A new volumetric CT machine for dental imaging based on the cone-beam technique: preliminary results.

The objective of this paper is to present a new type of volumetric CT which uses the cone-beam technique instead of traditional fan-beam technique. The machine is dedicated to the dento-maxillo-facial imaging, particularly for planning in the field of implantology. The main characteristics of the unit are presented with reference to the technical parameters as well as the software performance. Images obtained are reported as various 2D sections of a volume reconstruction. Also, measurements of the geometric accuracy and the radiation dose absorbed by the patient are obtained using specific phantoms. Absorbed dose is compared with that given off by spiral CT. Geometric accuracy, evaluated with reference to various reconstruction modalities and different spatial orientations, is 0.8-1% for width measurements and 2.2% for height measurements. Radiation dose absorbed during the scan shows different profiles in central and peripheral axes. As regards the maximum value of the central profile, dose from the new unit is approximately one sixth that of traditional spiral CT. The new system appears to be very promising in dentomaxillo-facial imaging and, due to the good ratio between performance and low cost, together with low radiation dose, very interesting in view of large-scale use of the CT technique in such diagnostic applications.

Small renal-cell carcinomas: clinical and imaging features.

The authors review the clinical, pathological and imaging characteristics of 20 patients with histological confirmation of 23 renal-cell carcinomas measuring < or = 3 cm in size. All lesions were unilateral. All patients were submitted to CT investigations, which identified 20 tumours (86%) and failed to identify 3 small-sized neoplastic nodular formations (0.4, 0.4, 0.8 cm) in patients with double tumour localisation in the same kidney. 15 patients underwent ultrasonography (US) which detected 11 carcinomas out of 17 (65%); of the 6 tumours (in 4 patients) not detected by US, 4 were identified by CT; 2 of these patients were subsequently re-examined by US with identification of the tumour. US failed to detect the 2 small tumours unidentified by CT (the third patient did not undergo US). 17 patients had no renal symptoms, and identification of the tumour was an incidental finding. The increasingly widespread use of US and CT enables a large number of kidneys to be examined and thus permits identification of a greater number of small-sized kidney tumours, allowing early surgical intervention with a greater chance of success. The technical options in surgical therapy may be multiple, though the use of any operation other than nephrectomy tends to be limited by the possible presence of small neoplastic nodular formations in the same kidney, which may not be detectable by US or CT owing to their very small size.

Multiplanar study of the mediastinum with electronically reconstructed computed tomography images.

Refinements of computer software permit electronic reconstructions of CT sagittal, parasagittal, and coronal planes, which have markedly improved our understanding of the relations among mediastinal structures, most of which present a vertical course, as well as between focal lesions and adjoining structures.