Mr. Raffaele Villa Profile

Raffaele Villa

at ASST Monza

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Proceedings Article | 13 July 2022 Paper

Normalized image noise as an absolute quantity for performance assessment in 2D mammography

Nicoletta Paruccini, Raffaele Villa, Nadia Oberhofer

Proceedings Volume 12286, 122861A (2022) https://doi.org/10.1117/12.2624538

KEYWORDS: Polymethylmethacrylate, Image quality, Mammography, Aluminum, Image processing, Photon counting, Contrast sensitivity

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A method is proposed to equate the measured noise to a thickness of Aluminium by exposing a simple test object which includes an Aluminium step-wedge sandwiched between PMMA slabs. The scaling process turns the Image Noise expressed in mmAl into an absolute quantity which reflects exposure conditions. A second quantity, the dose independent Normalized Image Noise is defined. It is a characteristic value for every mammography unit/model and phantom setup and represents a measure of a system’s overall detection efficiency in clinical conditions. 8 mammography units of different manufacturers and detector technologies have been evaluated for PMMA thickness 3, 5 and 7 cm over a wide average glandular dose (AGD) range. The calculated Normalised Image Noise values were reproducible (uncertainty 3-5%) and coherent with known physical characteristics of the detector-grid combinations. Image Noise resulted sensitive to radiation spectra and scatter amount. Starting from threshold contrast detection with the CDMAM ver. 3.4 phantom, it was possible to identify Image Noiseacceptable/achievable thresholds which correspond to adequate image quality. Signal difference to noise (SDNR) analysis based on the proposed test object was in good agreement with SDNR evaluation according to the EUREF guideline (difference 1- 7%). Conversion coefficient, Image Noise and Normalised Image Noise could all be derived from a single exposure without having to determine the detector's response curve beforehand which is particularly advantageous for non-linear response. Given the sensitivity of Image Noise to radiation quality and dose, it is a suitable metric for optimization.

Proceedings Article | 22 May 2020 Paper

Validation of a statistical method for low contrast detectability as a simple tool for QC in digital mammography

Raffaele Villa, Nadia Oberhofer, Nicoletta Paruccini

Proceedings Volume 11513, 115131K (2020) https://doi.org/10.1117/12.2563987

KEYWORDS: Aluminum, LCDs, Statistical methods, Digital mammography, Image quality, Gold, Image analysis, Mammography

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The aim of this work was to validate an innovative and simplified method for threshold contrast evaluation in digital mammography based on a single exposure of a homemade test tool. A homogeneous region was used to calculate threshold contrast for details of varying size with a statistical approach. An included aluminium step wedge permitted to express the threshold contrast also as an absolute quantity in terms of mm Al. The method has been applied to 9 mammography systems from 5 vendors with different acquisition geometries and detector characteristics in a variety of exposure setups. MTF data were used to correct statistical threshold contrast results for different spatial resolution properties. Validation of the statistical method was carried out as comparison with the widespread method of CDMAM image analysis. Threshold contrasts LC_th obtained with the two methods showed good correspondence. For all systems the ratio, averaged over all exposure conditions, laid within ± 15% from the mean. With respect to the overall figure of merit IQF_inv a linear correlation between the two methods was demonstrated in every unit (r > 0.94 units 1-8, r = 0.89 unit 9). The ratio between the IQF_inv values determined with CDMAM analysis and the statistical analysis was calculated for every exposure condition and averaged for each system. Theses average ratios laid within ± 10% from the mean IQF_inv determined from all units. This is equivalent to a universal angular coefficient between the IQF_inv determined with the two methods, valid for all systems. Finally, mean LC_th ratio values calculated from all data were used to propose reference values for acceptable and achievable threshold contrasts LC_th expressed in terms of mm of aluminium, in analogy to threshold contrasts in terms of gold thickness for CDMAM evaluation.

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