JPS63503118A - Device that separates nuclear magnetic signals from a limited area - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Low noise NMR positioning system Gaikyu H again Mame color separation The present invention relates to a contrast imaging system and a spectroscopic system using nuclear magnetic resonance. In its primary application, it extracts NMR from areas of the body with an improved signal-to-noise ratio. Concerning deriving information.

Nine Hill Five Powers In currently implemented magnetic resonance imaging systems, the main noise source is the body. losses in the coil, which far exceed the losses in the coil and the noise in the first amplifier. spin. Therefore, in order to improve the signal-to-noise ratio, it is necessary to connect only one part of the body. surface coils are designed to reduce noise caused by These are from 1982 Clarendon Press (C1arendo) n Press) Publishing Nori, G. Gadian (Nihon Press) Conveniently, these coils perform only on the epidermis, which is close to the surface of the body. Moreover, in September 1985, Medical Physics (Med C published in Volume 12, pages 604-607 of ical Physics), E, high() Iayes) and rl by Axel, 5T magnetism Noise performance of surface coil for resonance imaging ce of 5 surface Coils for Magnetic Re5o Nance Imaging at 1.5T) J As such, the shape of the sensing volume is essentially defined by the diameter of the coil. It is difficult to As a result, it is possible to observe the internal region with a high signal-to-noise ratio or to observe the external and external regions. Currently, it is useful when it is desired to perform localized spectroscopic analysis in a similar area. There are no methods available.

rProceedings published in London in 1985 5ociety of Magnetic Re5onance in Me dicinel shows surface coils using coupled coil pairs in multiple configurations. Two papers have been published. These configurations exhibit several desirable properties. However, it is still concentrated in the epidermal structure. In each case, the most A large sensitivity is shown, and this sensitivity monotonically decreases as the region gets deeper. Therefore, The deeper the region is, the signal is received with a relatively poor signal-to-noise ratio. This is because these This is because the illumination also derives noise signals from the region near the surface. of these coils The combination is not configured to cancel out undesired areas.

And bean scream! i An object of the present invention is to provide a spectral signal with improved magnetic resonance imaging and signal-to-noise ratio. It is.

Yet another object of the invention is to have a sensitivity region that is primarily limited to the desired region. The object of the present invention is to provide an improved system of surface coils that can be used.

Yet another object of the invention is to provide a system of surface coils and a controllable sensitivity area. and associated control amplifiers.

Yet another object of the present invention is to have sensitivity primarily to internal areas of the body and other areas of the body. We provide a system of surface coils with negligible sensitivity over Is Rukoto.

Briefly, according to the present invention, a sensor having different but overlapping sensing regions An array of separated coils is used. The signals from these coils are Demonstrates maximum sensitivity in this region and only marginal sensitivity elsewhere. It is weighted and combined so that it does not occur. This combination and weighting is This can be achieved by directly connecting the signals, or by amplifying and increasing each signal. This can also be achieved by combining widened signals. In this latter case can control the gain or weight of the amplifier to control the area of sensitivity. Ru.

Simple 1 For a more complete understanding of the invention, details of some embodiments may be taken in conjunction with the accompanying drawings. See detailed explanation.

FIG. 1 is a schematic diagram of an embodiment of the invention; FIG. 2 is a diagram illustrating the operation of an embodiment of the invention. Here is a set of curves to illustrate: FIG. 3 is a schematic diagram of an embodiment of the invention using series connected coils; FIG. 4 is a schematic diagram of an embodiment of the invention using a controlled amplifier; and FIG. 5 is a schematic diagram of another embodiment of the invention.

delicious mouth FIG. 1 is a basic block diagram of an embodiment of the invention.

Here each array of one surface coil 11.12.13 is typically a human body. They are spaced at different distances from the object 1o. The signals from these coils are Combined as shown below, they form a sensing area within the object 10. mentioned above As such, the size of this sensing area primarily determines the amount of noise. I mean, This is because human body loss is the main noise source. Therefore, the area in which this area is investigated Existing surface coils should preferably surround this maximum sensitivity near the surface. sensitivity decreases for internal regions. Therefore, these coils , relatively poor signal-to-noise ratio in internal regions for either spectroscopic or chemical shift imaging. Or not give.

This positioning of the sensing region is compatible with NMR positioning procedures using various gradient configurations. It is irrelevant. In these steps, the signal is separated from the volume 10. It will be done. However, these do not affect noise pickup, which basically depends on each component. determined by the combined magnetic field action of the illumination.

In order to receive the signal in the internal region with a good signal-to-noise ratio, the output of the coil is are combined to cancel out the areas. The same noise signal is generated in the connected coils. It is important to understand that this cancellation applies to noise since is important.

As a simple explanation, use only coils 11 and 12 and connect their outputs to the back. It is assumed that they are combined in a matching or canceling relationship. Further, the coil 12 is the coil 1 Assume that it is separated by a distance d from 1 and has twice as many turns as that. 1 individual sensitivity curves are shown in FIG. 2, with the curve for coil 11 indicated at 31. and the curve for coil 12 is shown at 30. The outputs are subtracted from each other. Therefore, the resulting sensitivity curve is shown by a dotted line 32. maximum sensitivity occurs in the desired internal region, and cancellation occurs near the surface of the human body. Note that only the integrated area under curve 32 affects the noise, and Nearby noise is eliminated.

FIG. 3 shows a more general solution for combining the coil signals. here , the outputs of the three coils are summed or combined with opposite polarities to obtain the desired sensing area. area is given. Furthermore, the number of turns of the coil is determined by the relative number of each component as shown in Figure 2. determine the weight. The sum of the coil signals 36 is determined by the classical NMR currently practiced. This becomes the received signal. This is sent to a synchronous demodulator 35, which typically It consists of a product detector driven by the cosine and sine of wave frequencies. revenge The tuned outputs are referred to as I and Q indicating the in-phase and quadrature components.

A more flexible configuration is shown in FIG. Here, the output of each coil is are sent to controlled amplifiers 40, 41 and 42, respectively. These amplifiers are positive or It is controlled to have a negative gain. These are control signals 45, 46 and 45, respectively. 47. These control signals determine the region to be selected . The area selector 43 manually or automatically selects the area with the maximum SN ratio. can be programmed.

The procedure for selecting optimal weights is well known in control theory. desired Assume that the region of interest is designated by f(X). Also, each coil has a sensitivity curve 5 Assume that (X) is formed.

The total sensitivity curve g(x) obtained thereby is expressed by the following equation.

g(x)=a, 5(x)+a, 5(x-x□)+a, 5(x-x,)+, , , ans(x-xn) where a6. ,, an is the weight added to each coil signal. In addition, xl, . . . , xn are the coil spacings. In general, these! Good, good is selected by a well-known procedure to minimize the square size of g(x)−f(x). It will be done. In the case of the system of FIG. 3, the weights a,.

, , an represent the number of turns of the coil.

In the system of Figure 1, the five selection regions are in one dimension perpendicular to the plane of the coil. obtained. However, there are nine examples in which a variety of coil shapes can be used within the scope of the present invention. For example, instead of placing the coil on only one side of the body as in Figure 1, Place coils on both sides of the body to provide flexibility in selecting sensing areas Can be done. Also, as shown in Figure 5, the axis of the coil is spaced perpendicular to the axis of the coil. It can be shifted to provide selectivity. Here, the coils 60, 61 and 62 are Its axis has been shifted. Their output can be assembled to suitably select the selection area. Can be matched.

In the system shown in Figure 4, especially when using high frequencies, the entire system The various cancellations are no longer accurate due to the various phase shifts across the body. Ru. To correct this, a compensating phase shift is introduced into the amplifier chain, and the phase error can be corrected. These can also be introduced into the system shown in Figure 3. Ru. They can also be introduced into the system of FIG. These phase differences It can also be used as part of a spatial selection mechanism.

Generally, resonant coils are used as surface coils to obtain maximum efficiency.

Therefore, in Figures 1, 3, 4, and 5, it is usually referred to as the Larmor frequency. The coil can be made to resonate at the resonant frequency of the system. This frequency is applied to the magnetic field Proportional. Alternatively, the system of FIG. 3 with a pair of coupled coils connected in series The system is a single resonant system. Self-inductance and mutual inductance of addition and subtraction A resonant circuit at the Larmor frequency can be formed using a combination with inductance. can.

Generally, this system provides an improved signal-to-noise ratio when receiving magnetic resonance signals. It is designed to However, a second switch can be placed at signal 36. Ru. In transmit mode, a transmit burst is sent to a series array of coils and the corresponding A spatially selective excitation is applied to the region.

In many imaging and spectroscopy fields, in order to sequence various regions of the body, For example, in projection angiography, where a gradient system is used, a series of parallel planes are Projection of a volume by sequencing and obtaining a projection of each plane each time can be obtained. In order to maximize the signal-to-noise ratio, use the system shown in Figure 4. It is possible to limit the sensing volume to the area of each plane and obtain information about that plane during that time. Wear. This solution can also be used for multiplanar cross-sectional imaging.

When the system is configured to receive signals from a relatively small volume, , the noise due to coil loss is comparable to or exceeds the loss of the human body. Ru. In this case, the signal-to-noise ratio can be further improved by supercooling the receiver coil array. can do good. This is the same cooling system used in the main magnet. This can be achieved using

Pure? (No change in content) FIG.-1 relative sensitivity Procedural amendment (formality) %formula% 1. Indication of incident: PCT/US871008632, title of invention: Low noise N MR positioning system 3, correction person Relationship to the case: Applicant 5. Date of amendment order: Self-issued international search report

Claims (15)

[Claims] 1. A method of receiving nuclear magnetic resonance signals from a volume, comprising: Receive signals from multiple coils, each coil superimposing different parts of the volume. The signal is received from the area where the area is located, and the area where the signal is received is separated. weighted signals, and to form a nuclear magnetic resonance signal with an increased signal-to-noise ratio from a portion of the volume. A method characterized by comprising the step of combining the received signals. . 2. The combining step includes combining at least one of the received signals with at least one Claim 1 comprising the step of subtracting from two other received signals. The method described in. 3. Claim 2, wherein said signals are weighted before the step of combining said signals. The method described in section. 4. The signal is weighted by the number of turns of each of the plurality of coils. The method described in section 3. 5. The step of combining includes the step of connecting the coils to each other. The method described in section. 6. The above combination stage involves feeding the output of each coil to the amplifier and combining the output of the amplifier. 4. A method as claimed in claim 3, including the step of matching. 7. The combining step is such that the region of the volume is imaged with a high signal-to-noise ratio. Claim 1, further comprising the step of sequentially synthesizing various coil combinations. the method of. 8. In a device for receiving a nuclear magnetic signal from a certain volume, a nuclear magnetic signal adjacent to the volume a plurality of coils arranged in the same manner, and means for receiving signals from each coil; Gives high sensitivity to the desired part of the volume and low sensitivity to the undesired part. Combine the received signals above to increase the signal-to-noise ratio of the desired part by giving A device characterized by comprising means. 9. The means for combining said at least one received signal into at least one The apparatus according to claim 8, comprising means for subtracting from other received signals. Place. 10. means for weighting the signals prior to the means for combining the signals; Apparatus according to claim 9. 11. The plurality of coils have a selected number of turns to weight the signals. 11. The device according to claim 10, having: 12. Said means for combining comprises means for connecting the coils to each other. 12. Apparatus according to paragraph 11. 13. The above combining means supplies the output of each coil to an amplifier and the output of the amplifier. 12. Apparatus according to claim 11, comprising means for combining forces. 14. 14. The amplifier according to claim 13, wherein the amplifier has a controlled gain. Device. 15. The above-mentioned combining means is such that various regions of the above-mentioned volume part exhibit high sensitivity. Claim 8, further comprising means for sequentially coupling various coil combinations to the equipment.