阅读说明：本技术 一种基于原子蒸气室阵列的心/脑磁测量装置 (Heart/brain magnetic measuring device based on atomic vapor chamber array ) 是由 周欣 娄昕 谭政 孙献平 叶朝辉 于 2021-09-28 设计创作，主要内容包括：本发明公开一种基于原子蒸气室阵列的心/脑磁测量装置,稳频激光器输出的偏振激光经保偏光纤入射光纤分束单元获得分束激光,各个分束激光经过偏振可调准直单元后入射原子蒸气室阵列单元中对应的原子蒸气室的入射端面并从原子蒸气室的出射端面出射,原子蒸气室的顶部端面作为探测端面,各个原子蒸气室出射的激光经光检偏单元后由对应的光探测单元将光信号转换为光强电信号。本发明原子蒸气室阵列由多个原子蒸气室阵列单元组成,集成布局在柔性基板上,易于获得较高的空间分辨率磁场测量；使用Cs原子及NMOR方式时,可工作在室温环境；仅使用一台激光器,操作简单,磁场测量灵敏度较高。本发明装置在生物微弱磁场测量领域具有重要应用价值。(The invention discloses a heart/brain magnetic measuring device based on an atomic vapor chamber array.A polarized laser output by a frequency stabilized laser enters an optical fiber beam splitting unit through a polarization maintaining fiber to obtain beam splitting lasers, each beam splitting laser enters the incident end face of a corresponding atomic vapor chamber in the atomic vapor chamber array unit after passing through a polarization adjustable collimation unit and is emitted from the emergent end face of the atomic vapor chamber, the top end face of the atomic vapor chamber is used as a detection end face, and the laser emitted by each atomic vapor chamber passes through a light polarization detection unit and is converted into a light intensity electric signal by the corresponding light detection unit. The atomic vapor chamber array consists of a plurality of atomic vapor chamber array units, is integrated and distributed on the flexible substrate, and is easy to obtain higher spatial resolution magnetic field measurement; when the Cs atom and the NMOR mode are used, the system can work in a room temperature environment; only one laser is used, the operation is simple, and the magnetic field measurement sensitivity is high. The device has important application value in the field of biological weak magnetic field measurement.)

1. The device comprises a frequency stabilized laser (1) and is characterized in that polarized laser output by the frequency stabilized laser (1) enters an optical fiber beam splitting unit (3) through a polarization maintaining fiber (2), the optical fiber beam splitting unit (3) splits the incident polarized laser into a plurality of split laser, each split laser enters an incident end face of a corresponding atomic vapor chamber in an atomic vapor chamber array unit (6) after passing through a polarization adjustable collimation unit (5) and is emitted from an emitting end face of the atomic vapor chamber, the top end face of each atomic vapor chamber is used as a detection end face, and the laser emitted by each atomic vapor chamber is converted into an optical signal into an optical intensity electric signal through a corresponding optical detection unit (9) after passing through an optical polarization detection unit (8).

2. The cardiac/cerebral magnetic measurement device based on the atomic vapor chamber array as claimed in claim 1, wherein the optical intensity electrical signals output by each optical detection unit (9) are transmitted by a bundled signal cable (10) and then are subjected to data acquisition by a multi-channel data acquisition card (11), and each path of optical intensity electrical signals acquired by the multi-channel data acquisition card (11) are input to a control and image processing computer (12).

3. The atomic vapor chamber array-based magnetocardiogram measuring device according to claim 2, wherein said atomic vapor chamber array unit (6) is located in a helmholtz coil unit (7), and the control and image processing computer (12) is connected to the helmholtz coil unit (7) via bundled control cables (10).

4. The atomic vapor cell array-based magnetocardiogram measuring device according to claim 3, wherein the atomic vapor cells in the atomic vapor cell array unit (6) are square, and the atomic vapor cell comprises a top end surface, a bottom end surface and four side end surfaces, wherein a pair of opposite side end surfaces are respectively an incident end surface and an emergent end surface, the top end surface is a detecting end surface, and the inner surface of the bottom end surface is attached with non-evaporated alkali metal.

5. The cardiac/cerebral magnetic measurement device based on the atomic vapor chamber array according to claim 3, characterized in that the atomic vapor chamber array (101) comprises a plurality of atomic vapor chamber array units (6), and the atomic vapor chambers in the atomic vapor chamber array units (6) are arranged in a straight line.

6. The cardiac/cerebral magnetic measurement device based on the atomic vapor cell array according to claim 1, characterized in that the polarized laser is a linearly polarized laser, the atomic vapor cell is filled with Cs atoms, and the frequency stabilized laser (1) operates at D1 linear wavelength 894.6nm of the Cs atoms.

7. The atomic vapor cell array-based magnetocardiogram measuring device according to claim 1, wherein the top end surfaces of the atomic vapor cells are disposed on a flexible substrate.

8. The atomic vapor chamber array-based cardiac/cerebral magnetic measurement device according to claim 7, wherein the flexible substrate is a teflon film or a woven cloth.

Technical Field

The invention relates to the field of measurement of weak biological magnetic field signals, magnetic field intensity, magnetic field distribution and the like, in particular to a cardiac/cerebral magnetic measurement device based on an atomic vapor chamber array for obtaining a human cardiac magnetic map or cerebral magnetic map.

Background

The significance of the biological magnetic field research is that important information such as physiological process, pathology and the like of organisms can be obtained. The biological magnetic signal is very weak, for example, the intensity of the magnetocardiogram generated by bioelectric current in the human body is of the order of pT, while the intensity of the magnetocardiogram is of the order of hundreds of fT. Therefore, a high-sensitivity magnetometric instrument is required to acquire a Magnetocardiogram (MCG) and a Magnetoencephalogram (MEG) of a human body.

The SQUID (superconducting Quantum interference device) magnetometer can reach-1 fT/Hz^1/2A sensitive commercial weak magnetic field measuring instrument, which works in a low temperature environment cooled by liquid helium, can be used for MCG measurement of human body [ Cohen D et al, magnetic imaging disks taken instrument a shield pole with a super connecting point-contact magnetic meter, Applied Physics Letters,1970,16(7): 278-.]And measurement of MEG in humans [ Cohen D, magnetic activity characterization of the blue' selective with a superconduction magnometer, Science,1972,175(4022): 664-.]。

The atomic magnetometer realizes magnetic field detection by measuring Larmor precession of spin polarized atoms in a magnetic field through a laser technology, and the sensitivity of the atomic magnetometer reaches a level which is comparable with the SQUID magnetometer. For example, the experimental measurement sensitivity of the current spin-exchange relaxation-free (SERF) atomic magnetometer reaches 0.16fT/Hz^1/2[Dang H B et al.,Ultrahigh sensitivity magnetic field and magnetization measurements with an atomic magnetometer,Applied Physics Letters,2010,97(15):151110.]. Therefore, one of the important applications of a highly sensitive atomic magnetometer is the measurement of weak biological magnetic fields, in particular, as a magnetic measuring instrument for the heart and brain of a human body in a magnetically shielded ultra-low field environment. For example, the heart magnetism of a pregnant fetus is measured using a SERF atomic magnetometer [ Wylie R et al, Optical magnetometer array forfetal magnetocardiography,Optics Letters,2012,37(12):2247-2249.]And performing a brain magnetic study [ Xia H et al, magnetic encyclopediy with an atomic magnetic mapper, Applied Physics Letters,2006,89(21):211104.]And the like.

In the existing methods and technologies, it is preferable to use a high-sensitivity atomic magnetometer that can work at normal temperature to measure a weak biological magnetic field. Measurements are usually made with partial coverage or full coverage of the human heart, brain combined with multiple atomic magnetometers, so that the MCG and MEG of the human body can be acquired. For example, when the current commercial zero field magnetometer (QZFM, Gen-2) of the U.S. qspin company is applied to the magnetic measurement of the heart/brain, a plurality of atomic magnetometer probes are combined, and each atomic magnetometer is independently integrated with a laser and other optical devices, and needs to be adjusted and calibrated respectively, so that the complexity of operation is increased; in addition, since each atomic magnetometer has its own independent working parameters (e.g., temperature, laser frequency, laser power, magnetic field compensation, detection sensitivity, etc.), it is very difficult to adjust the working parameters of the combined atomic magnetometers uniformly; finally, the acquired cardiac/cerebral magnetic signals of the human body measured by a plurality of independent atomic magnetometer probes also need complex multiple data post-processing and calibration to obtain the MCG and the MEG of the human body. Because the size of the single integrated atomic magnetometer probe is large, the measurement of a magnetic field with high spatial resolution cannot be realized, and the accurate positioning or imaging of the heart/brain position is not facilitated; in addition, because of its weight, it is not suitable to fix a large number of atomic magnetometer probes on a flexible substrate to achieve close contact with a human body part, which affects the acquisition of high magnetic field measurement sensitivity. Therefore, the development of a novel human body heart/brain magnetic field measuring device based on an atomic magnetometer is urgently needed, so that the measurement of a weak biological magnetic field is more convenient and accurate.

Disclosure of Invention

The invention aims to provide a heart/brain magnetic measuring device based on an atomic vapor chamber array, aiming at the defects in the prior art.

The above object of the present invention is achieved by the following technical means:

a core/brain magnetic measuring device based on an atom vapor chamber array comprises a frequency stabilized laser, wherein polarized laser output by the frequency stabilized laser enters an optical fiber beam splitting unit through polarization maintaining optical fibers, the optical fiber beam splitting unit splits the incident polarized laser into a plurality of beam splitting lasers, each beam splitting laser enters an incident end face of a corresponding atom vapor chamber in the atom vapor chamber array unit after passing through a polarization adjustable collimation unit and is emitted from an emitting end face of the atom vapor chamber, the top end face of each atom vapor chamber serves as a detection end face, and the laser emitted by each atom vapor chamber is converted into light intensity electric signals through a corresponding light detection unit after passing through a light polarization detection unit.

The light intensity electric signals output by each light detection unit are transmitted by the bundled signal cable and then are subjected to data acquisition by the multi-channel data acquisition card, and all paths of light intensity electric signals acquired by the multi-channel data acquisition card are input to the control and image processing computer.

The atomic vapor chamber array unit is arranged in the Helmholtz coil unit, and the control and image processing computer is connected with the Helmholtz coil unit through a bundling control cable.

The atomic vapor chamber in the atomic vapor chamber array unit is square, and the atomic vapor chamber includes a top end surface, a bottom end surface, and four side end surfaces, wherein a pair of opposite side end surfaces are respectively used as an incident end surface and an emergent end surface, the top end surface is used as a detection end surface, and the inner surface of the bottom end surface is attached with non-evaporated alkali metal.

The above-described atomic vapor cell array includes a plurality of atomic vapor cell array units, and the atomic vapor cells in the atomic vapor cell array units are arranged in a straight line.

The polarized laser is linearly polarized laser, the atom vapor chamber is filled with Cs atoms, and the frequency stabilized laser works at D1 linear wavelength 894.6nm of the Cs atoms.

The top end face of the atom vapor chamber as described above is provided on the flexible substrate.

The flexible substrate is a polytetrafluoroethylene film or woven cloth.

Compared with the prior art, the invention has the following beneficial effects:

1. compared with the mode of combining a plurality of atomic magnetometer probes, the atomic magnetometer probe array has the advantages that a plurality of lasers are not needed, the atomic vapor chamber array which is integrally distributed on the flexible substrate is used, the structure is simple, the miniaturization is easy, and the wearable type cardiac/cerebral magnetograph equipment is favorably developed;

2. the atomic vapor chamber integrally distributed on the flexible substrate has small size, and is beneficial to realizing magnetic field measurement with high spatial resolution; the number of the atomic vapor chambers can be changed according to actual measurement requirements, so that more complete magnetic field distribution information can be acquired;

3. only one laser is used as the light source. For the atomic vapor cell array, the laser wavelength, the power magnitude, the polarization direction and the noise level of each atomic vapor cell are the same, so that system noise caused by using different lasers is effectively eliminated;

4. for the human body heart/brain magnetic measurement, the data obtained by each atom vapor chamber in the atom vapor chamber array is comparable, the comprehensive post-processing is simpler and more reliable, and errors caused by the parameter calibration, the data processing and other processes are avoided;

5. the system can work in a room temperature environment by using Cs atoms and NMOR modes. Compared with a magnetic measurement mode based on a SERF atomic magnetometer (which needs to work at a higher temperature), the method does not need to use a vacuum or thick heat insulation plate or other modes to isolate an atomic vapor chamber from a measured organism, reduces the measurement distance, can obtain higher magnetic induction signal intensity of the organism, and is favorable for realizing the magnetic detection of the human heart/brain with higher sensitivity.

Drawings

Fig. 1 is a schematic diagram of the present invention.

In the figure: 1-a frequency stabilized laser; 2-polarization maintaining fiber; 3-an optical fiber beam splitting unit; 4-a bundle polarization fiber; 5-a polarization adjustable collimation unit; 6-atomic vapor cell array unit; 7-Helmholtz coil unit; 8-an optical polarization detection unit; 9-a light detection unit; 10-bundled signal cable wires; 11-a multi-channel data acquisition card; 12-a control and image processing computer; 13-bundling control cables; 101-array of atomic vapor cells.

Fig. 2 is a schematic diagram of an embodiment of the present invention.

Detailed Description

To facilitate understanding and practice of the present invention by those of ordinary skill in the art, the present invention is described in further detail below with reference to the embodiments of fig. 1 and 2, it being understood that the embodiments described herein are for purposes of illustration and explanation only and are not intended to be limiting.

Example (b):

in the embodiment, alkali metal Cs atoms are used in the atom vapor chambers in the atom vapor chamber array 101, the frequency stabilized laser 1 operates at the linear wavelength 894.6nm of the D1 atom of the alkali metal Cs, and a single beam of linearly polarized laser (which is formed by sigma lasers with opposite rotation directions and the same frequency) is used⁺Circularly polarized light sum σ^-Circularly polarized light) to provide pump light and probe light for each atomic vapor chamber in NMOR working mode through a polarization maintaining fiber 2, a fiber beam splitting unit 3, a cluster polarization fiber 4 and a polarization adjustable collimation unit 5.

The invention provides a heart/brain magnetic measuring device based on an atomic vapor chamber array, which can be further expanded to be used for measuring other weak biological magnetic fields by adopting a mode of 'one laser + the atomic vapor chamber array'. The atomic magnetometer structure based on the atomic vapor chamber array 101 can greatly improve the working performance and the efficiency for measuring weak biological magnetic fields (including human heart/brain magnetism and the like).

A kind of heart/brain magnetic measuring device based on atom steam chamber array, including the frequency stabilized laser 1, also include the polarization maintaining fiber 2, the polarized laser that the frequency stabilized laser 1 outputs is incident to the fiber beam splitting unit 3 through the polarization maintaining fiber 2, the fiber beam splitting unit 3 splits the incident polarized laser into a plurality of beam splitting lasers, each beam splitting laser is incident to the incident end of the corresponding atom steam chamber in the atom steam chamber array unit 6 and emergent from the emergent end of the atom steam chamber after passing through the polarization adjustable collimation unit 5, the top end of each atom steam chamber is used as the detection end, the laser that each atom steam chamber emits is converted into the optical signal intensity into the electrical signal by the corresponding optical detection unit 9 after passing through the optical detection unit 8, the optical signal intensity electrical signal that each optical detection unit 9 outputs is transmitted by the signal cable 10 of bundling and then is carried on the data acquisition by the multi-channel data acquisition card 11, each path of light intensity electric signal acquired by the multi-channel data acquisition card 11 is input to the control and image processing computer 12, the atomic vapor chamber array unit 6 is located at the center of the Helmholtz coil unit 7, the control and image processing computer 12 is connected with the Helmholtz coil unit 7 through a bundling control cable, and each atomic vapor chamber array unit 6 forms an atomic vapor chamber array 101.

The atomic vapor cell array 101 is formed by combining a plurality of atomic vapor cell array units 6, and in the present embodiment, as shown in fig. 2: each atomic vapor chamber array unit 6 comprises 7 atomic vapor chambers which are integrally distributed on a flexible substrate to serve as a weak biological magnetic field measuring probe, wherein 1 atomic vapor chamber array unit is used for calibrating the working parameters of the atomic vapor chamber; the number of atomic vapor chambers used is specifically determined based on cardiac magnetic field or brain magnetic field measurements for different human bodies, and the exemplary atomic vapor chamber array 101 includes 28 atomic vapor chambers in total, including 4 atomic vapor chamber units 6, which are only part of the coverage for the heart or brain when measuring cardiac/brain magnetism.

When the atomic vapor cell array 101 is in operation, the top end face of each atomic vapor cell faces the heart or brain of the human body as a detection end face, and the laser light from the polarization-adjustable collimation unit 5 passes through the atomic vapor in the atomic vapor cell from the incident end face of the side face of the atomic vapor cell along the optical axis direction and leaves the atomic vapor cell from the emergent end face of the opposite side face.

The polarization adjustable collimation unit 5, the optical polarization detection unit 8 and the optical detection unit 9 are matched with the atomic vapor chamber array 101 for use.

The atom-vapor-cell array unit 6 may be constructed as an atom magnetometer including a plurality of (7 in this embodiment) atom-vapor cells.

The frequency stabilized laser 1 works on the wavelength of an alkali metal Cs atom D1 line 894.6nm, is integrated into a cylindrical Cs atom vapor chamber, is frequency stabilized in a saturation absorption mode, is used together with the polarization maintaining optical fiber 2 as a frequency stabilizing optical fiber laser unit, and has the laser output power range of 40-250 mW typically;

the polarization maintaining optical fiber 2 is a polarization optical fiber with Cs atoms working at 894.6nm wavelength and is matched with the frequency stabilized laser 1 for use;

the optical fiber beam splitting unit 3 is composed of 1 or a plurality of optical fiber beam splitters, uses a hologram method, has the function of splitting a polarized laser into a plurality of laser beams with the same working parameters (power, polarization, mode and the like), and in application, the number of the beam splitting is the same as that of the atomic vapor chambers in the atomic vapor chamber array 101, as shown in the embodiment shown in fig. 2,1 to 2 plus four 1 to 7 are used, and the total number of the beam splitting is 28 to dozens of mu W laser beams, which corresponds to 28 atomic vapor chambers in the atomic vapor chamber array 101;

the bundling polarization optical fiber 4 is used for transmitting a plurality of beams of beam splitting laser from the optical fiber beam splitting unit 3, and the number of polarization optical fibers in the bundling polarization optical fiber 4 is the same as the beam splitting number of the optical fiber beam splitting unit 3 in application;

the polarization adjustable collimation unit 5 comprises a prism, a polarizing plate, a collimating mirror and other devices, and has the functions of collimating the laser from the bundling polarization optical fiber 4 and outputting the laser to the incident end face of the side face of each atomic vapor chamber in the atomic vapor chamber array 101 in a collimating way;

the atomic vapor cell array unit 6 is formed by combining a plurality of atomic vapor cells, and 7 atomic vapor cells are provided in this embodiment. The atomic steam chamber is made of optical cement, the material is parylene glass, the inner wall of the atomic steam chamber is coated with a coating for reducing atomic wall relaxation, and the inside of the atomic steam chamber is packaged with alkali metal Cs as a working medium in a hot melting mode. In the present embodiment, a typical atomic vapor chamber is square (not limited to this shape, and may be, for example, rectangular, cross-shaped, cylindrical, etc.), and has a size of 3mm × 3mm × 3mm (not limited to this size). Each atom vapor chamber consists of six flat plate end surfaces including a top end surface, four side end surfaces and a bottom end surface, wherein: the top end face is used as a weak biological magnetic field (such as heart and brain magnetism) detection end face; two end faces of the side face along the optical axis direction are a laser incident end face and an emergent end face which are plated with antireflection films. In this embodiment, the top end surfaces of the atom vapor chambers in the atom vapor chamber array unit 6 are connected to the flexible substrate, and as an embodiment, the atom vapor chambers in the atom vapor chamber array unit are arranged in a straight line, the atom vapor chambers may be arranged in other configurations, and the inner surface of the bottom end surface of the atom vapor chamber is attached with a trace amount of non-evaporated alkali metal Cs, and the atom vapor chamber pitch in each row is the same. The atomic vapor cell array unit 6 is located in a helmholtz coil unit 7 for magnetic field compensation, pulse sequence operation.

The helmholtz coil unit 7, which is a square structure (not limited to this shape), includes two sets of three-dimensional helmholtz coils, whose operation is ensured by the control and image processing computer 12 through the bundled control cable 13, and provides operations such as magnetic field compensation, pulse sequence, etc. for the atomic vapor cell array unit 6.

The light polarization detection unit 8 is composed of optical devices such as a polarization beam splitter and a wave plate, has the function of distinguishing emergent light with different polarization angles after the pump light and the detection light pass through each atomic vapor chamber in the atomic vapor chamber array 101, and respectively outputs the emergent light to the corresponding light detection units 9;

the optical detection unit 9 is composed of a plurality of four-quadrant detectors or a plurality of balanced photoelectric detectors, has the function of converting optical signals into electric signals, and is matched with the optical polarization detection unit 8 for use;

a cluster signal cable 10 for transmitting the electrical signal from each detector of the optical detection unit 9;

the multi-channel data acquisition card 11 and the control and image processing computer 12 are used for acquiring, calculating and processing the measured human body heart/brain magnetic field data to give the MCG and MEG of the human body.

The atomic vapor chamber array 101 is composed of a plurality of atomic vapor chamber array units 6, the atomic vapor chamber array units 6 comprise a plurality of atomic vapor chambers, the number of the atomic vapor chambers included in the atomic vapor chamber array 101 is typically 14-126, and the number of the atomic vapor chambers is specifically determined according to the surface area size measured by the heart magnetic field or the brain magnetic field of different human bodies. Fig. 2 shows an embodiment of 28 atomic vapor chambers in total, which is a 4 atomic vapor chamber array unit 6, and can be used for magnetocardiogram measurement or magnetoencephalography (partial coverage) measurement. If used for brain magnetic (full coverage) measurement, a total of 126 atomic vapor chambers can be used by 18 atomic vapor chamber array units 6, wherein one atomic vapor chamber in each array unit is used in advance for calibration of the operation parameters of the array unit.

The working process of the invention is expressed as follows:

first, the number of atomic vapor chambers included in the array of atomic vapor chambers 101 to be used is specifically determined in accordance with the surface area size measured for the cardiac magnetic field or the brain magnetic field of different human bodies; typically, the number of atomic vapor chambers is 14 (chest part) to 63 (chest plus back) for the human magnetocardiogram measurements, and 14 (partial coverage) to 126 (full coverage) for the human magnetocardiogram measurements;

in addition, the heart/brain magnetic measurement device based on the atomic vapor chamber array works in a magnetic shielding room environment (a magnetic shielding room, a magnetic shielding cylinder and the like), and each instrument and part in the device are in a normal working state;

a flexible substrate (insulating, heat insulating material such as typically teflon film, woven cloth, etc.) integrated with the atomic vapor cell array 101, which is in operation to be brought into close contact with a measured human body;

the frequency stabilized laser 1 and the polarization maintaining fiber 2 are used jointly, and the polarized laser which is emitted out and stabilized in the line spectral line of Cs atoms D1 enters the fiber splitting unit 3;

then, according to the standard that the number of the split beams of the polarized laser is consistent with the number of the atomic vapor chambers in the atomic vapor chamber array 101, a beam of the polarized laser with the wavelength of 894.6nm is split into a plurality of beams of laser with the same working parameters, and each beam of the split laser is used as a pumping light and a detection light of atomic vapor in each atomic vapor chamber;

a plurality of beams of laser light output from the cluster polarization optical fiber 4 pass through the polarization adjustable collimation unit 5 to respectively irradiate the atomic vapor in each atomic vapor chamber in the atomic vapor chamber array 101;

meanwhile, the control and image processing computer 12 performs operations such as magnetic field compensation and pulse sequence on the atomic vapor chamber region through the bundling control cable 13 and the Helmholtz coil unit 7;

the pump light, the detection light and the Cs atomic vapor interact with each other, work in a room temperature and NMOR mode, are represented as emergent light with different polarization angles after passing through each atomic vapor chamber, and are respectively output to the optical detection unit 9 through the optical polarization detection unit 8;

after the optical signal is converted into an electrical signal, the bundled signal cable 10 transmits the electrical signal from each detector in the optical detection unit 9 to the multi-channel data acquisition card 11;

finally, the control and image processing computer 12 calculates the magnetocardiogram or magnetocardiogram data of the human body measured by each atomic vapor chamber in the atomic vapor chamber array 101, and performs comprehensive processing such as time-frequency transformation and spectrum analysis to obtain the MCG or MEG of the human body.

The specific embodiments described in this specification are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments, or alternatives may be employed in a similar manner, by those skilled in the art, without departing from the spirit of the invention or exceeding the scope of the invention as defined in the appended claims.