Mauro Gambaccini

Dual-energy tissue cancellation in mammography with quasi-monochromatic x-rays

Dual-energy radiography has not evolved into a routine clinical examination yet due to intrinsic limitations of both dual-kVp imaging and single-exposure imaging with conventional x-ray sources. The recent introduction of novel quasi-monochromatic x-ray sources and detectors could lead to interesting improvements, especially in mammography where the complex structure of healthy tissues often masks the detectability of lesions. A dual-energy radiography technique based on a tissue cancellation algorithm has been developed for mammography, with the aim of maximizing the low intrinsic contrast of pathologic tissues while being able to minimize or cancel the contrast between glandular and fat tissues. Several images of a plastic test object containing various tissue equivalent inserts were acquired in the energy range 17-36 keV using a quasi-monochromatic x-ray source and a scintillator-coated CCD detector. Images acquired at high and low energies were nonlinearly combined to generate two energy-independent basis images. Suitable linear combinations of these two basis images result in the elimination of the contrast of a given material with respect to another. This makes it possible to selectively cancel certain details in the processed image.

An ultrasound model to calculate the brain blood outflow through collateral vessels: a pilot study

BackgroundThe quantification of the flow returning from the head through the cervical veins and the collaterals of the internal jugular vein (IJV), is becoming of prominent interest in clinical practice. We developed a novel model to calculate the cerebral venous return, normalized to the arterial inflow, in the different segments of the IJV.MethodsWe assessed, by established Echo Colour Doppler (ECD) methodology, the head inflow (HBinF) defined as the sum of common carotids and vertebral arteries, as well as the cerebral flow (CBF) defined as the sum of internal carotid and vertebral arteries. We also assessed the head outflow (HBoutF) defined as the sum of the measurements at the junction of the IJV and the vertebral veins. In addition, we also calculated the collateral flow index (CFI) by estimating the flow which re-enters directly into the superior vena cava as the amount of blood extrapolated by the difference between the HBinF and the HBoutF. We preliminarily tested the model by comparing ten healthy controls (HC) with ten patients affected by chronic cerebral spinal venous insufficiency (CCSVI), a condition characterized by some blockages in the IJV which are bypassed by collateral circulation.ResultsIn HC the HBinF was 956+-105ml/min, whereas the HBoutF was > 90% of the HBinF, leading to a final CFI value of 1%. The last result shows that a very small amount of blood is drained by the collaterals. In upright we confirmed a reduction of the outflow through the IJV which increased CFI to 9%. When we applied the model to CCSVI, the HBinF was not significantly different from controls. In supine, the flow of CCSVI patients in the IJV junction was significantly lower (p < 0.001) while the correspondent CFI value significantly increased (61%, p < 0.0002).ConclusionsOur preliminary application of the novel model in the clinical setting suggests the pivotal role of the collateral network in draining the blood into the superior vena cava under CCSVI condition.

Narrow energy band X-rays via mosaic crystal for mammography application

Abstract Monochromatic X-ray beams are desirable in various fields of diagnostic radiology. We are investigating an imaging system based on a narrow energy band X-ray source for mammography application. The narrow energy band is obtained by making use of a mosaic crystal that reflects X-rays from a conventional X-ray tube via Bragg diffraction. In this paper the characteristics of the system in terms of energy resolution and fluence rate are reported. Small field (1.1 × 3.0 cm 2 ) radiographs of Plexiglas phantoms with a thickness up to 3.6 cm have been obtained with 18, 20 and 22 keV quasi-monochromatic beams. The field size is limited by the crystal size along one dimension and by the desired energy spread along the other one. A digital imaging system has been used to correct for non-uniformity of the X-ray beam.

Does thoracic pump influence the cerebral venous return

We assessed the hemodynamic effects induced by the thoracic pump in the intra- and extracranial veins of the cerebral venous system on healthy volunteers. Activation of the thoracic pump was standardized among subjects by setting the deep inspiration at 70% of individual vital capacity. Peak velocity (PV), time average velocity (TAV), vein area (VA), and flow quantification (Q) were assessed by means of echo color Doppler in supine posture. Deep respiration significantly increases PV, TAV, and Q, but it is limited to the extracranial veins. To the contrary, no significant hemodynamic changes were recorded at the level of the intracranial venous network. Moreover, at rest TAV in the jugular veins was significantly correlated with Q of the intracranial veins. We conclude that the modulation of the atmospheric pressure operated by the thoracic pump significantly modifies the hemodynamics of the jugular veins and of the reservoir of the neck and facial veins, with no effect on the vein network of the intracranial compartment.

Use of silicon and GaAs pixel detectors for digital autoradiography

Solid state detectors made of Si (4.8/spl times/8 mm/sup 2/) and GaAs (6.4/spl times/8 mm/sup 2/) pixel matrices bump-bonded to the Omega2 and Omega3 electronic read-out systems, developed at CERN for H.E.P. experiments, have been used to obtain autoradiographic images of clusters of human epithelial cells and DNA fragments separated via electrophoresis, both labeled with /sup 32/P. The system has shown a good minimum detectable activity per unit area of 2.10/sup -4/ cps mm/sup -2/, and has proved linear for a count rate in the range 0.2-20 cpa, typical of autoradiography. The pixel dimensions are 75/spl times/500 /spl mu/m/sup 2/ (Si-Omega2) and 50/spl times/500 /spl mu/m/sup 2/ (GaAs-Omega3), respectively. We are able to clearly localize clusters of cells which have incorporated the radioactive tracer and DNA fragments on an electrophoretic gel on paper (blots).

AUTORADIOGRAPHY WITH SILICON STRIP DETECTORS

A digital autoradiography system based on double sided silicon strip detectors (1.6 × 1.6 mm2 active surface with 100 μm pitch) has been developed and successfully tested with beta-emitting tracers. It is shown here that the system is able to perform imaging of organic material with specific sensitivity as small as 0.002 nCi/mm2, and to record activity measurements with good linearity in the range 0.002–20 nCi/mm2. Autoradiographic images of clusters of mammary cells marked with ortho-(32P)phosphate, obtained with an exposure time of about 10 min are presented.

A Monte Carlo simulation of the possible use of Positron Emission Tomography in proton radiotherapy

Abstract We have used the Monte Carlo technique to evaluate the applicability of Positron Emission Tomography to in vivo dosimetry for proton radiotherapy. A fair agreement has been found between Monte Carlo results and experimental data. The simulation shows that PET can be useful especially for in vivo Braggs peak localization.

A new hemodynamic model for the study of cerebral venous outflow

We developed a mathematical model of the cerebral venous outflow for the simulation of the average blood flows and pressures in the main drainage vessels of the brain. The main features of the model are that it includes a validated model for the simulation of the intracranial circulation and it accounts for the dependence of the hydraulic properties of the jugular veins with respect to the gravity field, which makes it an useful tool for the study of the correlations between extracranial blood redistributions and changes in the intracranial environment. The model is able to simulate the average pressures and flows in different points of the jugular ducts, taking into account the amount of blood coming from the anastomotic connections; simulate how the blood redistribution due to change of posture affects flows and pressures in specific points of the system; and simulate redistributions due to stenotic patterns. Sensitivity analysis to check the robustness of the model was performed. The model reproduces average physiologic behavior of the jugular, vertebral, and cerebral ducts in terms of pressures and flows. In fact, jugular flow drops from ∼11.7 to ∼1.4 ml/s in the passage from supine to standing. At the same time, vertebral flow increases from 0.8 to 3.4 ml/s, while cerebral blood flow, venous sinuses pressure, and intracranial pressure are constant around the average value of 12.5 ml/s, 6 mmHg, and 10 mmHg, respectively. All these values are in agreement with literature data.

Spatial resolution measurements in quasimonochromatic x rays with mosaic crystals for mammography application

A novel x-ray source for mammography application is being investigated. Quasimonochromatic x rays have been produced via Bragg diffraction with a W-anode x-ray tube and a graphite mosaic crystal array. The system provides 18 keV x rays with an energy resolution deltaE/E approximately equals 0.12. A thorough analysis of the spatial resolution of the system has been performed in order to understand and quantify the effect of the introduction of an active optical element such as a mosaic crystal in the x-ray path. The focal spot of the source and its emission properties have been studied by using the slit camera method. Experiments have shown that the introduction of a mosaic crystal in the optical path modifies the resolution properties of the Bragg diffraction-based radiography system. Along the direction perpendicular to the diffraction plane the resolution properties of the imaging system mainly depend on the x-ray tube focal spot size and position. Along the diffraction plane the focal spot size depends on mosaic characteristics and on the geometrical setup. Hence, it could be modified by setting the appropriate experimental conditions.

Focusing properties of mosaic crystals

X-ray instruments with mosaic crystals are proposed and used in many applications in synchrotron radiation, medical physics and astrophysics. These crystals present a parafocusing of the x-ray beam in the diffraction plane, which is thoroughly analyzed in this paper. We studied the evolution of the cross- section of the diffracted beam, using several samples of Highly Oriented Pyrolythic Graphite crystals coming from different suppliers. The experiment has been performed at the European Synchrotron Radiation Facility (beamline BM5). The results clearly show a parafocusing effect in the 1:1 magnification ratio along the diffraction plane and a defocusing effect along the perpendicular plane. The secondary extinction coefficient is also measured.