Patent Application
20120126810
The present application relates to the magnetic resonance arts. It finds particular application in using magnetic resonance (MR) to measure pH, and will be described with particular reference thereto.
Typically when measuring pH in a patient, a fluid sample is collected from the patient and taken to a laboratory which measures the pH of the fluid using bench-top laboratory equipment. This approach, however, is limited to samples from a single time point and the measurement may not accurately reflect the pH levels inside an organ of interest.
An electrode directly inserted into the organ of interest can make continuous pH measurements over an extended period of time directly from inside the organ of interest. However, this approach requires an invasive procedure to implant the electrode. pH can also be measured using a magnetic resonance imaging (MRI) or a magnetic resonance spectroscopy (MRS) system. MRI scanners and MRS spectrometers are able to measure pH by measuring the changes in T2 relaxation rate or chemical shift frequency. The changes in the T2 relaxation rate or the chemical shift frequency are proportionally correlated to changes in pH. Unfortunately, this approach requires routine testing and screening using an MRI or MRS scanner which is cumbersome and expensive.
The present application provides a new and improved pH measurement device which overcomes the above-referenced problems and others.
In accordance with one aspect, a pH measurement system is provided. A magnet defines a B0 magnetic field with which selected dipoles preferentially align in an examination region. A orbital angular momentum system endows electromagnetic (EM) radiation with orbital angular momentum (OAM) and transmits the OAM endowed EM radiation to the examination region to at least one of (1) enhance the preferential alignment of the selected dipoles with the B0 magnetic field and (2) excite the aligned dipoles to resonate. A receive coil receives resonance signals from the resonating dipoles. An analysis or measurement unit determines a pH in the examination region by analyzing the resonance signals.
In accordance with another aspect, a method of measuring pH is provided. A B0 magnetic field is defined with which selected dipoles preferentially align in an examination region. Electromagnetic (EM) radiation X is endowed with orbital angular momentum (OAM). The OAM endowed EM radiation is transmitted to the examination region to at least one of (1) enhance the preferential alignment of the selected dipoles with the B0 magnetic field and (2) excite the aligned dipoles to resonate. The resonance signals are received from the resonating dipoles and a pH in the examination region is determined by analyzing the resonance signals.
One advantage resides in the real-time measurement of pH.
Another advantage resides in the reduced size of a MR scanner to measure pH.
Another advantage resides in the reduced cost of MR based pH measurement.
Still further advantages of the present invention will be appreciated to those of ordinary skill in the art upon reading and understand the following detailed description.
The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention.
Orbital angular momentum (OAM) is an intrinsic property of all azimuthal phase-bearing light, independent of the choice of axis about which the OAM is defined. When interacting with an electronically distinct and isolated system, such as a free atom or molecule, OAM can be transferred from the electromagnetic (EM) radiation, such as light, x-rays, or the like to the center of mass of motion.
Various experiments used the interaction of OAM endowed light with matter, for example, optical tweezers, high throughput optical communications channels, optical encryption techniques, optical cooling, entanglements of photons with OAM, and entanglement of molecule quantum numbers with interacting photons' OAM. Because angular momentum is a conserved quantity, the OAM of absorbed photons is transferred in whole to interacting molecules. As a result, the electron states reach saturation spin states, angular momentum of the molecule about its own center of mass is increased and oriented along the propagation axis of the incident light, and magnetrons precession movement of the molecules are oriented along the propagation axis of the incident light. These effects make it possible to hyperpolarize nuclei within fluids by illuminating them with EM carrying spin and OAM.
An analysis of electromagnetic (EM) fields shows that there is a flow of EM energy with a first component that travels along the vector of the beam propagation, and a second component of EM energy that rotates about the axis of the beam propagation. The second component is proportional to the angular change of the potential vector around the beam propagation. This is signification because the rotational energy flow is proportional to the “l”, the OAM value, and the rotational energy transferred to the molecules with which the EM interacts is increase according to the value of the OAM.
When EM carrying spin and OAM is absorbed by molecules, the angular momentum is conserved and the total angular momentum of the system (both the radiation and the matter) is not changed during absorption and emission of the radiation. When a photon is absorbed by an atom, the resulting angular momentum of the atom is equal to the vector sum of its initial angular momentum plus the angular momentum of the absorbed photon.
When a photon interacts with a molecule, only the OAM of the electrons is directly coupled to the optical transitions. The different types of angular momentum are coupled to each other by various interactions such as spin-orbit, spin rotation, hyperfine,
OAM-rotation, and the like. The polarization of the photon flows through the electron orbital to molecule's the nuclear spin, electron spin, and molecular spin via these interactions. The magnitude of the interaction between the photon and the molecule is proportional to the OAM of the photon. Resultantly, the molecular moment aligns in the direction of the propagation axis of the incident light endowed with spin and OAM proportional to that of the OAM content of the incident light.
It is understood that any electromagnetic radiation can be endowed with OAM, not necessarily only visible light. The described embodiment uses visible light, which interacts with the molecules of living tissue without any damaging effects; however, light/radiation above or below the visible spectrum, e.g. infrared, ultraviolet, x-ray, or the like, is also contemplated.
With reference to
After the beam is expanded, the light beam is circularly polarized. A linear polarizer 16 gives the unpolarized light a single linear polarization. A quarter wave plate 18 circularly polarizes the linearly polarized beam by shifting the phase of the linearly polarized light by 1/4 wavelength. Using circularly polarizing light has the added benefit of polarizing electrons.
The circularly polarized light is passed through an adjustable phase hologram 20 which imparts a selectable amount of OAM and spin to an incident beam. The phase hologram 20 maybe physically embodied in a spatial light modulator as a liquid crystal on silicon (LCoS) panel, or it can be embodied in other optics, such as combinations of cylindrical lens or wave plates, or as a fixed phase hologram.
A spatial filter 22 is placed after the phase hologram to selectively block 0th order diffracted beams, i.e. light with no OAM, and allows light with only one OAM value to pass. Since OAM of the system is conserved, it would be counterproductive to let the entire light pass, because the net OAM transferred to the target molecule would be zero.
The diffracted beams endowed with OAM are collected using concave mirrors 24 and focused on an examination region 30 with an objective lens 26. Alternatively, the mirrors 24 may not be necessary if coherent light is employed. Furthermore, the lens may be replaced or supplemented with an alternate light guide, fiber optics, or the like.
The examination region 30 is defined adjacent to the objective lens 26. Magnets 32 are disposed adjacent to the examination region 30 to generate a B0 magnetic field traverse to the path of the OAM endowed radiation emitted by the objective lens 26. The OAM system 10 is pulsed to excite resonance in selected polarized dipoles in the examination region 30 which are preferentially aligned with the B0 field.
In the illustrated embodiment, a second OAM system 10′ directs OAM endowed EM into the examination region 30 to enhance polarization of the selected dipoles. The second OAM system 10′ can be the same as the first OAM system 10 or can include mirrors to re-direct OAM endowed EM radiation from the first OAM system 10 into the examination region 30.
Receive coils 34 receive resonance signals from the polarized dipoles excited to resonance by the OAM endowed EM radiation from the first OAM system 10. A receiver 36 demodulates the signals and a processor 38 in one embodiment determines the magnetic resonance (MR) frequency. The same or another processor 38′ compares the determined resonance frequency with a table, chart, graph, equation, algorithm, or the like from a memory 40 that correlates resonance frequency of the selected dipole with pH. A display 42 displays the pH corresponding to the determined MR frequency for the selected dipole.
In another embodiment, a controller 54 controls the first OAM system 10 to induce spin echoes in the MR signals from the resonating dipoles. The processor 38 determines a rate of decay of the spin echoes, particularly a T2 or T2* relation time, which is compared with relaxation values from a table, chart, graph, equation, algorithm, or the like in the memory 42 which correlate relaxation time values with pH. Alternatively, other types of echoes are contemplated. As another alternative, the relaxation value of the induced resonance signal is measured without inducing echoes.
In another embodiment, the examination region 30 is divided into a plurality of voxels whose pH is each measured. One voxel might correspond to blood and another to a neighboring organ. Spatial encoding is achieved, for example, by gradient magnetic fields produced by weaker, homogeneous magnets, an electromagnetic, or the like. Alternately, the magnets 32 are permanent or electromagnets configured to provide the B0 field with a permanent gradient in one of more directions to achieve spatial encoding or frequency encoding.
With reference to
To acquire a pH measurement of the examination region in a subject, the subject is placed inside the imaging region of the MR scanner. A sequence controller 60 communicates with gradient amplifiers 62 and the OAM device 10″ to induce and manipulate resonance in selected dipoles in the region of interest, for example, repeated echo, steady-state, or other resonance sequences, selectively manipulate or spoil resonances, or otherwise generate selected magnetic resonance signals characteristic of the dipoles in the examination region. The generated resonance signals detected by the RF coil assembly 54, 56 are communicated to an analysis or measurement unit 64. The measurement unit 64 determines the pH value by measuring a change in the relaxation value, e.g. a T2 relaxation rate, determined from the detected resonance signals. A measurement processor 66 of the measurement unit 64 acquires echoes from of the region of interest periodically. The processor 66 compares the T2 relaxation value to a look up table, chart, graph, equation, algorithm, or the like stored in a memory 68 that includes T2 relaxation rate values and corresponding pH values and determines the pH value corresponding to the T2 relaxation value of the received MR signal.
In another embodiment, the pH of unknown dipoles is measured by injecting a known reference dipole into the patient. The sequence controller 60 controls the OAM system 10″ to induce resonance concurrently in both the known and unknown dipoles. Typically, the known and unknown dipoles have different characteristic MR frequencies at the strength of the B0 field. The pH of the reference dipoles is measured as described above and used to correlate relaxation rate of the unknown molecules with pH. The relaxation values of the known reference dipoles is calculated and compared to the look up table stored in memory 68 and a similar table or the like is derived for the unknown dipole by interpolation and extrapolation of a plurality of measured pH values.
In another embodiment, the pH measurement is acquired by measuring changes in the chemical shift values. The processor 66 of the measurement unit 64 calculates the difference between the frequency of the detected resonance signal and the frequency of a reference resonance signal frequency, e.g. the resonance frequency of the measured dipole in the given B0 field at a pH of 7.0. The chemical shift value is determined from a ratio of the frequency difference over the frequency of the reference signal. When measuring the pH of known molecules, the determined chemical shift value is compared to a look up table, chart, graph, equation, algorithm, or the like stored in memory 68 that includes chemical shift values and corresponding pH values.
In another embodiment, the pH of unknown dipoles is measured by injecting a known reference dipole into the patient. The chemical shift of the unknown and reference dipoles are calculated and the chemical shift of the reference dipole is compared to the look up table stored in memory 68. The determined pH for the reference dipole is then attributed to the measured chemical shift of the unknown dipole.
The resultant pH measurement is processed by a video processor 70 and displayed on a user interface 72 equipped with a human readable display. The interface 72 is, for example, a personal computer or workstation. Rather than producing a video image, the pH measurement can be processed by a printer driver and printed, transmitted over a computer network or the Internet, converted to a digital or analog readout, or the like.
In another embodiment, the surface probe device 58 that carries the OAM device is pressed against the carotid artery(s) where it is sufficiently close that the light endowed with OAM will penetrate to the blood inside. As previously mentioned, the OAM device can be used to excite resonance as well as to align or hyperpolarize the nuclei of dipoles in the blood flowing through the region of interest. The resonance from hyperpolarized nuclei is measured with the device 56 as they flow through the subject's bloodstream.
In another embodiment, with reference to
The light from the light source is endowed with OAM by the OAM endowing unit 13. The light endowed with OAM encounters a partially mirrored plate 88 that allows a portion of light to pass to a first objective lens 90. Another portion of light is reflected to a first mirror 92 and on to a second mirror 94 where it then passes through a second objective lens 96, which is oriented orthogonally to the first objective lens. Other optical orientations are possible to arrive at the same result and are also contemplated. Alternatively, the partially mirrored plate 88 can be a fully mirrored shutter which selectively passes the OAM endowed light to each of the objective lens.
In another embodiment, with reference to
The invention has been described with reference to the preferred embodiments. Modifications and alterations may occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be constructed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB2010/053147 | 7/9/2010 | WO | 00 | 1/24/2012 |
| Number | Date | Country | |
|---|---|---|---|
| 61232814 | Aug 2009 | US |
