Large aperture superconducting magnet (benkei)

Benkei, which was a large window frame conventional magnet at KEK has been converted to a superconducting magnet. In the conversion, the pole gap has been doubled from 0.5 m to 1.0 m retaining an analysing power at 2 T m. Several new techniques were applied to coil windings and cryostat fabrication. The superconducting Benkei has shown satisfactory performances for long term operation.     

Response of human insulinoma cells to extracellular calcium is different from normal B cells

The preoperative determination of the localization of a small insulinoma is sometimes difficult using routine imaging techniques. We have used the selective arterial calcium injection (SACI) test to determine the location of the tumor preoperatively. The pathophysiologic basis of the SACI test is based on the responsiveness of insulinomas to calcium injected into the feeding artery. In this study, we demonstrated the in vitro response of the insulinoma cells to the extracellular calcium challenge by using primary-cultured insulinoma cells. Human insulinoma cells were obtained from three patients. MIN6 cells (normal pancreatic B cells) were used as a control; their insulin response to various stimuli resembles that of normal B cells. The insulin secretory dynamics in response to extracellular calcium were observed using a perfusion system. Second, the change of the concentration of cytosolic free calcium ([Ca2+]i) was monitored by fluorometry using fura-2/AM. When the concentration of extracellular calcium ([Ca2+]o) was changed from 2.54 mM to 10 mM, insulin secretion from the insulinoma cells was markedly increased within 6 min (10- to 18-fold at maximum), and rapidly returned to the basal level; at the same time, [Ca2+]i was immediately elevated and reached a peak within 1 min. In contrast, in the MIN6 cells, the insulin secretion and [Ca2+]i were not significantly changed when [Ca2+]o was switched to 10 mM. The results of these in vitro experiments agreed with the clinical results of the SACI test. The positive response of the insulinoma to the SACI test is probably due to the different response of insulinoma cells to the extracellular calcium challenge compared with normal B cells. The role of [Ca2+]i may be important in the mechanism underlying the SACI test.     

Optimally weighted wavelet transform based on supervised training for detection of microcalcifications in digital mammograms

We are developing a computer-aided diagnosis (CAD) scheme for detection of clustered microcalcifications in digital mammograms. The use of an empirically chosen wavelet and scale combination for detection of microcalcifications as an initial step of the CAD scheme has been reported by us previously. In this study, we developed a technique for optimizing the weights at individual scales in the wavelet transform to improve the performance of our CAD scheme based on the supervised learning method. In the learning process, an error function was formulated to represent the difference between a desired output and the reconstructed image obtained from weighted wavelet coefficients for a given mammogram. The error function was then minimized by modifying the weights for wavelet coefficients by means of a conjugate gradient algorithm. The Least Asymmetric Daubechies' wavelets were optimized with 297 regions of interest (ROIs) as a training set by a jackknife method. The performance of the optimally weighted wavelets was evaluated by means of receiver-operating characteristic (ROC) analysis by use of the above set of ROIs. The analysis yielded an average area under the ROC curve of 0.92, which outperforms the difference-image technique used in our existing CAD scheme, as well as the partial reconstruction method used in our previous study.     

Usefulness of percutaneous cardiopulmonary bypass support in patients with difficulties in weaning from cardiopulmonary bypass

A percutaneous cardiopulmonary support system (PCPS) was used in 12 patients (mean age 68 years) between March 1991 and June 1996 for difficulties weaning from ordinary cardiopulmonary bypass. Cardiac procedures preceding the placement of the PCPS were coronary artery bypass grafting in 8 patients, aortic valve replacement in 1, double valve replacement in 1, and ascending aortic replacement for acute aortic dissection in 1. These procedures were elective in 6 patients and emergent in 6. Intraaortic balloon pumps were used in all cases except in two cases with atherosclerotic occlusive disease. Nine (75%) of the patients were weaned from PCPS, and seven (58%) were discharged. There were no complications due to the placement of PCPS except for three episodes of lower leg ischemia. We conclude that PCPS is useful in addressing difficulties in weaning from ordinary cardiopulmonary bypass and there should be further discussion about the limitations of PCPS in cases of severe circulatory failure.     

Development of ultra high strength steels based on spinodal decomposition

A new idea for the development of ultra high strength steels by utilizing the spinodal decomposition of the Fe-Mo binary system is proposed. The idea comprises the restraint of the brittleness of the Fe-Mo alloy by reducing the Mo-content necessary to spinodal decomposition and by microstructure refining such as grain refining, subgrain refining etc; the former is realized by the alloying with some elements which, in general, have a tendency towards ordering (i.e., negative interchange energy between the nearest neighbour atoms) when combined with iron, and the latter by thermomechanical treatment and/or cold rolling. On the basis of the idea, that hidden properties indispensable to high strength materials are successfully drawn from the Fe-Mo alloy; we have obtained a 4GPa grade high tensile steel of Fe-Mo-Co-V. This idea is sure to contribute new suggestions to the development of high strength materials.     

The hyperthermophilic archaeon Pyrodictium occultum has two alpha-like DNA polymerases

We cloned two genes encoding DNA polymerases from the hyperthermophilic archaeon Pyrodictium occultum. The deduced primary structures of the two gene products have several amino acid sequences which are conserved in the alpha-like (family B) DNA polymerases. Both genes were expressed in Escherichia coli, and highly purified gene products, DNA polymerases I and II (pol I and pol II), were biochemically characterized. Both DNA polymerase activities were heat stable, but only pol II was sensitive to aphidicolin. Both pol I and pol II have associated 5'-->3' and 3'-->5' exonuclease activities. In addition, these DNA polymerases have higher affinity to single-primed single-stranded DNA than to activated DNA; even their primer extension abilities by themselves were very weak. A comparison of the complete amino acid sequences of pol I and pol II with two alpha-like DNA polymerases from yeast cells showed that both pol I and pol II were more similar to yeast DNA polymerase III (ypol III) than to yeast DNA polymerase II (ypol II), in particular in the regions from exo II to exo III and from motif A to motif C. However, comparisons region by region of each polymerase showed that pol I was similar to ypol II and pol II was similar to ypol III from motif C to the C terminus. In contrast, pol I and pol II were similar to ypol III and ypol II, respectively, in the region from exo III to motif A. These findings suggest that both enzymes from P. occultum play a role in the replication of the genomic DNA of this organism and, furthermore, that the study of DNA replication in this thermophilic archaeon may lead to an understanding of the prototypical mechanism of eukaryotic DNA replication.     

Computer-aided diagnosis in chest radiography. Preliminary experience

RATIONALE AND OBJECTIVES: Computer-aided diagnosis (CAD) schemes for chest radiography are being developed with which to alert radiologists to possible lesions, and thus potentially improve diagnostic accuracy. However, CAD schemes have not been tested on a large number of clinical cases. The authors identify design parameters that would be required for development of an intelligent workstation. METHODS: Computer-aided diagnosis programs were applied for the automated detection of lung nodules, cardiomegaly, and interstitial infiltrates to 310 consecutive chest radiographs, and were analyzed for potential usefulness and limitations. Computer-aided diagnosis output was evaluated by radiologists and physicists for accuracy and technical problems, respectively. RESULTS: Approximately 70% of the results were judged to be potentially acceptable; however, the number of false-positive findings was relatively high. Technical problems included failure to detect subtle abnormalities and the occurrence of false-positive detections caused by normal anatomical structures. CONCLUSION: Computer-aided diagnosis has the potential to be a valuable aid to radiologists in clinical practice, if certain technical problems can be overcome and if optimal operating points can be defined for clinical use.