CN108765513B

CN108765513B - Relaxation parameter imaging method for inhibition of cardiac blood pool

Info

Publication number: CN108765513B
Application number: CN201810569792.2A
Authority: CN
Inventors: 王成彦; 杜一平
Original assignee: Shanghai Jiaotong University
Current assignee: Shanghai Jiaotong University
Priority date: 2018-06-05
Filing date: 2018-06-05
Publication date: 2022-06-28
Anticipated expiration: 2038-06-05
Also published as: CN108765513A

Abstract

The invention provides a relaxation parameter imaging method for inhibiting heart blood pool signals, which specifically comprises the step of applying partial saturation radio frequency pulses and double inversion pulses adaptive to different heart rates in sequence, so that the aims of inverting blood signals and retaining cardiac muscle signals are fulfilled. The method of the invention combines the blood inhibition technology with the T2 relaxation parameter imaging technology, obviously reduces partial volume artifact and improves the myocardial-blood contrast.

Description

Relaxation parameter imaging method for inhibition of cardiac blood pool

Technical Field

The invention relates to the technical field of medical image processing, and particularly provides a heart blood pool suppression relaxation parameter imaging method adaptive to different heart rates.

Background

Magnetic Resonance Imaging (MRI) is a non-invasive imaging technique and is widely used in cardiac imaging. Quantitative T1 and T2 relaxation parameter imaging can detect myocardial lesions more accurately and is gradually concerned by researchers due to high repeatability and low variability. Taking T2 parameter imaging as an example, there are a number of studies showing a significant increase in T2 values in acute myocardial infarction, myocarditis, etc. [1,2 ]. Although the conventional T2 weighted pulse sequence can also be used to detect impaired myocardial edema, it has the problem of being unable to quantify. Myocardial T2 parameter imaging reduces inter-subject and inter-study variability while having high sensitivity and specificity, with greater diagnostic accuracy for the T2 parameter compared to T2 weighted imaging [3,4 ].

However, the current T2 relaxation parameter imaging technology has the advantages of obvious partial volume effect of images due to the priority of spatial resolution, difficult T2 quantification for the adjacent region of the myocardium and the blood pool, and large measurement error. After the myocardial signal receives the image of the blood signal, the measurement result is significantly higher and is easily confused with the true edema. For thinner regions such as the left atrium, right ventricle, etc., current bright blood imaging techniques are far from meeting clinical requirements. Although motion correction may improve measurement accuracy to some extent, partial volume artifacts cannot be fully addressed.

One way to address the partial volume limitation is to suppress the signal within the blood pool. There are many methods of blood suppression currently available, with the Double Inversion Recovery (DIR) sequence being the most widely used technique [5-10 ]. The technology firstly applies non-selective 180 DEG inversion pulse to invert all signals, then uses selective 180 DEG inversion pulse consistent with an imaging plane to invert and recover the signals in the imaging plane, and finally achieves the purpose of inverting only blood signals outside the imaging plane. However, achieving blood suppression by DIR pulses requires a longer delay time for blood magnetization recovery (longer relaxation time for blood T1), which is not feasible within a single R-R interval. Moreover, the delay time of the method is uncontrollable, and the scanning requirements of people with different heart rates cannot be met, so that the method cannot be applied to relaxation parameter imaging of cardiac muscle. In addition, the DIR technique has poor signal suppression effects on slow blood flow velocities, which can lead to additional residual artifacts. Spatial saturation pulses are another method of blood suppression [11,12] whose principle is to excite and dephase all signals upstream of the imaging plane, and after waiting a certain time all blood inflow is suppressed by the saturation pulses, which is the most "old" magnetic resonance angiography technique. However, this method has problems in that since the heart moves significantly during the beating cycle, the position of the saturation pulse application is difficult to control; the efficiency is low for the region with complicated flow direction, and the effect of upstream signal suppression is poor; the inhibitory effect of the saturation pulse on the blood is restored to some extent after a certain period of blood flow, and thus the blood cannot be completely inhibited. The motion-sensitized magnetization preparation (MSDE) technique [13,14] achieves blood suppression by applying a high-intensity gradient field to rapidly dephase all moving tissues. However, due to the characteristics of cardiac motion, the technology also inhibits the myocardial signals, the signal-to-noise ratio of myocardial imaging can be obviously reduced, and further additional errors are brought to fitting of relaxation parameters.

In summary, myocardial blood pressure inhibition is a very challenging problem, and there is no method that can realize relaxation parameter imaging under blood inhibition at present, and this requirement is very urgent in clinical diagnosis, so it is of great clinical significance to develop a stable and efficient blood inhibition relaxation parameter imaging method.

Disclosure of Invention

The invention aims to provide a stable and efficient blood suppression relaxation parameter imaging method which has important clinical significance.

In a first aspect of the invention, a cardiac blood pool suppression relaxation parameter imaging method is provided, the method comprising the steps of:

(1) detecting the heart rate of the object to be detected to obtain a detection result; wherein, the detection result comprises a P peak, a QRS peak and a T peak;

(2) applying a partially saturated radio frequency pulse beta according to the detection result obtained in the step (1), and then calculating the reduction of the longitudinal magnetization vector (Mz) of the object to the initial magnetization M₀Cos (. beta.) then according to T₁The relaxation time coefficient calculates the recovered magnetization vector:

wherein M is₀Is the initial longitudinal magnetization, beta is the flip angle of the pre-excitation pulse, TD_βIs the duration between the pre-excitation pulse and the non-selective 180 ° pulse in the double inversion pulse; t is a unit of ₁The relaxation time coefficient is the intrinsic relaxation time of the imaged object;

(3) applying double inversion pulses, wherein the double inversion pulses sequentially comprise a non-selective 120-180 DEG inversion pulse and a 120-180 DEG inversion pulse with a layer selection function; wherein the width of the 120-180 DEG inversion pulse with the layer selection is 3-5 times of the thickness of the imaging layer;

(4) during the TI time, blood and myocardial signals are recovered according to the following formula:

wherein M is_0，bloodAnd M_0，myoRespectively representInitial longitudinal magnetization vectors, Mz, of blood and myocardium without pulse_blood(TD_β) And Mz_myo(TD_β) Respectively representing the magnetization vectors of the blood and the myocardium after the application of the partially saturated radio-frequency pulse beta;

wherein the TI time is the duration between the non-selective 120-180 DEG pulse and the beginning of a relaxation preparation (T2prep) pulse (i.e., T2prep)_dia-TD_β-TE_T2prep)；M_0，bloodAnd M_0，myoRespectively representing the initial longitudinal magnetization vectors, Mz, of the blood and myocardium without pulse application_blood(TD_β) And Mz_myo(TD_β) Representing the magnetization vectors of the blood and the myocardium, respectively, after application of the partially saturated radio-frequency pulse beta.

(6) Carrying out relaxation preparation so as to obtain 3-20 groups of T1/T2 weighted images with different echo Times (TE);

(7) and acquiring signals to obtain relaxation weighted images of blood inhibition.

In another preferred example, the TI value and the β value are determined by:

TI≈60(s)/HR-T_rest. [4]

wherein T is_restIs the remaining time (ms) of each R-R interval, including signal acquisition, trigger delay time and pulse duration, HR being the heart rate;

when a pulse is actually applied, the relationship between the TI time and other pulses and delay times is:

TI＝T_dia-TD_β-TE_T2prep [5]

wherein T is_diaIs the heart rate trigger delay time, TE_prepIs the echo time of the magnetization preparation pulse; TE_T2prepIs the relaxation preparation time.

Calculating solution beta according to the equation [1], the equation [2] and the equation [5], and obtaining the following beta:

in another preferred embodiment, the duration of the applied pre-excitation pulse is 0.1-0.5 ms, the dispersed phase gradient time is 1.0-3.5 ms, the non-selective inversion pulse time is 3.3-6.1 ms, and TD_βThe time is 5-80 ms;

in another preferred example, the TI time is a parameter calculated by adjusting the heart rate, and the adjusting includes:

in the case of a slower heart rate (heart rate below 40 beats/second), the TI time is extended;

the TI time is shortened under the condition of a faster heart rate (the heart rate is between 40 and 120 times/second);

in the case of an ultra-fast heart rate (heart rate over 120 beats/second), two cardiac cycles are selected for one complete excitation and acquisition.

In another preferred example, the method further comprises: by calculating SI _blood/SI_blood,0And SI_myo/SI_myo,0To reflect the efficiency of blood and myocardial inhibition, wherein SI_blood(or SI)_myo) Is residual blood (or myocardial) signal after reversal recovery, and SI_blood,0(or SI)_myo,0) Indicating the initial blood (or myocardial) signal intensity prior to inhibition.

In another preferred embodiment, in the step (6), the relaxation preparation includes: an initial 90 ° x pulse is applied, then 2-8 composite 180 ° y pulses are applied, and finally a final 90 ° -x inversion pulse is applied.

In another preferred example, in the step (6), 4 to 16 different echo times are set.

In another preferred example, in the step (7), the relaxation weighted image is obtained by using a single-pass bSSFP.

In another preferred embodiment, the single-pass bSSFP parameters include: the reverse rotation angle is 5-25 degrees, the pulse number is 80-180, and the acquisition time is 50-250 ms.

In another preferred example, 3-6 heartbeat intervals are waited after each image acquisition.

In another preferred example, the method further comprises: (8) and performing registration on the same group of images by using an affine registration algorithm according to the obtained relaxation weighted images.

In another preferred example, the step (8) further includes: removing residual blood signals using a thresholding process under an empirical threshold selected as TE _T2prepAnd (3) removing and reconstructing the areas with the signal intensity lower than the threshold value, wherein the signal intensity of the myocardium in the image is 10-50% of that in the image with the signal intensity of 0.

In another preferred embodiment, a three-parameter fitting model is used for quantification of relaxation parameters, and then a voxel-wise curve fitting is performed on the original image according to the following equation:

wherein TE_T2prepIs the echo time, A is the signal function at full recovery, T₂Is the myocardium T₂The relaxation time, B, characterizes the signal of the central k-space line position of the bSSFP readout gradient.

In another preferred example, the method further comprises: and carrying out quantitative analysis on the reconstructed image.

In another preferred embodiment, the quantitative analysis comprises: the region-of-interest signal analysis (ROI of arbitrary shape) was performed for each region, and the mean and standard deviation thereof were recorded.

In another preferred embodiment, the same ROI is used in all original pictures of the same individual.

In another preferred embodiment, in TE_T2prepThe signal-to-noise ratio (SNR) of the image is calculated in the source image at 0ms, i.e. the mean signal in the phantom divided by the standard deviation of the noise region.

In another preferred embodiment, the myocardium is tracked by manually mapping epicardial and endocardial contours.

In another preferred embodiment, the signal curve of the cross section in the ventricle is obtained on the original map.

In another preferred embodiment, the cardiac image is subdivided using a six-segment method, and the mean and its standard deviation are calculated in each segment.

In a second aspect of the invention, a cardiac blood pool suppression relaxation parameter imaging apparatus is provided, said imaging apparatus performing cardiac imaging according to the method according to the first aspect of the invention.

In another preferred embodiment, the image forming apparatus includes: the device comprises an imaging module, an image reconstruction module and a quantitative analysis module.

It is to be understood that within the scope of the present invention, the above-described features of the present invention and those specifically described below (e.g., in the examples) may be combined with each other to form new or preferred embodiments. Not to be reiterated herein, but to the extent of space.

Drawings

FIG. 1 is a block diagram of a method of adaptive cardiac blood pool suppression relaxation parameter imaging for different heart rates;

FIG. 2. imaging module of a heart blood pool suppression relaxation parameter imaging method adaptive to different heart rates;

FIG. 3. automatic selection of imaging delay time based on different heart rates;

FIG. 4 water model imaging results of different T1, T2 relaxation times;

FIG. 5T 1, T2 relaxation time measurements (mean and standard deviation) of water phantom imaging;

FIG. 6.2 is the result of short axis bit imaging;

FIG. 7 comparison of the results of bright blood and blood suppression in long axis imaging (arrows indicate atrial wall).

Detailed Description

The inventor provides a heart blood pool inhibition relaxation parameter imaging method through long-term and intensive research. The method can effectively deduct blood signals in imaging, so that stable and efficient blood suppression relaxation parameter imaging can be obtained. Based on the above findings, the inventors have completed the present invention.

Aiming at the problems in the prior art, the invention solves the difficulty of the traditional myocardial relaxation parameter imaging from the following two aspects:

1) the blood suppression technology is combined with the T2 relaxation parameter imaging technology, so that partial volume artifacts are obviously reduced, and the myocardial-blood contrast is improved;

2) the method realizes a real-time heart rate self-adaptive blood-keeping method, and can achieve sufficient blood inhibition and maximum signal-to-noise ratio retention for a subject with any heart rate.

The invention comprises three modules: the device comprises an imaging module, an image reconstruction module and an image analysis module.

1. Imaging module

The imaging module mainly functions to calculate and optimize scanning parameters according to the heart rate detected in real time, and achieve blood signal suppression and imaging data acquisition in a complete cardiac cycle. The device mainly comprises the following five parts:

1) Presaturation pulse

After a P peak, a QRS peak and a T peak are obtained based on an electrocardio detection device, a partial saturation radio frequency pulse (beta) is applied at an interval of specific time (5-100 ms), the magnetization vector is reversed by beta degree (0-90 degrees), and the pulse duration is 0.2-5 ms. After the pulse application is completed, the dephasing gradient fields are applied along the x, y, z directions, respectively, to achieve complete dephasing of the horizontal remanent magnetization vector.

The partially saturated radio frequency pulse (beta) is designed as a pre-excitation pulse with an adaptive flip angle. The flip angle of the pre-excitation pulse is adaptively selected based on the heart rate of the patient to ensure that the blood signal is completely suppressed for two adjacent beat intervals (R-R).

After the pre-excitation pulse, the longitudinal magnetization vector (Mz) of the test object is reduced to an initial magnetization M₀Cos (. beta.) then according to T₁Recovery of relaxation time coefficient:

wherein M is₀Is the initial longitudinal magnetization, beta is the flip angle of the pre-excitation pulse, TD_βIs the duration between the pre-excitation pulse and the non-selective 180 deg. pulse in the double inversion pulse.

2) Double inversion pulse

After the pre-excitation pulse beta, a pair of inversion pulses (DIR, 120-180 DEG) is applied, including a non-selective 120-180 DEG inversion pulse followed by a 120-180 DEG inversion pulse with slice selection, with the purpose of inverting the blood signal that is about to flow into the imaging slice in preparation for blood signal suppression. The width of the selective inversion pulse is 3-5 times the thickness of the imaging layer.

Immediately after the DIR pulse is applied, the blood signal is inverted while the myocardial signal is preserved. During the TI time (i.e., the time between the onset of the non-selective 180 ° pulse and the T2prep pulse), blood and myocardial signal recovery are expressed as follows:

according to the formula, if imaging at the moment TI is chosen, the blood signal can disappear completely before the T2prep pulse. However, since the heart rate varies from patient to patient, it is difficult to determine the time of TI. Therefore, we propose an adaptive time design in which TI and β are automatically calculated from the patient heart rate detected by the device. TI is set to T_dia-TD_β-TE_prepAcquiring data at diastole of the heart, wherein T_diaIs the trigger delay time, TE_T2prepIs the echo time of the magnetization preparation pulse. Then according to equation [1 ]]And equation [2 ]]Calculate β, obtain β as follows:

the invention applies the duration of the pre-excitation pulse (0.1-0.5 ms), the dispersed phase gradient (1.0-3.5 ms), the non-selective inversion pulse (3.3-6.1 ms) and the TD of 5-80 ms_β。

TI is calculated from Heart Rate (HR):

TI≈60(s)/HR-T_rest., [4]

wherein T is_restIs the remaining time (ms) of each R-R interval, including signal acquisition, trigger delay time and pulse duration, HR being the heart rate. By calculating SI_blood/SI_blood,0And SI_myo/SI_myo,0To reflect the blood and myocardial inhibitory efficiency, with SI _blood(or SI)_myo) Is residual blood (or myocardial) signal after reversal recovery, and SI_blood,0(or SI)_myo,0) Indicating the initial blood (or myocardial) signal intensity prior to inhibition.

In practical application, the calculation parameters can be automatically adjusted according to the heart rate (as shown in fig. 3): in the case of a slower heart rate, the TI time is extended; in the case of a faster heart rate, the TI time is shortened; in the case of an ultrafast heart rate, two cardiac cycles are selected as one complete excitation and acquisition.

3) Preparation for relaxation

The relaxation preparation consists of an initial 90 x pulse followed by 2-8 composite 180 y pulses and a final 90-x inversion pulse, with the aim of obtaining a T2 weighting of the variable echo Time (TE), setting 4-16 different echo times.

4) Signal acquisition

A relaxation weighted image of blood inhibition is obtained by using a single bSSFP reading gradient, the inversion angle is 5-25 degrees, the pulse number is 80-180, and the acquisition time is 50-250 ms, so that the loss of magnetization vectors in inversion recovery is reduced, and a higher signal-to-noise ratio is obtained. Waiting 3-6 heartbeat intervals after each image acquisition to ensure adequate magnetization recovery.

2. Image reconstruction module

After the original image of the volume is acquired, the registration of the images of the same group is performed using an affine registration algorithm. To remove residual blood signals in blood suppressed cardiac images, a thresholding process under an empirical threshold, chosen as TE, is used _T2prepAnd (5) eliminating the reconstruction process of the region with the signal intensity lower than the threshold value, wherein the signal intensity of the myocardium in the image is 10-50% of that in the image with the signal intensity of 0. Applied to the quantification of relaxation parameters using a three parameter fitting model, thenAccording to equation [6]The original image is subjected to a voxel-wise curve fit.

Wherein TE_T2prepIs the echo time, A is the signal function at full recovery, T₂Is the myocardium T₂The relaxation time, B, characterizes the signal of the central k-space line position of the bSSFP readout gradient. The reconstructed image is saved to the workstation together with all the original images.

3. Quantitative analysis module

In the quantitative analysis module, a region-of-interest signal analysis (ROI of arbitrary shape) is performed for each region, and the mean value and standard deviation thereof are recorded. The same ROI was used in all original pictures of the same individual. In TE_T2prepThe signal-to-noise ratio (SNR) of the image is calculated in the source image at 0ms, i.e. the mean signal in the phantom divided by the standard deviation of the noise region.

The myocardium is tracked by manually mapping the epicardial and endocardial contours. Signal curves of cross-sections in the ventricles were obtained on the original graph. The cardiac images were studied in segments according to the American Heart Association (AHA) segmentation guidelines, and analyzed in slice slices of the ventricles using the six-segment method, with the mean and standard deviation calculated in each segment.

The invention has the advantages that:

1) the invention provides a method for combining a blood inhibition technology with a relaxation parameter imaging technology for the first time, which effectively realizes blood inhibition in a complete cardiac cycle, can improve myocardial-blood contrast, and obviously reduces partial volume effect artifacts existing in the traditional bright blood relaxation parameter imaging, so that the T2 measurement of the left atrium and the right ventricle becomes possible.

2) The invention provides a method for carrying out self-adaptive blood suppression on real-time heart rate, which can achieve sufficient blood suppression on a subject with any heart rate and maximally reserve the signal-to-noise ratio of a myocardial image by updating the scanning delay time and the pre-pulse inversion angle according to the interval of heartbeat intervals.

The invention will be further illustrated with reference to the following specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. The experimental procedures, in which specific conditions are not noted in the following examples, are generally carried out under conventional conditions or conditions recommended by the manufacturers. Unless otherwise indicated, percentages and parts are by weight.

General procedure

The imaging platform can be selected from 1.5T/3.0T clinical standard magnetic resonance imaging systems of any manufacturers. Specific embodiments of The present invention are described below by way of example with reference to The 1.5T MR system (Philips Achieva, Philips Healthcare, Best, The Netherlands).

1. Water model scanning

The imaging sequence designed by the invention is arranged in an imaging platform to complete all imaging preparation including shimming, pre-scanning and positioning. The maximum amplitude of the imaging system is 40mT/m, the slew rate is 150 mT/m/ms, and a 32-channel cardiac coil is used for signal reception.

For standard containing 6 NiCl₂Was scanned in an agar water phantom having a T2 value similar to that of myocardium

And sets of different T1 values. The blood suppression imaging and the traditional bright blood imaging methods proposed by the invention are respectively used for scanning. The scan parameters were as follows: field of view (FOV) 320 x 320mm²Resolution 2 x 2mm²The number of layers is 1, the thickness is 8mm, the SENSE acceleration factor is 2.5, the bSSFP read repetition time/echo time (TR/TE) is 2.8/1.4ms, the flip angle is 60 °, 10 linear ramp-up pulses, a linear k-space filling method is adopted, and the acquisition window is 150 ms. A total of 9 different sets of T2prep echo times, including TE, are used_T2prep＝0，TE_T2prepTE with a linear step of 10ms and a sum ranging from 25ms to 95ms_T2prepThe value is obtained. TE_T2prepInfinity by applying saturation pulses prior to image acquisitionThe echo time of T2prep is now long. For conventional bright blood relaxation parameter imaging, a heart rate of 60bpm is simulated. For the BEATS scan, heart rates of 60, 70, 80, 90, 110 and 130bpm were simulated to test whether they would affect the T2 measurement accuracy. To assess the repeatability of the T2 measurements, scans were repeated every 10 minutes between scans for a total of 3 BEATS sequence scans.

The reference T2 relaxation time was obtained using a 32 echo Spin Echo (SE) sequence. The scan parameters were as follows: field of view 320 x 320mm²Resolution 2 x 2mm²The thickness is 8mm, the flip angle is 90 °, TR is 10s, TEs is from 10ms to 320ms, the interval is 10ms, and the signal average (NSA) is 4. The reference T1 relaxation times were obtained using an inverted SE sequence, with 16 inversion times of 50,100,200,300,400,500,600,700,800,900,1000,1250,1500,1750,2000 and 3000 ms. Other imaging parameters were: FOV 320 × 320mm²Resolution 2 x 2mm²The slice thickness is 8mm, the flip angle is 90 °, TR/TE is 10s/10ms, and NSA is 4. Three-parameter models were used to fit the T1 and T2 values of the images.

The blood suppression relaxation parameter imaging results obtained using the imaging method proposed by the present invention are shown in fig. 4 and 5. The mean T2 measurement in the blood suppression T2 graph proposed by the present invention is very accurate over heart rates in the range of 60 to 110bpm compared to the conventional bright blood T2 measurement, while higher heart rates somewhat reduce the accuracy of the measurement (an increase in standard deviation can be observed). The signal-to-noise ratio in different vials decreased with increasing heart rate due to insufficient time for signal recovery. The standard deviations (

heart rate

60, 70, 80, 90, 100bpm, 0.29ms, 0.35ms, 0.35ms, 0.29ms, 0.42ms, respectively) of the repeated scans of the present invention have good repeatability. The T2 relaxation parameter measured using the method of the invention was not different from the conventional bright blood measurement in heart rates of 60 to 130 bpm.

2. Volunteer scanning

The imaging sequence designed by the invention is arranged in an imaging platform to complete all imaging preparation including shimming, pre-scanning and positioning. The imaging system has a maximum amplitude of 40mT/m, a slew rate of 150 mT/m/ms, and uses a 32-channel cardiac coil for signal reception.

Imaging studies were performed on healthy adult subjects. For each subject, scout images are first acquired with the ventricular center short axis slice as the imaging plane. An electrocardio triggering mode of free breathing is adopted, and a single-excitation bSSFP sequence is used as a data acquisition mode. The sequence parameters are as follows: field of view 320 x 320mm²Resolution 2 x 2mm²Number of layers 3, thickness/gap 8/4mm, SENSE acceleration factor 2.5, TR/TE 2.8/1.4 ms, flip angle 60 °, 9T 2prep echo times (including TE)_T2prep0,25,35,45,55,65,75,85,95, ∞ ms). The heart motion is detected by adopting a two-dimensional spiral beam navigation mode, and a navigation echo is placed at the right diaphragm and is detected by adopting a 5mm window. The scan time for each slice of cardiac imaging is approximately 40 seconds. To evaluate the reproducibility of imaging sequences using the blood suppression proposed by the present invention, each scan was repeated 3 times with 10 minute intervals.

Fig. 6 shows short axis raw images and T2 relaxation parameter plots for two healthy subjects of different heart rates. In both cases, the original images obtained by the blood suppression relaxation parameter method have no significant artifacts and a relatively high contrast between the myocardium and the blood pool. The ratio of blood to myocardial signals was from 3.03[ 2.56; 3.72] to 0.15[ 0.13; 0.17] (P ═ 0.01). The method proposed by the present invention allows the partial volume effect of the myocardium to be significantly reduced due to the suppression of the blood signal in the ventricle. Compared with the traditional bright blood T2 image, the new method can better depict the myocardial structure, and the image edge is sharper and clearer. Fig. 7 shows a long axis image of an example of a subject, which shows that the blood suppression effect is good, the atrial structure is not easily observed in the bright blood image, and the atrium is clearly visible in the blood suppression image.

All documents referred to herein are incorporated by reference into this application as if each were individually incorporated by reference. Furthermore, it should be understood that various changes and modifications of the present invention can be made by those skilled in the art after reading the above teachings of the present invention, and these equivalents also fall within the scope of the present invention as defined by the appended claims.

Reference:

1.Mcnamara MT,Higgins CB,Schechtmann N,Botvinick E,Lipton MJ, Chatterjee K,Amparo EG.Detection and characterization of acute myocardial infarction in man with use of gated magnetic resonance.Circulation 1985；71(4):717-724.

2.Payne AR,Casey M,McClure J,McGeoch R,Murphy A,Woodward R, Saul A,Bi X,Zuehlsdorff S,Oldroyd KG.Bright-blood T2-weighted MRI has higher diagnostic accuracy than dark-blood short tau inversion recovery MRI for detection of acute myocardial infarction and for assessment of the ischemic area at risk and myocardial salvage.Circ Cardiovasc Imaging 2011；4(3):210-219.

3.Huang T-Y,Liu Y-J,Stemmer A,Poncelet BP.T₂measurement of the human myocardium using a T₂-prepared transient-state trueFISP sequence.Magn Reson Med 2007；57(5):960-966.

4.Baeβler B,Schaarschmidt F,Stehning C,Schnackenburg B,Giolda A, Maintz D,Bunck AC.Reproducibility of three different cardiac T₂-mapping sequences at 1.5T.J Magn Reson Imaging 2016；44(5):1168-1178.

5.Edelman RR,Chien D,Kim D.Fast selective black blood MR imaging. Radiology 1991；181(3):655-660.

6.Debbins JP,Riederer SJ,Rossman PJ,Grimm RC,Felmlee JP,Breen JF, Ehman RL.Cardiac magnetic resonance fluoroscopy.Magn Reson Med 1996；36(4):588-595.

7.Nguyen TD,de Rochefort L,Spincemaille P,Cham MD,Weinsaft JW, Prince MR,Wang Y.Effective motion-sensitizing magnetization preparation for black blood magnetic resonance imaging of the heart.J Magn Reson Imaging 2008；28(5):1092-1100.

8.Newbould RD,Owen DR,Shalhoub J,Brown AP,Gambarota G. Motion-sensitized driven equilibrium for blood-suppressed T₂*mapping.J Magn Reson Imaging 2011；34(3):702-709.

9.Saranathan M,Savin GS.Multi-slice MR data acquisition in successive heartbeats with black blood contrast.US Patent 7,412,277.Aug 12,2008.

10.Fayad ZA,Itskovich VV,Mani V,Szimtenings MM.Rapid multislice black blood double-inversion recovery technique for blood vessel imaging.US Patent 7,369,887.May 6,2008.

11.Felmlee JP,Ehman RL.Spatial presaturation:a method for suppressing flow artifacts and improving depiction of vascular anatomy in MR imaging. Radiology 1987；164(2):559-564.

12.Nayak KS,Rivas PA,Pauly JM,Scott GC,Kerr AB,Hu BS,Nishimura DG.Real-time black-blood MRI using spatial presaturation.J Magn Reson Imaging 2001；13(5):807-812.

13.Srinivasan S,Hu P,Kissinger KV,Goddu B,Goepfert L,Schmidt EJ, Kozerke S,Nezafat R.Free-breathing 3D whole-heart black-blood imaging with motion sensitized driven equilibrium.J Magn Reson Imaging 2012；36(2):379-386.

14.Wang J,Yarnykh VL,Hatsukami T,Chu B,Balu N,Yuan C.Improved suppression of plaque-mimicking artifacts in black-blood carotid atherosclerosis imaging using a multislice motion-sensitized driven-equilibrium(MSDE)turbo spin-echo(TSE)sequence.Magn Reson Med 2007；58(5):973-981。

Claims

1. a method for cardiac blood pool suppression relaxation parameter imaging, said method comprising the steps of:

(2) according to the detection result obtained in the step (1), applying a partial saturation radio frequency pulse, wherein the partial saturation radio frequency pulse is a pre-excitation pulse with an adaptive flip angle beta, and then calculating the longitudinal magnetization vector Mz of the object to be reduced to cos (beta) of the initial magnetization, wherein the initial longitudinal magnetization of the initial magnetization is M₀Then according to T₁Magnetization restored by relaxation time coefficient calculationVector:

wherein M is₀Is the initial longitudinal magnetization, beta is the flip angle of the pre-excitation pulse, TD_βIs the duration between the pre-excitation pulse and the non-selective 180 ° pulse in the double inversion pulse; t is₁The relaxation time coefficient is the intrinsic relaxation time of the imaged object;

(4) During the TI time, for the blood signal Mz, the following formula is used_blood(TI) and myocardial signal Mz_myo(TI) recovery:

wherein the TI time is the duration T between the non-selective 120-180 DEG pulse and the beginning of the relaxation preparation, T2prep pulse_dia-TD_β-TE_T2prep；M_0，bloodAnd M_0，myoRespectively representing the initial longitudinal magnetization vectors, Mz, of the blood and myocardium without pulse application_blood(TD_β) And Mz_myo(TD_β) Representing the magnetization vectors of the blood and the myocardium, respectively, after application of the partially saturated radio-frequency pulse β;

(5) carrying out relaxation preparation so as to obtain 3-20 groups of T1/T2 weighted images with different echo times TE;

(6) and acquiring signals to obtain relaxation weighted images of blood inhibition.

2. The method of claim 1, wherein the TI and β values are determined by:

TI≈60/HR-T_rest [4]

wherein T is_restIs the remaining time of each R-R interval in ms, including signal acquisition, trigger delay time and pulse duration, HR being the heart rate; units of 60 are seconds;

when a pulse is actually applied, the relationship between TI time and other pulses and delay times is:

TI＝T_dia-TD_β-TE_T2prep [5]

wherein T is_diaIs the heart rate trigger delay time; TD_βIs the duration between the pre-excitation pulse and the non-selective 180 ° pulse in the double inversion pulse; TE _T2prepIs the relaxation preparation time;

wherein TE_prepIs the echo time of the magnetization preparation pulse; TD_βIs the duration between the pre-excitation pulse and the non-selective 180 ° pulse in the double inversion pulse; t1_bloodRefers to blood T₁A relaxation time coefficient.

3. The method of claim 1, wherein the TI time is a parameter calculated by heart rate fast and slow adjustments, and the adjustments comprise:

in the case of a slower heart rate, i.e. a heart rate below 40 beats/second, the TI time is prolonged;

when the heart rate is higher, namely the heart rate is between 40 and 120 times/second, the TI time is shortened;

in the case of an ultrafast heart rate, i.e. a heart rate exceeding 120 beats/second, two cardiac cycles are selected for one complete excitation and acquisition.

4. The method of claim 1, wherein the method further comprises: by calculating SI_blood/SI_blood,0And SI_myo/SI_myo,0To reflect the blood and myocardial inhibitory efficiency, with SI_bloodIs the residual blood signal after inversion recovery, and SI_blood,0Representing the initial blood signal intensity before inhibition; SI (Standard interface)_myoIs the residual myocardial signal after inversion recovery, and SI_myo,0Indicating the initial myocardial signal intensity prior to inhibition.

5. The method of claim 1, wherein in step (5), the relaxation preparation comprises: an initial 90 x pulse is applied, then 2-8 composite 180 y pulses are applied, and finally a final 90-x inversion pulse is applied.

6. The method of claim 1, wherein in step (6), the relaxation weighted images are obtained using a single pass bSSFP.

7. The method of claim 1, wherein the method further comprises: (7) and according to the obtained relaxation weighted images, carrying out registration on the images in the same group by using an affine registration algorithm.

8. The method of claim 7, wherein said step (7) further comprises: removing residual blood signals, wherein said removing uses a thresholding process under an empirical threshold, the threshold being chosen to be TE_T2prepAnd (3) eliminating and reconstructing the area with the signal intensity lower than the threshold value, wherein the signal intensity of the area is 10-50% of the myocardial signal intensity in the image with the value of 0.

9. The method of claim 7, wherein the method further comprises: and carrying out quantitative analysis on the reconstructed image.

10. A cardiac blood pool suppression relaxation parameter imaging apparatus, wherein said imaging apparatus performs cardiac imaging according to the method of claim 1;

The imaging device comprises: the device comprises an imaging module, an image reconstruction module and a quantitative analysis module;

wherein the imaging module is to perform: calculating and optimizing the parameters of scanning according to the heart rate detected in real time, and realizing blood signal suppression and imaging data acquisition in a complete cardiac cycle;

and the imaging module performs the following sub-steps:

(S1) according to the detection result, which is the heart rate detection result and which includes the P peak, the QRS peak and the T peak, applying a partially saturated rf pulse, which is a pre-excitation pulse with an adaptive flip angle β, and then calculating the decrease of the longitudinal magnetization vector Mz of the object to cos (β) of the initial magnetization, which is the M magnetization₀Then according to T₁The relaxation time coefficient calculates the recovered magnetization vector:

(S2) applying double inversion pulses, which sequentially include a non-selective 120-180 ° inversion pulse and a 120-180 ° inversion pulse with slice selection; wherein the width of the 120-180 DEG inversion pulse with the layer selection is 3-5 times of the thickness of the imaging layer;

(S3) during the TI time, for the blood signal Mz according to the following formula_blood(TI) and myocardial signal Mz_myo(TI) recovery:

(S4) carrying out relaxation preparation so as to obtain 3-20 groups of T1/T2 weighted images with different echo times TE;

(S5) acquiring signals to obtain relaxation weighted images of blood inhibition;

the image reconstruction module is configured to perform: after an original image of a body is obtained, carrying out registration on images in the same group by using an affine registration algorithm; and

the quantitative analysis module is used for executing: the signals of interest were analyzed for each region and the mean and standard deviation thereof were recorded.