Source: http://www.google.com/patents/US20090174405?dq=7069184
Timestamp: 2017-11-24 22:26:42
Document Index: 108521109

Matched Legal Cases: ['art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 101', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10', 'art 10']

Patent US20090174405 - Magnetic resonance imaging apparatus and magnetic resonance imaging method - Google Patents
A magnetic resonance imaging apparatus includes a generation unit configured to generate a magnetic field, a reconstruction unit configured to reconstruct an image for a subject on the basis of a magnetic resonance signal radiated from the subject in the magnetic field, a presumption unit configured...http://www.google.com/patents/US20090174405?utm_source=gb-gplus-sharePatent US20090174405 - Magnetic resonance imaging apparatus and magnetic resonance imaging method
Publication number US20090174405 A1
Application number US 12/389,700
Also published as US7843194, WO2009072619A1
Publication number 12389700, 389700, US 2009/0174405 A1, US 2009/174405 A1, US 20090174405 A1, US 20090174405A1, US 2009174405 A1, US 2009174405A1, US-A1-20090174405, US-A1-2009174405, US2009/0174405A1, US2009/174405A1, US20090174405 A1, US20090174405A1, US2009174405 A1, US2009174405A1
Inventors Yoshimori Kassai
Original Assignee Yoshimori Kassai
US 20090174405 A1
A magnetic resonance imaging apparatus includes a generation unit configured to generate a magnetic field, a reconstruction unit configured to reconstruct an image for a subject on the basis of a magnetic resonance signal radiated from the subject in the magnetic field, a presumption unit configured to presume a distribution of an image quality deterioration degree occurring in the image on the basis of a precision at which the generation unit generates the magnetic field, and a creation unit configured to create a display image showing the distribution of the image quality deterioration degree on the image.
wherein the creation unit creates a display image showing the distribution of the image quality deter oration degree on the positioning image.
13. The magnetic resonance imaging apparatus according to claim 9, wherein the creation unit creates the display image by partially changing at least one of brightness and chrome of the positioning image in accordance with the distribution of the image quality deterioration degree.
15. The magnetic resonance imaging apparatus according to claim 14, further comprising
This is a Continuation Application of PCT Application No. PCT/JP2008/072179, filed Dec. 5, 2008, which was published under PCT Article 21(2) in Japanese.
Likewise, since the region capable of carrying out the satisfactory imaging is limited, it is important to efficiently use the region for the efficient imaging, but it is difficult to appropriately set the imaging region.
FIG. 1 is a diagram showing a configuration of a magnetic resonance imaging apparatus (MRI apparatus) according to an embodiment of the invention.
FIG. 16 is a diagram showing a Z-axis-direction brightness distribution at a certain position of the image shown in FIG. 15 and the RE magnetic field map obtained on the basis of the brightness distribution.
The receiving unit 9 creates a magnetic resonance signal data on the basis of the output signal obtained from the receiving RE coil 8.
The computer system 10 includes an interface part 10 a, a data collecting part 10 b, a reconstruction part 10 c, a storage part 10 d, a display part 10 e, an input part 10 f, and a main control part 10 g.
The interface part 10 a is connected to the gradient magnetic field power source 3, the bed control unit 5, the sending unit 7, the receiving RF coil 8, the receiving unit 9, and the like. The interface part 10 a is used to input and output signals sent and received between the respective connected units and the computer system 10.
The data collecting part 10 b collects a digital signal output from the receiving unit 9 via the interface part 10 a. The data collecting part 101 stores the collected digital signal, that is, the magnetic resonance signal data in the storage part 10 d.
The reconstruction part 10 c performs a post-process, that is, a reconstruction such as a Fourier transform on the magnetic resonance signal data stored in the storage part 10 d, and obtains a spectrum data or an image data of a desired nuclear spin in the subject 200. The reconstruction part 10 c creates mask data in which a distribution of a static magnetic field strength or a distribution of an RE magnetic field strength is reflected with respect to a region having a reconstructed image with reference to a gradient magnetic field map, a static magnetic field map, and an RF magnetic field map stored in the storage part 10 d.
The storage part 10 d stores the magnetic resonance signal data, the spectrum data, or the image data for each subject. Additionally, the storage part 10 d stores the gradient magnetic field map, the static magnetic field map, and the RE magnetic field map.
The gradient magnetic field map is a data table showing a distortion of an actual gradient magnetic field, generated by the gradient magnetic field coil 2, with respect to an ideal gradient magnetic field. The static magnetic field map shows a spatial distribution of the static magnetic field strength. The RE magnetic field map shows a spatial distribution of the REF magnetic field strength.
The main control part 10 g includes a CPU, a memory, and the like which are not shown in the drawings, and generally controls the MRI apparatus 100. The main control part 10 g has a variety of functions described below as well as a control function for realizing known functions in the known MRI apparatus. One of the functions is to input an allowable deviation amount designated by the operator via the input part 10 f. Another of the functions is to create display data by means of the image data and the mask data obtained by the reconstruction part 10 c.
The gradient magnetic field map shows a relationship for multiple positions in a space where the gradient magnetic field is formed and shows a physical deviation amount between a coordinate (hereinafter, referred to as “a detected coordinate”) obtained from the gradient magnetic field strength for each position and an actual coordinate (hereinafter, referred to as “an actual coordinate”) an the corresponding position. The deviation of the detected coordinate with respect to the actual coordinate occurs respectively in the X-axis, Y-axis, and Z-axis directions. That is, the deviation amount is expressed as a vector amount including deviation amounts dx, dy, and dz in the X-axis, Y-axis, and Z-axis directions. However, in this embodiment, since it is necessary to obtain only the deviation magnitude for the detected coordinate with respect to the actual coordinate, the deviation amount may be expressed as a scalar amount.
FIG. 2 is a diagram showing an example of the gradient magnetic field map. This gradient magnetic field map shows a deviation amount for each position from a position P (0, 0, 0) to a position P (32, 32, 32), where the position P (0, 0, 0) denotes a center of a space where the gradient magnetic field is formed. Additionally, a coordinate value is decided by dividing the width in the X-axis, Y-axis, and Z-axis directions as a target of the gradient magnetic field map by the same interval. Specifically, a region of 3.28×107 mm3 is divided by an interval of 10 mm in the X-axis, Y-axis, and Z-axis directions to thereby obtain the coordinate values up to the coordinate value 32. Then, the deviation amount for each position is expressed by the scalar amount using the unit of mm. For example, at the position P (32, 0, 0), the deviation amount for the detected coordinate with respect to the actual coordinate is 5 mm. Additionally, the range of the coordinate value shown in the gradient magnetic field map may be arbitrarily set. That is, the coordinate value may be expressed as a negative value or a value having a positive value and a negative value. The region indicated by the coordinate value may be smaller or larger than 320 mm3. The interval corresponding to a variation for one coordinate value may be smaller or larger than 10 mm.
Incidentally, the static magnetic field map and the RE magnetic field map are changed due to the influence of the subject 200. Thus, it is desirable that the static magnetic field map an the RF magnetic field map are created on the basis of the magnetic resonance signal collected in a state where the subject 200 is disposed in the imaging space. However, the static magnetic field map and the RF magnetic field map created without considering the existence of the subject 200 substantially show a distribution of an image quality deterioration degree caused by the nonuniformity of the static magnetic field strength distribution or the nonuniformity of the RF magnetic field strength distribution. Accordingly, the static magnetic field map and the RF magnetic field map created without considering the existence of the subject 200 are prepared in advance as a default static magnetic field map and a default RF magnetic field map, and may be used.
Next an operation of the MRI apparatus 100 with the above-described configuration according to a first embodiment will be described.
Before the subject 200 is imaged to obtain a medical diagnostic Image, in Step Sa1, the main control part 10 g controls the respective units so as to image a positioning mage.
That is, the reconstruction part 10 c obtains the deviation amount for the position included in the imaging region from the gradient magnetic field map. Then, the reconstruction part 10 c calculates the deviation amount (hereinafter, referred to as “a pixel distortion”) for each position of pixels forming a reconstruction image on the basis of the deviation amount obtained for each position. Accordingly, the reconstruction part 10 c obtains a map data in which one scalar amount shows the deviation amount for each position of the pixels forming the reconstruction image. Then, the reconstruction part 10 c creates the mask data by performing a binarization process, in which an allowable level (a default value or an operator's designated value) is set to a threshold value, on the map data.
The main control part 10 g creates the display data by combining the mask data with the data showing the positioning image. At this time, it is possible to create the display data showing, for example, the image shown in FIG. 7 by masking the positioning image with the mask data. Additionally, it is possible to create the display data showing, for example, the image shown in FIG. 8 in such a manner that a pixel value for each pixel is adjusted so that a brightness for each pixel on the positioning image is set to n % and a brightness for each pixel shown by the mask data is set to (100−n) %, and the pixel values for the same pixels of both data are added. Additionally, FIG. 8 shows a case where n is set to “70”. In all cases, the brightness for the pixel in the region where the deviation amount is less than the allowable level is 100%. The brightness for the pixel in the region where the deviation amount is not less than the allowable level is reduced to n %. Additionally, in FIGS. 7 and 8, text information showing an imaging condition and the like is displayed while overlapping with the information shown by the mask data and the positioning image.
The above-described image shown by the display data is displayed by the display part 10 e under the control of the main control part 10 g.
(Display of Image Quality Deterioration State Caused by Nonuniformity of Static Magnetic Field Strength)
The static magnetic field map shows a tendency of the static magnetic field strength distribution. Thus, in the same manner as the case of the gradient magnetic field, the main control part 10 g basically creates the mask data by performing the binarization process, in which the allowable level (the default value or the operator's designated value) is set to the threshold value, on the static magnetic field map; creates the display data by combining the mask data with the data showing the positioning image; and then carries out the display based on the display data in terms of the display part 10 e.
However, the gradient magnetic field has, for example, the nonlinearity shown in FIG. 10, and the nonlinearity of the gradient magnetic field is not reflected in the static magnetic field map shown in FIG. 9. Accordingly, FIG. 9 shows the static magnetic field strength distribution for each position of, for example, the image which is shown in FIG. 11 and in which the nonlinearity of the gradient magnetic field is corrected. Then, for this reason, it is not possible to correctly show the static magnetic field strength distribution of, for example, the image which is shown in FIG. 12 and in which the nonlinearity of the gradient magnetic field is not corrected. Additionally, the positioning image is an image in which the nonlinearity of the gradient magnetic field is not corrected.
FIG. 13 is a diagram showing an example of the image obtained by imaging a phantom for a calibration upon installing the MRI apparatus 100. Upon imaging the image shown in FIG. 13, the correction of the nonlinearity of the gradient magnetic field is carried out .
Then, in the same manner as the case of the gradient magnetic field, the main control part 10 g basically creates the mask data by performing the binarization process, in which the allowable level (the default value or the operator's designated value) is set to the threshold value, on the RF magnetic field map; creates the display data by combining the mask data with the data showing the positioning image; and then carries out the display based on the display data in terms of the display part 10 e.
However, in the RF magnetic field map, the influence of the nonlinearity of the gradient magnetic field strength is corrected as above. Accordingly, in the RF magnetic field map shown in FIG. 14, the static magnetic field strength distribution for each position of, for example, the image, which is shown in FIG. 12 and in which the nonlinearity of the gradient magnetic field is not corrected, is not correctly shown.
In FIG. 16, the gentle curve depicted by the dashed line indicates the RE magnetic field strength distribution obtained on the basis of the brightness distribution depicted by the small bent curve shown in FIG. 16. Additionally, in FIG. 16, the gentle curve depicted by the solid line indicates the strength distribution reflected in the RF magnetic field map. For this reason, the RF magnetic field map stored in the storage part 10 d is different from the RE magnetic field strength distribution without the correction of the nonlinearity of the gradient magnetic field.
Thus, the reconstruction part 10 c creates the mask data in such a manner that the influence of the nonlinearity of the gradient magnetic field is removed from the RE magnetic field map stored in the storage part 10 d, and the same binarization process as that of the gradient magnetic field is carried out.
Accordingly, since both the positioning image and the mask data have the distortion caused by the nonlinearity of the gradient magnetic field, it is possible to obtain the display data correctly showing a state where the positioning image is influenced by the nonuniformity of the RE magnetic field strength.
Incidentally, the influence of the nonuniformity of the RF magnetic field is small in an EASE (fast advanced spin echo) and a T2 emphasis (T2W) of a FSE capable of utilizing the condition of a FE and a CPMG (Carr-Purcell-Meiboom-Gill) of a low flip angle, and it is supposed that an attenuation of about 30 to 40% corresponding to an PA (flip angle) is substantially an allowable range. In an SE in which an SNR (signal to noise ratio) is dependent on the pulse of 180°, a signal value is hardly influenced by a variation of about 10 to 20%. Meanwhile, an IR (inversion recovery) pulse and a fat suppression (Fatsat) pulse are largely influenced by the nonuniformity, and the influence is large since the suppression of the fat signal is nonuniform within an error of 10%. The RF magnetic field distribution is changed in accordance with the subject 200.
Next, an operation of the MRI apparatus 100 according to a second embodiment of the invention will be described.
In Step Sa1, after the positioning image is imaged, the main control part 10 g moves the current process to Step Sb1. In Step Sb1, the main control part 10 g determines a region which is not appropriate for imaging the medical diagnostic image (hereinafter, referred to as “an inappropriate region). It is possible to determine the inappropriate region, for example, as a region not more than the threshold value of the mask data according to the first embodiment.
In Step Sb2, the main control part 10 g displays the positioning image obtained in Step Sa1 on the display part 10 e without carrying out the same process as that of the first embodiment. Then, the main control cart 10 g allows the operator to designate a region for imaging the medical diagnostic image on the positioning images. Thus, in Step Sa4, the main control part 10 g sets the imaging region in accordance with the operator's instruction. At this time, the operator designates the imaging region without checking any of the image quality deterioration state caused by the nonuniformity of the RE magnetic field, the nonuniformity of the static magnetic field, or the nonlinearity of the gradient magnetic field. For this reason, the imaging region may be set together with the inappropriate region.
In Step Sb5, the main control part 10 g checks whether the operator requires the change of the imaging region. Then, when the change of the imaging region is required, the main control part 10 g moves the current process from Step Sh5 to Step Sb6.
(1) The reconstruction part 10 c may use a value arbitrarily designated by the operator as the threshold value applied upon creating the mask data showing the range of the image quality deterioration caused by the nonuniformity of the RE magnetic field or the static magnetic field strength. Specifically, it may be supposed that the reconstruction part 10 c uses the threshold value in accordance with the parameter set in advance for a distortion amount or a signal reduction amount which is allowed to designate a precision guarantee range of the MRI apparatus 100. Additionally, the brightness of the mask data upon combining the positioning image with the mask data showing the range of the image quality deterioration caused by the nonuniformity of the RE magnetic field or the static magnetic field strength may be changed in the same manner as the case of the mask data showing the range of the image quality deterioration caused by the nonlinearity of the gradient magnetic field. Specifically, in consideration of the distortion (includes a determination of these directions of the frequency encode and the phase encode) caused by the uniformity of the magnetic field and the distortion caused by the gradient magnetic field as the image quality deterioration degree, for example, the position precision of 3 mm, is set with respect to the distortion caused by the linearity of the magnetic field, and in a portion having the larger distortion on the positioning image, the pixel brightness is reduced by, for example, 50%. Accordingly, it is possible to display a boundary region of a hairline shape and to obtain information on a region having the larger distortion.
On the contrary, in a single-shot EPI method, the requirement for the uniformity of the RE magnetic field is not strict, but the requirement for the uniformity of the static magnetic field is strict due to the image distortion.
(4) The mask data may be created in such a manner that the influence of the nonlinearity of the gradient magnetic field is applied to the static magnetic field map to be distorted, the distorted static magnetic field map is stored in the storage part 10 d, and then the binarization process is performed on the static magnetic field map stored in the storage part 10 d.
(5) The mask data may be created in such a manner that the storage part 10 d stores the distorted static magnetic field map obtained by applying the influence of the nonlinearity of the gradient magnetic field thereto, and the binarization process is performed on the distorted static magnetic field map.
US6144202 * Mar 9, 1998 Nov 7, 2000 Kabushiki Kaisha Toshiba Reduction of MR image degradation due to added gradient field pulse
US8779771 Aug 19, 2011 Jul 15, 2014 Siemens Aktiengesellschaft Magnetic resonance imaging system and method embodying a magnetic resonance marking system and method
US9704053 * Sep 15, 2015 Jul 11, 2017 Siemens Aktiengesellschaft Method and magnetic resonance apparatus for planning a spectroscopy measurement
US20160078616 * Sep 15, 2015 Mar 17, 2016 Siemens Aktiengesellschaft Method and magnetic resonance apparatus for planning a spectroscopy measurement
CN102843965A * Apr 6, 2012 Dec 26, 2012 株式会社东芝 Magnetic resonance imaging device, magnetic resonance imaging method, and medical system
CN103181763A * Dec 29, 2011 Jul 3, 2013 上海联影医疗科技有限公司 Self-adaptive correcting method for magnetic resonance imaging deformation
DE102010039555A1 * Aug 20, 2010 Feb 23, 2012 Siemens Aktiengesellschaft Magnetresonanz-Markierungssystem, Magnetresonanzsystem, Verfahren zum Steuern eines Magnetresonanz-Markierungssystems und Verfahren zur Erzeugung von Magnetresonanzaufnahmen
Cooperative Classification G01R33/56572, G01R33/5659, A61B5/055, G01R33/56563
European Classification G01R33/565P
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:KASSAI, YOSHIMORI;REEL/FRAME:022290/0109