ULTRASONIC INVESTIGATION OF THE EYE WITH A NEW CONTACT METHOD AND WITH THREE DIFFERENT REAL‐TIME PRESENTATIONS
The ultrasound examination was carried out by means of a crystal with a 40° sector scan, which was pressed either against the eyelid or directly against the sclera. The real‐time display was obtained by either A‐mode, B‐mode or combined A/B‐mode scanning. In clinical applications, both the resolution capacity and the sensitivity of the device were good. A‐mode scanning gave the greatest accurary in amplitude measurement, while the A/B‐mode yielded the most concrete topographic picture of the target.
The application of ultrasonic locating techniques to ophthalmology. II. Ultrasonic slit lamp in the ultrasonic visualization of soft tissues.
Introduction This is a preliminary report of the visualization of the interior of the lightopaque eye and the retro-ocular areas by pulsed ultrasonic echographic methods. Non-radio-opaque foreign materials, such as wood and plastics, may also be visualized, as well as soft tissue pathology. At present no other method can yield the information obtained by the technique to be described. A comparison of the visual appearance of a normal beef eye, the x-ray appearance, and the sonic appearance graphically illustrates this contention (Fig. 1). The x-ray demonstrates only the gross outline of the eye. The ultrasonogram reveals a cross section of the internal structure of the eye equivalent in detail to a low-power photomicrograph. Serial ultrasonic tomograms (Figs. 13 to 21) yield a composite picture of the eye at all levels without in any way altering the tissues. Precise direct measurement of the depth within the tissue is possible with this
Thermal incompatibility analysis of metal-ceramic systems based on flexural displacement data.
The feasibility of simple tests or analytical methods for prediction of residual stress states in metal-ceramic (MC) prostheses has not been demonstrated. Biomaterial metal-ceramic strips have been proposed to provide sensitive measures of transient and residual stress states through the measurement of midpoint deflection after cooling from the ceramic sintering temperature. The objective of this study was to apply the elastic-viscoelastic analogy to calculate transient and residual midpoint deflections in MC biomaterial strips and to compare these values with deflections measured with a beam-bending viscometer (BBV). Calculations and measurements were made for five MC systems that were found from a clinical study to be "thermally compatible" systems. Metal strips, 64 mm in length, 3 mm wide, and either 0.5 mm, 1.0 mm, or 2.0 mm in thickness, were veneered with four 0.25-mm thick layers of opaque porcelain. Midpoint deflection of the MC strips (ceramic oriented in the posterior position) was measured during cooling from an initial temperature of 700 degrees C. In general, the directions of the measured residual deflections did not agree with the "textbook" convention that negative deflections are associated with positive thermal contraction mismatch (alpha(M) - alpha(c) > 0) regardless of metal thickness. For a metal thickness of 0.5 mm, the residual midpoint deflection for all thermal contraction mismatch cases, except one, was positive (upward deflection) whereas the residual midpoint deflections were all negative when the metal thickness was increased to 1 or 2 mm, independent of the thermal contraction mismatch. The best agreement between calculated and measured values of residual midpoint deflection (+16 microns vs. +14 +/- 2.3 microns, respectively was obtained for MC biomaterial strips with a Ni-Cr alloy (0.5 mm thick) while the largest difference (+346 microns vs. +61 +/- 43.8 microns) was obtained for MC bimaterial strips with a Au-Pd allow (0.5 mm thick). In all but one case, changes in deflection direction as a function of metal thickness were correctly predicted by the viscoelastic analysis. The results of this study indicate that a viscoelastic model is useful for estimating thermal compatibility conditions of MC systems.