Increase In Signal-to-noise Ratio Research Articles

Integrating photoacoustic tomography into a multimodal automated breast ultrasound scanner.

.Significance: Photoacoustic tomography (PAT) is a promising emergent modality for the screening and staging of breast cancer. To minimize barriers to clinical translation, it is common to develop PAT systems based upon existing ultrasound hardware, which can entail significant design challenges in terms of light delivery. This often results in inherently non-uniform fluence within the tissue and should be accounted for during image reconstruction.Aim: We aim to integrate PAT into an automated breast ultrasound scanner with minimal change to the existing system.Approach: We designed and implemented an illuminator that directs spatially non-uniform light to the tissue near the acquisition plane of the imaging array. We developed a graphics processing unit-accelerated reconstruction method, which accounts for this illumination geometry by modeling the structure of the light in the sample. We quantified the performance of this system using a custom, modular photoacoustic phantom and graphite rods embedded in chicken breast tissue.Results: Our illuminator provides a fluence of at the tissue surface, which was sufficient to attain a signal-to-noise ratio (SNR) of 8 dB at 2 cm in chicken breast tissue and image 0.25-mm features at depths of up to 3 cm in a medium with moderate optical scattering. Our reconstruction scheme is faster than a CPU implementation; it provides a 25% increase in SNR at 2 cm in chicken breast tissue and lowers image error by an average of 31% at imaging depths compared with a method that does not account for the inhomogeneity of the illumination or the transducer directivity.Conclusions: A fan-shaped illumination geometry is feasible for PAT; however, it is important to account for non-uniform fluence in illumination scenarios such as this. Future work will focus on increasing fluence and further optimizing the ultrasound hardware to improve SNR and overall image quality.

The Sensitivity Improvement Characterization of Distributed Strain Sensors Due to Weak Fiber Bragg Gratings.

Weak fiber Bragg gratings (WFBGs) in a phase-sensitive optical time-domain reflectometer (phi-OTDR) sensor offer opportunities to significantly improve the signal-to-noise ratio (SNR) and sensitivity of the device. Here, we demonstrate the process of the signal and noise components’ formation in the device reflectograms for a Rayleigh scattering phi-OTDR and a WFBG-based OTDR. We theoretically calculated the increase in SNR when using the same optical and electrical components under the same external impacts for both setups. The obtained values are confirmed on experimental installations, demonstrating an improvement in the SNR by about 19 dB at frequencies of 20, 100, and 400 Hz. In this way, the minimum recorded impact (at the threshold SNR = 10) can be reduced from 100 nm per 20 m of fiber to less than 5 nm per 20 m of fiber sensor.

Restoration of the electrocardiogram during mechanical cardiopulmonary resuscitation

Objective: An artefact-free electrocardiogram (ECG) is essential during cardiac arrest to decide therapy such as defibrillation. Mechanical cardiopulmonary resuscitation (CPR) devices cause movement artefacts that alter the ECG. This study analyzes the effectiveness of mechanical CPR artefact suppression filters to restore clinically relevant ECG information. Approach: In total, 495 10 s ECGs were used, of which 165 were in ventricular fibrillation (VF), 165 in organized rhythms (OR) and 165 contained mechanical CPR artefacts recorded during asystole. CPR artefacts and rhythms were mixed at controlled signal-to-noise ratios (SNRs), ranging from –20 dB to 10 dB. Mechanical artefacts were removed using least mean squares (LMS), recursive least squares (RLS) and Kalman filters. Performance was evaluated by comparing the clean and the restored ECGs in terms of restored SNR, correlation-based similarity measures, and clinically relevant features: QRS detection performance for OR, and dominant frequency, mean amplitude and waveform irregularity for VF. For each filter, a shock/no-shock support vector machine algorithm based on multiresolution analysis of the restored ECG was designed, and evaluated in terms of sensitivity (Se) and specificity (Sp). Main results: The RLS filter produced the largest correlation coefficient (0.80), the largest average increase in SNR (9.5 dB), and the best QRS detection performance. The LMS filter best restored VF with errors of 10.3% in dominant frequency, 18.1% in amplitude and 11.8% in waveform irregularity. The Se/Sp of the diagnosis of the restored ECG were 95.1/94.5% using the RLS filter and 97.0/91.4% using the LMS filter. Significance: Suitable filter configurations to restore ECG waveforms during mechanical CPR have been determined, allowing reliable clinical decisions without interrupting mechanical CPR therapy.

Quality of service (QoS): measurements of image formats in social cloud computing

With the development of multimedia and the popularity of social cloud (SC), Quality of Service (QoS) is used to measure the technical parameters of service delivery. QoS is mostly used for measuring various kinds of multimedia data. Sharing (uploading) on SC has become the daily activity of end-users. As a result of this activity, it provides an open challenge for service providers. As a service provider, the host delivers productive infrastructure, allowing end-users to upload and share their high-quality images. To evaluate the QoS of image compression, we conduct objective QoS techniques to measure the efficiency of image quality and QoS performance of service delivery via uploading /downloading of images on three popular SC, (Facebook, Twitter, and Instagram). These social clouds and image services are compared by the mean, standard deviation (STDEV),mean square error (MSE), and signal-to-noise ratio (SNR). So we can achieve better results about the SC image quality. The results show that Instagram and Facebook compressed images more as compared to Twitter. However, Twitter less supports image formats and provides an acceptable quality of compressed images as compared to others. Therefore, Facebook supports all image file formats and enhanced (QoE) levels of end-users, but Twitter provided the best QoS of compressed images as compared to Instagram. Further, we found that the decrease of MSE and increase of SNR both have a high impact on image resolutions as compared to original image parameters, which has a higher effect on quality. For the specific quality assurance of image tasks acquired for robust automated image analysis research, we are also using deep learning techniques (DLT) to classify the quality of images. We also have identified the opportunity to simplify the Convolutional Neural network (CNN) with smaller resampling grids and making this process more suitable for at least five thousand (5000) of the enormous datasets available in the future.

High-sensitivity multispeckle diffuse correlation spectroscopy.

.Significance: Cerebral blood flow is an important biomarker of brain health and function as it regulates the delivery of oxygen and substrates to tissue and the removal of metabolic waste products. Moreover, blood flow changes in specific areas of the brain are correlated with neuronal activity in those areas. Diffuse correlation spectroscopy (DCS) is a promising noninvasive optical technique for monitoring cerebral blood flow and for measuring cortex functional activation tasks. However, the current state-of-the-art DCS adoption is hindered by a trade-off between sensitivity to the cortex and signal-to-noise ratio (SNR).Aim: We aim to develop a scalable method that increases the sensitivity of DCS instruments.Approach: We report on a multispeckle DCS (mDCS) approach that is based on a 1024-pixel single-photon avalanche diode (SPAD) camera. Our approach is scalable to independent speckle measurements since large-pixel-count SPAD cameras are becoming available, owing to the investments in LiDAR technology for automotive and augmented reality applications.Results: We demonstrated a 32-fold increase in SNR with respect to traditional single-speckle DCS.Conclusion: A mDCS system that is based on a SPAD camera serves as a scalable method toward high-sensitivity DCS measurements, thus enabling both high sensitivity to the cortex and high SNR.

Physical Layer Security Over Mixture Gamma Distributed Fading Channels With Discrete Inputs: A Unified and General Analytical Framework

Physical layer security is investigated over mixture Gamma (MG) distributed fading channels with discrete inputs. By the Gaussian quadrature rules, closed-form expressions are derived to characterize the average secrecy rate (ASR) and secrecy outage probability (SOP), whose accuracy is validated by numerical simulations. To show more properties of the finite-alphabet signaling, we perform an asymptotic analysis on the secrecy metrics in the large limit of the average signal-to-noise ratio (SNR) of the main channel. Leveraging the Mellin transform, we find that the ASR and SOP converge to some constants as the average SNR increases and we derive novel expressions to characterize the rates of convergence. This work establishes a unified and general analytical framework for the secrecy performance achieved by discrete inputs.

Imaging of Stroke in Rodents Using a Clinical Scanner and Inductively Coupled Specially Designed Receiver Coils.

Imaging of small laboratory animals in clinical MRI scanners is feasible but challenging. Compared with dedicated preclinical systems, clinical scanners have relatively low B0 field (1.5-3.0 T) and gradient strength (40-60 mT/m). This work explored the use of wireless inductively coupled coils (ICCs) combined with appropriate pulse sequence parameters to overcome these two drawbacks, with a special emphasis on the optimization of the coil passive detuning circuit for this application. A Bengal rose photothrombotic stroke model was used to induce cortical infarction in rats and mice. Animals were imaged in a 3T scanner using T2 and T1-weighted sequences. In all animals, the ICCs allowed acquisition of high-quality images of the infarcted brain at acute and chronic stages. Images obtained with the ICCs showed a substantial increase in SNR compared to clinical coils (by factors of 6 in the rat brain and 16-17 in the mouse brain), and the absence of wires made the animal preparation workflow straightforward.

Frontiers of Sodium MRI Revisited: From Cartilage to Brain Imaging.

Sodium magnetic resonance imaging (23Na‐MRI) is a highly promising imaging modality that offers the possibility to noninvasively quantify sodium content in the tissue, one of the most relevant parameters for biochemical investigations. Despite its great potential, due to the intrinsically low signal‐to‐noise ratio (SNR) of sodium imaging generated by low in vivo sodium concentrations, low gyromagnetic ratio, and substantially shorter relaxation times than for proton (1H) imaging, 23Na‐MRI is extremely challenging. In this article, we aim to provide a comprehensive overview of the literature that has been published in the last 10–15 years and which has demonstrated different technical designs for a range of 23Na‐MRI methods applicable for disease diagnoses and treatment efficacy evaluations. Currently, a wider use of 3.0T and 7.0T systems provide imaging with the expected increase in SNR and, consequently, an increased image resolution and a reduced scanning time. A great interest in translational research has enlarged the field of sodium MRI applications to almost all parts of the body: articular cartilage tendons, spine, heart, breast, muscle, kidney, and brain, etc., and several pathological conditions, such as tumors, neurological and degenerative diseases, and others. The quantitative parameter, tissue sodium concentration, which reflects changes in intracellular sodium concentration, extracellular sodium concentration, and intra–/extracellular volume fractions is becoming acknowledged as a reliable biomarker. Although the great potential of this technique is evident, there must be steady technical development for 23Na‐MRI to become a standard imaging tool. The future role of sodium imaging is not to be considered as an alternative to 1H MRI, but to provide early, diagnostically valuable information about altered metabolism or tissue function associated with disease genesis and progression.Level of Evidence1Technical Efficacy Stage1

A 32-channel receive array coil for bilateral breast imaging and spectroscopy at 7T.

This work describes the construction and evaluation of a bilateral 32-channel receive array for breast imaging at 7T. The receive array consisted of 32 receive coils, placed on two 3D-printed hemispherical formers. Each side of the receive array consisted of 16 receive loops, each loop having a corresponding detachable board with match/tune capacitors, active detuning circuitry, and a balun. Coil performance was evaluated on homogeneous canola oil phantoms using a Philips Achieva 7T system. Array coil performance was compared with a bilateral forced current excitation volume coil in transmit/receive mode and with a previously reported 16-channel unilateral coil with a similar design. The 32-channel array had an increase in average SNR throughout both phantoms by a factor of five as compared with the volume coil, with SNR increases up to 10 times along the periphery and three times in the center. Noise measurements showed low interelement noise correlation (average: 5.4%; maximum: 16.8%). Geometry factor maps were acquired for various acceleration factors and showed mean geometry factors<1.2, for combined acceleration factors of up to six. The improvements achieved demonstrate the clear potential for use in dynamic contrast-enhanced or diffusion-weighted MR studies, while maintaining diagnostically relevant spatial and temporal resolutions.

A variable resolution approach for improved acquisition of hyperpolarized 13 C metabolic MRI.

To ameliorate tradeoffs between a fixed spatial resolution and signal-to-noise ratio (SNR) for hyperpolarized 13 C MRI. In MRI, SNR is proportional to voxel volume but retrospective downsampling or voxel averaging only improves SNR by the square root of voxel size. This can be exploited with a metabolite-selective imaging approach that independently encodes each compound, yielding high-resolution images for the injected substrate and coarser resolution images for downstream metabolites, while maintaining adequate SNR for each. To assess the efficacy of this approach, hyperpolarized [1-13 C]pyruvate data were acquired in healthy Sprague-Dawley rats (n = 4) and in two healthy human subjects. Compared with a constant resolution acquisition, variable-resolution data sets showed improved detectability of metabolites in pre-clinical renal studies with a 3.5-fold, 8.7-fold, and 6.0-fold increase in SNR for lactate, alanine, and bicarbonate data, respectively. Variable-resolution data sets from healthy human subjects showed cardiac structure and neuro-vasculature in the higher resolution pyruvate images (6.0 × 6.0 mm2 for cardiac and 7.5 × 7.5 mm2 for brain) that would otherwise be missed due to partial-volume effects and illustrates the level of detail that can be achieved with hyperpolarized substrates in a clinical setting. We developed a variable-resolution strategy for hyperpolarized 13 C MRI using metabolite-selective imaging and demonstrated that it mitigates tradeoffs between a fixed spatial resolution and SNR for hyperpolarized substrates, providing both high resolution pyruvate and coarse resolution metabolite data sets in a single exam. This technique shows promise to improve future studies by maximizing metabolite SNR while minimizing partial-volume effects from the injected substrate.

Increased sensitivity and signal-to-noise ratio in diffusion-weighted MRI using multi-echo acquisitions

Post-mortem diffusion MRI (dMRI) enables acquisitions of structural imaging data with otherwise unreachable resolutions - at the expense of longer scanning times. These data are typically acquired using highly segmented image acquisition strategies, thereby resulting in an incomplete signal decay before the MRI encoding continues. Especially in dMRI, with low signal intensities and lengthy contrast encoding, such temporal inefficiency translates into reduced image quality and longer scanning times. This study introduces Multi Echo (ME) acquisitions to dMRI on a human MRI system - a time-efficient approach, which increases SNR (Signal-to-Noise Ratio) and reduces noise bias for dMRI images. The benefit of the introduced ME-dMRI method was validated using numerical Monte Carlo simulations and showcased on a post-mortem brain of a wild chimpanzee. The proposed Maximum Likelihood Estimation echo combination results in an optimal SNR without detectable signal bias. The combined strategy comes at a small price in scanning time (here 30% additional) and leads to a substantial SNR increase (here white matter: ~ 1.6x, equivalent to 2.6 averages, grey matter: ~ 1.9x, equivalent to 3.6 averages) and a general reduction of the noise bias.

Reducing Quantizer Distortion Due to Insufficient Resolution in Massive MIMO Receivers

Use of low-resolution (1-4 bits) Analog-to-Digital Converters (ADCs) can reduce power consumption in Massive Multiple-Input, Multiple-Output (MIMO) receivers. Ordinary linear beamforming may suffice for low-resolution ADCs under conditions on the Signal-to-Noise Ratio (SNR) and number of antennas that may be called low but sufficient resolution. However, if the SNR increases or number of antennas decreases, an error floor will typically occur. We introduce three low-complexity iterative algorithms to reduce quantization noise in such low but insufficient resolution cases. These algorithms process the raw quantizer outputs prior to detection, achieving up to two orders-of-magnitude reduction in Bit Error Rate (BER). Our algorithms are based on the new `equivalent model' for quantizers developed in our prior work. These algorithms can be applied to any number of bits and any modulation format. We focus on Orthogonal Frequency-Division Multiplexing (OFDM) to show that quantizer distortion can be corrected without going to the frequency domain.

Practical Recommendations for Hyperspectral and Thermal Proximal Disease Sensing in Potato and Leek Fields

Thermal and hyperspectral proximal disease sensing are valuable tools towards increasing pesticide use efficiency. However, some practical aspects of the implementation of these sensors remain poorly understood. We studied an optimal measurement setup combining both sensors for disease detection in leek and potato. This was achieved by optimising the signal-to-noise ratio (SNR) based on the height of measurement above the crop canopy, off-zenith camera angle and exposure time (ET) of the sensor. Our results indicated a clear increase in SNR with increasing ET for potato. Taking into account practical constraints, the suggested setup for a hyperspectral sensor in our experiment involves (for both leek and potato) an off-zenith angle of 17°, height of 30 cm above crop canopy and ET of 1 ms, which differs from the optimal setup of the same sensor for wheat. Artificial light proved important to counteract the effect of cloud cover on hyperspectral measurements. The interference of these lamps with thermal measurements was minimal for a young leek crop but increased in older leek and after long exposure. These results indicate the importance of optimising the setup before measurements, for each type of crop.

Combined Denoising and Suppression of Transient Artifacts in Arterial Spin Labeling MRI Using Deep Learning.

Arterial spin labeling (ASL) is a useful tool for measuring cerebral blood flow (CBF). However, due to the low signal-to-noise ratio (SNR) of the technique, multiple repetitions are required, which results in prolonged scan times and increased susceptibility to artifacts. To develop a deep-learning-based algorithm for simultaneous denoising and suppression of transient artifacts in ASL images. Retrospective. 131 pediatric neuro-oncology patients for model training and 11 healthy adult subjects for model evaluation. 3T / pseudo-continuous and pulsed ASL with 3D gradient-and-spin-echo readout. A denoising autoencoder (DAE) model was designed with stacked encoding/decoding convolutional layers. Reference standard images were generated by averaging 10 pairwise ASL subtraction images. The model was trained to produce perfusion images of a similar quality using a single subtraction image. Performance was compared against Gaussian and non-local means (NLM) filters. Evaluation metrics included SNR, peak SNR (PSNR), and structural similarity index (SSIM) of the CBF images, compared to the reference standard. One-way analysis of variance (ANOVA) tests for group comparisons. The DAE model was the only model to produce a significant increase in SNR compared to the raw images (P < 0.05), providing an average SNR gain of 62%. The DAE model was also effective at suppressing transient artifacts, and was the only model to show a significant improvement in accuracy in the generated CBF images, as assessed using PSNR values (P < 0.05). In addition, using data from multiple inflow time acquisitions, the DAE images produced the best fit to the Buxton kinetic model, offering a 75% reduction in the fitting error compared to the raw images. Deep-learning-based algorithms provide superior accuracy when denoising ASL images, due to their ability to simultaneously increase SNR and suppress artifactual signals in raw ASL images. 3 TECHNICAL EFFICACY STAGE: 1.

Clinical Value of Noncontrast-Enhanced Radial Quiescent-Interval Slice-Selective (QISS) Magnetic Resonance Angiography for the Diagnosis of Acute Pulmonary Embolism Compared to Contrast-Enhanced Computed Tomography and Cartesian Balanced Steady-State Free Precession.

Free-breathing noncontrast-enhanced (non-CE) magnetic resonance angiography (MRA) techniques are of considerable interest for the diagnosis of acute pulmonary embolism (APE), due to the possibility for repeated examinations, avoidance of side effects from iodine-based contrast agents, and the absence of ionizing radiation exposure as compared to CE-computed tomographic angiography (CTA). To analyze the clinical performance of free-breathing and electrocardiogram (ECG)-gated radial quiescent-interval slice-selective (QISS)-MRA compared to CE-CTA and to Cartesian balanced steady-state free precession (bSSFP)-MRA. Prospective. Thirty patients with confirmed APE and 30 healthy volunteers (HVs). Radial QISS- and bSSFP-MRA at 1.5T. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were computed to compare the pulmonary imaging quality between MRA methods. The pulmonary arterial tree was divided into 25 branches and an ordinal scoring system was used to assess the image quality of each pulmonary branch. The clinical performance of the two MRA techniques in accurately assessing APE was evaluated with respect to CE-CTA as the clinical reference standard. Wilcoxon signed-rank and Spearman's correlation tests were performed. Sensitivity and specificity of the MRA techniques were determined using CE-CTA as the clinical reference standard. Thrombus-mimicking artifacts appeared more frequently in lobar and peripheral arteries of patients with Cartesian bSSFP than with radial QISS-MRA (pulmonary trunk: 12.2% vs. 14.0%, P = 0.64; lobar arteries: 35.6% vs. 22.0%, P = 0.005, peripheral arteries: 74.4% vs. 49.0%, P < 0.001). The relative increases in SNR and of CNR provided by radial QISS-MRA with respect to Cartesian bSSFP-MRA were 30-35% (P-values of SNR/CNR, HVs: 0.09/0.09, patients: 0.03/0.02). The image quality of pulmonary arterial branches was considered good to excellent in 77.2% of patients with radial QISS-MRA and in 43.2% with Cartesian bSSFP-MRA (P < 0.0001). The clinical performance of radial QISS-MRA was higher than Cartesian bSSFP-MRA for grading embolism, with a total sensitivity of 86.0% vs. 80.6% and a specificity of 93.3% vs. 84.0%, respectively. Radial QISS-MRA is a reliable and safe non-CE angiographic technique with promising clinical potential compared to Cartesian bSSFP-MRA and as an alternative technique to CE-CTA for the diagnosis of APE. 1 TECHNICAL EFFICACY STAGE: 3.

Assessing spatial resolution, acquisition time and signal-to-noise ratio for commercial microimaging systems at 14.1, 17.6 and 22.3 T

This work provides a systematic comparison of the signal-to-noise ratio (SNR), spatial resolution, acquisition time and metabolite limits-of-detection for magnetic resonance microscopy and spectroscopy at three different magnetic field strengths of 14.1 T, 17.6 T and 22.3 T (the highest currently available for imaging), utilizing commercially available hardware. We find an SNR increase of a factor 5.9 going from 14.1 T to 22.3 T using 5 mm radiofrequency (saddle and birdcage) coils, which results in a 24-fold acceleration in acquisition time and deviates from the theoretically expected increase of factor 2.2 due to differences in hardware. This underlines the importance of not only the magnetic field strengths but also hardware optimization. In addition, using a home-built 1.5 mm solenoid coil, we can achieve an isotropic resolution of (5.5 µm)3 over a field-of-view of 1.58 mm × 1.05 mm × 1.05 mm with an SNR of 12:1 using 44 signal averages in 58 h 34 min acquisition time at 22.3 T. In light of these results, we discuss future perspectives for ultra-high field Magnetic Resonance Microscopy and Spectroscopy.

Performance Analysis of FBMC O-QAM System Using Varied Modulation Level

Communication channels that are affected by various disturbances will cause a high Bit Error Rate (BER). To maximize the performance of the channel in the future, Filter Bank Multicarrier (FBMC) technique is used as a renewal of Orthogonal Frequency Division Multiplexing (OFDM). FBMC has better spectrum efficiency properties due to the nature of orthogonality which only divides bandwidth for sub-channels. The purpose of the research was to knowing the performance of FBMC Offset QAM (FBMC O-QAM) which has a variation of modulation levels of 4-QAM, 16-QAM, and 64-QAM. The Zero Forcing (ZF) method is used to detect the original signal sent by the transmitting antenna. System performance in this study was measured by parameter Bit Error Rate (BER) and channel capacity. The results showed that the FBMC O-QAM system with ZF has decreased BER value on each modulation. At the time of modulation 4 QAM has a BER value of 0.0008945 with an SNR value of 20 dB. Modulation 16 QAM also experienced the same thing when the SNR value of 20 dB has BER value of 0.001856, and at modulation 64 QAM has BER value of 0.01766 at a SNR of 20 dB. Besides decreasing the BER parameters, the FBMC O-QAM ZF system has own characterize in channel capacity. For the 4-QAM has 4.808 b/s/Hz, 16-QAM has 4.627 b/s/Hz, and 64-QAM has 3.903 b/s/Hz at SNR 20 dB. It conclude that 4-QAM has a best channel capacity enhancement. The value of channel capacity generated based on simulations using Zero Forcing shows an increase in value along with an increase in SNR, but has a smaller value compared to channel capacity in theory.

A Frequency Translation System for Multi-Channel, Multi-Nuclear MR Spectroscopy.

Most MRI scanners are equipped to receive signals from 1H array coils but few support multi-channel reception for other nuclei. Using receive arrays can provide significant SNR benefits, usually exploited to enable accelerated imaging, but the extension of these arrays to non-1H nuclei has received less attention because of the relative lack of broadband array receivers. Non-1H nuclei often have low sensitivity and stand to benefit greatly from the increase in SNR that arrays can provide. This paper presents a cost-effective approach for adapting standard 1H multi-channel array receivers for use with other nuclei - in this case, 13C. A frequency translation system has been developed that uses active mixers residing at the magnet bore to convert the received signal from a non-1H array to the 1H frequency for reception by the host system receiver. This system has been demonstrated at 4.7T and 7T while preserving SNR and isolation. 1H decoupling, particularly important for 13C detection, can be straightforwardly accommodated. Frequency translation can convert 1H-only multi-channel receivers for use with other nuclei while maintaining SNR and channel isolation while still enabling 1H decoupling. This work allows existing multi-channel MRI receivers to be adapted to receive signals from nuclei other than 1H, allowing for the use of receive arrays for in vivo multi-nuclear NMR.

Increased SNR in acousto-optic imaging via coded ultrasound transmission.

Acousto-optic imaging (AOI) is a non-invasive method that uses acoustic modulation to map the light fluence inside biological tissue. In many AOI implementations, ultrasound pulses are used in a time-gated measurement to perform depth-resolved imaging without the need for mechanical scanning. However, to achieve high axial resolution, it is required that ultrasound pulses with few cycles are used, limiting the modulation strength. In this Letter, we develop a new approach to pulse-based AOI in which coded ultrasound transmission is used. In coded-transmission AOI (CT-AOI), one may achieve an axial resolution that corresponds to a single cycle, but with a signal-to-noise ratio (SNR) that scales as the square root of the number of cycles. Using CT-AOI with 79 cycles, we experimentally demonstrate over four-fold increase in SNR in comparison to a single-cycle AOI scheme.

The speech intelligibility and applicability of the speech transmission index in large spaces

This paper aims to explore the influence factors of speech intelligibility and the applicability of the speech transmission index (STI) in large spaces, where the sound energy is unevenly distributed and non-exponentially decays. The subjective speech intelligibility tests were conducted in Mandarin (China mainland) in two large spaces with volumes of 97,000 m3 and 246,000 m3. Objective indicators such as the Reverberation Time (RT), Early Decay Time (EDT), Definition (D50), and Speech Transmission Index (STI) under different signal-to-noise ratio (SNRs) were also measured in these two spaces. The results showed that both the SNR and room acoustics had significant effect on the speech intelligibility in these two spaces, but the effect of room acoustics on speech intelligibility was also affected by SNR. The speech intelligibility scores significantly increased with the increase in SNR when the SNR was less than 14.4 dB. In terms of room acoustics, D50 was more relevant to speech intelligibility than RT and EDT in these two large spaces when SNR ranged from −5dB to 15 dB. The STI value in large spaces should not be used as in ordinary spaces to evaluate the speech intelligibility. Based on the tests in this paper, the corresponding relation between STI and speech intelligibility in large spaces was modified, and a new rating threshold of STI was also proposed according to the revised relation, which indicated a necessity to modify the rating criteria of using STI to predict speech intelligibility in large spaces.