The Threaded Dental Implant as a Reference Object for Image Alignment

This paper presents a method that uses the threaded dental implant as a reference object for the inter-image alignment necessary for digital subtraction radiography. The implant is furthermore used to define a measurement coordinate system and to automate the placement of reference areas used for contrast correction. The method is intended for studies of diffuse bone density changes in the vicinity of the implant. The method is shown to be insensitive to large variations in exposure time and geometry, and is together with the contrast correction method of Ruttimann et at., able to detect clinically invisible simulated bone density changes.     

An international survey of imaging practices in radiotherapy

Improvements in delivery of radiation dose to target tissues in radiotherapy have increased the need for better image quality and led to a higher frequency of imaging patients. Imaging for treatment planning extends to function and motion assessment and devices are incorporated into medical linear accelerators (linacs) so that regions of tissue can be imaged at time of treatment delivery to ensure dose distributions are delivered as accurately as possible. A survey of imaging in 97 radiotherapy centres in nine countries on six continents has been undertaken with an on-line questionnaire administered through the International Commission on Radiological Protection mentorship programme to provide a snapshot of imaging practices. Responses show that all centres use CT for planning treatments and many utilise additional information from magnetic resonance imaging and positron emission tomography scans. Most centres have kV cone beam CT attached to at least some linacs and use this for the majority of treatment fractions. The imaging options available declined with the human development index (HDI) of the country, and the frequency of imaging during treatment depended more on country than treatment site with countries having lower HDIs imaging less frequently. The country with the lowest HDI had few kV imaging facilities and relied on MV planar imaging intermittently during treatment. Imaging protocols supplied by vendors are used in most centres and under half adapt exposure conditions to individual patients. Recording of patient doses, a knowledge of which is important in optimisation of imaging protocols, was limited primarily to European countries.     

Validation of image analysis for enzyme histochemical and immunocytochemical staining

Immunocytochemical and enzyme histochemical analyses of cells and tissues are used to detect changes in the extent of injury and the expression of various molecules. Image analysis quantitation offers an easier, more efficient technique to evaluate these changes. We studied the application of image analysis for evaluating enzyme histochemistry and immunocytochemistry of cells and tissues as a way to assess stroke. Using brain sections, we compared investigator and computer-generated image analysis of 2,3,5-triphenyltetrazolium chloride stained cerebral infarcts in rats subjected to 2 h middle cerebral artery occlusion and 22 h re-perfusion. Both methods documented the infarct volumes with a comparison of means of less then 5%. This suggests no difference between computer- and hand-calculated values. Computer-generated analysis was easier and faster to use. Using endothelial cell monolayers, immunocytochemical staining of a time course of heat shock protein expression was compared to a grading system using fast red chromagen counterstained with hematoxylin. Results demonstrated greater ease and efficiency with computer-generated image analysis compared to other subjective systems of analysis. Image analysis is more useful for detecting small differences in staining, especially when using 3,3-diaminobenzidine as a chromagen. Investigator bias is also reduced using this system. Our comparisons validate the use of this versatile technology to assess more easily both cell and tissues in stroke research.     

Optimization-based region-of-interest reconstruction for X-ray computed tomography based on total variation and data derivative

Region-of-interest (ROI) and interior reconstructions for computed tomography (CT) have drawn much attention and can be of practical value for potential applications in reducing radiation dose and hardware cost. The conventional wisdom is that the exact reconstruction of an interior ROI is very difficult to be obtained by only using data associated with lines through the ROI. In this study, we propose and investigate optimization-based methods for ROI and interior reconstructions based on total variation (TV) and data derivative. Objective functions are built by the image TV term plus the data finite difference term. Different data terms in the forms of L1-norm, L2-norm, and Kullback–Leibler divergence are incorporated and investigated in the optimizations. Efficient algorithms are developed using the proximal alternating direction method of multipliers (ADMM) for each program. All sub-problems of ADMM are solved by using closed-form solutions with high efficiency. The customized optimizations and algorithms based on the TV and derivative-based data terms can serve as a powerful tool for interior reconstructions. Simulations and real-data experiments indicate that the proposed methods can be of practical value for CT imaging applications.     

The first optic ganglion of the bee

Summary The synaptic relationships between and within receptor-cell axons (RCAs), first-order interneurones (L-fibres) and accessory fibres (acc) in the first optic ganglion (the lamina) of the worker bee were studied in serial sections with Golgi-EM and routine transmission electron microscopy. The ommatidium contains nine retinular (photoreceptor) cells all of which project as RCAs to a single optical cartridge in the lamina. Six of the RCAs end as short visual fibres (svf) in the lamina, while the remaining three, the so-called long visual fibres (lvf), pass the lamina and end in the second optic ganglion, the medulla. In addition to the RCAs and an unknown number of accessory fibres, the cartridge also contains four L-fibres (L 1–4). The spatial arrangement of the RCAs and L-fibres within a cartridge is constant throughout the depth of the lamina. Serial sections reveal a great number of chemical synapses interconnecting RCAs, L-and acc fibres. Double T-shaped presynaptic dense projections are surrounded and in close association with either spherical or flattened synaptic vesicles. The finding of gap junctions between and within identified RCAs and L-fibres suggest that these axons may be electronically coupled. A model for information processing in the lamina of the bee is suggested from observations of synaptic connectivity between and within fibres of one cartridge.     

The stromal processing peptidase activities from Chlamydomonas reinhardtii and Pisum sativum: unexpected similarities in reaction specificity

We have partially purified the stromal processing peptidase from Chlamydomonas reinhardtii and compared the properties of this activity with those of the pea counterpart. Whereas previous studies have suggested that the two enzymes may have significantly different reaction specificities, we find that they are in fact very similar. Both enzymes process precursors of two higher-plant thylakoid lumen proteins, and one C. reinhardtii lumenal protein, to similar intermediate-size forms. However, whereas the algal enzyme processes the precursor of C. reinhardtii Rubisco small subunit to the correct mature size, this precursor is cleaved only to an intermediate size by the pea enzyme. The small subunit precursor from pea appears to be cleaved by both enzymes in a similar manner. In terms of sensitivity to inhibitors, the two activities are notably different; the pea enzyme has previously been shown to be inhibited by several types of heavy-metal chelator, but we have found that none of these compounds affect the algal activity.     

Human face processing is tuned to sexual age preferences

Human faces can motivate nurturing behaviour or sexual behaviour when adults see a child or an adult face, respectively. This suggests that face processing is tuned to detecting age cues of sexual maturity to stimulate the appropriate reproductive behaviour: either caretaking or mating. In paedophilia, sexual attraction is directed to sexually immature children. Therefore, we hypothesized that brain networks that normally are tuned to mature faces of the preferred gender show an abnormal tuning to sexual immature faces in paedophilia. Here, we use functional magnetic resonance imaging (fMRI) to test directly for the existence of a network which is tuned to face cues of sexual maturity. During fMRI, participants sexually attracted to either adults or children were exposed to various face images. In individuals attracted to adults, adult faces activated several brain regions significantly more than child faces. These brain regions comprised areas known to be implicated in face processing, and sexual processing, including occipital areas, the ventrolateral prefrontal cortex and, subcortically, the putamen and nucleus caudatus. The same regions were activated in paedophiles, but with a reversed preferential response pattern.     

Defining the Determinants for Dual Targeting of Amino Acyl-tRNA Synthetases to Mitochondria and Chloroplasts

Most of the organellar amino acyl-tRNA synthetases (aaRSs) are dually targeted to both mitochondria and chloroplasts using dual targeting peptides (dTPs). We have investigated the targeting properties and domain structure of dTPs of seven aaRSs by studying the in vitro and in vivo import of N-terminal deleted constructs of dTPs fused to green fluorescent protein. The deletion constructs were designed based on prediction programs, TargetP and Predotar, as well as LogoPlots derived from organellar proteomes in Arabidopsis thaliana. In vitro import was performed either into a single isolated organelle or as dual import (i.e., into a mixture of isolated mitochondria and chloroplasts followed by reisolation of the organelles). In vivo import was investigated as transient expression of the green fluorescent protein constructs in Nicotiana benthamiana protoplasts. Characterization of recognition determinants showed that the N-terminal portions of TyrRS-, ValRS- and ThrRS-dTPs (27, 22 and 23 amino acids, respectively) are required for targeting into both mitochondria and chloroplasts. Surprisingly, these N-terminal portions contain no or very few arginines (or lysines) but very high number of hydroxylated residues (26-51%). For two aaRSs, a domain structure of the dTP became evident. Removal of 20 residues from the dTP of ProRS abolished chloroplastic import, indicating that the N-terminal region was required for chloroplast targeting, whereas deletion of 16 N-terminal amino acids from AspRS-dTP inhibited the mitochondrial import, showing that in this case, the N-terminal portion was required for the mitochondrial import. Finally, deletion of N-terminal regions of dTPs for IleRS and LysRS did not affect dual targeting. In summary, it can be concluded that there is no general rule for how the determinants for dual targeting are distributed within dTPs; in most cases, the N-terminal portion is essential for import into both organelles, but in a few cases, a domain structure was observed.     

A hybrid image processing system for X-ray images of an external fixator

In the field of orthopaedics, treatment of extremity deformities can be realised by means of external fixators. However, control of such biomedical system is very difficult. Some different mathematical models have been developed to improve quality of this service. Most of the parameters, which are used in these models, have been obtained from two orthogonal X-ray images: one from anteroposterior, AP, direction and the other from a lateral, L, direction. The quality of the results of this model is dependent on the accuracy of the input parameters. Measuring these parameters is a time-consuming issue, and the accuracy of the results is also low. To increase the quality of the measurement, the reference points should be chosen from the edges of the biomedical system, and it is important to find the edges without noise. To achieve this purpose, Sobel edge detector, binary large object analysis, thresholding and inverting are applied as image processing steps. The results are compared with manual measurement values which have been obtained earlier. The results show that semi-automatic measurement of the parameters is more accurate and faster than manual measurement. It shows that the efficiency of the fixator method has been improved.