Analysis of patient dose in full field digital mammography

THE IMPORTANCE OF FEEDBACK IN MONITORING PATIENTS' RADIATION DOSES IN MAMMOGRAPHY

The majority of medical facilities in the Slovak Republic archive diagnostic images of their patients in a picture archiving and communicating system (PACS). Data from the PACS system can be used to analyse patient radiation dose and perform internal and external quality control through dose monitoring software systems. However, appropriate use of such systems requires the provision of feedback and the ability of staff to identify causes of diagnostic reference level exceedances. The present pilot study evaluated the use of a Dose quality control system (DQC) for monitoring the radiation dose of the patients in the ongoing mammography screening, with subsequent identification of alerts triggered by the system.

The Effect of Breast Size and Density in Turkish Women on Radiation Dose in Full-Field Digital Mammography

Objective

The purpose of this study was to look into the relationship between breast size and mammographic breast density in women and breast radiation dose on full-field digital mammography (FFDM), as well as the factors that influence radiation dose.

Materials and Methods

The study included a total of 2,060 FFDM images from 515 consecutive participants. The participants were divided into two groups: those exposed to high doses (>3 mGy) and those exposed to low doses (<3 mGy). Moreover, the researchers analyzed the relationship between mean glandular dose (MGD) of the breast and patient age, compressed breast thickness, compression force, mammographic breast composition, and mammographic breast size.

Results

The mean mammographic breast volume was 936.2 ± 425.2 (114.5-3,018) mL, and the mean compressed breast tissue thickness was 56.75 ± 10.44 mm. Moreover, the mean MGD in the high-dose group was 3.51 ± 0.48 mGy and 1.92 ± 0.56 mGy in the low-dose group. The high-dose group had greater breast thickness, diameters, volume, compression pressure, and surgical rate. However, the high-dose group was younger and had less dense breasts. In multivariate logistic regression analysis, the most important predictors of dose determination were breast thickness [odds ratio (OR): 1.178, 95% confidence interval (CI): 1.156-1.200, p<0.001], history of previous surgery (OR: 2.210, 95% CI: 1.417-3.447, p<0.001), compression force (OR: 1.008, 95% CI: 1.004-1.013, p<0.001), and breast density (OR: 1.873, 95% CI: 1.359-2.580, p<0.001).

Conclusion

Women with larger breast volumes are subjected to higher doses of radiation. Therefore, breast-screening programs can be individualized to young women with larger breast volumes and women who have had breast-conserving surgery.

Comparison of spectra and mean glandular dose (MGD) with tube voltage used in digital mammography for simulated, metrological and clinical cases

Mammography has a crucial role in breast cancer detection. The National Cancer Institute (INCA) estimates that 29.7% of the cancer cases in Brazil are related specifically to the breast. It is necessary to evaluate the mean glandular dose with a new solid-state detector in a digital radiography system, utilizing PMMA phantoms and spacers for different thicknesses. The Selenia Dimensions (Hologic, Bedford) direct radiography (DR) system can perform full-field digital mammographies through digital detectors. This system uses new technologies, such as the digital breast tomosynthesis system (DBT), and employs a sequence of projections acquired over the breast, resulting in images with low contrast. The estimation of breast dose is an important part of mammographic quality control for x-ray mammography. Nevertheless, there are currently no standard protocols for the dosimetry of breast imaging in 3D. Additionally, a x-ray spectra function is crucial to measure a considerable output in x-ray spectrometry. The purpose of this work was to assess the mean glandular dose (MGD) and the spectra in slabs of polymethyl methacrylate (PMMA) and breast equivalent thickness through digital mammography using four experiments: a Hologic Selenia Dimensions mammograph with a solid-state detector; a spectrometer (only for the spectra, in this case); a clinical COMET x-ray tube with a solid-state detector; and the MCNPX code. References recommend that the real environments that work well with digital mammography are in the following tube voltages: 25 kVp; 26 kVp; 28 kVp; 31 kVp and 33 kVp. Taking into account several thicknesses of PMMA, the results of both the MGD in metrological, clinical and simulated cases were in accordance with the references, from 30 mm of PMMA. All the spectra for all cases have indicated good agreement with the references.

Patient-Assisted Compression in Screening Mammography: Patient Experience and Image Quality

OBJECTIVE

Screening mammography is critical to reduce breast cancer mortality, yet many women cite pain from compression as a reason they avoid this test. We evaluated patient experience and image quality in screening patients opting for a handheld patient-assisted compression (PAC) device.

METHODS

After institutional review board approval, women screened between February and July 2018 with a synthetic 2D/tomosynthesis mammography unit were offered use of a handheld PAC device. Patient experience through survey, image quality, compression thickness, compression force, and average glandular dose were evaluated and compared between women opting for PAC and women opting for technologist-controlled compression (TC). Multivariable ordinal logistic and linear regression models were estimated to control for age and breast density. In addition, for women opting for PAC, image quality obtained with their current PAC mammogram was compared with that obtained with their prior TC mammogram, by using Wilcoxon/Pearson tests.

RESULTS

Seventy-three percent of women preferred their mammogram experience with PAC compared with their prior mammogram without PAC. Women using PAC reported decreased anxiety compared with those using TC, after controlling for age and breast density (adjusted odds ratio [aOR] 0.22 [95% confidence interval (CI): 0.09-0.49]). There were no significant differences in image quality, compression thickness, or average glandular dose in exams for women using PAC compared with exams for women using TC. Women using PAC had significantly more compression force than women using TC had (P = 0.012).

CONCLUSIONS

Mammography with PAC improves patient experience and results in similar image quality compared with mammography with TC.

A biomechanical breast model evaluated with respect to MRI data collected in three different positions

BACKGROUND

Mammography is a specific type of breast imaging that uses low-dose X-rays to detect cancer in early stage. During the exam, the women breast is compressed between two plates in order to even out the breast thickness and to spread out the soft tissues. This technique improves exam quality but can be uncomfortable for the patient. The perceived discomfort can be assessed by the means of a breast biomechanical model. Alternative breast compression techniques may be computationally investigated trough finite elements simulations.

METHODS

The aim of this work is to develop and evaluate a new biomechanical Finite Element (FE) breast model. The complex breast anatomy is considered including adipose and glandular tissues, muscle, skin, suspensory ligaments and pectoral fascias. Material hyper-elasticity is modeled using the Neo-Hookean material models. The stress-free breast geometry and subject-specific constitutive models are derived using tissues deformations measurements from MR images.

FINDINGS

The breast geometry in three breast configurations were computed using the breast stress-free geometry together with the estimated set of equivalent Young's modulus (E_breast^r = 0.3 kPa, E_breast^l = 0.2 kPa, E_skin = 4 kPa, E_fascia = 120 kPa). The Hausdorff distance between estimated and measured breast geometries for prone, supine and supine tilted configurations is equal to 2.17 mm, 1.72 mm and 5.90 mm respectively.

INTERPRETATION

A subject-specific breast model allows a better characterization of breast mechanics. However, the model presents some limitations when estimating the supine tilted breast configuration. The results show clearly the difficulties to characterize soft tissues mechanics at large strain ranges with Neo-Hookean material models.

Influence of breast compression pressure on the performance of population-based mammography screening

BACKGROUND

In mammography, breast compression is applied to reduce the thickness of the breast. While it is widely accepted that firm breast compression is needed to ensure acceptable image quality, guidelines remain vague about how much compression should be applied during mammogram acquisition. A quantitative parameter indicating the desirable amount of compression is not available. Consequently, little is known about the relationship between the amount of breast compression and breast cancer detectability. The purpose of this study is to determine the effect of breast compression pressure in mammography on breast cancer screening outcomes.

METHODS

We used digital image analysis methods to determine breast volume, percent dense volume, and pressure from 132,776 examinations of 57,179 women participating in the Dutch population-based biennial breast cancer screening program. Pressure was estimated by dividing the compression force by the area of the contact surface between breast and compression paddle. The data was subdivided into quintiles of pressure and the number of screen-detected cancers, interval cancers, false positives, and true negatives were determined for each group. Generalized estimating equations were used to account for correlation between examinations of the same woman and for the effect of breast density and volume when estimating sensitivity, specificity, and other performance measures. Sensitivity was computed using interval cancers occurring between two screening rounds and using interval cancers within 12 months after screening. Pair-wise testing for significant differences was performed.

RESULTS

Percent dense volume increased with increasing pressure, while breast volume decreased. Sensitivity in quintiles with increasing pressure was 82.0%, 77.1%, 79.8%, 71.1%, and 70.8%. Sensitivity based on interval cancers within 12 months was significantly lower in the highest pressure quintile compared to the third (84.3% vs 93.9%, p = 0.034). Specificity was lower in the lowest pressure quintile (98.0%) compared to the second, third, and fourth group (98.5%, p < 0.005). Specificity of the fifth quintile was 98.4%.

CONCLUSION

Results suggest that if too much pressure is applied during mammography this may reduce sensitivity. In contrast, if pressure is low this may decrease specificity.

Mammographic compression in Asian women

OBJECTIVES

To investigate: (1) the variability of mammographic compression parameters amongst Asian women; and (2) the effects of reducing compression force on image quality and mean glandular dose (MGD) in Asian women based on phantom study.

METHODS

We retrospectively collected 15818 raw digital mammograms from 3772 Asian women aged 35-80 years who underwent screening or diagnostic mammography between Jan 2012 and Dec 2014 at our center. The mammograms were processed using a volumetric breast density (VBD) measurement software (Volpara) to assess compression force, compression pressure, compressed breast thickness (CBT), breast volume, VBD and MGD against breast contact area. The effects of reducing compression force on image quality and MGD were also evaluated based on measurement obtained from 105 Asian women, as well as using the RMI156 Mammographic Accreditation Phantom and polymethyl methacrylate (PMMA) slabs.

RESULTS

Compression force, compression pressure, CBT, breast volume, VBD and MGD correlated significantly with breast contact area (p<0.0001). Compression parameters including compression force, compression pressure, CBT and breast contact area were widely variable between [relative standard deviation (RSD)≥21.0%] and within (p<0.0001) Asian women. The median compression force should be about 8.1 daN compared to the current 12.0 daN. Decreasing compression force from 12.0 daN to 9.0 daN increased CBT by 3.3±1.4 mm, MGD by 6.2-11.0%, and caused no significant effects on image quality (p>0.05).

CONCLUSIONS

Force-standardized protocol led to widely variable compression parameters in Asian women. Based on phantom study, it is feasible to reduce compression force up to 32.5% with minimal effects on image quality and MGD.

Optimization of Image Quality and Dose in Digital Mammography

Nowadays, the optimization in digital mammography is one of the most important challenges in diagnostic radiology. The new digital technology has introduced additional elements to be considered in this scenario. A major goal of mammography is related to the detection of structures on the order of micrometers (μm) and the need to distinguish the different types of tissues, with very close density values. The diagnosis in mammography faces the difficulty that the breast tissues and pathological findings have very close linear attenuation coefficients within the energy range used in mammography. The aim of this study was to develop a methodology for optimizing exposure parameters of digital mammography based on a new Figure of Merit: FOM ≡ (IQFinv)2/AGD, considering the image quality and dose. The study was conducted using the digital mammography Senographe DS/GE, and CDMAM and TORMAM phantoms. The characterization of clinical practice, carried out in the mammography system under study, was performed considering different breast thicknesses, the technical parameters of exposure, and processing options of images used by the equipment's automatic exposure system. The results showed a difference between the values of the optimized parameters and those ones chosen by the automatic system of the mammography unit, specifically for small breast. The optimized exposure parameters showed better results than those obtained by the automatic system of the mammography, for the image quality parameters and its impact on detection of breast structures when analyzed by radiologists.

Conformance of mean glandular dose from phantom and patient data in mammography

In mammography dosimetry, phantoms are often used to represent breast tissue. The conformance of phantom- and patient-based mean glandular dose (MGD) estimates was evaluated mainly from the aspect of diagnostic reference levels. Patient and phantom exposure data were collected for eight diagnostic and three screening mammography devices. More extensive assessments were performed for two devices. The average breast thickness was close to the nationally used reference of 50 mm in diagnostic (50 mm, SD = 13 mm, n = 5342) and screening (47 mm, SD = 13 mm, n = 395) examinations. The average MGD for all breasts differed by 2% from the MGD determined for breasts in the limited compressed thickness range of 40-60 mm. The difference between phantom- and patient-based MGD estimations was up to 30%. Therefore, phantom measurements cannot replace patient dose data in MGD determination.

Dosimetry and image quality assessment in a direct radiography system

OBJECTIVE

To evaluate the mean glandular dose with a solid state detector and the image quality in a direct radiography system, utilizing phantoms.

MATERIALS AND METHODS

Irradiations were performed with automatic exposure control and polymethyl methacrylate slabs with different thicknesses to calculate glandular dose values. The image quality was evaluated by means of the structures visualized on the images of the phantoms.

RESULTS

Considering the uncertainty of the measurements, the mean glandular dose results are in agreement with the values provided by the equipment and with internationally adopted reference levels. Results obtained from images of the phantoms were in agreement with the reference values.

CONCLUSION

The present study contributes to verify the equipment conformity as regards dose values and image quality.

Effect of anode/filter combination on average glandular dose in mammography

A comparative analysis of the mean glandular doses was conducted in 100 female patients who underwent screening mammography in 2011 and 2013. Siemens Mammomat Novation with the application of the W/Rh anode/filter combination was used in 2011, whereas in 2013 anode/filter combination was Mo/Mo or Mo/Rh. The functioning of mammography was checked and the effectiveness of the automatic exposure control (AEC) system was verified by measuring compensation of changes in the phantom thickness and measuring tube voltage. On the base of exposure parameters, an average glandular dose for each of 100 female patients was estimated. The images obtained by using AEC system had the acceptable threshold contrast visibility irrespective of the applied anode/filter combination. Mean glandular doses in the females, examined with the application of the W/Rh anode/filter combination, were on average 23.6% lower than that of the Mo/Mo or Mo/Rh anode/filter combinations. It is recommended to use a combination of the W/Rh anode /filter which exhibited lower mean glandular doses.

Towards personalized compression in mammography: a comparison study between pressure- and force-standardization

OBJECTIVE

To compare a conventional 14 decanewton (daN) force-standardized compression protocol with a personalized 10kilopascal (kPa) pressure-standardized protocol.

METHODS

A new add-on contact area detector, which enables pressure-standardized compression, is validated in a double-blinded intra-individual comparison study. Breast screening participants (433) received one craniocaudal (CC) and one mediolateral oblique (MLO) compression for both breasts. Three of these compressions were force-standardized, and one, blinded and randomly assigned, was pressure-standardized. Participants scored their pain experience on an 11-point numerical rating scale (NRS). Three experienced breast-screening radiologists, blinded for compression protocol, indicated which images required retakes.

RESULTS

An unanticipated under-compression issue that occurred at forces below 5daN was effectively solved with minimal extra radiographer training during the study. For pressure-standardized compressions obtained at 5daN or more, the compressed breasts thickness increased on average 4.2% (MLO)-6.3% (CC), average pain scores were reduced by 10% (MLO)-17% (CC) and the proportion of women experiencing severe pain (NRS≥7) was reduced by 27% (MLO)-32% (CC), compared with force-standardized compressions (all p-values <0.05). Average glandular dose (AGD) and proportions of retakes were similar for both protocols.

CONCLUSION

Pressure-standardized compressions resulted in AGD values and a retake proportion similar to force-standardized compressions, while pain was significantly reduced.

Dose reduction in automatic optimization parameter of full field digital mammography: breast phantom study

Purpose

We evaluated the impact of three automatic optimization of parameters (AOP) modes of digital mammography on the dose and image quality.

Methods

Computerized Imaging Reference Systems phantoms were used. A total of 12 phantoms with different thickness and glandularity were imaged. We analyzed the average glandular dose (AGD) and entrance surface exposure (ESE) of 12 phantoms imaged by digital mammography in three modes of AOP; namely standard mode (STD), contrast mode (CNT), and dose mode (DOSE). Moreover, exposure factors including kVp, mAs, and target/filter combination were evaluated. To evaluate the quality of the obtained digital image, two radiologists independently counted the objects of the phantoms.

Results

According to the AOP modes, the score of masses and specks was sorted as CNT>STD=DOSE. There was no difference in the score of fiber among the three modes. The score of image preference was sorted as CNT>STD>DOSE. The AGD, ESE, and mAs were sorted as CNT>STD>DOSE. The kVp was sorted as CNT=STD>DOSE. The score of all test objects in the phantom image was on a downtrend with increasing breast thickness. The score of masses was different among the three groups; 20-21%>30%>50% glandularity. The score of specks was sorted as 20-21%=30%>50% glandularity. The score of fibers was sorted as 30%>20-21%=50% glandularity. The score of image preference was not different among the three glandularity groups. The AGD, ESE, kVp, and mAs were correlated with breast thickness, but not correlated with glandularity.

Conclusion

The DOSE mode offers significant improvement (19.1-50%) in dose over the other two modes over a range of breast thickness and breast glandularity with acceptable image quality. Owning knowledge of the three AOP modes may reduce unnecessary radiation exposure by utilizing the proper mode according to its purpose.