Quantitative assessment of portal hypertension with bi-parametric dual-frequency hepatic MR elastography in mouse models.

OBJECTIVES: To determine the potential of bi-parametric dual-frequency hepatic MR elastography (MRE) for predicting portal pressure (PP) in mouse models of portal hypertension (PHTN) with the presence of varying hepatic fibrosis. METHODS: We studied 73 wild-type male mice, including 22 mice with hepatic congestion, 20 mice with cholestatic liver injury, and 31 age-matched sham mice. Hepatic shear stiffness (SS) and volumetric strain (VS) were calculated by 3D MRE acquired at 80 and 200 Hz. We measured PP immediately after MRE. Liver fibrosis was verified by hydroxyproline assay. We predicted PP by fitting generalized linear models with single- and dual-frequency SS and VS, respectively. The relationship between predicted and actual PP was evaluated by Spearman's correlation. We compared the prediction accuracy of portal hypertension for all models with DeLong tests at a significance level of 0.05. RESULTS: Animals with congestive or cholestatic liver disease developed significant PHTN and hepatic fibrosis to varying degrees. In both models, SS increased, while VS decreased significantly compared with shams. All bi-parametric models had high diagnostic accuracy for PHTN. The dual-frequency models (AUCs: 0.90 [81-95%], 0.91 [81-95%]) had substantially or significantly higher accuracy than single-frequency ones (AUCs: 0.83 [71-91%], and 0.78 [66-87%]). The predicted PP of dual-frequency models also showed stronger correlations with actual PP than single-frequency predictions. CONCLUSIONS: The bi-parametric dual-frequency model improved the diagnostic accuracy of liver MRE in diagnosing PHTN in preclinical models. This technical advance has the potential to monitor PHTN progression and treatment efficacy in the presence of varying fibrosis. KEY POINTS: • Bi-parametric hepatic MR elastography can predict portal pressure. • The prediction models of shear stiffness and volumetric strain with dual-frequency measurements demonstrate high diagnostic accuracy (AUCs > 0.9) in two different portal hypertension mouse models with varying fibrosis.

Cost effective wavelength reused MDM system for bidirectional mobile fronthaul.

In this paper, we propose a cost-effective wavelength-reused mode-division-multiplexing (MDM) system for high speed symmetrical bidirectional mobile fronthaul application. At the base band unit (BBU) pool, one of the spatial modes is used to transmit signal carrier while the others are used for downstream (DS) signal channels. At the remote radio unit (RRU) side, the signal carrier is split and reused as modulation carrier for all the upstream (US) signal channels after mode demultiplexing. Thanks to the low mode crosstalk characteristic of the mode multiplexer/demultiplexer (MUX/DEMUX) and few-mode fiber (FMF), the signal carrier and each signal channel can be effectively separated. The spectral efficiency (SE) is significantly enhanced when multiple spatial channels are used. Compared with other wavelength reused scheme in which the downstream and upstream be modulated in orthogonal dimension, the modulation format of both directions are independent in the proposed wavelength reused MDM system. Therefore, it can easily achieve symmetrical bidirectional transmission without residual re-modulation crosstalk. The proposed scheme is scalable to multi-wavelength application when wavelength MUX/DEMUX is utilized. With the proposed scheme, we demonstrate a proof of concept intensity modulated 4 × 25-Gb/s 16-QAM orthogonal frequency division multiplexing (OFDM) transmission over 10-km FMF using low modal-crosstalk two-mode FMF and MUX/DEMUX with error free operation. The downstream receiver sensitivity is -21 dBm while the upstream receiver sensitivity is -18 dBm for bidirectional transmission. Due to the Rayleigh backscattering and other spurious reflections, the upstream suffers 2 dB power penalty compared with unidirectional transmission without downstream. To mitigate bidirectional transmission impairments, we propose a simple and effective method to suppress Rayleigh backscattering by shifting the downstream subcarrier frequency. A receiver sensitivity improvement of up to 2.5 dB is achieved for upstream with different downstream power.