Method for simulating dose reduction in digital mammography using the Anscombe transformation.

Lucas R Borges,Polyana F Nunes,Helder C R De Oliveira,Andrew D A Maidment,Predrag R Bakic,Marcelo A C Vieira

doi:10.1118/1.4948502

Abstract

Purpose:This work proposes an accurate method for simulating dose reduction in digital mammography starting from a clinical image acquired with a standard dose.Methods:The method developed in this work consists of scaling a mammogram acquired at the standard radiation dose and adding signal-dependent noise. The algorithm accounts for specific issues relevant in digital mammography images, such as anisotropic noise, spatial variations in pixel gain, and the effect of dose reduction on the detective quantum efficiency. The scaling process takes into account the linearity of the system and the offset of the detector elements. The inserted noise is obtained by acquiring images of a flat-field phantom at the standard radiation dose and at the simulated dose. Using the Anscombe transformation, a relationship is created between the calculated noise mask and the scaled image, resulting in a clinical mammogram with the same noise and gray level characteristics as an image acquired at the lower-radiation dose.Results:The performance of the proposed algorithm was validated using real images acquired with an anthropomorphic breast phantom at four different doses, with five exposures for each dose and 256 nonoverlapping ROIs extracted from each image and with uniform images. The authors simulated lower-dose images and compared these with the real images. The authors evaluated the similarity between the normalized noise power spectrum (NNPS) and power spectrum (PS) of simulated images and real images acquired with the same dose. The maximum relative error was less than 2.5% for every ROI. The added noise was also evaluated by measuring the local variance in the real and simulated images. The relative average error for the local variance was smaller than 1%.Conclusions:A new method is proposed for simulating dose reduction in clinical mammograms. In this method, the dependency between image noise and image signal is addressed using a novel application of the Anscombe transformation. NNPS, PS, and local noise metrics confirm that this method is capable of precisely simulating various dose reductions.

Highlights

To validate studies of radiation dose reduction, it is necessary to have a set of clinical images acquired from the same patient at different radiation levels
Using the Anscombe transformation, a relationship is created between the calculated noise mask and the scaled image, resulting in a clinical mammogram with the same noise and gray level characteristics as an image acquired at the lower-radiation dose
The performance of the proposed algorithm was validated using real images acquired with an anthropomorphic breast phantom at four different doses, with five exposures for each dose and 256 nonoverlapping ROIs extracted from each image and with uniform images

Summary

Introduction

To validate studies of radiation dose reduction, it is necessary to have a set of clinical images acquired from the same patient at different radiation levels The availability of such images is limited, since these require repeated irradiation of patients. One way to overcome this limitation is to use realistic breast phantoms; anthropomorphic phantoms are capable of mimicking the appearance of breast tissues, either as physical models or through digital simulation.. One way to overcome this limitation is to use realistic breast phantoms; anthropomorphic phantoms are capable of mimicking the appearance of breast tissues, either as physical models or through digital simulation.3–5 Another approach to validate dose reduction methods is to simulate the reduced dose by postprocessing clinical images.. Counting values are considerably higher in mammography images (λ ≫ 10), in this work, we used the unbiased exact inverse, available online.

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Results

Conclusion