A New Approach to Image Reconstruction in Positron Emission Tomography Using Artificial Neural Networks

This study investigates the possibility of using an Artificial Neural Network (ANN) for reconstructing Positron Emission Tomography (PET) images. The network is trained with simulated data which include physical effects such as attenuation and scattering. Once the training ends, the weights of the network are held constant. The network is able to reconstruct every type of source distribution contained inside the area mapped during the learning. The reconstruction of a simulated brain phantom in a noiseless case shows an improvement if compared with Filtered Back-Projection reconstruction (FBP). In noisy cases there is still an improvement, even if we do not compensate for noise fluctuations. These results show that it is possible to reconstruct PET images using ANNs. Initially we used a Dec Alpha; then, due to the high data parallelism of this reconstruction problem, we ported the learning on a Quadrics (SIMD) machine, suited for the realization of a small medical dedicated system. These results encourage us to continue in further studies that will make possible reconstruction of images of bigger dimension than those used in the present work (32 × 32 pixels)

SYSTEM FOR AUTOMATIC DETECTION OF CLUSTERED MICROCALCIFICATIONS IN DIGITAL MAMMOGRAMS

In this paper, we investigate the performance of a Computer Aided Diagnosis (CAD) system for the detection of clustered microcalcifications in mammograms. Our detection algorithm consists of the combination of two different methods. The first, based on difference-image techniques and gaussianity statistical tests, finds out the most obvious signals. The second, is able to discover more subtle microcalcifications by exploiting a multiresolution analysis by means of the wavelet transform. We can separately tune the two methods, so that each one of them is able to detect signals with similar features. By combining signals coming out from the two parts through a logical OR operation, we can discover microcalcifications with different characteristics. Our algorithm yields a sensitivity of 91.4% with 0.4 false positive cluster per image on the 40 images of the Nijmegen database

Sviluppo di una SPECT Camera per lo studio di Radiofarmaci “intelligenti” su piccoli animali

L'uso di radiofarmaci, tra le molteplici applicazioni delle radiazioni, trova completa giustificazione in campo medico. I radiofarmaci sono sostanze chimiche che, in quanto farmaci, hanno la proprietà di interagire specificatamente con il sistema biologico e che, contenendo nella loro struttura un atomo di un nuclide radioattivo emittente gamma (radiazione scarsamente assorbita dai tessuti biologici), consentono di seguirne il percorso biologico per mezzo di idonei rivelatori esterni. È così possibile costruire una serie di immagini, raccolte in tempi successivi, che individua la distribuzione del radiofarmaco nel corpo e ne evidenzia il progredire del metabolismo. In questo modo è possibile avere indicazioni, non solo morfologiche di organi e apparati, ma soprattutto informazioni sulla loro funzionalità. L'informazione clinica che si ottiene dall'analisi delle immagini scintigrafiche, dipende sostanzialmente dalle proprietà biologiche che il radiofarmaco possiede una volta iniettato in vivo. Se il radiofarmaco ha inoltre la proprietà di fissarsi specificamente in cellule tumorali, esso può diventare anche radioterapeutico. Basta infatti utilizzare nella "marcatura" un radionuclide che emetta radiazioni adatte alla distruzione delle cellule tumorali (radiazioni corpuscolari a corto range nella materia biologica) perché il radiofarmaco affine ad esse, iniettato in vivo, trasporti l'agente terapeutico specificamente nella zona di azione

Scintillation camera control of a computer-guided manipulator for biomedical applications

In our previous studies we have presented a method to measure the detector-to-object distance using a tiltedcollimator (TC) technique. It exploits the shift of the imaged object in the image plane, obtained for tilted positions of a parallel-hole lead collimator. In this work we present the design and first test results of an instrument, which combines the localization of a small-size gamma-ray source with computer-guided precise object manipulation

Novel X-ray source for dual-energy subtraction angiography

In angiography practice an iodate contrast medium is injected in patient vessels with catheters. The absorption of x-rays raises immediately after the iodine K-edge energy. In digital subtraction angiography, two images are used, acquired before and after the injection of the contrast medium, respectively. The vessels morphology result from the difference of images so obtained. This technique involves a non-negligible risk of morbidity or mortality, due to high concentration of injected contrast agent. We are investigating a new source which produces two thin parallel quasi-monochromatic beams - having peak energies centered before and after the iodine K-edge energy, respectively - by using a conventional x-ray tube and a highly oriented pyrolytic graphite mosaic crystal. The polychromatic x-rays incident on the crystal are monochromatized by Bragg diffraction and split in two thin parallel beams, by means of a collimating system. These two beams impinge on the phantom simulating patient vessels and are detected with solid-state array detectors. The image results as difference between the remaining intensities of two beams. We report a preliminary study of the new technique performed both with theoretical stimulations and experimental measurements. Results of computer simulation give information about characteristics as size and quality of the quasi- monochromatic beams, that should be considered in detail to design a system dedicated to the clinical practice. Experimental measurements have been performed on a small- field detector in order to shows the enhancement of image contrast obtained with the application of the new technique