The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform
O. Beuf - One of the best experts on this subject based on the ideXlab platform.
-
Design of a Four-Channel Surface Receiver Coil Array Without Preamplifiers for the Decoupling Between Elements: Validation for High-Resolution Rat Knee MR Imaging
IEEE Sensors Journal, 2013Co-Authors: A.-l. Perrier, J.-c. Goebel, Astrid Pinzano-watrin, Emilie Roeder, Pierre Gillet, Denis Grenier, O. BeufAbstract:In magnetic resonance imaging, multichannel coil arrays are increasingly being used to improve signal-to-noise ratio in order to increase spatial and/or temporal image resolution. A recent decoupling technique allows conception of two-channel surface transceiver coil arrays. This technique, based on a common conductor, does not require an additional preamplifier for the decoupling between elements. In this case, the coil array loops are directly connected to the independent transmit/receive switches and Preamplifiers of the MR system. Using this common conductor decoupling technique, a topology of a four-channel coil array is developed and described in this paper. A four-channel surface receiver coil array is designed to perform the simultaneous acquisition of both rat knee joints at 7 T. Without the use of additional Preamplifiers, a good decoupling between channels is obtained and very high spatial resolution 3-D images with a voxel size of $49\times 49\times 98~\mu{\rm m}^{3}$ is achieved in 1 h 22 min scan time. Acquisitions allow the quantification of cartilage morphological parameters such as thickness and volume.
-
Design of a Four-Channel Surface Receiver Coil Array Without Preamplifiers for the Decoupling Between Elements: Validation for High-Resolution Rat Knee MR Imaging
IEEE Sensors Journal, 2013Co-Authors: A.-l. Perrier, J.-c. Goebel, Astrid Pinzano-watrin, Emilie Roeder, Pierre Gillet, Denis Grenier, O. BeufAbstract:In Magnetic Resonance Imaging (MRI), multi-channel coil arrays are increasingly being used to improve Signal-to-Noise Ratio (SNR) in order to increase spatial and/or temporal image resolution. Recent decoupling technique allows conception of two-channel surface transceiver coil arrays; this technique based on common conductor does not require additional preamplifier for the decoupling between elements. In this case the coil array loops are directly connected to the independent transmit/receive switches and Preamplifiers of the MR system. Using this common conductor decoupling technique, a topology of a four-channel coil array was developed and described in this paper. A four-channel surface receiver coil array was designed to perform the simultaneous acquisition of both rat knee joints at 7T. Without the use of additional Preamplifiers, a good decoupling between channels was obtained and very high spatial resolution 3D images with a voxel size of 49 × 49 × 98 µm 3 were achieved in 1h22min scan time. Acquisitions allowed the quantification of cartilage morphological parameters such as thickness and volume
Maxim Zaitsev - One of the best experts on this subject based on the ideXlab platform.
-
Direct matching methods for coils and Preamplifiers in MRI.
Journal of Magnetic Resonance, 2018Co-Authors: Elmar Fischer, Jurgen Hennig, Maxim ZaitsevAbstract:Abstract In this paper, direct matching methods for coils and Preamplifiers in receiver arrays are presented. Instead of compensating the reactance of the input impedance of Preamplifiers, in our method, the reactance was used to resonate with the coil matching networks and thus to decouple the coils. Furthermore, coil matching networks and preamplifier input matching networks were combined, meaning the coil loop can be matched to the transistor in the preamplifier directly. These matching methods and, for comparison, the conventional matching method were implemented with custom-made Preamplifiers and coils. Decoupling and noise-matching performance were compared between these three configurations. Phase shifting networks between coils and Preamplifiers are not necessary in our matching methods. With fewer components, these matching networks showed lower noise factors, while similar preamplifier-decoupling performance was found for all three methods.
-
Design of a 3T preamplifier which stability is insensitive to coil loading.
Journal of Magnetic Resonance, 2016Co-Authors: Elmar Fischer, O. G. Gruschke, Jan G. Korvink, Jurgen Hennig, Maxim ZaitsevAbstract:In MRI (magnetic resonance imaging), Preamplifiers are needed to amplify signals obtained from MRI receiver coils. Under various loading conditions of the corresponding receiver coils, Preamplifiers see different source impedance at their input and may become unstable. Therefore Preamplifiers which stability is not sensitive to coil loading are desirable. In this article, a coil-loading-insensitive preamplifier for MRI is presented, derived from an unstable preamplifier. Different approaches to improve stability were used during this derivation. Since a very low noise factor is essential for MRI Preamplifiers, noise contributions from passive components in the MRI preamplifier have to be considered during the stabilization process. As a result, the initially unstable preamplifier became stable with regard to coil loading, while other MRI requirements, as the extremely low noise factor, were still fulfilled. The newly designed preamplifier was manufactured, characterized and tested in the MRI spectrometer. Compared to a commercially available preamplifier, the newly designed preamplifier has similar imaging performance but other advantages like smaller size and better stability. Furthermore, presented stabilization approaches can be generalized to stabilize other unstable low-noise amplifiers.
Vitaliy Zhurbenko - One of the best experts on this subject based on the ideXlab platform.
-
three element matching networks for receive only mri coil decoupling
Magnetic Resonance in Medicine, 2021Co-Authors: Wenjun Wang, Vitaliy Zhurbenko, Juan D Sanchezheredia, Jan Henrik ArdenkjaerlarsenAbstract:Purpose Preamplifier decoupling is useful for minimizing interaction between MRI array elements. The purpose of this work is to propose a general approach to designing networks for preamplifier decoupling while keeping the number of elements to a minimum. The approach is applicable to arbitrary impedance Preamplifiers and arbitrary coil impedances. Methods Closed form design equations for decoupling networks are derived based on maximum decoupling and minimum preamplifier noise conditions. The analytical solutions are verified using numerical simulations. Design examples at 32.1, 64, 128, and 298 MHz are shown. One of the examples is realized on a test bench. The fabricated circuit is tested for decoupling and minimum noise properties. Results The design equations are verified numerically and experimentally. The fabricated network demonstrates 30.7 dB of decoupling and minimum output noise at the design frequency. Conclusion The design equations lead to four alternative network solutions. Each network is realized as a T-shape or Π-shape three elements circuit topology. All four networks are identical in performance providing minimum amplifier noise and maximum decoupling for a given preamplifier and coil combination. An MRI array designer can choose any solution out of four. The considerations for choosing the most practical solution are given. The presented method enables the use of arbitrary impedance Preamplifiers or transistors (not necessary 50 Ω) and provides the most compact design possible (with the least number of components), which is particularly useful in multi-element systems.
-
Cryogenic Preamplifiers for Magnetic Resonance Imaging
IEEE Transactions on Biomedical Circuits and Systems, 2018Co-Authors: Daniel H. Johansen, Juan D. Sanchez-heredia, Jan R. Petersen, Vitaliy Zhurbenko, Tom K. Johansen, Jan Henrik Ardenkjaer-larsenAbstract:Pursuing the ultimate limit of detection in magnetic resonance imaging (MRI) requires cryogenics to decrease the thermal noise of the electronic circuits. As cryogenic coils for MRI are slowly emerging cryogenic Preamplifiers are required to fully exploit their potential. A cryogenic preamplifier operated at 77 K is designed and implemented for 13 C imaging at 3 T (32.13 MHz), using off-the-shelves components. The design is based on a high electron mobility transistor (ATF54143) in a common source configuration. Required auxiliary circuitry for optimal cryogenic preamplifier performance is also presented consisting of a voltage regulator (noise free supply voltage and optimal power consumption), switch, and trigger (for active detuning during transmission to protect the preamplifier). A gain of 18 dB with a noise temperature of 13.7 K is achieved. Performing imaging experiments in a 3 T scanner showed an 8% increased signal-to-noise ratio from 365 to 399 when lowering the temperature of the preamplifier from 296 to 77 K while keeping the coil at room temperature. This paper thus enables the merger of cryogenic coils and Preamplifiers in the hopes of reaching the ultimate limit of detection for MRI.
-
Towards new vistas in preamplifier design for MRI
2017 12th European Microwave Integrated Circuits Conference (EuMIC), 2017Co-Authors: Daniel H. Johansen, Juan D. Sanchez-heredia, Vitaliy Zhurbenko, Jan H. Ardenkjsr-larsenAbstract:High signal to noise ratio (SNR) in magnetic resonance imaging is vital for ensuring accurate diagnosis and treatment. Arrays of surface coils for receive only purposes is a well established way to increase SNR. However, due to crosstalk between the array elements, the SNR can be severely degraded. For that reason, arrays often do not exploit their full potential. By using a series decoupling network with non-conventional matching and preamplifier impedances the decoupling between elements can be increased significantly. In the presented design example, almost 6 dB additional decoupling can be achieved with no impairment of preamplifier noise figure. The decoupling changes as a function of both coil and preamplifier performance. Thus, the fundamental trade-off between noise and decoupling is discussed. This work embarks on the path towards new vistas in design of Preamplifiers for surface coil arrays for magnetic resonance imaging.
Tomasz Starecki - One of the best experts on this subject based on the ideXlab platform.
-
improving the signal to noise ratio of qtf Preamplifiers dedicated for qepas applications
Applied Sciences, 2020Co-Authors: Piotr Z Wieczorek, Tomasz Starecki, Frank K TittelAbstract:The signal-to-noise ratio (SNR) is a major factor that limits the detection sensitivity of quartz-enhanced photoacoustic spectroscopy (QEPAS) sensors. The higher the electrical signal level compared to the noise amplitude is the lower the concentration of gases that can be detected. For this reason the preamplifier circuits used in QEPAS should be optimized for low-frequency narrow-band applications. Moreover, special care should be taken when choosing a particular operational amplifier in either a transimpedance or voltage (differential) configuration. It turns out that depending on the preamp topology different operational amplifier parameters should be carefully considered when a high SNR of the whole QEPAS system is required. In this article we analyzed the influence of the crucial parameters of low-noise operational Preamplifiers used in QEPAS applications and show the resulting limitations of transimpedance and voltage configurations.
-
a high sensitivity preamplifier for quartz tuning forks in qepas quartz enhanced photoacoustic spectroscopy applications
Sensors, 2017Co-Authors: Tomasz Starecki, Piotr Z WieczorekAbstract:All the Preamplifiers dedicated for Quartz Enhanced PhotoAcoustic Spectroscopy (QEPAS) applications that have so far been reported in the literature have been based on operational amplifiers working in transimpedance configurations. Taking into consideration that QEPAS sensors are based on quartz tuning forks, and that quartz has a relatively high voltage constant and relatively low charge constant, it seems that a transimpedance amplifier is not an optimal solution. This paper describes the design of a quartz QEPAS sensor preamplifier, implemented with voltage amplifier configuration. Discussion of an electrical model of the circuit and preliminary measurements are presented. Both theoretical analysis and experiments show that use of the voltage configuration allows for a substantial increase of the output signal in comparison to the transimpedance circuit with the same tuning fork working in identical conditions. Assuming that the sensitivity of the QEPAS technique depends directly on the properties of the preamplifier, use of the voltage amplifier configuration should result in an increase of QEPAS sensitivity by one to two orders of magnitude.
-
Ultra-low-noise preamplifier for condenser microphones
Review of Scientific Instruments, 2010Co-Authors: Tomasz StareckiAbstract:The paper presents the design of a low-noise preamplifier dedicated for condenser measurement microphones used in high sensitivity applications, in which amplifier noise is the main factor limiting sensitivity of the measurements. In measurement microphone Preamplifiers, the dominant source of noise at lower frequencies is the bias resistance of the input stage. In the presented solution, resistors were connected to the input stage by means of switches. The switches are opened during measurements, which disconnects the resistors from the input stage and results in noise reduction. Closing the switches allows for fast charging of the microphone capacitance. At low frequencies the noise of the designed preamplifier is a few times lower in comparison to similar, commercially available instruments.
Kofi M. Odame - One of the best experts on this subject based on the ideXlab platform.
-
A Bandwidth-Adaptive Preamplifier
IEEE Journal of Solid-State Circuits, 2013Co-Authors: Dingkun Du, Kofi M. OdameAbstract:We propose an adaptive microphone preamplifier that adjusts its power consumption according to the input signal's bandwidth. A chip prototype of the adaptive preamplifier for speech processing was fabricated in a 0.5-μm CMOS process. The adaptive preamplifier's measured input referred noise is 3 μV rms and its total harmonic distortion is -40 dBc for an 80-mV rms input amplitude. These noise and distortion specifications remain virtually constant over the preamplifier's range of bandwidth adaptation. The adaptive preamplifier consumes 65 μW of power. This is achieved with no degradation in speech quality, when compared to a conventional preamplifier of fixed bandwidth, and as measured by the perceptual evaluation of speech quality (PESQ) score.
-
ISCAS - An adaptive microphone preamplifier for low power applications
2012 IEEE International Symposium on Circuits and Systems, 2012Co-Authors: Kofi M. OdameAbstract:In this paper, we present a microphone preamplifier that adapts its power consumption according to the input signal's instantaneous bandwidth. The preamplifier's dynamic range and gain keep reasonably constant, regardless of the power consumption. The preamplifier was fabricated with a 0.5-µm CMOS process. The measurement results show it has over 79.5-dB dynamic range with 53.4% power saving compared to its non-adaptive counterpart.