Can diffusion tensor imaging noninvasively detect IDH1 gene mutations in astrogliomas? A retrospective study of 112 cases

BACKGROUND AND PURPOSE

IDH1 mutational status probably plays an important role in the predictive response for patients with astroglioma. This study explores whether DTI metrics are able to noninvasively detect IDH1 status in astrogliomas.

MATERIALS AND METHODS

The DTI data of 112 patients with pathologically proven astroglioma (including 25, 12, and 10 cases with IDH1 mutation and 11, 11, and 43 cases without mutation in grades II, III, and IV, respectively) were retrospectively reviewed. The maximal fractional anisotropy, minimal ADC, ratio of maximal fractional anisotropy, and ratio of minimal ADC in the tumor body were measured. In the same World Health Organization grading, the imaging parameters of patients with and without IDH1 R132H mutation were compared by means of optimal metrics for detecting mutations. Receiver operating characteristic curve analysis was performed.

RESULTS

The maximal fractional anisotropy and ratio of maximal fractional anisotropy values had statistical significance between patients with IDH1 R132H mutation and those without mutation in astrogliomas of grades II and III. The areas under the curve for maximal fractional anisotropy and ratio of maximal fractional anisotropy were both 0.92 in grade II and 0.80 and 0.82 in grade III. The minimal ADC value and ratio of minimal ADC value also demonstrated statistical significance between patients with mutation and those without mutation in all astroglioma grades. The areas under the curve for minimal ADC were 0.94 (II), 0.76 (III), and 0.66 (IV), and the areas under the curve for ratio of minimal ADC were 0.93 (II), 0.83 (III), and 0.70 (IV).

CONCLUSIONS

Fractional anisotropy and ADC from DTI can noninvasively detect IDH1 R132H mutation in astrogliomas.

Cardiac autonomic function and insulin resistance for the development of hypertension: a six-year epidemiological follow-up study

BACKGROUND AND AIMS

To explore the impact of cardiac autonomic function (CAF) and insulin resistance (IR) on incident hypertension.

METHODS AND RESULTS

In 1996, 1638 subjects finished baseline examination, which included anthropometry, blood pressures, CAF, blood biochemistry, plasma insulin, urine examination and electrocardiogram. CAF included standard deviation of normal-to-normal intervals or RR intervals (SDNN), low- and high-frequency power spectrum (LF and HF), and LF/HF ratio at supine for 5 min, the RR interval changes during lying-to-standing maneuver, and the ratio between the longest RR interval during expiration and the shortest RR interval during inspiration (E/I ratio). We used homeostasis model assessment to define beta cell function (HOMA-B) and insulin resistance (HOMA-IR). In total, 992 non-hypertensive participants completed the follow-up assessment in 2003 and 959 participants were included for the final analysis. Incident hypertension was determined by blood pressure status at follow-up. In unadjusted model, both square root of HOMA-IR (OR:3.37, 95%CI: 2.10-6.64) and HOMA-B (OR:0.996, 95%CI: 0.992-0.999) were related to incident hypertension. In multivariate model, square root of HOMA-IR (OR:1.97, 95%CI: 1.05-3.70), but not HOMA-B, was associated with incident hypertension. After further adjustment for baseline CAF, the positive relationship between the square root of HOMA-IR and incident hypertension disappeared. In contrast, LF/HF ratio (OR:1.18, 95%CI: 1.01-1.37), HF power (OR:0.98, 95%CI: 0.96-0.999), and E/I ratio (OR:0.71, 95%CI: 0.54-0.95) were each independently associated with incident hypertension after further adjustment for HOMA measures.

CONCLUSION

Sympathovagal imbalance with an apparently decreased parasympathetic tone is an important predictor of incident hypertension independent of IR.

Imaging and elemental mapping of biological specimens with a dual-EDS dedicated scanning transmission electron microscope

A dedicated analytical scanning transmission electron microscope (STEM) with dual energy dispersive spectroscopy (EDS) detectors has been designed for complementary high performance imaging as well as high sensitivity elemental analysis and mapping of biological structures. The performance of this new design, based on a Hitachi HD-2300A model, was evaluated using a variety of biological specimens. With three imaging detectors, both the surface and internal structure of cells can be examined simultaneously. The whole-cell elemental mapping, especially of heavier metal species that have low cross-section for electron energy loss spectroscopy (EELS), can be faithfully obtained. Optimization of STEM imaging conditions is applied to thick sections as well as thin sections of biological cells under low-dose conditions at room and cryogenic temperatures. Such multimodal capabilities applied to soft/biological structures usher a new era for analytical studies in biological systems.

Design and implementation of a versatile and variable-frequency piezoelectric coefficient measurement system

We present a simple but versatile piezoelectric coefficient measurement system, which can measure the longitudinal and transverse piezoelectric coefficients in the pressing and bending modes, respectively, at different applied forces and a wide range of frequencies. The functionality of this measurement system has been demonstrated on three samples, including a PbZr(0.52)Ti(0.48)O(3) (PZT) piezoelectric ceramic bulk, a ZnO thin film, and a laminated piezoelectric film sensor. The static longitudinal piezoelectric coefficients of the PZT bulk and the ZnO film are estimated to be around 210 and 8.1 pC/N, respectively. The static transverse piezoelectric coefficients of the ZnO film and the piezoelectric film sensor are determined to be, respectively, -0.284 and -0.031 C/m(2).

The effect of soy isoflavone on bone mineral density in postmenopausal Taiwanese women with bone loss: a 2-year randomized double-blind placebo-controlled study

The treatment of 300-mg/day isoflavones (aglycone equivalents) (172.5 mg genistein + 127.5 mg daidzein) for 2 years failed to prevent lumbar spine and total proximal femur bone mineral density (BMD) from declining as compared with the placebo group in a randomized, double-blind, two-arm designed study enrolling 431 postmenopausal women 45-65 years old.

INTRODUCTION

This study evaluated the effects of soy isoflavones on bone metabolism in postmenopausal women.

METHODS

Four hundred and thirty-one women, aged 45-65 years, orally consumed 300-mg/day isoflavones (aglycone equivalents) or a placebo for 2 years in a parallel group, randomized, double-blind, two-arm study. Each participant also ingested 600 mg of calcium and 125 IU of vitamin D(3) per day. The BMD of the lumbar spine and total proximal femur were measured using dual-energy X-ray absorptiometry at baseline and every half-year thereafter. Serum bone-specific alkaline phosphatase, urinary N-telopeptide of type 1 collagen/creatinine, and other safety assessments were examined regularly.

RESULTS

Two hundred out of 217 subjects in the isoflavone group and 199 out of 214 cases in placebo group completed the treatment. Serum concentrations of isoflavone metabolites, genistein and daidzein, of the intervention group were remarkably elevated following intake of isoflavones (p < 0.001). However, differences in the mean percentage changes of BMD throughout the treatment period were not statistically significant (lumbar spine, p = 0.42; total femur, p = 0.39) between the isoflavone and placebo groups, according to the generalized estimating equation (GEE) method. A significant time trend of bone loss was observed at both sites as assessed by the GEE method following repeated measurement of BMD (p < 0.001). Differences in bone marker levels were not significant between the two treatment groups.

CONCLUSION

Treatment with 300-mg/day isoflavones (aglycone equivalents) failed to prevent a decline in BMD in the lumbar spine or total femur compared with the placebo group.

Hypoglycemic effect and mechanism of a proteoglycan from ganoderma lucidum on streptozotocin-induced type 2 diabetic rats

BACKGROUND AND OBJECTIVES

Diabetes mellitus inducing a leading cause of morbidity are widespread in the entire globe. The present study was to investigate the antidiabetic potency and mechanism of a proteoglycan extract, named FYGL (Fudan-Yueyang-G. lucidum), from the fruiting bodies of Ganoderma Lucidum as published recently, using streptozotocin-induced type 2 diabetic mellitus (T2DM) rats.

MATERIAL AND METHODS

The T2DM model rats were treated with FYGL as well as metformin and rosiglitazone. The levels of plasma glucose and insulin were measured, and the expression and activity of the protein tyrosine phosphatase 1B (PTP1B) and the tyrosine phosphorylation level of the insulin receptor (IR) 3-subunit in the livers and skeletal muscles of the T2DM rats were analyzed by immunoprecipitation and Western blotting methods. In addition, the levels of free fatty acid and serum lipid profile were measured using commercial kits for those trailed rats.

RESULTS

The decrease in fasting plasma glucose and the increase in insulin concentration dose- and time-dependently in the T2DM rats treated by FYGL, comparable with that by the clinical drugs, metformin and rosiglitazone. The levels of the PTP1B expression and activity were decreased, and the tyrosine phosphorylation level of the IR 1-subunit was increased in the skeletal muscles of the T2DM rats. Furthermore, FYGL significantly decreased the levels of free fatty acid, triglyceride, total cholesterol and low density lipoprotein-cholesterol as well as increased the level of high density lipoprotein-cholesterol.

DISCUSSION

It is suggested that the hypoglycemic mechanisms of FYGL are caused by inhibition of the PTP1B expression and activity, consequently, regulation of the tyrosine phosphorylation level of the IR 13-subunit. As those results, FYGL also controlled the plasma biochemistry indexes relative to the type 2 diabetes-accompanied metabolic disorders. This is possibly the first report on the underlying mechanisms responsible for the antidiabetic effect of Ganoderma lucidum.

Construction of the HBV S-ecdCD40L fusion gene and effects of HBV S-ecdCD40L modification on function of dendritic cells

We examined the effect of dendritic cells engineered to express an HBV S antigen CD40L fusion gene (HBV S-ecdCD40L). The DNA of HBV S gene and the cDNA of the extracellular domain of human CD40 ligand were linked by cloning. Peripheral blood mononuclear cells (PBMC) from healthy adults were incubated and induced into dendritic cells (DC) in presence of granulocyte/macrophage colony-stimulating factor (GM-CSF) and interleukin-4(IL-4). The DCs were transfected the novel construct, and the impact of the expressed clone assessed. We find that, compared with control groups, modification of DCs with HBV S-ecdCD40L fusion gene resulted in the activation of DCs with upregulated expression of immunologically important cell surface molecules (CD80, CD86 and HLA-DR) and proinflammatory cytokines (IL-12). The DCs modified with HBV S-ecdCD40L are able to stimulate enhanced allogeneic T-cell proliferation in vitro. Thus, the fusion gene HBV S-ecdCD40L can promote DC's activation and enhance its function and may prove to be the foundation for a new type of hepatitis B vaccine.

Chemically defined media for cultivation of Naegleria gruberi

Cultivation of amebae of the axenic strain of Naegleria gruberi, NEG-M, was achieved in media consisting entirely of chemically defined components. A complete medium that contains 31 components allows growth with yields up to 5 x 10(6) amebae per ml. A minimal medium gives lower yields but defines 22 components that are essential for continuous cultivation: 11 amino acids, 6 vitamins, hematin, guanosine, D-glucose, Mg(2+), and inorganic phosphate. These media allow precise studies of the metabolism and differentiation of this unusual eukaryote.

A Risk Assessment Model for Importation of United States Milling Wheat Containing Tilletia contraversa

Dwarf bunt of wheat, caused by the fungus Tilletia contraversa, is a pathogen historically limited in distribution by its very specific climatic requirements for establishment. In an effort to both address the need for adequate protection and eliminate unwarranted trade barriers, a number of countries have examined restrictions on importing milling wheat containing teliospores of T. contraversa. Pest risk analysis (PRA), under the guidelines of the World Trade Organization and Food and Agriculture Organization, has become an internationally accepted process for evaluating such issues. As a component of a dwarf bunt PRA, our objective was to develop a quantitative mathematical model to evaluate and communicate the potential risk of dwarf bunt establishment from the importation of U.S. milling wheat containing teliospores of T. contraversa. A T. contraversa–risk model (TCK-risk model) was developed using new data, historic literature, and industry statistics to estimate teliospore diversion from transport and milling processes, spore contamination levels, grain handling, and end-product usage. A climatic model was developed to identify potential regions where the environment was favorable for disease development. The likelihood of disease establishment and wheat yield loss was determined using the model to conduct Monte Carlo simulations of 100,000 wheat shipping-years. The model is dynamic in that individual components can be easily updated or modified in order to determine the effect of numerous scenarios (e.g., climate changes, shipping tonnage, contamination levels, mitigation strategies) on the probability of dwarf bunt establishment. TCK-risk model evaluation scenarios previously conducted for the People's Republic of China, Brazil, Mexico, and Peru are presented as examples.

The optimal time-window for surgical treatment of spontaneous intracerebral hemorrhage: result of prospective randomized controlled trial of 500 cases

The aim of this clinical study was to determine the optimal time-window for surgical treatment of spontaneous intracerebral hemorrhage (ICH). From January 1998 to September 2000, 17 hospitals in Shanghai participated in a prospective randomized controlled trial. Among a consecutive series of 500 patients with spontaneous ICH, 234 underwent medical treatment and 266 patients received surgical treatment. According to the interval from initial onset to treatment, they were divided into 3 stages: ultra-early (< or =7 h), early (7-24 h), and delayed (> 24 h). Perioperative evaluation (Glasgow Outcome Score), long-term outcome (the activities of daily living [ADL] score), mortality, as well as incidence of associated complications were compared respectively. We found that: a) in the ultra-early and early stages, both the perioperative and long-term outcome of surgical treatment was definitely better than medical treatment; b) for the outcome of surgical treatment, there was no significant difference between ultra-early and early stages; c) in ultra-early stage, risk of postoperative rebleeding was significantly higher, and decreased henceforth; d) in delayed stage, incidence of associated respiratory, urinary, and gastrointestinal system complications was higher in surgery group than in medication group. In summary, our study yielded conclusive evidence that the early stage (within 7-24 h) was the optimal time-window for surgical intervention of spontaneous ICH.

The impact of clinical risk factors in the conversion from acute lung injury to acute respiratory distress syndrome in severe multiple trauma patients

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are different stages of the same disease, the aggravated stage of ALI leading to ARDS. Patients with ARDS have higher hospital mortality rates and reduced long-term pulmonary function and quality of life. It is, therefore, important to prevent ALI converting to ARDS. This study evaluated 17 risk factors potentially associated with the conversion from ALI to ARDS in severe multiple trauma. The results indicate that the impact of pulmonary contusion, APACHE II score, gastrointestinal haemorrhage and disseminated intravascular coagulation may help to predict conversion from ALI to ARDS in the early phase after multiple-trauma injury. Trauma duration, in particular, strongly impacted the short- and long-term development of ALI. Being elderly (aged > or = 65 years) and undergoing multiple blood transfusions in the early phase were independent risk factors correlated with secondary sepsis, deterioration of pulmonary function and transfusion-related acute lung injury due to early multiple fluid resuscitation.

Optimal design of integrally gated CNT field-emission devices using a genetic algorithm

A method to optimize the focusing quality of integrally gated CNT field-emission (FE) devices by combining field-emission modeling and a computational intelligence technique, genetic algorithm (GA), is proposed and demonstrated. In this work, the e-beam shape, as a characteristic parameter of electron-optical properties, is calculated by field-emission simulation modeling. Using a design tool that combines GA and physical modeling, a set of structural and electrical parameters for four FE device groups, including double-gate, triple-gate, quadruple-gate and quintuple-gate type, were optimized. The resultant FE devices exhibit satisfactory e-beam focusabilities and the extracted parameters with the best performance for each type of FE device were represented to be fabricated by a VLSI technique. The GA-based automatic design parameter extraction will significantly benefit the design of integrated electron-optical systems for versatile vacuum micro- and nano-electronic applications.

The effect of activation treatments on the development of reconstructed bovine oocytes

The purpose of this study was to investigate the effect of different activation treatments on the development of IVM-derived and cloned bovine embryos. The effect of oocyte age (20h versus 24h after IVM) on the blastocyst rate was also investigated. No differences in the percentage of blastocyst development were observed between the oocytes matured for 20 and 24h (15% versus 27%, p>0.05). Reconstructed oocytes activated 4h after fusion (fusion before activation, FBA) had a higher blastocyst rate than those oocytes activated immediately after electrofusion (fusion and activation simultaneously, FAS) (26% versus 5%, p<0.01). Blastocyst rates were significantly greater (p<0.01) for the reconstructed oocytes activated by calcium ionophore (A23187) combined with 6-dimethylaminopurine (6-DMAP) (51.6%) than for those activated with cycloheximide (CHX) plus cytochalasin B (CB) treatment (1h, 8.2%; 5h, 14.3%). However, the blastocyst rates were similar among reconstructed oocytes activated by electric pulses and A23187 (30.5% versus 42.2%) or by A23187 and ionomycin (36.7% versus 33.3%) combined with 6-DMAP, respectively. Blastocysts that developed from reconstructed oocytes activated by A23187 and 6-DMAP resulted in three pregnancies (3/9) and one live birth from 18 embryos transferred to recipient cows. Genotypic analysis of six bovine microsatellite markers by polymerase chain reaction confirmed that the cloned calf was genetically identical to the nuclear donor. In conclusion, reconstructed oocytes that derived from oocytes exposed to activation treatment 4h after electrofusion are more likely to develop to the blastocyst stage. The best treatment to activate reconstructed bovine oocytes in this study was A23187 combined with 6-DMAP.

Practical and simple circuitry for the measurement of small capacitance

Practical and cost-effective circuitry with high sensitivity has been developed to measure a small capacitance using current compensation method. The circuitry uses an electronic switch to periodically connect or separate the capacitor under test (C(x)) from a reference capacitor (C(r)). When C(x) is connected in parallel with C(r) the total capacitance becomes C(x)+C(r). On the other hand, as C(x) is separated from C(r), the total capacitance is only C(r). This periodic change of the capacitance generates a periodic square-wave output with an amplitude in proportion to the capacitance of C(x). A high sensitivity of DeltaV/DeltaC=202.2 mV/pF has been achieved, making the circuitry a powerful tool in measuring small capacitances. Three applications have been performed to present its capability: (a) displacement, (b) height of liquid, and (c) angle of tilt. The experimental results demonstrate the performance of the circuitry.

Angular distribution of polarized photon-pairs in a scattering medium with a Zeeman laser scanning confocal microscope

A novel confocal microscope designed for use with turbid media is proposed. We use a Zeeman laser as the light source. Based on the properties of two-frequency polarized photon-pairs and the common-path feature of polarized photon-pairs with heterodyne detection employed in the proposed confocal microscope, three gatings (spatial filtering gating, polarization gating and spatial coherence gating) are thus simultaneously incorporated in the microscope. Experimental results for the angular distribution of polarized photon-pairs in a scattering medium indicate that polarization gating and spatial coherence gating preclude the detection of multiply scattered photons, whereas the pinhole selects the least scattered photon-pairs. Thus, better performance for axial resolution than can be obtained with a conventional confocal microscope is demonstrated experimentally. In addition, the proposed microscope is able to either look deeper into a turbid medium or work with a denser medium; furthermore, the axial resolution is improved.

Factors Affecting Growth Factor Activity in Goat Milk

Growth factors that are present in goat milk may be responsible for its beneficial effects on the digestive system as described in ancient Chinese medical texts. To develop a nutraceutical product rich in growth factors for promoting gastrointestinal health, it is essential to collect milk with consistently high growth factor activity. Therefore, we investigated the factors affecting growth factor activity in goat milk. Among the 5 breeds of dairy goats tested, milk from Nubian goats had the highest growth factor activity. Tight-junction leakage induced by a 24-h milking interval did not increase growth factor activity in the milk. Milk collected from pregnant does had a significantly higher growth factor activity than milk collected postpartum. Growth factor activity decreased during the first 8 wk of lactation, fluctuated thereafter, and then increased dramatically after natural mating. During wk 1 to 8, growth factor activity was inversely correlated with milk yield and week of lactation. No correlation was observed during wk 9 to 29. After natural mating of the goats, the growth factor activity in the milk correlated significantly with somatic cell count and conductivity (a measure of membrane permeability), and correlated inversely with milk yield. Based on the above data, goat milk with higher growth factor activity could be selectively collected from Nubian pregnant does.

The effect of electrical field strength on activation and development of cloned caprine embryos

The activation procedure used in nuclear transfer (NT) is one of the critical factors affecting the efficiency of animal cloning. The purpose of this study was to compare the effect of two electrical field strengths (EFS) for activation on the developmental competence of caprine NT embryos reconstructed from ear skin fibroblasts of adult Alpine does. The NT embryos were obtained by transfer of the quiescent fibroblasts at the fourth passage into the enucleated metaphase II (M II) oocytes. Four to five hours after electrical fusion, the NT-embryos were activated by EFS either at 1.67 or at 2.33 kV/cm and immediately incubated in 6-DMAP (2 mM) for 4 h. The cleavage rate of the NT-embryos activated with 2.33 kV/cm was greater than that activated with 1.67 kV/cm after in vitro culture for 18 h (65.6% versus 19.6%, p < 0.001). No pregnancy was found in 14 recipient does after transferring 51 NT embryos at 1-2 cell stages activated with 1.67 kV/cm. In contrast, two of the seven recipients were pregnant and gave birth to three kids after transferring 61 NT embryos at 1-2 cell stages activated by 2.33 kV/cm. The birth weights of three cloned kids were within the normal range of Alpine goats. However, one kid died 1h after birth while the remaining two are still healthy. DNA analysis by polymerase chain reaction (single-strand conformation polymorphism, SSCP) confirmed that the three kids were genetically identical to the nuclear donor.

Compliance with childhood immunizations in Kern County, California

A rapid survey was conducted to describe the immunization status of the 0- to 2-year-old population in selected communities of Kern County, California, and identify reasons for noncompliance with immunization recommendations. Households were selected by two-stage cluster sampling. Among 860 children, 38% had received immunizations on schedule, while 44% had not received the recommended doses for their age. Compliance with the immunization schedule worsened dramatically after the first year of life. Among 2 year olds, the proportion that had the recommended number of vaccine doses was 81% for MMR, 82% for polio, 65% for DTP, and 47% for Hib. Parents' main reasons for noncompliance included child's illness, procrastination, and limited access to information and services. The low levels of compliance reflect lack of active follow-up in preventive health care across socioeconomic levels. The results show the importance of aiming immunization messages at parents and physicians of 12- to 18-month-old children. The rapid survey approach offers public health agencies an efficient means of assessing community health problems and targeting programs according to need.

Damped and thermal motion of laser-aligned hydrated macromolecule beams for diffraction

We consider a monodispersed Rayleigh droplet beam of water droplets doped with proteins. An intense infrared laser is used to align these droplets. The arrangement has been proposed for electron- and x-ray-diffraction studies of proteins which are difficult to crystallize. This paper considers the effect of thermal fluctuations on the angular spread of alignment in thermal equilibrium, and relaxation phenomena, particularly the damping of oscillations excited as the molecules enter the field. The possibility of adiabatic alignment is also considered. We find that damping times in a high-pressure gas cell as used in x-ray-diffraction experiments are short compared with the time taken for molecules to traverse the beam and that a suitably shaped field might be used for electron-diffraction experiments in vacuum to provide adiabatic alignment, thus obviating the need for a damping gas cell.

Meshless repair of perineal hernia after abdominoperineal resection: case report

Perineal hernia is a rare complication after major pelvic surgery. Placing non-biodegradable mesh across the pelvic inlet is the best method of repair. A 72-year-old man presented with a perineal hernia 8 years after undergoing an abdominoperineal resection because of rectal cancer. During the repair operation, intestinal spillage occurred, making it impossible to place permanent mesh as planned. Instead, we used the bladder to cover the pelvic inlet. The patient recovered well and after 35 months of follow-up, there was no evidence of hernia recurrence. When mesh placement is not feasible, this bladder mobilization technique can replace it.

Reconstruction of complex single-particle images using charge-flipping algorithm

An iterative algorithm is developed to retrieve the complex exit-face wavefunction for a two-dimensional projection of a nanoparticle from a measurement of the oversampled modulus of its Fourier transform in reciprocal space. The algorithm does not require the support (boundary) of the object to be known. A loose support for the complex object is gradually found using the Oszlanyi-Suto charge-flipping algorithm, and a compact support is then iteratively developed using a dynamic Gerchberg-Saxton-Fienup algorithm. At the same time, the complex object is reconstructed using this compact support. The algorithm applies to the reconstruction of complex images with any distribution of phase values from 0 to 2pi. Modification of the algorithm by using real-value constraints for a complex object in the charge-flipping algorithm leads to faster reconstruction of the object whose phase value is smaller than pi/2.

Diffraction and imaging from a beam of laser-aligned proteins: resolution limits

The effect of the limited alignment of hydrated molecules is considered in a laser-aligned molecular beam, on diffraction patterns taken from the beam. Simulated patterns for a protein beam are inverted using the Fienup-Gerchberg-Saxton phasing algorithm, and the effect of limited alignment on the resolution of the resulting potential maps is studied. For a typical protein molecule (lysozyme) with anisotropic polarizability, it is found that up to 1 kW of continuous-wave near-infrared laser power (depending on dielectric constant), together with cooling to liquid-nitrogen temperatures, may be needed to produce sufficiently accurate alignment for direct observation of the secondary structure of proteins in the reconstructed potential or charge-density map. For a typical virus (TMV), a 50 W continuous-wave laser is adequate for subnanometre resolution at room temperature. The dependence of resolution on laser power, temperature, molecular size, shape and dielectric constant is analyzed.

Iterative phase retrieval without support

An iterative phase retrieval method for nonperiodic objects has been developed from the charge-flipping algorithm proposed in crystallography. A combination of the hybrid input-output (HIO) algorithm and the flipping algorithm has greatly improved performance. In this combined algorithm the flipping algorithm serves to find the support (object boundary) dynamically, and the HIO part improves convergence and moves the algorithm out of local minima. It starts with a single intensity measurement in the Fourier domain and does not require a priori knowledge of the support in the image domain. This method is suitable for general image recovery from oversampled diffuse elastic x-ray and electron-diffraction intensities. The relationship between this algorithm and the output-output algorithm is elucidated.