Application of Monte Carlo Algorithms to Cardiac Imaging Reconstruction.

Monte Carlo algorithms have a growing impact on nuclear medicine reconstruction processes. One of the main limitations of myocardial perfusion imaging (MPI) is the effective mitigation of the scattering component, which is particularly challenging in Single Photon Emission Computed Tomography (SPECT). In SPECT, no timing information can be retrieved to locate the primary source photons. Monte Carlo methods allow an event-by-event simulation of the scattering kinematics, which can be incorporated into a model of the imaging system response. This approach was adopted in the late Nineties by several authors, and recently took advantage of the increased computational power made available by high-performance CPUs and GPUs. These recent developments enable a fast image reconstruction with improved image quality, compared to deterministic approaches. Deterministic approaches are based on energy-windowing of the detector response, and on the cumulative estimate and subtraction of the scattering component. In this paper, we review the main strategies and algorithms to correct the scattering effect in SPECT and focus on Monte Carlo developments, which nowadays allow the threedimensional reconstruction of SPECT cardiac images in a few seconds.

DUAL-PARTICLE DOSEMETER BASED ON ORGANIC SCINTILLATOR.

Traditionally available handheld dosemeters are generally sensitive to only one type of radiation: neutrons or photons. Some dosemeters also rely on very specific attenuation correlations between response and dose, are not scalable in size and multiple dosemeters are required to characterise mixed-particle fields. The research presented here serves as a proof-of-concept for a method to simultaneously measure dose rates from neutrons and photons using a particle discriminating organic scintillation detector without the need for spectral deconvolution. The method was compared with traditional instruments and to simulation. Isotopic photon dose rates measured with this method were within 4% of simulated truth, whereas fission spectrum neutron dose rates were measured within 21%. Measurements of dose rates from both particles agree with simulated truth better than traditional instruments. This new method allows for measurement of dose equivalent from both neutrons and photons with a single instrument and no reliance on spectral deconvolution.

Angular distribution of neutron production by proton and carbon-ion therapeutic beams.

Carbon-ion beams are increasingly used in the clinical practice for external radiotherapy treatments of deep-seated tumors. At therapeutic energies, carbon ions yield significant secondary products, including neutrons, which may be of concern for the radiation protection of the patient and personnel. We simulated the neutron yield produced by proton and carbon-ion pencil beams impinging on a clinical phantom at three different angles: 15°, 45° and 90°, with respect to the beam axis. We validated the simulated results using the measured response of organic scintillation detectors. We compared the results obtained with FLUKA 2011.2 and MCNPX 2.7.0 based on three different physics models: Bertini, Isabel, and CEM. Over the different ions, energies, and angles, the FLUKA simulation results agree better with the measured data, compared to the MCNPX results. Simulations of carbon ions at low angles exhibit both the highest deviation from measured data and inter-model discrepancy, which is probably due to the different treatment of the pre-equilibrium stage. The reported neutron yield results could help in the comparison of carbon-ion and proton treatments in terms of secondary neutron production for radiation protection applications.

Advanced readout methods for superheated emulsion detectors.

Superheated emulsions develop visible vapor bubbles when exposed to ionizing radiation. They consist in droplets of a metastable liquid, emulsified in an inert matrix. The formation of a bubble cavity is accompanied by sound waves. Evaporated bubbles also exhibit a lower refractive index, compared to the inert gel matrix. These two physical phenomena have been exploited to count the number of evaporated bubbles and thus measure the interacting radiation flux. Systems based on piezoelectric transducers have been traditionally used to acquire the acoustic (pressure) signals generated by bubble evaporation. Such systems can operate at ambient noise levels exceeding 100 dB; however, they are affected by a significant dead time (>10 ms). An optical readout technique relying on the scattering of light by neutron-induced bubbles has been recently improved in order to minimize measurement dead time and ambient noise sensitivity. Beams of infra-red light from light-emitting diode (LED) sources cross the active area of the detector and are deflected by evaporated bubbles. The scattered light correlates with bubble density. Planar photodiodes are affixed along the detector length in optimized positions, allowing the detection of scattered light from the bubbles and minimizing the detection of direct light from the LEDs. A low-noise signal-conditioning stage has been designed and realized to amplify the current induced in the photodiodes by scattered light and to subtract the background signal due to intrinsic scattering within the detector matrix. The proposed amplification architecture maximizes the measurement signal-to-noise ratio, yielding a readout uncertainty of 6% (±1 SD), with 1000 evaporated bubbles in a detector active volume of 150 ml (6 cm detector diameter). In this work, we prove that the intensity of scattered light also relates to the bubble size, which can be controlled by applying an external pressure to the detector emulsion. This effect can be exploited during the readout procedure to minimize shadowing effects between bubbles, which become severe when the latter are several thousands. The detector we used in this work is based on superheated C-318 (octafluorocyclobutane), emulsified in 100 µm ± 10% (1 SD) diameter drops in an inert matrix of approximately 150 ml. The detector was operated at room temperature and ambient pressure.

Application of a Bonner sphere spectrometer for the determination of the angular neutron energy spectrum of an accelerator-based BNCT facility.

Experimental activities are underway at INFN Legnaro National Laboratories (LNL) (Padua, Italy) and Pisa University aimed at angular-dependent neutron energy spectra measurements produced by the (9)Be(p,xn) reaction, under a 5MeV proton beam. This work has been performed in the framework of INFN TRASCO-BNCT project. Bonner Sphere Spectrometer (BSS), based on (6)LiI (Eu) scintillator, was used with the shadow-cone technique. Proper unfolding codes, coupled to BSS response function calculated by Monte Carlo code, were finally used. The main results are reported here.

Angle and energy differential neutron spectrometry for the SPES BNCT facility.

An accelerator-driven thermal neutron facility for boron neutron capture therapy of skin melanoma is currently under construction at the Legnaro National Laboratories, Italy. The installation relies on the production of neutrons from a thick beryllium target bombarded with 5 MeV protons. A complete set of double differential data, i.e. angle- and energy-differential neutron spectra produced by the beryllium target, is necessary for the Monte Carlo-based design of the installation. For this purpose, double differential fluence measurements are currently performed with the "BINS" neutron spectrometer using 5 MeV protons at the "CN" Van de Graaf accelerator. This spectrometer uses a superheated emulsion of dichlorotetrafluoroethane which is sequentially operated at 25, 30, 35, 40, 45, 50 and 55 degrees C and thus provides a series of seven sharp thresholds covering the 0.1-10 MeV neutron energy interval. Deconvolution of the data is performed with the code "MAXED", which is based on the maximum entropy principle. The analysis of our first neutron spectrometry measurements at angles of 0 degrees, 40 degrees, 80 degrees and 120 degrees supports the viability of the BINS spectrometry method for the generation of the required double differential data.

[Endoscopic endoprosthesis insertion in the treatment of digestive diseases]. / L'utilizzo delle protesi endoscopiche nella patologia dell'apparato digerente.

Over the last few years the use of endoscopically placed endoprostheses for benign and malignant digestive diseases has considerably developed. The endoscopic placement of prostheses is usually well tolerated by patients; it does not require anaesthesia and it is a relatively low-risk procedure. New self-expandable metallic prostheses allow to treat even very tight stenoses; they do not usually require dilatation, therefore reducing the risks involved in dilatation procedure. This study presents a review of experience with prostheses placement in digestive diseases. Indications, limits and complications will be discussed according to data reported in the international literature.

[Modern indications on the medical treatment of symptomatic diverticular disease]. / Moderni orientamenti nel trattamento medico della malattia diverticolare sintomatica.

Authors refer about their experience on treatment of symptomatic diverticular disease both with antibiotic and anti-inflammatory drugs. They confirm the observation of other Authors on effectiveness of this new therapeutic approach versus traditional antibiotic therapy.

[Study of fecal antigens against Helicobacter pylori as non-invasive test compared with the 13C-urea breath-test. Personal experience]. / La ricerca dell'antigene fecale dell'Helicobacter Pylori come test non invasivo in confronto al 13C-urea Breath-Test. Esperienza personale.

The target of this study is the evaluation of two different noninvasive tests: 13C-urea Breath-Test, as gold standard, versus the HpSA test, as new method to research the faecal antigen of Helicobacter Pylori (HP). Thirty patients, affected by dyspeptic symptomatology and never treated before by antibiotic therapy to eradicate the HP, was subjected, by Authors, to this evaluation. This study say that the 13C-urea Breath-test represent the gold standard in the pre-endoscopic research of HP presence concerning specificity and sensibility. However, the HpSA test need more improvement.

[Breath test as non-invasive assessment for the initial screening of non-ulcerous dyspepsia]. / Il Breath Test come indagine non invasiva di scelta per lo screening iniziale della dispepsia non ulcerosa.

Considering the important role of Helicobacter Pylori (Hp) in the most common gastro-intestinal pathologies, the Authors want to test the effectiveness of a non-invasive diagnostic technique for detection of the Hp in the gastric mucosa. At the end of experience they think, like the most of Literature, that the Breath Test, concerning sensibility and specificity, represent the gold standard for detection of the Hp.

[Endoscopic prosthesis in colonic malignant pathology]. / Le protesi endoscopiche nella patologia maligna del colon.

The utilization of stents in neoplastic colon pathology finds a correct location in the therapeutic panorama. Authors report the use of enteric stents as definitive treatment in acute intestinal occlusion with inoperable malignant neoplasia as well as palliative treatment in intestinal occlusion with non-surgically resectable neoplasia.

[Esophageal perforations and fistulas: clinical management]. / Perforazioni e fistole esofagee: importanza nella pratica clinica.

Aim of this study was the literature review regarding esophageal perforations and fistulas. We examined the most common causes, clinical findings (symptoms and signs), laboratory and imaging studies for differential diagnosis and complications. Finally, we examined the surgical or endoscopic treatment and the prognosis.

[Our experience with the appropriate use of esophagogastroduodenoscopy]. / Nostra esperienza sull'utilizzo appropriato dell'esofagogastroduodenoscopia.

Many studies emphasize the right indications about the execution of an EGDS showing that a lot of requests are inappropriate. We have wanted to report our experience too, that showed more comfortable results than that checked, by other Authors moreover we have emphasized that the inappropriate requestsare justly divided between generical and specialized physicians.

[Endoscopic treatment of non-neoplastic cholestasis]. / L'approccio endoscopico alla colestasi ad etiopatogenesi non neoplastica.

Now, draining the cholestasis by endoscopic way is a safe and effective solution. The most of Authors think that the non neoplastic cholestasis find her substantial solution by endoscopic methodology. We reported the most important endoscopic techniques used in these cases, especially the papillosphincterotomy, the pneumatic dilatation and the placing of endoprosthesis.

[H. pylori infection. Our experience with the quadruple and triple therapy as first pharmacologic approach]. / Infezione da H. pylori. Nostra esperienza con l'uso della quadruplice terapia versus triplice come prima istanza farmacologica.

For now the most used pharmacological treatment of first instance to eradication of Hp foresees utilization of triple therapy (PPI + two antibiotics). In our study we have compared this kind of treatment with the quadruple therapy (PPI + three antibiotics), that have showed a taller percentage of eradication at the end of first therapeutical cycle with a shorter time and lower price of treatment.