Toward a Standardization of Ultrasound Scanners for Dynamic Contrast-Enhanced Ultrasonography: Methodology and Phantoms

The standardization of ultrasound scanners for dynamic contrast-enhanced ultrasonography (DCE-US) is mandatory for evaluation of clinical multicenter studies. We propose a robust method using a phantom for measuring the variation of the harmonic signal intensity obtained from the area under the time-intensity curve versus various contrast-agent concentrations. The slope of this measured curve is the calibration parameter. We tested our method on two devices from the same manufacturer (AplioXV and Aplio500, Toshiba, Tokyo, Japan) using the same settings as defined for a French multicenter study. The Aplio500's settings were adjusted to match the slopes of the AplioXV, resulting in the following settings on the Aplio500: at 3.5 MHz: MI = 0.15; CG = 35 dB and at 8 MHz: MI = 0.10; CG = 32 dB. This calibration method is very important for future DCE-US multicenter studies.     

Design and Fabrication of Phantoms Using Stereolithography for Small-Animal Imaging Systems

PURPOSE: We have investigated a new technology for fabricating phantoms with fine details for use in small-animal imaging. PROCEDURES: We used a high-resolution, 3-D stereolithography (SL) system to produce performance-evaluation phantoms such as cold-rod Derenzo, hot-channel Derenzo, and Defrise phantoms. SL performance was estimated by measuring the dimensions of many structures using a microscope. We also evaluated the degree of water absorption by two different SL resins, Somos(R) 11120 and Accura(R) 40, after curing. RESULTS: The average bias and precision of the cold-rod structures over the size range 0.5 to 1.0 mm, were -0.4% and 1.74%, respectively. The water absorption study showed that Somos(R) 11120 is a more suitable material for nuclear medicine applications. CONCLUSION: We have demonstrated that SL is a robust and accurate method for fabrication of phantoms for small-animal imaging systems.     

A Review of Tissue Substitutes for Ultrasound Imaging

The characterization and calibration of ultrasound imaging systems requires tissue-mimicking phantoms with known acoustic properties, dimensions and internal features. Tissue phantoms are available commercially for a range of medical applications. However, commercial phantoms may not be suitable in ultrasound system design or for evaluation of novel imaging techniques. It is often desirable to have the ability to tailor acoustic properties and phantom configurations for specific applications. A multitude of tissue-mimicking materials and phantoms are described in the literature that have been created using a variety of materials and preparation techniques and that have modeled a range of biological systems. This paper reviews ultrasound tissue-mimicking materials and phantom fabrication techniques that have been developed over the past four decades, and describes the benefits and disadvantages of the processes. Both soft tissue and hard tissue substitutes are explored. (E-mail: mculjat@mednet.ucla.edu)     

Evaluation of Intravascular Ultrasound Catheter-Based Transducers Using the Resolution Integral

Intravascular ultrasound (IVUS) catheters are a specialist imaging modality used in the assessment of cardiovascular disease. The ultrasound transducer may either be of single-element mechanical or phased-array design. Because of their design and operating frequencies (10–45 MHz), evaluation of the imaging performance is not possible with commercially available ultrasound test objects. An existing test object, the Edinburgh Pipe Phantom, was modified to allow measurement of resolution integral (R), depth of field (Lr) and characteristic resolution (Dr) of IVUS catheters. In total, seven IVUS catheters, from two manufacturers and of both single-element mechanical and phased-array design, were tested to provide a measure of performance over different frequencies and technologies. Measurements of R for the tested IVUS catheters ranged from 11.9 to 18.8. The modified Edinburgh Pipe Phantom therefore allows catheter-based ultrasound probes to be evaluated scientifically and their performance to be seen in relation to other similar ultrasound technologies such as pre-clinical ultrasound and endoscopic ultrasound.     

Comparison of Two Inexpensive Rapid Prototyping Methods for Manufacturing Filament Target Ultrasound Phantoms

Current use of 3-D printers to manufacture ultrasound phantoms is limited to relatively expensive photopolymer jetting printers. The present work investigates the feasibility of using two common and inexpensive 3-D printer technologies, fused deposition modeling (FDM) and digital light processing (DLP), to print custom filament target phantoms. Acoustic characteristics obtained from printed solid blocks indicated that the printing materials—acrylonitrile butadiene styrene and polylactic acid for FDM and a photopolymer for DLP printing—were appropriate for use as scatterers. A regular grid of filaments was printed to study printing accuracy. As a proof of concept of the phantom manufacturing process, a complex pattern of filament targets was placed in de-ionized water to create a phantom, which was then imaged using an ultrasound imager. The pattern was clearly identifiable, although multiple reflections were observed, which underscores the importance of future work to enhance printing resolution. This goal is deemed possible using improvement of the DLP printing setup.     

The validity of Rehabilitative Ultrasound Imaging for measurement of trapezius muscle thickness

The purpose of the study was to establish the validity of Rehabilitative Ultrasound Imaging (RUSI) against Magnetic Resonance Imaging (MRI) for measuring trapezius muscle thickness. Participants were asymptomatic subjects recruited from Trinity College Dublin and associated teaching hospitals. Four MRI axial slices were made through each of the C6, T1, T5 and T8 spinous processes, with the subject supine. RUSI was performed immediately after MRI at the same vertebral levels, with the subject prone. Linear measurements of trapezius muscle thickness were made off-line on both the MRI and Ultrasound scans, in three regions: lower, middle and upper trapezius. Bland and Altman limits of agreement and Pearson's correlation coefficient were used to analyse the relationship between thickness measures taken from MRI and RUSI. Eighteen subjects (9 women) participated, (age-range 21–42 years). Results demonstrated good agreement between MRI and RUSI measurements of the lower trapezius muscle at T8 (r = 0.77) and moderate agreement at T5, (r = 0.62). Results were poor for the middle (T1) and upper (C6) trapezius muscles, (r = −0.22 to 0.52) but may be explained by differences in both positioning and imaging planes between the 2 modalities.It was concluded that RUSI is a valid method of measuring lower trapezius muscle thickness.     

Assessing the Imaging Capabilities of Radial Mechanical and Electronic Echo-endoscopes Using the Resolution Integral

Over the past decade there have been significant advances in endoscopic ultrasound (EUS) technology. Although there is an expectation that new technology will deliver improved image quality, there are few methods or phantoms available for assessing the capabilities of mechanical and electronic EUS systems. The aim of this study was to investigate the possibility of assessing the imaging capability of available EUS technologies using measurements of the resolution integral made with an Edinburgh Pipe Phantom. Various radial EUS echo-endoscopes and probes were assessed using an Edinburgh Pipe Phantom. Measurements of the resolution integral (R), depth of field (L_R) and characteristic resolution (D_R) were made at all operating frequencies. The mean R value for Fuji miniprobes was 16.0. The GF-UM20 and GF-UM2000 mechanical radial scopes had mean R values of 24.0 and 28.5, respectively. The two electronic radial echo-endoscopes had similar mean R values of 34.3 and 34.6 for the Olympus GF-UE260 and Fujinon EG-530 UR scopes, respectively. Despite being older technology, the mechanical GF-UM2000 scope had superior characteristic resolution (D_R), but could not compare with the depths of field (L_R) delivered by the current generation of electronic radial scopes, especially at the standard operating frequencies of 7.5 and 12 MHz.     

血管应变显像软件的研制及应用的初步研究

目的 探讨评价血管及斑块应变的新方法。 方法 根据理论分析，自行设计了血管应变显像的软件程序。在兔动脉粥样硬化的模型中，进行了腹主动脉血管内超声检查，应用软件程序分析腹主动脉的应变分布。 结果 应用软件程序可自动识别血管内膜及外膜的边界，血管及斑块的应变值大小可以彩色编码显示，并显示应变的三维分布，脂质型斑块应变值大于纤维型斑块（P〈0．05）。 结论 应用计算机应变软件程序可用于显示血管及斑块的应变分布，为进一步研究斑块的弹性提供了新方法。     

3M和5M液晶显示器对不同分辨率乳腺体模图影像显示质量的研究

目的比较不同分辨率乳腺机获得的专用模体测试结果,评估3M与5M医用专业显示器对乳腺影像显示质量的影响。方法使用70μm和100μm分辨率乳腺机分别拍摄对比度细节乳腺摄影(CDMAM)。由4名放射诊断医师和2名技师在标准和放大显示模式下,评估2种显示器所能显示的最小圆盘直径(Di)与厚度(Ci,th),并计算出影像质量因子反数值(IQFinv)。2种显示器及2种显示模式的比较均采用配对t检验。结果在使用100μm分辨率乳腺影像数据时,无论是标准显示模式还是放大显示模式,2种显示器的影像细节显示能力相仿(P>0.05);使用70μm分辨率乳腺影像数据时,在标准显示模式下,5M显示器可识别最小直径为(0.130±0.000)mm,小于3M显示器的(0.155±0.012)mm(P=0.004)。5M显示器的IQFinv值显著高于3M显示器(P=0.036)。在放大显示模式下,3M与5M显示器的可识别最小直径相同[(0.125±0.012)mm],5M显示器的IQFinv值高于3M显示器,但差异无统计学意义(P>0.05)。无论哪种分辨率图像与显示器组合,在放大模式下阅片的影像质量均优于标准模式(P=0.010)。结论 70μm分辨率数据配备5M显示器可获得高质量图像,利用阅读时的放大模式在一定程度上可改善3M显示器对各种细节的显示。     

A Semi-automated 3-D Annotation Method for Breast Ultrasound Imaging: System Development and Feasibility Study on Phantoms

Spatial annotation is an essential step in breast ultrasound imaging, because the follow-up diagnosis and treatment are based on this annotation. However, the current method for annotation is manual and highly dependent on the operator's experience. Moreover, important spatial information, such as the probe tilt angle, cannot be indicated in the clinical 2-D annotations. To solve these problems, we developed a semi-automated 3-D annotation method for breast ultrasound imaging. A spatial sensor was fixed on an ultrasound probe to obtain the image spatial data. Three-dimensional virtual models of breast and probe were used to annotate image locations. After the reference points were recorded, this system displayed the image annotations automatically. Compared with the conventional manual annotation method, this new annotation system has higher accuracy as indicated by the phantom test results. In addition, this new annotation method has good repeatability, with intra-class correlation coefficients of 0.907 (average variation: ≤3.45%) and 0.937 (average variation: ≤2.85%) for the intra-rater and inter-rater tests, respectively. Breast phantom experiments simulating clinical breast scanning further indicated the feasibility of this system for clinical applications. This new annotation method is expected to facilitate more accurate, intuitive and rapid breast ultrasound diagnosis.     

Effects of Nonlinear Propagation in Ultrasound Contrast Agent Imaging

This paper investigates two types of nonlinear propagation and their effects on image intensity and contrast-to-tissue ratio (CTR) in contrast ultrasound images. Previous studies have shown that nonlinear propagation can occur when ultrasound travels through tissue and microbubble clouds, making tissue farther down the acoustic path appear brighter in pulse inversion (PI) images, thus reducing CTR. In this study, the effect of nonlinear propagation through tissue or microbubbles on PI image intensity and CTR are compared at low mechanical index. A combination of simulation and experiment with SonoVue microbubbles were performed using a microbubble dynamics model, a laboratory ultrasound system and a clinical prototype scanner. The results show that, close to the bubble resonance frequency, nonlinear propagation through a bubble cloud of a few centimeter thickness with a modest concentration (1:10000 dilution of SonoVue microbubbles) is much more significant than through tissue-mimicking material. Consequently, CTR in regions distal to the imaging probe is greatly reduced for nonlinear propagation through the bubble cloud, with as much as a 12-dB reduction compared with nonlinear propagation through tissue-mimicking material. Both types of nonlinear propagation cause only a small change in bubble PI signals at the bubble resonance frequency. When the driving frequency increases beyond bubble resonance, nonlinear propagation through bubbles is greatly reduced in absolute values. However because of a greater reduction in nonlinear scattering from bubbles at higher frequencies, the corresponding CTR is much lower than that at bubble resonance frequency. (E-mail: mengxing.tang@imperial.ac.uk)     

脊柱爆裂型骨折影像学表现及检查价值分析

目的：评价DR平片、CT、MRI三种影像学检查对脊柱爆裂型骨折诊断价值和限度。材料与方法：对35例脊柱不同部位爆裂骨折影像平片表现进行分析，比较其优缺点。结果：爆裂型骨折以胸腰段最常见，占脊柱骨折的77％，常伴有骨碎片突入椎管致椎管狭窄，椎间盘突出，脊髓受压、水肿、出血。脊髓横断是最严重的脊髓创伤。结论：影像学检查是脊柱、脊髓创伤的重要手段。DR平片是脊柱爆裂骨折的基本诊断方法，CT对判断椎体纵行、矢状方向骨折、椎管狭窄及移位有着重要价值。MRI是准确判断脊髓损伤程度的首选最佳方法。     

Temperature Measurement by Thermal Strain Imaging with Diagnostic Power Ultrasound,with Potential for Thermal Index Determination

Over the years, there has been a substantial increase in acoustic exposure in diagnostic ultrasound as new imaging modalities with higher intensities and frame rates have been introduced; and more electronic components have been packed into the probe head, so that there is a tendency for it to become hotter. With respect to potential thermal effects, including those which may be hazardous occurring during ultrasound scanning, there is a correspondingly growing need for in vivo techniques to guide the operator as to the actual temperature rise occurring in the examined tissues. Therefore, an in vivo temperature estimator would be of considerable practical value. The commonly-used method of tissue thermal index (TI) measurement with a hydrophone in water could underestimate the actual value of TI (in one report by as much as 2.9 times). To obtain meaningful results, it is necessary to map the temperature elevation in 2-D (or 3-D) space. We present methodology, results and validation of a 2-D spatial and temporal thermal strain ultrasound temperature estimation technique in phantoms, and its apparently novel application in tracking the evolution of heat deposition at diagnostic exposure levels. The same ultrasound probe is used for both transmission and reception. The displacement and thermal strain estimation methods are similar to those used in high-intensity focused ultrasound thermal monitoring. The use of radiofrequency signals permits the application of cross correlation as a similarity measurement for tracking feature displacement. The displacement is used to calculate the thermal strain directly related to the temperature rise. Good agreement was observed between the temperature rise and the ultrasound power and scan duration. Thermal strain up to 1.4% was observed during 4000-s scan. Based on the results obtained for the temperature range studied in this work, the technique demonstrates potential for applicability in phantom (and possibly in vivo tissue) temperature measurement for the determination of TI. (E-mail: Haidong.Liang@UHBristol.nhs.uk)     

Iterative Minimum Variance Beamformer with Low Complexity for Medical Ultrasound Imaging

Minimum variance beamformer (MVB) improves the resolution and contrast of medical ultrasound images compared with delay and sum (DAS) beamformer. The weight vector of this beamformer should be calculated for each imaging point independently, with a cost of increasing computational complexity. The large number of necessary calculations limits this beamformer to application in real-time systems. A beamformer is proposed based on the MVB with lower computational complexity while preserving its advantages. This beamformer avoids matrix inversion, which is the most complex part of the MVB, by solving the optimization problem iteratively. The received signals from two imaging points close together do not vary much in medical ultrasound imaging. Therefore, using the previously optimized weight vector for one point as initial weight vector for the new neighboring point can improve the convergence speed and decrease the computational complexity. The proposed method was applied on several data sets, and it has been shown that the method can regenerate the results obtained by the MVB while the order of complexity is decreased from O(L³) to O(L²).     

Automatic Methods for Carotid Contrast-Enhanced Ultrasound Imaging Quantification of Adventitial Vasa Vasorum

Adventitial vasa vasorum are physiologic microvessels that nourish artery walls. In the presence of cardiovascular risk factors, these microvessels proliferate abnormally. Studies have reported that they are the first stage of atheromatous disease. Contrast-enhanced ultrasound (CEUS) of the carotid allows direct, quantitative and non-invasive visualization of the adventitial vasa vasorum. Hence, the development of computer-assisted methods that speed image analysis and eliminate user subjectivity is important. We developed methods for automatic analyses and quantification of vasa vasorum neovascularization in CEUS and tested these methods in a cohort of 186 individuals, 63 of whom were healthy volunteers. We implemented alternative automatic strategies for using the images to stratify patients according to their risk group and compare the strategies with respect to diagnostic performance. An automatic single-parameter strategy performs less effectively than the corresponding Arcidiacono method based on manual interpretation of the images (68 < area under the receiver operating characteristic curve [AUROC] for the manual Arcidiacono method < 82; 60 < AUROC for the automatic single-parameter strategy < 63). However, by use of additional image parameters, an automatic multiparameter strategy has significantly improved performance with respect to the manual Arcidiacono method (78 < AUROC < 90). The automatic multiparameter strategy is a valuable alternative to the manual Arcidiacono method, improving both diagnostic speed and diagnostic accuracy.     

Ultrasound Molecular Imaging of Atherosclerosis Using Small-Peptide Targeting Ligands Against Endothelial Markers of Inflammation and Oxidative Stress

The aim of this study was to evaluate a panel of endothelium-targeted microbubble (MB) ultrasound contrast agents bearing small peptide ligands as a human-ready approach for molecular imaging of markers of high-risk atherosclerotic plaque. Small peptide ligands with established affinity for human P-selectin, VCAM-1, LOX-1 and von Willebrand factor (VWF) were conjugated to the surface of lipid-stabilized MBs. Contrast-enhanced ultrasound (CEUS) molecular imaging of the thoracic aorta was performed in wild-type and gene-targeted mice with advanced atherosclerosis (DKO). Histology was performed on carotid endarterectomy samples from patients undergoing surgery for unstable atherosclerosis to assess target expression in humans. In DKO mice, CEUS signal for all four targeted MBs was significantly higher than that for control MBs, and was three to sevenfold higher than in wild-type mice, with the highest signal achieved for VCAM-1 and VWF. All molecular targets were present on the patient plaque surface but expression was greatest for VCAM-1 and VWF. We conclude that ultrasound contrast agents bearing small peptide ligands feasible for human use can be targeted against endothelial cell adhesion molecules for inflammatory cells and platelets for imaging advanced atherosclerotic disease.