Impact of dopants on X‑ray attenuation of 3D‑printed polymers for mammography and tomosynthesis spectra.
3D-printing enables the production of anthropomorphic breast phantoms for assessing image quality in digital mammography (DM) and breast tomosynthesis (DBT). 3D-printing materials must be selected carefully to mimic breast tissue attenuation for clinical spectra.
This study investigates the impact on the effective X-ray attenuation coefficient (µeff) of polymer formulation and dopants (e.g., colorants) used in 3D-printing materials. It also analyses the impact on their equivalent glandular ratios (BR) relative to commercial materials (CIRS).
Five base polymers (PLA, ABS, PETG, HIPS, RESIN) were selected among the catalogue of five manufacturers. A collection of nineteen variants (base polymer + color) was 3D-printed as step-wedges with thicknesses (t) from 0.5 to 5.5 cm and imaged on a clinical mammography system (DM: W/Rh with the anti-scatter grid, DBT: W/Al without grid, at 27, 29 and 31 kVp). The µeff(t) values were derived from the mean pixel value measured at each step of the logarithmically transformed images. As reference, µeff values were measured for the CIRS materials with well-known BR. A two-parameter empirical model was used to fit the values as: µeff(t) = µ0 /(1+kt), where µ0 corresponds to µeff at thickness tending to zero, and k is the decrease rate with thickness due to beam hardening and scatter. The impact of dopants on polymer attenuation was evaluated by analyzing both µeff and µ0 values. Based on µ0-BR relationships of CIRS materials, the corresponding BR values were computed for the investigated materials.
For all acquisition conditions, some color variants of 3D-printed materials with the same base polymer exhibit noticeable differences in µeff, independently of the thickness, particularly for DM. For this modality, the maximum differences within µeff values of materials sharing polymer base decreased by 62% for PLA-based, 44% for PETG-based and 30% for ABS-based materials, when the thickness increases from 1.5 to 5.5 cm. For DBT, a lower variability of µeff values was observed. The materials best mimicking purely glandular and adipose tissues were selected based on µeff, µ0 and BR results. Specifically, relative differences in µ0 (averaged across kVp), reported as paired values (DM, DBT) were: (-3%, +1%) and (-1%, +4%) for PLA crystal silver and PLA blue versus CIRS with BR = 100% (glandular tissue); (+3%, +1%) for ABS white versus CIRS with BR = 0% (adipose tissue). According to the BR values derived for all acquisition conditions, PLA blue and PLA crystal silver mimicked glandular tissue (BR: 101%-109%, 95%-100%, respectively), while ABS white mimicked adipose tissue (BR: -2% to 8%). PETG translucent blue and RESIN corresponded to intermediate glandular ratios (BR ≈ 50%-70%).
3D-printed materials sharing the same polymer base can exhibit substantially different attenuation for DM/DBT spectra, resulting in different BR equivalences due to formulation variations (e.g., pigments and dopants). Therefore, phantom developers should not rely solely on base polymer designations and declared density when selecting materials for production of breast phantoms; instead, the attenuation of each specific formulation needs to be verified and periodically re-evaluated under the intended mammography conditions.
This study investigates the impact on the effective X-ray attenuation coefficient (µeff) of polymer formulation and dopants (e.g., colorants) used in 3D-printing materials. It also analyses the impact on their equivalent glandular ratios (BR) relative to commercial materials (CIRS).
Five base polymers (PLA, ABS, PETG, HIPS, RESIN) were selected among the catalogue of five manufacturers. A collection of nineteen variants (base polymer + color) was 3D-printed as step-wedges with thicknesses (t) from 0.5 to 5.5 cm and imaged on a clinical mammography system (DM: W/Rh with the anti-scatter grid, DBT: W/Al without grid, at 27, 29 and 31 kVp). The µeff(t) values were derived from the mean pixel value measured at each step of the logarithmically transformed images. As reference, µeff values were measured for the CIRS materials with well-known BR. A two-parameter empirical model was used to fit the values as: µeff(t) = µ0 /(1+kt), where µ0 corresponds to µeff at thickness tending to zero, and k is the decrease rate with thickness due to beam hardening and scatter. The impact of dopants on polymer attenuation was evaluated by analyzing both µeff and µ0 values. Based on µ0-BR relationships of CIRS materials, the corresponding BR values were computed for the investigated materials.
For all acquisition conditions, some color variants of 3D-printed materials with the same base polymer exhibit noticeable differences in µeff, independently of the thickness, particularly for DM. For this modality, the maximum differences within µeff values of materials sharing polymer base decreased by 62% for PLA-based, 44% for PETG-based and 30% for ABS-based materials, when the thickness increases from 1.5 to 5.5 cm. For DBT, a lower variability of µeff values was observed. The materials best mimicking purely glandular and adipose tissues were selected based on µeff, µ0 and BR results. Specifically, relative differences in µ0 (averaged across kVp), reported as paired values (DM, DBT) were: (-3%, +1%) and (-1%, +4%) for PLA crystal silver and PLA blue versus CIRS with BR = 100% (glandular tissue); (+3%, +1%) for ABS white versus CIRS with BR = 0% (adipose tissue). According to the BR values derived for all acquisition conditions, PLA blue and PLA crystal silver mimicked glandular tissue (BR: 101%-109%, 95%-100%, respectively), while ABS white mimicked adipose tissue (BR: -2% to 8%). PETG translucent blue and RESIN corresponded to intermediate glandular ratios (BR ≈ 50%-70%).
3D-printed materials sharing the same polymer base can exhibit substantially different attenuation for DM/DBT spectra, resulting in different BR equivalences due to formulation variations (e.g., pigments and dopants). Therefore, phantom developers should not rely solely on base polymer designations and declared density when selecting materials for production of breast phantoms; instead, the attenuation of each specific formulation needs to be verified and periodically re-evaluated under the intended mammography conditions.
Authors
Belarra Belarra, Hernández-GirĂłn Hernández-GirĂłn, Castillo-GarcĂa Castillo-GarcĂa, Homolka Homolka, Chevalier Chevalier
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