Comparison of micro-CT imaging and histology for approximal caries detection.

Histological sectioning is a generally accepted in vitro validation method for caries detection techniques. However, it requires cumbersome sample preparation and induces irreversible sample destruction. Micro-Computer Tomography (micro-CT) allows non-destructive imaging of tooth structure. The aim of this study was to compare the performance of histological sectioning and micro-CT imaging in detecting approximal carious lesions. Unlike previous studies, evaluation is objectified by comparing visual appearance of exactly corresponding anatomical regions. Sixty extracted human teeth were scanned with a desktop micro CT system. Axial histological slices were prepared and photographed. Sample preparation, combined with dedicated image processing, ensured selection of identical anatomical regions on radiographic and histological images. Evaluation of the presence and extent of carious lesions was performed by four dentists using custom-designed software. Each section was scored independently (histo or micro CT). Scores of approximal surfaces were retained for further analysis. Spearman's correlation coefficients (0.738 to 0.829, p < 0.0001) showed a good agreement between signs of carious lesions in the identical region obtained with both methods. Bland-Altman plots showed that 90.76% of the data points were within the limits of agreement. Micro-CT imaging was shown to provide an interesting alternative to histological sectioning as detection method for carious lesions.

Possibilities and limits of X-ray microtomography for in vivo and ex vivo detection of vascular calcifications.

In the present paper, vascular calcifications due to chronic renal failure in rats are studied by X-ray microtomography (micro-CT). Although micro-CT is traditionally used as an imaging technique, a quantitative analysis of data obtained by in vivo and ex vivo micro-CT is described and discussed. By comparison with traditional destructive methods, such as histomorphometry and atomic absorption, the detection limits for calcium were determined in living rats and in extracted aortas. micro-CT proved to be an effective non-invasive imaging technique allowing non-destructive quantification of ectopic calcifications.

High resolution micro-CT scanning as an innovative tool for evaluation of the surgical positioning of cochlear implant electrodes.

X-ray microtomography (micro-CT) is a new technique allowing for visualization of the internal structure of opaque specimens with a quasi-histological quality. Among multiple potential applications, the use of this technique in otology is very promising. Micro-CT appears to be ideally suited for in vitro visualization of the inner ear tissues as well as for evaluation of the electrode damage and/or surgical insertion trauma during implantation of the cochlear implant electrodes. This technique can greatly aid in design and development of new cochlear implant electrodes and is applicable for temporal bone studies. The main advantage of micro-CT is the practically artefact-free preparation of the samples and the possibility of evaluation of the interesting parameters along the whole insertion depth of the electrode. This paper presents the results of the first application of micro-CT for visualization of the inner ear structures in human temporal bones and for evaluation of the surgical positioning of the cochlear implant electrodes relative to the intracochlear soft tissues.

In vivo assessment of emphysema in mice by high resolution X-ray microtomography.

High resolution X-ray microtomography (micro-CT) was used for the detection of emphysema in live mice. Emphysema was induced in C57BL/6 J mice by intratracheal instillation of different amounts of porcine pancreatic elastase. This emphysema could be clearly detected by micro-CT seven weeks post-treatment: analysis of the whole data set of virtual cross-sections showed the presence of a dose-dependent level of emphysema.

Detecting and tracking local changes in the tibiae of individual rats: a novel method to analyse longitudinal in vivo micro-CT data.

In this study we present the analysis of in vivo micro-CT scans using a new method based on image registration that accurately evaluates longitudinal micro-CT studies. We tested if detailed changes in the bone architecture could be detected and tracked in individual animals. A prototype in vivo micro-CT scanner (Skyscan 1076) was developed in which tibiae of rats that are lying on a bed under gas anaesthesia were scanned. For this study, three female Wistar rats were used: a sham-operated rat, an ovariectomised (OVX) rat and one rat that served as a reproducibility control. The reproducibility control rat was scanned twice in 1 day. The other animals were scanned at week 0, just before surgery, at week 4 and at week 14 after surgery. Architectural changes over time were detected by overlaying two data sets made at different time points using an algorithm that uses mutual information for optimal registration. The scans were segmented into binary data sets using a local thresholding algorithm. The reproducibility test showed small errors of less than 3% in bone volume measurements and errors less than 0.5% in measurements of trabecular thickness. The sham-operated rat showed no changes in total bone volume, though thinning and eventual loss of some small trabeculae could be detected, which could be related to the age of the animal. The OVX rat lost much trabecular bone volume, especially in the metaphysis (60% at week 4, 75% at week 14). The remaining trabeculae slowly increased in thickness. Following the different scans in time showed the forming of new trabecular structures. Additionally, small longitudinal growth at the growth plate could be detected after the first 4 weeks. Further, the OVX rat showed extensive modelling at the proximal endosteal lateral cortex. We have shown a new method that can detect and track changes in the local bone architecture and individual trabeculae in time, in an individual living animal. This method enables longitudinal in vivo micro-CT studies and has the potential to greatly contribute to experimental rat or mouse studies on pharmacological intervention and transgenic models.

Quantitative analysis of bone mineral content by x-ray microtomography.

A new non-destructive method based on x-ray microtomography (micro-CT) was developed to measure calcium density in bone. X-ray micro-CT was used as a quantitative approach to acquire and reconstruct virtual cross-sections through the sample. Accurate beam-hardening correction was implemented. Grey values in the virtual cross-sections were calibrated as calcium mineral density in bone. From these cross-sections, three-dimensional models were created. Calcium content was calculated directly from images and expressed as percentage per volume and per weight. Calcium mineral density was studied by this method in a unique set of bones isolated from newts (Pleurodeles waltlii Michah) that had travelled into space. A demineralization of 10% was shown as a consequence of sustained micro-gravity.

3D in-vivo X-ray microtomography of living snails.

In this paper we report the first in-vivo scanning of living snails by desktop X-ray microtomograph with a resolution up to 10 m. Consecutive cross-sections were acquired without destroying the specimen. Subsequently, 3D images were reconstructed. The results clearly demonstrate the possibilities of in-vivo scanning. Processes of growth and regeneration of living snails were visualized over a period of time.

Molecular identification of foreign inclusions in inflammatory tissue surrounding metal implants by Fourier transform laser microprobe mass spectrometry.

Fourier transform laser microprobe mass spectrometry (FT LMMS) is a novel technique for micro-analysis of solids with a lateral resolution in the 5 microns range. One of the major advantages of the technique is the capability to perform characterisation of the molecular composition of both organic and inorganic compounds. The information is directly deduced from the signals without the aid of reference spectra. FT LMMS was applied to the characterisation of black tissue fragments in a biopsy from a patient, in which a constrained condylar nodular knee system was implanted ten years ago. The tissue contained numerous foreign giant cells with a black non-birefringent pigment in their cytoplasm. FT LMMS analysis allowed us to detect directly by means of molecular signals, that the debris consisted primarily of titanium oxide and not metallic titanium, while the implant itself only contained titanium.

Increased force levels after shortening and restretching skinned cardiac muscle.

At steady calcium activation, changes in loading conditions were imposed on single skinned cardiac myocytes and on multicellular skinned cardiac muscle. Despite the initial steady level of activation, an increase in isometric force (i.e. force gain) was observed after stretching following a period of shortening. Force gain was most pronounced at low levels of free activating calcium, but it was present at any level of free calcium, including maximal activation. The extent of shortening did not influence the amount of force gain. An increased level of shortening (i.e. shortening gain) was observed after clamping a single myocyte under afterloaded conditions. Since no membranous systems were present, the mechanism causing force and shortening gain were shown to be located at the level of the contractile proteins. The hypothesis is suggested that different steady states of the crossbridges could exist despite a constant steady level of calcium activation.

Effects of ryanodine on relaxation in isolated myocardium from different animal species.

Relaxation in mammalian ventricular cardiac muscle is sensitive to the prevailing load. This "load dependence of relaxation" (LD) can be demonstrated only when an efficient sarcoplasmic reticulum (SR) is present. To define further the role of the SR in LD, we studied contraction and relaxation in cat, rat and frog cardiac muscle after exposure to ryanodine. Ryanodine is a selective inhibitor of calcium release from the SR. This view was confirmed in the present study in single cardiac rat myocytes with functioning SR. Ryanodine did not affect LD in multicellular mammalian myocardium even though it had already significantly depressed contractility, suggesting that calcium release from the SR plays no role in establishing LD. Calcium accumulation in the SR as a consequence of the inhibited release can account for the late depression of LD in the presence of ryanodine.

Effects of prostacyclin on contractile properties of isolated mammalian cardiac muscle.

We studied the influence of prostacyclin (PGI2) on the contractile performance of isolated mammalian ventricular muscle. PGI2 had no direct influence on myocardial contractility, as evidenced by experiments on single cardiac cells and papillary muscle. Moreover, PGI2 did not interfere with the inotropic action of isoproterenol. In comparison, neither prostaglandin E1 nor E2 appeared to have any cardiotonic action.

Uniform sarcomere behaviour during twitch of intact single cardiac cells.

Behaviour of sarcomere length was analysed in different regions of single cardiac cells (n = 249) of the ventricle, both at rest (n = 144) and during twitch contractions (n = 57). At rest, regional distribution of sarcomere length proved to be uniform. In the leaky cell (n = 48), resting sarcomere length was not affected over longer periods of time (up to 2 h), nor by lowering the ATP concentration (from 5 mM to 2.5 mM and 500 microM), nor by increasing free calcium within subactivating ranges (5, 20, 60 microM). No statistical differences could be detected between resting cell dimensions and sarcomere length between cells isolated from left and right ventricle (n = 64), nor between cells from epicardial or endocardial layers (n = 80). During twitch contraction in the intact unloaded cardiac cell (n = 32), sarcomere lengths in different regions were analysed every 20 ms and behaved synchronously, presenting arguments for uniformity during the myocardial contraction-relaxation cycle in the free-lying intact cardiac cell.

Effects of AQA39 on contractile performance of isolated mammalian ventricular myocardium.

AQA39 is a new cardioactive agent with, at low dosages, a minute positive inotropic action on ventricular myocardial tissue probably mediated through the calcium sequestering membraneous systems. At higher concentrations AQA39 depressed myocardial performance probably due to inhibition of the slow calcium channels.

Activation stabilization--further support for a new class of cardioactive substances.

Alinidine, a new compound with a bradycardic action, has a rate-decreasing and stabilizing action on the spontaneous contractions of single rat ventricular cardiac cells with a partially skinned and leaky sarcolemmal membrane but with a well-functioning sarcoplasmic reticulum. In the intact multicellular cat papillary muscle, alinidine delays the onset of mechanical activation at concentrations that hardly affect peak mechanical performance and the relaxation phase. From these results, we postulate that alinidine has a stabilizing action on activation, in particular on the release of calcium from the intracellular membranous system, with minimal effects on the total amount released and on the calcium reuptake or process of inactivation.

Effects of AR-L 115 on contraction and relaxation of isolated mammalian cardiac muscle.

We studied the mode of action of a new cardiotonic agent (AR-L115) contractile performance of isolated cardiac muscle. We analyzed its effects on the contraction and relaxation of partially skinned, single cardiac cells of rat ventricle, and of intact papillary muscles of the right ventricle of the cat. AR-L115 (30-100 micrograms/ml) reversibly increased the frequency, but not the amplitude, of spontaneous isotonic and isometric contractions of the single cells with functioning sarcoplasmic reticulum (SR), thereby resembling the action of caffeine. It did not affect contractions of mechanically skinned and detergent-pretreated cells without functioning SR, which were activated through iontophoretic calcium pulses. In papillary muscles, AR-L115 (1-40 micrograms/ml) significantly increased directly measured maximum unloaded velocity of shortening at zero load, peak velocity of isotonic shortening and lengthening, peak total isometric tension development, and peak rate of tension development, indicating augmented contractility. These effects were less pronounced than those of increasing the calcium concentration in the bathing solution from 2.5 to 7.5 mM. After beta-adrenergic blockade (propranolol or toliprolol 10(-5) M), the maximal effects of AR-L115 were markedly diminished. Load dependence of isotonic relaxation and the time of half-isometric relaxation were not affected by the drug. Accordingly, AR-L115 is a mild positive inotropic agent, which mainly increases contractility during the contraction phase without markedly affecting load dependence of relaxation. These effects are probably mediated both through a catecholaminelike action on beta-receptors and through a separate caffeinelike action on the calcium-sequestering membrane systems. In contrast to digitalis glycosides, AR-L115 does not exhibit tachyphylaxis in chronically AR-L115-loaded animals.

Sarcomere distribution patterns in single cardiac cells.

Sarcomeres of single cardiac cells isolated either by microdissection or by enzymatic dissociation were visualized on a television screen, through the objective (63 X) of an inverted microscope and a television camera. A distinct line of the television picture was positioned on the preparation and the frequency content, corresponding to the dark and light areas of the striations was tracked by a phase-locked loop. This technique permitted the measurement of the length of successive sarcomeres and hence the sarcomere distribution pattern over the entire preparation.

Effect of temperature on the mechanical behaviour of single skinned cardiac cells.

The effect of changes in temperature (16-35 degrees C) on the contractile behaviour of single, skinned cardiac cells was analysed. Lowering the temperature decreased force development, extent of shortening and velocity of shortening. The effects of altering temperature on the calcium sensitivity of velocity of shortening were more pronounced than the temperature effect upon the calcium dependence of force and extent of shortening. At maximal activation force-velocity curves showed a marked shift in peak velocity, with hardly any effect on peak isometric force.