CT parameters in pure orbital wall fractures and their relevance in the choice of treatment and patient outcome: a systematic review

Computed tomography (CT) is commonly used for the diagnosis, treatment planning, and prognosis of pure orbital fractures of the orbital floor and medial wall. The aim of this study was to systematically review the current literature in order to establish an overview of CT parameters relevant to the choice of treatment and (long-term) clinical outcome for patients treated operatively and conservatively. The PRISMA guidelines were followed. Databases were searched using the terms 'orbital fracture' and 'computed tomography'. Studies evaluating the relationship between CT parameters and the treatment decision or clinical outcome (enophthalmos, diplopia, and/or limitation of ocular movement) were included. The search yielded 4448 results of which 31 were included (except for three, all were retrospective). The systematic use of CT imaging in orbital fractures of the floor and the medial wall can be of great value in the treatment decision and prediction of (long-term) clinical outcomes for both conservatively and surgically treated patients. The following parameters were found to be the most relevant: fracture size, fracture location, orbital volume, soft tissue involvement, and craniocaudal dimension. Although some show great individual potential, it is likely that incorporating all parameters into an algorithm will provide the best predictive power and thus would be the most practically applicable tool.

Natural killer cell infiltration is discriminative for antibody-mediated rejection and predicts outcome after kidney transplantation

Despite partial elucidation of the pathophysiology of antibody-mediated rejection (ABMR) after kidney transplantation, it remains largely unclear which of the involved immune cell types determine disease activity and outcome. We used microarray transcriptomic data from a case-control study (n=95) to identify genes that are differentially expressed in ABMR. Given the co-occurrence of ABMR and T-cell-mediated rejection (TCMR), we built a bioinformatics pipeline to distinguish ABMR-specific mRNA markers. Differential expression of 503 unique genes was identified in ABMR, with significant enrichment of natural killer (NK) cell pathways. CIBERSORT (Cell type Identification By Estimating Relative Subsets Of known RNA Transcripts) deconvolution analysis was performed to elucidate the corresponding cell subtypes and showed increased NK cell infiltration in ABMR in comparison to TCMR and normal biopsies. Other leukocyte types (including monocytes/macrophages, CD4 and CD8 T cells, and dendritic cells) were increased in rejection, but could not discriminate ABMR from TCMR. Deconvolution-based estimation of NK cell infiltration was validated using computerized morphometry, and specifically associated with glomerulitis and peritubular capillaritis. In an external data set of kidney transplant biopsies, activated NK cell infiltration best predicted graft failure amongst all immune cell subtypes and even outperformed a histologic diagnosis of acute rejection. These data suggest that NK cells play a central role in the pathophysiology of ABMR and graft failure after kidney transplantation.

Investigation of fatigue crack initiation facets in Ti-6Al-4V using focused ion beam milling and electron backscatter diffraction

In the very high cycle fatigue regime, internal crack initiation can occur in Ti-6Al-4V because of the formation of facets, which are α grains that have fractured in a transcrystalline and planar manner. Because this crack initiation phase occupies most of the fatigue life, it is essential to understand which mechanisms lead to facet formation. Fatigue tests have been performed on drawn and heat-treated Ti-6Al-4V wires, and the facets at internal crack initiation sites have been analysed in detail in terms of their appearance, their spatial orientation and their crystallographic orientation. The facets were not smooth, but showed surface markings at the nanoscale. In nearly all cases, these markings followed a linear pattern. One anomalous facet, in a sample with the largest grain size, contained a fan-shaped pattern. The facets were at relatively steep angles, mostly between 50° and 70°. Cross-sections of the fracture surfaces have been made by focused ion beam milling and were used to measure the crystallographic orientation of facets by electron backscatter diffraction. Most facet planes coincided with a prismatic lattice plane, and the linear markings were parallel to the prismatic slip direction, which is a strong indication that prismatic slip and slip band formation led to crack initiation. However, the anomalous facet had a near-basal orientation, which points to a possible cleavage mechanism. The cross-sections also exposed secondary cracks, which had formed on prismatic lattice planes, and in some cases early stage facet formation and short crack growth phenomena. The latter observations show that facets can extend through more than one grain, and that there is crack coalescence between facets. The fact that drawn wires have a specific crystallographic texture has led to a different facet formation behaviour compared to what has been suggested in the literature.

Characterization of stable and transient cavitation bubbles in a milliflow reactor using a multibubble sonoluminescence quenching technique

The bubble type, generated by an ultrasonic field, was studied in a batch and flow reactor using a multibubble sonoluminescence (MBSL) quenching technique with propanol and acetone. The influence of frequency and transducer configuration was evaluated using the same piezoelectric element in both setups. Results show that the bubble type not only depends on the frequency, but also on the input power or transducer configuration. Additionally, the effect of flow on sonoluminescence yield and bubble type was studied in the continuous setup at various frequencies. As the flow becomes turbulent, the sonoluminescence signal reaches a plateau for three out of four frequencies, and a transition from transient to stable cavitation occurs for frequencies below 200 kHz.

A novel multimodular methodology to investigate external cervical tooth resorption

AIM

To introduce a multimodular combination of techniques as a novel minimal invasive approach to investigate efficiently and accurately external cervical resorption (ECR).

METHODOLOGY

One case of a central incisor with extensive external cervical resorption was selected to demonstrate the potential of a comparative novel study methodology. ECR diagnosis was based on clinical inspection, digital radiography and cone-beam computed tomography (CBCT). After extraction, the tooth was investigated using microfocus computed tomography (micro-CT), nano-CT and hard tissue histology. These techniques were compared for their accuracy and applicability to highlight their advantages and disadvantages.

RESULTS

Nano-CT was more effective than micro-CT and CBCT for detailed ex vivo exploration of ECR. The reparative tissue, pericanalar resorption resistant sheet (PRRS), pulp tissue reactions, resorption channels and their interconnection with the periodontal ligament space were accurately visualized by detailed processing and analysis of the nano-CT data set with Dataviewer and CTAn software. Nano-CT analysis provided better insight in the true extent of the resorption, based on quantitative measurements and 3D visualization of the tooth structure. Nano-CT imaging results were similar to hard tissue histology at the mineralized tissue level. To clarify the dynamic phenomenon of reparative tissue formation and substitution of the resorbed tissues, nano-CT needed to be associated with hard tissue histology.

CONCLUSION

Nano-CT is a fast and minimal invasive technique for the ex vivo analysis and understanding of ECR and is complementary with hard tissue histology. A combined approach of clinical and CBCT examination, with nano-CT and histological mapping measurements, can provide an ideal platform for future ECR imaging and exploration studies.

Contrast-enhanced nanofocus computed tomography images the cartilage subtissue architecture in three dimensions

We describe a non-destructive imaging method, named contrast-enhanced nanofocus X-ray computed tomography (CE-nanoCT), that permits simultaneously imaging and quantifying in 3D the (sub)tissue architecture and (biochemical) composition of cartilage and bone in small animal models at a novel contrast and spatial resolution. To demonstrate the potential of this novel methodology, a newborn mouse was scanned using CE-nanoCT. This allowed simultaneously visualising the bone and cartilage structure much like the traditional alcian blue-alizarin red skeletal stain. Additionally, it enabled a 3D visualisation at such a high spatial image resolution that internal, micro-scale structures could be digitally dissected and evaluated for size, structure and composition. Ex vivo treatment with papain, that is known to specifically remove the non-calcified cartilage layer but keep the calcified cartilage intact, proved CE-nanoCT to be applicable to visualise the subdivisions within the hyaline cartilage of the articular joint of mice. The quantitative power of CE-nanoCT in vivo was evaluated using a mouse model for osteoarthritis (OA), where OA-like cartilage lesions are induced by meniscus destabilisation surgery. The thickness of both the non-calcified and calcified cartilage layer in the knee joint of such mice was visualised and quantified in 3D and compared to unaffected mice. Finally, to show that different forms of cartilage and tissue combinations can be distinguished using CE-nanoCT, different cartilaginous body parts of the mouse were imaged. In conclusion, CE-nanoCT can provide novel insights in preclinical research by quantifying in a non-destructive 3D manner pathological differences, in particular in developing mice, newborns or adults.

Mental and motor development before and during growth hormone treatment in infants and toddlers with Prader-Willi syndrome

BACKGROUND

Prader-Willi syndrome (PWS) is a neurogenetic disorder characterized by muscular hypotonia, psychomotor delay, feeding difficulties and failure to thrive in infancy. GH treatment improves growth velocity and body composition. Research on the effects of GH on psychomotor development in infants with PWS is limited.

OBJECTIVE

To evaluate psychomotor development in PWS infants and toddlers during GH treatment compared to randomized controls.

DESIGN/PATIENTS

Forty-three PWS infants were evaluated at baseline. Twenty-nine of them were randomized into a GH group (n = 15) receiving 1 mg/m(2)/day GH or a non-GH-treated control group (n = 14). At baseline and after 12 months of follow-up, analysis with Bayley Scales of Infant Development II (BSID-II) was performed. Data were converted to percentage of expected development for age (%ed), and changes during follow-up were calculated.

RESULTS

Infants in the GH group had a median age of 2.3 years [interquartile range (IQR) 1.7-3.0] and in the control group of 1.5 years (IQR 1.2-2.7) (P = 0.17). Both mental and motor development improved significantly during the first year of study in the GH group vs. the control group: median (IQR) change was +9.3% (-5.3 to 13.3) vs.-2.9% (-8.1 to 4.9) (P < 0.05) in mental development and +11.2% (-4.9 to 22.5) vs.-18.5% (-27.9 to 1.8) (P < 0.05) in motor development, respectively.

CONCLUSION

One year of GH treatment significantly improved mental and motor development in PWS infants compared to randomized controls.

Validation of x-ray microfocus computed tomography as an imaging tool for porous structures

X-ray microfocus computed tomography (micro-CT) is recently put forward to qualitatively and quantitatively characterize the internal structure of porous materials. However, it is known that artifacts such as the partial volume effect are inherently present in micro-CT images, thus resulting in a visualization error with respect to reality. This study proposes a validation protocol that in the future can be used to quantify this error for porous structures in general by matching micro-CT tomograms to microscopic sections. One of the innovations of the protocol is the opportunity to reconstruct an interpolated micro-CT image under the same angle as the physical cutting angle of the microscopic sections. Also, a novel thresholding method is developed based on matching micro-CT and microscopic images. In this study, titanium porous structures are assessed as proof of principle. It is concluded for these structures that micro-CT visualizes 89% of the total amount of voxels (solid and pore) correctly. However, 8% represents an overestimation of the real structure and 3% are real structural features not visualized by micro-CT. When exclusively focusing on the solid fraction in both the micro-CT and microscopic images, only an overestimation of about 5% is found.

Micro-rotary fatigue of tooth–biomaterial interfaces

The bonding effectiveness of restorative materials to tooth tissue is typically measured statically. Clinically tooth/composite bonds are however subjected to cyclic sub-critical loads. Therefore, in vitro fatigue testing of dental adhesives should predict better the in vivo performance of adhesives. The objective of this study was to determine the fatigue resistance of two representative adhesives, a self-etch and an etch&rinse adhesive, bonded to enamel and dentin. Therefore, tooth/composite interfaces were cyclically loaded using a miniaturized version of a rotating beam fatigue testing device. Subsequently, the load at which 50% of the specimens fail after 10(5) cycles, was determined as the median micro-rotary fatigue resistance (microRFR). For both adhesives, the microRFR was about 30-40% lower than the corresponding micro-tensile bond strength (microTBS) to both enamel and dentin. Analysis of the fracture surfaces by Feg-SEM revealed typical fatigue fracture patterns. It is concluded that resin/tooth interfaces are vulnerable to progressive damage by sub-critical loads, with the 3-step etch&rinse adhesive being more resistant to fatigue than the 2-step self-etch adhesive.

Individualised, micro CT-based finite element modelling as a tool for biomechanical analysis related to tissue engineering of bone

Load-bearing tissues, like bone, can be replaced by engineered tissues or tissue constructs. For the success of this treatment, a profound understanding is needed of the mechanical properties of both the native bone tissue and the construct. Also, the interaction between mechanical loading and bone regeneration and adaptation should be well understood. This paper demonstrates that microfocus computer tomography (microCT) based finite element modelling (FEM) can have an important contribution to the field of functional bone engineering as a biomechanical analysis tool to quantify the stress and strain state in native bone tissue and in tissue constructs. Its value is illustrated by two cases: (1) in vivo microCT-based FEM for the analysis of peri-implant bone adaptation and (2) design of biomechanically optimised bone scaffolds. The first case involves a combined animal experimental and numerical study, in which the peri-implant bone adaptive response is monitored by means of in vivo microCT scanning. In the second case microCT-based finite element models were created of native trabecular bone and bone scaffolds and a mechanical analysis of both structures was performed. Procedures to optimise the mechanical properties of bone scaffolds, in relation to those of native trabecular bone are discussed.

Effect of backyard burning on dioxin deposition and air concentrations

The influence from open burning of garden and household waste on locally measured dioxin deposition and air concentrations was evaluated in three sets of experiments: the combustion of garden waste in barrels and in open fires, and the incineration of household waste in an empty oil drum. Each set was composed of eight individual experiments over 4 h. Deposition gauges were located 20 m NE, SE, SW and NW with respect to the source and on a background location at 400 m SW. Air samples were taken in the plume with a medium volume sampler equipped with a quartz filter and a polyurethane plug. The results illustrate deposition increments in the wind direction at a distance of 20 m from the source of 0.8 pg TEQ/m2 day for garden waste and 2.5 pg TEQ/m2 day for household waste. Concentrations in the plume were increased by 160-580 fg TEQ/m3 over a period of 12 and 31 h respectively. Expressed at a reference CO2 concentration of 9% this corresponds with a range from 0.8 to 3.6 ng TEQ/m3, which is comparable with a poorly controlled MSWI. Emission factors in the order of magnitude of 4.5 ng TEQ/kg combusted garden waste and 35 ng TEQ/kg burned municipal waste were determined.

MRI and x-ray CT study of spatial distribution of core breakdown in ‘Conference’ pears

Two non-destructive tomographic techniques, X-ray CT imaging and magnetic resonance imaging (MRI), were applied to study the development of core breakdown disorder in 'Conference' pears (Pyrus communis cv. Conference). This disorder, which is characterized by brown discoloration of the tissue and development of cavities, is induced by elevated CO(2) and decreased O(2) levels during controlled atmosphere storage. Tomographic images of pears stored for 10 months under disorder inducing conditions, were acquired with both techniques and compared to the actual slices. Both X-ray and MRI were able to differentiate between unaffected tissue, brown tissue and cavities. A simple image-processing program, based on threshold values, was developed to determine the area percentage of affected and unaffected tissue as well as the cavity and core area per slice. For all three imaging techniques the area percentage brown tissue per slice increased with the diameter of the pear, but was systematically underestimated by 12% and 6% for, respectively, X-ray and MRI, compared to the actual slices. The area percentage cavity corresponded very well for all techniques. It was also found that the contours of the brown tissue were parallel to the fruit boundaries, suggesting a relation between the disorder symptoms and gas diffusion properties of the fruit. It was concluded that MRI is the most appropriate technique to study the development of core breakdown disorder during postharvest storage in future experiments.

Progressive versus constant tapered shaft design using NiTi rotary instruments

AIM

To evaluate the influence of a progressive versus constant tapered shaft design on canal preparation by NiTi rotary techniques.

METHODOLOGY

A XMCT-scanner and custom-made software were used to nondestructively analyse the mesial canals of 10 extracted mandibular molars in 3D with a spatial resolution of 12.5 microm. Specimens (n = 10 per group) were scanned before and after preparation using ProTaper (progressive tapered) or K3 (constant tapered) files. Numerical values for volume, curvature, dentine removal and centring ratio were obtained in addition to a visual inspection for canal aberrations. Data were analysed by (multiway factorial) anova, Wilcoxon tests and t-tests.

RESULTS

The volume of total dentine removal (mean +/- SD) was 1.21 +/- 0.66 mm(3) (ProTaper) and 1.06 +/- 0.23 mm(3) (K3) (P > 0.05), and the amount of dentine removal at all separate horizontal regions examined was comparable for both groups. The mean linear dentine removal (transportation) was in the range of 8-212 microm (ProTaper) and 4-187 microm (K3). The resultant centring ratio varied from 0.01 to 0.24 (ProTaper) and from 0.01 to 0.17 (K3), whilst different straightening patterns were observed. A centre displacement towards the furcation coronally was most pronounced for the ProTaper group whereas a centre displacement towards the outer side of the curvature more apically was only observed for the K3 group. No severe canal aberrations were found.

CONCLUSIONS

The progressive tapered shaft design of the ProTaper instrument was less influenced by the mid-root curvature than the constant tapered design of the K3 instrument thereby providing a good centred apical preparation. However, ProTaper instruments tended to transport towards the furcation in the coronal region.

Cervical external root resorption in vital teeth

External resorptions associated with inflammation in marginal tissues present a difficult clinical situation. Many times, lesions are misdiagnosed and confused with caries and internal resorptions. As a result inappropriate treatment is often initiated. This paper provides three-dimensional representations of cervical external resorption, based on X-ray microfocus-tomographical scanning of a case, which will aid the dental practitioner in recognizing characteristic features during clinical inspection. In addition, histopathological examination reveals the cellular morphology of the adjacent tissues.

Smooth flexible versus active tapered shaft design using NiTi rotary instruments

AIM

The aim of this study was to evaluate the influence of a smooth flexible versus active tapered shaft design on canal preparation by NiTi rotary techniques.

METHODOLOGY

A XMCT-scanner (SkyScan 1072) and developed software (Bergmans et al. 2001) were used to nondestructively analyze the mesial canals of 10 extracted mandibular molars in 3D with a spatial resolution of 30 microm. Specimens (n = 10 per group) were scanned before (PRE) and after (POST) preparation using Lightspeed (smooth flexible) or GT-rotary (active tapered) files. Numerical values for volumes, dentine removal (net) transportation and centring ability were obtained in addition to a visual inspection on canal aberrations. Data were analyzed by Shapiro Wilk test, multiway factorial anova, Tukey-Kramer test, Wilcoxon test and t-test.

RESULTS

Results indicated that the active tapered shaft removed significantly more dentine in the middle to apical portion of the root compared to the smooth flexible design. Both groups demonstrated some straightening, but no significant differences were found with respect to instrument types. However, absolute values for net transportation and centering ratio were small and no canal aberrations could be found.

CONCLUSIONS

The smooth flexible shaft design did not improve the morphological characteristics of canal preparation by NiTi rotary instruments when compared with the active tapered design. Therefore, system selection should be based upon other criteria.

Use of microfocus computerized tomography as a new technique for characterizing bone tissue around oral implants

Qualitative and quantitative analysis of peri-implant tissues around retrieved oral implants is typically done by means of light microscopy on thin histological sections containing the metal surface and the undecalcified bone. It remains, however, a labor-intensive and thus time-consuming job. Moreover, it is a destructive technique that allows tissue quantification in only a limited number of two-dimensional sections. As an alternative, we evaluated the bone structure around screw-shaped titanium implants by means of microfocus computerized tomography (micro-CT) because it presents a number of advantages compared to conventional sectioning techniques: micro-CT is nondestructive, fast, and allows a fully three-dimensional characterization of the bone structure around the implant. Images can be reconstructed in an arbitrary plane, and three-dimensional reconstructions are also possible. Because of its high resolution, individual trabeculae can be visualized. The accuracy of micro-CT was qualitatively evaluated by comparing histological sections with the corresponding CT slices for the same specimen. The overall trabecular structure is very similar according to both techniques. Even very close to the interface, the titanium implant does not seem to produce significant artifacts. Furthermore, because the complete digital data on the trabecular bone structure around the implant is available, it is possible to create finite-element models of the bone-implant system that model the trabeculae in detail so that mechanical stress transfer at the interface can be studied at the level of individual trabeculae. Therefore, micro-CT seems to be very promising for the in vitro assessment of the three-dimensional bone structure around oral implants. Further research will be needed to evaluate its accuracy in a more quantitative way.

Structural and radiological parameters for the nondestructive characterization of trabecular bone

Trabecular bone is characterized by compositional and organizational factors. The former include porosity at microlevel and mineralization. The latter refer to the trabecular architecture. Both determine the mechanical properties of the trabecular bone. The aim of this study is to investigate the relationship between the mechanical properties and the local HU value, the bone mineral density, the in vitro histomorphometric properties assessed by means of microcomputed tomography, and the Young's modulus determined by ultrasound measurement. Also the correlation between local HU values based on CT data of the full bone and HU values based on CT data of excised trabecular bone cylinders is investigated. Therefore density and strength related parameters of 22 trabecular bone cylinders retrieved from a fresh cadaver femur were measured by using different techniques. The mean HU value of the excised bone samples is very highly correlated with the pQCT density (R2=0.95) and the microCT-based morphometric parameter BV/TV (R2=0.95). The mean HU values, determined from the CT images of the planned and excised bone samples, are less highly correlated (R2=0.75). The Young's modulus E(US) determined from the ultrasound measurement is highly correlated with the maximal stress sigmamax (R2 = 0.88) but not with the mechanically determined Young's modulus Emech (R2 = 0.67). The maximal stress sigmamax correlates well with the density parameters (R2 varies between 0.76 and 0.86). On the contrary the mechanically determined Young's modulus Emech does not correlate well with the density parameters (R2 varies between 0.52 and 0.56). The absorbed energy Eabs during the deformation is only highly correlated with the maximal stress sigmamax (R2 = 0.83). The inclusion of structural parameters besides a density related parameter did improve the prediction of the Young's modulus and the maximal stress. In conclusion, it seems that the HU value from clinical CT scanning is a good predictor of the local bone density and volume fraction. A combination of local density and a measure of the structural anisotropy is clearly needed to achieve good predictions of bone mechanics.

Mechanical root canal preparation with NiTi rotary instruments: rationale, performance and safety. Status report for the American Journal of Dentistry

The growing use of NiTi rotary instruments in dental practice demands a good understanding of their concept of alloy and design in relation to improved properties and inherent limitations. Nickel titanium's super elasticity allows more centered canal preparations with less transportation and a decreased incidence of canal aberrations. Furthermore, the production of files with increased taper became possible. This is of special importance because of concerns on the achievement of adequate irrigation and close adaptation of the filling material during endodontic treatment. Unique shaft and tip designs should permit the use of a rotary handpiece allowing different tactile awareness. On the other hand, special attention is paid to maximize cutting efficiency and cutting control throughout instrumentation. NiTi rotary instruments are generally used in a crown-down approach and a continuous reaming motion. Consequently, rounder root canal preparations, with less straightening and a smaller amount of apical extrusion is achievable. In spite of their increased flexibility, separation is still a concern with NiTi files. The phenomenon of repeated cyclic metal fatigue and the variable of torsional loading are two important factors in instrument fracture. However, with awareness of the appropriate manipulation and special attention to the equipment used, NiTi systems are safe with a minimal incidence of instrument failure.

A methodology for quantitative evaluation of root canal instrumentation using microcomputed tomography

AIM

The aim of this paper was to present an objective methodology for quantitative evaluation of root canal instrumentation using microcomputer tomography, together with developed software based on a constructed mathematical model.

METHODOLOGY

A desktop X-ray micro-CT scanner (SkyScan 1072) was used to provide data sets of an extracted mandibular molar before and after instrumentation (ProFile 0.04 Taper instruments, Dentsply Maillefer, Ballaigues, Switzerland) that were stored for later use by software. A volume visualization package (T3D) was applied to obtain 3D renderings of the molar to illustrate the qualitative visualization capacity. Next, medical image volume fusion software was used to allow alignment of pre and post image volumes. Finally, software was developed to make quantitative measurements and to provide additional qualitative information on the registered image volumes. This procedure implemented a true 3D mathematical model for quantification of instrumentation effects. Using a local co-ordinate frame, perpendicular reslices were made at five different levels within the mesio-buccal canal to evaluate transportation and centring ability.

RESULTS

At first accurate and detailed 3D renderings were obtained. The general and local canal shape before and after preparation could visually be examined in 360 degrees rotation. Numerical values were obtained for volume, volume changes and transportation. Centring ability was calculated by centring ratio and centre movement.

CONCLUSIONS

This methodology is a new and objective way for quantitative evaluation of root canal instrumentation using microcomputer tomography and dedicated software.

Health risk assessment of dioxin emissions from municipal waste incinerators: the Neerlandquarter (Wilrijk, Belgium)

Two municipal waste incinerators in the vicinity of a residential area close to the city of Antwerp caused concern to local habitants. Risk assessment was performed combining chemical, toxicological measurements and model calculations. As the first step in risk assessment an inventory was made of historic emissions from both incinerators with emphasis on dioxins. The operational atmospheric transport and deposition model for priority substances (OPS) was used to calculate the deposition of dioxins in the vicinity of incinerators. The observed soil contamination pattern did not correspond to the calculated deposition pattern, indicating that other sources may contribute at least partly to the local PCDD/PCDF contamination of the area. Dioxin exposure of people in the Neerlandquarter as a function of the food consumption behavior was calculated using a mathematical model (VLIER-HUMAAN) combined with transfer factors. According to the results of these calculations, just residing in the impact area does not result in a meaningful risk. Only if locally produced food was consumed (milk, meat and vegetables), exposure in the Neerlandquarter was enhanced compared to the average dioxin exposure estimated for the Flemish population. Exposure in 1997 was below the exposure in 1980. As a consequence of different eating habits and lower bodyweight, children are subjected to significantly higher exposure than adults. Adverse health outcomes from dioxin exposure in the past cannot be excluded. There was no evidence for enhanced exposure to genotoxicants based on a comparison of chromosomal damage to blood cells of children from the study area to those from a control group.

Schlieren photography study of energy absorption by uric acid nuclei

Previous studies using microfocus x-ray radiography on concentric laminated uric acid calculi following in vitro extracorporeal shock-wave lithotripsy (ESWL) has demonstrated the enlargement of the matrix layers. The Schlieren technique was used to verify the hypothesis that the incident energy would be concentrated in the matrix layers by total internal reflection. Because of the rough surface of the stone, the ultrasonic beam (4 MHz) was incident at various angles. At the critical Rayleigh angle (45.9 degrees +/- 0.5 degrees ), the reflected beam consisted of a spectacularly reflected lobe and a reradiated leaky Rayleigh wave. Different critical Lamb angles, theta(L), of 30.8 degrees, 38.1 degrees and 50.8 degrees (experimental uncertainty 0.5 degrees ) were also determined. Depending on the angle of incidence on the stone surface, a Rayleigh wave can be produced and/or one or more layers, as a whole, are set into vibration (Lamb excitation), with the result that shell-like fragments consisting of one or more layers, break off the stones at sites of weaker bonding, as has been noted in previous in vitro lithotripsy experiments by our group.

Ultrasonic velocities of concentric laminated uric acid stones

In concentric laminated uric acid samples two different sound velocities are observed with very different values, the one in the organic matrix varies from 670 to 1170 m s(-1), the other in the crystalline layers between 3200 and 5300 m s(-1). This large difference illustrates the importance of the internal stone structure on the fracture behaviour of urinary stones and reveals the weakness of the actual disintegration models, attributing the destructive effect of shock waves on the differences in acoustical impedance at the water/stone interface and not on the differences in acoustical impedance at the matrix/crystalline interfaces inside the urinary calculus.

Detection and characterization of primary liver cancer in rats by MS-264-enhanced MRI

A new MR contrast agent, MS-264 (Gd(1RS)-1-(p-butylbenzyl)-DTPA), was developed to achieve hepatobiliary specificity and its potential evaluated for detecting and characterizing liver tumors in rats with chemically induced hepatocellular carcinoma (HCC). In seven rats with 66 HCC lesions, enhancements of different abdominal organs and tumors were compared on T1-weighted images after intravenous administration of Gd-DTPA (0.3 mmol/kg) and MS-264 (0.05 mmol/kg). MR images were correlated with postmortem microangiographic and histological findings. An overall enhancement of different organs, which normalized within 24 h, was observed after Gd-DTPA and MS-264 injection. MS-264 caused a higher relative enhancement (RE) in liver (60%), compared with that of Gd-DTPA (40%), which resulted in a prompt negative contrast enhancement in 59 of 66 HCCs. All were moderately to poorly differentiated (Grades II-IV) tumors. Six of these 59 negative contrast-enhancing lesions showed a positively enhanced peritumoral rim, which corresponded histologically to malignant infiltration (n = 2) or compression (n = 4). On the other hand, six well differentiated HCCs showed prolonged positive enhancement. However, one well differentiated HCC was not positively enhanced by MS-264, probably due to poor access of the agent to the lesion. In comparison to that of the precontrast images, enhancement with Gd-DTPA and MS-264 increased the number of detected lesions by 22 and 42%, respectively. In this animal study, MS-264 proved to be useful in detection and characterization of primary liver cancers.

Localization of metalloporphyrin-induced "specific" enhancement in experimental liver tumors: comparison of magnetic resonance imaging, microangiographic, and histologic findings

RATIONALE AND OBJECTIVES

We investigated the tumor specificity of gadolinium mesoporphyrin (Gd-MP) and manganese tetraphenylporphyrin (Mn-TPP) as magnetic resonance (MR) imaging contrast agents.

METHODS

Fifteen rats with multiple hepatocellular carcinomas and eight rats with implanted Novikoff hepatomas were given intravenous injections of either Gd-MP or Mn-TPP at 0.05 mmol/kg, which was compared with nonspecific gadopentetate dimeglumine (0.3 mmol/kg). T1-weighted spin-echo images were obtained before and up to 48 hr after injection and compared with corresponding microangiograms and histologic specimens. The relative enhancement of organs and tumors was plotted as a function of time.

RESULTS

Initially, both metalloporphyrins behaved as nonspecific agents, similar to gadopentetate dimeglumine, and enhanced the tumor by perfusion and diffusion. However, metalloporphyrins, but not gadopentetate dimeglumine, caused a delayed (> or = 3 hr) enhancement in some compartments of certain lesions. The MR imaging-microangiography-histology matching technique revealed that those compartments were actually nonviable components, including necrosis (n = 10), thrombosis (n = 7), and cystic secretion (n = 3), but not viable tumor tissue.

CONCLUSION

Metalloporphyrins did not prove to be tumor specific. However, the observed affinity for nonviable tissue has elicited other potential applications for these agents.

Nitrous oxide emissions from waste water

The estimation of nitrous oxide emissions is complicated by the high degree of uncertainty on the emission factors involved and by the limited acquaintance with all significant nitrous oxide sources. A potentially important source for which emission data are lacking is the sewage system transporting waste water from human activities. For this study an experimental measurement campaign has been carried out on waste water sampled at different sewage treatment plants. The nitrous oxide developing from the water samples was monitored by means of gas chromatography. The methodological analysis was based on the concentration/time curves obtained. Our results indicate that the formation of nitrous oxide from the waste water matrices results from microbiological denitrification. We deduced tentative emission factors for the waste water types studied.

The influence of internal stone structure upon the fracture behaviour of urinary calculi

In vitro extracoporeal shock wave lithotripsy (ESWL) on different types of urinary calculi, in combination with microfocus x-ray and microphotography, illustrates the importance of the internal stone structure. Calculi with a rough surface layered structure (calcium oxalate monohydrate) and untextured calculi (cystine) are characterized by a low stone fragility, whereas coarse-grain calculi (calcium oxalate dihydrate, struvite), and calculi with a smooth surface layered structure (uric acid), are very fragile. Shell-like fragmentation in layered calculi, with smooth surface of the crystalline laminations, suggests that the stone matrix influenced the propagation of the shock wave energy inside the stone.

Fatigue properties of implant materials in hip prosthesis form: a standardized test

The determination of the fatigue properties on small specimens is not accurate. It does not take into account the considerable scatter in fatigue properties which may arise in the implants. Therefore, testing of the properties on the actual implant is needed. The working hypothesis of the present article is that four-point bending fatigue tests allow determination of the fatigue limit of the femoral component material in total hip prostheses. It eliminates the disadvantages of the previously proposed load on head test because (1) the reproducibility of the stress pattern is easy; (2) the fatigue testing is over the whole critical part of the stem; and (3) the stresses do not change during the test. Testing of a series of hip prostheses shows that (1) the measured fatigue limit is typical for the material tested; (2) the location of the fatigue fractures is over the critical medial third of the stem; and (3) the fractographic aspects correspond to those of in vivo failed prostheses. The four-point bending procedure is proposed as a standard method.