A technique for enhancing the perceptual sharpness of an image is described. The enhancement algorithm augments the frequency content of the image using shape-invariant properties of edges across scale by using a nonlinearity that generates phase coherent higher harmonics. The procedure utilizes the Laplacian transform and the Laplacian pyramid image representation. Results are presented depicting the power-spectra augmentation and the visual enhancement of several images. Simplicity of computations and ease of implementation allow for real-time applications such as high-definition television (HDTV).

Radiation quality indices (QI), tumor control probability (TCP), and normal tissue complication probability(NTCP) were evaluated for ideal single and double plane HDR interstitial implants. In the analysis, geometrically-optimized at volume (GOV) treatment plans were generated for different values of inter-source-spacing (ISS) within the catheter, inter-catheter-spacing (ICS), and inter-plane-spacing (IPS) for single -and double -plane implants. The dose volume histograms (DVH) were generated for each plan, and the coverage volumes of 100%, 150%, and 200% were obtained to calculate QIs, TCP, and NTCP. Formulae for biologically effective equivalent uniform dose (BEEUD), for tumor and normal tissues, were derived to calculate TCP and NTCP. Optimal values of QIs, except external volume index (EI), and TCP were obtained at ISS = 1.0 cm, and ICS = 1.0 cm, for single-plane implants, and ISS = 1.0 cm, ICS = 1.0 cm, and IPS = 0.75 to 1.25 cm, for double -plane implants. From this study, it is assessed that ISS = 1.0 cm, ICS = 1.0 cm, for single -plane implant and IPS between 0.75 cm to 1.25 cm provide better dose conformity and uniformity.

Electron beam dosimetry at low monitor unit (MU) settings is important for dosimetric applications. Dose linearity, beam flatness, and beam energies were studied at low MU settings with various dose rates for different types of linear accelerators. It is observed that for the scattering foil units, the dose/MU is a smooth function of MU for all beam energies. Discrepancies in dose/MU are highest at the lowest MU. Significant variation (5%-245%) in dose linearity is observed among various linear accelerators at low MU settings. Dose rate has no effect on the dose linearity for all energies for the scattering foil units tested. On the contrary, for the scanned beam, there is no predictable pattern as dose/MU is random in nature and varies with time and beam energy. The maximum dosimetric error is observed for the highest energy beam where the beam width is most narrow. Using film, the beam uniformity was noticed to be very poor at low MU and high energy for scanned beams. The beam uniformity and dose linearity are random at low MU due to the random nature of the scan cycle. Under the adverse conditions, the deviation in dosimetric parameters was observed up to 200 MU.

The concerted effort to minimize the radiation exposure to normal human tissues while delivering a high radiation dose to the tumor often results in complications. This limits the efficacy of radiation treatment. Analysis of radiation tolerance dose with organ weight in 15 human organs yields a correlation coefficient of 0.62, whereas the correlation of radiation tolerance dose with blood and water content yields correlation coefficients of 0.82 and 0.60, respectively. Results indicate that as the organ weight and/or blood and water content increases, radiation tolerance dose decreases.

Exposure measurements with ionization chambers are dependent on the correction factors related to the beam energy (ke), temperature and pressure (ktp), ionization recombination (Pion), and polarity (kpol) effects. In this work, six different chambers commonly used in diagnostic radiology were investigated for the Pion and kpol at various exposure rates by changing the tube voltage, beam current, exposure time, and distance. A special triaxial connector was used to connect chambers to an electrometer capable of measuring positive and negative polarity and 150 V and 300 V electrode potentials to measure the kpol and Pion, respectively. A mammography unit (24-35 kVp) and a diagnostic x-ray unit (60-125 kVp) were used. Results indicate that the magnitude of the Pion is linearly dependent on kVp for large volume (> 150 cm3) chambers and independent for small volume (< or = 150 cm3) chambers. In general, Pion is higher at higher exposures (increasing kVp, mAs, and decreasing distance); however, kpol is independent of exposure rate and kVp, but strongly depends on the sensitive volume of an ion chamber. Pion and kpol vary between 1-48% and 1-16%, respectively, among various chambers and exposure conditions. Chambers with larger volumes have higher values of Pion and kpol. The desired accuracy of +/- 5% in exposure measurements might not be feasible unless both the polarity and recombination effects are known and accounted accurately.