JP6173757B2 - MRI equipment - Google Patents

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JP6173757B2
JP6173757B2 JP2013089395A JP2013089395A JP6173757B2 JP 6173757 B2 JP6173757 B2 JP 6173757B2 JP 2013089395 A JP2013089395 A JP 2013089395A JP 2013089395 A JP2013089395 A JP 2013089395A JP 6173757 B2 JP6173757 B2 JP 6173757B2
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張　延平
延平 張
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Sumitomo Heavy Industries Ltd
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Description

本発明は、ＭＲＩ装置に関する。   The present invention relates to an MRI apparatus.

ＳＱＵＩＤセンサを用いたＭＲＩ装置として、例えば特許文献１に記載されたものが知られている。この特許文献１に記載されたＭＲＩ装置では、感知コイル及びＳＱＵＩＤ（Ｓｕｐｅｒｃоｎｄｕｃｔｉｎｇ Ｑｕａｎｔｕｍ Ｉｎｔｅｒｆａｃｅ Ｄｅｖｉｃｅ：超伝導量子干渉素子）センサと、これらを適切な温度に冷却するための冷却器と、が用いられている。感知コイルは、被検体からの磁気信号を感知し、ＳＱＵＩＤセンサは、感知コイルで感知された磁気信号に起因する電流を感知する。そして、ＳＱＵＩＤセンサにより感知された電流に基づいて、ＭＲＩ画像が構築される。   As an MRI apparatus using a SQUID sensor, for example, an apparatus described in Patent Document 1 is known. In the MRI apparatus described in Patent Literature 1, a sensing coil, a SQUID (Superconducting Quantum Interface Device) sensor, and a cooler for cooling them to an appropriate temperature are used. . The sensing coil senses a magnetic signal from the subject, and the SQUID sensor senses a current caused by the magnetic signal sensed by the sensing coil. Then, an MRI image is constructed based on the current sensed by the SQUID sensor.

特表２０１０−５２５８９２号公報Special table 2010-525892 gazette

ところで、通常、ＭＲＩ装置は１．５Ｔ以上の高磁場を有するものが多く、例えば手術中に利用し難い等のため、中低磁場化されたＭＲＩ装置が求められる場合がある。この場合、磁場を小さくすると検出コイルの感度が悪くなることから、ＭＲＩ画像の画質が劣化する。この点、上記従来のＭＲＩ装置では、前述のようにＳＱＵＩＤセンサを用いることにより、画質の維持と中低磁場化との両立を図っている。しかしながら、市販のＳＱＵＩＤセンサは、いわゆる磁束トラップ（外部の弱い磁場にさらされるとセンサのある場所に磁束がトラップされ、外部に排出されずに残る現象）によって外部の磁場の影響を受けやすいおそれがあり、磁場耐性に改善の余地がある。   By the way, normally, many MRI apparatuses have a high magnetic field of 1.5 T or more. For example, an MRI apparatus with a low magnetic field may be required because it is difficult to use during surgery. In this case, if the magnetic field is reduced, the sensitivity of the detection coil is deteriorated, so that the image quality of the MRI image is deteriorated. In this regard, the conventional MRI apparatus uses the SQUID sensor as described above to achieve both the maintenance of the image quality and the low magnetic field. However, a commercially available SQUID sensor may be easily affected by an external magnetic field due to a so-called magnetic flux trap (a phenomenon in which a magnetic flux is trapped in a place where the sensor is located and exposed without being discharged to the outside). There is room for improvement in magnetic field resistance.

そこで、本発明は、画質を維持しつつ中低磁場化を実現可能であり、かつ、磁場耐性を向上させることができるＭＲＩ装置を提供することを課題とする。   Accordingly, it is an object of the present invention to provide an MRI apparatus that can realize a medium-low magnetic field while maintaining image quality and can improve magnetic field resistance.

上記課題を解決するため、本発明に係るＭＲＩ装置は、被検体における原子核の核磁気共鳴により放出される核磁気共鳴信号を検出するＭＲＩ装置であって、被検体を含む空間に、静磁場を少なくとも発生させる磁場発生手段と、核磁気共鳴信号の検出を行うための非高温超電導ＳＮＳ型ＳＱＵＩＤセンサと、このセンサを冷却する冷却手段と、を備える。   In order to solve the above problems, an MRI apparatus according to the present invention is an MRI apparatus that detects a nuclear magnetic resonance signal emitted by nuclear magnetic resonance of a nucleus in a subject, and applies a static magnetic field to a space including the subject. It comprises at least a magnetic field generating means for generating, a non-high temperature superconducting SNS SQUID sensor for detecting a nuclear magnetic resonance signal, and a cooling means for cooling the sensor.

本発明のＭＲＩ装置では、核磁気共鳴信号の検出のために非高温超電導ＳＮＳ型ＳＱＵＩＤセンサが用いられる。この非高温超電導ＳＮＳ型ＳＱＵＩＤセンサは、中低磁場で高感度な性質を有するため、中低磁場においても画質を維持できる。さらに、この非高温超電導ＳＮＳ型ＳＱＵＩＤセンサにあっては、磁束トラップが発生しにくい性質を有するため、外部の磁場からの影響を受け難くすることができる。したがって、画質を維持しつつ中低磁場化を実現可能であり、かつ、磁場耐性を向上させることができる。   In the MRI apparatus of the present invention, a non-high temperature superconducting SNS SQUID sensor is used for detection of nuclear magnetic resonance signals. Since this non-high temperature superconducting SNS SQUID sensor has a high sensitivity property in a medium and low magnetic field, it can maintain image quality even in a medium and low magnetic field. Furthermore, since this non-high temperature superconducting SNS SQUID sensor has the property that magnetic flux traps are difficult to occur, it can be made less susceptible to the influence of an external magnetic field. Therefore, it is possible to realize a medium and low magnetic field while maintaining the image quality, and to improve the magnetic field resistance.

また、冷却手段は、極低温冷凍機であることが好ましい。このように構成することで、例えば冷却のために液体ヘリウムを用いる必要性を抑制することができる。   The cooling means is preferably a cryogenic refrigerator. With this configuration, it is possible to suppress the necessity of using liquid helium for cooling, for example.

また、ＭＲＩ装置は、手術中に用いられることが好ましい。このように、本発明では、ＭＲＩ装置を用いて手術を行うことができる。   The MRI apparatus is preferably used during surgery. Thus, in the present invention, surgery can be performed using the MRI apparatus.

本発明によれば、画質を維持しつつ中低磁場化を実現可能であり、かつ、磁場耐性を向上させることができるＭＲＩ装置を提供することができる。   According to the present invention, it is possible to provide an MRI apparatus that can realize a medium-low magnetic field while maintaining image quality and can improve magnetic field resistance.

一実施形態に係るＭＲＩ装置の構成を示す概略模式図である。1 is a schematic diagram illustrating a configuration of an MRI apparatus according to an embodiment. 従来の検出コイルとＳＱＵＩＤセンサとの感度を比較するグラフである。It is a graph which compares the sensitivity of the conventional detection coil and a SQUID sensor. 非高温超電導ＳＮＳ型ＳＱＵＩＤセンサを構成するジョセフソン接合素子を示す斜視図である。It is a perspective view which shows the Josephson junction element which comprises a non-high temperature superconducting SNS type | mold SQUID sensor. 図３に示すジョセフソン接合素子の縦断面図である。It is a longitudinal cross-sectional view of the Josephson junction element shown in FIG.

以下、添付図面を参照して、本発明の好適な実施形態について詳細に説明する。なお、以下の説明において同一又は相当要素には同一符号を付し、重複する説明を省略する。   Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, the same or equivalent elements will be denoted by the same reference numerals, and redundant description will be omitted.

まず、一実施形態に係るＭＲＩ装置の概略構成について説明する。図１は、一実施形態に係るＭＲＩ装置の構成を示す概略模式図である。図１に示すように、ＭＲＩ装置１は、被検体２が配置される撮像空間５が開放された開放型の構造をなしている。このＭＲＩ装置１は、磁場発生手段３と、非高温超電導ＳＮＳ型ＳＱＵＩＤセンサ６と、極低温冷凍機７と、を備える。   First, a schematic configuration of an MRI apparatus according to an embodiment will be described. FIG. 1 is a schematic diagram illustrating a configuration of an MRI apparatus according to an embodiment. As shown in FIG. 1, the MRI apparatus 1 has an open structure in which an imaging space 5 in which a subject 2 is arranged is opened. The MRI apparatus 1 includes a magnetic field generating means 3, a non-high temperature superconducting SNS type SQUID sensor 6, and a cryogenic refrigerator 7.

磁場発生手段３は、撮像空間５を挟んで配置されており、撮像空間５に静磁場を発生させる静磁場磁石、撮像空間５に傾斜磁場を発生させる傾斜場コイル、及び撮像空間５に高周波磁場を発生させる高周波コイル等を少なくとも含んでいる。磁場発生手段３の静磁場磁石は、被検体２の体軸に対し垂直方向に静磁場を発生させる。この静磁場磁石は、主に常伝導磁石又は永久磁石であり、例えば地磁気（５０μＴ）より高くて手術中に使い易い０．２Ｔ以下の中低磁場を撮像空間５に発生させる。   The magnetic field generation means 3 is disposed with the imaging space 5 interposed therebetween, and a static magnetic field magnet that generates a static magnetic field in the imaging space 5, a gradient field coil that generates a gradient magnetic field in the imaging space 5, and a high-frequency magnetic field in the imaging space 5. Including at least a high-frequency coil for generating the. The static magnetic field magnet of the magnetic field generating means 3 generates a static magnetic field in a direction perpendicular to the body axis of the subject 2. The static magnetic field magnet is mainly a normal conducting magnet or a permanent magnet, and generates, for example, a medium to low magnetic field of 0.2 T or less, which is higher than the geomagnetism (50 μT) and easy to use during surgery, in the imaging space 5.

磁場発生手段３の傾斜磁場コイルは、互いに直交する３軸方向のコイル（不図示）によって３軸方向に磁場勾配を生じさせる。この傾斜磁場コイルとしては、例えば開放型の構造を妨げないよう平板状のコイルが用いられている。磁場発生手段３の高周波コイルは、撮像空間５の被検体２に高周波磁場を照射し、水素原子の核スピンをほぼ一様に共鳴励起させる。この高周波コイルとしては、例えば開放型の構造を妨げないよう平板状のコイルが用いられている。   The gradient magnetic field coil of the magnetic field generating means 3 generates a magnetic field gradient in three axial directions by means of coils (not shown) orthogonal to each other. As this gradient magnetic field coil, for example, a flat coil is used so as not to disturb the open structure. The high-frequency coil of the magnetic field generating unit 3 irradiates the subject 2 in the imaging space 5 with a high-frequency magnetic field and resonantly excites the nuclear spins of hydrogen atoms almost uniformly. As this high frequency coil, for example, a flat coil is used so as not to disturb the open structure.

非高温超電導ＳＮＳ型ＳＱＵＩＤセンサ６は、被検体２の近傍に配置され、被検体２における原子核の核磁気共鳴信号を検出する。具体的には、被検体２における原子核の核磁気共鳴により放出される核磁気共鳴信号を受信し、電気信号に変換する。非高温超電導ＳＮＳ型ＳＱＵＩＤセンサ６が検出した信号は、ＭＲＩ画像の構築に利用され、例えば、電磁遮蔽壁８に覆われているディスプレイ９に被検体２の断層像や三次元画像等として表示される。非高温超電導ＳＮＳ型ＳＱＵＩＤセンサ６は、９Ｋ未満の低温において動作が可能である。なお、非高温超電導ＳＮＳ型ＳＱＵＩＤセンサ６の詳細については、後述する。   The non-high temperature superconducting SNS type SQUID sensor 6 is disposed in the vicinity of the subject 2 and detects nuclear magnetic resonance signals of nuclei in the subject 2. Specifically, a nuclear magnetic resonance signal emitted by nuclear magnetic resonance of a nucleus in the subject 2 is received and converted into an electrical signal. The signal detected by the non-high temperature superconducting SNS type SQUID sensor 6 is used to construct an MRI image, and is displayed as a tomographic image or a three-dimensional image of the subject 2 on the display 9 covered with the electromagnetic shielding wall 8, for example. The The non-high temperature superconducting SNS type SQUID sensor 6 can operate at a low temperature of less than 9K. Details of the non-high temperature superconducting SNS type SQUID sensor 6 will be described later.

極低温冷凍機７は、非高温超電導ＳＮＳ型ＳＱＵＩＤセンサ６を冷却するための冷却手段であり、例えばＧＭ（ギフォード・マクマホン）冷凍機等が用いられている。極低温冷凍機７は、圧縮された冷媒ガスを膨張空間に供給して膨張させることによって、４Ｋ程度の極低温まで冷却でき、これにより非高温超電導ＳＮＳ型ＳＱＵＩＤセンサ６を動作可能に冷却する。すなわち、極低温冷凍機７は、液体ヘリウムを用いることなく、冷媒ガスを循環させることにより冷却を行っている。   The cryogenic refrigerator 7 is a cooling means for cooling the non-high temperature superconducting SNS type SQUID sensor 6, and for example, a GM (Gifford McMahon) refrigerator or the like is used. The cryogenic refrigerator 7 can cool the non-high temperature superconducting SNS SQUID sensor 6 in an operable manner by supplying the compressed refrigerant gas to the expansion space and allowing it to expand to a cryogenic temperature of about 4K. That is, the cryogenic refrigerator 7 performs cooling by circulating the refrigerant gas without using liquid helium.

次に、一実施形態に係るＭＲＩ装置が備える非高温超電導ＳＮＳ型ＳＱＵＩＤセンサ６について、更に詳細に説明する。   Next, the non-high temperature superconducting SNS type SQUID sensor 6 included in the MRI apparatus according to the embodiment will be described in more detail.

非高温超電導ＳＮＳ型ＳＱＵＩＤセンサ６は、一般的なＭＲＩ装置におけるＲＦ検出コイルの代わりに用いられている。図２は、従来のＲＦ検出コイルとＳＱＵＩＤセンサとの感度を比較するグラフである。図２の横軸は静磁場強度β０（Ｔ）を示し、縦軸はＳＮＲ（Ｓｉｇｎａｌ ｔо Ｎｏｉｓｅ Ｒａｔｉо：信号雑音比）を示している。ＳＮＲは、その値が高ければ伝送におけるノイズの影響が小さく、その値が低ければノイズの影響が大きいことを意味する。 The non-high temperature superconducting SNS type SQUID sensor 6 is used in place of an RF detection coil in a general MRI apparatus. FIG. 2 is a graph comparing the sensitivity of a conventional RF detection coil and a SQUID sensor. The horizontal axis of FIG. 2 indicates the static magnetic field strength β 0 (T), and the vertical axis indicates the SNR (Signal to Noise Ratio). If the value of SNR is high, the influence of noise in transmission is small, and if the value is low, it means that the influence of noise is large.

図２の曲線ａは従来のＲＦ検出コイルを用いた場合の静磁場強度β０に対するＳＮＲ値、図２の直線ｂはＳＱＵＩＤセンサを用いた場合の静磁場強度β０に対するＳＮＲ値を示している。図２の曲線ａに示すように、従来のＲＦコイルを用いた場合には、静磁場強度β０に対しＳＮＲは指数関数的に増加している。この場合、静磁場強度β０とＳＮＲとの関係は、以下の数式（１）で示される。
ＳＮＲ∝４２．６・β0 2 …（１）
すなわち、従来のＲＦコイルを用いた場合、ＳＮＲは静磁場強度β０が小さくなるにつれてその二乗に比例して減少し、静磁場強度β０が中低磁場（ここでは、０．６４Ｔ以下）の範囲では、高いＳＮＲを得ることが困難とされている。 A curve a in FIG. 2 indicates an SNR value with respect to the static magnetic field intensity β 0 when the conventional RF detection coil is used, and a straight line b in FIG. 2 indicates an SNR value with respect to the static magnetic field intensity β 0 when the SQUID sensor is used. . As shown by the curve a in FIG. 2, when the conventional RF coil is used, the SNR increases exponentially with respect to the static magnetic field strength β 0 . In this case, the relationship between the static magnetic field strength β 0 and the SNR is expressed by the following formula (1).
SNR∝42.6 · β 0 2 (1)
That is, when a conventional RF coil, SNR decreases in proportion to the square as the static magnetic field strength beta 0 decreases (here, 0.64T or less) static magnetic field strength beta 0 is a medium downfield In the range, it is difficult to obtain a high SNR.

一方、図２の直線ｂに示すように、ＳＱＵＩＤセンサを用いた場合には、静磁場強度β０に対しＳＮＲは直線的に増加している。この場合、静磁場強度β０とＳＮＲとの関係は、以下の数式（２）で示される。
ＳＮＲ∝β0 …（２）
すなわち、低温ＳＮＳ型ＳＱＵＩＤセンサを用いた場合、ＳＮＲは静磁場強度β０に比例する。よって、ＳＱＵＩＤセンサは、従来のＲＦ検出コイルと比べて、中低磁場の範囲における静磁場強度β０に対するＳＮＲの変化が小さく、当該範囲におけるＳＮＲの値が高い。換言すると、静磁場強度β０が中低磁場の場合には、従来のＲＦ検出コイルよりもＳＱＵＩＤセンサの方がノイズの影響が小さく、得た画質が高い。 On the other hand, as shown in line b of FIG. 2, in the case of using the SQUID sensor, SNR relative to the static magnetic field strength beta 0 is increased linearly. In this case, the relationship between the static magnetic field strength β 0 and the SNR is expressed by the following formula (2).
SNR∝β 0 (2)
That is, when the low temperature SNS type SQUID sensor is used, the SNR is proportional to the static magnetic field strength β 0 . Therefore, the SQUID sensor has a small change in SNR with respect to the static magnetic field intensity β 0 in the range of medium and low magnetic fields and a high SNR value in the range compared to the conventional RF detection coil. In other words, when the static magnetic field strength β 0 is a medium to low magnetic field, the SQUID sensor is less affected by noise than the conventional RF detection coil, and the obtained image quality is high.

また、ここでは、非高温超電導ＳＮＳ型ＳＱＵＩＤセンサ６を利用する。この非高温超電導ＳＮＳ型ＳＱＵＩＤセンサ６は、ジョセフソン接合素子によって構成される。図３は非高温超電導ＳＮＳ型ＳＱＵＩＤセンサを構成するジョセフソン接合素子を示す斜視図、図４は図３に示すジョセフソン接合素子の縦断面図である。   Here, the non-high temperature superconducting SNS type SQUID sensor 6 is used. This non-high temperature superconducting SNS type SQUID sensor 6 is composed of a Josephson junction element. FIG. 3 is a perspective view showing a Josephson junction element constituting the non-high temperature superconducting SNS SQUID sensor, and FIG. 4 is a longitudinal sectional view of the Josephson junction element shown in FIG.

図３及び図４に示すように、ジョセフソン接合素子１０は、矩形膜状の第１の超伝導膜１２と、第１の超伝導膜１２に対しその長手方向を直交して跨ぐように重ね合わされた矩形膜状の第２の超伝導膜１３と、を備えている。第１の超伝導膜１２と第２の超伝導膜１３とが重なる部分には、これら２つの超伝導膜１２，１３を互いに電気的に絶縁するための絶縁膜１４が設けられている。第２の超伝導膜１３は、第１の超伝導膜１２を跨ぐことから、第１の超伝導膜１２の形状に沿って曲げられている。このため、ジョセフソン接合素子１０の縦断面は、凸型をなしている（図４参照）。   As shown in FIGS. 3 and 4, the Josephson junction element 10 includes a first superconducting film 12 having a rectangular film shape, and the first superconducting film 12 so as to cross the longitudinal direction of the first superconducting film 12 at right angles. And a rectangular superconducting film 13 having a rectangular shape. In the portion where the first superconducting film 12 and the second superconducting film 13 overlap, an insulating film 14 for electrically insulating the two superconducting films 12 and 13 from each other is provided. Since the second superconducting film 13 straddles the first superconducting film 12, it is bent along the shape of the first superconducting film 12. For this reason, the longitudinal section of the Josephson junction element 10 has a convex shape (see FIG. 4).

第１の超伝導膜１２及び第２の超伝導膜１３は、９Ｋよりも低い温度で超伝導現象を起こす非高温超伝導物質により構成されている。非高温超伝導物質としては、例えば、Ｎｂが挙げられる。第１の超伝導膜１２及び第２の超伝導膜１３の寸法は、幅が４０００ｎｍ程度であり、厚さが１００ｎｍ〜２５０ｎｍの薄膜である。絶縁膜１４は絶縁性を有する物質により構成され、例えばＮｂ２Ｏ５等のＮｂの酸化物が挙げられる。絶縁膜１４の厚さは、１０ｎｍ程度である。ジョセフソン接合素子１０は、第１の超伝導膜１２、絶縁膜１４及び第２の超伝導膜１３の順で積層されている。最上位に積層された第２の超伝導膜１３には断面円形の有底穴１５が設けられている。この有底穴１５は、第２の超伝導膜１３の面のうち絶縁膜１４が設けられている側とは反対側の表面（以下、単に「上面」という）１３ａから第１の超伝導膜１２側へ向かって延びており、絶縁膜１４に達する手前において第２の超伝導膜１３の内部に底部１５ａを形成している。ここで、有底穴１５の径は２０〜２００ｎｍであり、有底穴１５のアスペクト比（穴の径に対する穴の深さの比）は６以下とされている。 The first superconducting film 12 and the second superconducting film 13 are made of a non-high temperature superconducting material that causes a superconducting phenomenon at a temperature lower than 9K. An example of the non-high temperature superconducting material is Nb. The dimensions of the first superconducting film 12 and the second superconducting film 13 are thin films having a width of about 4000 nm and a thickness of 100 nm to 250 nm. The insulating film 14 is made of an insulating material, and examples thereof include Nb oxides such as Nb 2 O 5 . The thickness of the insulating film 14 is about 10 nm. The Josephson junction element 10 is formed by laminating a first superconducting film 12, an insulating film 14, and a second superconducting film 13 in this order. The second superconducting film 13 stacked at the top is provided with a bottomed hole 15 having a circular cross section. The bottomed hole 15 extends from the surface of the second superconducting film 13 opposite to the side on which the insulating film 14 is provided (hereinafter simply referred to as “upper surface”) 13 a to the first superconducting film. The bottom portion 15 a is formed in the second superconducting film 13 before reaching the insulating film 14. Here, the diameter of the bottomed hole 15 is 20 to 200 nm, and the aspect ratio of the bottomed hole 15 (ratio of the hole depth to the hole diameter) is 6 or less.

絶縁膜１４は、上記有底穴１５の底部１５ａから更に所定の深さに位置する部分（有底穴１５の底部１５ａに対向する部分）に、イオンビームの照射によるイオン注入により形成された弱接合部１４ａを有している。この弱接合部１４ａは、第１の超伝導膜１２及び第２の超伝導膜１３の間を導電化し、電子対が通過できるようにしたものである。つまり、２つの超伝導膜１２，１３の間における弱接合部１４ａにおいて、超伝導電子対のトンネル効果が発揮される。注入されているイオンとしては、Ｎｂ、Ａｕ、Ｃｕ、Ａｌ、Ｐ、Ｎ等のイオンが挙げられる。   The insulating film 14 is a weak portion formed by ion implantation by ion beam irradiation at a portion located at a predetermined depth from the bottom portion 15a of the bottomed hole 15 (a portion facing the bottom portion 15a of the bottomed hole 15). It has a joint 14a. This weakly bonded portion 14a conducts between the first superconducting film 12 and the second superconducting film 13 so that electron pairs can pass therethrough. That is, the tunnel effect of the superconducting electron pair is exhibited at the weak junction 14 a between the two superconducting films 12 and 13. Examples of the implanted ions include Nb, Au, Cu, Al, P, and N ions.

ここで、上述したように、本実施形態に係る非高温超電導ＳＮＳ型ＳＱＵＩＤセンサ６を構成するジョセフソン接合素子１０は、低温ＳＮＳ型の接合とされている。低温とは、液体窒素で冷却できる温度（７７Ｋ）未満をいう。ＳＮＳ型とは、二つの超伝導（Ｓ）の電極に挟まれた接合層が導電性（Ｎ）を有する接合種類である。   Here, as described above, the Josephson junction element 10 constituting the non-high temperature superconducting SNS type SQUID sensor 6 according to the present embodiment is a low temperature SNS type junction. Low temperature refers to a temperature lower than 77 K that can be cooled with liquid nitrogen. The SNS type is a bonding type in which a bonding layer sandwiched between two superconducting (S) electrodes has conductivity (N).

ＳＮＳ型の接合の場合、接合部分が導電性を有しているため、当該接合部分の電気抵抗率ρの値は非常に小さい。よって、ＳＮＳ型の接合の場合、数式（３）に示すように、理論的には電気抵抗Ｒをほとんど有していない。しかし、電気抵抗Ｒが小さすぎると電圧の測定ができなくなり実用性に乏しい。
Ｒ＝ρ・（Ｌ／Ｓ）…（３）
ただし、Ｒ：電気抵抗［Ω］、ρ：電気抵抗率［Ω・ｍ］、Ｌ：物体の長さ［ｍ］、Ｓ：物体の断面積［ｍ２］ In the case of an SNS type junction, since the junction portion has conductivity, the value of the electrical resistivity ρ of the junction portion is very small. Therefore, in the case of an SNS type junction, theoretically, it has almost no electrical resistance R as shown in Equation (3). However, if the electric resistance R is too small, the voltage cannot be measured and the practicality is poor.
R = ρ · (L / S) (3)
Where R: electrical resistance [Ω], ρ: electrical resistivity [Ω · m], L: object length [m], S: object cross-sectional area [m 2 ]

そこで、非高温超電導ＳＮＳ型ＳＱＵＩＤセンサ６としてのジョセフソン接合素子１０にあっては、前述のようにイオン注入によって接合部分を形成することにより、当該接合部分の断面積Ｓを小さくしている。すなわち、接合部分の断面積Ｓを小さくすることで、一定の電気抵抗Ｒを持たせている（数式（３）参照）。これにより、実用可能な非高温超電導ＳＮＳ型ＳＱＵＩＤセンサ６を実現している。   Therefore, in the Josephson junction element 10 as the non-high temperature superconducting SNS type SQUID sensor 6, the junction area is formed by ion implantation as described above, thereby reducing the sectional area S of the junction area. That is, by reducing the cross-sectional area S of the joint portion, a certain electric resistance R is given (see Formula (3)). Thereby, the practical non-high temperature superconducting SNS type SQUID sensor 6 is realized.

以上、本実施形態のＭＲＩ装置１によれば、核磁気共鳴信号の検出のために非高温超電導ＳＮＳ型ＳＱＵＩＤセンサ６が用いられる。この非高温超電導ＳＮＳ型ＳＱＵＩＤセンサ６は、従来のＲＦ検出コイルと比較して中低磁場で高感度な性質を有するため、中低磁場においても画質を維持できる。さらに、非高温超電導ＳＮＳ型ＳＱＵＩＤセンサ６にあっては、接合の断面及び周りの面積が小さく、かつ、高温超電導材料に比べ結晶欠陥が少なく均一性の高いものとなっており、すなわち、磁束トラップが発生しにくい性質を有するジョセフソン接合素子１０により構成されている。このため、外部の磁場からの影響を受け難くすることができる。したがって、画質を維持しつつ中低磁場化を実現可能であり、かつ、磁場耐性を向上させることができる。   As described above, according to the MRI apparatus 1 of the present embodiment, the non-high temperature superconducting SNS SQUID sensor 6 is used for detection of nuclear magnetic resonance signals. Since this non-high temperature superconducting SNS type SQUID sensor 6 has a high sensitivity property in a medium and low magnetic field as compared with a conventional RF detection coil, the image quality can be maintained even in a medium and low magnetic field. Further, in the non-high temperature superconducting SNS type SQUID sensor 6, the cross section of the junction and the area around it are small, and there are few crystal defects and high uniformity compared with the high temperature superconducting material. It is composed of the Josephson junction element 10 having a property that is difficult to generate. For this reason, it can be made hard to receive the influence from an external magnetic field. Therefore, it is possible to realize a medium and low magnetic field while maintaining the image quality, and to improve the magnetic field resistance.

また、本実施形態は、上述したように、冷却手段として極低温冷凍機７を備えている。この極低温冷凍機７は、冷媒ガスを循環させているため、例えば冷却のために液体ヘリウムを用いる必要性を抑制することができる。よって、液体ヘリウムを維持するためのコストを減らし、低コスト化を図ることができる。   Further, as described above, this embodiment includes the cryogenic refrigerator 7 as a cooling means. Since the cryogenic refrigerator 7 circulates the refrigerant gas, it is possible to suppress the necessity of using liquid helium for cooling, for example. Therefore, the cost for maintaining liquid helium can be reduced and the cost can be reduced.

また、本実施形態に係るＭＲＩ装置１は、手術中に用いることにより、上記作用効果を好適に発揮することができる。具体的には、高磁場のＭＲＩ装置を手術中に用いると、医療器具等が磁力によって強く引っ張られる等の悪影響が生じ得る。これに対し、本実施形態に係るＭＲＩ装置１は、非高温超電導ＳＮＳ型ＳＱＵＩＤセンサ６を用いているため、地磁気（５０μＴ）より高くて手術中に使い易い０．２Ｔ以下の磁場範囲として、好適に利用可能となる。よって、高磁場のＭＲＩ装置を用いた場合に想定される悪影響を抑制し、安全に手術を行うことができる。   Moreover, the MRI apparatus 1 according to the present embodiment can exert the above-described effects effectively when used during surgery. Specifically, when a high magnetic field MRI apparatus is used during surgery, adverse effects such as a medical instrument being strongly pulled by a magnetic force may occur. On the other hand, since the MRI apparatus 1 according to the present embodiment uses the non-high temperature superconducting SNS type SQUID sensor 6, it is suitable as a magnetic field range of 0.2 T or less that is higher than the geomagnetism (50 μT) and easy to use during surgery. Will be available. Therefore, it is possible to suppress an adverse effect assumed when a high magnetic field MRI apparatus is used, and to perform surgery safely.

以上、本発明の好適な実施形態について説明したが、本発明は上記実施形態に限定されるものではなく、各請求項に記載した要旨を変更しない範囲で変形し、又は他のものに適用したものであってもよい。   As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to the said embodiment, It changed within the range which does not change the summary described in each claim, or applied to the other thing It may be a thing.

例えば、上記実施形態では、開放型のＭＲＩ装置１としたが、これに限られず、閉鎖型のＭＲＩ装置としてもよい。また、必要に応じて、磁場発生手段３の冷却にも極低温冷凍機７を用いる構成としてもよい。   For example, in the above embodiment, the open type MRI apparatus 1 is used. However, the present invention is not limited to this, and a closed type MRI apparatus may be used. Moreover, it is good also as a structure which uses the cryogenic refrigerator 7 for cooling of the magnetic field generation means 3 as needed.

また、上記実施形態のジョセフソン接合素子１０は、図３及び図４に示すような積層構造に限られない。例えば、第１の超伝導膜１２、絶縁膜１４及び第２の超伝導膜１３がこれらの積層方向から見たときに同一形状となるように単純に積層されていてもよい。また、ジョセフソン接合素子１０の有底穴１５が積層部分の中央部に設けられていなくてもよく、例えば、有底穴１５は、積層部分の中央部からずれた位置に設けられていてもよい。   Further, the Josephson junction element 10 of the above embodiment is not limited to the laminated structure as shown in FIGS. For example, the first superconducting film 12, the insulating film 14, and the second superconducting film 13 may be simply laminated so as to have the same shape when viewed from the laminating direction. Further, the bottomed hole 15 of the Josephson junction element 10 may not be provided in the central portion of the laminated portion. For example, the bottomed hole 15 may be provided at a position shifted from the central portion of the laminated portion. Good.

また、非高温超電導ＳＮＳ型ＳＱＵＩＤセンサ６に含まれる非高温超伝導物質としては、Ｎｂに限られず、７７Ｋよりも遥かに低い温度で超伝導現象を起こす限り、その他の金属又はＮｂＮ等であってもよい。   Further, the non-high temperature superconducting material included in the non-high temperature superconducting SNS type SQUID sensor 6 is not limited to Nb, and may be other metals or NbN as long as the superconducting phenomenon occurs at a temperature much lower than 77K. Also good.

１…ＭＲＩ装置、２…被検体、３…磁場発生手段、６…非高温超電導ＳＮＳ型ＳＱＵＩＤセンサ、７…極低温冷凍機（冷却手段）。   DESCRIPTION OF SYMBOLS 1 ... MRI apparatus, 2 ... Subject, 3 ... Magnetic field generation means, 6 ... Non-high temperature superconducting SNS type SQUID sensor, 7 ... Cryogenic refrigerator (cooling means).

Claims (1)

被検体における原子核の核磁気共鳴により放出される核磁気共鳴信号を検出するＭＲＩ装置であって、
前記被検体を含む空間に、静磁場を少なくとも発生させる磁場発生手段と、
前記核磁気共鳴信号の検出を行うための非高温超電導ＳＮＳ型ＳＱＵＩＤセンサと、
前記非高温超電導ＳＮＳ型ＳＱＵＩＤセンサを冷却する冷却手段と、を備える、ＭＲＩ装置。 An MRI apparatus for detecting a nuclear magnetic resonance signal emitted by nuclear magnetic resonance of a nucleus in a subject,
Magnetic field generating means for generating at least a static magnetic field in a space including the subject;
A non-high temperature superconducting SNS SQUID sensor for detecting the nuclear magnetic resonance signal;
And a cooling means for cooling the non-high temperature superconducting SNS type SQUID sensor.
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