Vahid Tavakoli

Assessment of Age-Related Changes in Left Ventricular Twist by 3-Dimensional Speckle-Tracking Echocardiography

The purpose of this study was to determine the normal value of left ventricular (LV) twist in 3‐dimensional (3D) geometry and to study the effects of aging on 3D LV twist by sophisticated newly developed 3D speckle‐tracking echocardiographic techniques.

Adaptive Multi-Resolution Myocardial Motion Analysis of B-Mode Echocardiography Images using Combined Local/Global Optical Flow

Since myocardial motion is directly related to cardiac vascular supply, it can be helpful in diagnosing the heart abnormalities. The most comprehensive and available imaging study of the cardiac function is echocardiography and therefore it is important to make the echocardiography motion more quantitative. To overcome the sensitivity to shear, rotation and wide range of motion, we propose an adaptive hybrid method based on combined local global (CLG) optical flow in combination with adaptive multi-resolution spatiotemporal spline moments. In adaptive multi-resolution strategy the coarse moments are applied on the coarse moving regions and the fine moments are applied on the fine moving areas. The fine and coarse moving regions are obtained using motion segmentation. The evaluation was performed on simulated, synthetic, real data. The proposed method achieved rotational error of 2.8 degrees per frame and amplitude error of 2.2 percent per frame. These results demonstrate a better performance with respect to other B-Mode echocardiography motion estimation techniques such as Lucas-Kanade, Horn-Shunck and spatiotemporal affine technique.

Optimized noninvasive monitoring of thermal changes on digital B-mode renal sonography during revascularization therapy.

Objective. Noninvasive real‐time thermal change monitoring of human internal organs can play a critical role in diagnosis and treatment of many disorders, including reperfusion of renal arteries during anticoagulation therapy. Methods. This article focuses on tissue temperature detection using ultrasound velocity changes in different structures and their related speckle shift from their primary locations on high‐quality B‐mode digital sonography. We evaluated different speckle‐tracking techniques and optimized them using appropriate motion estimation methods to determine the best algorithm and parameters. Results. Performing thermal detection methods on simulated phantoms showed a good correlation between speckle shifts and the ground truth temperature. For the simulated images, average thermal error was 0.5°C with an SD of 0.5°C, where lower errors can be obtained in noiseless (motionless) data. The proposed technique was evaluated on real in vivo cases during surgical occlusion and reopening of the renal segmental artery and showed the potential of the algorithm for observation of internal organ changes using only digital ultrasound systems for diagnosis and therapy. Conclusions. The adaptive Rood pattern search proved to be the best block‐matching technique, whereas the multiresolution Horn‐Schunck technique was the best gradient optical flow method. The extracted thermal change during in vivo revascularization therapy is promising. In addition, we present an evaluation of several block‐matching and optical flow motion estimation techniques.

A new variational technique for combining affine registration and optical flow in echocardiography images

Since myocardial motion is directly related to cardiac vascular supply, it can be helpful in diagnosing the heart abnormalities. The most comprehensive and available imaging study of the cardiac function is B-Mode echocardiography. However diagnostic systems are expert dependent and motion is not clear in the B-mode echocardiography images and therefore many efforts are pointed toward proposing new methods to measure the motion accurately. So far there have been many methods for myocardial motion estimation such as affine registration, elastic registration or optical flow but each method suffers from lack of accuracy. To increase the accuracy of motion detection techniques, we propose a new algorithm based on a variational technique to combine the efficiencies of optical flow methods and affine registration in combination with multi-resolution spatiotemporal Spline moments. The evaluation was performed on simulated, synthetic and real data. A comparison between the proposed method and several other methods shows its better performance to measure the motion more accurately in the presence of shear, rotation and noise. The proposed method achieved rotational error of 2.6 degrees per frame and amplitude error of 3.7 percent per frame. These results demonstrate a better efficiency with respect to other B-Mode echocardiography motion estimation techniques such as Lucas-Kanade, Horn-Schunck and spatiotemporal affine technique.

FPGA-core defibrillator using wavelet-fuzzy ECG arrhythmia classification

An electrocardiogram (ECG) feature extraction and classification system has been developed and evaluated using Quartus II 7.1 belong to Altera Ltd. In wavelet domain QRS complexes were detected and each complex was used to locate the peaks of the individual waves. Then, fuzzy classifier block used these features to classify ECG beats. Three types of arrhythmias and abnormalities were detected using the procedure. The completed algorithm was embedded into Field Programmable Gate Array (FPGA). The completed prototype was tested through software-generated signals, in which test scenarios covering several kinds of ECG signals on MIT-BIH Database. For the purpose of feeding signals into the FPGA, a software was designed to read signal files and import them to the LPT port of computer that was connected to FPGA. From the results, it was achieved that the proposed prototype could do real time monitoring of ECG signal for arrhythmia detection. We also implemented algorithm in a sequential structure device like AVR microcontroller with 16 MHZ clock for the same purpose. External clock of FPGA is 50 MHZ and by utilizing of Phase Lock Loop (PLL) component inside device, it was possible to increase the clock up to 1.2 GHZ in internal blocks. Final results compare speed and cost of resource usage in both devices. It shows that in cost of more resource usage, FPGA provides higher speed of computation; because FPGA makes the algorithm able to compute most parts in parallel manner.

Chemostratigraphy of the Permian–Triassic Strata of the Offshore Persian Gulf, Iran

This study focuses on the geochemistry of the Permian–Triassic boundary (PTB) of three wells in the Persian Gulf region. The δ 18 O shows a negative shift at the PTB that is due to meteoric diagenesis. The δ 13 C shows a decrease to about −1.4‰ in this event, which is comparable with the other Permian–Triassic sections elsewhere. The negative δ 13 C excursion could be used as a marker and represents an input of the 12 C to the sediments. The subsequent gradual positive shift after the boundary is related to the biotic recovery following the end-Permian mass extinction. Changes in the Th/U ratio of the studied wells indicate an anoxic environment at the end-Permian time, followed by a sudden increase of oxygen content at the PTB. This was coupled with the increasing PCO 2 and the presumably acidic conditions that were increasing toward the PTB. The Sr concentration shows a decreasing trend toward the PTB indicating normal acidity and PCO 2 conditions at the Dzhulfian (Wuchiaingian), and change of acidic conditions below the PTB in Dorashamian (Changhsingian) are inferred from the deposition of aragonite or calcite as primary dominant mineral, respectively. After this boundary, both redox and acidic conditions have been changed, and the environment was favorable for biotic restoration. Concurrent with these situations, the sea level was falling and reached its lowest level at the end-Permian time as inferred from the increase in Fe elemental content and Sr isotope as well as the decrease in oxygen isotope data.

The end-Permian regression in the western Tethys: sedimentological and geochemical evidence from offshore the Persian Gulf, Iran

Detailed sedimentological and geochemical records across the Permian–Triassic boundary (PTB) in five offshore wells of the central Persian Gulf served to interpret the end-Permian sea-level change in this region. A decrease in sea level at the PTB was established by petrographical and geochemical study of the boundary. Thin sections showed that Upper Permian strata are composed of dolomite with minor anhydrite, changing into limestone in Lower Triassic sediments. Brine dilution toward the boundary supports sea-level fall in the Permian–Triassic transition, reflected by a decrease in anhydrite content and a shallowing-upward trend from lagoonal to peritidal facies. Isotopic changes at the boundary are in favor of sea-level fall. Changes in both carbon (from about 4 to –1‰) and oxygen (from 2 to –5‰) stable isotopes show negative excursions. The shift in carbon isotope values is a global phenomenon and is interpreted as resulting from carbonate sediment interaction with 12C-rich waters at the end-Permian sea-level fall. However, the oxygen isotope shift is attributed to the effect of meteoric waters with negative oxygen isotope values. The increase in strontium isotope ratios is also consistent with the high rate of terrestrial input at the boundary. The effect of meteoric conditions during diagenesis is evident from vuggy and moldic porosities below the PTB. The following transgression at the base of the Triassic is evident from the presence of reworked fossils and intraclasts resulting from deposition from agitated water.

A Hybrid Fuzzy Based Algorithm for 3D Human Airway Segmentation

Segmentation of the human airway tree from volumetric computed tomography images is an important stage for many clinical applications such as virtual bronchoscopy. The main challenges of previously developed methods are to deal with two problems namely, leaking into the surrounding lung parenchyma during segmentation and the need to manually adjust the parameters. To overcome these problems, a multi- seeded fuzzy based region growing approach in conjunction with the spatial information of voxels is proposed. Comparison with a commonly used region growing segmentation algorithm shows that the proposed method retrieves more accurate results by achieving the specificity and sensitivity of 98.81% and 85.18%, respectively. The proposed algorithm needs no manually adjustment of parameters as well as any pre-filtering process, while leading to deliver the clinically accepted segmentation result with no leakage.

Ultrasound thermal change detection based on steerable filters

Growing tendency toward utilization of Laser and RF knives has opened a new port for thermal control applications in which ultrasound thermal detection is crucial. Ultrasound velocity is dependent on the thermal properties of the environment. In this paper we focus on tissue temperature detection using multiresolution steerable filter-based motion estimation. The proposed technique was evaluated on simulated and real in-vivo cases during surgical occlusion and reopening of renal segmental artery and demonstrated promising results for observation of internal organ temperature changes using only digital ultrasound systems for diagnosis and therapy. It is proved that being oriented in space and time, steerable filters can achieve more accurate results. Performing thermal detection methods on synthetic phantoms demonstrated good correlation between speckle shifts and the ground truth temperature. For the simulated images average thermal error was 0.68 degrees Celsius with a standard deviation of 0.79.

Design of an Optimized Mother Wavelet Function for TEOAE Signal Denoising

The aim of this work is to provide a quantitative approach to the problem of matching a mother wavelet to Transient Evoked Otoacoustic Emission (TEOAE) signals by using tuning. A tuning curve was used as a template for designing a mother wavelet that has the maximum matching to the tuning curve. The scaling function was calculated from the matched mother wavelet and by using these functions, lowpass and highpass filters were designed for a filter bank and otoacoustic emissions signal analysis and synthesis. After signal analyzing, denoising is performed by time windowing the signals time-frequency components. By using the matched wavelet in otoacoustic emission signal denoising, it is possible to enhance signal to noise ratio up to 7 dB. The wavelet generated from this algorithm was remarkably similar to the Biorthogonal wavelets. Therefore, a high resolution time-frequency analysis for the otoacoustic emission signals is possible.