35 results about "Partial fourier" patented technology

The invention relates to a Fourier parallel magnetic resonance imaging method based on a one-dimensional part of a deep convolutional network, and belongs to the technical field of magnetic resonance imaging. The method comprises the following steps: a sample set for training and a sample label set are created; an initial deep convolutional network is built; a training sample of the sample set is input into an initial deep convolutional network model to perform forward propagation, an output result of the forward propagation is compared with an expect result in the sample label set, and training is performed using a gradient descent algorithm until various layer parameters maximizing the consistency between the output result and the expect result are obtained; an optimal deep convolutional network model is established by utilizing the obtained various layer parameters; and a multi-coil under-sampling image obtained through online sampling is input into the optimal deep convolutional network model, forward propagation is performed on the optimal deep convolutional network model, and a rebuilt single-channel whole-sampling image is output. A noise of the rebuilt image can be removed well, a magnetic resonance image having a good visual effect is rebuilt, and the Fourier parallel magnetic resonance imaging method has high practical value.

A system and method for reducing the scan time of an MR imaging system using a data acquisition technique that combines partial Fourier acquisition and compressed sensing includes a computer programmed to acquire a partial MR data set in k-space along a phase encoding direction, the data set having missing data in the phase encoding direction due to the omission of phase encoding steps. The computer is further programmed to generate an estimate of a reconstructed image, compensate the partial MR data set for the missing data, and reconstruct an MR image by iteratively minimizing the total squared difference between the k-space data of the estimate of the reconstructed image and the measured k-space data of the compensated partial MR data set.

A method for moving table MR imaging with partial Fourier imaging is disclosed. MR data is acquired from a subject to partially fill k-space. The partially filled k-space is then reconstructed to form an image space having a first resolution. The image space is then transformed back into k-space followed by additional processing of the transformed k-space into an image space having a second resolution. A system to implement such a method is also disclosed.

The invention discloses a method for processing Doppler expansion of underwater sound high-speed OFDM communication. The method relates to a Doppler estimation and compensation module, a channel estimation module based on compression sensing and a part fast Fourier transform demodulation module, wherein the key portion is the part fast Fourier transform demodulation module and output of the other two modules serves as input of the part fast Fourier transform demodulation module. According to the method for processing Doppler expansion of underwater sound high-speed OFDM communication, a traditional OFDM demodulation method is modified, part Fourier transform is firstly adopted to serve as a demodulation method and part of Doppler expansion can be eliminated in the process of demodulation; due to the fact that Doppler expansion is processed for twice, influence on signals by Doppler expansion can be reduced to a lower range and the method is particularly high in adaptation to a rapidly-changed underwater sound channel. Therefore, the high processing performance of Doppler expansion is achieved.

In a method and an apparatus for magnetic resonance guided high intensity focused ultrasound (HIFU), precise localization of the focal point of the HIFU is determined by imaging an examination subject in parallel with GRE sequences that respectively include a positive monopolar gradient pulse and a negative monopolar gradient pulse, that respectively encode the acoustic radiation force (ARF)-induced phase shift that is induced by the simultaneous activation of HIFU during the sequences. A GRE phase image is reconstructed from each acquisition sequence, and a difference image is formed between the two GRE phase images, from which the HIFU focal point is determined. An average image is formed of the two GRE phase images from which PRFS temperature map is determined simultaneously to ARFI map. The use of parallel imaging and the use of partial Fourier reconstruction for reconstructing the GRE phase images allows the data to be acquired sufficiently rapidly so as to minimize the adverse effect of tissue heating that occurs with conventional longer-duration, and repetitious, techniques.

An improved technique is described for acquiring MR image data such as needed for FSE-based Dixon imaging techniques. A gradient-induced echo shift is produced in the pulse sequences by a small gradient applied along the readout axis prior to a readout pulse. When necessary, another small pulse is applied along the readout axis, equal in area and opposite in polarity to the first, to compensate for the shifting effect. Similar pulses are applied for each acquisition window. While data with non-zero phase shifts between water and fat signals are collected as fractional echoes, no increase in echo spacing is necessary with the modified acquisition strategy. Images corresponding to different phase shifts are reconstructed using phase-sensitive partial Fourier reconstruction algorithms whenever necessary. These images are then used to separate different chemical species (such as water and fat) in the object to be imaged. Increased time efficiency is therefore achieved with the improved technique, with a significant reduction in degradation due to losses in slice coverage and increased image blurring and sensitivity to flow and motion due to T2-modulation along the echo train in conventional techniques.

In an imaging method and device for water/fat separation in MRI using a two-point Dixon FSE sequence, each refocusing RF pulse corresponds to two readout gradients of the same polarity, each being center-divided into a smaller rear part and a larger front part, and one rephasing gradient of opposite polarity. In running the FSE sequence, each echo signal acquired is subjected to an FFT, to reconstruct an image with water and fat in phase and an image with water and fat in opposed phases. Data of each echo signal are subjected to a partial Fourier transform; and the in-phase water/fat image and the opposite-phase water/fat image are subjected to a water/fat separation algorithm, to obtain a pure water image and a pure fat image.

The invention relates to a time domain channel estimation method of a multiple-input multiple-output orthogonal frequency-division multiplexing down system. A pilot frequency symbol sequence using orthogonal virtual pilot frequency symbol and code domain is assumed to be used; firstly, a receiving terminal estimates the frequency response of each sub-channel at the actual pilot frequency symbol sub-carrier; then, the channel estimation for the virtual pilot frequency symbol sub-carrier is obtained through the linear interpolation of channel estimation of adjacent symbols used for orthogonal frequency division; the received symbol is re-constructed by utilizing the virtual pilot frequency symbol and the channel estimation thereof, the impulse response estimation of each sub-channel is obtained by ranking the received symbol of the actual pilot frequency symbol sub-carrier in ascending order according to the index value of the sub-carrier and then applying the least square method for time domain regularization, and the channel estimation of all the pilot frequency symbol sub-carriers is obtained after partial Fourier transformation; and finally, the channel frequency response of each user data symbol sub-carrier is obtained through the linear interpolation of channel estimation of the pilot frequency symbol sub-carrier. The invention has the advantages that the channel estimation precision is high, and larger quantity of transmitting antenna can be supported.

A modulator and modulation method are provided, which output an OQAM multi-carrier signal. The method implements a step of transforming, from the frequency domain to the time domain, a set of M symbols of real data so as to output M transformed symbols. The complete transformation includes the following sub-steps: applying a partial Fourier transform to the set of M symbols of real data, outputting a first subset of C transformed symbols, where C is strictly less than M; and obtaining, from the first subset, a second subset of (M-C) transformed symbols that is complementary to the first subset.

Magnetic resonance (MR) data are acquired by applying magnetic fields to an examination region concurrent with stimulated echo signals, such that trajectories, which are not straight lines, are generated in k-space. For this purpose, sequence of RF pulses is applied to generate the stimulated echo signals in the examination object, undersampled MR measurement data are detected during reception of the stimulated echo signals in the at least two receiving coils, along the curved k-space trajectories, and fully sampled MR measurement are generated from the undersampled MR measurement data using sensitivity information of the at least two receiving coils. Alternatively, the MR measurement data are fully sampled in a central region of k-space, and a region outside the central region is not fully sampled, and a phase correction with a Partial Fourier technique is executed on the MR measurement data using fully sampled MR measurement data from the central region of k-space.

An asymmetric 3D shells k-space trajectory design with partial Fourier acceleration is described. A non-iterative homodyne reconstruction framework is also described.

The invention relates to an observation matrix construction method based on a low-coherence unit norm tight frame, and belongs to the technical field of signal processing, and the method comprises thesteps: S1, initializing an initial observation matrix phi 0 into a random part Fourier matrix, and enabling the initial observation matrix phi 0 to serve as an initial alpha tight frame F; s2, calculating a Gram matrix corresponding to the framework F, and projecting the matrix to a structure constraint set of a tight framework by using a contraction function to generate a new Gram matrix; s3, updating the Gram matrix through a weighted iteration process; s4, reducing the rank of the new Gram matrix, calculating the square root of the new Gram matrix, and finding out a tight frame closest toa unit norm tight frame; and S5, solving the optimal target function to obtain an observation matrix. According to the method, the mutual interference coefficient between the observation matrix and the sparse basis is reduced, the dependence degree on signal sparsity is reduced, the problem that an ETF frame is difficult to construct is avoided, the initial observation matrix is initialized into apart of Fourier matrix, the calculation complexity is reduced, and the pressure of storage and processing equipment is reduced.

The invention discloses a pilot design method in compressed sensing channel estimation and mainly solves the problem that an existing design method cannot obtain a comparatively-good pilot pattern in limited-time searches. The method includes the steps of firstly, selecting P carrier positions from N subcarriers of an orthogonal frequency division multiplexing (OFDM) system to serve as a pilot pattern S; secondly, calculating a partial Fourier matrix WL according to the subcarrier number N and the maximum multipath delay L in the system; thirdly, using a random searching method to optimize the pilot pattern S, that is to say, using the partial Fourier matrix WL to calculate a measuring matrix T to obtain an optimized pilot patter Smin serving as the final pilot design result. Compared with an existing pilot design method, the pilot design method has the advantages that the method is good in search stability, better pilot can be obtained, and the method can be used for compressed sensing channel estimation and offline calculation.