Volume 64, Issue 3

Due to the declining instances of organ donation, total artificial heart (TAH) therapy is of increasing importance for the management of end-stage biventricular heart failure. We introduce the currently most important established and novel TAH systems (SynCardia, CARMAT, ReinHeart, BiVACOR), report clinical outcomes and discuss technical requirements for the successful implementation of TAH therapy as an alternative to cardiac transplantation.

Bioresorbable scaffolds (BRS) promise to be the treatment of choice for stenosed coronary vessels. But higher thrombosis risk found in current clinical studies limits the expectations. Three hemodynamic metrics are introduced to evaluate the thrombosis risk of coronary stents/scaffolds using transient computational fluid dynamics (CFD). The principal phenomena are platelet activation and effective diffusion (platelet shear number, PSN), convective platelet transport (platelet convection number, PCN) and platelet aggregation (platelet aggregation number, PAN) were taken into consideration. In the present study, two different stent designs (thick-strut vs. thin-strut design) positioned in small- and medium-sized vessels (reference vessel diameter, RVD=2.25 mm vs. 2.70 mm) were analyzed. In both vessel models, the thick-strut design induced higher PSN, PCN and PAN values than the thin-strut design (thick-strut vs. thin-strut: PSN=2.92/2.19 and 0.54/0.30; PCN=3.14/1.15 and 2.08/0.43; PAN: 14.76/8.19 and 20.03/10.18 for RVD=2.25 mm and 2.70 mm). PSN and PCN are increased by the reduction of the vessel size (PSN: RVD=2.25 mm vs. 2.70 mm=5.41 and 7.30; PCN: RVD=2.25 mm vs. 2.70 mm=1.51 and 2.67 for thick-strut and thin-strut designs). The results suggest that bulky stents implanted in small caliber vessels may substantially increase the thrombosis risk. Moreover, sensitivity analyses imply that PSN is mostly influenced by vessel size (lesion-related factor), whereas PCN and PAN sensitively respond to strut-thickness (device-related factor).

Oscillometry is the most popular technique for automatic blood pressure (BP) estimation. This method relies on recording the cuff deflation curve (CDC) from a high suprasystolic BP (SSBP) to a low subdiastolic BP (SDBP) and is very sensitive to noise caused by breathing, motion artifacts, muscle contraction and the environment. We developed a unified BP estimation method involving two integrated sub-procedures based on the arterial lumen area (ALA) model and applied it for continuous BP measurement. Our proposed method is coefficient free and continuous. No empirical coefficients are applied, and the CDC varies within a low-pressure range of 40–80 mm Hg, which can be sustainably imposed on our wrists. The first sub-procedure estimates the mean arterial pressure (MAP) and arterial compliance parameter b under a complete CDC period. In the second sub-procedure, the systolic BP (SBP) and diastolic BP (DBP) are estimated based on the dynamic-updated oscillometric waveform. We applied this method on 300 continuously oscillometric traces recorded from 20 male and female healthy subjects aged 20–60 years. The validated results were compared with those from a double stethoscope check. We observed mean absolute errors of 4.77 and 4.24 mm Hg in estimating the SBP and DBP, respectively.

The presence of high-frequency velocity fluctuations in aneurysms have been confirmed by in-vivo measurements and by several numerical simulation studies. Only a few studies have located and recorded wall vibrations in in-vitro experiments using physiological patient models. In this study, we investigated the wall fluctuations produced by a flowing perfusion fluid in a true-to-scale elastic model of a cerebral fusiform aneurysm using a laser Doppler vibrometer (LDV). The model was obtained from patient data. The experimental setup reproduced physiologically relevant conditions using a compliant perfusion system, physiological flow parameters, unsteady flow and a non-Newtonian fluid. Three geometrically identical models with different wall elasticities were used for measurements. The influence of five different flow rates was considered. Wall vibrations were predominantly found at frequencies in the range 40–60 Hz and 255–265 Hz. Their amplitude increased with increasing elasticity of the model, but the spectral peaks remained at about the same frequency. Varying the flow rate produced almost no changes in the frequency domain of the models. The frequency of the spectral peaks varied slightly between points at the lateral wall and at the bottom of the aneurysm. Indeed, embedding the model in a fluid during measurements produced higher and smoother amplitude fluctuations.

The physiological modeling of retinal layers to provide an insight into how the incoming image is converted into its equivalent spike train that can be decoded by the human brain is a key issue. Most of the retinal layer models concentrate mainly on image compression, edge detection and image reconstruction. A retinal layer model to generate spike waveform corresponding to the visual information is not covered much in the literature. The aim of this study was to develop a mathematical model of retinal layers that has complex neural structures, that can detect the incoming signal and transform the signal into the equivalent spike train. The proposed retinal layer model includes a photoreceptor, an outer plexiform (OPL), an inner plexiform (IPL) and ganglion cell layers exhibiting the properties of compression, luminance and spatial temporal filtering in the processing of visual information. The photoreceptor layer enhances the contrast visibility in the dark region and maintains the same in the bright regions. The OPL is modeled to enhance the contour of the image. The finer detail of the image is extracted by mathematically modeling the IPL. The ganglion cell layer is modeled using the Hodgkin-Huxley model to generate the spike train for the incoming information. The spike train was generated for color deficient individuals namely protanopia, deuteranopia, tritanopia and for individuals suffering from night blindness. Simulation results showed a spike train was generated only for a certain threshold stimulus value. The differences in spike pattern for a normal and visually impaired individual were studied. This may lead to a methodology for earlier diagnosis.

Diabetes mellitus is an enduring disease related with significant morbidity and mortality. The main pathogenesis behind this disease is its numerous micro- and macrovascular complications. In developing countries, diabetic retinopathy (DR) is one of the major sources of vision impairment in working age population. DR has been classified into two categories: proliferative diabetic retinopathy (PDR) and non-proliferative diabetic retinopathy (NPDR). NPDR is further classified into mild, moderate and severe, while PDR is further classified into early PDR, high risk PDR and advanced diabetic eye disease. DR is a disease caused due to high blood glucose levels which result in vision loss or permanent blindness. High-level advancements in the field of bio-medical image processing have speeded up the automated process of disease diagnoses and analysis. Much research has been conducted and computerized systems have been designed to detect and analyze retinal diseases through image processing. Similarly, a number of algorithms have been designed to detect and grade DR by analyzing different symptoms including microaneurysms, soft exudates, hard exudates, cotton wool spots, fibrotic bands, neovascularization on disc (NVD), neovascularization elsewhere (NVE), hemorrhages and tractional bands. The visual examination of the retina is a vital test to diagnose DR-related complications. However, all the DR computer-aided diagnostic systems require a standard dataset for the estimation of their efficiency, performance and accuracy. This research presents a benchmark for the evaluation of computer-based DR diagnostic systems. The existing DR benchmarks are small in size and do not cover all the DR stages and categories. The dataset contains 1445 high-quality fundus photographs of retinal images, acquired over 2 years from the records of the patients who presented to the Department of Ophthalmology, Holy Family Hospital, Rawalpindi. This benchmark provides an evaluation platform for medical image analysis researchers. Furthermore, it provides evaluation data for all the stages of DR.

Human activity recognition (HAR) is a research hotspot in the field of artificial intelligence and pattern recognition. The electrooculography (EOG)-based HAR system has attracted much attention due to its good realizability and great application potential. Focusing on the signal processing method of the EOG-HAR system, we propose a robust EOG-based saccade recognition using the multi-channel convolutional independent component analysis (ICA) method. To establish frequency-domain observation vectors, short-time Fourier transform (STFT) is used to process time-domain EOG signals by applying the sliding window technique. Subsequently, we apply the joint approximative diagonalization of eigenmatrix (JADE) algorithm to separate the mixed signals and choose the “clean” saccadic source to extract features. To address the problem of permutation ambiguity in a case with a six-channel condition, we developed a constraint direction of arrival (DOA) algorithm that can automatically adjust the order of eye movement sources according to the constraint angle. Recognition experiments of four different saccadic EOG signals (i.e. up, down, left and right) were conducted in a laboratory environment. The average recognition ratios over 13 subjects were 95.66% and 97.33% under the between-subjects test and the within-subjects test, respectively. Compared with “bandpass filtering”, “wavelet denoising”, “extended infomax algorithm”, “frequency-domain JADE algorithm” and “time-domain JADE algorithm, the recognition ratios obtained relative increments of 4.6%, 3.49%, 2.85%, 2.81% and 2.91% (within-subjects test) and 4.91%, 3.43%, 2.21%, 2.24% and 2.28% (between-subjects test), respectively. The experimental results revealed that the proposed algorithm presents robust classification performance in saccadic EOG signal recognition.

Brain-computer interface (BCI) applications such as keyboard control and vehicular navigation present significant assistive merit for disabled individuals. However, there are limitations associated with BCI paradigms which restrict a wider adoption of BCI technology. For example, rapid serial visual presentation (RSVP) paradigms can induce seizures in photosensitive epileptic subjects. This paper evaluates the novel mirrored-word reading paradigm (MWRP) for BCI implementation using an offline experimental study. The offline study obtained an average single-trial classification accuracy of 74.10%. The results also demonstrate that the use of multiple trials for classification can increase the accuracy as is common with BCIs. The developed MWRP-based BCI also utilized a low presentation frequency which averts the possibility of paradigm induced photosensitivity. However, there are multiple avenues for future work. The MWRP can be implemented in the online format for real-time device control. For example, a vehicular application platform can be used where the word orientation represents directions for travel. The MWRP can also be investigated across a wider range of stimulus presentation parameters such as timing, color and stimulus size. Such studies can be used to suggest further improvements to the paradigm which can enhance its applicability for online device control.

Spinal implants are commonly used in the treatment of spinal disorders or injuries. However, the biomechanical analyses of them are rarely investigated in terms of both biomechanical and clinical perspectives. Therefore, the main purpose of this study is to investigate the effects of rod diameter on the biomechanical behavior of spinal implants and to make a comparison among them. For this purpose, three spinal implants composed of pedicle screws, setscrews and rods, which were manufactured from Ti6Al4V, with diameters of 5.5 mm, 6 mm and 6.35 mm were used and a bilateral vertebrectomy model was applied to spinal systems. Then, the obtained spinal systems were tested under static tension-compression and fatigue (dynamic compression) conditions. Also, failure analyses were performed to investigate the fatigue behavior of spinal implants. After static tension-compression and fatigue tests, it was found that the yield loads, stiffness values, load carrying capacities and fatigue performances of spinal implants enhanced with increasing spinal rod diameter. In comparison to spinal implants with 5.5 mm rods, the fatigue limits of implants showed 13% and 33% improvements in spinal implants having 6 mm and 6.35 mm rods, respectively. The highest static and fatigue test results were obtained from spinal implants having 6.35 mm rods among the tested implants. Also, it was observed that the increasing yield load and stiffness values caused an increase in the fatigue limits of spinal implants.

Purpose For the treatment of malignant diseases of the oral cavity and the larynx, a total or partial resection is the standard therapy, while in special cases chemo- and/or external radiation therapy is considered. Transoral access reduces trauma and hospitalization time. Transoral surgery is usually executed using external microscopic imaging. Therefore, the microscope is placed in the visual line of the opening of the mouth and throat. However, specific anatomical structures like the posterior commissure (dorsal end of the vocal cords) are not visible in these procedures. An endoscopic approach can improve this problem. We introduce a new prototype system for endoscopic assisted transoral surgery. Methods Based on clinical observation and discussions with professional users and surgeons, the clinical need was identified and specified. A general concept or an endoscopic manipulator to assist microlaryngeal surgery was designed. For that a steerable rigid endoscope was combined with an actuator that allows translational and rotational movement. A quick release fastener was designed allowing for fast change of the endoscope and independence from its shape and type. The actuator was fixed on a commercially available, semi-active medical holding arm for easy positioning. The holder can be fixed to the standard rails of the surgical table. The piezoelectric drives integrated in the actuator are activated with a foot pedal. This allows easy and fast fine positioning, while the hands are free to perform the surgery with standard instruments for microlaryngeal surgery. Results A prototype of the system for endoscopic assisted transoral surgery was developed. The entire technical setup was tested in terms of usability and performance in a simulated surgical scenario. A basic phantom, representing the throat and vocal cords was created and placed on a surgical table. The system was installed on the table and the clinical workflow of a simulated endoscopic assisted surgery on the vocal cords was performed. The performance of the setup and the procedure success was evaluated by clinical users. Conclusion Fixture of the system on the surgical table is fast and easy due to its low weight and compact design. The medical holder allows a fast initial positioning of the system in front of the phantom patient. An easy insertion and removal of the endoscope was realized using the quick release fastener. The developed endoscope fixation is universally adaptable and not limited to a single type of endoscope. The piezoelectric drives, combined with the foot pedal, allow a precise placement and readjustment of the endoscope during surgery. The use of a multi view endoscope enables a variable view on the surgical situs. The size and shape of the whole setup offer excellent access to the targeted structures. The development was classified beneficial by the clinical users.

Digital silicon photomultiplier (dSiPM) is introduced for diffuse optical imaging (DOI) applications instead of conventional photomultiplier tubes and avalanche photodiodes (APDs) as a state-of-the-art detector. According to the low-level light regime in DOI applications, high sensitivity and high dynamic range (DR) image sensors are needed for DOI systems. dSiPM is proposed as a developing detector which can detect low-level lights. Also, an accurate equation is obtained for calculating the DR of dSiPMs. Different dSiPMs and the corresponding benefits are studied for DOI applications. Furthermore, a 120 dB DR dSiPM is chosen for use in DOI systems. It is shown that dSiPMs can be utilized in DOI configurations such as time domain (TD), frequency domain (FD) and continuous wave (CW) systems. Ultimately, by utilizing dSiPM in DOI systems, the DOI method can be used for thoracic imaging due to the high DR and signal-to-noise ratio (SNR) of the detector.

The gold standard for estimating blood alcohol content (BAC) after alcohol consumption is a blood sample analysis. An innovative technology to estimate BAC is based on impedance cardiography and bioimpedance spectroscopy (BIS). This study investigated whether it is possible to estimate increasing blood alcohol levels during a drinking trial with bioimpedance measurement techniques. Twenty-one healthy volunteers were assigned to a test (ethanol) group (ETH) or a reference group (H 2 O). After baseline measurements, the ETH group ingested 120 ml of vodka, followed by a resorption phase of 50 min. Then, bioimpedance and breath alcohol measurements were performed. Thereafter, 60 ml of vodka was ingested and another resorption phase of 50 min was followed by bioimpedance and breath alcohol measurements. This procedure was repeated until alcohol levels exceeded 0.4 mg/l. The H 2 O group performed in the same way with water. For all measurements, extracellular resistance (R e ) and the base impedance (Z 0 ) were computed. Regarding BIS, several parameters differed significantly between the ETH and the H 2 O group. R e increased in ETH (p=0.005), but not in the H 2 O group when comparing the first and last measurements. Z 0 also increased significantly in the ETH group (p=0.001). To conclude, with BIS measurements, it is possible to measure increasing blood alcohol levels.