G. Iurlaro

Double‐blind randomized controlled trial study on post‐extraction immediately restored implants using the switching platform concept: soft tissue response. Preliminary report

AIM To evaluate the soft tissue response to immediately placed implants using the platform switching concept. MATERIAL AND METHODS In 22 patients, 22 implants of 5.5 mm platform diameter were placed immediately into fresh extraction sockets in maxillae without compromised bone tissue. Eventual post-extraction bone defects were filled using bovine bone matrix mixed with collagen. Immediately after insertion, implants were randomly divided: 11 implants were connected with a 3.8 mm diameter abutment (test group) and 11 with a 5.5 mm diameter abutment (control group). A provisional crown was adapted and adjusted for non-functional immediate positioning. Two months later, definitive prosthetic rehabilitation was performed. Periodontal parameter, buccal peri-implant mucosal changes (REC), mesial and distal papilla height (PH) and vertical height of jumping distance (VHG) were measured at the time of implant placement, of definitive prosthesis insertion and every 6 months thereafter. RESULTS The mean follow-up was 25 months. All implants were clinically osseointegrated. The test group showed a +0.18 mm REC gain. PH gain was +0.045 mm on average. The mean values were statistically significant (P< or =0.005) compared with the control group (PH=-0.88 mm; REC=-0.45 mm). No difference between the two groups in periodontal parameters was found. The mean value of bone filling was 7.51 mm in the test group (97.4% of VHG) and 8.57 mm in the control group (95.2% of VHG). No statistically significant difference was found between the two groups. CONCLUSIONS This study suggests that, in a limited time period of 2 years, immediately placed implants with subsequent platform switching can provide peri-implant tissue stability.

Design of compact pinhole SPECT system based on flat panel PMT

The present development of new gamma imagers has allowed to realize detectors with ultra high spatial resolution and very compact size for PET as well as for SPET application. In this paper we analyze and discuss the possible design of new pinhole SPECT scanners based on heads which consist of flat panel PSPMT and different design of scintillation arrays like NaI(Tl), 1 mm pixel size, and CsI(Tl) multi layers array, mounted in off centered configuration to improve the intrinsic spatial resolution of the imagers. The results show that an array configuration 2/spl times/2 Hamamatsu flat panel PSPMTs coupled to NaI(Tl) scintillation array with 1 mm pixel size, represents the best trade off between compactness and spatial resolution of pinhole SPET scanner. The use of off centered CsI(Tl) scintillation array coupled to a single flat panel PSPMT allows to arrange a high sensitivity and very compact pinhole SPET scanner at very low cost only worsening of 50% spatial resolution than an Anger gamma camera pinhole SPECT.

Factors affecting flat panel PMT calibration for gamma ray imaging

Hamamatsu H8500 Flat Panel PMT represents the last technological advancement in gamma ray imaging. Compact size makes it attractive for medical imaging application. To study and compare image performance two Flat Panel PMTs were coupled to CsI(Tl) and NaI(Tl) scintillation arrays with 3 mm and 1.8 mm pixel size respectively and they were connected to multi-anode electronic readout (64 channel). Furthermore a pulsed blue LED coupled to an optical fiber was utilized to scan the tube with different light distribution spreading. The study took into account how PMT anode gain uniformity response, light distribution and intensity, influence spatial resolution, position linearity and image noise. Gain calibration was firstly studied because of PMT gain anode non uniformity response, which range between 27:100 and between 45:100 respectively. Furthermore each crystal pixel produces different charge distribution and this depends on the matching between anode and scintillation array lattice. The amount of anode charge can change more than a factor five for narrow light distributions. Tube gain setting results critical, in fact because of energy resolution of each anode spectra, only a factor five pulse height variation can be adequately converted by ADC. In addition there is a further gain anode variation due to PMT non uniformity response of a factor 3. This mentioned two elements, do not allow to convert all pulses in the useful pulse height ADC range. As a consequence image position distortion and background are produced. Flat Panel shows good image performance. However, because of the big anode size and PMT gain non uniformity response, the gain setting can be critical to obtain the best image performance for scintillation light distribution comparable with anode size.

Factors Affecting Hamamatsu H8500 Flat Panel PMT Calibration for Gamma Ray Imaging

The Hamamatsu H8500 Flat Panel PMT is the latest technological advancement in gamma ray imaging. Its compact size makes it attractive for medical imaging applications. To study and compare image performance a Flat Panel PMT, representing the present production, was coupled to CsI(Tl) and Nal(Tl) scintillation arrays with 3 mm and 1.8 mm pixel size respectively and connected to a multi-anode electronic readout. Furthermore, a pulsed blue LED coupled to an optical liber was utilized to scan the tube with different light distributions. This study investigated how PMT anode gain uniformity response, scintillation light distribution and intensity influence the spatial resolution, the position linearity and the image noise. Each crystal in the scintillation array produces a different charge distribution, which depends on the match between the anode size and the scintillation array lattice. The Nal(Tl) array demonstrated to fit both PMT characteristics and dynamic range of electronic read out, due to the charge distribution adequate to the anode size. For CsI(Tl) crystal, the pulse height calibration resulted more critical, due to the narrow light distribution. In conclusion, the use of Flat Panel tube with selected anode gain uniformity could represent the cheapest and easiest solution to obtain the best image quality, in particular for scintillator array with smaller pixel size.

DISIS&#8212;Discrete Scintillation Imager Simulator

To foresee the response of a discrete scintillation imager, operating in single-photon modality, a computer simulation code has been developed and tested. The simulator, whose acronym is DISIS, may be used for designing and/or evaluating devices based on scintillation arrays coupled to a position sensitive light sensors by light guides. The simulator can be classified as a deterministic code because it is based on: (i) an analytical model describing the scintillation light distribution for charge integrals calculation, (ii) an algorithm using charge values for event centroiding and (iii) a Gaussian model for spreading the events on the image according to the inherent imager resolution. Particularly, DISIS allows one to study the influence of each setup parameter on the device spatial response. The imager optimization can be achieved by improving the pixel identification. To this aim the best trade-off has to be found between: (a) the light distribution at photocathode, (b) the light sampling capability over the photocathode area and (c) the centroiding algorithm

CATHECTOR: A GAMMA-RAY DETECTOR IN A CATHETER

This work is aimed to study the feasibility of a low energy gamma-ray detector for nuclear medicine to be inserted into a body cavity, duct, or vessel. The small dimension detector concept is based on a CsI:Tl scintillation crystal coupled to a Si Avalanche Photodiode (APD) mounted in a catheter. Due to the availability of Tc in nuclear medicine departments, 140 keV photons have been considered for detector design. At this energy the response concerns a more extended volume nearby the cathector than in the case of beta emitting radiotracers. Monte Carlo simulations have been performed and results have then been compared to experimental ones. The latter have been obtained using a Co radioisotopic source and a laboratory setup including a detector having dimensions not optimized coupled to a low-noise conventional electronics. Count rates and sensitivities have been measured approaching a point source to the detector along some paths and considering different background irradiation levels.

DISIS - a computer simulation code for discrete scintillation imagers

A computer simulation code has been developed in order to foresee the response of discrete scintillation imaging devices. Discrete Scintillation Imager Simulator (DISIS) has been designed for imagers based on a scintillation array coupled to a position sensitive light sensor (like position sensitive photomultiplier tube or avalanche photodiode array) by a planar light guide. The simulator is a deterministic code that uses: (i) a model describing the single photon light distribution emerging from a crystal pixel for charge integrals evaluation; (ii) the assigned algorithm for centroid calculation; and (iii) the Gaussian spread for localizing, crystal by crystal, the events on the image. In particular DISIS allows us to study the spatial response over the imager field of view changing parameters individually. The imager optimization can be obtained searching an acceptable pixel identification. To this aim a good trade-off between the spread of light distribution, the light sampling capability over the light-sensor area and the centroiding algorithm has to be found.