A Cryogenic Engineering Conference Publication, 1988
Measurements of the magnetic field of the human brain in a clinical setting require a higher leve... more Measurements of the magnetic field of the human brain in a clinical setting require a higher level of performance from the instrumentation than is generally acceptable for laboratory research. We describe several significant advances that are intended for such neuromagnetic applications as well as for a broader range of biomagnetic studies. We report the development of a closed-cycle refrigerator capable of sustaining a SQUID-based sensor without introducing significant deterioration of the noise level. This eliminates the need for liquid cryogen and permits the sensor to be operated in various orientations, including inverted. The performance of a new type of magnetically shielded room is then evaluated for neuromagnetic studies. It has the advantages of being pre-fabricated and of providing a large interior for convenient clinical studies. Its ceiling supports a versatile gantry that holds one or two sets of magnetic sensors. This arrangement, when used with a magnetic system for precisely determining the sensor positions with respect to the patient’s head, is feasible for precise localization of neural sources within the brain. We end with an example of the kinds of clinical studies that are now being carried out with the aid of neuromagnetic measurements.
Measurements of superfluid density in 3He via fourth sound in an open parallel plate “superleak” ... more Measurements of superfluid density in 3He via fourth sound in an open parallel plate “superleak” show an unexpected pressure and pore size dependence and an unexpectedly small change at the B → A transition.
IEEE Transactions on Appiled Superconductivity, 1999
For HTS dc-SQUID sensors operating in high magnetic fields we have used quasiplanar HTS Josephson... more For HTS dc-SQUID sensors operating in high magnetic fields we have used quasiplanar HTS Josephson junctions, HTS films prepared at optimized conditions with a high oxygen pressure dc-sputtering technique, a capsulation with a heater, and a proper dc-SQUID layouts. DC-SQUIDS tested in magnetic fields up to about 1 kG demonstrate no reduction of the critical current. A model is proposed, which gives a satisfactory explanation of the experimental results. With the use of a digital feedback a dynamic range of about 160 dB was achieved. Highly sensitive devices were prepared with flip-chip flux antennas. For the magnetometers a resolution of about 40 flldHz was obtained in unshielded environment.
Abstract: wafer.To subtract high magnetic background noise onecan use a gradiometric configuratio... more Abstract: wafer.To subtract high magnetic background noise onecan use a gradiometric configuration of the pick-upcoil. Tian et al. [4] have achieved a field gradientsensitivity of 73 fT/cm#Hz in the white noise regionand 596 fT/cm#Hz at 1Hz with a single layergradiometric flux antenna on a 5 cm Si wafer. Wehave demonstrated [5] a planar HTS flip-chipgradiometer having multilayer gradiometric fluxantenna prepared on a 3 cm wafer. A resolution ofabout 40 fT/cm#Hz at frequencies above 1o...
... Abstract We discuss the use of a new SQUID magnetometer for non-invasive measurements of hepa... more ... Abstract We discuss the use of a new SQUID magnetometer for non-invasive measurements of hepatic (liver) iron stores. Placement of the SQUID, detection coil, and magnet in the dewar vacuum region significantly reduced system noise. ...
Neurology & Clinical Neurophysiology, Nov 30, 2004
High temperature superconducting (HTS) SQUID sensors have adequate magnetic field sensitivity for... more High temperature superconducting (HTS) SQUID sensors have adequate magnetic field sensitivity for adult magnetocardiography (MCG) measurements, but it remains to be seen how well they perform for fetal MCG (fMCG), where the heart signals are typically ten times smaller than the adult signals. In this study, we assess the performance of a prototype HTS SQUID system; namely, a three-SQUID gradiometer formed from three vertically-aligned HTS dc-SQUID magnetometers integrated into a fiberglass liquid nitrogen dewar of diameter 12.5 cm and height 30 cm. Axial gradiometers with short or long baseline, as well as a second order gradiometer, can be formed out of these magnetometers via electronic subtraction. The calibrated magnetometer sensitivities at 1 kHz are 109 fT/square root of Hz, 155 fT/square root of Hz and 51 fT/square root of Hz. Direct comparison is made between the HTS SQUID system and a LTS SQUID system by making recordings with both systems during the same session on adult a...
Introduction Iron overload from genetic disorders and/or regular blood transfusions is a serious ... more Introduction Iron overload from genetic disorders and/or regular blood transfusions is a serious health problem in many regions of the world. As liver and spleen iron stores account for more than 70 % of total body iron stores, the precise quantification and the continuous monitoring of these stores is of particular importance in the diagnosis and treatment of these disorders. During the last two decades several noninvasive methods have been explored for the assessment of elevated liver iron stores in patients with primary (genetic hemochromatosis) or with iron loading anemias (e.g., -thalassemia major, leukemia after bone marrow transplantation). Of these different methods only quantitative magnetic resonance imaging (qMRI) [1] and SQUID biomagnetic liver susceptometry (BLS) [2] have achieved a broader clinical acceptance. The noninvasive determination of liver iron concentration (LIC) by BLS has become now a routine method in iron overload monitoring. While serum ferritin has been s
Pressure waves propagate through a superleak in both $^{3}\mathrm{He}$-$A$ and $^{3}\mathrm{He}$-... more Pressure waves propagate through a superleak in both $^{3}\mathrm{He}$-$A$ and $^{3}\mathrm{He}$-$B$, showing that both are superfluids below ${T}_{c}$. Superfluid relative density is obtained from velocity measurements over a wide pressure range above and below the polycritical point.
A Cryogenic Engineering Conference Publication, 1988
Measurements of the magnetic field of the human brain in a clinical setting require a higher leve... more Measurements of the magnetic field of the human brain in a clinical setting require a higher level of performance from the instrumentation than is generally acceptable for laboratory research. We describe several significant advances that are intended for such neuromagnetic applications as well as for a broader range of biomagnetic studies. We report the development of a closed-cycle refrigerator capable of sustaining a SQUID-based sensor without introducing significant deterioration of the noise level. This eliminates the need for liquid cryogen and permits the sensor to be operated in various orientations, including inverted. The performance of a new type of magnetically shielded room is then evaluated for neuromagnetic studies. It has the advantages of being pre-fabricated and of providing a large interior for convenient clinical studies. Its ceiling supports a versatile gantry that holds one or two sets of magnetic sensors. This arrangement, when used with a magnetic system for precisely determining the sensor positions with respect to the patient’s head, is feasible for precise localization of neural sources within the brain. We end with an example of the kinds of clinical studies that are now being carried out with the aid of neuromagnetic measurements.
Measurements of superfluid density in 3He via fourth sound in an open parallel plate “superleak” ... more Measurements of superfluid density in 3He via fourth sound in an open parallel plate “superleak” show an unexpected pressure and pore size dependence and an unexpectedly small change at the B → A transition.
IEEE Transactions on Appiled Superconductivity, 1999
For HTS dc-SQUID sensors operating in high magnetic fields we have used quasiplanar HTS Josephson... more For HTS dc-SQUID sensors operating in high magnetic fields we have used quasiplanar HTS Josephson junctions, HTS films prepared at optimized conditions with a high oxygen pressure dc-sputtering technique, a capsulation with a heater, and a proper dc-SQUID layouts. DC-SQUIDS tested in magnetic fields up to about 1 kG demonstrate no reduction of the critical current. A model is proposed, which gives a satisfactory explanation of the experimental results. With the use of a digital feedback a dynamic range of about 160 dB was achieved. Highly sensitive devices were prepared with flip-chip flux antennas. For the magnetometers a resolution of about 40 flldHz was obtained in unshielded environment.
Abstract: wafer.To subtract high magnetic background noise onecan use a gradiometric configuratio... more Abstract: wafer.To subtract high magnetic background noise onecan use a gradiometric configuration of the pick-upcoil. Tian et al. [4] have achieved a field gradientsensitivity of 73 fT/cm#Hz in the white noise regionand 596 fT/cm#Hz at 1Hz with a single layergradiometric flux antenna on a 5 cm Si wafer. Wehave demonstrated [5] a planar HTS flip-chipgradiometer having multilayer gradiometric fluxantenna prepared on a 3 cm wafer. A resolution ofabout 40 fT/cm#Hz at frequencies above 1o...
... Abstract We discuss the use of a new SQUID magnetometer for non-invasive measurements of hepa... more ... Abstract We discuss the use of a new SQUID magnetometer for non-invasive measurements of hepatic (liver) iron stores. Placement of the SQUID, detection coil, and magnet in the dewar vacuum region significantly reduced system noise. ...
Neurology & Clinical Neurophysiology, Nov 30, 2004
High temperature superconducting (HTS) SQUID sensors have adequate magnetic field sensitivity for... more High temperature superconducting (HTS) SQUID sensors have adequate magnetic field sensitivity for adult magnetocardiography (MCG) measurements, but it remains to be seen how well they perform for fetal MCG (fMCG), where the heart signals are typically ten times smaller than the adult signals. In this study, we assess the performance of a prototype HTS SQUID system; namely, a three-SQUID gradiometer formed from three vertically-aligned HTS dc-SQUID magnetometers integrated into a fiberglass liquid nitrogen dewar of diameter 12.5 cm and height 30 cm. Axial gradiometers with short or long baseline, as well as a second order gradiometer, can be formed out of these magnetometers via electronic subtraction. The calibrated magnetometer sensitivities at 1 kHz are 109 fT/square root of Hz, 155 fT/square root of Hz and 51 fT/square root of Hz. Direct comparison is made between the HTS SQUID system and a LTS SQUID system by making recordings with both systems during the same session on adult a...
Introduction Iron overload from genetic disorders and/or regular blood transfusions is a serious ... more Introduction Iron overload from genetic disorders and/or regular blood transfusions is a serious health problem in many regions of the world. As liver and spleen iron stores account for more than 70 % of total body iron stores, the precise quantification and the continuous monitoring of these stores is of particular importance in the diagnosis and treatment of these disorders. During the last two decades several noninvasive methods have been explored for the assessment of elevated liver iron stores in patients with primary (genetic hemochromatosis) or with iron loading anemias (e.g., -thalassemia major, leukemia after bone marrow transplantation). Of these different methods only quantitative magnetic resonance imaging (qMRI) [1] and SQUID biomagnetic liver susceptometry (BLS) [2] have achieved a broader clinical acceptance. The noninvasive determination of liver iron concentration (LIC) by BLS has become now a routine method in iron overload monitoring. While serum ferritin has been s
Pressure waves propagate through a superleak in both $^{3}\mathrm{He}$-$A$ and $^{3}\mathrm{He}$-... more Pressure waves propagate through a superleak in both $^{3}\mathrm{He}$-$A$ and $^{3}\mathrm{He}$-$B$, showing that both are superfluids below ${T}_{c}$. Superfluid relative density is obtained from velocity measurements over a wide pressure range above and below the polycritical point.
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Papers by D. Paulson