Quality control in dual head gamma-cameras: Comparison between methods and software used for image analysis.

Patient radiation dose and image quality are primary issues in the conduct of nuclear medicine (NM) procedures. A range of protocols are currently used in image acquisition and analysis of quality control (QC) tests, with National Electrical Manufacturers Association (NEMA) methods and protocols widely accepted in providing an accurate description, measurement and report of γ-camera performance parameters. However, no standard software is available for image analysis. Present study compares vendor QC software analysis and three types of software freely downloadable from the internet: NMQC, NM Toolkit and ImageJ-NM Toolkit software. These were used for image analysis of QC tests of γ-cameras based on NEMA protocols including non-uniformity evaluation. Ten non-uniformity QC images were obtained using a dual head γ-camera installed in Trieste General Hospital and then analyzed. Excel analysis was used as the baseline calculation for the non-uniformity test according to NEMA procedures. The results of non-uniformity analysis showed good agreement between the independent types of software and Excel calculations (the average differences were 0.3%, 2.9%, 1.3% and 1.6% for the Useful Field of View (UFOV) integral, UFOV differential, Central Field of View (CFOV) integral and CFOV differential, respectively), while significant differences were detected following analysis using the company QC software when compared with Excel analysis (the average differences were 14.6%, 20.7%, 25.7% and 31.9% for the UFOV integral, UFOV differential, CFOV integral and CFOV differential, respectively). Compared to use of Excel calculations use of NMQC software was found to be in close accord. Variation in results obtained using the three types of software and γ-camera QC software was due to the use of different pixel sizes. It is important to conduct independent analyses tests in addition to using the vendor QC software in order to determine the differences between values.

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.

Evaluation of image quality and dose in renal colic: comparison of different spiral-CT protocols.

The aim of this study was to test different technical spiral-CT parameters to obtain optimal image quality with reduced X-ray dose. Images were acquired with a spiral-CT system Philips Tomoscan AVE1, using 250 mA, 120 kV, and 1-s rotational time. Three protocols were tested: protocol A with 5-mm thickness, pitch 1.6, slice reconstruction every 2.5 mm; protocol B with 3-mm thickness, pitch 1.6, slice reconstruction every 1.5 mm; and protocol C with 3-mm thickness, pitch 2, slice reconstruction every 1.5 mm. Two phantoms were employed to evaluate the image quality. Axial images were acquired, then sagittal and coronal images were reconstructed. Finally, the absorbed X-ray dose for each protocol was measured. Regarding image quality, 5-mm-thick images (protocol A) showed greater spatial resolution and lower noise compared with 3-mm-thick images (protocols B and C) on the axial plane; 3-mm reconstructed sagittal and coronal images (protocols B and C) showed an improved image quality compared with 5-mm reformatted images (protocol A). Concerning X-ray dose, the mean dose was: protocol A 19.6 +/- 0.8 mGy; protocol B 14.4 +/- 0.6 mGy; protocol C 12.5 +/- 1.0 mGy. Our study supports the use of thin slices (3 mm) combined with pitch of 1.6 or 2 in renal colic for X-ray dose reduction to the patient and good image quality.

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 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.

[Evaluation of the performance of 8 computerized tomographs in clinical use in Italy]. / Valutazione delle prestazioni di 8 tomografi computerizzati in uso clinico in Italia.

In the past few years the use of CT scanners has widely spread in Italian health care institutions. This methodology has thus become an important part of our national health service--which creates the need for an accurate study of the various aspects of the phenomenon, e.g. technological, diagnostic and economic. In order to evaluate the quality of the CT scanners used in our country, we asked the majors suppliers of the Italian market to provide us with a unit from their production. Six out of 7 companies complied with our request. A standard protocol was used to evaluate the performance of 8 CT scanners, currently used in Italy. The following parameters were evaluated: spatial resolution, contrast resolution, noise, slice thickness, uniformity, linearity and radiation dose. Five currently-used operating modalities were employed. The results allow an overall assessment of the performance of the 8 CT scanners.

[Preprocessing programs of CT images for three-dimensional reconstruction]. / Programmi di pre-elaborazione di immagini TC per ricostruzioni tridimensionali.

Up to now three-dimensional reconstructions in computed tomography have been applied mainly to the skeleton. This limitation is due to technical difficulties when dealing with images of the soft tissues. In order to overcome these limitations three new softwares were developed, thus enabling the operator to pre-elaborate and modify the axial CT images. The first program allows the operator to isolate the lesion and/or the anatomical structures of interest from the surrounding areas. The second program eliminates the areas of isodensity with the lesion it is obtained by means of a trackball. The third program enables the operator to write the modified axial images on the original file. The lesion and/or the structures of interest can thus be processed more easily by the 3D reconstructive program. The new softwares have been applied to 3D reconstructions of brain lesions, and two significant cases are presented. Furthermore, since the new softwares can enhance the quality of 3D images of the skeleton, the programs were also tested in cases of acetabular traumas.

The use of retinal fluorangiography techniques in the study of cerebral circulation.

Retinal fluorangiographic techniques can be employed in the study of cerebrovascular disorders in relation to the embryological, anatomic and functional affinities between the cerebral and retinal circulation. The techniques currently used have been improved by means of the computer analysis of the photographic image, thus allowing qualitative evaluations of the vascular dynamics and quantitative evaluations referred to remarkable variations. These improved techniques can be summed up as follows: equidensitometry with arbitrary colors, computerized fluorangiography for the evaluation of the vascular caliber, computer analysis of mean transit time (m.t.t.). A new type of qualitative evaluation not considering the fluorangiographic image has recently been introduced: the fluorophotometric analysis.

[Computed tomography of the femur head. Normal aspects and appearance in aseptic necrosis]. / Tomografia computerizzata delle teste femorali. Aspetti normali ed in corso di necrosi asettica.

The diagnostic value of Computed Tomography (CT) in the diagnosis of the aseptic necrosis of the femoral head is discussed. The CT findings in the different evolutive stages are reported and the respective diagnostic value of Conventional Radiology and CT are discussed. The CT findings of femoral head necrosis in the early phases are emphasized. The capability of CT to demonstrate structural changes in femoral heads with regular morphology allows to consider this technique when there exists a clinical doubt of osteonecrosis of the femoral head and in risk patients.