Low polarization dependent diffraction grating for wavelength demultimlexing.

A low polarization dependent, high diffraction efficiency grating for wavelength demultiplexer is proposed, manufactured by standard crystallographic etching of Si surface. Light is incident and diffracted inside the wafer, which is covered with reflecting metal. Optimized groove form results in a flat spectral response for TE and TM polarizations.

Measurement of glomerular filtration rate with technetium-99m DTPA: comparison of plasma clearance techniques.

We have compared several techniques for measuring [99mTc]DTPA plasma clearance following single injection to estimate glomerular filtration rate (GFR). Half hourly measurements of disappearance of plasma activity were used to calculate a reference GFR corrected for one-pool assumption and body surface area. Alternative methods involving (i) single blood sample, (ii) two blood samples, (iii) external detector clearance rate, and (iv) a combination of (i) and (iii) were then compared. Closest correlations were obtained with (i) two blood samples at 2 hr and 4 hr (s.e.e. 2.8 ml/min) and (i.v.) external rate constant from 2-5 hr with a blood sample at 3 hr (s.e.e. 3.0 ml/min). Correlations with single blood sample were closest at 3 hr and 4 hr postinjection (s.e.e. 5.4 and 4.5 ml/min, respectively). External detector disappearance rate constant alone was least accurate (s.e.e. greater than 10 ml. min).

Measurement of glomerular filtration rate with 99mTc-DTPA: a comparison of gamma camera methods.

A comparison has been made between three gamma camera methods for estimation of glomerular filtration rate (GFR) using 99mTc-DTPA in a group of 27 patients with widely different renal function. Plasma clearance of 99mTc-DTPA by multiple blood sampling was used as the reference. Percentage uptake of chelate in the bladder and kidneys at 20 min after injection gave the lowest standard error of 8.0 ml/min. Techniques using early uptake of isotope in the kidneys at 2 min after injection gave less accurate estimates. Correction for the vascular activity in the renal region of interest improved the results for the 2 min uptake technique. Gamma camera techniques provide rapid estimates of GFR which are less accurate than those obtained by plasma clearance of labelled chelate.

Use of the flexible film isolator as a single circuit hypoxic chamber for small animals.

PVC isolators are now widely used for housing animals and provide a readily available pretested air-tight chamber (Pendry, 1984; Trexler, 1984). We have adapted a flexible film isolator for use as a hypoxic chamber for small animals. The environment within the chamber can be easily and continuously monitored with indwelling probes, obviating the need for a separate circuit for gas analysis. This design has been used for long-term studies of chronic hypoxia.