Characterization of the spatial resolution of different high-frequency imaging systems using a novel anechoic-sphere phantom.
Characterization of the spatial resolution of different high-frequency imaging systems using a novel anechoic-sphere phantom.
复制标题
DOI：
10.1109/tuffc.2011.1990
复制
发表时间：
2011-05
期刊：
影响因子：
--
通讯作者：
Ketterling JA
中科院分区：
文献类型：
--
作者：
Filoux E;Mamou J;Aristizábal O;Ketterling JA
高频超声（HFU，>20 MHz）成像系统的空间分辨率通常使用垂直于波束的导线来确定。最近，两个仿组织体模（TMP）被开发来估计三维（3D）分辨率。每个TMP由9个1 cm宽的组织模拟材料板组成，其中包含随机分布的消声球。一个平板中的所有消声球具有相同的尺寸，并且它们的直径从第一个平板中的0.1 mm增加到最后一个平板中的1.09 mm。一组平板的散射背景是用3.5 μm的玻璃珠制作的，而第二组平板的散射背景是6.4 μm。HFU系统针对斑点背景检测这些球体的能力提供了其3D空间分辨率的现实估计。在本研究中，这些TMP与使用单元件换能器、线性阵列和环形阵列的HFU系统一起使用。将TMP浸入水中，并使用VisualSonics™ Vevo 770和Vevo 2100以及基于5元件环形阵列的定制HFU系统扫描每个板。环形阵列的标称中心频率为40 MHz，焦距为12 mm，总孔径为6 mm。使用合成聚焦算法形成景深增加的图像。穿透深度通过使用跨越15至65 MHz的线性啁啾信号在4 µs内增加。将定制系统获得的结果与Vevo系统（40 MHz探头RMV-704和MS-550 D）的球体检测结果进行比较，即，3D空间分辨率和对比度噪声比（CNR）。结果B型图像表明，只有线阵换能器未能清楚地解决0.2毫米的球体，这表明，单元素和环形阵列换能器的三维空间分辨率上级线阵。单元件换能器只能在狭窄的1.5 mm景深内检测这些球体，而环形阵列能够检测到至少7 mm的深度。对于任何尺寸的消声球体，由线性调频编码信号激发的环形阵列提供了最高对比度的图像，焦点处的最大CNR为1.8，相比之下，使用脉冲激励时为1.3，使用单元件换能器和线性阵列时为1.6。该成像配置还在8 mm的宽深度范围内提供了高于1.2的CNR，而CNR将在其他配置的聚焦区之外迅速降至低于1。
The spatial resolution of high-frequency ultrasound (HFU, >20 MHz) imaging systems is usually determined using wires perpendicular to the beam. Recently, two tissue-mimicking phantoms (TMPs) were developed to estimate the three-dimensional (3D) resolution. Each of the TMPs consist of nine, 1 cm wide slabs of tissue-mimicking material containing randomly distributed anechoic spheres. All anechoic spheres in one slab have the same dimensions, and their diameter is increased from 0.1 mm in the first slab to 1.09 mm in the last. The scattering background for one set of slabs was fabricated using 3.5 µm glass beads, while those of the second set were 6.4 µm. The ability of a HFU system to detect these spheres against a speckle background provides a realistic estimation of its 3D spatial resolution. In the present study, these TMPs were used with HFU systems using single-element transducers, linear arrays and annular arrays. The TMPs were immersed in water and each slab was scanned using a VisualSonics™ Vevo 770 and Vevo 2100, and a custom HFU system based on a 5-element annular array. The annular array had a nominal center frequency of 40 MHz, a focal length of 12 mm, and a total aperture of 6 mm. A synthetic-focusing algorithm was used to form images with an increased depth-of-field. The penetration depth was increased by using a linear-chirp signal spanning 15 to 65 MHz over 4 µs. Results obtained with the custom system were compared to those of the Vevo systems (40 MHz probes RMV-704 and MS-550D) in terms of sphere detection, i.e., 3D spatial resolution, and contrast-to-noise ratio (CNR). Resulting B-mode images indicated that only the linear-array transducer failed to clearly resolve the 0.2 mm spheres, which showed that the 3D spatial resolution of the single-element and annular-array transducers was superior to that of the linear array. The single-element transducer could only detect these spheres over a narrow 1.5 mm depth-of-field, while the annular array was able to detect them to depths of at least 7 mm. For any size of the anechoic spheres, the annular array excited by a chirp-coded signal provided images of the highest contrast, with a maximum CNR of 1.8 at the focus, compared to 1.3 when using impulse excitation and 1.6 with the single-element transducer and linear array. This imaging configuration also provided CNRs above 1.2 over a wide depth range of 8 mm, while CNRs would quickly drop below 1 outside the focal zone of the other configurations.