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New magnetic field measurement technique for medical research

The measurement of magnetic fields in living organisms is of increasing importance in biomedical diagnostics. In order to detect the very low fields, they have to be extensively shielded against external perturbations. A novel magnetic field measuring device enables the shielding to be improved with reduced effort. Furthermore, the device is transportable and thus applicable in a clinical environment..

The structure of the new measuring device

The most sensitive sensors for magnetic fields are currently superconducting quantum interferometers, so-called SQUIDs. They are used in biomedical engineering, among other things, to detect the magnetic fields of living organisms. The high sensitivity of a SQUID measurement requires extensive shielding to reduce the Earth’s magnetic field and further perturbations, for example from electrical cables or mobile radio. Up to now, this shielding has been achieved by the use of special cabins made of highly magnetically permeable metal, which is associated with high costs of material and resources.

With the completion of the measuring device, PTB has broken new ground. In the process, the fact was exploited that some metals (such as niobium or lead) are, at very low temperatures, completely impermeable for magnetic fields (Meissner-Ochsenfeld effect). The new measuring device consists of a niobium cylinder with a horizontal bore, externally accessible. Small samples or also small test animals can be placed here. Via a vertical access, 18 SQUIDs are inserted on a flexible chain into the interior of the niobium cylinder, so that they enclose the sample annularly. The niobium cylinder, together with the SQUIDs, is kept in liquid helium at a temperature of 4 K. External interfering magnetic fields, which can enter the niobium shielding cylinder and reach the SQUIDs only through the open ends of the cylinder, are reduced by up to eight orders of magnitude at the site of the sensors. This by far exceeds the shielding obtained by conventional methods.

With the new measuring device, non-contact observation is possible, for example, of the electrical activity in the heart of a mouse via magnetic field measurement. Due to its compact construction, it is transportable. Thus, in future it will enable highly accurate magnetic field measurements in clinical laboratories.

Contact at PTB:

Phone: +49-531-592-0