Parameters Of Imaging System Research Articles

Lower bound on average mean-square error for image restoration

An average mean-square error bound that is applicable to general image observation models involving degradations of blur, signal-dependent and signal-independent noise, and sensor nonlinearity is derived. A Cramer-Rao lower bound on average mean-square errors for any unbiased image restoration scheme is derived. This bound is analytically expressed as a function of degradation parameters of imaging systems. Potential performance improvements by incorporating signal-dependent noise or sensor nonlinearity into algorithmic design are discussed. >

Stochastic analysis of stereo quantization error

The probability density function of the range estimation error and the expected value of the range error magnitude are derived in terms of the various design parameters of a stereo imaging system. In addition, the relative range error is proposed as a better way of quantifying the range resolution of a stereo imaging system than the percent range error when the depths in the scene lie within a narrow range. >

A Monte Carlo program for the simulation of scintillation camera characteristics

There is a need for mathematical modelling for the evaluation of important parameters for photon imaging systems. A Monte Carlo program which simulates medical imaging nuclear detectors has been developed. Different materials can be chosen for the detector, a cover and a phantom. Cylindrical, spherical, rectangular and more complex phantom and source shapes can be simulated. Photoelectric, incoherent, coherent interactions and pair production are simulated. Different detector parameters, e.g. the energy pulse-height distribution and pulse pile-up due to finite decay time of the scintillation light emission, can be calculated. An energy resolution of the system is simulated by convolving the energy imparted with an energy-dependent Gaussian function. An image matrix of the centroid of the events in the detector can be simulated. Simulation of different collimators permits studies on spatial resolution and sensitivyt. Comparisons of our results with experimental data and other published results have shown good agreement. The usefulness of the Monte Carlo code for the accurately simulation of important parameters in scintillation camera systems, stationary as well as SPECT (single-photon emission computed tomography) systems, has been demonstrated.

Motion and structure from two perspective views: algorithms, error analysis, and error estimation

Deals with estimating motion parameters and the structure of the scene from point (or feature) correspondences between two perspective views. An algorithm is presented that gives a closed-form solution for motion parameters and the structure of the scene. The algorithm utilizes redundancy in the data to obtain more reliable estimates in the presence of noise. An approach is introduced to estimating the errors in the motion parameters computed by the algorithm. Specifically, standard deviation of the error is estimated in terms of the variance of the errors in the image coordinates of the corresponding points. The estimated errors indicate the reliability of the solution as well as any degeneracy or near degeneracy that causes the failure of the motion estimation algorithm. The presented approach to error estimation applies to a wide variety of problems that involve least-squares optimization or pseudoinverse. Finally the relationships between errors and the parameters of motion and imaging system are analyzed. The results of the analysis show, among other things, that the errors are very sensitive to the translation direction and the range of field view. Simulations are conducted to demonstrate the performance of the algorithms and error estimation as well as the relationships between the errors and the parameters of motion and imaging systems. The algorithms are tested on images of real-world scenes with point of correspondences computed automatically. >

Reconstruction in diffraction imaging

The problem of reconstruction in imaging systems that are modeled using the Helmholtz wave equation (diffraction imaging) is addressed. A spectral analysis of the available diffraction data is presented to help develop algorithms and constraints on a diffraction imaging system's parameters for accurate reconstruction of the desired image. Means of reducing the execution time of these algorithms and their relationship to currently available filtered backpropagation and unified Fourier reconstruction methods are also discussed.

Subtraction of simultaneously acquired dual radionuclide images.

The physical aspects of a simultaneous dual radionuclide technique incorporating computer subtraction for the diagnosis of infection using 67Ga citrate and 99mTc methylene diphosphonate (MDP) or sulfur colloid are considered. The efficacy of the data acquisition protocol and the interpretation of the subtracted images are shown to depend significantly on fundamental imaging system parameters. Measurement of these parameters using simple phantoms and their role in elucidating the technique is detailed. Subtracted images produced by three variations of the basic method arising from different normalization algorithms in current usage are compared. Simple phantoms are again used in assessing the accuracy of each variation. Clinical results are reported elsewhere.

Noise in stenosis measurement using digital subtraction angiography.

This paper examines statistical errors in the measurement of arterial stenoses by digital videodensitometry. Images of vessel phantoms were acquired using digital subtraction angiographic techniques with low concentrations of an iodine contrast medium and low levels of x-ray exposure. Effects of the spatial and temporal averaging of image information on signal-to-noise ratios in the stenosis measurement were of primary interest. The influences of iodine concentration, x-ray scatter, veiling glare, x-ray energy spectrum, x-ray exposure, and detective quantum efficiency of the system were also included in the theoretical analysis. The agreement between theoretical calculation and experimental measurement of a simulated vessel was verified using measured values of the imaging system parameters. With a 14.2 mg/ml iodine concentration, using 20 mR per image at the entrance to a 13-cm water phantom, and averaging over a 6-mm length of a vessel 6.2 mm in diameter, the standard deviation in a measurement of a vessel's relative cross-sectional area was about 0.05. The extension of these results to practical applications in vivo is discussed.

Transformation of visual target acquisition data between different meteorological and optical sight parameters: a simple method

A simple method is described for transforming field visual target acquisition data (the standard data) to apply to different meteorological conditions, imaging system parameters, and visual acquisition levels (e.g., detection and recognition). For each probability of target acquisition in the standard data, a new value of range is computed which is appropriate to the new conditions. As an example, the method is applied to the case of optical sights for different values of magnification and for different meteorological visibilities and ambient luminances.

Spaceborne and airborne imaging radar observations of sand dunes

Seasat and aircraft radar imagery of five areas of sand dunes in the southwestern United States and northwestern Mexico have been studied and compared to Landsat imagery and air photos. Radar imaging system parameters included two wavelengths (23.5 cm and 3.0 cm) and incidence angles ranging from 0° through 70°. Horizontal polarization was used on both transmit and receive for all radar imagery. Resolution ranged from 12 m for the best aircraft imagery to about 40 m for Seasat. Sand dunes studied behave as smooth surfaces for both 23.5 cm and 3.0 cm wavelength radars and the reflection of the radar energy from the dunes is specular. Measured surface irregularities of sand dunes are inadequate to cause either Bragg or incoherent scattering of the incident radar beam in the 3.0 to 23.5 cm wavelength region. This results in dunes that appear dark when imaged at incidence angles greater than the angle of repose because none of the dune faces are oriented properly (normal to the incident radar beam) to give a specular return to the antenna. A scattering model based on specular return from randomly oriented flat dune faces was used and experimentally verified using aircraft data. Imaging radar resolution must be adequate to define the changing distribution of dune faces that characterize the dune morphology. Linear dune features with interdune spacing of less than 3–4 resolution elements are not recognizable. Distributed dune types such as barchans or stars must be more than about 10 resolution elements in each direction to be defined on the imagery. Illumination direction of the radar beam is important; directional dune features must be oriented within about 60° of perpendicular to the radar illumination direction in order to be imaged. If such features have considerable topographic relief, the direction of radar illumination is less important. Because directional trends in unexplored regions cannot be predicted, availability of radar imagery from two directions greatly facilitates interpretation of dune morphology and hence conclusions about causative wind regimes.

Infrared Imaging Using Nonlinear Optical Upconversion

This paper presents the phenomenology of different approaches to the frequency-shifting (upconversion) of infrared radiation into the visible and discusses the practical aspects of designing systems to upconvert IR images. The recently discovered process of upconverting infrared radiation into the visible or the ultraviolet using two-photon-pumped alkalimetal vapors and the more familiar method of frequency mixing using single-photon-pumped nonlinear crystals are described and compared. In addition to these coherent processes, the use of quantum-counter action in certain crystals to convert an IR photon into a visible photon by an incoherent process is discussed. The important performance parameters of an IR imaging system are discussed briefly and the considerations and constraints involved in the design of coherent and incoherent image upconverter systems are presented. Using this background, practical system designs are developed for both active and passive imaging. The expected performances of these systems are compared with those of IR imaging systems based on direct-detection of IR photons with semiconductor detectors.