No abstract

No abstract

We present a novel scheme to separate spatially twin beams generated by a type-I lithium niobate (LNB) optical parametric oscillator near frequency degeneracy. The system is based on a holographic diffraction grating acting as a beam splitter in a balanced detector. The fast and easy temperature tuning of LNB index of refraction allows an easy control of the twin-beam wavelength distance in a range of the order of similar to 100 nm. We report correlation spectra measured for different twin-beam wavelength separations (15-60 nm) with a maximum noise reduction of 3.2 dB at 3.5 MHz. The described system exhibited a pump resonance stability longer than 6 h with infrared output power fluctuations within 4% around an average value of similar or equal to 2 mW in each beam. The measured oscillation threshold pump power was lower than 31 mW

We have assembled a prototype system for multimodal (radionuclide and optical) in vivo planar imaging of small animals (mice) using single photon emission radiotracers (Tc-99m) and a fluorescent marker (hematoporphyrin). Preliminary tests of the separate (optical and radionuclide) prototype imaging systems are presented, aimed at assessing their features and at determining the experimental protocol for in vivo imaging. Tests were performed on anesthetized healthy or tumor bearing mice. The gamma radiation detector is a small area (11 11 mm 2 ) hybrid pixel detector based on the Medipix1 ASIC readout technology (64 64 square pixels of 170 m by side), bump-bonded to a 300 m thick silicon detector. High spatial resolution in radioimaging (in the order of 1 mm) is achieved in vivo with a pinhole tungsten collimator (0.35 mm diameter, 90 acceptance angle, field of view of over 20 mm at 10 mm source distance). A future setup will use the Medipix2 hybrid detector (256 256 square pixels, 55 m by side) bump-bonded to a 1 mm thick CdTe pixel detector. The laser-induced in vivo fluorescence imaging system comprises a pulsed light source (Nd : YAG laser, = 532 nm, energy/pulse = 30 mJ, pulse width = 50 ps, repetition rate = 10 Hz) used to excite the fluorescence emission (600-760 nm) of injected hematoporphyrin compound, a low sensitivity CCD camera and a commercial image analysis system. Images of normal and tumor regions are acquired by using a cut-on filter ( 600 nm). Digital image subtraction then enhances the tumor contrast with respect to the background. The final experimental protocol, only partly implemented here, includes independent and then combined optical/radio imaging of control mice and of a solid tumoral area (human thyroid derived anaplastic carcinoma) after injection of the radiotracer and/or of the fluorophore. In this work, the accumulation of the radionuclide in selected organs and of the fluorophore in the tumor provides the signal contrast in the two imaging modalities. Fluorescence spectroscopy of excised tissue samples is also performed to help the interpretation of fluorescence images. Results of in vivo combined imaging on tumor in mice will be shown in a next paper.

We report on tests of a radionuclide imaging system for in vivo investigations in small animals with low energy gamma-rays as from 125I (27-35 keV). The system imaging optics features a high resolution coded aperture mask and a fine pitch silicon hybrid pixel detector of the Medipix2 series (55 μm pitch). The coded aperture (no-two-holes-touching MURA 62×62) had 70 μm holes in 75 μm tungsten, and was used in a 2:1 magnification for a field of view of about 7 mm. Laboratory tests with a 109Cd 22-keV source and in vivo mouse thyroid imaging tests with 125I show a system resolution of about 110 μm. This low energy, semiconductor-based, compact gamma camera is the basic imaging unit of a small animal single photon emission computed tomography system with deep sub-millimeter resolution