[en] Short communication

[en] Comparative evaluation of radiographic filmscreen systems presents several problems from both the theoretical and the experimental point of view. From the theoretical point of view the main difficulties are related to the choice of the parameters best suited to express the 'overall quality' of a system. From the practical point of view the main problem is that to measure some basic quantities (resolution and noise) sophisticated and expensive instruments are required. This paper deals with both these problems. To express image quality we have assumed the signal-to-noise power ration: this index depends in a explicit way on contrast, resolution and noise of the system. The dependence on sensitivity is implicit and was derived using literature data. From a knowledge of the dependence of image quality on sensitivity it is possible to develop an 'overall quality' index which is considered to express the 'technological level' of the systems. In this work some basic phisical quantities (characteristic curve, sensitivity) were evaluated using standard instruments. To measure spatial resolution and noise an inexpensive, PC-based, TV-digitizer system was developed. As an example, both image and overall quality indices were evaluated on three mammographic systems which are typical of the three different 'phases' of the development of this technique

[en] Spatial resolution, statistical noise, and patient dose are important parameters for the evaluation of the performances of computerized tomography (CT) scanners. These parameters are combined to develop some ''synthetic indices'', and to describe intrinsic properties of a CT scanner (the maximum obtainable spatial resolution and dose efficiency). This type of analysis has been applied to the evaluation of four CT scanners, three of third, and one of fourth generation

[en] The paper presents the methods used by Working Group ENEA-EDP (Experts in Personal Dosimetry) to control the reliability of the Dosimetric Services operating in Italy and asking for the above controls on voluntary basis. Testing and irradiation test methods are explained as well as the evaluation criteria. The paper includes suggestions and guide-lines to gain the status of 'Reliable Service'. Technical equipment and operating procedures needed to pass the test are also illustrated. (author)

[en] A recent, commercially available computer programme for the three-dimensional (3D) display of single-photon emission tomography (SPET) data was used to study myocardial perfusion in patients with coronary artery disease (CAD). To enable the detection of small ischemic lesions, the authors proposed a new 'distance-subtraction' method: After suitable centering of the axial slices, 3D 'distance-shaded' images of the stress study were subtracted from the corresponding views of the rest study. With this technique, small changes in surface-to-observer distance were high-lighted, thus enabling us to detect nontransmural ischemic areas of the myocardium. General characteristics and possibilities of the subtraction technique were tested on a simple myocardial phantom. Some clinical results of the application of this method on CAD patients are presented and discussed. In CAD patients in whom only nontransmural ischemic lesions are present, the subtraction of 'distance-shaded' images is decisive for a correct diagnosis. (orig.)

No abstract available

[en] For thermal modeling to play a significant role in treatment planning, monitoring, and control of magnetic resonance-guided focused ultrasound (MRgFUS) thermal therapies, accurate knowledge of ultrasound and thermal properties is essential. This study develops a new analytical solution for the temperature change observed in MRgFUS which can be used with experimental MR temperature data to provide estimates of the ultrasound initial heating rate, Gaussian beam variance, tissue thermal diffusivity, and Pennes perfusion parameter. Simulations demonstrate that this technique provides accurate and robust property estimates that are independent of the beam size, thermal diffusivity, and perfusion levels in the presence of realistic MR noise. The technique is also demonstrated in vivo using MRgFUS heating data in rabbit back muscle. Errors in property estimates are kept less than 5% by applying a third order Taylor series approximation of the perfusion term and ensuring the ratio of the fitting time (the duration of experimental data utilized for optimization) to the perfusion time constant remains less than one. (paper)

[en] Background: Digital mammography systems, thanks to a physical performance better than conventional screen-film units, have the potential of reducing the dose to patients, without decreasing the diagnostic accuracy. Purpose: To achieve a physical and clinical comparison between two systems: a screen-film plate and a dual-side computed radiography system (CRM; FUJIFILM FCR 5000 MA). Material and Methods: A unique feature of the FCR 5000 MA system is that it has a clear support medium, allowing light emitted during the scanning process to be detected on the 'back' of the storage phosphor plate, considerably improving the system's efficiency. The system's physical performance was tested by means of a quantitative analysis, with calculation of the modulation transfer function, detective quantum efficiency, and contrast-detail analysis; subsequently, the results were compared with those achieved using a screen-film system (SFM; Eastmann Kodak MinR-MinR 2000). A receiver operating characteristic (ROC) analysis was then performed on 120 paired clinical images obtained in a craniocaudal projection with the conventional SFM system under standard exposure conditions and also with the CRM system working with a dose reduced by 35% (average breast thickness: 4.3 cm; mean glandular dose: 1.45 mGy). CRM clinical images were interpreted both in hard copy and in soft copy. Results: The ROC analysis revealed that the performances of the two systems (SFM and CRM with reduced dose) were similar (P>0.05): the diagnostic accuracy of the two systems, when valued in terms of the area underneath the ROC curve, was found to be 0.74 for the SFM, 0.78 for the CRM (hard copy), and 0.79 for the CRM (soft copy). Conclusion: The outcome obtained from our experiments shows that the use of the dual-side CRM system is a very good alternative to the screen-film system

[en] The high cost of virgin ¹⁸O-enriched water has forced many researchers to study methods to purify and recycle enriched water after the first irradiation for the production of radiopharmaceuticals. In our study, [¹⁸O]H₂O was purified by ozonolysis and distillation. Analyses showed a large decrease in impurities after this treatment. The purification procedure was carried out after the production of 94 batches of [¹⁸F]-FDG, which were manufactured using a GE Minitrace cyclotron and a GE Mx TracerLab synthesizer. Saturation yields after bombardment, using virgin and re-purified water were, respectively, 2864±204 MBq/μA and 2727±167 MBq/μA, a decrease of 5.5%. The decrease in [¹⁸F]-FDG yield, from 67.2±0.7% to 65.5±0.9%, can be ascribed to the irradiation step only