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2 Methodology
The experimentation has been developed in collaboration with the Thoracic
Surgery Unit of the Istituto Nazionale Tumori (INT - National Cancer Institute),
Milan. The study involved a total of 52 volunteers, of which 22 healthy and 30
suffering from different types of primary lung cancer. Patients were enrolled from
who underwent tumor resection at the Thoracic Surgery Unit of INT and they
were eligible to participate if they were more than 18 years old, could understand
the breath collection procedure and could give written informed consent. The
healthy volunteers were recruited from the candidates of a randomized study
with multislice spiral CT, named Multicentric Italian Lung Detection (MILD)
trial for early lung cancer detection promoted by INT from 2005. Control people
have no pulmonary disease or respiratory symptoms and have negative chest
CT scan. All volunteers were assessed for their eligibility and asked to sign a
consent form to participate in the study, including a detailed information sheet.
A tobacco smoking history was obtained from all subjects. All volunteers were
asked to sign a written consent form, and the study was approved by the Ethical
Committee of the INT.
The breath acquisition has been made by inviting all volunteers to blow into a
nalophan bag of approximately 500
cm
3
of volume. Considering that the breath
exhaled directly from lung is contained only in the last part of exhalation, using
a spirometer to evaluate each volunteer exhalation capacity, we diverted the flow
at the end of the exhalation into the bag in order to collect only the final portion
of forced expiratory volume and analyze only a portion of alveolar air. Finally,
the air contained in the bag has been input to the electronic nose and analyzed.
Before connecting the bags to the electronic nose, it has been necessary to define
the parameters of the instrument: in particular we chose a sample frequency
of 1 Hz with a flow equal to 150
cm
3
per minute and the total duration of a
measure has been set to 8 minutes (of which one minute and a half for stimulus
acquisition). From each bag we took two measures, obtaining a total of 104
measurements, of which 44 correspond to the breath of healthy people and 60
to patients breath.
3 Basic Functioning of the Electronic Nose
An electronic nose is an instrument able to detect and recognize odors, namely
the volatile organic compounds present in an analyzed substance [2]. Its func-
tioning is strongly inspired by the biological olfactory system (Figure 1). In
human olfaction, odor sensations are induced by the interaction of odorants
with specialized receptors in the olfactory epithelium in the top of the nasal
cavity; this interaction creates signals that are transmitted to the olfactory bulb
and, ultimately, to the brain, which analyzes the received signals and performs
the classification or recognition of the odor. Following the same principles, the
electronic nose is composed of three fundamental modules (Figure 2):
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