Preclinical SPECT offers a powerful means to understand the molecular pathways of metabolic activity in animals.
SPECT cameras using pinhole collimators offer high resolution that is needed for visualizing small structures in
laboratory animals. One of the limitations of pinhole geometries is that increased magnification causes some rays to
travel through the scintillator detector at steep angles, introducing parallax errors due to variable depth-of-interaction
in the scintillator, especially towards the edges of the detector field of view. These parallax errors
ultimately limit the resolution of pinhole preclinical SPECT systems, especially for higher energy isotopes that can
easily penetrate through millimeters of scintillator material. A pixellated, focused-cut scintillator, with its pixels
laser-cut so that they are collinear with incoming rays, can potentially compensate for these parallax errors and thus
open up a new regime of sub-mm preclinical SPECT. We have built a 4-pinhole prototype gamma camera for
preclinical SPECT imaging, using an EMCCD camera coupled to a 3 mm thick CsI(Tl) scintillator whose pixels are
focused towards each 500 μm-diameter pinhole aperture of the four pinholes. The focused-cut scintillator was
fabricated using a laser ablation process that allows for cuts with very high aspect ratios. We present preliminary
results from our phantom experiments.
We describe a time-integrating acousto-optic correlator (TIAOC) developed for imaging and target detection using a wideband random-noise radar system. This novel polarization interferometric in-line TIAOC uses an intensity-modulated laser diode for the random noise reference and a polarization-switching, self-collimating acoustic shear-mode gallium phosphide (GaP) acousto-optic device for traveling-wave modulation of the radar returns. The time-integrated correlation output is detected on a 1-D charge-coupled device (CCD) detector array and calibrated and demodulated in real time to produce the complex radar range profile. The complex radar reflectivity is measured in more than 150 radar range bins in parallel on the 3000 pixels of the CCD, improving target acquisition speeds and sensitivities by 150 over previous serial analog correlator approaches. The polarization interferometric detection of the correlation using the undiffracted light as the reference allows us to use the full acousto-optic device (AOD) bandwidth as the system bandwidth. Also, the experimental result shows the fully complex random-noise signal correlation and coherent demodulation without an explicit carrier, demonstrating that optically processed random-noise radars do not need a stable local oscillator.
We present an optimized design of an acousto-optic tunable filter (AOTF) using a phased-array transducer for a spectrally-multiplexed
ultrafast pulse-shaping RF beamformer application. The momentum-space interaction geometry is used to optimize an AOTF using acoustic beam-steering techniques in combination with acoustic anisotropy in order to linearly map the applied RF frequency to the filtered output optical frequency. The appropriate crystal orientation and phased-array transducer design are determined to linearize the RF to optical frequency mapping even in the presence of optical dispersion of the birefringence. After optimizing the phased-array transducer, acoustic anisotropy, and optical anisotropic diffraction geometry, the designed AOTF will compensate for the birefringent dispersion of TeO<sub>2</sub> to give a linear modulation of RF frequencies onto the corresponding optical frequencies. This linearized frequency mapped AOTF is required for a squint-compensated, wavelength-multiplexed, optically processed RF imager.
A time-integrating acousto-optic correlator (TIAOC) is a good candidate for imaging and target detection using a wideband random noise radar system. We have developed such a correlator for
a random noise radar with a signal frequency range of 1-2 GHz. This
system has demonstrated good wideband signal correlation performance with good dynamic range and fine tuning of delays.