Photon-enhanced thermionic emission from heterostructures with low interface recombination.

Photon-enhanced thermionic emission is a method of solar-energy conversion that promises to combine photon and thermal processes into a single mechanism, overcoming fundamental limits on the efficiency of photovoltaic cells. Photon-enhanced thermionic emission relies on vacuum emission of photoexcited electrons that are in thermal equilibrium with a semiconductor lattice, avoiding challenging non-equilibrium requirements and exotic material properties. However, although previous work demonstrated the photon-enhanced thermionic emission effect, efficiency has until now remained very low. Here we describe electron-emission measurements on a GaAs/AlGaAs heterostructure that introduces an internal interface, decoupling the basic physics of photon-enhanced thermionic emission from the vacuum emission process. Quantum efficiencies are dramatically higher than in previous experiments because of low interface recombination and are projected to increase another order of magnitude with more stable, low work-function coatings. The results highlight the effectiveness of the photon-enhanced thermionic emission process and demonstrate that efficient photon-enhanced thermionic emission is achievable, a key step towards realistic photon-enhanced thermionic emission based energy conversion.

Differential serotonin transport is linked to the rh5-HTTLPR in peripheral blood cells.

The human serotonin transporter (SERT) gene possesses a 43-base pair (bp) insertion-deletion promoter polymorphism, the h5-HTTLPR. Genotype at this locus correlates with variation in anxiety-related personality traits and risk for major depressive disorder in many studies. Yet, the complex effects of the h5-HTTLPR, in combination with closely associated single-nucleotide polymorphisms (SNPs), continue to be debated. Moreover, although SERT is of high clinical significance, transporter function in vivo remains difficult to assess. Rhesus express a promoter polymorphism related to the h5-HTTLPR. The rh5-HTTLPR has been linked to differences in stress-related behavior and cognitive flexibility, although allelic variations in serotonin uptake have not been investigated. We studied the serotonin system as it relates to the 5-HTTLPR in rhesus peripheral blood cells. Sequencing of the rh5-HTTLPR revealed a 23-bp insertion, which is somewhat longer than originally reported. Consistent with previous reports, no SNPs in the rh5-HTTLPR and surrounding genomic regions were detected in the individuals studied. Reductions in serotonin uptake rates, cell surface SERT binding, and 5-hydroxyindoleacetic acid/serotonin ratios, but not SERT mRNA levels, were associated with the rh5-HTTLPR short allele. Thus, serotonin uptake rates are differentiable with respect to the 5-HTTLPR in an easily accessible native peripheral tissue. In light of these findings, we foresee that primary blood cells, in combination with high sensitivity functional measurements enabled by chronoamperometry, will be important for investigating alterations in serotonin uptake associated with genetic variability and antidepressant responsiveness in humans.

Novel fluorescence-based approaches for the study of biogenic amine transporter localization, activity, and regulation.

Pre-synaptic norepinephrine (NE) and dopamine (DA) transporters (NET and DAT) terminate catecholamine synaptic transmission through reuptake of released neurotransmitter. Recent studies reveal that NET and DAT are tightly regulated by receptor and second messenger-linked signaling pathways. Common approaches for studying these transporters involve use of radiolabeled substrates or antagonists, methods possessing limited spatial resolution and that bear limited opportunities for repeated monitoring of living preparations. To circumvent these issues, we have explored two novel assay platforms that permit temporally resolved quantitation of transport activity and transporter protein localization. To monitor the binding and transport function of NET and DAT in real-time, we have investigated the uptake of the fluorescent organic compound 4-(4-diethylaminostyryl)-N-methylpyridinium iodide (ASP+). We have extended our previous single cell level application of this substrate to monitor transport activity via high-throughput assay platforms. Compared to radiotracer uptake methods, acquisition of ASP+ fluorescence is non-isotopic and allows for continuous, repeated transport measurements on both transfected and native preparations. Secondly, we have extended our application of small-molecule-conjugated fluorescent CdSe/ZnS nanocrystals, or quantum dots (Qdots), to utilize antibody and peptide ligands that can identify surface expressed transporters, receptors and other membrane proteins in living cell systems. Unlike typical organic fluorophores, Qdots are highly resistant to bleaching and can be conjugated to multiple ligands. They can also be illuminated by conventional light sources, yet produce narrow, gaussian emission spectra compatible with multiple target visualization (multiplexing). Together, these approaches offer novel opportunities to investigate changes in transporter function and distribution in real-time with superior spatial and temporal resolution.

Ultrasonography for the evaluation of forearm interosseous membrane disruption in a cadaver model.

Recognition of interosseous membrane disruption associated with radial head injury and Essex-Lopresti injury is important, especially if radial head excision is contemplated. Because a widely accepted method to diagnose interosseous membrane disruption does not exist, we evaluated the accuracy of ultrasonography to diagnose this injury in a cadaver model. Nine pairs of cadaver forearms were randomized into 2 groups. The central third of the interosseous membrane of forearms of group 1 was cut, whereas it was visualized but not cut in group 2. A dynamic ultrasound examination was performed to determine interosseous membrane integrity, and static images were made. The static images were evaluated by 2 other radiologists and interpretations were recorded. One radiologist incorrectly interpreted 1 pair of forearms; the other 2 radiologists were 100% accurate. The accuracy of ultrasonography in detecting interosseous injuries was 96% with our methods.

Phase inversion tissue harmonic sonographic imaging: a clinical utility study.

OBJECTIVE: We evaluated the utility of phase inversion tissue harmonic sonographic imaging in a variety of clinical applications. SUBJECTS AND METHODS: Two hundred randomly selected patients were scanned with both fundamental and tissue harmonic methods on a sonography system. The following transducers were used: 2.5 MHz, 20 mm phased array; 3 MHz, 40 mm curved array; 6.5 MHz, 13 mm curved array transvaginal; and 7.5 MHz, 40 mm linear. Operators evaluated visualization of normal and pathologic tissues by tissue harmonic versus fundamental imaging using scores ranging from 1 for much worse visualization to 5 for much better visualization. They also assessed the overall utility of tissue harmonic imaging in the diagnosis of the patient's condition. The studies were saved on magnetooptical disc and were independently reviewed by one of the authors. RESULTS: Tissue harmonic imaging was helpful for all types of examination. Tissue harmonic imaging improved visualization of normal tissue in 49% of the cases and pathologic tissue in 73% of the cases. Tissue harmonic imaging was found to be diagnostically helpful in 43% of the cases and essential to the diagnosis in 6% of the cases. CONCLUSION: Tissue harmonic imaging significantly improves visualization of both normal and pathologic tissues and its selective use has major diagnostic utility in a wide variety of clinical applications.

The measurement of proton stopping power using proton-cone-beam computed tomography.

A cone-beam computed tomography (CT) system utilizing a proton beam has been developed and tested. The cone beam is produced by scattering a 160 MeV proton beam with a modifier that results in a signal in the detector system, which decreases monotonically with depth in the medium. The detector system consists of a Gd2O2S:Tb intensifying screen viewed by a cooled CCD camera. The Feldkamp-Davis-Kress cone-beam reconstruction algorithm is applied to the projection data to obtain the CT voxel data representing proton stopping power. The system described is capable of reconstructing data over a 16 x 16 x 16 cm3 volume into 512 x 512 x 512 voxels. A spatial and contrast resolution phantom was scanned to determine the performance of the system. Spatial resolution is significantly degraded by multiple Coulomb scattering effects. Comparison of the reconstructed proton CT values with x-ray CT derived proton stopping powers shows that there may be some advantage to obtaining stopping powers directly with proton CT. The system described suggests a possible practical method of obtaining this measurement in vivo.

Vena caval occlusion after bird's nest filter placement.

BACKGROUND: Inferior vena caval thrombosis as a result of intracaval barrier devices occurs in 6.5% of patients with Greenfield filters. The incidence is less well defined in patients in whom bird's nest filters have been placed. We reviewed our experience with bird's nest filters to determine the incidence of filter-induced caval thrombosis. METHODS: The records of 140 patients with bird's nest filters were reviewed, living patients were interviewed, and the inferior vena cava examined in 37 patients by duplex scanning. RESULTS: Ninety-three patients were available for evaluation. Five of these patients were found to have caval thrombosis by duplex scanning and 2 had clinical symptoms and signs compatible with caval thrombosis. The majority of these patients were on anticoagulants at the time of filter thrombosis. CONCLUSION: The incidence of filter-induced vena caval thrombosis in patients with bird's nest filters (7%) is comparable with that of Greenfield filters. Because of the catastrophic manifestations of this complication and the increasing application of vena caval filters, the role of these filters in the treatment of thrombotic disease needs further critical evaluation.

Comparison of proton and x-ray conformal dose distributions for radiosurgery applications.

Highly focused dose distributions for radiosurgery applications are successfully achieved using either multiple static high-energy particle beams or multiple-arc circular x-ray beams from a linac. It has been suggested that conformal x-ray techniques using dynamically shaped beams with a moving radiation source would offer advantages compared to the use of only circular beams. It is also thought that, generally, charged particle beams such as protons offer dose deposition advantages compared to x-ray beams. A comparison of dose distributions was made between a small number of discrete proton beams, multiple-arc circular x-ray beams, and conformal x-ray techniques. Treatment planning of a selection of radiosurgery cases was done for these three techniques. Target volumes ranged from 1.0-25.0 cm3. Dose distributions and dose volume histograms of the target and surrounding normal brain were calculated. The advantages and limitations of each technique were primarily dependent upon the shape and size of the target volume. In general, proton dose distributions were superior to x-ray distributions; both shaped proton and shaped x-ray beams delivered dose distributions which were more conformal than x-ray techniques using circular beams; and the differences between all proton and x-ray distributions were negligible for the smallest target volumes, and greatest for the larger target volumes.

A precision cranial immobilization system for conformal stereotactic fractionated radiation therapy.

PURPOSE: Conformal radiotherapy has been shown to benefit from precision alignment of patient target to therapy beam (1, 6, 13). This work describes an optimized immobilization system for the fractionated treatment of intracranial targets. A study of patient motion demonstrates the high degree of immobilization which is available. METHODS AND MATERIALS: A system using dental fixation and a thermoplastic mask that relocates on a rigid frame is described. The design permits scanning studies using computed tomography (CT) and magnetic resonance imaging (MR), conventional photon radiotherapy, and high precision stereotactic proton radiotherapy to be performed with minimal repositioning variation. Studies of both intratreatment motion and daily setup reliability are performed on patients under treatment for paranasal sinus carcinoma. Multiple radiographs taken during single treatments provide the basis for a three-dimensional (3D) motion analysis. Additionally, studies of orthogonal radiographs used to setup for proton treatments and verification port films from photon treatments are used to establish day to day patient position variation in routine use. RESULTS: Net 3D patient motion during any treatment is measured to be 0.9 +/- 0.4 mm [mean +/- standard deviation (SD)] and rotation about any body axis is 0.14 +/- 0.67 degrees (mean +/- SD). Day-to-day setup accuracy to laser marks is limited to 2.3 mm (mean) systematic error and 1.6 mm (mean) random error. CONCLUSION: We conclude that the most stringent immobilization requirements of 3D conformal radiotherapy adjacent to critical normal structures can be met with a high precision system such as the one described here. Without the use of pretreatment verification, additional developments in machine and couch design are needed to assure that patient repositioning accuracy is comparable to the best level of patient immobility achievable.

Doppler US of helical flow in the portal vein.

In helical portal venous blood flow, the usual laminar flow in the portal vein is replaced by a spiral. This changes the color Doppler ultrasound (US) appearance to one of alternating or parallel red and blue bands. Duplex US may appear to show hepatopetal, hepatofugal, or simultaneous bidirectional flow depending on placement of the cursor within the helix. Helical portal venous flow is unusual in normal individuals (2.2% of 135 patients). Its presence should prompt further scrutiny for signs of liver disease, particularly portosystemic shunts, as in 20% of 41 patients who subsequently underwent liver transplantation. It is a normal finding immediately after liver transplantation (43% of 35 patients) and transjugular intrahepatic portosystemic shunt (TIPS) creation (28% of 36 patients). In both liver transplant and TIPS recipients, helical flow is usually transient. Its persistence long after transplantation in association with a prolonged increase in portal venous velocity is a useful sign of portal vein stenosis. Helical flow may also occur in cases of neoplastic invasion or displacement of the portal vein.

Femtosecond spontaneous-emission studies of reaction centers from photosynthetic bacteria.

Spontaneous emission from reaction centers of photosynthetic bacteria has been recorded with a time resolution of 50 fs. Excitation was made directly into both the special-pair band (850 nm) and the Qx band of bacteriochlorophylls (608 nm). Rhodobacter sphaeroides R26, Rhodobacter capsulatus wild type, and four mutants of Rb. capsulatus were studied. In all cases the fluorescence decay was not single exponential and was well fit as a sum of two exponential decay components. The short components are in excellent agreement with the single component detected by measurements of stimulated emission. The origin of the nonexponential decay is discussed in terms of heterogeneity, the kinetic scheme, and the possibility of slow vibrational relaxation.

Computers in ultrasonic imaging.

This article describes the role of computers and digital electronics in state-of-the-art diagnostic ultrasound scanners. An overview of the computational requirements is provided, and limits on color flow image frame rates are discussed. The new scanner architectures emerging may be used to extend current limitations of ultrasonography, making features such as automatic phase aberration correction, speckle reduction, and tissue characterization available.

Wide area networks for teleradiology.

Teleradiology networks transmit digital radiographic images from one location to another. These networks are wide area networks. Teleradiology networks are used for diagnostic purposes and preview tasks. Wide area networks for teleradiology use public service switching. The use of fiber optics networks provide reduced costs and increased flexibility. An example is presented that compares the cost of teleradiology networks.

Prenatal and postnatal consequences in the brain and behavior of rats exposed to ultrasound in utero.

As a result of a prior experiment demonstrating damage to the developing cortex of the fetal rat 24 hours after maternal exposure to ultrasound, postnatal consequences of similar exposure on rat behavior were examined. No decrease in postnatal weight or growth rate was found and no significant decrease in cortical thickness was present postnatally at 28 days. In two of four behavioral tests, rats exposed to ultrasound in utero resembled similarly treated controls. In one test, ultrasound-exposed rats showed slower performance, and in one, faster performance. These data provide no consistent evidence that ultrasound exposure resulted in deleterious postnatal effects.

Teleradiology: an assessment.

A teleradiology system acquires radiographic images at one location and transmits them to one or more remote sites, where they are displayed and/or converted to hard copy. These systems often employ wide area networks. Their goal is to provide improved radiologic services at all sites on the network. Experience in the use of teleradiology systems has demonstrated the need for a laser film digitizer, an optical disk, and a high-quality display and/or laser film printer at each site. Single-site hardware purchase costs average $196,000, plus an additional 20% for yearly network services. Hardware purchased for a consultation or central referral facility approximates $344,000.

Chest radiography: comparison of high-resolution digital displays with conventional and digital film.

This study was performed to compare the performances of observers using three display formats for chest radiography. The display formats were conventional radiographs, digitized radiographs (2,048 X 2,048 X 12 bits) printed on laser film, and digitized radiographs (2,048 X 2,048 X 12 bits) displayed on a high-resolution (2,560 X 2,048 X 12-bit) gray-scale display. The test set for the study consisted of 163 cases. Sixty-four of the cases were normal, whereas the 99 remaining cases demonstrated one or more common radiographic abnormalities. Nine abnormalities were selected for analysis: costophrenic angle blunting, interstitial disease, atelectasis, pneumothorax, parenchymal mass, consolidation, obstructive disease, hilar/mediastinal mass, and apical scarring. Six experienced general radiologists participated in the evaluation. Receiver operating characteristic curves were generated for each abnormality and display format. The results indicate that, while the three display formats are equivalent for the detection of some abnormalities, detectable differences in observer performance may be seen even at 2,048 X 2,048 X 12 bits for the detection of obstructive disease, pneumothorax, interstitial disease, and parenchymal masses.