～（23）Na磁共振成像的实现及初步研究
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摘要
磁共振成像(MRI)无疑是物理学对生物医学领域最重要的贡献之一，现已成为临床诊断和生物医学基础研究中最重要的手段之一。MRI对身体基本无害，图像空间分辨率和组织对比度好，并可三维立体的对任意方向上的层面行成像。现阶段运用最广泛的MRI技术是质子磁共振成像，以检测生物体内水分子中质子的磁共振信号为基础。随着MRI技术及应用需求的快速发展，一些以~(23)Na为代表的杂核MRI研究已经开始体现出其重要作用。
钠离子(Na~+)是生物体中普遍存在的电解质之一，其细胞外浓度比细胞内浓度高大约8-10倍。由钠-钾泵控制的细胞内外钠浓度梯度对维持细胞结构和功能的完整性起重要作用，也是神经元细胞静息电位产生的基础。组织钠-浓度对病理变化十分敏感，可以用来指示细胞完整性，组织代谢和离子动态平衡的改变。~(23)Na磁共振成像检测组织中钠离子的浓度与分布，可提供许多常规MRI无法提供的重要信息。然而，与水相比，生物组织中Na~+的浓度相对较低，导致~(23)Na磁共振成像往往只能获得较低的信噪比和空间分辨率，且成像时间一般较长。但这些问题都可以通过提高场强和使用性能的探头来加以改善。
在本研究中，我们开展了一些有关~(23)Na MRI的初步的、探索性的工作，以期为在本实验室开展深入系统的~(23)Na MRI研究奠定基础。首先，我们自制了一个在4.7T的场强下用于~(23)Na射频发射和信号接收的表面线圈。其步骤包括1)根据表面线圈的基本原理设计出合适的电路，并通过实验证明其有效性；2)选用合适的高频、无磁性、耐高压的电容、电感材料制作出~(23)Na MRI表面线圈的实物；3)归纳了实际制作时出现的一些问题，为今后类似工作的开展积累经验。其次，我们用所制表面线圈在Bruker Biospec 47／30磁共振成像仪进行了~(23)Na MRI初步实验，分别采集了不同浓度NaCl溶液，盐腌制鹌鹑蛋和大鼠头部的~(23)Na密度像。此项研究为本实验室深入开展~(23)Na磁共振成像的生物医学应用研究奠定了基础。
MRI is undoubtedly one of the most important contributions made by physiciststo the field of medicine. Nowadays MRI has become one of the most importanttechnology used in clinical diagnosis of diseases and basic research in all braches ofbiomedicine. There is no evidence showing that the static magnetic field, pulsedgradient field and radiofrequency(RF) pulses used in MRI have harmful effects onanimals or humans. It can provide high spatial resolution 2D and 3D images at anyslice orientation and real time information about biological systems with differentcontrasts. MRI examination is noninvasive so that it causes no damage to thesample/subject and enables longitudinal studies on the same sample/subject. Currentlyproton MRI, which detects the signal from tissue water, is the most widely used MRItechnique in the field of biomedicine. With the advances in MRI technology andincreased demands from practical applications, imaging with non-proton nuclei, suchas sodium, has attracted more and more research interests.
Sodium is one of the most common electrolytes in biological organisms. Theextracellular sodium concentration is roughly 8 to 10 times of that in the intracellularspace. The sodium concentration gradient is tightly regulated by sodium-potassiumpumps, and plays very important roles in maintaining cellular integrity andfunctionality. Tissue sodium concentration is sensitive to pathological conditions andcan be used as an indicator for cellular integrity, tissue metabolic activity and ionhomeostasis. Using ~(23)Na MRI to measure the concentration and distribution of tissue sodium can provide lots of important biological information that is not obtainableusing ~1H MRI. However, tissue sodium concentration is much lower than water sothat it is often true that ~(23)Na MRI requires long acquisition time and can only yieldimages with low spatial resolution and low signal-to-noise ratio. Using higher fieldstrength magnets and high performance RF coils to image can partially ameliorate theaforementioned problems.
The work described in this thesis is a set of exploratory experiments performedin attempt to implement, for the first time, ~(23)Na MRI in our laboratory. First, asingle-loop surface coil specially designed for ~(23)Na MRI was made by the followingsteps: 1) design a proper circuit for the surface coil based on the principlessummarized by others; 2) the validity of the design was proven by experiments; 3)choose appropriate non-magnetic materials (i.e., wire, capacitors and circuit board) tofabricate the coil; 4) summarize the problems encountered and experiencesaccumulated in making the coil. As the next step, we then use the coil to acquire ~(23)Nadensity-weighted images on tubes filled with NaCl solution, boiled salted quail eggand rat brain on a Bruker Biospec 47/30 MRI scanner. The studies represent the veryfirst step towards many ~(23)Na MRI application studies to come, especially in the fieldof biomedicine.
钠离子(Na~+)是生物体中普遍存在的电解质之一，其细胞外浓度比细胞内浓度高大约8-10倍。由钠-钾泵控制的细胞内外钠浓度梯度对维持细胞结构和功能的完整性起重要作用，也是神经元细胞静息电位产生的基础。组织钠-浓度对病理变化十分敏感，可以用来指示细胞完整性，组织代谢和离子动态平衡的改变。~(23)Na磁共振成像检测组织中钠离子的浓度与分布，可提供许多常规MRI无法提供的重要信息。然而，与水相比，生物组织中Na~+的浓度相对较低，导致~(23)Na磁共振成像往往只能获得较低的信噪比和空间分辨率，且成像时间一般较长。但这些问题都可以通过提高场强和使用性能的探头来加以改善。
在本研究中，我们开展了一些有关~(23)Na MRI的初步的、探索性的工作，以期为在本实验室开展深入系统的~(23)Na MRI研究奠定基础。首先，我们自制了一个在4.7T的场强下用于~(23)Na射频发射和信号接收的表面线圈。其步骤包括1)根据表面线圈的基本原理设计出合适的电路，并通过实验证明其有效性；2)选用合适的高频、无磁性、耐高压的电容、电感材料制作出~(23)Na MRI表面线圈的实物；3)归纳了实际制作时出现的一些问题，为今后类似工作的开展积累经验。其次，我们用所制表面线圈在Bruker Biospec 47／30磁共振成像仪进行了~(23)Na MRI初步实验，分别采集了不同浓度NaCl溶液，盐腌制鹌鹑蛋和大鼠头部的~(23)Na密度像。此项研究为本实验室深入开展~(23)Na磁共振成像的生物医学应用研究奠定了基础。
MRI is undoubtedly one of the most important contributions made by physiciststo the field of medicine. Nowadays MRI has become one of the most importanttechnology used in clinical diagnosis of diseases and basic research in all braches ofbiomedicine. There is no evidence showing that the static magnetic field, pulsedgradient field and radiofrequency(RF) pulses used in MRI have harmful effects onanimals or humans. It can provide high spatial resolution 2D and 3D images at anyslice orientation and real time information about biological systems with differentcontrasts. MRI examination is noninvasive so that it causes no damage to thesample/subject and enables longitudinal studies on the same sample/subject. Currentlyproton MRI, which detects the signal from tissue water, is the most widely used MRItechnique in the field of biomedicine. With the advances in MRI technology andincreased demands from practical applications, imaging with non-proton nuclei, suchas sodium, has attracted more and more research interests.
Sodium is one of the most common electrolytes in biological organisms. Theextracellular sodium concentration is roughly 8 to 10 times of that in the intracellularspace. The sodium concentration gradient is tightly regulated by sodium-potassiumpumps, and plays very important roles in maintaining cellular integrity andfunctionality. Tissue sodium concentration is sensitive to pathological conditions andcan be used as an indicator for cellular integrity, tissue metabolic activity and ionhomeostasis. Using ~(23)Na MRI to measure the concentration and distribution of tissue sodium can provide lots of important biological information that is not obtainableusing ~1H MRI. However, tissue sodium concentration is much lower than water sothat it is often true that ~(23)Na MRI requires long acquisition time and can only yieldimages with low spatial resolution and low signal-to-noise ratio. Using higher fieldstrength magnets and high performance RF coils to image can partially ameliorate theaforementioned problems.
The work described in this thesis is a set of exploratory experiments performedin attempt to implement, for the first time, ~(23)Na MRI in our laboratory. First, asingle-loop surface coil specially designed for ~(23)Na MRI was made by the followingsteps: 1) design a proper circuit for the surface coil based on the principlessummarized by others; 2) the validity of the design was proven by experiments; 3)choose appropriate non-magnetic materials (i.e., wire, capacitors and circuit board) tofabricate the coil; 4) summarize the problems encountered and experiencesaccumulated in making the coil. As the next step, we then use the coil to acquire ~(23)Nadensity-weighted images on tubes filled with NaCl solution, boiled salted quail eggand rat brain on a Bruker Biospec 47/30 MRI scanner. The studies represent the veryfirst step towards many ~(23)Na MRI application studies to come, especially in the fieldof biomedicine.
引文
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[1] R. Ouwcrkcrk, K.B. Blcich. Tissue Sodium Concentration in Human Brain Tumors as Measured with ~(23)Na MR Imaging. Radiology, 2003 (227): 529-537.
[2] J.D. Delayre, J.S. Ingwall, C. Maloy. Gated Sodium-23 Nuclear Magnetic Resonance Images of an Isolated Perfused Working Rat Heart. Science, 1981(212): 935-936.
[3] M.E. Mosclcy, W.M. Chew, M.C. Nishimura. In vivo Sodium-23 Magnetic Resonance Surface Coil Imaging: Observing Experimental Cerebral Ischemia in the Rat. Magn Reson Imaging, 1985(3): 383-387.
[4] T. Shimizu, H. Naritomi, T. Sawada. Sequential Changes on ~(23)Na MRI after Cerebral Infarction. Ncuroradiology, 1993(35): 416-419.
[5] R. Barthaa, T.Y. Leca, M.J. Hoganb. Sodium T_2~*-wcightcd MR Imaging of Acute Focal Cerebral Ischemia in Rabbits. Magn Reson Imaging, 2004(22): 983-991.
[6] R.J. Kim, J.A.C. Lima, E.L Chen. Fast ~(23)Na Magnetic Resonance Imaging of Acute Reperfused Myocardial Infarction. Potential to Assess Myocardial Viability. Circulation, 1997(95): 1877-1885.
[7] M. Beer, J. Sandstede, T. Pabst. Assessment of Myocardial Viability by ~(31)p-MR-spectroscopy and ~(23)Na-MR Imaging. Magn Reson Mater Phys, Biol Med, 2000(11): 44-46.
[8] T. Nishimura, M. Sada, H. Sasaki. Sodium Nuclear Magnetic Resonance Imaging of Acute Cardiac Rejection in Heterotopic Heart Transplantation. Cardiovasc Res, 1989(23): 561-566.
[9] K.R. Thulborn, D. Davis. Quantitative Tissue Sodium Concentration Mapping of the Growth of Focal Cerebral Tumors With Sodium Magnetic Resonance Imaging. Magn Reson Med, 1999(41): 351-359.
[10] J.I. Shapiro, A. Borthakur, R. Dandora. Sodium Visibility and Quantitation in Intact Bovine Articular Cartilage Using High Field (23) Na MRI and MRS. J Magn Reson, 1999(142): 24-31.
[11] G. Steidle, H. Graf, F. Schick. Sodium 3-D MRI of the Human Torso Using a Volume Coil. Magn Reson Imaging, 2004(22): 171-180.
[12] M.A. Brown, R.C. Semelka. Mri Basic Principles and Applications. A John Wiley& Sons, Inc., Publication, 2003, 67-69.
[13] 赵喜平．磁共振成像系统的原理及应用．北京：科学出版社，2000．
[14] 陈星荣，沈天真．脑梗死的影像学．中国医学计算机成像杂志，2000(6)：2-36．
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[6] 王秀彬．磁共振矩形表面线圈的研制．医疗卫生装备，2004(11)：69．
1．丁炜，孟平，刘朝阳，裘鉴卿，雷皓．~(23)Na成像的初步实验研究．波谱学杂志(已接收)．
2．孟平，丁炜，刘朝阳，正交检波系统的校正．波谱学杂志(已接收)．
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[1] R. Ouwcrkcrk, K.B. Blcich. Tissue Sodium Concentration in Human Brain Tumors as Measured with ~(23)Na MR Imaging. Radiology, 2003 (227): 529-537.
[2] J.D. Delayre, J.S. Ingwall, C. Maloy. Gated Sodium-23 Nuclear Magnetic Resonance Images of an Isolated Perfused Working Rat Heart. Science, 1981(212): 935-936.
[3] M.E. Mosclcy, W.M. Chew, M.C. Nishimura. In vivo Sodium-23 Magnetic Resonance Surface Coil Imaging: Observing Experimental Cerebral Ischemia in the Rat. Magn Reson Imaging, 1985(3): 383-387.
[4] T. Shimizu, H. Naritomi, T. Sawada. Sequential Changes on ~(23)Na MRI after Cerebral Infarction. Ncuroradiology, 1993(35): 416-419.
[5] R. Barthaa, T.Y. Leca, M.J. Hoganb. Sodium T_2~*-wcightcd MR Imaging of Acute Focal Cerebral Ischemia in Rabbits. Magn Reson Imaging, 2004(22): 983-991.
[6] R.J. Kim, J.A.C. Lima, E.L Chen. Fast ~(23)Na Magnetic Resonance Imaging of Acute Reperfused Myocardial Infarction. Potential to Assess Myocardial Viability. Circulation, 1997(95): 1877-1885.
[7] M. Beer, J. Sandstede, T. Pabst. Assessment of Myocardial Viability by ~(31)p-MR-spectroscopy and ~(23)Na-MR Imaging. Magn Reson Mater Phys, Biol Med, 2000(11): 44-46.
[8] T. Nishimura, M. Sada, H. Sasaki. Sodium Nuclear Magnetic Resonance Imaging of Acute Cardiac Rejection in Heterotopic Heart Transplantation. Cardiovasc Res, 1989(23): 561-566.
[9] K.R. Thulborn, D. Davis. Quantitative Tissue Sodium Concentration Mapping of the Growth of Focal Cerebral Tumors With Sodium Magnetic Resonance Imaging. Magn Reson Med, 1999(41): 351-359.
[10] J.I. Shapiro, A. Borthakur, R. Dandora. Sodium Visibility and Quantitation in Intact Bovine Articular Cartilage Using High Field (23) Na MRI and MRS. J Magn Reson, 1999(142): 24-31.
[11] G. Steidle, H. Graf, F. Schick. Sodium 3-D MRI of the Human Torso Using a Volume Coil. Magn Reson Imaging, 2004(22): 171-180.
[12] M.A. Brown, R.C. Semelka. Mri Basic Principles and Applications. A John Wiley& Sons, Inc., Publication, 2003, 67-69.
[13] 赵喜平．磁共振成像系统的原理及应用．北京：科学出版社，2000．
[14] 陈星荣，沈天真．脑梗死的影像学．中国医学计算机成像杂志，2000(6)：2-36．
[1] 曾晓庄．医学影像服务市场．世界医疗器械，2000(6)：59-60．
[2] 田建广，夏照帆，叶朝辉．活体~(23)Na NMR及在生物医学中的应用．波谱学杂志，2000(17)：419-424．
[3] 夏防汛，谭北旋，佟海涛．颞下颌关节磁共振表面线圈临床成像的研究．中国医学影像技术，1999(15)：185-186．
[4] 张兴伟，凤伟，陈晓海．前列腺MRI检查：直肠内表面线圈与体线圈的对比研究．实用放射学杂志，2003(19)：165-167．
[5] 丁美新．MRI射频线圈的发射效率．电工技术杂志，1999(3)：7-9．
[6] 王秀彬．磁共振矩形表面线圈的研制．医疗卫生装备，2004(11)：69．
1．丁炜，孟平，刘朝阳，裘鉴卿，雷皓．~(23)Na成像的初步实验研究．波谱学杂志(已接收)．
2．孟平，丁炜，刘朝阳，正交检波系统的校正．波谱学杂志(已接收)．