Jochen Edrich

Human magnetic auditory evoked fields.

Magnetoencephalographic (MEG) averaged auditory evoked fields to click stimuli (N = 512) were recorded from four human subjects. The MEG was recorded with an asymmetric second derivative SQUID gradiometer located in an aluminum shielded room. Unlike conventional EEG auditory evoked potentials, which have a widespread distribution, evoked magnetic fields appear to be localized to the general area of the primary auditory cortex and diminish rapidly in amplitude as the gradiometer is moved away in any direction.

The human magnetoencephalogram: some EEG and related correlations

Simultaneous magnetoencephalographic (MEG) and electroencephalographic (EEG) data were recorded from six normal adult subjects. MEG signal strength and EEG voltage level appear to be linearly correlated. Spectral analysis suggested that the MEG and EEG data were produced by similar but non-identical generator systems. A vertex region magnetic averaged evoked response to flash was recorded in one (of four) subjects, consisting of a waveform similar to but out of phase with the simultaneous EEG averaged evoked response, such that cortical negativity was correlated with a magnetic field directed into the scalp. Eye movement artifact, which can seriously compromise EEG recordings, does not appear to be a major problem in MEG recordings.

Auditory evoked magnetic fields: Response amplitude vs. stimulus intensity

Abstract Auditory evoked magnetic fields (AEFs) and EEG auditory evoked potentials (AEPs) were recorded from the right hemisphere of 24 normal subjects. MEG and EEG recordings were made from a point 1/4 of the distance from T4 to C4, in response to contralateral ear stimulation by irregularly spaced 100 msec long 1 kHz tone bursts at 40, 60, 80 and 100 dB sound pressure level (SPL). A figure-8 SQUID gradiometer was used for magnetic recordings. MEG and EEG, bandpassed between 2 and 40 Hz, were averaged for 500 msec following 128 stimuli. A mean response was computed for the group of 24 subjects at each stimulus intensity, and the integrated area under the curve of this mean response for the first 200 msec was obtained. The amplitudes of the largest responses occurring within the first 250 msec after stimulus delivery were also measured, as was the amplitude of a biological noise (no stimulus) control. The amplitude of AEFs increased rapidly to approximately 60% of maximum at 60 dB SPL, with the field amplitudes produced by 60, 80 and 100 dB stimuli tending to plateau or even decrease slightly. In contrast, the amplitude of the simultaneously recorded AEPs increased linearly with increasing stimulus intensity. It is suggested that the plateau effect or decrease of the AEF amplitude with increasing stimulus intensity may be caused by an inward movement of the current dipole with increasing stimulus intensity and/or may reflect primarily local intracellular currents associated with single unit activation patterns in auditory cortical regions, whereas AEPs may reflect more widespread extracellular currents.

Microwave Absorption of Living Human Skin Between 8 and 96 GHz

For the study of mm wave thermography and hazards the absorption characteristics of living human skin are determined between 8 and 95 GHz by placing the skin against a thin dielectric film suspended across a rectangular horn and measuring its return loss. The resulting absorption curve increases from 75% at 8 GHz to 95% at 96 GHz. These values are almost twice as high as compared to earlier predictions based on dielectric measurements; however, they agree fairly well with radiometric measurements and provide the basis for very sensitive mm wave thermographs.

Millimeter Wave Thermograph as Subcutaneous Indicator of Joint Inflammation

Noninvasive imaging of inflammations of human joints using a new remote scanning technique is described; it uses the mm wave radiation emitted by the human body. This method overcomes the depth limitations of conventional infrared thermographs and can measure to subcutaneous depths of several mm with a temperature resolution of 0.25°C. Measurements on rheumatoid arthritic knee joints are presented which show little correlation with simultaneously measured skin temperatures. Significant long term thermographic changes induced by steroid injection indicate a potential for objective patient monitoring and development of new treatment methods.

Auditory evoked magnetic fields: a replication, with comments on the magneticP50 analog

SummaryAuditory evoked magnetic fields (AEFs) and EEG auditory evoked potentials (AEPs) were recorded from left and right auditory cortical regions of 12 normal adult subjects. The magnetic sensor was a figure-eight SQUID gradiometer with a 4 cm baseline oriented so as to be maximally sensitive to a current dipole oriented normal to the Sylvian fissure. Stimuli were 100 ms long 1 kHz tone pips with a modal interstimulus interval of 700 ms delivered at sound pressure levels of 40, 60, 80 and 100 dB. AEF amplitude was found to be related to stimulus intensity in a quadratic fashion, AEP amplitude in a linear fashion. AEFs were of larger amplitude in response to contralateral as compared to ipsilateral stimulation. AEPs did not exhibit such a relationship. In a second experiment right-hemisphere AEFs and AEPs in response to contralateral ear tone stimulation in these 12 subjects were combined with similar previous data from 24 subjects, providing a total of 36 subjects, to examine the comparability of the AEPP50 wave form and the AEFP50 analog. The latency of theP50 was found to decrease as a function of increasing stimulus intensity for both AEFs and AEPs, and theP50 latency was consistently shorter in magnetic compared to potential recordings.RiassuntoSono stati registrati campi magnetici uditivi indotti (AEF) e potenziali uditivi indotti EEG (AEP) dalle regioni corticali uditive destra e sinistra di 12 soggetti normali adulti. Il sensore magnetico era un gradiometro SQUID a forma di otto con una linea di base di 4 cm orientato in modo da essere massimamente sensibile a un dipolo di corrente orientato perpendicolarmente alla fissure di Sylvio. Gli stimoli erano impulsi sonori di 1 kHz, lunghi 100 ms con un intervallo modale tra stimoli di 700 ms emessi a livelli di pressione sonora di 40, 60, 80 e 100 dB. Si è trovato che l’ampiezza AEF è correlata all’intensità dello stimolo in modo quadratico, l’ampiezza AEP in modo, lineare. Gli AEF erano di ampiezza maggiore in risposta alla stimolazione contralaterale che in risposta alla stimolazione ipsilaterale. Gli AEP non presentano questa relazione. In un secondo esperimento gli AEF e AEP dell’emisfero destro in risposta al tono di stimolazione nell’orecchio controlaterale in questi 12 soggetti sono stati combinati con dati simili precedenti su 24 soggetti, ottenendo cosí un totale di 36 soggetti, per esaminare la comparabilità della forma dell’onadaP50 di AEP e dell’analogaP50 di AEF. Si è trovato che la latenza dellaP50 decrese in funzione dell’intensità crescente dello stimolo sia per AEF che per AEP, e che la latenza diP50 è decisamente inferiore nelle registrazioni magnetiche rispetto alle registrazioni del potenziale.

Microwave Techniques in the Diagnosis and Treatment of Cancer

Naturally emitted thermal radiation of the human body at cm and mm wavelengths can be utilized to image subcutaneous temperature distributions and detect thermally active tumors. Contacting thermographs that were developed for such point-by-point measurements at long cm wavelengths are compared with remotely focussed, imaging thermographs for short cm and mm wavelengths in regard to instrumentation, measurement methods and clinical results in the detection of breast cancer and other tumors. For treatment of cancer microwave irradiation can produce hyperthermia in a more localized region than conventional methods. Various forms of controlling hyperthermia using subcutaneous probes are discussed, and potentials. preliminary animal experiments and limitations of new forms of noninvasive controls using microwave radiometry are given.

Thermographic Imaging At Millimeter And Centimeter Wavelengths

Theoretical considerations and experiments show that thermography at centimeter wavelengths offers an attractive penetration depth of more than one centimeter; however it is not well suited for remote imaging of the temperature of the human body because of its marginal spatial resolution and the required large distance between the receiver and the object. Millimeter wave thermography tests around 45 GHz show that a spatial resolution of a few millimeters and a temperature resolution of 0.1°K can be achieved. A penetration depth of several millimeters makes millimeter wave thermography more attractive for remote temperature sensing of deeper lying body tissues than infrared thermography.

A Millimeter-Wave Thermograph for Human Breast and Spine Scans

Millimeter-wave thermographs for remote, noninvasive temperature sensing of the human body are described. Their penetration depth ranges from 0.1 mm to 1 cm thus overcoming the depth limitations of conventional infrared thermographs by several orders of magnitude. Potentially useful applications of this new method include clinical studies of the injured human spine and early detection of subcutaneous tumors such as breast cancer. Design details of an optimized, beam- or load switched thermograph for 69.5 GHz are presented which is presently undergoing clinical tests. It exhibits a temperature resolution of 0.25 °c for an integration time of 1 sec.

A Sensitive and Permanent Josephson Mixer for Millimeter Waves

A new method to construct permanent Josephson mixers for millimeter waves is described. In contrast to conventional point contacts which are mechanically unstable and require adjustments after each cooldown, these point contact junctions are set at room temperature, stay mechanically stable and can be temperature cycled without readjustments. The junctions are packaged in a modified Sharples mixer wafer and exhibit a single-sideband noise temperature of 71° K at 47 GHz. Based on these results system noise temperatures of less than 100° K are predicted for practical broadband radiometers, radar and communications receivers up to at least 100 GHz.