Base distance optimization for SQUID gradiometers

Conference · Thu Dec 31 04:00:00 EST 1998

OSTI ID:350912

Garachtchenko, A ^[1]; Matlashov, A; Kraus, R ^[2]

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1. Applied Materials, Santa Clara, CA (United States)
2. Los Alamos National Lab., NM (United States)

The measurement of magnetic fields generated by weak nearby biomagnetic sources is affected by ambient noise generated by distant sources both internal and external to the subject under study. External ambient noise results from sources with numerous origins, many of which are unpredictable in nature. Internal noise sources are biomagnetic in nature and result from muscle activity (such as the heart, eye blinks, respiration, etc.), pulsation associated with blood flow, surgical implants, etc. Any magnetic noise will interfere with measurements of magnetic sources of interest, such as magnetoencephalography (MEG), in various ways. One of the most effective methods of reducing the magnetic noise measured by the SQUID sensor is to use properly designed superconducting gradiometers. Here, the authors optimized the baseline length of SQUID-based symmetric axial gradiometers using computer simulation. The signal-to-noise ratio (SNR) was used as the optimization criteria. They found that in most cases the optimal baseline is not equal to the depth of the primary source, rather it has a more complex dependence on the gradiometer balance and the ambient magnetic noise. They studied both first and second order gradiometers in simulated shielded environments and only second order gradiometers in a simulated unshielded environment. The noise source was simulated as a distant dipolar source for the shielded cases. They present optimal gradiometer baseline lengths for the various simulated situations below.

• Research Organization: Los Alamos National Lab., NM (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: W-7405-ENG-36
• OSTI ID: 350912
• Report Number(s): LA-UR--98-4044; CONF-9809130--; ON: DE99002591
• Country of Publication: United States
• Language: English

Related Subjects

55 BIOLOGY AND MEDICINE
BASIC STUDIES
BRAIN
DIAGNOSTIC TECHNIQUES
DIAGNOSTIC USES
MAGNETIC FIELDS
MAGNETOMETERS
MEDICINE
OPTIMIZATION
SENSITIVITY
SIGNAL-TO-NOISE RATIO
SQUID DEVICES