Perivascular color artifact: pathologic significance and appearance on color Doppler US images

Clinical outcomes of endovascular therapy with vascular stents for central venous obstruction in hemodialysis patients

BACKGROUND

Symptomatic central venous obstruction (CVO) is sometimes observed in patients undergoing hemodialysis. Angioplasty is generally performed for salvage purposes, and stent implantation is performed as a last resort to prevent permanent venous occlusion. However, published reports about the clinical outcomes of stenting for CVO have been limited by the small number of included patients and the relatively old generation of analyzed stents. This study aimed to clarify the safety and efficacy of endovascular therapy (EVT) using stents for symptomatic CVO in contemporary practice.

METHODS

This retrospective review was performed between May 2012 and August 2021. We retrospectively analyzed consecutive 31 lesions (31 patients, 64 ± 10.7 years old) treated with a vascular stent for elastic recoil after balloon angioplasty or recurrent stenosis <3 months after angioplasty. The primary outcome was primary patency, defined as freedom from target lesion revascularization. The secondary outcome was assisted primary patency, defined as freedom from permanent occlusion of the target stents.

RESULTS

In all cases, stents were successfully deployed on the target lesions. No EVT-related complications were observed. Self-expandable and balloon-expandable stents were used in 26 and 5 lesions, respectively. The median follow-up period was 18 months (interquartile range, 7-40). Kaplan-Meier analysis revealed that the primary patency rates were 66.1 % at 6 months, 61.7 % at 12 months, and 38.4 % at 24 months after EVT. The assisted primary patency rate was 70.3 % 24 months after EVT. In the multivariate analysis, younger age was the only independent predictor of target lesion revascularization (hazard ratio: 0.92, 95 % CI: 0.85-0.99, p = 0.04).

CONCLUSIONS

Stent implantation for CVO that is resistant to standard angioplasty seems safe and effective.

Computational fluid dynamics simulation of hemodynamic changes in a hemodialysis patient with central venous stenosis treated with stent

BACKGROUND

It has not been demonstrated that computational fluid dynamics (CFD) can be used to model central venous stenosis (CVS), nor that hemodynamic changes in CVS treated with stent placement can be anticipated. The purpose of this study was to demonstrate the hemodynamic performance of CVS patients treated with stent placement.

METHODS

Patient-specific geometric models were constructed using computed tomography images of veins from hemodialysis patients treated with stent placement. CFD simulation based on geometry was performed using ANSYS-15 to compare pressure quantitatively, wall shear stress (WSS), and flow velocity in the brachial vein before and after stent placement.

RESULTS

Following a covered stent placement, the swelling of the left upper extremity was relieved. Prior to stent implantation, the maximum and mean brachial vein wall pressures were 465.2 Pa and 224.609 Pa, respectively. It was determined that the maximum WSS value was 8.449 Pa and that the mean WSS value was 0.743 Pa. The maximum and mean flow velocities were 1.16 and 0.173 m/s, respectively. After stent placement, the maximum wall pressure, maximum WSS, and maximum flow velocity dropped by 59.4%, 71.2%, and 57.8%, respectively. The mean wall pressure, mean WSS, and mean flow rate decreased by 43.5%, 52.7%, and 17.6%, respectively.

CONCLUSION

Hemodynamics of CVS in hemodialysis patients exhibited turbulent, imbalances and disorders, which can be improved by stent placement.

Endovascular treatments of tunneled central venous catheter-induced superior vena cava complete occlusion via through-and-through technique

BACKGROUND

Superior vena cava occlusion (SVCO) induced by tunneled central venous catheter (tCVC) is an uncommon but challenging complication of hemodialysis patients. The aim of this study was to access the efficacy, safety, and patency of stents in tCVC-related SVCO via through-and-through technique.

METHOD

We retrospectively identified seven patients with benign SVCO secondary to tCVC treated with endovascular approaches successfully between 1 March 2013 and 31 October 2019. Patients' demographic data, clinical signs and symptoms, and imaging data were followed up and recorded.

RESULTS

Technical success was achieved in all cases. All the patients were performed with percutaneous transcatheter angioplasty (PTA) and subsequently stent placement via the through-and-through technique. During follow-up, four patients underwent secondary interventions, including PTA and/or stent placement. The primary patency after 3, 6, 9 and 12 months was 100%, 100%, 86% and 86%, and secondary patency after 12 months was 100%. No procedure-related deaths occurred.

CONCLUSIONS

Endovascular management of SVCO is a safe and effective approach. CT examination can provide a direction for endovascular treatment and periodic surveillance.

Transjugular percutaneous endovascular treatment of dysfunctional hemodialysis access

PURPOSE

To evaluate the feasibility and the outcomes of transjugular percutaneous endovascular treatment of dysfunctional hemodialysis access in patients with chronic kidney disease.

METHODS

A total of 50 transjugular treatments in 38 patients with arteriovenous fistulas or arteriovenous grafts from September 2011 to May 2015 were included in this study. Medical records and angiographies were retrospectively reviewed. Success rate, patency rate, procedure time, and complications including internal jugular vein stenosis were evaluated.

RESULTS

A total of 50 sessions of transjugular treatments were performed in 38 patients. There were 31 native arteriovenous fistulas including 10 immature cases and 19 arteriovenous grafts. Among the 50 cases, technical success was achieved in 45 and clinical success was achieved in 44; 37 cases (74%) with multiple stenotic sites were treated by the transjugular approach without placement of cross-sheaths. The mean time from puncture of the internal jugular vein to first fistulography was 10 min, and the mean total procedure time was 64 min. The primary patency rate at 6 months was 77%, while the secondary patency rate at 6 months was 97%. Perforation occurred in two cases during conventional percutaneous transluminal angioplasty after failure of the transjugular approach. One dissection occurred during the transjugular approach. There was no newly developed internal jugular vein stenosis during a mean follow-up period of 19.3 months.

CONCLUSION

For the treatment of dysfunctional or immature hemodialysis access, the transjugular approach is a feasible and effective option that avoids injury to the graft or draining vein, especially in immature fistulas.

Comparison of Open-Cell Stent and Closed-Cell Stent for Treatment of Central Vein Stenosis or Occlusion in Hemodialysis Patients

Background

Central vein stenosis or occlusion is a common complication that can lead to significant morbidity and dysfunction of access in the hemodialysis patient. More lesions can develop over time, and preserving access becomes a challenge as life expectancy of the hemodialysis patient increases.

Objectives

The goal was to compare long-term results and determine the outcomes of open-cell stent versus closed-cell stent for central vein stenosis or occlusion in hemodialysis patients.

Patients and Methods

From 1997 to 2015, in 401 hemodialysis patients, stent placement for central vein stenosis or occlusion was performed if balloon angioplasty was unsatisfactory, due to elastic recoil or occurrence of restenosis within 3 months. When thrombus was present, primary stenting was performed. A total of 257 open-cell stents and 144 closed-cell stents were used. Angiographic findings including lesion site, central vein stenosis or occlusion, and presence of thrombosis and complication were evaluated. Primary patency rate and mean patency rate of the stent were compared between two stent groups by Kaplan-Meier survival analysis.

Results

For the open-cell stent group, 159 patients were diagnosed as central vein stenosis and 98 were occlusion. For the closed-cell stent group, 78 were stenosis and 66 were occlusion. There were two complications for central migration and two for procedure-related vein rupture. Open-cell stents and closed-cell stents had mean patency rates of 10.9 ± 0.80 months and 8.5 ± 10.87 months, respectively (P = 0.002).

Conclusion

The open-cell stent is effective and its performance is higher than that obtained with the closed-cell stent for treating central vein stenosis or occlusion in hemodialysis patients.

Central venous disease in hemodialysis patients: an update

Central venous occlusive disease (CVD) is a common concern among the hemodialysis patient population, with the potential to cause significant morbidity. Endovascular management of CVD, comprising percutaneous balloon angioplasty and bare-metal stenting, has been established as a safe alternative to open surgical treatment. However, these available treatments have poor long-term patency, requiring close surveillance and multiple repeat interventions. Recently, covered stents have been proposed and their efficacy assessed for the treatment of recalcitrant central venous stenosis and obstruction. Moreover, newly proposed algorithms for the surgical management of CVD warrant consideration. Here, we seek to provide an updated review of the current literature on the various treatment modalities for CVD.

Central venous disease in hemodialysis patients: prevalence, etiology and treatment

A common problem in the management of hemodialysis patients is central venous occlusive disease. There has been extensive literature on the treatment of this important and prevalent problem. Treatment options to date include percutaneous balloon angioplasty, bare metal stents and surgical bypass. Unfortunately, all the available treatment options have poor long-term patency, requiring repetitive intervention. More recently, covered stents have been mentioned in the literature for the treatment of central venous stenosis and obstruction. There is very little data to date on this technology, and further randomized controlled trials will be needed to compare the efficacy of percutaneous balloon angioplasty, bare metal stents and covered stents. It appears prevention of this difficult problem is paramount, by limiting venous access or intervention of the central venous system.

Review of central venous disease in hemodialysis patients

A common problem in the management of patients who are undergoing hemodialysis is central venous occlusive disease. There has been extensive literature on the treatment of this important and prevalent problem. Treatment options to date include percutaneous balloon angioplasty, bare metal stents, and surgical bypass. Unfortunately, all the available treatment options have poor long-term patency, requiring repeated interventions. More recently, covered stents have been mentioned in the literature for the treatment of central venous stenosis and obstruction. There are very few data to date on this technology, and further randomized controlled trials will be needed to compare the efficacy of percutaneous balloon angioplasty, bare metal stents, and covered stents. It appears that it is of paramount importance to prevent this difficult problem by limiting access to, or intervention in, the central venous system.

Tissue vibration pulsatility for arterial bleeding detection using Doppler ultrasound

Trauma is the number one cause of death among Americans between 1 and 44 years old, and exsanguination due to internal bleeding resulting from arterial injuries is a major factor in trauma deaths. We have evaluated the feasibility of using tissue vibration pulsatility in arterial bleeding detection. Eight femoral arteries from four juvenile pigs were punctured transcutaneously with a 6 or 9-French catheter. Also, 11 silicone vessels wrapped with turkey breast were placed in a pulsatile flow phantom and penetrated with an 18-gauge needle. The tissue vibration pulsatility was derived as a ratio of the maximum spectral energy from 200 to 2500 Hz of tissue vibration in systole over a baseline value in diastole. Then, the tissue vibration pulsatility index (TVPI) was defined as the maximum tissue vibration pulsatility value for each experimental condition. Both in vitro and in vivo results showed that the TVPI from injured vessels is significantly higher (p<0.005) than that of intact vessels. In addition, we constructed the 2D map of tissue vibration pulsatility during in vitro studies and found that it could be used for spatial localization of the puncture site. Our preliminary results indicate that the tissue vibration pulsatility may be useful for detecting arterial bleeding and localizing the bleeding site.

Doppler vibrometry: assessment of arterial stenosis by using perivascular tissue vibrations without lumen visualization

PURPOSE

To correlate vibration frequency and duration at Doppler vibrometry with stenosis severity determined at catheter angiography.

MATERIALS AND METHODS

Sixteen patients (eight women) scheduled to undergo abdominal or pelvic angiography were recruited after providing informed consent. An ultrasonography (US) scanner was customized to acquire raw echo data before conventional Doppler processing. Data were acquired from perivascular tissue regions proximal to stenoses, close to the most narrow lumen, and distal to stenoses in the renal, hepatic, common iliac, and superior mesenteric arteries. The data were processed to quantify vibration frequency and duration. The minimum lumen diameter and the pre- and poststenotic lumen diameters were quantified from angiograms. One patient with a hepatic artery stenosis did not yield measurable vibrometry data due to significant bowel gas.

RESULTS

Stenoses (diameter reduction, 43%-91%) were angiographically measured in the six renal arteries, four hepatic arteries, three iliac arteries, and one superior mesenteric artery yielding vibrometry data. Three iliac arteries were normal (<30% diameter reduction at angiography). For these 17 arteries, the vibration frequency was higher with a greater percentage of stenosis [Pearson r = .75; P < .001) and a smaller minimum lumen diameter (r = .72; P < .001). The vibration duration increased with a greater percentage of stenosis (r = .7; P < .001).

CONCLUSIONS

Preliminary results indicate that the vibration frequency and duration can be used to quantitatively estimate stenosis severity. Doppler vibrometry is complementary to duplex US and does not require lumen visualization.

Central venous obstruction management

A major challenge in the management of hemodialysis patients is central venous stenosis and obstruction. Placement of central venous catheters has been shown to result in a high incidence of central venous stenosis or obstruction. There has been extensive literature on the treatment of this important and prevalent problem. Treatment options include percutaneous balloon angioplasty and bare metal stents. Unfortunately, all the available treatment options have variable rates of patency, requiring repeated intervention. More recently, covered stents have been mentioned in the literature for the treatment of central venous stenosis and obstruction. There is very little data to date, and further randomized controlled trials will be needed to compare the efficacy of percutaneous balloon angioplasty, bare metal stents, and covered stents. It appears prevention of this difficult problem is paramount, by limiting use of central venous catheters.

A rare complication of hemodialysis catheters: superior vena cava syndrome

Central venous catheters in hemodialysis patients may result in superior vena cava (SVC) syndrome. With the increasing use of these catheters, the SVC syndrome will probably be more common among hemodialysis patients. This report describes 3 cases of SVC syndrome due to central venous catheters that developed in hemodialysis patients with previous multiple catheter placements.

Central vein stenosis: a nephrologist's perspective

Central vein stenosis is commonly associated with placement of central venous catheters and devices. Central vein stenosis can jeopardize the future of arteriovenous fistula and arteriovenous graft in the ipsilateral extremity. Occurrence of central vein stenosis in association with indwelling intravascular devices including short-term, small-diameter catheters such as peripherally inserted central catheters, long-term hemodialysis catheters, as well as pacemaker wires, has been recognized for over two decades. Placement of multiple catheters, longer duration, location in subclavian vein, and placement on the left-hand side of neck seem to predispose to the development of central vein stenosis. Endothelial injury with subsequent changes in the vessel wall results in development of microthrombi, smooth muscle proliferation, and central vein stenosis. Central vein stenosis is often asymptomatic in nondialysis patients, but can result in edema of ipsilateral extremity and breast when challenged by increased flow from an arteriovenous fistula or arteriovenous graft. Bilateral central vein stenosis or superior vena cava stenosis can produce a clinical picture of superior vena cava syndrome, associated with engorgement of face and neck. Endovascular interventions are the mainstay of management of central vein stenosis. Percutaneous angioplasty and stent placement for elastic and recurring lesions can restore the functionality of the vascular access, at least temporarily. Frequent or multiple interventions are usually required. In recalcitrant cases, surgical bypass of the obstruction is an option. In resistant cases with severe symptoms, occlusion of the functioning vascular access will usually provide relief of symptoms. Further study of mechanisms of development of central vein stenosis and search for a targeted therapy is likely to lead to better ways of managing central vein stenosis. Prevention of central vein stenosis is the key to avoid access failure and other complications from central vein stenosis and relies upon avoidance of central vein stenosis placement and timely placement of arteriovenous fistula in prospective dialysis patient.

Doppler Artifacts and Pitfalls

With increasing technologic advances in ultrasound, its applications have continued to grow for the detection of pathology and physiology. To avoid misinterpretation of results, however, the Doppler US practitioner must understand the factors that produce a Doppler signal, whether vascular, motion, or artifact. Color or power Doppler artifacts can be verified by their atypical spectral waveform. Some artifacts, such as aliasing (for rapid detection of stenoses or arteriovenous fistulae) and the twinkle artifact (for identification of renal calculi and verification of other stones or crystals), are extremely useful diagnostically. Careful attention to the technical parameters of frequency, gain, filter and scale is required to correctly identify vascular patency or thrombosis, especially in slow-flowing vessels.

Ultrasonic interrogation of tissue vibrations in arterial and organ injuries: preliminary in vivo results

Soft tissues surrounding vascular injuries are known to vibrate at audible and palpable frequencies, producing bruits and thrills. We report the results of a feasibility study where Doppler ultrasound (US) was used to quantitatively estimate the tissue vibrations after induced trauma in an animal model. A software-programmable US system was used to acquire quadrature-demodulated ensembles of received US echoes bypassing clutter filtering and other conventional Doppler processing stages. The waveforms of tissue velocity surrounding the injury site were then estimated from the clutter data using autocorrelation and analyzed to determine vibration characteristics. Six New Zealand white rabbits and two juvenile pigs were used for the study. The femoral artery of the anesthetized animal was punctured with an 18-gauge needle to model a peripheral arterial trauma, and the liver was surgically exposed and incised to model organ trauma. Two types of oscillatory tissue motion were observed: "vibrations" with high frequency (>50 Hz) and low peak-peak amplitude (<1 microm) and "flutter" with low frequency (<50 Hz) and high peak-peak amplitude (>1 microm). Active bleeding in femoral artery punctures produced tissue vibrations at the frequency of 323 +/- 214 Hz (mean +/- standard deviation, pooled for both rabbits and pigs) and the amplitude of 0.24 +/- 0.15 microm. Active bleeding in liver incisions produced vibrations at the frequency of 120 +/- 47 Hz and the amplitude of 0.33 +/- 0.25 microm. Flutter was observed in punctured arteries at the frequency of 28 +/- 13 Hz the amplitude of 2.92 +/- 1.75 microm, and in incised livers at the frequency of 26 +/- 6 Hz and the amplitude of 1.53 +/- 0.76 microm. In a punctured artery, the vibration frequency and phase of tissue surrounding the artery were highly correlated between neighboring locations in tissue (correlation coefficient = 0.98), and with the flow oscillations in the lumen (correlation coefficient = 0.96). This preliminary study indicates that tissue vibrations could provide additional physiologic information for detecting, localizing and monitoring internal bleeding using US.

B-flow sonographic evaluation of hemodialysis fistulas: a comparison with low- and high-pulse repetition frequency color and power Doppler sonography

OBJECTIVE

The purpose of this study was to determine the effectiveness of B-flow sonography in the evaluation of hemodialysis fistulas and to compare this new technique with color and power Doppler sonography.

METHODS

In this study, 32 randomly selected patients (mean age, 46 years; age range, 18-87 years) with normally functioning hemodialysis fistulas were evaluated with low- and high-pulse repetition frequency (PRF) color and power Doppler sonography (PRF values of 3 and 10 kHz) and B-flow sonography. All images were reviewed and graded independently by 2 observers for luminal filling with flow signals, visibility of the intimal layer, and overall image quality. The study was approved by the Institutional Review Board, and informed consent was obtained from all patients.

RESULTS

Statistical analysis with Friedman and Wilcoxon signed rank tests revealed that B-flow sonography was superior to other techniques for luminal filling and visibility of the intimal layer (P = .000). For overall image quality, B-flow sonography was also the best method according to the Friedman test (P = .000). However, the Wilcoxon test showed no significant difference between B-flow and high-PRF (10-kHz) color and power Doppler sonography (P = .131). The kappa scores reflected moderate to good interobserver agreement (kappa = 0.285-0.784).

CONCLUSIONS

B-flow sonography is a relatively new and superior imaging technique that provides direct visualization of the blood echoes and the morphologic characteristics of the surrounding vessel wall simultaneously. During the evaluation of hemodialysis shunts, the major advantage of this technique is its ability to avoid artifacts such as aliasing and overwriting.

Ultrasonic technique for imaging tissue vibrations: preliminary results

We propose an ultrasound (US)-based technique for imaging vibrations in the blood vessel walls and surrounding tissue caused by eddies produced during flow through narrowed or punctured arteries. Our approach is to utilize the clutter signal, normally suppressed in conventional color flow imaging, to detect and characterize local tissue vibrations. We demonstrate the feasibility of visualizing the origin and extent of vibrations relative to the underlying anatomy and blood flow in real-time and their quantitative assessment, including measurements of the amplitude, frequency and spatial distribution. We present two signal-processing algorithms, one based on phase decomposition and the other based on spectral estimation using eigen decomposition for isolating vibrations from clutter, blood flow and noise using an ensemble of US echoes. In simulation studies, the computationally efficient phase-decomposition method achieved 96% sensitivity and 98% specificity for vibration detection and was robust to broadband vibrations. Somewhat higher sensitivity (98%) and specificity (99%) could be achieved using the more computationally intensive eigen decomposition-based algorithm. Vibration amplitudes as low as 1 mum were measured accurately in phantom experiments. Real-time tissue vibration imaging at typical color-flow frame rates was implemented on a software-programmable US system. Vibrations were studied in vivo in a stenosed femoral bypass vein graft in a human subject and in a punctured femoral artery and incised spleen in an animal model.

The diagnostic relevance of colour Doppler artefacts in carotid artery examinations

PURPOSE

Physical and technical artefacts of the colour Doppler method are examined with regard to their diagnostic relevance for the carotid artery.

MATERIALS AND METHODS

After recording all diagnostic problems arising from physical and technical artefacts in 30,000 consecutively carotid arteries, the quantitative significance of relevant artefacts was determined in minor subgroups of the collective.

RESULTS

Acoustic shadowing causes diagnostic problems in morphological and haemodynamic evaluation of stenoses. Mirror image artefacts simulate flow in cases of actual vessel occlusion or mimic vessel wall ulceration in carotid plaques and stenoses. Insonation angle artefacts inhibit detection of flow or mimic flow reversal. Problems of spatial resolution lead to incorrect demonstration of the vessel lumen in stenotic findings. Aliasing, perivascular colour artefacts, and ghosting do not cause any diagnostic problems. Relevant shadowing artefacts occurred in 14.7%, and relevant mirror image artefacts in 2.5% of the pathological cases. Insonation angle artefacts occurred in 17.3% of the cases (when using standard apparatus setting). However, with an exact knowledge of the artefact phenomena, insonation angle artefacts could be eliminated and mirror image artefacts were recognized in all cases. Resolution artefacts resulted in underestimation of carotid stenoses by on average 13.3% of the degree of stenosis.

CONCLUSION

In principle, four artefact phenomena give rise to diagnostic problems; however, with a good knowledge of the phenomena, only artefacts due to acoustic shadowing and limited spatial resolution are of diagnostic significance.

Pediatric abdominal applications of color Doppler ultrasonography

Color Doppler ultrasonography (US) is a valuable imaging method because of the important information it provides with respect to organ perfusion, vessel patency, and tumor characterization. In addition, it is a noninvasive technique that does not use ionizing radiation. This review summarizes current applications of color Doppler US in the diagnosis of diseases or abnormalities of the liver and biliary tree, the urinary and gastrointestinal tracts, and the inguinal region.

Twinkling artifact in color Doppler imaging of the orbit

OBJECTIVE

To show an artifact related to color Doppler flow imaging of the orbit.

METHODS

Three patients with strongly reflective structures in the orbit were selected from those routinely referred by clinicians for color Doppler ultrasonography of the orbit. Gray scale and color flow images were obtained with a 7.5-MHz linear array probe for a region with strongly reflective structures. A spectral display was acquired to confirm the presence of blood flow.

RESULTS

One patient had a metallic foreign body just behind the bulb; another had calcification within the irregular mass of phthisis bulbi; and the third had hyperechoic drusen in the periphery of the intraocular melanoma. The color mosaic, suggesting the presence of blood flow, was detected beyond all hyperechoic structures. Close vertical bands with no outer wrapping were detected in the spectrum display, obtained by placing the sample volume on the region of color flow. The artificial color flow was recognized as a color Doppler twinkling artifact.

CONCLUSIONS

The color flow beyond the strongly reflecting structures in the orbit might be mistakenly interpreted as real blood flow if an examiner is not familiar with the artifact. It should prompt further imaging with spectral Doppler ultrasonography.

Effect of color Doppler system on the twinkling sign associated with urinary tract calculi

PURPOSE

The aim of this study was to assess the effect of the color Doppler system on the artifact known as the "twinkling sign."

METHODS

Sixty-five patients with at least 1 urinary tract calculus seen on sonography were examined with color Doppler sonography. Two color Doppler systems of 2 different generations were used. Examinations included gray-scale, color Doppler, power Doppler, and spectral evaluations of the calculus with various settings of Doppler gain, velocity range, color filter, focal depth, and acoustic power.

RESULTS

A color artifact was present within and/or distal to 29 (39%) of 75 urinary tract calculi when the old generation system was used. Use of the new generation system produced this color artifact within and/or distal to 72 (96%) of the urinary tract calculi. The intensity of the artifact was affected by the acoustic output of the equipment.

CONCLUSIONS

The twinkling sign is an artifact that can not only lead to misdiagnosis of vascular flow within a structure but also help differentiate a very small stone from other small echogenic structures when later generation "all-digital" systems are used. The color sensitivity of the system and acoustic power used are important technical factors that affect the production of this artifact.

Doppler sonography of the native liver

Doppler sonography is being used routinely in evaluating the vascular structures of the native liver because of its ease of use, lower cost, easier availability, lack of need for X-ray and accuracy. Doppler sonography can well demonstrate the vascularization of liver tumors, portal vein thrombosis, portal vein abnormalities in patients with portal hypertension and hepatic venous findings in patients with Budd Chiari syndrome. The purpose of this article is to present information about Doppler sonography of the native liver and to show its usefulness in the evaluation of hepatic vascular diseases.

Renovascular disease: Doppler ultrasound

Color Doppler ultrasound (CDUS) seems to be an effective imaging technique for the diagnosis of renal vascular diseases. It is already the modality of choice for the detection of acute renal vein thrombosis and nonocclusive intrarenal vascular disorders including iatrogenic arteriovenous fistula and false aneurysm, particularly in patients with impaired renal function that precludes the use of iodinated contrast agents. Although proximal Doppler interrogation remains an important step in diagnosing renal artery (RA) stenosis, useful hemodynamic information can be obtained from the distal arterial bed. When CDUS fails in identifying proximal RAs, normal waveform velocity and morphology obtained from intrarenal arteries enable one to rule out RA occlusion and most of the severe stenoses (> or = 80%). Such information, which is not subject to a significant risk of technical failure, seems to be particularly useful in studying patients with acute renal failure of suspected vascular origin. Despite the extreme variability in reported performance between studies, CDUS has seemed to be a valuable tool compared with other noninvasive modalities in the diagnosis of RA stenosis. Whereas a CDUS-based strategy is already accepted in numerous specialized centers, a thorough evaluation of diagnostic criteria and extensive training of operators will allow CDUS to be widely accepted for the screening of patients at high risk for renovascular hypertension.

Color flow mapping

Color flow mapping systems have become widely used in the short time since their development. These systems overlay a pseudo-color velocity map upon the gray-scale two-dimensional image. Between 4 and 16 pulses are directed to each line-of-sight, and this requirement reduces the frame rate in comparison with the gray-scale image. Other limitations of color flow mapping include its ability to estimate only the velocity toward or away from the transducer and an increase in the variance in comparison with spectral Doppler. Potential artifacts include aliased velocities and the detection of flow in hypoechoic or hyperechoic nonvascular structures. Clinical applications include cardiology, studies of the abdominal and peripheral vasculature, evaluation of organ perfusion and the differentiation of tumors. Most current systems use narrowband estimators that examine a fixed sample volume and detect a change in phase between two pulses. Wideband estimators that can track red blood cells in two or three dimensions are under evaluation. Narrowband estimators, including the autocorrelator, the short Fourier transform and second order autoregressive filters, are compared with wideband estimators including cross-correlation, sum-absolute-difference and the wideband maximum likelihood estimator. Because the intensity of blood echoes is far smaller than echoes from surrounding tissue, high pass filters have been developed that can reject the larger signal from tissue using the return from a small number of pulses. Other areas of research include strategies for flow estimation with contrast agents, three-dimensional color flow mapping and power Doppler flow mapping.

Vascular ultrasound: a radiologist perspective

Color Doppler flow imaging (CDFI) is an evolutionary technical development that has considerably improved the diagnostic efficacy and clinical role of vascular ultrasound. The appropriate use of CDFI rests on an understanding of the instrumentation, factors affecting image quality and artifact, as well as the pathophysiology of the central and peripheral circulation. The modality has reached a relative plateau of performance. In this review, applications of CDFI for studies of the neck, abdomen, and extremities are evaluated.