A complication of Fourier domain optical coherence tomography (OCT) methods, such as spectral domain and swept
source OCT, is the complex conjugate ambiguity due to inverse Fourier transform of real-valued data. As a result, the
image is symmetric to the zero plane, and only half of the theoretical imaging depth range is used to avoid overlapping
"mirror images" that confuse the image. We have previously demonstrated harmonic detection in a video-rate spectral
domain OCT system using a high speed line scan camera. Harmonic detection removes the complex conjugate
ambiguity by providing the real and imaginary components of the spectral interferogram. In this work, we show that
harmonic detection is easily applied to swept source OCT to remove the complex conjugate ambiguity while maintaining the imaging performance of the original swept source instrument. Harmonic detection swept source OCT allows simultaneous experimental determination of the real and imaginary components of each spectral interferogram without the need to measure consecutive A-scans at differing phase. This harmonic detection swept source optical coherence tomography system exhibits 110 dB sensitivity, up to 55 dB dynamic range, ≥ 50 dB complex conjugate rejection, and operates at the full 16 kHz sweep rate of the swept source laser for real-time video rate imaging.
Acetone is a good marker of metabolic stress as it is the most volatile and rapidly equilibrated of the ketone bodies
produced by human metabolism. If the body utilizes predominately fat to meet its energy requirements, blood and
breath acetone concentrations will increase. Elevated concentrations of breath acetone can indicate a normal response to
caloric imbalances in the diet, or a diseased state such as untreated diabetes. This paper describes a novel method of
acetone detection that uses a gas-solid chemical reaction of acetone with a hydroxylamine hydrochloride (HA) to
produce an easily detectable chemical species, HCl. Breath samples are passed through a reactor filled with solid HA
and the amount of HCl gas released is measured by sensitive near infrared diode laser spectroscopy. The breath acetone
instrument described is compact, low power and portable.
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