Superconductor imaging surface magnetometry

Hulsteyn, D. B. van; Petschek, A. G.; Flynn, E.R.; Overton, W.C.

doi:10.1063/1.1145437

Cited by 19 publications

(13 citation statements)

References 2 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…We have now constructed a flat SQUID-array system utilizing 12 thin-film button SQUIDS that were specifically designed for this effort by Conductus, Inc. in collaboration with and under contract to Los Alamos [6] for use in imagesurface systems (Fig. 2).…”

Section: Resultsmentioning

confidence: 99%

“…5 in [6]). This is a consequence of 8, the angle formed between the phantom source axis and the magnetometer, being large for smaller values of R. As R increases, the R-3 term dominates once again and the data from all channels converge.…”

Section: B System Measurementsmentioning

confidence: 99%

“…THEORY The theory for superconducting imaging gradiometry was first described by van Hulsteyn, et al [6]. He showed that analytic expressions could only be derived for unconstrained geometries (e.g.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

First results for a novel superconducting imaging-surface sensor array

Kraus

Flynn

Espy

et al. 1999

IEEE Trans. Appl. Supercond.

View full text Add to dashboard Cite

RECEIVEDAbstract-A superconducting imaging-surface system was constructed using 12 coplanar thin-am SQUID magnetometers located parallel to and spaced 2 cm from a 25 cm diameter l a d imaging-plane. Some measurements included two additional sensors on the "back" side of the superconducting imaging-plane to study the field symmetry for our system. Performance was measured in a shielded can and in the open laboratory environment. Data from this system has been used to: (a) A phantom source field was measured at the sensors as a function of phantom distance from the sensor array to verify the imaging theory. Both the shape and absolute values of the measured and predicted curves agree very well indicating the system is behaving as a gradiometer in accordance with theory. The output from SQUIDS located behind the imaging surface that sense background fields can be used for software or analog background cancellation. Fields arising from sources close to the imaging plane were shielded form the background sensors by more than a factor of 1000. Measurement of the symmetry of sensor sensitivity to uniform fields exactry followed theoreticaI predictions.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: B System Measurementsmentioning

confidence: 99%

See 1 more Smart Citation

First results for a novel superconducting imaging-surface sensor array

Kraus

Flynn

Espy

et al. 1999

IEEE Trans. Appl. Supercond.

View full text Add to dashboard Cite

show abstract

“…Analytic solutions are known for simple geometries such as the sphere or infinite plane [4], but for finite geometries the field is difficult or impossible to determine analytically. Consequently, we have implemented a finite element model (FEM) description of the SIS forward physics using the exact as-built geometry.…”

Section: Methodsmentioning

confidence: 99%

Performance of a novel SQUID-based superconducting imaging-surface magnetoencephalography system

Kraus

Volegov

Maharajh

et al. 2002

Physica C: Superconductivity

View full text Add to dashboard Cite

Abstract-Performance for a recently completed whole-head magnetoencephalography system using a superconducting imaging-surface (SIS) surrounding an array of 150 SQUID magnetometers is reported. The helmetlike SIS is hemispherical in shape with a brim. Conceptually, the SIS images nearby sources onto the SQUIDs while shielding sensors from distant "noise" sources. A finite element method (FEM) description using the as-built geometry was developed to describe the SIS effect on source fields by imposing B ⊥ (surface)=0. Sensors consist of 8mm × 8mm SQUID magnetometers with 0.84nT/Φ sensitivity and <3fT/√Hz noise. A series of phantom experiments to verify system efficacy have been completed. Simple dry-wire phantoms were used to eliminate model dependence from our results. Phantom coils were distributed throughout the volume encompassed by the array with a variety of orientations. Each phantom coil was precisely machined and located to better than 25µm and 10mRad accuracy. Excellent agreement between model-calculated and measured magnetic field distributions of all phantom coil positions and orientations was found. Good agreement was found between modeled and measured shielding of the SQUIDs from sources external to the array showing significant frequency-independent shielding. Phantom localization precision was better than 0.5mm at all locations with a mean of better than 0.3mm. IntroductionWeak magnetic fields are a direct consequence of neuronal activity in the brain that causes ionic currents to flow in the neurons [1]. Magnetoencephalography (MEG) is the technique that measures the weak magnetic fields that emanate from the brain[2] as a direct consequence of the neuronal currents resulting from brain activity. The extraordinarily weak magnetic fields, typically 10-100 femtoTesla (fT), are measured by an array of SQUID (Superconducting QUantum Interference Device) sensors. The position and vector characteristics of these neuronal sources can be estimated from the inverse solution of the field distribution at the surface of the head. In addition to locating the sources of neuronal activity, MEG temporal resolution is unsurpassed by any other method currently used for brain imaging. Although MEG is not truly tomographic and source reconstruction is limited by solutions of the electromagnetic inverse problem, constraints used for source localization produce reliable and accurate results. Current MEG instrumental source location accuracy reported in the literature is approximately 2 to 4 mm, depending on source parameters, and typically 5-10 mm accuracy is attained in most medical applications with the latest instruments.A unique whole-head MEG system incorporating a superconducting imaging-surface (SIS) has been designed and built at Los Alamos with the goal of dramatically improving source localization accuracy while mitigating limitations of current systems (e.g. low signal-to-noise, cost, bulk). The Los Alamos SIS-MEG system[3] is based on the principal that Meissner currents flow in the surface of superconduc...

show abstract

“…The theoretical basis of superconducting imaging surface (S1S) magnetometry was introduced by van Hulsteyn et al in [1]. The primary concept is that a single coil detector located in the vicinity of a superconducting surface can be made to act like a first-order gradlometer.…”

Section: Introductionmentioning

confidence: 99%