MRI device

Abstract

To provide an MRI system coil insert for use with an MRI system, an MRI system arrangement comprising an MRI system together with a coil insert or an MRI system together with other components, as well as an echo planar spectroscopic imaging system comprising the MRI system arrangement and a method for operating the MRI system.SOLUTION: An MRI system coil insert 2 for use within a bore B of a main MRI system 1 is provided, the coil insert 2 comprises at least one gradient coil for creating a spatially varying magnetic field along a respective axis and being arranged to be electrically driven at an ultrasonic frequency.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an MRI apparatus, and more particularly to an MRI system coil insert for use with an MRI system, an MRI system apparatus including an MRI system including the coil insert or other components, and an echo-planar spectroscopic imaging system including the MRI system apparatus, and a method of operating the MRI system.

Background Art

[0002] Magnetic Resonance Imaging (MRI) systems are widely used for imaging a subject and also for obtaining spectral information in the case of Magnetic Resonance Spectroscopy Imaging (MRSI). An MRI system generally includes a magnet configuration that creates a large static magnetic field B0, a set of high-frequency coils or antennas that generate an alternating magnetic field B1 and collect magnetic resonance signals (i.e., acquire magnetic resonance data), and a set of gradient magnetic field coils that enable spatial encoding in the B0 magnetic field to allow tomographic imaging. Further, in the case of MRSI, the gradient magnetic field coils are also used to enable spectroscopic encoding.

[0003] Spatial encoding of magnetic resonance signals is generally achieved by rapid switching of three magnetic field gradients (X, Y, Z) created by gradient magnetic field coils located around a scanner bore in which the subject to be examined is positioned.

[0004] Generally, in existing systems, the gradient magnetic field coils are driven in the range of 0 to 10 kHz. Since the gradient magnetic field coils are driven within the audible range (20 Hz to 20 kHz), considerable effort has been made to reduce the noise generated at the switching gradients and by the Lorentz forces induced thereby. Such methods include using materials that attenuate the generated noise.

[0005] To enhance the spatial resolution of MRI, the gradient system can be driven "faster" and "more powerfully". That is, it has a larger gradient slew rate (T / m / s) and a larger gradient strength (mT / m). The current gradient performance may be limited mainly by unpleasant peripheral nerve stimulations (PNS) induced by the too-fast switching of strong magnetic field gradients. The switching of the gradient can induce electric fields and currents in conductive tissues such as muscles and nerves, which may lead to nerve depolarization and ultimately nerve stimulation.

Summary of the Invention

Problems to be Solved by the Invention

[0006] Therefore, it is desirable to develop an MRI apparatus and a method of operating an MRI apparatus that can improve performance without increasing the physical discomfort to the patient due to auditory effects and / or peripheral nerve stimulations. Similarly, it would be desirable to create an MRI apparatus and a method of using an MRI apparatus that can reduce the auditory effects and / or peripheral nerve stimulations and / or other causes of discomfort, regardless of whether the performance of the MRI process itself is improved. Also, it may be interesting to be able to complete the scan more quickly in order to minimize the patient's discomfort and / or obtain a result that is less affected by the time taken to acquire the scan.

Means for Solving the Problems

[0007] According to a first aspect of the present invention, there is provided a coil insert for an MRI system used within the bore of an MRI system, the coil insert comprising at least one gradient magnetic field coil arranged to create a spatially varying magnetic field along respective axes and to be electrically driven at an ultrasonic frequency.

[0008] This enables the functionality of the main MRI system to be used in combination with the insert to perform examinations. The use of ultrasonic frequencies has various advantages. First, since the time dominated by the Lorentz force is less, the force applied to the coil itself can be reduced. This means that the coil can be lighter than when driven at more conventional frequencies, so the coils can be physically different and the structures supporting them can be different. Second, the gradient switching becomes inaudible to the patient. Third, it has been found that when ultrasonic frequencies are used, the peripheral nerve stimulation (PNS) of the patient undergoing the examination can be reduced. This is presumably because there is not enough time for the nerves to respond to the switching magnetic field.

[0009] The coil insert may have a central region without gradient magnetic field coil windings. This can enable a window to be provided in the insert through which the patient can see when the patient's head is positioned within the insert. This can be facilitated by using less force on the lighter coil / coils.

[0010] The insert may be substantially cylindrical. The insert may have a main axis. The main axis may be arranged to be aligned with the main axis of the bore of the main MRI system in which the insert is used. In such a case, the axes of the insert and the main MRI system may be aligned by being parallel to each other or coinciding with each other.

[0011] At least one gradient magnetic field coil may comprise a Z-gradient magnetic field coil that creates a spatially varying magnetic field along the main axis of the insert. At least one gradient magnetic field coil may comprise an X-gradient magnetic field coil or a Y-gradient magnetic field coil that creates a spatially varying magnetic field transverse to the main axis of the insert.

[0012] The coil insert may comprise a first gradient magnetic field coil that creates a spatially varying magnetic field along a first respective axis, and a second gradient magnetic field coil that creates a spatially varying magnetic field along a second respective axis.

[0013] The first gradient magnetic field coil may be a Z-gradient magnetic field coil that creates a spatially varying magnetic field along the main axis of the insert, and the second gradient magnetic field coil may be an X-gradient magnetic field coil or a Y-gradient magnetic field coil that creates a spatially varying magnetic field in a transverse direction with respect to the main axis of the insert.

[0014] When the coil insert comprises a first gradient magnetic field coil and a second gradient magnetic field coil, the coil insert may still have a central region without gradient magnetic field coil windings.

[0015] The coil insert may comprise a third gradient magnetic field coil that creates a spatially varying magnetic field along a third respective axis that is transverse to the first axis and the second axis. However, generally, it is easier to provide a central region without gradient magnetic field coil windings, so it is preferred to provide one or two gradient magnetic field coils and not provide a third gradient magnetic field coil.

[0016] The main MRI system will have its own gradient magnetic field coils, which may be used in cooperation with the gradient magnetic field coils of the insert during operation. Thus, for example, if the insert does not have a gradient magnetic field coil that creates a spatially varying magnetic field along a particular axis, spatial encoding along that axis may be performed using the gradient magnetic field coils of the main MRI system.

[0017] The Z-gradient magnetic field coil may comprise at least one set of windings.

[0018] The Z-gradient magnetic field coil may comprise a first set of windings provided at the first end of the insert and a second set of windings provided at the second end of the insert. In a series of embodiments, the region between the first and second sets of windings may not have Z-gradient magnetic field coil windings.

[0019] Creating a central region without windings may be associated with a low linearity magnetic field, but has been determined to be acceptable for this type of insert. In particular, when the insert is used in an examination involving a patient's head. Here, the insert need not have a long length.

[0020] In some examples, the Z-gradient magnetic field coil may comprise more than two sets of windings. For example, four or more sets of windings may be provided.

[0021] The windings may be arranged to enable providing a segmented gradient on the Z-axis. That is, instead of providing a continuous, i.e., linear, gradient along the Z-axis, a series of gradient segments along the axis is provided. This means that a smaller maximum absolute magnetic field may be used to set the gradient along the entire Z-axis. This may then help to minimize peripheral nerve stimulation (PNS) of the patient undergoing the examination. This arrangement is more useful in the case of a longer insert, i.e., when the Z-axis is longer. Such an insert may be for examining a longer region of the patient or may be a whole-body insert.

[0022] In other words, the windings may be arranged to enable providing a spatially non-monotonic gradient along the Z-axis.

[0023] The windings may be arranged to enable providing a spatially multi-lobed gradient along the Z-axis.

[0024] The windings may be arranged to enable providing a spatially oscillating gradient along the Z-axis.

[0025] The winding may be arranged to enable it to provide a gradient having a polynomial or sinusoidal spatial variation along the Z-axis.

[0026] Here, when referring to these gradient patterns, it will be understood that reference is being made to the variation in the amplitude / size of the magnetic field as seen along the Z-axis.

[0027] The winding of the Z-gradient magnetic field coil may be provided in two layers, and the winding of the first layer among the two layers is provided without being aligned with the winding of the second layer among the two layers. This may help to improve the achievable spatial encoding.

[0028] The winding of the first set of the Z-gradient magnetic field coil may be provided in two layers, and the winding of the first layer among the two layers is provided without being aligned with the winding of the second layer among the two layers. The winding of the second set of the Z-gradient magnetic field coil may be provided in two layers, and the winding of the first layer among the two layers is provided without being aligned with the winding of the second layer among the two layers.

[0029] The X-gradient magnetic field coil or the Y-gradient magnetic field coil may comprise at least one set of windings.

[0030] The X-gradient magnetic field coil or the Y-gradient magnetic field coil may comprise a pair of windings provided on opposite sides in the radial direction of the insert. Each winding of the pair may comprise a plurality of helically wound turns, and each turn has, respectively, an inner arcuate segment, a first end segment extending outwardly to an outer arcuate segment, and a second end segment extending inwardly from the outer arcuate segment to the corresponding inner arcuate segment of the next turn. Each inner arcuate segment may be along the side wall of the insert. Each outer arcuate segment may be along the side wall of the insert.

[0031] When a Z-gradient magnetic field coil is provided and comprises the first and second sets of windings as described above, an X or Y-gradient magnetic field coil may be provided and disposed within the insert axially between the first and second sets of windings of the Z-gradient magnetic field coil.

[0032] The X or Y gradient magnetic field coil may include a third set of windings and a fourth set of windings provided on opposite sides in the radial direction of the insert and between the first and second windings of the Z gradient magnetic field coil in the axial direction. Accordingly, the third and fourth sets of windings may be provided in a region where there are no Z gradient magnetic field coil windings. Here, the third and fourth sets of windings are the same windings as described above as a pair of windings, and in this series of embodiments, note that they are the third and fourth in the sense that the first and second windings are defined in relation to the Z gradient magnetic field coil.

[0033] A circumferential gap may be provided between the third and fourth sets of windings so that there is a region in the insert where there are no windings of the Z gradient magnetic field coil and no windings of the X or Y gradient magnetic field coil. This region may be arranged as a window that a patient can see through when the patient's head is disposed within the insert.

[0034] Each of the third set of windings and the fourth set of windings may each include a plurality of helically wound turns, and each turn has an inner arcuate segment, a first end segment extending outward to the outer arcuate segment, and a second end segment extending inward from the outer arcuate segment to the corresponding inner arcuate segment of the next turn.

[0035] Each inner arcuate segment may be along the side wall of the insert. Each outer arcuate segment may be along the side wall of the insert.

[0036] Such an arrangement can help maximize the axial length of the insert, where the X or Y gradient magnetic field coil can generate a linear magnetic field over its length. It can also make it possible to maximize the circumferential gap between the ends of the third and fourth sets of windings and create a window for the patient.

[0037] The insert may include a partial shielding coil for at least one gradient magnetic field coil, or may further not include a shielding coil. When the insert includes a first gradient magnetic field coil and a second gradient magnetic field coil, the insert may include a partial shielding coil for the first gradient magnetic field coil and the second gradient magnetic field coil, or may further not include a shielding coil.

[0038] The insert may include at least one capacitor electrically connected to at least one gradient magnetic field coil so as to resonate each gradient magnetic field coil at a predetermined ultrasonic frequency. This helps to efficiently drive the gradient magnetic field coil at a predetermined frequency. It also means that the gradient magnetic field coil can be driven using a low current from a high impedance signal source, thereby reducing inductive coupling to other coils / metal objects in the area.

[0039] When the insert includes a first gradient magnetic field coil and a second gradient magnetic field coil, at least one first capacitor may be electrically connected to the first gradient magnetic field coil so as to resonate the first gradient magnetic field coil at a first predetermined ultrasonic frequency, and at least one second capacitor may be electrically connected to the second gradient magnetic field coil so as to resonate the second gradient magnetic field coil at a second predetermined ultrasonic frequency.

[0040] The first predetermined ultrasonic frequency may be the same as the second predetermined ultrasonic frequency.

[0041] However, preferably, the first predetermined ultrasonic frequency is different from the second predetermined ultrasonic frequency.

[0042] This makes it easy to operate the two gradient magnetic field coils at different frequencies, which in turn results in the generation of Lissajous encoding rather than circular or helical encoding by this combination, which can lead to sampling more spatial frequencies during imaging. This can then increase the potential for accelerating the imaging.

[0043] It has been determined that there is a potential problem that audible sound can occur by using two frequencies. This is determined to be due to the occurrence of "beats" between the sounds created by the two frequencies.

[0044] Preferably, the frequency difference between the first predetermined ultrasonic frequency and the second predetermined ultrasonic frequency is an inaudible frequency. That is, it is either an extremely low frequency or an ultrasonic frequency. Generally, in practice, the first predetermined ultrasonic frequency and the second predetermined ultrasonic frequency are selected such that the frequency difference between them is an extremely low frequency.

[0045] According to another aspect of the present invention, there is provided a coil insert device for an MRI system, comprising a coil insert as described above and a signal generator device for electrically driving at least one gradient magnetic field coil at an ultrasonic frequency.

[0046] When at least one gradient magnetic field coil includes a Z-gradient magnetic field coil, the coil windings and the signal generator device may be arranged to provide a gradient that is segmented on the Z-axis.

[0047] The windings and the signal generator device may be arranged to provide a spatially non-monotonic gradient along the Z-axis.

[0048] The windings and the signal generator device may be arranged to provide a spatially multi-lobed gradient along the Z-axis.

[0049] The winding and the signal generator device may be arranged to provide a spatially oscillating gradient along the Z-axis.

[0050] The winding and the signal generator device may be arranged to provide a gradient having a polynomial or sinusoidal spatial variation along the Z-axis.

[0051] When the insert includes a first gradient magnetic field coil and a second gradient magnetic field coil, the signal generator device may be arranged to drive the first gradient magnetic field coil at a first selected ultrasonic frequency and the second gradient magnetic field coil at a second selected ultrasonic frequency. The first and second frequencies may be the same as each other. The first and second frequencies may be different from each other.

[0052] Preferably, the frequency difference between the first selected ultrasonic frequency and the second selected ultrasonic frequency is a non-audible frequency. That is, it is either an ultra-low frequency or an ultrasonic frequency. Generally, in practice, the first selected ultrasonic frequency and the second selected ultrasonic frequency are selected such that the frequency difference between them is an ultra-low frequency.

[0053] The first selected frequency may be the same as a first predetermined frequency. The second selected frequency may be the same as a second predetermined frequency.

[0054] Therefore, the first and second coils may be driven at the selected frequencies regardless of whether a capacitor for resonating the coils at the selected frequencies is provided, but it is noted that it is preferable that a capacitor is provided and the coils are driven at their respective resonance frequencies.

[0055] According to another aspect of the present invention, there is provided an MRI system device including an MRI system having a main bore and a coil insert for an MRI system as described above used within the bore.

[0056] According to another aspect of the present invention, there is provided an MRI system apparatus comprising an MRI system having a main bore and a coil insert device for an MRI system as described above, wherein the coil insert is arranged for use within the bore.

[0057] Although the above features have been described in the context of a coil insert for an MRI system, the above features and concepts can be used for the MRI system itself if the context permits.

[0058] Thus, according to another aspect of the present invention, there is provided an MRI system comprising a coil device, the coil device comprising at least one gradient magnetic field coil arranged to create a spatially varying magnetic field along respective axes and to be electrically driven at an ultrasonic frequency.

[0059] Generally, any of the above features is also a feature for this aspect of the present invention if the context permits. For the sake of brevity, not all are repeated herein, but some are explicitly described by way of example.

[0060] The MRI system may comprise a signal generator device for electrically driving at least one gradient magnetic field coil at an ultrasonic frequency.

[0061] In a series of embodiments, the at least one gradient magnetic field coil comprises a Z-gradient magnetic field coil, and the windings of the coil and the signal generator device are arranged to provide a gradient segmented along the Z-axis.

[0062] In other words, the windings and the signal generator device may be arranged to provide a non-monotonic gradient along the Z-axis.

[0063] The windings and the signal generator device may be arranged to provide a spatially multi-lobed gradient along the Z-axis.

[0064] The windings and the signal generator device may be arranged to provide a spatially oscillating gradient along the Z-axis.

[0065] The winding and the signal generator device may be arranged to provide a gradient having a polynomial or sinusoidal spatial variation along the Z-axis.

[0066] The MRI system may include at least one capacitor electrically connected to at least one gradient magnetic field coil so as to resonate each gradient magnetic field coil at a predetermined ultrasonic frequency.

[0067] The coil device may include a first gradient magnetic field coil and a second gradient magnetic field coil. At least one first capacitor may be electrically connected to the first gradient magnetic field coil so as to resonate the first gradient magnetic field coil at a first predetermined ultrasonic frequency. At least one second capacitor may be electrically connected to the second gradient magnetic field coil so as to resonate the second gradient magnetic field coil at a second predetermined ultrasonic frequency.

[0068] The first predetermined ultrasonic frequency may be the same as the second predetermined ultrasonic frequency.

[0069] However, preferably, the first predetermined ultrasonic frequency is different from the second predetermined ultrasonic frequency.

[0070] Preferably, the frequency difference between the first predetermined ultrasonic frequency and the second predetermined ultrasonic frequency is a non-audible frequency. That is, it is either an ultra-low frequency or an ultrasonic frequency. Generally, in practice, the first predetermined ultrasonic frequency and the second predetermined ultrasonic frequency are selected such that the frequency difference between them is an ultra-low frequency.

[0071] When the coil device includes a first gradient magnetic field coil and a second gradient magnetic field coil, the signal generator device may be arranged to drive the first gradient magnetic field coil at a first selected ultrasonic frequency and the second gradient magnetic field coil at a second selected ultrasonic frequency. The first and second frequencies may be the same as each other. The first and second frequencies may be different from each other.

[0072] Preferably, the frequency difference between the first selected ultrasonic frequency and the second selected ultrasonic frequency is a non-audible frequency. That is, it is either an ultra-low frequency or an ultrasonic frequency. In general, in practice, the first selected ultrasonic frequency and the second selected ultrasonic frequency are selected such that the frequency difference between them is an ultra-low frequency.

[0073] The first selected frequency may be the same as the first predetermined frequency. The second selected frequency may be the same as the second predetermined frequency.

[0074] According to another aspect of the present invention, a method of operating an MRI system apparatus as described above is provided.

[0075] According to a further aspect of the present invention, an echo-planar spectroscopic imaging system is provided, comprising an MRI system apparatus having an acquisition unit that acquires magnetic resonance data and a reconstruction unit that reconstructs an image and spectroscopic information from the acquired magnetic resonance data. The acquisition unit is arranged to output a single-band or multi-band RF pulse, an RF transmitter; a first gradient magnetic field coil arranged to be driven at an ultrasonic frequency to create a spatially varying magnetic field along a first respective axis, and a second gradient magnetic field coil arranged to be driven at an ultrasonic frequency to create a spatially varying magnetic field along a second respective axis; and a signal generator device configured to electrically drive the first gradient magnetic field coil at a first selected ultrasonic frequency and the second gradient magnetic field coil at a second selected ultrasonic frequency. The signal generator device is configured to apply a plurality of chirp pulses to the first gradient magnetic field coil and a plurality of chirp pulses to the second gradient magnetic field coil during a readout period as part of acquiring magnetic resonance data, to achieve spectral encoding and spatial encoding on the first and second respective axes. The acquisition unit is arranged to read out magnetic resonance data during the readout period, and the reconstruction unit is arranged to reconstruct an image and spectral information related to the image from the magnetic resonance data read out during the readout period.

[0076] This enables spatial encoding over the duration of each chirp and over the duration of the readout period. By using ultrasonic frequencies and a series of chirps, it is possible to acquire MRSI data, i.e., MRI images and related spectral data, related to a significantly shorter examination period than achieved using existing techniques. This can avoid information loss or confusion due to time-dependent changes, such as metabolite flow or chemical changes in the subject during the examination period.

[0077] Each chirp pulse may have a length of less than 100 milliseconds, preferably less than 10 milliseconds. In one embodiment, each chirp pulse has a length of about 1 millisecond. In another embodiment, each chirp pulse has a length of about 0.5 millisecond.

[0078] The signal generator device may be configured to apply at least 10 chirp pulses, preferably at least 50 pulses, during the readout period. In one embodiment, 200 chirp pulses may be applied during the readout period.

[0079] Thus, it can be seen that the readout period may be, for example, about 100 milliseconds, for example 200 chirp pulses each of 0.5 milliseconds, or 200 milliseconds, for example 200 chirp pulses each of 1 millisecond. This can in turn lead to bandwidths of 2 kHz and 1 kHz respectively, and spectral data resolutions of about 10 Hz and 5 Hz respectively.

[0080] The acquisition unit may be arranged to acquire magnetic resonance data during a plurality of readout periods to generate a set of magnetic resonance data.

[0081] The acquisition unit may be arranged to cause the RF transmitter to output a single-band or multi-band RF pulse before the start of each read period. The acquisition may be configured to apply each of the plurality of chirp pulses to a first gradient magnetic field coil and each of the plurality of chirp pulses to a second gradient magnetic field coil during each read period to achieve spectral encoding and spatial encoding on the first and second respective axes.

[0082] The reconstruction unit may be arranged to reconstruct an image and spectral information regarding the image from a set of magnetic resonance data read during the plurality of read periods.

[0083] The first selected ultrasonic frequency and the second selected ultrasonic frequency may be the same frequency.

[0084] Preferably, the first selected ultrasonic frequency is different from the second selected ultrasonic frequency.

[0085] Preferably, the frequency difference between the first selected ultrasonic frequency and the second selected ultrasonic frequency is a non-audible frequency. That is, it is either an ultra-low frequency or an ultrasonic frequency. Generally, in practice, the first selected ultrasonic frequency and the second selected ultrasonic frequency are selected such that the frequency difference between them is an ultra-low frequency.

[0086] The acquisition unit may include at least one first capacitor electrically connected to the first gradient magnetic field coil to resonate the first gradient magnetic field coil at a first predetermined ultrasonic frequency, and at least one second capacitor electrically connected to the second gradient magnetic field coil to resonate the second gradient magnetic field coil at a second predetermined ultrasonic frequency.

[0087] The first predetermined ultrasonic frequency may be the same as the second predetermined ultrasonic frequency.

[0088] However, preferably, the first predetermined ultrasonic frequency is different from the second predetermined ultrasonic frequency.

[0089] Preferably, the frequency difference between the first predetermined ultrasonic frequency and the second predetermined ultrasonic frequency is a non-audible frequency. That is, it is either an ultra-low frequency or an ultrasonic frequency. Generally, in practice, the first predetermined ultrasonic frequency and the second predetermined ultrasonic frequency are selected such that the frequency difference between them is an ultra-low frequency.

[0090] The first selected frequency may be the same as the first predetermined frequency. The second selected frequency may be the same as the second predetermined frequency.

[0091] The acquisition unit may further include a third gradient magnetic field coil that is arranged to be electrically driven to create a spatially varying magnetic field along each of the third axes. The signal generator device may be arranged to electrically drive the third gradient magnetic field coil, and in particular, to provide spatial encoding along each of the third axes to enable selection of a slice of the subject being examined during each readout period or during each of a plurality of readout periods, during which the above-described magnetic resonance data or a set of magnetic resonance data is acquired.

[0092] The acquisition unit may be arranged to acquire further magnetic resonance data or a further series of magnetic resonance data in a subsequent process to facilitate improvement of the signal-to-noise ratio of the acquired data.

[0093] The acquisition unit may acquire further magnetic resonance data or a further series of magnetic resonance data in a subsequent process such that different slices of the subject being examined are selected using spatial encoding along each of the third axes.

[0094] The MRI system device may include an MRI system having a main bore and an MRI system coil insert device used within the bore.

[0095] The insert may include a first gradient magnetic field coil and a second gradient magnetic field coil.

[0096] The insert may include a coil insert according to the first aspect of the present invention.

[0097] The third gradient magnetic field coil may be a gradient magnetic field coil of the MRI system itself. This can help to ensure that this gradient magnetic field coil is moved away from the patient so that the window of the insert is not blocked.

[0098] Generally, an MRI system also includes additional respective gradient magnetic field coils arranged to create a spatially varying magnetic field along each of the first axes and to create a spatially varying magnetic field along each of the second axes. However, when acquiring magnetic resonance data in accordance with the above-described further aspect of the present invention, in at least some instances, these additional respective gradient magnetic field coils may remain unused.

[0099] In other embodiments, there may be no insert, and rather, the first and second gradient magnetic field coils of the above-described further aspect of the present invention may be provided in the main body of the MRI system.

[0100] In other embodiments, gradient magnetic field coils may be utilized in both the main MRI system and the insert, and even on the same axis. Thus, for example, the Z gradient magnetic field coils within the insert and within the main MRI system may both be used for encoding.

[0101] According to another aspect of the present invention, there is provided an echo-planar spectroscopic imaging method using an MRI system device having an acquisition unit that acquires magnetic resonance data and a reconstruction unit that reconstructs image and spectral information from the acquired magnetic resonance data. The method is Applying a single-band or multi-band RF pulse to a subject under examination, Electrically driving a first gradient magnetic field coil at a first ultrasonic frequency to create a spatially varying magnetic field along each of the first axes, and electrically driving a second gradient magnetic field coil at a second ultrasonic frequency to create a spatially varying magnetic field along each of the second axes, As part of acquiring magnetic resonance data, during a readout period, applying a plurality of chirp pulses to the first gradient magnetic field coil and applying a plurality of chirp pulses to the second gradient magnetic field coil to achieve spectral encoding and spatial encoding along the first and second respective axes, Reading out magnetic resonance data during the readout period, Reconstructing an image and spectral information related to the image from the magnetic resonance data read out during the readout period.

[0102] It should be noted that, in general terms and including any necessary amendments to the language, all of the additional features defined above according to any aspect of the present invention described above are applicable as additional features of all other aspects of the present invention defined above. For the sake of brevity, these additional features are not restated after each aspect of the present invention.

[0103] Hereinafter, embodiments of the present invention will be described by way of example only with reference to the accompanying drawings.

Brief Description of the Drawings

[0104]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

DETAILED DESCRIPTION OF THE INVENTION

[0105] FIG. 1 schematically shows an MRI system apparatus including, in this example, a main MRI system 1 and a coil insert 2 for an MRI system. In this embodiment, most of the structure and operation of the main MRI system 1 are conventional. Accordingly, while various aspects of the main MRI system are illustrated in the drawings and described below, other aspects of the MRI system 1 are not illustrated or described in detail, although of course these details are well known and understood in the field of MRI examinations.

[0106] The MRI system insert 2 is arranged to be supplied and used in cooperation with an existing MRI system. Of course, this means that rather than having to develop an entirely new MRI system, an existing MRI system may be adapted to utilize the inventive concept, which is commercially advantageous. That is, in an alternative example, the MRI system apparatus shown in FIG. 1 may be manufactured from the start, and in a further alternative example, if desired, the features and functions of the insert 2 may be incorporated into the main body of the MRI system 1.

[0107] In FIG. 1, for clarity, the coil insert 2 for the MRI system is shown outside the main MRI system 1. However, during operation, the insert 2 is moved to a position within the main bore B of the main MRI system 1, to the position indicated by the dotted line in FIG. 1. FIG. 2 schematically shows an insert 2 of the type shown in FIG. 1 attached to the bed 3 of the MRI system 1 such that the insert 2 is slidably movable between the position shown in FIG. 2 corresponding to the position shown in FIG. 1 where the insert 2 is outside the bore B of the MRI system 1 and the position inside the bore B of the MRI system 1.

[0108] Various different forms of inserts may be provided.

[0109] The insert 2’ shown in FIG. 2 comprises an insert Z-gradient magnetic field coil 2z having a first set of windings 2z1 and a second set of windings 2z2 provided one at each end of the insert 2.

[0110] The fact that the Z-coil windings are not in the central region between the first set of windings 2z1 and the second set of windings 2z2 can lead to a suboptimal magnetic field, but in at least some situations, these imperfections have been judged to be acceptable. As an example, in an insert used for examining a human head, the space between the first set of windings 2z1 and 2z2 is relatively small, so these imperfections are acceptable.

[0111] The insert 2 shown in FIG. 1 comprises a similar insert Z-gradient magnetic field coil 2z having the first and second sets of windings 2z1 and 2z2, and further comprises an insert X-gradient magnetic field coil 2x having the first and second sets of windings 2x1 and 2x2. These sets of windings are shown separately and more clearly in FIG. 3.

[0112] In both the inserts 2 of FIGS. 1 and 3 and the insert 2' of FIG. 2, each set of Z windings 2z1, 2z1 itself comprises two sets of helically wound turns 2z1a, 2z1b, 2z2a, 2z2b. The second layers 2z1b, 2z2b are wound on top of their respective first layers 2z1a, 2z2a, but not quite in alignment, so that the outer set of conductors can provide an opposite current direction. This has been found to improve the shielding of the gradient magnetic field and minimize eddy currents in the surrounding conductor material.

[0113] The winding patterns of the windings 2x1, 2x2 of the X-gradient magnetic field coil 2x in the inserts 2 of FIGS. 1 and 3 become more apparent by considering FIG. 4 in combination with FIG. 3.

[0114] FIG. 4 shows the sets of windings 2x1, 2x2 of the X-insert gradient magnetic field coil 2x in comparison with the inner layer of a more conventionally wound X-gradient magnetic field coil (named "prior art" in FIG. 4). Each set of windings 2x1, 2x2 is helically wound, and each turn of the winding comprises an inner arcuate segment 2x1a, 2x2a that is connected to an outer arcuate segment 2x1c, 2x2c via a first end segment 2x1b, 2x2b. The turn is completed by a second end segment 2x1d, 2x2d that returns inward toward the start of the next turn. The next turn begins at the corresponding inner arcuate segments 2x1a, 2x2a of the subsequent turn and continues similarly.

[0115] It can be seen that the arcs of each inner arcuate segment have the same radius as the other inner arcuate segments. Similarly, the arcs of each outer arcuate segment have the same radius as the other outer arcuate segments. The radius of the arc of the inner segment is smaller than the radius of the arc of the outer segment.

[0116] This winding arrangement leads to a linear region that is longer in the axial direction of the insert than the winding arrangement of the prior art, allowing for a circumferential gap that is larger than the prior art pattern between the ends of the two sets of windings 2x1, 2x2. There may be a compromise in the nature of the magnetic field created by such windings, but it has been found that the benefits of the system of the present invention outweigh these problems.

[0117] The insert 2 shown in FIGS. 1 and 3 is designed for use in examining a patient's head, and in particular, for examining the brain. Accordingly, the insert 2 is arranged such that the patient's head is disposed within the bore of the insert. The arrangement of the Z-gradient magnetic field coil and the X-gradient magnetic field coils 2z, 2x in the insert makes it possible to provide a window W (shown schematically in FIG. 3 and its position is shown schematically in FIG. 1) in the insert 2 through which the user's head can be seen when inserted into the insert 2. This window W may be an opening in the insert if desired, or an opening filled with a transparent material.

[0118] Furthermore, in the insert 2' of the type shown in FIG. 2 without an X-gradient magnetic field coil, there is also a possibility of creating one or more windows W through which the user's head can be seen when it is within the insert 1. Naturally, providing such windows helps to counter the patient's feeling of claustrophobia.

[0119] The MRI system apparatus includes a signal generator device 4 provided for driving the gradient magnetic field coils 2z, 2x of the insert 2.

[0120] In commercial terms, this signal generator device 4 may be provided together with the insert 2, and these may be considered together as a coil-insert device for an MRI system that can be used in an existing MRI system 1. Naturally, in other alternatives, when a complete system is developed, a separate signal generator device may not be necessary and instead it may be incorporated into the system provided within the main MRI system.

[0121] The signal generator device 4 is arranged to drive the gradient magnetic field coils 2z and 2x of the insert 2 at ultrasonic frequencies. That is, the frequencies are beyond the audible range.

[0122] When two or more gradient magnetic field coils are in the insert 2, for example, the insert 2 of the type shown in FIGS. 1 and 3, in some examples, the same ultrasonic frequency may be used to drive each of the gradient magnetic field coils 2z and 2x.

[0123] Alternatively, preferably, when there are two gradient magnetic field coils, for example, two gradient magnetic field coils 2z and 2x in the insert 2, the signal generator device 4 is arranged to drive them at different ultrasonic frequencies.

[0124] As an example, in some embodiments, a single ultrasonic frequency may be used and set at 20.2 kHz. In other embodiments where two different frequencies are used, these may be, for example, 22 kHz on one hand and 19.9 kHz on the other hand, where one is used to drive the X-gradient magnetic field coil 2x and the other is used to drive the Z-gradient magnetic field coil 2z. In practice, as can be appreciated, there is a great deal of freedom as to which frequencies may be selected.

[0125] However, it has been determined to be particularly advantageous that, firstly, two different frequencies are selected and, secondly, the difference between these two different frequencies itself is in the inaudible frequency range. As mentioned in the introduction, when two frequencies are different, favorable spatial encoding can be achieved, and by having a frequency difference in the inaudible range, the generation of an audible "beating" signal created between the sounds generated at the two selected inaudible frequencies can be avoided. Generally, the two frequencies may be selected such that the frequency difference is below the human audible range. That is, the frequency difference is 20 Hz or less.

[0126] As schematically shown in FIG. 1, a signal generator device 4 is arranged to drive each of the gradient magnetic field coils 2x, 2z of the insert via respective capacitors Cx, Cz. The values of these capacitors are selected to resonate the respective gradient magnetic field coils 2x, 2z at the frequency driven by the signal generator device 4. This facilitates the use of a high-impedance signal generator and delivering a lower current to the gradient magnetic field coils 2x, 2c, which can then help reduce the coupling between them.

[0127] It should be noted that the idea of resonating the gradient magnetic field coil at a predetermined frequency encompasses both the situation where the gradient magnetic field coil is one electrical entity driven by one signal generator and the situation where the gradient magnetic field coil is composed of a plurality of separate electrical entities that may be driven individually. Thus, for example, if the gradient magnetic field coil has a plurality of individual windings, each is made to resonate by providing an appropriate capacitor.

[0128] In the device of the present invention, RF shielding is not provided in the insert 2 or between the insert 2 and the main MRI system. This helps minimize losses due to the generation of eddy currents, such as would occur if the insert gradient magnetic field coils 2x, 2z were driven at ultrasonic frequencies. At the same time, the insert, and particularly the gradient magnetic field coils 2x, 2z, are relatively transparent to the signals transmitted and received by the main MRI system. Thus, the operation of the main MRI system may continue with the insert 2 in a fixed position within the bore B of the main MRI system.

[0129] In general terms, minimizing the amount of conductive material in the vicinity of the insert gradient magnetic field coils 2x, 2z (or any gradient magnetic field coil operating at ultrasonic frequencies) helps improve efficiency by minimizing the effects of eddy currents. The problem is reduced as the spacing between the gradient magnetic field coil driven at ultrasonic frequencies and the metal object increases. Thus, in the apparatus of the present invention, active gradient magnetic field shielding is not optimal or even present for the main MRI system, and the fact that other metal objects are within the main MRI system is acceptable. This requirement to minimize the metal in the vicinity of the ultrasonic-driven gradient magnetic field coil makes it unclear that the use of such frequencies is practical, and including them in the insert rather than in the main MRI machine is more convenient in at least some situations.

[0130] FIG. 5 schematically shows an alternative form of the Z-gradient magnetic field coil that may be provided in an alternative form of the insert. Similarly, in the alternative example, the Z-gradient magnetic field coil of this form may be provided in the main body of the newly constructed MRI machine 1.

[0131] Here, the Z-gradient magnetic field coil includes four sets of windings 2z1 to 2z4, each having the same structure as the set of Z windings 2z1, 2z2 described above. Again, these windings are arranged to be driven by the signal generator device 4 and are arranged to resonate at a selected drive frequency by including one or more capacitors (not shown).

[0132] In this case, rather than monotonically varying the Z-gradient magnetic field in the insert by means of a Z-gradient magnetic field coil as in the conventional case, nor as described above with respect to FIGS. 1 to 4, here, a segmented Z-gradient is created. That is, rather than monotonically varying the Z-gradient magnetic field, the insert of FIG. 5 is arranged to create a more complexly varying Z-gradient magnetic field. In particular, this may be set to be multi-leafed, or for example, to have a polynomial or sinusoidal variation along the Z-axis. This means that, while still providing an appropriate variation of the gradient per unit length along the insert, the maximum amplitude of the difference in the gradient magnetic field from one end of the axis to the other can be controlled. Providing a segmented Z-gradient magnetic field can be particularly advantageous when longer inserts are used, i.e., when examining a region longer than just the head, for example when the insert is used for whole-body examinations or when the gradient windings are incorporated into a whole-body MRI machine. Further, the SENSE (Sensitivity Encoding) reconstruction technique, as is well known in the field of MRI, can successfully clarify the information obtained when acquiring magnetic resonance data using a segmented Z-gradient of the type generated by the insert shown in FIG. 5. Further, it is judged that by using such a segmented Z-gradient, the manifestation of PNS in the subject being examined can be reduced, or the use of a stronger Z-gradient can be enabled before the manifestation of PNS is obtained.

[0133] Following a brief introduction of the main MRI system 1, the operation of the MRI system apparatus is described below.

[0134] In general terms, the main MRI system 1 comprises an acquisition unit I for acquiring magnetic resonance data and a reconstruction unit R for reconstructing images and spectroscopic information regarding those images from the acquired magnetic resonance data. In the apparatus shown in FIG. 1, the insert 2 and the signal generator device 4 form part of the acquisition unit I. That is, they cooperate with the acquisition unit I of the main MRI machine to acquire magnetic resonance data, and the data may then be reconstructed by the reconstruction unit R.

[0135] The elements of the acquisition unit I of the main MRI machine 1 generally include a magnet and a coil device 5 and a control system 6. The control system 6 has an output unit 61 for controlling the operation of the magnet and the coil device 5 and a reception unit 62 for receiving information returning from the magnet and the coil device 5. In the device of the present invention where the coil insert 2 is used, the output unit 61 also issues a control signal to the signal generator device 4, and in some embodiments, the reception unit 62 also receives the output from the insert 2, but this is optional. In the device described herein, the reception of magnetic resonance data is performed by the main MRI machine 1 itself.

[0136] As suggested above, in an alternative example, the components of the insert 2 and the signal generator device may be incorporated into the MRI machine itself.

[0137] It will be recognized that an MRI machine generally includes one or more "computers" that control the operation and process the received data. Each such computer may include a processor, a memory, and at least one data storage device. The control system 6 may be computer-implemented. The reconstruction unit R may be computer-implemented.

[0138] The magnet and coil device 5 includes a main magnet 51 that creates a static magnetic field, X, Y, and Z gradient magnetic field coils 52, a high-frequency transmission coil 53, and a high-frequency reception coil 54.

[0139] During operation, the output unit 61 delivers a drive current to the gradient magnetic field coil 52, causes an appropriate high-frequency transmission pulse to be output by the transmission coil 53, and the reception unit 62 receives the input from the reception coil 54.

[0140] In an embodiment of the present invention, the output unit 61 also provides a control trigger signal to the signal generator device 4 to enable taking appropriate timing to generate a gradient drive signal for driving the insert gradient magnetic field coils 2x, 2z.

[0141] In principle, any combination of the gradient magnetic field coils 52 of the main MRI system 1 and the gradient magnetic field coils 2x, 2z of the insert 2 may be used to achieve the desired encoding effect.

[0142] Most commonly, perhaps when the insert 2 includes an X gradient magnetic field coil 2x and a Z gradient magnetic field coil 2z, these may be used in combination with the Y gradient magnetic field coil 52y of the main MRI machine 1.

[0143] Thus, in a specific example, the gradient magnetic field coil 52y of the main MRI machine 1 may be used for spatial encoding to select and examine a specific slice of the subject, and the Z and X gradient magnetic field coils 2z, 2y of the insert 2 can be used for spatial encoding within that slice.

[0144] In a situation where the insert includes only a Z gradient magnetic field coil (e.g., the insert shown in FIG. 2), the X and Y gradient magnetic field coils 52x, 52y of the main MRI machine 1 may be used in cooperation with the Z gradient magnetic field coil 2z of the insert 2.

[0145] In other situations, both gradient magnetic field coils on one specific axis of the main MRI machine 1 and the insert 2 may be used together.

[0146] For example, the insert shown in FIG. 2 may be used in a situation where the X, Y, and Z gradient magnetic field coils 52x, 52y, 52z from the MRI machine 1 are used in combination with the Z gradient magnetic field coil 2z of the insert. This can provide different options for spatial encoding.

[0147] In the situations described above, the gradient magnetic field coils 52 of the main MRI machine 1 are driven at a conventional frequency, while the gradient magnetic field coils of the insert 2 are driven at an ultrasonic frequency.

[0148] Figure 6 shows a timing diagram of Echo Planar Spectroscopic Imaging (EPSI) technology that can be implemented using the MRI system apparatus of the type described above. In particular, the MRI system apparatus of FIG. 1, when used in conjunction with the insert of the type described with respect to FIGS. 1-3 above, can be used as an echo planar spectroscopic imaging system and operated according to the timing diagram shown in FIG. 6.

[0149] In this technique, the Z-gradient magnetic field coil 2z of the insert 2 is used together with the X-gradient magnetic field coil of the insert 2x and the Y-gradient magnetic field coil 52y of the main MRI machine 1. The timing diagram 6 schematically shows the signals applied to these gradient magnetic field coils when the technique of FIG. 6 is implemented. As will be appreciated, "Gz insert" refers to the signal applied to the Z-gradient magnetic field coil 2z of the insert, "Gx insert" refers to the signal applied to the X-gradient magnetic field coil 2x of the insert, and "Gy body" refers to the signal applied to the Y-gradient magnetic field coil 52y of the main MRI machine.

[0150] Furthermore, in the timing diagram, RF indicates the signal applied using the transmit coil 53 of the main MRI machine 1.

[0151] At the start of each repetition period (TR), a multi-band pulse is applied by the RF transmit coil 53 and a slice selection pulse is applied to the Y-gradient magnetic field coil 52y of the MRI machine 1. Next, during the subsequent readout period, a plurality of respective chirp pulses are applied to the Z-gradient magnetic field coil 2z of the insert 2 on the one hand and to the X-gradient magnetic field coil 2x of the insert 2 on the other hand. In an embodiment of the present invention, each chirp has a length of 500 microseconds and a total of 200 such chirps are applied to the Z-gradient magnetic field coil and the X-gradient magnetic field coils 2z, 2x respectively during the readout period.

[0152] In an embodiment of the present invention, the chirps are each of the same waveform as each of the other chirps, and the chirps of the Z-gradient magnetic field coil 2z and the chirps of the X-gradient magnetic field coil 2x are applied in the same phase with each other. However, other possibilities are available.

[0153] The purpose of applying the chirps is to obtain a large K-space (the amplitude per axis defines the spatial resolution of that axis), and the distance between points / circles in the K-space (the decaying amplitude defines the field of view).

[0154] Using this technique, all spatial encoding can be defined in each chirp, while spectral information is encoded across the chirp group, i.e., across 200 chirps in this example. The spectral bandwidth and resolution are determined by the number of chirps and their lengths, as well as the total length of the chirps. Thus, in this example, when the length of each chirp is 500 microseconds, the bandwidth is 2 kHz, the total length of the chirps is 100 milliseconds, and this results in a resolution of about 10 Hz (excluding the effects of relaxation and other small units).

[0155] In another embodiment, each chirp may be 1 millisecond in length. In such an example, if 200 chirps are still applied, this results in a bandwidth of 1 kHz and a resolution of about 5 Hz instead of 10 Hz as in the above example.

[0156] Each chirp consists of the application of a limited time-varying amplitude of an ultrasonic frequency configured such that the respective insert gradient magnetic field coils 2z, 2x are operative. In this example, the two ultrasonic frequencies are the same, but in other examples, they are different and may provide the additional benefits described above.

[0157] In this embodiment, four shots are used to improve the accuracy of the results as shown in the timing diagram. The second multi-band pulse in MB2 is provided at the start of the second shot, and a further appropriate slice selection signal is applied to the Y-gradient magnetic field coil 52y of the main MRI machine 1. Subsequently, a second sequence of chirps is applied to the Z-gradient magnetic field coil and the X-gradient magnetic field coils 2z, 2x of the insert 2 during the readout period of this second shot. Since the whole process is repeated again with the third and fourth shots, the acquired magnetic resonance data may be supplied to the reconstruction unit R in order to reconstruct an image and spectral data associated with the image. The reconstruction system R may be configured under software that performs SENSE (Sensitivity Encoding) reconstruction.

[0158] If desired, further processes as described above may be carried out to obtain more data for the purpose of improving the signal-to-noise ratio.

[0159] As another method, or in addition thereto, further processes may be carried out for different "Y slices" of the subject. That is, a different set of offset frequencies for slice selection may be applied to the RF coil 54 of the MR machine 1, for example, to select a second batch of slices for the examination.

[0160] It is noted that spatial encoding is carried out with each chirp using this technique, and complete spatial encoding and spectral encoding for a set of slices may be carried out in about 100 milliseconds if only one shot is used, or in about 400 milliseconds if four shots are used as in the example shown in FIG. 6.

[0161] This means that it can take into account image data and spectral data collected over a very short period. This can help avoid information loss or confusion in the results, which would occur with more conventional techniques that require a much longer encoding time. In more conventional echo-planar spectroscopic imaging techniques, the data is encoded one voxel at a time across the entire region of interest, where spatial encoding effectively first selects a particular voxel and then spectroscopic sampling is performed for that voxel before moving on to the next voxel. This leads to a much longer examination period of several seconds.

Claims

1. An MRI system coil insert for use within the bore of a main MRI system, comprising a spindle, and at least one gradient magnetic field coil arranged to create a spatially varying magnetic field along each axis which is any one of an axis parallel to the spindle, an axis coinciding with the spindle, and an axis angled with respect to the spindle, and to be electrically driven at an ultrasonic frequency of 19.9 kHz or more. The MRI system coil insert includes a first gradient magnetic field coil and a second gradient magnetic field coil. At least one first capacitor is electrically connected to the first gradient magnetic field coil to resonate the first gradient magnetic field coil at a first predetermined ultrasonic frequency, and at least one second capacitor is electrically connected to the second gradient magnetic field coil to resonate the second gradient magnetic field coil at a second predetermined ultrasonic frequency. The MRI system coil insert, wherein the first predetermined ultrasonic frequency is different from the second predetermined ultrasonic frequency.

2. The MRI system coil insert according to claim 1, having a central region without gradient magnetic field coil windings.

3. The MRI system coil insert according to claim 2, having a window in the MRI system coil insert through which the patient can see when the patient's head is positioned within the MRI system coil insert.

4. The MRI system coil insert according to any one of claims 1 to 3, comprising a Z-gradient magnetic field coil for creating a spatially varying magnetic field along the spindle of the MRI system coil insert.

5. The Z-gradient magnetic field coil of the coil insert for an MRI system according to claim 4 comprises a first set of windings provided at a first end of the coil insert for an MRI system and a second set of windings provided at a second end of the coil insert for an MRI system.

6. The Z-gradient magnetic field coil of the coil insert for an MRI system according to claim 4 comprises more than two sets of windings, and the windings are arranged to enable the provision of a magnetic field gradient divided on the Z axis.

7. The coil insert for an MRI system according to any one of claims 1 to 6 comprises an X-gradient magnetic field coil or a Y-gradient magnetic field coil that creates a spatially varying magnetic field in a transverse direction with respect to the main axis of the coil insert for an MRI system.

8. The coil insert for an MRI system according to any one of claims 1 to 7 comprises a first gradient magnetic field coil that creates a spatially varying magnetic field along a first axis among the respective axes, and a second gradient magnetic field coil that creates a spatially varying magnetic field along a second axis among the respective axes.

9. The coil insert for an MRI system according to claim 5 further comprises an X-gradient magnetic field coil or a Y-gradient magnetic field coil that creates a spatially varying magnetic field in a transverse direction with respect to the main axis, and the X or Y gradient magnetic field coil comprises a third set of windings and a fourth set of windings provided on a side facing in a radial direction with respect to the main axis of the coil insert for an MRI system and between the first and second sets of windings of the Z-gradient magnetic field coil in an axial direction with respect to the main axis of the coil insert for an MRI system.

10. A circumferential gap of the coil insert for an MRI system is provided between the third and fourth sets of windings such that there is a region in the coil insert for an MRI system where there are no windings of the Z-gradient magnetic field coil and no windings of the X or Y gradient magnetic field coil.

11. The winding of the third set and the winding of the fourth set each include a plurality of helically wound turns, and each turn of one revolution includes an inner arcuate segment, a first end segment extending outwardly to the outer arcuate segment, and a second end segment extending inwardly from the outer arcuate segment to the corresponding inner arcuate segment of the next turn. The coil insert for an MRI system according to claim 9 or claim 10.

12. The difference in frequency between the first predetermined ultrasonic frequency and the second predetermined ultrasonic frequency is a non-audible frequency outside the audible range of 20 Hz to 20 kHz. The coil insert for an MRI system according to any one of claims 1 to 11.

13. A coil insert device for an MRI system, comprising the coil insert for an MRI system according to any one of claims 1 to 12, and a signal generator device for electrically driving the at least one gradient magnetic field coil at an ultrasonic frequency of 19.9 kHz or higher.

14. The signal generator device is arranged to drive the first gradient magnetic field coil at a first selected ultrasonic frequency and the second gradient magnetic field coil at a second selected ultrasonic frequency. The coil insert device for an MRI system according to claim 13.

15. The difference in frequency between the first selected ultrasonic frequency and the second selected ultrasonic frequency is a non-audible frequency outside the audible range of 20 Hz to 20 kHz. The coil insert device for an MRI system according to claim 14.

16. The first selected ultrasonic frequency is the same as the first predetermined ultrasonic frequency, and the second selected ultrasonic frequency is the same as the second predetermined ultrasonic frequency. The coil insert device for an MRI system according to claim 14 or claim 15.

17. The coil insert device for an MRI system according to claim 13, when dependent on claim 6, wherein each set of the windings of the Z-gradient magnetic field coil and the signal generator device are arranged to provide a spatially varying magnetic field gradient on the Z-axis.

18. An MRI system device comprising an MRI system having a main bore and an MRI coil insert for an MRI system according to any one of claims 1 to 12 used within the main bore.

19. An MRI system device comprising an MRI system having a main bore and an MRI coil insert device for an MRI system according to any one of claims 13 to 16 arranged to be used within the main bore.

20. An echo planar spectroscopic imaging system comprising an MRI system device having an acquisition unit for acquiring magnetic resonance data and a reconstruction unit for reconstructing images and spectroscopic information from the acquired magnetic resonance data, wherein the acquisition unit comprises an RF transmitter arranged to output a single-band or multi-band RF pulse, a first gradient magnetic field coil arranged to be driven at an ultrasonic frequency of 19.9 kHz or higher to create a spatially varying magnetic field along a first axis, and a second gradient magnetic field coil arranged to be driven at an ultrasonic frequency of 19.9 kHz or higher to create a spatially varying magnetic field along a second axis, and a signal generator device configured to electrically drive the first gradient magnetic field coil at a first selected ultrasonic frequency and the second gradient magnetic field coil at a second selected ultrasonic frequency, wherein the signal generator device is configured to apply a plurality of chirp pulses to the first gradient magnetic field coil and a plurality of chirp pulses to the second gradient magnetic field coil during a readout period as part of acquiring the magnetic resonance data to achieve spectral encoding and spatial encoding on the first and second axes. The acquisition unit is arranged to read out magnetic resonance data during the readout period, and the reconstruction unit is arranged to reconstruct an image and spectral information regarding the image from the magnetic resonance data read out during the readout period. An echo-planar spectroscopic imaging system in which the first selected ultrasonic frequency is different from the second selected ultrasonic frequency.

21. The echo-planar spectroscopic imaging system according to claim 20, wherein each chirp pulse has a length of less than 10 milliseconds.

22. The echo-planar spectroscopic imaging system according to claim 20 or 21, wherein the signal generator device is configured to apply at least 10 chirp pulses during the readout period.

23. The acquisition unit is arranged to acquire magnetic resonance data during a plurality of readout periods to generate a set of magnetic resonance data, the acquisition unit is arranged to cause the RF transmitter to output a single-band or multi-band RF pulse before the start of each readout period, and the acquisition is such that during each readout period, a plurality of respective chirp pulses are applied to the first gradient magnetic field coil and a plurality of respective chirp pulses are applied to the second gradient magnetic field coil to achieve spectral encoding and spatial encoding on the first and second axes. The echo-planar spectroscopic imaging system according to any one of claims 20 to 22.

24. The echo-planar spectroscopic imaging system according to any one of claims 20 to 23, wherein the frequency difference between the first selected ultrasonic frequency and the second selected ultrasonic frequency is a non-audible frequency outside the audible range of 20 Hz to 20 kHz.

25. The echo-planar spectroscopic imaging system according to any one of claims 20 to 24, wherein the acquisition unit includes at least one first capacitor electrically connected to the first gradient magnetic field coil so as to resonate the first gradient magnetic field coil at a first predetermined ultrasonic frequency, and at least one second capacitor electrically connected to the second gradient magnetic field coil so as to resonate the second gradient magnetic field coil at a second predetermined ultrasonic frequency.

26. The echo-planar spectroscopic imaging system according to claim 25, wherein the first selected ultrasonic frequency is the same as the first predetermined ultrasonic frequency, and the second selected ultrasonic frequency is the same as the second predetermined ultrasonic frequency.

27. The echo-planar spectroscopic imaging system according to any one of claims 20 to 26, wherein the acquisition unit further includes a third gradient magnetic field coil arranged to be electrically driven to create a spatially varying magnetic field along a third axis, and the signal generator device is arranged to electrically drive the third gradient magnetic field coil to provide spatial encoding on the third axis, enabling selection of a slice of the subject under examination during each readout period or each of a plurality of readout periods during which the magnetic resonance data or a set of magnetic resonance data is acquired.

28. The echo-planar spectroscopic imaging system according to any one of claims 20 to 27, wherein the MRI system device includes an MRI system having a main bore and an MRI system coil insert device used within the main bore, and the MRI system coil insert includes the first gradient magnetic field coil and the second gradient magnetic field coil.

29. The echo planar spectroscopic imaging system according to any one of claims 20 to 27, wherein the MRI system apparatus comprises an MRI system having a main bore and a coil insert for an MRI system according to any one of claims 1 to 12 used within the main bore.

30. An echo planar spectroscopic imaging method using an MRI system apparatus, the method comprising an acquisition unit that acquires magnetic resonance data, and a reconstruction unit that reconstructs an image and spectral information from the acquired magnetic resonance data, the method comprising: applying a single-band or multi-band RF pulse to a subject being examined; electrically driving a first gradient magnetic field coil at a first ultrasonic frequency to create a spatially varying magnetic field along a first axis, and electrically driving a second gradient magnetic field coil at a second ultrasonic frequency to create a spatially varying magnetic field along a second axis; as part of acquiring the magnetic resonance data, applying a plurality of chirp pulses to the first gradient magnetic field coil and applying a plurality of chirp pulses to the second gradient magnetic field coil during a readout period to achieve spectral encoding and spatial encoding on the first and second axes; reading out the magnetic resonance data during the readout period; reconstructing an image and spectral information regarding the image from the magnetic resonance data read out during the readout period; and wherein the first ultrasonic frequency is different from the second ultrasonic frequency.

Images