H. Cho

Mean curvature as a major determinant of β-sheet propensity

Motivation: Despite the importance of β-sheets as building blocks in proteins and also toxic elements in the pathological disorders, ranging from Alzheimers disease to mad cow diease, the principles underlying their stability are not well understood. Non-random β-sheet propensities of amino acids have been revealed both by their distinct statistical preferences within known protein structures and by the relative thermodynamic scales through the experimental host-guest systems. However, recent fitting analysis has proved that a native β-sheet conforms to a minimal surface with zero mean curvature, like the physical model of soap films. Results: We here suggest that the stability of a residue in the all β-sheet proteins can be measured with its mean curvature parameter, using discrete differential geometry. The sharply decreasing mean curvature with increasing number of β-strands identifies a significant cooperative effect whereby the interstrand interaction increases in strength with the number of β-strands. Furthermore, strong correlations of mean curvatures with previous β-sheet propensities of amino acids show that their intrinsic differences in adopting the ideal β-sheet structure are affected by the water-accessible area of side-chains, and result in the distinct statistical and thermodynamic β-sheet propensities. Therefore, we conclude that mean curvature should be considered as the significant stability index of a β-sheet structure. Contact: ehkoh@yonsei.ac.kr

Development of a digital panoramic X-ray imaging system for dental applications

As a continuation of our digital radiographic sensor R&D, we have developed a prototyped digital panoramic X-ray imaging system for dental applications. The imaging system consists of a slit-collimated X-ray generator with a 0.4 mm focal spot size and a 3.5 mm Al filtration, a linear-array typed CMOS imager with a 48 times 48 mum2 pixel size and a 128 (in the scan direction) times 3072 (in the vertical direction) pixel format, a series of microstep motors for the precise motion control of the imaging system, and the designed sequences for the motion control and pixel readout required to make a specific plane of interest (POI) to be focused. With the several test phantoms we designed, we, for the first time, succeeded in obtaining useful digital panoramic X-ray images by moving the X-ray generator and the CMOS imager along a continuously-sliding rotational center. In this study, we demonstrated that the prototype system can be applicable to any shaped POI or multi-POIs simultaneously to be focused, provided that adequate sequences for motion control and pixel readout are designed. We expect that the imaging system will be useful for our ongoing applications of dental panoramic radiography and nondestructive testings.

Performance of a Digital Gamma-Imaging System Based Upon CdTe-CMOS Sensor and

As a continuation of our digital radiographic sensor R&D, we have developed a digital gamma-imaging system based upon the commercially-available CdTe-CMOS sensor (AJAT, SCAN1000) and the 75Se gamma source (MDS, Gamma Mat@ SE) for our ongoing application of nondestructive testing. Here the sensor has a 750-mum-thick CdTe photoconductor as an efficient radiation converter and a CMOS pixel array having 100times100 mum2 pixel size and 5.41times51.0 mm2 active area, bump-bonded to the photoconductor for signal readout. The source has about 62.8 Ci activity and a physical size of 3.0 mm in diameter. For the first time in this project, we have succeeded in obtaining useful gamma images from the imaging system and evaluated the imaging performance in terms of the resolving power, the line spread function (LSF), the modulation transfer function (MTF), the noise power spectrum (NPS), and the detective quantum efficiency (DQE). For comparison, we also evaluated the image quality by using a microfocus X-ray source (Hamamatsu, L9121-01) having a focal spot size of about 5 mum.

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As a continuation of our digital X-ray imaging sensor R&D, we have developed a cost-effective, portable, digital radiographic system based on the CMOS image sensor coupled with a fiber optic plate (FOP) and a conventional scintillator. The imaging system mainly consists of a commercially available CMOS image sensor of 48times48 mum2 pixel size and 49.2times49.3 mm2 active area (RadEyetrade2 from Rad-icon Imaging Corp.), a FOP bundled with several millions of glass fibers of about 6 mum in diameter, a phosphor screen such as Min-R or Lanex series, a readout IC board and a GUI software we developed, and a battery-operated X-ray generator (20-60 kVp; up to 1 mA). Here the FOP was incorporated into the imaging system to reduce the performance degradation of the CMOS sensor and the readout IC board caused by irradiation, and also to improve image qualities. In this paper, we describe each imaging component of the fully-integrated portable digital radiographic system in detail, and also present its performance analysis with experimental measurements and acquired X-ray images in terms of system response with exposure, contrast-to-noise ratio (CNR), modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE).

Se Source for Nondestructive Testing

The performance of gas avalanche pixel detectors of square and circular geometry, with and without semiconducting surface coating, was characterized in terms of gas gain and active region. Although the electric field profile of the square geometry cannot be radially uniform, a 200 /spl mu/m pitch detector of this type exhibited a maximum gain of /spl sim/12000 which is comparable to that of the circular counterpart. Due to the existence of the anode bus lines passing under the cathodes, there is a defocusing effect of the drift field lines converging to the anodes, resulting in inactive regions where electrons produced from gas ionization are not collected at the anodes. Variation of the count rate with the drift field was measured to probe these defocusing effects. The p-type a-Si:C:H surface coating was effective in reducing these inactive regions.

Development of a portable digital radiographic system based on FOP-coupled CMOS image sensor and its performance evaluation

PURPOSE Primary central nervous system lymphoma (PCNSL) is an aggressive and rare extranodal non-Hodgkin lymphoma (NHL). Absolute lymphocyte count (ALC) has been suggested to have a prognostic value in several subtypes of NHL. We evaluated the prognostic significance of clinical factors, including ALC, in patients with PCNSL to develop a new prognostic model. METHODS We analysed prognostic factors, including ALC, at diagnosis in 81 PCNSL patients receiving high-dose methotrexate-based therapy. RESULTS The median ALC at diagnosis was 1210 × 10(6)/L (range, 210-3610), with lymphopenia (≤ 875 × 10(6)/L) being detected in 27 (33.3%) patients. In the multivariate analysis, Eastern Cooperative Oncology Group performance status (ECOG PS) >1 (hazard ratio [HR] 3.18, P=0.003), age >50 years (HR 4.23, P=0.012), and lymphopenia at diagnosis (HR 2.83, P=0.008) remained independent prognostic factors for low overall survival (OS). Lymphopenia was also a significant prognostic factor for progression-free survival (HR 3.17, P=0.001). By means of a new three-factor prognostic model using ECOG PS >1, age >50 years, and presence of lymphopenia, with 1 point assigned to each factor, we successfully classified the patients into three risk groups: low (0 and 1), intermediate (2), and high (3). The 5-year OS rates of the patients in the low-, intermediate-, and high-risk groups were 74.3%, 21.7%, and 12.5%, respectively (P<0.001). CONCLUSIONS Low ALC is a useful indicator of poor prognosis in patients with PCNSL. The proposed three-factor model should be validated in large-scale studies.

Gas avalanche pixel detectors with amorphous silicon carbide (a-Si:C:H) overcoating

Upfront autologous stem cell transplantation (ASCT) has shown favourable outcome in patients with primary central nervous system lymphoma (PCNSL), but the role of risk‐adapted upfront ASCT consolidation has not been evaluated in PCNSL. As PCNSL patients with the International Extranodal Lymphoma Study Group (IELSG) prognostic score ≥2 or those who did not achieve complete response after two courses of induction chemotherapy (non‐CR1) have shown inferior outcomes, we retrospectively analysed the role of upfront ASCT in 66 high‐risk (IELSG ≥2 and/or non‐CR1) younger (age <65 years) immunocompetent PCNSL patients who achieved at least partial response after initial high‐dose methotrexate‐based chemotherapy. Nineteen patients who received upfront ASCT exhibited significantly better overall survival (OS, P = 0·021) and progression‐free survival (PFS, P = 0·005) compared to 47 patients who did not. In univariate and multivariate analyses, upfront ASCT was associated with better OS (P = 0·037 and P = 0·025, respectively) and PFS (P = 0·009 and P = 0·007, respectively). In a propensity score‐matched cohort (n = 36), patients who received upfront ASCT also showed better outcome (P = 0·037 for OS, P = 0·001 for PFS). Our results suggest that upfront ASCT consolidation might be especially beneficial for high‐risk PCNSL patients.

A new prognostic model using absolute lymphocyte count in patients with primary central nervous system lymphoma

Pacemaker lead endocarditis is treated with total removal of the infected device and proper antibiotics. The outcomes of patients undergoing percutaneous lead extraction for large vegetations (>2 cm) have not yet been shown. In this case report, we present two patients with pacemaker lead endocarditis with large vegetations of maximum diameter 2.4 cm and 3.2 cm. The first patient had multiple vegetations attached to the tricuspid and mitral valves and developed septic emboli to the brain, lung, and liver. The second patient had a large, persistent vegetation on the tricuspid valve, even two weeks after complete removal of the leads. Both patients were successfully treated with transvenous pacemaker lead removal and antibiotics.

The role of upfront autologous stem cell transplantation in high-risk younger patients with primary central nervous system lymphoma

Abstract To evaluate the feasibility of selecting a mobilization regimen based on the response to induction therapy, we retrospectively analyzed 179 multiple myeloma patients who underwent stem cell mobilization. In comparison with patients who achieved at least a very good partial response (VGPR) to induction therapy and received granulocyte-colony stimulating factor (G-CSF) alone and patients who did not achieve a VGPR and received cyclophosphamide (CY) + G-CSF, treatment-related toxicity was greater and neutrophil engraftment was slower in the CY than the G-CSF group. The rate of requisite mobilization (≥ 2.0 × 106/kg) was similar in both groups. Overall and progression-free survival was not different between patients in the G-CSF group and patients who achieved at least VGPR and received CY + G-CSF. In conclusion, response-adapted selection of a mobilization regimen is appropriate. G-CSF alone should be the preferred treatment for patients who achieved at least a VGPR to induction therapy.

Transvenous pacemaker lead removal in pacemaker lead endocarditis with large vegetations: a report of two cases.

The aim of this study was to identify the risk factors associated with severe bacterial infection (SBI) in multiple myeloma (MM) patients during treatment with bortezomib-based regimens. A total of 98 patients with MM were evaluated during 427 treatment courses. SBI occurred in 57.1% (56/98) of the patients and during 19.0% (81/427) of the treatment courses. In the multivariate analysis for the factors associated with the development of SBI in each treatment course, poor performance status (Eastern Cooperative Oncology Group ≥ 2, P < 0.001), early course of therapy (≤ 2 courses, P < 0.001), and pretreatment lymphopenia (absolute lymphocyte count < 1.0 × 109/L, P = 0.043) were confirmed as independent risk factors. The probability of developing SBI were 5.1%, 14.9%, 23.9% and 59.5% in courses with 0, 1, 2, and 3 risk factors, respectively (P < 0.001). In conclusion, we identified three pretreatment risk factors associated with SBI in each course of bortezomib treatment. Therefore, MM patients with these risk factors should be more closely monitored for the development of SBI during bortezomib-based treatment.