MR imaging providing tissue/blood contrast image

• US 20070265522A1
• Filed: 06/28/2007
• Published: 11/15/2007
• Est. Priority Date: 04/17/1998
• Status: Active Grant

• Current Assignee: Toshiba Medical Systems Corporation (Canon Inc.)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Miyazaki, Mitsue, Kassai, Yoshimori, Sugiura, Satoshi
• Granted Patent: US 8,131,338 B2
• Time in Patent Office: Days
• US Class Current: 600/411
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging
• CPC Class Codes: A61B 5/352 Detecting R peaks, e.g. for synchronising diagnostic apparatus; Estimating R-R interval
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: A61B 5/7285 for synchronising or triggering a physiological measurement or image acquisition with a physiological event or waveform, e.g. an ECG signal A61B6/5205, A61B6/541, A61B8/5207, A61B8/543 take precedence
• CPC Class Codes: G01R 33/4828 Resolving the MR signals of different chemical species, e.g. water-fat imaging
• CPC Class Codes: G01R 33/5605 by transferring coherence or polarization from a spin species to another, e.g. creating magnetization transfer contrast [MTC], polarization transfer using nuclear Overhauser enhancement [NOE]
• CPC Class Codes: G01R 33/5607 by reducing the NMR signal of a particular spin species, e.g. of a chemical species for fat suppression, or of a moving spin species for black-blood imaging
• CPC Class Codes: G01R 33/5615 Echo train techniques involving acquiring plural, differently encoded, echo signals after one RF excitation, e.g. using gradient refocusing in echo planar imaging [EPI], RF refocusing in rapid acquisition with relaxation enhancement [RARE] or using both RF and gradient refocusing in gradient and spin echo imaging [GRASE]
• CPC Class Codes: G01R 33/5617 using RF refocusing, e.g. RARE
• CPC Class Codes: G01R 33/5635 Angiography, e.g. contrast-enhanced angiography [CE-MRA] or time-of-flight angiography [TOF-MRA]
• CPC Class Codes: G01R 33/5673 Gating or triggering based on a physiological signal other than an MR signal, e.g. ECG gating or motion monitoring using optical systems for monitoring the motion of a fiducial marker

Abstract

A magnetic resonance imaging (MRI) system includes an ECG detector for the patient object being imaged and an element for performing an MRI pulse sequence. An imaging unit defined by the pulse sequence is longer in temporal length than one heart beat represented by the ECG signal. An MR signal is acquired from the object in response to the pulse sequence and an MR image based on the acquired MR signal is produced. A plurality of divided MT pulses can be applied instead of the conventional single MT pulse. In this case, an SE-system pulse sequence having a shorter echo train spacing is used, to generate sounds by applying gradient pulses incorporated in an imaging pulse sequence so as to automatically instruct a patient to perform an intermittent breath hold during three-dimensional scanning.

Claims

1. A magnetic resonance imaging (MRI) system comprising:

a scanning unit configured to repeatedly perform a three-dimensional scan to acquire echo data corresponding to a predetermined slice encoding and delay time from a triggering signal that is synchronized with a reference signal representing cardiac phase of an object being scanned; and

an image producing unit configured to produce a three dimensional image of a region of interest of the object based on the acquired echo data.

2. The MRI system of claim 1, further comprising:

a sequence performing unit configured to perform a pulse sequence including (a) a pre-sequence for applying an MT (magnetization transfer) pulse causing MT effects in spins of the object and (b) a data acquisition SE (spin echo) sequence performed after the pre-sequence for generating echo signals in response to a single excitation of the spins by an RF (radio frequency) magnetic field;

wherein said image producing unit is configured to acquire the echo signals generated by performing the pulse sequence for imaging.

3. The MRI system of claim 2, wherein the MT pulse consists of divided MT pulses composing a pulse train, at least one parameter of the number of the divided MT pulses being changeable and chosen from a group of parameters comprising, (a) a flip angle assigned to each of the divided MT pulses and (b) an off-resonance frequency assigned to each of the divided MT pulses.

4. The MRI system of claim 2, wherein the pre-sequence includes a fat-saturation pulse applied after applying the MT pulse for suppressing an echo signal to be acquired from fat of the object.

5. The MRI system of claim 4, wherein the pre-sequence includes a gradient spoiler pulse applied after applying the fat-saturation pulse for dephasing spins of the object.

6. The MRI system of claim 4, wherein at least one of RF pulses forming the MT pulse and the fat-saturation pulse is applied slice-selectively or slice-non-selectively.

7. The MRI system of claim 4, wherein at least one of RF pulses forming the MT pulse and the fat-saturation pulse is applied with a gradient magnetic field for a slice regarding a region to be imaged.

8. The MRI system of claim 2, further comprising:

an electrocardiogram synchronizing unit configured to start the pulse sequence synchronized with an electro cardiogram signal of the object; and

a breath-hold instructing unit configured to instruct the object to stop breathing intermittently according to the electro cardiogram signal.

9. The MRI system of claim 8, wherein said breath-hold instructing unit is configured to supply a pulse for generating a sound by applying a gradient magnetic field to a gradient coil, the pulse for generating the sound being incorporated into the pulse sequence in time series.

10. The MRI system of claim 9, wherein said electro cardiogram synchronizing unit is configured to start the pulse sequence with the predetermined time delay after timing determined by a reference wave of the electro cardiogram signal, and

said breath-hold instructing unit is configured to apply the pulse for generating sound within the predetermined time delay.

11. The MRI system of claim 9 wherein said electro cardiogram synchronizing unit is configured to start the pulse sequence with the predetermined time delay after a reference time determined by the electro cardiogram signal, and

said breath-hold instructing unit is configured to apply the pulse for generating sound in a period of time calculated based on timing of the electro cardiogram signal reference time, the period of time being between two pulse sequences performed intermittently.

12. The MRI system of claim 9, wherein said breath-hold instructing unit is configured to instruct the object to stop breathing intermittently using the sound caused by applying the gradient magnetic field together with a message transmitted to the object by another process.

13. The MRI system of claim 12 wherein said message transmitted b y another process includes at least one of:

(a) a sound signal synthesized by a computer or (b) a visual signal.

14. The MRI system of claim 9, wherein said breath-hold instructing unit is configured to change at least one parameter of:

(a) a switching frequency of a pulse for the gradient magnetic field,

(b) an intensity of the gradient magnetic field to be applied,

(c) a switching duration of the gradient magnetic field and

(d) the number of gradient magnetic fields to be applied.

15. The MRI system of claim 2, wherein the data acquisition SE sequence is formed by a train of pulses in accordance with Fast SE method employing a half-Fourier method.

16. The MRI system of claim-2, wherein the data acquisition SE sequence has refocus RF pulses between which a time interval is set to be a value not more than 6 milliseconds.

17. The MRI system of claim 2, wherein the data acquisition SE sequence is a sequence of which an interval between echoes due to RF pulses is set to be a value not more than 8 milliseconds.

18. The MRI system of claim 1, wherein said scanning unit is configured to perform the three-dimensional scan after applying a fat-saturation pulse for suppressing an echo signal from fat of the object.

19. The MRI system of claim 1, wherein said scanning unit is configured to perform the three-dimensional scan according to a pulse sequence having a gradient magnetic field spoiler for dispersing phases of spins.

20. The MRI system of claim 1, wherein said scanning unit is configured to perform the three-dimensional scan so as to start imaging from a vicinity of k-space center with the predetermined time delay.

21. The MRI system of claim 1, wherein said scanning unit is configured to set an arbitrary value into the predetermined time delay for synchronization with an ECG.

22. The MRI system of claim 1 wherein said image producing unit is configured to obtain a combined image from images of echo data acquired with a chance of phase encoding direction.

23. The MRI system of claim 1, wherein said image producing unit is configured to perform maximum intensity projection processing to data of the three dimensional image.

24. A magnetic resonance imaging method comprising:

repeatedly performing a three-dimensional scan in which echo data is acquired for a corresponding predetermined slice encoding amount and predetermined time delay from a triggering signal synchronized with a reference cardiac wave representing cardiac phase of an object being scanned; and

producing a three dimensional image of a region of interest of the object based on the echo data acquired by the three dimensional scan.