Aims and objectives
Theoretical indexes of detectability,
such as signal-difference-to-noise ratio (SDNR) and threshold gold thickness obtained from c-d analysis,
show a decrease of object detectability/visibility as compressed breast thickness increases.
This is the consequence of the automatic exposure control (AEC) setup of most digital mammographic system which are currently programmed to maintain constant pixel value at the detector as a function of thickness [1,2]. While simple AEC tests,
for example using a thin square of Aluminium imaged on a uniform background,
show a reduction in object detectability,...
Methods and materials
Simulated microcalcification clusters and masses were inserted into unprocessed mammograms,
processed and then scored by four radiologists.
Images were visualized using the ViewDEX software [3,4].
The radiologists performed a free search study and rated their confidence of the detection of a lesion using a five-point rating scale.
a JAFROC analysis was applied .
Screening patient data,
acquired on two identical digital mammography systems,
were collected during one year and the images were divided into 4 thickness groups,
defined as ‘T-groups’ (T1≤29mm; T2=30-49mm; T3=50-69mm; T4≥70mm)....
Results of the study were calculated using the JAFROC software (JAFROC,
The overall significant difference test result for the study was found to be < 0.0001,
showing that at least two of the compared ‘modalities’ i.e.
the T-groups are significantly different.
The alternative free-response receiver operating characteristic curves (AFROC)for the 4 readers are presented in figure 3.
In going from T1 to T4,
the area under the AFROC curve was 0.80,
0.55 and 0.56,
indicating a decrease in detectability...
These clinical data confirm results found in simple QA tests for many mammography systems - that detectability falls as breast thickness increases,
especially for compressed breast thicknesses above 49 mm.
This result can be due to the specific set up of the mammographic system that keeps doses rather low for thicker breasts.
Another contributing factor could be the increased amount of tissue overlap in thicker breasts.
Both aspects are currently under study,
with the aim of improving lesion detectability for thicker breasts.
European Commission: European Guidelines for Quality Assurance in Breast Cancer Screening and Diagnosis.
Struelens L,Verdun F,
The use of detectability indices as a means of Automatic Exposure Control for a digital mammography system.
Observer studies involving detection and localization: Modeling,
analysis and validation.
Van Ongeval C,