In vivo dosimetry for estimation of effective doses in multislice CT coronary angiography.

In vivo dosimetry represents a technique that has been widely employed to evaluate the dose to the patient mainly in radiotherapy. Considering the increment in dose to the population due to new high-dose multislice CT examinations, such as coronary angiography, it is becoming important to more accurately know the dose to the patient. The desire to know patient dose extends even to radiological examinations. Thermoluminescent dosimeters are considered the gold standard for in vivo dosimetry, but their use is time consuming. A rapid, less labor-intensive method has been developed to perform in vivo dosimetry using radiochromic film positioned next to the patient's skin. Multislice CT scanners allow the estimation of the effective dose to the patient from the dose length product (DLP) parameter, the value of which is displayed on the acquisition console, simply multiplying the DLP by published conversion factors. The method represents only an approximation based on standard size circular phantoms and neglects the actual size of the patient. More accurate evaluations can be carried out using software-based Monte Carlo simulations. However, these methods do not consider possible dose reduction techniques, such as automatic tube-current modulation. For 22 patients effective doses measured by in vivo dosimetry and calculated by software were compared. The technique of using in vivo dosimetry measured with radiochromic film appears a promising procedure for improving the assessment of the effective dose to the patient.

[Effective dose in X-ray examinations: comparison between spiral CT and urography in the study of renal colic]. / Dose efficace in indagini radiologiche: confronto tra TC spirale ed urografia nello studio della colica renale.

AIM: The aim of this study was to calculate the effective dose in patients with renal colic undergoing spiral CT examination and IVU examination, and to verify the ability of the systems to measure the effective dose. MATERIAL AND METHODS: Dose measurements were carried out for both diagnostic techniques by employing an anthropomorphic phantom with thermoluminescence detectors (TLDs) fitted inside the phantom. The data so obtained were compared with dose estimations based on published tables, which allow to obtain the effective dose on the basis of the experimental value of common dose indicators, the performance of the equipment and the setting of the acquisition parameters for such examinations. RESULTS: The absorbed dose inside the phantom had an homogeneous distribution during the spiral CT examination, while during the IVU there were significant differences in the absorbed dose between different zones of the body, due to the geometry of the x-ray beam. The mean effective dose, which corresponds to the average of values absorbed by males and females, measured by TLD dosimeters for spiral CT examination was 3.3 time that for IVU. For both spiral CT and IVU the dose to the male was significantly lower than that to the female, owing to the anatomic position of female gonads that are completely exposed to the x-ray radiations during the study, while male gonads lie outside of the exposed area. Both methods for estimating the effective dose in spiral CT, based on CTDI value, significantly underestimated the value derived from experimental TLDs measurement. The evaluation of effective dose in IVU, based on the measurement of the skin dose in air, overestimated the measurement performed by TLDs. DISCUSSION AND CONCLUSIONS: Dose measurement performed by TLD dosimeters fitted inside an anthropomorphic phantom has the advantage of calculating experimentally the absorbed dose in different anatomic districts. However, the method is quite difficult, and introduces some imprecisions due to the simplified morphology of the phantom and the measuring system of TLDs (+/- 10%). Another possibility is to make theoretical estimations on the basis of simple dose measurements. Also these methods are affected by many factors that may introduce imprecisions, such as the patient geometry which has a considerable effect on the dose distribution inside the body. Therefore the methods of measurement based on CTDI value can provide only rough estimations of effective dose. The same considerations can be applied to IVU; in this case the theoretical estimations are based on skin dose measurements, which are very accurate but cannot foresee the behaviour of x-rays inside the patient. As regards the diagnostic procedures evaluated, the gonadic absorbed dose has a greater effect on the effective dose value as a consequence of the weight tissue ratio Wt. In this respect we should underline that, while female gonads are completely irradiated during spiral CT and IVU examinations, the male gonads are exposed only to diffuse radiation; this entails a great difference between the effective dose to the male and that to the female. For this reason the effective dose should be expressed not only for the average man (that is the mean value between males and females), but also distinguishing by patient sex. Although the comparison of different evaluating methods confirmed the difficulties in obtaining the exact effective dose, all the measurements performed with IVU and spiral CT showed that the effective dose for CT is 3.3 times that for IVU. However, the excellent image quality obtained by spiral CT and the high intrinsic contrast of stones probably makes it possible to reduce the dose with this technique, preserving an acceptable quality of the diagnostic images.

Inhibition of trophoblast adhesion to endothelial cells by the sera of women with recurrent spontaneous abortions.

PROBLEM: May anti-phospholipid or other autoantibodies interfere with trophoblast-endothelial cells interaction in women with unexplained pregnancy losses? METHODS OF STUDY: The sera of 72 women with recurrent spontaneous abortions (RSA) containing antibodies to endothelial cells (28), trophoblast (14), and cardiolipin (10) or lacking antibodies (25), and 26 controls were examined in an inhibition assay of trophoblast adhesion to endothelial cells using an ELISA based on the recognition of trophoblast by antibodies to cytokeratin. RESULTS: Adhesion of trophoblast to endothelial cells was time- and dose-dependent. Patients and control sera inhibited trophoblast adhesion with mean values of 37% and 7%, respectively. Inhibition above 2SD of the mean control value was still observed in 58% of the patients sera and 8% of the control sera. Sera containing antibodies to endothelial cells had higher inhibitory effect (38%) than those with antibodies to trophoblast (23%) and cardiolipin (28%) or lacking antibodies (26%). CONCLUSIONS: Antibodies and other undefined factors in the sera of women with RSA inhibit adhesion of trophoblast to endothelial cells.

Wiener spectrum of radiographic systems: comparison of different evaluation methods.

The noise power spectrum, or Wiener spectrum, of the radiographic mottle is a fundamental quantity in film-screen image quality evaluation. In this paper, using a high-quality computerized microdensitometer, two different acquisition and calculation methods for noise evaluation are compared. The first one is the classic (unidimensional) method used in film noise evaluation: a long and narrow slit (10 x 400 microns2) is used to delimit the microdensitometer light beam and the transmission data are collected by scanning the sample in a rectilinear pattern. A section of the two-dimensional Wiener spectrum is thus obtained. The second (two-dimensional) method is similar to that used in digital image noise evaluation: a square slit is used on the microdensitometer window and data are collected by scanning the sample on a square pattern. To evaluate the effect of different sampling frequencies, our data were acquired both selecting a 50 x 50 microns2 square slit and a 20 x 20 microns2 square slit. The two-dimensional Wiener spectrum thus obtained is then reduced to a unidimensional function. The measurements were made on two different films (Kodak Ortho G e Kodak T-MAT G) exposed with the same screen (Kodak Lanex Regular). These films have the same sensitivity but a different emulsion structure. One film (Ortho G) is made of irregular halide silver grains and the other (T-MAT G) of tabular grains. A satisfactory agreement between the two procedures was found which makes the comparison of data from the laboratories using microdensitometers and those using TV-grabbing system for film-screen evaluation meaningful.

[The dose and quality program in mammography (DQM). Results of the study carried out in 20 Fruili-Venezia Giulia centers]. / Programma dose e qualità nella mammografia (DQM). Risultati dell'indagine svolta in 20 centri del Friuli-Venezia Giulia.

Recently, 20 breast centers in Friuli Venezia Giulia have been investigated for the mammography optimization program known as DQM (Dose and Quality in Mammography). This was the second trial, the first one dating 1987-1988 and including only 10 centers. The chosen parameters were evaluated by means of a performance phantom containing 15 details, a Victoreen 660 ionizing camera, a star pattern and several plexiglass phantoms of different thickness. Statistical-methodological data were collected by means of a questionnaire. The results of the trial were communicated to each center as well as directions for future improvements. All centers were found to use mammographic equipment with a molybdenum anode and the film-screen combination; 18 center use grids daily, while 11 can perform direct radiographic magnification. Only 40% of the examined centers use a dedicated daylight printer. The overall quality of the radiographic image was seen to be acceptable, as 8 or more details of 15 hidden in the phantom were visualized, in 16 of 20 centers. The mean glandular dose was below the minimum threshold in all centers: in 45% of cases it was below 1.5 mGy. The setting of the automatic exposition control system was found to be poor, especially that of the adjustment related to breast thickness. Acceptability thresholds were met only by 31% of the examined centers (density variations < 20%). Notwithstanding the identification of areas where improvements can be made also from a methodological point of view, we can conclude that the quality provided by regional breast centers is definitely adequate. Good image quality and acceptable doses were observed in 80% of the centers. The results are significant and encouraging when compared with those from the first DQM trial carried out in our region, which confirms the value of periodical quality programs.

The choice of radiographic film-screen systems: quality evaluation and purchasing specifications drafting. Report on A.I.F.B. Working Group activity.

The comparative evaluation of radiographic screen-film systems presents several problems from both the theoretical and the experimental points 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. This quantity is expressed as a product of image quality index and system sensitivity. As image quality index we assumed the signal-to-noise power ratio: this index depends in an explicit way on contrast, resolution and noise of the system. From the experimental point of view the main problem is that to measure some basic quantities, sophisticated and expensive equipment, like computer-controlled microdensitometers, is generally required. In this paper, we report the Italian Association of Biomedical Physicists Task group suggestions for measuring the basic physical parameters (with particular reference to the use of cost-effective equipment and for purchasing specification drafting). Using synthetic quality indices, the evaluation criteria of radiographic materials are directly derived from the general theory of radiographic image perception.

[A protocol for evaluating screen-film systems]. / Protocollo per la valutazione dei sistemi schermo-pellicola.

When a competition is made for the supply of sensitive photographic material, each USL is asked, in a time scan of one or more years, to evaluate the characteristics of the screen-film systems proposed by the various companies. In the last years the authors had several opportunities to check different screen-film systems for many Friuli-Venezia Giulia hospitals. For this reason they have set an evaluation form tested after following changes and recently employed in its final version. The check form is reported on in this paper with some personal considerations originated by the authors' experience. The technical parameters which must be evaluated are reported, together with the instrumentation needed to perform the technical examination, the examination modality, and the score-attributing criteria. The evaluation form is very flexible for it allows each Radiology Department to evaluate each parameter in a personal way and to fit it to its own needs.