Electricity: measuring and testing – Particle precession resonance – Determine fluid flow rate
Reexamination Certificate
2000-09-11
2003-04-15
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Determine fluid flow rate
C324S303000, C324S318000
Reexamination Certificate
active
06549007
ABSTRACT:
The present invention relates to nuclear magnetic resonance phenomena and in particular to the use thereof in imaging and analysis techniques.
This present application describes the development of a low-cost, robust, and fast, on-line nuclear magnetic resonance (NMR) imager (and associated protocols) suitable for imaging a solid object undergoing continuous translational motion. To date, conventional NMR and MRI measurements on solid objects are performed when they are stationary. This prevents the application of NMR imaging methods to objects moving continuously on conveyor belts, or to semi-solid materials being extruded or otherwise ejected. This severely limits the development of MRI as a sensor in an on-line industrial process. In contrast, the NMR techniques and protocols described in this specification are specifically designed to apply to objects in motion and do not succeed unless the object is translating. This distinguishes the present application from previous NMR and MRI approaches.
Conventional MRI velocity measurements on flowing fluids are a possible exception to the statement that conventional NMR methods are performed only on stationary objects. However the protocols used to image fluid flow are not applicable to solid objects moving with constant velocity. In contrast, the techniques described in the present specification can be applied both to solid translating objects and also to flowing fluids.
An on-line imaging technique which is fast, low-cost, robust and fully automated is important in a number of commercial environments. Some conventional MRI techniques, such as echo planar imaging (EPI), are “fast”, with image acquisition times of 100 milliseconds or less, but they require expensive equipment, such as rapidly switched (500 to 2000 Hz), low inductance, strong (10-40 mT m
−1
) gradient generating units, and are not suitable for application in a factory environment and cannot easily be automated. Moreover, motion of an object being imaged during the EPI acquisition time has an adverse effect on EPI image quality. For example, an object of size 5 cm, moving with a velocity of 1 m/s would move its own length (5 cm) if the EPI image acquisition time is 50 ms. In contrast the present specification shows that object motion is essential to the success of the present invention and does not degrade image quality. Moreover the hardware is low cost (relative to today's commercial NMR spectrometers), robust, and can be fully automated.
The present invention exploits a fundamental physical principle of motional relativity, namely, that a time varying magnetic field (or time-varying field gradient) can be applied to an object in either of two equivalent ways. In the first, conventional, way, the object is stationary and the magnetic field is varied in time. In the second way, exploited by the present invention, the magnetic field (or field gradient) is steady, and instead, the object is moved through the field (or field gradient). The latter way has not, hitherto, been exploited for on-line magnetic resonance imaging.
It is an object of the present invention to provide a method for obtaining magnetic resonance imaging data in respect of an object which is undergoing translational motion.
It is a further object of the present invention to provide apparatus for gathering magnetic resonance imaging data on objects passing therethrough.
It is a further object of the invention to provide a method and apparatus for real time monitoring of objects passing through an imaging unit using magnetic resonance imaging techniques.
According to one aspect, the present invention provides a method of nuclear magnetic resonance imaging comprising the steps of:
conveying an object to be imaged through an imaging module at predetermined velocity, v;
generating, within the imaging module, a spatially characterised, constant magnetic field B
0
substantially parallel to the direction of the velocity, v;
generating, within the imaging module, a spatially characterised magnetic field gradient, G
z
substantially parallel to the direction of the velocity, v;
generating, within the imaging module, a radiofrequency field B
1
pulse transverse to field B
0
;
detecting nuclear magnetic resonance signals weighted with at least one selected nuclear magnetic resonance parameter from said object.
According to another aspect, the present invention provides an apparatus for gathering nuclear magnetic resonance imaging data comprising:
a first field generating means for generating a spatially characterised, constant magnetic field B
0
in an imaging unit volume having a predetermined length along a longitudinal axis thereof, the B
0
field being parallel to said longitudinal axis;
a second field generating means for generating, in said imaging unit volume, a spatially characterised magnetic field gradient G
z
substantially parallel to B
0
;
a third field generating means for generating, within the imaging unit volume, radiofrequency field B
1
pulses transverse to field B
0
;
receiver means for detecting nuclear magnetic resonance signals weighted with at least one selected nuclear magnetic resonance parameter from said object;
wherein at least said second field generating means comprises a coil having cylindrical geometry.
According to a further aspect, the present invention provides an apparatus for gathering nuclear magnetic resonance imaging data comprising:
a first field generating means for generating a spatially characterised, constant magnetic field B
0
in an imaging unit volume having a predetermined length along a longitudinal axis thereof, the B
0
field being parallel to said longitudinal axis;
a second field generating means for generating, in said imaging unit volume, a spatially characterised magnetic field gradient G
z
substantially parallel to B
0
;
a third field generating means for generating, within the imaging unit volume, radiofrequency field B
1
pulses transverse to field B
0
;
receiver means for detecting nuclear magnetic resonance signals weighted with at least one selected nuclear magnetic resonance parameter from said object;
wherein at least said second field generating means comprises a coil having adjacent loops thereof separated by a distance which increases or decreases as a function of the distance along the coil axis.
Embodiments of the present invention will now be described, by way of example, and with reference to the accompanying drawings in which:
FIG. 1
shows a schematic diagram showing principles of a nuclear magnetic resonance imaging apparatus according to the present invention;
FIG. 2
shows a schematic diagram of an exemplary RF field generating unit suitable for use in the present invention;
FIG. 3
shows a schematic diagram of an exemplary G
z
field generating unit according to the present invention;
FIG. 4
shows a schematic diagram of an exemplary G
x
field generating unit suitable for use in the present invention;
FIG. 5
shows a schematic diagram of an exemplary G
&phgr;
field generating unit suitable for use in the present invention;
FIG. 6
shows an exemplary pulse sequence suitable for T
2
weighting based on motionally modified spin echoes;
FIG. 7
shows an exemplary pulse sequence suitable for T
1
weighting based on motionally modified inversion recovery;
FIG. 8
shows an exemplary pulse sequence suitable for T
1
and diffusive weighted imaging based on motionally modified stimulated echoes;
FIG. 9
shows an exemplary pulse sequence suitable for diffusion weighting based on motionally modified spin echoes;
FIG. 10
shows an exemplary pulse sequence suitable for T
1
and diffusive weighted imaging based on motionally modified stimulated echoes;
FIG. 11
shows an exemplary arrangement suitable for weighting motional echoes with T
1
(low field) relaxation;
FIG. 12
shows an exemplary pulse sequence suitable for three-dimensional imaging based on motional echoes;
FIG. 13
shows an on-line variation of an echo planar imaging pulse sequence of imaging in the x-y plane;
FIG. 14
is a plot of signal intensity versus time showing pse
Hills Brian Philip
Wright Kevin Michael
Dickstein , Shapiro, Morin & Oshinsky, LLP
Fetzner Tiffany A.
Institute of Food Research
Lefkowitz Edward
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