We developed a 375-channel, whole-head magnetoencephalography (MEG) system ("BabyMEG") for studying the electrophysiological development of human brain during the first years of life. The helmet accommodates heads up to 95% of 36-month old boys in the USA. The unique two-layer sensor array consists of: (1) 270 magnetometers (10 mm diameter, ∼15 mm coil-to-coil spacing) in the inner layer, (2) thirty-five three-axis magnetometers (20 mm × 20 mm) in the outer layer 4 cm away from the inner layer. Additionally, there are three three-axis reference magnetometers. With the help of a remotely operated position adjustment mechanism, the sensor array can be positioned to provide a uniform short spacing (mean 8.5 mm) between the sensor array and room temperature surface of the dewar. The sensors are connected to superconducting quantum interference devices (SQUIDs) operating at 4.2 K with median sensitivity levels of 7.5 fT/√Hz for the inner and 4 fT/√Hz for the outer layer sensors. SQUID outputs are digitized by a 24-bit acquisition system. A closed-cycle helium recycler provides maintenance-free continuous operation, eliminating the need for helium, with no interruption needed during MEG measurements. BabyMEG with the recycler has been fully operational from March, 2015. Ongoing spontaneous brain activity can be monitored in real time without interference from external magnetic noise sources including the recycler, using a combination of a lightly shielded two-layer magnetically shielded room, an external active shielding, a signal-space projection method, and a synthetic gradiometer approach. Evoked responses in the cortex can be clearly detected without averaging. These new design features and capabilities represent several advances in MEG, increasing the utility of this technique in basic neuroscience as well as in clinical research and patient studies.

We discuss the use of a new SQUID magnetometer for noninvasive measurements of hepatic (liver) iron stores. Placement of the SQUID, detection coil, and magnet in the dewar vacuum region significantly reduced system noise. In addition, the system incorporates multiple magnets and detection coils which may allow thc discrimination of the surface skin layer from the deeper (weaker signal) true liver iron concentration. Measurements indicate an instrumental noise level < 20 pgfg of equivalent iron concentration.

In the presence of a magnetic field the 3 He A phase is interposed between the normal liquid and the 3 He B phase for all pressures measured, including pressures below that of the polycritical point. This can be understood on the basis of known nuclear paramagnetic properties if at a given pressure both 3 He A and 3 He B have the same critical temperature and if there are plausible small differences in the heat capacties of the two phases.We have discovered that a rather weak magnetic field acting on the weak nuclear paramagnetism of 3 He has a profound effect on the Tj^ line separating 3 He A and 3 He B in the phase diagram of the superfluid. As shown in Fig. 1 for a field of 378 G, the field produces its largest effect in the vicinity of the pressure of the polycritical point (PCP) but it also acts to interpose the 3 He A phase between the normal liquid and 3 He B down to our lowest pressure of less than 8 bars. Both this remarkable effect and the lowfield T AB line may be quantitatively understood on the basis of the known magnetic properties of 1.9 2.0 2.1 2.2 2.3 2.4 2.5 2.6 T-mK FIG. 1. Phase diagram of liquid 3 He in a field of 378 G using the provisional temperature scale of Ref. 4. The low-field T^ line found in Ref. 3 is shown for reference. The PCP occurs at about 21.5 bars.each of the phases if one assumes that both 3 He A and 3 He B have the same pressure-dependent critical temperature and that there is a particularly simple form for the small thermal differences between the two phases. We believe that this result will be important in determining the nature and the relationship of the A and B phases. In particular, in a context of BCS-like pairing theories of the superfluidity, the results suggest that both 3 He A and 3 He B represent triplet states in the same I manifold. 1 The effect of a magnetic field on the A and B features of the pressurization curve has been reported by Gully et al., 2 who find a small splitting of the A feature and a substantial depression of the B feature by a magnetic field. The dependence of the transition temperature T AB from 3 He B to 3 He A on pressure was determined by Paulson, Johnson, and Wheatley 3 by measurements of the magnetization discontinuity in the JB-A transition in a field of 49 G. The present measurements were also made using static nuclear magnetization measurements. The experimental method, apparatus, calibration technique, and accuracy are the same as those described briefly in Ref. 3. The precision of measurement is, however, substantially improved at higher fields, partly because of increased sensitivity but mostly as a result of the reduced magnetometer background, which is thus principally a manifestation of weak electronic magnetism. Furthermore, the transition A* B reported here in 378-and 480-G fields is reversible in the sense that by careful manipulation of temperature [via adjustments in the magnetic field applied to the main cerium magnesium nitrate (CMN)J this transition could be partly effected, then reversed. Once the transition on coolin...

Abdrwt-We have fabricated HTS &SQUID flip-chip the magnetometers could be additionally improved by a sensors with a large area multilayer flux transformers. larger Pickup loop with the flux transformer made on a Different layouts of the flux transformers provide a large largerwafer. variety of magnetometers and planar gradiometers. For the To subtract high magnetic background noise one can use a magnetometers a resolution-6 tT/.\IHz and the planar gradiometric configuration of the pickup coil. Tian et al. [4] gradiometers a resolution of about ,. , 30 fT/cm..\IHz were have achieved a field gradient sensitivity of 73 fT/cm& in routinely obtained at 77 K The noise was nearly white down to the white noise region and 596 fl/cm,,/fi at 1 fi with a frequencies of few Hz. The sensors were vacuum-tight layer gradiometfic flux antenna on a 50 mm si wafer. We have demonstrated [5] a planar HTS flip-chip encapsulated together with a heater and a feedback coil. This makes the handling of the sensors more reproducible and convenient. Production of the magnetometers and gradiometers gradiometer having padometric flux antenna in small series was proven. prepared on a 30 mm wafer. A resolution of-40 ff/cmdHz

We developed a prototype of a mobile, high-resolution, multichannel magnetoencephalography ͑MEG͒ system, called babySQUID, for assessing brain functions in newborns and infants. Unlike electroencephalography, MEG signals are not distorted by the scalp or the fontanels and sutures in the skull. Thus, brain activity can be measured and localized with MEG as if the sensors were above an exposed brain. The babySQUID is housed in a moveable cart small enough to be transported from one room to another. To assess brain functions, one places the baby on the bed of the cart and the head on its headrest with MEG sensors just below. The sensor array consists of 76 first-order axial gradiometers, each with a pickup coil diameter of 6 mm and a baseline of 30 mm, in a high-density array with a spacing of 12-14 mm center-to-center. The pickup coils are 6 ± 1 mm below the outer surface of the headrest. The short gap provides unprecedented sensitivity since the scalp and skull are thin ͑as little as 3 -4 mm altogether͒ in babies. In an electromagnetically unshielded room in a hospital, the field sensitivity at 1 kHz was ϳ17 fT/ ͱ Hz. The noise was reduced from ϳ400 to 200 fT/ ͱ Hz at 1 Hz using a reference cancellation technique and further to ϳ40 fT/ ͱ Hz using a gradient common mode rejection technique. Although the residual environmental magnetic noise interfered with the operation of the babySQUID, the instrument functioned sufficiently well to detect spontaneous brain signals from babies with a signal to noise ratio ͑SNR͒ of as much as 7.6:1. In a magnetically shielded room, the field sensitivity was 17 fT/ ͱ Hz at 20 Hz and 30 fT/ ͱ Hz at 1 Hz without implementation of reference or gradient cancellation. The sensitivity was sufficiently high to detect spontaneous brain activity from a 7 month old baby with a SNR as much as 40:1 and evoked somatosensory responses with a 50 Hz bandwidth after as little as four averages. We expect that both the noise and the sensor gap can be reduced further by approximately half with a gain in SNR of about four. Thus, we conclude from the performance of the prototype that it should be feasible to improve the babySQUID to detect cortical activity in infants in real time with high spatial resolution.