Three-dimensional anatomy setup verification by correlation of orthogonal portal images and digitally reconstructed radiographs.

A method for three-dimensional verification of anatomy setup that uses the correlation of portal images and reference megavoltage digitally reconstructed radiographs (MDRRs) is presented. Prior to a treatment, an orthogonal pair of portal images is acquired from which subimages containing anatomical features are selected. These subimages are consequently matched to MDRRs that represent different rotations of the anatomy around axes going through the treatment isocenter. The Pearson correlation coefficient is employed for the matching since it is invariant with respect to global scaling and shifting of the image intensities. Furthermore, it does not require feature extraction or point-pair identification. The greatest value of the correlation coefficient corresponds to the proper rotational alignment of the anatomy and the location of the correlation maximum in each view indicates the translational shifts of the anatomy. The mean accuracy of translation and rotation registrations tests were a fraction of a millimeter and a fraction of a degree, respectively, for MDRR-to-MDRR matching. For portal-to-MDRR matching, the mean translation registration error is on the order of 1 mm and the mean error in radial displacement is of the order of 2.7 mm.

Group foraging in snowshoe hares (Lepus americanus): Aggregation or social group?

We investigated the behavioural mechanisms involved in group formation at a feeding site in a captive snowshoe hare population. The analysis showed that grouping resulted most often from a feeding attraction which led individuals to use the feeding site independently of each other. However social attraction and especially social repulsion among hares were also involved in group size dynamics. As group size increased, social repulsion underlined by an autocatalytic process led the hares to collectively leave the feeding site. Consequently, the social interactions rates and distance covered per hare increased non-linearly with hare number present at the feeding site. The results suggest that hare behaviour underlined by these mechanisms may influence the risks of starvation and predation. From these results, further field studies are suggested to test in the framework of a multi-factor hypothesis how hare behaviour, food supply and predation may interact simultaneously in population regulation.

[Diagnosis of genital Chlamydia trachomatis infections using antigen detection and cell culture]. / Dépistage des infections génitales à Chlamydia trachomatis par la détection antigénique et la culture cellulaire.

The purpose of this study is: 1. comparing the immuno-enzymatic method (E.L.I.S.A. Abbott) and the cellular culture in the screening of the chlamydial genital infections; 2. evaluating these two tests in post-treatment control. During a 3 month period, 825 patients of our S.T.D. Clinic are considered a risk group and 144 have a positive culture. The E.L.I.S.A. method presents a sensitivity of 70.8% and a specificity of 98.5%. On the other hand, the sensitivity rises up to 80.9% if we retain only the primary culture. Interesting fact: if the reading on the spectrophotometer (E.L.I.S.A. Quantum) is greater than 0.7, the culture is always positive. Being a sexual contact of an infected person, having more than one partner or an history of a S.T.D. in the past, all these factors increase the risk of a chlamydial positivity, but in female only. We observe that 76.5% of patients suffering from gonorrhea have also a chlamydial infection proven by culture. Following a post-treatment control of one week, 5 cases remain positive, that is 3 by E.L.I.S.A. and 2 by culture, while three weeks later all cases are negative. The E.L.I.S.A. method has a good correlation with culture, is highly specific and the reading of optic density seems useful in predicting a positive culture. Risk factors are not the same in male and female. The post-treatment controls by both methods are not always similar if they are performed after one or three weeks.