Optical diagnosis of breast tumour has been of growing interest in the
last few years due to its non invasive character and to the chance of
obtaining information complementary to x-ray mammograms. In fact, the
principal tissue components, as oxy- and deoxy-haemoglobin, lipid and
water, exhibit different light absorption properties in the spectral range
from 600 nm to 1000 nm. Thus in principle, it is possible to distinguish
different breast structures on the basis of their light absorption. It
must be noted, however, that tissues are turbid media and a simple light
attenuation measurement is influenced by both absorption and scattering
properties, which cannot be discriminated.
A new time-resolved transmittance technique has been developed to measure
simultaneously both absorption and scattering coefficients. This approach
is based on the detection of the time distribution of photons transmitted
by a tissue slab following the injection of a short light pulse. The
arrival time delay of the transmitted photons and in general the time
shape of the emerging light pulse are correlated to the optical properties
(absorption and scattering) of the medium. Absorption provides information
about tissue composition and scattering is related to tissue structure.
The clinical diagnosis is based on the possibility to detect a tumour
inside the breast on the basis of the different optical properties of the
neoplastic tissue with respect to the healthy one.
Based on this technique the first two clinical prototypes operating in the
time domain have been developed both at Milan and Berlin (Physikalisch-Technische Bundesanstalt). These two instruments are actually operating in
an experimental phase in clinic, in the frame of a multi-centre clinical
trial of the European project OPTIMAMM. This project is aims at providing
in the next years a clear picture of the potentialities of optical
mammography.
The Milan mammograph (MAMMOT; MAMMograph for Optical Tomography) has been
realized through a well established cooperation among the researchers of
the Sezione Politecnico di Milano of the Institute of Photonics and
Nanotechnologies (CNR) and those of the Physics Department at the
Politecnico di Milano. The mammography image is obtained by scanning the
breast, slightly compressed between two Plexiglas plates, with two coaxial
fibres (for light injection and collection, respectively) set at the
opposite sides of the tissue. In order to obtain more specific information
on the different tissue components, four light pulses with time duration
of 200-400 ps set at different wavelengths (685 nm, 785 nm, 915 nm and 975
nm) are launched in the injection fibre. By sampling every millimetre,
four waveforms are acquired in each point, by an advanced detection system
with high time resolution and single photon sensitivity. By suitable data
analysis it is then possible to build optical images of absorption and
scattering at the four wavelengths.
During the present clinical trial running at the "Clinica S. PIO X" in
Milan, 119 patients have been examined so far, bearing either benign or
malignant pathologies. Together with the patients examined in Berlin, this
is the largest trial at international level. The results obtained are very
encouraging and show the possibility of discriminating different lesion
types. A data bank of the optical properties of the different pathologies
is building up.
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