In the present study, we describe a fingerprinting approach to analyze the time evolution of the MR signal and retrieve quantitative information about the microvascular network. We used a Gradient ...Echo Sampling of the Free Induction Decay and Spin Echo (GESFIDE) sequence and defined a fingerprint as the ratio of signals acquired pre- and post-injection of an iron-based contrast agent. We then simulated the same experiment with an advanced numerical tool that takes a virtual voxel containing blood vessels as input, then computes microscopic magnetic fields and water diffusion effects, and eventually derives the expected MR signal evolution. The parameter inputs of the simulations (cerebral blood volume CBV, mean vessel radius R, and blood oxygen saturation SO2) were varied to obtain a dictionary of all possible signal evolutions. The best fit between the observed fingerprint and the dictionary was then determined by using least square minimization. This approach was evaluated in 5 normal subjects and the results were compared to those obtained by using more conventional MR methods, steady-state contrast imaging for CBV and R and a global measure of oxygenation obtained from the superior sagittal sinus for SO2. The fingerprinting method enabled the creation of high-resolution parametric maps of the microvascular network showing expected contrast and fine details. Numerical values in gray matter (CBV=3.1±0.7%, R=12.6±2.4μm, SO2=59.5±4.7%) are consistent with literature reports and correlated with conventional MR approaches. SO2 values in white matter (53.0±4.0%) were slightly lower than expected. Numerous improvements can easily be made and the method should be useful to study brain pathologies.
•We propose an MR fingerprinting approach to measure microvascular characteristics.•High-resolution parametric maps show expected contrast and fine details.•Numerical values correlate with conventional MR approaches.•Numerous improvements can easily be made.•The method should be useful to study brain pathologies.
A software-defined radio (SDR) receiver with improved robustness to out-of-band interference (OBI) is presented. Two main challenges are identified for an OBI-robust SDR receiver: out-of-band ...nonlinearity and harmonic mixing. Voltage gain at RF is avoided, and instead realized at baseband in combination with low-pass filtering to mitigate blockers and improve out-of-band IIP3. Two alternative ¿iterative¿ harmonic-rejection (HR) techniques are presented to achieve high HR robust to mismatch: a) an analog two-stage polyphase HR concept, which enhances the HR to more than 60 dB; b) a digital adaptive interference cancelling (AIC) technique, which can suppress one dominating harmonic by at least 80 dB. An accurate multiphase clock generator is presented for a mismatch-robust HR. A proof-of-concept receiver is implemented in 65 nm CMOS. Measurements show 34 dB gain, 4 dB NF, and + 3.5 dBm in-band IIP3 while the out-of-band IIP3 is +16 dBm without fine tuning. The measured RF bandwidth is up to 6 GHz and the 8-phase LO works up to 0.9 GHz (master clock up to 7.2 GHz). At 0.8 GHz LO, the analog two-stage polyphase HR achieves a second to sixth order HR > 60 dB over 40 chips, while the digital AIC technique achieves HR > 80 dB for the dominating harmonic. The total power consumption is 50 mA from a 1.2 V supply.
We performed small-scale demonstrations at GSFC of high-resolution Xray TES microcalorimeters read out using a microwave SQUID multiplexer. This work is part of our effort to develop detector and ...readout technologies for future space-based X-ray instruments such as the microcalorimeter spectrometer envisaged for Lynx, a large mission concept under development for the Astro 2020 Decadal Survey. In this paper we describe our experiment, including details of a recently designed, microwave-optimized low-temperature setup that is thermally anchored to the 55mKstage of our laboratory ADR. Using aROACH2 FPGA at room temperature, we read out pixels of a GSFC-built detector array via a NIST-built multiplexer chip with Nb coplanar waveguide resonators coupled to rf-SQUIDs. The resonators are spaced 6 MHz apart (at ∼ 5.9 GHz) and have quality factors of ∼ 15,000. In our initial demonstration, we used flux-ramp modulation frequencies of 125 kHz to read out 5 pixels simultaneously and achieved spectral resolutions of 2.8-3.1 eV FWHM at 5.9 keV. Our subsequent work is ongoing: to-date we have achieved a median spectral resolution of 3.4 eV FWHM at 5.9 keV while reading out 28 pixels simultaneously with flux-ramp frequencies of 160 kHz. We present the measured system-level noise and maximum slew rates and briefly describe our future development work.
Current analog harmonic rejection mixers typically provide 30-40 dB of harmonic rejection, which is often not sufficient. We present a mixed analog-digital approach to harmonic rejection mixing that ...uses a digital interference canceler to reject the strongest interferer. Simulations indicate that, given a practical RF scenario, the digital canceler is able to improve the signal-to-interference ratio by 30-45 dB.
OBJECTIVES Conventional T2 weighted MRI studies have highlighted the fact that the presence of clinically silent brain lesions increases the risk of developing clinically definite multiple sclerosis ...after an isolated syndrome of the optic nerve, brain stem, or spinal cord. The objectives of the present study are: (1) to show whether or not these patients also have asymptomatic abnormalities of the spinal cord, and (2) to recruit a new cohort of such patients using high resolution MRI of both brain and spinal cord. METHODS The brain was imaged in the axial plane with 3 mm thick contiguous slices using a proton density and T2 weighted fast spin echo (FSE) sequence; a T1 weighted sequence after the injection of gadolinium-DTPA; and a fast fluid attenuated inversion recovery (fFLAIR) sequence. The spinal cord was imaged in the sagittal plane with 3 mm thick slices using a T2 weighted FSE and a T1 weighted gadolinium enhanced sequence. RESULTS Thirty three patients, mean age 31 (16–46) were recruited. There were 14 men and 19 women. Brain MRI was abnormal in 22 (67%); no patient was seen with abnormalities on only one or other sequence. Six patients (18%) displayed one or more gadolinium enhancing lesions on brain MRI. In the spinal cord, nine (27%) patients displayed one or more clinically silent lesions on FSE. Two patients showed one and two gadolinium enhancing lesions in the spinal cord respectively. CONCLUSION This high incidence of spinal cord lesions emphasises that asymptomatic demyelinating lesions may also involve clinically eloquent pathways. Follow up studies are required to determine their prognostic importance.
Objectives Peripherally inserted central catheters (PICCs) may be complicated by upper extremity (UE) superficial (SVT) or deep venous thrombosis (DVT). The purpose of this study was to determine ...current PICC insertion patterns and if any PICC or patient characteristics were associated with venous thrombotic complications. Methods All UE venous duplex scans during a 12-month period were reviewed, selecting patients with isolated SVT or DVT and PICCs placed ≤30 days. All UE PICC procedures during the same period were identified from an electronic medical record query. PICC-associated DVTs, categorized by insertion site, were compared with all first-time UE PICCs to determine the rate of UE DVT and isolated UE SVT. Technical and clinical variables in patients with PICC-associated UE DVT also were compared with 172 patients who received a PICC without developing DVT (univariable and multivariable analysis). Results We identified 219 isolated UE SVTs and 154 UE DVTs, with 2056 first-time UE PICCs placed during the same period. A PICC was associated with 44 of 219 (20%) isolated UE SVTs and 54 of 154 UE DVTs (35%). The rates of PICC-associated symptomatic UE SVT were 1.9% for basilic, 7.2% for cephalic, and 0% for brachial vein PICCs. The rates of PICC-associated symptomatic UE DVT were 3.1% for basilic, 2.2% for brachial, and 0% for cephalic vein PICCs (χ 2 P < .001). Univariate analysis of technical and patient variables demonstrated that larger PICC diameter, noncephalic insertion, smoking, concurrent malignancy, diabetes, and older age were associated with UE DVT ( P < .05). Multivariable analysis showed larger catheter diameter and malignancy were the only variables associated with UE DVT ( P < .05). Conclusions The incidence of symptomatic PICC-associated UE DVT is low, but given the number of PICCs placed each year, they account for up to 35% of all diagnosed UE DVTs. Larger-diameter PICCs and malignancy increase the risk for DVT, and further studies are needed to evaluate the optimal vein of first choice for PICC insertion.
A novel low-mast low-power terrestrial digital audio broadcasting (T-DAB) single frequency network topology is described and evaluated in this paper. For this purpose, a pilot network (band III and ...L-band) was constructed in Amsterdam, the Netherlands. The performance of the band III pilot network (channel 12B) is compared with the existing traditional high-power high-mast T-DAB network (channel 12C) of the public service broadcaster. An important goal is to investigate whether the pilot network can co-exist with an existing traditional T-DAB network. The field trial shows that a gap filler can effectively neutralize the adjacent channel interference of the pilot network on the existing T-DAB network. Moreover, the L-band pilot network is compared with both band III networks by assessing the indoor coverage of every network. For estimation of the indoor coverage, 34 objects were investigated. Both the indoor penetration loss for band III and L-band was determined for each object. Indoor coverage in a region is reached if 95% of the buildings or more have indoor coverage. Using this definition, the loss for band III is 21.6 dB and for L-band 24.6 dB. As a result we consider the indoor penetration loss values reported in literature as too optimistic. Also other parameters of the pilot network were measured, such as the frequency re-use distance.
The Spitzer Extended Deep Survey (SEDS) is a very deep infrared survey within five well-known extragalactic science fields: the UKIDSS Ultra-Deep Survey, the Extended Chandra Deep Field South, ...COSMOS, the Hubble Deep Field North, and the Extended Groth Strip. SEDS covers a total area of 1.46 deg super(2) to a depth of 26 AB mag (3sigma) in both of the warm Infrared Array Camera (IRAC) bands at 3.6 and 4.5 mum. Because of its uniform depth of coverage in so many widely-separated fields, SEDS is subject to roughly 25% smaller errors due to cosmic variance than a single-field survey of the same size. SEDS was designed to detect and characterize galaxies from intermediate to high redshifts (z = 2-7) with a built-in means of assessing the impact of cosmic variance on the individual fields. Because the full SEDS depth was accumulated in at least three separate visits to each field, typically with six-month intervals between visits, SEDS also furnishes an opportunity to assess the infrared variability of faint objects. This paper describes the SEDS survey design, processing, and publicly-available data products. Deep IRAC counts for the more than 300,000 galaxies detected by SEDS are consistent with models based on known galaxy populations. Discrete IRAC sources contribute 5.6 + or - 1.0 and 4.4 + or - 0.8 nW m super(-2) sr super(-1) at 3.6 and 4.5 mum to the diffuse cosmic infrared background (CIB). IRAC sources cannot contribute more than half of the total CIB flux estimated from DIRBE data. Barring an unexpected error in the DIRBE flux estimates, half the CIB flux must therefore come from a diffuse component.
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