- Email: [email protected]
A preliminary study on the possibility to diagnose urinary tract cancers by an electronic nose
Available online at www.sciencedirect.com
Sensors and Actuators B 131 (2008) 1–4
A preliminary study on the possibility to diagnose urinary tract cancers by an electronic nose M. Bernabei a,∗ , G. Pennazza a , M. Santonico a , C. Corsi c , C. Roscioni d , R. Paolesse b , C. Di Natale a , A. D’Amico a b
a Department of Electronic Engineering, University of Rome Tor Vergata, Via del Politecnico 1, 00133 Rome, Italy Department of Chemical Science and Technology, University of Rome Tor Vergata, Via della Ricerca Scientifica, 00133 Rome, Italy c Villa Pia Hospital, Via B. Ramazzini 93, 00149 Rome, Italy d San Camillo-Forlanini Hospital, Via Portuense 332, 00149 Rome, Italy
Available online 23 December 2007
Abstract In this paper a study about the possibility of an early and non-invasive diagnosis of urinary tract cancers with an electronic nose is presented. Measurements of urine headspace were performed by means of an electronic nose based on eight quartz crystal microbalance (QCM) gas sensors coated with different metalloporphyrins. A total of 113 patients affected by various urological pathologies were involved in the experiment, 19 of them were measured twice, before and after the surgical treatment of the cancer. 18 healthy volunteers were used as a reference population. The e-nose data were processed by both principal component analysis (PCA) and discriminant analysis solved by partial least square (PLS-DA). The PLS-DA model related to the data of the healthy and the ills individuals, except the post-surgery samples, shows a complete discrimination between these two groups and a gradual differentiation between prostate and bladder cancer. The application of PCA to the whole data set, shows a migration of the post-surgery class towards the healthy group, suggesting that the headspace of urine samples of patients with the urinary tract cancer is different from that of healthy individuals. These preliminary results confirm a strict correlation between urine headspace and urological pathologies, enhancing the possibility to perform early diagnosis, considered of upmost importance along the medical diagnostic path. © 2007 Elsevier B.V. All rights reserved. Keywords: Urinary tract cancer; Electronic nose; Diagnosis; Quartz crystal microbalance
1. Introduction In the last years, in medicine there has been an increased interest for inexpensive, non-invasive, simple and early diagnostic tests with a high sensitivity and specificity for selected diseases. At this scope new diagnostic tools based on the analysis of the biological fluids have been considered. In fact, each pathology modifies chemical composition of human body and biological fluids, so if we were in a position to find these alterations of the chemical composition, we could diagnose all the diseases. This principle is used by clinical chemistry to diagnose some diseases by means of the chemical analysis of body fluids, such as blood, urine and breath, known to be correlated to a certain disease.
∗
Corresponding author. Tel.: +39 06 49934581; fax: +39 06 49934066. E-mail address: [email protected] (M. Bernabei).
0925-4005/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2007.12.030
Unfortunately with the current instruments used in medical field, it is not possible to determine the concentration of all the compounds inside the human body. On the other hand volatile organic compounds (VOCs) found in the air surrounding living beings and in the headspace of the biological fluids contain information about the internal biochemistry of the body and then they can provide a mean for the identification of diseases. The progresses in chemical sensors technology have opened the possibility to use electronic noses for non-invasive, inexpensive and early diagnosis based on the analysis of the odour of skin, exhaled breath, urine, and saliva [1]. In fact these instruments are arrays of different non-selective sensors and their responses are not correlated to a specific compound, but rather to the whole chemical information about samples. Then if we analyzed by means of an electronic nose the headspace of samples that contains unlike combinations of VOCs, the different sensitivity and the absence of selectivity of the sensors of the e-nose permit to detect these alterations of the
2
M. Bernabei et al. / Sensors and Actuators B 131 (2008) 1–4
whole headspace composition, and to discriminate between samples. Its ability to detect gynaecological infections [2], Helicobacter pylori infection [3] and to identify bacteria [4] was verified in principle. More recently, the possibility to identify lung cancer by analyzing the breath of patients with such devices was also demonstrated [5]. The detection of diseases from urine odour analysis with the artificial olfactory system was also verified in the case of bacterial infections where the different metabolic products of the colonizing bacterial population allows recognition of diseases [6]. The treatment of urinary tract cancers is expected to find benefits from the introduction of such diagnostic methods. Indeed, these pathologies, in particular bladder cancer, require frequent checks that, with the current technology, are particularly painful for the patient. Various urinary markers for bladder cancer have been found out, but none of these are able to develop a diagnostic test with sufficient sensitivity and specificity to replace the actual diagnostic examination. The possibility to use the volatile compounds of urine as indicators of the presence of bladder cancer was also demonstrated by training dogs to recognize the urine of diseased subjects [7]. On the basis of these studies, we have investigated the suitability of an electronic nose to characterize the headspace of urine samples for the identification of subjects affected by urological pathologies, such as in particular bladder cancer. 2. Experimental Measurements were performed with the ENQBE, one of the last prototypes of the electronic noses developed at the University of Rome Tor Vergata. The instrument is based on eight quartz crystal microbalances (QCMs) gas sensors coated by sensing layers of metalloporphyrins. Most of odours compounds are excellent ligands for metal ions and so metalloporphyrins are good candidates for odour sensing. The sensing properties of sensors based on these compounds depend on the nature of both the central metals and peripheral substituents of the metalloporphyrin complex [8]. In this way, small variations in porphyrin structure give sensors with different adsorption properties. This flexibility is extremely important in the e-nose technology that requires sensors with broad and overlapping sensitivities [9]. QCM sensors response is expressed in Hz as difference between the oscillation frequency when the sensor is exposed to the reference air and when it is exposed to headspace sample. In fact, adsorption or desorbtion of molecules from the gas phase on the quartz surface causes a variation of the oscillating mass (m), which induces a variation of the oscillation frequency (f). The relation between f and m can be described, in the first approximation, by the Sauerbrey equation [10] Cf f02 m (1) A where A is the coated area, Cf the mass sensitivity constant and f0 the fundamental frequency.
f = −
This instrument is utilized since 7 years in medical researches [11,12]. A total of 131 individuals were involved in the experiment. Twenty-five of them were affected by bladder cancer, twelve by prostate cancer, twenty-nine by benign prostatic hypertrophy (BPH) and thirty-three by various urological pathologies. Fifteen patients were measured twice, before and after the surgical treatment of cancer. Eighteen healthy volunteers were used as a reference population. Measurements of patients were performed on urine samples provided by the Department of Urology of ‘Villa Pia’ hospital in Rome. For each patient, medical staff has provided the collection of all that informations useful for data analysis, in particular if they are smokers, if they usually drink alcohol and which drugs they take. Each individual involved in the experiment was informed about the scope of the measurements and their consents were collected before the measurement campaign. The study was then approved by the ethical committee of the Villa Pia hospital. Urines were collected in the morning, before any food intake. They were stored in sealed vials and kept at 25 ◦ C for the necessary time to obtain a steady headspace. Then 10 ml of the headspace of each sample was extracted and injected into a 2 l sterile bag pre-filled with N2 . This procedure was performed by means of a chromatographic syringe. The content of the bag was then flown at the constant speed of 0.3 l/min into the sensor chamber. All measurements were performed on site. In order to minimize the influence of possible instrumental drift, the measurement sequence was randomized. 3. Results and discussion Electronic nose data were processed by both principal component analysis (PCA) and discriminant analysis solved by partial least squares (PLS-DA). Initially, the data related to post surgery class were omitted. This class included not only patients measured with e-nose some weeks after surgical removal of tumour, but also patients measured during a routine hospital check. In fact people who have had bladder cancer are at very high risk of getting it again and they have to be checked for a relapse every 3 to 6 months for the first few years after their initial treatment, and every year after that. So we have tested them during one of these controls. Their data could contain not only the information about the presence of an illness, but also the influence of post surgery treatment and of the drugs that they usually take to avoid bladder cancer recurrences. This makes those samples particular. The remaining data were processed by PLS-DA choosing the two large classes of reference and diseased. Fig. 1 shows the plot of the first two latent variables of PLS-DA model related to this classification. In order to valuate the identification performances of the method, a leave-one-out validation method has been adopted. It is evident by the score plot, a complete discrimination between the data related to patients and to the healthy controls, 100% of the samples were correctly classified.
M. Bernabei et al. / Sensors and Actuators B 131 (2008) 1–4
Fig. 1. Plot of the two first latent variables of the PLS-DA model built without the post-surgery patients.
These results confirm that the volatile part of urine gives information about the presence of a urological pathology and demonstrate that the ENQBE, with a suitable sampling protocol, can detect this information. As a second step we have considered the samples related to healthy controls and patients affected by bladder and prostate cancer to verify if it is possible to discriminate the two kinds of the urological cancer that we have measured. These data were processed by PCA and the resulting score plot is shown in Fig. 2. As it can be seen, there is not a complete discrimination between the two tumours, but rather a sort of gradual differentiation. An interesting result is obtained examining the whole data set, including the post-surgery patients. The whole data set was processed by PCA and the score plot is shown in Fig. 3. In the plot the post-surgery samples lay across the two groups of reference and diseased.
Fig. 2. Score plot of the two first principal components analysis of the data related to controls and patients affected by bladder and prostate cancer. Data are labeled as (1) subjects with bladder cancer, (2) subjects with prostate cancer, and (3) healthy controls.
3
Fig. 3. Score plot of the first two principal components of the whole data set. Data are labeled as (1) subjects with urological diseases, (2) healthy controls, and (3) bladder cancer post-surgery patients.
We did not expect that all post-surgery samples were recognized as healthy samples for various reasons, first of all many of them were affected (BPH) and the removal of tumour do not eliminate BPH; second, some patients were measured a week after the treatment and some even after 3 months. This migration of post-surgery patients towards the healthy class can be considered an important result. All this encourages us to think that an early odour diagnosis of urinary tract cancers seems possible. 4. Conclusions Preliminary results confirm that there is an anomalous composition of the volatile part of urine of patients affected by a urological pathology and show that the electronic nose is able to detect this anomalous composition of urine headspace, in fact 100% of patients were classified as ills and 100% of healthy volunteers were correctly classified too. The findings related to the post-surgery patients show that the related class tends to overlap that of healthy people, so it can be supposed that an early diagnosis of urinary tract cancer appears possible. To this regard, more studies are necessary to evaluate at which stage we can diagnose the urological tumour. For this purpose we are designing a plan to follow the same patient during the disease evolution. The PCA of the samples related to prostate and bladder cancer, the two kinds of urological tumours that we have analyzed, points out that the two classes are not totally separated, but their statistical distribution has different mean and variance. This indicates that discrimination between the different tumours can be done, and so we are designing a new sampling protocol to eliminate noise in urine odour due to the variability of the biological sample. In fact in this way we can reduce the interclass variance and distinguish between different urological pathologies. This is a preliminary experiment that shows us that an early odours diagnosis of urinary tract cancers is possible, but more
4
M. Bernabei et al. / Sensors and Actuators B 131 (2008) 1–4
studies are necessary both from physiological and from instrumental point of view, to understand which modifications of chemical composition are directly related to the diseases and which are the mechanisms producing these correlations. References [1] A. Turner, N. Magan, Electronic nose and disease diagnostics, nature review, Microbiology 2 (2004) 161–166. [2] S. Chandiok, B.A. Crawley, B.A. Oppenheim, P.R. Chadwick, S. Higgins, K.C. Persaud, Screening for bacterial vaginosis: a novel application of artificial nose, J. Clin. Pathol. 50 (1997) 790–791. [3] A.K. Pavlou, N. Magan, D. Sharp, J. Brown, H. Barr, A.P.F. Turner, An intelligent rapid odour recognition model in discrimination of Helicobacter pylori and other gastroesophageal isolates in vitro, Biosens. Bioelectron. 15 (2000) 333–342. [4] J.W. Gardner, M. Craven, C. Dow, E.L. Hines, The prediction of bacteria type and culture growth phase by an electronic nose with a multi-layer perceptron network, Meas. Sci. Technol. 9 (1998) 120–127. [5] C. Di Natale, A. Macagnano, E. Martinelli, R. Paolesse, G. D’Arcangelo, C. Roscioni, A. Finazzi-Agr`o, A. D’Amico, Lung cancer identification by the analysis of breath by means of an array of non-selective gas sensors, Biosens. Bioelectron. 18 (2003) 1209–1218. [6] A.K. Pavlou, N. Magan, C. McNulty, J.M. Jones, D. Sharp, J. Brown, A.P.F. Turner, Use of an electronic nose system for diagnoses of urinary tract infections, Biosens. Bioelectron. 17 (2002) 893–899. [7] C.M. Willis, S.M. Church, C.M. Guest, W.A. Cook, N. McCarthy, A.J. Bransbury, M.R. Church, J.C. Church, Olfactory detection of human bladder cancer by dogs: proof of principles study, Br. Med. J. 329 (2004) 712–718. [8] J.A.J. Brunink, C. Di Natale, F. Bulgaro, F.A.M. Davide, A. D’Amico, R. Paolesse, T. Boschi, M. Faccio, G. Ferri, The application of metalloporphyrins as coating material for QMB based chemical sensor, Anal. Chim. Acta 325 (1996) 53–64. [9] C. Di Natale, R. Paolesse, A. Macagnano, A. Mantini, C. Goletti, A. D’Amico, Characterization and design of porphyrins-based broad selectivity chemical sensors for electronic nose applications, Sens. Actuator B 52 (1998) 162–168. [10] G. Sauerbrey, Verwendung von Schwingquarzen zur Wagung dunner Schichten und zur Mikrowagung, Zeitschrift fur Physik 155 (1959) 206–222. [11] C. Di Natale, A. Macagnano, R. Paolesse, A. Mantini, A. D’Amico, Electronic nose approach to human skin odour analysis, Sens. Actuator B 65 (2000) 216–219. [12] C. Di Natale, A. Mantini, A. Magagnano, D. Antuzzi, R. Paolesse, A. D’Amico, Electronic nose analysis of urine samples containing blood, Physiol. Meas. 20 (1999) 377–384.
Biographies Mara Bernabei received an electronics engineering degree from the University of Rome Tor Vergata in 2004. Since 2004, she has cooperated with the sensors and microsystems group of the University of Rome Tor Vergata, for the
development of chemical sensor arrays and their applications in food, medical, environment and space field. Currently she is a PhD student at the University of Manchester, England. Her research project concerned with the development of large scale sensor arrays for neuromorphic modeling. Giorgio Pennazza received an electronics engineering degree from the University of Rome Tor Vergata in 2001, he obtained his PhD degree on “Engineering of sensorial and learning systems” from University of Rome Tor Vergata, in 2004. Currently he has a post-doc position at the sensors group of the University of Rome Tor Vergata. His research interests are concerned with the development of chemical sensor arrays applications, in particular for medical diagnosis. He authored more than 20 papers on international journals and conferences. Marco Santonico received an electronics engineering degree from the University of Rome Tor Vergata, in 2003. Currently he is a PhD student on “Engineering of sensorial and learning systems” at the University of Rome Tor Vergata. His research interest is in the development of chemical sensor arrays for food and medical applications. Claudio Corsi received the Laurea degree in medicine and surgery from the University La Sapienza, Rome, Italy. He specialized in urology and currently he is head physician of the Department of ‘Villa Pia’ Hospital in Rome. Claudio Roscioni is an emeritus head physician of the San Camillo-Forlanini Hospital in Rome and he has been a professor in phthisiology at the University La Sapienza, Rome, Italy. He is author of more than 100 papers in medical journals and conference proceedings. Since 1994, he has cooperated with the sensors and microsystems group of the University of Rome Tor Vergata in research activities concerning with the development of chemical sensors arrays as a medical diagnostic tool. Roberto Paolesse is an associate professor of general chemistry at the faculty of engineering of the University of Rome Tor Vergata. His research interests include the synthesis and reactivity of transition metal complexes with porphyrins and related macrocycles and the development and application of chemical sensors. He authored more than 250 papers on international journals and conferences. Corrado Di Natale is an associate professor at the faculty of engineering of the University of Rome Tor Vergata where he teaches courses on Sensors and Detectors. His research activities are concerned with the development of chemical and bio-sensors, artificial sensorial systems (olfaction and taste) and their applications, and the study of the optical and electronic properties of organic and molecular materials. He authored more than 330 papers on international journals and conference proceedings. Arnaldo D’Amico received the Laurea degree in physics and electronic engineering from the University La Sapienza, Rome, Italy. For several years, he has been with the National Research Council (CNR) leading the semiconductors laboratory at the Solid State Electronic Institute, Rome. In 1988, he was appointed full professor of electronics at the University of L’Aquila, and, since 1990, he has been with the University of Rome Tor Vergata where he leads the Sensors and Microsystems Group and is full professor of electronics, faculty of engineering. Currently, he is also director of the Corbino Institute of Acoustic of the National Research Council (CNR). His main research activities are concerned with the research and development of physical and chemical sensors, low voltage electronics, noise and advanced electronic devices. He is author of more than 350 papers in international journals and conference proceedings.
Sensors and Actuators B 131 (2008) 1–4
A preliminary study on the possibility to diagnose urinary tract cancers by an electronic nose M. Bernabei a,∗ , G. Pennazza a , M. Santonico a , C. Corsi c , C. Roscioni d , R. Paolesse b , C. Di Natale a , A. D’Amico a b
a Department of Electronic Engineering, University of Rome Tor Vergata, Via del Politecnico 1, 00133 Rome, Italy Department of Chemical Science and Technology, University of Rome Tor Vergata, Via della Ricerca Scientifica, 00133 Rome, Italy c Villa Pia Hospital, Via B. Ramazzini 93, 00149 Rome, Italy d San Camillo-Forlanini Hospital, Via Portuense 332, 00149 Rome, Italy
Available online 23 December 2007
Abstract In this paper a study about the possibility of an early and non-invasive diagnosis of urinary tract cancers with an electronic nose is presented. Measurements of urine headspace were performed by means of an electronic nose based on eight quartz crystal microbalance (QCM) gas sensors coated with different metalloporphyrins. A total of 113 patients affected by various urological pathologies were involved in the experiment, 19 of them were measured twice, before and after the surgical treatment of the cancer. 18 healthy volunteers were used as a reference population. The e-nose data were processed by both principal component analysis (PCA) and discriminant analysis solved by partial least square (PLS-DA). The PLS-DA model related to the data of the healthy and the ills individuals, except the post-surgery samples, shows a complete discrimination between these two groups and a gradual differentiation between prostate and bladder cancer. The application of PCA to the whole data set, shows a migration of the post-surgery class towards the healthy group, suggesting that the headspace of urine samples of patients with the urinary tract cancer is different from that of healthy individuals. These preliminary results confirm a strict correlation between urine headspace and urological pathologies, enhancing the possibility to perform early diagnosis, considered of upmost importance along the medical diagnostic path. © 2007 Elsevier B.V. All rights reserved. Keywords: Urinary tract cancer; Electronic nose; Diagnosis; Quartz crystal microbalance
1. Introduction In the last years, in medicine there has been an increased interest for inexpensive, non-invasive, simple and early diagnostic tests with a high sensitivity and specificity for selected diseases. At this scope new diagnostic tools based on the analysis of the biological fluids have been considered. In fact, each pathology modifies chemical composition of human body and biological fluids, so if we were in a position to find these alterations of the chemical composition, we could diagnose all the diseases. This principle is used by clinical chemistry to diagnose some diseases by means of the chemical analysis of body fluids, such as blood, urine and breath, known to be correlated to a certain disease.
∗
Corresponding author. Tel.: +39 06 49934581; fax: +39 06 49934066. E-mail address: [email protected] (M. Bernabei).
0925-4005/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2007.12.030
Unfortunately with the current instruments used in medical field, it is not possible to determine the concentration of all the compounds inside the human body. On the other hand volatile organic compounds (VOCs) found in the air surrounding living beings and in the headspace of the biological fluids contain information about the internal biochemistry of the body and then they can provide a mean for the identification of diseases. The progresses in chemical sensors technology have opened the possibility to use electronic noses for non-invasive, inexpensive and early diagnosis based on the analysis of the odour of skin, exhaled breath, urine, and saliva [1]. In fact these instruments are arrays of different non-selective sensors and their responses are not correlated to a specific compound, but rather to the whole chemical information about samples. Then if we analyzed by means of an electronic nose the headspace of samples that contains unlike combinations of VOCs, the different sensitivity and the absence of selectivity of the sensors of the e-nose permit to detect these alterations of the
2
M. Bernabei et al. / Sensors and Actuators B 131 (2008) 1–4
whole headspace composition, and to discriminate between samples. Its ability to detect gynaecological infections [2], Helicobacter pylori infection [3] and to identify bacteria [4] was verified in principle. More recently, the possibility to identify lung cancer by analyzing the breath of patients with such devices was also demonstrated [5]. The detection of diseases from urine odour analysis with the artificial olfactory system was also verified in the case of bacterial infections where the different metabolic products of the colonizing bacterial population allows recognition of diseases [6]. The treatment of urinary tract cancers is expected to find benefits from the introduction of such diagnostic methods. Indeed, these pathologies, in particular bladder cancer, require frequent checks that, with the current technology, are particularly painful for the patient. Various urinary markers for bladder cancer have been found out, but none of these are able to develop a diagnostic test with sufficient sensitivity and specificity to replace the actual diagnostic examination. The possibility to use the volatile compounds of urine as indicators of the presence of bladder cancer was also demonstrated by training dogs to recognize the urine of diseased subjects [7]. On the basis of these studies, we have investigated the suitability of an electronic nose to characterize the headspace of urine samples for the identification of subjects affected by urological pathologies, such as in particular bladder cancer. 2. Experimental Measurements were performed with the ENQBE, one of the last prototypes of the electronic noses developed at the University of Rome Tor Vergata. The instrument is based on eight quartz crystal microbalances (QCMs) gas sensors coated by sensing layers of metalloporphyrins. Most of odours compounds are excellent ligands for metal ions and so metalloporphyrins are good candidates for odour sensing. The sensing properties of sensors based on these compounds depend on the nature of both the central metals and peripheral substituents of the metalloporphyrin complex [8]. In this way, small variations in porphyrin structure give sensors with different adsorption properties. This flexibility is extremely important in the e-nose technology that requires sensors with broad and overlapping sensitivities [9]. QCM sensors response is expressed in Hz as difference between the oscillation frequency when the sensor is exposed to the reference air and when it is exposed to headspace sample. In fact, adsorption or desorbtion of molecules from the gas phase on the quartz surface causes a variation of the oscillating mass (m), which induces a variation of the oscillation frequency (f). The relation between f and m can be described, in the first approximation, by the Sauerbrey equation [10] Cf f02 m (1) A where A is the coated area, Cf the mass sensitivity constant and f0 the fundamental frequency.
f = −
This instrument is utilized since 7 years in medical researches [11,12]. A total of 131 individuals were involved in the experiment. Twenty-five of them were affected by bladder cancer, twelve by prostate cancer, twenty-nine by benign prostatic hypertrophy (BPH) and thirty-three by various urological pathologies. Fifteen patients were measured twice, before and after the surgical treatment of cancer. Eighteen healthy volunteers were used as a reference population. Measurements of patients were performed on urine samples provided by the Department of Urology of ‘Villa Pia’ hospital in Rome. For each patient, medical staff has provided the collection of all that informations useful for data analysis, in particular if they are smokers, if they usually drink alcohol and which drugs they take. Each individual involved in the experiment was informed about the scope of the measurements and their consents were collected before the measurement campaign. The study was then approved by the ethical committee of the Villa Pia hospital. Urines were collected in the morning, before any food intake. They were stored in sealed vials and kept at 25 ◦ C for the necessary time to obtain a steady headspace. Then 10 ml of the headspace of each sample was extracted and injected into a 2 l sterile bag pre-filled with N2 . This procedure was performed by means of a chromatographic syringe. The content of the bag was then flown at the constant speed of 0.3 l/min into the sensor chamber. All measurements were performed on site. In order to minimize the influence of possible instrumental drift, the measurement sequence was randomized. 3. Results and discussion Electronic nose data were processed by both principal component analysis (PCA) and discriminant analysis solved by partial least squares (PLS-DA). Initially, the data related to post surgery class were omitted. This class included not only patients measured with e-nose some weeks after surgical removal of tumour, but also patients measured during a routine hospital check. In fact people who have had bladder cancer are at very high risk of getting it again and they have to be checked for a relapse every 3 to 6 months for the first few years after their initial treatment, and every year after that. So we have tested them during one of these controls. Their data could contain not only the information about the presence of an illness, but also the influence of post surgery treatment and of the drugs that they usually take to avoid bladder cancer recurrences. This makes those samples particular. The remaining data were processed by PLS-DA choosing the two large classes of reference and diseased. Fig. 1 shows the plot of the first two latent variables of PLS-DA model related to this classification. In order to valuate the identification performances of the method, a leave-one-out validation method has been adopted. It is evident by the score plot, a complete discrimination between the data related to patients and to the healthy controls, 100% of the samples were correctly classified.
M. Bernabei et al. / Sensors and Actuators B 131 (2008) 1–4
Fig. 1. Plot of the two first latent variables of the PLS-DA model built without the post-surgery patients.
These results confirm that the volatile part of urine gives information about the presence of a urological pathology and demonstrate that the ENQBE, with a suitable sampling protocol, can detect this information. As a second step we have considered the samples related to healthy controls and patients affected by bladder and prostate cancer to verify if it is possible to discriminate the two kinds of the urological cancer that we have measured. These data were processed by PCA and the resulting score plot is shown in Fig. 2. As it can be seen, there is not a complete discrimination between the two tumours, but rather a sort of gradual differentiation. An interesting result is obtained examining the whole data set, including the post-surgery patients. The whole data set was processed by PCA and the score plot is shown in Fig. 3. In the plot the post-surgery samples lay across the two groups of reference and diseased.
Fig. 2. Score plot of the two first principal components analysis of the data related to controls and patients affected by bladder and prostate cancer. Data are labeled as (1) subjects with bladder cancer, (2) subjects with prostate cancer, and (3) healthy controls.
3
Fig. 3. Score plot of the first two principal components of the whole data set. Data are labeled as (1) subjects with urological diseases, (2) healthy controls, and (3) bladder cancer post-surgery patients.
We did not expect that all post-surgery samples were recognized as healthy samples for various reasons, first of all many of them were affected (BPH) and the removal of tumour do not eliminate BPH; second, some patients were measured a week after the treatment and some even after 3 months. This migration of post-surgery patients towards the healthy class can be considered an important result. All this encourages us to think that an early odour diagnosis of urinary tract cancers seems possible. 4. Conclusions Preliminary results confirm that there is an anomalous composition of the volatile part of urine of patients affected by a urological pathology and show that the electronic nose is able to detect this anomalous composition of urine headspace, in fact 100% of patients were classified as ills and 100% of healthy volunteers were correctly classified too. The findings related to the post-surgery patients show that the related class tends to overlap that of healthy people, so it can be supposed that an early diagnosis of urinary tract cancer appears possible. To this regard, more studies are necessary to evaluate at which stage we can diagnose the urological tumour. For this purpose we are designing a plan to follow the same patient during the disease evolution. The PCA of the samples related to prostate and bladder cancer, the two kinds of urological tumours that we have analyzed, points out that the two classes are not totally separated, but their statistical distribution has different mean and variance. This indicates that discrimination between the different tumours can be done, and so we are designing a new sampling protocol to eliminate noise in urine odour due to the variability of the biological sample. In fact in this way we can reduce the interclass variance and distinguish between different urological pathologies. This is a preliminary experiment that shows us that an early odours diagnosis of urinary tract cancers is possible, but more
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Biographies Mara Bernabei received an electronics engineering degree from the University of Rome Tor Vergata in 2004. Since 2004, she has cooperated with the sensors and microsystems group of the University of Rome Tor Vergata, for the
development of chemical sensor arrays and their applications in food, medical, environment and space field. Currently she is a PhD student at the University of Manchester, England. Her research project concerned with the development of large scale sensor arrays for neuromorphic modeling. Giorgio Pennazza received an electronics engineering degree from the University of Rome Tor Vergata in 2001, he obtained his PhD degree on “Engineering of sensorial and learning systems” from University of Rome Tor Vergata, in 2004. Currently he has a post-doc position at the sensors group of the University of Rome Tor Vergata. His research interests are concerned with the development of chemical sensor arrays applications, in particular for medical diagnosis. He authored more than 20 papers on international journals and conferences. Marco Santonico received an electronics engineering degree from the University of Rome Tor Vergata, in 2003. Currently he is a PhD student on “Engineering of sensorial and learning systems” at the University of Rome Tor Vergata. His research interest is in the development of chemical sensor arrays for food and medical applications. Claudio Corsi received the Laurea degree in medicine and surgery from the University La Sapienza, Rome, Italy. He specialized in urology and currently he is head physician of the Department of ‘Villa Pia’ Hospital in Rome. Claudio Roscioni is an emeritus head physician of the San Camillo-Forlanini Hospital in Rome and he has been a professor in phthisiology at the University La Sapienza, Rome, Italy. He is author of more than 100 papers in medical journals and conference proceedings. Since 1994, he has cooperated with the sensors and microsystems group of the University of Rome Tor Vergata in research activities concerning with the development of chemical sensors arrays as a medical diagnostic tool. Roberto Paolesse is an associate professor of general chemistry at the faculty of engineering of the University of Rome Tor Vergata. His research interests include the synthesis and reactivity of transition metal complexes with porphyrins and related macrocycles and the development and application of chemical sensors. He authored more than 250 papers on international journals and conferences. Corrado Di Natale is an associate professor at the faculty of engineering of the University of Rome Tor Vergata where he teaches courses on Sensors and Detectors. His research activities are concerned with the development of chemical and bio-sensors, artificial sensorial systems (olfaction and taste) and their applications, and the study of the optical and electronic properties of organic and molecular materials. He authored more than 330 papers on international journals and conference proceedings. Arnaldo D’Amico received the Laurea degree in physics and electronic engineering from the University La Sapienza, Rome, Italy. For several years, he has been with the National Research Council (CNR) leading the semiconductors laboratory at the Solid State Electronic Institute, Rome. In 1988, he was appointed full professor of electronics at the University of L’Aquila, and, since 1990, he has been with the University of Rome Tor Vergata where he leads the Sensors and Microsystems Group and is full professor of electronics, faculty of engineering. Currently, he is also director of the Corbino Institute of Acoustic of the National Research Council (CNR). His main research activities are concerned with the research and development of physical and chemical sensors, low voltage electronics, noise and advanced electronic devices. He is author of more than 350 papers in international journals and conference proceedings.