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A laser induced fluorescence (LIF) instrument has been developed to measure tropospheric NO 2 with low detection limit. The instrument design, development and first measurements are reported. There are also details of the temporal gate system built for the fluorescence acquisition. The instrument is able to make fast measurements (up to 4 Hz) and shows a limit of detection of 10 pptv/60 s. Continuous observations (2 weeks in summer 2007) in a small town in central Italy were used to test the performance of the instrument and to study the photochemistry of ozone in a background site. LIF and a commercial chemiluminescence (CL) instrument simultaneous observations of NO 2 show a good linearity (LIF = 1.02 CL + 0.6 (ppb), R 2 = 0.98) but there is a bias of the commercial instrument of about 0.60 ppbv on average. The overestimation of the CL system is probably due to conversion of NO y species into NO by the molybdenum converter used in the CL instrument to detect NO 2 . Analysis of 1 s data is used to test the instrument response and the coupling between nitrogen oxides and ozone.

The suitability of sandwich holography for displacement derivative measurement is demonstrated. Holographic carrier fringes are produced by shearing one plate relative to the other in a sandwich pair. Some experimental results are presented.

Sandwich hologram interferometry and sandwich speckle photography tend to complement each other as displacement measuring methods; a sandwich hologram is best suited for out-of-plane movements, while speckle photography is used to determine in-plane components. The two techniques can be combined and both holographic and speckle photographic data can be stored on the same sandwich pair. Fringes caused by in-plane rigid body motion can be compensated for and local displacement evaluated.

A simple method of fringe control in HNDT is described; some experimental results in defects diagnostic are shown.

A simple and compact method of optical differentiation of displacement patterns is proposed. It utilizes sandwich-double exposure holograms. Some typical experimental results are presented.

Although chemodectomas of the mediastinum are uncommon lesions, they have very characteristic arteriographic findings. When a vascular tumor mass is found in the region of the aortic bodies, mediastinal chemodectoma should be considered. Angiography is valuable in defining the vascular supply and determining the resectability of mediastinal chemodectomas.

Water soluble contrast myelography has been associated with a variety of complications. The inadvertant injection of air into the thecal sac may produce an apparent extramedullary, intradural defect on myelography. Post myelography CT examination should be used to confirm the presence of such a pseudolesion.

An upside-down configuration of the spleen can be mistaken for a left suprarenal mass. A radioisotopic liver-spleen scan will demonstrate a characteristic appearance of the spleen with its hilus superiorly and its convex border medially and adjacent to the kidney. When a left suprarenal mass is identified, we advocate the liver-spleen scan as the first step in the diagnostic workup. If the typical configuration is found, no further studies are necessary.