▁tracking ▁is ▁limited ▁to ▁the ▁relatively ▁low ▁frame ▁rate ▁of ▁B - mode . ▁If ▁the ▁frame ▁rate ▁is ▁too ▁low , ▁the ▁tracking ▁quality ▁becomes ▁reduced , ▁due ▁to ▁frame - to - frame ▁decor relation . ▁This ▁may ▁also ▁be ▁a ▁problem ▁if ▁the ▁heart ▁rate ▁is ▁high , ▁( which ▁in ▁fact ▁is ▁a ▁relative ▁decrease ▁in ▁frame ▁rate ▁- ▁fewer ▁frames ▁per ▁heart ▁cycle ). ▁ ▁In cre asing ▁frame ▁rate ▁in ▁B - mode ▁is ▁done ▁by ▁reducing ▁line ▁density , ▁i . e . ▁later al ▁resolution , ▁and ▁thus ▁making ▁the ▁method ▁more ▁angle ▁dependent . ▁Finally , ▁the ▁method ▁on ▁some ▁applications ▁is ▁dependent ▁on ▁the ▁RO I ▁( Region ▁Of ▁Interest ) ▁size ▁and ▁shape . ▁In ▁principle ▁Spe ck le ▁tracking ▁is ▁available ▁for ▁de formation ▁measurement ▁in ▁all ▁directions , ▁however , ▁due ▁to ▁the ▁limitation ▁of ▁later al ▁resolution ▁in ▁ap ical ▁images , ▁meas uring ▁circum fer ential ▁and ▁transm ural ▁de formation ▁needs ▁par as ternal ▁cross ▁section al ▁views . ▁On ▁the ▁other ▁hand , ▁compared ▁to ▁T issue ▁Do pp ler , ▁that ▁method ▁is ▁mainly ▁only ▁available ▁for ▁longitud inal ▁measures ▁from ▁the ▁ap ical ▁position . ▁ ▁In ▁the ▁study ▁by ▁Cho ▁et ▁al , ▁both ▁TV I ▁derived ▁and ▁spe ck le ▁tracking ▁derived ▁longitud inal ▁stra in ▁showed ▁mod est ▁correlation ▁with ▁M RI ▁derived ▁stra in . ▁The ▁RO C ▁analysis ▁showed ▁significantly ▁higher ▁A UC ▁for ▁spe ck le ▁tracking ▁for