▁the ▁on set ▁of ▁relax ation ▁similar ▁to ▁a ▁spring ▁un co iling ▁and ▁results ▁in ▁su ction ▁forces . ▁These ▁forces ▁are ▁then ▁used ▁for ▁rapid ▁early ▁di ast ol ic ▁rest oration . ▁ ▁App lications ▁and ▁Lim itations ▁The ▁util ities ▁of ▁S TE ▁are ▁increasing ly ▁recognized . ▁St rain ▁results ▁derived ▁from ▁S TE ▁have ▁been ▁valid ated ▁using ▁son omic rom etry ▁and ▁tag ged ▁M RI ▁and ▁results ▁correlate ▁significantly ▁with ▁T issue ▁Do pp ler – der ived ▁measurements . ▁T issue ▁Do pp ler ▁technology , ▁the ▁alternative ▁method ▁for ▁stra in ▁rate ▁imag ing ▁to ▁spe ck le ▁tracking ▁technology , ▁requires ▁ach ieving ▁sufficient ▁parallel ▁orientation ▁between ▁the ▁direction ▁of ▁motion ▁and ▁the ▁ul tras ound ▁beam . ▁Its ▁use ▁has ▁remained ▁limited ▁due ▁to ▁angle ▁dependency , ▁substantial ▁int ra ob server ▁and ▁inter ob server ▁vari ability ▁and ▁noise ▁inter ference . ▁Spe ck le ▁tracking ▁technology ▁has ▁to ▁a ▁certain ▁degree ▁overcome ▁these ▁limitations . ▁ ▁In ▁order ▁to ▁achieve ▁sufficient ▁tracking ▁quality ▁when ▁single ▁markers ▁are ▁used , ▁however ▁commercial ▁algorithms ▁very ▁often ▁resort ▁to ▁vari eties ▁of ▁spl ine ▁sm o othing ▁using ▁available ▁information ▁from ▁the ▁strong est ▁echo es , ▁very ▁oft ▁the ▁mit ral ▁ann ulus , ▁so ▁the ▁regional ▁measurements ▁are ▁not ▁pure ▁regional , ▁but ▁rather ▁to ▁a ▁degree , ▁spl ine ▁functions ▁of ▁the ▁global ▁average . ▁AS ▁the ▁method ▁uses ▁B - mode , ▁frame ▁rate ▁of ▁spe ck le