Background. Image post-processing gives computed radiography (CR) a considerable advantage over film-screen systems. After digitisation of information from CR plates, data are routinely processed using manufacturer-specific software. Agfa CR readers use MUSICA software, and an upgrade with significantly different image appearance was recently released: MUSICA2. Aim. This study quantitatively compares the image quality of images acquired without post-processing (flatfield) with images processed using these two software packages. Methods. Four aspects of image quality were evaluated. An aluminium step-wedge was imaged using constant mA at tube voltages varying from 40 to 117kV. Signal-to-noise ratios (SNRs) and contrast-to-noise Ratios (CNRs) were calculated from all steps. Contrast variation with object size was evaluated with visual assessment of images of a Perspex contrast-detail phantom, and an image quality figure (IQF) was calculated. Resolution was assessed using modulation transfer functions (MTFs). Results. SNRs for MUSICA2 were generally higher than the other two methods. The CNRs were comparable between the two software versions, although MUSICA2 had slightly higher values at lower kV. The flatfield CNR values were better than those for the processed images. All images showed a decrease in CNRs with tube voltage. The contrast-detail measurements showed that both MUSICA programmes improved the contrast of smaller objects. MUSICA2 was found to give the lowest (best) IQF; MTF measurements confirmed this, with values at 3.5 lp/mm of 10% for MUSICA2, 8% for MUSICA and 5% for flatfield. Conclusion. Both MUSICA software packages produced images with better contrast resolution than unprocessed images. MUSICA2 has slightly improved image quality than MUSICA.

Background. Mammography aims to obtain mammograms of best possible image quality with least possible radiation dose.1 Theoretically, an increase in breast compression gives a reduction in thickness, without changing the density, resulting in improved image quality and reduced radiation dose. Aim. This study aims to investigate the relationship between compression force, phantom thickness, image quality and radiation dose. The existence of a compression point beyond which increased compression gives a change in density rather than thickness is also considered. Method. Image quality is assessed with a contrast-detail phantom within Superflab phantom on a computed radiography (CR) mammography unit using automatic exposure control (AEC). Image quality is determined by visual inspection and image quality figure (IQF) scoring. The effect of compression and lesion depth on image quality is determined. Entrance and exit doses are calculated. The relationship between entrance dose, compression and thickness is investigated, as is the existence of a compression point beyond which a change in phantom density occurs. The average glandular dose (AGD) is calculated from the scanning average level (SAL) and logarithmic mean (LgM) according to Koen et al,2 and compared to the allowable limit. Results. The geometry effect was not observed. An improvement in image quality with increased compression was found. Entrance dose did decrease with increased compression. This trend was not observed with exit dose as AEC was used and exit dose was calculated from SAL values. The “change-in-density” point of compression was determined. Both LgM and SAL could be used successfully for AGD calculation.

Background. Radiologists analyse both standard mammographic views of a breast to confirm the presence of abnormalities and reduce false-positives. However, at present, no computer-aided diagnosis system uses ipsilateral mammograms to confirm the presence of suspicious features. Aim. The aim of this study was to develop image-processing algorithms that can be used to match a suspicious feature from one mammographic view to the same feature in another mammographic view of the same breast. This algorithm can be incorporated into a computer-aided diagnosis package to confirm the presence of suspicious features. Method. The algorithms were applied to 68 matched pairs of craniocaudal and mediolateral-oblique mammograms. The results of this pilot study take the form of maps of similarity. A novel method of evaluating the similarity maps is presented, using the area under the receiver operating characteristic curve (AUC) and the contrast (C) between the area of the matched region and the background of the similarity map. Results and conclusions. The first matching algorithm (using texture measures extracted from a grey-level co-occurrence matrix (GLCM) and a Euclidean distance similarity metric) achieved an average AUC of 0.80±0.17 with an average C of 0.46±0.26. The second algorithm (using GLCMs and a mutual information similarity metric) achieved an average AUC of 0.77±0.25 with an average C of 0.50±0.42. The latter algorithm also performed remarkably well with the matching of malignant masses and achieved an average AUC of 0.96±0.05 with an average C of 0.90±0.21. In conclusion, texture analysis methods used with suitable similarity metrics allow a suspicious feature from one mammographic view to be matched with the same suspicious feature in other mammographic views of the same breast.

Studies indicate that computed radiography (CR) can lead to increased radiation dose to patients. It is therefore important to relate the exposure indicators provided by CR manufacturers to the radiation dose delivered so as to assess the radiation dose delivered to patients directly from the exposure indicators. The aim of this study was to investigate the performance of an Agfa CR system in order to characterize the dose indicators provided by the system. The imaging plate response was characterized in terms of entrance exposure to the plate and the digital signal indicators generated by the system (SAL - Scanning Average Level and lgM - Logarithmic median) for different beam qualities. Several exposures were performed on a mammography unit and the digital signal, expressed as SAL and lgM for each image was correlated with the entrance exposure on a standard ACR phantom. From this, the relationship between the Agfa dose indices (SAL and lgM) and the average glandular dose (AGD) in mammography was established. An equation was derived to calculate the AGD delivered to the patient as a function of the exposure indicator, lgM, and the kV. The results indicated that the measured AGD at 28kV for a standard breast thickness during routine calibration with the ACR phantom was 1.58mGy (lgM = 1.99), which is within 1.5% of the value calculated using the derived equation for a standard Perspex thickness of 4.2cm using the AEC (1.56mGy). The standard error in using this equation was calculated to be 8.3%.

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