Technical advances in motion-robust MR thermometry.

Proton resonance frequency shift (PRFS) MR thermometry is the most common method used in clinical thermal treatments because of its fast acquisition and high sensitivity to temperature. However, motion is the biggest obstacle in PRFS MR thermometry for monitoring thermal treatment in moving organs. This challenge arises because of the introduction of phase errors into the PRFS calculation through multiple methods, such as image misregistration, susceptibility changes in the magnetic field, and intraframe motion during MRI acquisition. Various approaches for motion correction have been developed for real-time, motion-robust, and volumetric MR thermometry. However, current technologies have inherent trade-offs among volume coverage, processing time, and temperature accuracy. These tradeoffs should be considered and chosen according to the thermal treatment application. In hyperthermia treatment, precise temperature measurements are of increased importance rather than the requirement for exceedingly high temporal resolution. In contrast, ablation procedures require robust temporal resolution to accurately capture a rapid temperature rise. This paper presents a comprehensive review of current cutting-edge MRI techniques for motion-robust MR thermometry, and recommends which techniques are better suited for each thermal treatment. We expect that this study will help discern the selection of motion-robust MR thermometry strategies and inspire the development of motion-robust volumetric MR thermometry for practical use in clinics.

MR-guided focused ultrasound therapy of extra-abdominal desmoid tumors: a multicenter retrospective study of 105 patients.

OBJECTIVE: To assess the safety and efficacy of magnetic resonance-guided focused ultrasound (MRgFUS) for the treatment extra-abdominal desmoids. METHODS: A total of 105 patients with desmoid fibromatosis (79 females, 26 males; 35 ± 14 years) were treated with MRgFUS between 2011 and 2021 in three centers. Total and viable tumors were evaluated per patient at last follow-up after treatment. Response and progression-free survival (PFS) were assessed with (modified) response evaluation criteria in solid tumors (RECIST v.1.1 and mRECIST). Change in Numerical Rating Scale (NRS) pain and 36-item Short Form Health Survey (SF-36) scores were compared. Treatment-related adverse events were recorded. RESULTS: The median initial tumor volume was 114 mL (IQR 314 mL). After MRgFUS, median total and viable tumor volume decreased to 51 mL (95% CI: 30-71 mL, n = 101, p < 0.0001) and 29 mL (95% CI: 17-57 mL, n = 88, p < 0.0001), respectively, at last follow-up (median: 15 months, 95% CI: 11-20 months). Based on total tumor measurements (RECIST), 86% (95% CI: 75-93%) had at least stable disease or better at last follow-up, but 50% (95% CI: 38-62%) of remaining viable nodules (mRECIST) progressed within the tumor. Median PFS was reached at 17 and 13 months for total and viable tumors, respectively. NRS decreased from 6 (IQR 3) to 3 (IQR 4) (p < 0.001). SF-36 scores improved (physical health (41 (IQR 15) to 46 (IQR 12); p = 0.05, and mental health (49 (IQR 17) to 53 (IQR 9); p = 0.02)). Complications occurred in 36%, most commonly 1st/2nd degree skin burns. CONCLUSION: MRgFUS reduced tumor volume, reduced pain, and improved quality of life in this series of 105 patients with extra-abdominal desmoid fibromatosis. CLINICAL RELEVANCE STATEMENT: Imaging-guided ablation is being increasingly used as an alternative to surgery, radiation, and medical therapy for the treatment of desmoid fibromatosis. MR-guided high-intensity focused ultrasound is an incisionless ablation technique that can be used to reduce tumor burden effectively and safely. KEY POINTS: • Desmoid fibromatosis was treated with MR-guided high-intensity focused ultrasound in 105 patients. • MR-guided focused ultrasound ablation reduced tumor volume and pain and improved quality of life. • MR-guided focused ultrasound is a treatment option for patients with extra-abdominal desmoid tumors.

Volumetric hyperthermia delivery using the ExAblate Body MR-guided focused ultrasound system.

OBJECTIVES: To investigate image-guided volumetric hyperthermia strategies using the ExAblate Body MR-guided focused ultrasound ablation system, involving mechanical transducer movement and sector-vortex beamforming. MATERIALS AND METHODS: Acoustic and thermal simulations were performed to investigate volumetric hyperthermia using mechanical transducer movement combined with sector-vortex beamforming, specifically for the ExAblate Body transducer. The system control in the ExAblate Body system was modified to achieve fast transducer movement and MR thermometry-based hyperthermia control, mechanical transducer movements and electronic sector-vortex beamforming were combined to optimize hyperthermia delivery. The experimental validation was performed using a tissue-mimicking phantom. RESULTS: The developed simulation framework allowed for a parametric study with varying numbers of heating spots, sonication durations, and transducer movement times to evaluate the hyperthermia characteristics for mechanical transducer movement and sector-vortex beamforming. Hyperthermic patterns involving 2-4 sequential focal spots were analyzed. To demonstrate the feasibility of volumetric hyperthermia in the system, a tissue-mimicking phantom was sonicated with two distinct spots through mechanical transducer movement and sector-vortex beamforming. During hyperthermia, the average values of Tmax, T10, Tavg, T90, and Tmin over 200 s were measured within a circular ROI with a diameter of 10 pixels. These values were found to be 8.6, 7.9, 6.6, 5.2, and 4.5 °C, respectively, compared to the baseline temperature. CONCLUSIONS: This study demonstrated the volumetric hyperthermia capabilities of the ExAblate Body system. The simulation framework developed in this study allowed for the evaluation of hyperthermia characteristics that could be implemented with the ExAblate MRgFUS system.

Motion-robust, multi-slice, real-time MR thermometry for MR-guided thermal therapy in abdominal organs.

PURPOSE: To develop an effective and practical reconstruction pipeline to achieve motion-robust, multi-slice, real-time MR thermometry for monitoring thermal therapy in abdominal organs. METHODS: The application includes a fast spiral magnetic resonance imaging (MRI) pulse sequence and a real-time reconstruction pipeline based on multi-baseline proton resonance frequency shift (PRFS) method with visualization of temperature imaging. The pipeline supports multi-slice acquisition with minimal reconstruction lag. Simulations with a virtual motion phantom were performed to investigate the influence of the number of baselines and respiratory rate on the accuracy of temperature measurement. Phantom experiments with ultrasound heating were performed using a custom-made motion phantom to evaluate the performance of the pipeline. Lastly, experiments in healthy volunteers (N = 2) without heating were performed to evaluate the accuracy and stability of MR thermometry in abdominal organs (liver and kidney). RESULTS: The multi-baseline approach with greater than 25 baselines resulted in minimal temperature errors in the simulation. Phantom experiments demonstrated a 713 ms update time for 3-slice acquisitions. Temperature maps with 30 baselines showed clear temperature distributions caused by ultrasound heating in the respiratory phantom. Finally, the pipeline was evaluated with physiologic motions in healthy volunteers without heating, which demonstrated the accuracy (root mean square error [RMSE]) of 1.23 ± 0.18 °C (liver) and 1.21 ± 0.17 °C (kidney) and precision of 1.13 ± 0.11 °C (liver) and 1.16 ± 0.15 °C (kidney) using 32 baselines. CONCLUSIONS: The proposed real-time acquisition and reconstruction pipeline allows motion-robust, multi-slice, real-time temperature monitoring within the abdomen during free breathing.

Therapeutic Potential of Human Fetal Mesenchymal Stem Cells in Musculoskeletal Disorders: A Narrative Review.

Mesenchymal stem cells (MSCs) have emerged as a promising therapeutic approach for diverse diseases and injuries. The biological and clinical advantages of human fetal MSCs (hfMSCs) have recently been reported. In terms of promising therapeutic approaches for diverse diseases and injuries, hfMSCs have gained prominence as healing tools for clinical therapies. Therefore, this review assesses not the only biological advantages of hfMSCs for healing human diseases and regeneration, but also the research evidence for the engraftment and immunomodulation of hfMSCs based on their sources and biological components. Of particular clinical relevance, the present review also suggests the potential therapeutic feasibilities of hfMSCs for musculoskeletal disorders, including osteoporosis, osteoarthritis, and osteogenesis imperfecta.

Ultrathin arrayed camera for high-contrast near-infrared imaging.

We report an ultrathin arrayed camera (UAC) for high-contrast near infrared (NIR) imaging by using microlens arrays with a multilayered light absorber. The UAC consists of a multilayered composite light absorber, inverted microlenses, gap-alumina spacers and a planar CMOS image sensor. The multilayered light absorber was fabricated through lift-off and repeated photolithography processes. The experimental results demonstrate that the image contrast is increased by 4.48 times and the MTF 50 is increased by 2.03 times by eliminating optical noise between microlenses through the light absorber. The NIR imaging of UAC successfully allows distinguishing the security strip of authentic bill and the blood vessel of finger. The ultrathin camera offers a new route for diverse applications in biometric, surveillance, and biomedical imaging.

Sonication strategies toward volumetric ultrasound hyperthermia treatment using the ExAblate body MRgFUS system.

PURPOSE: The ExAblate body MRgFUS system requires advanced beamforming strategies for volumetric hyperthermia. This study aims to develop and evaluate electronic beam steering, multi-focal patterns, and sector vortex beamforming approaches in conjunction with partial array activation using an acoustic and biothermal simulation framework along with phantom experiments. METHODS: The simulation framework was developed to calculate the 3D acoustic intensity and temperature distribution resulting from various beamforming and scanning strategies. A treatment cell electronically sweeping a single focus was implemented and evaluated in phantom experiments. The acoustic and thermal focal size of vortex beam propagation was quantified according to the vortex modes, number of active array elements, and focal depth. RESULTS: Turning off a percentage of the outer array to increase the f-number increased the focal size with a decrease in focal gain. 60% active elements allowed generating a sonication cell with an off-axis of 10 mm. The vortex mode number 4 with 60% active elements resulted in a larger heating volume than using the full array. Volumetric hyperthermia in the phantom was evaluated with the vortex mode 4 and respectively performed with 100% and 80% active elements. MR thermometry demonstrated that the volumes were found to be 18.8 and 29.7 cm3, respectively, with 80% array activation producing 1.58 times larger volume than the full array. CONCLUSIONS: This study demonstrated that both electronic beam steering and sector vortex beamforming approaches in conjunction with partial array activation could generate large volume heating for HT delivery using the ExAblate body array.

Prenatal prognostic factors for isolated right congenital diaphragmatic hernia: a single center's experience.

BACKGROUND: Right-sided congenital diaphragmatic hernia (RCDH) is relatively rare compared with left-sided congenital diaphragmatic hernia (LCDH). Clinical data of RCDH, especially with respect to antenatal prediction of neonatal outcome, are lacking. The aim of this study was to report the treatment outcomes of patients with antenatally diagnosed RCDH and to evaluate the predictability of observed-to-expected lung area-to-head circumference ratio (O/E LHR) for perinatal outcomes, focused on mortality or extracorporeal membrane oxygenation (ECMO) requirement. METHODS: We retrospectively reviewed the medical records of newborn infants with isolated RCDH. We analyzed and compared the clinical and prenatal characteristics including the fetal lung volume, which was measured as the O/E LHR, between the survivors and the non-survivors. RESULTS: A total of 26 (66.7%) of 39 patients with isolated RCDH survived to discharge. The O/E LHR was significantly greater in survivors (64.7 ± 21.2) than in non-survivors (40.5 ± 23.4) (P =.027). It was greater in survivors without ECMO requirement (68.3 ± 15.1) than non-survivors or those with ECMO requirement (46.3 ± 19.4; P = .010). The best O/E LHR cut-off value for predicting mortality in isolated RCDH was 50. CONCLUSIONS: The findings in this study suggest that O/E LHR, a well-characterized prognostic indicator in LCDH, could be applied to a fetus with antenatally diagnosed RCDH. A large cohort study is required to verify the association between O/E LHR values and the graded severity of RCDH.

Functional and structural evaluation in the lungs of children with repaired congenital diaphragmatic hernia.

BACKGROUND: To evaluate the long-term functional and structural pulmonary development in children with repaired congenital diaphragmatic hernia (CDH) and to identify the associated perinatal-neonatal risk factors. METHODS: Children with repaired CDH through corrective surgery who were born at gestational age ≥ 35 weeks were included in this analysis. Those who were followed for at least 5 years were subjected to spirometry and chest computed tomography for evaluation of their functional and structural growth. Main bronchus diameters and lung volumes (total, left/right) were measured. According to total lung volume (TLV) relative to body surface area, children were grouped into TLV ≥ 50 group and TLV < 50 group and the associations with perinatal-neonatal factors were analyzed. RESULTS: Of the 28 children (mean age, 6.2 ± 0.2 years) with left-sided CDH, 7 (25%) had abnormal pulmonary function, of whom 6 (87%) showed restrictive patterns. All pulmonary functions except FEF25-75% were worse than those in matched healthy control group. Worse pulmonary function was significantly associated with small head and abdominal circumferences at birth. The mean TLV was 1339.1 ± 363.9 mL and LLV/TLV was 47.9 ± 2.5 mL. Children with abnormal pulmonary function were more likely to have smaller lung volumes. In multivariate analysis, abdominal circumference at birth was significantly associated with abnormal lung volume. CONCLUSIONS: A quarter of children with repaired CDH showed abnormal pulmonary function. Small abdominal circumference at birth was associated with abnormal pulmonary function and lower TLV. .

Simultaneous fat-referenced proton resonance frequency shift thermometry and MR elastography for the monitoring of thermal ablations.

PURPOSE: Simultaneous fat-referenced proton resonance frequency shift (FRPRFS) thermometry combined with MR elastography (MRE) is proposed, to continuously monitor thermal ablations for all types of soft tissues, including fat-containing tissues. Fat-referenced proton resonance frequency shift thermometry makes it possible to measure temperature even in the water fraction of fat-containing tissues while enabling local field-drift correction. Magnetic resonance elastography allows measuring the mechanical properties of tissues that are related to tissue structural damage. METHODS: A gradient-echo MR sequence framework was proposed that combines the need for multiple TE acquisitions for the water-fat separation of FRPRFS, and the need for multiple MRE phase offsets for elastogram reconstructions. Feasibility was first assessed in a fat-containing gelatin phantom undergoing moderate heating by a hot water circulation system. Subsequently, high intensity focused ultrasound heating was conducted in porcine muscle tissue ex vivo (N = 4; 2 samples, 2 locations/sample). RESULTS: Both FRPRFS temperature maps and elastograms were updated every 4.1 seconds. In the gelatin phantom, FRPRFS was in good agreement with optical fiber thermometry (average difference 1.2 ± 1°C). In ex vivo high-intensity focused ultrasound experiments on muscle tissue, the shear modulus was found to decrease significantly by 34.3% ± 7.7% (experiment 1, sample 1), 17.9% ± 10.0% (experiment 2, sample 1), 55.1% ± 8.7% (experiment 3, sample 2), and 34.7% ± 8.4% (experiment 4, sample 2) as a result of temperature increase (ΔT = 22.5°C ± 4.2°C, 14.0°C ± 2.8°C, 14.7°C ± 3.7°C, and 14.5°C ± 3.0°C, respectively). CONCLUSION: This study demonstrated the feasibility of monitoring thermal ablations with FRPRFS thermometry together with MRE, even in fat-containing tissues. The acquisition time is similar to non-FRPRFS thermometry combined with MRE.

Multifocal microlens arrays using multilayer photolithography.

We report a new microfabrication method of multifocal microlens arrays (MF-MLAs) for extended depth-of-field (DoF) using multilayer photolithography and thermal reflow. Microlenses of different focal lengths were simultaneously fabricated on a single glass wafer by using repeated photolithography with multiple photomasks to define microposts of different thicknesses and concurrent thermal reflow of multi-stacked microposts. The diverse lens curvatures of MF-MLAs are precisely controlled by the thickness of the micropost. Hexagonally packaged MF-MLAs clearly show three different focal lengths of 249 µm, 310 µm, and 460 µm for 200 µm in lens diameter and result in multifocal images on a single image sensor. This method provides a new route for developing various three-dimensional (3D) imaging applications such as light-field cameras or 3D medical endoscopes.

Neonatal exchange transfusion: Experience in Korea.

BACKGROUND: Exchange transfusion (ET) is an established, efficacious, and reliable practice for severe neonatal hyperbilirubinemia, hemolytic disease of the newborn, and neonatal sepsis. This study assessed the indications and clinical outcomes of ET performed in a tertiary hospital in Korea. MATERIALS AND METHODS: We studied 64 ET sessions performed on 23 neonates between March 1999 and March 2018. ET was performed based on estimated double volume exchange transfusion using fresh red blood cells and fresh frozen plasma. Patients' clinical information, including demographic data and ET indication, and laboratory data were collected pre- and post-ET. RESULTS: The most common ET indication was hyperbilirubinemia with hemolytic anemia due to non-ABO maternal blood group discrepancies. In three preterm babies, ETs were performed for severe anemia, leukocytosis, and hyperkalemia cases. Before ET, the patients showed slightly high WBC counts, low hemoglobin levels, and low platelet counts. After ET, blood examination revealed normal WBC counts, increased hemoglobin levels, and decreased platelet counts (all P < 0.001). Bilirubin levels decreased immediately after ET (P < 0.001). Electrolyte and C-reactive protein levels showed no significant changes after ETs. Adverse events occurred in 11 (47.8 %) patients; the most common were hypoxemia and hypotension. One infant experienced cardiorespiratory arrest due to hypercalcemia and was successfully resuscitated. No one died within 24 h of ET. However, five infants showed hyperbilirubinemia aggravation. CONCLUSIONS: ET is an effective treatment modality for leukocytosis and hyperbilirubinemia with low mortality but involves common adverse events post-ET. This report provides an overview of current ET practices in Korea.

Challenges of acute peritoneal dialysis in extremely-low-birth-weight infants: a retrospective cohort study.

BACKGROUND: Peritoneal dialysis (PD) has been used occasionally in extremely-low-birth-weight (ELBW) infants with acute kidney injury (AKI). This study aimed to evaluate the clinical characteristics and outcomes of ELBW infants with AKI treated with PD. METHODS: In this retrospective cohort study, the medical records of ELBW infants with AKI, who underwent PD from January 2008 to February 2018, were reviewed. A PD catheter (7.5-9.0 Fr) or central venous catheter (4 Fr) was used for the peritoneal access. Treatment with PD solutions (2.5 or 4.25%) was started at 10 mL/kg, which was increased to 20-30 mL/kg for 60-120 min/cycle continuing for 24 h. RESULTS: Twelve ELBW infants (seven male and five female infants) were treated, and their mean (±SD) gestational age and birth weight were 27.2 (±3.3) weeks and 706.5 (±220.5) g, respectively. Two patients had severe perinatal asphyxia (5-min Apgar score ≤ 3). The most important indication for starting PD was AKI due to sepsis. The average (±SD) duration of PD was 9.4 (± 7.7) days. The potassium levels in the ELBW infants with hyperkalemia decreased from 6.8 to 5.0 mg/mL after 9.3 (± 4.4) days. The most common complication of PD was mechanical dysfunction of the catheters, such as dialysate leakage (75%). Two patients were successful weaned off PD. The mortality rate of the infants treated with PD was 91.7%. CONCLUSIONS: In this series, the mortality rate of ELBW infants with AKI treated with PD was relatively high because of their incompletely developed organ systems. Therefore, the use of PD should be carefully considered for the treatment of ELBW infants with AKI in terms of decisions regarding resuscitation.

Physical exercise enhances adult cortical plasticity in a neonatal rat model of hypoxic-ischemic injury: Evidence from BOLD-fMRI and electrophysiological recordings.

Neuroplasticity is considered essential for recovery from brain injury in developing brains. Recent studies indicate that it is especially effective during early postnatal development and during the critical period. The current study used functional magnetic resonance imaging (fMRI) and local field potential (LFP) electrophysiological recordings in rats that experienced neonatal hypoxic-ischemic (HI) injury during the critical period to demonstrate that physical exercise (PE) can improve cortical plasticity even when performed during adulthood, after the critical period. We investigated to what extent the blood oxygen level-dependent (BOLD)-fMRI responses were increased in the contralesional spared cortex, and how these increases were related to the LFP electrophysiological measurements and the functional outcome. The balance of excitation and inhibition was assessed by measuring excitatory and inhibitory postsynaptic currents in stellate cells in the primary somatosensory (S1) cortex, which was compared with the BOLD-fMRI responses in the contralesional S1 cortex. The ratio of inhibitory postsynaptic current (IPSC) to excitatory postsynaptic current (EPSC) at the thalamocortical (TC) input to the spared S1 cortex was significantly increased by PE, which is consistent with the increased BOLD-fMRI responses and improved functional outcome. Our data clearly demonstrate in an experimental rat model of HI injury during the critical period that PE in adulthood enhances neuroplasticity and suggest that enhanced feed-forward inhibition at the TC input to the S1 cortex might underlie the PE-induced amelioration of the somatosensory deficits caused by the HI injury. In summary, the results of the current study indicate that PE, even if performed beyond the critical period or during adulthood, can be an effective therapy to treat neonatal brain injuries, providing a potential mechanism for the development of a potent rehabilitation strategy to alleviate HI-induced neurological impairments.

ER stress attenuation by Aloe-derived polysaccharides in the protection of pancreatic ß-cells from free fatty acid-induced lipotoxicity.

Insulin resistance, a pathophysiology of type 2 diabetes, is associated with obesity. Lipotoxicity in obesity leads to the dysfunction and death of pancreatic ß-cells and inadequate insulin production, thereby aggravating type 2 diabetes. The present study was conducted to determine the effect of Aloe vera polysaccharides (APs) as an anti-hyperglycemic agent and their mechanisms of action. Gel polysaccharides from Aloe extracts were separated using ultrafiltration devices with molecular weight-cutoff membranes, and the protective effect of APs on pancreatic ß-cells in response to free fatty acids (FFAs) was determined. Hamster pancreatic ß-cell line HIT-T15 was treated with palmitate and APs to analyze cellular responses. We observed a large number of apoptotic ß-cell death after treatment with high levels of palmitate, but this was efficiently prevented by the addition of APs in a dose-dependent manner. It was found that the anti-apoptotic properties of APs were largely due to the relief of endoplasmic reticulum (ER) stress signaling. APs were effective in interfering with the FFA-induced activation of the PERK and IRE1 pathways as well as ROS generation, thereby protecting pancreatic ß-cells from lipotoxicity. Although variation in the chain length of APs can influence the activity of FFA-mediated ER stress signaling in different ways, polysaccharide mixtures with molecular weights higher than 50 kDa showed greater antiapoptotic and antioxidant activity in ß-cells. After oral administration of APs, markedly lowering fasting blood glucose levels were observed in db/db mice, providing evidence of the potential of APs as an alternative insulin sensitizer. Therefore, it was concluded that APs have a protective effect against type 2 diabetes by modulating obesity-induced ER stress in pancreatic ß-cells.

Exogenous ß-Hydroxybutyrate Treatment and Neuroprotection in a Suckling Rat Model of Hypoxic-Ischemic Encephalopathy.

ß-Hydroxybutyrate (BHB) is a representative ketone body that may play a role in the mitigation of neonatal hypoxic-ischemic encephalopathy by altering energy metabolism. This study aimed to investigate the neuroprotective efficacy of exogenous BHB administration in a suckling rat model after hypoxia-ischemia (HI). Thirteen-day-old (P13) rat pups were subjected to 120 min of hypoxia according to the Rice-Vannucci model. BHB (5.0 mmol/kg, HI-BHB) or vehicle (0.9% saline, HI-Veh) was administered 0, 2, 4, and 6 h after HI induction. Pathologic injury scores and the number of TUNEL-positive cells were evaluated on P15. Residual hemispheric volume was measured with T2-weighted MRI (on P27) and functional tests, such as the negative geotaxis test, rope suspension test, rotarod test, novel object recognition test, and cylinder test, were performed. Systemic ketosis (approx. 2.0-3.0 mM/L) was well tolerated by the rat pups with no difference in the mortality rate between both groups. Compared with the HI-Veh group, the HI-BHB group demonstrated significantly lower pathological scores as well as fewer TUNEL-positive cells. The intact residual hemispheric and hippocampal volumes were greater in the HI-BHB group than the HI-Veh group. However, the results of functional tests did not differ between both groups. Postischemic BHB administration reduced brain injury in suckling rats after HI. The safe clinical application of our animal model to human infants with HI requires further investigation.

Proposal of novel structure for wide wavelength tuning in distributed Bragg reflector laser diode with single grating mirror.

We report a novel structure that is capable of wide wavelength tuning in the distributed Bragg reflector laser diode (DBR-LD) with a single grating mirror. This device's DBR section has two tuning elements, plasma, and heater tunings, which are implemented simultaneously on the top of a single waveguide by using an in-between dielectric layer. For the proposed structure, a three-dimensional thermal simulation was conducted. The results showed that the temperature profile within the waveguide is highly affected by the position of heater metal and thermal conductivity of the p-cladding layer. As a result, it is important to use a uniform temperature region in the DBR section for a wide tuning range and stable single-mode operation. For a 550-µm long DBR-LD with a 250-µm long DBR section, a tuning range of 26 nm (i.e., 7 nm for plasma tuning and 19 nm for heater tuning); an SMSR of more than 45 dB; and a peak power variation of less than ± 2.5 dB were obtained. From the comparisons of two DBR-LDs with only one tuning element, we confirmed that using the dielectric layer is a very effective way of achieving a wide tuning under the independent tuning operation.

Overcoming the efficiency limit of organic light-emitting diodes using ultra-thin and transparent graphene electrodes.

We propose an effective way to enhance the out-coupling efficiencies of organic light-emitting diodes (OLEDs) using graphene as a transparent electrode. In this study, we investigated the detrimental adsorption and internal optics occurring in OLEDs with graphene anodes. The optical out-coupling efficiencies of previous OLEDs with transparent graphene electrodes barely exceeded those of OLEDs with conventional transparent electrodes because of the weak microcavity effect. To overcome this issue, we introduced an internal random scattering layer for light extraction and reduced the optical absorption of the graphene by reducing the number of layers in the multilayered graphene film. The efficiencies of the graphene-OLEDs increased significantly with decreasing the number of graphene layers, strongly indicating absorption reduction. The maximum light extraction efficiency was obtained by using a single-layer graphene electrode together with a scattering layer. As a result, a widened angular luminance distribution with a remarkable external quantum efficiency and a luminous efficacy enhancement of 52.8% and 48.5%, respectively, was achieved. Our approach provides a demonstration of graphene-OLED having a performance comparable to that of conventional OLEDs.

Neuroplasticity for spontaneous functional recovery after neonatal hypoxic ischemic brain injury in rats observed by functional MRI and diffusion tensor imaging.

For infants and children, an incredible resilience from injury is often observed. There is growing evidence that functional recovery after brain injury might well be a consequence of the reorganization of the neural network as a process of neuroplasticity. We demonstrate the presence of neuroplasticity at work in spontaneous recovery after neonatal hypoxic ischemic (HI) injury, by elucidating a precise picture in which such reorganization takes place using functional MRI techniques. For all 12 siblings, 6 rats were subjected to severe HI brain injury and 6 rats underwent sham operation only. Severe HI brain injury was induced to postnatal day 7 (p7) Sprague-Dawley rats according to the Rice-Vannucci model (right carotid artery occlusion followed by 150min of hypoxia with 8% O2 and 92% of N2). Brain activation maps along with anatomical and functional connectivity maps related to the sensory motor function were obtained at adult (p63) using blood oxygen level dependent (BOLD)-functional MRI (fMRI), resting state-functional MRI (rs-fMRI) and diffusion tensor imaging (DTI); each of these MRI data was related to sensory motor functional outcome. In-depth investigation of the functional MRI data revealed: 1) intra-hemispheric expansion of BOLD signal activation in the contralesional undamaged hemisphere for ipsilesional forepaw stimuli to include the M2 and Cg1 in addition to the S1 and M1 wide spreading in the anterior and posterior directions, 2) inter-hemispheric transfer of BOLD signal activation for contralesional forepaw stimuli, normally routed to the injured hemisphere, to analogous sites in the contralesional undamaged hemisphere, localized newly to the M1 and M2 with a reduced portion of the S1, 3) inter-hemispheric axonal disconnection and axonal rewiring within the undamaged hemisphere as shown through DTI, and 4) increased functional interactions within the cingulate gyrus in the HI injured rats as shown through rs-fMRI. The BOLD signal amplitudes as well as DTI and rs-fMRI data well correlate with behavioral tests (tape to remove). We found that function normally utilizing what would be the injured hemisphere is transferred to the uninjured hemisphere, and functionality of the uninjured hemisphere remains not untouched but is also rewired in an expansion corresponding to the newly formed sensorimotor function from both the contralesional and the ipsilesional sides. The conclusion drawn from the data in our current study is that enhanced motor function in the contralesional hemisphere governs both the normal and damaged sides, indicating that active plasticity with brain laterality was spontaneously generated to overcome functional loss and established autonomously through normal experience via modification of neural circuitry for neonatal HI injured brain.

Role of micropillar arrays in cell rolling dynamics.

In this study, we present a role of arrayed micropillar structures in cell rolling dynamics. Cell rolling on a ligand coated surface as a means of cell separation was demonstrated using a micropillar-integrated microfluidic channel. This approach allows the separation of cells according to characteristic surface properties, regardless of cell size. In these experiments, different moving trajectories of the cells between a ligand-coated micropost structure and a 1% BSA coated micropost structure were observed using sequential images. Based on the analysis of the angle of travel of cells in the trajectory, the average angles of travel on the ligand-coated microposts were 1.5° and -3.1° on a 1% BSA-coated micropost structure. The overall force equivalent applied to a cell can be analyzed to predict the cell rolling dynamics when a cell is detached. These results show that it will be possible to design chip geometry for delicate operations and to separate target cells. Furthermore, we believe that these control techniques based on a ligand coated micropillar surface can be used for enhancing cell rolling-based separation in a faster and more continuous manner.