Manfred Säbel

Recent developments in breast imaging

A review of breast imaging has already appeared in 1982 in this journal. Consequently, the present article concentrates on a discussion of only those developments of a more recent nature. Although the emphasis is placed on the physical aspects of the different imaging methods concerned, the essential factors relating to the clinical background and the associated radiation risk are also outlined. The completeness of detail depends on the present clinical importance of the method under discussion. X-ray mammography, which is still the most important breast imaging technique and has proved to be an effective method for breast cancer screening, is therefore treated in greater detail. Since the early 1980s, ultrasound B-mode scanning has evolved to an indispensable adjunct to x-ray mammography. For Doppler sonography, diaphanography, contrast-enhanced MRI, CT and DSA, the visualization of a tumour depends essentially on the enhanced vascularity of the lesion. Whether this will prove to be a reliable indicator for malignancy remains to be shown in controlled clinical studies. Common to all imaging systems is the increasing use of digital methods for signal processing, which also offers the possibility of computer-aided diagnosis by texture analysis and pattern recognition.

Determination of average glandular dose with modern mammography units for two large groups of patients

Until recently, for mammography Mo anode-Mo filter x-ray tube assemblies were almost exclusively used. Modern mammography units provide the possibility to employ a variety of anode-filter combinations with the aim of adapting the x-ray spectrum to compressed breast thickness and composition. The present contribution provides information on the radiation exposure of two large groups of patients (one of 1678 and one of 945 women) who were mammographed with modern x-ray equipment, and on the dosimetry necessary for the evaluation. For dosimetric purposes spectral information is essential. X-ray spectra have been determined for various anode-filter combinations from measurements with a Ge detector. Based on these spectra, conversion factors from air kerma free in air to average glandular dose (g factors) have been calculated for different anode-filter combinations, compressed breast thickness ranging from 2 to 9 cm and breast compositions varying from 0 to 100% glandular tissue. Determinations of various quantities, including entrance surface air kerma (ESAK), tube output, tube loading (TL), fraction of glandular tissue (FGL) and compressed breast thickness, were made during actual mammography. Average glandular dose (AGD) was determined using g factors corrected for tissue composition as well as g values for standard breast composition, i.e. 50% adipose tissue and 50% glandular tissue by mass. It is shown that, on average, the influence of the actual breast composition causes variations of the order of about 15%. For group 1 and group 2, the mean values of average glandular dose (using g factors corrected for tissue composition) were 1.59 and 2.07 mGy respectively. The number of exposures per woman was on average 3.4 and 3.6 respectively. The mean value of compressed breast thickness was 55.9 and 50.8 mm respectively. The mean age of group 1 was 53.6 years (for group 2 the age was not recorded). The fraction by mass of glandular tissue FGL decrease with increasing compressed breast thickness and age of patient (from 75% at 25 mm to 20% at 80 mm, and from 65% at 20 years to 30% at 75 years). For a medium-sized breast, i.e. a compressed breast thickness of 55 mm, FGL is about 35%, indicating that the standard mix (FGL = 50%) might need some modification, particularly because of additional evidence from another investigation with similar results on FGL.

Radiation Exposure and Image Quality in X-Ray Diagnostic Radiology

Radiation exposure and image quality in X-ray diagnostic radiology , Radiation exposure and image quality in X-ray diagnostic radiology , کتابخانه دیجیتالی دانشگاه علوم پزشکی و خدمات درمانی شهید بهشتی

On the Mechanism of Radioprotection by Cysteamine: I. Relationship between Cysteamine-induced Mitotic Inhibition and Radioprotective Effects in the Livers of Young and Senile White Mice

SummaryThe incorporation of 3H-thymidine into liver DNA, the weight of the liver, its DNA-, RNA- and protein content and the body-weight were investigated in white NMRI mice at the age of five weeks or two years after(1) intraperitoneal application of 150 mg/kg cysteamine,(2) whole-body irradiation with 500 rads 60Co γ-rays,(3) combined application of cysteamine and irradiation.The i.p. application of cysteamine results in a transient decrease of the 3H-thymidine incorporation into liver DNA of the five-week-old mice. In two-year-old animals, the incorporation rate is temporarily increased; partial hepatectomy, however, results in a decrease similar to that in the young animals. Whole body irradiation causes an initial decrease of the incorporation rate in both animal groups; subsequently it increases and reaches the control values after seven days. At this time, however, the DNA-, RNA-, and protein content is significantly lower in the irradiated animals.Cysteamine given 15 min before irradiation acceler...

Inhibition of estrogen-induced radioprotection of placental nucleic acids and proteins by the antiestrogen clomiphene

Abstract The 500 rad total body irradiation of pregnant rats on 20th day of gestation as well as the treatment of the animals with 0.5 mg Clomiophene per kg and day between the 18th and 21st day was ineffective on placental weight and its contents of DNA, RNA, and proteins, measured on 22nd day of pregnancy. The combination of both treatments however led to a significant decrease in placental weight and its contents of DNA, RNA, and proteins. As Clomiphene, a 1(p-β-diethylaminoethoxy-phenyl)-2.2-diphenyl-2-chloro-ethylencitrate, in the presence of estrogen shows antiestrogenic effects by blocking estrogen-specific receptors, our experiments provide evidence that endogenous estrogens are radioprotective during pregnancy, when the content of endogenous estrogen is increased 300 to 500 times. On account of functional relations to the nucleo-proteins estrogens may decrease the effect of radiation-induced radicals on the DNA.

Image Quality and Dose

The radiological image is composed of the spatial variations of a physical quantity, e.g. the X-ray fluence at the input of the imaging chain (radiation image). When using a film-screen system then this spatial variation is represented by the resulting distribution of the optical density on the film (radiograph), when using a digital imaging system it is – after corrections of the raw data with reference to IEC 62494 (see IEC 62494, 2008) and postprocessing – shown by the resulting grey-scale values e.g. on the monitor of the viewing station (X-ray image). The radiological image represents the projection of the spatial distribution of the patient tissue components within the field of view. Visualisation of important details requires separation of the ‘structures of interest’ against the ‘background’ (e.g. in mammography, micro-calcifications in the breast glandular tissue). Loosely speaking, the difference between structures of interest and background is referred to as the signal.

Patient Dose Estimation

Dose output Y100 of X-ray tube assemblies with W/Re-anode at a target angle of 10° and various additional filtration; focus distance of 100 cm (the figure is equivalent to Fig. 10.3)

Production and Measurement of X-Rays

X-rays are produced when a beam of fast electrons strikes a target. The electrons lose, on this occasion, most of their energy in collisions with atomic electrons in the target, causing ionisation and excitation of atoms. In addition they can be sharply deflected by the electric field of the atomic nuclei, thereby losing energy by emitting X-ray photons.

Characteristics of the Imaging Radiation Field

Typical geometrical and physical characteristics of anti-scatter grid Pb 12/40 Typical geometrical and physical characteristics of anti-scatter grid Pb 13/75 Typical geometrical and physical characteristics of anti-scatter grid Pb 15/80

Radiation Field and Dosimetric Quantities

The physical characteristics of the radiation source and the exposure parameters, which together determine the radiation quality, are the anode material of the X-ray tube and the filtration of the primary radiation beam, the X-ray peak tube voltage selected, its temporal course (e.g. especially at short exposure times or, in pulsed exposure techniques, its rise and drop) and the inherent waveform of the tube voltage (2-, 6-, 12-, multi-pulse or DC). The radiation quality (i.e. the photon energy spectrum) influences both patient dose and image quality. An increase in the X-ray tube voltage for a certain anode-filter combination at a definite image receptor dose (see Sect. 5.2) will result in an increased penetration of the X-ray beam and consequently in a reduction of the absorbed dose and the contrast observed in the image.