A　semiautomatic　segmentation　method　based　on　level　set　is　proposed　to　solve　the　weak　boundaries　problem　in　segmentation　of　myocardial　DE-MRI　(delayed　enhancement　magnetic　resonance　Image).　This　method　uses　multiphase　level　sets　and　the　Chan-Vese　model　to　simultaneously　extract　the　boundaries　of　endocardium,　epicardium　and　infarction.　It　relies　on　the　circular　shape　of　the　cardiac　left　ventricle　that　a　circular　penalized　term　is　introduced　to　keep　the　shape　of　the　evolving　contour　close　to　a　circle,　and　thus　the　difficulty　caused　by　the　weak　boundaries　between　the　endocardium　and　trabeculation　is　overcome.　A　dynamic　balloon　force　is　introduced　according　to　the　distance　between　the　myocardial　borders　to　preserve　the　distance　between　the　two　evolving　contours　within　a　given　range,　therefore　the　segmentation　accuracy　of　the　epicardium　is　improved.　Since　the　gray　level　of　the　normal　myocardium　is　significantly　different　from　that　of　the　infarcted　myocardium,　the　Chan-Vese　model　is　used　to　extract　the　infarction　region　of　myocardium　and　to　obtain　smooth　object　boundaries.　The　proposed　method　is　validated　on　the　data　set　from　STACOM　2012　challenge.　The　average　Dice　similarity　coefficient　of　the　method　is　0.72,　and　is　0.07-0.12　bigger　than　those　of　other　methods.　Experimental　results　also　show　that　the　proposed　method　obtains　better　reproducibility,　and　is　more　robust　than　those　compared　methods.　©　2017,　Editorial　Office　of　Journal　of　Xi＇an　Jiaotong　University.　All　right　reserved.