The response of an optical systems to a point source, known as the point-spread function (PSF), represents one of the
most fundamental characteristics of an optical system. The PSF varies as a function of source spectral composition as
well as position with respect to the optical axis. PSF characterization of optical systems can be used to predict their
performance in imaging and non-imaging applications.
In this paper we describe an electro-optical setup for automated characterization of the PSF of optical systems over a
broad range of operating conditions and radiance levels, with spectral compositions ranging from ultraviolet (UV) to
long-wave infrared (LWIR). Our test setup includes interchangeable radiance sources and computer controlled motion
stages which allows for automated characterization of the optical system under test. The software-controlled
characterization process provides quantitative analysis of the system’s chromatic and monochromatic aberrations,
including axial chromatism, field curvature, and field distortion. The developed process also defines system level
characteristics, such as relative illumination, field of regard and magnification. Finally, we demonstrate
characterization of the operational dynamic range of imaging and non-imaging sensors employing the described setup,
including their threshold responsivity, as well as their saturation performance under intense illumination conditions.
Ischemic stroke accounts for nearly 80% of all stroke cases. Although proton diffusion and perfusion magnetic
resonance imaging (MRI) are the gold standards in ischemic stroke diagnostics, the use of hyperpolarized 129Xe MRI has
a potential role to contribute to the diagnostic picture. The highly lipophilic hyperpolarized 129Xe can be non-invasively
delivered via inhalation into the lungs where it is dissolved into the blood and delivered to other organs such as the brain.
As such, we expect hyperpolarized 129Xe to act as a perfusion tracer which will result in a signal deficit in areas of blood
deprived tissue. In this work, we present imaging results from an animal model of transient ischemic stroke
characterized through 129Xe MRI. In this model, a suture is used to occlude the middle cerebral artery (MCA) in the rat
brain, thus causing an ischemic event. After a period of MCA occlusion, the suture can then be removed to reperfuse the
ischemic area. During the ischemic phase of the stroke, a signal void was observed in the MCA territory; which was
subsequently restored by normal 129Xe MRI signal once perfusion was reinstated. Further, a higher resolution one-dimensional
chemical shift image shows a sharp signal drop in the area of ischemia. Validation of ischemic damage was
shown through both proton diffusion-weighted MRI (DWI) and by 2,3,5-triphenyltetrazoliumchloride (TTC) staining.
The results show the potential of 129Xe to act as a perfusion tracer; information that may add to the diagnostic and
prognostic utility of the clinical picture of stroke.
The features used in the ABCD rule for characterization of skin lesions suggest that the spatial and frequency information in the nevi changes at various stages of melanoma development. To analyze these changes wavelet transform based features have been reported. The classification of melanoma using these features has produced varying results. In this work, all the reported wavelet transform based features are combined to form a single feature set. This feature set is then optimized by removing redundancies using principal component analysis. A feed forward neural network trained with the back propagation algorithm is then used in the classification process to obtain better classification results.