SQUIDs in biomagnetism: A roadmap towards improved healthcare
Artikel i vetenskaplig tidskrift, 2016

Globally, the demand for improved health care delivery while managing escalating costs is a major challenge. Measuring the biomagnetic fields that emanate from the human brain already impacts the treatment of epilepsy, brain tumours and other brain disorders. This roadmap explores how superconducting technologies are poised to impact health care. Biomagnetism is the study of magnetic fields of biological origin. Biomagnetic fields are typically very weak, often in the femtotesla range, making their measurement challenging. The earliest in vivo human measurements were made with room-temperature coils. In 1963, Baule and McFee (1963 Am. Heart J. 55 95-6) reported the magnetic field produced by electric currents in the heart ('magnetocardiography'), and in 1968, Cohen (1968 Science 161 784-6) described the magnetic field generated by alpha-rhythm currents in the brain ('magnetoencephalography'). Subsequently, in 1970, Cohen et al (1970 Appl. Phys. Lett. 16 278-80) reported the recording of a magnetocardiogram using a Superconducting QUantum Interference Device (SQUID). Just two years later, in 1972, Cohen (1972 Science 175 664-6) described the use of a SQUID in magnetoencephalography. These last two papers set the scene for applications of SQUIDs in biomagnetism, the subject of this roadmap. The SQUID is a combination of two fundamental properties of superconductors. The first is flux quantization - the fact that the magnetic flux ? in a closed superconducting loop is quantized in units of the magnetic flux quantum, ?0 ? h/2e, ? 2.07 × 10-15 Tm2 (Deaver and Fairbank 1961 Phys. Rev. Lett. 7 43-6, Doll R and Nabauer M 1961 Phys. Rev. Lett. 7 51-2). Here, h is the Planck constant and e the elementary charge. The second property is the Josephson effect, predicted in 1962 by Josephson (1962 Phys. Lett. 1 251-3) and observed by Anderson and Rowell (1963 Phys. Rev. Lett. 10 230-2) in 1963. The Josephson junction consists of two weakly coupled superconductors separated by a tunnel barrier or other weak link. A tiny electric current is able to flow between the superconductors as a supercurrent, without developing a voltage across them. At currents above the 'critical current' (maximum supercurrent), however, a voltage is developed. In 1964, Jaklevic et al (1964 Phys. Rev. Lett. 12 159-60) observed quantum interference between two Josephson junctions connected in series on a superconducting loop, giving birth to the dc SQUID. The essential property of the SQUID is that a steady increase in the magnetic flux threading the loop causes the critical current to oscillate with a period of one flux quantum. In today's SQUIDs, using conventional semiconductor readout electronics, one can typically detect a change in ? corresponding to 10-6 ?0 in one second. Although early practical SQUIDs were usually made from bulk superconductors, for example, niobium or Pb-Sn solder blobs, today's devices are invariably made from thin superconducting films patterned with photolithography or even electron lithography. An extensive description of SQUIDs and their applications can be found in the SQUID Handbooks (Clarke and Braginski 2004 Fundamentals and Technology of SQUIDs and SQUID Systems vol I (Weinheim, Germany: Wiley-VCH), Clarke and Braginski 2006 Applications of SQUIDs and SQUID Systems vol II (Weinheim, Germany: Wiley-VCH)). The roadmap begins (chapter 1) with a brief review of the state-of-the-art of SQUID-based magnetometers and gradiometers for biomagnetic measurements. The magnetic field noise referred to the pick-up loop is typically a few fT Hz-1/2, often limited by noise in the metallized thermal insulation of the dewar rather than by intrinsic SQUID noise. The authors describe a pathway to achieve an intrinsic magnetic field noise as low as 0.1 fT Hz-1/2, approximately the Nyquist noise of the human body. They also descibe a technology to defeat dewar noise. Chapter 2 reviews the neuroscientific and clinical use of magnetoencephalography (MEG), by far the most widespread application of biomagnetism with systems containing typically 300 sensors cooled to liquid-helium temperature, 4.2 K. Two important clinical applications are presurgical mapping of focal epilepsy and of eloquent cortex in brain-tumor patients. Reducing the sensor-to-brain separation and the system noise level would both improve spatial resolution. The very recent commercial innovation that replaces the need for frequent manual transfer of liquid helium with an automated system that collects and liquefies the gas and transfers the liquid to the dewar will make MEG systems more accessible. [...]

MRI

SQUID

MEG-MRI

MEG

Biomagnetism

magnetic nanoparticles

ULF MRI

Författare

Rainer Körber

Physikalisch-Technische Bundesanstalt (PTB)

Jan Hendrik Storm

Physikalisch-Technische Bundesanstalt (PTB)

Hugh Seton

University of Aberdeen

Jyrki P. Makela

Helsingin Yliopisto

Ritva Paetau

Helsingin Yliopisto

Lauri Parkkonen

Aalto-Yliopisto

Christoph Pfeiffer

Chalmers, Mikroteknologi och nanovetenskap (MC2), Kvantkomponentfysik

Bushra Riaz

Göteborgs universitet

Justin Schneiderman

Göteborgs universitet

Hui Dong

Chinese Academy of Sciences

University of California

Seong Min Hwang

Korea Research Institute of Standards and Science

University of California

Lixing You

Chinese Academy of Sciences

University of California

Ben Inglis

University of California

John Clarke

University of California

Michelle A. Espy

Los Alamos National Laboratory

Risto J. Ilmoniemi

Aalto-Yliopisto

Per Magnelind

Los Alamos National Laboratory

Andrei N. Matlashov

Los Alamos National Laboratory

Jaakko O. Nieminen

Aalto-Yliopisto

Petr L. Volegov

Los Alamos National Laboratory

Koos C J Zevenhoven

Aalto-Yliopisto

Nora Höfner

Physikalisch-Technische Bundesanstalt (PTB)

Martin Burghoff

Physikalisch-Technische Bundesanstalt (PTB)

Keiji Enpuku

Kyushu University

S. Y. Yang

MagQu Co., Ltd.

Jen Jei Chieh

National Taiwan Normal University

Jukka Knuutila

Elekta Oy

Petteri Laine

Elekta Oy

Jukka Nenonen

Elekta Oy

Superconductor Science and Technology

0953-2048 (ISSN) 1361-6668 (eISSN)

Vol. 29 11 Art. no. 113001-

DOI

10.1088/0953-2048/29/11/113001

Mer information

Senast uppdaterat

2018-05-23