Abstracts – BMT 2019 – Frankfurt am Main, September 25–26 • DOI 10.1515/bmt-2019-6008 Biomed. Eng.-Biomed. Tech. 2019; 64(s2): S36–S40 • © by Walter de Gruyter • Berlin • Boston S36

Quantitative 1d-reconstruction of magnetic nanoparticles using magnetorelax- ometry and optically pumped

Aaron Jaufenthaler, Institute of Electrical and Biomedical Engineering, Private University for Health Sciences, Medical Informatics and Technology (UMIT), Hall in Tirol, Austria, [email protected] Thomas Middelmann, Department Biosignals, Physikalisch-Technische Bundesanstalt, Berlin, Germany, [email protected] Maik Liebl, Department Biosignals, Physikalisch-Technische Bundesanstalt, Berlin, Germany, [email protected] Dietmar Eberbeck, Department Biosignals, Physikalisch-Technische Bundesanstalt, Berlin, Germany, [email protected] Daniel Baumgarten, Institute of Electrical and Biomedical Engineering, Private University for Health Sciences, Medical Informatics and Technology (UMIT), Hall in Tirol, Austria, [email protected]

Magnetic nanoparticles (MNP) offer a large variety of promising applications in medicine thanks to their exciting phys- ical properties, e.g. magnetic hyperthermia and magnetic drug targeting. For most applications, it is crucial to spatially quantify the amount of MNP. In magnetorelaxometry (MRX), the magnetic moments of the MNP are aligned by an external , forming a net magnetic moment. After switching-off this field, the relaxation of this net mo- ment is commonly detected by a superconducting quantum interference device (SQUID). The amplitude of this relaxa- tion curve is directly proportional to the MNP quantity and thus, MRX with multiple sensors and/or varying excitation fields allows for spatial quantitative reconstruction of MNP amount. Since the latest developments in OPM technology allow sensitivities comparable to those of SQUID, OPM may be used in MRX, offering a reduced sensor-target- distance and the omission of cryogenic cooling. Our setup consists of a single QuSpin zero field OPM and four excita- tion coils, fabricated on a printed circuit board and placed at a distance of 11 mm in front of the OPM, both positioned in a magnetically shielded room (BMSR-2 at the PTB in Berlin). The MNP samples consist of Resovist ® (Schering, Berlin, Germany), diluted and freeze dried in a sugar matrix, with a volume of 140 µl and an iron concentration ranging from 3 mmol/L to 15 mmol/L. Three MNP samples were placed in a row between the OPM and the excitation coils. The MNP were partially aligned by the field of one of the subsequently switched activation coils. The field pulses have a duration of one second and a strength of < 1 mT, during which the OPM saturates. After switching off the field, the relaxation of the MNP is measured by the OPM after a dead time of 15 ms. This process is repeated with the other coils. By fitting the relaxation model to the measurement data and solving the inverse problem, accurate quantitative recon- struction of the three iron concentrations could be achieved.

Abstracts – BMT 2019 – Frankfurt am Main, September 25–26 • DOI 10.1515/bmt-2019-6008 Biomed. Eng.-Biomed. Tech. 2019; 64(s2): S36–S40 • © by Walter de Gruyter • Berlin • Boston S37

Multichannel Exercise MCG with Optically Pumped Magnetometers

Thomas Middelmann, Department Biosignals, Physikalisch-Technische Bundesanstalt, Berlin, Germany, [email protected] Stefan Hartwig, Department Biosignals, Physikalisch-Technische Bundesanstalt, Berlin, Germany, [email protected] Tilmann Sander, Department Biosignals, Physikalisch-Technische Bundesanstalt, Berlin, Germany, tilmann.sander- [email protected] Lutz Trahms, Department Biosignals, Physikalisch-Technische Bundesanstalt, Berlin, Germany, [email protected]

Recent advances in commercial production of miniaturized optically pumped magnetometers (OPMs) enable a new level of biomagnetic investigations. Now magnetic field sensors can be directly attached to the body, while the subject is still allowed to move. Also, the sensitivity level reached by commercial OPMs enables them to compete with SQUID based systems in biomedical applications like (MCG) and (MEG). For these measurements, a bandwidth from 0.1 Hz to 100 Hz is often sufficient. OPM based systems gain from their higher flexi- bility, that enables their direct attachment to the body, comparable to electrodes in Electrocardiography (ECG) or Elec- troencephalography (EEG). This offers new opportunities for field mapping e.g. in terms of higher spatial resolution and closer distance to the field sources, as well as realization of personalized and complex geometries. Here, we show that the flexibility of OPMs enables, first, the registration of exercise MCG even when the subject is moving and, second, the attachment of sensors on the chest and on the back of the subject at the same time. We used commercially available zero-field OPMs with a sensitivity of about 15 fT/rtHz and a bandwidth of 135 Hz to perform exercise MCG measurements in PTB’s magnetically shielded room BMSR-2. A set of 8 sensors (16 channels) was at- tached to the chest and another set of 8 sensors (16 channels) was attached to the back of the subject. MCG was recorded before, while and after the subject was exercising on a nonmagnetic ergometer. The OPMs were fixed on the subject’s body only separated from the skin by a thin layer of cloth. We obtained an SNR of up to 300, that allows for distinguishing details in recorded data already without averaging. These measurements demonstrate the ease of handling and high flex- ibility of OPMs combined with good signal quality.

Abstracts – BMT 2019 – Frankfurt am Main, September 25–26 • DOI 10.1515/bmt-2019-6008 Biomed. Eng.-Biomed. Tech. 2019; 64(s2): S36–S40 • © by Walter de Gruyter • Berlin • Boston S38

Magnetic field camera for bio-magnetic sensing

Christian B. Schmidt, Magnetometry - Leibniz Institute of Photonic Technology (IPHT)), Jena, Germany, chris- [email protected] Florian Wittkämper, Magnetometry - Leibniz Institute of Photonic Technology (IPHT), Jena, Germany, flori- [email protected] Gregor Oelsner, Magnetometry - Leibniz Institute of Photonic Technology (IPHT), Jena, Germany, greg- [email protected] Rob IJsselsteijn, Magnetometry – Supracon AG, Jena, Germany, [email protected] Roland Eichhardt, BMTI of the Technical University Illmenau, Germany, [email protected] Uwe Graichen, BMTI of the Technical University Illmenau, Germany, [email protected] Volkmar Schultze, Magnetometry - Leibniz Institute of Photonic Technology (IPHT), Jena, Germany, [email protected] Jens Haueisen, BMTI of the Technical University Illmenau, Germany, [email protected] Ronny Stolz, Magnetometry - Leibniz Institute of Photonic Technology (IPHT), Jena, Germany, ronny.stolz@leibniz- ipht.de

The reconstruction of bio-magnetic sources for cardiography and electroencephalography of small animals requires a magnetic field sensor array with a spacing of a few millimeters, while being able to detect the field as close as possible to the sources origin. While superconducting quantum interference devices (SQUIDs) provide the needed sensitivity of a few femtotesla and are able to achieve the required pixel density, the thermal isolation in the centimeter regime dis- qualifies them for the given task. Here, we present a magnetic field sensor array based on optically pumped Cesium va- por gas that features 52 pixels arranged in a matrix with a circular field of view. This magnetic field camera (MC) has a pixel distance as well as a sensor-mid-to-housing-distance of about 3 mm. This design allows a theoretical resolution of 2.5 mm at adistance of 7 mm below the sensor housing. The MC is based on the light shift dispersed Mz-mode (LSD- Mz) and is therefore theoretically able to reach a sensitivity in the tens of femtotesla even at Earth magnetic field strengths. To achieve the requirements of the MCs, we constructed a large vapor cell containing all pixels and use a sin- gle laser combined with a diffractive optical element instead of combining single cells and 52 lasers. These changes call for a new generation of vapor cells, being able to work in reflection geometry and with direct heating of the optical windows, e.g., via transparent semiconductors. The complete design will be presented as well as first characterizations of the MC.

Abstracts – BMT 2019 – Frankfurt am Main, September 25–26 • DOI 10.1515/bmt-2019-6008 Biomed. Eng.-Biomed. Tech. 2019; 64(s2): S36–S40 • © by Walter de Gruyter • Berlin • Boston S39

Magnetic Measurement of Electrically Evoked Muscle Responses with Optical- ly-Pumped Magnetometers (OPMs)

Eric Elzenheimer, Kiel University, Digital Signal Processing and System Theory, Kiel, Germany, [email protected] Helmut Laufs, UKSH, Department of Neurology, Kiel, Germany, [email protected] Wilhelm Schulte-Mattler, University Hospital Regensburg, Regensburg, Germany, Wilhelm.Schulte- [email protected] Gerhard Schmidt, Kiel University, Digital Signal Processing and System Theory, Kiel, Germany, [email protected]

Electroneurography is an essential method for the assessment of peripheral nerve disorders. For electrophysiological diagnostics, muscle signals are recorded with surface electrodes. The signals are triggered by electrical stimulation of efferent nerve fibers at different sites along the nerve. The recorded waveforms are analyzed by measuring quantities such as nerve conduction velocity, signal amplitude, distal motor latency. These are compared with age-matched refer- ence values. These objective data are a relevant contribution to the diagnosis of nerve pathologies in addition to the clinical examination. Magnetic sensing offers potential advantages compared to the current recording technique with surface electrodes, e.g. it does not require electrode skin contact thus avoiding skin preparation, potential infection or allergic reactions, and the body tissue does not influence the biological signals. Currently, optically pumped magnetometers (OPMs) provide an uncooled sensor technology that is promising in many respects for medical applications. Yet, a shielded chamber meet- ing high technical standards is a prerequisite for OPM measurements. Furthermore, the limited bandwidth that is presently provided by OPMs is a challenge and influences broadband signals to a most relevant degree. We successfully performed both averaged and un-averaged magnetic muscle measurements of a hand muscle (Musculus abductor pollicis brevis) innervated by a peripheral nerve (N. medianus) with a proximal electrical stimulation in a shielded environment. To minimize mechanical couplings into the magnetometers, we at- tached the OPMs to a stable self-constructed sensor platform and used a vacuum cushion for fixation of the subject’s arm. We report in detail on the results of the magnetic measurements and their validation with electroneurography data as reference. Finally, we discuss the suitability of OPMs for clinical application in the context of diagnostic value in comparison with the current electrical gold standard. This exemplary measurement demonstrates the usability of this new sensor for electrically evoked signals. Abstracts – BMT 2019 – Frankfurt am Main, September 25–26 • DOI 10.1515/bmt-2019-6008 Biomed. Eng.-Biomed. Tech. 2019; 64(s2): S36–S40 • © by Walter de Gruyter • Berlin • Boston S40

Optical pumped for magnetomyography to study the nerval in- nervation pattern of the hand

Philip Julian Broser, Kinderspital, Neuropädiatrie, St. Gallen, Switzerland, [email protected] Svenja Knappe, University of Colorado, Boulder , United States Diljit-Singh Kajal, Universität Tübingen , MEG Zentrum Nima Noury, Universität Tübingen , MEG Zentrum Christoph Braun, Universität Tübingen , MEG Zentrum, [email protected]

Motor control by the central nervous system is exerted to the peripheral via a dense network of nerve fibers targeting each individual muscle. There are numerous clinical situation were a detailed assessment of the nerval-innervation pat- tern is required for diagnosis and treatment. Especially deep muscles are hard to examine and are as yet only accessible by uncomfortable and painful needle EMG techniques. Just recently, a new and flexible method and device became available to measure the small magnetic fields generated by the contraction of the muscles. Optical pumped magnetom- eters (OPM) are small devices that measure the zero-field level crossing resonance of spinpolarized rubidium atoms. The resonance is dependent on the local magnetic field strength and therefore these devices are able to measure even the small magnetic fields generated by contracting muscle fibres.In this study, we demonstrate as a proof of principle that these OPMs can be used to measure the low magnetic field generated by the small hand muscles after electric stimula- tion of the ulnar or median nerve. We show that using this technique we are able to analyze the detailed innervation pat- tern of small palmar hand muscles and are capable to differentiate between areas innervated by the median or ulnar nerve. We expect that the new approach will have an important impact on the diagnosis of nerval entrapement syn- droms, spinal cord lesions and neuro muscular diseases.