NL2025766B1 - METHOD FOR SIMULTANEOUSLY OBTAINING T1 WEIGHTED IMAGE OF MAGNETIC RESONANCE Dual-SIGNAL NANOPROBE BY USING RAREVTR SEQUENCE - Google Patents

METHOD FOR SIMULTANEOUSLY OBTAINING T1 WEIGHTED IMAGE OF MAGNETIC RESONANCE Dual-SIGNAL NANOPROBE BY USING RAREVTR SEQUENCE Download PDF

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NL2025766B1
NL2025766B1 NL2025766A NL2025766A NL2025766B1 NL 2025766 B1 NL2025766 B1 NL 2025766B1 NL 2025766 A NL2025766 A NL 2025766A NL 2025766 A NL2025766 A NL 2025766A NL 2025766 B1 NL2025766 B1 NL 2025766B1
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Sun Xilin
Wang Kai
Yang Lili
Jiang Meng
A Rong
Jiang Weiqi
Qiao Wenju
Sun Xiaohong
Cheng Lixin
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Univ Harbin Medical
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Abstract

The present invention relates to the technical field of optimization of medical imaging sequence parameters, in particular to a method for simultaneously obtaining a Tl weighted image of magnetic resonance dual-signal nanoprobe by using a RAREVTR sequence. The method includes the following steps: (l) preparing nanoprobes With Tl and T2 dual magnetic resonance contrast signals at different concentrations; (2) fixing the prepared phantoms together, and placing the phantoms in a magnet scanning bed, tuning to its resonance frequency, and then scanning RAREVTR and MSME sequences to obtain Tl values and T2 values corresponding to the probes, (3) Determining and setting an optimal TE value and optimal TR value for dual-signal nanoprobe solution according to an equation Y=[A+C * (l-exp (-TlU Tl))] * exp (-TE/ T2) . The RAREVTR sequence with the optimized parameters could not only obtain an accurate Tl value, but also could obtain an approximate TlWl image.

Description

METHOD FOR SIMULTANEOUSLY OBTAINING T1 WEIGHTED IMAGE OF MAGNETIC RESONANCE Dual-SIGNAL NANOPROBE BY USING RAREVTR
SEQUENCE
FIELD OF TECHNOLOGY The present invention relates to the technical field of optimization of medical imaging sequence parameters, in particular to a method for simultaneously obtaining an ideal T1 (longitudinal relaxation time) weighted image and T1 relaxation time of magnetic resonance dual- signal nanoprobe by using a RAREVTR (Rapid Acquisition Relaxation Enhancement with Variable Repetition Time) sequence. Specifically, a method for eliminating the influence of T2 (transverse relaxation time) confusing signals of a dual-signal nanoprobe by using a RAREVTR sequence performed on a 9.4T (9.4 Tesla) magnetic resonance imaging (BioSpec94/20USR) system.
BACKGROUND In the existing imaging technology, the magnetic resonance imaging (MRI) is an imaging technology in the field of medical imaging that has both the advantages of non-invasive and high spatial resolution. It has broad prospects in basic biomedical researches and clinical diseases. Among various kinds of imaging methods, the magnetic resonance imaging is one of the indispensable tools in biomedical research.
The development of novel clinical contrast agents, such as nanoprobes and novel drugs has received a lot of attention from scientific researchers. MRI/MRS (magnetic resonance imaging/magnetic resonance spectrum) systems with high field intensity and high uniformity provide fast and effective observation conditions for the characterization of the signal feature , functions and performance of these new drugs and new nano-matertals, as well as the assessment of preclinical biosafety.
T1, T2, and T2 mapping measurements could provide multiple anatomical information of soft tissues with high spatial resolution, which are used to clinical disease diagnoses; T1 weighted image (TIWI) highlights the differences in T1 relaxation (longitudinal relaxation) of tissues, which could better display the anatomical structures of tissues and organs while T2 weighted image (T2WI) highlights the differences in the T2 relaxation (transverse relaxation) of the tissues, which can better display diseased tissues. such as tumors. The T1 weighted image is characterized by short TR (Repetition Time) and short TE (Echo Time). The shorter the T1 of the tissue is, the faster the recovery is, and the stronger the signal is; and the longer the T1 of the tissue is, the slower the recovery 1s, and the weaker the signal is. The T2 weighted image is characterized by long TR
(Repetition Time) and long TE (Echo Time), the longer the T2 of the tissue is, the slower the recovery is, and the stronger the signal is; and the shorter the T2 of the tissue is, the faster the recovery is, and the weaker the signal is. MRI T1 Mapping image can be obtained by RAREVTR (Rapid Acquisition Relaxation Enhancement with Variable Repetition Time) sequence, signal weighting is performed by using a T1 relaxation time to obtain a T1 (longitudinal relaxation time) value of each point of the image, and the T1 value is used as grayscale of the point of the image. The signal collected by MR is not only related to the exponential attenuation of T1, but also related to a T2 value, therefore, an image signal obtained by RAREVTR in vitro imaging of the dual-signal probe is not a real T1 weighted signal, that is, the signal intensity of a k space actually collected instead of the signal of an actual image. This signal is linked to the actual image through an exponential form of time. Therefore, when the nanoprobe research used has dual-signal (T1 weighted signal, T2 weighted signal) characteristics, the actually obtained image is affected by the T2 value and cannot reflect the T1 weighted approximate image, the same is true for MSME (Multi Slice Multi Echo) sequences used to determine T2 relaxation time of tissues or samples.
SUMMARY The main purpose of the present invention is to solve the influence of confusing signals of dual-signal nanoprobes appeared in the imaging result of RAREVTR (Rapid Acquisition Relaxation Enhancement with Variable Repetition Time) or MSME (Multi Slice Multi Echo) sequences, which is used to normative Tlmapping and T2mapping imaging. And simultaneously to obtain a T1 weighted image while getting a conventional T1 value by optimizing sequence parameters on ParaVision 6.0.1 imaging system. The technical solution of the present invention is as follows: a method for simultaneously obtaining a T1 weighted image of magnetic resonance dual-signal nanoprobe by using a RAREVTR sequence, which is characterized by including the following steps: (preparing nanoprobes with T1 and T2 dual contrast signals at different concentrations, 0.05 mM, 0.1 mM, 0.2 mM and 0.4 mM (millimole) respectively; (2) fixing the prepared phantoms of nanoprobe together, placing the phantoms in a magnet resonance scanning bed, and tuning the nanoprobe to its resonance frequency, and then scanning RAREVTR and MSME sequences on a ParaVision6.0.1 imaging system conventionally to obtain T1 values and T2 values corresponding to the probes with different concentrations; and (3) after the step (2), setting an optimal TE value and TR value forthe probe solutions according to an equation Y= [A+C * (l-exp (-TR/ T1)}] * exp (-TE/ T2). In the equation described in the step (3):
The A represents an absolute deviation.
The C represents the signal intensity, which is in direct proportion to the proton density.
The TR refers to a repetition time between two excitation pulse during magnetic resonance imaging.
The TR determines the magnitude of longitudinal magnetization vector recovery before the excitation pulse is emitted, and is a factor that determines the signal intensity.
TE represents an echo time, the time interval from the initial generation of the transverse magnetization intensity to the reception of a signal after the action of an excitation radio frequency pulse, and the echo time is also known as an echo delay time.
The beneficial effects of the present invention are as follows: I. When T1 mapping the double-signal nanoprobe with magnetic resonance imaging system , the RAREVTR (Rapid Acquisition Relaxation Enhancement with Variable Repetition Time) sequence with the optimized parameters could eliminate the influence of the T2 (transverse relaxation) signal of dual-signal nanoprobe.
2. When T2 mapping the double-signal nanoprobe with magnetic resonance imaging system, the MSME (Multi Slice Multi Echo) sequence with the optimized parameters could eliminate the influence of the T1 (longitudinal relaxation) signal of dual-signal nanoprobe.
3. The RAREVTR (Rapid Acquisition Relaxation Enhancement with Variable Repetition Time) sequence with the optimized parameters not only could obtain an accurate T1 (longitudinal relaxation) value, but also could obtain an approximate TIWI (T1 weighted) image.
4. The MSME (Multi Slice Multi Echo) sequence with the optimized parameters not only could obtain an accurate T2 (transverse relaxation) value, but also could obtain an approximate T2WI (T2 weighted) image.
BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1is a T1 mapping image. a signal intensity image and a longitudinal relaxation time image before the optimization of imaging parameters of a RAREVTR sequence.
Fig. 2 is a T1 mapping image. a signal intensity diagram and a longitudinal relaxation time image after the optimization of imaging parameters of the RAREVTR sequence.
Fig. 3 is a T2 mapping image, a signal intensity image and a transverse relaxation time image of MSME sequence.
Fig. 4 is a T1 weighted image obtained by FLASH (Fast Low Angle Shot) sequence according to an optimal TE value and an optimal TR value.
DETAILED DESCRIPTION OF THE EMBODIMENTS Referring to Fig. 1, the signal intensity related to the proton density is extremely inhomogeneous, and the pixel values of an obtained T1 mapping image cannot reflect T1 weighted signal.
Referring to Fig. 2, the signal intensity related to the proton density is highly homogeneous, and the pixel values of the obtained T1 mapping image can reflect the T1 weighted signal.
Referring to Fig. 3, In the same way, a T2 contrast effect image can be obtained by MSME (Multi Slice Multi Echo) sequence at the same time, and its signal intensity is inversely proportional to the concentration of a probe solution.
Referring to Fig. 4, the results show that the image obtained by T1 mapping sequence, RAREVTR sequence, with optimized parameters does not has much differences that obtained by T1 weighted FLASH sequence, which means a T1WI image of dual-signal nanoprobe could be obtained from the T1 mapping RAREVTR sequence by parameter optimization properly, and also conventional T1 value is obtained at the same time. Finally, the optimization and efficient use of a T1 mapping imaging sequence are realized in this work.
A method for simultaneously obtaining a T1 weighted image of magnetic resonance dual- signal nanoprobe by using a RAREVTR sequence includes the following steps: (1) preparing nanoprobes with T1 and T2 dual contrast signals at different concentrations, 0.05 mM, 0.1 mM, 0.2 mM and 0.4 mM (millimole) respectively; (2) fixing the prepared phantoms of nanoprobes together, and placing sample phantoms in a magnet resonance scanning bed, and tuning the nanoprobe to its resonance frequency, then scanning RAREVTR (Rapid Acquisition Relaxation Enhancement with Variable Repetition Time, T1 mapping imaging) and MSME (Multi Slice Multi Echo, T2 mapping imaging) sequences on a 9.4T magnetic resonance imaging system. Using related ParaVision6.0.1 software to obtain T1 values and T2 values corresponding to the probes with different concentrations conventially; and (3) after the step (2). setting an optimal TE (Echo Time) value and an optimal TR (Repetition Time) value for the probe solutions according to an equation Y= [A+C * (1-exp (-TR/ T1))] * exp (- TE/T2) to eliminate the influence of the T2 signal of the nanoprobe solutions on the pixel values of the T1 mapping image and also to eliminate the influence of the T1 signal of the nanoprobe solutions on the pixel values of the T2 mapping image similarly. Therefore, the RAREVTR or MSME (T1 mapping or T2 mapping imaging) sequence could also obtain a T1 weighted image or a T2 weighted image in addition to the obtaining of conventional T1 value or T2 value regularly, that is, the pixel values of the image obtained by the T1 mapping or T2 mapping sequences not only could reflect the T1 or T2 weighted signal of the dual-signal nanoprobe respectively but also could obtain the T1 or T2 relaxation time regularly.
In the equation described in the step (3): The A represents an absolute deviation.
5 The C represents the signal intensity (proportional to the proton density).
The TR refers to the time interval between two excitations magnetic resonance pulse. The TR determines the magnitude of longitudinal magnetization vector recovery before the excitation pulse is emitted, and is a factor that determines the signal intensity. The magnitude of the echo signal depends on the magnitude of a transverse magnetization vector at the time of reading out the signal, and the magnitude of the transverse magnetization vector depends on the magnitude of a flipped longitudinal magnetization vector, so that the extension of the TR can increase the recovery of the longitudinal magnetization. Therefore, more transverse magnetization is generated during the next excitation, the intensity of the generated signal would be increased. and the signal-to-noise ratio of the image would be improved; on the contrary, if the TR is shortened, only a part of longitudinal magnetization would recover, the transverse magnetization during the next excitation would be reduced, the number of signals would decrease , and the signal-to-noise ratio of image would be low.
TE represents an echo time, the time interval from the initial generation of the transverse magnetization intensity to the reception of a signal after the excitation of radio frequency pulse, and the echo time is also known as an echo delay time.
The optimal TE value needs to consider the T2 value of the dual-signal nanoprobe. For RAREVTR sequence, a short TE value (1/5 to 1/4 of the T2 value of the dual-signal probe) is set according to the T2 value of the nanoprobe, which relates to the exp (-TE/T2) portion of the equation, and reduces the influence on the signal intensity C, thereby eliminating the influence of the confusing signals of the T2 (transverse relaxation) signal in the RAREVTR (Rapid Acquisition Relaxation Enhancement with Variable Repetition Time. T1 mapping imaging) sequence to obtain an approximate T1WI image of the dual-signal probe.
The optimal TR value shold consider the T1 value of the dual-signal nanoprobe. For T2 mapping MSME (Multi Slice Multi Echo) sequence, a long TR value (4-5 times of the T1 value of the dual-signal probe) is set according to the T1 value, which relates to the exp(-TR/T1) portion of the equation, and reduces the influence on the signal intensity C, thereby eliminating the influence of the confusing signals of the T2 signal in the MSME (the dual-signal probe .,T2 mapping imaging) sequence to obtain an approximate T2WI (T2 weighted) image of the dual-signal probe.
Exemplary embodiment 1: In order to eliminate the influence of T2 confusing signals of dual- signal nanoprobe and to realize the T1 weighted image simultaneously, based on the original imaging sequence parameters, the maximum TR is set to a value less than 1/5 of the T1 value. The T1 represents the longitudinal relaxation time of the probe solution.
Exemplary embodiment 2: in order to eliminate the influence of T2 confusing signals of dual- signal nanoprobe and to realize the T1 weighted image simultaneously, based on the original imaging sequence parameters, the TE is set to be less than 1/5 of the T2 value of dual-signal nanoprobe ; and the maximum TR is set to a value less than 1/5 of the T1 value. The T1 represents the longitudinal relaxation time of the probe solution, and the T2 represents the transverse relaxation time of the probe solution.
Exemplary embodiment 3: in order to eliminate the influence of T2 confusing signals of dual- signal nanoprobe and to realize the T1 weighted image simultaneously, based on the original imaging sequence parameters, the TE is set to be less than 1/5 of the T2 value; and the TR is set to various values, the maximum value is 4000ms. The T1 represents the longitudinal relaxation time of the probe solution, and the T2 represents the transverse relaxation time of the probe solution.
The specific implementation parameters in examplary embodiments 1. 2 and 3 are as follows: Exemplary Embodiment 1 Embodiment 2 Embodiment 3 ee VTR(ms) 47.88.80.120,160, | 43.035,80,120,160, | 43.035.80.120,160,200.260, een enen | sons er Echo 521 4.64 4.64 ee Excitation 90° 90° 90°
EO Acquisition 1.280 1.280 1.280 ama OO
*VTR (before optimization) of the original RAREVTR sequence are 254.383, 450, 900, 1200, 2000, 3000, 4000, 5000 (ms, milliseconds) respectively. ema James TI saturation 61.68, 49.03, 42.97, 29.2, 15.87 56.15, 5342, 51.38, 46.83, 49.94 recovery (signal intensity) T1 mapping 5.729, 8.147, 9.106, 9.582, 8.085 | 4.677, 7.992, 10.17, 14.67, 23.46 (TE: image pixel value | (TE: 28.84, TR : 254.383, no 4.64, TR : 260, the signal trend was obvious signal trend was observed with | obvious with the increase of probe solution the increase of probe solution concentration.
The higher the concentration, concentration.) the better T1 contrast effect, the signal more brighter.) Longitudinal 2546.5, 1238.7. 936.2, 547.7, 302 2826.2, 1435.6, 1039.7, 599.1, 352.6 (There is relaxation time ( | (There is a trend) a trend) T1,ms) * The order of the measurement are control (water), 0.05mM, 0.1mM. 0.2mM. 0.4mM ( different concentrations of T1 and T2 dual-signal nanoprobes.
The above description is only a specific embodiment of the present invention, and various illustrations do not limit the essential contents of the present invention.
The following numbered clauses include embodiments that are contemplated and nonlimiting:
1. A method for simultaneously obtaining a T1 weighted image of magnetic resonance dual- signal nanoprobe by using a RAREVTR sequence, which is characterized by the following steps: (1) preparing nanoprobes with T1 and T2 dual magnetic resonance contrast signals at different concentrations, 0.05 mM. 0.1 mM, 0.2 mM and 0.4 mM respectively; (2) fixing the prepared phantoms of nanoprobe together, and placing the phantoms in a magnet scanning bed, tuning the probe to its resonance frequency and then scanning RAREVTR and MSME sequences on 9.4T magnetic resonance imaging system, then using a related ParaVision6.0.1 software to obtain T1 values and T2 values corresponding to the probes with different concentrations; and (3) after the step (2), determining and setting an optimal TE (Echo Time) value and an optimal TR (Repetition Time) value for dual magnetic resonance signal nanoprobe solution according to an equation Y=[A+C * (l-exp (-TR/ T1))] * exp (-TE/ T2); wherein in the equation described in the step (3), the A represents an absolute deviation; the C represents the signal intensity, which is direct proportional to the proton density; the TR refers to the time interval between two magnetic resonance excitation pulse during MR imaging; the TR determines the magnitude of longitudinal magnetization vector recovery before the excitation pulse is emitted, and also is a factor that determines the signal intensity; the TE represents an echo time, the time interval from the initial generation of the transverse magnetization intensity to the reception of a signal after the excitation of radio frequency pulse, the echo time is also known as an echo delay time.

Claims (1)

ConclusiesConclusions 1. Werkwijze voor gelijktijdig verkrijgen van een T 1-gewogen beeld van magnetische resonantie dubbelsignaals nanoprobe met behulp van een RAREVTR-sequentie, welke gekenmerkt wordt door de volgende stappen: (1) voorbereiden van nanoprobes met T1 en T2 dubbele magnetische resonantie contrastsignalen bij verschillende concentraties, respectievelijk 0.05 mM, 0.1 mM, 0.2 mM en 0.4 mM; (2) samen fixeren van de voorbereide fantomen van nanoprobe, en plaatsen van de fantomen in een magnetisch scanbed, afstemmen van de probe op zijn resonantiefrequentie en vervolgens scannen van RAREVTR- en MSME-sequenties met een 9.4T magnetische-resonantie beeldvormingssysteem, vervolgens gebruiken van een gerelateerde ParaVision6.0.1 software om T1-waarden en T2-waarden te verkrijgen die overeenkomen met de probes met verschillende concentraties; en (3) na de stap (2). bepalen en instellen van een optimale TE (Echo Time)-waarde en een optimale TR (Repetition Time)-waarde voor dubbele magnetische resonantiesignaal nanoprobe-oplossing volgens de vergelijking Y=[A+C*(1-exp (-TR/T1)]*exp(-TE/T2)}; waarbij in de vergelijking beschreven in de stap (3), de A staat voor een absolute afwijking: de C staat voor de signaalintensiteit, die recht evenredig is met de protondichtheid; de TR staat voor het tijdsinterval tussen twee magnetische resonantie-excitatiepulsen tijdens MR- beeldvorming; de TR de grootte bepaalt van longitudinale magnetisatie vector herstel voordat de excitatiepuls uitgestoten wordt, en ook een factor is die de signaalintensiteit bepaalt; de TE staat voor een echotijd, het tijdsinterval vanaf het initieel genereren van de transversale magnetisatie-intensiteit tot de ontvangst van een signaal na de excitatie van radiofrequentiepuls, de echotijd is tevens gekend als een echovertragingstijd.A method for simultaneously obtaining a T1-weighted image of magnetic resonance double-signal nanoprobe using a RAREVTR sequence, which is characterized by the following steps: (1) preparing nanoprobes with T1 and T2 double magnetic resonance contrast signals at different concentrations, 0.05 mM, 0.1 mM, 0.2 mM and 0.4 mM, respectively; (2) fix the prepared nanoprobe phantoms together, and place the phantoms in a magnetic scanning bed, tune the probe to its resonance frequency, and then scan RAREVTR and MSME sequences with a 9.4T magnetic resonance imaging system, then use from a related ParaVision6.0.1 software to obtain T1 values and T2 values corresponding to the probes with different concentrations; and (3) after the step (2). determining and setting an optimal TE (Echo Time) value and an optimal TR (Repetition Time) value for dual magnetic resonance signal nanoprobe solution according to the equation Y=[A+C*(1-exp (-TR/T1)) ]*exp(-TE/T2)}; where in the equation described in step (3), the A stands for an absolute deviation: the C stands for the signal intensity, which is directly proportional to the proton density; the TR stands for the time interval between two magnetic resonance excitation pulses during MR imaging; the TR determines the magnitude of longitudinal magnetization vector recovery before the excitation pulse is ejected, and is also a factor determining signal intensity; the TE stands for an echo time, the time interval from the initial generation of the transverse magnetization intensity until the reception of a signal after the excitation of radio frequency pulse, the echo time is also known as an echo delay time.
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