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IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control vol 56 no 7 July 2009 1327 An Ultrasonic Imaging Speckle Suppression and Contrast Enhancement Technique by Means of Frequency Compounding and Coded Excitation Jose R Sanchez Student Member IEEE and Michael L Oelze Member IEEE Abstract A method for improving the contrast resolution of B mode images is proposed by combining the speckle reduction technique of frequency compounding FC and the codedexcitation and pulse compression technique called resolution enhancement compression REC FC suppresses speckle but at the expense of a reduction in axial resolution Using REC the axial resolution and bandwidth of the imaging system was doubled Therefore by combining REC with FC REC FC the tradeoff between axial resolution and contrast enhancement was extended significantly Simulations and experimental measurements were conducted with a single element transducer f 2 66 having a center frequency of 2 25 MHz and a 3 dB bandwidth of 50 Simulations and measurements of hyperechoic 6 dB tissue mimicking targets were imaged Four FC cases were evaluated full half third and fourth width of the true impulse response bandwidth The image quality metrics used to compare REC FC to conventional pulsing CP and CP FC were contrast to noise ratio CNR speckle signalto noise ratio histogram pixel intensity and lesion signal tonoise ratio Increases in CNR of 121 231 302 and 391 were obtained in experiments when comparing REC FC for the full half third and fourth width cases to CP Furthermore smaller increases in CNR of 112 233 and 309 were obtained in experiments when comparing CP FC for the half third and fourth width cases to CP Improved lesion detectability was observed by using REC FC I Introduction S peckle the granular structure in ultrasonic images reduces the ability to detect low contrast targets Speckle is formed by subresolution scatterers that cause constructive and destructive interference of backscattered ultrasonic signals within the resolution cell volume of an ultrasonic source 1 Furthermore speckle is considered to be a deterministic process because when an object is imaged under the same operating conditions no changes in the speckle pattern occur Because of this nature speckle is not reduced by signal averaging Therefore a considerable amount of work and effort has been spent over the last few decades developing techniques to reduce speckle in ultrasound images Manuscript received November 16 2008 accepted April 15 2009 This work was supported by a grant from the NIH R21 EB006741 The authors are with the Department of Electrical and Computer Engineering University of Illinois at Urbana Champaign Urbana IL e mail jsanch27 uiuc edu Digital Object Identifier 10 1109 TUFFC 2009 1189 0885 3010 25 00 In imaging small structures or an object could be identified if the contrast between the target and the surrounding area are different 2 In ultrasound the difference in contrast between different



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