What is a doppler ultrasound

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    07-May-2015

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  • 1.What is a Doppler ultrasound?Answerfrom Sheldon G. Sheps, M.D.Doppler ultrasound is a noninvasive test that can be used to measure your blood flow and blood pressureby bouncing high-frequency sound waves (ultrasound) off circulating red blood cells. A regular ultrasounduses sound waves to produce images, but cant show blood flow.A Doppler ultrasound may help diagnose many conditions, including:Blood clotsPoorly functioning valves in your leg veins, which can cause blood or other fluids to pool in your legs(venous insufficiency)Heart valve defects and congenital heart diseaseA blocked artery (arterial occlusion)Decreased blood circulation into your legs (peripheral artery disease)Bulging arteries (aneurysms)Narrowing of an artery, such as those in your neck (carotid artery stenosis)A Doppler ultrasound can estimate how fast blood flows by measuring the rate of change in its pitch(frequency). During a Doppler ultrasound, a technician trained in ultrasound imaging (sonographer)presses a small hand-held device (transducer), about the size of a bar of soap, against your skin over thearea of your body being examined, moving from one area to another as necessary. This test may be doneas an alternative to more-invasive procedures such as arteriography and venography, which involveinjecting dye into the blood vessels so that they show up clearly on X-ray images.A Doppler ultrasound test may also help your doctor check for injuries to your arteries or to monitorcertain treatments to your veins and arteries.Doppler ultrasoundDoppler ultrasound is a well established technique used to diagnose problems during pregnancy. In thesame way that a speed radar measures how fast cars are travelling, Doppler ultrasound can monitor howfast blood is moving in the umbilical blood flow. Professionals can then look to see whether the blood flowis normal, indicating that the fetus is healthy, or abnormal, indicating that the fetus is under stress. Thehealth professionals can then decide which high-risk pregnancies need assistance in delivering the baby,and which women can be left to deliver without assistance.

2. The aim of using Doppler is to reduce risk to the baby. However, some experts argue that it may promptsome unnecessary early interventions.The review included 18 studies which together included 10,000 women in "high risk" groups. High riskwomen included those who had previously lost babies during pregnancy, those carrying growth restrictedbabies and women with hypertension or diabetes. Women who were examined with Doppler ultrasoundwere compared with those who had no Doppler or with those who had cardiotocography (CTG), whichmonitors the babys heartbeat. According to the results, Doppler reduced infant deaths, possibly throughbetter timing of caesarean sections, as well as reducing the number of caesarean sections themselves,and inductions of labour. However, the researchers say the studies included were of questionable quality."A case could certainly be made for a higher quality, multi-centre trial of Doppler ultrasound than we haveso far seen," said lead researcher Zarko Alfirevic, who is based at the Division of Perinatal andReproductive Medicine at the University of Liverpool. "It is quite possible that for some so-called high riskgroups fetal Doppler offers little or no benefit. Women with diabetes are one such group where fetalDoppler may, in fact, give false reassurance."It is important to point out, of course, that it is the clinical decision that follows a Doppler ultrasoundexamination that changes the outcome for the baby, and currently there is little agreement on whatintervention should follow an abnormal Doppler finding."New Placenta Screening For High-Risk PregnanciesScienceDaily (Apr. 2, 2007) For the first time ever, a team of Torontoresearchers are using a combination of ultrasound and blood tests to screenhigh-risk pregnant mothers for placental damage. By completing these non-invasive tests, most high-risk mothers can be reassured that their placenta isformed and functioning properly, so they can expect a healthy pregnancy.See Also:Health & Medicine Pregnancy and Childbirth Hypertension Gynecology Womens Health Teen Health MenopauseReference Stillbirth Placenta Maternal bond Nutrition and pregnancyThe tests are done early enough, at 16 to 23 weeks gestation, so if results are abnormal, physicians havetime to improve pregnancy outcomes. "Close to 40 per cent of high-risk mothers we see in our clinicexperience placental damage," says Dr. John Kingdom, Principal Investigator of the study and Maternal-Fetal Medicine Specialist at Mount Sinai Hospital. The research is among the first to look at placentahealth -- a vital life line between mother and fetus through which nutrients, oxygen, antibodies andhormones pass. 3. "By identifying early on if there is a potential risk of complications, we can do everything possible toensure the safety of both the mother and fetus," says Dr. Kingdom, who is also a Professor in theDepartment of Obstetrics and Gynaecology at the University of Toronto. "We can reassure those withnormal test results that their placentas are functioning well and they can expect a healthy pregnancy andbirth."If the placenta is not functioning properly it could be a potential danger to the health of the mother andfetus. Abnormalities can lead to conditions such as preeclampsia, which is maternal high blood pressure,stillbirth or the need for a pre-term delivery.The screening tests include: a maternal serum screening test used to detect Downs syndrome, whichmeasures the hormone levels in the mothers blood; a uterine artery Doppler blood flow test, whichchecks the maternal blood flow in the placenta; and an ultrasound of the placental shape. Of the 212high-risk women in the study, 19 delivered early due to poor fetal growth. None of these women hadnormal placental function test results. Likewise, only two of 22 stillbirths occurred in women with normaltests, and these losses were not related to abnormal placental function. This data demonstrates that theplacenta screening tests can provide a good indication of which women may experience complicationsduring pregnancy."This is an important first step in identifying placental abnormalities in early pregnancy, at a time when anumber of interventions can be used to improve outcomes for those with the highest risk" says Dr.Kingdom. "This study will lead the way for future research in placenta screening and help us providequality care for all mothers."The research will be published in the American Journal of Obstetrics and Gynecology in April 2007. 4. Doppler Ultrasound Findings in the Hepatic Artery Shortly After Liver Transplantation1. ngeles Garca-Criado1,2. Rosa Gilabert1,3. Annalisa Berzigotti1 and4. Concepcin Br1 + Author Affiliations1. 1Department of Radiology, Clinic Hospital of Barcelona, Villarroel 170, 08036 Barcelona,Spain. Next Section Abstract OBJECTIVE. The purpose of this article is to describe the Doppler waveform findings in the hepatic artery in the early posttransplantation period, both in the absence and presence of arterial complications. CONCLUSION. The presence of transient high-resistance Doppler waveforms in normal hepatic arteries is a common finding after grafting. Hepatic artery thrombosis and stenosis, and arterial steal syndromes can be diagnosed by Doppler in the early liver transplantation period. Doppler sonography 5. hepatic artery liver transplantation sonographyultrasoundPrevious SectionNext SectionIntroductionHepatic artery complications are one of the most frequent causes of morbidity and graft loss in theimmediate period after liver transplantation because they can lead to liver graft ischemia [1]. The earlydetection of these complications is critical to treat them promptly and to reduce the liver damage. Asurveillance program based on color Doppler ultrasound (CDUS) in the first days after liver transplantationhas proven to be effective for the early diagnosis of hepatic artery complications, and it is now considered astandard of care [2, 3]. However, the interpretation of Doppler findings in the immediateposttransplantation phase may be difficult because the hepatic artery waveform also is commonly altered inthe absence of complications [4]. Moreover, the same Doppler findings can be observed in differentcomplications. The aim of this article is to describe the Doppler waveforms of the hepatic artery in theimmediate posttransplantation period, both in patients with a normal artery and in those with arterialcomplications.Previous SectionNext SectionDoppler Arterial Findings in the Immediate PosttransplantationPeriodThe normal hepatic artery shows a low-resistance waveform with continuous diastolic blood flow. Theresistive index (RI) is the most commonly used Doppler parameter in hepatic artery evaluation. It allows asemiquantitative estimation of the resistance to arterial flow into the liver and its normal value, both inhealthy individuals and those with transplants, and it ranges from 0.55 to 0.80 [5] (Fig. 1).In the first days after liver transplantation, almost half of patients have a transient high RI at the hepaticartery that will return to normal in a few days if there are no complications [4]. According to the degree ofresistance, the high RI has been classified by Garca-Criado et al. [4] into four types: type 1, RI > 0.80 withcontinuous blood flow in the diastolic phase (Fig. 2); type 2, RI = 1, complete absence of the diastolicsignal and preserved systolic velocity (Fig. 3); type 3, absence of diastolic signal and diminished systolicvelocity (Fig. 4); and, in severe cases, type 4, undetectable Doppler flow. The last two types are a furtherprogression of the transient high-resistance flow, but these spectral waveforms are indistinguishable fromthe arterial hypoperfusion secondary to some arterial complications. Therefore, when a type 3 patternappears in the immediate postoperative period, it is mandatory to be alert and to perform daily CDUS,suspecting a complication when the waveform does not become normal within 4 days. In these cases, CTangiography (CTA), MR angiography (MRA), or arteriography is indicated. In patients with a type 4waveform indicating undetectable arterial CDUS flow, CDUS (if possible), CTA, or MRA is indicated toexclude hepatic artery thrombosis. If a patent artery is seen, a daily CDUS examination is mandatory untilthe flow becomes normal. 6. Early and transient high RI, which has been shown to be related to an older donor and a prolonged periodof ischemia, lacks clinical repercussions and long-term prognostic implications [4].Previous SectionNext SectionDoppler Findings in Posttransplantation Hepatic ArteryComplicationsHepatic Artery ThrombosisEarly hepatic artery thrombosis is the most serious arterial complication after liver transplantation and hasan incidence of 5-7% in adults and 11% in children. Because the blood supply to the biliary tree is entirelyarterial, abnormal results on liver function tests are often its first manifestation. However, hepatic arterythrombosis can be diagnosed at CDUS in the presymptomatic phase, allowing early reperfusion thatobviates retransplantation [6]. Patients with hepatic artery thrombosis who are treated by revascularizationbefore the development of clinical or laboratory alterations have a lower incidence of late biliarycomplications [2], which emphasizes the importance of performing close Doppler monitoring after livertransplantation.The ultrasound diagnosis of hepatic artery thrombosis is based on the absence of Doppler arterial signal atthe hilus as well as in the intrahepatic arterial branches (Figs. 5A, 5B, 5C, 5D, and 5E). A high-resistanceflow at the hilus (RI = 1) may be observed if the Doppler waveform is obtained in the main hepatic arterybefore the thrombus.Occasionally, low arterial flow may provoke a false-positive diagnosis of hepatic artery thrombosis.Contrast-enhanced ultrasound can be useful in these cases because it improves the sensitivity and accuracyof Doppler ultrasound for hepatic artery flow detection. Moreover, contrast-enhanced ultrasound helps todecrease the scanning time [7, 8] (Figs. 5A, 5B, 5C, 5D, and 5E). When contrast-enhanced ultrasoundcannot be used, other noninvasive imaging techniques such as MRA or CTA can be performed afterDoppler ultrasound and before arteriography.False-negative diagnoses of hepatic artery thrombosis have been described in late phases after graftingwhen periportal collateral arteries develop at the site of thrombosis. Unfortunately, the collateral flow isoften inadequate to allow satisfactory intrahepatic biliary perfusion. To correctly establish the diagnosis,remember that the Doppler signal in the arterial collateral vessels shows a pattern with prolonged systolicacceleration time and low RI [9]. This pattern is nonspecific of hepatic artery thrombosis and can also befound in hepatic artery stenosis.Hepatic Artery StenosisHepatic artery stenosis is a frequent complication after liver transplantation, with an incidence of 4-10%[10]; in severe cases it may cause liver ischemia and graft loss. However, this complication frequentlycauses a subtle form of graft dysfunction, which delays the diagnosis.Hepatic artery stenosis may be suspected when an intrahepatic Doppler waveform shows a prolongedsystolic acceleration time ( 0.08 second) and a low RI (< 0.5) [9] (Figs. 6A and 6B). In these cases, ameticulous Doppler study along the course of the main hepatic artery is mandatory because the detection ofa focal peak velocity greater than 2 m/s is diagnostic for hepatic artery stenosis [9] (Fig. 6C). When anincreased focal peak systolic velocity is not detected along the course of the hepatic artery, the differentialdiagnosis must include hepatic artery thrombosis with the development of collateral vessels. In these cases,contrast-enhanced ultrasound examination has been advised, although it does not obviate an angiographicstudy to establish the diagnosis [11].Pseudoaneurysm of the Hepatic ArteryEven if pseudoaneurysm of the hepatic artery is an infrequent complication after liver transplantation, itspotential for rupture and subsequent fatal hemorrhage makes early diagnosis important. The ultrasounddiagnosis is based on detection of a predominantly cystic lesion at the hepatic hilus, which fills with coloron CDUS and presents an arterial Doppler waveform (Figs. 7A, 7B, and 7C).Arterial Steal SyndromesThe arterial steal syndromes have only recently been recognized as a cause of hepatic hypoperfusion afterliver transplantation. These syndromes are characterized by low arterial flow toward the graft caused by ashift of flow into the splenic artery, called splenic artery steal syndrome, the most frequent; or into thegastroduodenal artery, called gastroduodenal artery steal syndrome. 7. Angiography is mandatory for the diagnosis. The criteria are the presence of an enlarged splenic artery ( 4mm or 150%...

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