ABSTRACT Ultrasound imaging is noninvasive realtime imaging tool that is finding increased usage in hospitals and clinics Ultrasound technology uses high frequency sound waves to reflect off changes in acoustic impedances between tis ID: 31233
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ApplicationReportSPRAB18A–December2008DigitalSignalProcessor(DSP)forPortableUltrasoundRamaPailoorandDevPradhan..........................................................................................................ABSTRACTUltrasoundimagingisanon-invasivereal-timeimagingtoolthatis Contents1Introduction..........................................................................................22PortableUltrasoundSystem......................................................................23DSPBasedPortableUltrasoundSolution.......................................................54SystemCharacteristics............................................................................8 ,DSP/BIOSaretrademarksofTexas Introduction2PortableUltrasoundSystem2.1DrivingRequirementsforaPortableSystem ultrasoundsystemsareconsideredtobeultrasoundsystemsthatweigharound10lbsorless,andcanrunonbatteries.Theybegantoappearinthemarketplaceinthelate90sandhaveseenaremarkablegrowthinsalesintherecentyears.ThisgrowthhasbeenadirectresultoftheirapplicabilityinareassuchasICUs,emergencymedicine,regionalanesthesiaandbattlefield.DSPsandSoCsarespeciallydesignedsingle-chipdigitalmicrocomputersthatprocessdigitizedelectricalsignalsgeneratedbyelectronicsensors(e.g.,cameras,transducers,microphones,etc.)thatwillhelptorevolutionizetheareaofdiagnosticultrasoundimaging.Adiagnosticultrasoundimagingsystemgeneratesandtransmitsacousticwavesandcapturesreflectionsthatarethentransformedintovisualimages.Thesignalprocessingonthereceivedacousticwavesincludeinterpolation,decimation,datafilteringandreconstruction.ProgrammableDSPsandSOCs,witharchitecturesdesignedforimplementingcomplexmathematicalalgorithmsinreal-time,canefficientlyaddressalltheprocessingneedsofsuchasystem.ThefollowinginformationintroducestheconceptofacompleteportableultrasoundsystemsolutionbasedonTexasInstruments'(TI)semiconductorcomponents,developmenttools,andsoftwaresolutions.Additionally,thevariousconceptsthatoutlinetheinherentadvantagesofaDSPandaSoCinaportableultrasoundsystem-efficientsignalprocessing,lowerpowerconsumptionandlowercost,allleadingtobetterultrasounddiagnosticimaging-willalsobecovered.Thekeydriverrequirementsforaportableultrasoundsystemarethesamewithanyportabledevice:size,weight,batterylife,costandperformance.OEMsaremakingtrade-offsintheseareas,forexample,providingjustabasicimagingsystemwithlessfeaturesbutwithmorebatterylife,(e.g.,8-channelblackandwhitesystemsvs.moresophisticated128channelcolorsystemsthatwouldneedtobere-chargedmoreoften).Thesizeoftheportablesystemvariesfromlaptopsizedsystemstohandhelds.ThesesizelimitationsaredrivingtheneedformoresystemintegrationonthesupportingSoCsandmoreautomaticimageenhancementfeaturesduetofewerfinecontrols.Therequirementsforportablesystemsisalsobeingdrivenfromgeographieswheretheinfrastructureismoreruralandaccesstothelargermoresophisticatedimagingsystemsislimited,andwherecliniciansmustnowtakethesystemtothepatient.Thismakescostacriticalfactoraswell.DigitalSignalProcessor(DSP)forPortableUltrasoundSPRAB18ADecember2008SubmitDocumentationFeedback CompleteSystemView Front-EndProcessing UltrasoundSystembasicfunctionalbuildingblocksofadiagnosticultrasoundimagingsystemare:thetransducer,processingblocksneededforimageformation,systemcontrollerandpowersupplymoduleasshowninFigure1.Figure1.UltrasoundImagingSystemFunctionalBlocksDelineationofsignalpathoperationsasfront-end,mid-endandback-endprocessingvariesfromonemanufacturertoanother.Italsodepends,tosomedegree,onthetypeoftechnologyusedforcarryingouttheseoperations:application-specificintegratedcircuit(ASIC),field-programmablegatearray(FPGA),DSPorPC.Ultrasoundimageformationbegins,inwhatiscommonlyreferredtoasthefrontend,usingpulse-echotechnique.Figure2showsthemaincomponentsofthisfunctionalblock.Figure2.ComponentsofFront-EndProcessingDecember2008DigitalSignalProcessor(DSP)forPortableUltrasound3SubmitDocumentationFeedback Mid-EndProcessing UltrasoundSystemtransmitbeamformerisresponsiblefortheorderlypulse-excitationoftransducerelements,whichresultsinemissionofacousticwavesintotheregionofinterest.Immediatelyfollowingthis,thetransmit/receive(T/R)switchispositionedtoputthefrontendinreceivemode.Transducerelementstransformthereflectionsorechoesintocorrespondingelectricalsignals.Theanalogfrontend(AFE)properlyamplifiesthesesignalsandconvertsthemintodigitaldatastreamsforfurtherprocessing.Byapplyingdynamicdelaysintothesedatastreams,thereceivebeamformercombinesthemtoformascanline,arepresentationoftheregionofinterestalongagivenlineofsight.Thisprocessisrepeatedeithersequentiallyorsimultaneouslytoformmultiplescanlinestocoveraregionofinterest.Thefront-endcontrollerisresponsibleforcontrollingthetimingandsequencingoftransmitandreceivebeams.Samplingratesusedforanalog-to-digital(A/D)conversioninthefrontendcanvaryfrom16MHzto50MHzdependingonsystemrequirements.Mostultrasoundimagingsystemsintroducedinrecentyearsarecapableofthreemajormodesofoperation:B-mode,color-flowandDoppler.B-modeoperationresultsinagrayscaleimagethatisusedforexaminingtissuestructuresandorgans.Color-flowoperationresultsinacolor-codeddisplayofspatialdistributionofmeanvelocityofbloodflowsuper-imposedongrayscaleimage.Dopplerprocessingproducesscrollingdisplayofbloodflowvelocitydistributionatauserspecifiedlocation.Somesystemsarecapableofdisplayingallthreemodessimultaneously.Figure3.Mid-EndProcessingFigure3showsmajorelementsofthemid-processingsectionforthethreemajormodesofoperation.CommontoallthreeistheinitialstagewherebeamformedRFdatagetsdownconvertedtobaseband,filtered,andinmostcases,decimated.Whatfollowsthisdependsonthemode.ForB-mode,itisenvelopedetectionandlogarithmiccompression.Whatneedstotakeplaceforcolor-flowisalotmorecomputeintensiveinvolvinghighpassfilteringofensemblesofscanlinestoremovecontributionsfromvesselwallortissuemotion.Outputofthewallfilteristhenusedtoestimatepower,meanvelocity,andturbulence.Dopplerprocessinginvolvesamuchsimplerwallfilterandestimationofvelocitydistributionusingshort-timeFouriertransformtechniques.DopplerprocessingalsoproducesastereoaudiosignalrepresentingtheDopplerspectrum.DigitalSignalProcessor(DSP)forPortableUltrasoundSPRAB18ADecember2008SubmitDocumentationFeedback Back-EndProcessing SystemControllerandMMI3DSPBasedPortableUltrasoundSolution3.1AdvantagesofDSPandSOCsinaPortableSystem BasedPortableUltrasoundSolution4showsanexampleofwhattakesplaceinthebackend.Figure4.Back-EndProcessingB-modeandcolor-flowestimatesaresubjectedtotemporalandspatialprocessingtoreducenoiseandenhancefeaturesofinterest.ScanconversionistheoperationwhereB-modeandcolor-flowestimatesareconvertedtodisplayrasterdata,pixelswith1:1aspectratio.Whencolor-flowison,B-modeandcolor-flowpixelshavetobeblendedtoproduceasingleimage.Thisblendingistypicallybasedonapplicationdependentthresholds.Justlikemostembeddedsystems,ultrasoundimagingsystemsneedasystemcontrollertocarryoutfunctionssuchas:·Configureandcontrolthesignalpath·Handleuserinputeventsandtakeappropriateactions·Monitoracousticpressureandintensitylevelsandensuresafetyofpatients·Inthecaseofportablesystems,carryoutsmartpowermanagementtomaximizescanningtimeinasinglecharge.·Storeandrecallimageclips·RunapplicationstoallowyoutomakeclinicallyrelevantmeasurementsonacquiredimagesequencesTraditionally,ultrasoundsystemshaveusedacombinationofASIC,FPGA,DSPandPCforcapturingandprocessingbeamformedultrasoundimagesandrenderingthemforvisualdisplay.Thesesystemswerecart-basedsystemsthatpluggedintoawallforpowerandtypicallydidnotmovefromlocationtolocation.Withultrasoundimagingsystemsnowgoingportable,thereisaneedforasimpleruserinterfaceandlowerpowerconsumption.Thesystemsalsoneedtoberugged,upgradeableinthefield,andhavegoodconnectivity(maybeevenwireless).Thesmallerformfactorontheportablesystemsalsomeansthattheyarenotexpectedtohavefeaturesneededfordetailedmanualmeasurementsandanalysis,andthatmoremustbedonewiththelimitedcontrolsavailable.DSPsandSOCstodayarepervasiveinhandheldportabledevices;theirstrengthistheirhighperformancepermWofpowerandthehighlevelofsystemintegrationforsupportfornearlyallstandardperipheraldevices(e.g.,USBstorage,LCDdisplay,Ethernet,802.11,etc.).CouplethatwiththeflexibilitytheyprovideviaprogrammabilitytosupportmoreintelligentprocessingandimageenhancementanalyticsanditiseasytoseehowDSPsandSOCsenableaverypowerfulsolutioninaportableultrasoundsystem.MostDSPsandSOCsarealsowellsupportedbyreal-timeoperatingsystemsthatabstractoutsomeofthecomplexitiesofthehardware,andprovideamorefamiliarsoftwaredevelopmentenvironmentthathavebeentunedtosupportapplicationswithreal-timedeterministicrequirementsandlimitedmemoryresources.December2008DigitalSignalProcessor(DSP)forPortableUltrasound5SubmitDocumentationFeedback ExampleSystemBlockDiagrams BasedPortableUltrasoundSolutionfollowingexamplesshowhowTexasInstruments'DSPandSoCdevicescanbeusedinportableultrasoundsystems.Figure5showssystemblockdiagramhighlightingtheuseofTMS320DM648andTMS320DM6446forcarryingoutmid-end,back-end,andsystemcontrollerfunctions.Figure5.DM648+DM6446BlockDiagramThecombinationoftwoC64x+coresandvideo/imagingcoprocessors(VICP)offercompellingcomputecapabilitytoaddresstheneedsofthethreemodesofultrasoundoperation.TheprimaryroleoftheARM9istoruntheoperatingsystemuponwhichthesystemcontrollerfunctionsanduserinterfacecanbeimplemented.SignalProcessor(DSP)forPortableUltrasound6SPRAB18ADecember2008SubmitDocumentationFeedback Real-TimeOperatingSystems(RTOS) BasedPortableUltrasoundSolution6showsanexampleofasystemrequiringhigherinput/output(I/O)bandwidthandcomputationsthanthesystemshowninFigure5.ATMS320C6455DSPisusedhere,withawiderEMIFAbus,whichallowshigherinputdatarates.LargerL2memoryandhigheroperatingclockfrequencyarethemajorcontributorstoincreasedcomputecapability.Inthisexample,theOMAP3530playsthedualroleofsystemcontrollerandback-endprocessor.Figure6.C6455+OMAP3530BlockDiagramTomakeapplicationdevelopmenteasier,moreportablefromonehardwareplatformtoanother,andfastertomarket,embeddedsystemstodayaregravitatingmoreandmoretooff-the-shelfembeddedoperatingsystems.OnecanleveragethemanymanyearsofeffortthatRTOSdevelopershaveputintomakethishardwareabstractionlayermorefeaturerich,morerobust,andmoreefficientinthesupportfunctionsoftheapplication.Besidesstandardoperatingsystemfeatureslikemulti-tasking,memorymanagement,interrupt,andeventhandling,embeddedoperatingsystemshavesomespecialcharacteristicsthatdifferentiatethemfromnon-embeddedOSes(likeWindowsForexample,embeddedOSesareusuallyconfigurabletoallowyoutoaddorremovefeaturesasneeded.Theynormallyhaveasmallmemoryfootprint,higherpredictability(realtime)withapre-emptivepriority-basedschedulingscheme,efficienttaskswitchinglatency,lightweight,predictableinter-processcommunicationmechanisms,powermanagementsupport,etc.Thesearekeyneedsforembeddedsystemsthatareoftenrealtimeinnature,costconscious,andpowerefficient.Inaportableultrasoundsystemmanyofthesefeaturescomeintoplay.Specifically,thereal-timenatureofanultrasoundsystemmakesitimportanttobeabletocaptureultrasoundimages,processthem,andrenderthemtobeseenonascreeninstantly.Systemstartup(boottime)isexpectedtobefast(10seconds)andthelatency,whenswitchingfromB-modeestimationtocolorflowandDopplerprocessing,isexpectedtobeminimal(1second).Longbatterylife(8hours)andpowersavingsmode,withquickwake-upcapability,isanimportantrequirement.SupportforstandardperipheralslikeUSBstorage,printers,LCDdisplays,etc.,isamust.AlloftheseneedsarewellsupportedinmostofftheshelfRTOSavailableonTISOCdevices.December2008DigitalSignalProcessor(DSP)forPortableUltrasound7SubmitDocumentationFeedback SystemCharacteristics4.1Benchmarks References CharacteristicsfollowingsectionsprovideC64x+cyclecountestimatesforseveralkeyfunctionsneededinmid-endandback-endprocessing.Theseestimatesarebasedeitheronstand-alonebenchmarkingorbenchmarksfromTIsdsplibandimglib.Formoredetailedanalysisofseveralfunctionsusedforsignalpathimplementation,seeEfficientImplementationofUltrasoundColorDopplerAlgorithmsonTexasInstrumentsC64x+TMPlatforms(SPRAB11 Thenumbersprovidedheregiveyouanideaaboutcomputepowerneededforeachmodeofoperation.Actualperformancenumbersmayvarydependingonsystemdesignandusageofsharedmemoryresources.Table1givesasummaryofCPUusageestimatesforvariousprocessingblocksdescribedinprevioussections.ThenumbersareforaC64x+corerunningat1GHz..Table1.KeyBenchmarksCPUUsageAssumptionsRFDemod£16%RFsamplingrate=50MHzImagingdepth~=25cm(scanlineinterval=325ms)FilterLength(L)=16(#oftapsperoutputsample)Numberofoutputsamples=512(decimationfactor(S)=32)Numberofcyclesperoutputsample=S+(0.625L+S)=74Color-FlowWall£5%Ensemblelength(N)=10FilterNumberofscanlinesperframe=128Numberofcolorflowsamplesperscanline=256Framerate=30HzNumberofcyclesperoutputsample=NCPUUsage=5%Color-Flow£6%Ensemblelength(N)=10ParameterNumberofscanlinesperframe=128EstimationNumberofcolorflowsamplesperscanline=256Framerate=30HzNumberofcycles/outputforcorrelationcomputation=(N+1)/2Numberofcycles/outputforvelocityestimation=37(approximate)Numberofcycles/outputforturbulenceestimation=16(approximate)SpectralDoppler£1%PulseRepetitionFrequency(P)=20kHzWallFilterWallFilterLength(L)=64Numberofcyclesperoutput=2*((L/4+4)+15)(dsplibbenchmark)SpectralDoppler£1%EstimationofvelocitydistributionistypicallydoneusingShortTimeFourierTransformEstimationtechniques.FFTSize=256RateofFFTcomputation=1kHzBenchmarkfor256point16x32complexFFT=1827cycles(intrinsicCversion)Numberofcyclesneededforwindowingandpowerestimation=512perspectralcolumn.ScanConversion£10%Sizeofoutputrasterusedfordisplayingultrasoundimage:512x512AcquisitionFrameRate:30HzThomasL.Szabo,DiagnosticUltrasoundImaging,ISBN-13:978-0-12-680145-3·TMS320C64x+DSPLittle-EndianDSPLibraryProgrammersReference(SPRUEB8 ·TMS320C64x+DSPImage/VideoProcessingLibrary(v2.0)Programmer'sReference(SPRUF30 ·SignalProcessingOverviewofUltrasoundSystemsforMedicalImaging(SPRAB12 ·EfficientImplementationofUltrasoundColorDopplerAlgorithmsonTexasInstrumentsC64x+Platforms(SPRAB11 DigitalSignalProcessor(DSP)forPortableUltrasoundSPRAB18ADecember2008SubmitDocumentationFeedback ATMS320DigitalSignalProcessorPlatform ATMS320DSPfamilyfromTIoffersthewidestselectionofsignalprocessorsavailableanywhere,withabalanceofgeneral-purposeandapplication-specificprocessorstosuityourneeds.Therearethreedistinctinstructionsetarchitecturesthatarecompletelycode-compatiblewithinthefollowingplatforms:·Highperformancemulti-coreDSPplatforms·HighperformancesinglecoreDSPplatforms·PowerefficientDSPandSOCplatformsFigureA-1.RoadmapforDSPArchitecturesDecember20089SubmitDocumentationFeedback BeXpressDSPSoftwareandDevelopmentTools Bsreal-timeeXpressDSPsoftwareanddevelopmenttoolstrategyincludesthreetightlyknitingredientsthatempowerdeveloperstotapthefullpotentialofTMS320DSPs:·TheworldsmostpowerfulDSPintegrateddevelopmenttools:CodeComposerStudio IDE·eXpressDSPSoftwareincluding:Scalable,real-timesoftwarefoundation:DSP/BIOSReal-TimeOperatingSystem(OS)Software Foundation Standardsforapplicationinteroperabilityandreuse:TMS320DSPAlgorithmStandardxDAISand DesignreadycodethatiscommontomanyapplicationstogetyoustartedquicklyonDSPdesign:eXpressDSPFrameworkSoftware AgrowingbaseofTIDSP-basedproductsfromTIsDSPThirdPartyProgram eXpressDSPcompliantproductsthatcanbeeasilyintegratedintosystems.EachelementisdesignedtosimplifyDSPprogrammingandmovedevelopmentfromacustomcraftedapproachtoanewparadigmofinteroperablesoftwarefrommultiplevendorssupportedbyaworldwideinfrastructure.Therehasbeenanexplosivegrowthinreal-timeapplicationsdemandingthereal-timeprocessingpowerofTIDSPs.eXpressDSPenablesinnovatorsandinventorstospeednewproductstomarketandturnideasintoreality.Previouslyunimaginedapplications,includingvirtualreality,medicalimaging,autonavigation,digitalaudio,andInternettelephonynowrelyonthecrucialreal-timecomputingpowerthatcanonlybefoundinaDSP.DSKandEVMDSPstarterkits(DSK)andevaluationmodules(EVM)aretoolsthatallowdeveloperstotesttheircodeinhardwarebeforeactuallybuildingprototypedesigns.DSKsareavailableforTMS320C6455andTMS320C6713DSP.EVMsareavailablefortheTMS320DM6446,TMS320C6474,TMS320DM648andOMAP35xxSOCs.SPRAB18ADecember2008SubmitDocumentationFeedback 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