VLSI Circuits for adaptive digital beamforming in ultrasound imaging

Cataloged from PDF version of article.For phased-array ultrasound imaging, alternative beamforming techniques and their VLSI circuits are studied to form a fully digital receive frontad hardware. In order to increase the timiig accuracy in beamforming, a computationally efficient interpolation scheme to increase the sampling rate is examined. For adaptive beamforming, a phase aberration correction method with very low computational complexity is described. Image quality performance of the method is examined by processing the non-aberrated and aberrated phased-array experimental data sets of an ultrasound resolution phantom. A digital beamforming scheme based on receive focusing at the raster focal points is examined. The sector images of the resolution phantom, reconstructed from the phased-array experimental data by beamforming at the radial and raster focal points, are presented for comparison of the image resolution performances of the two beamforming schemes. VLSI circuits and their implementations for the proposed techniques are presented

A phase aberration correction method for ultrasound imaging

Cataloged from PDF version of article.A computationally efficient method for phase aberration correction in ultrasound imaging is presented. The method is based on time delay estimation via minimization of the sum of absolute differences between radio frequency samples of adjacent array elements. Effects of averaging estimated aberration patterns over scan angles, and truncation to a single bit wordlength are examined. Phase distortions due to near-field inhomogeneities are simulated using silicone rubber aberrators. Performance of the method is tested using experimental data. Simulation studies addressing different factors affecting efficiency of the method, such as the number of iterations, window length, and the number of scan angles used for averaging, are presented. Images of a standard resolution phantom are reconstructed and used for qualitative testing

Influence of missing array elements on phase aberration correction for medical ultrasound

Cataloged from PDF version of article.The influence of missing array elements on aberration correction based on time delay estimation using radio frequency signals of neighboring elements is experimentally investigated. Normalized cross correlation and sum of absolute differences are employed as the cost functions in aberration estimation. Their performance is tested through various measurements using radio frequency data acquired with a 3.3 MHz, 64-element phased array. Variation of cost functions and phase estimation error are obtained for different combinations of number of missing elements, amount of aberration, and noise level. For a particular combination of these parameters, a set of B-scan images is reconstructed and presented to examine the effects of residual phase errors on image quality

Left Renal Vein Abnormalities Detected During Routine Abdominal Computed Tomography Imaging: Clinico-radiological Significance

Purpose: Preoperative knowledge of the presence of major venous anomalies facilitates the safe performance of aortic surgery. The purpose of the study was to estimate the incidence, as detected by abdominal computed tomography (CT), of major left renal vein anomalies related to the abdominal aorta in an adult population. Materials and methods: Seven hundred and fifty abdominal CT examinations were reviewed retrospectively for the presence of left renal vein anomalies. Eleven CT scans were excluded from the study because of technical or patient-related factors. The course of the left renal vein was assessed on the CT slices to detect any anomalies. Results: Left renal vein anomaly was detected in 23 (3.1%) of 739 cases. Seventeen (2.3%) of them were a retro-aortic and six (0.8%) of them were a circum-aortic left renal vein. Conclusion: It is important to detect left renal vein anomalies before retroperitoneal surgery or interventional procedures. These anomalies can be identified in routine abdominal CT examinations with a careful inspection

Radiation Impedance of an Array of Circular Capacitive Micromachined Ultrasonic Transducers

Cataloged from PDF version of article.The radiation impedance of a capacitive micromachined ultrasonic transducer (cMUT) with a circular membrane is calculated analytically using its velocity profile for the frequencies up to its parallel resonance frequency for both the immersion and the airborne applications. The results are verified by finite element simulations. The work is extended to calculate the radiation impedance of an array of cMUT cells positioned in a hexagonal pattern. A higher radiation resistance improves the bandwidth as well as the efficiency of the cMUT. The radiation resistance is determined to be a strong function of the cell spacing. It is shown that a center-to-center cell spacing of 1.25 wavelengths maximizes the radiation resistance, if the membranes are not too thin. It is also found that excitation of nonsymmetric modes may reduce the radiation resistance in immersion applications

Central region morphometry in a child brain; Age and gender differences

Background: Data on central region morphometry of a child brain is  important not only in terms of providing us with information about central region anatomy of the brain but also in terms of the help of this  information for the plans to be applied in neurosurgery.Objective: In the present study, central region morphometry of a child  brain in mid.sagittal MR images was analyzed in age and gender groups.Materials and Methods: Different points determined previously,  commissura posterior (PC) and the distances between cerebral cortex point (VCS) vertical to commissura anterior. commissura posterior line, sulcus centralis (CS), sulcus marginalis (MS), and the angle (α) between   CS-PC-MS were determined and measured together with difference of gender in three different age groups (aged 6.9, 10.13, and 14.17).Results: Central region measures of the brains of boys aged 6.17 are  higher than girls except for MS.PC distance. While VCS.PC, CS.PC, and MS-PC measures display a significant difference in the girls aged 14.17  when compared to the other age groups of 6.9 and 10.13 (P < 0.05), angle α is not significantly different in age and gender groups (P > 0.05). However, while VCS-PC, CS-PC and MS-PC distances show a significant  increase in girls beginning from the age of 14, this increase is limited in boys.Conclusion: Morphometric differences observed in different age groups in boys and girls shall contribute our evaluation of the alterations in brain development in both of genders and shall be useful in preparation of  surgical operation plans to be applied to the central region.Key words: Brain, central region, child, morphometry, magnetic resonance Imagin

Reduction of effects of inactive array elements in phase aberration correction

Phase aberration correction based on time delay estimation via minimization of sum of absolute difference (SAD) between radio frequency (RF) signals of neighboring elements is studied in the presence of missing elements. To examine the influence of inactive elements, phase estimation error is measured for various combinations of different number of missing elements, aberration level, and SNR. The measurements are performed on an experimental RF data set. Aberration delays of missing elements are interpolated using the phase estimate between the nearest active elements. The B-scan images are reconstructed for qualitative examination

Evaluation of the length and angulation of the styloid process in the patient with pre-diagnosis of Eagle syndrome

Clinical symptoms caused by the elongated styloid process (SP) or calcified stylohyoid ligament were first described by W. Eagle and they are now known as Eagle syndrome (ES). Normal length of SP was stated by Eagle as 2.5 cm. The objective of this study was to determine and discuss the length of SP and medial angulation degree with computed tomography (CT), which is an affective modality in the identification of ES, and a comparison with related studies. Three-dimensional (3D) images obtained from the axial CT scans of 22 cases (11 males and 11 females) aged between 24 and 80 years, who referred to Cumhuriyet University Hospital, Department of Radiology for multi slice CT with the pre-diagnosis of ES, were used. Lengths of the SP and medial angulations were measured on the obtained images. Inter- and intra-group comparisons were carried out using Wilcoxan and Mann-Whitney U tests. The mean length of the SP was found as 4.1 &#177; 1.1 cm. When inter- and intra-group lengths of the right and left SP were compared, the difference was not significant (p > 0.05). The mean medial angulation of the SP was found as 67.5 &#177; 5.1°. There was a significant difference found between the right side medial angulation and left side medial angulation in all persons (p < 0.05). Lengths of the right and left SP of the patients with pre-diagnosis of ES were close to each other. However, the right-side angulation was observed to be smaller than the left medial angulation in all the patients. Similarly, right side medial angulation of the females was smaller than the left side medial angulation, but this difference was absent in the males. Eagle syndrome should be kept in mind in patients with a sore throat radiating to the ears with swallowing and an observed non-compliance between the complaints such as feeling a foreign body in the throat and facial pain, and physical examination of those who do not have a response to long-term medical therapy should be performed. (Folia Morphol 2011; 70, 4: 295&#8211;299

Peptide functionalized superparamagnetic iron oxide nanoparticles as MRI contrast agents

Cataloged from PDF version of article.Magnetic resonance imaging (MRI) attracts great attention in cellular and molecular imaging due to its non-invasive and multidimensional tomographic capabilities. Development of new contrast agents is necessary to enhance the MRI signal in tissues of interest. Superparamagnetic iron oxide nanoparticles (SPIONs) are used as contrast agents for signal enhancement as they have revealed extraordinary magnetic properties at the nanometre size and their toxicity level is very low compared to other commercial contrast agents. In this study, we developed a new method to functionalize the surface of SPIONs. Peptide amphiphile molecules are used to coat SPIONs non-covalently to provide water solubility and to enhance biocompatibility. Superparamagnetic properties of the peptide-SPION complexes and their ability as contrast agents are demonstrated. In vitro cell culture experiments reveal that the peptide-SPION complexes are biocompatible and are localized around the cells due to their peptide coating

Optimization of a Collapsed Mode CMUT Receiver for Maximum Off-Resonance Sensitivity

We propose an airborne collapse capacitive micromachined ultrasonic transducer (CMUT) as a practical viable ultrasound transducer capable of providing a stable performance at the off-resonance frequencies. Traditional practice is to bias the CMUT plate close to collapse voltage to achieve high coupling coefficient and sense the incoming ultrasound as an open-circuit receive voltage signal of the transducer or short-circuit receive current (SCRC). Maintaining CMUT plate in the vicinity of collapse threshold is rather difficult. In this paper, an analytic approach to design an airborne collapsed-mode CMUT for maximum off-resonance sensitivity is presented. We use small-signal circuit model to evaluate the performance of a collapsed CMUT for varying operating conditions. CMUT operational parameters that yield the highest off-resonance SCRC are directly obtained from performance design curves. Collapsed CMUT plate is then biased in a critical biasing region that produces a stable and maximum off-resonance sensitivity. We experimentally verify and measure a stable sensitivity of a fabricated collapsed CMUT cell of -60 dB V/Pa at 100 kHz when biased between 50 to 65 V. We characterize our linear circuit model performance against the measured performance of collapsed CMUT in air within 4-dB tolerance. [2018-0058