Ultrasound　Nakagami　parametric　imaging　is　a　useful　tool　for　tissue　characterization.　Previous　literature　has　suggested　using　a　square　with　side　lengths　corresponding　to　3　times　the　transducer　pulse　length　as　the　minimum　window　for　constructing　the　Nakagami　image.　This　criterion　does　not　produce　sufficiently　smooth　images　for　the　Nakagami　image　to　characterize　homogeneous　tissues.　To　improve　image　smoothness,　we　proposed　window-modulated　compounding　(WMC)　Nakagami　imaging　based　on　summing　and　averaging　the　Nakagami　images　formed　using　sliding　windows　with　varying　window　side　lengths　from　1　to　N　times　the　transducer　pulse　length　in　1　pulse　length　step.　Simulations　(the　number　densities　of　scatterers:　2-16　scatterers/mm(2))　and　experiments　on　fully　developed　speckle　phantoms　(the　scatterer　diameters:　20-106　mu　m)　were　conducted　to　suggest　an　appropriate　number　of　frames　N　and　to　evaluate　the　image　smoothness　and　resolution　by　analyzing　the　full　width　at　half　maximum　(FWHM)　of　the　parameter　distribution　and　the　widths　of　the　image　autocorrelation　function　(ACF),　respectively.　In　vivo　ultrasound　measurements　on　rat　livers　without　and　with　cirrhosis　were　performed　to　validate　the　practical　performance　of　the　WMC　Nakagami　image　in　tissue　characterization.　The　simulation　results　showed　that　using　a　range　of　N　from　7　to　10　as　the　number　of　frames　for　image　compounding　reduces　the　estimation　error　to　less　than　5%.　Based　on　this　criterion,　the　Nakagami　parameter　obtained　from　the　WMC　Nakagami　image　increased　from　0.45　to　0.95　after　increasing　the　number　densities　of　scatterers　from　2　to　16　scatterers/mm(2).　The　FWHM　of　the　parameter　distribution　(bins　=　40)　was　13.5　+/-　1.4　for　the　Nakagami　image　and　9.1　+/-　1.43　for　the　WMC　Nakagami　image,　respectively　(p-value　＜　.05).　The　widths　of　the　ACF　for　the　Nakagami　and　WMC　Nakagami　images　were　454　+/-　5.36　and　458　+/-　4.33,　respectively　(p-value　＞　.05).　In　the　phantom　experiments,　we　also　found　that　the　FWHM　of　the　parameter　distribution　for　the　WMC　Nakagami　image　was　smaller　than　that　of　the　conventional　Nakagami　image　(p-value　＜　.05),　and　there　was　no　significant　difference　of　the　ACF　width　between　the　Nakagami　and　WMC　Nakagami　images　(p-value　＞　.05).　In　the　animal　experiments,　the　Nakagami　parameters　obtained　from　the　WMC　Nakagami　image　for　normal　and　cirrhotic　rat　livers　were　0.62　+/-　0.08　and　0.92　+/-　0.07,　respectively　(p-value　＜　.05).　The　results　demonstrated　that　the　WMC　technique　significantly　improved　the　image　smoothness　of　Nakagami　imaging　without　resolution　degradation,　giving　Nakagami　model-based　imaging　the　ability　to　visualize　scatterer　properties　with　enhanced　image　quality.　(C)　2014　Elsevier　B.V.　All　rights　reserved.