Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Reexamination Certificate
1999-11-24
2002-04-02
Patidar, Jay (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
C324S307000, C324S322000
Reexamination Certificate
active
06366091
ABSTRACT:
TECHNICAL FIELD
This invention relates to a nuclear magnetic resonance imaging (MRI) method for measuring nuclear magnetic resonance (hereinafter referred to as “NMR”) signals from hydrogen, phosphorus, and so forth, in an object, and imaging a density distribution of nuclei and a relaxation time. More particularly, the present invention relates to a method of, and an apparatus for, imaging perfusion of distal blood vessels, etc, with high resolution.
BACKGROUND ART
FMRI (Functional MRI) for extracting local activation of the brain from a slight local signal change of time-series MR images has been put into practical application in recent years. A spin tagging method that applies IR (Inversion Recovery) pulses and then executes imaging by EPI (Echo Planar Imaging) sequences has been studied as one of the FMRI, and methods of applying various IR pulses have been examined, too. Such prior art technologies include SG. Kim “Qualification of relative cerebral flow change by flow-sensitive alternating inversion recovery (FAIR) technique: application to functional mapping”, Magnetic Resonance in Medicine, 34, pp. 293-301(1995), and SG. Kim et al. “Fast interleaved echo-planar imaging with navigator: high-resolution anatomic and functional images at 4 Tesla”, Magnetic Resonance in Medicine, 35, pp. 895-902(1996).
FIG. 9
shows an example of the sequences by the spin tagging method. Initially, an inversion radio frequency pulse (the radio frequency pulse will be hereinafter referred to as the “RF pulse”)
901
is applied simultaneously with a slice selecting gradient magnetic field
902
. The inversion RF pulse, that is known as an adiabatic inversion RF pulse, is employed as the inversion RF pulse
901
because an accurate rectangular excitation shape can be obtained. A slice becomes thinner when the intensity of the slice selecting gradient magnetic field
902
is higher and becomes thicker when the intensity is lower. When the intensity is zero, that is, when no gradient magnetic field is applied, no slice is selected. A region having a desired thickness can thus be excited selectively (tagging).
After the passage of a predetermined time TI
905
from the end of the application of this inversion RF pulse, an EPI sequence
904
shown in
FIG. 2
is executed. In this EPI sequence
904
, after the RF pulse
201
is applied simultaneously with the slice selecting gradient magnetic field
202
, a phase encode gradient magnetic field
203
is applied in the pulse form so that the application amount is different each time. At the same time, a gradient magnetic field
205
in a readout direction is applied repeatedly and inversely so as to measure echo signals
207
. Referring to
FIG. 9
, a time TI
905
from the end of the application of the inversion RF pulse
901
to the irradiation timing of the RF pulse of an imaging sequence
904
is referred to as a “time of inversion”.
In such a spin tagging method, while magnetization of the region selected by the inversion RF pulse is inverted (tagged), spins of bloodstream, etc, migrate from other regions. In consequence, the signals containing the tagged spins and the non-tagged spins in mixture can be acquired in the imaging sequence. Images of perfusion can be acquired by utilizing these signals.
FIG. 10
shows an example of the imaging sequence by applying the spin tagging method to perfusion imaging. This imaging sequence executes once, or iterates continuously, the sequence shown in
FIG. 9
in a predetermined repetition time Tr
906
. In this instance, the first inversion RF pulse (IR pulse
101
) is for slice selection and the second inversion RF pulse (IR pulse
102
) is for slice non-selection. The difference of the image data obtained by these two imaging sequences is calculated, and the local perfusion of the brain in the slice selecting region (slice
1
) can be imaged. Assuming that the repetition time Tr
906
is 2 seconds and the inversion time TI
905
is 1 second in this case, an about 3-second time is necessary because an ordinary single-shot EPI sequence needs about 100 msec time. One image can be acquired for one slice in the predetermined inversion time.
In the slice selecting RF pulse
903
and imaging (
904
) of the slice
1
in
FIG. 10
, the echo signals obtained by imaging are processed by known image processing (such as two-dimensional Fourier transform), giving the image of the slice
1
. This image is generally referred to as the “IR (Inversion Recovery) image”. It is known that the IR image has various texture contrasts depending on the size of TI. When the artery flows from below to up in the object in this image (for example, the cerebral artery branching from the main artery when the transaxial image of the head is imaged), signals resulting from the bloodstream (perfusion) are imparted to the IR image. In imaging of the slice non-selecting RF pulse and the slice
1
shown in
FIG. 10
, too, the echo signals obtained by imaging are processed by known image processing (such as two-dimensional Fourier transform), giving the image of the slice
1
. This image is also a kind of the IR (Inversion Recovery) images. When the artery flows from below to up in the object, however, the signals resulting from the bloodstream (perfusion) of the blood inverted by the IR pulses are imparted to the IR image. The difference of the data between the first image and this image is calculated, and the signals resulting from the object itself can be removed. Inconsequence, only the signals that depend on the bloodstream (perfusion) are imaged.
In order to obtain this IR image, it has been necessary in the past to apply the IR pulses whenever the slice is changed.
In the spin tagging method described above, the inversion time TI from the end of the application of the inversion RF pulse to the application of the RF pulse of the imaging sequence reflects the regions at which the blood arrives during that period of time. Therefore, when setting of the inversion time TI is changed, the image changes, as well. In perfusion imaging by the existing spin tagging method, imaging is conducted by setting appropriately the inversion time TI (for example, to 0.75 seconds) in accordance with the velocity of the bloodstream to be observed. In order to observe the region of a diseased part having a certain expansion such as the cerebral apoplexy, it is preferred that the TI time can be set in various ways to acquire the images.
It has been required to acquire not only one slice but also multiple slices, or three-dimensional images. When the images each having a various TI time are acquired for the multiple slices, for example, the imaging time of (Tr+TI+EPI imaging time)×(number of TI setting times)×(number of slices) is necessary as the time required for a series of imaging, and the imaging time gets elongated.
DISCLOSURE OF INVENTION
In perfusion imaging by utilizing the spin tagging method, therefore, it is an object of the present invention to provide an MRI method, and an apparatus for the method, that can image the moving condition of a bloodstream, the flow velocity of which changes as it flows towards distal ends, over a broad range, and can acquire multi-slices or three-dimensional images within a short imaging time.
It is another object of the present invention to provide an MRI method, and an apparatus for the method, that can acquire perfusion images with high spatial resolution.
An MRI method according to the present invention for accomplishing the objects described above comprises an inversion longitudinal magnetization generation step for generating inversion longitudinal magnetization by applying radio frequency pulses to an object containing magnetization to be detected, and an imaging step for executing continuously a plurality of signal acquisition steps in succession to the inversion longitudinal magnetization generation step.
Here, the signal acquisition step may comprise a sequence capable of acquiring a plurality of signals by one-time excitation of magnetization, and includes a step for irradiating at lea
Shimizu Hiromichi
Takahashi Tetsuhiko
Hitachi Medical Corporation
Patidar Jay
Shrivastav Brij B.
LandOfFree
Nuclear magnetic resonance imaging method and apparatus... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Nuclear magnetic resonance imaging method and apparatus..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Nuclear magnetic resonance imaging method and apparatus... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2830731