Characterization of the imaging settings in screening mammography using a tracking and reporting system: A multi-center and multi-vendor analysis

Audit of data from examination image headers collected for quality assurance in the ECOG-ACRIN EA1151 tomosynthesis mammographic imaging screening trial (TMIST)

PURPOSE

A comprehensive, centrally-monitored physics quality control (QC) program was developed for the Tomosynthesis Imaging Screening Trial (TMIST), a randomized controlled trial of digital breast tomosynthesis (TM) versus digital mammography (DM) for cancer screening. As part of the program, in addition to a set of phantom-based tests, de-identified data on image acquisition and processing parameters were captured from the DICOM headers of all individual patient images in the trial. These data were analyzed to assess the potential usefulness of header data from digital mammograms and tomosynthesis images of patients for quality assurance in breast imaging.

METHODS

Data were automatically extracted from the headers of all de-identified patient mammograms and tomosynthesis images in the TMIST study. Image acquisition parameters and estimated radiation doses were tracked for individual sites, systems and across system types. These parameters included (among others) kV, target/filter use, number of acquired views per examination, AEC mode, compression thickness and force and detector temperature. Consistency of manually entered study data parameters (subject ID, screening time-point) from TMIST was evaluated. Preliminary observations from the program are presented.

RESULTS

We report on data from 812 651 images from 135 525 examinations acquired between October, 2017 and December, 2022. Data came from 6 system models from 3 manufacturers. There was greater variability both in the number of views used and in the estimated (proxy) doses received in DM exams compared to TM. Mean proxy doses per examination varied among manufacturers from 2.76-4.54 mGy for DM and 3-4.84 mGy for the tomosynthesis component in the TM arm with maximum examination proxy doses of 20 and 26 mGy for DM and TM respectively. Mean proxy doses per examination for the combination examination in TM (tomosynthesis plus digital mammography) varied from 6.6 to 7.6 mGy among manufacturers with a maximum of 44.5 mGy.

CONCLUSIONS

Overall, modern digital mammography and tomosynthesis systems used in TMIST have operated very reliably. Doses vary considerably due to variation in the number of views per examination, thickness and fibro-glandularity of the breast, and choices in the use of synthesized versus actual 2D mammography in the TM examination. These data may also be useful in predicting equipment problems. Header information is valuable not only for automated QC, but also for cross-checking accuracy and consistency of data in a clinical study.

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.

Optimization of the exposure parameters in digital mammography for diverse glandularities using the contrast-detail metric

PURPOSE

This investigation aims to study the optimization in digital mammography, considering a diverse percentage of breast glandularity using the contrast-detail metric.

METHODS

The Figure of Merit (FOM), defined as the ratio of the square of the Inverted Image Quality Figure (IQF_INV) by the Mean Glandular Dose (MGD), was used. A Monte Carlo simulation study was carried out to calculate the Normalized Glandular Dose (D_gN). A contrast detail analysis employing the test object Contrast-Detail Mammography Phantom (CDMAM, type 3.4) was performed in the Hologic digital mammography system-model Selenia located in the Research Center in Radiation Sciences and Technologies (CPqCTR) facilities (Brazil). It employed the CIRS phantom with 20 %, 30 %, 50 % of glandularity, and 6.0 cm in thickness.

RESULTS

It was obtained new acquisition parameters for all glandularities that achieved a decrease in the MGD up to ∼ 50 %, maintaining the same image quality. The study was validated using the CIRS, TORMAM, and ACR phantoms through the contrast-to-noise ratio (CNR), the signal-to-noise ratio (SNR), and the MGD values obtained with the optimized parameters and the four AEC modes, which are the optimization proposed by the manufacturer.

CONCLUSIONS

In this work, a new procedure was proposed that estimated the IQF_INV value using the equivalence criterion between the CIRS phantom and the CDMAM test object with their respective PMMA plates. Based on the optimization carried out in this investigation, the AEC parameters, considering diverse glandularities, could be improved. This achievement permits the implementation of new protocols that optimize the ratio between the image's quality and the breast dose with 6.0 cm in thickness and 20 %, 30 %, and 50 % glandularity using contrast-detail metric.

Noise modeling and variance stabilization of a computed radiography (CR) mammography system subject to fixed-pattern noise

In this work we model the noise properties of a computed radiography (CR) mammography system by adding an extra degree of freedom to a well-established noise model, and derive a variance-stabilizing transform (VST) to convert the signal-dependent noise into approximately signal-independent. The proposed model relies on a quadratic variance function, which considers fixed-pattern (structural), quantum and electronic noise. It also accounts for the spatial-dependency of the noise by assuming a space-variant quantum coefficient. The proposed noise model was compared against two alternative models commonly found in the literature. The first alternative model ignores the spatial-variability of the quantum noise, and the second model assumes negligible structural noise. We also derive a VST to convert noisy observations contaminated by the proposed noise model into observations with approximately Gaussian noise and constant variance equals to one. Finally, we estimated a look-up table that can be used as an inverse transform in denoising applications. A phantom study was conducted to validate the noise model, VST and inverse VST. The results show that the space-variant signal-dependent quadratic noise model is appropriate to describe noise in this CR mammography system (errors< 2.0% in terms of signal-to-noise ratio). The two alternative noise models were outperformed by the proposed model (errors as high as 14.7% and 9.4%). The designed VST was able to stabilize the noise so that it has variance approximately equal to one (errors< 4.1%), while the two alternative models achieved errors as high as 26.9% and 18.0%, respectively. Finally, the proposed inverse transform was capable of returning the signal to the original signal range with virtually no bias.

Comparison of radiation dose between 2D digital stereotactic versus digital breast tomosynthesis-guided breast biopsies

RATIONALE AND OBJECTIVE

Use of digital breast tomosynthesis (DBT) in breast imaging has necessitated DBT-guided biopsy, however, a single DBT acquisition may result in a greater radiation dose than a single DM acquisition. Our objective was to compare the number of images acquired and the resulting radiation dose of DBT versus DM-guided breast biopsies.

METHOD

All biopsies performed on our DM unit from 8/2016 to 1/2017 and on our DM-DBT unit from 8/2017 to 1/2018 were retrospectively reviewed. The number of image acquisitions, average glandular dose (AGD) per acquisition and per procedure were computed and stratified by guidance modality and lesion type.

RESULTS

25 DM-guided biopsies were performed on the DM-only unit, 58 biopsies were performed with DM guidance on the dual unit (DM-DU) and 29 were performed with DBT. The average number of images acquisitions was 10.9 for DM-only unit biopsies, 9.3 images for DM-DU biopsies and 4.3 images for DBT-guided biopsies. Mean procedure AGD for DM-only unit biopsies was 28.77 mGy, versus 22.06 mGy for DM-DU and 10.18 mGy for DBT biopsies. Mean procedure AGD for biopsied calcification-only lesions was 22.3 mGy for DM-DU versus 10.7 mGy for DBT guidance (p < 0.001), with an average of 8.1 images per procedure for DM-DU versus 4.2 for DBT.

CONCLUSION

Fewer image acquisitions were obtained with DBT compared with DM guidance, therefore, the overall dose of DBT-guided procedures was less. The dose reduction obtained with DBT is possible across all lesion types, even for calcification-only lesions.