Showing papers on "Parametric Image published in 1997"

Parametric Images of Benzodiazepine Receptor Concentration Using a Partial-Saturation Injection:

Abstract: The in vivo quantification of the benzodiazepine receptor concentration in human brain using positron emission tomography (PET) and 1l C-flumazenil ( 11 C-FMZ), is usually based on a three-compartment model and on PET curves measured in a small number of large regions of interest; however, it should be interesting to estimate the receptor concentration for each pixel and to build quantified images of the receptor concentration. The main advantage is to allow screening of the receptor site localization and visual observation of the possible abnormalities. Up to now, all the methods described include complex experimental protocols, difficult to use in routine examinations. In this paper, we propose the partial-saturation approach to obtain parametric images of benzodiazepine receptor concentration and FMZ affinity. It consists of a single FMZ injection with a low specific activity, followed by Scatchard analysis. Like other parametric imaging methods, this partial-saturation approach can lead to a small percentage (<1%) of unrealistic values in receptor-poor regions; however, it is the only method that allows receptor concentration and affinity images to be obtained from a single-injection 40-min experiment without blood sampling. We also propose a second method in which the receptor concentration map is directly deduced from the PET image acquired 5 to 10 min after a partial-saturation injection. This method assumes a known and constant FMZ affinity value but requires only very simple corrections of this PET image. It is robust (negative values are never found) and quite simple to use in routine examination of patients (no blood sampling, single injection, only 10-min experiment).

Imaging through scattering media by parametric amplification of images: study of the resolution and the signal-to-noise ratio.

Abstract: An imaging scheme through scattering media in which parametric image amplification is used is presented. An image of a resolution chart through a solution of latex microspheres with an attenuation of 22 mean free paths is obtained with a resolution of 20 µm. The evolution of the signal-to-noise ratio with respect to the medium attenuation is studied and compared with a rough modeling of the imaging process.

Toward retinal vessel parameterization

Abstract: The reliable measurement of retinal vessel geometry in ordinary red-free fundus photographs is a challenging issue. Quite apart from refractive effects which can distort absolute measures, the existence of the central light reflex poses some interesting problems in vessel modelling and segmentation. One aim of our research is to obtain subpixel vessel width precision from digitised retinal photographs. For this purpose, we require a reasonable physical and mathematical model for the vessel intensity profile. In this paper, we review physical principles behind the image formation, leading to a twin Gaussian model. We test 4 non-linear parametric models based on Gaussian forms. Some applications of this model-based approach are introduced, including the parametric detennination of vessel centre and the accurate determination of vessel width in typical noisy clinical images. Key Words : retinal imaging. non-linear parametric models, parametric image models, sub-pixel resolution

Parametric imaging of patient pharmacokinetics

Abstract: This paper presents an approach to extracting patient pharmacokinetic information from a set of longitudinal scintigraphic images and representing the kinetic information in parametric image form. In this approach, three or four pairs of simultaneously acquired anterior and posterior images, for internal dosimetry with iodine-131, are obtained at 24-h intervals. Each pair of anterior and posterior images is converted to a ”conjugate-view” image. The sequential conjugate-view images are then spatially registered to each other using a symmetric phase-only matched filter technique. With the registered images, the value at each pixel location, over time, is fitted to a monoexponential function. The resulting decay constant and intercept parameters are then represented as ”decay-constant” and ”intercept” images. Further analytical integration of the exponential function results in a ”cumulated-activity” image. Phantom studies demonstrated that the proposed method is accurate and reliable in the registration and kinetic data extraction of the longitudinal images. Clinical application of the approach to patients with thyroid carcinoma showed that regions of rapid uptake or clearance that would not otherwise be highlighted were easily identified and some regions with unexpected kinetics were observed. It is concluded that decay-constant, intercept, and cumulated-activity images provide a rapid and comprehensive visual assessment of patient pharmacokinetics. The technique may have a greater impact on the care of patients with extensive and distributed disease.

Parametric image coding by means of polynomial transforms

Abstract: In this paper we propose an image coding scheme based on the polynomial transform and multiresolution analysis. The polynomial transform is an image representation model that mimics some properties of the human vidual system, and which we use in order to model edges in terms of their characteristic parameters. Based on the polynomial transform, we build a pyramidal hierarchical predictive scheme for image coding. The feature parameters that we encode are: local average, edge orientation, edge position and edge magnitude.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Observation of quantum noise correlations in parametric image amplification

Abstract: There has recently been increased interest in the application of squeezed light to phenomena in the spatial domain. In particular, it was shown that spatially broadband squeezed light can be used to image faint objects with subshot noise sensitivity.’ Since an optical parametric amplifier (OPA) generates correlated photons that are spatially broadband, it is an ideal process for the initial demonstration of quantum correlations in image amplification. Quantum-noise reduction of more than 6 dB has previously been achieved by use of twin beams of light generated by a traveling-wave 0PA.Z Also, parametric amplification has been shown to have practical applications in timegated image r e~overy .~ ,~ An example is the amplification of ballistic photons through turbid media for biomedical imaging.5 Here we report what we believe to be the first observation of quantum noise correlations between the spatial frequencies of a parametrically amplified image and the generated conjugate image. As shown in Fig. la, an object is placed in the signal (1064 nm) path and imaged via a X 1 telescope into the OPA. The image inside the OPA is formed by light traveling at many different spatial frequencies. Since the pump beam (532 nm) is aligned on axis, we can assume it to be a plane wave at zero spatial frequency. Because the OPA is spatially broadband, a range of spatial frequencies of the image are amplified and, additionally, an idler image with similar spatial frequencies is generSoliton Energy (pJ)