Patent Description:
Magnetic resonance imaging ("MRI") is a widely accepted and commercially available technique for obtaining digitized visual images representing the internal structure of objects having substantial populations of atomic nuclei that are susceptible to nuclear magnetic resonance ("NMR"). Many MRI systems use superconductive magnets to scan a subject/patient via imposing a strong main magnetic field on the nuclei in the subject to be imaged. The nuclei are excited by a radio frequency ("RF") signal at characteristics NMR (Larmor) frequencies. By spatially disturbing localized magnetic fields surrounding the subject and analyzing the resulting RF responses from the nuclei as the excited protons relax back to their lower energy normal state, a map or image of these nuclei responses as a function of their spatial location is generated and displayed. An image of the nuclei responses provides a non-invasive view of a subject's internal structure.

Many MRI systems require a subject to be scanned for an extended period of time, hereinafter referred to as a "scanning time", "scanning period", and/or simply "scan", which may last for several minutes or more while data regarding the RF responses is collected. The scanning period of such MRI systems may be long enough for subjects that are alive, e.g., a patient, to undergo several respiratory cycles. Respiratory cycles, however, can potentially cause some MRI systems to suffer "motion error" which may reduce the quality of images generated from the scan. For example, in some instances, the motion error resulting from a patient's respiratory cycles may produce motion artifacts, e.g., blurring and/or "ghosting", within generated MRI images.

Accordingly, some MRI systems avoid motion error by requiring a patient to hold their breath during various parts of the scanning period to mitigate motion error resulting from the patient's respiratory cycle. Other MRI systems, hereinafter referred to as "free-breathing" MRI systems, allow a patient to breath continuously during the scanning period and utilize respiratory gating to reduce the effects of motion error. Respiratory gating, however, often requires the use of acceptance windows, i.e., designated region(s) of a respiratory cycle from which data acquired during a scan may be used to generate an image. Generally, acceptance windows function as hard-thresholds by limiting the data used to generate an image to data acquired within an acceptance window - data acquired outside of the acceptance window is often discarded.

Typically, the smaller an acceptance window becomes, the smaller the motion error in the generated image becomes. It is often the case, however, that the smaller an acceptance window becomes, the larger the discarded portion of data to the portion of data used to generate an image becomes, and as a result, the longer the scan time becomes. Accordingly, many free-breathing MRI systems must balance image quality against scanning time. As such, many free-breathing MRI systems have small acceptance windows which typically discard as much as <NUM>% or more of the acquired data and may have scan times on the order of ten (<NUM>) minutes or more.

Additionally, the small acceptance windows and long scan times of some free-breathing MRI systems make such MRI systems sensitive to respiratory drifting and cardiac variations, which often not only increases patient discomfort, but may also reduce scan robustness. Further, many free-breathing MRI systems ignore intra-window motion corruption and/or are unable to utilize the discarded data to improve the reconstruction of k-space.

What is needed, therefore, is an improved MRI system and method for imaging a free-breathing subject.

In a first aspect of the invention, a method for magnetic resonance imaging of a moving subject is provided in accordance to claim <NUM>, said method comprising: directing a MRI imaging system to acquire using a plurality of coil channels k-space data of a k-space region via free-breathing scanning the subject, the k-space data including a plurality of data, each datum having a motion error due to respiratory motion of the subject and each being associated with a respective position of respiratory motion; estimating the motion error and a relationship between the motion error and the respective respiratory position to produce a soft gating filter; constructing a motion regularization matrix based at least in part on the estimated soft-gating filter and containing values based upon the motion error of the acquired k-space data; calculating a coil weight for each coil channel of the plurality of coil channels based at least in part on the constructed motion regularization matrix; and synthesizing unacquired k-space data from the acquired k-space data in a non-iterative manner, without the need to repeat k-space acquisition via additional scans, based on the coil weights, each datum in the unacquired k-space data set being synthesized from neighboring data in the acquired k-space data, wherein the coil weights are calculated so as to reduce contributions to the synthesizing of datum of the unacquired k-space data from data of the acquired k-space data having motion errors that are large, and increase contributions to the reconstruction of datum of the unacquired k-space data from data of the acquired k-space data having motion errors that are small.

In another aspect of the invention, an MRI controller of an MRI imaging system is provided in accordance with claim <NUM>.

In yet another aspect of the invention, a computer readable medium is provided in accordance with claim <NUM>.

Reference will be made below in detail to exemplary embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference characters used throughout the drawings refer to the same or like parts, without duplicative description.

As used herein, the terms "substantially," "generally," and "about" indicate conditions within reasonably achievable manufacturing and assembly tolerances, relative to ideal desired conditions suitable for achieving the functional purpose of a component or assembly. As used herein, "electrically coupled", "electrically connected", and "electrical communication" mean that the referenced elements are directly or indirectly connected such that an electrical current may flow from one to the other. The connection may include a direct conductive connection, i.e., without an intervening capacitive, inductive or active element, an inductive connection, a capacitive connection, and/or any other suitable electrical connection. Intervening components may be present.

Further, the embodiments disclosed herein are described with respect to an MRI system used to analyze tissue generally and are not limited to human tissue.

Referring now to <FIG>, the major components of an MRI system <NUM> incorporating an embodiment of the invention are shown. Operation of the system <NUM> is controlled from the operator console <NUM>, which includes a keyboard or other input device <NUM>, a control panel <NUM>, and a display screen <NUM>. The console <NUM> communicates through a link <NUM> with a separate computer system <NUM> that enables an operator to control the production and display of images on the display screen <NUM>. The computer system <NUM> includes a number of modules, which communicate with each other through a backplane <NUM>. These include an image processor module <NUM>, a CPU module <NUM> and a memory module <NUM>, which may include a frame buffer for storing image data arrays. The computer system <NUM> communicates with a separate system control or control unit <NUM> through a high-speed serial link <NUM>. The input device <NUM> can include a mouse, joystick, keyboard, track ball, touch activated screen, light wand, voice control, or any similar or equivalent input device, and may be used for interactive geometry prescription. The computer system <NUM> and the MRI system control <NUM> collectively form an "MRI controller" <NUM>.

The MRI system control <NUM> includes a set of modules connected together by a backplane <NUM>. These include a CPU module <NUM> and a pulse generator module <NUM>, which connects to the operator console <NUM> through a serial link <NUM>. It is through link <NUM> that the system control <NUM> receives commands from the operator to indicate the scan sequence that is to be performed. The pulse generator module <NUM> operates the system components to execute the desired scan sequence and produces data which indicates the timing, strength and shape of the RF pulses produced, and the timing and length of the data acquisition window. The pulse generator module <NUM> connects to a set of gradient amplifiers <NUM>, to indicate the timing and shape of the gradient pulses that are produced during the scan. The pulse generator module <NUM> can also receive patient data from a physiological acquisition controller <NUM> that receives signals from a number of different sensors connected to the patient, such as ECG signals from electrodes attached to the patient. And finally, the pulse generator module <NUM> connects to a scan room interface circuit <NUM>, which receives signals from various sensors associated with the condition of the patient and the magnet system. It is also through the scan room interface circuit <NUM> that a patient positioning system <NUM> receives commands to move the patient to the desired position for the scan.

The pulse generator module <NUM> operates the gradient amplifiers <NUM> to achieve desired timing and shape of the gradient pulses that are produced during the scan. The gradient waveforms produced by the pulse generator module <NUM> are applied to the gradient amplifier system <NUM> having Gx, Gy, and Gz amplifiers. Each gradient amplifier excites a corresponding physical gradient coil in a gradient coil assembly, generally designated <NUM>, to produce the magnetic field gradients used for spatially encoding acquired signals. The gradient coil assembly <NUM> forms part of a magnet assembly <NUM>, which also includes a polarizing magnet <NUM> (which in operation, provides a homogenous longitudinal magnetic field B<NUM> throughout a target volume <NUM> that is enclosed by the magnet assembly <NUM>) and a whole-body (transmit and receive) RF coil <NUM> (which, in operation, provides a transverse magnetic field B<NUM> that is generally perpendicular to B<NUM> throughout the target volume <NUM>).

The resulting signals emitted by the excited nuclei in the patient may be sensed by the same RF coil <NUM> and coupled through the transmit/receive switch <NUM> to a preamplifier <NUM>. The amplifier MR signals are demodulated, filtered, and digitized in the receiver section of a transceiver <NUM>. The transmit/receive switch <NUM> is controlled by a signal from the pulse generator module <NUM> to electrically connect an RF amplifier <NUM> to the RF coil <NUM> during the transmit mode and to connect the preamplifier <NUM> to the RF coil <NUM> during the receive mode. The transmit/receive switch <NUM> can also enable a separate RF coil (for example, a surface coil) to be used in either transmit or receive mode.

The MR signals picked up by the RF coil <NUM> are digitized by the transceiver module <NUM> and transferred to a memory module <NUM> in the system control <NUM>. A scan is complete when an array of raw k-space data (<NUM> in <FIG>) has been acquired in the memory module <NUM>. This raw k-space data/datum is rearranged into separate k-space data arrays for each image to be reconstructed, and each of these is input to an array processor <NUM> which operates to Fourier transform the data into an array of image data. This image data is conveyed through the serial link <NUM> to the computer system <NUM> where it is stored in memory <NUM>. In response to commands received from the operator console <NUM>, this image data may be archived in long-term storage or it may be further processed by the image processor <NUM> and conveyed to the operator console <NUM> and presented on the display <NUM>.

Referring now to <FIG>, a schematic side elevation view of the magnet assembly <NUM> is shown in accordance with an embodiment of the invention. The magnet assembly <NUM> is cylindrical in shape having a center axis <NUM>. The magnet assembly <NUM> includes a cryostat <NUM> and one or more radially aligned longitudinally spaced apart superconductive coils <NUM>. The superconductive coils <NUM> are capable of carrying large electrical currents and are designed to create the B<NUM> field within the patient/target volume <NUM>. As will be appreciated, the magnet assembly <NUM> may further include both a terminal shield and a vacuum vessel (not shown) surrounding the cryostat <NUM> in order to help insulate the cryostat <NUM> from heat generated by the rest of the MRI system (<NUM> in <FIG>). The magnet assembly <NUM> may still further include other elements such as covers, supports, suspension members, end caps, brackets, etc. (not shown). While the embodiment of the magnet assembly <NUM> shown in <FIG> and <FIG> utilizes a cylindrical topology, it should be understood that topologies other than cylindrical may be used. For example, a flat geometry in a split-open MRI system may also utilize embodiments of the invention described below. As further shown in <FIG>, a patient / imaged subject <NUM> is inserted into the magnet assembly <NUM>.

As illustrated in <FIG>, in embodiments, the k-space region <NUM> may include a plurality of datum (represented by circles/dots <NUM>). As is to be understood, at the end of a scan, some datum <NUM> may be acquired (represented by the solid dots) while other datum <NUM> may remain unacquired (represented by the hollow dots). As used herein, an "acquired datum" is a datum <NUM> for which a value has been obtained, and an "unacquired datum" is a datum <NUM> for which a value has not been obtained. As is to be understood, a set of datum <NUM> may be acquired collectively as a single echo obtained by sensing a complex signal emitted by the nuclei stimulated in the subject <NUM> during a scanning period. Such a scanning period is referred to as readout period. As such, the set of datum acquired in a single echo forms a readout line in k-space. Accordingly, while <FIG> depicts the k-space region <NUM> as two-dimensional ("2D"), it is to be understood that in reality, the k-space region <NUM> is three-dimensional ("3D") with the readout direction perpendicular to the ky-kz plane and thus each dot or circle in the ky-kz plane is in effect a readout line. Further, while the k-space region <NUM> shown in <FIG> depicts an undersampled rate of <NUM>, other rates may be used.

Turning now to <FIG>, the MRI system <NUM> is used to perform free-breathing MRI. Accordingly, chart <NUM> depicts a series of respiratory cycles <NUM> of the subject <NUM> during a scanning period having start time t<NUM> and end time tp. As is to be understood, line <NUM> represent the position of the subject <NUM> between an end expiration positon PEE and an end inspiration position PEI at various k-space acquisition/sampling/echo times. For example, points P<NUM> and P<NUM> represent acquisitions of k-space near the beginning of inhalation and near the beginning of exhalation, respectively. As is to be further understood, the position <NUM> of the subject <NUM> at the end of each expiration period (shown as the peaks of line <NUM>) may vary from one period to the next. Similarly, the position <NUM> of the subject <NUM> at the end of each inspiration period (shown as the valleys of line <NUM>) may also vary from one period to the next. In other words, the "depths" / "sizes" of the subject's <NUM> breaths may vary during the scanning period. As a result, in embodiments, PEE and PEI may be a range of positions, shown as bands <NUM> and <NUM>, respectively, that encompasses a range of positions that are at or near an averaged and/or reference end expiration position and averaged and/or reference end inspiration position, respectively.

As stated above, the respiratory motion <NUM> of the subject <NUM> during the scanning period t<NUM> to tp may result in motion error. Accordingly, in embodiments, the datum <NUM> which make up the k-space region <NUM> may each have a motion error, i.e., a variation to their value that has been induced by the motion of the subject <NUM> during the scan.

As shown in <FIG>, however, the relationship between motion error and the respiratory positions/movement <NUM> of the subject <NUM> is estimated to produce a respiratory soft gating threshold/filter <NUM>. Therefore, as will be appreciated, in embodiments, the MRI controller <NUM> may be configured to suppress the motion error of each datum <NUM> by reconstructing the k-space region <NUM> via the soft gating threshold <NUM> in a "non-iterative" manner, i.e., the MRI controller <NUM> can correct k-space for motion error without the need to repeat k-space acquisition via additional scans.

Accordingly, referring now to <FIG>, a method <NUM> for imaging the free-breathing subject <NUM> utilizing the MRI system <NUM> according to an embodiment is shown. As will be appreciated, in certain embodiments, an imaging application may be stored in the memory device <NUM>, <NUM> which may be loaded into the CPU <NUM>, <NUM> such that the MRI controller <NUM> is adapted by the imaging application to perform all, or part, of method <NUM>. Accordingly, as shown in <FIG>, the method <NUM> includes acquiring <NUM>-space data from a k-space region <NUM> via scanning the subject <NUM> with the MRI system <NUM>; calculating <NUM> a coil weight x; and reconstructing <NUM> a datum and/or a line of the plurality of datum within the k-space region <NUM> based at least in part on the coil weight x and the plurality of datum <NUM> of the acquired k-space data. As further shown in <FIG>, in embodiments, the method <NUM> further includes estimating <NUM> the respiratory soft gating filter <NUM> and constructing <NUM> a motion regularization matrix based at least in part on the estimated soft-gating filter <NUM>. Therein, calculating <NUM> the coil weight x is based at least in part on the motion regularization matrix, and the motion regularization matrix contains values based upon the motion error of the datum <NUM>. In embodiments, the regularization matrix may be a diagonal matrix containing motion errors of the acquired data included in a reconstruction, and each diagonal element of the regularization matrix may be equal to the motion error in the soft-gating filter corresponding to the respiratory position of an acquired datum in a reconstruction. As will also be appreciated, according to the invention, the coil weight x is calculated to reduce contributions to the reconstruction of the datum <NUM> and/or the line from datum <NUM> of the plurality having motion errors that are large and increases contribution to the reconstruction of the datum <NUM> and/or the line from datum <NUM> of the plurality having motion errors that are small. Moreover, it is to be understood that the coil weight x may be a single weight and/or a plurality of weights, e.g., a list, vectors, and/or matrix.

For example, embodiments of the invention may utilize an autocalibrating parallel imaging style method to synthesizes unacquired/target datum <NUM> from neighboring acquired/source datum <NUM> (Sj, j=<NUM>,<NUM>,. ), i.e., one or more unacquired datum <NUM> may be reconstructed based on information contained by one or more acquired datum <NUM> that are in close proximity within k-space to the one or more unacquired datum <NUM>. The reconstruction weights, x, for a synthesis pattern may be calculated by solving: <MAT> where A and b are source and target calibration data matrixes, respectively. As such, x may be calculated by minimizing the L<NUM>-norm error of: <MAT> As will appreciated, the j-th column in A (A. ,j) may include concatenated calibration data with a k-space shifting corresponding to Sj in reconstruction. Further, in free-breathing imaging, Sj may be collected with motion displacement and, accordingly, A. ,j may need to be updated with A. ,j to calculate the optimal x in the existence of motion, where ej represents the change in calibration data with the corresponding motion of Sj. Alternatively, according to equation <NUM>, motion at Sj may increase the L<NUM>-norm error by xj∥e. ,j∥<NUM> and the entire reconstruction error due to motion may then be approximated by Σ(xj∥e. Therefore, equation <NUM> turns to:
<MAT> where Δ is a diagonal matrix with Δj,j=sqrt(δj) and δj=∥e. As is to be further appreciated, this Tikhonov regularization has the following analytical solution:
<MAT>.

Accordingly, as can be seen, in embodiments, equation <NUM> reduces xj for "bad" datum <NUM> with large ðj to suppress motion (min∥Δx∥<NUM>) and accordingly increases xj for "good" datum <NUM> with small δj to improve data fitting (min∥Ax-b∥<NUM>). For example, in embodiments datum <NUM> acquired at P<NUM> (shown in <FIG> and <FIG>) in the respiration cycle <NUM> which is close to PEE (and, as a result, likely to have a low motion error) may contribute more to the reconstruction than datum <NUM> acquired at P<NUM> (shown in <FIG> and <FIG>) which is far away from PEE (and therefore likely to have a high motion error).

As is to be understood, while embodiments disclosed herein utilize the coil weight x as being based on the Tikhonov regularization solution shown by equation <NUM>, as is to be appreciated, other embodiments may utilize a coil weight x based at least in part on other Tikhonov regularization solutions, and/or a coil weight x based on a regularization method that is not a Tikhonov regularization solution, but which still ensures that the coil weight x reduces contributions to the reconstructed datum and/or line from datum <NUM> that have large motion errors and increases contributions to the reconstructed datum <NUM> and/or line from datum <NUM> that have small motion errors.

Referring now to <FIG>, the respiratory soft gating filter <NUM> is based at least in part on the motion error of a respiration position <NUM> of the subject <NUM>. In such embodiments, estimating <NUM> the respiratory soft gating filter <NUM> may be combined with the acquisition <NUM> of k-space data. For example, embodiments of the invention may acquire/obtain <NUM> the k-space data via a free-breathing 3D cardiac CINE with k-t sampling and a pseudo-random vieworder. In such embodiments, acquisition <NUM> of center <NUM>% k-space may be repeated by four (<NUM>) or more times for estimating Δ (see equation <NUM> above). A histogram may be generated <NUM> from a simultaneously recorded respiratory signal, and the most consistent position near end-expiration PEE and end-inspiration PEI may then be derived <NUM>. As shown in <FIG>, in the repeatedly acquired <NUM> center k-space, two datasets at PEE (KEE) and PEI (KEI), respectively, may also be generated (<NUM> in <FIG>). The motion error from PEE to PEI, ∥KEE-KEI∥<NUM>, may be calculated (<NUM> in <FIG>). As is to be appreciated, δP at a respiratory position, P (not shown), may then be estimated (<NUM> in <FIG>) as shown below:<MAT> While equation <NUM> assumes that δP increases linearly with off-PEE displacement, it is to be appreciated that equation <NUM> may be altered to incorporated scenarios where δP does not increases linearly with off-PEE displacement. As is to be further appreciated, different coil channels may sense motion differently and create different δ's, e.g., lower for elements near the subject's <NUM> dorsal and higher for elements near the subject's <NUM> chest wall. Therefore, in embodiments, ∥KEE-KEI∥<NUM> is calculated individually for each coil channel to generate coil-specific δP's.

The datum and/or line that is reconstructed <NUM> is an unacquired datum <NUM> (hollow dots) and/or line. Additionally, and as shown by decision block <NUM> in method <NUM>, the MRI controller <NUM> is configured to reconstruct multiple/additional datum <NUM> and/or lines within the k-space <NUM>, such that the entirety of the k-space region <NUM> is reconstructed.

Accordingly, in an embodiment, the MRI system <NUM> may be based on a GE 3T (MR750), configured to obtain a free-breathing 3D CINE scan with an acceleration factor of <NUM>, and/or further configured to operate at <NUM>/450W. As exemplary image taken by such an embodiment is shown in <FIG>. In such an embodiment, the acquired k-space <NUM> may be processed via a k-t auto-calibrating parallel imaging method, kat ARC wherein static-tissue-removal may be utilized to identify and remove signals from static tissues, e.g., chest wall, dorsal, in the acquired k-space data to improve kat ARC at high acceleration. As such, the static tissue image may be generated from a time-projection dataset with weighted averaging based on δP to obtain motion-suppressed reconstruction in static tissues. Accordingly, in kat ARC, all k-space lines, including those acquired to correct motion corruption from acquisition, are synthesized based on equation <NUM>, and Δ is constructed based on the P of each source line for each synthesis and the prior-calculated δP. Because each k-space neighborhood contains a mix of 'good' and 'bad' data/datum <NUM>, equation <NUM> synthesizes each line in the entire k-space region <NUM> with an L<NUM>-norm-optimal balance between data fitting and motion suppression.

As will be appreciated, to the extent that such an approach would fall within the claims, the presented reconstruction method could be generally applied to MRI systems with other types of motion, e.g., cardiac motion.

Finally, it is also to be understood that the MRI system <NUM> may include the necessary electronics, software, memory, storage, databases, firmware, logic/state machines, microprocessors, communication links, displays or other visual or audio user interfaces, printing devices, and any other input/output interfaces to perform the functions described herein and/or to achieve the results described herein. For example, as previously mentioned, the MRI system <NUM> may include at least one processor <NUM>, <NUM> and system memory <NUM>, <NUM>, which may include random access memory (RAM) and read-only memory (ROM). The MRI system <NUM> may further include an input/output controller, and one or more data storage structures. All of these latter elements may be in communication with the at least one processor <NUM>, <NUM> to facilitate the operation of the MRI system <NUM> as discussed above. Suitable computer program code may be provided for executing numerous functions, including those discussed above in connection with the MRI system <NUM> and methods disclosed herein. The computer program code may also include program elements such as an operating system, a database management system and "device drivers" that allow the MRI system <NUM>, to interface with computer peripheral devices, e.g., sensors, a video display, a keyboard, a computer mouse, etc..

The at least one processor <NUM>, <NUM> of the MRI system <NUM> may include one or more conventional microprocessors and one or more supplementary co-processors such as math co-processors or the like. Elements in communication with each other need not be continually signaling or transmitting to each other. On the contrary, such elements may transmit to each other as necessary, may refrain from exchanging data at certain times, and may cause several steps to be performed to establish a communication link there-between.

The data storage structures such as memory discussed herein may include an appropriate combination of magnetic, optical and/or semiconductor memory, and may include, for example, RAM, ROM, flash drive, an optical disc such as a compact disc and/or a hard disk or drive. The data storage structures may store, for example, information required by the MRI system <NUM> and/or one or more programs, e.g., computer program code such as the imaging application and/or other computer program product, adapted to direct the MRI system <NUM>. The programs may be stored, for example, in a compressed, an uncompiled and/or an encrypted format, and may include computer program code. The instructions of the computer program code may be read into a main memory of a processor from a computer-readable medium. While execution of sequences of instructions in the program causes the processor to perform the process steps described herein, hard-wired circuitry may be used in place of, or in combination with, software instructions for implementation of the processes of the present invention. Therefore, embodiments of the present invention are not limited to any specific combination of hardware and software.

The program may also be implemented in programmable hardware devices such as field programmable gate arrays, programmable array logic, programmable logic devices or the like. Programs may also be implemented in software for execution by various types of computer processors. A program of executable code may, for instance, includes one or more physical or logical blocks of computer instructions, which may, for instance, be organized as an object, procedure, process or function. Nevertheless, the executables of an identified program need not be physically located together, but may include separate instructions stored in different locations which, when joined logically together, form the program and achieve the stated purpose for the programs such as preserving privacy by executing the plurality of random operations. In an embodiment, an application of executable code may be a compilation of many instructions, and may even be distributed over several different code partitions or segments, among different programs, and across several devices.

The term "computer-readable medium" as used herein refers to any medium that provides or participates in providing instructions to at least one processor <NUM>, <NUM> of the MRI system <NUM> (or any other processor of a device described herein) for execution. Such a medium may take many forms, including but not limited to, non-volatile media and volatile media. Non-volatile media include, for example, optical, magnetic, or opto-magnetic disks, such as memory. Volatile media include dynamic random access memory (DRAM), which typically constitutes the main memory. Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any other optical medium, a RAM, a PROM, an EPROM or EEPROM (electronically erasable programmable read-only memory), a FLASH-EEPROM, any other memory chip or cartridge, or any other medium from which a computer can read.

Various forms of computer readable media may be involved in carrying one or more sequences of one or more instructions to at least one processor for execution. For example, the instructions may initially be borne on a magnetic disk of a remote computer (not shown). The remote computer can load the instructions into its dynamic memory and send the instructions over an Ethernet connection, cable line, or telephone line using a modem. A communications device local to a computing device, e.g., a server, can receive the data on the respective communications line and place the data on a system bus for at least one processor. The system bus carries the data to main memory, from which the at least one processor retrieves and executes the instructions. The instructions received by main memory may optionally be stored in memory either before or after execution by the at least one processor. In addition, instructions may be received via a communication port as electrical, electromagnetic or optical signals, which are exemplary forms of wireless communications or data streams that carry various types of information.

It is further to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. Additionally, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope, provided they fall under the scope of the appended claims.

For example, in an embodiment, an MRI system for imaging a moving subject is provided. The MRI system includes a magnet assembly and an MRI controller. The magnet assembly is configured to acquire-space data via scanning the subject. The acquired k-space data includes a plurality of data each having a motion error. The MRI controller is configured to receive the acquired k-space data from the magnet assembly. The MRI controller is further configured to suppress the motion error of each datum by reconstructing the k-space region via a soft gating threshold in a non-iterative manner. The MRI controller is further configured to: estimate the soft gating threshold; construct a motion regularization matrix based at least in part on the respiratory soft gating threshold; calculate a coil weight based at least in part on the motion regularization matrix; and reconstruct a datum of the plurality based at least in part on the coil weight and the plurality of datum. The coil weight reduces contributions to the synthesizing of datum of the unacquired k-space data from data of the acquired k-space data having motion errors that are large, and increases contributions to the reconstruction of datum of the unacquired k-space data from data of the acquired k-space data having motion errors that are small. The estimated soft gating threshold is based at least in part on a motion error of a motion position of the subject during scanning. In certain embodiments, the reconstructed datum is acquired or unacquired. The MRI controller is further configured to reconstruct additional datum of the plurality so as to completely reconstruct the entire k-space region. In certain embodiments, the calculated coil weight is further based at least in part on a Tikhonov regularization solution. In certain embodiments, the Tikhonov regularization solution is x=(ATA+ΔTΔ)-<NUM>ATb.

Other embodiments provide for a method for magnetic resonance imaging a moving subject. The method includes: acquiring -space data of a k-space region via scanning the subject with a magnetic resonance imaging system, the k-space data including a plurality of data each having a motion error; calculating a coil weight; and reconstructing an unacquired datum of the k-space region based at least in part on the coil weight and the plurality of acquired k-space data. The coil weight reduces contributions to the synthesizing of datum of the unacquired k-space data from data of the acquired k-space data having motion errors that are large, and increases contributions to the reconstruction of datum of the unacquired k-space data from data of the acquired k-space data having motion errors that are small. The method further includes: estimating a soft gating filter; and constructing a motion regularization matrix based at least in part on the estimated soft-gating filter. Therein, calculating a coil weight is based at least in part on the motion regularization matrix. The soft gating filter is based at least in part on an estimated motion error of a motion position of the subject during scanning. The method further includes reconstructing additional datum of the plurality so as to completely reconstruct the entire k-space region in a non-iterative manner. In certain embodiments, calculating a coil weight is based at least in part on a Tikhonov regularization solution. In certain embodiments, the Tikhonov regularization solution is x=(ATA+ΔTΔ)-<NUM>ATb.

Yet still other embodiments provide for an MRI controller for a MRI imaging system that images a moving subject. The MRI controller is configured to: direct a magnet assembly of the MRI imaging system to acquire k-space data of a k-space region via scanning the subject, the acquired k-space data including a plurality of data each having a motion error; estimate a soft gating filter; construct a motion regularization matrix based at least in part on the estimated soft-gating filter; calculate a coil weight based at least in part on the constructed motion regularization matrix; and reconstruct a datum of the plurality based at least in part on the coil weight and the acquired k-space data in a non-iterative manner. Accordingly, the coil weight reduces contributions to the synthesizing of datum of the unacquired k-space data from data of the acquired k-space data having motion errors that are large, and increases contributions to the reconstruction of datum of the unacquired k-space data from data of the acquired k-space data having motion errors that are small. The soft gating filter is based at least in part on an estimated motion error of a motion position of the subject during scanning. In certain embodiments, the coil weight is based at least in part on a Tikhonov regularization solution. In certain embodiments, the Tikhonov regularization solution is x=(ATA+ΔTΔ)-<NUM>ATb. In certain embodiments, the plurality of datum includes at least one of acquired datum and unacquired datum.

Accordingly, as will be appreciated, by utilizing a soft respiratory gating threshold/filter <NUM>, the present invention utilize the available information contained within datum <NUM> that would be discarded by hard thresholding acceptance windows. As a result, the invention is able to reduce/suppress motion error from data within the acceptance window within a free-breathing MRI scan in a non-iterative manner, i.e., the invention can correct k-space for motion error by synthesizing datum <NUM> based on neighboring datum <NUM> without the need to fill/complete k-space via additional scans in an iterative manner. In some embodiments of the invention provide for increased motion suppression, shorter scanning times, and/or more efficient use of acquired data, than traditional free-breathing MRI systems using respiratory gating based on hard threshholding. Further, by utilizing a soft respiratory gating threshold/filter <NUM>, some embodiments of the invention are able to account for intra-window motion error.

Moreover, embodiments of the invention may be implemented in 3D cine and 4D flow MRI systems. As will be appreciated, some embodiments enable free-breathing 3D cine MRI procedures while eliminating the need for the subject <NUM> to breath-hold during cardiac evaluations/imaging, and/or significantly improve the quality of 4D flow anatomy imagery. Accordingly, such embodiments may provide for compressive cardiac evaluations (anatomy, function, angiography, and/or flow) utilizing a single 4D flow scan.

Additionally, while the dimensions and types of materials described herein are intended to define the parameters of the invention, they are by no means limiting and are exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms "including" and "in which" are used as the plain-English equivalents of the respective terms "comprising" and "wherein. " Moreover, in the following claims, terms such as "first," "second," "third," "upper," "lower," "bottom," "top," etc. are used merely as labels, and are not intended to impose numerical or positional requirements on their objects.

This written description uses examples to disclose several embodiments of the invention, including the best mode, and also to enable one of ordinary skill in the art to practice the embodiments of invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to one of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Claim 1:
A method (<NUM>) for magnetic resonance imaging of a moving subject, the method
comprising:
directing a MRI imaging system (<NUM>) to acquire (<NUM>) using a plurality of coil channels k-space data of a k-space region (<NUM>) via free-breathing scanning the subject, the k-space data including a plurality of data, each datum having a motion error due to respiratory motion of the subject and each being associated with a respective position of respiratory motion;
estimating (<NUM>) the motion error and a relationship between the motion error and the respective respiratory position to produce a soft gating filter;
constructing (<NUM>) a motion regularization matrix based at least in part on the estimated soft-gating filter and containing values based upon the motion error of the acquired k-space data ;
calculating (<NUM>) a coil weight for each coil channel of the plurality of coil channels based at least in part on the constructed motion regularization matrix; and synthesizing (<NUM>) unacquired k-space data from the acquired k-space data in a non-iterative manner, without the need to repeat k-space acquisition via additional scans, based on the coil weights, each datum in the unacquired k-space data being synthesized from neighboring data in the acquired k-space data, wherein the coil weights are calculated so as to reduce contributions to the synthesizing of datum of the unacquired k-space data from data of the acquired k-space data having motion errors that are large, and increase contributions to the reconstruction of datum of the unacquired k-space data from data of the acquired k-space data having motion errors that are small.