JP2003190113A - Navigation imaging method and magnetic resonance imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To avoid an artifact caused by passing a navigator slice through the portion of an imaging target included in an imaging slice. <P>SOLUTION: The imaging slice Si is located only on the right lung Lr. Two navigator slices N1 and N2 are located so that a crossing X can be located on the left lung Ll and can not pass through the right lung Lr included in the imaging slice Si. The left lung Ll is imaged by inverting the locations symmetrically. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a navigation imaging method and a magnetic resonance imaging apparatus, and more particularly, navigation capable of avoiding an artifact caused by a navigator slice passing through an imaging target portion included in an imaging slice. The present invention relates to an imaging method and a magnetic resonance imaging device.

[0002]

2. Description of the Related Art A conventional navigation imaging method will be described with reference to FIGS. It is assumed that the heart H is imaged by the SE (Spin Echo) method in synchronization with the respiratory phase. First, as shown in FIG. 12, the right lung Lr
A 90 ° pulse is applied to the first navigator slice N1 that passes through the body (which may be the left lung Ll) in the axial direction and does not pass through the heart H. Subsequently, a second navigator slice N2 that intersects the first navigator slice N1 at the right lung Lr and the intersection passes through the right lung Lr in the body axis direction and does not pass through the heart H.
180 degree pulse is added to. Then, the navigation echo is emitted from the intersection X of the first navigator slice N1 and the second navigator slice N2, and this is collected.

Next, as shown in FIG. 13, a one-dimensional profile is created from the navigation echo with the vertical axis representing the strength of an MR (Magnetic Resonance) signal and the horizontal axis representing the longitudinal position of the intersection X. This one-dimensional profile has a step shape in which the MR signal on the head side is small and the MR signal on the foot side is large. The head side is the right lung Lr, the foot side is the liver, etc., and the portion where the MR signal intensity changes corresponds to the diaphragm. Then, the right lung Lr expands during inspiration and the right lung Lr contracts during expiration, so that the changing portion of the intensity of the MR signal of the one-dimensional profile periodically moves. Therefore, if the moment at which the MR signal intensity exceeds an appropriate threshold value at an appropriate detection position Po within the range in which the MR signal intensity changing portion periodically moves is monitored, the respiratory phase in which the heart H should be imaged. Can be detected.

Then, as shown in FIG. 14, the imaging slice Si is imaged in synchronization with the respiratory phase. The heart H moves due to respiration, but by imaging in synchronization with the respiratory phase, it is possible to always image at the same position.

[0005]

In the conventional magnetic resonance imaging apparatus, the relative positions of the two navigator slices N1 and N2 are fixed, but the position of the intersection X can be designated by the operator. . Therefore, as conceptually shown in FIG. 15, the operator has designated the position of the intersection X so that the navigator slices N1 and N2 do not pass through the heart H included in the imaging slice Si.

However, when it is desired to image the lung field itself, even if the position of the intersection X is moved, as shown in FIG. 16, the navigator slices N1 and N2 select the lung field included in the imaging slice S1 at the intersection F. As a result,
The intensity of the MR signal at the intersection F changes, and as shown in FIG. 17, the artifact f appears on the MR image.

Therefore, an object of the present invention is to provide a navigation imaging method and a magnetic resonance imaging apparatus capable of avoiding an artifact caused by a navigator slice passing through an imaging target portion included in an imaging slice.

[0008]

SUMMARY OF THE INVENTION In a first aspect, the present invention provides for the one-dimensional acquisition of MR signals on the intersection of two navigator slices in either the right or left lung. A navigation imaging method characterized by creating a profile, detecting a periodical motion of the lung from the one-dimensional profile, and imaging an imaging slice arranged in the other of the right lung or the left lung in synchronization with the motion. provide. In the navigation imaging method according to the first aspect, the imaging target region is narrowed down to only one of the right lung and the left lung, and the intersection of the two navigator slices is arranged in the other of the right lung and the left lung that are not the imaging target region. . As a result, the area of the imaging target region included in the imaging slice becomes small, so that it is possible to prevent the navigator slice from passing through the area. That is, artifacts can be avoided. If the right lung or the left lung is imaged in the same manner after the right lung or the left lung is imaged, the entire lung field can be imaged.

[0009] In a second aspect, the present invention arranges the intersection of two navigator slices in one of the anterior lung and the posterior lung and collects MR signals on the intersection to create a one-dimensional profile. There is provided a navigation imaging method characterized by detecting a periodical motion of a lung from a one-dimensional profile and imaging an imaging slice arranged in the other of the anterior lung and the posterior lung in synchronization with the motion. In the navigation imaging method according to the second aspect, the imaging target region is narrowed down to only one of the anterior lung and the posterior lung, and the intersection of the two navigator slices is arranged in the other of the anterior lung and the posterior lung that are not the imaging target region. . As a result, the area of the imaging target region included in the imaging slice becomes small, so that it is possible to prevent the navigator slice from passing through the area. That is, artifacts can be avoided. In addition, if one of the anterior lung and the posterior lung is imaged and then the other of the anterior lung and the posterior lung is similarly imaged, the entire lung field can be imaged.

In a third aspect, the present invention provides a one-dimensional profile in which the intersection of two navigator slices is located in one of the right lung or the left lung and MR signals on the intersection are collected to create a one-dimensional profile. Profile creating means, motion detecting means for detecting a periodical motion of the lung from the one-dimensional profile, and synchronous imaging means for imaging an imaging slice arranged in the other of the right lung or the left lung in synchronization with the motion. There is provided a magnetic resonance imaging apparatus characterized by being provided. The magnetic resonance imaging apparatus according to the third aspect can preferably implement the navigation imaging method according to the first aspect.

In a fourth aspect, the present invention provides a one-dimensional profile in which the intersection of two navigator slices is placed in one of the anterior or posterior lungs and MR signals on the intersection are collected to create a one-dimensional profile. Profile creating means, motion detecting means for detecting a periodical motion of the lung from the one-dimensional profile, and synchronous imaging means for imaging an imaging slice arranged in the other of the anterior lung and the posterior lung in synchronization with the motion. There is provided a magnetic resonance imaging apparatus characterized by being provided. The magnetic resonance imaging apparatus according to the fourth aspect can suitably implement the navigation imaging method according to the second aspect.

In a fifth aspect, the present invention comprises a one-dimensional profile creating means for collecting MR signals on the intersection of two navigator slices to create a one-dimensional profile,
Motion detection means for detecting a periodic movement of an imaging target region from the one-dimensional profile, synchronous imaging means for imaging an imaging slice arranged on the imaging target region in synchronization with the motion, and imaging included in the imaging slice A magnetic resonance imaging apparatus comprising: a navigator slice setting means for setting a navigator slice so as not to overlap a target region. In the magnetic resonance imaging apparatus according to the fifth aspect, since the navigator slice can be set so that the navigator slice does not pass through the region of the imaging target region included in the imaging slice, the navigator slice passes through the imaging target region included in the imaging slice. It is possible to avoid artifacts caused by this.

According to a sixth aspect of the present invention, in the magnetic resonance imaging apparatus having the above structure, the navigator slice setting means is means for an operator to specify a position of the navigator slice. Provide a device. In the magnetic resonance imaging apparatus according to the sixth aspect, since the operator can specify the position of the navigator slice, the navigator slice can be set so that the navigator slice does not pass through the region of the imaging target region included in the imaging slice.

In a seventh aspect, the present invention provides a slice thickness setting for automatically setting the thickness of the navigator slice so that the cross-sectional area of the intersecting portion has a target area in the magnetic resonance imaging apparatus having the above structure. There is provided a magnetic resonance imaging apparatus including the means. In the magnetic resonance imaging apparatus according to the seventh aspect, the thickness of the navigator slice is automatically adjusted to make the cross-sectional area of the intersection constant at the target area. Therefore, even if the intersection angle between the two navigator slices is changed, the same navigation accuracy can be maintained.

According to an eighth aspect of the present invention, in the magnetic resonance imaging apparatus having the above structure, the slice thickness setting means is
There is provided a magnetic resonance imaging apparatus characterized by obtaining an intersection angle of two navigator slices and then calculating a slice thickness from the intersection angle and a target area. In the magnetic resonance imaging apparatus according to the eighth aspect, it is possible to preferably calculate the thickness of the navigator slice for keeping the cross-sectional area of the intersection of the two navigator slices constant at the target area.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described in more detail with reference to the embodiments shown in the drawings. The present invention is not limited to this.

FIG. 1 is a block diagram showing a magnetic resonance imaging apparatus according to an embodiment of the present invention. In this magnetic resonance imaging apparatus 100, the magnet assembly 1 has a space portion (hole) for inserting a subject therein, and a constant main magnetic field is applied to the subject so as to surround this space portion. A permanent magnet 1p, a gradient magnetic field coil 1g for generating a gradient magnetic field of X-axis, Y-axis, and Z-axis, a transmission coil 1t for applying an RF pulse for exciting spins of nuclei in a subject, and a subject And a receiving coil 1r for detecting the MR signal from. The gradient magnetic field coil 1
g is connected to the gradient magnetic field drive circuit 3. The transmitter coil 1t is connected to the RF power amplifier 4. The receiving coil 1r is connected to the preamplifier 5.
A superconducting magnet may be used instead of the permanent magnet 1p.

The sequence storage circuit 8 operates the gradient magnetic field drive circuit 3 based on the stored pulse sequence in accordance with a command from the computer 7 to generate a gradient magnetic field from the gradient magnetic field coil 1g of the magnet assembly 1. The gate modulation circuit 9 is operated to modulate the carrier wave output signal of the RF oscillation circuit 10 into a pulsed signal having a predetermined timing and a predetermined envelope shape, which is applied as an RF pulse to the RF power amplifier 4 and then by the RF power amplifier 4. After power amplification, it is applied to the transmitter coil 1t of the magnet assembly 1 to selectively excite a desired slice.

The preamplifier 5 includes a magnet assembly 1
The MR signal from the subject detected by the receiving coil 1 r is amplified and input to the phase detector 12. Phase detector 12
Uses the carrier wave output signal of the RF oscillation circuit 10 as a reference signal, phase-detects the MR signal from the preamplifier 5, and
It is given to the D converter 11. The A / D converter 11 converts the analog signal after phase detection into digital data and inputs it to the computer 7.

The computer 7 reads the digital data from the A / D converter 11 and performs an image reconstruction operation to generate an MR image. The computer 7 is responsible for overall control such as receiving information input from the console 13. The generated MR image and the like are displayed on the display device 6.

FIG. 2 is a flow chart showing a navigation imaging process by the magnetic resonance imaging apparatus 100. It is assumed that the right lung Lr is imaged by the SE method in synchronization with the respiratory phase. In step J1, the pre-scan slice orthogonal to the imaging slice plane is imaged and displayed on the display device 6. FIG. 3 shows a prescan image. Lr is the right lung,
Ll is the left lung.

At step J2, the operator operates the console 13
Is operated to set an imaging slice Si on the prescan image as shown in FIG. At this time, the imaging slice S
i includes the right lung Lr, which is the imaging target site.

At step J3, the operator operates the console 13
Is operated to set the first navigator slice N1 on the prescan image as shown in FIG. At this time, the first navigator slice N1 does not pass through the left lung Ll in the body axis direction and does not pass through the right lung Lr that is the imaging target site included in the imaging slice Si.

At step J4, the operator operates the console 13
Is operated to set the second navigator slice N2 on the pre-scan image as shown in FIG. At this time, the second navigator slice N2 intersects with the first navigator slice N1 and the intersection X passes through the left lung Ll in the body axis direction and the right lung Lr which is the imaging target site included in the imaging slice Si. Do not pass through.

At step J5, as shown in FIG. 7, an intersection angle θ between the first navigator slice N1 and the second navigator slice N2 is obtained. Here, the intersection angle θ is an angle of 90 ° or less among the interior angles of the parallelogram that is the cross section of the intersection X.

At step J6, the intersection angle θ and the target area A
Based on and, the slice thickness d of the navigator slice is calculated.
That is, d = √ {A · sin θ}

At step J7, a 90 ° pulse is applied to the first navigator slice N1 and then a 180 ° pulse is applied to the second navigator slice N2 to collect the navigation echo emitted from the intersection X. At step J8, based on the collected navigation echo,
As shown in, a one-dimensional profile is created with the vertical axis representing the strength of the MR signal and the horizontal axis representing the position of the intersection X in the lengthwise direction. This one-dimensional profile has a step shape in which the MR signal on the head side is small and the MR signal on the foot side is large. Head side is left lung Ll, foot side is liver etc., MR
The changing portion of the signal strength corresponds to the diaphragm. Then, the left lung Ll expands during inspiration and the left lung Ll contracts during expiration, so that the changing portion of the MR signal intensity of the one-dimensional profile moves cyclically. In step J9, it is judged whether or not the MR signal intensity at an appropriate detection position Po within the range in which the MR signal intensity changing portion periodically moves exceeds an appropriate threshold value. Return to step J7,
If so, proceed to Step J10.

In step J10, the imaged slice Si is imaged. Thereby, the right lung Lr can be imaged in synchronization with the respiratory phase.

At step J11, as shown in FIG.
The imaging slice Si and the navigator slices N1 and N2 are symmetrically left-right reversed and set, and the above steps J7 to J10 are performed.
Perform the same processing as. Thereby, the right lung Lr can be imaged in synchronization with the respiratory phase.

10 and 11 are explanatory views of setting examples of the imaging slice Si and the navigator slices N1 and N2 when the lung field is divided into the anterior lung and the posterior lung for imaging. When imaging the anterior lung, as shown in FIG. 10, the imaging slice Si is set to include the anterior lung, and the first navigator slice N is set.
1 is set so as to pass through the rear lung in the body axis direction and not pass through the front lung included in the imaging slice Si. When imaging the posterior lung, as shown in FIG. 11, the imaging slice Si is set to include the posterior lung, and the first navigator slice N1 passes through the anterior lung in the body axis direction and is included in the imaging slice Si. Set it so that it does not pass through the rear lung.

In general, the present invention is applicable to navigation imaging of a part that moves by breathing (eg, lung, heart, pancreatic duct, bile duct).

[0032]

According to the navigation imaging method and the magnetic resonance imaging apparatus of the present invention, it becomes possible to avoid the artifact caused by the navigator slice passing through the imaging target portion included in the imaging slice.

[Brief description of drawings]

FIG. 1 is a block diagram showing a magnetic resonance imaging apparatus according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a navigation imaging process according to an embodiment of the present invention.

FIG. 3 is a view showing an example of a prescan image.

FIG. 4 is an explanatory diagram showing setting of an imaging slice for imaging the left lung.

FIG. 5 is an explanatory diagram showing setting of a first navigator slice.

FIG. 6 is an explanatory diagram showing setting of a second navigator slice.

FIG. 7 is an explanatory diagram of an intersection.

FIG. 8 is a view showing an example of a one-dimensional profile.

FIG. 9 is an explanatory diagram showing setting of an imaging slice for imaging the right lung.

FIG. 10 is an explanatory diagram showing setting of an imaging slice and a navigator slice for imaging the anterior lung.

FIG. 11 is an explanatory diagram showing setting of an imaging slice and a navigator slice for imaging the posterior lung.

FIG. 12 is an explanatory diagram showing setting of a navigator slice for imaging a heart.

FIG. 13 is a view showing an example of a one-dimensional profile.

FIG. 14 is an explanatory diagram showing setting of an imaging slice for imaging a heart.

FIG. 15 is an explanatory diagram showing setting of an imaging slice and a navigator slice for imaging the heart.

FIG. 16 is an explanatory diagram showing setting of an imaging slice and a navigator slice for imaging a lung.

FIG. 17 is a conceptual diagram of an artifact caused by a navigator slice passing through an imaging target portion included in an imaging slice.

[Explanation of symbols]

100 magnetic resonance imaging apparatus 1 Magnet assembly 1g gradient magnetic field coil 1t transmitter coil 1p permanent magnet 1r receiver coil 6 Display device 7 calculator 8 Sequence memory circuit N1 first navigator slice N2 Second Navigator Slice Si, S1 imaging slice Lr right lung Ll left lung X Navigator slice intersection f artifact

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Katsuya Hirano             127, 4-7 Asahigaoka, Hino City, Tokyo             GE Yokogawa Medical System Co., Ltd.             Within F-term (reference) 4C096 AA20 AB11 AB50 AC04 AC05                       AD12 AD24 AD26 BB32 CA05                       DA03 DA19

Claims (8)

[Claims] 1. A cross section of two navigator slices is arranged in one of the right lung and the left lung, and MR signals on the cross section are collected to create a one-dimensional profile. Navigation image pickup method, characterized in that a different motion is detected, and an imaging slice arranged in the other of the right lung and the left lung is imaged in synchronization with the motion. 2. An intersection of two navigator slices is arranged in one of the anterior lung and the posterior lung, MR signals on the intersection are collected to create a one-dimensional profile, and the one-dimensional profile is used to periodically analyze the lung. Navigation imaging method, characterized by detecting a specific movement, and capturing an imaging slice arranged in the other of the front lung and the rear lung in synchronization with the movement. 3. A one-dimensional profile creating means for arranging an intersection of two navigator slices in one of the right lung and the left lung and collecting MR signals on the intersection to create a one-dimensional profile, and the one-dimensional profile. A magnetic field comprising motion detection means for detecting a periodic motion of the lung from the profile, and synchronous imaging means for imaging an imaging slice arranged in the other of the right lung and the left lung in synchronization with the motion. Resonance imaging device. 4. A one-dimensional profile creating means for arranging an intersection of two navigator slices in one of an anterior lung and a posterior lung and collecting MR signals on the intersection to create a one-dimensional profile, and the one-dimensional profile. A magnetic field detecting means for detecting a periodical movement of the lung from the profile; and a synchronous imaging means for imaging an imaging slice arranged in the other of the anterior lung and the posterior lung in synchronization with the motion. Resonance imaging device. 5. A one-dimensional profile creating means for creating a one-dimensional profile by collecting MR signals on the intersection of two navigator slices, and a motion for detecting a periodic motion of an imaging target region from the one-dimensional profile. Detecting means, synchronous imaging means for imaging an imaging slice arranged on the imaging target site in synchronization with the movement, and navigator slice setting for setting the navigator slice so as not to overlap the imaging target site included in the imaging slice And a magnetic resonance imaging apparatus. 6. The magnetic resonance imaging apparatus according to claim 5, wherein the navigator slice setting means is means for an operator to specify a position of the navigator slice. 7. The magnetic resonance imaging apparatus according to claim 5 or 6, wherein slice thickness setting means for automatically setting the thickness of the navigator slice so that the cross-sectional area of the intersection portion becomes a target area. A magnetic resonance imaging apparatus comprising: 8. The magnetic resonance imaging apparatus according to claim 5 or 6, wherein the slice thickness setting means obtains a crossing angle of two navigator slices, and then the slice thickness is calculated from the crossing angle and the target area. A magnetic resonance imaging apparatus characterized by: