Mustafa Zahid Yildiz

An Optoelectromechanical Tactile Sensor for Detection of Breast Lumps

We developed a compact tactile imaging (TI) system to guide the clinician or the self-user for noninvasive detection of breast tumors. Our system measures the force distribution based on the difference in stiffness between a palpated object and an abnormality within. The average force resolution, force range, and the spatial resolution of the device are 0.02 N, 0-4 N, and 2.8 mm, respectively. To evaluate the performance of the proposed TI system, compression experiments were performed to measure the sensitivity and specificity of the system in detecting tumor-like inclusions embedded in tissue-like cylindrical silicon samples. Based on the experiments performed with 11 inclusions, having two different sizes and two different stiffnesses located at three different depths, our TI system showed an average sensitivity of 90.8 ± 8.1 percent and an average specificity of 89.8 ± 12.7 percent. Finally, manual palpation experiments were performed with 12 human subjects on the same silicon samples and the results were compared to that of the TI system. The performance of the TI system was significantly better than that of the human subjects in detecting deep inclusions while the human subjects performed slightly better in detecting shallow inclusions close to the contact surface.

Relationship between vibrotactile detection threshold in the Pacinian channel and complex mechanical modulus of the human glabrous skin

The goal of this study was to investigate the relationship between the psychophysical vibrotactile thresholds of the Pacinian (P) channel and the mechanical properties of the skin at the fingertip. Seven healthy adult subjects (age: 23–30) participated in the study. The mechanical stimuli were 250-Hz sinusoidal bursts and applied with cylindrical contactor probes of radii 1, 2, and 3.5 mm on three locations at the fingertip. The duration of each burst was 0.5 s (rise and fall time: 50 ms). The subjects performed a two-interval forced-choice task while the stimulus levels changed for tracking the threshold at 75% probability of detection. There were significant main effects of contactor radius and location (two-way ANOVA, values of p < 0.001). The thresholds decreased as the contactor radius increased (i.e., spatial summation effect) at all locations. The thresholds were lowest near the whorl at the fingertip. Additionally, we measured the mechanical impedance (specifically, the storage and loss moduli) at the contact locations. The storage moduli did not change with the contactor location, but the loss moduli were lowest near the whorl. While the loss moduli decreased, the storage moduli increased (e.g., more springiness) as the contactor radius increased. There was moderate and barely significant correlation between the absolute thresholds and the storage moduli (r = 0.650, p = 0.058). However, the correlation between the absolute thresholds and the loss moduli was high and very significant (r = 0.951, p < 0.001). The results suggest that skin mechanics may be important for locally shaping psychophysical detection thresholds, which would otherwise be expected to be constant due to uniform Pacinian innervention density at the fingertip.

Effects of passive and active movement on vibrotactile detection thresholds of the Pacinian channel and forward masking

Abstract We investigated the gating effect of passive and active movement on the vibrotactile detection thresholds of the Pacinian (P) psychophysical channel and forward masking. Previous work on gating mostly used electrocutaneous stimulation and did not allow focusing on tactile submodalities. Ten healthy adults participated in our study. Passive movement was achieved by swinging a platform, on which the participant’s stimulated hand was attached, manually by a trained operator. The root-mean-square value of the movement speed was kept in a narrow range (slow: 10–20 cm/s, fast: 50–60 cm/s). Active movement was performed by the participant him-/herself using the same apparatus. The tactile stimuli consisted of 250-Hz sinusoidal mechanical vibrations, which were generated by a shaker mounted on the movement platform and applied to the middle fingertip. In the forward-masking experiments, a high-level masking stimulus preceded the test stimulus. Each movement condition was tested separately in a two-interval forced-choice detection task. Both passive and active movement caused a robust gating effect, that is, elevation of thresholds, in the fast speed range. Statistically significant change of thresholds was not found in slow movement conditions. Passive movement yielded higher thresholds than those measured during active movement, but this could not be confirmed statistically. On the other hand, the effect of forward masking was approximately constant as the movement condition varied. These results imply that gating depends on both peripheral and central factors in the P channel. Active movement may have some facilitatory role and produce less gating. Additionally, the results support the hypothesis regarding a critical speed for gating, which may be relevant for daily situations involving vibrations transmitted through grasped objects and for manual exploration.

A novel tactile sensor for detecting lumps in breast tissue

We developed a compact tactile sensor in order to guide the clinician or the self-user for non-invasive detection of lumps. The new design has an advantage over the existing discrete tactile sensors and detection methods by efficiently sensing force distribution over an area without any side effects. The sensor consists of 10×10 infrared emitter-detector pairs, a silicon-rubber elastic pad, and a contoured tactile interface (25×21 moving pins) for palpating three-dimensional objects. To demonstrate the practical use of the sensor, first a cylindrical tissue-like silicon phantom was prepared, then a 13 mm diameter rigid spherical object was placed at varying depths of 0-20 mm to simulate cancerous lumps in breast tissue, and finally the tactile sensor was systematically pressed on the phantom to successfully detect the lumps for compression depths of 10- 24 mm. The location and the estimated radius of each lump were calculated from the recorded tactile images.

İnme Rehabilitasyonunda Kullanılabilecek Kablo ve Yay Tahrikli Giyilebilir Bir El Bileği Egzersiz Cihazı Tasarımı

Inme, her yil milyonlarca kisiyi etkilemektedir. Bu kisilerin cogu, hareket kabiliyetlerini geri kazanabilmek icin rehabilitasyona ihtiyac duymaktadirlar. El kaslarinin robotik temelli rehabilitasyonuna yonelik cok sayida cihaz onerilmis olmasina ragmen bu cihazlarin hala gelistirilmesi gereken yonleri vardir. Onceki cihazlarda kuvvet ve hareket aktarimi icin kullanilan yontemlerin bir takim olumsuz yonleri bulunmaktadir. Bunlardan biri, cihazlarda kullanilan mafsallar ile el ve el bilegi eklemlerinin donme merkezlerinin tam olarak hizalanamamasidir. Bu durum, vucut eklemleri uzerinde kesme kuvvetleri olusturmaktadir. Donme merkezlerini hizalamak icin uygulanan yontemlerin bazi dezavantajlari bulundugundan yeni uygulamalara ihtiyac vardir. Bu calismada, el bilegi egzersizlerini gerceklestirmek amaciyla yeni bir cihaz onerilmektedir. Cihaz, hareket ve kuvvet aktarimini kablo ve yay tahriki ile yapmaktadir. Boylece donme merkezlerinin hizalanmasi sorunu yasanmamaktadir. Cihaz, pasif ve aktif egzersizlere olanak saglamaktadir. Cihazin ev ortaminda kullanima uygun, tasinabilir ve dusuk maliyetli olmasi amaclanmistir. Gelistirilen cihazin, rehabilitasyon maliyetlerini azaltmasi ve tedavi surecini kisaltmasi beklenmektedir. Cihaz, inme rehabilitasyonun yani sira sinir yaralanmasi, sinir sikismasi, tendon yaralanmasi, kiriklar ve spor yaralanmalari gibi durumlarda da kullanilabilir. Dusuk maliyetli olmasi beklenen cihazin, ticarilestirilmesi durumunda tibbi cihazlar alaninda dis pazarlara bagimli ulkemizin rekabet gucune katki yapmasi beklenmektedir .

Gömülü Sistem Tabanlı EKG Holter Cihazının Tasarlanması

Ulkemizde ve dunyada nufusun giderek yaslanmasi ve kalp rahatsizliklarinin artmasi, bu hayati organimizin faaliyetlerini surekli kontrol altinda tutma, tedavi surecinde ve oncesinde tum etkileri gozlemleme gibi ihtiyaclari dogurmaktadir. Calismanin temel amaci, acik kaynak kodlu, gelistirilmeye acik gomulu sistem tabanli tasinabilir bir EKG Holter cihazini gerceklestirmektir. Yapmis oldugumuz calisma uc asamadan olusmaktadir: Ilk asamada, bireyin Elektrokardiyografi (EKG) sinyalleri tasarladigimiz biyoenstrumantasyon yukseltici devresi ile toplanarak yaklasik 200 kat kuvvetlendirilmis ve sonraki sinyal isleme asamasina uygun hale getirilmistir. Şebeke gurultusunu bastirmak uzere EKG sinyallerine 50 Hz ‘lik centik filtre ve bant genisligi 0,01 – 130 Hz arasinda olan bant geciren filtre uygulanmistir. Ikinci asamada ise analog EKG isareti Analog Dijital Ceviriciler kullanilarak sayisallastirilmistir. Haberlesme protokolleri yazilarak gomulu sistem kartlariyla baglantisi kurulmustur. Uc farkli gomulu sistem karti ile sinyal isleme algoritmalari uygulanacak hale getirilmistir. Tasarladigimiz arayuz ilk olarak cok sayida kutuphane destegi olmasi sebebiyle Python dilinde gelistirilmis. Ancak bu dilin yazdigimiz sinyal isleme algoritmasini calistirma hizi yeterli olmadigindan C++ dilinde programlama yapilmaya gecilmistir. Ucuncu asamada, 10 farkli katilimcidan 100 sn. suresince 3’er adet a- dinlenme halinde ve b- merdiven inme cikma hareketinin ardindan EKG verileri kaydedilmistir. Daha sonra, Raspberry Pi, Beaglebone ve Odroid gomulu sistem kartlari arasindaki hiz farklari ve performanslari analiz edilerek karsilastirilmasi yapilmis ve sonuclar incelenmistir. Beaglebone kullanilarak ornekleme hizi 35 Hz’i gecemediginden EKG icin kullaniminin uygun olmadigi saptanmistir. Raspberry Pi ile ornekleme hizi 80 Hz civarinda kalmakta ve sadece nabiz hesabi icin kullanilabilecegi saptanmistir. Odroid’ de ise ornekleme hizi 250 Hz civarina cikabildiginden ECG analizi icin en uygun mikrobilgisayar olarak belirlenmistir.

The effect of psychophysical forward masking in the tactile Pacinian channel on somatosensory evoked responses

Tactile perception originates in the four psychophysical tactile channels. These channels are mediated by four corresponding receptor systems. Particularly, for the Pacinian tactile channel, the lowest tactile threshold of humans is approximately at 250 Hz. In this study, we measured frequency-following brain responses to 250-Hz vibratory stimuli with intensities at varying sensation levels. Initially, the absolute threshold of the Pacinian channel was measured using the two-interval forced-choice paradigm. The experiments were repeated with a masking stimulus (frequency: 250 Hz; intensity: SL+10, SL+20, SL+30 dB) which preceded the test-stimulus interval. As a result, the masked thresholds were elevated as a function of the masking-stimulus level, consistent with previous studies. Then, EEG signals were recorded over the somatosensory cortex (CPc-CPi) during vibrotactile stimulation, using the same protocol as described in psychophysical part of the experimets. The EEG signals were averaged 500 times, and analyzed by using Fourier and wavelet transforms. The difference between the total area of power spectrum during the masked test-stimulus and during the unmasked test stimulus interval was significant for SL+30 masking level (Wilcoxon signrank test p=0.013). In addition, the difference of power spectrum area at driving frequency between two cases was significant for SL+20 and SL+30 masking level p=0.013 and p=0.019 respectively. This is the first time that a neural correlate of psychophysical forward masking is demonstrated in the tactile system.

Frequency following brain oscillations evoked by vibrotactile stimulation of the distal phalanx in normal subjects

The sensory response upon vibrotactile stimuli is still not entirely understood. Previously, the responses of single units from mechanoreceptive afferents and cortical neurons have been studied. There is a thorough psychophysical literature on judgements of the presence, magnitude, and frequency of vibrotactile stimuli [1–3]. However, non-invasive recording of evoked responses on the scalp have solely been determined for electrical stimuli.In this study, psychophysical detection thresholds of adult subjects were measured at various mechanical frequencies. These values were found to be consistent with the literature. To measure the frequency following brain responses, stimulus intensities were determined based on psychophysical sensation levels. Data recorded from the somatosensory cortex area via electrodes placed on scalp, were analysed with wavelet transform. The results show that, as the mechanical stimulus intensity was increased, the background activity was suppressed and the frequency-following activity during stimulus period increased. This finding was statistically significant