Terahertz heterodyne imager for biomedical applications

Terahertz heterodyne imaging is an established technique that offers the potential for extremely large dynamic range and high signal-to-noise ratio while maintaining fast data acquisition, stable magnitude and phase measurements, reasonable frequency flexibility and mm level penetration in tissue and other materials. The authors have set up an imaging system based around a custom fabricated 2.5 THz planar Schottky diode mixer pair and two optically pumped far IR lasers. One laser is used for the signal beam and supplies as much as 70mW at 2.5 THz. The other laser acts as a local oscillator (LO) source for the two mixers. Line pairs very close to each other (CH3OH and CH2F2) are chosen to provide a workable intermediate frequency output (IF=24 GHz). Broader RF bandwidth is possible with tunable signal sources and wider IF band amplifiers. A novel frequency stabilization scheme has been implemented to track and calibrate the laser power (magnitude and phase) over a sample run. The system uses the second THz mixer, a low frequency (GHz) reference oscillator and a lock-in amplifier to monitor and normalize the two lasers (LO and Signal). Stability of ~0.1 dB and <5 degrees have been achieved with a dynamic range of more than 90dB. The present system scans the sample through the focused beam and measures transmission or reflection at a fixed RF frequency. Applications to date include establishing contrast mechanisms in a range of test and biological materials. The measurement system is described and the merits and demerits discussed. Early results on a variety of samples are presented as well as plans to enhance the performance in the near future

Confocal Ellipsoidal Reflector System for a Mechanically Scanned Active Terahertz Imager

We present the design of a reflector system that can rapidly scan and refocus a terahertz beam for high-resolution standoff imaging applications. The proposed optical system utilizes a confocal Gregorian geometry with a small mechanical rotating mirror and an axial displacement of the feed. For operation at submillimeter wavelengths and standoff ranges of many meters, the imaging targets are electrically very close to the antenna aperture. Therefore the main reflector surface must be an ellipse, instead of a parabola, in order to achieve the best imaging performance. Here we demonstrate how a simple design equivalence can be used to generalize the design of a Gregorian reflector system based on a paraboloidal main reflector to one with an ellipsoidal main reflector. The system parameters are determined by minimizing the optical path length error, and the results are validated with numerical simulations from the commercial antenna software package GRASP. The system is able to scan the beam over 0.5 m in cross-range at a 25 m standoff range with less than 1% increase of the half-power beam-width

A planar quasi-optical SIS receiver for array applications

A planar, quasi-optical SIS receiver operating at 230 GHz is described. The receiver consists of a 2 x 5 array of half wave dipole antennas with ten niobium-aluminum oxide-niobium SIS junctions on a quartz dielectric-filled parabola. The 1.4 GHz intermediate frequency is coupled from the mixer via coplanar strip transmission lines and 4:1 balun transformers. The receiver is operated at 4.2 K in a liquid helium immersion cryostat. We report accurate measurements of the performance of single receiver elements. A mixer noise temperature of 89 K DSB, receiver noise temperature of 156 K DSB, and conversion loss of 3 dB into a matched load have been obtained

Time-Delay Multiplexing of Two Beams in a Terahertz Imaging Radar

We demonstrate a time-delay multiplexing technique that doubles the frame rate of a 660–690-GHz imaging radar with minimal additional instrument complexity. This is done by simultaneously projecting two offset, orthogonally polarized radar beams generated and detected by a common source and receiver. Beam splitting and polarization rotation is accomplished with a custom designed waveguide hybrid coupler and twist. A relative time lag of approximately 2 ns between the beams’ waveforms is introduced using a quasi-optical delay line, followed by spatial recombination using a selectively reflective wire grid. This delay is much longer than the approximately 20-ps time-of-flight resolution of the 30-GHz bandwidth radar, permitting the two beams’ reflected signals from a compact target to be easily distinguished in digital post-processing of the single receiver channel

Inactivity/sleep in two wild free-roaming African elephant matriarchs - Does large body size make elephants the shortest mammalian sleepers?

The current study provides details of sleep (or inactivity) in two wild, free-roaming African elephant matriarchs studied in their natural habitat with remote monitoring using an actiwatch subcutaneously implanted in the trunk, a standard elephant collar equipped with a GPS system and gyroscope, and a portable weather station. We found that these two elephants were polyphasic sleepers, had an average daily total sleep time of 2 h, mostly between 02:00 and 06:00, and displayed the shortest daily sleep time of any mammal recorded to date. Moreover, these two elephants exhibited both standing and recumbent sleep, but only exhibited recumbent sleep every third or fourth day, potentially limiting their ability to enter REM sleep on a daily basis. In addition, we observed on five occasions that the elephants went without sleep for up to 46 h and traversed around 30 km in 10 h, possibly due to disturbances such as potential predation or poaching events, or a bull elephant in musth. They exhibited no form of sleep rebound following a night without sleep. Environmental conditions, especially ambient air temperature and relative humidity, analysed as wet-bulb globe temperature, reliably predict sleep onset and offset times. The elephants selected novel sleep sites each night and the amount of activity between sleep periods did not affect the amount of sleep. A number of similarities and differences to studies of elephant sleep in captivity are noted, and specific factors shaping sleep architecture in elephants, on various temporal scales, are discussed

Renal function and cortical blood flow during the recovery phase of acute renal failure

Renal function and cortical blood flow during the recovery phase of acute renal failure. The characteristics of the recovery process in dichromate-induced acute renal failure were determined. Rats were studied 1, 4, 7, and 14 days after the s.c. injection of either saline or potassium dichromate. In the sham-injected control animals, all values at each interval were similar. The typical pattern of acute renal failure was seen one day after dichromate injection: glomerular filtration rate (GFR) fell 80%, total renal blood flow (TRBF) was reduced 35%, the proportional flow to the outer cortex was diminished, and the urinary to plasma (U/P) inulin clearance was reduced. The early recovery phase, days 4 and 7, was characterized by: 1) a mild but significant diuresis, 2) progressive improvement in GFR and an increase in the proportional flow to the outer cortex, which actually exceeded control values, 3) a dissociation between improvement in renal function and changes in TRBF, since GFR increased progressively while TRBF remained relatively fixed, and 4) improvement in GFR that was associated with a progressive and parallel increase in absolute perfusion of the outer cortex. The present data suggest that the recovery process occurs in two stages. In the first stage, the restoration of outer cortical perfusion and renal function precedes the recovery of TRBF and tubular function, which occur during the second stage of the recovery process.Fonction rénale et débit sanguin rénal cortical au cours de la période de récupération de l'insuffisance rénale aiguë. Les caractéristiques du processus de récupération après une insuffisance rénale aiguë induite par le dichromate, ont été déterminées. Des rats ont été étudiés 1, 4, 7, et l4 jours après l'injection s.c. de dichromate de potassium ou de soluté salé. Chez les animaux contrôles, toutes les valeurs obtenues sont semblables. L'aspect typique de l'insuffisance rénale aiguë est observée un jour après l'injection de dichromate: GFR diminue de 80%, le débit sanquin rénal (TRBF) est réduit de 35%, la fraction de ce débit délivrée au cortex superficiel diminue et le U/P de l'inuline est abaissé. La phase de récupération précoce, aux jours 4 et 7, est caractérisée par: 1) une diurèse peu importante mais significativement plus grande, 2) une amélioration progressive de GFR et une augmentation de la fraction du débit délivrée au cortex superficiel, qui devient supérieure aux valeurs contrôles, 3) une dissociation entre l'amélioration de la fonction rénale indiquée par l'augmentation progressive de GFR, et TRBF qui reste relativement bas, 4) et une amélioration de GFR qui est associée à une augmentation progressive et parallèle du débit absolu de perfusion du cortex superficiel. Ces résultats suggèrent que le processus de récuparation survient en deux étapes. A la première étape, la récupération du débit cortical superficiel et de la fonction rénale précède la récupération de TRBF et de la fonction tubulaire qui constitue la deuxième étape

The Evolution of Percutaneous Mitral Valve Repair Therapy Lessons Learned and Implications for Patient Selection

AbstractMitral regurgitation (MR) is the most common valve disease in the United States. However, a significant number of patients are denied surgery due to increased age, poor ventricular function, or associated comorbidities, putting them at high risk for adverse events. Moreover, the benefit of surgery for MR is unclear in patients with functional (secondary) MR. Recently, percutaneous repair of the mitral valve with a particular device (MitraClip, Abbott, Menlo Park, California) has emerged as a novel therapeutic option for patients with secondary MR or those deemed to be high risk for surgery. We review data from its initial concept through clinical trials and current data available from several registries. We focused on lessons learned regarding adequate patient selection, along with current and future perspectives on the use of device therapy for the treatment of MR