Characterization of breast calcification types using dual energy x-ray method.

Calcifications are products of mineralization whose presence is usually associated with pathological conditions. The minerals mostly seen in several diseases are calcium oxalate (CaC2O4), calcium carbonate (CaCO3) and hydroxyapatite (HAp). Up to date, there is no in vivo method that could discriminate between minerals. To this aim, a dual energy x-ray method was developed in the present study. An analytical model was implemented for the determination of the Calcium/Phosphorus mass ratio ([Formula: see text]). The simulation was carried out using monoenergetic and polyenergetic x-rays and various calcification thicknesses (100-1000 [Formula: see text]) and types (CaC2O4, CaCO3, HAp). The experimental evaluation of the method was performed using the optimized irradiation conditions obtained from the simulation study. X-ray tubes, combined with energy dispersive and energy integrating (imaging) detectors, were used for the determination of the [Formula: see text] in phantoms of different mineral types and thicknesses. Based on the results of the experimental procedure, statistical significant difference was observed between the different types of minerals when calcification thicknesses were 300 [Formula: see text] or higher.

Polynomial dual energy inverse functions for bone Calcium/Phosphorus ratio determination and experimental evaluation.

An X-ray dual energy (XRDE) method was examined, using polynomial nonlinear approximation of inverse functions for the determination of the bone Calcium-to-Phosphorus (Ca/P) mass ratio. Inverse fitting functions with the least-squares estimation were used, to determine calcium and phosphate thicknesses. The method was verified by measuring test bone phantoms with a dedicated dual energy system and compared with previously published dual energy data. The accuracy in the determination of the calcium and phosphate thicknesses improved with the polynomial nonlinear inverse function method, introduced in this work, (ranged from 1.4% to 6.2%), compared to the corresponding linear inverse function method (ranged from 1.4% to 19.5%).

Dual Energy Method for Breast Imaging: A Simulation Study.

Dual energy methods can suppress the contrast between adipose and glandular tissues in the breast and therefore enhance the visibility of calcifications. In this study, a dual energy method based on analytical modeling was developed for the detection of minimum microcalcification thickness. To this aim, a modified radiographic X-ray unit was considered, in order to overcome the limited kVp range of mammographic units used in previous DE studies, combined with a high resolution CMOS sensor (pixel size of 22.5 µm) for improved resolution. Various filter materials were examined based on their K-absorption edge. Hydroxyapatite (HAp) was used to simulate microcalcifications. The contrast to noise ratio (CNR tc ) of the subtracted images was calculated for both monoenergetic and polyenergetic X-ray beams. The optimum monoenergetic pair was 23/58 keV for the low and high energy, respectively, resulting in a minimum detectable microcalcification thickness of 100 µm. In the polyenergetic X-ray study, the optimal spectral combination was 40/70 kVp filtered with 100 µm cadmium and 1000 µm copper, respectively. In this case, the minimum detectable microcalcification thickness was 150 µm. The proposed dual energy method provides improved microcalcification detectability in breast imaging with mean glandular dose values within acceptable levels.

Bone calcium/phosphorus ratio determination using dual energy X-ray method.

Non-invasive dual energy methods have been used extensively on osteoporosis diagnosis estimating parameters, such as, Bone Mineral Density (BMD) and Bone Mineral Content (BMC). In this study, an X-ray dual energy method (XRDE) was developed for the estimation of the bone Calcium-to-Phosphorous (Ca/P) mass ratio, as a bone quality index. The optimized irradiation parameters were assessed by performing analytical model simulations. X-ray tube output, filter material and thickness were used as input parameters. A single exposure technique, combined with K-edge filtering, was applied. The optimal X-ray spectra were selected according to the resulted precision and accuracy values. Experimental evaluation was performed on an XRDE system incorporating a Cadmium Telluride (CdTe) photon counting detector and three bone phantoms with different nominal mass Ca/P ratios. Additionally, the phantoms' mass Ca/P ratios were validated with energy-dispersive X-ray spectroscopy (EDX). Simulation results showed that the optimum filter atomic number (Z) ranges between 57 and 70. The optimum spectrum was obtained at 100 kVp, filtered with Cerium (Ce), with a surface density of 0.88 g/cm(2). All Ca/P ratio measurements were found to be accurate to within 1.6% of the nominal values, while the precision ranged between 0.91 and 1.37%. The accuracy and precision values of the proposed non-invasive method contributes to the assessment of the bone quality state through the mass Ca/P ratio determination.

A novel easy-to-use phantom for the determination of MTF in SPECT scanners.

PURPOSE: To evaluate modulation transfer function (MTF) in single photon emission computed tomography (SPECT) systems using the line spread function (LSF) method and a novel flood source which can be easily fabricated with materials accessible in hospital facilities. METHODS: A Tc-99m-based flood source (E(γ) = 140 keV) consisting of a radiopharmaceutical bound to the grains of a radiographic film was prepared in laboratory. Various films and radiopharmaceuticals were examined, in order to obtain a thin homogenous and reproducible flood source. The source showing best uniformity and reproducibility was placed between two PMMA blocks and images were obtained by using the brain tomographic acquisition protocol (brain) and the myocardial perfusion tomographic acquisition protocol (heart). MTF was evaluated by determining the LSF for various reconstruction methods and filters. MTF calculation was obtained by the utilization of a custom made software in which a method similar to the one proposed by Boone [Med. Phys. 28, 356-360 (2001)] was implemented. All imaging experiments were performed in a Siemens e-Cam γ-camera. Furthermore, MTF was assessed through the point spread function (PSF) following conventional methods. RESULTS: The optimum homogeneity was obtained by immersing an Agfa MammoRay HDR Medical x-ray film in a solution of dithiothreitol (DTT, 10(-3) M)/Tc-99m(III)-DMSA (DMSA: trivalent technetium-99m-dimercapto-succinic acid, 40 mCi/40 ml) for 30 min in the dark. These films exhibited better uniformity (CV < 1.9%). Higher MTF values were obtained for the brain scan protocol with iterative 3D with eight iterations reconstruction method. MTF of the brain protocol was in all cases better than the heart protocol. MTFs derived from LSF were more precise compared with those obtained from PSF since their reproducibility was better in all cases, providing a mean standard deviation of 0.0065, in contrary to the PSF method which gave 0.0348. CONCLUSIONS: The method presented here is novel and easy to implement, requiring materials commonly found in clinical practice. Furthermore, this technique which is based on the LSF method reduces measurement noise levels due to the larger amount of data averaging than in the conventional PSF method. Furthermore, MTF can be assessed easily, in three dimensions (3D), by placing the flood source either in sagittal or coronal direction.