Magnetomotive probe system and method of use thereof

A magnetomotive imaging probe system is disclosed comprising a movable probe, a magnet arranged on the probe, and an ultra sound transducer, wherein the magnet is arranged to generate a time-varying magnetic field (T) at an imaging plane (304) of the ultrasound transducer, distally of the ultra sound transducer and the probe, when the probe has a proximal first position adjacent the ultra sound transducer.

FIELD OF THE INVENTION

This invention pertains in general to the field of magnetomotive imaging. More particularly the invention relates to a magnetomotive imaging probe system, a magnetomotive imaging probe assembly, and a method of magnetomotive imaging with such imaging probe system or assembly.

BACKGROUND OF THE INVENTION

Magnetomotive imaging is a new imaging technique where superparamagnetic iron oxide nanoparticles can be used as ultrasound contrast agents. The main idea of this imaging technique is the application of a time-varying magnetic field (pulsed or sinusoidal) to the volume where the nanoparticles are deposited. The magnetic field induces movement of the particles and thereby the surrounding tissue. Previous techniques, such as disclosed in Evertsson, M. et al, IEEE, Transactions on ultrasonic, ferroelectrics, and frequency control, vol. 60, no. 3, 1 Mar. 2013, pages 481-491, that has been used to create the time-varying magnetic field has been employing an electromagnet, which consists of a coil around a cone-shaped iron-core, seeFIG.1. When a current is applied, a magnetic field is formed from the tip of the core. The force acting on the particles is dependent on the field strength, and on the field gradient. A problem with such previous techniques is that the displacement amplitude of the nanoparticle-laden regions is higher closer to the tip, and the resulting image data therefore gives misleading information about the nanoparticle concentration. This inevitable leads to problems in providing accurate analysis of the properties of the material or tissue in which the nanoparticles has been collected, e.g. in the situation where the nanoparticles have been labeled with tumor- or tissue specific targeting agents. The information available for e.g. detecting cancer in tissue therefore becomes flawed. Problems with prior art thus includes insufficient accuracy in detecting these targeting nanoparticles, and consequently insufficient accuracy in detecting, resolving and analyzing the material which the nanoparticles targets and binds.

Further problems with prior art is that the tissue which is analyzed is affected by the analyzing equipment, for example by heat, which also decreases the possibilities for performing a complete analysis of the tissue.

Jia Congxian et al, Photons plus ultrasound: Imaging and sensing, 2011, Proc. of SPIE, vol. 7899, no. 1, 10 Feb. 2011, discloses a method for magnetomotive photoacoustic imaging where magnetic particles in a tube where placed in a water tank containing magnets for manipulation of the particles, and an ultrasound device placed on top of the water tank. Thus another problem with prior art is the unsuitability of these setups for applications in humans or larger animals due to restrictions or limitations in positioning the various components such as the magnet in relation to the ultrasound transducer.

Problems with prior art, if at all possible to implement, may accordingly lead to reduced patient safety, more time consuming and expensive diagnosis, and less possibilities for an individualized treatment in the patient care.

Hence an improved device or assembly, and/or system, and method, for providing improved magnetomotive imaging would be advantageous.

SUMMARY OF THE INVENTION

Accordingly, embodiments of the present invention preferably seek to mitigate, alleviate or eliminate one or more deficiencies, disadvantages or issues in the art, such as the above-identified, singly or in any combination by providing a magnetomotive imaging probe assembly and a method for magnetomotive imaging with a probe assembly according to the appended patent claims.

According to a first aspect of the invention a magnetomotive imaging probe system is provided comprisinga movable probe, a magnet arranged on the probe, and an ultra sound transducer, wherein the magnet is arranged to generate a time-varying magnetic field (T) at an imaging plane (304) of the ultrasound transducer, distally of the ultra sound transducer and the probe, when the probe has a proximal first position adjacent the ultra sound transducer.

According to a second aspect of the invention, a method of magnetomotive imaging with a probe system is provided, the system comprising a movable probe, an ultra sound transducer, and a magnet arranged on the probe. The method comprises positioning the probe at a proximal first position adjacent the ultra sound transducer, generating, with said magnet, a time-varying magnetic field (T) at an imaging plane of the ultrasound transducer, distally of the ultra sound transducer and the probe, and detecting motion of magnetic nanoparticles in response to said time-varying magnetic field with the ultrasound transducer in the imaging plane.

According to a third aspect of the invention, a magnetomotive imaging probe assembly is provided comprising a probe support and a magnet arranged on said probe support. The probe support is adapted to connect to an ultra sound transducer and fixate the position of the ultra sound transducer in relation to, and adjacent, the magnet, whereby in use the magnet is arranged to generate a time-varying magnetic field (T) at an imaging plane of the ultrasound transducer.

According to a fourth aspect of the invention, a method of magnetomotive imaging with a probe assembly is provided, the probe support being adapted to connect to an ultrasound transducer and having a magnet movably arranged on the probe support, the method comprising rotating the magnet to generate a time-varying magnetic field (T) at an imaging plane of the ultrasound transducer when connected to the probe support, and detecting a motion of magnetic nanoparticles in response to the time-varying magnetic field with the ultrasound transducer in the imaging plane.

According to another aspect of the invention, use of a magnetomotive imaging probe assembly or system according to the first or third aspect of the invention for magnetomotive ultrasound imaging of magnetic nanoparticles is provided.

Further embodiments of the invention are defined in the dependent claims, wherein features for the second and subsequent aspects of the invention are as for the first aspect mutatis mutandis.

Some embodiments of the invention provide for increased accuracy in resolving the concentration of nanoparticles in a material.

Some embodiments of the invention provide for increased accuracy in analyzing material properties in magnetomotive imaging.

Some embodiments of the invention provide for imaging that with less impact on the analyzed material.

Some embodiments of the invention provide for converting ultrasound imaging equipment to a magnetomotive imaging device.

Some embodiments of the invention provide for a compact and easy to use magnetomotive imaging probe assembly or system.

Further embodiments of the invention are defined in the dependent claims, wherein features for the second and subsequent aspects of the invention are as for the first aspect mutatis mutandis.

DESCRIPTION OF EMBODIMENTS

The following description focuses on an embodiment of the present invention applicable to a probe assembly for magnetomotive imaging. However, it will be appreciated that the invention is not limited to this application but may be applied to many other fields and applications.

FIG.1shows a prior art magnetomotive imaging setup as discussed in the background of invention.

FIG.2shows a magnetomotive imaging probe assembly100according to an embodiment of the invention. The probe assembly100comprises a probe support101, and a magnet,102,103, arranged on the probe support101. The probe support101is adapted to connect to an ultrasound transducer115and fixate the position of the ultrasound transducer115in relation to, and adjacent, the magnet102,103. The ultrasound transducer115may connect to the probe support in various ways, such as by a “snapping-in” function that provides for an engaging and disengaging connection, i.e. a releasable connection, and/or by using fixation means116to connect the probe support101to the ultrasound transducer115. The magnet102,103, may be connected to the probe support101by a second fixation means117,117′. The magnet102,103, may thereby be fixed in relation to the ultrasound transducer115via the probe support101. The probe support101may be adapted to connect to a variety of ultrasound transducers115by being shaped to conform to the geometries of such varying ultrasound transducers, i.e. ultrasound probes. In use, i.e. when the ultrasound transducer115is fixated by the probe support101, the magnet102,103, is arranged to generate a time-varying magnetic field (T) at an imaging plane104of the ultrasound transducer115. Due to the probe support101being arranged to fixate the position of the ultra sound transducer115adjacent the magnet102,103, a compact and versatile magnetomotive imaging probe assembly is provided, as the magnet102,103, and transducer115are integrated in the probe assembly100via the probe support101. I.e. the magnet102,103, generates a time-varying magnetic field at the same location at the imaging plane104of the transducer wherever the probe100is positioned spatially relative the imaged subject. Imaging and analysis of tissue of humans and large animals is therefore possible without having to repeatedly repositioning the magnet to the current location of the ultra sound transducer as in the case with previous techniques. Indeed, the most hampering drawback with the prior techniques, is that the magnetic field is designed to emanate from the other side of the object to be imaged such as fixated at a position under the object, as seen inFIG.1, or even more complex techniques where magnets are arranged on either side of the object and in fixed arrangement thereto, which does not allow for repositioning and/or imaging of larger objects. This makes currently proposed designs unsuitable for applications in humans or larger animals. Further, the larger and more powerful magnet of previous designs can be dispensed with as it is only necessary to provide a localized magnetic field at the position of the transducer, on contrary to having to provide a stronger field to cover a sufficient portion of the imaged object as in previous solutions. This allows for less interference with the imaged object, e.g. less heating issues during imaging. The previously described advantages may be provided with any type of magnet that is arranged to generate a time-varying magnetic field at the imaging plane104of the ultrasound transducer115.

The magnet may be movably arranged on the probe support101, and, whereby in use, the magnet102,103may be arranged to generate the time-varying magnetic field (T) in response to a motion of the magnet102,103, relative the probe support101and the ultrasound transducer115. The magnet102,103, may thus be movably connected to the probe support101such that it can provide such motion relative the ultrasound transducer115, which is fixed in the probe support101. Due to the motion of the magnet102,103, a time-varying magnetic field (T) is provided at a target location110in the imaging plane104of the ultrasonic transducer115. Magnetic nanoparticles that are located at the target location110in the imaging plane104thus exhibits the fluctuations in the time-varying magnetic field (T) and are therefore forced to oscillate under the influence of the magnetic field (T). Because of the creation of the time-varying magnetic field in the axial direction105of the imaging plane104(see alsoFIG.4b), the displacement amplitude of the nanoparticles can be detected by the ultrasonic transducer115, when the probe assembly101is used to scan the object under examination. Imaging can thus be provided without the use of electromagnets. The magnet102,103, thus creates a time-varying magnetic field at the imaging plane104as it moves relative to the transducer115. This provides for detection with high sensitivity as there is no need for applying a high current as for the prior art magnetomotive setup with an electromagnet, to achieve a strong magnetic field. Hence, there will be no problems with increased temperature which is the case when applying a high current trough an electromagnet. The probe assembly101thus allows for the analyzed sample to be less affected by the imaging probe and a more accurate analysis can be performed. Hence, the magnet102,103, may be a permanent magnet.

The magnet102,103, may be arranged on said support101to extend parallel to a lateral direction118, as seen inFIG.2andFIG.4b. The lateral direction118is perpendicular to the axial direction105of the imaging plane104. The probe support102may be adapted to connect to, and fixate the position of, an ultrasound transducer115such that the width119of the imaging plane104extends in the lateral direction118. The magnet102,103may thus be arranged to extend along the width119of the imaging plane104, as seen inFIGS.2and4b. This removes previous problems with inhomogeneous magnetic fields in the lateral direction of the image plane that are created from fixating the tip of an electromagnets under the object to be imaged, which thereby, due to the dependency of the displacement amplitude of the nanoparticles on the field gradient from the tip, result in a larger displacement amplitude close to the position of the tip, compared to further away from the tip in the lateral direction, irrespectively of the actual concentration of the nanoparticles that is set out to be detected. This situation is illustrated inFIGS.7a-c, where ultrasound and magnetomotive images on a tissue phantom are shown for a prior art magnetomotive imaging setup, such as illustrated inFIG.1, using a magnetic solenoid excitation voltage at 4 Hz, 30 Vpp excitation voltage. The nanoparticle-laden inserts401,402,403, as illustrated inFIG.4a, are outlined in the figure, as well as the mapping of the detected nanoparticle concentration, c.f.FIG.7cand scale704for indication of the detected concentration in the corresponding magnetomotive images701,702,703, for the inserts401,402,403. In more detail, the top row,FIG.7a, shows ultrasonic B-mode images, and the middle row,FIG.7b, show color-coded images representing displacement magnitude of the nanoparticles across the B-mode images. The middle row shows the total movement where the displacements at all frequencies are color-coded. The color of each pixel represents the displacement magnitude in that position and is coded according to the color bar scale704on the right of the FIGS. The bottom row,FIG.7c, displays frequency tracked and phase-discriminative imaging, i.e. displacement was only color coded when occurring with frequency 8 Hz (two times the excitation frequency on the magnetic field) and the phase difference was less than ±1.15 radians relative to the center phase in the nanoparticle-laden regions. The concentration of nanoparticles in insert401is 0.5 mg Fe3O4per ml, in insert402it is 0.3 mg Fe3O4per ml, and in insert403it is 0.4 mg Fe3O4per ml.

In particular fromFIG.7c, it can be clearly seen that in this prior art setup the movement of the inserts401,402,403, moves towards the center of the image where the electromagnetic tip is located. The insert moving the most is therefore the middle one, i.e. insert402, as seen from the corresponding magnetomotive image702, which actually has the lowest concentration of nanoparticles (0.3 mg Fe3O4/ml). As mentioned before this is due to the inhomogeneous magnetic field, where the insert being closest to the tip of the electromagnet, which in this case is insert402, has larger force acting on it compared to inserts401and403. It is thus not possible to relate the measured displacement amplitude of the nanoparticles to properties such as the concentration of nanoparticles with this prior art setup, which can be crucial for performing an accurate and complete analysis of the targeted material.

FIGS.8a-cillustrates the corresponding magnetomotive images obtained from using the magnetomotive imaging probe assembly101according to the present invention. Due to the laterally homogeneous magnetic field created by the magnets102,103, arranged on the probe support to extend along the width119of the image plane104in the lateral direction118there is only movement of the nanoparticles parallel to the imaging plane104along the axial direction105. Hence, the displacement of the nanoparticles gives an accurate representation of the concentration in the lateral direction118, which now correctly reveals the left insert401, outlined as object801in the corresponding magnetomotive image ofFIG.8c, as the insert having the highest concentration of nanoparticles (0.5 mg Fe3O4/l), and the right insert403/803as having the second highest concentration (0.4 mg Fe3O4/ml), and the middle insert402/802as having the lowest concentration (0.3 mg Fe3O4/ml). Hence, with the magnetomotive imaging probe assembly100the movement of the nanoparticles is increased with increasing nanoparticle concentration independent of the lateral position of the insert in the background material. The ultrasonic transducer115may have a distal edge120, i.e. the transducer face. The probe support101may fixate the ultrasound transducer such that the distal edge120is arranged substantially parallel to the magnet102,103, and the lateral direction118, and/or substantially parallel to the plane108.

The previously described advantages may be provided with any type of magnet that is arranged to extend along the width of the image plane104, parallel to lateral direction118, and generating a time-varying magnetic field at the imaging plane104of the ultrasound transducer115. In the examples inFIGS.2-4, the magnet102,103, is movably arranged on the probe support101and is arranged to generate the time-varying magnetic field (T) being homogeneous in the lateral direction in response to a motion of the magnet relative the probe support101and the ultrasound transducer115.

The setup of the magnetomotive probe assembly100is illustrated inFIG.4, showing the cylindrical inserts401,402,403, with different nanoparticle concentrations positioned in a tissue phantom404, in relation to a target imaging location110of the probe assembly100.

The fixation means116may be arranged to allow for connecting the ultrasonic transducer115to the probe support101at different distances from the magnet102,103. The distance may be variable along the axial direction105to optimize the excitation signal. The displacement of the nanoparticles is dependent on the distance between the magnet102,103, and the inserts401,402,403.FIGS.5a-fillustrates the displacement amplitude of the nanoparticles versus frequency for various concentrations of the inserts and for two different distances between the magnet and the inserts. The triangles represent the measurement values from the probe assembly100with the magnet102,103, close to the sample, the squares represent the same setup but the magnet102,103, is 3 mm farther away from the inserts, and the circles represent the prior art electromagnetic coil setup. Each symbol is a mean value of three cross-sections and the standard deviation is marked with error bars. It can be seen fromFIGS.5a-fthat the probe assembly100induces a higher displacement than the prior art electromagnetic coil setup. The highest displacement is achieved when the magnet102,103, is close to the phantom/inserts (triangles). The increased displacement amplitude of the nanoparticles with the probe assembly100according to the present invention is also seen fromFIG.6, showing the measured displacement amplitude on axis601versus nanoparticle concentration on axis602for the probe assembly100(squares) and the prior art electromagnetic coil setup (circles). The probe assembly100provides accordingly for detection with a better signal to background ratio, which enhances e.g. the imaging and analysis of samples with low nanoparticle concentration. FromFIG.6it is again seen that the laterally inhomogeneous magnetic field of the prior art setup gives a non-linear dependence of the displacement amplitude on the nanoparticle concentration, where the insert402with a concentration of 0.3 mg Fe3O4/ml has the highest displacement. This is in contrast to the more linear dependence obtained with the present imaging probe assembly100as seen inFIG.6(squares).

The arrangement of the magnet102,103, on the probe support101according to the above disclosure further reduces the influence of the axial coordinate in the axial direction105of the image plane104on the displacement amplitude. Hence a more accurate detection of the displacement amplitude is possible also in this direction of the image plane104.

The imaging probe assembly100may comprise the ultrasound transducer115, being arranged adjacent said magnet102,103. It should be realized that the inventive features as described above provides the aforementioned advantages irrespectively of the probe assembly100functions as a “snap-on” accessory to existing ultrasound transducers/probes, or has an ultrasound transducers/probe fixedly mounted to the probe support101as part of the probe assembly100. In each case the probe support101provides for fixating the position of the ultrasonic transducer115in relation to the magnet102,103, which may be movably mounted on the probe support101to thereby create a time-varying magnetic field at the imaging plane104of the ultrasonic transducer115. Alternatively or in addition the probe support101provides for fixating the position of the ultrasonic transducer115in relation to the magnet102,103, such that the magnet102,103, extend along the width of the imaging plane104.

The magnet102,103, may be rotationally arranged on the probe support101and adjacent the ultrasound transducer115when connected to the probe support101. The motion may thereby be a rotating motion. By rotating the magnet102,103, the magnetic field at the target location110is varied. The magnetic poles, N and S, of a permanent magnet102,103, may thus be displaced over time from a target location110at the imaging plane104by the motion of the magnet102,103, and thereby create a fluctuation in the magnetic field (T). The displacement may be provided by the aforementioned rotating motion, or any other motion that provides an oscillation of the magnetic field (T) over time at the target location110. Hence, the magnetic poles (N, S) of the permanent magnet102,103, are upon said motion displaceable from a target location110in the imaging plane104with an oscillating motion.

As illustrated inFIG.2the magnet102,103, may comprise a first102and a second magnet103, each being rotationally arranged on the probe support101and adjacent the ultrasound transducer115, when connected to the probe support101. Having a first101and a second102magnet may provide for an improved laterally homogeneous time-varying magnetic field (T). The first102and second103magnets may be rotatable in opposite directions, as illustrated by arrows (w1, w2) inFIG.2. Alternatively, each of the first102and second103magnets may be rotatable in a direction opposite to that illustrated inFIG.2, i.e. the first102and second103magnets would still be rotated in opposite directions in such case. As illustrated, the poles of each permanent magnet are arranged to rotate such that identical poles are facing each other to create a magnetic field gradient along the imaging plane104. E.g. the N-poles of magnets102,103, are momentarily facing each other in the situation shown inFIG.2. Subsequent rotation of the magnets102,103, will position the S-poles towards each other, and during the rotation the magnetic field at the target location110will undergo a fluctuation to move the magnetic particles. It may be conceivable that such fluctuation may be possible to generate from moving or oscillating a different number of magnets in relating to each other, and with oscillations in various directions. The symmetry of the arrangement illustrated inFIG.2may provide for an optimal time-varying magnetic field (T) at a target location110in the imaging plane104. The imaging and analysis of an object at the target location110may thus be accurately performed, and further without influence from undesired lateral gradients in the magnetic field (T) as described above.

The probe support101may be adapted to connect to, and fixate the position of, an ultrasonic transducer115such that the imaging plane104of the ultrasonic transducer115extends along the axial direction105between the first102and second103magnets, as seen inFIG.2. The first102and second103magnets are thus positioned on either side of the imaging plane104to provide a homogeneous time-varying magnetic field (T). The distance between the first magnet102and the imaging plane104may be the same as the distance between the second magnet103and the imaging plane104. The first102and second103magnets have respective first and second rotational axes106,107, spanning, and being separated along, a plane108. The axial direction105may be substantially normal to the plane108, and/or the rotational axes106,107, may be substantially parallel to the lateral direction118. This may further provide for a time-varying magnetic field (T) that has a minimal amount of undesired gradients. The nanoparticles will be displaced with an amplitude that is extending along the axial direction105of the ultrasound image plane104. The rotational axes106,107, of magnets102,103, may thus extend in the plane108so that the distance from each of the magnets102,103, to a distal portion109of the ultrasonic transducer115is the same if the magnets102,103, have a uniform cross-sectional dimension along the rotational axes106,107. This provides for a time-varying magnetic field (T) that has the same characteristics along the width119of the imaging plane104, where the width extends in the same direction as the rotational axes106,107. The relative positions of the magnets102,103, and the ultrasound transducer115, when fixed to the probe support101, may be varied to provide for customization according to the particular imaging application and thereby optimized to such varying applications. Hence it may be conceivable to vary the angle between the ultrasound transducer115and the plane108defined by the rotational axes106,107, and vary the distance between the magnets102,103.

Further, the probe support101may be adapted to connect to, and fixate the position of, an ultrasonic transducer115such that a distal portion109of said ultrasonic transducer is arranged between the first102and second magnets103when connected to the probe support101, as illustrated inFIG.2, to provide for an adequate detection signal. The distance between the distal portion109,120, i.e. the transducer face, and the plane108may be varied for example by either lowering or raising the ultrasonic transducer115along a height variable fixation means116in the probe support101. The ultrasound transducer115may thus be positioned at varying vertical locations in the magnetic field (T) produced by the magnets102,103. As mentioned above, further relative adjustments may be possible, to position the transducer115and imaging plane104in any location of the magnetic field (T).

As discussed above, the first102and second103magnets may extend substantially along the width119of the imaging plane104. The magnetic field may accordingly be homogeneous along the entire width of the imaging plane104to improve the imaging abilities.

As illustrated inFIG.2, each of the first102and second103magnets may comprise cylindrically shaped magnets102,103, having respective first and second rotational axes106,107, extending in a lateral direction (118) and each having opposite magnetic poles (N, S) separated along a diameter of each of the magnets in the radial direction (r), whereby rotation of the magnets102,103, create a time-varying magnetic field (T) from each of the magnets102,103, at the target location110. It is conceivable that other shapes of the magnets102,103, may provide the same effect.

The magnetomotive imaging probe assembly100may comprise a control unit111and a motor112. The motor112is coupled to the control unit111and to the magnet102,103, to power the motion of the magnet102,103. The control unit112may be adapted to vary the speed of motion (w1, w2) of the magnet102,103, according to a predetermined pattern to thereby vary the frequency of the time-varying magnetic field (T) as a predetermined frequency impulse to generate a frequency impulse response of magnetic nanoparticles at the target location110. This provides for determining an impulse response from the nanoparticles that may be indicative of the material properties, such as viscosity and density. Hence the nanoparticles may be displaced by the magnetic impulse and the material properties will affect how the displacement varies over time, such as the dominant frequency, maximum amplitude, and speed of damping may be indicative of material density, the elasticity and viscosity.

The control unit112may be adapted to vary the speed of motion w1, w2) of the magnet102,103, such as by increasing the speed linearly up to a certain maximum speed, and thereafter decrease the speed, to provide a sweep throughout frequencies and detect the resulting displacement amplitude of the nanoparticles. The control unit112may thus be adapted to vary the speed of motion (w1, w2) of the magnet102,103, according to such predetermined pattern to provide for detection of a frequency impulse response. The control unit may be adapted to set a constant speed of motion (w1, w2) of the magnet102,103. The control unit112may thus employ a magnetic force compensating control signal that varies the momentum of each of the magnets102,103, such that the varying magnetic force between the N and S poles of the magnets102,103, is compensated to provide for a constant rotational speed. Otherwise the angular speed may not be kept constant, as the magnetic S-pole of first magnet102has a tendency to lock to the magnetic N pole of the second magnet103due to the magnetic force between the poles. Depending on the position of the S-pole relative the N-pole during rotation of the magnets the magnetic force will vary, which thus may be compensated by the control unit111.

The control unit112may be further adapted to synchronize the frequency or speed of motion (w1, w2) of the magnets102,103, to the ultrasound imaging in order to provide for ultrasound detection at the correct frequency, and further to allow for detection at the right phase relative the ultrasound imaging.

The ultrasound transducer115also has an ultrasound control unit114that provides for the necessary control and analysis related to the ultrasound equipment.

FIG.3illustrates a schematic of an example of a probe assembly100, showing the magnets102,103, connected to a motor112, and an ultrasonic transducer115. The probe support101has been omitted for clarity of presentation.FIG.4illustrates a schematic of another example of a probe assembly100showing the ultrasonic transducer115and magnets102,103, fixated in a probe support101, which also may function as a casing of the probe assembly to isolate any subject to be imaged from the interior of the probe assembly100, i.e. the magnets will be in the casing for avoiding interference with the subject.

FIG.9illustrates a flow-chart of a method200of magnetomotive imaging with a probe assembly100, the probe assembly100comprising a probe support101adapted to connect to an ultrasound transducer115and a magnet102,103, movably arranged on the probe support101. The method200comprises rotating201the magnet102,103, to generate a time-varying magnetic field (T) at an imaging plane104of the ultrasound transducer115when connected to the probe support101. The method further comprises detecting205motion of magnetic nanoparticles in response to the time-varying magnetic field with the ultrasound transducer115in the imaging plane104. As mentioned above, this provides for an accurate determination of nanoparticle concentration, and further improved analysis of the examined material.

The method200may comprise rotating202first102and second103cylindrical permanent magnets, each having opposite magnetic poles (N, S) separated along a diameter of each of said magnets in the radial direction (r), in opposite rotational directions on either side of the imaging plane.

The method200may comprise rotating203first102and second103cylindrical permanent magnets according to a predetermined pattern to thereby vary the frequency of said time-varying magnetic field (T) as a predetermined frequency impulse to generate a frequency impulse response of the magnetic nanoparticles. The properties of the material of the analyzed object may thus me determined. The predetermined pattern may for example include rotating the magnets with a certain number of turns, or fractions of turns, such as half a turn, during a period of time such as a certain number, or fractions of seconds or minutes, to subsequently detect the response from the nanoparticles.

The method200may alternatively or in addition comprise rotating204first102and second103cylindrical permanent magnets with a constant rotational speed.

The magnetomotive imaging probe assembly100according to the above disclosure may be used for magnetomotive ultrasound imaging of magnetic nanoparticles.

FIG.10illustrates a magnetomotive imaging probe system300of the present invention. The system300comprises a movable probe301, a magnet302,303, arranged on the probe, and an ultra sound transducer315. The magnet302,303, is arranged to generate a time-varying magnetic field (T) at an imaging plane304of the ultrasound transducer315, distally of the ultra sound transducer315and the probe301, when the probe301has a proximal first position305adjacent the ultra sound transducer315. Since the probe is movable it can be freely positioned in various positions relative the ultra sound transducer315, which allows for probing different regions in the imaging plane304, i.e. displacing the magnetic particles in various regions and in different directions in the imaging plane304. This facilitates and optimizes detection in the region of interest, thereby improving accuracy and extraction of material properties in targeted region. Further, since the ultra sound transducer315may also be moved to various positions relative the analysed object, the system300provides for improved flexibility e.g. during surgery when it is desired to characterize a tissue region of a complex anatomy. Having the probe301in a proximal position305adjacent the ultra sound transducer, and arranged to generated the time-varying magnetic field (T) distally of the ultrasound transducer and the probe301, improved imaging and tissue characterization is provided for when frequent repositioning in relation to the object and/or the region of interest is required, such as in aforementioned complex anatomies or procedures involving several interventions at several target sites and regions of interest. Both the probe301and the ultra sound transducer315may thus be positioned proximally of the analysed object, and being movable in relation thereto, and without limitation with respect to the size of analysed object.

The probe301may thus be movable in relation to the ultra sound transducer315, and the probe may be a handheld probe301.

The magnet302,303, may be movably arranged on the probe301, whereby in use, the magnet302,303, is arranged to generate said time-varying magnetic field (T) in response to a motion of the magnet relative the ultrasound transducer315. Thus, the magnet302,303, may be a permanent magnet, with the previously aforementioned advantages as described for the embodiments relating toFIGS.2-9. The magnet may comprise a first magnet302, and a second magnet303as described inFIG.2with reference to first and second magnets102,103. Alternatively, a single magnet may be used, movably arranged in the probe301. Generally, the magnet302,303, may have any arrangement as described for the embodiments relating to FIGS.2-9, with the added feature in the system300ofFIG.10that the magnet302,303, is repositionable in relation to the ultrasound transducer315, by being arranged on a movable probe301as described previously.

The magnet302,303, may be displaceable from a target location110in the imaging plane304with an oscillating motion. This may provide for improved imaging and/or characterization of the analysed object at the target location110. It may also provide for a compact and easy to use probe301. Alternatively or in addition the magnet302,303, may have a rotating motion relative the probe301, as described in relation toFIG.2.

Alternatively the magnet302,303, may be an electromagnet.

The system300may comprise a control unit111and a motor112coupled to the probe301. The motor being coupled to the control unit and to the magnet302,303, to power a motion of the magnet, wherein the control unit is adapted to vary the speed of motion (w1, w2) of the magnet302,303, according to a predetermined pattern to thereby vary the frequency of said time-varying magnetic field (T) as a predetermined frequency impulse to generate a frequency impulse response of magnetic nanoparticles at the target location110, as described previously. Alternatively or in addition the control unit may be adapted to set a constant speed of motion (w1, w2) of the magnet302,303.

FIG.11illustrates a method400of magnetomotive imaging with a probe system300comprising a movable probe301and an ultra sound transducer315, and a magnet302,303arranged on the probe. The method400comprises; positioning401the probe at a proximal first position305adjacent the ultra sound transducer, generating402, with the magnet, a time-varying magnetic field (T) at an imaging plane104of the ultrasound transducer, distally of the ultra sound transducer and the probe, and detecting403motion of magnetic nanoparticles in response to the time-varying magnetic field with the ultrasound transducer in said imaging plane.

Generating the time-varying magnetic field (T) may comprise moving404the magnet302,303, relative the ultrasound transducer315. Moving the magnet302,303, may comprise displacing405the magnet302,303, from a target location110in the imaging plane304with an oscillating motion.

As will be appreciated by one of skill in the art, the present invention may be embodied as device, system, or method.

The present invention has been described above with reference to specific embodiments. However, other embodiments than the above described are equally possible within the scope of the invention. Different method steps than those described above, may be provided within the scope of the invention. The different features and steps of the invention may be combined in other combinations than those described. The scope of the invention is only limited by the appended patent claims.

More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the teachings of the present invention is/are used.