Device for generating vibrations in human tissue for magnetic resonance elastography

Abstract

The invention relates to a device for generating vibrations in human tissue for magnetic resonance elastography, comprising a housing with a central housing portion (2) and two outer housing portions (3, 4), a turbine (6) which is rotatably mounted in the central housing portion (2) about a rotational axis (13) and which can be driven by a fluid flowing into the central housing portion (2), and two unbalance elements (7, 8) which are driven by the turbine (6) and each of which is rotatably mounted in a respective outer housing portion (3, 4) about a rotational axis (13) that is aligned with the rotational axis (13) of the turbine (6) such that the turbine (6) is positioned between the two unbalance elements (7, 8) in the axial direction.

Description

[0001] Device for generating vibrations in human tissue for magnetic resonance elastography

[0002] The invention relates to a device for generating vibrations in human tissue for magnetic resonance elastography.

[0003] Vibration generators, also known as transducers or wave generators, are used in magnetic resonance elastography to direct mechanical waves into the tissue under examination. Shear waves are relevant due to their lower phase velocity. When they hit, these cause shifts in the micrometer range, which can be made visible using magnetic resonance imaging. Bipolar gradient pulses allow the wave amplitude to be encoded in the phase of the MR signal. If the image is repeated at a different time than the oscillation, wave patterns are produced that serve as the basis for calculating the elasticity of the tissue. The mechanical properties of the tissue, such as elasticity, and any changes in these properties are an important indicator for diagnosing or classifying various diseases, such as fibrosis.Furthermore, changes in muscle stiffness are a direct function of muscle tension and thus a measure of the activity level.

[0004] There are several key factors to consider when using the vibration generator for magnetic resonance elastography.

[0005] It is crucial that the vibration generator operates at a stable frequency, which typically varies between 20 and 200 Hz depending on the specific application. Low-frequency waves are less attenuated and can therefore penetrate deeper into the body, while higher frequencies, with shorter wavelengths, allow for more precise localization and a more accurate depiction of tissue stiffness. It should be noted that the shear modulus is directly related to the square root of the wave propagation velocity, which, however, is not constant for all frequencies. This is why multifrequency elastography is also used.

[0006] Frequency stability throughout the entire measurement is of great importance. The generated wave amplitude is equally critical to ensure adequate penetration depth into the tissue. A suitable combination of amplitude and frequency must be found depending on the depth and properties of the tissue being examined, as well as existing structures and boundary layers. Higher frequencies suffer less attenuation but offer a shorter penetration depth. It is therefore advantageous if the vibration generator offers a wide selection of frequency and amplitude settings. Other essential features include MR compatibility, i.e. the absence of magnetic or metallic components, biocompatibility to ensure that the vibration generator material has no negative influence on living tissue, and appropriate size.The vibration generator should be dimensioned to fit between the RF coil and the patient in order to keep the distance between them as short as possible.

[0007] EP 3384844 A1 discloses a mechanical actuator for the

[0008] Magnetic resonance elastography has become known, which uses the principle of centrifugal force to generate vibrations. The mechanical actuator comprises a passive drive with a rotating turbine vibrator equipped with an eccentric weight, where the turbine vibrator is driven by a fluid, such as compressed air or water, and an active drive configured to control the pressure of the fluid that drives the turbine vibrator. A disadvantage here is the coaxial arrangement of the turbine and eccentric weight, such that the turbine surrounds the eccentric weight.

[0009] This results in a high construction, so that the actuator cannot easily be placed between the RF coil and the patient.

[0010] For mechanically excited vibration generators that operate with an eccentric weight, there is a conflict between the need for a compact, flat design and the provision of sufficient mass to generate effective centrifugal forces. A flat vibration generator offers less space for the necessary mass to generate sufficient vibration amplitudes.

[0011] A larger design, in turn, increases the distance between the RF coil and the patient, which leads to a weakening of the received signal and a deterioration of the image quality.

[0012] Therefore, one object of the present invention is to improve a vibration generator for magnetic resonance elastography by resolving the aforementioned conflict of objectives. The vibration generator should combine a flat design with sufficient mass for vibration generation to generate effective centrifugal forces without compromising the arrangement between the RF coil and the patient.To achieve this object, the invention provides, according to a first aspect, a vibration generator comprising a housing with a central housing section and two outer housing sections, a turbine which is mounted in the central housing section so as to be rotatable about an axis of rotation and which can be driven by a fluid flowing into the central housing section, and two unbalance elements which are driven by the turbine and which are each mounted in the outer housing sections so as to be rotatable about an axis of rotation which is aligned with the axis of rotation of the turbine, so that the turbine is arranged in the axial direction between the two unbalance elements.

[0013] The axial arrangement of the turbine between the unbalanced weight elements results in a significantly lower overall height of the vibration generator. At the same time, the use of two unbalanced weights, as opposed to a single eccentric weight, provides sufficient vibration mass.

[0014] The design of the vibration generator with the turbine in the middle and the symmetrical arrangement of the unbalance elements on both sides of the turbine also enables a balanced distribution of mass and vibration forces.

[0015] Because the turbine is located in a central housing section and therefore separate from the imbalance elements located in the outer housing sections, the fluid flow to and from the turbine is not affected by the imbalance elements. The fluid-driven turbine provides a reliable and adjustable vibration generation mechanism, allowing precise control of the frequency and amplitude of the vibrations, which is critical for high-quality imaging.

[0016] According to a preferred development of the invention, the transmission of the rotary movement from the turbine to the two unbalance elements takes place in that the unbalance elements are each coupled to the turbine in a rotationally fixed manner by means of a positive plug connection.

[0017] The plug-in connection allows the respective unbalance element to be easily plugged onto and removed from the turbine. When plugged or pushed onto the turbine, a positive connection is created that is effective in the direction of rotation. The plug-in connection ensures simple assembly and also enables the unbalance elements to be replaced. This can be useful, for example, to use unbalance elements with different eccentric masses as required. It also makes it easier to change the turbine, allowing a wide variety of turbine types to be used if necessary.

[0018] It is preferably provided that the positive plug-in connection has an axial section with a non-circular cross-section on one element selected from the turbine and the unbalance element and a receptacle for the positive axial insertion of the axial section on the other element selected from the turbine and the unbalance element. The non-circular cross-section can, for example, be triangular, rectangular, square or star-shaped. A particularly advantageous embodiment with a star-shaped cross-section comprises a cross-section in the shape of an internal or external hexalobular screw ("Torx®"). This type of cross-sectional shape ensures good power transmission with low material wear.

[0019] A further preferred embodiment provides that the non-circular cross-section has a rotational symmetry of order > 2. This allows the unbalance elements to be positively connected to the turbine in various angular positions, creating, for example, the possibility of an angular offset between the two unbalance elements in order to generate vibration superpositions if necessary.

[0020] The unbalance elements can advantageously have axial bores for receiving weight rods. The bores are arranged eccentrically so that the total mass of the unbalance of the unbalance elements can be adjusted by varying the weight of the weight rods or by varying the number of weight rods. The weight rods can, for example, be made of a plastic with a higher density than the material of the unbalance elements, such as PTFE. The unbalance elements preferably have a plurality of bores distributed in the circumferential direction for receiving weight rods. By varying different combinations of weights, the force development of the vibration generator can be controlled in addition to the selection of the frequency.

[0021] As already mentioned, the housing is divided into a central housing section and two outer housing sections. In order to separate the central housing section from the outer housing sections, a preferred development of the invention provides that the central housing section delimits a chamber for accommodating the turbine, which is closed off from the unbalance elements and is in particular fluid-tight. This ensures that the fluid introduced into the central housing section or into the chamber delimited by it to drive the turbine does not come into contact with the unbalance elements. The seal required for this can, for example, comprise a sealing cord which is arranged on the mutually facing sealing surfaces of two housing halves.

[0022] The turbine can, in principle, be driven by any fluid. Water or air is preferred. The chamber housing the turbine is therefore designed to be watertight or airtight.

[0023] In order to transmit the vibrations generated by the unbalanced elements as directly as possible to the patient's body region to be examined, it is preferably provided that the unbalanced elements are mounted at their opposite ends in rolling bearings, which transmit the vibrations generated by the rotation of the unbalanced elements to the housing. For this purpose, the rolling bearings are immovably mounted, for example, in suitable annular grooves in the housing, such as by positive engagement.

[0024] Preferably, the rolling bearings facing the turbine form an axis passage between the chamber of the middle housing section accommodating the turbine and the chambers of the outer housing section accommodating the unbalance elements.

[0025] Housing sections made of . In order to ensure the MR compatibility of the vibration generator, it is preferably provided that the device including the housing, the turbine, the unbalance elements and the rolling bearings consists of non-magnetizable, in particular non-metallic materials, such as e.g. polymers (polyamide, polyurethane, polypropylene, polycarbonate), ceramics, non-ferromagnetic metals.

[0026] According to a further aspect, the present invention relates to the use of a device according to the first aspect of the invention for generating vibrations in human tissue in the context of magnetic resonance elastography. The vibration generator is placed on the patient's body region to be examined and activated so that the generated vibrations are introduced into the body region. The vibration generator is arranged in particular between an excitation coil of a magnetic resonance tomograph and the body region to be examined.

[0027] The invention is explained in more detail below with reference to an exemplary embodiment shown schematically in the drawing. In this drawing: Fig. 1 shows a vibration generator according to the invention with the upper housing shell removed, Fig. 2 shows a representation of the upper housing shell, Fig. 3 shows the turbine of the vibration generator shown in Fig. 1 and Fig. 4 shows an unbalance element of the vibration generator shown in Fig. 1.

[0028] Fig. 1 shows a vibration generator according to the invention, the housing of which consists of two housing shells. The lower housing shell is designated 1 in Fig. 1, whereas the upper housing shell has been removed and is not shown in order to better show the components arranged inside the housing. The housing comprises a central housing section 2 and two outer housing sections 3 and 4. In the central housing section 2 there is arranged a turbine 6 which is mounted so as to be rotatable about an axis 13. A fluid inlet 5 is provided for driving the turbine 6, via which fluid inlet 5 a drive fluid, such as water or compressed air, is introduced into the chamber enclosed by the central housing section, where the drive fluid strikes the turbine blades and drives the turbine to rotate. The drive fluid is led out of the chamber via a fluid outlet which is not visible in Fig. 1.

[0029] The turbine drives the two unbalance elements 7 and 8, which are each mounted in the two outer housing sections 3 and 4 around the same axis of rotation 13. The turbine 6 is thus arranged in the axial direction between the two unbalance elements 7 and 8. As will be explained in more detail with reference to Figs. 3 and 4, the turbine 6 and the unbalance elements 7 and 8 are connected to one another in a rotationally fixed manner by means of a positive plug-in connection and thus form a common axis of rotation. The bearings are provided by means of the rolling bearings 9, 10, 11 and 12, which are all received in a form-fitting manner in annular receiving grooves 15 in the housing shells 1 and 14 (Fig. 2), so that the vibrations generated by the unbalance elements 7 and 8 are transmitted directly to the housing.

[0030] The turbine 6 is shown separately in Fig. 3 and comprises an axle section 16 with a non-circular, namely star-shaped, cross-section. The axle section 16 is inserted into a receptacle 17 (Fig. 4) arranged on the unbalance element 7 or 8, which has a cross-section corresponding to the cross-section of the axle section 16, so that the axle section 16 fits positively into the receptacle

[0031] 17 and a rotationally fixed connection is established. The receptacle 17 is formed on an axle section 18 of the unbalance element 7 or 8.

[0032] As can be seen in Fig. 4, the unbalance element 7 or 8 comprises an eccentric mass 19 in which radially distributed bores 20 are provided which serve to accommodate weight rods.

Claims

Patent claims:

1. Device for generating vibrations in human tissue for magnetic resonance elastography, comprising a housing with a central housing section (2) and two outer housing sections (3, 4), a turbine (6) which is mounted in the central housing section (2) so as to be rotatable about an axis of rotation (13) and which can be driven by a fluid flowing into the central housing section (2), and two unbalance elements (7, 8) which are driven by the turbine (6) and which are each mounted in the outer housing sections (3, 4) so ​​as to be rotatable about an axis of rotation (13) which is aligned with the axis of rotation (13) of the turbine (6), so that the turbine (6) is arranged in the axial direction between the two unbalance elements (7, 8).

2. Device according to claim 1, characterized in that the unbalance elements (7, 8) are each coupled to the turbine (6) in a rotationally fixed manner by means of a positive plug connection.

3. Device according to claim 2, characterized in that the positive plug connection has an axial section (16) with a non-circular cross-section on one element selected from the turbine (6) and the unbalance element (7, 8) and a receptacle (17) for the positive axial insertion of the axial section (16) on the other element selected from the turbine (6) and the unbalance element (7, 8).

4. Device according to claim 3, characterized in that the non-circular cross-section has a rotational symmetry of order > 2.

5. Device according to one of claims 1 to 4, characterized in that the unbalance elements (7, 8) have axial bores (20) for receiving weight rods.

6. Device according to one of claims 1 to 5, characterized in that the central housing section (2) delimits a chamber for receiving the turbine (6) which is closed off from the unbalance elements (7, 8), in particular a fluid-tight chamber.

7. Device according to one of claims 1 to 6, characterized in that the unbalance elements (7, 8) are mounted at their opposite end regions in rolling bearings (9, 10, 11, 12) which transmit the vibrations generated by the rotation of the unbalance elements (7, 8) to the housing.

8. Device according to claim 7, characterized in that the rolling bearings (9, 10) each facing the turbine (6) form an axle passage between the chamber of the middle housing section (2) receiving the turbine (6) and the chambers of the outer housing sections (3, 4) receiving the unbalance elements (7, 8).

9. Device according to one of claims 1 to 8, characterized in that the device including the housing (1, 14), the turbine (6), the unbalance elements (7, 8) and the rolling bearings (9, 10, 11, 12) consists of non-magnetizable, in particular non-metallic materials, such as polymers (polyamide, polyurethane, polypropylene, polycarbonate), ceramics, non-ferromagnetic metals.

10. Use of a device according to one of claims 1 to 9 for generating vibrations in human tissue in the context of magnetic resonance elastography.

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