Investigation of a new light imaging technique to detect incipient caries in teeth.

At the present time dental X-rays are the best method to locate carious lesions, however, small lesions can be detected only with difficulty. Even though investigations in the past have shown that light imaging systems are more sensitive to small lesions than X-rays it is difficult to determine the characteristics of these lesions with any of these systems. We developed a new light imaging technique that makes it much easier to determine the size and depth of these lesions on most areas of the teeth even though modifications on the present setup will still be necessary to detect them as easily on occlusal surfaces. This technique is based on raster scans of the teeth with narrow collimated light beams. The results of this investigation show that the areas ( greater than 0.1 mm 2) of small incipient lesions can be measured and their depths estimated.

Increased spatial resolution in transillumination using collimated light.

In traditional transillumination of the breast (diaphanography), the abundance of diffuse light resulting from the use of extended noncollimated sources reduces the visibility of deep seated lesions. A prototype scanning imaging system has been developed to investigate the effectiveness of thin collimated light beams (1.5 mm cross section) synchronized with a similarly collimated detector to increase contrast in lesions normally lost due to the detection of diffuse light. The study demonstrates that detection of opaque 1.5 mm details is possible in phantoms simulating breast tissues 6 mm thick regardless of depth. This is about 10 times better than images obtained on the same samples using present transillumination methods. Furthermore, this study indicates that internal structures (lesions, cysts) in up to 12 mm thick excised breast sections can be visualized by exploiting their frequency-dependent attenuation. This is accomplished by inserting 50 nm interference filters in the input light path, which can be varied in a stepwise manner in the range of 400 nm to 1000 nm. These results demonstrate for the first time that images of lesion-bearing 1 cm or larger tissues can be obtained, thus opening promising possibilities for whole-breast imaging.

Stable xenon versus radiolabeled microsphere cerebral blood flow measurements in baboons.

Regional cerebral blood flow was simultaneously determined using the stable xenon computed tomographic and the radioactive microsphere techniques over a wide range of blood flow rates (less than 10-greater than 300 ml/100 g/min) in 12 baboons under conditions of normocapnia, hypocapnia, and hypercapnia. A total of 31 pairs of determinations were made. After anesthetic and surgical preparation of the baboons, cerebral blood flow was repeatedly determined using the stable xenon technique during saturation with 50% xenon in oxygen. Concurrently, cerebral blood flow was determined before and during xenon administration using 15-microns microspheres. In Group 1 (n = 7), xenon and microsphere determinations were made repeatedly during normocapnia. In Group 2 (n = 5), cerebral blood flow was determined using both techniques in each baboon during hypocapnia (PaCO2 = 20 mm Hg), normocapnia (PaCO2 = 40 mm Hg), and hypercapnia (PaCO2 = 60 mm Hg). Xenon and microsphere values in Group 1 were significantly correlated (r = 0.69, p less than 0.01). In Group 2, values from both techniques also correlated closely across all levels of PaCO2 (r = 0.92, p less than 0.001). No significant differences existed between the slopes or y intercepts of the regression lines for either group and the line of identity. Our data indicate that the stable xenon technique yields cerebral blood flow values that correlate well with values determined using radioactive microspheres across a wide range of cerebral blood flow rates.

Xenon/computed tomography cerebral blood flow measurements. Methods and accuracy.

We performed a series of five baboon experiments to compare cerebral blood flow measured with an improved stable xenon/CT method and the radiolabelled microsphere technique at a PaCO2 of 40 mm Hg. The xenon/CT method was implemented by fitting the arterial xenon uptake with a double exponential function, by measuring the oxygen and carbon dioxide concentrations continuously during each breath and by taking into account the lung-to-brain transit time of xenon. The time of xenon inhalation was extended to 30 minutes to obtain more reliable estimates of CBF in white matter regions. The results indicate an overall correlation coefficient of 0.92 between the two methods and good numeric agreement.

Systematic errors in bone-mineral measurements by quantitative computed tomography.

Bone-mineral measurements using quantitative computed tomography (QCT) are commonly based on comparisons with solutions in water of known concentrations of K2HPO4. In this paper are described theoretical and experimental studies that have led to the conclusion that large systematic errors can arise in these measurements, depending on the soft-tissue and fat concentrations in the vertebral spongiosa. In the case of single energy scanning, such large errors have been identified to be due to the varying water content (displacement effect) in the calibration samples and the varying fat content in the region of interest (ROI) within the patient. In the case of dual energy scanning, the error arises because when normalized to that of water, the mass attenuation coefficient of fat increases with photon energy while the reverse is true for K2HPO4. Our studies have also revealed that total trabecular bone density (which includes the mineral, soft tissue, and fat) can be much more accurately determined by the dual energy QCT method than bone mineral alone. This finding is especially interesting since there have been several reports in the literature suggesting that bone density rather than bone-mineral content is a better predictor of the risk of osteoporosis-related fractures.

Regional cerebral blood flow measurements using stable xenon enhanced computed tomography: a theoretical and experimental evaluation.

Several theoretical and practical aspects of regional cerebral blood flow measurements using stable xenon gas and CT are discussed. It is shown that by comparing the enhancement at any time T1 with that at saturation or any other time T2, the need to use arbitrary means to bring the arterial concentration data and the CT enhancement data to the same system of measurement units can be eliminated. If CT is performed continuously during the washin phase, say at intervals of 1 min, least squares analysis of the enhancement data can be used to obtain the best possible estimates for the flow rate constant kappa and the saturation enhancement. However, if only a limited number of scans can be performed, as may be the case in human studies, it is also possible to get a good estimate of kappa from a knowledge of the ratio of the enhancement at any time T1 with that at any other time T2. Combinations of T1 = 2.0 min and T2 = 4.0 min, T1 = 1.0 min and T2 = 6.0 min, or T1 = 2.0 min and T2 = 5.0 min were found to be the most convenient. It is also shown that the end-tidal xenon concentration in the exhaled air can be accurately assessed indirectly by measuring the oxygen, CO2, and water vapor concentrations, thereby eliminating the need for more expensive methods involving the use of a mass spectrometer or a thermal conductivity gas analyzer.

A dual-channel signal averager for spontaneous signals.

This signal averager has been developed for spontaneous transients of tension and of aequorin bioluminescence in skinned cardiac cells. The signal with the largest signal-to-noise ratio (generally the tension transient) is entered in Channel 1 and triggers the system. Then the averager will unmask the signal entered in Channel 2 if it was buried in the noise during the direct recording. This signal averager uses an inexpensive microcomputer and a program written in Assembly Language. To facilitate its use, the averager is remotely controlled by a potentiometer for the adjustment of the threshold voltage above which the signal in Channel 1 will be collected and by three push buttons for starting the data collection, for averaging and displaying the results, and for resetting the system. The display is purely analog on the recorder, including averaged signals and interval for the signals in both channels together with a graphical representation of the standard deviations and of the number of observations. This signal averager could be used for any preparations developing spontaneous signals with variable intervals, provided that at least one of the synchronous signals has a large enough signal-to-noise ratio to trigger the system.

Fluid-percussion model of mechanical brain injury in the cat.

Mechanical brain injury was produced in 36 cats with a fluid-percussion model in which brain damage or dysfunction is produced by a single, brief, hydraulically-induced pressure transient that is conducted through the brain. Fluid-percussion injury induce elastic deformation of the brain resembling the brain deformation known to occur following head impact. Physiological responses and pahtological changes following injury were expressed as a function of peak pressure. Macroscopic central nervous system lesions concentrated at the pontomesencephalic junction, cervicomedullary junction, and in the cerebellar tonsils were consistently observed at and above 2.6 atmospheres (atm). At higher levels of injury (greater than or equal to 3.2 atm) there was extensive basal subarachnoid hemorrhage. At very high levels of injury (greater than 4.0 atm) hemorrhagic contusions were noted at the cerebral hemisphere impact site. A spectrum of neuronal alterations was identified in the damaged areas. Computer analysis showed correlation of electroencephalographic (EEG) changes with the neuropathological changes, since EEG recovery became severely impaired above 2.6 atm. No EEG changes were noted below 1.5 atm. From 1.5 to 2.2 atm there was a physiological response to injury but no significant changes were seen on neuropathological examination. This range of injury should permit further studies of the more subtle changes following mechanical brain injury without intraparenchymal hemorrhage or subarachnoid hemorrhage. The fluid-percussion model relates brain deformation following mechanical loading to a single pressure transient that is easily measured and controlled. Further quantitative investigation into the pathobiology of mechanical brain injury following graded brain deformation is thus made possible.