Three dimensional ultrasonic elasticity imaging

Lead Research Organisation: University of Cambridge
Department Name: Engineering

Abstract

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.

Publications

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Chen L (2010) A hybrid displacement estimation method for ultrasonic elasticity imaging. in IEEE transactions on ultrasonics, ferroelectrics, and frequency control

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Chen L (2010) A normalization method for axial-shear strain elastography. in IEEE transactions on ultrasonics, ferroelectrics, and frequency control

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Housden RJ (2011) A new method for the acquisition of ultrasonic strain image volumes. in Ultrasound in medicine & biology

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Housden RJ (2010) 3-D ultrasonic strain imaging using freehand scanning and a mechanically-swept probe. in IEEE transactions on ultrasonics, ferroelectrics, and frequency control

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Ijaz U (2013) Multidirectional Scattering Models for 3-Dimensional Ultrasound Imaging in Journal of Ultrasound in Medicine

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Ijaz UZ (2013) Multidirectional scattering models for 3-dimensional ultrasound imaging. in Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine

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Neale E (2011) A pilot study using transvaginal real-time ultrasound elastography to evaluate the postmenopausal endometrium. in Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology

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Treece GM (2009) Uniform precision ultrasound strain imaging. in IEEE transactions on ultrasonics, ferroelectrics, and frequency control

 
Description Ultrasonic imaging is a safe, inexpensive way of looking inside the body. Unfortunately, not everything shows up clearly; tumours often reflect sound in much the same way as surrounding tissues and their boundaries can be indistinct. This makes it difficult to plan surgery and assess how well a tumour is responding to treatment. However, tumours are often stiffer than their surroundings. Ultrasonic elastography aims to show the tissue's stiffness, instead of the way it reflects sound, so that tumours should be easier to spot and delineate. There are several flavours of elastography, but we have focused on one which involves taking a series of ultrasound pictures while the clinician applies a varying pressure. For any two images in the sequence, stiff structures (like tumours) do not change much, whereas soft structures are deformed. Image processing algorithms deduce the deformations, building a map of the tissue's elasticity. Clinicians can already purchase real-time elastography equipment, but what they get are two-dimensional (2D) pictures, corresponding to anatomical slices, and not a 3D map of the tissue's elasticity. Unfortunately, without the 3D map, it is difficult to plan surgery and monitor a tumour's response to treatment. This is where this research project made its primary contribution. It brought together internationally leading groups in the areas of ultrasonic elastography (London) and 3D ultrasound (Cambridge) to develop 3D ultrasonic elastography. The research progressed on parallel high and low risk paths. The low risk work looked at ways of recording a series of 2D elastograms, and stacking them together to make a 3D image. We asked the clinician to sweep a conventional 2D probe over the area of interest, recording elastograms all the while: this is the freehand approach. We also used a special 3D probe, which the clinician holds still while a stepper motor sweeps a 2D probe (inside the 3D probe) over the target area. We implemented both approaches and compared their effectiveness in terms of imaging quality and ease of use. We discovered that a hybrid approach, with a 3D probe that the clinician moves gently up and down, makes it easier to produce good 3D elastograms. The concept was tested clinically, producing the first published 3D elastograms of the brain and the testis. Meanwhile, the high risk path, by measuring tissue deformation in 3D, attempted to build better elastograms that contain more useful information about the tissue's properties (previously, elastography had assessed tissue deformation only in the direction of the applied pressure). But measuring 3D deformation is hard, mostly because we can only make high resolution measurements in the direction of the ultrasound wave. To measure deformation in other directions, we needed to control the ultrasound scanner to steer the waves more tangentially. We achieved this using specially modified scanning hardware and novel image processing algorithms, and succeeded in producing far more accurate maps of 3D deformation than was previously possible, resulting in improved ability to define tumour boundaries, determine their slipperiness, and detect changes in tissue permeability to fluids (important for disease detection, drug access and monitoring response to treatment). This work is now ripe for commercial exploitation: it sits well with the new generation of 3D ultrasound probes being released by the major equipment manufacturers. During the project we also (a) used the methods developed to generate data to solve the so-called inverse problem and thereby determine the Young's modulus of the medium, which was used with radiosensitive gels to measure complex 3D radiation dose distributions, (b) showed that our elastograms compared favourably with those obtained using acoustically applied pressure and with some advantages, and (c) demonstrated 3D tissue tracking for motion compensated radiotherapy.
Exploitation Route The technology has clear uses in Healthcare. The technology is already being used in hospitals for clinical research.
Sectors Healthcare

URL http://mi.eng.cam.ac.uk/~rjh80/elast3D/elast3D.html
 
Description Elastography is now a common feature of top-end medical ultrasound systems. Our research contributed to the technical realisation of this technology. Clinical applications of elastography are now emerging, and will most likely continue to emerge over the next several decades. Current applications include lesion detection and classification, fibrosis staging, treatment monitoring and vascular imaging.
First Year Of Impact 2012
Sector Healthcare
Impact Types Societal,Economic

 
Title Cambridge ultrasound elastography database 
Description RF data for 2D and 3D elastography research, covering a wide variety of anatomical areas and pathologies. 
Type Of Material Database/Collection of data 
Year Produced 2011 
Provided To Others? Yes  
Impact The database is used in the ongoing work of around 30 research groups. 
URL http://mi.eng.cam.ac.uk/projects/elastography/
 
Title Stradwin 
Description Stradwin is freely available research software for medical imaging. All our successful research outcomes are implemented in Stradwin, including freehand 3D ultrasound, 2D and 3D ultrasound elastography, and CT cortical bone analysis. 
Type Of Technology Software 
Year Produced 2011 
Impact Stradwin is used by around 50 research teams around the world. 
URL http://mi.eng.cam.ac.uk/~rwp/stradwin/