提高B超图像质量的新途径

本文论述了一种提高B超图像质量的新途径。文中介绍了1/2间距波束扫描,电子多级聚焦,接收可变孔径控制等几种操作原理。在此基础上提出了高密集型用56阵元发射55阵元接收的探头新方案设想。     

一种新的超声成像方法振动声成像

文章介绍一种新的超声成像方法———振动声成像。首先从理论上分析了振动声成像的基本原理;然后分别介绍了该方法在钙化动脉血管成像、乳房中微钙化灶的检测以及受热疗和HIFU治疗的肿瘤组织焦斑检测等方面的应用;最后比较了振动声成像与传统超声成像不同点并指出了振动声成像独特的优势。     

A ring transducer system for medical ultrasound research.

An ultrasonic ring transducer system has been developed for experimental studies of scattering and imaging. The transducer consists of 2048 rectangular elements with a 2.5-MHz center frequency, a 67% -6 dB bandwidth, and a 0.23-mm pitch arranged in a 150-mm-diameter ring with a 25-mm elevation. At the center frequency, the element size is 0.30lambda x 42lambda and the pitch is 0.38lambda. The system has 128 parallel transmit channels, 16 parallel receive channels, a 2048:128 transmit multiplexer, a 2048:16 receive multiplexer, independently programmable transmit waveforms with 8-bit resolution, and receive amplifiers with time variable gain independently programmable over a 40-dB range. Receive signals are sampled at 20 MHz with 12-bit resolution. Arbitrary transmit and receive apertures can be synthesized. Calibration software minimizes system nonidealities caused by noncircularity of the ring and element-to-element response differences. Application software enables the system to be used by specification of high-level parameters in control files from which low-level hardware-dependent parameters are derived by specialized code. Use of the system is illustrated by producing focused and steered beams, synthesizing a spatially limited plane wave, measuring angular scattering, and forming b-scan images.     

A new hydroxyapatite-based biocomposite for bone replacement

Since the 1970s, various types of ceramic, glass and glass–ceramic materials have been proposed and used to replace damaged bone in many clinical applications. Among them, hydroxyapatite (HA) has been successfully employed thanks to its excellent biocompatibility. On the other hand, the bioactivity of HA and its reactivity with bone can be improved through the addition of proper amounts of bioactive glasses, thus obtaining HA-based composites. Unfortunately, high temperature treatments (1200 °C ÷ 1300 °C) are usually required in order to sinter these systems, causing the bioactive glass to crystallize into a glass–ceramic and hence inhibiting the bioactivity of the resulting composite. In the present study novel HA-based composites are realized and discussed. The samples can be sintered at a relatively low temperature (800 °C), thanks to the employment of a new glass (BG_Ca) with a reduced tendency to crystallize compared to the widely used 45S5 Bioglass®. The rich glassy phase, which can be preserved during the thermal treatment, has excellent effects in terms of in vitro bioactivity; moreover, compared to composites based on 45S5 Bioglass® having the same HA/glass proportions, the samples based on BG_Ca displayed an earlier response in terms of cell proliferation.     

一种新型的平面度检定方法

提出一种采用传感器技术测量平板平面度的方法,检测过程简单,数据处理简化,该方法的应用将较大地提高劳动效率,降低劳动强度,是值得推广的一种新型平面度检测方法。     

超声造影早期评价HIFU治疗兔移植性骨肿瘤的初步研究

目的:观察兔VX2移植性骨肿瘤经高强度聚焦超声(High Intensity Focused Ultrasound,HIFU)治疗前后超声造影的图像变化,以评价高强度聚焦超声治疗骨肿瘤的疗效。方法:将VX2瘤块植入20只兔的右侧胫骨髓腔内,三周后进行HIFU治疗。治疗前后均推注超声微泡造影剂,对肿瘤治疗前后的超声造影图像进行比较。结果:治疗前超声造影显示,右侧胫骨髓内肿瘤快速、明显强化,与周边组织分界清楚,测得病灶平均大小为,上下径(17.614±0.955)mm,前后径(10.414±1.142)mm。治疗后造影,治疗区域显示为造影剂灌注缺损区,平均范围为上下径(8.010±0.584)mm,前后径(7.540±0.499)mm,未经治疗的肿瘤组织仍有超声造影剂灌注。结论:超声造影成像清楚地显示肿瘤范围以及治疗后灌注缺损区的大小,通过反映治疗后肿瘤的血供改变来评价HIFU治疗肿瘤的疗效。     

单频超声和双频复合超声的空化效应实验研究

从超声电功率、超声作用时间和溶液温度来研究超声的空化效应,采用碘化钾溶液中碘的释放量来测定超声的空化产额,研究结果表明：在相同的电功率输入情况下,双频复合超声（25kHz/40kHz）释放碘的量远大于单频25kHz超声和单频40kHz超声释放的碘的量,双频复合超声的空化产额高于单频超声。     

A new high intensity focused ultrasound applicator for surgical applications

Improved high-intensity focused ultrasound (HIFU) surgical applicators are required for use in a surgical environment. We report on the performance and characteristics of a new solid-cone HIFU applicator. Previous HIFU devices used a water-filled stand-off to couple the ultrasonic energy from the transducer to the treatment area. The new applicator uses a spherically-focused element and a solid aluminum cone to guide and couple the ultrasound to the tissue. Compared with the water-filled applicators, this new applicator is simpler to set up and manipulate, cannot leak, prevents the possibility of cavitation within the coupling device, and is much easier to sterilize and maintain during surgery. The design minimizes losses caused by shear wave conversion found in tapered solid acoustic velocity transformers operated at high frequencies. Computer simulations predicted good transfer of longitudinal waves. Impedance measurements, beam plots, Schlieren images, and force balance measurements verified strong focusing and suitable transfer of acoustic energy into water. At the focus, the -3 dB beam dimensions are 1.2 mm (axial)×0.3 mm (transverse). Radiation force balance measurements indicate a power transfer efficiency of 40%. In vitro and in vivo tissue experiments confirmed the applicator's ability to produce hemostasis     

Choosing the best set of quality judges: A new quality tool

This article presents a technique which allows one to choose the ‘best’ set of quality judges. The methodology can be applied to any situation requiring discernment of a qualified inspector of products or service. The approach presented in this article selects judges who align their quality criteria with the prevailing expert. Multidimensional scaling is conducted on a disagreement matrix formed by executing multiple pairwise comparisons. An example of voice quality judging is included in the article as a practical example of the technique.     

A new coded-excitation ultrasound imaging system. I. Basicprinciples

A new approach to ultrasound imaging with coded-excitation is presented. The imaging is performed by reconstruction of the scatterer strength on an assumed grid covering the region of interest (ROI). Our formulation is based on an assumed discretized signal model which represents the received sampled data vector as a superposition of impulse responses of all scatterers in the ROI. The reconstruction operator is derived from the pseudo-inverse of the linear operator (system matrix) that produces the received data vector. The singular value decomposition (SVD) method with appropriate regularization techniques is used for obtaining a robust realization of the pseudo-inverse. Under simplifying (but realistic) assumptions, the pseudo-inverse operator (PIO) can be implemented using a bank of transversal filters with each filter designed to extract echoes from a specified image line. This approach allows for the simultaneous acquisition of a large number of image lines. This could be useful in increasing frame rates for two-dimensional imaging systems or allowing for real-time implementation of three-dimensional imaging systems. When compared to the matched filtering approach to similar coded-excitation systems, our approach eliminates correlation artifacts that are known to plague such systems. Furthermore, the lateral resolution of the new system can exceed the diffraction limit imposed on conventional imaging systems utilizing delay-and-sum beamformers. The range resolution is compared to that of conventional pulse-echo systems with resolution enhancement (our PIO behaves as a pseudo-inverse Wiener filter in the range direction). Both simulation and experimental verification of these statements are given     

A new bioadhesive for in vivo bone adhesion

A new bone adhesive was used to facilitate the union of bone fragments detached and repositioned on the tibia of dogs. The sites were X-rayed and histologically examined 1 and 6 weeks post-operatively. By 6 weeks, the bone fragments were found to be solidly attached in their original sites. Histological examination revealed no signs of inflammation, infection or any other adverse reactions, neither on the operated bone, nor in remote tissues of internal organs (spleen, lung, liver, kidney, and lymph nodes). The tested specimens exhibit, de novo bone growth into the adhesive, concomitant with clear signs of biodegradation of the adhesive. Additional in vivo experiments were carried out in white rats, whereby the adhesive was implanted subcutaneously and it became evident that the implanted material enabled new bone formation (ectopic), with no adverse effects within the immediate site as well as in the remote areas. Moreover, the biocompatible nature of the material revealed distinct signs of biodegradability.     

Heating of bone and soft tissue by ultrasound

Abstract

The absorption of ultrasound in human tissue always causes some local increase in temperature. In the case of ultrasound imaging, the power is usually much less than that used therapeutically and is unlikely to produce any significant physiological effect. However, a reliable means of calculating the maximum temperature rise to be expected in any given case will assist in both the development and the safe use of new ultrasound devices. To validate earlier work on ultrasonic tissue heating, including both experiment and finite element modelling (FEM), an analytical method is described for calculating the steady-state temperature rise along the axis of an axially symmetrical beam of ultrasound incident through water on a two-layer phantom consisting of agar gel and a bone mimic, the practical beam profile being modelled by a pair of coaxial Gaussian functions. It is shown that, in the absence of perfusion, the steady-state temperature distribution for the extended heat source generated by the ultrasound absorption can be obtained by integrating the point-source solution to the Bioheat transfer equation (BHTE). The boundary conditions associated with the difference in thermal properties of the mimic materials are satisfied by introducing images of the extended heat source in the gel/bone–mimic interface.     

A new imaging strategy using wideband transient response of ultrasound contrast agents

High-resolution clinical systems operating near 15 MHz are becoming more available; however, they lack sensitive harmonic imaging modes for ultrasound contrast agent (UCA) detection, primarily due to limited bandwidth. When an UCA is driven to nonlinear oscillation, a very wideband acoustic transient response is produced that extends beyond 15 MHz. We propose a novel strategy using two separate transducers at widely separated frequencies and arranged confocally to simultaneously excite and receive acoustic transients from UCAs. Experiments were performed to demonstrate that this new mode shows similar resolution, higher echo amplitudes, and greatly reduced attenuation compared to transmission at a higher frequency, and superior resolution compared to transmission and reception at a lower frequency. The proposed method is shown to resolve two 200 microm tubes with centers separated by 400 microm. Strong acoustic transients were detected for rarefaction-first 1-cycle pulses with peak-negative pressures above 300 kPa. The results of this work may lead to uses in flow and/or targeted imaging in applications requiring very high sensitivity to contrast agents.     

A new synthetic aperture focusing method to suppress the diffraction of ultrasound

Spatial resolution of an ultrasound image is limited by diffraction of ultrasound as it propagates along the axial direction. This paper proposes a method for reducing the diffraction spreading effect of ultrasound by using a synthetic aperture focusing (SAF) method that uses plane waves instead of spherical waves. The new method performs data acquisition and beamforming in the same manner as conventional SAF methods. The main difference is that all array elements are used on each firing to generate a plane wave, the traveling angle of which varies with the position of a receive subaperture. On reception, each scan line is formed by synthesizing RF samples acquired by relevant receive subapertures with delays to force the plane waves to meet at each imaging point. Theoretical analysis and computer simulation with infinite transmit aperture show that the proposed method is capable of suppressing the diffraction of ultrasound and especially causing the lateral beam width to remain unchanged beyond a certain depth determined by the size of a receive subaperture and the maximum traveling angle of plane waves. It is demonstrated that the proposed method is realizable using a linear array transducer. It is also shown that the lateral radiation pattern produced by the proposed method has smaller beam width than that using conventional SAF methods in the region of interest because it suppresses the diffraction of ultrasound.     

The electromechanical properties of fluid-filled bone: A new dimension

The current understanding of electromechanical effects in fully hydrated bone is that they are electrokinetic (streaming potential) in nature. The presence of a second competing mechanism, piezoelectricity, which dominates in dry conditions, has been denied in conditions of full hydration based on the absence of a piezoelectric response from wet collagen. Since the mineralized collagenous matrix of bone can only absorb 26 wt% water (Relative Humidity (RH)=60%), there seems no reason to dismiss a piezoelectric component entirely and experimental evidence was sought using a new measuring technique. A comprehensive analysis has been developed to relate both mechanisms to bone structure at different levels of hydration. Our results indicate the presence of both mechanisms at full hydration, with the piezoelectric effect leading streaming potential in the time domain. The immediate implication of this finding is that it is the piezoelectric effect which determines the characteristics of the generated electrical signal and may subsequently influence bone generation and remodelling.     

A conceptually new type of bio-hybrid scaffold for bone regeneration

Magnetic bio-hybrid porous scaffolds have been synthesized, nucleating nano-apatite in situ on self-assembling collagen, in the presence of magnetite nano-particles. The magnetic phase acted as a sort of cross-linking agent for the collagen, inducing a chemico-physical-mechanical stabilization of the material and allowing us to control the porosity network of the scaffold. Gradients of bio-mineralization and magnetization were also developed for osteochondral application. The good potentiality of the material as a biomedical device, able to offer assistance to bone regeneration through scaffold reloading with specific factors guided by an external magnetic field, has been preliminarily investigated. Up to now the proof of this concept has been realized through in vitro assessments.     

Promoting quality improvement research

The authors show how an internal grant program can stimulate quality improvement research by providing technical and financial support to clinicians and employees.     

A programmable real-time system for development and test of new ultrasound investigation methods

In vitro and/or in vivo experimental tests represent a crucial phase in the development of new ultrasound (US) investigation methods for biomedical applications. Such tests frequently are made difficult by the lack of flexibility of general purpose instruments and commercial US machines typically available in research laboratories. This paper presents a novel, real-time development system specifically designed for US research purposes. Main features of the system are the limited dimensions (it is based on a single electronic board), the capability of transmitting arbitrary waveforms to two probes, of storing the received radio-frequency (RF) echo data in a file and/or of processing them in real-time according to programmable algorithms. As an example of application, results of simultaneous hemodynamic and mechanic investigations in human arteries are reported. However, the high system flexibility and portability make it suitable for a large class of US applications.     

Effects of non-optimal focusing on dual-frequency ultrasound measurements of bone

In pulse-echo (PE) ultrasound measurements, the use of focused transducers is desirable for quantitative assessment of bone characteristics because of the attenuation in the overlying soft tissues. However, the variable thickness and composition of the soft tissue overlying bone affect the focal depth of the ultrasound beam and induce errors into the measurements. To compensate for the attenuation-related effects caused by the interfering soft tissue (i.e., fat and lean tissue), a dual-frequency ultrasound (DFUS) technique was recently introduced. The aim of this study was to investigate the effect of non-optimal focal depth of the ultrasound beam on the determination of the integrated reflection coefficient (IRC) of bone when overlaid by an interfering layer composed of oil and water. The feasibility of the DFUS-based correction of the IRC was evaluated through numerical simulations and experimental measurements. Even when the interfering layer-bone interface was out of focus, the total thickness of the interfering layer could be accurately determined with the technique. However, based on the simulations, the errors in the determination of the composition of the interfering layer increased (0.004 to 113.8%) with the increase in distance between the interfering layer-bone interface and the focus of the ultrasound beam. Attenuation compensation, based on the true composition of the interfering layer, resulted in an average relative error of 22.3% in the IRC values calculated from the simulations. Interestingly, the attenuation compensation with the interfering layer composition estimated using the DFUS technique resulted in a smaller average relative error of 14.9% in the IRC values. The simulations suggest that DFUS can reduce the errors induced by soft tissue in bone PE ultrasound measurements. The experimental measurements indicate that the accuracy of the IRC measurements is rather similar when using DFUS correction or correction based on the true composition of the interfering layer. However, the results suggest that accurate determination of soft tissue composition may be difficult without optimal focusing of the ultrasound beam on the soft tissue-bone interface.