The risk-based breast screening (RIBBS) study protocol: a personalized screening model for young women

The optimal mammography screening strategy for women aged 45-49 years is a matter of debate. We present the RIBBS study protocol, a quasi-experimental, prospective, population-based study comparing a risk- and breast density-stratified screening model (interventional cohort) with annual digital mammography (DM) screening (observational control cohort) in a real-world setting. The interventional cohort consists of 10,269 women aged 45 years enrolled between 2020 and 2021 from two provinces of the Veneto Region (northen Italy). At baseline, participants underwent two-view digital breast tomosynthesis (DBT) and completed the Tyrer-Cuzick risk prediction model. Volumetric breast density (VBD) was calculated from DBT and the lifetime risk (LTR) was estimated by including VBD among the risk factors. Based on VBD and LTR, women were classified into five subgroups with specific screening protocols for subsequent screening rounds: (1) LTR ≤ 17% and nondense breast: biennial DBT; (2) LTR ≤ 17% and dense breast: biennial DBT and ultrasound; (3) LTR 17-30% or LTR > 30% without family history of BC, and nondense breast: annual DBT; (4) LTR 17-30% or > 30% without family history of BC, and dense breast: annual DBT and ultrasound; and (5) LTR > 30% and family history of BC: annual DBT and breast MRI. The interventional cohort is still ongoing. An observational, nonequivalent control cohort of 43,000 women aged 45 years participating in an annual DM screening programme was recruited in three provinces of the neighbouring Emilia-Romagna Region. Cumulative incidence rates of advanced BC at three, five, and ten years between the two cohorts will be compared, adjusting for the incidence difference at baseline.Trial registration This study is registered on Clinicaltrials.gov (NCT05675085).

Phantom-based analysis of variations in automatic exposure control across three mammography systems: implications for radiation dose and image quality in mammography, DBT, and CEM

BACKGROUND

Automatic exposure control (AEC) plays a crucial role in mammography by determining the exposure conditions needed to achieve specific image quality based on the absorption characteristics of compressed breasts. This study aimed to characterize the behavior of AEC for digital mammography (DM), digital breast tomosynthesis (DBT), and low-energy (LE) and high-energy (HE) acquisitions used in contrast-enhanced mammography (CEM) for three mammography systems from two manufacturers.

METHODS

Using phantoms simulating various breast thicknesses, 363 studies were acquired using all available AEC modes 165 DM, 132 DBT, and 66 LE-CEM and HE-CEM. AEC behaviors were compared across systems and modalities to assess the impact of different technical components and manufacturers' strategies on the resulting mean glandular doses (MGDs) and image quality metrics such as contrast-to-noise ratio (CNR).

RESULTS

For all systems and modalities, AEC increased MGD for increasing phantom thicknesses and decreased CNR. The median MGD values (interquartile ranges) were 1.135 mGy (0.772-1.668) for DM, 1.257 mGy (0.971-1.863) for DBT, 1.280 mGy (0.937-1.878) for LE-CEM, and 0.630 mGy (0.397-0.713) for HE-CEM. Medians CNRs were 14.2 (7.8-20.2) for DM, 4.91 (2.58-7.20) for a single projection in DBT, 11.9 (8.0-18.2) for LE-CEM, and 5.2 (3.6-9.2) for HE-CEM. AECs showed high repeatability, with variations lower than 5% for all modes in DM, DBT, and CEM.

CONCLUSIONS

The study revealed substantial differences in AEC behavior between systems, modalities, and AEC modes, influenced by technical components and manufacturers' strategies, with potential implications in radiation dose and image quality in clinical settings.

RELEVANCE STATEMENT

The study emphasized the central role of automatic exposure control in DM, DBT, and CEM acquisitions and the great variability in dose and image quality among manufacturers and between modalities. Caution is needed when generalizing conclusions about differences across mammography modalities.

KEY POINTS

• AEC plays a crucial role in DM, DBT, and CEM. • AEC determines the "optimal" exposure conditions needed to achieve specific image quality. • The study revealed substantial differences in AEC behavior, influenced by differences in technical components and strategies.

Using automated software evaluation to improve the performance of breast radiographers in tomosynthesis screening

OBJECTIVE

To improve breast radiographers' individual performance by using automated software to assess the correctness of breast positioning and compression in tomosynthesis screening.

MATERIALS AND METHODS

In this retrospective longitudinal analysis of prospective cohorts, six breast radiographers with varying experience in the field were asked to use automated software to improve their performance in breast compression and positioning. The software tool automatically analyzes craniocaudal (CC) and mediolateral oblique (MLO) views for their positioning quality by scoring them according to PGMI classifications (perfect, good, moderate, inadequate) and checking whether the compression pressure is within the target range. The positioning and compression data from the studies acquired before the start of the project were used as individual baselines, while the data obtained after the training were used to test whether conscious use of the software could help the radiographers improve their performance. The percentage of views rated perfect or good and the percentage of views in target compression were used as overall metrics to assess changes in performance.

RESULTS

Following the use of the software, all radiographers significantly increased the percentage of images rated as perfect or good in both CCs and MLOs. Individual improvements ranged from 7 to 14% for CC and 10 to 16% for MLO views. Moreover, most radiographers exhibited improved compression performance in CCs, with improvements up to 16%.

CONCLUSION

Active use of a software tool to automatically assess the correctness of breast compression and positioning in breast cancer screening can improve the performance of radiographers.

CLINICAL RELEVANCE STATEMENT

This study suggests that the use of a software tool for automatically evaluating correctness of breast compression and positioning in breast cancer screening can improve the performance of radiographers on these metrics, which may ultimately lead to improved screening outcomes.

KEY POINTS

• Proper breast positioning and compression are critical in breast cancer screening to ensure accurate diagnosis. • Active use of the software increased the quality of craniocaudal and mediolateral oblique views acquired by all radiographers. • Improved performance of radiographers is expected to improve screening outcomes.

Exploratory radiomic analysis of stage III non-small cell lung cancer CT images: Correlation with clinical-pathological characteristics

e20574

Background: Recent evidences have suggested potential applications of radiomics in early diagnosis, prognostic stratification and treatment outcome prediction of Non-Small Cell Lung Cancer (NSCLC) patients. The purpose of this study is to evaluate the ability of radiomic analysis to discriminate between different clinical-pathological conditions in patients with stage III NSCLC. Methods: Baseline CT studies from 59 patients with stage III NSCLC referred to our Institution from 2010 and 2020 were retrospectively reviewed, and the segmentation of the main lung lesion and the extraction of 517 radiomic features performed using a commercial software. The number of features was reduced to 46 by means of principal component analysis applied using the R package “RadAR” (Radiomics Analysis with R). The Kruskal-Wallis test was applied to all the radiomic features in order to evaluate which of them can discriminate between 7 clinical dichotomous characteristics: tumor stage, type, presence of mutation, treatment response, relapse free survival (RFS), smoking habit, patient outcome. P < 0.05 means that there is a statistically significant difference between the two subgroups. Results: The median age at diagnosis was 69 years (range 43-83). Most patients were males (40/59 = 67.8%) and heavy smokers (36/59 = 61.0%). Adenocarcinoma was the most common histology (41/59 = 70.7%), while cases were almost equally splitted between stage IIIA (45.8%) and stage IIIB or IIIC (54.2%). Most selected radiomic features (29/46 = 63.0%) showed a statistically significant difference between patients with and without mutations. Ten (10/46 = 21.7%) radiomic features were associated with patient sex. Seven features (7/45 = 15.2%) were “sensitive” to the tumor clinical stage (stage IIIA vs. stage IIIB+IIIC), 4 (4/46 = 8.7%) to the histological type, and 2 (2/46 = 4.3%) to the patient outcome. None of the selected radiomic features was able to discriminate between responder and non-responder patients, current/previous smokers and never smokers, and patients with RFS lower than 12 months versus RFS equal or higher than 12 months. Conclusions: This preliminary analysis showed that radiomics has the potential of identifying mathematical features associated with clinical and histopathological characteristics in stage III NSCLC patients, which might feed multiparametric predictive models. Larger datasets and further analysis are necessary in order to confirm initial results.

Artifact reduction in contrast-enhanced mammography

OBJECTIVE

To evaluate the effectiveness of a new algorithm developed to reduce artifacts in dual-energy subtraction (DES) contrast-enhanced mammography (CEM) images while preserving contrast enhancement of possible lesions.

METHODS

A retrospective multi-reader paired study was performed by using 134 CEM studies obtained from the first 134 women enrolled in a prospective clinical study aiming to compare the clinical performance of CEM to those of breast MRI in screening of women at increased risk of breast cancer. Four experienced readers compared independently the standard (STD) DES images with those obtained by reprocessing the raw images by a new algorithm (NEW), expected to reduce the DES artifact intensity. The intensity of three types of artifacts (breast-in-breast, ripple, and skinfold enhancement) and the intensity of possible contrast uptake were assessed visually and rated using a categorical ordinal scale. Proportions of images rated by the majority of readers as "Absent", "Weak", "Medium", "Strong" in each artifact intensity category were compared between the two algorithms. P-values lower than 0.05 were considered statistically significant.

RESULTS

The NEW algorithm succeeded in eliminating 84.5% of breast-in-breast artifacts, 84.2% of ripple artifacts, and 56.9% of skinfold enhancement artifacts versus STD DES images, and reduced the artifact intensity in 12.1%, 13.0%, and 28.8% of the images, respectively. The visibility of lesion contrast uptake was the same with the STD and the NEW algorithms.

CONCLUSION

The new dual-energy subtraction algorithm demonstrated to be effective in reducing/eliminating CEM-related artifacts while preserving lesion contrast enhancement.

Repeat Screening Outcomes with Digital Breast Tomosynthesis Plus Synthetic Mammography for Breast Cancer Detection: Results from the Prospective Verona Pilot Study

Background Few results are available about subsequent outcomes after screening with digital breast tomosynthesis (DBT). Purpose To compare the diagnostic accuracy of a screening round with DBT plus synthetic mammography (SM) (hereafter, DBT+SM) and the repeat screening round with DBT with SM (hereafter, DBT+SM) or full-field digital mammography (FFDM) with FFDM screening. Materials and Methods This prospective study (Verona Pilot Study, clinical trial identification: 2015/1238) included women screened with DBT+SM between April 2015 and March 2017 and rescreened with DBT+SM or FFDM between April 2017 and March 2019. Screening performance (recall rate, cancer detection rate [CDR], and positive predictive value of recall [PPV1]) was compared with that obtained from 28 680 women screened with FFDM between 2013 and 2014 (control group). Cancer stages were compared between modalities and screening rounds. A χ² test was used to evaluate differences. P < .05 was indicative of a statistically significant difference. Results Of 34 638 women enrolled, 32 870 (median age, 58 years; age range, 52-71 years) underwent repeat screening-16 198 with DBT+SM and 16 672 with FFDM. The CDR was higher for repeat screening with DBT+SM than for the control group with FFDM (8.1 per 1000 women screened vs 4.5 per 1000 women screened, respectively; P < .01) and was not significantly lower for repeat screening with FFDM (3.5 per 1000 women screened vs 4.5 per 1000 women screened, respectively; P = .11). Compared with the control group, there was no difference in the recall rate at repeat screening with both DBT+SM (3.71% vs 3.40%, respectively; P = .10) and FFDM (3.71% vs 3.69%, P = .92), whereas PPV1 was higher only when repeat screening was performed with DBT+SM (23.8% vs 12.0%, P < .01). At repeat screening, the proportion of cancers stage II or higher was 14.5% (19 of 131 cancers) with DBT+SM and 8.5% (five of 59 cancers) with FFDM, both of which were lower than the proportion in the control group with FFDM (30 of 110 cancers, 27.3%) (P ≤ .01). Conclusion At repeat screening, digital breast tomosynthesis plus synthetic mammography depicted more cancers than full-field digital mammography (FFDM) and found a lower number of stage II cancers compared with FFDM. © RSNA, 2020 See also the editorial by Bae in this issue.

Stand-Alone Artificial Intelligence for Breast Cancer Detection in Mammography: Comparison With 101 Radiologists

BACKGROUND

Artificial intelligence (AI) systems performing at radiologist-like levels in the evaluation of digital mammography (DM) would improve breast cancer screening accuracy and efficiency. We aimed to compare the stand-alone performance of an AI system to that of radiologists in detecting breast cancer in DM.

METHODS

Nine multi-reader, multi-case study datasets previously used for different research purposes in seven countries were collected. Each dataset consisted of DM exams acquired with systems from four different vendors, multiple radiologists' assessments per exam, and ground truth verified by histopathological analysis or follow-up, yielding a total of 2652 exams (653 malignant) and interpretations by 101 radiologists (28 296 independent interpretations). An AI system analyzed these exams yielding a level of suspicion of cancer present between 1 and 10. The detection performance between the radiologists and the AI system was compared using a noninferiority null hypothesis at a margin of 0.05.

RESULTS

The performance of the AI system was statistically noninferior to that of the average of the 101 radiologists. The AI system had a 0.840 (95% confidence interval [CI] = 0.820 to 0.860) area under the ROC curve and the average of the radiologists was 0.814 (95% CI = 0.787 to 0.841) (difference 95% CI = -0.003 to 0.055). The AI system had an AUC higher than 61.4% of the radiologists.

CONCLUSIONS

The evaluated AI system achieved a cancer detection accuracy comparable to an average breast radiologist in this retrospective setting. Although promising, the performance and impact of such a system in a screening setting needs further investigation.

Accuracy of mammography dosimetry in the era of the European Directive 2013/59/Euratom transposition

PURPOSE

To evaluate the impact of increasing levels of accuracy for mean glandular dose (MGD) evaluation in the era of the European Directive 2013/59/Euratom transposition.

METHOD

4028 women who had a mammography examination by one of five mammography units using different detector technologies were included in this study. 16,006 images were processed by a software algorithm that determines breast glandularity quantitatively and uses this to estimate patient-specific MGD (psMGD). Entrance dose (ED) values and half value layers (HVLs) measured for each mammography system were collected to evaluate the effect of equipment calibration in psMGD calculation. The psMGD values adjusted for system calibration were compared with organ dose (OD) provided by manufacturers as image metadata.

RESULTS

Overall median relative difference between calibrated psMGD and organ dose was below 3%, with larger differences for individual systems. The psMGD adjustment for system calibration was particularly useful for one system for which ED had an evident miscalibration issue. The mean difference between psMGD with calibration and organ dose provided by manufacturers was 4.1 %, ranging from -16.3 % to +24.5 %. The proportion of images for which organ dose was more than 10 % 'inaccurate' compared to psMGD was between 11 % and 46 %, depending on the mammography system.

CONCLUSION

Patient-specific mean glandular dose, possibly adjusted for system calibration, allows more accurate individual breast dosimetry than what would be performed using organ dose provided by manufacturers. Conversely, definition of diagnostic reference levels could be achieved using either psMGD or organ dose.

Interaction of Cd(ii) and Ni(ii) terpyridine complexes with model polynucleotides: a multidisciplinary approach

The study of the intercalation of both complexes, evidenced by CD and fluorescence spectroscopy and supported by QM/MM calculations, broadens the experimental and theoretical background on drugs/DNA interactions.

Optimal follow-up intervals in active surveillance of renal masses in patients with von Hippel-Lindau disease

OBJECTIVES

To estimate an optimal follow-up (FU) interval for von Hippel-Lindau (VHL) patients with renal masses (RMs) by determining tumour growth rates from growth curves.

METHODS

Thirty lesions (47.6%) were classified as solid tumours (STs) and 33 (52.4%) as complex cysts (CCs). Variations in lesion volume over time were analyzed. For 53 lesions, we calculated the growth rate during the period when the volume of the lesion changed most rapidly, and called this the fast growth rate (FGR).

RESULTS

The STs initially grew fast, followed by a period of slower growth. The CCs varied in volume over time, associated with variable amounts of their fluid component. The FGR correlated better with the latest volume for STs (r = 0.905) than for CCs (r = 0.780). An optimal FU interval between 3 and 12 months was derived by combining the FGR calculated from the curve with the latest volume measured.

CONCLUSIONS

Analyzing growth curves and related kinetic parameters for RMs in VHL patients could be useful with a view to optimizing the subsequent FU interval and improving the active surveillance program.

KEY POINTS

• Measuring volume changes over time enables tumour growth curves to be charted. • Renal solid tumours increase in volume with a typical sigmoidal curve. • Complex cysts may increase and decrease in volume spontaneously over time. • The fast growth rate of solid tumours correlates with their latest volume. • The fast growth rate can orient the scheduling of subsequent follow-ups.

Performance comparison of single-view digital breast tomosynthesis plus single-view digital mammography with two-view digital mammography

OBJECTIVE

To determine the performance of combined single-view mediolateral oblique (MLO) digital breast tomosynthesis (DBT) plus single-view cranio-caudal (CC) mammography (MX) compared with that of standard two-view digital mammography.

METHODS

A multi-reader multi-case (MRMC) receiver-operating characteristic (ROC) study was conducted, involving six breast radiologists. Two hundred fifty patients underwent bilateral MX and DBT imaging. MX and DBT images with the adjunct of the CC-MX view from 469 breasts were evaluated and rated independently by six readers. Differences in mean areas under the ROC curves (AUCs), mean sensitivity and mean specificity were analysed by analysis of variance (ANOVA) to assess clinical performance.

RESULTS

The combined technique was found to be non-inferior to standard two-view mammography (MX((CC+MLO))) in mean AUC (difference: +0.021;95 % LCL = -0.011), but was not statistically significant for superiority (P = 0.197). The combined technique had equivalent sensitivity to standard mammography (76.2 % vs. 72.8 %, P = 0.269) and equivalent specificity (84.9 % vs. 83.0 %, P = 0.130). Specificity for benign lesions was significantly higher with the combination of techniques versus mammography (45.6 % vs. 36.8 %, P = 0.002).

CONCLUSION

In this enriched study population, the combination of single-view MLO tomosynthesis plus single-view CC mammography was non-inferior to that of standard two-view digital mammography in terms of ROC curve area, sensitivity and specificity.

Improvement of ESR dosimetry for thermal neutron beams through the addition of gadolinium

In this paper, the addition of gadolinium is proposed as a useful tool to enhance the electron spin resonance (ESR) sensitivity of organic compounds to thermal neutrons. The target of this work is the detection, through the ESR technique, of the thermal neutron fluence in a mixed field of photons and neutrons. Gadolinium was chosen because it has a very high capture cross section to thermal neutrons; its nuclear reaction with thermal neutrons induces complex inner shell transitions that generate, besides other particles, Auger electrons, which in turn release their energy in the neighborhood (only several nanometers) of the place of reaction. Gadolinium was added to two organic molecules: alanine and ammonium tartrate. The main result obtained was a greater neutron sensitivity for dosimeters with gadolinium than for those without gadolinium for both organic molecules used. Since a dosimeter pair is required to discriminate between the two components of a mixed field, we studied the response of each dosimeter pair irradiated in a mixed field. Through a blind test we verified the usefulness of this dosimetric system and we obtained an estimate of the fluence in the mixed field with a relative uncertainty of 3%, when the pair composed of an alanine dosimeter and a dosimeter with alanine and gadolinium is used.

Grid removal and impact on population dose in full-field digital mammography

The study purpose was to determine the impact of anti-scatter grid removal on patient dose, in full field digital mammography. Dose saving, phantom based, was evaluated with the constraint that images acquired with and without grid would provide the same contrast-to-noise ratio (CNR). The digital equipment employed a flat panel detector with cesium iodide for x-ray to light conversion, 100 microm pixel size; the x-ray source was a dual-track tube with selectable filtration. Poly(methyl-emathocrylate) (PMMA) layers in the range 20-70 mm were used to simulate the absorption of different breast thickness, while two Al foils, 0.1 and 0.2 mm thick were used to provide a certain CNR. Images with grid were acquired with the same beam quality as selected in full automatic exposure mode and the mAs levels as close as possible, and the CNR measured for each thickness between 20 and 70 mm. Phantom images without grid were acquired in manual exposure mode, by selecting the same anode/filter combination and kVp as the image with grid at the same thickness, but varying mAs from 10 to 200. For each thickness, an image without aluminum was acquired for each mAs value, in order to obtain a flat image to be used to subtract the scatter nonuniformity from the phantom images. After scatter subtraction, the CNR was measured on images without grid. The mAs value that should be set to acquire a phantom image without grid so that it has the same CNR as the corresponding grid image was calculated. Therefore, mAs reduction percentage was determined versus phantom thickness. Results showed that dose saving was lower than 30% for PMMA equivalent breast thinner than 40 mm, decreased below 10% for intermediate thickness (45-50 mm), but there was no dose gain for thickness beyond 60 mm. By applying the mAs reduction factors to a clinical population derived from a data base of 4622 breasts, dose benefit was quantified in terms of population dose. On the average, the overall dose reduction was about 8%. It was considered small, not sufficient to justify a clinical implementation, and the anti-scatter grid was maintained.

ESR response to γ-rays of alanine pellets containing B(OH)3 or Gd2O3

ESR response to gamma-irradiation (1-50 Gy) of blends containing alanine and either B(OH)(3) or Gd(2)O(3) is reported. The sensitivity of the alanine--B(OH)(3) blend is comparable to the sensitivity of pure alanine, although its lowest detectable dose, LDD, is smaller ( approximately 1.3 Gy) than that of pure alanine ( approximately 2.9 Gy). Alanine with Gd(2)O(3) is about two times more sensitive than pure alanine, and its LDD is 0.8 Gy. The better sensitivity and LDD are probably due to the high atomic number (Z=64) of gadolinium, which enhances the interaction probability with photons and, consequently, the radical yield. This study suggests that other high-Z atoms may be useful for increasing the sensitivity of the response of alanine to gamma-radiation.

Automated analysis of phantom images for the evaluation of long-term reproducibility in digital mammography

The performance of an automatic software package was evaluated with phantom images acquired by a full-field digital mammography unit. After the validation, the software was used, together with a Leeds TORMAS test object, to model the image acquisition process. Process modelling results were used to evaluate the sensitivity of the method in detecting changes of exposure parameters from routine image quality measurements in digital mammography, which is the ultimate purpose of long-term reproducibility tests. Image quality indices measured by the software included the mean pixel value and standard deviation of circular details and surrounding background, contrast-to-noise ratio and relative contrast; detail counts were also collected. The validation procedure demonstrated that the software localizes the phantom details correctly and the difference between automatic and manual measurements was within few grey levels. Quantitative analysis showed sufficient sensitivity to relate fluctuations in exposure parameters (kV(p) or mAs) to variations in image quality indices. In comparison, detail counts were found less sensitive in detecting image quality changes, even when limitations due to observer subjectivity were overcome by automatic analysis. In conclusion, long-term reproducibility tests provided by the Leeds TORMAS phantom with quantitative analysis of multiple IQ indices have been demonstrated to be effective in predicting causes of deviation from standard operating conditions and can be used to monitor stability in full-field digital mammography.

Study of the glow curves of TLD exposed to thermal neutrons

The glow curves of thermoluminescent dosimeters (TLD600, TLD700 and MCP), exposed to a mixed field of thermal neutrons and gamma photons are analysed. The fluence values of thermal neutrons used, comparable with those used in radiotherapy, allow one to define the reliability of the TLDs, in particular the most sensitive MCP, in this radiation field and to get information on the dose absorbed values. The glow curves obtained have been deconvoluted using general order kinetics and the observed differences for the different LET components have been analysed. In particular, the ratio of the n(0) parameter of two different peaks seems to allow to discriminate the different contributions of neutrons and gamma photons in the beam.

Alanine blends for ESR measurements of thermal neutron fluence in a mixed radiation field

In this paper, the results of a study on the electron spin resonance (ESR) dosimetry to measure thermal neutron fluence in a mixed radiation field (neutron and photons) are presented. The ESR responses of alanine dosemeters with different additives are compared. In particular, the (10)B-acid boric and the Gd-oxide were chosen to enhance the sensitivity of alanine dosemeters to thermal neutrons. Irradiations were carried out inside the thermal column of the TAPIRO reactor of the ENEA center, Casaccia Rome. The main results are a greater neutron sensitivity and a smaller lowest detectable fluence for the dosemeters with gadolinium than for dosemeters of alanine with (10)B, which is well known to be much more sensitive to thermal neutrons than simple alanine.

Evaluation of the minimum iodine concentration for contrast-enhanced subtraction mammography

Early manifestation of breast cancer is often very subtle and is displayed in a complex and variable pattern of normal anatomy that may obscure the disease. The use of dual-energy techniques, that can remove the structural noise, and contrast media, that enhance the region surrounding the tumour, could help us to improve the detectability of the lesions. The aim of this work is to investigate the use of an iodine-based contrast medium in mammography with two different double exposure techniques: K-edge subtraction mammography and temporal subtraction mammography. Both techniques have been investigated by using an ideal source, like monochromatic beams produced at a synchrotron radiation facility and a clinical digital mammography system. A dedicated three-component phantom containing cavities filled with different iodine concentrations has been developed and used for measurements. For each technique, information about the minimum iodine concentration, which provides a significant enhancement of the detectability of the pathology by minimizing the risk due to high dose and high concentration of contrast medium, has been obtained. In particular, for cavities of 5 and 8 mm in diameter filled with iodine solutions, the minimum concentration needed to obtain a contrast-to-noise ratio of 5 with a mean glandular dose of 2 mGy has been calculated. The minimum concentrations estimated with monochromatic beams and K-edge subtraction mammography are 0.9 mg ml(-1) and 1.34 mg ml(-1) for the biggest and smallest details, respectively, while for temporal subtraction mammography they are 0.84 mg ml(-1) and 1.31 mg ml(-1). With the conventional clinical system the minimum concentrations for the K-edge subtraction mammography are 4.13 mg ml(-1) (8 mm diameter) and 5.75 mg ml(-1) (5 mm diameter), while for the temporal subtraction mammography they are 1.01 mg ml(-1) (8 mm diameter) and 1.57 mg ml(-1) (5 mm diameter).

Dose comparison between screen/film and full-field digital mammography

The study purpose was the comparison between doses delivered by a full-field digital mammography system and a screen/film mammography unit, both using the same type of X-ray tube. Exposure parameters and breast thickness were collected for 300 screen/film (GE Senographe DMR) and 296 digital mammograms (GE Senographe 2000D). The entrance surface air kerma (ESAK) was calculated from anode/filter combination, kV(p) and mAs values and breast thickness, by simulating spectra through a program based on a catalogue of experimental X-ray spectra. The average glandular dose (AGD) was also computed. Results showed an overall reduction of average glandular dose by 27% of digital over screen/film mammography. The dose saving was about 15% for thin and thick breasts, while it was between 30% and 40% for intermediate thicknesses. Full-field digital mammography dose reduction is allowed by wider dynamic range and higher efficiency of digital detector, which can be exposed at higher energy spectra than screen/film mammography, and by the separation between acquisition and displaying processes.

Are phantoms useful for predicting the potential of dose reduction in full-field digital mammography?

A phantom study was performed in full-field digital mammography to investigate the opportunity and the magnitude of a possible dose reduction that would leave the image quality above the accepted thresholds associated with some classical phantoms. This preliminary work is intended to lay the groundwork for a future clinical study on the impact of dose reduction on clinical results. Three different mammography phantoms (ACR RMI 156, CIRS 11A and CDMAM 3.4) were imaged by a full-field digital mammography unit (GE Senographe 2000D) at different dose levels. Images were rated by three observers with softcopy reading and scoring methods specific to each phantom. Different types of data analysis were applied to the ACR (American College of Radiology) and the other two phantoms, respectively. With reference to the minimum acceptance score in screen/film accreditation programmes, the ACR phantom showed that about 45% dose reduction could be applied, while keeping the phantom scores above that threshold. A relative comparison was done for CIRS and CDMAM, for which no threshold is defined. CIRS scoring remained close to the reference level down to 40% dose reduction, the inter- and intra-observer variability being the main source of uncertainty. Contrast-detail curves provided by CDMAM overlapped down to 50% dose reduction, at least for object contrast values ranging between 30% and 3%. This multi-phantom study shows the potential of further reducing the dose in full-field digital mammography beyond the current values. A common dose reduction factor around 50% seems acceptable for all phantoms. However, caution is required before extrapolating the results for clinical use, given the limitations of these widely used phantoms, mainly related to their limited dynamic range and uniform background.

Digital mammography: quality and dose control

PURPOSE

For almost 3 years, Radiologists and Physicists from Padova and Ferrara Universities have collaborated together, with the aim of collecting and comparing experimental data useful to define the most significant parameters for quality controls in digital mammography. Successively, radiologists and physicists working in other sites where a digital mammography unit was installed joined the work-group.

MATERIALS AND METHODS

In this study we report the results obtained from measurements of linearity, uniformity, short- and long-term reproducibility, AEC stability performed on 5 digital equipment by using a simple test object. X-ray beam quality and tube yield were preliminarily checked in such a way that possible uncertainties of digital system responses could be separated from those due to differences among X-ray tubes.

RESULTS

Results showed that the equipment considered, comparable in terms of both beam quality (HVL) and tube yield, always displayed linear response and reproducibility errors lower than 5%. Uniformity was very good and the grey level compensation as a function of exposure parameters remained within 5%. Differences in choice of parameters by exposure control system (AOP) were emphasised, especially for crossing between track/filter combinations (from Mo/Mo to Mo/Rh and from Mo/Rh to Rh/Rh); those differences were attributed to the +/-2 mm tolerance of breast thickness measurement (mechanically obtained) greater than the AOP tolerance (+/-1 mm).

DISCUSSION AND CONCLUSIONS

Obtained results can be useful, as comparison and reference values, for users employing a digital mammography unit of the same kind reported in this paper. Moreover, the same results could be used as "orientation" also by other users having different digital mammography technologies, whose operation should be nevertheless specifically studied and understood in order to find the most useful parameters for quality controls. The acquired experience clearly showed us that years of investigations will be necessary in order to be able to write reliable protocols. This should induce people to contemplate the necessity of not improvising "theoretical" protocols, that are unreliable and dangerous for their negative clinical implications.

Patient dose in full-field digital mammography: an Italian survey

The aim of this study was to compare performance and patient dose of full-field digital mammography units for clinical use. Measurements of linearity and automatic exposure control stability were performed on four units installed in as many Italian sites. The tube output was also obtained by the same ionization chamber, permitting to evaluate ratios mGy/mAs for each available spectrum. The entrance air-kerma was calculated over a sample of 800 cranio-caudal mammograms and the average glandular dose obtained, assuming two mean glandular compositions of 50 and 30%, respectively. Digital systems showed very good linearity and comparable responses. The stability of the automatic exposure control was better than 5% for all systems. Regarding doses, the two mammography units that work mainly in contrast mode deliver, respectively, 17 and 28% more dose compared with those working in standard mode. For the latter mode, the mean average glandular dose was in the range 1.25-1.37 mGy and 1.37-1.49 mGy for the 50 and 30% glandular composition, respectively. Results of this study were compared with those of other surveys, showing that full-field digital mammography allows a significant clinical dose reduction compared with screen/film mammography.

Dual-energy imaging in full-field digital mammography: a phantom study

A dual-energy technique which employs the basis decomposition method is being investigated for application to digital mammography. A three-component phantom, made up of plexiglas, polyethylene, and water, was doubly exposed with the full-field digital mammography system manufactured by General Electric. The 'low' and 'high' energy images were recorded with a Mo/Mo anode-filter combination and a Rh/Rh combination, respectively. The total dose was kept within the acceptable levels of conventional mammography. The first hybrid images obtained with the dual-energy algorithm are presented in comparison with a conventional radiograph of the phantom. Image-quality characteristics at contrast cancellation angles between plexiglas and water are discussed. Preliminary results show that a combination of a standard Mo-anode 28 kV radiograph with a Rh-anode 49 kV radiograph provides the best compromise between image-quality and dose in the hybrid image.

Changes of lipocalin type prostaglandin D-synthase in the seminal plasma of subfertile man

It was proposed that lipocalin type prostaglandin D synthase (L-PGD-S), a bifunctional protein both synthesizing PGD2 and transporting retinoids and other lipophilic ligands, could be involved in the development and the maturation of sperm. In the present study, the seminal plasma (SP) of 59 adult males was analyzed by standard WHO methods and immunoblotting, using a monospecific polyclonal antibody directed against L-PGD-S. Briefly, aliquots of SP (2.5 microl), were fractionated by polyacrylamide electrophoresis in the presence of sodium dodecyl sulfate, the blots were stained and densitometrically analyzed. To obtain quantitative data, the aliquot of SP was selected within the linear part of the dose/band intensity curve and a proper quality control was analyzed in all blots to normalize the intensity of the bands of different experiments. A significant reduction (p<0.05) of the L-PGD-S levels was observed in severe oligozoospermic patients compared to normozoospermic subjects and a significant correlation between L-PGD-S levels and sperm concentration was found, as reported by other authors. Further studies are warranted to evaluate the possible diagnostic and pharmacological applications of these observations.

Stopped-flow kinetic studies of low potential electron carriers of the photosynthetic bacterium, Rhodobacter capsulatus: ferredoxin I and NifF

The kinetics of electron-transfer reactions involving nif-specific proteins from Rhodobacter capsulatus; ferredoxin I, NifF, Fe-protein of nitrogenase and dithionite were studied using stopped-flow spectrophotometry. Kinetic evidence was obtained for the formation of a tight (0.44 microM) complex between NifF and Fe-protein. Under the same conditions, FdI interacted only weakly (Kd > 325 microM) with Fe-protein. There was no evidence for complex formation between NifF and FdI since the reaction NifFSQ + FdIred had a bimolecular rate constant of 12.5 +/- 1.2 x 10(3) M-1 s-1. These results suggest that NifF, which is present in only small quantities in the cell, can make a significant contribution to the overall rate of nitrogen fixation due its high reactivity with Fe-protein. Moreover, the apparent lack of specific interaction between NifF and FdI suggest that they act in vivo in parallel to reduce Fe-protein and not in series.

[Quality control of mammography: potential use of a new device for testing the image quality and the dose]

The authors tested a new equipment containing a phantom to check quality mammographic image and an electronic instrument to measure incident radiation (Phan-EX). The phantom contains objects which have similar characteristics to the details of diagnostic interest and allows an easy and accurate estimation of image quality on the basis of the number of objects detected. The radiation detector, consisting of a solid state photodiode, provides an integer proportional to the input exposure. The results obtained highlighted a good reproducibility of instrument output and a good relationship between these values and the exposure ones obtained with a much more expensive ionization chamber. The device response was linear in varying both the anodic exposure (mAs) and the x-ray tube voltage (varying the energy, the calibration factor varied only by a small percent). The authors conclude that the Phan-EX may be useful for quality assurance of the mammographic unit. Furthermore, they suggest some of its practical applications: daily tests of qualitative of the mammographic unit and the treatment system performance, control of the automatic exposure probe, choice and optimization of exposure and treatment of the film parameters, the determination of the output of the x-ray tube, the evaluation of the sensitivity of different screen/film systems.

Cloning, characterization, and regulation of nifF from Rhodobacter capsulatus

The Rhodobacter capsulatus nifF gene and upstream sequence were cloned by using a probe based on the N-terminal sequence of NifF. nifF was found to not be contained in the previously described nif regions I, II, and III. Comparison of the deduced amino acid sequence showed that it is highly similar to NifF from Azotobacter vinelandii and NifF from Klebsiella pneumoniae. Analysis of translational fusions demonstrated that the regulation of transcription was the same as previously reported at the protein level. Insertional mutagen esis showed that NifF contributes significantly to nitrogenase activity under normal nitrogen-fixing conditions and that it is absolutely required for nitrogen fixation under iron limitation.

Purification and properties of a nif-specific flavodoxin from the photosynthetic bacterium Rhodobacter capsulatus

A flavodoxin was isolated from iron-sufficient, nitrogen-limited cultures of the photosynthetic bacterium Rhodobacter capsulatus. Its molecular properties, molecular weight, UV-visible absorption spectrum, and amino acid composition suggest that it is similar to the nif-specific flavodoxin, NifF, of Klebsiella pneumoniae. The results of immunoblotting showed that R. capsulatus flavodoxin is nif specific, since it is absent from ammonia-replete cultures and is not synthesized by the mutant strain J61, which lacks a nif-specific regulator (NifR1). Growth of cultures under iron-deficient conditions causes a small amount of flavodoxin to be synthesized under ammonia-replete conditions and increases its synthesis under N2-fixing conditions, suggesting that its synthesis is under a dual system of control with respect to iron and fixed nitrogen availability. Here we show that flavodoxin, when supplemented with catalytic amounts of methyl viologen, is capable of efficiently reducing nitrogenase in an illuminated chloroplast system. Thus, this nif-specific flavodoxin is a potential in vivo electron carrier to nitrogenase; however, its role in the nitrogen fixation process remains to be established.