Friedrich Semturs

Factors for conversion between human and automatic read-outs of CDMAM images.

PURPOSE According to the European protocol for the quality control of the physical and technical aspects of mammography screening (EPQCM) image quality of digital mammography devices has to be assessed using human evaluation of the CDMAM contrast-detail phantom. This is accomplished by the determination of threshold thicknesses of gold disks with different diameters (0.08-2 mm) and revealed to be very time consuming. Therefore a software solution based on a nonprewhitening matched filter (NPW) model was developed at the University of Nijmegen. Factors for the conversion from automatic to human readouts have been determined by Young et al. [Proc. SPIE 614206, 1-13 (2006) and Proc. SPIE 6913, 69131C1 (2008)] using a huge amount of data of both human and automatic readouts. These factors depend on the observer groups and are purely phenomenological. The authors present an alternative approach to determine the factors by using the Rose observer model. METHODS Their method uses the Rose theory which gives a relationship between threshold contrast, diameter of the object and number of incident photons. To estimate the conversion factors for the five diameters from 0.2 to 0.5 mm they exposed with five different current-time products which resulted in 25 equations with five unknowns. RESULTS The theoretical conversion factors (in dependence of the diameters) amounted to be 1.61 ± 0.02 (0.2 mm diameter), 1.67 ± 0.02 (0.25 mm), 1.85 ± 0.02 (0.31 mm), 2.09 ± 0.02 (0.4 mm), and 2.28 ± 0.02 (0.5 mm). The corresponding phenomenological factors found in literature are 1.74 (0.2 mm), 1.78 (0.25 mm), 1.83 (0.31 mm), 1.88 (0.4 mm), and 1.93 (0.5 mm). CONCLUSIONS They transferred the problem of determining the factors to a well known observer model which has been examined for many years and is also well established. This method reveals to be reproduceable and produces factors comparable to the phenomenological ones.

Image Quality of a Wet Laser Printer Versus a Paper Printer for Full-Field Digital Mammograms

OBJECTIVE The purpose of our study was to compare the image quality of a wet laser printer with that of a paper printer for full-field digital mammography (FFDM). MATERIALS AND METHODS For both a wet laser printer and a paper printer connected to an FFDM system, image quality parameters were evaluated using a standardized printer test image (luminance density, dynamic range). The detectability of standardized objects on a phantom was also evaluated. Furthermore, 640 mammograms of 80 patients with different breast tissue composition patterns were imaged with both printers. Subjective image quality parameters (brightness, contrast, and detection of details of anatomic structures-that is, skin, subcutis, musculature, glandular tissue, and fat), the detectability of breast lesions (mass, calcifications), and the diagnostic performance according to the BI-RADS classification were evaluated. RESULTS Both the luminance density and the dynamic range were superior for the wet laser printer. More standardized objects were visible on the phantom imaged with the wet laser printer than with the paper printer (13/16 vs 11/16). Each subjective image quality parameter of the mammograms from the wet laser printer was rated superior to those of the paper printer. Significantly more breast lesions were detected on the wet laser printer images than on the paper printer images (masses, 13 vs 10; calcifications, 65 vs 48; p < 0.05). With the paper printer images, BI-RADS 4 and 5 categories were underestimated for 10 (43.5%) of 23 patients. CONCLUSION For FFDM, images obtained from a wet laser printer show superior objective and subjective image quality compared with a paper printer. As a consequence, the paper printer should not be used for FFDM.

Teleradiology with uncompressed digital mammograms: Clinical assessment

PURPOSE The purpose of our study was to demonstrate the feasibility of sending uncompressed digital mammograms in a teleradiologic setting without loss of information by comparing image quality, lesion detection, and BI-RADS assessment. MATERIALS AND METHODS CDMAM phantoms were sent bidirectionally to two hospitals via the network. For the clinical aspect of the study, 200 patients were selected based on the BI-RAD system: 50% BI-RADS I and II; and 50% BI-RADS IV and V. Two hundred digital mammograms (800 views) were sent to two different institutions via a teleradiology network. Three readers evaluated those 200 mammography studies at institution 1 where the images originated, and in the two other institutions (institutions 2 and 3) where the images were sent. The readers assessed image quality, lesion detection, and BI-RADS classification. RESULTS Automatic readout showed that CDMAM image quality was identical before and after transmission. The image quality of the 200 studies (total 600 mammograms) was rated as very good or good in 90-97% before and after transmission. Depending on the institution and the reader, only 2.5-9.5% of all studies were rated as poor. The congruence of the readers with respect to the final BI-RADS assessment ranged from 90% and 91% at institution 1 vs. institution 2, and from 86% to 92% at institution 1 vs. institution 3. The agreement was even higher for conformity of content (BI-RADS I or II and BI-RADS IV or V). Reader agreement in the three different institutions with regard to the detection of masses and calcifications, as well as BI-RADS classification, was very good (κ: 0.775-0.884). Results for interreader agreement were similar. CONCLUSION Uncompressed digital mammograms can be transmitted to different institutions with different workstations, without loss of information. The transmission process does not significantly influence image quality, lesion detection, or BI-RADS rating.

Physical aspects of different tomosynthesis systems

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.ZusammenfassungDie digitale Brusttomosynthese (DBT) ist eine auf der digitalen Mammographie aufbauende neuartige Bildverarbeitungstechnologie. Dabei werden durch bogenförmige Bewegung der Röntgenröhre mehrere Aufnahmen der komprimierten Brust angefertigt, um daraus Schichtbilder der Brust zu rekonstruieren. Es wird eine Gesamtdosis ähnlich der Dosis einer herkömmlichen digitalen Mammographie angestrebt. Einer der wesentlichen Vorteile von DBT besteht darin, dass Läsionen nicht mehr durch überlagernde Gewebeteile verdeckt werden und dadurch die Befundungsqualität, insbesondere bei dichten Brüsten, gesteigert werden kann.Die jetzigen DBT-Implementierungen verschiedener Hersteller unterscheiden sich in mehrfacher Hinsicht. Es werden die Vor- und Nachteile der verschiedenen DBT-Charakteristiken wie Scanwinkel, Anzahl der Projektionen, Scanzeit, Pixelgröße, Rekonstruktionsmethoden und Art der Röhrenbewegung gegenübergestellt sowie die Anzahl der empfohlenen Aufnahmeebenen und der damit verbundene Dosisbedarf verglichen.AbstractDigital 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.

Quality Controls in Digital Mammography protocol of the EFOMP Mammo Working group

This article aims to present the protocol on Quality Controls in Digital Mammography published online in 2015 by the European Federation of Organisations for Medical Physics (EFOMP) which was developed by a Task Force under the Mammo Working Group. The main objective of this protocol was to define a minimum set of easily implemented quality control tests on digital mammography systems that can be used to assure the performance of a system within a set and acceptable range. Detailed step-by-step instructions have been provided, limiting as much as possible any misinterpretations or variations by the person performing. It is intended that these tests be implemented as part of the daily routine of medical physicists and system users throughout Europe in a harmonised way so allowing results to be compared. In this paper the main characteristics of the protocol are illustrated, including examples, together with a brief summary of the contents of each chapter. Finally, instructions for the download of the full protocol and of the related software tools are provided.

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.

Perspectives of the digital mammography platform

ZusammenfassungEtwa jede neunte Frau in Europa erkrankt im Laufe ihres Lebens an Brustkrebs. Durch die Einführung von Mammographiescreeningprogrammen werden immer mehr kleine Brustkarzinome in einem frühen Stadium entdeckt. Die Einführung der digitalen Mammographie erzielt insbesondere bei bestimmten Patientinnengruppen eine weitere kontinuierliche Senkung der Brustkrebsmortalität. Zusätzlich ermöglicht die digitale Mammographie die Entwicklung neuer und Fusion bereits existierender bildgebender Methoden. Zu dieser „digitalen Mammographieplattform“ gehören die digitale Brusttomosynthese, die digitale Kontrastmittelmammographie und die digitale Kontrastmittel-Brusttomosynthese sowie fusionierte Datensätze der digitalen Mammographie mit dem Ultraschall oder der MRT. Diese innovativen Techniken bieten die Möglichkeit, die Sensitivität der Mammographie zu steigern und die Brustkrebsmortalität weiter zu senken. Der folgende Artikel fasst diese neuen Anwendungen zusammen, beschreibt die Stärken der digitalen Plattform und veranschaulicht den potenziellen Vorteil einer verbesserten Brustkrebsfrüherkennung durch die digitale Mammographie.AbstractIn 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.

Conversion factors between human and automatic readouts of CDMAM phantom images of CR mammography systems

In mammography screening, profound assessment of technical image quality is imperative. The European protocol for the quality control of the physical and technical aspects of mammography screening (EPQCM) suggests using an alternate fixed choice contrast-detail phantom-like CDMAM. For the evaluation of technical image quality, human or automated readouts can be used. For automatic evaluation, a software (cdcom) is provided by EUREF. If the automated readout indicates unacceptable image quality, additional human readout may be performed overriding the automated readout. As the latter systematically results in higher image quality ratings, conversion factors between both methods are regularly applied. Since most image quality issues with mammography systems arise within CR systems, an assessment restricted to CR systems with data from the Austrian Reference Center in the mammography screening program has been conducted. Forty-five CR systems were evaluated. Human readouts were performed with a randomisation software to avoid bias due to learning effects. Additional automatic evaluation allowed for the computation of conversion factors between human and automatic readouts. These factors were substantially lower compared to those suggested by EUREF, namely 1.21 compared to 1.62 (EUREF UK method) and 1.42 (EUREF EU method) for 0.1 mm, and 1.40 compared to 1.83 (EUREF UK) and 1.73 (EUREF EU) for 0.25 mm structure size, respectively. Using either of these factors to adjust patient dose in order to comply with image quality requirements results in differences in the dose increase of up to 90%. This necessitates a consensus on their proper application and limits the validity of the assessment methods. Clear criteria for CR systems based on appropriate studies should be promoted.

Spectrum optimization for computed radiography mammography systems.

PURPOSE Technical quality assurance is a key issue in breast screening protocols. While full-field digital mammography systems produce excellent image quality at low dose, it appears difficult with computed radiography (CR) systems to fulfill the requirements for image quality, and to keep the dose below the limits. However, powder plate CR systems are still widely used, e.g., they represent ∼30% of the devices in the Austrian breast cancer screening program. For these systems the selection of an optimal spectrum is a key issue. METHODS We investigated different anode/filter (A/F) combinations over the clinical range of tube voltages. The figure-of-merit (FOM) to be optimized was squared signal-difference-to-noise ratio divided by glandular dose. Measurements were performed on a Siemens Mammomat 3000 with a Fuji Profect reader (SiFu) and on a GE Senograph DMR with a Carestream reader (GECa). RESULTS For 50mm PMMA the maximum FOM was found with a Mo/Rh spectrum between 27kVp and 29kVp, while with 60mm Mo/Rh at 28kVp (GECa) and W/Rh 25kVp (SiFu) were superior. For 70mm PMMA the Rh/Rh spectrum had a peak at about 31kVp (GECa). FOM increases from 10% to >100% are demonstrated. CONCLUSION Optimization as proposed in this paper can either lead to dose reduction with comparable image quality or image quality improvement if necessary. For systems with limited A/F combinations the choice of tube voltage is of considerable importance. In this work, optimization of AEC parameters such as anode-filter combination and tube potential was demonstrated for mammographic CR systems.

Comparison of two CDMAM generations with respect to dose sensitivity

A contrast-detail phantom like the CDMAM phantom (Artinis Medical Systems, Zetten, NL) is suggested by the ’European protocol for the quality control of the physical and technical aspects of mammography screening’ to evaluate image quality of digital mammography systems. In a recent paper the commonly used CDMAM 3.4 was evaluated according to its dose sensitivity in comparison to other phantoms. The successor phantom (CDMAM 4.0) features other disc diameters and thicknesses that were adapted to be more closely to the image quality which can be found in modern mammography systems. It seems to be obvious to compare this two generations of phantoms with respect to a potential improvement. The time-current product was varied within a range of clinically used values (40-160 mAs). Image evaluation was performed using the automatic evaluation software provided by Artinis. The relative dose sensitivity was compared in dependence of different diameters. Additionally, the IQFinv parameter, which averages over the diameters was computed to get a more global conclusion. We found that the dose is of a considerable smoother dependence with the CMDAM 4.0 phantom. Also the IQFinv parameter shows a more linear behaviour than with the CDMAM 3.4. As the automatic evaluation shows different results on the two phantoms, conversion factors from automatic to human readouts have to be adapted consequently.