6th International Workshop on Breast Densitometry and Breast ...

6 th <strong>International</strong> <strong>Workshop</strong> on Breast Densitometry
and Breast Cancer Risk Assessment
P46 NON-INVASIVE OPTICAL ASSESSMENT OF BREAST DENSITY AND
IDENTIFICATION OF HIGH-RISK SUBJECTS
Paola Taroni, 1 * Giovanna Quarto, 1 Antonio Pifferi, 1,2 Lorenzo Spinelli, 2 Alessandro Torricelli, 1 Francesca
Ieva, 3 Anna Maria Paganoni, 3 Francesca Abbate, 4 Nicola Balestreri, 5 Simona Menna, 4 Enrico Cassano, 4 and
Rinaldo Cubeddu 1,2
1 Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy; 2 Istituto di
Fotonica e Nanotecnologie, Consiglio Nazionale delle Ricerche, Piazza Leonardo da Vinci 32, 20133 Milano,
Italy; 3 Dipartimento di Matematica, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy;
4 European Institute of Oncology, Breast Imaging Unit, Via G. Ripamonti, 435, 20141 Milano, Italy ;
5 European Institute of Oncology, Department of Radiology, Via G. Ripamonti, 435, 20141 Milano, Italy
We propose the assessment of breast density by non-invasive optical means using time domain diffuse optical
spectroscopy.
Optical techniques can provide functional and structural information on biological tissue in an absolutely noninvasive
way, and they have already been successfully applied to the characterization of breast tissue in vivo.
We have further exploited the potential of diffuse optical spectroscopy operating in the time domain to assess
both tissue composition in terms of key constituents and scattering parameters that are related to the
microscopic structure of tissue and specifically to breast density.
ABSTRACTS
Time domain multi-wavelength (635-1060 nm) optical mammography was performed on 147 subjects, and
average breast tissue composition (water, lipid, collagen, oxy- and deoxyhemoglobin) and scattering
parameters (amplitude a and slope b) were estimated using the diffusion approximation to the radiative transfer
theory to model photon propagation in tissue. Mammographic density was classified through BI-RADS
categories.
The dependence of optically derived tissue composition and scattering parameters on BI-RADS categories was
investigated. All parameters show highly significant difference for BI-RADS category 2 vs 3, and 3 vs 4 (nonparametric
Wilcoxon test, p < 0.005), while for most parameters the difference between category 1 and 2 is not
statistically significant. Specifically, increasing breast density corresponds to progressively increasing average
amounts of water and collagen, while the lipid content decreases gradually. An increase with BI-RADS
category is also observed in both scattering amplitude a and slope b, in agreement with differences in
microscopic structure expected between fatty and fibroglandular tissue. The blood parameters (i.e. total
hemoglobin content tHb and oxygenation level SO 2 ) are less sensitive, with only tHb showing a slight increase
with mammographic density.
The linear correlation between optically derived parameters was also investigated. In particular, lipid content
shows strong negative correlation with both water and collagen content. Moreover, positive (negative)
correlation exists between scattering amplitude a and concentrations of water and collagen (lipid). Such
observations are consistent with the hypothesis that the major contribution to scattering comes from
fibroglandular tissue components.
To develop a procedure for the identification of high-risk women, the mammographic density was
dichotomized, comparing subjects in BI-RADS categories 1 to 3 to subjects in category 4. The p-values of the
Wilcoxon test showed that tHb, lipid, water, collagen, a e b are significantly different in the two populations
considered (at least p < 0.001), while SO 2 is not. The best regression logistic model for the risk probability was
found via a stepwise variables selection minimizing the AIC (Akaike Information Criterion) and resulted to
depend on collagen content and scattering parameters. The model provides a total misclassification error of
12.3%, corresponding to a simple kappa of 0.84, which compares favorably with the reproducibility of BI-
RADS measures among radiologists and even intra-radiologist.
These results qualify the optical technique as a potential candidate for non-invasive, relatively simple, and
operator-independent assessment of breast-density related risk.
81