CN115429250B - MRI (magnetic resonance imaging) gating method and system based on multi-channel pressure induction - Google Patents

Abstract

The present application discloses an MRI gating method and system based on multi-channel pressure sensing. The method includes: collecting the pressure change between the lower body surface of the human body and the contact surface of the examination bed through multiple signal acquisition channels to obtain multiple respiratory signals; performing signal processing on the multiple respiratory signals to obtain signals representing the signal levels of the corresponding channels. multiple recommended indicators; the recommended indicators include stability indicators, sensitivity indicators and signal-to-noise ratio indicators; based on the multiple recommended indicators, select the optimal channel that meets the preset requirements from multiple signal acquisition channels; based on the optimal channel The acquired respiratory signal was gated by MRI. The method and system disclosed in the present application can improve the quality of MRI imaging by selecting the respiratory signal of the optimal acquisition channel for MRI gating.

Description

MRI gating method and system based on multi-channel pressure sensing

technical field

The present invention relates generally to the field of MRI gating. More specifically, the present invention relates to an MRI gating method based on multi-channel pressure sensing and an MRI gating system based on multi-channel pressure sensing.

Background technique

In modern medicine, MRI (magnetic resonance imaging) technology is used to image the internal structure of the human body. It uses the principle of nuclear magnetic resonance (nuclear magnetic resonance, referred to as NMR), according to the different attenuation of the released energy in different structural environments inside the material, and through the detection of the emitted electromagnetic waves by an external gradient magnetic field, it can be known that the atomic nucleus that constitutes this object The position and type of the object can be drawn as a structural image inside the object.

During the imaging process using MRI, it is necessary to use patient respiratory information, including respiratory phase and respiratory cycle information, to perform MRI gating for imaging. Accurate acquisition of respiratory information is an important factor in determining the effect of imaging or treatment.

In the first application CN201810399008.8 (a method and system for obtaining respiratory information), it is disclosed that the respiratory signal can be obtained by collecting the pressure changes of the lower body surface of the human body and the examination bed, and filtering after analog-to-digital conversion. However, in actual use, due to the large difference in the size of the patient, the measurement value difference between different channels is large, so that the accuracy of the respiration measurement is not enough. Therefore, how to improve the accuracy of the respiratory signal required for MRI gating to improve the quality of MRI imaging has become an urgent problem to be solved.

Contents of the invention

In order to at least solve the technical problems described in the background technology section above, the present invention proposes an MRI gating method and system based on multi-channel pressure sensing. The solution of the present invention can effectively improve the accuracy of respiratory signals required for MRI gating, thereby improving the quality of MRI imaging. In view of this, the present invention provides solutions in the following aspects.

The first aspect of the present invention provides an MRI gating method based on multi-channel pressure sensing, comprising: collecting pressure changes between the lower body surface of the human body and the contact surface of the examination bed through multiple signal acquisition channels to obtain multiple respiratory signals; Perform signal processing on the plurality of respiratory signals to obtain a plurality of recommended indicators representing the signal level of the corresponding channel; the recommended indicators include stability indicators, sensitivity indicators and signal-to-noise ratio indicators; based on the plurality of recommended indicators from multiple The optimal channel that meets the preset requirements is selected from the signal acquisition channels; the MRI gating is performed based on the respiratory signal collected by the optimal channel.

In one embodiment, signal processing is performed on the multiple breathing signals, specifically including a primary conditioning step and a secondary conditioning step; the primary conditioning step is used to reduce the sampling noise of the multiple breathing signals to obtain noise-removed breathing signal; the secondary conditioning step is used to obtain the multiple recommended indicators according to the difference in signal frequency in the noise-removed respiratory signal.

In one embodiment, the primary conditioning step specifically includes: sampling the pressure value at a sampling rate higher than the breathing frequency of the human body, and smoothing a plurality of consecutive sampling points, so as to reduce the noise of the preliminary sampling.

In one embodiment, the secondary conditioning step specifically includes: extracting the direct current and ultra-low frequency part of the signal, defined as the static pressure component Fs; extracting the ultra-high frequency part of the signal, defined as the noise component Fn of the measurement signal; extracting the signal The rest of the intermediate frequency in the middle frequency is used as the dynamic pressure component Fd; the change level of the static pressure component Fs is used to represent whether the patient has obvious movement, which is used as a recommended indicator of stability; the ratio between the static pressure component Fs and the dynamic pressure component Fd is used, that is, Fd /Fs, to characterize the measurement sensitivity of the signal, as a recommended sensitivity index; use the calculation relationship between the dynamic pressure Fd and the noise component Fn, that is, 10lg(Fd/Fn), to characterize the signal-to-noise ratio of the acquisition channel, as the signal-to-noise ratio Index; the ultra-high frequency is greater than the respiratory cut-off frequency, and the ultra-low frequency is less than the respiratory cut-off frequency.

In one embodiment, the selection of the optimal channel that meets the preset requirements includes selecting one or more of the following conditions for gated imaging: maximum stability, maximum sensitivity, and maximum signal-to-noise ratio.

The second aspect of the present invention provides an MRI gating system based on multi-channel pressure sensing, including; a pressure acquisition module, which is used to collect pressure changes between the lower body surface of the human body and the contact surface of the examination bed through multiple signal acquisition channels, to Acquire multiple respiratory signals; the signal processing module performs signal processing on the multiple respiratory signals to obtain multiple recommended indicators representing the signal level of the corresponding channel; the recommended indicators include stability indicators, sensitivity indicators and signal-to-noise ratio indicators The channel selection module selects the optimal channel that meets the preset requirements from multiple signal acquisition channels based on the multiple recommended indicators; the MRI gating module performs MRI gating based on the respiratory signal collected by the optimal channel.

In one embodiment, signal processing is performed on the multiple breathing signals, specifically including a primary conditioning step and a secondary conditioning step; the primary conditioning step is used to reduce the sampling noise of the multiple breathing signals to obtain noise-removed breathing signal; the secondary conditioning step is used to obtain the multiple recommended indicators according to the difference in signal frequency in the noise-removed respiratory signal.

In one embodiment, the primary conditioning step specifically includes: sampling the pressure value at a sampling rate higher than the breathing frequency of the human body, and smoothing a plurality of consecutive sampling points, so as to reduce the noise of the preliminary sampling.

In one embodiment, the secondary conditioning step specifically includes: extracting the direct current and ultra-low frequency part of the signal, defined as the static pressure component Fs; extracting the ultra-high frequency part of the signal, defined as the noise component Fn of the measurement signal; extracting the signal The rest of the intermediate frequency in the middle frequency is used as the dynamic pressure component Fd; the change level of the static pressure component Fs is used to represent whether the patient has obvious movement, which is used as a recommended indicator of stability; the ratio between the static pressure component Fs and the dynamic pressure component Fd is used, that is, Fd /Fs, to characterize the measurement sensitivity of the signal, as a recommended sensitivity index; use the calculation relationship between the dynamic pressure Fd and the noise component Fn, that is, 10lg(Fd/Fn), to characterize the signal-to-noise ratio of the acquisition channel, as the signal-to-noise ratio Index; the ultra-high frequency is greater than the respiratory cut-off frequency, and the ultra-low frequency is less than the respiratory cut-off frequency.

In one embodiment, the selection of the optimal channel that meets the preset requirements includes selecting one or more of the following conditions for gated imaging: maximum stability, maximum sensitivity, and maximum signal-to-noise ratio.

Using the solution provided by the present invention, the optimal signal acquisition channel is selected by using the stability index, sensitivity index and signal-to-noise ratio index, and MRI gating is performed based on the respiratory signal collected by the optimal signal acquisition channel. It can meet the needs of patients of different sizes, improves the accuracy of the collected respiratory signals, and then improves the quality of MRI imaging.

Description of drawings

The above and other objects, features and advantages of exemplary embodiments of the present invention will become readily understood by reading the following detailed description with reference to the accompanying drawings. In the drawings, several embodiments of the present invention are shown by way of illustration and not limitation, and the same or corresponding reference numerals indicate the same or corresponding parts, wherein:

FIG. 1 is a schematic diagram showing a multi-channel MRI gating method according to an embodiment of the present invention;

2 is a schematic diagram illustrating a signal processing method according to an embodiment of the present invention;

Fig. 3 is a schematic diagram showing a secondary conditioning step method according to an embodiment of the present invention;

Fig. 4 is a schematic diagram showing a multi-channel MRI gating system according to an embodiment of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of them. Based on the implementation manners in the present invention, all other implementation manners obtained by those skilled in the art without creative efforts shall fall within the protection scope of the present invention.

It should be understood that the terms "first", "second", "third" and "fourth" in the claims, description and drawings of the present invention are used to distinguish different objects, rather than to describe a specific order . The terms "comprising" and "comprising" used in the description and claims of the present invention indicate the presence of described features, integers, steps, operations, elements and/or components, but do not exclude one or more other features, integers , steps, operations, elements, components, and/or the presence or addition of collections thereof.

It should also be understood that the terms used in the description of the present invention are for the purpose of describing specific embodiments only, and are not intended to limit the present invention. As used in the specification and claims herein, the singular forms "a", "an" and "the" are intended to include the plural forms unless the context clearly dictates otherwise. It should be further understood that the term "and/or" used in the description and claims of the present invention refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

As used in this specification and claims, the term "if" may be construed as "when" or "once" or "in response to determining" or "in response to detecting" depending on the context. Similarly, the phrase "if determined" or "if [the described condition or event] is detected" may be construed, depending on the context, to mean "once determined" or "in response to the determination" or "once detected [the described condition or event] ]” or “in response to detection of [described condition or event]”.

The specific implementation manner of the present invention will be described in detail below in conjunction with the accompanying drawings.

The first aspect of the present invention provides an MRI gating method based on multi-channel pressure sensing. Fig. 1 is a schematic diagram illustrating a multi-channel MRI gating method according to an embodiment of the present invention. An MRI gating method based on multi-channel pressure sensing in the present invention can be implemented as steps S100-S400 as described below:

Step S100, collect the pressure change between the lower body surface of the human body and the contact surface of the examination bed, so as to obtain multiple breathing signals.

In the embodiment of the present invention, the pressure change between the lower body surface of the human body and the contact surface of the examination bed is collected through multiple signal collection channels. When the human body breathes, there will be multiple muscle groups in the back to participate in cooperation, and the breathing state is characterized by the relaxation and contraction process of the back muscles and the pressure changes generated by the inspection window.

In a preferred embodiment of the present invention, pressure sensors are used in multiple signal acquisition channels to sense pressure changes on the contact surface between the back of the human body and the examination table during breathing. The arrangement of the pressure sensors may be that one signal collection channel corresponds to one pressure sensor, or that one signal collection channel corresponds to multiple pressure sensors, or that multiple signal collection channels correspond to one pressure sensor. In the present invention, through the multi-channel network arrangement of the pressure sensors, as much pressure change data as possible on the contact surface between the back of the human body and the examination bed during breathing is collected to improve the accuracy of subsequent data processing.

In a preferred embodiment of the present invention, the pressure sensor can be installed or embedded in the examination bed to reduce the steps for patients to put on and take off the instrument and improve the patient's medical experience; Wearing it, in this configuration, it is convenient for the doctor to adjust the key parts that need to be checked, and it has higher flexibility.

In a preferred embodiment of the present invention, according to the collected pressure signal, the system performs analog-to-digital conversion on the above-mentioned pressure signal. is a digital signal, that is, the initial breathing signal.

Step S200, performing signal processing on the plurality of respiratory signals to obtain a plurality of recommended indicators representing signal levels of corresponding channels.

In the embodiment of the present invention, digital signal processing needs to be performed after the initial respiratory signal is acquired to obtain the recommended index. The recommended indexes include stability indexes, sensitivity indexes and signal-to-noise ratio indexes. Among them, the stability index is used to represent whether the patient has obvious movement, and whether the signal channel is stable. It is predictable that if the patient has obvious movement during the examination process, it will affect the clarity of the MRI imaging; the sensitivity index is used to represent the measurement sensitivity of the signal. It can be expected that if the sensitivity of the acquisition channel is low, it will affect the quality of MRI imaging; the signal-to-noise ratio index is used to characterize the signal-to-noise ratio of the channel. It can be expected that if the signal-to-noise ratio of the acquisition channel is low, it will affect the quality of MRI imaging. The speed of MRI imaging.

In a preferred embodiment of the present invention, performing signal processing on the plurality of respiratory signals includes a primary conditioning step and a secondary conditioning step. Please refer to FIG. 2. FIG. 2 is a schematic diagram showing a signal processing method for a respiratory signal according to an embodiment of the present invention, which can be implemented as steps S210-S220 as described below:

Step S210, a primary conditioning step, for reducing the sampling noise of the plurality of respiratory signals to obtain denoised respiratory signals;

In a preferred embodiment of the invention, the primary signal conditioning step aims at smoothing the primary signal. Since the breathing cycle of the human body is about 3-6 seconds per time, you can use a high sampling rate, such as 50Hz for pressure value sampling (sampling interval is 40ms), to smooth multiple continuous sampling points (such as 5 sampling points) ( or median filter) to reduce the initial sampling noise.

Step S220, a secondary conditioning step, used to obtain the multiple recommended indicators according to the difference in signal frequency in the noise-removed respiratory signal.

In a preferred embodiment of the present invention, refer to FIG. 3 for details of the secondary conditioning steps. Fig. 3 is a schematic diagram illustrating a method of secondary conditioning steps according to an embodiment of the present invention, which may be implemented as steps S221-S226 as described below.

Step S221, extracting the direct current and ultra-low frequency part of the signal, which is defined as the static pressure component Fs;

Step S222, extracting the ultrahigh frequency part in the signal, defined as the noise component Fn of the measurement signal;

Step S223, extracting the remaining intermediate frequency part in the signal, which is defined as the dynamic pressure component Fd.

After the required signal is extracted according to the different signal frequencies, the signal needs to be processed to obtain multiple recommended indicators representing the signal level of each acquisition channel. The specific signal processing process is as follows:

Step S224, using the change level of the static pressure component Fs to characterize whether the patient has obvious movement, as a recommended indicator of stability;

Step S225, using the ratio between the static pressure component Fs and the dynamic pressure component Fd, that is, Fd/Fs, to characterize the measurement sensitivity of the signal, as a sensitivity recommendation index;

Step S226, using the calculation relationship between the dynamic pressure Fd and the noise component Fn, ie, 10lg(Fd/Fn), to characterize the signal-to-noise ratio of the acquisition channel as the signal-to-noise ratio index.

It should be noted that the ultra-high frequency and ultra-low frequency are compared relative to the normal respiratory frequency range. The human breathing cycle is about 3-6 seconds/time. For example, if it is greater than 0.5Hz (that is, the breathing cycle is 2s/each time), it can be judged as an ultra-high frequency. The specific values of ultra-high frequency and ultra-low frequency are not specifically limited in the present invention, and any frequency considered to exceed the range of normal respiratory frequency can be regarded as ultra-high frequency and ultra-low frequency within a reasonable range.

Continue to return to Figure 1 below. Step S300, selecting an optimal channel that meets preset requirements from multiple signal acquisition channels based on the multiple recommended indicators.

In the embodiment of the present invention, considering the large difference in the size of the patients, when the obtained respiratory signal is used for MRI gating, there will be a large difference in the measurement results. For example, when measuring an overweight patient, the static force Fs may be too large and the signal amplitude Fd is relatively small, so the measurement sensitivity Fs/Fd is small; on the contrary, for an overweight patient, although the measurement sensitivity is high, the measurement signal may be The noise ratio is poor. Therefore, according to different patient sizes, it is necessary to select the measurement results of the acquisition channels that meet the preset requirements, so as to ensure the accuracy of the respiratory signal.

In a preferred embodiment of the present invention, the selection of the optimal channel that meets the preset requirements includes selecting one or more of the following conditions for gated imaging: maximum stability value, maximum sensitivity value, signal-to-noise ratio value maximum. It can be understood that when selecting the optimal channel, it needs to be adjusted according to the actual body size of the patient. For example, to detect a fat patient, the respiratory signal collected by the channel with the highest signal-to-noise ratio and/or the highest sensitivity can be selected for gating; For thin patients, the respiration signal acquired by the channel with the highest stability and/or the highest signal-to-noise ratio can be selected for gating. The present invention performs manual selection or automatic selection of the final signal channel through recommended indicators, such as manual or automatic selection of the most stable/sensitive/optimal signal-to-noise ratio channel according to preferences, for subsequent gated imaging, making it suitable for patient populations (height, weight , physique) wider.

Step S400, performing MRI gating based on the respiratory signal collected by the optimal channel.

In the embodiment of the present invention, the respiratory signal collected by the optimal channel is transmitted to the MRI controller, so that the MRI controller uses the respiratory signal collected by the optimal channel to perform MRI gating.

Based on the multi-channel pressure sensing-based MRI gating method described in Fig. 1, Fig. 2 and Fig. 3, the second aspect of the present invention also provides an MRI gating system based on multi-channel pressure sensing; the MRI gating system An MRI gating method based on multi-channel pressure sensing described in Figure 1, Figure 2 and Figure 3 can be implemented, so as to obtain the respiratory signal obtained by the optimal acquisition channel through multiple recommended indicators for MRI gating Purpose; As shown in Figure 4, the acquisition system of a kind of breathing information of the present invention comprises:

The pressure collection module 100 is used to collect pressure changes between the lower body surface of the human body and the contact surface of the examination bed through multiple signal collection channels, so as to obtain multiple breathing signals;

The signal processing module 200 performs signal processing on the plurality of respiratory signals to obtain a plurality of recommended indicators representing the signal level of the corresponding channel; the recommended indicators include stability indicators, sensitivity indicators and signal-to-noise ratio indicators;

The channel selection module 300, based on the multiple recommended indicators, selects the optimal channel that meets the preset requirements from multiple signal acquisition channels;

The MRI gating module 400 performs MRI gating based on the respiratory signal collected by the optimal channel.

In a preferred embodiment of the present invention, the signal processing of the plurality of respiratory signals specifically includes a primary conditioning step and a secondary conditioning step;

The primary conditioning step is used to reduce the sampling noise of the plurality of respiratory signals to obtain denoised respiratory signals;

The secondary conditioning step is used to obtain the multiple recommended indexes according to the signal frequency difference in the noise-removed respiratory signal.

In a preferred embodiment of the present invention, the primary conditioning step specifically includes;

Use a sampling rate higher than the human respiratory frequency to sample the pressure value, and smooth multiple consecutive sampling points to reduce the initial sampling noise.

In a preferred embodiment of the present invention, the secondary conditioning step specifically includes;

Extract the DC and ultra-low frequency part of the signal, which is defined as the static pressure component Fs;

Extract the ultra-high frequency part of the signal, which is defined as the noise component Fn of the measurement signal;

Extract the remaining intermediate frequency part of the signal, which is defined as the dynamic pressure component Fd;

Use the change level of the static pressure component Fs to characterize whether the patient has significant movement, as a recommended indicator of stability;

Use the ratio between the static pressure component Fs and the dynamic pressure component Fd, that is, Fd/Fs, to characterize the measurement sensitivity of the signal, as a recommended index for sensitivity;

Use the calculation relationship between the dynamic pressure Fd and the noise component Fn, that is, 10lg(Fd/Fn), to characterize the signal-to-noise ratio of the channel as the signal-to-noise ratio index;

The ultra-high frequency is greater than the respiratory cut-off frequency, and the ultra-low frequency is less than the respiratory cut-off frequency.

In a preferred embodiment of the present invention, the selection of the optimal channel that meets the preset requirements includes selecting one or more of the following conditions for gated imaging:

The maximum value of stability;

The maximum sensitivity value;

The signal-to-noise ratio is the largest.

While various embodiments of the invention have been illustrated and described, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Many modifications, changes and substitutions will occur to those skilled in the art without departing from the idea and spirit of the present invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the appended claims define the scope of the invention and therefore cover modular compositions, equivalents or alternatives within the scope of these claims.

Claims (2)

1. An MRI gating method based on multi-channel pressure induction is characterized by comprising the following steps of;

acquiring pressure change between the lower body surface of a human body and a contact surface of an examination bed through a plurality of signal acquisition channels to acquire a plurality of respiratory signals;

performing signal processing on the plurality of respiratory signals to obtain a plurality of recommendation indexes representing signal levels of corresponding channels; the recommendation indexes comprise stability indexes, sensitivity indexes and signal-to-noise ratio indexes;

selecting an optimal channel meeting preset requirements from a plurality of signal acquisition channels based on the plurality of recommendation indexes;

performing MRI gating on the basis of respiratory signals acquired by the optimal channel;

performing signal processing on the plurality of respiratory signals, wherein the signal processing specifically comprises a primary conditioning step and a secondary conditioning step;

the primary conditioning step is used for reducing the sampling noise of the plurality of respiratory signals to obtain noise-removed respiratory signals;

the secondary conditioning step is used for obtaining the plurality of recommended indexes according to different signal frequencies in the de-noising breathing signal;

the primary conditioning step specifically comprises;

sampling pressure values by using a sampling rate higher than the respiratory frequency of a human body, and smoothing a plurality of continuous sampling points to reduce initial sampling noise;

the secondary conditioning step specifically comprises;

extracting direct current and ultralow frequency parts in the signal, and defining the parts as static pressure components Fs;

extracting an ultrahigh frequency part in the signal, and defining the ultrahigh frequency part as a noise component Fn of the measurement signal;

extracting the residual intermediate frequency part in the signal, and defining the residual intermediate frequency part as a dynamic pressure component Fd;

using the variation level of the static pressure component Fs to represent whether the patient has obvious movement or not as a stability recommendation index;

using the ratio between the static pressure component Fs and the dynamic pressure component Fd, namely Fd/Fs, to represent the measurement sensitivity of the signal, and using the measurement sensitivity as a sensitivity recommendation index;

using a calculation relation between the dynamic pressure Fd and the noise component Fn, namely 10lg (Fd/Fn), to represent the signal-to-noise ratio of the acquisition channel as a signal-to-noise ratio index;

the ultra-high frequency is greater than the respiratory cut-off frequency, and the ultra-low frequency is less than the respiratory cut-off frequency;

the selecting of the optimal channel meeting the preset requirements comprises selecting one or more of the following conditions for gated imaging:

the stability value is maximum;

the sensitivity value is maximum;

the signal-to-noise ratio is the largest.

2. An MRI gating system based on multi-channel pressure sensing, comprising;

the pressure acquisition module is used for acquiring pressure change between the contact surface of the lower body surface of the human body and the examination bed through a plurality of signal acquisition channels so as to acquire a plurality of respiratory signals;

the signal processing module is used for carrying out signal processing on the plurality of respiratory signals so as to obtain a plurality of recommendation indexes representing corresponding channel signal levels; the recommendation indexes comprise stability indexes, sensitivity indexes and signal-to-noise ratio indexes;

the channel selection module is used for selecting an optimal channel which meets the preset requirement from a plurality of signal acquisition channels based on the recommendation indexes;

the MRI gating module is used for performing MRI gating on the basis of the respiratory signals acquired by the optimal channel;

performing signal processing on the plurality of respiratory signals, wherein the signal processing specifically comprises a primary conditioning step and a secondary conditioning step;

the primary conditioning step is used for reducing the sampling noise of the plurality of respiratory signals to obtain noise-removed respiratory signals;

the secondary conditioning step is used for obtaining the plurality of recommendation indexes according to different signal frequencies in the de-noising breathing signal;

the primary conditioning step specifically comprises;

sampling pressure values by using a sampling rate higher than the respiratory frequency of a human body, and smoothing a plurality of continuous sampling points to reduce initial sampling noise;

the secondary conditioning step specifically comprises;

extracting direct current and ultralow frequency parts in the signal, and defining the parts as static pressure components Fs;

extracting an ultrahigh frequency part in the signal, and defining the ultrahigh frequency part as a noise component Fn of the measurement signal;

extracting the residual intermediate frequency part in the signal, and defining the residual intermediate frequency part as a dynamic pressure component Fd;

using the variation level of the static pressure component Fs to represent whether the patient has obvious movement or not as a stability recommendation index;

using the ratio between the static pressure component Fs and the dynamic pressure component Fd, namely Fd/Fs, to represent the measurement sensitivity of the signal, and using the measurement sensitivity as a sensitivity recommendation index;

the signal-to-noise ratio of an acquisition channel is represented by using a calculation relation between the dynamic pressure Fd and the noise component Fn, namely 10lg (Fd/Fn), and is used as a signal-to-noise ratio index;

the ultra-high frequency is greater than the respiratory cut-off frequency, and the ultra-low frequency is less than the respiratory cut-off frequency;

the selecting of the optimal channel meeting the preset requirements comprises selecting one or more of the following conditions for gated imaging:

the stability value is maximum;

the sensitivity value is maximum;

the signal-to-noise ratio is the largest.

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