▁detect ing ▁d ys function al ▁segments . ▁However , ▁this ▁study ▁only ▁included ▁patients ▁with ▁coron ary ▁disease . ▁The ▁lower ▁frame ▁rate ▁has ▁been ▁seen ▁to ▁be ▁a ▁problem ▁in ▁stress ▁echo , ▁as ▁the ▁peak ▁stress ▁shows ▁a ▁fairly ▁high ▁frame ▁rate . ▁ ▁The ▁main ▁problem ▁with ▁spe ck le ▁tracking , ▁however , ▁is ▁increasing ly ▁recogn ised : ▁The ▁lack ▁of ▁standard isation . ▁Each ▁vendor ▁of ▁ul tras ound ▁equipment , ▁or ▁analysis ▁software , ▁has ▁different ▁algorithms , ▁that ▁will ▁perform ▁differently ▁during ▁analysis . ▁In ▁head ▁to ▁head ▁compar isons , ▁bi ases ▁between ▁analysis ▁may ▁be ▁substantial , ▁especially ▁when ▁compared ▁to ▁an ▁external ▁reference . ▁Thus , ▁measurements , ▁normal ▁limits ▁and ▁cut ▁off ▁values ▁are ▁only ▁vendor ▁specific . ▁Due ▁to ▁industrial ▁secre cy , ▁the ▁details ▁of ▁the ▁different ▁algorithms ▁may ▁also ▁be ▁largely ▁un available , ▁so ▁a ▁detailed ▁investigation ▁in ▁mod elling ▁is ▁difficult . ▁ ▁References ▁ ▁Further ▁reading ▁ ▁S uther land ; ▁Hat le ; ▁Cla us ; ▁D ' ho oge ; B ijn ens ▁( 2 0 0 6 ) ▁Do pp ler ▁My oc ard ial ▁Im aging . ▁B SW K , ▁Belg ium . ▁ ▁Mar wick ; ▁Yu ; ▁Sun ▁( 2 0 0 7 ) ▁My oc ard ial ▁Im aging : ▁T issue ▁Do pp ler ▁and ▁Spe ck le ▁Track ing . ▁W iley - Black well . ▁ ▁External ▁links ▁As b j orn ▁Sto