Correction: Selective area growth of GaN nanowires and nanofins by molecular beam epitaxy on heteroepitaxial diamond (001) substrates

[This corrects the article DOI: 10.1039/D1NA00221J.].

Environmental sensitivity of GaN nanofins grown by selective area molecular beam epitaxy

Nanostructures exhibit a large surface-to-volume ratio, which makes them sensitive to their ambient conditions. In particular, GaN nanowires and nanofins react to their environment as adsorbates influence their (opto-) electronic properties. Charge transfer between the semiconductor surface and adsorbed species changes the surface band bending of the nanostructures, and the adsorbates can alter the rate of non-radiative recombination in GaN. Despite the importance of these interactions with the ambient environment, the detailed adsorption mechanisms are still not fully understood. In this article, we present a systematic study concerning the environmental sensitivity of the electrical conductivity of GaN nanofins. We identify oxygen- and water-based adsorbates to be responsible for a quenching of the electrical current through GaN nanofins due to an increased surface band bending. Complementary contact potential difference measurements in controlled atmospheres on bulkm- andc-plane GaN reveal additional complexity with regard to water adsorption, for which surface dipoles might play an important role besides an increased surface depletion width. The sensitive reaction of the electrical parameters to the environment and surface condition underlines the necessity of a reproducible pre-treatment and/or surface passivation. The presented results help to further understand the complex adsorption mechanisms at GaN surfaces. Due to the sensitivity of the nanofin conductivity on the environment, such structures could perform well as sensing devices.

Influence of environmental conditions and surface treatments on the photoluminescence properties of GaN nanowires and nanofins

Due to their intrinsically large surface-to-volume ratio, nanowires and nanofins interact strongly with their environment. We investigate the role of the main air constituents nitrogen, oxygen and water on the efficiency of radiative recombination in GaN nanostructures as a function of different surface treatments and at temperatures up to 200 °C. Oxygen and water exposures exhibit a complex behavior as they can both act quenching and enhancing on the photoluminescence intensity dependent on the temperature. For oxygen, these characteristics are already observed for low concentrations of below 0.5% in nitrogen. While the photoluminescence intensity changes induced by oxygen occur independently of illumination, the influence of water is light-induced: it evolves within tens of seconds under ultraviolet light exposure and is heavily influenced by the nanostructure pre-treatment. In contrast to observations in dry atmospheres, water prevents a recovery of the photoluminescence intensity in the dark. Combined measurements of the electrical current through GaN nanofins and their photoluminescence intensity reveal the environmental influence on the interaction of non-radiative recombination processes and changes in the surface band bending of the nanostructures. Several investigated solvents show an enhancing effect on the PL intensity increase, peaking in c-hexane with a 26-fold increase after 6 min of light exposure. Stabilization of the PL intensity was achieved by a passivation of the GaN surface with Ga_xO_y, and ZnO shells. Surprisingly, Al₂O₃coatings resulted in a highly instable PL intensity during the first minutes of illumination. Our findings reveal the high importance of controlled environmental conditions for the investigation of nanostructures, especially when aimed at their applications in the fields of environmental sensing, photo-catalysis and light-emitting diodes.

Selective area growth of GaN nanowires and nanofins by molecular beam epitaxy on heteroepitaxial diamond (001) substrates

GaN-on-diamond is a promising route towards reliable high-power transistor devices with outstanding performances due to better heat management, replacing common GaN-on-SiC technologies. Nevertheless, the implementation of GaN-on-diamond remains challenging. In this work, the selective area growth of GaN nanostructures on cost-efficient, large-scale available heteroepitaxial diamond (001) substrates by means of plasma-assisted molecular beam epitaxy is investigated. Additionally, we discuss the influence of an AlN buffer on the morphology of the GaN nanostructures. The nanowires and nanofins are characterized by a very high selectivity and controllable dimensions. Low temperature photoluminescence measurements are used to evaluate their structural quality. The growth of two GaN crystal domains, which are in-plane rotated against each other by 30°, is observed. The favoring of a certain domain is determined by the off-cut direction of the diamond substrates. By X-ray diffraction we show that the GaN nanostructures grow perpendicular to the diamond surface on off-cut diamond (001) substrates, which is in contrast to the growth on diamond (111), where the nanostructures are aligned with the substrate lattice. Polarity-selective wet chemical etching and Kelvin probe force microscopy reveal that the GaN nanostructures grow solely in the Ga-polar direction. This is a major advantage compared to the growth on diamond (111) and enables the application of GaN nanostructures on cost-efficient diamond for high-power/high-frequency applications.

Metastable Ta2N3 with highly tunable electrical conductivity via oxygen incorporation

The binary Ta-N chemical system includes several compounds with notable prospects in microelectronics, solar energy harvesting, and catalysis. Among these, metallic TaN and semiconducting Ta3N5 have garnered significant interest, in part due to their synthetic accessibility. However, tantalum sesquinitride (Ta2N3) possesses an intermediate composition and largely unknown physical properties owing to its metastable nature. Herein, Ta2N3 is directly deposited by reactive magnetron sputtering and its optoelectronic properties are characterized. Combining these results with density functional theory provides insights into the critical role of oxygen in both synthesis and electronic structure. While the inclusion of oxygen in the process gas is critical to Ta2N3 formation, the resulting oxygen incorporation in structural vacancies drastically modifies the free electron concentration in the as-grown material, thus leading to a semiconducting character with a 1.9 eV bandgap. Reducing the oxygen impurity concentration via post-synthetic ammonia annealing increases the conductivity by seven orders of magnitude and yields the metallic characteristics of a degenerate semiconductor, consistent with theoretical predictions. Thus, this inverse oxygen doping approach - by which the carrier concentration is reduced by the oxygen impurity - offers a unique opportunity to tailor the optoelectronic properties of Ta2N3 for applications ranging from photochemical energy conversion to advanced photonics.

Disrupted Neural Synchrony Mediates the Relationship between White Matter Integrity and Cognitive Performance in Older Adults

Our main goal was to determine the influence of white matter integrity on the dynamic coupling between brain regions and the individual variability of cognitive performance in older adults. Electroencephalography was recorded while participants performed a task specifically designed to engage working memory and inhibitory processes, and the associations among functional activity, structural integrity, and cognitive performance were assessed. We found that the association between white matter microstructural integrity and cognitive functioning with aging is mediated by time-varying alpha and gamma phase-locking value. Specifically, better preservation of the inferior fronto-occipital fasciculus in older individuals drives faster task-related modulations of alpha and gamma long-range phase-locking value between the inferior frontal gyrus and occipital lobe and lower local phase-amplitude coupling in occipital lobes, which in turn drives better cognitive control performance. Our results help delineate the role of individual variability of white matter microstructure in dynamic synchrony and cognitive performance during normal aging.

Photo-induced selective etching of GaN nanowires in water

Nanowire (NW) based devices for solar driven artificial photosynthesis have gained increasing interest in recent years due to the intrinsically high surface to volume ratio and the excellent achievable crystal qualities. However, catalytically active surfaces often suffer from insufficient stability under operational conditions. To gain a fundamental understanding of the underlying processes, the photochemical etching behavior of hexagonal and round GaN NWs in deionized water under illumination are investigated. We find that the crystallographic c-plane remains stable, whereas the m-planes are photochemically etched with rates up to 11 nm min-1, depending on the applied UV light intensity. By investigating nanowalls, we achieve control of the exposed crystallographic facets and find an enhanced stability of the a-plane compared to the m-plane. Photo-excited holes, which drift to the side facets due to the upward surface band bending in nominally n-type (not intentionally doped) GaN, are identified as the driving force of the process, which allows the development of concepts for the stabilization of the nanostructures. A geometrically enhanced absorption of periodic NW arrays is correlated with a dependence of the etch rate on the NW pitch and diameter. Further, we find selective photochemical etching of the NW base in the presence of sub-band gap illumination, which is attributed to defect-related absorption in this region. These results provide improved understanding of the roles of inhomogeneous defect distribution, light excitation profiles, and different surface facets on the photochemical stability of nanostructures and provide viable strategies for improving stabilities under light-driven reaction conditions.

Selectively grown GaN nanowalls and nanogrids for photocatalysis: growth and optical properties

In this work, the selective area growth of GaN nanowalls and nanogrids on sapphire and GaN on sapphire by molecular beam epitaxy is investigated. We demonstrate the fabrication of homogeneous GaN nanowall arrays with different widths, distances and specific crystallographic side facets. Photoluminescence spectroscopy of as-grown GaN nanowalls reveals a high crystal quality and low defect density. Moreover, a distinct dependence of the nanowall width and the intensity of the donor-bound exciton emission on the crystal orientation of the sidewall facets is found and explained by different surface states for a-plane and m-plane GaN. The waveguide character of the GaN nanowalls, given by the large refractive index of GaN and the subwavelength size of the structures, is analysed by experimental transmission measurements and numerical simulations. Our results and the high epitaxial control achieved by selective area growth show the potential of tailor-made nanowall-based devices, e.g., in photocatalysis or nanofluidics.

GaN Nanowire Arrays for Efficient Optical Read-Out and Optoelectronic Control of NV Centers in Diamond

Solid-state quantum emitters embedded in a semiconductor crystal environment are potentially scalable platforms for quantum optical networks operated at room temperature. Prominent representatives are nitrogen-vacancy (NV) centers in diamond showing coherent entanglement and interference with each other. However, these emitters suffer from inefficient optical outcoupling from the diamond and from fluctuations of their charge state. Here, we demonstrate the implementation of regular n-type gallium nitride nanowire arrays on diamond as photonic waveguides to tailor the emission direction of surface-near NV centers and to electrically control their charge state in a p-i-n nanodiode. We show that the electrical excitation of single NV centers in such a diode can efficiently replace optical pumping. By the engineering of the array parameters, we find an optical read-out efficiency enhanced by a factor of 10 and predict a lateral NV-NV coupling 3 orders of magnitude stronger through evanescently coupled nanowire antennas compared to planar diamond not covered by nanowires, which opens up new possibilities for large-scale on-chip quantum-computing applications.

Experience in Using Fetal Membranes: The Present and New Perspectives

INTRODUCTION

The placenta is an accessible source of tissues for transplantation. Placental transplants have been used in wound treatment because of the basic function of the placenta and its nutritious properties and structure.

PATIENTS AND METHODS

The aim of this work is to present the clinical usage of fetal membranes, including human amnion, on the basis of the burn treatment center's experience. The clinical use of amnion and different types of placental transplants are described. The initial results of research work within the MEDPIG project are presented regarding the application of placenta from transgenic pigs as a source of tissues for transplantation.

RESULTS

From August 2011 to March 2017, 252,592 cm² of biostatic human amnion transplants were prepared in our tissue bank. During this period they were transplanted to 528 patients, including 10 patients with Lyell syndrome. Initial studies were conducted in which placentas were collected from 5 transgenic pigs and 27,426 cm² of amniotic grafts were prepared from them.

DISCUSSION

The authors' own experience as well as the literature confirm the extraordinary efficiency of transplants prepared from placental tissues, especially from the amniotic membrane.

CONCLUSIONS

The clinical effects confirm the effectiveness of using human amnion in wound treatment. Amniotic transplant is a new treatment standard in toxic epidermal necrolysis TEN (Lyell's syndrome), which has found confirmation in very good clinical outcomes. The collected placentas from transgenic animals enabled the preparation of significantly more grafts than in the case of human material, which is a great advantage of this source of placenta over human tissues.

Polarity Control of Heteroepitaxial GaN Nanowires on Diamond

Group III-nitride materials such as GaN nanowires are characterized by a spontaneous polarization within the crystal. The sign of the resulting sheet charge at the top and bottom facet of a GaN nanowire is determined by the orientation of the wurtzite bilayer of the different atomic species, called N and Ga polarity. We investigate the polarity distribution of heteroepitaxial GaN nanowires on different substrates and demonstrate polarity control of GaN nanowires on diamond. Kelvin Probe Force Microscopy is used to determine the polarity of individual selective area-grown and self-assembled nanowires over a large scale. At standard growth conditions, mixed polarity occurs for selective GaN nanowires on various substrates, namely on silicon, on sapphire and on diamond. To obtain control over the growth orientation on diamond, the substrate surface is modified by nitrogen and oxygen plasma exposure prior to growth, and the growth parameters are adjusted simultaneously. We find that the surface chemistry and the substrate temperature are the decisive factors for obtaining control of up to 93% for both polarity types, whereas the growth mode, namely selective area or self-assembled growth, does not influence the polarity distribution significantly. The experimental results are discussed by a model based on the interfacial bonds between the GaN nanowires, the termination layer, and the substrate.

Surface passivation and self-regulated shell growth in selective area-grown GaN-(Al,Ga)N core-shell nanowires

The large surface-to-volume ratio of GaN nanowires implicates sensitivity of the optical and electrical properties of the nanowires to their surroundings. The implementation of an (Al,Ga)N shell with a larger band gap around the GaN nanowire core is a promising geometry to seal the GaN surface. We investigate the luminescence and structural properties of selective area-grown GaN-(Al,Ga)N core-shell nanowires grown on Si and diamond substrates. While the (Al,Ga)N shell allows a suppression of yellow defect luminescence from the GaN core, an overall intensity loss due to Si-related defects at the GaN/(Al,Ga)N interface has been observed in the case of Si substrates. Scanning transmission electron microscopy measurements indicate a superior crystal quality of the (Al,Ga)N shell along the nanowire side facets compared to the (Al,Ga)N cap at the top facet. A nucleation study of the (Al,Ga)N shell reveals a pronounced bowing of the nanowires along the c-direction after a short deposition time which disappears for longer growth times. This is assigned to an initially inhomogeneous shell nucleation. A detailed study of the proceeding shell growth allows the formulation of a strain-driven self-regulating (Al,Ga)N shell nucleation model.

Strain-Induced Band Gap Engineering in Selectively Grown GaN-(Al,Ga)N Core-Shell Nanowire Heterostructures

We demonstrate the selective area growth of GaN-(Al,Ga)N core-shell nanowire heterostructures directly on Si(111). Photoluminescence spectroscopy on as-grown nanowires reveals a strong blueshift of the GaN band gap from 3.40 to 3.64 eV at room temperature. Raman measurements relate this shift to compressive strain within the GaN core. On the nanoscale, cathodoluminescence spectroscopy and scanning transmission electron microscopy prove the homogeneity of strain-related luminescence along the nanowire axis and the absence of significant fluctuations within the shell, respectively. A comparison of the experimental findings with numerical simulations indicates the absence of a significant defect-related strain relaxation for all investigated structures, with a maximum compressive strain of -3.4% for a shell thickness of 50 nm. The accurate control of the nanowire dimensions, namely, core diameter, shell thickness, and nanowire period, via selective area growth allows a specific manipulation of the resulting strain within individual nanowires on the same sample. This, in turn, enables a spatially resolved adjustment of the GaN band gap with an energy range of 240 meV in a one-step growth process.

Infections in the tissue material and their impact on the loss of transplants in the Laboratory of in vitro Cell and Tissue Culture with Tissue Bank in the years 2011-2015

Radiation sterilization eliminates microbiological infections but causes the degradation of the cell factor. The negative result of microbiological examination for tissue transplants is one of the conditions for approval for distribution in patients. The study attempts to verify impact of the presence of microbes onto material for transplant loss. In the 2011-2015 period, we analyzed 293 donors of skin and amnion. Microbiological sampling was performed. The total of 21 strains of bacteria, molds and fungi was identified in collected tissue. The widest spectrum of strains was found in skin (17), followed by amnia (8). The total number of positive findings was 147 and was again highest in skin (129), while the number of positive findings in amnia was 18 only. The general percentage of fungal infections was very low. The presence of fungal strains was only observed in allogeneic skin (2%). Large number of microorganisms isolated from the skin before sterilization was observed, so it seems impossible to use allogeneic intravital skin. However, the intravital application of allogeneic amnion obtained from cesarean section remains to be considered.

Lithographically fabricated silicon microreactor for in situ characterization of heterogeneous catalysts—Enabling correlative characterization techniques

We report on a new modular setup on a silicon-based microreactor designed for correlative spectroscopic, scattering, and analytic on-line gas investigations for in situ studies of heterogeneous catalysts. The silicon microreactor allows a combination of synchrotron radiation based techniques (e.g., X-ray diffraction and X-ray absorption spectroscopy) as well as infrared thermography and Raman spectroscopy. Catalytic performance can be determined simultaneously by on-line product analysis using mass spectrometry. We present the design of the reactor, the experimental setup, and as a first example for an in situ study, the catalytic partial oxidation of methane showing the applicability of this reactor for in situ studies.

Longitudinal pattern of regional brain volume change differentiates normal aging from MCI

BACKGROUND

Neuroimaging measures have potential as surrogate markers of disease through identification of consistent features that occur prior to clinical symptoms. Despite numerous investigations, especially in relation to the transition to clinical impairment, the regional pattern of brain changes in clinically normal older adults has not been established. We predict that the regions that show early pathologic changes in association with Alzheimer disease will show accelerated volume loss in mild cognitive impairment (MCI) compared to normal aging.

METHODS

Through the Baltimore Longitudinal Study of Aging, we prospectively evaluated 138 nondemented individuals (age 64-86 years) annually for up to 10 consecutive years. Eighteen participants were diagnosed with MCI over the course of the study. Mixed-effects regression was used to compare regional brain volume trajectories of clinically normal individuals to those with MCI based on a total of 1,017 observations.

RESULTS

All investigated volumes declined with normal aging (p < 0.05). Accelerated change with age was observed for ventricular CSF (vCSF), frontal gray matter, superior, middle, and medial frontal, and superior parietal regions (p < or = 0.04). The MCI group showed accelerated changes compared to normal controls in whole brain volume, vCSF, temporal gray matter, and orbitofrontal and temporal association cortices, including the hippocampus (p < or = 0.04).

CONCLUSION

Although age-related regional volume loss is apparent and widespread in nondemented individuals, mild cognitive impairment is associated with a unique pattern of structural vulnerability reflected in differential volume loss in specific regions. Early identification of patterns of abnormality is of fundamental importance for detecting disease onset and tracking progression.

Serum uric acid and brain ischemia in normal elderly adults

BACKGROUND

Uric acid (UA) has antioxidant properties yet when elevated is associated with vascular disease and stroke. Further, even high normal UA is associated with increased risk of mild cognitive dysfunction in elderly adults.

METHOD

In this cross-sectional, observational study, we examined the relationship between serum UA and aggregate volume of white matter hyperintense (WMH) signals observed on proton density and T2-weighted brain MR images in a community sample of 177 adults ages 20 to 92. Using logistic regression, we tested whether participants with UA concentrations in the highest quartile of the sample--but still normal--would have increased WMH volumes.

RESULTS

Compared with those with low to moderate levels, participants with high normal serum UA were more likely to fall in the highest quartile of WMH volume. The odds ratios (95% CIs) of increased WMH were 2.6 (1.2 to 5.4) for total, 2.5 (1.2 to 5.1) for periventricular, and 2.8 (1.4 to 5.9) for subcortical WMH volume. After controlling for age, sex, race, education, body mass, hypertension, and diabetes, the multivariate-adjusted odds of large total and subcortical WMH volumes remained elevated. Finally, high normal UA increased the odds of having excessive ischemic burden four- to fivefold in adults ages 60 and older.

CONCLUSIONS

These findings demonstrate that mildly elevated serum uric acid is associated with increased burden of cerebral ischemic pathology, particularly in older adults. We outline the potential pathogenesis of this association. A clinical trial of antihyperuricemic medication to treat or prevent chronic brain ischemia might be warranted.

Advanced bronchioloalveolar carcinoma: a phase II trial of paclitaxel by 96-hour infusion (SWOG 9714): a Southwest Oncology Group study

BACKGROUND

There are no published prospective trials of chemotherapy for advanced bronchioloalveolar carcinoma (BAC), a subtype of non-small-cell lung cancer for which there is no current standard therapy. This phase II study assesses the efficacy and toxicity of 96-h paclitaxel in chemotherapy-naive patients with advanced BAC.

PATIENTS AND METHODS

Patients with histologically confirmed stage IIIB (with pleural effusion) or stage IV BAC were eligible. Treatment consisted of paclitaxel 35 mg/m2/24 h continuously infused over 96 h (days 1-4) every 21 days for up to six courses.

RESULTS

A total of 58 eligible patients were enrolled. The objective response rate was 14% (all partial responses, 9% confirmed); 40% of patients demonstrated stable disease. The median progression-free and overall survivals were 5 and 12 months, respectively. Grade 3 or greater toxicities included neutropenia/granulocytopenia (43%), febrile neutropenia (12%), infection (22%), and stomatitis/pharyngitis (10%); there were five treatment-related deaths.

CONCLUSIONS

S9714 represents the first prospective multi-institutional cooperative group trial focusing on treatment outcomes in BAC. Studies targeting this population are feasible, and while first-line paclitaxel administered as a prolonged infusion is active in this setting, toxicities limits the utility of this regimen. S9714 serves as a historical control for BAC patients against which future therapeutic approaches can be compared.

Inverse T(2) contrast at 1.5 Tesla between gray matter and white matter in the occipital lobe of normal adult human brain

T(2) of cortical gray matter is generally assumed to be longer than that of white matter. It is shown here that this is not the case in the occipital lobe, but that this effect is often obscured at lower resolution and concealed in standard T(2)-weighted images. Using a high-resolution (1 x 1.3 x 2 mm(3)) segmented EPI Carr-Purcell-Meiboom-Gill sequence, T(2) relaxation times of the brain were measured at 1.5 T for eight healthy adult volunteers. The average T(2) values of cortical gray and white matter were found to be 88 +/- 2 and 84 +/- 3 msec in the frontal lobe, 84 +/- 2 and 83 +/- 3 msec in the parietal lobe, and 79 +/- 1 and 87 +/- 3 msec in the occipital lobe, respectively. This unexpected occipital T(2) contrast between gray and white matter is attributed to regional differences in iron concentration.

A weighted least-squares algorithm for estimation and visualization of relative latencies in event-related functional MRI

The properties of the hemodynamic latencies in functional maps have been relatively unexplored. Accurate methods of estimating hemodynamic latencies are needed to take advantage of this feature of fMRI. A fully automated, weighted least-squares (WLS) method for estimating temporal latencies is reported. Using a weighted linear model, the optimal latency and amplitude of the fMRI response can be determined for those voxels that pass a detection threshold. There is evidence from previous studies that the hemodynamic response may be time-locked to the stimulus within certain limits, less variable earlier in its evolution, and able to resolve information about relative hemodynamic timing. This information can be used to test hypotheses about the sequence and spatial distribution of neural activity. The method can be used to weight the earliest evolution of the hemodynamic response more heavily and decrease bias resulting from the hemodynamic response function. Additionally, the WLS method can control for varying response shapes across the brain and improve latency comparisons between brain regions. The WLS method was developed to study the properties of hemodynamic latencies, which may be increasingly important as event-related fMRI continues to be advanced.

White matter hyperintensity volume in late-onset and early-onset schizophrenia

BACKGROUND

Late life onset schizophrenia (sometimes termed "late paraphrenia") has been theorized to be due to neuro-degenerative processes affecting individuals with latent vulnerability to schizophrenia. However, neuro-imaging studies using computed tomography (CT) and magnetic resonance imaging (MRI) investigating possible degenerative anatomic correlates (atrophy, white matter disease, and strokes) to late onset psychoses have yielded conflicting findings. The variation in these findings may be due to differences in study design, case ascertainment, and measurement methods.

OBJECTIVE

The present study compares a continuous measure of total volume of white matter hyperintensities (WMHs) in age, race, and gender-ratio matched groups of late-onset schizophrenic, elderly, early-onset schizophrenic and control subjects.

METHOD

Our method of WMH measurement yielded an explicit volume and is an alternative to frequently used ordinal measures.

RESULTS

We found no significant differences in the WMH volumes between these three groups. This finding is consistent with a prior study (Symonds et al., 1997. J Neuropsychiat Clin Neurosci 9: 251 - 258), that used ordinal measures.

Current opinions for the treatment of syringomyelia and chiari malformations: survey of the Pediatric Section of the American Association of Neurological Surgeons

INTRODUCTION

A variety of surgical interventions have been recommended for patients with syringomyelia and Chiari malformation. To obtain a better understanding of currently used management strategies and surgical interventions, this study evaluates current opinions in the treatment of these entities.

METHODS

Members of the Pediatric Section of the American Association of Neurological Surgeons (AANS) were surveyed in July of 1998. A questionnaire was designed to assess (1) management of asymptomatic and symptomatic cases; (2) signs and symptoms that warrant surgical intervention, and (3) surgical strategies. Seventy-seven of 234 surveys (33%) were returned. Responses were entered in a Microsoft Excel spreadsheet for data analysis.

RESULTS

Each year, respondents evaluated on average 10 patients with confirmed syringomyelia and operated on 7. There was substantial agreement to operate on patients with syringomyelia who had progressive scoliosis or progressive motor/sensory loss. For isolated syringomyelia without a Chiari malformation, the majority of respondents recommended shunting of the syrinx. Opinion was mixed concerning physical restrictions for asymptomatic patients with syringomyelia and Chiari malformations. For Chiari malformations, the majority of respondents recommended a minimum cervicomedullary decompression with dural patch grafting. No consensus was obtained on whether dural patch grafting should be done alone or in combination with intradural dissection or manipulation of the tonsils.

CONCLUSION

Although many respondents agreed on the management and surgical treatment of symptomatic patients with syringomyelia and/or Chiari malformations, there was disagreement with regard to the optimal surgical procedure. Respondents rejected prophylactic surgery for their asymptomatic patients, choosing to follow them conservatively with serial imaging and neurological examinations.

Phase II trial of gemcitabine in patients with previously untreated metastatic cancer of the esophagus or gastroesophageal junction

BACKGROUND

There were approximately 12,500 cases of esophageal carcinoma diagnosed in the US in 1992 and 12,200 deaths. The impact of chemotherapy on patients with metastatic disease is marginal with a median survival of only five months. Gemcitabine (LY188011,2,2,-difluorodeoxycytidine: dFdC), an analog of cytosine arabinoside (ara-C), is a pyrimidine antimetabolite. Gemcitabine has shown interesting clinical activity in initial phase II clinical trials in a variety of malignancies, including the aerodigestive malignancies, squamous-cell carcinoma of the head/neck and both non-small-cell and small-cell lung cancer.

PATIENTS AND METHODS

A total of 21 patients with chemotherapy-naïve metastatic esophageal carcinoma were entered. Nineteen patients were evaluable for toxicity and seventeen patients were evaluable for response. Gemcitabine was administered intravenously at 1250 mg/m2 over 30-60 minutes on days 1, 8, and 15 followed by 1 week of rest. This four-week schedule defined a cycle of treatment. Patients may have received a maximum of six cycles.

RESULTS

Gemcitabine was well tolerated with minimal non-hematologic toxicity and grade 3-4 anemia, granulocytopenia, and thrombocytopenia occurring in 10.5%, 21%, and 0% of patients, respectively. No responses were seen in the seventeen evaluable patients.

CONCLUSIONS

At the dose and schedule studied it would appear that gemcitabine has no activity in patients with chemotherapy-naïve esophageal carcinoma.

Asymptomatic Chiari Type I malformations identified on magnetic resonance imaging

OBJECT

Chiari Type I malformation (CMI) is a congenital disorder recognized by caudal displacement of the cerebellar tonsils through the foramen magnum and into the cervical canal. Frequently, associated findings include abnormalities of nearby bony and neural elements as well as syringomyelia. Cerebellar tonsillar ectopia is generally considered pathological when greater than 5 mm below the foramen magnum. However, asymptomatic tonsillar ectopia is an increasingly recognized phenomenon, the significance of which is poorly understood.

METHODS

The authors retrospectively reviewed the records of all brain magnetic resonance (MR) images obtained at our hospital over a 43-month period in an attempt to ascertain the relative prevalence and MR imaging characteristics of asymptomatic CMIs. Of 22,591 patients who underwent MR imaging of the head and cervical spine, 175 were found to have CMIs with tonsillar herniation extending more than 5 mm below the foramen magnum. Of these, 25 (14%) were found to be clinically asymptomatic. The average extent of ectopia in this population was 11.4 +/- 4.86 mm, and was significantly associated with a smaller cisterna magna. Syringomyelia and osseous anomalies were found in only one asymptomatic patient.

CONCLUSIONS

The authors suggest that the isolated finding of tonsillar herniation is of limited prognostic utility and must be considered in the context of all available clinical and radiographic data. Strategies for treating patients with asymptomatic CMIs are discussed.

Estrogen replacement therapy and MRI-demonstrated cerebral infarcts, white matter changes, and brain atrophy in older women: the Cardiovascular Health Study

OBJECTIVE

We studied the relationship between the use of estrogen replacement therapy (ERT) and cerebral magnetic resonance imaging (MRI) abnormalities among older women.

DESIGN

A population-based prospective study (Cardiovascular Health Study).

SETTING

Four regions in the United States.

PARTICIPANTS

A total of 2133 (62.9% of the eligible) women aged 65 to 95 years (mean age 74.8), on whom MRI was performed in 1992-1994.

MEASUREMENTS

Presence of global brain atrophy, white matter changes, small infarct-like lesion (ILL) (<3 mm), MRI infarcts (> or =3 mm, mostly small and asymptomatic), and cognitive function as measured by Mini-Mental State Exam (MMSE), and by ERT use (current/past/never), adjusted for a number of socioeconomic, lifestyle, and reproductive covariates.

RESULTS

Current use of ERT was reported by 15% and past use by another 23% of participants; 35% of all women had MRI infarcts. The prevalence of MRI infarcts did not differ in current or past users from those who had never used ERT (nonusers). Bifrontal distance, the largest distance between frontal horns, and the size of ventricles were larger among current ERT users compared to past users or nonusers (P (trend) = .01), adjusted for all other covariates, but no dose-response relationship to current or past ERT use was found. Duration of estrogen use was not associated with any atrophy measure. Cortical atrophy measure, sulcal widening, or white matter disease did not differ significantly by ERT use or duration of use. Central measures of atrophy, bifrontal distance, and ventricular size were significantly associated with cognition as measured by MMSE.

CONCLUSIONS

Current ERT users had much more clinically significant central atrophy than nonusers, but the implications remained unclear.

Determination of oxygen extraction ratios by magnetic resonance imaging

The oxygen extraction ratio (OER) of a tissue describes the interplay between oxygen delivery and consumption and, as such, directly reflects the viability and activity of any organ. It is shown that OER can be quantified using a single magnetic resonance imaging observable, namely the relaxation time T2 of venous blood draining from the tissue. This principle is applied to study local OER changes in the brain on visual stimulation in humans, unambiguously demonstrating a mismatch between changes in blood flow and oxygen metabolism on activation.

Venous blood effects in spin-echo fMRI of human brain

The spin-echo response to visual activation was studied as a function of spatial resolution at a field of 1.5 T. The results showed that the increase in absolute T(2) upon activation was as large as 22.8 +/- 3.1% (P < 0.05) at the highest resolution (5.3 mm(3)), while it was as small as 3.5 +/- 0.2% (P < 0.05) at the lowest resolution (42.2 mm(3)). In addition, upon increasing resolution, the spin-echo signal decay as a function of echo time changed from monoexponential to nonexponential. These data indicate that, when using the standard resolution for fMRI studies at 1.5 T, the effects of spin-echo changes in the draining veins are of major contribution to the total blood oxygenation level-dependent (BOLD) signal changes measured in voxels encompassing the activated brain areas. The data can be quantitatively accounted for using a model based on the intravascular origin of the spin-echo effect including both macrovascular and microvascular effects. Existing theories for the spin-echo BOLD effect based on diffusion through field gradients predict negligible spin-echo effects inside the large vessels and are therefore incompatible with the data. Magn Reson Med 42:617-626, 1999.

Kinetic analysis of [11C]McN5652: a serotonin transporter radioligand

The impulse response function of a radioligand is the most fundamental way to describe its pharmacokinetics and to assess its tissue uptake and retention pattern. This study investigates the impulse response function of [11C](+)McN5652, a radioligand used for positron emission tomography (PET) imaging of the serotonin transporter (SERT) in the brain. Dynamic PET studies were performed in eight healthy volunteers injected with [11C](+)McN5652 and subsequently with its pharmacologically inactive enantiomer [11C](-)McN5652. The impulse response function was calculated by deconvolution analysis of regional time-activity curves, and its peak value (f(max)), its retention value at 75 minutes (fT), and its normalized retention (f(rel) = fT/f(max)) were obtained. Alternatively, compartmental models were applied to calculate the apparent total distribution volume (DV(T)) and its specific binding component (DV(S)). Both the noncompartmental (fT,f(rel)) and the compartmental parameters (DV) were investigated with and without correction for nonspecific binding by simple subtraction of the corresponding value obtained with [11C](-)McN5652. The impulse response function obtained by deconvolution analysis demonstrated high tracer extraction followed by a slow decline in the form of a monoexponential function. Statistical analysis revealed that the best compartmental model in terms of analysis of variance F and condition number of the parameter variance-covariance matrix was the one that was based on a single tissue compartment with parameters k1 and k2 and that also included the parameter of regional cerebral blood volume (BV). The parameter f(rel) demonstrated low between-subject variance (coefficient of variation [CV] = 19%), a midbrain to cerebellum ratio of 1.85, and high correlation with the known density of SERT (r = 0.787 where r is the coefficient of linear correlation between the parameter and the known density of SERT). After correction for nonspecific binding, f(rel) demonstrated further improvement in correlation (r = 0.814) and midbrain to cerebellum ratio (3.09). The variance of the distribution volumes was acceptable when the logarithmic transform lnDV was used instead of DV (17% for the three-parameter model), but correlation of this compartmental parameter was slightly less (r = 0.652 for the three-parameter model) than the correlation of the noncompartmental f(rel) with the known density of SERT, and the midbrain to cerebellum ratio was only 1.5 (uncorrected) and 1.8 (corrected). At the expense of increasing variance, the correlation was increased after correction for nonspecific binding using the inactive enantiomer (r = 0.694; CV = 22%). These results indicate that the kinetics of [11C](+)McN5652 can best be described by a one-tissue compartment model with three parameters (k1, k2, and BV), and that both the noncompartmental parameter f(rel) and the compartmental distribution volumes have the potential for quantitative estimation of the density of SERT. Further validation of the radioligand in experimental and clinical situations is warranted.

Randomized study of CODE versus alternating CAV/EP for extensive-stage small-cell lung cancer: an Intergroup Study of the National Cancer Institute of Canada Clinical Trials Group and the Southwest Oncology Group

PURPOSE

To determine whether an intensive weekly chemotherapy regimen plus thoracic irradiation is superior to standard chemotherapy in the treatment of extensive-stage small-cell lung cancer (ESCLC).

PATIENTS AND METHODS

Patients with ESCLC were considered eligible for the study if they were younger than 68 years, had a performance status of 0 to 2, and were free of brain metastases. Patients were randomized to receive cisplatin, vincristine, doxorubicin, and etoposide (CODE) or alternating cyclophosphamide, doxorubicin, vincristine/etoposide and cisplatin (CAV/EP). Consolidative thoracic irradiation and prophylactic cranial irradiation were given to patients responding to CODE and according to investigator discretion on the CAV/EP arm.

RESULTS

The fidelity of drug delivery on both drug regimens was equal, and more than 70% of all patients received the intended protocol chemotherapy. Although rates of neutropenic fever were similar, nine (8.2%) of 110 patients on the CODE arm died during chemotherapy, whereas one (0.9%) of 109 patients died on the CAV/EP arm. Response rates after chemotherapy were higher (P =.006) with CODE (87%) than with CAV/EP (70%). However, progression-free survival (median of 0.66 years on both arms) and overall survival (median, 0.98 years for CODE and 0. 91 years for CAV/EP) were not statistically different.

CONCLUSION

The CODE regimen increased two-fold the received dose-intensity of four of the most active drugs in small-cell lung cancer compared with the standard CAV/EP regimen while maintaining an approximately equal total dose. Despite supportive care (but not routine prophylactic use of granulocyte colony-stimulating factor), there was excessive toxic mortality with the CODE regimen. The response rate with CODE was higher than that of CAV/EP, but progression-free and overall survival were not significantly improved. In view of increased toxicity and similar efficacy, the CODE chemotherapy regimen is not recommended for treatment of ESCLC.

Neural pathways in tactile object recognition

OBJECTIVE

To define further the brain regions involved in tactile object recognition using functional MRI (fMRI) techniques.

BACKGROUND

The neural substrates involved in tactile object recognition (TOR) have not been elucidated. Studies of nonhuman primates and humans suggest that basic motor and somatosensory mechanisms are involved at a peripheral level; however, the mechanisms of higher order object recognition have not been determined.

METHODS

The authors investigated 11 normal volunteers utilizing fMRI techniques in an attempt to determine the neural pathways involved in TOR. Each individual performed a behavioral paradigm with the activated condition involving identification of objects by touch, with identification of rough/smooth as the control.

RESULTS

Data suggest that in a majority of individuals, TOR involves the calcarine and extrastriatal cortex, inferior parietal lobule, inferior frontal gyrus, and superior frontal gyrus-polar region.

CONCLUSIONS

TOR may utilize visual systems to access an internal object representation. The parietal cortices and inferior frontal regions may be involved in a concomitant lexical strategy of naming the object being examined. Frontal polar activation likely serves a role in visuospatial working memory or in recognizing unusual representations of objects. Overall, these findings suggest that TOR could involve a network of cortical regions subserving somatosensory, motor, visual, and, at times, lexical processing. The primary finding suggests that in this normal study population, the visual cortices may be involved in the topographic spatial processing of TOR.

Genistein-induced G2-M arrest, p21WAF1 upregulation, and apoptosis in a non-small-cell lung cancer cell line

Lung cancer is the leading cause of cancer-related death in the world, with increasing incidence in many developed countries. Epidemiological data suggest that consumption of soy products (the isoflavone genistein) may be associated with a decreased risk of breast and prostate cancer; however, such studies are not available for lung cancer. We investigated cell growth inhibition, modulation in gene expression, and induction of apoptosis by genistein in H460 non-small lung cancer cells. Genistein inhibited H460 cell growth in a dose-dependent manner. Flow-cytometric analysis showed that 30 microM genistein arrested cell cycle progression at the G2-M phase. 4,6-Diamidino-2-phenylindole staining, flow-cytometric analysis, and DNA laddering were used to investigate apoptotic cell death, and the results show that 30 microM genistein can cause typical DNA laddering, a hallmark for apoptosis. In addition, flow cytometry and 4,6-diamidino-2-phenylindole staining showed induction of apoptosis by genistein. Our investigation also demonstrated the modulation of p21WAF1 by Western blot analysis of cell lysates obtained from cultured cells treated with 30 and 50 microM genistein for 24, 48, and 72 hours. Simultaneously, immunocytochemical staining was conducted for the expression of p21WAF1 protein. Our results showed that genistein can upregulate p21WAF1 expression in genistein-treated cells. From these results, we conclude that genistein may act as an anticancer agent, and further studies may prove its efficacy in non-small lung cancer cells. Thus the biological effects of genistein may, indeed, be due to the modulation of cell growth, cell death, and cell cycle regulatory molecules.

Evaluation of pyrazoloacridine in patients with advanced pancreatic carcinoma

PURPOSE

Pyrazoloacridine (PZA) is an acridine derivative selected for clinical development because of broad pre-clinical antitumor activity and solid tumor selectivity. Phase I evaluations with PZA have demonstrated predictable toxicity and suggested clinical efficacy. A phase II trial in patients with previously untreated advanced pancreatic cancer was conducted.

METHODS

PZA was administered at a dose of 750 mg/m2 intravenously over 3 hours every 21 days. Seventeen patients were treated receiving a total of 46 courses of PZA.

RESULTS

Of the 15 patients evaluable for response, no responses were observed (0% response rate, 95% confidence interval 0-22%). Major toxicities directly attributable to PZA included moderate neutropenia and mild neurotoxicity.

CONCLUSION

PZA at this dose and schedule of administration was inactive in patients with pancreatic carcinoma.

Inhibition of tumor cell growth by p21WAF1 adenoviral gene transfer in lung cancer

Gene replacement therapy is potentially a very powerful tool, targeting specific molecular mediators of cancer development and progression. p21WAF1 (p21) is a cyclin-dependent kinase inhibitor that is induced by p53 upon DNA damage or p53 overexpression, resulting in cell cycle arrest at the G1 checkpoint and inhibition of further cell proliferation. Using a replication-deficient recombinant adenovirus (AdV) ((rAd)-p21) as a p21 gene delivery system, we have evaluated the effect of p21 introduction in lung cancer cells in vitro as well as in vivo. In in vitro experiments, two human non-small cell lung cancer (NSCLC) cell lines, NCI-H460 and NCI-H322, showed dose-dependent p21 induction and concomitant cell growth inhibition following rAd/p21 infection. Flow cytometric analysis of the cell cycle revealed a significant increase in the percentage of NCI-H460 cells in G0/G1 following rAd/p21 infection compared with untreated cells, suggesting that p21-induced growth inhibition was due to G0/G1 arrest. We also tested the therapeutic efficacy of rAd/p21 in an in vivo human NSCLC model in SCID mice. Tumor-bearing mice were established by subcutaneous injections of NCI-H460 cells and treated by repeated intratumoral injections of rAd/p21. Intratumoral delivery of rAd/p21 significantly suppressed tumor growth and prolonged survival in rAd/p21-treated mice. Our in vitro and in vivo results provide strong preliminary evidence for the growth inhibition of NSCLC by rAd/p21. Collectively, these results justify further studies to evaluate the efficacy of rAd/p21 for gene therapy in human lung cancer.

Object shape processing in the visual system evaluated using functional MRI

We used functional MRI (fMRI) to determine the cortical regions activated during processing of visual object shape in humans in six men and three women, using a paradigm with a baseline condition of simple shape detection and an activated condition of object/nonobject shape discrimination. Eight of the nine subjects studied showed significant signal changes. Seven of eight showed changes in the occipital lobes (five bilateral, two right only, one left only). All eight subjects with signal changes exhibited changes in the parietal lobes bilaterally. In the occipitotemporal gyri, there were signal changes bilaterally in seven subjects and unilaterally, on the right, in one. Activation-related fMRI signal increases were also present in the posterior superior and middle temporal gyri in seven of the subjects, with four showing bilateral signal changes, two showing signal changes on the left only, and one only on the right. The data strongly suggest that processing of object shape information in humans activates both the ventral and dorsal visual processing pathways ("what" and "where" pathways), described previously both in humans and in nonhuman primates.