JP6389039B2 - Slab setting device, magnetic resonance device, and program - Google Patents

Description

  The present invention relates to a slab setting device for setting a slab, a magnetic resonance device having the slab setting device, and a program applied to the slab setting device.

  As an MRA (MR angiography) method for imaging a blood flow without using a contrast agent, a TOF (time-of-flight) method using the inflow effect of blood is known.

  The TOF method includes a two-dimensional method (2D-TOF method) and a three-dimensional method (3D-TOF method). The 2D-TOF method is suitable for rendering blood with a relatively low flow rate, but has a problem that the resolution in the slice direction is low. On the other hand, the 3D-TOF method has a merit that the resolution in the slice direction can be increased because the slab is set and the slab is imaged by the 3D imaging method, and is mainly used for imaging of blood vessels in the head. Has been.

  However, the 3D-TOF method has a drawback that the blood flow signal is easily saturated because it is necessary to set the slab to a certain thickness. As a method for eliminating this drawback, a 3D-TOF method using a multi-slab is known (see Patent Document 1).

JP 2002-253527 A

  In the multi-slab 3D-TOF method, an operator inputs information necessary for setting a plurality of slabs (for example, the number of slices, slice thickness, and number of slabs included in one slab).

  By inputting these pieces of information, a plurality of slabs are set. After setting a plurality of slabs, the operator determines whether or not the slab setting conditions need to be changed. When it is determined that there is no need to change the slab setting conditions, scanning by the multi-slab 3D-TOF method is executed.

  However, the operator may want to change the slab setting conditions before executing the multi-slab 3D-TOF scan. For example, when the operator confirms the scan time before performing the scan by the multi-slab 3D-TOF method and the scan time is longer than expected, the operator wants to reduce the number of slices in order to shorten the scan time. Sometimes. However, when the number of slices is changed, the slab thickness changes accordingly, and there is a problem that it is not possible to take an image within the range of the imaging area originally considered by the operator. Therefore, when it is not desired to change the range of the imaging region, the operator needs to adjust not only the number of slices but also other parameters such as the slice thickness, and there is a problem that it takes time to adjust the parameters.

  For this reason, there is a demand for a technique for preventing the range of the imaging region from changing as much as possible even when the parameters for setting the slab are changed.

A first aspect of the present invention is a slab setting device for setting a plurality of slabs,
Setting means for setting the plurality of slabs based on the number of slices included in each of the plurality of slabs and the slice thickness of the slices;
The setting means includes
The slab setting device changes the slice thickness so that the slab thickness of the slab does not change when the number of the plurality of slices is changed.

  The 2nd viewpoint of this invention is a magnetic resonance apparatus which has said slab setting apparatus.

A third aspect of the present invention is a program applied to a slab setting device that sets a plurality of slabs,
A setting process for setting the plurality of slabs based on the number of slices included in each of the plurality of slabs and the slice thickness of the slices, wherein the number of slices is changed A setting process for changing the slice thickness so that the slab thickness of the slab does not change,
Is a program for causing a computer to execute.

  When the number of slices is changed, the slice thickness is changed so that the slab thickness does not change, so the range of the imaging region is not changed (or the range of the imaging region is not changed as much as possible). be able to.

It is the schematic of the magnetic resonance apparatus of this form of this invention. It is explanatory drawing of the process which the processor 8 performs. It is a figure which shows the scan performed with this form. It is a figure which shows the flow when performing the scan of FIG. It is a figure which shows sagittal image SA schematically. It is a figure showing an example of a plurality of slabs. It is explanatory drawing of slab a and b. It is a figure for demonstrating an example which shows how a slab changes when the number of slices is reduced from NS = 10 to NS = 5. It is a figure which shows slab a 'and b' reset. It is a figure which shows slab a 'and b' at the time of changing the number NS of slices from 10 to 8.

  Hereinafter, although the form for inventing is demonstrated, this invention is not limited to the following forms.

FIG. 1 is a schematic diagram of a magnetic resonance apparatus of this embodiment of the present invention.
A magnetic resonance apparatus (hereinafter referred to as “MR apparatus”, MR: Magnetic Resonance) 100 includes a magnet 2, a table 3, a receiving coil 4, and the like.

  The magnet 2 has a bore 21 in which the subject 12 is accommodated. The magnet 2 includes a superconducting coil, a gradient coil, an RF coil, and the like.

  The table 3 has a cradle 3 a that supports the subject 12. The cradle 3a is configured to be able to move into the bore 21. The subject 12 is transported to the bore 21 by the cradle 3a.

  The reception coil 4 is attached to the head of the subject 12. The receiving coil 4 receives a magnetic resonance signal from the subject 12.

  The MR apparatus 100 further includes a transmitter 5, a gradient magnetic field power source 6, a receiver 7, a processor 8, a memory 9, an operation unit 10, a display unit 11, and the like.

The transmitter 5 supplies current to the RF coil, and the gradient magnetic field power source 6 supplies current to the gradient coil.
The receiver 7 performs signal processing such as detection on the signal received from the receiving coil 4.

  The processor 8 transmits necessary information to the display unit 11 and reconstructs an image based on data received from the receiving coil 4 so as to realize various operations of the MR apparatus 100. Control the operation of each part. The memory 9 stores a program executed by the processor 8 and the like. The processor 8 reads the program stored in the memory 9 and executes the process described in the program. FIG. 2 shows processing executed by the processor 8. The program describes a setting process for setting a plurality of slabs based on information input from the operation unit 10 described later. The processor 8 configures a setting unit 81 for executing the setting process described in the program by reading the program. This setting process will be described later in detail.

The operation unit 10 is operated by an operator and inputs various information to the processor 8. The display unit 11 displays various information.
The MR apparatus 100 is configured as described above.

FIG. 3 is a diagram showing a scan executed in this embodiment.
In this embodiment, a localizer scan LS and a main scan MS are executed.

The localizer scan LS is a scan for acquiring an image used when setting a slab.
The main scan MS is a scan for acquiring a blood flow image by the multi-slab 3D-TOF method.
The flow when executing the scan of FIG. 3 will be described below.

FIG. 4 is a diagram showing a flow when the scan of FIG. 3 is executed.
In step S1, a localizer scan LS is executed. By executing the localizer scan LS, an axial image, a sagittal image, and a coronal image are acquired. FIG. 5 schematically shows a sagittal image SA as an example of an image acquired by the localizer scan LS. After executing the localizer scan LS, the process proceeds to step S2.

In step S2, the operator inputs information necessary for setting the slab on the head of the subject with reference to the image acquired by the localizer scan LS. For example, the following information is input.
(1) Number of slices NS included in one slab
(2) Slice thickness ST
(3) Number of slabs V
(4) Number of slices that overlap between adjacent slabs (overlap number) NO
(5) Slab position

  Such information can be input using a graphic tool, for example. The setting means 81 sets a slab based on the information (1) to (5). FIG. 6 is a diagram illustrating an example of a plurality of set slabs. FIG. 6 shows an example in which two slabs a and b are set.

  The upper side of FIG. 6 shows slabs a and b set on the head, and the lower side of FIG. 6 shows an enlarged view of slabs a and b. Although the upper slabs a and b in FIG. 6 are shown as being vertically long, the lower slabs a and b in FIG. 6 are shown as a substantially square for convenience of explanation.

  The slabs a and b are set so that some regions R0 overlap in order to reduce the signal intensity step at the joint of the slabs.

  FIG. 7 is a detailed explanatory diagram of the slabs a and b. The upper side of FIG. 7 shows the slabs a and b partially overlapped, and the lower side of FIG. 7 shows the slabs a and b shifted in the AP (Anterior-Posterior) direction. ing.

In FIG. 7, the number of slices NS included in one slab is set to 10, the slice thickness ST = 5 mm, and the number of slabs V = 2. Further, the overlap number NO of the overlap region R0 of the slabs a and b is set to NO = 4.
After inputting the above information, the process proceeds to step S3.

  In step S3, the operator determines whether or not the slab setting condition needs to be changed. When it is determined that it is not necessary to change the slab setting conditions, the process proceeds to step S6, and the main scan MS is executed according to the slabs a and b shown in FIG.

  However, the operator may want to change the slab setting conditions before executing the main scan MS. For example, when the operator confirms the scan time before executing the main scan MS and the scan time is longer than expected, the operator may want to reduce the number of slices NS in order to shorten the scan time. In this case, the process proceeds to step S4.

  In step S4, the operator changes the condition input in step S2. Here, it is assumed that the operator changes the slice number NS from NS = 10 to NS = 5 in order to shorten the scan time. The operator operates the operation unit 10 and inputs information for changing the slice number NS from NS = 10 to NS = 5. By inputting this information, the slice number NS can be changed from NS = 10 to NS = 5. FIG. 8 is a diagram for explaining an example of how the slab changes when the number of slices is reduced from NS = 10 to NS = 5.

  FIG. 8A shows slabs a and b when NS = 10 sheets, and FIG. 8B shows slabs a ′ and b ′ when NS = 5 sheets.

  In FIG. 8, the slab thickness is reduced by the amount of reduction in the number of slices. Specifically, when NS = 10 sheets (see FIG. 8A), the slab thickness T of the slabs a and b is T = 5 (mm) × 10 (sheets) = 50 mm, but NS = 5 sheets. Then (see FIG. 8B), the slab thickness T ′ of the slabs a ′ and b ′ is changed to T ′ = 5 (mm) × 5 (sheets) = 25 mm. Therefore, since the slab thickness is halved, the imaging region range R2 defined by the slabs a ′ and b ′ in FIG. 8B is narrower than the imaging region range R1 in FIG. For this reason, in the slabs a ′ and b ′ in FIG. 8B, there is a problem that it is not possible to take an image in the range R1 of the imaging region originally considered by the operator.

Further, in FIG. 8A, since the number of overlaps NS = 10 with respect to the number of slices NS = 10 included in one slab, the overlap number NO = 4, the ratio NO / NS of NO to NS is as follows: Value.
NO / NS = 4/10 = 2/5 (1)

On the other hand, in FIG. 8B, since the number of slices NS = 5 included in one slab is the number of overlaps NO = 4, the ratio NO / NS is as follows.
NO / NS = 4/5 (2)

  Therefore, it can be seen from equations (1) and (2) that the ratio NO / NS value is doubled by changing the number of slices. Since the value of the ratio NO / NS affects the image quality, if the ratio NO / NS value is doubled, the image quality may be deteriorated.

  Therefore, in this embodiment, when the number of slices is changed in step S4, step S5 is provided in order to prevent as much as possible the change in the range of the photographing region and the deterioration of the image quality. Below, step S5 is demonstrated.

  In step S5, the setting means 81 changes the slice thickness and the number of overlaps. Hereinafter, how to change the slice thickness and the number of overlaps will be described.

First, the setting means 81 changes the slice thickness using the following equation (3).
ST2 = ST1 * (NS1 / NS2) (3)
NS1: Number of slices before change
NS2: Number of slices after change
ST1: Slice thickness before changing the number of slices
ST2: Slice thickness after changing the number of slices

In this embodiment, the number of slices before the change is NS1 = 10, and the number of slices after the change is NS2 = 5. The slice thickness before changing the number of slices is ST1 = 5 mm. Therefore, the slice thickness ST2 after changing the number of slices has the following value.
ST2 = 5 * (10/5)
= 10 (mm) (4)

After changing the slice thickness, the setting means 81 changes the overlap number using the following equation (5).
NO2 = NO1 * (ST1 / ST2) (5)
Here, ST1: Slice thickness before changing the number of slices
ST2: Slice thickness after changing the number of slices
NO1: Number of overlaps before changing the number of slices
NO2: Number of overlaps after changing the number of slices

In this embodiment, the slice thickness before changing the number of slices is ST1 = 5 mm. The slice thickness after changing the number of slices is ST2 = 10 (mm) (see formula (4)). Further, the number of overlaps before changing the number of slices is NO1 = 4. Therefore, the overlap number NO2 after changing the number of slices becomes the following value.
NO2 = 4 * (5/10)
= 2 (6)

  Therefore, by changing the number of slices, the slice thickness is changed from ST1 = 5 mm to ST2 = 10 mm, and the overlap number is changed from NO1 = 4 to NO2 = 2. The setting means 81 resets the slabs a and b based on the changed values (5 slices, 10 mm slice thickness, and 2 overlaps). FIG. 9 shows the reset slabs a ′ and b ′.

  FIG. 9A shows slabs a and b before changing the number of slices, slice thickness, and number of overlaps, and FIG. 9B shows the result of changing the number of slices, slice thickness, and number of overlaps. The reset slabs a ′ and b ′ are shown.

  In FIG. 9A, the slab thickness T is T = 5 (mm) × 10 (sheets) = 50 mm, while in FIG. 9B, the slab thickness T ′ is T ′ = 10 (mm). × 5 (sheets) = 50 mm. Therefore, even if the number of slices is reduced, the slab thickness can be maintained by changing the slice thickness using Equation (3).

In FIG. 9A, since the number of overlaps N0 = 4 with respect to the number of slices NS = 10 included in one slab, the ratio N0 / N between NO and NS is as follows: Become.
NO / NS = 4/10 = 2/5 (7)

On the other hand, in FIG. 9B, since the number of overlaps NS = 2 with respect to the number of slices NS = 5 included in one slab, the ratio NO / NS is as follows.
NO / NS = 2/5 (8)

  Comparing equations (7) and (8), it can be seen that the ratio NO / NS is maintained even if the number of slices is changed.

  Therefore, even if the number of slices changes, the imaging region range R2 is held in the same range as the imaging region range R1 by changing the slice thickness and the number of overlaps using equations (3) and (5). be able to. Further, since the ratio N0 / NS is also maintained, it is possible to prevent degradation of image quality as much as possible.

  After changing the slice thickness to 10 mm and further changing the number of overlaps to 2, the process proceeds to step S6, and the main scan is executed. In this way, the flow ends.

  In the present embodiment, as described above, when the operator changes the number of slices, the setting unit 81 changes the slice thickness and the number of overlaps using equations (3) and (5). Therefore, even if the number of slices is changed, the slab thickness T ′ is maintained at the same value as the slab thickness T, and the imaging region range R2 can be maintained in the same range as the imaging region range R1. Further, since the ratio N0 / NS is also maintained, it is possible to prevent degradation of image quality as much as possible.

In the above example, the case where the number of slices NS is changed from 10 to 5 is described, but the case where the number of slices NS is changed from 10 to 8 will be considered below. In this case, the slice thickness ST2 in Expression (3) has the following value.
ST2 = ST1 * (NS1 / NS2)
= 5 * (10/8)
= 6.25 (mm) (9)

Therefore, the overlap number NO2 in the equation (5) is the following value.
NO2 = NO1 * (ST1 / ST2)
= 4 * (5 / 6.25)
= 3.2 (10)

  Therefore, the overlap number is calculated as NO2 = 3.2. However, since the number of overlaps must be an integer, if the number of overlaps is not calculated as an integer value, as shown in equation (10), the first decimal place can be rounded off, rounded down, or rounded up Good. For example, when the first decimal place is rounded off, NO2 = 3. Therefore, the setting unit 81 resets the slabs a and b based on the changed values (eight slices, slice thickness 6.25 mm, and three overlaps). FIG. 10 shows reset slabs a ′ and b ′.

  FIG. 10A shows slabs a and b before changing the number of slices, slice thickness, and number of overlaps, and FIG. 10B shows the result of changing the number of slices, slice thickness, and number of overlaps. The reset slabs a ′ and b ′ are shown.

  In FIG. 10A, the slab thickness T is T = 5 (mm) × 10 (sheets) = 50 mm, while in FIG. 10B, the slab thickness T ′ is T ′ = 6.25 ( mm) × 8 (sheets) = 50 mm. Therefore, even if the number of slices is reduced, the slab thickness can be maintained by changing the slice thickness using Equation (3).

  In FIG. 10, the shooting area range R2 is wider than the shooting area range R1 by ΔR. However, since the value of ΔR is sufficiently smaller than the slice thickness ST, even if the number of slices is changed from 10 to 8, the range R2 of the imaging region is hardly changed from the range R1 of the imaging region. it can.

Further, in FIG. 10A, since the number of overlaps N0 = 4 with respect to the number of slices NS = 10 included in one slab, the ratio N0 / N between NO and NS is the following value: Become.
NO / NS = 4/10 = 2/5 (11)

On the other hand, in FIG. 10B, since the overlap number NO = 3 with respect to the number of slices NS = 8 included in one slab, the ratio NO / NS is as follows.
NO / NS = 3/8 (12)

Therefore, a difference ΔD expressed by the following equation is generated between the equations (11) and (12).
ΔD = (2/5) − (3/8)
= 0.025 (13)

  However, since it can be considered that the value of ΔD (0.025) is sufficiently small, even if NO / NS is increased by ΔD, it is considered that the deterioration in image quality is sufficiently small.

  In this embodiment, an example in which two slabs are set is shown. However, the present invention is not limited to the case where two slabs are set, and can be applied to the case where three or more slabs are set.

  In this embodiment, a case is described in which the number of slices is reduced from 10 to 5 (8). However, the present invention is not limited to the case where the number of slices is reduced, and can be applied to the case where the number of slices is increased. When the number of slices is increased, the slice thickness is reduced so that the slab thickness does not change. Therefore, even when the number of slices increases, the range of the imaging region can be prevented from changing (or the range of the imaging region is not changed as much as possible).

  In this embodiment, a case where adjacent slabs overlap is described. However, the present invention can also be applied when adjacent slabs do not overlap.

2 Magnet 3 Table 3a Cradle 4 Receiving coil 5 Transmitter 6 Gradient magnetic field power supply 7 Receiver 8 Processor 9 Memory 10 Operation unit 11 Display unit 12 Subject 21 Bore 100 MR apparatus

Claims (3)

A slab setting device for setting a plurality of slabs,
Setting means for setting the plurality of slabs based on the number of slices included in each of the plurality of slabs and the slice thickness of the slices;
The setting means includes
When information for changing the number of the plurality of slices is input from an operation unit operated by an operator, the slab thickness of the slab does not change , and the first slab of the plurality of slabs A slab setting device that changes the slice thickness so that a ratio of the number of slices included in a region overlapping with a second slab and the number of slices does not change . A magnetic resonance apparatus comprising the slab setting device according to claim 1 . A program applied to a slab setting device for setting a plurality of slabs,
A setting process for setting the plurality of slabs based on the number of slices included in each of the plurality of slabs and the slice thickness of the slices, from the operation unit operated by an operator, If the information for changing the number of the slice is inputted, slab thickness of the slab is not changed, and the first slab and a region overlapping with a second slab of the plurality of slabs A setting process for changing the slice thickness so that the ratio between the number of included slices and the number of slices does not change ,
A program to make a computer execute.