Three dimensional ultrasonic elasticity imaging

超声波成像是一种安全、廉价的观察身体内部的方法。不幸的是，并不是所有的东西都能在超声波扫描中清晰地显示出来。肿瘤很难被发现，因为它们经常以与周围组织相同的方式反射声音。即使它们可以被探测到，它们的边界也很模糊。这使得外科医生很难精确地计划切除什么，或者临床医生很难评估肿瘤对治疗的反应。然而，肿瘤通常比它们周围的环境更坚硬。如果超声波可以显示组织的硬度，而不是它反射声音的方式，那么肿瘤将更容易被发现和描绘。这就是超声弹性成像要实现的目标。弹性成像有几种方法，但我们将重点关注其中一种，它包括在临床医生用不同的压力按压时拍摄一系列常规超声图像。如果我们比较序列中的两张图像，僵硬的结构（如肿瘤）不会发生太大变化，而不那么僵硬的结构则会变形。图像处理算法可以查看这两张图像并推断出每个组织的变形。因此，我们可以建立一个组织弹性的地图。临床医生已经可以购买提供实时弹性成像的设备，但他们得到的是二维（2D）图像，对应于解剖切片，而不是组织弹性的三维地图。不幸的是，没有3D地图，很难计划手术和监测肿瘤对治疗的反应。这就是这个研究计划的由来。它汇集了超声成像（伦敦）和3D超声（剑桥）领域的国际领先团队，目标是开发3D超声弹性成像。研究将在平行的高风险和低风险路径上进行。这项低风险的工作将着眼于在空间中紧密排列的位置记录一系列的二维星图，然后将它们堆叠在一起形成3D图像。我们可以让临床医生在感兴趣的区域扫描探针，同时记录弹性图：这是徒手方法。或者我们可以使用一种特殊的3d探头，其中二维探头的内部安装在由步进电机驱动的摇杆机构上。在这种机械方法中，临床医生保持探头不动，而电机将光束扫过目标区域。我们将实施这两种方法，并比较它们在成像质量和易用性方面的有效性。我们还将研究利用数据的3D特性来提高弹性图清晰度的方法。这项低风险研究将与该项目的临床目标密切相关，以评估乳腺癌和脑癌背景下的三维造影。如果工程师们要开发能够真正影响癌症患者日常管理的技术，来自合作临床医生的反馈是很重要的。同时，高风险路径将尝试通过测量三维组织变形来构建更详细的edelastogram。目前，弹性成像算法仅在施加压力的方向上评估组织变形。然而，组织实际上在三个维度上都发生了变形，通过测量这一点，我们可以得到更好的弹性图，并收集更多关于材料特性的临床有用信息。但是测量三维变形是很困难的，主要是因为我们只能在超声波传播的方向上进行高分辨率的测量，这个方向垂直于皮肤表面。为了测量其他方向的变形，我们需要控制超声波扫描仪，使其更接近方向。我们的目标是在施加压力不同的情况下，从不同的方向对每个组织进行成像。然后，我们需要开发算法，从这些丰富的数据中推断出3D变形。

Ultrasonic imaging is a safe, inexpensive way of looking inside thebody. Unfortunately, not everything shows up clearly in anultrasound scan. Tumours can be hard to see, becausethey often reflect sound in much the same way as the surroundingtissue. Even when they are detectable, their boundaries can beindistinct. This makes it difficult for surgeons to plan preciselywhat to cut out, or for clinicians to assess how well a tumour isresponding to treatment. However, tumours are often stiffer thantheir surroundings. If ultrasound could show the tissue'sstiffness, instead of the way it reflects sound, then tumours would bemuch easier to spot and delineate.This is what ultrasonic elastography sets out to achieve. There areseveral flavours of elastography, but we're going to focus on onewhich involves taking a series of conventional ultrasound pictureswhile the clinician presses down with varying pressure. If we comparetwo images in the sequence, stiff structures (like tumours) won'tchange much, whereas less stiff structures will be deformed. Imageprocessing algorithms can look at the two images and deduce thedeformation of each bit of tissue. We can therefore build up a map ofthe tissue's elasticity.Clinicians can already purchase equipment offering real-timeelastography, but what they get are two-dimensional (2D) pictures,corresponding to slices through the anatomy, and not a 3D map of thetissue's elasticity. Unfortunately, without the 3D map, it isdifficult to plan surgery and monitor a tumour's response totreatment. This is where this research proposal comes in. It bringstogether internationally leading groups in the areas of ultrasonicelastography (London) and 3D ultrasound (Cambridge) with the goal ofdeveloping 3D ultrasonic elastography.The research will progress on parallel high and low risk paths. Thelow risk work will look at ways of recording a series of 2Delastograms, at closely packed locations in space, and then stackingthem together to make a 3D image. We could get the clinician to sweepthe probe over the area of interest, recording elastograms all thewhile: this is the freehand approach. Or we could use a special 3Dprobe, inside which the innards of a 2D probe are mounted on a rockermechanism driven by a stepper motor. In this mechanical approach, theclinician holds the probe still, while the motor sweeps the beam overthe target area. We will implement both approaches and compare theireffectiveness in terms of imaging quality and ease of use. We willalso look at ways of exploiting the 3D nature of the data to improvethe clarity of the elastograms. This low risk research will interfaceclosely with the project's clinical objectives, to evaluate 3Delastography in the context of cancers of the breast andbrain. Feedback from the collaborating clinicians is important if theengineers are to develop technology which could actually affect theeveryday management of cancer patients.Meanwhile, the high risk path will attempt to build more detailedelastograms by measuring tissue deformation in 3D. Currently,elastography algorithms assess tissue deformation only in thedirection of the applied pressure. However, the tissue actuallydeforms in all three dimensions, and by measuring this weshould be able to make better elastograms and glean moreclinically useful information about the material's properties. Butmeasuring 3D deformation is hard, mostly because we can only make highresolution measurements in the direction of the ultrasound wave'spropagation, which is perpendicular to the skin surface. Tomeasure deformation in other directions, we will need tocontrol the ultrasound scanner to steer the waves moretangentially. Our aim is to image each bit of tissue from differentdirections while the applied pressure is varied. We will then need todevelop algorithms to deduce the 3D deformation from this rich data.