A remote-control datalogger for large-scale resistivity surveys and robust processing of its signals using a software lock-in approach

We present a new versatile datalogger that can be used for a wide range of possible applications in geosciences. It is adjustable in signal strength and sampling frequency, battery saving and can remotely be controlled over a Global System for Mobile Communication (GSM) connection so that it saves running costs, particularly in monitoring experiments. The internet connection allows for checking functionality, controlling schedules and optimizing pre-amplification. We mainly use it for large-scale electrical resistivity tomography (ERT), where it independently registers voltage time series on three channels, while a square-wave current is injected. For the analysis of this time series we present a new approach that is based on the lock-in (LI) method, mainly known from electronic circuits. The method searches the working point (phase) using three different functions based on a mask signal, and determines the amplitude using a direct current (DC) correlation function. We use synthetic data with different types of noise to compare the new method with existing approaches, i.e. selective stacking and a modified fast Fourier transformation (FFT)-based approach that assumes a 1∕f noise characteristics. All methods give comparable results, but the LI is better than the well-established stacking method. The FFT approach can be even better but only if the noise strictly follows the assumed characteristics. If overshoots are present in the data, which is typical in the field, FFT performs worse even with good data, which is why we conclude that the new LI approach is the most robust solution. This is also proved by a field data set from a long 2-D ERT profile

Implementasi Penguat Lock-in Digital Untuk Deteksi Gas

Pengukuran yang tidak akurat akibat sinyal data yang tertumpuk oleh derau merupakan salah satu permasalahan yang sering dijumpai di bidang elektronika. Terdapat beberapa cara untuk mengatasi permasalahan tersebut, salah satunya adalah dengan menggunakan digital lock-in amplifier. Pada tugas akhir ini dirancang digital lock-in amplifier untuk meningkatkan performa pengukuran dari sebuah sensor. Pemilihan lock-in amplifer dalam bentuk digital dikarenakan memiliki kelebihan biaya pembuatan yang lebih murah dan fisik yang lebih sederhana dibanding dengan lock-in amplifier analog. Semua proses pengolahan sinyal dilakukan pada komputer. Perangkat keras yang dibutuhkan adalah sensor gas MQ-7 yang sensitif terhadap konsentrasi gas karbon monoksida (CO) sebagai objek uji pada sistem. Mikrokontroler Arduino Mega digunakan untuk membangkitkan sinyal pembawa dan untuk komunikasi serial dengan komputer. Pada sistem penguat pengunci digital, sensor MQ-7 yang tengganggu oleh derau akan dimodulasi tegangan suplainya dengan sinyal kotak 100 Hz dengan amplitudo 5 V. Pada pengujian dengan sensor MQ-7 sebagai objek uji dilakukan dua pengujian. Perngujian pertama dengan menambahkan 23 ppm gas CO. Dari pengujian didapatkan hasil SNR keluaran sensor sebelum diproses di penguat lock-in adalah -11,59 dB dan SNR keluaran sensor dengan penguat lock-in adalah 11,79 dB. Pada pengujian kedua diberikan gas buang kendaraan dengan konsentrasi CO sebesar 62 ppm, didapatkan SNR sebelum dilewatkan penguat lock-in sebesar -6,94 dB dan ketika dilewatkan penguat lock-in adalah 15,7 dB. ============================================================================================================= Inaccurate measurements due to the data signal accumulated by noise are one of the most common problems in the field of electronics. There are several ways to solve the problem, one of them is by using digital lock-in amplifier. In this final project, adigital lock-in amplifier is designed to improve the measurement performance of a sensor. Selection of lock-in amplifer in digital form because it has the cost advantages of making cheaper in cost and physically simpler than the analog lock-in amplifier. All signal processing is done on the computer. The required hardware is the MQ-7 gas sensor which is sensitive to the concentration of carbon monoxide (CO) gas as the test object in the system. Arduino Mega microcontroller is used to generate carrier signal and for serial communication with computer. In a digital locking amplifier system, the distorted MQ-7 sensor by noise will be modulated its supply voltage with a 100 Hz box signal with an amplitude of 5 V. In the test with the MQ-7 sensor as the test object two tests are performed. First test by adding 23 ppm CO gas. From the test results obtained SNR sensor output before being processed in the lock-in amplifier is -11.59 dB and SNR sensor output with a lock-in amplifier is 11.79 dB. In the second test the vehicle exhaust gas with CO concentration of 62 ppm, was obtained SNR before passed the lock-in amplifier of -6.94 dB and when passed the lock-in amplifier is 15.7 dB

Desain Penguat Lock-In Digital Untuk Deteksi Gas Berkonsentrasi Rendah

Penelitian ini merancang dan membuat penguat lock-in digital (DLIA) yang diperuntukkan untuk sensor gas berkonsentrasi rendah. DLIA adalah penguat yang mampu untuk memulihkan sinyal yang terbenam di dalam derau. Tujuan dari penelitian ini untuk meningkatkan signal-to-noise ratio (SNR) dari sinyal kecil yang berasal dari sensor gas. Digital Signal Processing (DSP) diimplementasikan pada mikroprosesor ARM STM32F4. Sistem ini mempuyai penguatan variabel DC yang berkisar antara 20 sampai 100 dB. Kinerja DLIA ditunjukkan dengan mengukur sinyal kecil 100 mV pada 1 Hz dengan frekuensi cut-off (fc) 5 Hz. Hasil percobaan menunjukkan bahwa nilai SNR untuk sinyal asli dan output DLIA dengan penguatan satu kali, masing-masing adalah -4.73 dan 4.08 dB. Pada penelitian ini juga dilakukan pengukuran gas karbon monoksida (CO) berkonsentrasi 30 ppm menggunakan sensor gas semikonduktor MQ7 sebagai input dari sistem DLIA. Hasil pengujian menunjukkan bahwa nilai SNR untuk sinyal asli dan output DLIA dengan penguatan satu kali, masing-masing adalah 3.9 dan 7.8 dB. Untuk DLIA dengan penguatan empat kali dapat menghasilkan SNR sebesar 15.6 dB. ================================================================= This study has designed and constructed a digital lock-in amplifier (DLIA) for low-concentration gas sensors. DLIA is an amplifier which capable of recovering signals buried in the noise. The purpose of this research is to improve signal-to-noise ratio (SNR) of small signal coming from a gas sensor. Digital Signal Processing (DSP) is implemented on ARM STM32F4 microprocessor. The system has the DC gain ranging from 20 to 100 dB. DLIA performance is indicated by measuring small signal 100 mV at 1 Hz with cut-off frequency (fc) of 5 Hz. The experimental results show that the SNR values for the original signal and the DLIA output with a unity gain are -4.73 and 4.08 dB, respectively. In this study, carbon monoxide (CO) gas with the concentration of 30 ppm was measured using MQ7 semiconductor gas sensor as input for DLIA system. The experimental results show that the SNR values for the original signal and DLIA output with a unity gain are 3.9 and 7.8 dB, respectively. For DLIA with the gain of four can produce SNR of 15.6 dB

Development of Portable Diffuse Optical Spectroscopic Systems For Treatment Monitoring

The goal of this dissertation is to demonstrate the utility of portable, small-scale diffuse optical spectroscopic (DOS) systems for the diagnosis and treatment monitoring of various diseases. These systems employ near-infrared light (wavelength range of 650nm to 950nm) to probe human tissue and are sensitive to changes in scattering and absorption properties of tissues. The absorption is mainly influenced by the components of blood, namely oxy- and deoxy-hemoglobin (HbO2 and Hb) and parameters that can be derived from them (e.g. total hemoglobin concentration [THb] and oxygen saturation, StO2). Therefore, I focused on diseases in which these parameters change, which includes vascular diseases such as Peripheral Atrial Disease (PAD) and Infantile Hemangiomas (IH) as well as musculoskeletal autoimmune diseases such as Rheumatoid Arthritis (RA). In each of these specific diseases, current monitoring techniques are limited by their sensitivity to disease progression or simply do not exist as a quantitative metric. As part of this project, I first designed and built a wireless handheld DOS device (WHDD) that can perform DOS measurements at various tissue depths. This device was used in a 15-patient pilot study for infantile hemangiomas (IH) to differentiate diseased skin from normal skin and monitor the vascular changes during intervention. In another study, I compare the ultra-small form- factor WHDD’s ability to monitor synovitis and disease progression during a patient’s treatment of RA against the capabilities of a proven frequency domain optical tomographic (FDOT) system that has shown to differentiate patients with and without RA. Learning from clinical utility of the WHDD from these two studies, I adapted the WHDD technology to develop a compact multi- channel DOS measurement system to monitor perfusion changes in the lower extremities before and after surgical intervention for patients with peripheral artery disease (PAD). Using this multi- channel system, which we called the vascular optical spectroscopic measurement (VOSM) system, our group conducted a 20-subject pilot study to quantify its ability to monitor blood perfusion before and after revascularization of stenotic arteries in the lower extremities. This proof-of- concept study demonstrated how DOS may help vascular surgeons perform revascularization procedures in the operating room and assists in post-operative treatment monitoring of vascular diseases

Mise en œuvre d'un système portable d'imagerie cérébrale fonctionnelle bimodalité

RÉSUMÉ Dans ce mémoire, un appareil portable d’imagerie fonctionnelle du cerveau bimodalité est présenté. Ces travaux, entrepris dans le cadre du projet IMAGINC au sein du laboratoire Polystim, ont pour objectif de combiner la spectroscopie par proche infrarouge (NIRS, pour Near Infrared Spectroscopy) et l’électroencéphalographie (EEG) dans un même système afin de répondre aux besoins cliniques pour des applications incluant l’épilepsie et les accidents vasculaires cérébraux. À l’heure actuelle, les technologies couramment utilisées pour l’imagerie fonctionnelle du cerveau sont peu portables, coûteuses et nécessitent d’immobiliser le patient. La NIRS et l’EEG ont le potentiel de contourner ces problématiques et certains appareils ont prouvé la validité du concept. Cependant, le nombre de canaux et la sensibilité en NIRS de ces derniers sont insuffisants pour répondre aux exigences cliniques. Afin de répondre à ces besoins, l’appareil conçu peu être porté par le patient, a assez de canaux de détection pour couvrir toute la tête, a une autonomie de plus de 24 heures et est assez sensible en NIRS pour obtenir des données de qualité, même en présence de cheveux foncés. Constitué de trois modules, soit une interface graphique sur un ordinateur distant, un module de contrôle porté à la ceinture et un casque d’acquisition, le prototype réalisé permet de transférer les données en temps réel et est complètement configurable et contrôlable à distance. Afin de valider les performances du système, des mesures sur fantôme ont été effectuées pour la NIRS ainsi que pour l’EEG. Par la suite, un protocole expérimental utilisant des adultes en santé a été effectué sur 5 sujets et les résultats ont été comparés à ceux de la littérature. Après analyse, il a été conclu que l’appareil présenté fonctionne correctement et permet de reproduire des protocoles expérimentaux déjà publiés. Certaines améliorations doivent toutefois être apportées afin de pouvoir mieux répondre aux besoins du milieu de la santé.----------ABSTRACT In this thesis, a portable functional brain imaging system using two modalities is presented. This work, which is part of the IMAGINC project and affiliated with the Polystim laboratory, has the objective to combine near infrared spectroscopy (NIRS) to electroencephalography (EEG) in a single system in order to answer the clinical needs in applications as epilepsy and stroke. At this moment, typical technologies used for functional brain imaging are not portable, costly and need the patient to be immobilized. NIRS and EEG have the potential to by-pass these problems and some systems have already proved the validity of that concept. These systems, however, have a low channel count and lack NIRS sensitivity. In order to provide a better solution, a device was designed with enough detection channels to cover the whole head, autonomy over 24 hours and sufficient NIRS sensitivity to obtain quality data even with dark hair. The prototype that was built is made of 3 modules: a graphical user interface, a control module that can be worn on a belt and an acquisition helmet. It can transfer its data in real time to a distant computer and is completely remote configurable and controllable. Validation of the system was made by first using NIRS and EEG phantoms. An in-vivo experimental protocol was then used with 5 healthy adult subjects and results were compared with available papers. Analysis showed that the prototype works correctly and allows reproducing the results found in other published works. However, further optimization is still needed to improve the ability of the device to answer clinical needs

Dynamic Digital Optical Tomography for Cancer Imaging and Therapy Monitoring

Diffuse optical tomography is a non-invasive imaging technique that uses near-infrared light to create three-dimensional images of tissue. This dissertation presents the design and validation of an instrument for rapid optical imaging using digital detection techniques. In addition to a detailed description of the instrument, three studies are presented: a clinical study detecting breast cancer using dynamic optical imaging; a pre-clinical study monitoring early tumor response to anti-angiogenic therapy; and a clinical study monitoring individual patient response to neoadjuvant chemotherapy. These studies show that diffuse optical tomography is a valuable imaging modality that can play an important role in cancer detection and treatment

Apport de nouvelles techniques dans l’évaluation de patients candidats à une chirurgie d’épilepsie : résonance magnétique à haut champ, spectroscopie proche infrarouge et magnétoencéphalographie

L'épilepsie constitue le désordre neurologique le plus fréquent après les maladies cérébrovasculaires. Bien que le contrôle des crises se fasse généralement au moyen d'anticonvulsivants, environ 30 % des patients y sont réfractaires. Pour ceux-ci, la chirurgie de l'épilepsie s'avère une option intéressante, surtout si l’imagerie par résonance magnétique (IRM) cérébrale révèle une lésion épileptogène bien délimitée. Malheureusement, près du quart des épilepsies partielles réfractaires sont dites « non lésionnelles ». Chez ces patients avec une IRM négative, la délimitation de la zone épileptogène doit alors reposer sur la mise en commun des données cliniques, électrophysiologiques (EEG de surface ou intracrânien) et fonctionnelles (tomographie à émission monophotonique ou de positrons). La faible résolution spatiale et/ou temporelle de ces outils de localisation se traduit par un taux de succès chirurgical décevant. Dans le cadre de cette thèse, nous avons exploré le potentiel de trois nouvelles techniques pouvant améliorer la localisation du foyer épileptique chez les patients avec épilepsie focale réfractaire considérés candidats potentiels à une chirurgie d’épilepsie : l’IRM à haut champ, la spectroscopie proche infrarouge (SPIR) et la magnétoencéphalographie (MEG). Dans une première étude, nous avons évalué si l’IRM de haut champ à 3 Tesla (T), présentant théoriquement un rapport signal sur bruit plus élevé que l’IRM conventionnelle à 1,5 T, pouvait permettre la détection des lésions épileptogènes subtiles qui auraient été manquées par cette dernière. Malheureusement, l’IRM 3 T n’a permis de détecter qu’un faible nombre de lésions épileptogènes supplémentaires (5,6 %) d’où la nécessité d’explorer d’autres techniques. Dans les seconde et troisième études, nous avons examiné le potentiel de la SPIR pour localiser le foyer épileptique en analysant le comportement hémodynamique au cours de crises temporales et frontales. Ces études ont montré que les crises sont associées à une augmentation significative de l’hémoglobine oxygénée (HbO) et l’hémoglobine totale au niveau de la région épileptique. Bien qu’une activation contralatérale en image miroir puisse être observée sur la majorité des crises, la latéralisation du foyer était possible dans la plupart des cas. Une augmentation surprenante de l’hémoglobine désoxygénée a parfois pu être observée suggérant qu’une hypoxie puisse survenir même lors de courtes crises focales. Dans la quatrième et dernière étude, nous avons évalué l’apport de la MEG dans l’évaluation des patients avec épilepsie focale réfractaire considérés candidats potentiels à une chirurgie. Il s’est avéré que les localisations de sources des pointes épileptiques interictales par la MEG ont eu un impact majeur sur le plan de traitement chez plus des deux tiers des sujets ainsi que sur le devenir postchirurgical au niveau du contrôle des crises.Epilepsy is the most common chronic neurological disorder after stroke. The major form of treatment is long-term drug therapy to which approximately 30% of patients are unfortunately refractory to. Brain surgery is recommended when medication fails, especially if magnetic resonance imaging (MRI) can identify a well-defined epileptogenic lesion. Unfortunately, close to a quarter of patients have nonlesional refractory focal epilepsy. For these MRI-negative cases, identification of the epileptogenic zone rely heavily on remaining tools: clinical history, video-electroencephalography (EEG) monitoring, ictal single-photon emission computed tomography (SPECT), and a positron emission tomography (PET). Unfortunately, the limited spatial and/or temporal resolution of these localization techniques translates into poor surgical outcome rates. In this thesis, we explore three relatively novel techniques to improve the localization of the epileptic focus for patients with drug-resistant focal epilepsy who are potential candidates for epilepsy surgery: high-field 3 Tesla (T) MRI, near-infrared spectroscopy (NIRS) and magnetoencephalography (MEG). In the first study, we evaluated if high-field 3T MRI, providing a higher signal to noise ratio, could help detect subtle epileptogenic lesions missed by conventional 1.5T MRIs. Unfortunately, we show that the former was able to detect an epileptogenic lesion in only 5.6% of cases of 1.5T MRI-negative epileptic patients, emphasizing the need for additional techniques. In the second and third studies, we evaluated the potential of NIRS in localizing the epileptic focus by analyzing the hemodynamic behavior of temporal and frontal lobe seizures respectively. We show that focal seizures are associated with significant increases in oxygenated haemoglobin (HbO) and total haemoglobin (HbT) over the epileptic area. While a contralateral mirror-like activation was seen in the majority of seizures, lateralization of the epileptic focus was possible most of the time. In addition, an unexpected increase in deoxygenated haemoglobin (HbR) was noted in some seizures, suggesting possible hypoxia even during relatively brief focal seizures. In the fourth and last study, the utility of MEG in the evaluation of nonlesional drug-refractory focal epileptic patients was studied. It was found that MEG source localization of interictal epileptic spikes had an impact both on patient management for over two thirds of patients and their surgical outcome