EP2467730A1

EP2467730A1 - Method for examining the nuclear magnetic resonance in a sample and device for carrying out the method

Info

Publication number: EP2467730A1
Application number: EP10751802A
Authority: EP
Inventors: Raiker Witter
Original assignee: Karlsruher Institut fuer Technologie KIT
Current assignee: Karlsruher Institut fuer Technologie KIT
Priority date: 2009-08-21
Filing date: 2010-08-17
Publication date: 2012-06-27
Also published as: US20120146635A1; DE102009038472A1; US8890520B2; WO2011020590A1

Abstract

The present invention relates to a method for examining the nuclear magnetic resonance in a sample volume located in a measuring volume and to a device for carrying out the method. By means of an excitation laser, a packet of laser pulses is created, which then acts on the measuring volume when a quasi-static magnetic field occurs therein. If the resonance conditions for nuclear spins contained therein are fulfilled, the sample volume emits a response signal that is received by a detector. The quasi-static magnetic field occurring within the measuring volume is provided as follows: i) the measuring volume is acted on by a low-frequency laser beam, the wavelength of which exceeds the wavelength of the excitation laser by at least 10². Thus a periodically variable magnetic field is created in the measuring volume. The amplitude of said field is at least 90% of the maximum thereof in the measuring volume; or ii) the measuring volume is acted on by a high-frequency laser beam, the frequency of which exceeds the frequency of the excitation laser by at least 10². The laser beam is subjected to rectification before acting on the measuring volume. Thus a quasi-static magnetic field is created in the measuring volume, having an effective mean constant flux density over at least 10 periods, wherein the spatial and time average of the flux density are not equal to zero.

Description

Method for investigating nuclear magnetic resonance in a sample and

Apparatus for carrying out the method

The invention relates to a method for investigating the interactions between molecules and electromagnetic fields by means of nuclear magnetic resonance (NMR) and an apparatus for carrying out this method.

Nuclear magnetic resonance spectroscopy and imaging, also referred to as MRI (magnetic resonance imaging), allow the characterization of molecular properties and the identification of atomic constituents of a sample due to interactions between the molecules contained in a sample and magnetic fields.

To generate external magnetic fields required to perform this method, high frequency pulsed fields having an amplitude of up to 100T are used, see e.g. B. Concepts in Magnetic Resonance 19B, 2003, page 9. Although magnetic fields with a higher amplitude would be desirable, but are not achievable in this way. The sensitivity of the nuclear magnetic resonance method is subject to Boltzman statistics and increases with increasing flux density. At room temperature and a flux density of approx. 20 T only one of approx. 10 ⁵ atomic nuclei contributes to the signal. The magnetic field gradients additionally required for spatial resolution are too low below the μm range for micro / nanoscopy and micro / nano-spectroscopy.

According to D. Suter and J. Mlynek, Laser Excitation and Detection of Magnetic Resonance, Adv. In Magn. And Opt. Resonance, 16, pp. 1-12, 1991, find that atomic nuclei in a constant magnetic field experience a break in the symmetry leading to Zeemann splitting. The energy levels formed thereby can be optically excited, manipulated and detected with their fine structure. The use of a This opens up the investigation of new properties, eg. B. another spatial extent, bandwidth or induced emission.

Thus, the invention has for its object to provide a method for studying the nuclear magnetic resonance in a sample and an apparatus for performing this method, which allows a high resolution in the study of nuclear magnetic resonance and in imaging.

In particular, the provision of magnetic fields with very high flux densities as well as magnetic field gradients with very high slopes are the object of the present invention.

The object is achieved with regard to the method by the steps of claim 1 and with respect to the device by the features of claim 6.

Radiation sources that emit synchronized, monochromatic electromagnetic radiation with high spatial and temporal coherence produce magnetic fields of high flux density and amplitude and magnetic field gradients of high slopes. In the frequency range of 10 ⁷ to 10 ¹⁵ Hz, which is of importance for the present invention, suitable lasers, including here the radiation sources referred to as maser in the microwave range, are available; Depending on the selected frequency range, the maser, Teherahertz laser, IR laser, laser in the visible spectral range

or UV laser. Due to their high intensities and frequencies, magnetic fields with an amplitude in the range of 10 ⁴ T to 10 ⁸ T and magnetic field gradients with high slopes in the nm range can be generated with these radiation sources. In this way, the detection of changes in the nuclear spin of individual atoms is possible.

The process according to the invention comprises the steps a) to c). According to step a), a laser suitable for this purpose, which is referred to as an excitation laser, generates at least one packet of laser pulses, but in practice a whole cascade of packets of laser pulses.

According to step b), the at least one packet of laser pulses is emitted in such a way that it acts on the measurement volume in which the sample volume is located at a time when a quasi-static magnetic field ≠ 0 (zero) occurs within the measurement volume. This condition ensures that precisely when there is a quasi-static magnetic field in the measurement volume on the time scale of the excitation laser, the sample is exposed approximately simultaneously to a laser pulse producing a time-varying magnetic field with a flux density B ^.

The basic prerequisite for the detection of a response signal from the sample volume is the fulfillment of the frequency condition, the so-called Larmor condition, for the energetic excitation of nuclear spin levels with an energy difference ΔE as a consequence of an excitation frequency f% _j = Pπ-ωi- irradiated onto the atomic nuclei.

according to

^ E = hγ _Kem B _ϋ , = hω _Xj = hf _{λJ I} (1) where h. is the gyromagnetic moment of the atomic nucleus and to respective B ₀₁ denote the Planck constant, / k _s, the flux density of a (quasi-) static (external) magnetic field.

Now meet at least some nuclear spins contained in the sample, the resonance condition according to Eq. (1), the sample, which is in the prevailing quasi-static magnetic field, emitting a response signal with the energy .DELTA.E in response to each irradiated excitation laser pulse received according to step c) of at least one detector and preferably forwarded to a data processing system for further processing becomes. ' - A -

The magnetic field occurring within the measurement volume is then quasi-static with respect to the time scale of the frequency of the excitation laser within the measurement volume, if it is at

a factor 10 ² , preferably 10 ³ , either slower or faster than the frequency of the excitation laser changes.

In case i), when the magnetic field in relation to the time scale of the

The frequency of the excitation laser changes slowly, is ensured in the following manner, that always a value ≠ 0 for the flux density Boi of the quasi-static magnetic field, in the resonance condition according to Eq. (1) is received

In accordance with measure i), a suitable laser, which is referred to as a field laser, generates a low-frequency first laser beam for this purpose. The wavelength of the low-frequency first laser beam is selected such that it reduces the wavelength of the excitation laser by at least a factor 10 ² , preferably 10 ³ ,

exceeds.

In a preferred embodiment, a field laser is used for this purpose, which emits a low-frequency first laser beam with a wavelength of 10 ⁷ Hz to 10 ¹³ Hz, while the at least one packet of laser pulses is generated by an excitation laser with a frequency of 10 ⁹ to 10 ¹⁵ Hz ,

The low-frequency first laser beam strikes the measurement volume in which the sample volume to be examined is located. As a result, a first, periodically variable magnetic field with a flux density Boi is generated in the measurement volume, and the amplitude of the magnetic field has at least 90%, preferably 95% of its maximum within the measurement volume. The value of the amplitude is determined according to where μo is the magnetic field constant and c is the speed of light.

In case ii), when the magnetic field changes rapidly with respect to the time scale of the frequency of the excitation laser, a vanishing effective flux density Boi _eff = 0 of the quasi-static magnetic field is present on average, so that according to Eq. (1) does not allow a response signal to be observed from the sample volume.

Nevertheless, a quasi-static magnetic field with an effective

To obtain flux density ≠ 0, according to measure ii) the measuring volume with a high-frequency first laser beam whose frequency exceeds the frequency of the excitation laser by at least a factor of 10 ² , preferably 10 ³ , applied. It is crucial that in this case ii) the high-frequency first laser beam is subjected to rectification before the measurement volume is applied, whereby a quasi-static magnetic field is generated in the measurement volume which has an effective mean constant flux density Boieff over at least 10 periods and time average

≠ 0 (zero). Waveforms required for this can be composed of several frequency components analogously to the Fourier analysis.

While in a preferred embodiment the at least one packet of laser pulses is generated by an excitation laser with a frequency of 10 ⁷ to 10 ⁹ Hz, a field laser is simultaneously used, which generates a high-frequency first laser beam with a wavelength of 10 ⁹ to 10 ¹¹ Hz, which is subjected to a conventional and known electronic rectification before it acts on the measuring volume. For higher frequencies, measure ii) is in principle equally suitable; however, no rectifier for the spectral optical range is currently known.

In a particular embodiment, the method according to the invention is configured in such a way that, in addition to the quasi-static magnetic field already present, at least one further quasi-static magnetic field is present in the measurement volume. static magnetic field of flux density Bo _t with 1 = 1, 2, ... is generated.

For this purpose, according to the additional step a ') at least one further laser beam is generated whose wavelength corresponds to the wavelength of the low-frequency first laser beam according to measure i), but the phases of the at least one further laser beam differ from the phase of the low-frequency first laser beam by 90 ° ± 5 °, preferably by 90 °

± 1 °, so that the flux density B _O i of the at least one further laser beam in the measurement volume then shows a zero crossing and thus the highest possible gradient if the flux density of the quasi-static magnetic field according to measure i) has a maximum in the measurement volume.

In the case of measure ii), if a low-frequency first laser beam according to measure i) has not already been used, at least one further low-frequency laser beam can be generated analogously, which then has a zero crossing and thus the highest possible gradient in the measuring volume.

In one embodiment, the first laser beam and the existing further laser beams are aligned parallel to one another.

In another embodiment, existing further laser beams are each aligned orthogonally to the first laser beam. Due to the three-dimensionality of the space, two further orthogonally aligned laser beams can be used to generate gradients in all x and y directions when the z direction is the direction of oscillation of the quasi-static magnetic field generated by the first laser beam.

The at least one further laser beam is either from

one or more other field lasers, each one

emitting a suitable wavelength, generated or by means of at least one in the beam path introduced beam splitter and a π / 2 delay line (phase shifter) from the first laser beam with the same wavelength branched.

In this embodiment, the at least one further laser beam acts on the measuring volume, whereby at least one further, periodically variable magnetic field with a flux density box with i = 1, 2,... Is generated in the measuring volume, each having a gradient. If during step b) a laser pulse with a time-varying magnetic field of flux density Bi hits the measuring volume, the additional presence of the quasi-static magnetic field gradient enables imaging (MRI) whose resolution is limited only by the gradient of the gradient itself.

It should be noted that the sample must be at least partially transparent or reflective in the frequency ranges of the laser beams and laser pulses acting on it in order to be able to generate a detectable response signal.

The invention further relates to an apparatus for carrying out the method according to the invention and includes at least

at least one field laser for generating a first laser beam,

an excitation laser for generating laser pulses, wherein the frequency of the excitation laser exceeds the frequency of the first laser beam by at least a factor of 10 ² or the wavelength of the excitation laser exceeds the wavelength of the first laser beam by at least a factor of 10 ² ,

- means for controlling the relative phase between the field laser and the excitation laser, in particular a trigger, and

- Means for guiding the first laser beam and the laser pulses in a beam path to a measurement volume for receiving a sample.

In a preferred embodiment is in the beam path

Beam splitter and a π / 2 delay line introduced, so that the output of a field laser on at least two laser beams, the then have a phase shift of π / 2, can be divided.

The method according to the invention and the device suitable for carrying it out allow the generation of local magnetic fields and magnetic field gradients with very high flux densities. The resulting sensitivity gain allows nuclear magnetic resonance examinations also on individual atomic nuclei.

The method according to the invention and the device for carrying it out are illustrated below using exemplary embodiments and the figures. Here are shown in detail:

Fig. 1 shows the general measuring principle according to measure i);

Fig. 2 is an enlarged view of Fig. 1;

Fig. 3 shows a simple means for spectroscopy according to

Measure i);

4 shows a device for microspectroscopy according to measure i); 5 shows the general measuring principle according to measure ii);

Fig. 6 enlarged view zυ Fig. 5;

7 shows a simple device for spectroscopy according to measure ii ^);

8 shows a device for microspectroscopy according to measure ii).

The principle of the invention using the measure i) is shown schematically in FIG. The first laser beam having a frequency f _O i, a period τoi and a wavelength γoi radiates on the measurement volume, whereby a quasistatic magnetic field having a flux density Boi is formed over the measurement volume on the time scale of the below-mentioned laser pulses in the z direction.

Furthermore, in FIG. 1, in the direction of the first laser beam, a further laser beam having a frequency f _O2 , a period τo ₂ and a wavelength Y _{02 is} irradiated onto the measuring volume, whereby a further magnetic field in the z-axis of the laser pulses is produced over the measuring volume. Direction with a flux density B ₀₂ forms. Of the second laser beam is offset with respect to its phase for the first laser beam so that a quasi-static zero crossing of the magnetic field B ₀₂ occurs as closely as possible in the center of the sample or at the location of the maximum of the magnetic field of the first laser beam. If the oscillation planes of the two magnetic fields Boi and Bo _{2 are} in the same plane, the gradient of the superposition at this point has the highest slope in the case of the sinusoidal course of the two magnetic fields. From Fig. 1 it can be seen that depending on the frequency fo _Σ , period τ ₀₂ and wavelength γo2, the strength of the magnetic field gradient can be set in the measurement volume.

In the direction of the two laser beams, the measuring volume is then applied with a sequence of laser pulses with a frequency fι, wavelength γi, period τ _lr pulse duration τ _pl and adjustable polarization p _% such that each laser pulse, the measuring volume at the location of the quasi-constant magnetic field B. _O i and the strongest magnetic field gradient - = max or - = max hits. The frequency fι was so dy dx

is chosen to be the frequencies fni and fn? of the two laser beams by at least a factor 10 ² , preferably 10 ³ , exceeds.

If the Larmor condition is in accordance with Eq. 1, at least one sample volume located within the measurement volume, in response to the application, transmits a nuclear magnetic resonance signal detected with a detector directed to the measurement volume.

Fig. 2 shows the situation with the sample volume to be examined and its close environment enlarged. The amplitude- _{constant input pulse} with a frequency f _lf a period T ₁ , a wavelength γi causes from the sample volume out the decaying response signal indicated on the right in the image, which is recorded with the detector.

While in FIGS. 1, 3 and 4 in each case a laser pulse sequence coming from the left in the image is drawn with three or four laser pulses, wherein the third or fourth laser pulse arrives just at the measuring volume, Fig. 2 shows contrast only highlighted this incident laser pulse.

FIG. 3 shows a simplified device for micro / nano-spectroscopy or micro / nanoscopy. About optical media, deflection mirror and semi-transparent mirror, the first laser beam (frequency fo, period τo, wavelength γo) with the laser pulses (frequency f _lr period τ _lr pulse duration τ _plr wavelength γi) together, so that in the measurement volume at the same time the quasi-constant Magnetic field Boi, which is aligned here in the z-direction, and centrally affect the laser pulse on the sample. The laser pulse has at least 10 ² lower period duration than the first laser beam. Also shown are the magnetic field components S _{2 of} the laser pulses with the respectively associated frequencies f _x .

Fig. 4 shows the same structure as Fig. 1, but extended to the representation of the beam sources. On the left in the picture, the two field lasers are shown at the top and bottom for generating the first and second laser beams and in the middle of the excitation laser for generating the laser pulses and four laser pulses, which are on the way to sample. About deflecting mirrors and semi-transparent mirror, the two light beams and the laser pulses are brought together and directed to the measurement volume. The type of beam deflection is exemplified, with a different arrangement is possible, as long as the merging and localization of the two laser beams and the laser pulses are guaranteed in the volume of the sample to be examined.

A model calculation for laser fields should clarify the functionality of the method according to the invention in relation to measure i) quantitatively. For local generation of the on the time scale of the laser pulses quasi-constant magnetic field B ₀ in the range of the measuring volume are as field lasers an IR laser with the operating frequency f _O i = 10 ¹³ Hz and as excitation laser a pulsed UV laser (τ _P1 = ICT ¹⁴ s) with an operating frequency

fi = 10 ¹⁵ Hz used.

Using Eq. 1 gives the magnetic field strength for proton resonance {γp _roton = 42.5 ^# 10 ⁶ MHz / T) at maximum laser amplitude

B _0] = ^ ± ~ \ SOAdT. (3)

ΥKern

The laser field intensity is

The magnetic field gradient can be calculated by assuming

B ₀ 2 ~ B ₀₁ and Y02 & Yoi too estimated. In order for the energy levels to be excited, there is a corresponding excitation width required, it is confirmed that the pulse is shorter than the period of B ₀ . This results in an estimated excitation pulse (90 ° pulse length) of 10 ^"14 s.

It follows for the value of the field strength B ₁

0.25 «/" £, -1 (T ¹⁴ S → B _x = 59OkT. (7) For the intensity of the UV laser thus arises

In the following Table 1, orders of magnitude of some field properties with non-rectified B _0I -FeId are given:

The principle of the invention using the measure ii) is shown schematically in Fig. 5. The first laser beam with a frequency foi, a period τoi and a wavelength γoi is rectified and radiates to the measurement volume, whereby ü over the measurement volume on the time scale of the below-mentioned laser pulses in the z-direction, a quasi-static magnetic field with a flux density Boieff trains.

Furthermore, 5, in FIG. Y ₀₂ irradiated in the direction of the first laser beam, a further non-rectified laser beam having a frequency Jf _02, a period τo ₂ and a wavelength on the measuring volume, whereby over the measurement volume on the time scale of the laser pulses, a further magnetic field in z-direction with a Flußdich- te B ₀₂ trains. The second laser beam is arranged so that a quasi-static zero crossing of the magnetic field B ₀₂ occurs as accurately as possible in the center of the sample volume.

From FIG. 5 it can be seen that, depending on the frequency f ₀₂ , period Xo ₂ and wavelength γo _Σ , the strength of the magnetic field gradient in the measurement volume can be set.

In the direction of the two laser beams, the measurement volume will now _lt comprising a sequence of laser pulses with a frequency f wavelength γ _lr period Ti, pulse duration τ _pl and adjustable polarization pι applied such that each laser pulse the measurement volume at the location of the quasi-constant magnetic field B _O i _eff and the strongest magnetic field gra- dB _m dB _m

served - = max or - = max hits. The frequency was fι dy δx

is chosen such that it exceeds the frequency fo _{2 of} the second laser beam by at least a factor 10 ² , preferably 10 ³ . In contrast, the frequency f ₀₁ exceeds the frequency f _λ by at least a factor 10 ² , preferably 10 ³ .

Fig. 6 shows the situation with the sample volume to be examined and its close environment enlarged. The magnified highlighted amplitude _{constant input pulse} with a frequency £ χ, a period τ _lf a wavelength γi causes from the sample volume out the decaying response signal indicated on the right in the image, which is recorded with the detector.

FIG. 7 shows a simplified device for micro / nano-spectroscopy or micro / nanoscopy. Optical media, deflecting mirrors, rectifiers and semitransparent mirrors make the first te laser beam (frequency fo, period τo, wavelength γo) with the

Laser pulses (frequency f _lr period τ _lt pulse duration τ _p i, wavelength Yi) together, so that in the measuring volume simultaneously the quasi-constant magnetic field Boi _eff , which is aligned here in the z-direction, and centrally the laser pulse acting on the sample. The laser pulse has at least 10 ² longer periods than the first

Laser beam. Also shown are the magnetic field components B ± the laser pulses with the respective associated frequencies f _± .

Fig. 9 shows the same structure as Fig. 5, but extended to the representation of the beam sources. On the left in the picture, the two field lasers are shown at the top and bottom for generating the first and second laser beams and in the middle of the excitation laser for generating the laser pulses. About deflecting mirror, a rectifier and semi-transparent mirror, the two light beams and the laser pulses are brought together and directed to the measurement volume. The nature of

Beam deflection is exemplified, with a different arrangement being possible as long as the merging and localization of the two laser beams and the laser pulses in the volume of the sample to be examined are ensured.

An exemplary calculation for the measure ii) under the conditions with rectification of Boi is intended to illustrate the inventive method quantitatively. For the local generation of the effective quasi-static magnetic field Boi _eff , an IR laser with the operating frequency foi = 10 ¹³ Hz and an for the

Excitation signal a pulsed maser (τ _P1 & 10 ^'10 s, foi ~ 101 ³ Hz) of the operating frequency fi = 10 ¹¹ Hz used.

Using Eq. 1 results in the magnetic field strength for proton nuclear magnetic resonance (γ _P ro _t on = 42.5 to 10 ⁶ MHz / T) ξ≤ and an averaging factor 1.0 to

B _ow = ξ-B ₀₁ = ^ - ISkT. 9)

7Kern The laser field intensity with ξ = 0.64 is:

/ ^• Oi -L ~ s. GW

B Ol «64

² Mo μm 2 ^* 10)

The magnetic field gradient can be measured using B ₀₂ ~ 10 -3 B _O i and γo ₂

10 ³ Vi are estimated as:

(H)

In order for the energy levels to be excited there is a corresponding excitation width of

Δ /; ~ IO- ³ / _ol = ¹⁰ Hz Hz. 12). The result is an estimated excitation pulse (90 ° pulse length) of 10 ^{~ 10} s. This results in a value of

0.25 "/" 5, -1 (T ¹⁰ S → B, = S9T (13)

For the intensity of the measles thus arises

B; kW

«410 i4)

2 μ ₀ μm 2 ^* : In the following Table 2, orders of magnitude of some field properties with the same B _0I -feed are given:

There is freedom of construction. If you set z. As optical fibers to produce laser radiation, not necessarily several laser sources are required, which must be triggered on each other, since the radiation of a single source with different fiber arrangements can be adjusted accordingly.

It is also possible to generate a defined phase position of different polarization states, such that the phase-sensitive quadrature detection customary in NMR (see, for example, US Pat.

Electronics Letters, 15, 1979, 615).

Claims

claims

Method for the examination of nuclear magnetic resonance in a sample volume which is located in a measuring volume

with the steps

a) generating at least one packet of laser pulses by means of an excitation laser,

b) applying the at least one packet of laser pulses to the measurement volume in such a way that it acts on the measurement volume if a quasi-static magnetic field occurs within the measurement volume, whereby the sample volume in the measurement volume, provided the resonance conditions for it are present containing nuclear spins are satisfied, a response signal is emitted to the at least one packet of laser pulses, and

c) receiving the response signal from the sample volume in at least one detector,

wherein the quasi-static occurring within the measuring volume

Magnetic field is provided by that

i) the measurement volume is applied to a low-frequency first laser beam whose wavelength exceeds the wavelength of the excitation laser by at least a factor 10 ² , whereby a periodically variable magnetic field with a flux density Boi is generated in the measurement volume, and at least the amplitude of the magnetic field within the measurement volume Has 90% of its maximum, or

ii) the measurement volume is subjected to a high-frequency first laser beam whose frequency exceeds the frequency of the excitation laser by at least a factor 10 ² , wherein the laser beam is subjected to rectification before the measurement volume is applied, whereby a quasi-static magnetic field is generated in the measurement volume , which has an effective mean constant flux density Boieff over at least 10 periods, their spatial and temporal mean is not equal to zero.

2. The method of claim 1, wherein the quasi-static magnetic field by measure (i) is provided by the at least one packet of laser pulses from an excitation laser having a frequency of 10 ⁹ to 10 ¹⁵ Hz is generated and the low-frequency first laser beam of a first field laser with a frequency of 10 ⁷ to 10 ¹³ Hz is generated.

3. The method of claim 1, wherein the quasi-static magnetic field by the measure (ii) is provided by the at least one packet of laser pulses from an excitation laser having a wavelength of 10 ⁷ to 10 ⁹ Hz is generated and the high-frequency first laser beam of a

first field laser with a wavelength of 10 ⁹ to 10 ¹¹ Hz generated and subjected to an electronic rectification.

4. The method according to any one of claims 1 to 3, wherein at least one further laser beam is generated whose wavelength corresponds to the wavelength of the low-frequency first laser beam and the phase of the at least one further laser beam from the phase of the low-frequency first laser beam by 90 ° ± 5 ° differs, and the measuring volume during step b) is applied simultaneously with the at least one further laser beam, whereby at least one further periodically varying magnetic field is generated in the measuring volume with a flux density B _O i with i = 1, or 3, which has a gradient.

5. The method of claim 4, wherein the at least one further laser beam either

- Is generated by at least one additional additional field laser or

by means of at least one beam splitter introduced into the beam path and a π / 2 delay line from the derfrequenzed first laser beam is diverted.

6. Apparatus for carrying out the method according to one of claims 1 to 5, comprising

at least one field laser for generating a first laser beam,

an excitation laser for generating laser pulses,

- means for controlling the relative phase between the field laser and the excitation laser and

7. Apparatus according to claim 6, wherein in the beam path in addition at least one beam splitter and at least one delay line are introduced.

8. Apparatus according to claim 6, further comprising at least one

Rectifier is present.