Biomedical subjects

J L Schiano

Publications and source records attributed to J L Schiano.

5 recordsLinked to original sources

PubMed2000

Detection of nuclear resonance signals: modification of the receiver operating characteristics using feedback.

The performance of a nuclear resonance detection system can be quantified using binary detection theory. Within this framework, signal averaging increases the probability of a correct detection and decreases the probability of a false alarm by reducing the variance of the noise in the average signal. In conjunction with signal averaging, we propose another method based on feedback control concepts that further improves detection performance. By maximizing the nuclear resonance signal amplitude, feedback raises the probability of correct detection. Furthermore, information generated by the feedback algorithm can be used to reduce the probability of false alarm. We discuss the advantages afforded by feedback that cannot be obtained using signal averaging. As an example, we show how this method is applicable to the detection of explosives using nuclear quadrupole resonance.

Algorithms↗

PubMed1999

Optimization of offset frequency in the SORC pulse sequence using feedback.

The low signal-to-noise ratio (SNR) of nuclear quadrupolar resonance measurements has motivated research on signal enhancement methods, including multipulse sequences that facilitate signal averaging, the development of interlaced pulse sequences, and super-Q coils. More recently, it has been shown that feedback can be used to automatically optimize pulse sequence parameters, maximizing the SNR. This paper extends this work by using feedback to optimize the offset frequency in the strong off-resonant comb pulse sequence. Analysis and results are presented for a sample of sodium nitrite at both liquid nitrogen and room temperatures.

Magnetic Resonance Spectroscopy↗

PubMed1999

Feedback optimization of pulse width in the SORC sequence.

A method for increasing the signal-to-noise ratio (SNR) of nuclear quadrupole resonance (NQR) measurements by automatically adjusting a pulse parameter in real-time is presented. This approach is useful in situations where the optimal pulse parameters cannot be chosen beforehand due to lack of knowledge regarding the system. For example, NQR provides a means for detecting explosives by revealing the presence of (14)N. In this particular application, the distance between the search coil and the explosive, as well as the temperature of the explosive, is unknown. As a result, a fixed set of pulse parameters will not yield the largest SNR for all possible search applications. This paper describes a feedback algorithm that uses measurements of the NQR signal to automatically adjust the pulse width in the strong off-resonant comb sequence to maximize the SNR of the NQR measurement. Experimental results obtained using a sample of sodium nitrite are presented.

Algorithms↗

PubMed1987

A programmable-delay line.

A relatively simple circuit is described which delays audio signals in 5 microseconds steps from 0 microsecond to 4000 microseconds. Delays are programmed via twelve TTL-level data lines. The magnitude response is flat and the phase response is linear from DC to 5 kHz. The gain of the circuit is fixed and independent of the selected delay. Delays are accurate to within 1 microsecond of the programmed value. The device is a nice alternative to other methods which have diverse shortcomings.

Acoustic Stimulation↗

PubMed1986

Lateralization of low-frequency tones and narrow bands of noise.

It is well known and universally accepted that people's ability to use ongoing interaural temporal disparities conveyed via pure tones is limited to frequencies below 1600 Hz. We wish to determine if this limitation is the result of the constant amplitude and periodic axis-crossings which characterize pure tones. To this end, an acoustic pointing task was employed in which listeners varied the interaural intensitive difference of a 500-Hz narrow-band noise (the pointer) so that the position of its intracranial image matched that of a second, experimenter-controlled stimulus (the target). Targets were either pure tones or narrow bands of noise (50 or 100 Hz wide). The narrow bands of noise were delayed interaurally in two distinct manners: Either the entire waveform or only the carrier was delayed. In the latter case, the envelopes and phase-functions of the bands of noise were identical interaurally. This resulted in noises which resemble the pure tone case in that the interaural delay is manifested as a constant phase-shift and resemble ordinary noises in that the envelope and phase are random functions of time. Surprisingly, it appears that all three targets were lateralized virtually identically regardless of frequency or bandwidth. Apparently, the dynamically changing envelopes and phases did not affect the listeners' use of interaural temporal disparities in any discernible fashion.

Acoustic Stimulation↗