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Biomedical subjects

A H de Vries

Publications and source records attributed to A H de Vries.

6 recordsLinked to original sources
PubMed2006

Feasibility of automated matching of supine and prone CT-colonography examinations.

Matching of prone and supine positions in CT colonography may improve accuracy of polyp detection. The purpose of this study was to investigate the feasibility of automatic prone-supine matching in CT-colonography using proven polyps as fixed points of reference. The method is based on similarities in the direction of centre-lines and allows for compression and extraction of the centre-lines in both positions. To illustrate the impact of the match error of the new method in practice, the visibility of the matched polyps in a primary three-dimensional unfolded cube setting was determined as well. The method was compared with a method that relies on the normalized distance along the centre-line (NDAC method). The median absolute match error was 14 mm (range 0-59 mm, average 20 mm) either proximal or distal from the actual polyp in prone position. In the observer study, 70% (26/37) of the polyps were directly visible in prone view. The overall difference in median absolute match error between both methods was small (2 mm), although half way along the centre-line there were polyps with substantial differences in match error (larger with NDAC). We concluded that automated prone-supine matching of CT-colonography studies is feasible and has a low match error. The difference with the NDAC method was small and not significant, although half way along the centre-line some differences were seen.

Algorithms↗
PubMed2002

Theoretical characterization of the ground and optically excited states of alpha'-NaV2O5.

The character of the ground and optically excited states was investigated by quantum chemical calculations. We propose a rung ground state with V 3d(1)(xy)-O 2p(1)(y)-V 3d(1)(xy) character, instead of the conventional picture of one unpaired electron shared by 2 V ions. The unpaired electron on O is low-spin coupled to the V d electrons and spin density is predicted to be localized on vanadium. The absorption peak at 0.9 eV is assigned to a state with similar orbital occupations but a different spin coupling scheme, resulting in spin density localized on the bridging oxygen.

Journal Article↗
PubMed1996

Dried sera for confirming blood-borne virus infections (HCV, HTLV-I, HIV & HBsAg).

For safe blood transfusion, developing countries face considerable problems including serological screening and confirmation of blood-borne virus infections (HCV, HTLV-I, HIV and HBsAg). Confirmation tests are not only costly but also require sophisticated techniques and expertise. In order to provide this support we have attempted to perform a virus antibody confirmation test on samples dried on blotting paper (BP). Forty-nine sera derived from selected patients and donors from Bombay, and nine donors' sera from Bellarussia were transported on BP. In control experiments, dilutions of antibody-positive sera (HIV, HTLV-I & HCV) and 'blinded' HTLV-I antibody-positive and antibody-negative donors were applied on BP. Eluates from snipped BP were tested initially by screening tests, and the reactives were subjected to confirmatory tests for three types of virus antibody tests (HCV, HTLV-I & HIV) by blotting methods and neutralisation tests for HBsAg. There was considerable reduction of titres in dry sera but all BP-derived dry specimens gave excellent qualitative concordance with their liquid-equivalent sera, and the HTLV-I-positive donor was identified and reconfirmed correctly. Presence of only HCV antibody was confirmed in all the nine selected Bellarussian donors. Blood donors in Bombay had 3% HIV antibody, 6% HBsAg and none had HCV antibody, while selected patients showed substantially higher levels of these markers: HIV-antibody 64%, HBsAg 57% and HCV-antibody 17% confirmed positive. The cause of this high level remains to be established. Dry samples received by post seem to be an economical approach to a first step in providing some levels of independent confirmation of reactives in developing countries.

Antibodies, Viral↗
PubMedDate not supplied

Perceptive errors in CT colonography.

Published results to date have indicated a good per patient sensitivity of computed tomographic colonography (CTC) for colorectal cancer and for polyps measuring 10 mm or more together with a very good specificity. Sensitivity and specificity for polyps in the range of 6-10 mm are moderate. These results, however, can be achieved only with meticulous attention to technique including adequate colonic distention, and acquisition of supine and prone thin-section computed tomographic (CT) images. Moreover, there is a significant learning curve involved in the interpretation of CTC studies, with performance statistics improving with operator experience. Radiologists must be comfortable in reporting directly from workstation monitors and have access to and be familiar with software for multiplanar and endoluminal reconstructions. In addition to maximize polyp detection and minimize false positive results, reporting radiologists must have a working knowledge of normal colorectal anatomy and pathology on CTC and be familiar with potential pitfalls in interpretation. Besides the description of several possible causes for perceptive errors, also a literature search of perceptive errors in CTC is included in this paper.

Algorithms↗