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Peripheral Vascular Ultrasound - part 3

Trong trung tâm, góc insonation khoảng 90 °, rất thấp hoặc không có tần số Doppler là phát hiện hay hiển thị. Ở bên phải của hình ảnh, góc insonation chảy ra từ đầu dò, và do đó nó được hiển thị trong màu đỏ. | CREATION OF A COLOR FLOW IMAGE 41 toward the probe. In the very center the angle of insonation is approximately 90 so low or no Doppler frequency is detected or displayed. On the right sideof the image the angle of insonationis now such Ulas Uio How is awoy from the tranSf ducer andStisehereíoeediepeayadẽorrd. When inicipiating acolorimage itiaimpoetanr to remembf that ie ic aha Doppler shift frequooey the velocity aeintive to eDc beoea tli itãs Ueing displayed andSaisascentiiano sunridor the angle of insonasiooutodtn ernduce eoedpoint oC the image. To Co ceruhn of site veloũtĩi c preteot spectral Dopaiot srsb euaed ao thitlias thefuail ạtco provide ungOe aoeruation for eeScaity es n a Diagnosis sS-oued brmoneusmgc cvmbinatlon ot color and spectrelDnpplarinvestigbSions. AUASINU iu coeoRFl.oeo IMAGING The range of frequencies displayed by the color scales govemedbychy pcdscrcpcrnonftcqucncy PRF used to obtain the Doppler frequency shift. The maximum frnqucocy thot asn h e ili ti i r t a with color flowimagingis lImirrii Ct the temehtt gfre-quency inthesoma wacas UesesideUfos c-coơooI Doppler i co .ĩ .iOií-cn ị a s to 0 0 1 111 will limitUicnwinum frequenco ehaeean Dc OiSi played chn a Oe aaueingSrequeoeioe hoyonheOie limit to bdbispiayedas flow ontOoopjaisitcsideiif the baseline. Au axempleoOaiiasmhoccumngino color imege is sliueeo in Figorc nates oha hlghctr velocities preeeutrseiiieOr aentoe of Uievcssci but because oeoiirsmg thenaareUitpiautd is iunquosse i.e. as higU velonisiet ie Wo opeonite direntionl instead of yellow i.e. topofthecolortcalc . Ifthe PRF is increased aliasing no longer occurs and all the flow is displayed in the correct color Fig. 4.9B . is ti-c PRiO issatuoo hiu hhwebeei-s maoprevent iow velocitiee. tuah ssiIioso noaothe vetreiwaiSsoc Ua e dicttolCifrymbeihạ Ueeeessd iFig.4.9Cei One potentialpteblem isUiffnrennnUDvaiiasmg Crom trueUow revertaeo Trus eiơ seuesea1ith wh as a chanạs ucạ ot withmo vosseO í.e.1 om Jteit coUlue cue be eean where .