Acceptable SNR Research Articles

VALIDATION OF 2HG-TARGETTED MR SPECTROSCOPY FOR IDENTIFYING IDH-MUTANT GLIOMAS

Abstract AIMS Diffuse gliomas, the most common adult primary brain tumour, are classified by their histological and molecular characteristics and genetic profile. Isocitrate dehydrogenase (IDH) mutant gliomas correlate with longer mean survival and progression-free survival time. In tumour cells, IDH mutations lead to metabolic changes and the production of oncometabolite 2-hydroxyglutarate (2HG). MR spectroscopy (MRS) can assess metabolic changes in disease states in-vivo and non-invasively. In this study, we demonstrate a validation pathway for two advanced MRS methods to be used as IDH-mutation biomarkers in clinic. METHOD Simulated, phantom, and healthy volunteer experiments were performed to optimise and validate three MRS sequences tuned for measuring 2HG. A PRESS sequence was used with TR/TE of 2500/97 ms aiming at the 2HG peaks around 2.25 ppm. An edited PRESS sequence, named MEGA-PRESS, tailored to 2HG 4.02 ppm peak was used with TR/TE of 3000/68 ms, 128 averages, and with editing pulses at 1.9 and 7.5 ppm. A long TE semi-LASER MRS sequence, with improved voxel localisation, was also used (TR/TE: 2500/110 ms). RESULTS Simulations were performed to find optimised sequence parameters and to develop basis sets for analysing the phantom and healthy volunteer acquisitions. Tumour-mimicking phantoms with variable concentrations of 2HG and cystathionine were created and validated with 800 MHz NMR spectroscopy. Phantoms were then used to assess the sensitivity and specificity of the MRS for 2HG and cystathionine. MEGA-PRESS proved Synthetic in-vivo 2HG spectra, combined from healthy volunteers and simulated or phantom-2HG spectra, were used to assess the spectral quality needed to reliably measure 2HG. CONCLUSION MEGA-PRESS proved to be the most robust MRS method and demonstrated accurate and precise measurement of phantom and synthetic 2HG with acceptable SNR. Clinical validation of the technique will need to be performed on LGG patient population, and the overall accuracy will be compared with patient IDH mutation status.

Performance analysis of 4QAM-OFDM-FSO link under rain weather conditions

Abstract Free space optical communication (FSO) is a technique based on transmission of data by propagating the light in free space. FSO is inexpensive, providing high data rates, high capacity, high security, and low power and uses the license free frequency spectrum. Nevertheless, FSO is still facing many problems such as bad weather conditions, atmospheric turbulence, and multipath fading. In this research work, orthogonal frequency division multiplexing (OFDM) FSO system is analyzed for low to heavy rain fall intensities. Different rain rates have been considered for low, moderate, heavy, very heavy, and torrential rains. For all the rain rates, a direct detection OFDM–FSO system and a coherent detection system have been simulated and results are compared. Analysis has been done on the basis of SNR, received power, and constellation diagrams. According to these parameters, link length of both the systems for different rain rates was found. Coherent detection is applied to improve the system sensitivity compared to conventional direct detection. In tropical regions where heavy rainfall is the main reason for the degradation of the system, the OFDM system with coherent detection can perform better with high data rates. Second, over a 11 km FSO, a 4-QAM wireless signal is successfully transmitted under very heavy rainfall conditions. The distance achieved by moderate and heavy rains is 25 km and 15.5 km with an acceptable SNR of 25 dB and a system sensitivity (received power) of −65.1 dBm.

Reliability of reward ERPs in middle-late adolescents using a custom and a standardized preprocessing pipeline.

Despite advantage of neuroimaging measures in translational research frameworks, less is known about the psychometric properties thereof, especially in middle‐late adolescents. Earlier, we examined evidence of convergent and incremental validity of reward anticipation and response event‐related potentials (ERPs) and here we examined, in the same sample of 43 adolescents (M age = 15.67 years; SD = 1.01; range: 14–18; 32.6% boys), data quality (signal‐to‐noise ratio [SNR]), stability (mean amplitude across trials), and internal consistency (Cronbach’s α and split‐half reliability) of the same ERPs. Further, because observed time course and peak amplitude of ERP grand averages and thus findings on SNR, stability, and internal consistency may depend on preprocessing method, we employed a custom and a standardized preprocessing pipeline and compared findings across those. Using our custom pipeline, reward anticipation components were stable by the 40th trial, achieved acceptable internal consistency by the 19th, and all (but the stimulus‐preceding negativity [SPN]) achieved acceptable SNR by the 41st trial. Initial response to reward components were stable by the 20th trial and achieved acceptable internal consistency by the 11th and acceptable SNR by the 45th trial. Difference scores had worse psychometric properties than parent measures. Time course and peak amplitudes of ERPs and thus results on SNR, stability, and internal consistency were comparable across preprocessing pipelines. In case of reward anticipation ERPs examined here, 41 trials (+4 artifacted and removed) and, in case of reward response ERPs, 45 trials (+5 artifacted) yielded stable and internally consistent estimates with acceptable SNR. Results are robust across preprocessing methods.

Differential Reflecting Modulation for Reconfigurable Intelligent Surface-Based Communications

Reconfigurable intelligent surface (RIS) based communications have emerged as a new paradigm. This letter proposes a differential reflecting modulation (DRM) scheme for RIS based communication systems. In DRM, information bits are jointly carried by the activation permutations of the reflecting patterns and the phases of the transmitted signals, leading to that DRM can work without any channel state information (CSI) at the transmitter, RIS or receiver. In other words, DRM can release the intricate and resource-consuming channel estimation in the transmission process. Simulation results show that the proposed DRM pays an acceptable SNR penalty compared to non-differential modulation with coherent detection.

Radio-Frequency Coil Array for Improved Concurrent Transcranial Magnetic Stimulation and Functional Magnetic Resonance Imaging.

To perform concurrent TMS-fMRI on difficult targets, such as the occipital lobe. a 3-channel flexible, thin RF coil was constructed that allows for whole head image coverage without impeding TMS placement. A custom MR-safe patient table which mates with typical 3T MR scanners was constructed for the purpose of face-down subject positioning to allow for access to posterior TMS targets. To counterbalance the loading effect of the TMS coil on the RF coil circuits "Dummy Loads" are introduced, which mimic the loading conditions of the TMS coil when it is not present. the designed RF coil performed as expected, achieving acceptable SNR values at depths equal to the center of the average human head, and high SNR values near the surface. The system allows for concurrent TMS-fMRI, targeting any area of the being while imaging the entire volume.

Physical-Layer Schemes for Wireless Coded Caching

We investigate the potentials of applying the coded caching paradigm in wireless networks. In order to do this, we investigate physical layer schemes for downlink transmission from a multiantenna transmitter to several cache-enabled users. As the baseline scheme, we consider employing coded caching on the top of max–min fair multicasting, which is shown to be far from optimal at high-SNR values. Our first proposed scheme, which is near-optimal in terms of DoF, is the natural extension of multiserver coded caching to Gaussian channels. As we demonstrate, its finite SNR performance is not satisfactory, and thus we propose a new scheme in which the linear combination of messages is implemented in the finite field domain, and the one-shot precoding for the MISO downlink is implemented in the complex field. While this modification results in the same near-optimal DoF performance, we show that this leads to significant performance improvement at finite SNR. Finally, we extend our scheme to the previously considered cache-enabled interference channels, and moreover we provide an ergodic rate analysis of our scheme. Our results convey the important message that although directly translating schemes from the network coding ideas to wireless networks may work well at high-SNR values, careful modifications need to be considered for acceptable finite SNR performance.

SERIAL transmit – parallel receive (STxPRx) MR imaging produces acceptable proton image uniformity without compromising field of view or SAR guidelines for human neuroimaging at 9.4 Tesla

PurposeNon-uniform B1+ excitation and high specific absorption rates (SAR) compromise proton MR imaging of human brain at 9.4 T (400.5 MHz). By combining a transmit/receive surface coil array using serial transmission of individual coils with a total generalized variation reconstruction of images from all coils, acceptable quality human brain imaging is demonstrated. MethodsB0 is shimmed using sodium MR imaging (105.4 MHz) with a birdcage coil. Proton MR imaging is performed with an excitation/receive array of surface coils. The modified FLASH pulse sequence transmits serially across each coil within the array thereby distributing SAR in time and space. All coils operate in receive mode. Although the excitation profile of each transmit coil is non-uniform, the sensitivity profile estimated from the non-transmit receive coils provides an acceptable sensitivity correction. Signals from all coils are combined in a total generalized variation (TGV) reconstruction to provide a full field of view image at maximum signal to noise (SNR) performance. ResultsHigh-resolution images across the human head are demonstrated with acceptable uniformity and SNR. ConclusionProton MR imaging of the human brain is possible with acceptable uniformity at low SAR at 9.4 Tesla using this serial excitation and parallel reception strategy with TGV reconstruction.

Higher-Order Motion-Compensation for In Vivo Cardiac Diffusion Tensor Imaging in Rats.

Motion of the heart has complicated in vivo applications of cardiac diffusion MRI and diffusion tensor imaging (DTI), especially in small animals such as rats where ultra-high-performance gradient sets are currently not available. Even with velocity compensation via, for example, bipolar encoding pulses, the variable shot-to-shot residual motion-induced spin phase can still give rise to pronounced artifacts. This study presents diffusion-encoding schemes that are designed to compensate for higher-order motion components, including acceleration and jerk, which also have the desirable practical features of minimal TEs and high achievable b-values. The effectiveness of these schemes was verified numerically on a realistic beating heart phantom, and demonstrated empirically with in vivo cardiac diffusion MRI in rats. Compensation for acceleration, and lower motion components, was found to be both necessary and sufficient for obtaining diffusion-weighted images of acceptable quality and SNR, which yielded the first in vivo cardiac DTI demonstrated in the rat. These findings suggest that compensation for higher order motion, particularly acceleration, can be an effective alternative solution to high-performance gradient hardware for improving in vivo cardiac DTI.

New Generation of Optical NoC System with Wireless CDMA Architecture

AbstractIn this paper, a new generation of Network-on-chip (NoC) system with CDMA code is proposed. A Bipolar CDMA code is used to provide a good system performance and to reduce MAI. Two structures of a detector are employed, which are the PIN and the APD detectors, while putting into consideration thermal noise. On one hand, we are proving, in this work, that system performance can achieve a good BER value in optical context with an acceptable node number. On the other hand, system bandwidth can reach 16 Gbit/s with an acceptable SNR compared to wired architecture.

Severe climate sway in coherent CDMA-OSSB-FSO transmission system

Free space optics (FSO) link at high transmission rate is delimited due to its perceptivity to diversified surroundings especially in hilly regions. A demonstration of CDMA-FSO coherent detection system is reported in this work to achieve a prolonged 10Gbps-FSO link with acceptable SNR under the impact profound haze, rain and fog environment. Further, the work is extended to weigh the proposed CO-CDMA-OSSB-FSO transmission system against OFDM-OSSB-FSO direct detection system [9,10].

Realization of free space optics with OFDM under atmospheric turbulence

Free space optics (FSO) technology provides a promising solution for future broadband networks, offering high data transmission compared to RF technology. This work is focused on investigating the performance of an FSO system with OFDM and QAM. A 10Gbps data stream is transmitted using a 4-level QAM sequence through the FSO system under different atmospheric conditions. Results indicate that the integration of SOA prolongs the maximum achievable distance with acceptable SNR to 185km under clear weather conditions whereas under atmospheric fog, the maximum distance is extended to 2.5km.

A Hybrid Radar-Camera Sensing System With Phase Compensation for Random Body Movement Cancellation in Doppler Vital Sign Detection

This paper presents a Doppler radar vital sign detection system with random body movement cancellation (RBMC) technique based on adaptive phase compensation. An ordinary camera was integrated with the system to measure the subject's random body movement (RBM) that is fed back as phase information to the radar system for RBMC. The linearity of the radar system, which is strictly related to the circuit saturation problem in noncontact vital sign detection, has been thoroughly analyzed and discussed. It shows that larger body movement does not necessarily mean larger radar baseband output. High gain configuration at baseband is required for acceptable SNR in noncontact vital sign detection. The phase compensation at radar RF front-end helps to relieve the high-gain baseband from potential saturation in the presence of large body movement. A simple video processing algorithm was presented to extract the RBM without using any marker. Both theoretical analysis and simulation have been carried out to validate the linearity analysis and the proposed RBMC technique. Two experiments were carried out in the lab environment. One is the phase compensation at RF front end to extract a phantom motion in the presence of another large shaker motion, and the other one is to measure the subject person breathing normally but randomly moving his body back and forth. The experimental results show that the proposed radar system is effective to relieve the linearity burden of the baseband circuit and help compensate the RBM.

Modeling and simulation of long reach high speed inter-satellite link (ISL)

A hybrid OFDM–IsOWC system incorporating diverse modulation schemes like optical double side band (ODSB), optical tandem side band (OTSB) and optical single side band (OSSB) is carried out to optimize a long reach high speed inter-satellite link (ISL) with acceptable SNR and BER. The proposed system is also reported under the influence of antenna efficiency and pointing error at varied values of power levels. Simulations point toward that the proposed hybrid OFDM–OSSB–IsOWC transmission system promises significantly enhanced ISL link compared to conventional IsOWC systems.

High speed, long reach OFDM-FSO transmission link incorporating OSSB and OTSB schemes

Free Space Optics (FSO) link is extremely responsive to the diverse climate state of affairs that bound the FSO range. A demonstration of fading resistant FSO system using a simulated test-bed employing OFDM scheme is reported in this work to realize the prolonged FSO link with acceptable SNR and BER with the highest stream rate of 5Gbps under the impact of diverse weather conditions. Simulations point toward that the proposed hybrid OFDM-FSO transmission system incorporating OTSB- and OSSB-schemes promises significantly enhanced FSO link compared to conventional FSO systems.

WE‐G‐WAB‐07: Commissioning of a Novel Integrated Platform for Online MRIgRT

Purpose: An integrated system for online MRIgRT comprising an MR scanner‐on‐rails proximal to a Varian TrueBeam linac is currently under installation at our institution. This study presents the development of a procedure to commission this platform along with the synthesis, testing, and validation of several unique tools/methods central to this challenging frontier. Methods: The commissioning procedure is organized into three phases: 1) the linac and a modified patient couch are commissioned in the absence of magnetic fields; 2) the MR magnet is energized, followed by experimental field mapping and verification of linac/couch performance proximal to the magnet; 3) MR imaging is evaluated and integrated guidance functionalities are tested. Novel methods/technologies embedded in these steps include: magnetic field finite element simulations to confirm magnetic decoupling of the MR scanner, linac, and couch; development of a novel harmonic distortion analysis/shim evaluation technique and associated phantom design incorporating comprehensive imaging QA; simulation of patient‐induced susceptibility distortions and pulse sequence optimization; development of a phantom/method to evaluate the accuracy/stability of MR scanner/couch travel. Results: The finite element simulations of the MRIgRT platform indicated acceptable magnetic forces on critical couch/linac components, undisturbed x‐ray beam production, and acceptable field uniformity within the MRI active volume (via active shimming). Validation of the harmonic distortion analysis demonstrated that complete volumetric mapping of the geometric distortion could be performed with an error bound by the imaging voxel size. Susceptibility‐induced distortions were simulated for various anatomical sites and can be reduced to within 1–2 mm by increasing the frequency encoding gradient strength with acceptable SNR losses. Lastly, the accuracy of translation and rotation measurements was established for evaluating MR scanner/couch travel. Conclusion: A comprehensive procedure has been established for the commissioning of an integrated MRIgRT platform, and various key tools/methods for assessing system performance have been developed and tested. J. Winter and L. Petropoulos are employees of IMRIS. J. Marle and M. Sweitzer are employees of Varian Medical Systems. IMRIS and Varian are companies co‐developing the MRgRT system. Funding for the MRgRT project at Princess Margaret Hospital was provided by the Canadian Foundation for Innovation.

자기공명영상장치에서 전자파흡수율 분석

본 연구는 자기공명영상장치의 특성변수인 숙임각(flip angle), 반복시간(repetition time, TR), 에코시간(echo time, TE)을 사용하여 전자파흡수율(specific absorption rate, SAR)을 알아보고자 하였다. 연구대상은 체중 10 kg부터 90 kg까지를 대상으로 하여 동일한 검사기법을 적용하였고, 매개변수의 변화에 따른 평균 SAR 및 peak SAR 값을 측정하였다. 체중에 따른 SAR는 TE에서 변화는 없지만 숙임각이 커지고 TR이 짧을수록 증가하였다. SAR 값은 두부 허용 기준치 범위에 포함이 되었고 분절별 체중에 따른 영상의 신호 대 잡음비(signal to noise ratio, SNR)는 체중이 증가함에 따라 SNR은 증가하지는 않았다. 본 결과를 바탕으로 적절한 특성변수를 사용하여 다양한 대조도와 SNR을 얻어 진단의 가치를 높일 수 있을 것이다. In this paper, we measured specific absorption rate (SAR) using characteristic variables such as flip angle, repetition time (TR) and echo time (TE) at magnetic resonance imaging. The subject was applied to same scan technique from body weight 10 kg to 90 kg, were measured for the average SAR and the peak SAR values according to the change of parameter. SAR with different body weight levels was not seen a significant change at TE but it increased in the larger flip angle and the shorter TR. SAR value was within the limits of human head acceptable standard and SNR in segmental body weights was not proportional to the increase of body weights. In conclusion, this study can be helpful for diagnosis by using appropriate parameters which obtained the various contrast and SNR.

Improved Fractional Channel Estimation for MIMO Systems in the Low SNR Regime

In this paper, we propose a novel fractional channel estimation technique for block faded MIMO systems. The existing channel estimation techniques perform the estimation in the time domain which is appropriate for acceptable SNR levels. At low SNR levels, noise which is a major source of errors cannot be separated effectively in time domain. However, fractional domain processing of signals has been shown to be effective in minimizing the errors due to noise. The signal which appears scattered in time domain due to noise appears to be compact in the optimum fractional domain where the effects of noise can be minimized. Based on this principle, a novel channel estimation algorithm is proposed for the low SNR applications. It is seen that the proposed technique clearly outperforms the existing channel estimation technique.DOI: http://dx.doi.org/10.5755/j01.eee.19.1.3259

Efficient DCT-based image compression technique

Although JPEG technique is considered as the most popular image compression standard, it behaves high visual degradation at low bit rates. In this paper, an efficient DCT–based image compression technique is proposed to achieve high Compression Ratio (CR) with high quality at both high and low bit rates. This technique uses switching between JPEG compression technique at high bit rates and a novel Adaptive Lossy Image Compression (ALIC) technique at low bit rates. ALIC is proposed to overcome the drawbacks of JPEG technique at low bitrates. The performance of the proposed technique is analysed at low and high bit rates on both grey and colour images. Performances of both JPEG and ALIC techniques are analysed and compared. The experimental results reveal that the proposed ALIC technique achieves better CR with acceptable SNR in comparison with JPEG technique. Also, the resultant CR of ALIC technique can be considerably increased with a slight decrease of its PSNR. This decrease in PSNR does not result in a noticeable visual degradation of the compressed image. On the other hand, increasing the CR of JPEG technique results in a noticeable visual degradation due to the appearance of blocking effect in the reconstructed image. Thus, it is greatly recommended to use ALIC technique in the applications that require high CR with stable PSNR. ALIC is a general purpose technique that can be applied, not only on images, but also on any data source which uses Huffman coding to achieve better CR. Therefore, it is suitable for compression of text, image and video.

Implementation of Hybrid OFDM-FSO Transmission System

novel design based on integration of OFDM and FSO system is reported in this work to prolong the FSO link at high transmission rate under clear weather conditions and evaluates the performance of such hybrid systems using ODSB, OSSB and OTSB schemes. Simulations indicate that the hybrid OFDM-FSO promises considerably improved free space link with acceptable SNR and BER compared to traditional FSO systems.

Assessment of Fiducial-based 2D kV Orthogonal Imaging, Fiducial-based CBCT, and Soft-tissue-based CBCT for Prostate Cancer Patients With Implanted Fiducial Markers

Purpose/Objective(s): To assess the geometric accuracy and imaging performance of a newly developed phased array coil system optimized for MR imaging of patients immobilized with the type S frame for head and neck radiation therapy. Materials/Methods: Protocol optimization for the novel coil was undertaken using a GE Optima450-GEM 70cm wide bore unit adapted for radiation therapy MR-SIM localization. Pulse sequence parameters for T1FSE, T2 FRFSE and T1 and T2 CUBE (including matrix, slice thickness, bandwidth) were optimized to maximize SNR while minimizing the effect of chemical shift. Phantom measurements were then performed to quantify system related residual geometric distortions after application of a 3D commercial gradient distortion correction algorithm for the effective FOV and the pulse sequences utilized. The optimized protocols were used to image seven volunteers positioned using an MR compatible type S system with neutral head supports. MRI images (from the base of brain to below the clavicles) were acquired using the novel phased array coil combination placed over the head, neck and thoracic region. The volunteers were re-imaged without immobilization in a standard diagnostic head coil, which served as the benchmark for image quality. Signal to noise, image homogeneity and image artifacts were compared between the two image datasets in a blinded study. Visibility of ten anatomical structures was evaluated. For statistical analysis, Cohen’s kappa, Wilcoxon matched pairs and t-testing were utilized. Results: A geometrically accurate, high resolution MR-SIM imaging protocol (T1/T2CUBE. 2D T1/T2 FSE) was developed with 3mm slice thickness/no gap that provides excellent image quality from the base of brain to below the clavicles in the treatment position. From phantom studies, residual distortions were found to be 1.0mm within a 10 cm radius and < 1.5 mm within a 15 cm radius of the scan centre. Using a RBWof 50-62.5 minimized chemical shift (<1mm within a 10cm radius) at 1.5T while providing acceptable SNR. The coil provided higher SNR values in all anatomical structures, but less uniformity than the standard diagnostic head coil (full comparative SNR/CNR/geometric data will be presented). No significant difference for image quality and artifacts were demonstrated between the coils in the blinded study. Conclusions: The novel open architecture purpose built phased coil array provides unparalleled coverage and good image quality of the subject immobilized for head and neck radiation therapy and is a promising solution for MR-SIM in the head and neck region. Author Disclosure: G. Perkins: None. R. Hammoud: None. S. Pienaar: None. S. Paloor: None. N. Al Hammadi: None.