Mammographic image restoration using maximum entropy deconvolution

A Review on MR Image Intensity Inhomogeneity Correction

Intensity inhomogeneity (IIH) is often encountered in MR imaging, and a number of techniques have been devised to correct this artifact. This paper attempts to review some of the recent developments in the mathematical modeling of IIH field. Low-frequency models are widely used, but they tend to corrupt the low-frequency components of the tissue. Hypersurface models and statistical models can be adaptive to the image and generally more stable, but they are also generally more complex and consume more computer memory and CPU time. They are often formulated together with image segmentation within one framework and the overall performance is highly dependent on the segmentation process. Beside these three popular models, this paper also summarizes other techniques based on different principles. In addition, the issue of quantitative evaluation and comparative study are discussed.

Investigation of a 2D two-point maximum entropy regularization method for signal-to-noise ratio enhancement: application to CT polymer gel dosimetry

This study presents a new method of image signal-to-noise ratio (SNR) enhancement by utilizing a newly developed 2D two-point maximum entropy regularization method (TPMEM). When utilized as an image filter, it is shown that 2D TPMEM offers unsurpassed flexibility in its ability to balance the complementary requirements of image smoothness and fidelity. The technique is evaluated for use in the enhancement of x-ray computed tomography (CT) images of irradiated polymer gels used in radiation dosimetry. We utilize a range of statistical parameters (e.g. root-mean square error, correlation coefficient, error histograms, Fourier data) to characterize the performance of TPMEM applied to a series of synthetic images of varying initial SNR. These images are designed to mimic a range of dose intensity patterns that would occur in x-ray CT polymer gel radiation dosimetry. Analysis is extended to a CT image of a polymer gel dosimeter irradiated with a stereotactic radiation therapy dose distribution. Results indicate that TPMEM performs strikingly well on radiation dosimetry data, significantly enhancing the SNR of noise-corrupted images (SNR enhancement factors >15 are possible) while minimally distorting the original image detail (as shown by the error histograms and Fourier data). It is also noted that application of this new TPMEM filter is not restricted exclusively to x-ray CT polymer gel dosimetry image data but can in future be extended to a wide range of radiation dosimetry data.

A prototype of a quasi-monochromatic system for mammography applications

Improvement in image contrast and dose reduction, in mammographic x-ray imaging, can be achieved using narrow energy band x-ray beams in the 16-24 keV range. As part of an Italian Government funded project, a quasi-monochromatic system for mammography applications has been developed. The system is based on a tunable narrow energy band x-ray source operating in the 16-24 keV energy range. The bremsstrahlung beam is monochromatized via Bragg diffraction by a highly oriented pyrolytic graphite mosaic crystal (HOPG). The scanning system provides a large field (18 x 24 cm2) of quasi-monochromatic x-rays with energy resolution ranging from 10% at 18 keV to 17.2% at 24 keV. The system has been characterized in terms of fluence rate and energy resolution. An x-ray tube developed ad hoc allows us to acquire images in a reasonable time to minimize the motion blur. A qualitative analysis has been performed in order to know if the prototype system performances are far from a clinical application, by evaluating the spatial resolution, the field uniformity and the image quality as a function of the quasi-monochromatic beam energy. Dose evaluation has been performed as a function of the energy and compared to a conventional system for mammography. The quasi-monochromatic prototype system can produce comparable image quality at half the dose.