Radio frequency receiving device

A device for receiving RF signal is provided. The device includes a receiving component configured to receive a radio frequency (RF) signal and a sampling component configured to sample the RF signal. The sampling component may include a plurality of filters, a demultiplexer, a clock synthesizer, an analog-to-digital converter (ADC), and a digital signal processing device. The sampling component may obtain an intermediate frequency (IF) signal based on the plurality of filters, the demultiplexer, the clock synthesizer, the ADC, and the digital signal processing device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to International Application No. PCT/CN2017/072293, filed on Jan. 23, 2017, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure generally relates to radio frequency (RF) receiving device, and more particularly to a device for receiving or sampling RF signals from multiple nuclei in magnetic resonance imaging (MRI).

BACKGROUND

Magnetic resonance imaging (MRI) is a medical diagnostic technology that has been widely used for inspecting a patient body. Traditional MRI system generates a magnetic resonance (MR) image based on hydrogen nuclei. However, in recent years MR spectroscopic studies using multiple species of nuclei such as3He,7Li,13C,17O,19F,23Na,31P,129Xe, etc., is getting more and more attention. Accordingly, a device for sampling MR signals from multiple nuclei is in demand.

SUMMARY

In a first aspect of the present disclosure, a device for receiving an RF signal is provided. The device may include a receiving component configured to receive a radio frequency (RF) signal and a sampling component configured to sample the RF signal. The RF signal may have a center frequency and a bandwidth. The sampling component may include: a plurality of filters configured to filter the RF signal, a demultiplexer, a clock synthesizer, an analog-to-digital converter (ADC), and a digital signal processing device. Each of the plurality of filters may have a pass band. The demultiplexer may be connected between the receiving component and the plurality of filters. The demultiplexer may transmit, based on the center frequency and bandwidth of the RF signal and the pass band of the one filter of the plurality of filters, the RF signal to one filter of the plurality of filters, the pass band of the one filter including the center frequency and the bandwidth of the RF signal. The clock synthesizer may generate a first clock signal. The analog-to-digital converter (ADC) may sample the RF signal filtered by the plurality of filters based on the first clock signal, and convert the sampled RF signal into a digital signal. The digital signal processing device may be connected to the ADC. The digital signal processing device may perform in-phase/quadrature (I/Q) demodulation on the digital signal to obtain an intermediate frequency (IF) signal based on the first clock signal.

In some embodiments, the RF signal may originate from hydrogen nuclei or non-hydrogen nuclei in an imaged subject by magnetic resonance imaging (MRI).

In some embodiments, the receiving component may further include a first filter configured to filter the RF signal, and a first amplifier configured to amplify the RF signal. The first filter may include at least one of a band pass filter (BPF). In some embodiments, the BPF may include an inductor capacitor filter (LC filter) or a surface acoustic wave filter (SAW filter).

In some embodiments, the sampling component may further include a second amplifier. The second amplifier may be located or connected between the receiving component and the demultiplexer. The second amplifier may amplify the RF signal.

In some embodiments, the number of the plurality of filters may correlate with or correspond to the additive white noise introduced by the second amplifier.

In some embodiments, the plurality of filters may be configured as AAFs.

In some embodiments, the clock synthesizer may receive a second clock signal from a clock outside of the device.

In some embodiments, the clock synthesizer may include a phase-locked loop (PLL) for generating the first clock signal based on the second.

In some embodiments, the I/Q demodulation may be performed according to the first clock signal.

In some embodiments, an image or a spectrum may be generated based on the IF signal.

In some embodiments, generating the image or the spectrum based on the IF signal may further include generating k-space data based on the IF signal.

In some embodiments, the digital signal processing device may include a first channel configured to process a first digital signal to obtain a first intermediate frequency (IF) signal with a first bit-width; and a second channel configured to divide a second digital signal to obtain a third signal with a third bit-width and a fourth signal with a fourth bit-width and combine the third signal with the fourth signal to obtain a second IF signal with the first bit-width.

In a second aspect of the present disclosure, a digital signal processing device is provided. The digital signal processing device may include a first channel and a second channel. The first channel may process a first signal to obtain a first intermediate frequency (IF) signal with a first bit-width. The second channel may divide a second signal to obtain a third signal with a third bit-width and a fourth signal with a fourth bit-width; and combine the third signal with the fourth signal to obtain a second IF signal with the first bit-width.

In some embodiments, the first signal originates from hydrogen nuclei in an imaged subject by MRI.

In some embodiments, the second signal originates from non-hydrogen nuclei in the same imaged subject by MRI.

In some embodiments, the digital signal processing device may further include a band pass decimation filter configured to process the first signal to obtain a first IF signal.

In some embodiments, I/Q demodulation may be employed to divide the second signal into the third signal and the fourth signal.

In some embodiments, the digital signal processing device may further include a low pass decimation filter configured to perform the I/Q demodulation.

In some embodiments, the first bit-width may be extended from a fifth bit-width by adding one or more zeros after the least significant bit (LSB) of the first IF signal, or adding one or more signs before the most significant bit (MSB) of the first IF signal.

In some embodiments, each of the third bit-width and the fourth bit-width may equal to a half of the fifth bit-width.

In some embodiments, an image or a spectrum may be generated based on the first IF signal or the second IF signal.

In some embodiments, generating the image or the spectrum based on the first IF signal or the second IF signal may further include generating k-space data based on the first IF signal or the second IF signal.

In a third aspect of the present disclosure, a method for receiving and sampling digital signals is provided. The method may include receiving a FID signal; determining that the FID signal is a first signal originating from a first species of nuclei; in response to the determination that the FID signal is the first signal, processing the first signal originating from a subject to obtain a first IF signal with a first bit-width; determining that the FID signal is a second signal originating from a second species of nuclei; and in response to the determination that the FID signal is the second signal, dividing the second signal originating from the subject to obtain a third signal with a third bit-width and a fourth signal with a fourth bit-width; and combining the third signal with the fourth signal to obtain a second IF signal with the first bit-width.

In some embodiments, the processing the first signal comprising extending the first signal from a fifth bit-width to the first bit-width.

In some embodiments, the method may further include generating k-space data based on the first IF signal or the second IF signal.

In some embodiments, the method may further include generating an image based on the k-space data.

In some embodiments, the method may further include determining a spectrum of the frequencies of the FID signal.

In a fourth aspect of the present disclosure, a method for receiving and sampling digital signals is provided. The method may include receiving an RF signal, the RF signal having a center frequency and a bandwidth; and sampling the RF signal, the sampling the RF signal may include selecting, based on the center frequency and the bandwidth of the RF signal, a filter from a plurality of filters, the pass band of the filter including the center frequency and the bandwidth of the RF signal; filtering the RF signal using the selected filter; acquiring a first clock signal; sampling the filtered RF signal based on the first clock signal; converting the sampled RF signal into a digital signal; and processing the digital signal to obtain an IF signal based on the first clock signal

In some embodiments, the processing the digital signal to obtain an IF signal based on the first clock signal may include determining that the digital signal is a first signal originating from a first species of nuclei; in response to the determination that the digital signal is the first signal, processing the first signal originating from a subject to obtain the IF signal with a first bit-width; determining that the digital signal is a second signal originating from a second species of nuclei; and in response to the determination that the digital signal is the second signal, dividing the second signal originating from the subject to obtain a third signal with a third bit-width and a fourth signal with a fourth bit-width; and combining the third signal with the fourth signal to obtain the IF signal with the first bit-width.

In some embodiments, the processing the first signal may include extending the first signal from a fifth bit-width to the first bit-width.

In some embodiments, the method may further include generating k-space data based on the IF signal.

In some embodiments, the method may further include generating an image based on the k-space data.

In some embodiments, the method may further include determining a spectrum of the frequencies of the RF signal.

DETAILED DESCRIPTION

It will be understood that when a unit, module or block is referred to as being “on,” “connected to,” or “coupled to” another unit, module, or block, it may be directly on, connected or coupled to the other unit, module, or block, or intervening unit, module, or block may be present, unless the context clearly indicates otherwise. It will be understood that the connection or coupling between units, modules, or blocks is operable. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

The terminology used herein is for the purposes of describing particular examples and embodiments only, and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “include,” and/or “comprise,” when used in this disclosure, specify the presence of integers, devices, behaviors, stated features, steps, elements, operations, and/or components, but do not exclude the presence or addition of one or more other integers, devices, behaviors, features, steps, elements, operations, components, and/or groups thereof.

FIG. 1is a schematic diagram illustrating an exemplary networked environment100including an imaging system110according to some embodiments of the present disclosure. In some embodiments, imaging system110may be a magnetic resonance imaging (MRI) system. The present disclosure may be implemented on any suitable systems or devices containing a receiver for sampling RF signals of multiple frequencies, for example, an astronomical observation system, a petroleum or natural gas exploration system, etc.

As illustrated inFIG. 1, imaging system110may include an MRI scanner111and a computing device112. MRI scanner111may perform an MR scan on a subject, and acquire magnetic resonance (MR) signals based on the scan. The scanned subject may be a patient, an animal, a non-living sample, or the like. In some embodiments, MRI scanner111may perform the scan by applying a radio frequency (RF) pulse to the imaged subject (for example, a patient). When the frequency of the RF pulse equals to the Larmor frequency of certain nuclei, an MR signal may originate from the subject. As used herein, the Larmor frequency may refer to the frequency at which a nucleus spins. According to the intrinsic quantum property, different species of nuclei may spin at different frequencies. Exemplary species of nuclei may include hydrogen nuclei (1H), or non-hydrogen nuclei (such as3He,7Li,13C,17O,19F,23Na,31P,129Xe, etc.). As used herein, non-hydrogen nuclei may refer to one or more species of nuclei other than hydrogen nuclei. In some embodiments, the MR signal originating from the subject may include an RF signal. MRI scanner111may receive the RF signal by, for example, a coil element. The received RF signal may cause MRI scanner111to generate an intermediate frequency (IF) signal. The operation may include noise elimination, analog-to-digital conversion, sampling rate reduction, or the like.

In some embodiments, imaging system110may be a single-modality system. For instance, imaging system110may include MRI scanner111. In some embodiments, imaging system110may be a multi-modality system including, e.g., a positron emission tomography-magnetic resonance imaging (PET-MRI) scanner, a single photon emission computed tomography-magnetic resonance imaging (SPECT-MRI) scanner, etc.

Computing device112may receive the IF signal from MRI scanner111to reconstruct an image. In some embodiments, computing device112may process the IF signal before image reconstruction. For instance, k-space data may be generated based on the IF signal before image reconstruction. In some embodiments, computing device112may include an operation console. Via the operation console, a user may control MRI scanner111to perform an MR scan. In some embodiments, computing device112may process other information. For example, computing device112may execute instructions for image reconstruction or signal processing that may relate to routines, programs, procedures, data structures, etc.

Computing device112may include a computer, a server, etc. In some embodiments, computing device112may be any of these devices that include suitable components such as a processor (for example, a microprocessor, a digital signal processor, a controller, etc.), a memory, a communication port, an input/output (for example, a touch screen), etc.

Imaging system110be may be connected to a network120. Network120may be a wireless network (e.g., Bluetooth, WLAN, WiMax, etc.), a mobile network (e.g., 2G, 3G, 4G signals, etc.), a virtual private network (VPN), a shared network, a near field communication (NFC), ZIGBEE, a telephone network, a metropolitan area network, a public switched telephone network (PSTN), etc., It should be noted that other known communication networks or methods which provide a medium for transmitting data between separate devices are also contemplated. Via network120, imaging system110may connect to a storage130, a server140, and one or more terminal devices150through a wired connection or a wireless connection, or a combination of both. In some embodiments, computing device112may connect to MRI scanner111via network120.

Storage130may store an image and/or other relevant information of imaging system110. For example, the stored information may include health history information of a patient, images of a patent's organ, scanning parameters of the MRI scanner, image processing techniques used by, for example, computing device112, etc. In some embodiments, storage130may be a database. The database may include a hierarchical database, a network database, a relational database, or the like, or a combination thereof. In some embodiments, the storage may be implemented by a device for storing information, such as a random access memory (RAM), a CD-ROM, a flash memory, a hard disk, a read only memory (ROM), or the like, or a combination thereof.

Server140may have storage capacities and/or computation capacities. Server140may store MRI images and/or other relevant information of the imaging system110, and/or process the stored information. Server140may be of various types. For example, server140may be an application server, a catalog server, a computing server, a file server, media server, etc. In some embodiments, server140may be a file server configured to store the MR images. In some embodiment, server140may be a computing server configured to process the MR images. For example, server140may reconstruct an image based on the data acquired from the MRI scanner111. As another example, server140may render the reconstructed image and send it to the computing device112or terminal devices150, via network120. Server140may be centralized or distributed. Server140may be a local one or a remote one. Merely by way of example, server140may include a cloud server.

Terminal devices150may communicate with imaging system110, storage130, and/or server140via network120. Terminal device150may include a laptop150-1, a mobile phone150-2, a tablet computer150-3, a wearable device (not shown in the figure), etc. In some embodiments, terminal devices150may be used, by a user (for example, a patient, a doctor, an imaging specialist), to acquire MR images from imaging system110, storage130, or server140. In some embodiments, a user may input control information via terminal devices150to control the operation of imaging system110. For example, a user may input designated control information via the terminal devices150to control the scanning process, data storage, and/or image processing of imaging system110. The input information received by imaging system110may be transmitted to the computing device112for further processing.

It should be noted that the above description of imaging system110is merely provided for the purposes of illustration, and not intended to limit the scope of the present disclosure. For persons having ordinary skills in the art, multiple variations and modifications may be made under the teachings of the present disclosure. For example, the assembly and/or function of imaging system110may be varied or changed according to specific implementation scenarios. For example, storage130may be part of server140. However, those variations and modifications do not depart from the scope of the present disclosure.

FIG. 2is a schematic diagram illustrating an exemplary MRI scanner according to some embodiments of the present disclosure. MRI scanner111may include a pulse sequence generator210and a receiver220. Pulse sequence generator210may generate a pulse sequence for scanning a subject (for example, a patient). Exemplary pulse sequence may include spin echo (SE) sequence, fast spin echo (FSE) sequence, ultrashort echo-time (UTE) sequence, gradient echo (GRE) sequence, etc.

Pulse sequence generator210may generate an electromagnetic pulse. In some embodiments, the electromagnetic pulse may be an RF pulse. In some embodiments, the RF pulse may be of a certain frequency. If the frequency of the RF pulse equals to the Larmor frequency of one or more nuclei, resonance may be achieved. In some embodiments, an MR signal may originate from the patient based on the resonance. In some embodiments, the MR signal may be induced from hydrogen nuclei. In some embodiments, the MR signal may be induced from non-hydrogen nuclei.

A gradient magnetic field in different directions may be driven by gradient waveform generated by pulse sequence generator210. The gradient magnetic field may be used to encode the MR signal. In some embodiment, the MR signal may be encoded in a three-dimensional manner, for example, in an x direction, a y direction, and a z direction. The x direction, the y direction, and the z direction may be defined by imaging system110or a user.

Receiver220may receive an MR signal. In some embodiments, the MR signal may be an RF signal. In some embodiments, the RF signal may also be referred to as free induction decay (FID) signal. Receiver220may acquire the MR signal induced in, for example, a receiver coil. In some embodiments, receiver220may receive the MR signal from a specific part of the patient body, for example, the head, the arms, the carotid artery, the spine, etc. The MR signal originating from a part of the patient body may be induced in the receiver coil. The receiver coil may be a quadrature coil, a surface coil, a special coil, or the like, or any combination thereof. When the MR signal is received, a current signal or a voltage signal may be induced in the receiver coil accordingly.

Receiver220may also sample the received MR signal. Various sampling techniques may be applied for sampling the MR signal. Exemplary sampling techniques may include simple random sampling, stratified sampling, probability-proportional-to-size sampling, accidental sampling, cluster sampling, or the like, or any combination thereof. In some embodiments, one or more signal processing techniques may be applied during the sampling process. Exemplary signal processing techniques may include time-frequency analysis, differential equations, spectral estimation, a linear time-invariant system theory, a transform theory, or the like, or any combination thereof. In some embodiments, the sampling and/or signal processing techniques may be performed by one or more electronic devices or components. Merely by ways of example, the devices may include filters, analog-to-digital convertors (ADCs), signal compressors, digital signal processors (DSPs), amplifiers, or the like. In some embodiments, receiver220may further include other devices (for example, a clock synthesizer, a demultiplexer, a multiplexer, etc.) that may facilitate the MR signal sampling. In some embodiments, an IF signal may be generated by receiver220based on the received RF signal.

It should be noted that the above description of MRI scanner111is merely provided for the purposes of illustration, and not intended to limit the scope of the present disclosure. For persons having ordinary skills in the art, multiple variations and modifications may be made under the teachings of the present disclosure. For example, MRI scanner111may further include some other components, such as a patient positioning bed, a scanner driving device, etc. However, those variations and modifications do not depart from the scope of the present disclosure.

FIG. 3Ais a schematic diagram illustrating an exemplary computing device according to some embodiments of the present disclosure. Computing device112may include a processor310, a memory320, an input/output330and a communication port340.

Processor310may process received information. Process310may process information received from MRI scanner111, storage130, server140, or terminal devices150. In some embodiments, processor310may process information received from memory320, input/output330. The information may include MR signals, MR images, pulse sequences, instructions from a user, or the like, or any combination thereof. In some embodiments, processor310may process the MR signals received from MRI scanner111to reconstruct an image. Various operations may be performed by processor310to reconstruct an image. For example, the operations may include linear fitting, least squares operation, 2D Fourier transform (2D FT), Z-transform, Laplace transform, principle component analysis (PCA), nearest neighbor interpolation, regridding, iteration, or the like, or any combination thereof. In some embodiments, processor310may execute computer instructions. The computer instructions may relate to routines, programs, procedures, data structures, etc.

Processor310may be a microcontroller, a microprocessor, a reduced instruction set computer (RISC), an application specific integrated circuits (ASICs), an application-specific instruction-set processor (ASIP), a central processing unit (CPU), a graphics processing unit (GPU), a physics processing unit (PPU), a microcontroller unit, an advanced RISC machine (ARM), a programmable logic device (PLD), any circuit or processor capable of executing one or more functions, or the like, or any combinations thereof. In some embodiments, processor310may be a specially designed processor. For example, processor310may be a processor designed in according with the digital imaging and communications in medicine (DICOM) protocol.

Memory320may store the images or other information relating to imaging system110. Memory320may store information received from MRI scanner111, processor310, input/output330, or other devices connected to the imaging system110via network120. The information stored in memory320may include programs, software, algorithms, data, text, number, images, or the like, or a combination thereof. Exemplary algorithms may include recursion, a bisection algorithm, a divide and conquer algorithm, a dynamic programming technique, an iterative algorithm, a branch-and-bound algorithm, a backtracking algorithm, the Otsu's algorithm, a fuzzy set algorithm, a two-dimensional entropy thresholding algorithm, the fuzzy C-means (FCM) clustering algorithm, or the like, or any combination thereof. These examples are provided here for illustration purposes, and not intended to limit the scope of the present disclosure. In some embodiments, memory320may share information with storage130and/or server140via network120.

Memory320may be a local device or a remote device (e.g., a cloud storage). Merely by ways of example, memory320may be a random access memory (RAM), a read only memory (ROM), a flash memory, a nano random access memory, a hard disk, a floppy disk, a compact disk (CD), or any other devices suitable for storing data.

Input/output330may provide an interface to communicate with a user. In some embodiments, input/output330may receive input from the user. For example, input/output330may receive instructions or parameters regarding to the operation of MRI scanner111from a user. The received input from the user through input/output330may be transmitted to processor310for further processing. In some embodiments, input/output330may send information to a user. For example, input/output330may send medical history information, or an MR image to a user. Input/output330may include an interface including a display, a keyboard, a mouse, a touch screen, a microphone, a sensor, a wireless communication unit or the like, or any combination thereof. In some embodiments, input/output330may be implemented on a control console of computing device112. In some embodiments, input/output330may support input/output flows between computing device112and other components therein, such as a user interface (e.g., a portable computer).

Communication port340may be connected to a network to facilitate data communications. Communication port340may establish connections between computing device112, MRI scanner111and network120. The connection may be a wired connection, or a wireless connection, or combination of both that enables data transmission and reception. Wired connection may include electrical cable, optical cable, telephone wire, or the like, or any combination thereof. Wireless connection may include Bluetooth, Wi-Fi, WiMax, WLAN, ZigBee, mobile network (e.g., 3G, 4G, 5G, etc.), or other wireless connections. In some embodiments, communication port340may be a standardized communication port, such as RS232, RS485, etc. In some embodiments, communication port340may be a specially designed communication port. For example, communication port340may be designed in accordance with the digital imaging and communications in medicine (DICOM) protocol.

It should be noted that the above description of computing device112is merely provided for the purposes of illustration, and not intended to limit the scope of the present disclosure. For persons having ordinary skills in the art, multiple variations and modifications may be made under the teachings of the present disclosure. For example, exemplary computer platform may include an internal communication bus, program storage and data storage of different forms, e.g., a disk, a read only memory (ROM), a or random access memory (RAM), for various data files to be processed and/or communicated by the computer, as well as possibly program instructions to be executed by the CPU. However, those variations and modifications do not depart from the scope of the present disclosure.

FIG. 3Billustrates the architecture of a mobile device that may be used to realize a specialized system implementing the present disclosure. In some embodiments, a mobile device350as illustrated inFIG. 3Bmay constitute a terminal device150. For instance, a user may receive or provide information, imaging system110, or otherwise interact with imaging system110, using mobile device350. Mobile device350may include a smart phone, a tablet, a handled console, and a wearable computing device (e.g., eyeglasses, wrist watch, etc.), or in any other form factor. In some embodiments, mobile device350may include one or more central processing units (CPUs)358, one or more graphic processing units (GPUs)356, a display354, a memory362, a communication platform352, such as a wireless communication module, storage368, and one or more input/output (I/O) devices360. Any other suitable components including, for example, o a system bus or a controller (not shown), may also be included in mobile device350. As shown inFIG. 3B, a mobile operating system364, e.g., iOS, Android, Windows Phone, etc., and one or more applications366may be loaded into the memory362from the storage368in order to be executed by the CPU358. The applications366may include a browser or any other suitable mobile apps for receiving and rendering information relating to information from or to imaging system110on mobile device350. User interactions with the information stream may be achieved via the I/O devices360and provided to imaging system110and/or other components of the system, e.g., via network120.

To implement various modules, units, and their functionalities described in the present disclosure, computer hardware platforms may be used as the hardware platform(s) for one or more of the elements described herein (e.g., the imaging system110, and/or other components of the system described with respect toFIG. 1throughFIG. 16). The hardware elements, operating systems and programming languages of such computers are conventional in nature, and it is presumed that those skilled in the art are adequately familiar therewith to adapt those technologies to the imaging processing or signal processing as described herein. A computer with user interface elements may be used to implement a personal computer (PC) or other type of work station or terminal device, although a computer may also act as a server if appropriately programmed. It is believed that those skilled in the art are familiar with the structure, programming and general operation of such computer equipment and as a result the drawings should be self-explanatory.

FIG. 4is a flowchart of an exemplary process for generating an MR image according to some embodiments of the present disclosure. In401, an MR scan may be performed. The MR scan may be performed by, for example, MRI scanner111. In some embodiments, one or more parameters may be sent to MRI scanner111before or during the MR scan. The parameters may include a region of interest (ROI), slice thickness, an imaging type (e.g., T1 weighted imaging, T2 weighted imaging, proton density weighted imaging, etc.), a flip angle value, acquisition time (TA), echo time (TE), repetition time (TR), echo train length (ETL), the number of phases, the number of excitations (NEX), inversion time, bandwidth (e.g., RF receiver bandwidth, RF transmitter bandwidth, etc.), or the like, or any combination thereof.

In some embodiments, a pulse sequence may be sent to the MRI scanner111as a parameter. Exemplary pulse sequence may include spin echo, fast spin echo (FSE), fast recovery FSE, single shot FSE, gradient recalled echo, fast imaging with stead-state procession, etc. The pulse sequence may be generated by, for example, pulse sequence generator210. The pulse sequence may include pulses of an excitation radio frequency (RF) motivating a resonance in the MR scan. In some embodiments, the frequency of the RF pulse may be set based on the Larmor frequency of a certain nucleus (for example,1H,3He,7Li,13C,17O,19F,23Na,31P,129Xe, etc.). In some embodiments, a patient, or a portion thereof (e.g., tissues or organs of the patient including, e.g., head, heart, lung, blood vessel, muscle, etc.) may be scanned by MRI scanner111.

In402, an MR signal may be acquired. The MR signal may be an RF signal. In some embodiments, the RF signal may also be referred to as FID signal. In some embodiments, the signal acquisition may be performed by, for example, receiver220. One or more coil elements may be used to receive the MR signal. In some embodiments, the one or more coil elements may receive an MR signal of a specific frequency or a narrow bandwidth that corresponds to a single nucleus species. In some embodiments, the one or more coil elements may receive an MR signal of a wide bandwidth that corresponds to multiple nuclei (for example,3He,7Li,13C, etc.). In some embodiments, an analog signal (for example, a voltage signal or a current signal) may be induced in the one or more coil elements in response to the received MR signal.

In some embodiments, various sampling techniques may be applied while sampling the MR signal. Exemplary sampling techniques may include simple random sampling, stratified sampling, accidental sampling, cluster sampling, or the like, or any combination thereof. In some embodiments, one or more signal processing techniques may be applied during the sampling process. Exemplary signal processing techniques may include time-frequency analysis, differential equations, spectral estimation, a linear time-invariant system theory, a transform theory, or the like, or any combination thereof. In some embodiments, the one or more signal processing techniques may be performed by one or more electronic devices or components. Merely by ways of example, the devices may include filters, ADCs, signal compressors, digital signal processors (DSPs), amplifier, or the like. In some embodiments, after the sampling and processing, an IF signal may be generated and sent to computing device112for further processing or image reconstruction.

In403, an image may be reconstructed based on the MR signal. Various image reconstruction techniques may be applied to reconstruct an image based on the acquired MR signal. Merely by way of example, the reconstruction technique may include linear fitting, Fourier transform (FT), fast Fourier transform (FFT), non-uniform fast Fourier transform (NUFFT), interpolation, or the like, or any combination thereof. In some embodiments, the acquired MR signal may be processed to fill into the k-space before image reconstruction.

In some embodiments, the image may be generated in an iterative process by repeating401and402for a certain number of times. During each of the repetitions, an MR signal may be acquired. The repetition times of the iterative process may be determined by the imaging system110or set by a user (e.g., a doctor). The reconstructed image may be a T1weighted image, a T2weighted image, a proton density weighted image, a FLAIR (fluid attenuated inversion recovery) image, or the like. In some embodiments, the image may be further processed to generate a medical report. In some embodiments, a MR spectrum may be generated based on the MR signal.

It should be noted that the above description is provided for the purposes of illustration, not intended to limit the scope of the present disclosure. For persons having ordinary skills in the art, multiple variations and modifications may be reduced to practice in the light of the present disclosure. However, those variations and modifications do not depart from the scope of the present disclosure. For example, the reconstructed image and/or the generated report may be output to a related device (e.g., input/out330, server140, terminal devices150, or any other devices disclosed in the present application). As another example, the acquired MR signal scan may be stored in a storage device (e.g., memory320, storage130, etc.) before image reconstruction.

FIG. 5is a schematic diagram illustrating an exemplary receiver according to some embodiments of the present disclosure. Receiver220may include a receiving component510and a sampling component520. Receiving component510may receive an MR signal. The MR signal may originate from one or more species of nuclei including, for example, hydrogen nuclei (i.e.,1H), or non-hydrogen nuclei (e.g.,3He,7Li,13C,17O,19F,23Na,31P,129Xe, etc.), in the patient. In some embodiments, the MR signal may be an RF signal. In some embodiments, the RF signal may have a certain bandwidth between a minimum frequency and a maximum frequency. In some embodiments, the center frequency of the RF signal may be referred to as the frequency of the RF signal. Receiving component510may receive the MR signal from a specific part of the patient body including, for example, the head, the lung, the arms, the carotid artery, the spine, etc.

In some embodiments, receiving component510may include a coil element. The MR signal from a part of a patient body may be detected or collected by the coil element. The coil element may be a quadrature coil, a surface coil, a special coil, or the like, or any combination thereof. In response to the received MR signal, a current signal or a voltage signal may be generated in the coil element accordingly. In some embodiments, receiving component510may further include an amplifier and/or a filter. The amplifier may increase the amplitude of the MR signal. In some embodiments, the amplified MR signal may be sent to the filter. The filter may remove, from the MR signal, specific interference frequency components or noise. In some embodiments, the filter may remove, from the MR signal, certain frequency components outside the imaging bandwidth to avoid the aliasing which appears in the frequency spectrum during the process of the following signal processing.

Sampling component520may sample the MR signal received by receiving component510. Various sampling techniques may be applied while sampling the MR signal. Exemplary sampling techniques may include simple random sampling, stratified sampling, probability-proportional-to-size sampling, accidental sampling, cluster sampling, or the like, or any combination thereof. In some embodiments, an oversampling and band pass sampling technique may be applied in the sampling process. As used herein, oversampling may refer to the sampling of a signal at a sampling rate higher than twice the bandwidth of the MR signal. Conversely, band pass sampling may refer to the sampling of a signal at a sampling rate lower than twice the center frequency of the MRI scanner111.

In some embodiments, various signal processing techniques may be applied during the sampling process. Exemplary signal processing techniques may include time-frequency analysis, differential equations, spectral estimation, a linear time-invariant system theory, numerical analysis, a transform theory, or the like, or any combination thereof. In some embodiments, the signal processing techniques may be performed by one or more electronic devices or components. Merely by ways of example, the devices may include filters, ADCs, signal compressors, digital signal processors (DSPs), or the like.

In some embodiments, sampling component520may further include other devices (for example, a clock synthesizer, a demultiplexer, a multiplexer, etc.) that contributes to the MR signal sampling. For example, sampling component520may further include a clock synthesizer. The clock synthesizer may generate a clock signal. In some embodiments, the clock signal may be received from a control software. The clock signal may be provided to an ADC, and the sampling rate of the ADC may be determined based at least partially on the clock signal. More description of the clock signal may be found elsewhere is the present application. See, for example,FIG. 7and the descriptions thereof. In some embodiments, sampling component520, including one or more devices mentioned above, may generate a digitized signal based on the received RF signal. The desired frequency of the digitized signal may fall into the frequency band between 0 and fs/2 (fs may denote the sampling rate)

FIG. 6is a schematic diagram illustrating an exemplary receiving component according to some embodiments of the present disclosure. Receiving component510may include an coil element610, an amplifier620, and a filter630.

Coil element610may receive an MR signal. The MR signal may be originate from one or more species of nuclei including, for example, hydrogen nuclei (i.e.,1H), or non-hydrogen nuclei (e.g.,3He,7Li,13C,17O,19F,23Na,31P,129Xe, etc.), in the patient. In some embodiments, the MR signal may be treated as an RF signal. In some embodiments, the RF signal may also be referred to as FID signal. The MR signal from a specific nucleus may have a center frequency and a bandwidth. The center frequency and the bandwidth of the MR signal may be included in the frequency band of the MRI scanner111. In some embodiments, the center frequency and the bandwidth of the MR signal may relate to the static magnetic field strength (Bo).

In some embodiments, coil element610may receive the MR signal of a specific frequency or a narrow bandwidth that corresponds to a single nucleus species. For example, coil element610may be configured to receive the hydrogen nuclei signal in a 3T static magnetic field. As used herein, the hydrogen nuclei signal may refer to an MR signal emitted from a patient body after an RF pulse with the hydrogen nuclei resonance frequency is applied. In some embodiments, coil element610may receive the MR signal of another narrow bandwidth that corresponds to non-hydrogen nuclei (for example,3He,7Li,13C, etc.). The MR signal, received from one or more nuclei, may induce a voltage signal or a current signal in coil element610. In some embodiments, coil element610may generate a time-varying analog signal based on the voltage signal or the current signal. The amplitude of the analog signal may relate to the intensity of the MR signal and the nucleus species.

Merely by way of example, coil element610may include a quadrature coil, a surface coil, a special coil, or the like, or any combination thereof. The quadrature coil may be used to detect or collect MR signals from a part of a body in a three-dimensional manner. The surface coil may be used to detect or collect MR signals from a part of a body in a two-dimensional manner. The special coil may include a body phased array coil, a surface phased array coil, an element-directed spectroscopy coil, or the like, or any combination thereof. In some embodiments, receiving component510may include a plurality of coil elements610(for example, a coil array). Each of the plurality of coil elements may have a specific receiving bandwidth that corresponds to a single nucleus species. The number, position, and shape of the plurality of coil elements610may relate to the request for an effective induction area or a signal-to-noise ratio (SNR).

Amplifier620may preserve or enhance the energy in the MR signal with little additive noise. Amplifier620may connect to coil element610and receive the MR signal from coil element610. In some embodiments, the MR signal may be in the form of an analog signal. Amplifier620may increase the amplitude of the analog signal. In some embodiments, amplifier620may multiply the analog signal with a factor that relates to the magnitude of the amplification. The factor may be a number (for example, 1000), set by a user (for example, a doctor), determined by imaging system110, etc.

In some embodiments, amplifier620may be implemented on a device or equipment stand-alone or an electrical circuit integrated in receiving component510. For example, amplifier620may be a low noise amplifier (LNA), a microwave low noise amplifier (WLNAXX), or the like, or any combination thereof. The LNA may include a transistor amplifier, a field effect transistor (FET) amplifier, or the like, or any combination thereof. The LNA may amplify the RF signals with very low amplitude without significantly degrading their signal-to-noise ratio (SNR). The WLNAXX may include a semiconductor diode parametric amplifier, or the like.

In some embodiments, amplifier620may introduce additive white noise into the MR signal. The noise may influence the frequency components and/or the amplitude of the MR signal. The noise may relate to the characteristics of amplifier620. To reduce the side effect of additive white noise, one or more filters may be needed. In some embodiments, the number of filters may be determined, at least partially, based on the additive white noise.

Filter630may remove some frequency components of the received MR signal. Filter630may have a pass band that is delimited by a lower limit and an upper limit. Filter630may remove, from the MR signal, certain frequency components (for example, components of certain frequencies, noise, etc.) that are outside the pass band. For example, filter630may suppress the components whose frequencies equal to half the ADC sampling rate. As another example, filter630may suppress noise power larger than a threshold. In some embodiments, filter630may remove the additive noise introduced by amplifier620as well as certain frequency components of the MR signal.

Filter630may include an anti-aliasing filter (AAF), an inductor capacitor filter (LC filter), a low-pass filter, a high-pass filter, a band-pass filter (BPF), a band-stop filter, a notch filter, or the like, or any combination thereof. Filter630may be operably (or electrically) connected to coil element610or amplifier620. In some embodiments, filter630may be operably (or electrically) connected to amplifier620to calibrate the amplified MR signal. In some embodiments, the MR signal may be filtered by one or more filters630to avoid folded or aliased components that may appear in the imaging bandwidth during an analog-to-digital conversion.

FIG. 7is a schematic diagram illustrating an exemplary sampling component according to some embodiments of the present disclosure. Sampling component520may be connected to or communicate with receiving component510and sample the received MR signal. Sampling component520may include a clock synthesizer710, a demultiplexer720, a filtration device730, an ADC740, and a digital signal processing device750.

Clock synthesizer710may generate a clock signal. The clock signal may be used to determine the sampling rate of sampling component520. One or more frequencies (for example, 300 MHz, 600 MHz, 1 GHz, etc.) may be provided by the clock signal. The clock signal may be acquired from a clock, an oscillator, another frequency synthesizer, or any other suitable clock source. In some embodiments, the clock signal may be acquired from a clock source outside of receiver220. In some embodiments, the clock signal may be received from a control software installed in computing device112. In some embodiments, the clock signal may be acquired from processor310. Clock synthesizer710may generate the clock signal base on a factor. In some embodiments, the factor may be an integer (for example, 5, 6, 10, etc.) The factor may be a value, set by a user via input/output330, or determined by imaging system110. In some embodiments, the factor may be determined based at least partially on the bandwidth of the MR signal.

One or more sampling rates may be provided by the clock signal. In some embodiments, the sampling rates may be generated based on the divide factor. For example, given a clock signal of 600 MHz, the sampling rate may be reduced to 100 MSPS by a factor of 6.

In some embodiments, the clock signal that may provide the sampling rates may be sent to ADC740. ADC740may choose a sampling rate (divide factor) to sample the received signals (e.g., the MR signal). In some embodiments, the clock signal providing one or more sampling rates may be further sent to digital signal processing device750. In some embodiments, the clock signal may be sent to a decimation filter in digital signal processing device750as main working frequency.

Clock synthesizer710may be composed of a direct digital synthesizer (DDS), a clock data recover (CDR) device, a phase-locked loop (PLL), a clock divider, a clock fan-out driver, or the like, or any combination thereof. In some embodiments, clock synthesizer710may be a local device within sampling component520, or a remote device connects to sampling component520in a wired connection or a wireless connection.

Demultiplexer720may receive an MR signal and forward the received signal to a data line. In some embodiments, demultiplexer720may be used on the receiving end of sampling component520. In some embodiments, demultiplexer720may be connected to receiving component510. In some embodiments, demultiplexer720may include a plurality of switches. Each of the plurality of switches may be connected to one of multiple data lines. Each of the multiple data lines may have a specific pass band. In some embodiments, one or more electronic devices or elements may be implemented in each of the multiple data lines. For example, at least one filter may be included in each of the multiple data lines. Demultiplexer720may select one of a plurality of switches and forward the MR signal to the data line that is connected to the selected switch. For example, each of the plurality of switches may be connected to a data line in which a filter and an amplifier are included. Demultiplexer720may select a switch and forward the MR signal to the filter.

Demultiplexer720may select a switch based on a default setting, an operation from a user, or a control signal provided by imaging system110. In some embodiments, the control signal provided by imaging system110may be generated based on the nucleus species of interest, a feature thereof (e.g., the center frequency of the MR signal, the bandwidth of the MR signal, etc.), the pass band of data line, or the like, or a combination thereof. In some embodiments, demultiplexer720may select one of a plurality of switches based on both the frequency of the RF signal and the pass band of the connected data line. For example, demultiplexer720may select a switch if the pass band, of the data line that connected to the switch, contains the center frequency of the RF signal.

In some embodiments, a multiplexer may be provided, as a complementary component, together with demultiplexer720. See, for example,FIG. 14and the description thereof. The multiplexer may receive the MR signal that has passed through demultiplexer720. The multiplexer may also include a plurality of switches. Each of the plurality of switches in the multiplexer may connect to one of the multiple data lines. The multiplexer may select one of a plurality of switches and receive the MR signal from the data line. In some embodiments, the multiplexer may select the switch based on the operation of demultiplexer720. More description of demultiplexer720may be found elsewhere in the present application. See, for example,FIG. 8and the description thereof.

Filtration device730may remove unwanted frequency components from the MR signal. In some embodiments, filtration device730may have a specific pass band. In some embodiments, filtration device730may remove some frequency components outside its pass band to avoid aliasing that may occur during the analog-to-digital conversion. The frequency components may be one or more discrete frequency components or successive frequency components within a certain range.

Filtration device730may remove unwanted frequency components of the MR signal. In some embodiments, the MR signal may be received from demultiplexer720. In some embodiments, filtration device730may be implemented in the multiple data lines. Filtration device730may have a pass band between an upper limit and a lower limit. Filtration device730may remove, from the MR signal, certain frequency components (for example, components of certain frequencies, noise, etc.) outside the pass band. In some embodiments, filtration device730may remove, from the MR signal, frequency components outside the pass band. For example, filtration device730may remove noise or scattering whose frequency is equal to half of an integral multiple of the sampling rate of ADC740. That is, filtration device730may remove noise or scattering whose frequency is f, f=n·fs/2, where n may be an integer, and fsmay denote the sampling frequencies of ADC740. The pass band of filtration device730may relate to the center frequency(ies) and the bandwidth(s) of one or more nuclei species. For example, the pass band of filtration device730may contain the center frequency or center frequencies of one or more nuclei species. In some embodiments, the pass band of filtration device730may be set at least partially based on the center frequency(ies) and the bandwidth(s) of one or more nuclei species. In some embodiments, the pass band of filtration device730may relate to the sampling rate of ADC740. For example, the pass band of selected data path could not include n·fs/2, in order to avoid the appearance of folded or aliased components in the frequency spectrum during the analog-to-digital conversion.

In some embodiments, filtration device730may be implemented on a hardware device (for example, an integrated circuit). In some embodiments, filtration device730may be an AAF. Filtration device730may include a low-pass filter, a high-pass filter, a band-pass filter (BPF), a band-stop filter, a notch filter, or the like, or any combination thereof.

In some embodiments, filtration device730may include one or more filters. In some embodiments, filtration device730may be connected to demultiplexer720by connecting each of the filters to a switch in demultiplexer720. The number of filters may be set by a user, or determined by imaging system110based on the MR signal. In some embodiments, the number of the filters may be determined by imaging system110based on the additive white noise of the amplifier in the sampling component520present in the MR signal chain. If there is no additive white noise in the MR signal, filtration device730may need just one filter. More description regarding filtration device730may be found elsewhere in the present application. See, for example,FIG. 9,FIG. 14, andFIG. 15, and the descriptions thereof.

ADC740may convert the MR signal into a digital signal. The MR signal received by receiving component510may be an analog signal. ADC740may discretize the analog signal into a digital signal. For example, ADC740may convert the MR signal in the form of a voltage signal or a current signal into a set of digital binaries based on (e.g., proportional to) the amplitude of the voltage or current. Merely by way of example, ADC740may be a flash ADC, a successive-approximation ADC, a ramp-compare ADC, a Wilkinson ADC, an integrating ADC, a delta-encoded ADC, a pipelined ADC, a sigma-delta ADC, a time-interleaved ADC, etc.

In some embodiments, ADC740may be provided with a specific sampling rate during the analog-to-digital conversion of the MR signal. In some embodiments, the MR signal may be oversampled by ADC740. As used herein, a signal being sampled at a frequency greater than twice the frequency of the signal may be referred to as oversampling. According to the Nyquist sampling theorem, a signal may need to be sampled at a frequency greater than twice its frequency to maintain the signal quality. For example, if the frequency of an MR signal is 70 MHz, the minimum sampling rate of ADC740may be 140 MSPS according to Nyquist criterion.

In some embodiments, the MR signal may be sampled by ADC740with band pass sampling technique. As used herein, band pass sampling may refer to the sampling at a rate that does not meet the Nyquist criterion. Merely by way of example, if ADC740samples an MR signal of 70 MHz at a sampling rate of 100 MSPS, the MR signal may be considered to be sampled with band pass sampling. During band pass sampling, some components of the MR signal may be folded. For example, if ADC740samples an MR signal of 70 MHz at a sampling rate of 100 MSPS, components of certain frequencies may be folded. The folded components may appear at 30 MHz. With the AAF in front of ADC740, there would be almost no SNR loss even if mirror folding happens. And the following digital signal processing device750may just process the 30 MHz signal. In some embodiments, an undersampling technique may be used to down convert (i.e., reduce the frequency of) an MR signal. ADC740may down convert the MR signal to a lower frequency.

In some embodiments, the sampling rate of ADC740may be determined based on a default value, an input from a user, or a clock signal provided by clock synthesizer710. In some embodiment, the sampling rate of ADC740may be provided by clock synthesizer710. Clock synthesizer710may generate the clock taking into consideration the nucleus species, a feature thereof (e.g., the center frequency of the MR signal, the bandwidth of the MR signal, etc.), the pass band of filtration device730, or the like, or a combination thereof. In some embodiments, the sampling rate may be generated by clock synthesizer710to achieve band pass sampling.

Digital signal processing device750may process the digitized MR signal. Digital signal processing device750may be connected to ADC740to receive the digitized MR signal. Various operations may be used to process the digitized MR signal in digital signal processing device750. Exemplary processing operations may include down conversion, filtering, decimation, I/Q demodulation, compression, or the like, or any combination thereof. In some embodiments, one or more electronic devices or elements may be included in digital signal processing device750. For example, digital signal processing device750may include a decimation filter, a numerically controller oscillator (NCO), a multiplier, a poly-phase decimation FIR low pass filter, etc.

In some embodiments, digital signal processing device750may further include a plurality of channels. At least two of the plurality of channels may be included in digital signal processing device750, within which different processing operations may be provided. In some embodiments, one of the plurality of channels may be selected based on the frequency of the MR signal or the nucleus species of interest. For example, the MR signal from hydrogen nuclei may be sent to a first channel, within which a poly-phase decimation FIR band pass filtering operation may be performed to generate an intermediate radio (IF) signal; the MR signal from non-hydrogen nuclei may be sent to a second channel, within which an I/Q demodulation may be performed to divide the MR signal into an in-phase signal (I signal) and a Quadrature signal (Q signal).

Merely by ways of example, an MR signal from hydrogen nuclei with a frequency of 128 MHz may be sampled by ADC740at a sampling rate of 100 MSPS. The MR signal may appear with 28 MHz after the analog-to-digital conversion. Subsequently, the MR signal may be sent to one of the plurality of channels. A decimation band pass filter, included in the channel, may sample the MR signal at a sampling rate of 10 MSPS, and the frequency of the MR signal be converted to 2 MHz. As another example, an MR signal from non-hydrogen nuclei with a frequency of 120.1 MHz may be sampled by ADC740at the same sampling rate of 100 MSPS. The MR signal may appear with 20.1 MHz after the analog-to-digital conversion. Assuming that the MR signal with a frequency of 20.1 MHz is sent to the same channel, the decimation band pass filter within the channel may sample the MR signal at 10 MSPS. It may be difficult for the decimation band pass filter to remove the frequency components of 19.9 MHz. Thus, another channel, within which an I/Q demodulation and a decimation low pass filtering may be provided to process such MR signal.

In some embodiments, digital signal processing device750may generate an IF signal. In some embodiments, digital signal processing device750may reduce data rate of the digitized MR signal.

In some embodiments, digital signal processing device750may be implemented on an electronic device or an electric circuit.FIG. 14and the description thereof illustrate exemplary electronic devices and electric circuits. For example, digital signal processing device750may be a field-programmable gate array (FPGA), a digital signal processor (DSP), an application specific integrated circuit (ASIC), an application-specific instruction-set processor (ASIP), a physics processing unit (PPU), a microcontroller unit, an advanced reduced instruction set computer (MSC) machine (ARM), a programmable logic device (PLD), or the like, or any combination thereof, in some embodiments, digital signal processing device750may be implemented by way of a software or a program, for example, the MATLAB.

It should be noted that the above description of the process for generating a corrected image is merely provided for the purposes of illustration, and not intended to limit the scope of the present disclosure. For persons having ordinary skills in the art, multiple variations or modifications may be made under the teachings of the present disclosure. For example, sampling component520may further include an amplifier. The additive noise of the amplifier may be removed by filtration device730. The number of filters included in filtration device730may relate to the additive noise of the amplifier. If there is almost no additive noise, filtration device730may just include one filter. However, those variations and modifications do not depart from the scope of the present disclosure.

FIG. 8is a schematic diagram illustrating an exemplary demultiplexer according to some embodiments of the present disclosure. As illustrated inFIG. 8, demultiplexer720may include a plurality of switches, like switch720-1, switch720-2, . . . , switch720-m. In some embodiments, each of the switches may be connected to a data line. Upon receiving an MR signal, demultiplexer720may select one of the m switches, and forward the MR signal to a data line that is connected to the selected switch. The data line connected to a specific switch may have a certain pass band. Demultiplexer720may select one of the multiple switches, switch720-1through switch720-m, based on a default setting, an operation or instruction from a user, or a control signal provided by imaging system110. In some embodiments, the control signal provided by imaging system110may be generated based on the center frequency and the bandwidth of the MR signal, and the pass band of a data line. For example, the control signal may be generated, and demultiplexer720may select, based on the control signal, a switch when the center frequency of the MR signal falls within the pass band of the data line connected with the switch.

The multiplexer, provided together with demultiplexer720, may also have multiple switches. In some embodiments, the number of switches included in the multiplexer may equal to that of demultiplexer720. The multiplexer may select the switch based on the operation of demultiplexer720.

FIG. 9is a schematic diagram illustrating an exemplary filtration device according to some embodiments of the present disclosure. As is illustrated inFIG. 9, filtration device730may include a plurality of filters, such as filter730-1, filter730-2, . . . , filter730-n. In some embodiments, filter730-1through filter730-nmay be of the same type. For example, all of the filters, filter730-1through filter730-n, may be AAFs. In some embodiments, each of the filters, filter730-1through filter730-n, may be any type of filter, such as a low-pass filter, a high-pass filter, a band-pass filter (BPF), a comb filter, an all-pass filter, or the like, or any combination thereof. In some embodiments, at least two of the filters may be of different types. For example, filter730-1may be a high-pass filter, filter730-nmay be a low-pass filter, and other filters may be BPFs.

In some embodiments, each of the plurality of filters, filter730-1through filter730-n, may have a pass band with a certain frequency range. In some embodiment, the pass band of filtration device730may be determined based on the pass bands of the plurality of filters. For example, the available bandwidth of filtration device730may equal to the sum of the pass band widths of filter 1 through filter n. In some embodiments, at least two of the plurality of filters, filter730-1through filter730-n, may have the same pass band with the same frequency range. In some embodiments, at least two of the plurality of filters, filter730-1through filter730-n, may have different pass bands with different frequency ranges. In some embodiments, the pass band of each filter may be different from each other. In some embodiments, the pass band of each filter may correspond to signals from one or more nuclei species. For example, the pass band of filter 1 may contain the center frequencies of1H and19F, and the pass band of filter 2 may only contain the center frequency of13C. More description of the pass band of the filters may be disclosed elsewhere in the present application. See, for exampleFIG. 15and the description thereof.

In some embodiments, the number of the filters in filtration device730may equal to the number of the switches in demultiplexer720. In some embodiments, filter730-1through filter730-nmay be connected to switch720-1through switch720-m, respectively.

FIG. 10is a schematic diagram illustrating an exemplary digital signal processing device according to some embodiments of the present disclosure. Digital signal processing device750may include a signal processing channel1010, a register1020, and a load interface1030. In some embodiments, signal processing channel1010, register1020, and load interface1030may be implemented on a field-programmable gate array (FPGA), a digital signal processor (DSP), or an application specific integrated circuit (ASIC).

Signal processing channel1010may provide one or more channels to process the MR signal. The one or more channels may receive the digitized MR signal from ADC740. In some embodiments, signal processing channel1010may include a single channel to process the MR signal. In some embodiments, signal processing channel1010may include a plurality of channels. At least two of the plurality of channels may process the MR signal by different operations. The processing operations performed in the plurality of channels may include down conversion, filtering, amplification, decimation, I/Q demodulation, compression, or the like, or any combination thereof. Signal processing channel1010may select a channel for processing an MR signal. In some embodiments, the channel may be selected based on the frequency of the MR signal. For example, the MR signal from hydrogen nuclei may be sent to a first channel, within which a decimation band pass filtering operation may be performed to generate an intermediate radio (IF) signal; the MR signal from non-hydrogen nuclei may be sent to a second channel, within which an I/Q demodulation may be performed to divide the MR signal into an in-phase signal (I signal) and a Quadrature signal (Q signal). More description of signal processing channel1010may be disclosed elsewhere in the present application. See, for example,FIG. 11and the description thereof.

Signal processing channel1010may include one or more electronic devices or elements in each channel to perform the operations mentioned above. The electronic devices or elements may include filters, multipliers, decimation filters, or the like, or any combination thereof. For example, each of the plurality of the channels may include a decimation filter. The decimation filter may be a low-pass decimation filter, a high-pass decimation filter, a band-pass decimation filter, etc. In some embodiments, the decimation filter may receive a clock signal, and decimate the MR signal based on the clock signal. After decimation, the data rate of the MR signal may be reduced. In some embodiments, the clock signal may be provided by clock synthesizer710.

Register1020may store information. The stored information may relate to MR signal processing, or other information generated by or provided for digital signal processing device750. Register1020may store clock signals (e.g., the clock signal generated by clock synthesizer710), logic information (e.g., logic information of digital signal processing device750), or the like, or any combination thereof. For example, register1020may store the clock signal received from the control software mentioned above. The clock signal may be used to determine the sampling rate of the decimation filters in signal processing channel1010. As another example, register1020may store logic information of digital signal processing device750. Logic information may be used to modify the signal processing operation of digital signal processing device750. For instance, logic information may be used to alter one or more channels and/or processing operation therein, reset the coefficients of the decimation filter, etc. In some embodiments, logic information may relate to the sampling rate of receiving component520(for example, divide factor of clock synthesizer710). For example, if the sampling rate of ADC740is changed, logic information may change accordingly.

In some embodiments, the digitized MR signal may be written to register1020. In some embodiments, the digitized MR signal may be a binary number with a certain bit-width. The bit-width of the signal may be referred to as the bit-width of a number (e.g., a binary number) that the signal corresponds to. In some embodiments, register1020may be used for bit-width extension, truncation, combination, etc. In some embodiments, register1020may be used as an extension element to extend the bit-width of the MR signal. In some embodiments, register1020may be used as a truncation element to truncate the bit-width of the MR signal. In some embodiments, register1020may be further used as a combination element to mix two MR signals, and the bit-width of the two MR signals may be added together. For example, a combination element may combine the a 12 bit first signal and a 12 bit second signal and generate a binary number of 24 bit corresponding to the combined signal.

Register1020may be a programmer-visible register, a programmable read-only memory, a Nano-RAM, a thin film memory, a magnetic-core memory, a magnetic drum memory, a magnetic resistance random access memory, a flash memory, an electronic erasable programmable read-only memory, an erasable programmable read-only memory, a race-track memory, a programmable metallization memory, or the like, or any combination thereof. In some embodiments, register1020may be a local device located within digital processing device750. In some embodiments, register1020may be a remote device external to digital processing device750. In some embodiments, register1020may be connected to and receive information from processor310, memory320, input/out330, or storage130via network120.

Load interface1030may be used to update logic information for digital processing device750. Load interface1030may be a device connected to a programmable device that inputs and/or modifies logic information of digital processing device750. In some embodiments, load interface1030may receive logic information from a memory or a programmable local device. In some embodiments, load interface1030may process logic information and send it to a component in digital signal processing device750to control the operation of the component. Load interface1030may connect with other components of digital processing device750in a wired or wireless connection.

NCO1040may generate one or more periodical signals, such as a cosinusoid signal, a sinusoid signal, etc. The periodical signals may be provided to signal processing channel1010. For example, orthogonal NCO outputs (e.g., a cosinusoid signal and a sinusoid signal) may be sent to two multipliers in signal processing channel1010respectively. The two multipliers may multiply the MR signal from non-hydrogen nuclei in two different channels with the cosinusoid signal and the sinusoid signal, respectively.

FIG. 11is a schematic diagram illustrating an exemplary signal processing channel according to some embodiments of the present disclosure. Signal processing channel1010may include an H channel1110and an X channel1120.

H channel1110may process a hydrogen nuclei signal. X channel1120may process a non-hydrogen nuclei signal. As used herein, the hydrogen nuclei signal may refer to an MR signal originating from hydrogen nuclei; non-hydrogen nuclei signal may refer to an MR signal originating from non-hydrogen nuclei (e.g., one or more nuclei species selected from3He,7Li,13C,17O,19F,23Na,31P,129Xe, etc.). In some embodiments, the processing of the non-hydrogen nuclei signal may be different compared with the processing of the hydrogen nuclei signal. In some embodiments, H channel1110may include a decimation filter. The decimation filter may down convert the frequency of the hydrogen nuclei signal to generate an IF signal

In some embodiments, X channel1120may include an I/Q demodulator. The I/Q demodulator may divide the non-hydrogen nuclei signal into two sub-channels (for example, an I sub-channel and a Q sub-channel). In some embodiments, the I/Q demodulator may demodulate the non-hydrogen nuclei signal in the sub-channels to an in-phase signal (also referred to as I signal) and a quadrature signal (also referred to as Q signal). Merely by way of example, the I/Q demodulator may include two multipliers, and two poly-phase low pass decimation filters. The I/Q demodulation may be performed by the two multipliers, and the two low pass decimation filters. The two multipliers may receive the orthogonal NCO outputs and multiply the non-hydrogen nuclei signal in the I sub-channel and Q sub-channel with the orthogonal NCO outputs (for example, a cosinusoid signal and a sinusoid signal, respectively). The multiplication may be performed to down mix the frequency of the non-hydrogen nuclei signal. As used herein, down mix may refer to a shift operation that may move the frequency components of an MR signal towards the negative direction, thereby reducing the frequency of the MR signal. The portion of the non-hydrogen nuclei signal in each of the two sub-channels may be further processed by the low pass decimation filters. In some embodiments, the low pass decimation filter may remove, from a portion of the non-hydrogen nuclei signal, components of negative frequency and noise, and/or reduce the data rate. After the demodulation, an IF signal may be generated.

In some embodiments, there may be differences in terms of human body abundance of hydrogen nuclei and non-hydrogen nuclei. The available bit-width of corresponding MR signals (hydrogen nuclei signal and non-hydrogen nuclei signal) may be different accordingly. In some embodiments, an operation to equalize the final bit-width of the hydrogen nuclei signal and the non-hydrogen nuclei signal may be performed.

An exemplary operation on the bit-width for the hydrogen nuclei signals and non-hydrogen nuclei signal may be described as follows. It should be noted that description below is provided for illustration purposes, not intended to limit the present application. In H channel1110, the bit-width of the hydrogen nuclei signal may be extended, for example, by an extender. In some embodiments, the bit-width of the hydrogen nuclei signal may be extended from M bits to M+k bits, where k may denote a natural number (for example, k=0, 1, 2, . . . ), M may denote the actual available bit-width of the hydrogen nuclei signal, and M+k may be an even number. In some embodiments, the extender may perform bit-width extension by, for example, adding zeros after the least significant bit (LSB) corresponding to the hydrogen nuclei signal or adding signs before the most significant bit (MSB) corresponding to the hydrogen nuclei signal, or a combination of both. For instance, the extension element may perform bit-width extension by adding k zeros after the LSB corresponding to the hydrogen nuclei signal. As another example, the extender may perform bit-width extension by adding k signs before the MSB corresponding to the hydrogen nuclei signal. As a further example, the extension element may perform bit-width extension by adding i zeros after the LSB corresponding to the hydrogen nuclei signal, and adding (k−i) signs before the MSB corresponding to the hydrogen nuclei signal, where i is an integer no greater than k. In X channel1120, the bit-widths of both I signal and Q signal may be truncated, for example, by two truncation elements. In some embodiments, bit-widths of both I signal and Q signal may be truncated to (M+k)/2. In some embodiments, the truncation elements may perform bit-width truncation by, for example, removing the MSB of the I signal and the Q signal. In some embodiments, a combination may be performed on the I signal and the Q signal after the truncation. The combination may be performed by, for example, a combination element. The combination element may combine the truncated I signal and the truncated Q signal and generate a M+k bits value corresponding to the non-hydrogen nuclei signal, whose bit-width equals to the bit-width of the extended hydrogen nuclei signal. In some embodiments, the extension element, the truncation element, and the combination element may be implemented in register1020.

In some embodiments, X channel1120may share some common hardware devices with H channel1110. For example, H channel1010and some X channel1120may share a decimation band pass filter. The hydrogen nuclei signal or non-hydrogen nuclei signal received from ADC740may be processed into IF signal using respective coefficients.

FIG. 12is a flowchart of an exemplary process for generating a digital signal based on an input RF signal according to some embodiments of the present disclosure. In1201, the frequency of the RF signal may be determined. In some embodiments, a coil element designed for a particular species of nuclei may be installed on receiver220. The coil element may have an ID that may indicate the receiving frequency range of the coil element. Imaging system110may determine the frequency of the RF signal to be generated according to the ID of the installed coil element. After the determination of the frequency of the RF signal to be generated, an MR scan may be performed accordingly.

In1202, an RF signal may be received. In some embodiments, the RF signal may also be referred to as FID signal. The RF signal may be an MR signal originating from hydrogen nuclei (1H) or non-hydrogen nuclei (such as3He,7Li,13C,17O,19F,23Na,31P,129Xe, etc.) The RF signal may be received by the coil element. The coil element may receive the RF signal by the way electromagnetic induction and induce analog signals (for example, a voltage signal or a current signal).

In1203, the RF signal may be filtered in at least one of multiple data lines. In some embodiments, filtration device730may be implemented in the multiple data lines. The RF signal may be filtered by filtration device730. In some embodiments, filtration730may include a plurality of filters. Each filter may correspond to a pass band. The filter may perform filtering on the RF signal by passing the frequency components within the pass band and suppressing the frequency components outside the pass band. In some embodiments, the RF signal may be filtered by filtration device730to remove the frequency components that does not meet the Nyquist-Shannon criterion.

In1204, the filtered RF signal may be converted to a digital signal. The conversion may be performed by, for example, ADC740. ADC740may digitize the analog signal. For example, ADC740may convert the RF signal, being in the form of an analog voltage signal, to a set of digital binaries.

According to the Nyquist-Shannon sampling theorem, which is a modified version of the Nyquist sampling theorem, the sampling rate of ADC740may be larger than twice the maximum frequency of an RF signal. Multiple sampling rates may be provided for the sampling of the RF signal pursuant to the Nyquist-Shannon criterion. In some embodiments, ADC740may choose a sampling rate, from the multiple sampling rates, to sample the RF signal. In some embodiments, the multiple sampling rates may be provided by clock synthesizer710.

In some embodiments, the conversion may be performed according to the band pass sampling technique. For example, ADC740may sample a narrow band RF signal with 70 MHz center frequency at a sampling rate of 120 MSPS. Some components of the RF signal may appear at 50 MHz (i.e. 120 MHz minus 70 MHz) due to mirror folding. Thus, ADC740may lower all the frequency components of the RF signal as well as convert the RF signal to a digital signal.

FIG. 13is a flowchart of an exemplary process for generating IF signal based on the digital signal according to some embodiments of the present disclosure. In1301, a digital signal may be received. In some embodiments, the digital signal may be an MR signal that is digitized by ADC740. The MR signal may originate from a patient after an RF pulse with resonance frequency of certain nuclei is applied. In some embodiments, the nuclei may include hydrogen nuclei (1H) or non-hydrogen nuclei (e.g., one or more nuclei species selected from3He,7Li,13C,17O,19F,23Na,31P,129Xe, etc.). The digital signal may be received by, for example, digital signal processing device750.

In1302, a determination as to whether the digital signal is from hydrogen nuclei or non-hydrogen nuclei may be made. If the digital signal is from hydrogen nuclei, the process may proceed to1303, and the digital signal may be decimated and filtered by, for example, the decimation filter in H channel1110. If the digital signal is from non-hydrogen nuclei, the process may proceed to1305, and the digital signal may be demodulated into I signal and Q signal by, for example, the demodulator in X channel1120.

In1303, the digital signal may be filtered and decimated. The digital signal may be filtered and decimated by, for example, a decimation filter in H channel1110. The decimation filter may be a band-pass decimation filter, a low-pass decimation filter, a high-pass decimation filter, or the like. In some embodiments, the decimation filter may be a band-pass decimation filter. In some embodiments, the decimation filter may remove, from the digital signal, certain frequency components (for example, negative frequencies) and noise. In some embodiments, the decimation filter may reduce the data rate. In some embodiments, the digital signal may be a value of a certain bit-width.

In1304, the digitized signal of hydrogen nuclei may be extended. In some embodiments, the digitized signal may be extended from M bit to M+k bit, where k may denote a natural number (for example, k=0, 1, 2, . . . ), M may denote the actual bit-width of the hydrogen nuclei signal, and M+k may be an even number. In some embodiments, the bit-width extension may be performed by, for example, adding zeros after the LSB or adding signs before MSB, or a combination of both. For instance, the extender may perform bit-width extension by adding k zeros after the LSB corresponding to the hydrogen nuclei signal. As another example, the extender may perform bit-width extension by adding k signs before the MSB corresponding to the hydrogen nuclei signal. As a further example, the extender may perform bit-width extension by adding i zeros after the LSB corresponding to the hydrogen nuclei signal, and adding (k−i) signs before the MSB corresponding to the hydrogen nuclei signal, where i is an integer no greater than k. In some embodiments, the digital signal may be extended, for example, by an extension element. The extension element may be implemented in register1020. In some embodiments, the signal after the processing operation may be an IF signal.

In1305, the digitalized signal of non-hydrogen nuclei may be I/Q demodulated. In some embodiments, the digital signal of non-hydrogen nuclei may be duplicated such that the same digital signal of non-hydrogen nuclei may be sent to each of two sub-channels (for example, I sub-channel and Q sub-channel) in X channel1120. In some embodiments, the I/Q demodulation may be performed by an I/Q demodulator. In some embodiments, the I/Q demodulator may include an NCO, two multiplier, and two low pass decimation filters. The I/Q demodulation may be performed by the NCO, the two multiplier, and the two low pass decimation filters. The NCO may generate one or more periodical signal, such as a cosinusoid signal and a sinusoid signal. The two multipliers may multiply the digital signal in the I sub-channel and the digital signal in the Q sub-channel with the cosinusoid signal and the sinusoid signal, respectively. The digital signal in the two sub-channels may be further processed by the low pass decimation filters. In some embodiments, the low pass decimation filter may remove, from the digital signal, negative frequency components and noise, and/or reduce the data rate. After I/Q demodulation, an I signal may be obtained in the I sub-channel, and a Q signal may be obtained in the Q sub-channel. Both the I signal and the Q signal are digital signals. In some embodiments, the I signal and Q signal may be values having the same bit-width.

In1306, the I signal and the Q signal may be truncated. In some embodiments, both the I signal and the Q signal may be truncated to (M+k)/2 bits. In some embodiments, the truncation may be performed by, for example, removing the MSB of the I signal and the Q signal. In some embodiments, the truncation may be performed by, for example, one or two truncation elements. The truncation elements may be implemented in register1020.

In1307, the I signal and the Q signal may be combined. In some embodiments, the I signal and the Q signal may be combined by frequency mixing. In some embodiments, the combined signal may be a binary number of M+k bits, which equals to the bit-width of the extended digital signal of hydrogen nuclei. In some embodiments, the combined signal may be an IF signal of M+k bits.

FIG. 14is a schematic diagram illustrating an exemplary receiver according to some embodiments of the present disclosure. Receiver220may include a receiving component1401and a sampling component1402. Receiving component1401may receive an RF signal. In some embodiments, the RF signal may also be referred to as FID signal. In some embodiments, the RF signal may be an MR signal originating from hydrogen nuclei (1H) and/or non-hydrogen nuclei (such as3He,7Li,13C,17O,19F,23Na,31P,129Xe, etc.). Receiving component1401may include a coil element1403, an amplifier1404, and a filter1405. Coil element1403may be a receiver coil element that may induce an analog signal (for example, a voltage signal, a current signal, etc.) in response to the RF signal. Amplifier1404may be connected to coil element1403and increase the amplitude of the analog signal. In some embodiments, amplifier1404may be an LNA. Filter1405may perform filtration on the amplified signal to avoid aliasing during the analog-to-digital conversion in ADC1410. In some embodiments, filter1405may be an anti-aliasing filter (AAF. In some embodiments, the AAF may include at least a band pass filter (BPF). The BPF may be an inductor capacitor filter (LC filter), a surface acoustic wave filter, or the like, or any combination thereof.

Sampling component1402may include electric circuits or electronic devices1406through1419. Sampling components1402may sample the MR signal received by receiving component1401to generate an IF signal. Wide band RF gain block1406may further increase the amplitude of the analog signal before sending it to demultiplexer1407.

Demultiplexer1407may include a plurality of switches. Filtration device1408may also include a plurality of filters. In some embodiments, the number of the filters may equal to that of the switches. Filtration device1408may be connected to demultiplexer1407such that each of the filters is connected to a switch. Demultiplexer1407may select a switch and send the MR signal to the filter connected to the switch. In some embodiments, the plurality of filters may be implemented in multiple data lines of the same number. Demultiplexer1407may select a switch and send the MR signal to the filter connected to the switch via the data line connected to the switch. In some embodiments, other electronic devices may be implemented in the data line, such as amplifiers, multipliers, etc. Each of the plurality of filters may have a specific pass band.

Demultiplexer1407may select a switch based on a default setting, an operation from a user, or a control signal provided by imaging system110. In some embodiments, the control signal provided by imaging system110may be generated based on the center frequency and the bandwidth of the MR signal and the pass band of the filter. For example, Demultiplexer1407may select a switch when the center frequency of the MR signal falls within the pass band of the filter connected with the switch. The filter in filtration device1408may remove, from the MR signal, certain frequency components to avoid frequency domain aliasing. In some embodiments, the filter in filtration device1408may remove noise with certain frequency from the MR signal. For example, during the process for sampling of an MR signal of 64 MHz at a sampling rate of 100 MSPS, noise with the frequency of 136 MHz may be suppressed. In some embodiments, the filters in filtration device1408may be an AAF, a BPF, an LC filter, or the like.

Multiplexer1409may receive the filtered signal and forward it to pipelined ADC1410. Multiplexer1409may also have a plurality of switches. In some embodiments, multiplexer1409may select a switch based on the control signal(s) provided by imaging system110.

ADC1410may convert the analog MR signal to a digital signal. Clock synthesizer1411may connect to pipelined ADC1410and provide at least two sampling rates to pipelined ADC1410. For example, clock synthesizer1411may receive a 600 MHz signal, and generate a sampling rate of 100 MSPS based on a factor of 6 and another sampling rate of 120 MSPS based on another factor of 5. In some embodiments, the factors may be set by a user via input/output330, or determined by the imaging system110. In some embodiments, the factor may be determined based at least partially on the frequency of the MR signal. Pipelined ADC1410may sample the MR signal at a sampling rate chosen from the at least two sampling rates. The sampling rate of pipelined ADC1410may be determined based on the frequency of the analog signal and/or the pass bands of the filters in filtration device1408. For example, pipelined ADC1410may sample a 60 MHz signal with the sampling rate of 100 MSPS. In some embodiments, pipelined ADC1410may sample the MR signal with a band pass sampling technique. In some embodiments, clock synthesizer1411may include a PLL, a clock divider, etc.

The digital signal output by pipelined ADC1410may be demodulated into an I signal and a Q signal. In some embodiments, I/Q demodulation may be realized by NCO1414, multipliers1412and1413, and decimation low pass filters (decimation LPFs)1415and1416. NCO1414may generate one or more periodical signals, such as a cosinusoid signal and a sinusoid signal. Multipliers1412and1413may multiply the MR signal with the cosinusoid signal and the sinusoid signal, respectively, to down mix the frequency of the MR signal. As used herein, down mix may refer to a shift operation that may move the frequency components of the MR signal towards the negative direction. The MR signal may be further processed by decimation filters1415and1416. In some embodiments, decimation LPFs1415and1416may be low pass decimation filters. In some embodiments, decimation LPFs1415and1416may remove, from the non-hydrogen nuclei signal, negative frequency components and noise, and/or reduce the data rate to generate an IF signal.

In some embodiments, PLL1419may receive clock signal from clock synthesizer1411. The received clock signal may be driven and distributed to decimation LPFs1415and1416. Decimation LPFs1415and1416may receive the clock signal and adjust the sampling rate of the MR signal based on the clock signal. In some embodiments, a factor may be used to determine the sampling rate. The factor may be stored in RAM1417. In some embodiments, RAM1417may further store the frequency, phase, or other related information of NCO1414. In some embodiments, RAM1417may take the form of register1020.

Post processor1424may receive the IF signal and further process the IF signal to generate a base band signal. In some embodiments, the based band signal may be sent to computing device112for further processing or image reconstruction. For instance, k-space data may be generated based on the base band signal before image reconstruction. In some embodiments, post processor1424may be omitted.

In some embodiments, logic information that controls the operation of the components in digital signal processing components1421may be stored in a flash1423or another nonvolatile logic device1422. Digital signal processing components1421may acquire logic information from load interface1418.

FIG. 15is a schematic diagram illustrating an exemplary frequency spectrum of filtration device according to some embodiments of the present disclosure. Filtration device730may include a plurality of filters, such as filter 1, filter 2, . . . , filter n. Each of the plurality of filters, filter 1 through filter n, may have a pass band with a certain frequency range. In some embodiments, at least the pass bands of two filters may be different from each other. In some embodiments, at least the pass bands of two filters may be the same. Two pass bands are considered different if they are different in at least one feature including, e.g., the frequency range, pass band ripple, the rejection band suppression, the transition band width, etc. For instance, filter 1 may have a pass band in a trapezoid shape1510, filter 2 may have a pass band in a trapezoid shape1520, filter 3 may have a pass band in a trapezoid shape1530, . . . , filter n may have a pass band in a trapezoid shape1540.

Upper-limit1550may refer to the upper cut-off frequency of filtration device730. In some embodiments, upper-limit1550may relate to the pass bands of the plurality of filters. For example, the upper cut-off frequency of filtration device730may equal to the highest upper cut-off frequency among all the filters including filter 1 through filter n. In some embodiments, upper-limit1550may be determined based on static magnetic field strength Bo. For example, when the magnetic field intensity Bo is 3 T, 5 T, 7 T, 9.4 T, or 14 T, the upper-limit1550may be 129 MHz, 215 MHz, 301 MHz, 404 MHz, and 600 MHz, respectively.

In some embodiments, there may be an overlapping area between two neighbor pass bands in frequency spectrum1500. For example, the pass bands of filter 1 and filter 2 may have an overlapping area having a shape of triangle filled with outlined diamonds. In some embodiments, the overlapping areas between two pass bands may allow a continuous frequency range of filtration device730. A continuous frequency spectrum may guarantee all available frequency components are included in the frequency spectrum of filtration device730.

Pass band1560may correspond to the analog input bandwidth of ADC740. Pass band1560may be greater than the pass band of filtration device730. For example, if the pass band of filtration device730is 600 MHz (corresponds to a magnetic field of 14 T), the pass band of ADC740may support up to 650 MHz.

FIG. 16is a schematic diagram illustrating an exemplary digital signal processing channel according to some embodiments of the present disclosure. Signal processing channel1601may connect to pipelined ADC1603and receive a digital signal. The digital signal may be a hydrogen nuclei signal or a signal originating from non-hydrogen nuclei. The hydrogen nuclei signal may refer to an MR signal from hydrogen nuclei (1H). A non-hydrogen nuclei signal may refer to an MR signal from one or more species of-nuclei other than hydrogen (e.g., including at least two nucleus species selected from3He,7Li,13C,17O,19F,23Na,31P,129Xe, etc.). Signal processing channel1601may include an H channels1604and an X channel1605. H channel1604may process a hydrogen nuclei signal. X channel1605may process a non-hydrogen nuclei signal.

In H channel1604, the hydrogen nuclei signal may be processed by decimation band pass filter (decimation BPF)1606. Decimation BPF1606may reduce the data rate as well as remove, from the hydrogen nuclei signal, some components (e.g., noise, interference frequency components). In some embodiments, decimation BPF1606may receive a clock signal from PLL1419. The clock signal may be used to provide the working clock and may equal to the sampling rate of signals from hydrogen nuclei. In some embodiments, the processed hydrogen nuclei signal may be an IF signal. In some embodiments, the processed hydrogen nuclei signal may be a m bits (for example, 18 bits) value. In some embodiments, the hydrogen nuclei signal may be provided to extension element1607. Extension element1607may extend the hydrogen nuclei signal from m bits to m+n bits. In some embodiments, the bit-width extension may be performed by, for example, adding zeros after the LSB of the hydrogen nuclei signal or adding signs before the MSB of the hydrogen nuclei signal, or a combination of both. In some embodiments, extension element1607may be implemented in register1020. Channel1604may output an IF signal of m+n bit-width after the processing.

In X channel1605, an I/Q demodulation may be performed. In some embodiments, the non-hydrogen nuclei signal may be duplicated such that the same non-hydrogen nuclei signal may be sent to two sub-channels (for example, I sub-channel and Q sub-channel) in X channel1605. The I/Q demodulation may be performed by NCO1610, multipliers1608and1609, and decimation low pass filters (decimation LPFs)1611and1612. NCO1610may generate one or more periodical signals, for example, a sinusoid signal and a cosinusoid signal. Multipliers1608and1609may multiply the non-hydrogen nuclei signal in the I sub-channel and Q sub-channel with the cosinusoid signal and the sinusoid signal, respectively. The non-hydrogen nuclei signal in the two sub-channels may be further processed by low pass decimation LPFs1611and1612. In some embodiments, low pass decimation LPFs1611and1612may remove, from the digital signal, negative frequency components and noise, and/or reduce the data rate. After the I/Q demodulation, a Q signal and an I signal may be generated. In some embodiments, both the I signal and Q signal may be values with m bit-width. Truncation element1613and1614may truncate each of m bits I signal and m bits Q signal to (m+n)/2-bits. The truncated I signal of (m+n)/2 bits and the truncated Q signal of (m+n)/2 bits may be combined by combiner1615to provide an (m+n) bits non-hydrogen nuclei signal. In some embodiments, truncation element1613, truncation element1614, and combination element1615may be implemented in register1030. Channel1605may output an IF signal of (m+n) bits after the processing.

Digital signal processing device1600may send the hydrogen nuclei signal and the non-hydrogen nuclei signal to reconstructor1602. In some embodiment, both of the signals may be sent via a transmitting line of (m+n) bits. Reconstructor1602may restore the hydrogen nuclei signal and the non-hydrogen nuclei signal. In some embodiments, the restoration of the hydrogen nuclei signal and the non-hydrogen nuclei signal may be performed by a separator1616, multipliers1619and1620, an NCO1621, and decimation filters1622and1623. Separator1616may divide the input signal to two sub-channels1617and1618. In some embodiments, the hydrogen nuclei signal may be duplicated such that the same hydrogen nuclei signal is sent to two sub-channels1617and1618. The non-hydrogen nuclei signal, in a form of an I signal and a Q signal in signal processing channel1605, is separated into the I signal and the Q signal by separator1619. The I signal may be sent to sub-channel1618, and the Q signal may be sent to sub-channel1617. NCO1621may generate one or more periodical signals, for example, a sinusoid signal and a cosinusoid signal. The periodical signals may be multiplied, by multipliers1619and1620, with the signals in sub-channels1617and1618. In non-hydrogen nuclei cases, a sinusoid signal may be multiplied with the signal in both sub-channels1617and1618. In hydrogen nuclei case, a sinusoid signal may be multiplied with the Q signal in sub-channel1617and a cosinusoid signal may be multiplied with the I signal in sub-channel1618. Decimation filters1622and1623may be applied to reduce data rate and/or remove or reduce noise from sub-channels1617and1618. After the restoration of the hydrogen nuclei signal or the non-hydrogen nuclei signal, k-space data may be generated in reconstructor1602. In some embodiments, an image may be generated based on the k-space data. In some embodiments, a spectrum may be generated based on the k-space data. The spectrum may refer to a spectrum of the frequencies of the RF signal. The spectrum may be used for magnetic resonance spectroscopy analysis. In some embodiments, reconstructor1602may be implemented on image processing device112.