RU2400135C1 - Magnetic resonance tomograph for ectremity examination - Google Patents

Abstract

FIELD: medicine. ^ SUBSTANCE: invention is applicable in medicine, namely in orthopaedic, traumatologic and surgical practice, and allows for the imaging of extremity joints, soft tissues and bones formed by nucleic magnetic resonance. A tomograph comprises a case permanent magnet with tips at the poles, gradient and radio-frequency coils fixed inside the permanent magnet cavity, a control unit with a control panel and a diagnostic image system, a bed for an examined extremity, a holder for a healthy extremity and a movable place for a patient. The permanent magnet represents an open top U-like with the cylindrical magnetic poles symmetrised on its profile planes composed of sectors of a magnetic material and closed-end polar tips each consisting of a base with an external collar and correction elements comprising a central disk and an external ring. Besides the correction elements are supplied with a turn mechanism concerning the polar tip base by an angle 0 to 5 degrees. The gradient coils of each profile plane are mounted on a flat disk fixed on an external collar of the polar tip and separated from the radio-frequency coil by a flat electromagnetic screen. Besides the radio-frequency coil is supplied with a automatic switch scheme of reception to transfer and back. ^ EFFECT: invention facilitates implemented MRT adjustment, and also provides the optimum conditions for the patient and the medical staff when positioning an examined extremity. ^ 4 cl, 6 dwg

Description

The alleged invention is intended for use in medicine, namely in orthopedic, traumatological and surgical practice, and allows to obtain images of joints, soft tissues and bones of limbs based on nuclear magnetic resonance.

Known magnetic resonance imaging (MRI) type for limb examination MAGNETOM C company "SIEMENS" containing a permanent magnet, radio frequency coil, electronics, patient table and control panel (www.medial.siemens.com) [1].

The main disadvantage of the known MRI [1] is the very large mass of a permanent magnet of 16 tons, which complicates the installation of the apparatus in the clinic and significantly increases the cost of the product.

Also known is an MRI containing a permanent magnet, a solenoidal radio frequency coil, the turns of which are connected mutually in parallel, a bed for the limb to be examined, an electronics unit and a control panel (US Patent No. 5543710 of 1994; CL 324/318) [2].

A disadvantage of the known object [2] is a noticeable decrease in sensitivity in the ankle and heel area when examining the patient's leg.

An MRI for examining limbs is also known, containing a permanent magnet, a bed for the examined leg in the form of a boot made of magnetically and electrically insulating material, on which a radio frequency coil, an electronics unit and a control panel are wound (patent RU No. 2192165, class A61B 5/055) [ 3].

Known MRI [3] is intended for the study of the ankle joint and heel of the patient’s leg; it is impossible to obtain images of the knee and elbow joints on it, which limits the scope of the apparatus [3].

The closest in design to the claimed object is an MRI for examination of the limbs ARTOSCAN-C "Artoscan-C et al. Dedicated MRI Systems" 04/03/2004, www.esaote.com/media/des / Cfs ... [4], containing a permanent enclosed casing O-shaped magnet in its vertical section, with tips on the poles, gradient coils, radio frequency transmitting and receiving coils installed in the gap between the poles, bed for the object of study, electronics box, control panel, holder for a healthy limb and a patient's mobile chair.

ARTOSCAN-C was chosen by us as a prototype.

The main disadvantage of the prototype is the complexity of its configuration when the apparatus is put into operation, due to the lack of a mechanism for correcting its magnetic field.

Another disadvantage of the prototype is expressed in the difficulty in positioning the studied limb in the working gap between the poles of the magnet, which is caused by the poor location of the holder for a healthy limb. This drawback creates inconvenience for the patient and staff and may adversely affect the accuracy of the study.

The aim of the present invention is to facilitate the adjustment of MRI when it is put into operation, as well as providing optimal conditions for the patient and medical personnel when positioning the examined limb on MRI.

To achieve the goal in an MRI for examining limbs, containing a permanent magnet enclosed with a casing with tips at the poles, gradient and radio frequency coils installed inside the cavity of the permanent magnet, a control unit with a control panel and a diagnostic image system, a bed for the limb under study, a holder for a healthy limb and a movable place for the patient, the permanent magnet is made in the form of a U-shaped yoke open from above with a magnet symmetrically mounted on its lateral planes with cylindrical poles drawn from magnetic material sectors and end caps closed at the end, each of which consists of a base with an external support ring and correction elements, including a central disk and an outer ring, equipped with a mechanism for their rotation relative to the base of the pole tip by an angle from 0 up to 5 degrees, the gradient coils of each side plane are mounted on a flat disk mounted on the outer support ring of the pole piece and are separated from the radio frequency ears flat electromagnetic shield, wherein the radio frequency coil is provided with an automatic circuit to switch from reception to transmission and vice versa.

The invention is further illustrated by the drawings and the explanation thereof. Figure 1 presents a General view of the apparatus (without a remote control); in FIG. 2 shows the position of the patient during examination of the lower leg; in FIG. 3 shows the design of a magnet with an RF coil; FIG. 4 is a view A-A of FIG. 3, and FIG. 5 is a block diagram of an MRI, and FIG. 6 shows the position of the patient during the examination of the knee joint.

The proposed magnetic resonance orthopedic tomograph is a medical diagnostic device designed to obtain images of limb joints in plane-parallel sections in three main sections (axial, sagittal and coronary), and in oblique sections with an angle of up to 45 degrees.

The tomograph allows you to visualize and examine the internal structures of the limbs and joints: lower leg, knee joint, foot, ankle, elbow joint, wrist, hand.

MRI for examining the extremities has a permanent magnet 1, made in the form of a U-shaped yoke open from above, the back of which is fixed on the supporting screws 2 (Fig. 3, 4). The magnet 1 is closed by a protective casing 3 (Fig. 1,2). The induction of the static field of magnet 1 in its working part within a sphere with a diameter of 180 mm is 0.23 T. The poles 4 and 5 of magnet 1 have a cylindrical shape and are drawn from sectors of magnetic material. This design of the poles 4, 5 of magnet 1 prevents the occurrence of induction currents (Foucault currents), which reduce the intensity and uniformity of the magnetic field. At the ends of poles 4, 5, pole pieces 6 are fixed. Each pole piece 6 consists of a flat base of cylindrical shape 7 with an external support ring 8 and correction elements containing a central disk 9 and an outer ring 10, equipped with a mechanism for their rotation relative to the base 7 at an angle from 0 to 5 degrees. The turning mechanism of the correction elements consists of a ball joint and three screws installed through 120 °. Correction of the inclination of the cylindrical disk 9 is carried out by three screws 11, the top of which rests at the base of the poles 4 (5), in the center of which the head of the ball joint 12 is movably fixed (see Fig. 3). The adjustment of the position of the outer ring 9 is made by three screws 13, the head 14 of which is spherical in shape and movably fixed in the ring 10. The pole pieces 6 are made of magnetoplast - a material with magnetic permeability µ = 100, saturation field 1.2-1.6 T and electric conductivity up to 20%. The reversal mechanism of the correction elements of the pole pieces is designed to fine-tune the magnet before putting the MRI into operation. When the cylindrical disk 9 and the outer ring 10 are tilted by an angle from 0 ° to 5 °, the shape of the magnetic field in the gap between the tips of the magnet changes, which facilitates its “fine” adjustment and allows to obtain a high-quality diagnostic image. Such a setting is made only once, with the introduction of MRI in the clinic. Gradient coils 15 in the amount of three pieces are deposited on a flat disk 16 and mounted on the outer support ring 8 of the pole pieces 6. Gradient coils are separated from the transmitter-receiver RF coil 17 by a flat electromagnetic screen (not shown in FIG.). The radio frequency solenoidal coil 17 is located between the pole pieces 6, in the working position, its geometric axis runs perpendicular to the geometric axis of the pole pieces 6 and parallel to the base of the MRI. The radio-frequency coil 17 has a built-in circuit for automatically switching from receiving to transmitting and vice versa, therefore it can rightfully be called a receiving-transmitting coil. Inside the RF coil 17 passes the bed 18 for the test limb, made of magnetically neutral material, such as plastic.

The use of a single receiving and transmitting RF coil in the proposed MRI is not accidental. The fact is that in the traditional scheme, when using two radio-frequency coils, the working gap of the magnet is reduced, which limits the size of the objects of study.

The automatism of the circuit with one transmitter-receiver radio frequency coil is performed as follows:

- at the time of transmission, a large voltage is applied to the coil circuit from the transmitter, which opens the control diode, commutes the transmitting mode of operation of the coil;

- at the time of reception, the signal is small, the diode is closed and the receiving mode of the coil is switched.

On the upper part of the protective casing 3, to the left and right of the cavity of the magnet 1, there is a holder 19, in the form of a recess, for a healthy limb 20 (Fig. 2, 6).

Gradient 15 and radiofrequency 17 coils are electrically connected to an electronic unit (not shown in FIG.), Including a personal computer whose tasks are to control shooting, generate a special electrical signal for gradient and radiofrequency coils, process an electrical signal taken from the radiofrequency coil, and generate a diagnostic Images. The electronic unit is controlled by a doctor through the operator’s console (Fig. 5).

Here is an example of the use of MRI in the study of the lower extremities (knee joint) (Fig. 6).

During the examination, for example, legs, the shin 21 of the patient is on the bed 18 inside the radio frequency coil 17, and the patient 22 is on a specialized trolley 23 (Fig. 2, 6). The free leg 20 is placed on the holder 19, made in the form of a recess on the upper part of the protective casing 3, to the left and to the right of the magnet gap.

When examining the knee joint, lower leg, foot, and ankle, a knee coil is used. The sequence of actions is as follows:

- position the patient with his feet to the magnet;

- push the coil on the patient’s leg in a position in which the center of the coil coincides with the center of the examination area;

- position the leg with the coil above the upper edge of the magnet above the U-shaped recess;

- lower the leg with the coil into the U-shaped recess of the magnet so that the coil fits into the centering trap and locks in the center of the magnet;

- for a more comfortable position of the legs, it is recommended to place the second leg on the casing of the magnet;

1 - to clarify the positioning of the legs relative to the coil, run the xscout program in the sagittal section and get an image;

2 - check whether the center of the study area matches the center of the received image;

3 - if necessary, with the coil stationary, move the patient forward or backward and repeat the xscout program;

4 - start scanning according to the selected protocol

During the examination, the limb 21 is always located in the coil 17 in a standard way, parallel to the base of the magnet. In order to get the cut plane at an angle, for example 45 °, it is enough to redistribute the currents in the gradient coils, the ratio of which determines the angle of inclination. So, if we consider the XOY plane, that is, Z will be directed vertically due to the fact that no current is supplied to the gradient coil Z. If now part of the winding current X is applied to Z, then the section plane will rotate about the Y axis.

The explanation of FIG. 5

The radio frequency cell is a closed Faraday cage, inside which a magnetic system is installed. The purpose of the radiofrequency cell is to suppress external radio interference received by the receiving coils on the air. To prevent radio interference from passing through the connecting cables, all connecting cables between the magnetic system on the one hand and the power rack and the operator’s console on the other hand are inserted into the radio frequency cage through the RF filter unit.

A gradient amplifier, a transmitter, a magnet thermostat control system and an external electromagnetic field compensation control system are mounted in the support rack.

The operator’s console includes a head personal computer (PC) and a spectrometer that controls the operation of tomographic systems and is structurally located in the system unit of the head PC.

The workstation is an auxiliary PC connected by a local network to the main PC. The workstation provides the possibility of parallel work - in the process of scanning the current patient, the doctor can analyze, describe and display solid copies of the images of patients already examined on the tomograph on the computer of the workstation.

An image archive is also maintained on the hard disk of the workstation.

To place the equipment of the tomograph requires a room with an area of at least 20 m ² .

The compactness of MRI in combination with the modest requirements for the working room and the ability to work from a standard 220 V network make it possible to use it effectively both in hospitals and in outpatient departments for the diagnosis of, first of all, traumatological (including sports) injuries of the extremities, and also orthopedic, rheumatological and other diseases of the musculoskeletal system.

Claims (4)

1. Magnetic resonance imaging tomograph for examining the limbs, comprising a cased permanent magnet with tips at the poles, gradient and radio frequency coils installed inside the cavity of the permanent magnet, a control unit with a control panel and a diagnostic image system, a bed for the limb under study, a holder for a healthy limb and a movable place for the patient, characterized in that the permanent magnet is made in the form of a U-shaped yoke open on top with symmetrically mounted on its side plates speeds with cylindrical magnetic poles drawn from sectors of magnetic material and pole tips closed from the end, each of which consists of a base with an external support ring and correction elements, including a central disk and an external ring, equipped with a mechanism for their rotation relative to the base of the pole tip at an angle from 0 to 5 °, the gradient coils of each side plane are mounted on a flat disk mounted on the outer support ring of the pole piece and are separated from the radio frequency hydrochloric electromagnetic coil flat screen, wherein the radio frequency coil is provided with an automatic circuit to switch from reception to transmission and vice versa. 2. The tomograph according to claim 1, characterized in that the rotation mechanism of the correction elements of the pole pieces consists of a ball joint and three screws. 3. The tomograph according to claim 1, characterized in that the pole pieces are made of magnetoplast. 4. The tomograph according to claim 1, characterized in that the holder for a healthy limb is mounted on the upper surface of the casing of the permanent magnet, on both sides of its cavity.

Images