Physica C 494 (2013) 199–202

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Physica C

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Feasibility study of contaminant detection for food withULF-NMR/MRI system using HTS-SQUID

0921-4534/$ - see front matter � 2013 Elsevier B.V. All rights reserved.http://dx.doi.org/10.1016/j.physc.2013.04.004

⇑ Corresponding author. Tel.: +81 532 44 6908; fax: +81 532 44 6929.E-mail address: hatukade@ens.tut.ac.jp (Y. Hatsukade).

Yoshimi Hatsukade ⇑, Shingo Tsunaki, Masaaki Yamamoto, Takayuki Abe, Junichi Hatta, Saburo TanakaToyohashi University of Technology, 1-1 Hibarigaoka, Tempaku-cho, Toyohashi, Aichi 441 8580, Japan

a r t i c l e i n f o

Article history:Received 18 January 2013Received in revised form 27 February 2013Accepted 5 April 2013Available online 15 April 2013

Keywords:ULF-NMR/MRIHTS-SQUIDContaminant detectionPermanent magnet

a b s t r a c t

We have developed an ultra-low frequency (ULF) nuclear magnetic resonance (NMR) and magnetic res-onance imaging (MRI) system utilizing an HTS-SQUID for an application of contaminant detection in foodand drink. In the system, a permanent magnet of 1.1 T was used to pre-polarize protons in a water sam-ple. We measured NMR signals from water samples with or without various contaminants, such as stain-less steel (SUS304), aluminum, and glass balls using the system. In the case that the contaminant was theSUS304 ball, the NMR signal intensity was reduced compared to that from the sample without the con-taminant due to the remnant field of the contaminant. One-dimensional (1D) MRIs of the samples werealso acquired to detect non-magnetic contaminants. In the 1D MRIs, changes of the MRI spectra weredetected, corresponding to positions of the contaminants. These results show that the feasibility of thesystem to detect various contaminants in foods.

� 2013 Elsevier B.V. All rights reserved.

1. Introduction electronics, Helmholtz-type measurement coil, AC pulse coil, three

In recent years, ultra-low filed (ULF) nuclear magnetic reso-nance (NMR) and magnetic resonance imaging (MRI) have at-tracted attention because it can be compact, easy to handle, andlow running cost, compared to conventional NMR/MRI [1–4]. In astatic field of lT order, the Larmor frequency of 1H proton rangesin kHz order. In such low frequency range, superconducting quan-tum interference devices (SQUIDs) have been used as detectors ofNMR signals, taking advantage of high sensitivity independentfrom frequency. In spite of higher magnetic noise levels than thoseof low-temperature superconductor (LTS) SQUIDs, high-tempera-ture superconductor (HTS) SQUIDs also have been used for theapplication because use of the HTS-SQUIDs would offer potentialmerits when it comes to practical use, such as lower cost, user-friendliness, compactness and portability [5–8]. So far, we haveutilized HTS-rf-SQUID to construct an ULF-NMR/MRI system aim-ing for application to detect contaminant in food and drink. In thispaper, we studied a feasibility of the application of the system bymeasuring 1H-NMR and one-dimensional (1D) MRI signals fromwater samples including various kinds of contaminants, such asstainless steel, aluminum, glass and ceramic.

2. ULF-NMR/MRI system using HTS-rf-SQUID and permanentmagnet

The ULF-NMR/MRI system constructed for this study is shownin Fig. 1. The system consists of an HTS-rf-SQUID, cryostat, SQUID

gradient field coils, permanent magnet, sample transfer apparatus,delay pulse generator, current sources, function generator, andspectrum analyzer. All of the coils in the system are room-temper-ature (RT) coils. The HTS-rf-SQUID is positioned at the bottom ofthe cryostat, in which liquid nitrogen is filled. The RT coils andthe cryostat are located in a magnetically shielded room (MSR)with door opened. The permanent magnet of 1.1 T is located out-side the MSR and about 2 m away from the SQUID. In order to re-duce influence of a leakage field from the magnet on themeasurement field Bm, yoke magnets are arranged around themagnet (see Fig. 1b). With this setting, measured gradients dBz/dx, dBz/dy, and dBz/dz of the leakage field from the magnet at themeasurement position were less than about 1.1 nT/cm, which cor-responded to 0.045 Hz/cm. In NMR measurements, a water sample,which is pre-polarized in the permanent magnet, is transferred tounder the SQUID, and then exposed in a measurement field Bm

from the measurement coil in the z direction. Subsequently, byapplying a 90� pulse field BAC in the y direction from the AC pulsecoil, a free induction decay (FID) signal from the sample is mea-sured by the SQUID. The FID signal is converted to a NMR spectrumby fast Fourier transform (FFT) and recorded by the spectrum ana-lyzer. The system noise level is about 100–120 fT/Hz1/2. The mini-mum liftoff distance between the HTS-rf-SQUID and a transferredsample is about 16 mm. For MRI measurements, one Maxwell coiland two Golay coils are used to generate field gradients dBz/dz, dBz/dx and dBz/dy, respectively. Detail of the coil configuration isdescribed elsewhere [8].

Fig. 2 shows the pulse sequence used to obtain the 1H-NMRsignals from water samples. The pre-polarization field Bp

(a)

1.1 T

200 mm

165

mm

100 mm

(b)

G

y z

x

Spectrum analyzer

Current source for Bm

Gradient adjuster

SQUID reset

TriggerMain trigger

Magnetically shielded room

Head amp.

Delay pulse generator

SQUID electronics

HTS-SQUID

LN2

FG

AC pulse trigger

Bm

BACBpSample

N2 gas

Valve switching

circuit

Valve

Permanentmagnet

Fig. 1. (a) Schematic diagram of HTS-SQUID ULF-NMR/MRI system. (b) Pairpermanent magnet of 1.1 T surrounded by yoke magnets.

16 ms

Transfer duration: 0.5 s

Bp

SQUID reset

Gyz

Measurement

1 ms

5 sor more

Main trigger

BAC

Bm

2 s

0.52 ms

Fig. 2. Pulse sequence for NMR/MRI measurement in ULF.

58 mm

20 m

m

Contaminant (ball)Water

Only Water Water and SUS304 ( 1.0 mm)

Mag

netic

fiel

d [p

T/H

z1/2 ]

Frequency [Hz]

(a)

(b)Fig. 3. (a) Water sample with contaminant (aluminum ball) in a glass bottle. (b)NMR spectra of only water, and water and SUS304 ball of 1 mm in diameter.

Spec

tral p

eak

ampl

itude

raito

Sig

con/S

igw

ater

Contaminant diameter [mm]

Spec

tral p

eak

ampl

itude

raito

Sig

con/S

igw

ater

Contaminant diameter [mm]

(a)

(b)Fig. 4. (a) Relationship between contaminant diameter and signal amplitude incase of SUS304 balls. (b) Relationship between contaminant diameter and signalamplitude in case of aluminum balls.

200 Y. Hatsukade et al. / Physica C 494 (2013) 199–202

pre-polarizes the sample in the magnet for five or more seconds.Then the sample is blown away by means of N2 gas pressure totransfer the sample under the SQUID in about 0.5 s. The measure-ment field Bm is applied always to the measurement position underthe SQUID. After the transfer, a 90� pulse field BAC is applied fromthe AC pulse coil. At 1 ms after applying the BAC, the SQUID is set inthe flux locked mode to measure a FID signal. At 16 ms after lock-ing the SQUID electronics unit, the spectrum analyzer starts to re-cord the signal for 2 s. After recording the FID signal, the spectrumanalyzer converts the FID signal to an NMR spectrum by FFT. In 1D-MRI measurements, a gradient field Gyz (dBz/dy) of 56 nT/cm (cor-responding to 2.4 Hz/cm) is applied to the sample, coincident withthe recording duration.

Only water

with ceramic

(a)

(b)

(c)

(d)Fig. 5. 1D-MRI measurement results. (a) Only water, and water with a ceramic. (b) Water with aluminum ball. (c) Water with glass ball. (d) Water with nylon ball. The balldiameters were 5 mm.

Y. Hatsukade et al. / Physica C 494 (2013) 199–202 201

3. Experiments and results

3.1. NMR measurements

We measured 1H-NMR spectra from tap water samples of 10 mlincluding contaminants using the above-mentioned system andsequence. A glass bottle of 10 ml with length of 58 mm and diam-eter of 20 mm was used as a container. Balls of various contami-nants were put inside of the bottles as shown in Fig. 3a. Eachcontaminant was set in the center of the bottle. In the measure-ments, the samples were pre-polarized for 5 s or more. The mea-surement field Bm of about 45 lT was applied to the samples,which corresponded to the Larmor frequency of about 1914 Hz.The gradient field was not applied. The amplitude and durationof the 90� pulse field BAC were carefully selected to obtain theFID signal with the maximum amplitude using the sample withonly water. The NMR spectra of the sample with only water andwith water and SUS304 ball of 1 mm in diameter are shown inFig. 3b. The NMR signal was measured at about 1914 Hz from thesample with only water, with the line width (full width half max-imum) of about 0.9 Hz. On the other hand, the peak intensity of theNMR signal from the sample with the SUS304 ball of 1 mm indiameter decreased to half value compared to that from onlywater. In the case of SUS304 balls of greater diameter than2 mm, no signal peaks were measured. The relationship betweenthe signal amplitude of the NMR signal from the samples withthe contaminants and size of the contaminant was investigated.The SUS304 balls of 1–2 mm in diameters, and aluminum balls of1–5 mm in diameters were put inside the water sample. The rela-tionship in the case of the SUS304 balls is shown in Fig. 4a. Thespectral peak amplitude was normalized by that of the NMR signalfrom only water. The NMR peak amplitude decreased with the

increase of the SUS304 ball size. Fig. 4b shows the NMR signal peakamplitude from the samples with the aluminum balls as a functionof ball size. In contrast to the SUS304 balls, the NMR peakamplitude did not change with the increase of the ball size. Inthe case of the SUS304 balls, it is thought that remnant magnetiza-tion of the balls disturbed the measurement field, to reduce thepeak amplitudes of the FID signals from the water. Because the alu-minum balls should have little remnant magnetization, it is shownthat it is difficult by the NMR measurements to detect the alumi-num contaminants. The other contaminants, such as glass, ceramic,and polymer, with various sizes were also tested with the NMRmeasurements. The results showed that NMR spectra from thesesamples changed little as the aluminum contaminants.

3.2. 1D-MRI measurements

In order to detect the non-magnetic contaminants, 1D-MRImeasurements were performed. In the measurements, the sameBm (45 lT) was applied to the samples, while the gradient fieldGyz (dBz/dy) of 56 nT/cm (corresponding to 4 Hz/cm) was also ap-plied. Averaging number of all the measurements was one. 1D-MRI spectra of the sample with only water and those with the con-taminants, ceramic, aluminum, glass, and nylon of 5 mm in diam-eters are shown in Fig. 5a–d. In the case of the only water, the linewidth of 1D-MRI signal (broken line) was about 4 Hz. This valuedid not agree with the sample length 5.8 cm, which correspondedto about 14 Hz. The narrow line width of the 1D-MRI signal mustbe attributed to the narrow sensitivity range of the SQUID with awasher ring of about 9 � 9 mm. Compared to the MRI spectrumfrom the only water, the spectra from those with the contaminantschanged around the central frequency of about 1914 Hz, wherecorresponded to the positions of the contaminants. This is because

at 2.4 Hz/cm

at 4 Hz/cm

Fig. 6. 1D-MRI measurement results of water with aluminum ball of 1 mm indiameter at gradient fields of 2.4 and 4 Hz/cm.

202 Y. Hatsukade et al. / Physica C 494 (2013) 199–202

distribution of protons of the water was changed with the exis-tence of the contaminants. It is worth noting that the spectrashapes differed with the different materials. The smallest changein the case of the sample with the nylon ball might be due to thatthe nylon includes 1H protons. From these results, it is shown thatexistence of non-magnetic contaminants can be distinguished andlocalized by the 1D-MRI measurements.

In order to study the detectability of the system, the smallercontaminant, an aluminum ball of 1 mm in diameter, was put in-side the water sample, and the 1D-MRI of the sample was mea-sured by the system, while increasing the field gradient from 2.4to 4 Hz/cm with step of 0.2 Hz/cm. Fig. 6 shows the results withdBz/dy of 2.4 and 4 Hz/cm. At 4 Hz/cm, the signal had a small splitat about 1914 Hz, where the aluminum ball was located, eventhough the maximum signal amplitude was decreased. With dBz/dy of less than 4 Hz/cm, such split did not appear. To detect smallercontaminants less than 1 mm, signal averaging and slice selectionwith another gradient field in x or z direction will be tested.

4. Conclusion

In this paper, the feasibility of the application of the ULF-NMR/MRI system using HTS-rf-SQUID to the contaminant detection wasstudied. The experimental results of the water samples with theSUS304 balls indicate that the magnetic contaminants could be de-tected by the NMR measurements although there has been alreadycontaminant detection system using HTS-SQUIDs [9]. The 1D-MRIexperiments with the non-magnetic contaminants, it was shownthat the non-magnetic contaminants could be detected and local-ized by the 1D-MRI measurements. From these results, the possi-bility of applying the ULF SQUID-NMR/MRI to the contaminantdetection for food and drink was successfully demonstrated.

Acknowledgement

This work was supported in part by the ‘‘Knowledge Hub Pro-ject’’ managed by Aichi prefecture in Japan.

References

[1] R. McDermott, A.H. Trabesinger, M. Mück, E.L. Hahn, A. Pines, J. Clarke, Science295 (2002) 2247.

[2] R. McDermott, N. Kelso, S.-K. Lee, M. Mößle, M. Mück, W. Myers, B. ten Haken,H.C. Seton, A.H. Trabesinger, A. Pines, J. Clarke, J. Low Temp. Phys. 135 (2004)793.

[3] A.N. Matlachov, P.L. Volegov, M.A. Espy, J.S. George, R.H. Kraus Jr., J. Magn.Reson. 170 (2004) 1.

[4] P.L. Volegov, A.N. Matlachov, M.A. Espy, J.S. George, R.H. Kraus Jr., Magn. Reson.Med. 52 (2004) 467.

[5] Y. Zhang, L.Q. Qiu, H.-J. Krause, S. Hartwig, M. Burghoff, L. Trahms, Appl. Phys.Lett. 90 (2007) 182503.

[6] L.Q. Qiu, Y. Zhang, H.-J. Krause, A.I. Braginski, A. Offenhäusser, J. Magn. Reson.196 (2009) 101.

[7] S.Y. Yang, K.W. Lin, J.J. Chieh, C.C. Yang, H.E. Horng, S.H. Liao, H.H. Chen, C.Y.Hong, H.C. Yang, IEEE Trans. Appl. Supercond. 21 (2011) 534.

[8] S. Fukumoto, M. Hayashi, Y. Katsu, M. Suzuki, R. Morita, Y. Naganuma, Y.Hatsukade, S. Tanaka, O. Snigirev, IEEE Trans. Appl. Supercond. 21 (2011) 522.

[9] S. Tanaka, Y. Kitamura, Y. Hatsukade, T. Ohtani, S. Suzuki, J. Magn. Magn. Mater.324 (2012) 3487.