Multicarrier Approaches for High-Baudrate Optical-Fiber Transmission Systems with a Single Coherent Receiver

In this paper, we show the remarkable timing error (TE) and residual chromatic dispersion (CD) tolerance improvements of the filter bank multicarrier (FBMC) over orthogonal frequency division multiplexing (OFDM) for high-baudrate spectral slicing transmitter and single coherent receiver transmissions. For a 512 Gb/s 16 quadrature amplitude modulated (16QAM) spectrum slicing system at 1600 km of fiber transmission, the FBMC-based system reduces TE and residual CD penalties by more than 1.5 dB and 3 dB, in comparison to the OFDM-based system, respectively

The use of dynamic tracer concentration in veins for quantitative DCE-MRI kinetic analysis in head and neck.

BACKGROUND: Head and neck Magnetic Resonance (MR) Images are vulnerable to the arterial blood in-flow effect. To compensate for this effect and enhance accuracy and reproducibility, dynamic tracer concentration in veins was proposed and investigated for quantitative dynamic contrast-enhanced (DCE) MRI analysis in head and neck. METHODOLOGY: 21 patients with head and neck tumors underwent DCE-MRI at 3T. An automated method was developed for blood vessel selection and separation. Dynamic concentration-time-curves (CTCs) in arteries and veins were used for the Tofts model parameter estimations. The estimation differences by using CTCs in arteries and veins were compared. Artery and vein voxels were accurately separated by the automated method. Remarkable inter-slice tracer concentration differences were found in arteries while the inter-slice concentration differences in veins were moderate. Tofts model fitting by using the CTCs in arteries and veins produced significantly different parameter estimations. The individual artery CTCs resulted in large (>50% generally) inter-slice parameter estimation variations. Better inter-slice consistency was achieved by using the vein CTCs. CONCLUSIONS: The use of vein CTCs helps to compensate for arterial in-flow effect and reduce kinetic parameter estimation error and inconsistency for head and neck DCE-MRI

Decreases in molecular diffusion, perfusion fraction and perfusion-related diffusion in fibrotic livers: a prospective clinical intravoxel incoherent motion MR imaging study.

PURPOSE: This study was aimed to determine whether pure molecular-based diffusion coefficient (D) and perfusion-related diffusion parameters (perfusion fraction f, perfusion-related diffusion coefficient D*) differ in healthy livers and fibrotic livers through intra-voxel incoherent motion (IVIM) MR imaging. MATERIAL AND METHODS: 17 healthy volunteers and 34 patients with histopathologically confirmed liver fibrosis patients (stage 1 = 14, stage 2 = 8, stage 3 & 4 = 12, METAVIR grading) were included. Liver MR imaging was performed at 1.5-T. IVIM diffusion weighted imaging sequence was based on standard single-shot DW spin echo-planar imaging, with ten b values of 10, 20, 40, 60, 80, 100, 150, 200, 400, 800 sec/mm2 respectively. Pixel-wise realization and regions-of-interest based quantification of IVIM parameters were performed. RESULTS: D, f, and D* in healthy volunteer livers and patient livers were 1.096±0.155 vs 0.917±0.152 (10(-3) mm2/s, p = 0.0015), 0.164±0.021 vs 0.123±0.029 (p<0.0001), and 13.085±2.943 vs 9.423±1.737 (10(-3) mm2/s, p<0.0001) respectively, all significantly lower in fibrotic livers. As the fibrosis severity progressed, D, f, and D* values decreased, with a trend significant for f and D*. CONCLUSION: Fibrotic liver is associated with lower pure molecular diffusion, lower perfusion volume fraction, and lower perfusion-related diffusion. The decrease of f and D* in the liver is significantly associated liver fibrosis severity

Blood Vessel Extraction and Labeling.

<p>(a) Arteries and veins labeled by the automated vessel extraction method. The isolated vertebral artery voxel (the yellow arrow) was excluded from the vessel extraction due to its proneness to partial volume effect. (b) The dynamic peak times for artery and vein voxels in image slices. The average peak time of arteries appeared around 7.5 s earlier than veins.</p

Comparison of Fitting Result in Primary Tumors and Metastatic Nodes.

<p>The Tofts model fitting results by using the slice-averaged dynamic CTCs in arteries and veins in primary tumors (a) and metastatic nodes (b). Except for k_ep, significant differences were found in the estimations of K^trans, v_e and v_p by using the dynamic CTCs in arteries and veins.</p

Inter-slice Variations of Consentration-time-curves in Arteries and Veins.

<p>(a) The dynamic concentration-time curves (CTCs) in arteries for image slices. The remarkable inter-slice concentration consistency was resulted by the severe in-flow effect. (b) Relatively consistent dynamic CTCs in veins. (c) The averaged dynamic CTCs in arteries and veins along with the time shifted CTC in veins with the peak time aligned to the peak time in arteries. The tracer concentration in arteries may be significantly underestimated due to the in-flow effect.</p

Inter-slice Variations of Intensity-time-curves in Arteries and Veins.

<p>(a) The dynamic intensity-time-curves (ITCs) in artery voxels for image slices. Severe in-flow effect resulted in the inter-slice ITC differences. (b) The dynamic ITCs in vein voxels for image slices. Inter-slice ITC differences were moderate due to the reduced in-flow effect in veins. (c) The baseline and peak intensities in arteries and veins for image slices. The baseline intensity in arteries decreased by a factor of two with the ascending image slices.</p

Kinetic Parameter Maps within a Metastatic Node.

<p>The kinetic parameter maps (goodness of fit R²> = 0.8) within a metastatic node overlaid on the first time point DCE image by using the slice-averaged CTCs in arteries (first row) and veins (second row).</p