RU175978U1 - Dynamic phantom for spatial resolution control in magnetic resonance angiography - Google Patents

Abstract

The utility model relates to the field of medical technology, namely to devices for assessing spatial resolution during angiographic studies and can be used to control parameters and quality characteristics of images in magnetic resonance angiography. A dynamic phantom for controlling spatial resolution in magnetic resonance (MP) angiography, characterized in that the phantom is a periodic structure formed by three equal parallel silicone tubes connected in an adapter ring with an MP contrast fluid and a linear velocity profile and partitions between them, located on two pulleys, one of which is filled with an MR-contrast agent and placed in the isocenter of the magnet, the other is outside the radio frequency Coils (RF coil). The movement of the tubes is ensured by the fact that a pair of pulleys is connected to the motor shaft by a belt drive. The spatial resolution control is carried out for images obtained by scanning the main pulley, which is placed inside the RF coil. The maximum overall dimensions of each pulley with supports 180 × 160 × 123 mm. Both pulleys are mounted on a stand with a length of 600 mm. The engine is located outside the magnet at a distance of 3.5 meters. Range of engine shaft speed from 0 to 60 rpm. The method of magnetic resonance angiography is used to scan a rotating main pulley, on the resulting image using standard or specialized software, build the profile of the boundary of the periodic structure, determine the spatial resolution coefficient from it and conclude that it can be reproduced on the magnetic resonance image obtained by this method, objects whose sizes correspond to a given step of the periodic structure.

Description

The utility model relates to the field of medical technology, namely to means for controlling spatial resolution (ORS) in magnetic resonance angiography.

Magnetic resonance angiography (MRA) is a diagnostic method for assessing the anatomical and functional features of blood flow and cerebrospinal fluid in the human body. This method consists in the use of special MRA pulse sequences to create a contrast between a moving biological fluid (blood, cerebrospinal fluid) and stationary tissues. There are three main types of MRA: time-of-flight, phase-contrast and with contrast enhancement. The phase-contrast MRA method is based on the occurrence of a phase shift of moving protons using a bipolar gradient. The magnitude of the shift depends on the velocity of the biological fluids, as well as on the characteristics of the gradient field (induction and duration of the bipolar gradient). Given the parameters of the pulse sequence, the blood flow (cerebrospinal fluid) velocity can be determined by the magnitude of the brightness of pixels within the region of interest. It is also possible to set the maximum recorded fluid flow rate corresponding to the most intense signal in the image.

Thus, MRA is widely used not only for the qualitative assessment of the vascular and cerebrospinal systems, but also for obtaining quantitative indicators, including in the study of small vessels, for example, in assessing the state of the cerebral vascular bed. The need to visualize vessels of various diameters, branches, the presence of anastomoses requires the use of high spatial resolution MPA methods (Bogolepova E.A., Netesova E.V., Shustrova G.E., Abalmasov V.G .: Experience in the clinical application of magnetic resonance angiography [Electronic resource]: electron, journal Angiologia.ru. - Electronic journal. - Moscow: Infomedia Publishers, 2011; No. 1: p. 51-59. - Access mode: http://www.angiologia.ru/journal_angiologia /).

To ensure the required quality of diagnostic data with a given ORS value, it is necessary to periodically evaluate this parameter using phantoms and test objects.

To control the parameters and characteristics of a magnetic resonance imager (MRI) using the spin echo sequence, the technique of obtaining control images of a specialized phantom and their subsequent processing using software is used (Zelikman M.I., Kruchinin S.A., Snopova K.A. : Methods and means of monitoring the operational parameters of magnetic resonance tomographs. Medical technology. 2010; 5: p. 27-31). This phantom is a hollow cylinder made of acrylic plastic filled with MP-contrast fluid. Inside it there are several inserts necessary to control the parameters and quality characteristics of MP images obtained using the spin echo sequence. To control the ORS, a periodic structure is used, formed from rectangular parallelepipeds and the gaps between them with a step equal to 2.5, 2.0, 1.5, 1.0, 0.7, 0.5, 0.4 mm.

Known phantom for assessing the parameters of magnetic resonance images when testing MRI under the accreditation program of the American College of Radiology (ACR) (Kaljuste D., Nigul M. Evaluation of the ACR MRI phantom for quality assurance tests of 1.5 T MRI scanners in Estonian hospitals // Proceedings of the Estonian Academy of Sciences. - 2014. - No. 63 (3). - P. 328-334). The design of this phantom is similar to the technical solution given above. ORS control is carried out using a structure of three pairs of sets of holes with diameters from 1.1 mm to 0.9 mm. A visual assessment is made of the distinguishability of the holes of the smallest possible diameter in the image. The studied object is in a stationary position, therefore, using it to evaluate ORS with MRA is impossible due to the immobility of the periodic structures of the phantom.

Known disk phantom for monitoring velocity measurements in phase contrast magnetic resonance imaging (Pat. 2579824 Russian Federation, IPC G01R 33/20. Disk phantom for monitoring velocity measurements in phase contrast magnetic resonance imaging and a method for monitoring linear and volume velocity measurements the movement of the phantom [Text] / Gromov A.I., Sergunova K.A., Petryaykin A.V., Polenok Y.A., Mikhailenko E.A .; applicant and patentee of GBUZ “NPTsMR DZM.” - No. 2014144054/28 ; publ. 04/10/2016, Bull. No. 10. - 10 p.). The essence of this invention lies in the presence of a rotating disk with a given angular speed, filled with a gadolinium compound GD-DTPA and mounted on a shaft that rotates freely in bushings supported by brackets. The disadvantage of this invention from the point of view of ORS control is the lack of a periodic structure.

As the closest analogue of the claimed utility model, a phantom for modeling myocardial perfusion can be considered (Amedeo Chiribiri et al. Perfusion phantom: an efficient and reproducible method to simulate myocardial first-pass perfusion measurements with cardiovascular magnetic resonance. Magnetic resonance in medicine, vol. 69 , no.3, 04.24.2012, pp. 698-707). This model includes the plastic design of the heart chambers and four silicone tubes of equal diameter that simulate the arteries and veins of the heart through which fluid moves through the pump. The disadvantage of this phantom is the need to connect a pump, which implies the use of long tubes with liquid, the presence of a parabolic velocity distribution in the cross section of the tube with such a liquid flow, which impedes the processing of the obtained images, and the absence of a periodic structure that requires at least three tubes located on one straight.

The medical problem that can be solved by using a phantom to control ORS in MRA is the need to evaluate ORS angiographic images in order to improve the quality of diagnostic data in MRA.

The technical problem consists in the absence at the moment of means of ORS control with MPA that satisfy the conditions of this study, which consists in the presence of a moving fluid stream with a given speed and a periodic structure of the signal intensity in the image.

The use of this utility model makes it possible to control ORS during MRI examinations in the MPA mode, and as a result, to improve the quality of diagnostic data in MPA.

The essence of the utility model is that three parallel silicone tubes of equal diameter are located on two pulleys, one of which is filled with an MR-contrast agent and placed in the isocenter of the magnet, the other is outside the radio frequency coil. The movement of the tubes is ensured by the fact that a pair of pulleys is connected to the motor shaft by a belt drive. The ORS control will be carried out for images obtained by scanning the main pulley, which is placed inside the radio frequency coil (RF coil) of the head. The maximum overall dimensions of each pulley with supports 180 × 160 × 123 mm. Both pulleys are mounted on a stand with a length of 600 mm. The engine is located outside the magnet at a distance of 3.5 meters. Range of engine shaft speed from 0 to 60 rpm.

A brief description of the drawings.

FIG. 1 - Scheme-drawing of a dynamic phantom for monitoring ORS

Figure 2 - Figure connecting pulleys

FIG. 3 - Appearance of a pulley with silicone tubes fixed on it

FIG. 4 - Section of a tube with MP-contrast fluid

FIG. 5 - Silicone tube on a pulley

FIG. 6 - Scheme of pulley positioning in MRI

FIG. 7 - Figure to obtain the necessary cut of the pulley when scanning in MRI

FIG. 8 - Section of a pulley with silicone tubes

FIG. 9 - Photograph of an experiment using a phantom

FIG. 10 - Photograph of the location of the phantom on the patient's table in the RF coil

FIG. 11 - MPA image of an axial section of the main pulley with silicone tubes: a) at rest; b) - in motion; c) - construction of the line

FIG. 12 - Profile of the boundary of the periodic structure of silicone tubes

Utility Model Implementation

In FIG. 1 is a drawing diagram of a dynamic phantom, where 1 is a silicone tube, 2 is a main pulley, 8 is a support disk, 4 is a drive belt, 3, 5 and 9 are stands, 6 is an engine pulley, 7 is an engine.

The dynamic phantom consists of a main pulley 2, mounted on a shaft that rotates in the stand 3, and a support disk 8, also mounted on a shaft, rotating in the stand 5. All parts are made of non-magnetic plastic materials. Silicone pulley 1 of equal diameter is fitted over the pulleys. The torque is transmitted to the phantom by means of a belt drive 4 from the pulley of the engine 6 located on the axis of the engine 7 outside the magnet at a distance of 3.5 meters.

In FIG. 2 drawing pulley connections. In FIG. 3 is a top view of a pulley mounted on a shaft with silicone tubes on.

The movement of fluid relative to the tomograph is provided by the movement of the sealed tube. In FIG. 4 shows a section of a section of a tube at the junction of its ends, where 1 is a silicone tube, 10 is a connecting adapter, 11 is an MP-contrast liquid, 12 is an elementary layer of liquid.

The portion of the tube 1 connected to the ring by the adapter 10 is filled with an MR-contrast fluid 11 and moves with a linear velocity V. Under conditions close to normal, the fluid can be considered incompressible [Fundamentals of Hydrodynamics: Textbook. allowance / S.D. Chizhiumov. - Komsomolsk-on-Amur: GOUVPO “KnAGTU”, 2007. - 106 pp.], Therefore, the elementary layer 12 also moves with speed V. Given the incompressibility, each subsequent elementary layer of liquid moves with speed V.

In FIG. 5 shows a section of a tube on a pulley, where 1 is a silicone tube, 2 is a pulley.

Since the main pulley rotates with an angular velocity w, the linear velocity V of the elementary section of the tube can be found:

where r is the distance from the axis of rotation of the pulley to the center of the elementary section;

ω is the angular speed of rotation of the pulley.

If the motor shaft rotates with a frequency of n rpm, then its angular velocity w ₀ is

We believe that the angular velocity of rotation of the main pulley is equal to the angular velocity of rotation of the support disk, since the value of the elastic slip of the silicone tubes can be neglected. This speed is determined from the gear ratio for belt transmission and is equal to

where b is the diameter of the engine pulley;

D is the diameter of the support pulley;

ω is the angular speed of rotation of the support pulley;

ω ₀ - the angular speed of rotation of the engine pulley.

Thus, the linear velocity of any elementary section of a silicone tube with a liquid can be calculated as follows:

It is proposed to use the main and supporting pulleys with a diameter of D = 0.100 m, an engine pulley with a diameter of b = 0.036 m, and an engine rotor speed of n = 1 r / s. In this case, the distance from the axis of rotation of the pulley to the center of the elementary section of the tube is r = 0.110 m. Then, the calculated velocity of the elementary section of the silicone tube with MP-contrast fluid will be V = 0.248 m / s.

For the diameter of the engine pulley equal to 0.018 m, the linear velocity will take the value V = 0.124 m / s.

To control spatial resolution, a periodic structure formed of three silicone tubes and partitions between them can be used. Before scanning, the RF coil should be mounted on the deck of the patient table and provided with electrical power. A phantom is placed inside the RF coil and centered relative to it along the midline of the pulley, as shown in FIG. 6. After this, it is necessary to achieve the coincidence of the center of the receiving RF coil with the MRI isocenter by accurately combining the midline of the pulley with the laser beam. Lack of accurate positioning will lead to distortion of the periodic structure and incorrect results. Then, the scanning procedure is started using the MPA of the pulse sequences and axial images are obtained along section AA (Fig. 7, 8) of the pulley with tubes. On Fig shows that the periodic structure is an alternation of the inner diameter of the tube ∅d and the gap (d), consisting of the walls of adjacent tubes and partitions.

For manufacturing the phantom, we used parts printed on a 3D printer with a layer thickness of 50 μm using FFF technology (Fused filament fabrication). The materials for the main pulley were selected plastics: ABS (acrylonitrile butadiene styrene) and SBS (styrene-butadiene-styrene). Drawings of all parts were performed in the SolidWorks environment. The main pulley was filled with a gel-based MP contrast agent. To fill the silicone tubes, distilled water with an MP-contrast agent was used; their connection was carried out with a silicone adapter, fixing the joint with silicone sealant. All supports were laser cut from plexiglass. The experiments were carried out on an Excelart Vantage Atlas-X MP tomograph (Toshiba, Japan) with a constant magnetic field induction of 1.5 T using the 3D-TOF mode (TE = 8 ms, TR = 32 ms, tilt angle 20 °, cut thickness 1.2 mm )

In FIG. 9 is a photograph of an experiment using a phantom. The phantom support pulley is placed in the head RF coil, as shown in FIG. 10.

The MPA images of the stationary and moving pulley with silicone tubes filled with MP-contrast fluid are shown respectively in FIG. 11a and FIG. 11b. A boundary profile is constructed along the central axis of the tubes (as shown in FIG. 11 c) (FIG. 12). Next, the spatial resolution coefficient (K _ol ) is determined:

where M _max - the average value of the maximum brightness of the pixels of the profile of the boundaries of the periodic structure;

M _min - the average value of the minimum brightness of the pixels of the profile of the boundaries of the periodic structure;

M _s - the average value of the brightness of the pixels of the signal inside the phantom outside the periodic structure.

If the calculated value of the coefficient of spatial resolution exceeds 50%, then the value of spatial resolution corresponds to d given by the step of the periodic structure.

The first scan is recommended to be done with a step of periodic structure d equal to the ORS value declared by the manufacturer. If the calculated K _ol with this step is less than 50%, it is necessary to scan with an increase in the step of the periodic structure, until K _ol exceeds 50%.

Claims (1)

 A dynamic phantom for controlling the spatial resolution of magnetic resonance angiography, containing three equal parallel silicone tubes filled with MR-contrast fluid, installed in the form of a periodic structure, characterized in that each of the silicone tubes is connected to the ring by an adapter, the silicone tubes are mounted on the main a pulley and a support disk with the ability to move the tubes by transmitting torque from the engine pulley to the support disk, while the tubes are placed on Kywe and disc through interlaces tubes and partitions between them, the main pulley MP-filled with contrast material and placed at the isocenter of the magnet, the support disk and the motor pulley mounted outside the RF coil.

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