoherent optical processing system for the pseudo-color encoding of black-white tomograms by density has been used in the clinical radiography. It is a useful method in showing some features of the lung lesions clinically espe- , cially peripheral bronchogenic carcinomas. 18 cases of round or oval-shaped peripheral bronchogenic carcinomas ranging from 1.0 to 4 cm in size and 4 cases of central cancers were studied. In addition, round-shaped pneumonia in 2 cases, tuberculoma in 1, and postinflammation pseudo-tumor and harmatoma were also examined as controls. It is often possible to observe some structures of the tumors preoperati-vely by its recognizing capability on the graydifferen-ce, such as carcinomatous infiltrations in 17 "V"sha-ped notch in 4, central necrosis in 6, scar-for-mations in 4 and lung collapse in another. It is shown that this procedure demonstrated irregularity of tumor masses and "V"shaped notch better than conventional tomograms. It is particularly useful in detecting significant scar formations which were almost indistinct on conventional tomograns. Furthermore, pseudo-color photographs are also of value in differentiating peripheral bronchogenic carcinomas from benign lesions such as round- shaped penumonia, tuberculoma, etc. Although it is not satisfactory in three cases of central cancers and one case of peripheral type, this new technique, as compapared with CT scan, seems to be a more sensitive and accurate diagnostic imaging procedure to help make a specific diagnosis. Ty pical cases are illustrated.

Objective To characterize the imaging features of mediastinal cysts and gain a better understanding of atypical manifestations of various mediastinal cysts and improve the level of diagnosis. Methods The CT and/or MR images(CT n=28, MRI n=26, CT and MRI n=10), surgical information, and pathologic material in 44 histopathologically proved cases of mediastinal cyst were retrospectively reviewed. Results The mediastinal cysts were located in the anterior mediastinum(n=13), middle mediastinum(n=18), anterior-middle mediastinum (n=2) and posterior mediastinum(n=11). Bronchogenic cysts and pericardial cysts were atypically located in 7/20(35%)and 5/6 respectively. The density of 42.9% cysts on CT was close to that of water. Each of the cysts had a high signal intensity that was equal to or greater than cerebrospinal fluid on T_2-weighted MR images. One cyst showed marked loss of signal on MR hydrography. The signal intensities of the cysts were variable on T_1-weighted images. The signal intensity of MRI was not homogeneous in 5 and the reasons were different. Fourteen cases were misdiagnosed. Conclusion 1.The cysts with soft-tissue attenuation on CT in the anterior and posterior mediastinum may be easily misdiagnosed as neoplasm. Pericardial cysts located in the paratrachea may be easily misdiagnosed as bronchogenic cysts .2. MRI can be used to diagnose the cysts with high density on CT.3. Heterogeneous signal on MRI and loss of signal on MR hydrography might be the reasons for misdiagnosis.