[The spatial resolution of the digital storage phosphor system. The monitor and film compared]. / La risoluzione spaziale del sistema digitale con fosfori a memoria. Monitor e pellicola a confronto.

The physical characteristics of radiographic images, namely spatial resolution and contrast, have obvious effects upon diagnostic image usefulness. We investigated the spatial resolution of both radiographs and magnified digital obtained with a storage phosphor system, in comparison with a film-screen combination. This study was carried out on the conventional radiographs of a phantom grid 0.5 mm thick, with resolution ranging from 0.5 to 10 lp/mm. Each examination was compared at naked eye and with the electronic evaluation of a region of interest on both standard and magnified views or by digitization with a charge coupled detector (CCD) television camera followed by the computing of the modulation transfer function curve. Our results demonstrate a higher spatial resolution of direct magnification, on both digital and film-screen pictures (over 5 lp/mm). On the contrary, the electronic magnification on the monitor yields the same spatial resolution as non-magnified digital images (up to 4.3 lp/mm). By selecting appropriate regions of interest, we could demonstrate the compression of the non-magnified images on the monitor. The modulation transfer curves show that direct magnification yields higher spatial resolution than electronic magnification and non-magnified views. Viewing electronically magnified images on the monitor yields the same resolution as contact radiographs: the monitor offers the advantage of an easier study of the regions of interest.

[Dosimetric evaluations in dental radiology: comparison of the digital system and the conventional system]. / Valutazioni dosimetriche nella radiologia odontoiatrica: sistema digitale con fosfori fotostimolabili e tradizionale a confronto.

The dosimetric values measured on digital dental examinations (panoramic radiography and cephalography) were compared with those obtained with screen-film combinations. The X-ray dose was measured at the critical organs (lens, thyroid, cervical cord) on an anthropomorphic phantom, using thermoluminescence dosimeters and an ionization chamber: the radiographic unit was set at the same exposure values used for standard human studies in adults and children. The mean thyroid dose for screen-film panoramic radiographs was 0.037 mGy in the child and 0.053 in the adult; the lens and the cord doses were 0.009-0.012 mGy and 0.096-0.135 mGy, respectively. Digital panoramic radiography gave the thyroid a dose of 0.013 mGy in the child and 0.016 mGy in the adult: such a marked dose reduction was observed for the lens and the cervical cord too (0.0044-0.0052 mGy and 0.035-0.042 mGy, respectively). With conventional film cephalography the thyroid was given a mean dose of 0.042-0.072 mGy according to age and to patient's size; the lens received higher doses (0.420-0.720 mGy). These values were markedly reduced with the digital technique; 0.032-0.034 mGy to the thyroid gland and 0.320-0.340 mGy to the lens; spinal cord doses became negligible with digital exposures (0.009-0.010 mGy). The overall analysis of dosimetric values demonstrated a mean dose reduction averaging 40-60% with respect to standard film exposure. This difference is more apparent in the adult, since the linear dose-response pattern of the digital system allows good images to be acquired in "thicker" people without markedly increasing exposure values.

[Radiographic enlargement in the study of hand diseases. Digital versus conventional techniques]. / L'ingrandimento radiografico nello studio delle malattie della mano. Tecniche digitale e tradizionale a confronto.

The electronic magnification of digital images was compared with direct digital magnification and with plain radiograph magnification. A whole-body computed radiographic system with photostimulable phosphor plates contained inside standard X-ray cassettes was used. The small bones of the hands and wrists of 18 patients with traumatic (10 cases) or degenerative (8 cases) bone conditions mainly due to chronic renal failure were studied. Each patient was examined with all three techniques: the images were retrospectively reviewed by four observers relative to resolution, contrast, visibility of the lesions and diagnostic value of each method. The statistical analysis of our results demonstrated better yield of direct digital magnification than of plain radiograph (p = 0.00043) and of electronic (p = 7.5 10(-13) magnification. This finding was mainly due to density and contrast optimization of digital images, in spite of their low spatial resolution. This feature allows good simultaneous representation of structures with different radiographic densities, as it happens in the hand and wrist. Electronic magnification yielded less brilliant results, even if compared with plain radiographic studies (p = 0.0032). However, this limitation was compensated for by the fact that this technique is easier and quicker to perform and that it does not require any additional X-ray exposure.