Monochromatic X-rays: The future of breast imaging

PURPOSE

To present details about the innovative and disruptive technology of monochromatic X-rays and its application to breast imaging.

METHODS

To analyze results of studies done using a prototype system for breast imaging that generates monochromatic X-rays through fluorescence emission. To assess signal-to-noise ratio (SNR) as a measure of image quality at different doses in breast phantoms of different sizes and review the comparison of parameters with a standard mammography system.

RESULTS

Monochromatic X-rays reduce the radiation dose per mammogram by a factor of 5 to 10 times. For phantom simulating thick breast (9 cm), the SNR for monochromatic system was 2.6 times higher and the dose 4.2 times lower than the respective values obtained with the conventional system within the same 5 mm × 5 mm square area of the 100% glandular step wedge. For the conventional broadband system to equal the SNR of the monochromatic system, it would require a dose of 19 mGy, 29 times higher than the dose delivered by the monochromatic system. Contrast-enhanced digital mammography with monochromatic X-rays is shown to provide a simpler and more effective technique at substantially lower radiation dose.

CONCLUSIONS

Lowering radiation dose by a factor of 5 to 10 while maintaining image quality implies a major reduction in total exposure from breast cancer screening and dramatically less risk of radiation-induced cancers in at-risk women. The high SNRs for very thick breast phantoms provide strong evidence that screening with lower breast compression is possible while maintaining image quality.

Pressure-based Compression Guidance of the Breast in Digital Breast Tomosynthesis Using Flexible Paddles Compared to Conventional Compression

OBJECTIVE

We investigated the effect of introducing a pressure-based flexible paddle on compression parameters and user and patient experience of digital breast tomosynthesis (DBT) combined with patient-assisted compression or technologist compression.

METHODS

After institutional review board approval, women with a DBT appointment who gave informed consent received pressure-based flexible paddle breast compression. Eight lights on the paddle were illuminated (1.9 kPa per light) as pressure was applied, aiming for an 8-13.9 kPa target range. The compression level was applied by the technologist or the participant utilizing a remote control device. The participant's and technologist's experiences were assessed by a questionnaire. Compression parameters were compared to previous examinations. Comparative statistics were performed using t-tests.

RESULTS

Pressure-based compression (PBC) was judged to be similar or more comfortable compared with previous traditional exams (80%, 83/103), and 87% (90/103) of participants would recommend PBC to friends. Pressure variability decreased for craniocaudal (CC) views (-55%, P < 0.001) and mediolateral oblique (MLO) views (-34%, P < 0.0001). Subgroup analysis showed a similar glandular dose for CC views, while breast thickness was reduced (-3.74 mm, P < 0.0001). For MLO views, both glandular dose (-0.13 mGy, P < 0.0001) and breast thickness were reduced (-6.70 mm, P < 0.0001). Mean compression parameters were similar for technologist compression and patient-assisted examinations.

CONCLUSION

Use of the pressure-based flexible paddle in DBT, with or without patient-assisted compression, improved participant and technologist experience and reduced compression pressure variability, mean breast thickness, and glandular dose.

Breast compression and reported pain during mammographic screening

INTRODUCTION

We aimed to investigate the association between breast compression and experienced pain during mammographic screening.

METHODS

Using a questionnaire, we collected information on pain experienced during mammography from 1155 women screened in Akershus, February-March 2018, as a part of BreastScreen Norway. The questionnaire provided information on pain using a numeric rating scale (NRS, 0-10) and related factors. Data on compression force (Newton, N), pressure (kilopascal, kPa) and breast characteristics were extracted from the DICOM-header and a breast density software. Log-binomial regression was used to determine the relative risk (RR) of severe versus mild/moderate experienced pain associated with compression parameters, adjusting for breast characteristics and related factors.

RESULTS

Mean score of experienced pain was 2.2, whereas 6% of the women reported severe pain (≥7) during the examination. High body mass index (BMI) (≥27.3 kg/m²) was associated with a higher RR of pain scores ≥7 (RR 1.86, 95%CI 1.02-3.36) compared to medium BMI (23.7-27.2 kg/m²). Low compression pressure (4.0-10.2 kPa) was associated with a higher RR of severe pain (RR 2.93, 95%CI 1.39-6.20), compared with medium compression pressure (10.3-13.5 kPa) after adjusting for contact area, age, compressed breast thickness, volumetric breast density and BMI. The risk of severe versus mild/moderate pain (≥7 versus <7) decreased by 2% with increasing compression force (RR 0.98, 95%CI 0.97-1.00).

CONCLUSION

Women reported low levels of pain during mammography. Further knowledge about factors affecting experienced pain is needed to personalize the examination to the individual woman.

IMPLICATIONS FOR PRACTICE

Pain in shoulder(s) and/or neck prior to screening should be considered by the radiographers in a practical screening setting. A compression force of 100-140 N and pressure of 10.3-13.5 kPa are acceptable with respect to reported pain during mammography.

Evaluation of pressure-controlled mammography compression paddles with respect to force-controlled compression paddles in clinical practice

Objectives

To reduce pain and discomfort associated with breast compression in mammography, a pressure-controlled compression paddle was recently introduced.

The objective was to evaluate the pressure-controlled paddle by comparing it to the standard force-controlled paddle.

Methods

Differences of compressed breast thickness (CBT), compression force, compression pressure, and average glandular dose (AGD) between annual follow-up full-field digital mammography exams of 3188 patients were retrospectively examined. Two groups were compared: (1) force-force group (FF-group), both examinations were performed with the force-controlled paddle, and (2) force-pressure group (FP-group), only the follow-up examination was performed with the pressure-controlled paddle.

In an additional group of patients, pain scores on a scale of 0 (no pain at all) to 10 (worst pain imaginable) were evaluated prospectively (n = 343) who were randomly assigned to either paddle.

Results

Median differences between follow-up exams in CBT, compression force, compression pressure, and AGD were for the FF- and FP-group respectively − 1.0 vs 0.0 mm (p < 0.001); 0.0 vs − 1.0 daN (p = 0.002); − 1.0 vs − 0.5 kPa (p = 0.005); and 0.05 vs − 0.02 mGy (p < 0.001). These differences were, although statistically significant, clinically non-relevant (defined as ΔCBT > ± 2 mm; Δforce > ± 2 daN; Δpressure > ± 1 kPa and ΔAGD > ± 0.1 mGy). The subanalysis dividing CBT into five categories revealed similar results. The median [interquartile range] pain scores were 6 [3, 7] and 5 [3, 7] for the force-controlled and pressure-controlled paddle, respectively, which was not significantly different (p = 0.113).

Conclusions

We observed no clinically relevant differences in CBT, compression force, compression pressure, AGD, or pain score between the force- and pressure-controlled paddle. As such, we found no basis for preferring one paddle over the other.

Key Points

• The pressure-controlled paddle did not show any clinically relevant changes in breast compression parameters compared to the force-controlled paddle.

• The pressure-controlled paddle did not lead to significant reduction in pain scores indicated by the patients compared to the force-controlled paddle.

• A large variation in compression force and compression pressure was observed in mammography exams for the both the force- and pressure-controlled compression paddle.

Electronic supplementary material

The online version of this article (10.1007/s00330-018-5953-6) contains supplementary material, which is available to authorized users.

The impact of compression force and pressure at prevalent screening on subsequent re-attendance in a national screening program

Adherence to screening may indirectly help assess whether a prior screening examination deters women from returning for a subsequent examination. We investigated whether compression force and pressure in mammography were associated with re-attendance among prevalently screened women in the organized breast cancer screening program in Norway. Data on compression force (kg) and pressure (kPa) from women's first screening examination in the program (prevalent screening) and subsequent re-attendance were available for 31,225 women aged 50-68, screened during 2007-2013. Crude re-attendance rates and log-binomial regression models estimating the prevalence ratio of re-attendance were used to identify the association between compression force or pressure and re-attendance two-years later. Age and year at prevalent screening, county of residence, screening result (negative or false positive), breast volume, and breast density were included in analyses. Overall, 27,197 (87.1%) women re-attended the program. Re-attendance was highest for women who received a compression force of 10.0-13.9 kg (87.5%) or pressure of 9.0-17.9 kPa (87.8%) and lowest for those who received a compression force of <10.0 kg (85.0%) or pressure of <9.0 kPa (84.7%). The adjusted prevalence of re-attendance was 3% lower for women who received low compression force (<10.0 kg) and 2% lower for women who received low compression pressure (<9.0 kPa) relative to the reference groups (10.0-13.9 kg and 9.0-17.9 kPa, respectively). Future research related to re-attendance should also include information about women's experience of pain, anxiety and stress, as well as image quality.