On the dose sensitivity of a new CDMAM phantom.

For the technical quality assurance of breast cancer screening protocols several phantoms have been developed. Their dose sensitivity is a common topic often discussed in literature. The European protocol for the quality control of the physical and technical aspects of mammography screening suggests a contrast-detail phantom like the CDMAM phantom (Artinis Medical Systems, Elst, NL). The CDMAM 3.4 was tested with respect to its dose sensitivity and compared to other phantoms in a recent paper. The CDMAM 4.0 phantom provides other disc diameters and thicknesses adapted more closely to the image quality found in modern mammography systems. This motivates a comparison of the two generations using the same exposure parameters. We varied the time-current (mAs) within a range of clinically used values (40-140 mAs). All evaluations were done using automatic evaluation software provided by Artinis (for CDMAM 4.0) and the National Coordinating Centre for the Physics of Mammography, Guildford UK (CDMAM 3.4). We compared the relative dose sensitivity with respect to the different diameters and also computed the IQFinv parameter, which averages over the diameters as suggested in the manual for the phantom. The IQFinv parameter linearly depends on dose for both phantoms. The CDMAM 4.0 shows a more monotonous dependence on dose, the total variation of the threshold thicknesses as functions of the dose are significantly smaller than with the CDMAM 3.4. As the automatic evaluation shows rather different threshold thicknesses for the two phantoms, conversion factors for human to automatic readout have to be adapted.

Dose sensitivity of three phantoms used for quality assurance in digital mammography.

Technical quality assurance (QA) is one of the key issues in breast cancer screening protocols. For this QA task, three different methods are commonly used to assess image quality. The European protocol suggests a contrast-detail phantom (e.g. the CDMAM phantom), while in North America the American College of Radiology (ACR) accreditation phantom is proposed. Alternatively, phantoms based on image quality parameters from applied system theory such as the noise-equivalent number of quanta (NEQ) are applied (e.g. the PAS 1054 phantom). The aim of this paper was to correlate the changes in the output of the three evaluation methods (CDMAM, ACR and NEQ) with changes in dose. We varied the time-current product within a range of clinically used values (40-140 mAs, corresponding to 3.5-12.4 mGy entrance dose and detector dose of 32-110 µGy). For the ACR phantom, the examined parameter was the number of detected objects. With the CDMAM phantom we chose the diameters 0.10, 0.13, 0.20, 0.31 and 0.5 mm and recorded the threshold thicknesses. With respect to the third method, we evaluated the NEQ at typical spatial frequencies to calculate the relative changes in NEQ. Plotting NEQ versus dose increment shows a linear relationship and can be described by a linear function (with R > 0.99). Every manually selectable current- time product increment can be detected. With the ACR phantom, the number of detected objects increases only in the lower dose range and reaches saturation at about 9 mGy entrance dose (80 µGy detector dose). The CDMAM can detect a 50% increase in dose over the examined dose range with all five diameters, although the increases of threshold thickness are not monotonous. We conclude that an NEQ-based method has the potential to replace the established detail phantom methods to detect dose changes in the course of QA.

[Needle crystal detector technology in mammography--relationship between image quality and dose depending on beam quality]. / Nadelkristalldetektor-Technologie in der Mammografie--Bildqualität und Dosisverhalten in Abhängigkeit von der Strahlenqualität.

PURPOSE: Compared with traditional CR storage phosphor plates, CR needle crystal technology used in mammography claims to allow for better image quality using a lower dose. Image quality and dose behavior are evaluated for multiple breast thicknesses (simulated with PMMA slabs) on the Agfa DX-M system with needle crystal detectors (HM5.0) and optimized for possible different beam qualities. MATERIALS AND METHODS: Technical image quality was determined using the CDMAM phantom with subsequent "automatic readout" by considering limiting values as specified in the EUREF guideline. For dose, the calculated average glandular dose was used. RESULTS: With CR needle crystal detectors, comparable image quality can already be achieved with an approximately 50% lower dose than required for traditional plates. In addition, CR needle crystal technology makes it possible to also reach the achievable EUREF limit values without exceeding the dose limit values specified in EUREF. It was also found that the usage of W/Rh instead of Mo/Rh is beneficial for a 50 mm as well as 70 mm PMMA with regards to better image quality and a lower dose. CONCLUSION: The needle crystal technology with the Agfa DX-M system supports equivalent CDMAM image quality with an approximately 50% lower AGD compared to powder-based CR. An additional dose reduction can be achieved by using W/Rh instead of Mo/Rh.

[Physical aspects of different tomosynthesis systems]. / Physikalische Aspekte der verschiedenen Tomosynthesesysteme.

Digital breast tomosynthesis (DBT) is a new image processing technique based on digital mammography technology. Image slices of the stationary compressed breast are reconstructed from multiple images taken at different angles of the X-ray tube at the same time. The main goal is to achieve a similar radiation dose exposure as common encountered in traditional digital mammography. One of the key advantages of DBT is that lesions are less likely to be hidden amongst normal tissues as they are in traditional digital mammography. This way the quality of diagnosis can be improved, especially for dense breasts. Current DBT implementations from several manufacturers differ in certain features such as scanning angle, number of projections, scanning time, pixel size, reconstruction methods and type of tube movement. A comparison and description of these different characteristics as well as a discussion on the proposed number of imaging planes and related radiation dose requirements are given.

[Perspectives of the digital mammography platform]. / Perspektiven der digitalen Mammographieplattform.

In Europe one out of every nine women suffers from breast cancer during her lifetime. Since the introduction of mammography screening programs more breast cancers are being diagnosed when they are still small and early stage cancers with a favourable prognosis. The introduction of digital mammography systems has led to a continuous reduction of breast cancer mortality especially in specific patient subgroups. Furthermore, the digital mammography platform enables the development of new, innovative breast imaging methods to increase sensitivity and decrease breast cancer mortality. This digital mammography platform includes digital breast tomosynthesis, digital contrast medium mammography and digital contrast medium breast tomosynthesis as well as fused data sets from digital mammography with ultrasound or MRI. The following article summarizes these new applications, describes the strengths of the digital platform and illustrates the potential advantages of an improved breast cancer diagnosis by digital mammography.

[Quality assurance of mammographic devices]. / Technische Qualitätssicherung in der Mammographie.

An account of the technical features of mammographic devices as a consequence of the radiological requirements for imaging the breast is given. For quality assurance of these features specific test procedures have been established which at least since the introduction of the MED-directive 97/43 of CEC have to be applied. A concise summary of these protocols is given.