Abstract:
A method for imaging neuromuscular coupling and sensory processing with magnetic resonance imaging (“MRI”) is provided. More specifically, a method for examining the control that a subject&#39;s brain has over muscular motion, including both prompted and incidental actions, is provided. A dynamic acquisition is performed to rapidly acquire anatomical images of a desired muscle. This dynamic acquisition is interleaved with a functional acquisition that targets the cortical areas that are responsible for controlling, or processing, signals from the desired muscular region. By interleaving these two acquisitions, synchronized image information about the motion of the muscle along with the neuronal activity associated with the control of the muscle is acquired. Interleaving these data acquisitions also allows imaging of brain and muscle at substantially the same time, thereby reducing errors and pinpointing activity.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/149,837 filed on Feb. 4, 2009, and entitled “Method for Dynamic Motion Guided Functional Magnetic Resonance Imaging.” 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The field of the invention is magnetic resonance imaging (“MRI”) methods and systems. More particularly, the invention relates to methods for functional MRI (“fMRI”). 
         [0003]    When a substance such as human tissue is subjected to a uniform magnetic field (polarizing field B 0 ), the individual magnetic moments of the nuclei in the tissue attempt to align with this polarizing field, but precess about it in random order at their characteristic Larmor frequency. If the substance, or tissue, is subjected to a magnetic field (excitation field B 1 ) that is in the x-y plane and that is near the Larmor frequency, the net aligned moment, M z , may be rotated, or “tipped,” into the x-y plane to produce a net transverse magnetic moment M xy . A signal is emitted by the excited nuclei or “spins,” after the excitation signal B 1  is terminated, and this signal may be received and processed to form an image. 
         [0004]    When utilizing these “MR” signals to produce images, magnetic field gradients (G x , G y , and G z ) are employed. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used. The resulting set of received MR signals are digitized and processed to reconstruct the image using one of many well known reconstruction techniques. 
         [0005]    The measurement cycle used to acquire each MR signal is performed under the direction of a pulse sequence produced by a pulse sequencer. Clinically available MRI systems store a library of such pulse sequences that can be prescribed to meet the needs of many different clinical applications. Research MRI systems include a library of clinically-proven pulse sequences and they also enable the development of new pulse sequences. 
         [0006]    The MR signals acquired with an MRI system are signal samples of the subject of the examination in Fourier space, or what is often referred to in the art as “k-space.” Each MR measurement cycle, or pulse sequence, typically samples a portion of k-space along a sampling trajectory characteristic of that pulse sequence. Most pulse sequences sample k-space in a raster scan-like pattern sometimes referred to as a “spin-warp,” a “Fourier,” a “rectilinear,” or a “Cartesian” scan. The spin-warp scan technique employs a variable amplitude phase encoding magnetic field gradient pulse prior to the acquisition of MR spin-echo signals to phase encode spatial information in the direction of this gradient. In a two-dimensional implementation (“2DFT”), for example, spatial information is encoded in one direction by applying a phase encoding gradient, G y , along that direction, and then a spin-echo signal is acquired in the presence of a readout magnetic field gradient, G x , in a direction orthogonal to the phase encoding direction. The readout gradient present during the spin-echo acquisition encodes spatial information in the orthogonal direction. In a typical 2DFT pulse sequence, the magnitude of the phase encoding gradient pulse, G y , is incremented, ΔG y , in the sequence of measurement cycles, or “views” that are acquired during the scan to produce a set of k-space MR data from which an entire image can be reconstructed. 
         [0007]    There are many other k-space sampling patterns used by MRI systems. These include “radial”, or “projection reconstruction” scans in which k-space is sampled as a set of radial sampling trajectories extending from the center of k-space. The pulse sequences for a radial scan are characterized by the lack of a phase encoding gradient and the presence of a readout gradient that changes direction from one pulse sequence view to the next. There are also many k-space sampling methods that are closely related to the radial scan and that sample along a curved k-space sampling trajectory rather than the straight line radial trajectory. 
         [0008]    An image is reconstructed from the acquired k-space data by transforming the k-space data set to an image space data set. There are many different methods for performing this task and the method used is often determined by the technique used to acquire the k-space data. With a Cartesian grid of k-space data that results from a 2D or 3D spin-warp acquisition, for example, the most common reconstruction method used is an inverse Fourier transformation (“2DFT” or “3DFT”) along each of the 2 or 3 axes of the data set. With a radial k-space data set and its variations, the most common reconstruction method includes “regridding” the k-space samples to create a Cartesian grid of k-space samples and then performing a 2DFT or 3DFT on the regridded k-space data set. In the alternative, a radial k-space data set can also be transformed to Radon space by performing a 1DFT of each radial projection view and then transforming the Radon space data set to image space by performing a filtered backprojection. 
         [0009]    Functional magnetic resonance imaging (“fMRI”) technology provides an approach to study neuronal activity. Conventional fMRI detects changes in cerebral blood volume, flow, and oxygenation that locally occur in association with increased neuronal activity that is induced by functional paradigms. This physiological response is often referred to as the “hemodynamic response.” The hemodynamic response to neuronal activity provides a mechanism for image contrast commonly referred to as the blood-oxygen level dependent (“BOLD”) signal contrast. An MRI system can be used to acquire signals from the brain over a period of time. As the brain performs a task, these signals are modulated synchronously with task performance to reveal which regions of the brain are involved in performing the task. The series of fMRI time course images must be acquired at a rate that is high enough to see the changes in brain activity induced by the functional paradigm. In addition, because neuronal activity may occur at widely dispersed locations in the brain, a relatively large 3D volume or multi-slice volume must be acquired in each time frame. 
         [0010]    Typically, functional paradigms employed by fMRI fall into one of two categories: block designs and event-related designs. In block paradigms, functional tasks are organized into blocks that alternate throughout the functional scan at regular intervals. In addition, block paradigms often employ a stimulus, such as a visual or auditory cue, to perform a given task, the stimulus being presented to the subject such that a desired task is initiated. This approach can confound functional analysis, however, since unwanted neuronal activation is often produced in response to the stimulus. For example, if a subject is presented with a visual cue, neuronal activation in response to processing the visual information is produced. This neuronal activation results in cognitive function being represented in the functional images in portions of the brain where activation may not be desired, such as the visual cortex, for the particular application at task. In contrast to block paradigms, functional tasks in event-related paradigms are typically pseudo-random single events or rapid repetitions thereof. While pseudo-random in presentation, event-related paradigms still rely on predetermined timing of when functional tasks are to occur. Moreover, in many cases, external stimuli are still required to induce the desired functional task. 
         [0011]    In general, fMRI analyses proceed by performing statistical analyses between estimates of the expected hemodynamic response and BOLD signal changes that are indicative of the functional paradigm design, that is, the timing of the functional tasks performed by the subject, utilized when acquiring the image data. A mathematical model produced around the functional paradigm thereby forms the basis for statistical analysis, focusing on voxels whose signal changes correspond to the timing of the functional task. Therefore, a priori information about the times at which a functional task is performed is required before a subject is imaged. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention provides a method for functional magnetic resonance imaging (“fMRI”), and the subsequent fMRI analyses, without the need for a priori information regarding the specific timing of the performance of a functional task. More specifically, the present invention provides a method for examining the control that a subject&#39;s brain has over muscular motion, including both prompted and incidental actions. For example, the subject may be instructed to swallow, or the subject may swallow incidentally, while being imaged. 
         [0013]    It is therefore an aspect of invention to provide an imaging method having the ability to assess the brain&#39;s command signals, or sensory processing of the muscular motion, for both prompted and incidental events. One area of impact of the method is in studying swallowing disorders. 
         [0014]    It is another aspect of the invention to provide a method for simultaneously studying the action of muscles and the cortical processing controlling the timing of these actions. Additionally, hemodynamic response estimation techniques can be applied to estimate the functional response to incidental swallows, to assess lag between the cortical signal and the initiation of the swallowing event, and to monitor sensory feedback during the swallowing process. By studying these items for incidental swallows, as opposed to prompted, irregularities in the normal swallowing process can be more accurately identified. 
         [0015]    It is yet another aspect of the invention to provide an extension of standard functional MRI methods, which rely on the so-called blood-oxygen level dependent (“BOLD”) effect. In particular, a dynamic acquisition is interleaved with a BOLD acquisition. The dynamic acquisition acquires rapid images of a muscle while the interleaved functional BOLD acquisition targets the cortical areas that are responsible for controlling or processing signals from the region. By interleaving these two acquisitions, synchronized image information about the motion of the muscle along with its corresponding brain function is acquired. Interleaving these data acquisitions also allows imaging of brain and muscle at substantially the same time, therefore, reducing errors and pinpointing activity. 
         [0016]    The foregoing and other aspects and advantages of the invention will appear from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown by way of illustration at least one embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention, however, and reference is made therefore to the claims and herein for interpreting the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a block diagram of an exemplary magnetic resonance imaging (“MRI”) system that employs the present invention; 
           [0018]      FIG. 2A  is a graphic illustration of a dynamic imaging portion of a preferred pulse sequence; 
           [0019]      FIG. 2B  is a graphic illustration of a functional imaging portion of a preferred pulse sequence; 
           [0020]      FIG. 2C  is a graphic illustration of a spiral-in k-space sampling pattern employed by the pulse sequence of  FIG. 2B ; 
           [0021]      FIG. 3A  is a graphic illustration of a data acquisition scheme utilizing the dynamic and functional imaging portions of the preferred pulse sequence of  FIGS. 2A and 2B ; 
           [0022]      FIG. 3B  is an graphic illustration of a volume of interest from which image data is acquired from a subject in accordance with the data acquisition scheme of  FIG. 3A ; 
           [0023]      FIG. 4  is a flowchart setting forth the steps of an embodiment of the present invention; and 
           [0024]      FIG. 5  is a flowchart setting forth the steps of an embodiment of the functional magnetic resonance imaging (fMRI) analysis performed in accordance with the embodiment of the present invention set forth in  FIG. 4 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0025]    Referring particularly to  FIG. 1 , the preferred embodiment of the invention is employed in a magnetic resonance imaging (“MRI”) system. The MRI system includes a workstation  110  having a display  112  and a keyboard  114 . The workstation  110  includes a processor  116  that is a commercially available programmable machine running a commercially available operating system. The workstation  110  provides the operator interface that enables scan prescriptions to be entered into the MRI system. The workstation  110  is coupled to four servers: a pulse sequence server  118 ; a data acquisition server  120 ; a data processing server  122 , and a data store server  123 . The workstation  110  and each server  118 ,  120 ,  122  and  123  are connected to communicate with each other. 
         [0026]    The pulse sequence server  118  functions in response to instructions downloaded from the workstation  110  to operate a gradient system  124  and a radiofrequency (“RF”) system  126 . Gradient waveforms necessary to perform the prescribed scan are produced and applied to the gradient system  124  that excites gradient coils in an assembly  128  to produce the magnetic field gradients G x , G y , and G z  used for position encoding MR signals. The gradient coil assembly  128  forms part of a magnet assembly  130  that includes a polarizing magnet  132  and a whole-body RF coil  134 . 
         [0027]    RF excitation waveforms are applied to the RF coil  134  by the RF system  126  to perform the prescribed magnetic resonance pulse sequence. Responsive MR signals detected by the RF coil  134  or a separate local coil (not shown in  FIG. 1 ) are received by the RF system  126 , amplified, demodulated, filtered and digitized under direction of commands produced by the pulse sequence server  118 . The RF system  126  includes an RF transmitter for producing a wide variety of RF pulses used in MR pulse sequences. The RF transmitter is responsive to the scan prescription and direction from the pulse sequence server  118  to produce RF pulses of the desired frequency, phase and pulse amplitude waveform. The generated RF pulses may be applied to the whole body RF coil  134  or to one or more local coils or coil arrays (not shown in  FIG. 1 ). 
         [0028]    The RF system  126  also includes one or more RF receiver channels. Each RF receiver channel includes an RF amplifier that amplifies the MR signal received by the coil to which it is connected and a detector that detects and digitizes the I and Q quadrature components of the received MR signal. The magnitude of the received MR signal may thus be determined at any sampled point by the square root of the sum of the squares of the I and Q components: 
         [0000]        M =√{square root over (I 2   +Q   2 )}, 
         [0029]    and the phase of the received MR signal may also be determined: 
         [0000]    
       
         
           
             φ 
             = 
             
               
                 
                   tan 
                   
                     - 
                     1 
                   
                 
                  
                 
                   ( 
                   
                     Q 
                     I 
                   
                   ) 
                 
               
               . 
             
           
         
       
     
         [0030]    The pulse sequence server  118  also optionally receives patient data from a physiological acquisition controller  136 . The controller  136  receives signals from a number of different sensors connected to the patient, such as ECG signals from electrodes or respiratory signals from a bellows. Such signals are typically used by the pulse sequence server  118  to synchronize, or “gate”, the performance of the scan with the subject&#39;s respiration or heart beat. 
         [0031]    The pulse sequence server  118  also connects to a scan room interface circuit  138  that 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  138  that a patient positioning system  140  receives commands to move the patient to desired positions during the scan. 
         [0032]    The digitized MR signal samples produced by the RF system  126  are received by the data acquisition server  120 . The data acquisition server  120  operates in response to instructions downloaded from the workstation  110  to receive the real-time MR data and provide buffer storage such that no data is lost by data overrun. In some scans the data acquisition server  120  does little more than pass the acquired MR data to the data processor server  122 . However, in scans that require information derived from acquired MR data to control the further performance of the scan, the data acquisition server  120  is programmed to produce such information and convey it to the pulse sequence server  118 . For example, during prescans MR data is acquired and used to calibrate the pulse sequence performed by the pulse sequence server  118 . Also, navigator signals may be acquired during a scan and used to adjust RF or gradient system operating parameters or to control the view order in which k-space is sampled. And, the data acquisition server  120  may be employed to process MR signals used to detect the arrival of contrast agent in a magnetic resonance angiography (MRA) scan. In all these examples the data acquisition server  120  acquires MR data and processes it in real-time to produce information that is used to control the scan. 
         [0033]    The data processing server  122  receives MR data from the data acquisition server  120  and processes it in accordance with instructions downloaded from the workstation  110 . Such processing may include, for example: Fourier transformation of raw k-space MR data to produce two or three-dimensional images; the application of filters to a reconstructed image; the performance of a backprojection image reconstruction of acquired MR data; the calculation of functional MR images; and the calculation of motion or flow images. 
         [0034]    Images reconstructed by the data processing server  122  are conveyed back to the workstation  110  where they are stored. Real-time images are stored in a data base memory cache (not shown) from which they may be output to operator display  112  or a display  142  that is located near the magnet assembly  130  for use by attending physicians. Batch mode images or selected real time images are stored in a host database on disc storage  144 . When such images have been reconstructed and transferred to storage, the data processing server  122  notifies the data store server  123  on the workstation  110 . The workstation  110  may be used by an operator to archive the images, produce films, or send the images via a network to other facilities. 
         [0035]    Currently, deficits in swallowing are evaluated with video fluoroscopy, which looks at the timing of a barium swallow. In these fluoroscopy-based methods, delays, displacements, or any other irregularities of the swallow are monitored. Additionally, pressure sensors can be placed in the pharynx to assess the function of the muscle. It would be advantageous, however, to provide a method for simultaneously acquiring information regarding the mechanics of a patient&#39;s swallowing and information regarding the underlying neural control of such mechanics. By interleaving a dynamic imaging pulse sequence portion with a functional imaging pulse sequence portion, images indicative of swallowing mechanics can be obtained substantially simultaneously with functional images indicative of neuronal activity. In turn, the dynamic images can be employed to retrospectively determine when the subject was swallowing, thereby allowing the retrospective production of a timing sequence to be used in analysis of the functional images. In this manner, the subject is allowed to freely swallow during the imaging study, and need not be cued to swallow. This allows a more accurate study of the subject&#39;s swallowing mechanics than was previously achievable. 
         [0036]    Referring now to  FIGS. 2A and 2B , an exemplary pulse sequence utilized when practicing at least one embodiment of the present invention includes a dynamic imaging portion  200  and a functional imaging portion  250 . A number of different pulse sequences can be used to direct the MRI system to acquire image data during the dynamic imaging portion  200 ; however, in one embodiment, a spiral-out gradient recalled echo pulse sequence is employed, such as the one shown in  FIG. 2A . The dynamic imaging portion  200  includes a radio frequency (“RF”) excitation pulse  202  that is played out in the presence of a slice selective gradient pulse  204  in order to produce transverse magnetization in a prescribed slice. The slice selective gradient  204  also includes a rephasing lobe  206  that acts to compensate for phase dispersions in transverse magnetization produced by the slice selective gradient  204 . As shown in  FIG. 2A , the slice selective gradient  204  is played out along the G x -axis, thus producing a sagittal slice in the subject. It will be appreciated by those skilled in the art, however, that appropriate changes can be made to the pulse sequence in  FIG. 2A  so that slices in different planes are selected. 
         [0037]    After excitation of the spins in the slice, a multi-shot spiral-out spoiled gradient recalled echo acquisition is used to sample k-space. Here, a phase encoding gradient pulse  208  is applied to position encode the MR signal along one direction in the slice. A readout gradient pulse  210  is also applied to position encode the MR signal along a second, orthogonal direction in the slice. The result of playing out the phase encoding gradient  208  and the readout gradient  210  together is the sampling of k-space in a spiral-out pattern. A multi-shot acquisition covers only a portion of k-space for each repetition of the acquisition. For the multi-shot spiral, the spiral interleaf is rotated by a small amount between repetitions so as to cover the whole k-space upon a specified number of multiple applications, referred to as the number of shots. In the at least one embodiment, a 6-shot spiral acquisition is used for the dynamic imaging. After the phase encode and readout gradients,  208  and  210 , are applied, a spoiler gradient  212  is applied to dephase any residual echo signal so that it does not contaminate signals acquired from later repetition time (“TR”) periods. In general, the spoiler gradient  212  can be played along any of the gradient axes. Moreover, a plurality of such spoiler pulses  212  may be played out along any combination of these gradient axes. 
         [0038]    The dynamic imaging portion  200  is repeated and the phase encoding and readout gradients,  208  and  210 , are altered by stepping through a set of values to sample 2D k-space in a prescribed manner. As discussed above, this effectively rotates the spiral sampling pattern so that a different “spiral interleaf” is sampled with each repetition. In at least one embodiment, the dynamic imaging portion  200  is repeated six times before proceeding with the functional imaging portion  250  of the pulse sequence. It is noted, however, that any number of repetitions of the dynamic imaging portion  200  may be employed depending on the desired imaging application. As will be described below in detail, the dynamic imaging portion acquires MR signal from the same imaging slice during each repetition. 
         [0039]    A number of different pulse sequences can be used to direct the MRI system to acquire functional image data during the functional imaging portion  250 ; however, in one embodiment, a spiral-in gradient recalled echo (“GRE”) pulse sequence is employed, such as the one shown in  FIG. 2B . By acquiring functional image data with a spiral-in sampling pattern, the more important central regions of k-space are sampled when the functional MRI contrast has been allowed to develop. The functional MRI contrast is based on the blood oxygenation level dependent (BOLD) contrast mechanism described above, which provides image contrast resultant from microscopic field gradients around hemoglobin that depend on its oxygenation state. The spiral-in GRE sequence includes an RF excitation pulse  252  that is played out in the presence of a slice selective gradient pulse  254  to produce transverse magnetization in a prescribed slice. The slice selective gradient  254  also includes a rephasing lobe  256  that acts to compensate for phase dispersions in transverse magnetization produced by the slice selective gradient  254 . 
         [0040]    After excitation of the spins in the slice, a prephasing gradient  257  is played out on both the phase encode and readout gradient axes to position the start of sampling at the periphery of k-space. Next, a phase encoding gradient pulse  258  is applied to position encode the MR signal along one direction in the slice. A readout gradient pulse  260  is also applied to position encode the MR signal along a second, orthogonal direction in the slice. The result of playing out the phase encoding gradient  258  and the readout gradient  260  together is the sampling of k-space in a spiral-in pattern, such as the one shown in  FIG. 2C . With such a sampling pattern, the peripheral regions of k-space are acquired before the central region. As mentioned above, this allows the transverse magnetization to develop functional contrast before image data is acquired from the central region of k-space. This is advantageous since the central region of k-space contains most of the information regarding MR signal changes in response to neuronal activation. After the phase encoding  258  and readout gradient  260  are applied, a spoiler gradient  262  is applied to dephase any residual echo signal so that it does not contaminate signals acquired from later TR periods. In general, the spoiler gradient  262  can be played along any of the gradient axes. Moreover, a plurality of such spoiler pulses  262  may be played out along any combination of these gradient axes. 
         [0041]    In at least one embodiment, the functional imaging portion  250  is repeated once before proceeding with subsequent repetitions of the dynamic imaging portion  200  of the pulse sequence. It is noted, however, that any number of repetitions of the functional imaging portion  250  may be employed depending on the desired imaging application. As will be described below in detail, the functional imaging portion acquires MR signal from a different imaging slice during each subsequent repetition. Additionally, after data has been acquired from each prescribed functional slice, further repetitions of the pulse sequence are employed to sample the slices again so that a time series of functional image data is acquired. Additionally, the dynamic portion  200  is repeated so that a time series of dynamic image data is acquired, as will be described below in detail. 
         [0042]    Referring particularly now to  FIGS. 3A and 3B , the data acquisition scheme for an embodiment of the present invention is illustrated. As shown in  FIG. 3A , the dynamic and functional imaging portions of the preferred pulse sequence are performed in an interleaved manner in order to acquire both dynamic and functional image data from a subject  300  ( FIG. 3B ). First, the dynamic acquisition  200  is repeated a plurality of times to acquire dynamic image data from a single “dynamic” slice  302  in the subject  300 . An exemplary dynamic slice  302  is a sagittal slice that lies along the midline of the subject. In at least one embodiment, the dynamic imaging portion  200  is repeated six times before proceeding with the functional imaging portion  250  of the pulse sequence. In such embodiments, each repetition of the dynamic imaging portion  200  corresponds to a different shot of a spiral gradient echo acquisition. These individual shots are preferably interleaved spiral acquisitions; however, in the alternative, the data need not be acquired using an interleaved sampling pattern. Furthermore, and as mentioned above, the dynamic image data is acquired from this same slice location throughout the imaging session. 
         [0043]    After the first set of dynamic image data has been acquired, the functional imaging portion  250  is performed once to acquire functional image data at a first slice location in an imaging volume  304 . Exemplary functional slices in the imaging volume  304  are transverse slices; however, in the alternative, the functional slices may be coronal, sagittal, or oblique slices. Another set of the dynamic imaging portion  200  is subsequently applied to acquire another dynamic image data set from the same dynamic slice location  302 . Likewise, after the set of the dynamic imaging portion  200  has been applied, one repetition of the functional imaging portion  250  is performed to acquire functional image data at a second slice location in the imaging volume  304 . In the alternative, functional image data may be acquired from the same slice location a plurality of times before acquiring data from a different location. This process repeats until functional image data has been acquired from the desired number of slice locations in the imaging volume  304 . After the functional imaging volume has been acquired, the aforementioned process repeats to acquire a time series of both the functional volume, or individual slices therein, and the dynamic images. 
         [0044]    Referring particularly now to  FIG. 4 , a flowchart setting forth the steps of an exemplary method for acquiring dynamic and functional image data in accordance with the present invention is illustrated. The method begins with the acquisition of dynamic image data, as indicated at step  400 . After a set of dynamic image data has been acquired, functional image data is acquired at step  402 . As discussed above, each functional image data set corresponds to one slice location in a volume of interest that encompasses the subject. Therefore, a decision is made at decision block  404  whether all of the desired functional image data slices have been acquired. If not, the process loops back to step  400  after selecting the next functional imaging slice location, as indicated at step  406 . In this manner, one dynamic image is obtained for every functional image obtained. It is noted, however, as described above, the dynamic image data is acquired from the same slice location during each repetition. In the alternative, different slice locations at which dynamic image data is acquired can be selected during each repetition, as may be called for by the desired application. After all of the functional image data for one imaging volume has been acquired, a determination is made at decision block  408  whether the scanning session is completed. If not, the process loops back to acquire the next functional imaging volume, and corresponding dynamic image data, for the next set of time points in a time series. In this manner, time series of dynamic and functional image data are acquired such that functional MRI analyses can be performed later. 
         [0045]    After all of the dynamic and functional image data has been acquired, corresponding dynamic and functional images are reconstructed, as indicated at step  410 . A series of dynamic images is reconstructed from the dynamic image data. This is a conventional image reconstruction such as, for example, a regridding and Fourier transformation of the acquired dynamic image data. This series of dynamic images depicts the dynamic motion in the prescribed slice that occurred during the course of the imaging session. For example, the motion of muscles including the tongue and the levator veli palatini is represented in the series of dynamic images. In this manner, the series of dynamic images is indicative of the swallowing that the subject performed while being imaged. This information is later utilized to perform fMRI analysis on the functional images. 
         [0046]    The series of functional images is reconstructed from the functional image data. This is a conventional image reconstruction. For example, the functional image data is regridded to a Cartesian grid and subsequently Fourier transformed to produce the functional images. Such a series of images includes images indicative of neuronal activation at a plurality of prescribed slice locations within the subject. Following the reconstruction of the dynamic and functional images, an fMRI analysis is performed on the functional images to determine the neuronal activity of the subject during the imaging session, as indicated at step  412 . 
         [0047]    Conventional fMRI analyses require a priori information regarding the timing of the performed functional task. Therefore, traditionally, functional paradigms are designed in either a block or event-related manner. However, when practicing the present invention, such a priori information is not necessary. Instead, the subject is allowed to freely perform a desired task, such as swallowing, throughout the acquisition of the image data. The reconstructed dynamic images are then utilized to retrospectively generate a timing sequence for the performed task. In this manner, the acquired functional image data is not confounded by extraneous neuronal activation corresponding to stimuli presented to the subject. 
         [0048]    Referring particularly now to  FIG. 5 , the steps of an embodiment of the functional MRI (“fMRI”) analysis performed when practicing the present invention are illustrated. First, as discussed above, the reconstructed dynamic images are utilized to produce a timing sequence of the performance of the desired task, as shown at step  500 . For example, the series of dynamic images is analyzed to determine time points during the data acquisition at which the subject swallowed. These time points are recorded and a timing sequence corresponding to the performance of the swallow task produced therefrom. This timing sequence is subsequently used to produce a mathematical model of the expected hemodynamic response produced by the neuronal activation, as shown at step  502 . It will be appreciated by those skilled in the art that an exemplary mathematical model includes the so-called general linear model (“GLM”) utilizing a standard BOLD response or hemodynamic response function. The functional images are then preprocessed prior to the statistical analysis, as shown at step  504 . Preprocessing includes smoothing the functional images with a Gaussian filter, correcting the functional images for subject motion, and normalization of the functional images to a reference atlas, such as a Talairach coordinate reference. It will be appreciated by those skilled in the art that any number of preprocessing steps can be performed or omitted, and the performance of such steps is dictated by user preference and the application at hand. 
         [0049]    After the functional images have been preprocessed, a statistical analysis is performed on the images to identify signal changes in voxels indicative of neuronal activation, as indicated at step  506 . For example, a statistical analysis is performed in accordance with the GLM. In such a method, each voxel is analyzed to detect those whose signal variation in time corresponds to the timing sequence produced earlier. Finally, the functional maps produced by the statistical analysis are displayed at step  508 . The functional maps can be displayed directly, or can be displayed as an overlay on a high resolution anatomical image of the corresponding slice location in the subject. With the latter method of display, it is easier to visually interpret the location of neuronal activation in the subject&#39;s brain, as is well know in the art. 
         [0050]    The present invention has been described in terms of one or more preferred embodiments, and it should be appreciated that many equivalents, alternatives, variations, and modifications, aside from those expressly stated, are possible and within the scope of the invention.