DD200936A1 - METHOD AND ARRANGEMENT FOR PRESENTING THE SPINDLE DISTRIBUTION IN PARAMAGNETIC SAMPLES - Google Patents

Abstract

The invention relates to the spatial investigation of paramagnetic samples. The aim of the invention is to carry out a non-destructive, spatial investigation of the distribution of paramagnetic centers in samples by means of the EPR. The task is to develop a method that, under the environment of complicated mathematical deconvolution operations, enables the regestration of the 1, 2 and 3-dimensional representation of the EPR center distribution, also of multi-line spectra and the different distribution of different types of centers. According to the invention, a resulting location-dependent and time-dependent field in the z-direction is created without the modulation with two fields of different frequency for the z-planes in phase-sensitive rectification of the signal with a frequency * indp = p ** indn (p = 1,2 , 3 ...) and a formation of the time average over i periods and the signal component from the z indo level is registered. 3a

Description

&. O

Method and arrangement for displaying the spin density distribution in paramagnetic samples

Field of application of the invention

The invention relates to the spatial investigation of paramagnetic samples, in particular

- Transport processes and stationary distributions of paramagnetic centers in solids, their spatial assignment and their diffusion

- studies of metabolic processes and pathological changes in the field of medicine (for example, free radicals in the tumor tissue) and for basic research in the field of molecular biology

- Investigations of real structures in crystals (eg »Distribution of dopants in laser crystals, stress fields at boundary layers)

- in the field of organic chemistry, to study the distribution of paramagnetic centers in high-polarity stability and diffusion measurements) «

Characteristic of the known technical solution

For the nondestructive spatial investigation of non-transparent samples, some have become available in recent years

Methods developed to commercial maturity * These include X-ray tomography, scintigraphy, thermography and ultrasound diagnostics ·

For a long time now, the field of MiR has been working to make this method available for medical whole body examinations. "Most of the research is limited to the study of the distribution of proton resonance of differently mobile water in the human body. Characteristically, the HMRs are significantly larger ₁ and T ₀ times (1O "* ^J S to a few seconds) than in the EPR (10" s to 10 s) * While in the IMR with frequencies in the MHz range (1.5 MHz to 100 MHz) the frequencies for the EPR are in the GHz range (2 GHz to 35 GHz). These differences have led to the development of different methods for acquiring witness -related criteria , so that the methods of MR-witnessmatography fij that were previously available can not or only to a limited extent be applied to the EPR. · An advantage of the EPR over the HMR is the some orders of magnitude higher sensitivity, which makes it possible to meaningfully study the spatial distribution of paramagnetic centers in small samples (- <1 cur) «

Currently known methods in EPR [2j operate with CW microwave irradiation and a constant static or pulsed gradient field. The generation of the gradient field takes place once by approximated Helmholtz coils / 2 J and on the other hand by one-sided beveled pole pieces.

By varying the DC magnetic field B, the resonance condition for each point of the sample is generated one after the other and thus the distribution of the desired centers along the gradient is measured as a function of the field B. The folding product I (B) is separated from the spectrometer by the spectrometer.

tral distribution function g (B), which is characteristic for the investigated center and is determined in the homogeneous field, and the distribution function of the paramagnetic centers S (B) in the sample, registered.

The determination of S (B) must be done by a deconvolution operation. The spatial distribution of the paramagnetic centers can then be determined from S (B). The deconvolution operation, which is not solvable, especially in the case of multi-line spectra and different centers of different distributions, is generally unclear so that the decisive shortcoming of the process is ·

Object of the invention

The aim of the invention is to carry out a non-destructive spatial investigation of the distribution of paramagnetic centers in samples by means of the EPR.

Presentation of the nature of. invention

The object of the invention is to develop a method which allows the registration of the 1-, 2- and 3-dimensional representation of the BPR center distribution, also of multi-line spectra and the different distribution of different types of centers, bypassing complicated mathematical deconvolution operations «

According to the invention, in a method for displaying spin density distributions in a paramagnetic sample in which a high-frequency magnetic field of the frequency coj and the amplitude Bj and a static magnetic field B are applied to the sample to generate the resonance condition and in the

Jr

furthermore a homogeneous alternating field of the amplitude B _n and a second alternating field with location-dependent amplitude in at least one coordinate direction s "B" B (z) long ,? he 7 _; -Aofrs & on. cb'.e Prob «= be laid? whereby the field lines of B, B _n and B _m in the same direction, for example in the z-direction and B ₁ perpendicular to it in the x-direction or y-direction run characterized.rereicht that, to create a location and time-dependent field in z Let the homogeneous field B _n with a frequency <v and the gradient field B (z) with a frequency modulate & _n *, this resulting spatially and time dependent field in the z direction of the mathematical relationship

corresponds, its function ^ ( ⁶ ^ _1n ^) has a periodic course, which corresponds for example to a sine-triangular or sawtooth curve and according to the course of the gradient field B ", (z) on the z-axis one

Zq plane exists, the so-called ITullebene, in which B "(z _n )« 0 and for all other planes z- ^ B (zi / # Z ^)> 0, that a modulation with two fields of different Freauenz o>< gos and co, ';

ΐΐ (ζ ~ · for the zif-planes at phase-sensitive

T2 '

Rectification of the signal with a frequency ω = ρ · ω (ρ = 1,2,3 ·. · ·) And a formation of the time average over i-periods t. ^ = - - (i = 1,2,3, 4 ...) is carried out, which leads to the ^ p-th derivative of a line widened with the modulation amplitude 1 $ , the course of which is determined inter alia by the fact that, for a field, B, the maximum signal amplitude of the pth Derivative of the absorption line not widened with the modulation amplitude B, the signal amplitude increases with increasing

Gendein B value, and from a certain

ΠΙ η

ratio -ψ ¹ - (Δ B _{1 / o} -line width) at the B-value disappears and that only the signal component from the z _n -plane is registered. The modulation amplitude jS determines the maximum signal amplitude of the p-th derivative and also leads to B> 4 B. ^ to a visible modulation broadening which, contrary to the curve for 1L, has a signal maximum at iSj * 2 δ B. _{/ o} for ρ = 1. The increase of Δ Β, however, requires larger modulation amplitudes B if the resolution is not to be degraded «

In order to determine the spin density distribution of a sample in the z-direction, the z- _Q plane is displaced along the z-axis according to the invention »

According to the invention, the displacement of the z _Q plane can be achieved by varying the currents generating the electrode B (z), by shifting the coil pair so that the gradient field is generated or by displacement of the sample along the z axis *

For targeted spectroscopic examination of a plane, according to the invention, the z _Q plane of the gradient field is placed on the plane to be examined and the spectrum for this plane is registered by variation of the static B field, wherein the modulation broadening components of adjacent planes are also registered and by selecting suitable modulation amplitudes B to be separated »

For samples with a multi-line spectrum, the value of the static magnetic field B is placed on the line, which is least influenced by the modulus broadening parts of the other and their signal amplitude at B is most likely to zero as a function of B to register the spin density distribution *

The examination of samples and types of centers of different g-pacts and different distribution is possible by setting the optimum B value for each type of center and recording the distribution of the respective type of center for each type of center.

Purely the representation of the distribution of types of centers of different g-pactors in a sample according to the invention, the B-PeId is set to the optimum for each type of center B value and for this the

Sr

Distribution of the respective center type registered.

An increase in the sensitivity of the method "with only one modulated gradient field v / according to the invention carried out so that its direction about an axis perpendicular to the gradient or the sample at an angle of 0 - rotated 180 °, for each angular position of the gradient direction or the sample 1- registered dimensional projection profiles and the individual projection profiles are assembled by mathematical reconstruction into a 2-dimensional image »

For the generation of 3-dimensional images, two modulated gradient fields are used, for example B _n , (z) and B 1 (y), and a sample rotation is performed about the y-axis so as to vary by gradient field.

starch B _n ; (y) the thickness of the then 2-dimen

sional sample cross-sections to optimize according to the existing in the sample center concentration to allow a 3-dimensional representation.

The rotation of the sample in an EPR resonator leads to projection profiles that are correlated with the By and Ej-Peld distribution in the resonator. "Purely a quick process implementation and evaluation, it is appropriate to use resonance modes that allow the sample in a plane Turning to the

Have symmetrical or approximately constant Bj- Peldverteilungen, so that, for example * when using a cylindrical resonator with a SB ₀₁₁ mode annular sample sections of the same Bj-Peldamplitude exist and that during the rotation of the sample about the cylinder axis (y-axis), the EPR -Zentren are equally spaced from the axis of rotation of the same Bj-Peldamplitude exposed. The rotation of a sample with a high dielectric loss factor and non-rotationally symmetrical sample measurements results in changes in the quality of the cavity resonator with a non-rotationally symmetrical '-field distribution. The use of non-rotationally symmetrical slides (sample receivers) also comes along with it

In a non-rotationally symmetric Ej-PeIdverteilung to shifts in the resonant frequency of the resonator and thus to shift the monetary value B · Both leads to a decrease in the signal intensity of the projection profiles. For non-symmetrical E _T ~ Peld distributions therefore rotationally symmetric slides and for damping samples rotationally symmetric sample measurements are to be used «

For highly attenuating (aqueous) samples, disc-shaped samples are conveniently used and the sample placed in the minimum Ej-PeId of the resonator, eg TE ^ o-mode or TM ^ Q-mode, and the rotation is performed only in the plane of the minimum Ey field in order to produce 2-dimensional images of high sensitivity. Purely a fast sample sampling, especially for 2-dimensional or 3-dimensional representations, the modulation frequency is chosen as large as possible, since the formation of the time average over a period of i-periods - £ ^ = ^ Ξ-ζ-ί = 1 , 2,3 * , which determines the speed of the entire scanning process.

To perform a quick spatial sample examination, the .Probe first with a total of

L Ι όΌ L L

coarse pitch and then selected areas scanned with a Feinrastermaß.

An arrangement for carrying out the method for the preparation of spin density distributions in a paramagnetic sample, in which in a microwave block ,,., Microwave energy in CT ₁ Y-operation is generated, in a resonator a B ^ -FIId the frequency Co ^ above the sample are generated and arranged in the coils for generating a required for the paramagnetic resonance DC magnetic field B, according to the invention constructed so that for generating a homogeneous alternating field B. coils and a modulation generator are arranged, that for generating a gradient field B (z) coaxially to the Coils two gradient coils are mounted, that for signal processing the microwave block in series a microwave detector, an amplifier and a phase-sensitive. Subordinate rectifier, that for controlling the phase relationships between the modulation generator and the phase-sensitive rectifier, a phase shifter is connected, that for forming the time average of the phase-sensitive rectifier is connected downstream of a filter element, that for 1-dimensional representations the Siebglied a DC amplifier is connected downstream, the a writing or viewing device is assigned, that for 2- and - ^ - dimensional representation of the screen member is associated with an analog-to-digital converter, which is followed by an arithmetic unit for further processing and image reconstruction and the visual display of the writing or viewing device of the arithmetic unit is assigned that for generating a modulation frequency co a generator is arranged, that for determining the size of the magnetic field gradient, a power amplifier is connected downstream of the generator, that for z _o ~ plane shift a control unit the Leistungsver is more subordinate, whereby both the generator, the conductor

tion amplifier and the control unit are also the arithmetic unit are assigned, that for sample scanning a device for sample rotation is associated with the resonator, and that for setting the B value, a magnetic field control is arranged _} which is associated with both the coils for the DC magnetic field and the arithmetic unit.

The particular advantage of the method is that it creates a possibility to produce a location-dependent representation of the spin density distribution in a paramagnetic sample by means of the EPR without any mathematical effort for deployment operations. "

Furthermore, there is the possibility of examining selected areas due to the selective nature of the method and recording the spectral distribution function for these areas. * Another particular advantage is the possibility of examining samples with different types of paramagnetic centers and multi-line spectra and their distribution »

embodiment

The invention will be explained on the basis of the 1-dimensional representation of the distribution S (z) of paramagnetic centers parallel to the B-field (z-direction). In the accompanying pictures shows:

Pig, 1 the 1 "derivative of an absorption curve with a Lorentzian shape

2 is a schematic representation of a center distribution of paramagnetic centers S (z) with a corresponding representation of the field distribution B (z, z, t)

£ ö £ O Ό L · 4L ίο

Pig · 3a is a schematic representation of the principle of modulation broadening for the 1 " derivative of a Lorentzian line

Pig. 3b shows a schematic representation of the principle of modulation broadening for the 2 × derivative of a Lorentzian line

Pig. 4a is a schematic representation of a spectrum for the pail that paramagnetic centers with a single-plane spectrum are present in the z _Q plane, according to the example chosen in Pig *

Pig. 4b is a schematic representation of the Pail that in the ζ-plane no paramagnetic centers are present

Pig «5 schematic representation of the sample rotation in a TEq ₁ ^ resonator

Pig. β schematic representation of the rotation of a

disc-shaped sample in a TS _1O p resonator or

Pig · 7 schematic representation of the rotation of a

disk-shaped sample in a TIvL ^ ₀ resonator

Pig. 8 shows a block diagram of an arrangement for rotational guidance of the method for determining the spin density distribution _e

As in Pig. 2, the sample consists of a plurality of strips b, extending perpendicular to the z-direction, of paramagnetic centers of the same type and the same concentration, which are at a distance b from each other.

The absorption curve of these centers should correspond to a Lorentz line.

At constant microwave frequency & / _, amplitude B _T, and variable B-PeId, first the EPR spectrum, whose 1 * derivative is described by function 7 '(B) as shown in Pig «1, for the entire sample registered. In this case, the JB ^ FeId is modulated with a frequency ^ _n and an amplitude β _ir - 3l s / h co ^ £. The SPR signal is detected by phase-sensitive rectification with ^, so that the first derivative of the absorption curve is registered * The value of the DC magnetic field is set to the value B., which corresponds to the maximum signal amplitude of the 1 "derivative, so that

B - B ₁ = B ₀ - (B ₀ = resonance field value)

where Δ Bf _{1 is} the inflection point width for the 1 × derivative of a Lorentz line *

for Lorentz {a - ⁶ I /? ~ Half width) lines and

- ^4B 1/2

This signal amplitude is proportional to the concentration of the paramagnetic centers in the entire sample. "Each volume element of the sample accordingly contributes to this signal amplitude in accordance with the concentration of paramagnetic centers.

To represent the one-dimensional distribution of the concentration of paramagnetic centers in the z-direction, a sinusoidally modulated magnetic field of frequency> and location-dependent amplitude is set B (z) in the z direction to the sample in addition, so that

the following assignment results for the spatially and time-dependent field distribution over the sample

% Ct _t z _9i Zf) -B ₁ * ψ si »C

where ζ = position of the Uull plane of the gradient field for the B _m (z) = 0

ζ ^ = running z-coordinate for the

"R (<7 ο ^> D

For Ct / ^, and tv>, the condition 60? ..; ολ ^ << Γ --- η m '2.

(2p = spin-spin relaxation time)

As the distance of the ζ-plane increases, so does the field increase ^ J ^ 2L. of the modulated gradient, the field change range B dh *, the modulation amplitude 5 * = -22 - S-a'i »ty. _{; i} , ffor the centers outside the ζ-plane »For each sample plane ζ ^ ([^ = + 1 ··· if), a modulation-broadened spectrum is formed according to the concentration of the paramagnetic centers

CS) * .f L t,

if signal processing takes place over a time constant ty ~ - .

Thus, each point of this spectrum represents the time-linear average signal amplitude of the first derivative of the absorption curve at the frequency co (where co _m -> co ) and the amplitude B sampled by the corresponding field point B.

The nature of the "method becomes clear" on the basis of the spectra for the individual levels z 1 shown in FIG. ₃ a. Thus, the modulation with a second frequency OJ ₁ ^ leads to a spectrum whose signal value at the field value B depends on "B _m IΔ B ^ y ₂ decreases.

ISI'Sbl 2

Purely large "B" disappears the signal value

Iu

at this point. In this way it is possible, with a correspondingly large gradient field, to broaden all absorption spectra arising outside the .lambda. Plane in such a way that they no longer contribute any signal at the field value B.sub.i and thus predominantly the signal value from the .sup.-plane can be registered. Shifting the ζ-plane along the z-axis registers the one-dimensional representation of the distribution of the paramagnetic centers in the z-direction *

A second variant of the method consists of determining the spectrum of the paramagnetic centers present there by variations of B for each ζ plane. * Thus, a special spectroscopic characterization of selected sample areas is possible. When recording the spectra, it should be noted that the modulation broadened components of the planes outside of ζ are also registered, the amplitudes of which can be kept sufficiently small with a sufficiently large gradient field. Pig. Figure 4a shows a spectrum for the pail that the ζ plane lies in a layer where paramagnetic centers are present while Pig. Figure 4b shows a spectrum for a ζ-plane lying in a layer in which no paramagnetic centers are present (corresponding to the example chosen in Pig. 2).

If paramagnetic centers with a measuring line spectrum are present in a sample, then the broadening behavior of the multi-line spectrum is used to select the young line which is least affected by the widened portions of the primary bars and whose signal amplitude at the field value B is dependent on the modulation amplitude B on most likely to go to Mull. The selection criterion depends on the size of the signal amplitude at B, the line width ΔB , _{/ o} and the distance from the other lines * The use of the second derivative Y "

However, this can lead to a better resolution at the expense of a lower signal amplitude, since the decrease in amplitude of the widened portions of the Τ · ώχώχώχρ "in the case of Pl Pl Pl ^ ^ MP MP is, in fact, greater than.,-. the first derivative, Pig «3b» The DC magnetic field is set to B = B ₂ = B _Q when registering the distribution of the paramagnetic centers with the 2 * derivative *

The representation of the distribution of different types of centers of different distribution in a sample is only possible if the spectral lines of the different types of centers in the homogeneous B-field are separated, d * h. if the center types possess clearly distinguishable g-factors, lifting a one-dimensional representation of the distribution of paramagnetic centers are also two- and three-dimensional representations of interest »

Taking advantage of the modulated magnetic field gradient, there are basically two ways to do it ». Thus, 2D and 3D demultiplies can be determined by using zv / ei or * three orthogonal modulated graphs.

s \ * S \ s S \ *

served B (z); B _n . (X); B _n , (y) are generated, where

ZZZ

the field line must point in the z direction and the field line density is inhomogeneous in the x or y direction. The scanning of the sample with the null lines or zero point elements produced in this way leads to immediate 2D or zero data processing without major computation.

3D displays. " , - _.

The choice of the modulation frequencies for the individual gradient fields can be different, but the condition ⁶ ^ _m ^< ^ ^co - _a must be observed. The advantage of this method lies in an immediate direct 2D or. 3D registration of the spin density distribution * A significant disadvantage of the method, however, is the decrease in sensitivity with the increase in the number of modulated gradient fields. Upon acceptance of a

£. <JL · OU LC

Sample with h-signaling centers inx, y and z-direction, ie h. Signal elements, is the sensitivity (Ξ)

E ^ - γ- k = 1; 2; 3

k = number of orthogonal gradient fields.

In addition, the technical realization of three orthogonal gradient fields with each y & * » y 0.1 T / cm is very difficult.

Another possibility is that one works only with a modulated gradient field, whose direction is rotated about an axis perpendicular to the gradient at an angle of 0-180 °, Technically easier is the rotation of the sample "Pur each angle setting arise corresponding 1D projection profiles that can be γ / grounded into a 2D image using a mathematical reconstruction program,

Since in the EPR the field and field distributions defined by cavity resonators are generally used for the purpose of increasing the microwave power at the sample location, the distribution of the paramagnetic centers must be greater than that in the resonator be taken into account in the exact determination of the intensity distribution of the paramagnetic centers. A rotation of the sample in this cavity then leads to projection profiles which are correlated according to the respective position of the sample with the associated Bj and Ej distribution. For rapid process performance and evaluation, it is appropriate to use resonant modes that allow the sample to be rotated in a plane having symmetrical or approximately constant Bj-Peld distributions with respect to the axis of rotation, such that der "Β" when using a cylindrical Resonator with TE ₀₁ ^ -Mode, Fig * 5, annular sample sections

and that during rotation of the sample about the cylinder axis (y-axis) the EPR centers are equidistant from the axis of rotation of the same Br field amplitude. "Rotation of a sample with high dielectric dissipation factor and non-rotationally symmetric sample dimensions results In a non-rotationally symmetric Ej ~ field distribution to quality changes of the resonator * Similarly, the use of non-rotationally symmetric slides (sampler) with £ / t ^ in a non-rotationally symmetric Ej field distribution to the shift of the resonant frequency -oj> _{t of} the resonator and thus to the shift of the field value B. Both result in a decrease in the signal intensity and in distortions of the projection profile. Therefore, rotationally symmetric sample dimensions are to be used when rotating the sample about an axis with a non-rotationally symmetric E - field distribution.

When examining highly attenuating (aqueous) samples, it is advisable to arrange them only in areas with low Ej-FeIdstärke, in order to avoid an excessive drop in the resonant quality of the resonator. "The use of resonators with a TE ₁₀₂ - or TlI ₁₁ Q -MOdO lends itself to such samples because they have a plane with a minimum Ej-FeIdstärke, Fig. Β and Fig. 7 »which allows a sensitive measurement of thin, disc-shaped samples * To avoid quality and frequency changes, it is makes sense to rotate the samples only in the plane of the minimum Ej field.

In this way it is possible to work with a high measuring sensitivity and to keep the computational effort for the image reconstruction within limits. Similarly, when determining 3D images, you can use the procedure «Thus z * B _e can be calculated using 2 mo-

dulierten orthogonal gradient fields B "(ζ) and β '(y) and rotation of the sample around the y-axis 2D-Bllder be recorded for each y-plane · According to the concentration of paramagnetic centers in the sample, the width of the y-plane optimized by varying the gradient field strength, in order to enable a meaningful three-dimensional scanning of the sample. The advantage of the last-mentioned approach is the increase in sensitivity. However, this is at the expense of an increased mathematical effort.

The technical realization of the stated method is mainly determined by the generation and control of modulated magnetic fields with high field strength change over the sample. In contrast to the method with static gradients, it is believed that the gradient increase is linear and homogeneous over the sample In the case of modulated gradients, it is important that the * field change is very large in the immediate vicinity of the ITulbene, in order to achieve a large line broadening and thus a high resolution. "It is not necessary for the gradient increase to be linear and homogeneous over the entire sample volume · For a uniform resolution, however, it is necessary that the once selected field change is maintained in the immediate vicinity of the Ifullebene, when moving along the gradient axis · The value of the gradient field strength by ζ depends on the required resolution ·

Since in the EPR generally ^ B-j / p ^ ^, 01 ml, a gradient of -i ~ fe> 0.1 T / cm results at a resolution of ^ i s ^ iO y.

The generation of such gradient fields is z "Z" technically possible only for RF frequencies in the range of 10 Hz to 5000 Hz possible because the frequencies for an optimal signal-to-noise ratio in general for the

C * S £. V VJ £. in the

1, derivative 6 ^ _n1 = 2 7 x 100 kHz or for the second derivative ^ _η2 = ^2ϊΓ 'x 50 kHz, the condition applies

Purely a fast data acquisition it is necessary^as large as possible, since the formation of the temporal linear mean value over at least a period t = must be done. This averaging can be technically realized by a sieve member, in the simplest case an RC element_s its time constantty ^ J "It is also possible from a procedural point of view

πι η

choose"

The time constant of the sieve member is then determined by - * »^^^. However, since the production of PeIdgradienten 0.1 T / cm is also technically very difficult for frequencies above 1 kHz, and the signal-noise performance for u> 7 2 * 1 kHz is cheaper to choose better ^ ™ "" ^ _n *

However, in the interest of rapid spatial detection of the paramagnetic centers in the sample, the method provides the ability to scan the sample with a coarse pitch, i. using low gradient field strengths to scan in a relatively short period »Then, areas of interest can then be scanned with a fine pitch (high gradient field strength)»

A possible arrangement for the implementation of the described method is shown in Pig "8. This involves the recording of 1D projections in each case." By rotating the sample 3 and then performing an image reconstruction with the aid of a computer, 2D and 3D representations can be registered "

In a microwave block 1, the microwave

generates energy (CW operation, which builds up a Βγ field of the frequency j over the sample 3 in a resonator 2. Coils 4 generate the necessary for the paramagnetic resonance C-type magnetic field B. In coils 6 is a modulation generator 5, the homogeneous alternating field B _n generated. The gradient field B _m (z) generate two gradient field coils. 8

The signal processing is effected by means of a microwave detector 9, an amplifier 10 and a phase-sensitive rectifier 11. A phase shifter 12 regulates the phase relationships between the tracking frequency co and the PED 11. The lateral average is formed in a sieve element 13 - in the simplest case an RC element ,

One-dimensional representations can be fed and imaged immediately via a DC amplifier 14 "to a recorder or display device 15. For the formation of 2D and 3D representations, it is necessary to input the obtained data of the individual projections via an analog-to-digital converter 16 into a computer and there to carry out the processing and image reconstruction with suitable mathematical programs. The visual representation then also takes place via a viewing device or a writer.

The second task of the arithmetic unit 17 is the control of the entire image acquisition process, i. 3a. the control of the responsible units. A generator 19 generates the modulation frequency o> of the magnetic field gradient and thus influences the speed of the scanning process. Via a power amplifier 20, the size of the magnetic field gradient and thus the image resolution is determined. The actual sample scanning then takes place with a control unit 21 for the ζ plane displacement and the device for sample rotation 7.

The 3 value is set by means of a magnetic field control 18 and the variation of the B field is carried out during specific spectroscopic investigations of individual sample locations.

Claims (3)

"" Ί S - * invention claim 1. A method for representing spin density distribution in a sample in which a high frequency magnetic field of frequency ° and the amplitude Bj and a static magnetic field B are applied to the sample for generating the resonance condition, and..... Und und und und und und und in which furthermore a homogeneous alternating field of the amplitude B and a second alternating field with location-dependent amplitude in at least one coordinate direction z * B * B (z) is placed along the z axis to the sample, wherein the field lines of B, B and B in the same Direction z 3 in z-direction and By perpendicular to it in the x-direction or y-direction, emei clone t by the fact that to create a location and time-dependent field in the z-direction, the homogeneous field B with a frequency w and the gradient field B (z) with a frequency <^, where oj φ to are modulated, this resulting spatially and time dependent field in the z direction of the mathematical relationship its function ^^ °° _η "^ has a periodic course which corresponds to a sinusoidal triangle or sawtooth curve and, according to the course of the gradient field B (z) on the z-axis, there exists a ζ-plane, the so-called Eullebene, in which B (z) = 0 and for all other planes z ^ -B (z ^ z £ £ ) > 0, that a modulation with two fields of different frequency co <- <r oj and ^ _n ; ^Co _m ^ t _1. ^^ ^ - ^e z ^ planes in the case of phase-sensitive rectification of the signal with a frequency ^ = ρ · ^ _n (ρ = 1,2,3 ···) and a formation of the mean of the average over i Periods (i = 1,2,3j4 ····), Y / as leads to the p-th derivative of a line widened with the modulation amplitude B, the course of which u * a «, being determined by the fact that at a field value B corresponding to the maximum signal amplitude of the p-th derivative of the absorption line, the signal amplitude decreases with increasing 'B value, and at a certain ratio B ** /' «^ ( δ B ₁ / p-line width) at field value B disappears and that only the signal component is registered from the ζ plane» 2β The method of claim 1, characterized in that for detecting the spin density distribution of a sample in the z-direction, the ζ-plane is moved along the z-axis « 3 »method according to claim 2, characterized in that the displacement of the ζ-plane by varying the field B (z) generating currents is performed« 4 »method according to claim 2" ", characterized in that the displacement of the ζ-plane by displacement of the coil pair, which generates the gradient field is performed« 5 «method according to claim 2, characterized in that the displacement of the ζ-plane is carried out by displacement of the sample along the z-axis» 6. The method according to claim 1, characterized in that for the purpose of specific spectroscopic examination of a plane, the ζ-plane of the gradient field is placed on the plane to be examined and by varying the static B-field, the spectrum is registered for this level, wherein the modulations broadening shares adjacent Levels are registered and separated by Y / ahl suitable modulation amplitudes B _m . 7. The method according to claim 1 to 6, characterized in that for the registration of the spin density distribution for a sample with a multi-line spectrum, the value of the static magnetic field B ^ on i. ' the line is least affected by the modulus widening parts of the other lines and whose signal amplitude at B depends on B _m most likely to UuIl » 8 »method according to claim 1 to 7, characterized in that for the representation of the distribution of types of centers of different g-pactors in a sample, the B-PeId set to the optimal for each type of center B value and registers for this the distribution of the respective type of center becomes" 9. Method according to claims 1 to 7, characterized in that in order to increase the sensitivity of the method using only one modulated gradient field whose direction is rotated about an axis perpendicular to the gradient or the sample is rotated from 0-180 ° for each angular position Gradient direction or sample 1-dimensional projection profiles registered and the individual projection profiles are assembled by mathematical reconstruction to a 2 ~ dimensional image * 10 «method according to claim 8 and 9, characterized in that when using SPR cavity resonators, a rotation of the sample is carried out in the resonator, wherein the projection profiles produced are correlated with the B ^ and E_ field distribution in the resonator« 11. The method according to claim 10, characterized in that disc-shaped samples are used for strongly attenuating samples and the sample in the minimal γ-field Z. »5 £« ^ O £ L · 23 of the resonator, ζ · Β · TE .. Q ₂ -Mo de or arranged and the rotation is performed only in the plane of the minimum E _T field. 12. The method of claim 1 'to 11, characterized in that for a fast sample scanning, in particular for 2-dimensional or 3-diinear representations, the modulation frequency is chosen as large as the formation of the time average over a period of i periods ² ^ ^ ZrZ * ^ ⁼ ^ s ² , 3 · »») takes place. 13. The method of claim 1 to 12, characterized in that the sample is first scanned with a coarse grid for rapid spatial sample examination and then selected areas scanned with a Feinrastermaß v / earth « 14 · arrangement for the representation of spin density distributions in a paramagnetic sample, is generated in which in a microwave block microwave energy in the CW operation, in.einem resonator a by-field of frequency - generated by the sample and with the coils for generating a for the paramagnetic resonance necessary Gleichmagnetfeldes B are arranged, characterized in that for generating a homogeneous alternating field B coils (6) and a modulation generator (5) are arranged such that for generating a gradient field B (z) coaxially with the coils (6) two gradient field coils (8) are mounted, that for signal processing the microwave block (1) in series a microwave detector (9), an amplifier (10) and a phase-sensitive rectifier (11) is arranged downstream, that Controlling the phase relationships between the modulation on rat gene or (5) and the phase-sensitive rectifier (11) a phase shifter (12) is connected, that for forming the time average value of the phase-sensitive rectifier (11) is followed by a sieve member (13) in that, for 1-dimensional representations, the filter element (13) is followed by a low-voltage amplifier (14), to which a writing or viewing device (15) is assigned, that for 2- and 3-dimensional representation Siebglied (13) an analog-to-digital converter (16) is assigned to the further processing and image reconstruction of a computing unit (17) is followed and for visual representation of the writing or viewing device (15) of the arithmetic unit (17) is assigned that zvcr Generation of a modulation frequency OJ a generator (19) is arranged, that for determining the size of iJagnetfeldgradien th a power amplifier (20) is connected downstream of the generator (19) t that for ζ -plane shift a control unit (21) the power amplifier (20) is arranged close na, both the generator (iS) j of the power amplifier (20) and the control unit (21) are also associated with the arithmetic unit (17), in that a device for sample rotation (7) is associated with the resonator (2), and in that a magnetic field control (18) is arranged for adjusting the B value, which is applied both to the coils (4) for the direct magnetic field and to the arithmetic unit (17 ) assigned. 15 ° method according to claim 1-7, characterized in that for the determination of 3-dimensional images two modulated gradient fields, e.g. B (z) and B (y) are used and a sample rotation is made about the y-axis. 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