Graphene oxide/α-Bi(2)O(3) composites for visible-light photocatalysis, chemical catalysis, and solar energy conversion.

The growing challenges of environmental purification by solar photocatalysis, precious-metal-free catalysis, and photocurrent generation in photovoltaic cells receive the utmost global attention. Here we demonstrate a one-pot, green chemical synthesis of a new stable heterostructured, ecofriendly, multifunctional microcomposite that consists of α-Bi2 O3 microneedles intercalated with anchored graphene oxide (GO) microsheets (1.0 wt %) for the above-mentioned applications on a large economical scale. The bare α-Bi2 O3 microneedles display two times better photocatalytic activities than commercial TiO2 (Degussa-P25), whereas the GO-hybridized composite exhibits approximately four to six times enhanced photocatalytic activities than the neat TiO2 photocatalyst in the degradation of colored aromatic organic dyes (crystal violet and rhodamine 6G) under visible-light irradiation (300 W tungsten lamp). The highly efficient activity is associated with the strong surface adsorption ability of GO for aromatic dye molecules, the high carrier acceptability, and the efficient electron-hole pair separation in Bi2 O3 by individual adjoining GO sheets. The introduction of Ag nanoparticles (2.0 wt %) further enhances the photocatalytic performance of the composite over eightfold because of a plasmon-induced electron-transfer process from Ag nanoparticles through the GO sheets into the conduction band of Bi2 O3 . The new composites are also catalytically active and catalyze the reduction of 4-nitrophenol to 4-aminophenol in the presence of borohydride ions. Photoanodes assembled from GO/α-Bi2 O3 and Ag/GO/α-Bi2 O3 composites display an improved photocurrent response (power conversion efficiency ∼20 % higher) over those prepared without GO in dye-sensitized solar cells.

Rates and appropriateness of antimicrobial prescribing at an academic children's hospital, 2007-2010.

OBJECTIVE AND DESIGN: Antimicrobial use in hospitalized children has not been well described. To identify targets for antimicrobial stewardship interventions, we retrospectively examined pediatric utilization rates for 48 antimicrobials from 2007 to 2010 as well as appropriateness of vancomycin and cefepime use in 2010. PATIENTS AND SETTING: All children hospitalized between 2007 and 2010 at the Mayo Clinic Children's Hospital, a 120-bed facility within a larger adult hospital in Rochester, Minnesota. METHODS: We calculated antimicrobial utilization rates in days of therapy per 1,000 patient-days. Details of vancomycin and cefepime use in 2010 were abstracted by chart review. Two pediatric infectious disease physicians independently assessed appropriateness of antibiotic use. RESULTS: From 2007 to 2010, 9,880 of 17,242 (57%) hospitalized children received 1 or more antimicrobials. Antimicrobials (days of therapy per 1,000 patient-days) used most frequently in 2010 were cefazolin (97.8), vancomycin (97.1), fluconazole (76.4), piperacillin-tazobactam (70.7), and cefepime (67.6). Utilization rates increased significantly from 2007 to 2010 for 10 antimicrobials, including vancomycin, fluconazole, piperacillin-tazobactam, cefepime, trimethoprim-sulfamethoxazole, caspofungin, and cefotaxime. In 2010, inappropriate use of vancomycin and cefepime was greater in the pediatric intensive care unit than ward (vancomycin: 17.8% vs 6.4%, P = .001; cefepime: 9.2% vs 3.9%, P = .142) and on surgical versus medical services (vancomycin: 20.5% vs 8.0%, P = .001; cefepime: 19.4% vs 3.4%, P ≤ .001). The most common reason for inappropriate antibiotic use was failure to discontinue or de-escalate therapy. CONCLUSIONS: In our children's hospital, use of 10 antimicrobials increased during the study period. Inappropriate use of vancomycin and cefepime was greatest on the critical care and surgical services, largely as a result of failure to de-escalate therapy, suggesting targets for future antimicrobial stewardship interventions.

SU-E-I-85: Evaluation of a Solid-State Dosimeter Module for Measuring Nuclear Medicine Radionuclides.

PURPOSE: A recently introduced solid-state dosimeter module (UDOS001, Teledyne Microelectronic Technologies, Los Angeles, CA) requires only external power (e.g., from two nine-volt batteries in series) and a battery- powered data recorder to assemble a compact, portable dosimeter. This device was developed for radiation detection and monitoring of a wide range of radiation types. It has a nominal minimum energy of 100 keV. The present study sought to determine its suitability for measuring the dose from radionuclides used in nuclear medicine. METHODS: Three radionuclides (initially 4.77 mCi of F-18, 3.86 mCi of I-131, and 12.4 mCi of Tc-99m) were measured at a distance of one meter and at several different angles of incidence. The most sensitive analog output of the dosimeter was digitized by a battery-powered data logging device (Track-It 5VDC, Monarch Instrument, Amherst NH). These data were transferred from the data logger into a Windows 7 personal computer, formatted as an Excel 2010 spreadsheet and converted from voltage to dose using the manufacturer's nominal calibration factor of 14 urad/19.5 mV step. The dose rate was determined from the slope of a linear fit to the cumulated dose as a function of time. RESULTS: The nominal calibration of the dosimeter gives dose rate measurements that are close to published gamma ray dose rate constants for these radionuclides (0.65 vs. 0.70, 0.25 vs. 0.28, and 0.071 vs. 0.078 mrad/mCi-hr respectively). The angular dependence of the response is greater at 140 keV than at 511 keV, but an acceptance angle of at least 90 degrees has uniform response with all three radionuclides. CONCLUSIONS: A better calibration factor would be 0.154 urad/19.5 mV step at these gamma ray energies. This dosimeter can be used to measure the dose from common radionuclides used in nuclear medicine.

Three-Dimensional Dosimetry of a Beta-Emitting Radionuclide Using PRESAGE Dosimeters.

Three-dimensional dose distributions from liquid brachytherapy were measured using PRESAGE(®) dosimeters. The dosimeters were exposed to Y-90 for 5.75 days and read by optical tomography. The distributions are consistent with estimates from beta dose kernels.

Deposition pattern of heliox-driven bronchodilator aerosol in the airways of stable asthmatics.

To compare the deposition patterns of heliox-driven and air-driven radiolabeled bronchodilator aerosol, a prospective randomized study was undertaken at the Ben Taub Hospital in Houston, Texas. The working hypothesis was that nebulization with heliox would improve the peripheral deposition of a bronchodilator aerosol. Twelve mild-moderate known asthmatics were recruited for the study. They were asked to withhold medications for 8-24 hours prior to reporting for the study. Each subject was randomized to receive either heliox or oxygen for delivery of albuterol labeled with Tc-99m DTPA. Prior to the nebulization, baseline spirometry was performed. Following nebulization, the subjects were scanned for 1,000,000 counts on the ADAC Genesis Scanner. A postbronchodilator spirometry was then performed. Subjects returned about a week later, this time to have the same process repeated with the other gas. The normalized pixel counts were obtained, and the frequency distribution histograms were constructed for each of the deposition images. Skew and kurtosis were calculated. A lower skew and kurtosis value suggests a more peripheral distribution of the bronchodilator, whereas a higher pixel count corresponds with an increased area and uniformity of deposition. There were no statistically significant differences in baseline PFTs on the 2 days of the study. The pixel count was statistically higher after the heliox-driven nebulization than the air-driven nebulization. The skew and kurtosis values were lower after the heliox-driven nebulization than after the air-driven nebulization of radiolabeled aerosol. All patients had a good bronchodilator response with either driving gas. However, the degree of improvement was more with heliox-driven nebulization than with air-driven nebulization. We conclude that aerosol delivery with heliox results in more uniform and peripheral deposition. Thus, this mode of delivery can be used when uniform, peripheral deposition is desired as with drug delivery during an exacerbation or with aerosolized gene therapy.

Sources of HIV-prevention information for individuals at high risk.

OBJECTIVES: To identify the best methods of reaching individuals at high risk with HIV-prevention messages. METHODS: Data were collected from 827 men who have sex with men, injection drug users, sex workers, HIV+ individuals, heterosexuals, migrant workers, and perinatal women. RESULTS: Over 70% of participants were exposed to HIV-prevention messages, but sources of exposure varied by risk group. CONCLUSIONS: Most methods examined were effective means of communicating prevention messages. As multifaceted approaches to intervention allow for more comprehensive dissemination, interventions can be tailored to the targeted risk group by using sources shown most effective for each group.

Eddy current correction in volume-localized MR spectroscopy.

The quality of volume-localized magnetic resonance spectroscopy is affected by eddy currents caused by gradient switching. Eddy currents can be reduced with improved gradient systems; however, it has been suggested that the distortion due to eddy currents can be compensated for during postprocessing with a single-frequency reference signal. The authors propose modifying current techniques for acquiring the single-frequency reference signal by using relaxation weighting to reduce interference from components that cannot be eliminated by digital filtering alone. Additional sequences with T1 or T2 weighting for reference signal acquisition are shown to have the same eddy current characteristics as the original signal without relaxation weighting. The authors also studied a new eddy current correction method that does not require a single-frequency reference signal. This method uses two free induction decays (FIDs) collected from the same volume with two sequences with opposite gradients. Phase errors caused by eddy currents are opposite in these two FIDs and can be canceled completely by combining the FIDs. These methods were tested in a phantom. Eddy current distortions were corrected, allowing quantitative measurement of structures such as the -CH = CH- component, which is otherwise undetectable.

Role of spin echo and cine magnetic resonance imaging in presurgical planning of heterotaxy syndrome. Comparison with echocardiography and catheterization.

BACKGROUND: Patients with heterotaxy syndrome frequently have complex congenital cardiac and noncardiac malformations requiring detailed diagnostic evaluation by noninvasive as well as invasive imaging modalities for management planning. Recent advances in magnetic resonance imaging (MRI) techniques allow detailed delineation of cardiovascular anatomy and blood flow in young infants with rapid heart rates. The present study was undertaken to prospectively evaluate the role of MRI in the presurgical evaluation of patients with heterotaxy syndrome. METHODS AND RESULTS: Between January 1 and December 31, 1992, 14 consecutive patients with heterotaxy syndrome and complex congenital heart disease were enrolled in a prospective protocol. After evaluation by echocardiography and cardiac catheterization, a tentative management plan was recorded. Subsequently, a MRI study was performed and surgical planning was reevaluated. MRI was found to be comparable to echocardiography in terms of length of examination and sedation requirements. Surgical planning was altered in four patients because MRI provided additional data not evident on echocardiography and catheterization. Comparison of diagnostic yield between echocardiography, catheterization, and MRI showed that MRI is superior to echocardiography and often to catheterization in delineation of systemic and pulmonary venous anatomy and their relation to mediastinal structures. When the anatomic and hemodynamic data obtained by echocardiography and MRI were considered together, cardiac catheterization data were necessary only to determination of pulmonary vascular resistance before Fontan operation. CONCLUSIONS: MRI provides excellent anatomic and functional information that in some patients was not available by echocardiography or catheterization. Combined with echocardiography, MRI provides the high-quality diagnostic information necessary for management planning in most patients with heterotaxy syndrome. Cardiac catheterization is indicated when determination of pulmonary vascular resistance is necessary for decision making or when an interventional procedures is indicated.

Automatic adjustment of contrast and brightness of magnetic resonance images.

Two statistics of the magnetic resonance (MR) image, the median and the standard deviation of the values of the significant pixels, can be used along with the type of image to adjust the contrast and brightness of the image (ie, to "window" it) automatically and robustly. The essential parts of this approach to automatic windowing are (1) avoidance of irrelevant pixels, (2) identification of the type of MR image from information stored in the image header, and (3) use of algorithms for the maximum and minimum values that reflect the preference of the intended viewer using a specific monitor and ambient lighting conditions for the different types of images. An evaluation in thirteen clinical studies yielded 91.5% (2312/2526) images requiring no further adjustment and the remaining 8.5% (214/2526) being improved by further adjustment.

Comparison of gradient echo with spin echo magnetic resonance imaging and echocardiography in the evaluation of major aortopulmonary collateral arteries.

This study compared gradient echo magnetic resonance imaging, spin echo magnetic resonance imaging, echocardiography, and echocardiography with x-ray cineangiography in the evaluation of major aortopulmonary collateral arteries. Twelve patients (ages 9 months to 35 years, mean 11 +/- 11 years) with known or suspected major aortopulmonary collateral arteries were studied. The aortic insertion and proximal course of 29 major aortopulmonary collateral arteries demonstrated by x-ray contrast angiography were shown in all 29 cases by gradient echo magnetic resonance imaging but in only 23 of the 29 cases by spin echo magnetic resonance imaging. Color Doppler-echocardiography detected aortopulmonary collateral arteries in four patients but did not define the proximal course or distal anatomy. Gradient echo images of distal aortopulmonary collateral anatomy were qualitatively superior to spin echo images. The contrast-to-noise ratio between the vessel lumen and adjacent lung was greater for gradient echo (6.06 +/- 2.91) than for spin echo (1.45 +/- 1.13)(p < 0.05). Gradient echo magnetic resonance imaging is a useful method for identification and characterization of aortopulmonary collateral arteries in patients of all ages and is superior to spin echo magnetic resonance imaging and echocardiography.

Changes in intervertebral disc cross-sectional area with bed rest and space flight.

STUDY DESIGN: We measured the cross-sectional area of the intervertebral discs of normal volunteers after an overnight rest; before, during, and after 5 or 17 weeks of bed rest; and before and after 8 days of weightlessness. OBJECTIVES: This study sought to determine the degree of expansion of the lumbar discs resulting from bed rest and space flight. SUMMARY OF BACKGROUND DATA: Weightlessness and bed rest, an analog for weightlessness, reduce the mechanical loading on the musculoskeletal system. When unloaded, intervertebral discs will expand, increasing the nutritional diffusion distance and altering the mechanical properties of the spine. METHODS: Magnetic resonance imaging was used to measure the cross-sectional area and transverse relaxation time (T2) of the intervertebral discs. RESULTS: Overnight or longer bed rest causes expansion of the disc area, which reaches an equilibrium value of about 22% (range 10-40%) above baseline within 4 days. Increases in disc area were associated with modest increases in disc T2. During bed rest, disc height increased approximately 1 mm, about one-half of previous estimates based on body height measurements. After 5 weeks of bed rest, disc area returned to baseline within a few days of ambulation, whereas after 17 weeks, disc area remained above baseline 6 weeks after reambulation. After 8 days of weightlessness, T2, disc area, and lumbar length were not significantly different from baseline values 24 hours after landing. CONCLUSIONS: Significant adaptive changes in the intervertebral discs can be expected during weightlessness. These changes, which are rapidly reversible after short-duration flights, may be an important factor during and after long-duration missions.

Magnetic resonance imaging for assessment of tissue rejection after heterotopic heart transplantation.

Detection of myocardial rejection is difficult in patients with heterotopic heart transplantation because of the complex vascular anatomy present after transplant surgery. To determine whether magnetic resonance imaging might be useful for the assessment of heart rejection, eight patients with heterotopic heart transplantation were serially studied on 27 occasions. One patient had two donor hearts implanted, which allowed the study of 33 donor hearts. Data acquisition was gated to the ECG signal of the donor heart. Heavily T2-weighted (TE = 90 ms) velocity compensated spin-echo images were obtained through the midportion of the donor heart to assess tissue rejection. Donor heart function was qualitatively measured by acquiring multiphasic gradient echo images at the same level. A myocardial/skeletal muscle signal intensity ratio was calculated for the donor heart and compared to results of right ventricular biopsy obtained within 24 hours of imaging. A change in signal intensity ratio of 0.14 or more exceeded normal signal variation. All three episodes of rejection detected by biopsy were detected by magnetic resonance imaging. In three instances a significant change in the signal intensity ratio was associated with clinical evidence of rejection and a negative biopsy. Two instances were treated with a steroid bolus, and the signal returned to baseline. In three other instances a significant change in the magnetic resonance imaging signal occurred without clinical or biopsy evidence of rejection. Cardiac toxoplasmosis was present in one of these cases, and signal intensity returned to baseline after treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of viable myocardium in segments with fixed defects on thallium-201 scintigraphy: usefulness of magnetic resonance imaging early after acute myocardial infarction.

To determine if magnetic resonance imaging (MRI) can be used to detect tissue viability in segments with persistent 201T1 defects early following acute myocardial infarction, 24 patients underwent MRI and adenosine 201T1 single photon emission computed tomography (SPECT) imaging at approximately 6 days. Infarction was demonstrated on MRI using a velocity-compensated, T2-weighted spin-echo pulse sequence. Wall thickening was assessed using a gradient-echo pulse sequence obtained in the same anatomic position. Viable myocardium was defined by MRI as a segment with increased signal intensity and preserved wall thickening. A fixed defect on the 201T1 SPECT images was defined as the absence of any redistribution 4 hours after the 201T1 infusion. Of 11 patients with redistribution on the 201T1 images in the infarction region, 10 (91%) had preserved wall thickening by MRI. Of 13 patients with fixed defects on the 201T1 images in the infarction region, 6 (46%) had preserved wall thickening by MRI. Of 7 patients with absent thickening, all had one or more segments with absent perfusion on redistribution imaging. Wall thickening tended to occur in patients who received thrombolytic therapy or who underwent revascularization procedures prior to imaging. The results of the present study suggest that spin-echo MRI with motion compensation can be used to identify viable myocardium in patients with fixed defects on 201T1 SPECT following acute myocardial infarction.

Nuclear magnetic resonance velocity spectra of pulsatile flow in a rigid tube.

Velocity spectra can be derived from velocity-encoded nuclear magnetic resonance (NMR) images. Velocity spectra are histograms showing the amounts of fluid flowing at different velocities in the sensitive volume of the measurement. Velocity spectra may prove to be useful in characterizing the flow of blood in small vessels, for example, in detecting the presence of stenoses and in evaluating their severity. NMR velocity spectra acquired in vivo are sufficiently complicated that a model system was designed and tested to investigate the velocity spectra of pulsatile flow. This study measured the NMR velocity spectra of pulsatile flow in a rigid tube and compared them to velocity spectra derived from Doppler ultrasound measurements and to velocity spectra inferred from a theoretical model driven by the measured pressure difference function. The experimental results from each technique agree.

Magnetic resonance velocity measurements in small arteries. Comparison with Doppler ultrasonic measurements in the aortas of normal rabbits.

RATIONALE AND OBJECTIVES: Magnetic resonance imaging (MRI) can be used to measure motion. This study compares MRI blood flow velocity measurements to Doppler ultrasound velocity measurements in an animal model. MATERIALS AND METHODS: Blood flow in the abdominal aortas of nine normal rabbits was measured using 16-frame, velocity-resolved MRI and Doppler ultrasound. The MRI data were processed into velocity spectra to aid in their interpretation. RESULTS: Maximum velocity measurements made by range-gated Doppler ultrasound were predicted by the maximum velocity values derived from MR velocity spectra with a slope of 0.861, an intercept of -2.78 cm/second, and an R-value of 0.935 in 70 measurements. CONCLUSIONS: Despite the longer time required for the MR measurement, the MR velocity measurement may be useful in the assessment of deep vessels or those obscured by other structures, which are difficult to measure with ultrasound.

Characterization of acute myocardial infarction by magnetic resonance imaging.

The T2-weighted spin-echo technique is currently the most frequently used magnetic resonance imaging (MRI) method to visualize acute myocardial infarction. However, image quality is often degraded by ghost artifacts from blood flow, and respiratory and cardiac contractile motion. To enhance the usefulness of this technique for detailed characterization of infarction, a velocity-compensated spin-echo pulse sequence was tested by imaging a flow phantom, 6 normal subjects and 17 patients with acute myocardial infarction. After preliminary studies were performed in 7 patients to determine optimal imaging parameters, a standardized imaging protocol was used in the next 10. The location of myocardial infarction identified by the electrocardiogram and coronary anatomy was correctly identified in 10 of 10 patients. Distribution of the injury within the left ventricle was clearly visualized, and showed that patients often had a mixture of transmural and nontransmural injury. Heterogenous distribution of signal intensity within the infarction suggested the presence of hemorrhage. Papillary muscle involvement was readily apparent. Signal intensity of the infarction (brightest segment) was increased by 89 +/- 31% compared with the mean of the remote segments. The myocardial/skeletal muscle ratio was significantly (p less than 0.001) increased for the infarction segments compared with that for remote myocardium, allowing quantitative analysis of segmental signal intensity. The MRI wall motion study obtained as part of this protocol demonstrated wall thickening in 58% of the infarction segments and in 6 of 10 patients. This finding suggested the presence of reversibly injured myocardium. In conclusion, the results demonstrate the potential of MRI for detailed tissue characterization after acute myocardial infarction.

An electrocardiograph-respiration gating device for MR studies.

A versatile gating device for magnetic resonance (MR) spectroscopy and imaging is presented. The device uses electrocardiograph (ECG) and respiration signals as input, applies appropriate signal conditioning, and generates control signals for ECG, respiration, or combined gating studies. In the combined ECG and respiration mode, in conjunction with a proper MR pulse program, one can acquire MR data gated by the ECG signal within a selected window of the respiration cycle, while maintaining a steady level of magnetization saturation during the remainder of the respiration cycle, by gating the radio-frequency excitation with the ECG while inhibiting data acquisition.