医用超声诊断仪超声探头的分类和主要特性

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                    <p><img data-type="gif" src="http://mmbiz.qpic.cn/mmbiz_gif/dx3KibwtDhvc6YBndBzrYvfAVPCGNAlsqB9f7SjRnXkibcO3P2CSjz7TnOO8RAArOGOjobic1D5DCTCzzAoxv9jfw/0?wx_fmt=gif" data-ratio="0.1703125" data-w="640"  /></p><p><img data-s="300,640" data-type="jpeg" src="http://mmbiz.qpic.cn/mmbiz_jpg/dx3KibwtDhvcib2dKq7SO4w1Fc95lQVG3PXv0QSbstlENTRGgc0rgiaYtcqZBgjibU2cFEBhxmYZokicgrLcgiatf1wQ/0?wx_fmt=jpeg" data-ratio="0.8020833333333334" data-w="576"  /></p><p>要使用和维护好超声诊断仪，<span style="line-height: 1.6;">了解探头的特性是十分重要的。本文主要对医用超声探头的特性和分类做了具体的阐述和说明。</span></p><p><br  /></p><p>　　医用超声探头是各型超声诊断仪将高频电能转换为<span style="line-height: 1.6;">超声机械能向外辐射，</span><span style="line-height: 1.6;">并接收超声回波将声能转换为电</span><span style="line-height: 1.6;">能的一种声—电转换器件。超声探头在各类超声诊断设</span><span style="line-height: 1.6;">备中占有非常重要的位置</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">其性能的优劣直接影响成像</span><span style="line-height: 1.6;">的质量。</span></p><p>1</p><p>　 医用超声探头的分类：</p><p>超声诊断仪所配用探头中的换能器基本都是采用压<span style="line-height: 1.6;">电陶瓷材料</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">所以超声探头一般又称为压电换能器。</span></p><p>超声探头可以从以下几个方面来分类<span style="line-height: 1.6;">:</span></p><p>(1)</p><p>按探头中换能器所用振元数目<span style="line-height: 1.6;">:</span><span style="line-height: 1.6;">单元探头和多元</span><span style="line-height: 1.6;">探头</span><span style="line-height: 1.6;">;</span></p><p>(2)</p><p>按波束控制方式<span style="line-height: 1.6;">:</span><span style="line-height: 1.6;">线扫探头、相控阵探头、机械扇</span><span style="line-height: 1.6;">扫</span><span style="line-height: 1.6;">(</span><span style="line-height: 1.6;">包括单元式、多元切换式和环阵</span><span style="line-height: 1.6;">)</span><span style="line-height: 1.6;">探头、方阵探头</span><span style="line-height: 1.6;">等</span><span style="line-height: 1.6;">;</span></p><p>(3)</p><p>按探头的几何形状<span style="line-height: 1.6;">:</span><span style="line-height: 1.6;">矩形探头、弧形探头</span><span style="line-height: 1.6;">(</span><span style="line-height: 1.6;">凸形探</span><span style="line-height: 1.6;">头</span><span style="line-height: 1.6;">)</span><span style="line-height: 1.6;">、柱形探头、圆形探头等</span><span style="line-height: 1.6;">;</span></p><p>(4)</p><p>按诊断部位<span style="line-height: 1.6;">:</span><span style="line-height: 1.6;">心脏探头、腹部探头、眼科探头、颅</span><span style="line-height: 1.6;">脑探头等</span><span style="line-height: 1.6;">;</span></p><p>(5)</p><p>按应用方式<span style="line-height: 1.6;">:</span><span style="line-height: 1.6;">体外探头、体内探头、穿刺活检探</span><span style="line-height: 1.6;">头</span><span style="line-height: 1.6;">;</span></p><p>2</p><p>　 医用超声探头的主要特性：</p><p>探头特性的好坏是决定仪器性能的重要因素之一<span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">了解探头特性对使用和维护超声诊断仪是十分重要的。</span><span style="line-height: 1.6;">医用超声探头的特性具有使用特性</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">同时又具有声学特</span><span style="line-height: 1.6;">性。</span></p><p>(1)</p><p>使用特性</p><p>使用特性是探头与仪器配合使用的综合性能<span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">它包</span><span style="line-height: 1.6;">括探头的工作频率、频带宽度、灵敏度和分辨力。</span></p><p>①探头的工作频率<span style="line-height: 1.6;">:</span><span style="line-height: 1.6;">即探头中的换能器与仪器联接</span><span style="line-height: 1.6;">后</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">实际辐射超声波的频率。工作频率的选择主要决定</span><span style="line-height: 1.6;">于临床诊断的要求</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">因为人体各部位对超声的衰减都不</span><span style="line-height: 1.6;">相同</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">其衰减系数随频率的升高增加很快。因此</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">对于衰</span><span style="line-height: 1.6;">减大的织或要求探测深度大时</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">应选取较低的工作频</span><span style="line-height: 1.6;">率</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">相反对于衰减小的组织或求探测深度小时则选取</span><span style="line-height: 1.6;">较高的工作频率。</span></p><p><br  /></p><p>②频带宽度<span style="line-height: 1.6;">:</span><span style="line-height: 1.6;">指换能器的工作频率响应的范围。为</span><span style="line-height: 1.6;">了使频带宽度展宽</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">往往要增加阻尼</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">但因此也会使换能</span><span style="line-height: 1.6;">效率有一定程度的降低。</span></p><p><br  /></p><p>③灵敏度<span style="line-height: 1.6;">:</span><span style="line-height: 1.6;">指探头与超声诊断仪配合使用时在最大</span><span style="line-height: 1.6;">探测深度上</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">可发现最小病灶的能力。它主要与探头中</span><span style="line-height: 1.6;">换能器的换能特性和辐射效率等声学特性有关。换能特</span><span style="line-height: 1.6;">性好、辐射效率高的换能器</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">探测灵敏度就高。这主要取</span><span style="line-height: 1.6;">决于压电材料的压电性能、压电振子的辐射面积和压电</span><span style="line-height: 1.6;">材料的机械品质因素等。</span></p><p><br  /></p><p>④分辨力<span style="line-height: 1.6;">:</span><span style="line-height: 1.6;">探头特性对仪器分辨力有很大的影响</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">就</span><span style="line-height: 1.6;">探头本身而言</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">分辨力的高低主要与以下因素有关。</span></p><p>a</p><p>探头中换能器的辐射特性。如果辐射特性好<span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">则</span><span style="line-height: 1.6;">声束截面尺寸小</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">扩散角小</span><span style="line-height: 1.6;">指向性好</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">横向分辨力就高</span><span style="line-height: 1.6;">;</span><span style="line-height: 1.6;">辐射特性好</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">声束能量集中</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">旁瓣小</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">近场区干扰小</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">也有</span><span style="line-height: 1.6;">利于提高分辨力。</span></p><p>b</p><p>换能器的辐射面积越大<span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">声束的扩散角越小</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">横向</span><span style="line-height: 1.6;">分辨力也将提高。</span></p><p><span style="line-height: 1.6;">c</span></p><p>换能器的频率响应好<span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">距离分辨力高。</span></p><p>d</p><p>换能器的机械品质因素低<span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">有利于纵向分辨力的</span><span style="line-height: 1.6;">提高。</span></p><p>e</p><p>换能器层间匹配的好坏直接影响分辨力<span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">因为如</span><span style="line-height: 1.6;">果层间匹配不好</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">超声在探头中来回反射</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">会造成回波</span><span style="line-height: 1.6;">的多次叠加</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">从而使纵向分辨力下降。</span></p><p>(2)</p><p>声学特性<span style="line-height: 1.6;">:</span></p><p>超声探头的声学特性主要与探头中超声换能器所用</p><p>材料的特性有关<span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">它包括辐射特性、吸收特性、频率特性、</span><span style="line-height: 1.6;">转换特性和暂态特性。</span></p><p>①辐射特性是指换能器的辐射声场在空间的分布状<span style="line-height: 1.6;">态</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">主要是通过指向性和声束尺寸来进行描述。换能器辐</span><span style="line-height: 1.6;">射的声束特性在很大程度上决定超声探测的横向分辨力。</span></p><p>②吸收特性实际是指压电振子垫衬的吸收特性。在<span style="line-height: 1.6;">换能器振元后都加有垫衬吸收块</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">并要求垫衬具有良好</span><span style="line-height: 1.6;">的吸收特性。</span></p><p>③频率特性指换能器阻抗频率和辐射频率特性的总<span style="line-height: 1.6;">称。阻抗频率特性是指换能器阻抗随频率的变化的特</span><span style="line-height: 1.6;">性</span><span style="line-height: 1.6;">;</span><span style="line-height: 1.6;">辐射频率特性是指换能器辐射状态的频率特性。</span></p><p>④转换特性指换能器发射和接收状态的能量转换特<span style="line-height: 1.6;">性。从理论上讲</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">换能器的电—声和声—电的能量转换</span><span style="line-height: 1.6;">是等效和可逆的。</span></p><p>⑤暂态特性指换能器对脉冲响应的随动能力。对于<span style="line-height: 1.6;">超声探测效果来说</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">为了提高距离分辨力</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">通常采用阶跃</span><span style="line-height: 1.6;">窄脉冲来激励能换工作</span><span style="line-height: 1.6;">,</span><span style="line-height: 1.6;">换能器在电脉冲激励下的振动</span><span style="line-height: 1.6;">与弹性体在脉冲敲击力作用下的振荡是相似的</span><span style="line-height: 1.6;">,</span><span 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