Stenosis of the renal artery: assessment of slowed systole in the downstream circulation with Doppler sonography

Computer-assisted detection of tardus parvus waveforms on Doppler ultrasound

OBJECTIVE

To determine if a novel computer-generated metric, effective acceleration time, improves accuracy for detecting tardus parvus waveforms on spectral Doppler ultrasound.

METHODS

Patients with echocardiography-confirmed aortic valve stenosis (n = 132; 60 mild, 44 moderate, 28 severe) and matched controls (n = 48) who underwent carotid Doppler ultrasound were identified through an imaging database search at a single medical center. A custom-built spectral analysis computer program generated effective acceleration time values for spectral Doppler waveforms in the carotid arteries and a receiver operating characteristic analysis was performed to determine the optimal median effective acceleration time cutoff value to detect tardus parvus waveforms. Two radiologists, blinded to subject disease status, reviewed and rated all carotid sonograms for presence of tardus parvus waveforms. Inter-rater variability was measured, and the accuracy of aortic valve stenosis detection with and without use of the effective acceleration time cutoff was calculated.

RESULTS

Receiver operating characteristic analysis revealed an optimal effective acceleration time cutoff of ≥ 48 ms with a corresponding area under the curve of 0.77 (95% CI: 0.70-0.84). Use of the effAT cutoff demonstrated an accuracy of 74%. Accuracy of visual waveform interpretation by raters ranged from 43% to 61%. Inter-rater agreement in detection of tardus parvus waveforms was 76% (136/180 cases, K = 0.44, p < 0.001).

CONCLUSIONS

Detection of tardus parvus waveforms through visual interpretation of spectral Doppler waveform morphology is limited by low accuracy and moderate inter-rater variability. Use of a computer-generated median effective acceleration time cutoff value markedly improves diagnostic accuracy and avoids observer variability.

Type 3 takayasu arteritis diagnosed by parvus-tardus renal Doppler signal modulation

Takayasu's arteritis is known to cover the youngest age group in the etiology of secondary hypertension. The type 3 pattern is rare and involves the thoraco-abdominal aorta and its main abdominal branches. Here, we present the imaging results of a patient who had been followed up for systemic arterial hypertension and was diagnosed with Takayasu's arteritis type 3 by CT and MR angiography following bilateral detection of a parvus-tardus Doppler signal modulation in the renal arteries. We discuss the differential diagnoses that should be considered when observing a tardus-parvus Doppler signal. © 2017 Wiley Periodicals, Inc. J Clin Ultrasound 45:612-615, 2017.

Doppler Ultrasound in the Diagnosis of Renal Transplant Artery Stenosis — Value of Resistive Index

Doppler ultrasound (DU) with angiographic correlation was performed in 19 hypertensive renal transplant recipients suspected for transplant artery stenosis. DU included calculation of the intrarenal resistive index (RI) and measurement of the maximum systolic velocity in the transplant artery. All 10 cases having a pathologically low RI (≤0.6) had a ≥ 50% stenosis; specificity and positive predictive values were thus 100%. There were 5 false-negative diagnoses, sensitivity 67%. The measurement of maximum systolic velocity was feasible in only 15 cases (79%). Using a cut-off point of 2 m/s the sensitivity was 91% and there were 4 false-positive cases and one false-negative case. Balloon percutaneous transluminal angioplasty (PTA) was performed in 13 cases, of which 9 were successful. In all successful cases RI was <0.6 after PTA. We conclude that low RI (<0.6) is highly suggestive for transplant artery stenosis. RI may serve as an indicator of the hemodynamic success of PTA.

Renal artery stenosis due to fibromuscular dysplasia in a transplanted kidney from a deceased donor: a difficult diagnosis at color Doppler ultrasonography

Atherosclerotic renal artery stenosis is a frequent cause of arterial hypertension and/or allograft dysfunction after kidney transplantation and is usually located at the iliac artery anastomosis. Fibromuscular dysplasia is a less frequent, nonatherosclerotic, vascular disease, inducing stenosis at the proximal/mid-distal part of the renal artery. We report the case of a 44-year-old woman, in whom serum creatinine concentration increased and arterial hypertension developed 3 months after renal transplantation. Color Doppler ultrasonography showed a low arterial resistance index and prolonged acceleration time in the interlobar arteries, and a significantly increased peak systolic velocity at the mid third of the renal artery, demonstrating hemodynamically significant stenosis. Percutaneous transluminal angioplasty allowed stenosis correction and was followed by creatinine concentration and arterial blood pressure normalization.

Reference Values and Factors Associated With Renal Resistive Index in a Family-Based Population Study

Increased renal resistive index (RRI) has been recently associated with target organ damage and cardiovascular or renal outcomes in patients with hypertension and diabetes mellitus. However, reference values in the general population and information on familial aggregation are largely lacking. We determined the distribution of RRI, associated factors, and heritability in a population-based study. Families of European ancestry were randomly selected in 3 Swiss cities. Anthropometric parameters and cardiovascular risk factors were assessed. A renal Doppler ultrasound was performed, and RRI was measured in 3 segmental arteries of both kidneys. We used multilevel linear regression analysis to explore the factors associated with RRI, adjusting for center and family relationships. Sex-specific reference values for RRI were generated according to age. Heritability was estimated by variance components using the ASSOC program (SAGE software). Four hundred women (mean age±SD, 44.9±16.7 years) and 326 men (42.1±16.8 years) with normal renal ultrasound had mean RRI of 0.64±0.05 and 0.62±0.05, respectively ( P <0.001). In multivariable analyses, RRI was positively associated with female sex, age, systolic blood pressure, and body mass index. We observed an inverse correlation with diastolic blood pressure and heart rate. Age had a nonlinear association with RRI. We found no independent association of RRI with diabetes mellitus, hypertension treatment, smoking, cholesterol levels, or estimated glomerular filtration rate. The adjusted heritability estimate was 42±8% ( P <0.001). In a population-based sample with normal renal ultrasound, RRI normal values depend on sex, age, blood pressure, heart rate, and body mass index. The significant heritability of RRI suggests that genes influence this phenotype.

Doppler ultrasound and renal artery stenosis: An overview

Renovascular disease is a complex disorder, most commonly caused by fibromuscular dysplasia and atherosclerotic diseases. It can be found in one of three forms: asymptomatic renal artery stenosis (RAS), renovascular hypertension, and ischemic nephropathy. Particularly, the atherosclerotic form is a progressive disease that may lead to gradual and silent loss of renal function. Thus, early diagnosis of RAS is an important clinical objective since interventional therapy may improve or cure hypertension and preserve renal function. Screening for RAS is indicated in suspected renovascular hypertension or ischemic nephropathy, in order to identify patients in whom an endoluminal or surgical revascularization is advisable. Screening tests for RAS have improved considerably over the last decade. While captopril renography was widely used in the past, Doppler ultrasound (US) of the renal arteries (RAs), angio-CT, or magnetic resonance angiography (MRA) have replaced other modalities and they are now considered the screening tests of choice. An arteriogram is rarely needed for diagnostic purposes only. Color-Doppler US (CDUS) is a noninvasive, repeatable, relatively inexpensive diagnostic procedure which can accurately screen for renovascular diseases if performed by an expert. Moreover, the evaluation of the resistive index (RI) at Doppler US may be very useful in RAS affected patients for predicting the response to revascularization. However, when a discrepancy exists between clinical data and the results of Doppler US, additional tests are mandatory.

[Doppler US of the urinary system and renal vessels in normal and pathologic conditions]

The interest of Doppler ultrasound (US) in urinary tract investigation has dramatically increased during the past 10 years. It can provide useful diagnostic informations in pedicular and intrarenal vascular disorders, some medical nephropathies, in the assessment of renal tumors and urinary tract disorders including urolithiasis, acute obstruction and ureteral reflux. Recent technical improvements including the development of US contrast agents (microbubbles) have contributed to increase the diagnostic accuracy of the technique.

Serendipitous diagnosis of aortic coarctation by bilateral parvus et tardus renal Doppler flow pattern

Background

Aorta Coarctation (AC) is uncommon condition that in most adult patients is asymptomatic. Diagnosis of AC is made during routine physical examination by detection of Blood Pressure (BP) difference between arm and leg.

Aim

To describe a novel renal artery Doppler flow pattern pathognomonic of aortic coarctation.

Methods

We enrolled 4 consecutive patients referred to renal artery Doppler Ultrasonography (DU) for diagnostic work-up of secondary arterial hypertension. All met the following inclusion criteria: 1) arterial hypertension at age <30 years; 2) referred for renal DU to rule out renovascular hypertension.

Results

We found in all 4 patients (age range 10 to 27 years) a bilateral "parvus-tardus" renal Doppler flow pattern. In all, echocardiographic and angiographic work-ups showed aortic coarctation.

Conclusion

Careful physical examination should be performed in all hypertensive patients. Furthermore, the suspicion of AC can be raised by a bilateral renal arteries "parvus-tardus" Doppler flow pattern in young hypertensive patients screened for secondary hypertension.

Evaluation of the tardus-parvus pattern in patients with atherosclerotic and nonatherosclerotic renal artery stenosis

OBJECTIVE

The aim of this study was to evaluate the differences in the tardus-parvus pattern between atherosclerotic and nonatherosclerotic renal artery stenosis (RAS) and to explore the causes of these differences.

METHODS

In 81 patients, including a nonatherosclerotic group (29 cases of Takayasu arteritis and 22 cases of fibromuscular dysplasia) and an atherosclerotic group (n = 30), RAS was detected by color Doppler sonography and confirmed by renal arteriography. Doppler spectra were obtained at the upper, middle, and lower pole interlobar arteries, and the one with the most prolonged acceleration time (AT) was selected for recording the AT and resistive index (RI).

RESULTS

Renal angiography revealed 16 moderate RASs, 80 severe RASs, and 15 occlusions. No statistically significant differences were found in the AT between the atherosclerotic and nonatherosclerotic groups in the mild (P = .24), moderate (P = .63), and severe stenotic (P = .41) subgroups; however, there were statistically significant differences in the RI between the atherosclerotic and nonatherosclerotic groups in the mild (P < .001), moderate (P < .01), and severe (P < .001) subgroups. The RI values in the atherosclerotic group were much higher than those in the nonatherosclerotic group for the 3 stenotic subgroups.

CONCLUSIONS

The AT measurement method used widely now cannot differentiate potential differences in pulsus-tardus waveforms between atherosclerotic and nonatherosclerotic RAS; however, it remains a useful approach to detect RAS. Different RI cutoff values should be established according to atherosclerotic and nonatherosclerotic RAS, and consideration of influencing factors for the RI will help reduce misdiagnosis.

Evaluation of renal artery stenosis with velocity parameters of Doppler sonography

OBJECTIVE

The purpose of this study was to evaluate the accuracy of velocity parameters for the diagnosis of renal artery stenosis (RAS) with color Doppler sonography and to determine the optimal threshold values for these parameters.

METHODS

The study group was composed of 187 renal arteries, which were examined by color Doppler sonography and angiography. Four Doppler parameters, including the peak systolic velocities (PSVs) in the renal and interlobar arteries, the renal-aortic ratio, and the renal-interlobar ratio (RIR), were measured. Receiver operating characteristic curve analysis was performed to determine the optimal parameter. The sensitivity, specificity, and negative and positive predictive values at various threshold values were calculated.

RESULTS

Doppler sonographic examination was technically successful in 96% of renal arteries (180/187). The RIR was determined to be the best parameter. With threshold values of RIR greater than 5, PSV greater than 150 cm/s in the renal artery, renal-aortic ratio greater than 2, and PSV less than 25 cm/s in the interlobar artery, the sensitivity values were 88%, 81%, 70%, and 74%, respectively. An RIR greater than 5 and PSV less than 15 cm/s in the interlobar artery provided the optimal combination of parameters, with sensitivity and specificity of 91% and 87%, respectively.

CONCLUSIONS

The RIR is the best velocity parameter in the detection of RAS (> or =50%), and its best cutoff is 5. Valuing influencing factors of PSV in the renal artery will help reduce misdiagnosis. The combination of RIR greater than 5 and PSV less than 15 cm/s in the interlobar artery provides the best diagnostic efficiency of RAS.

Changes in cerebral and ocular hemodynamics in Behçet's disease assessed by color-coded duplex sonography

AIM

To quantify the cerebral and retrobulbar hemodynamics in Behçet's disease with and without ocular involvement and compared with that of healthy controls.

MATERIALS AND METHODS

Of 51 people studied, 17 had Behçet's disease with ocular involvement, 17 had Behçet's disease without ocular involvement, and 17 were healthy controls. A single eye was examined in each patient. Peak systolic velocity (PSV), end-diastolic velocity (EDV), time-averaged maximum velocity (Tamax), and resistance index (RI) were evaluated in the ophthalmic (OA), posterior ciliary (PCA), central retinal (CRA) and middle cerebral artery (MCA). Additionally, the average blood flow velocities in the central retinal vein (CRV), and acceleration time (AT) and pulsatility index (PI) in the MCA were calculated.

RESULTS

The mean EDV in the PCA was 25% lower and RI was higher in patients with ocular involvement of BD than in patients without involvement (p = 0.006 and p = 0.005, respectively) and in healthy controls (p = 0.003 and p = 0.004, respectively). Differences were smaller in comparisons of the CRA and absent on comparisons of the OA and MCA. The acceleration time of the MCA was significantly higher in patients with Behçet's disease than in healthy controls (p = 0.03).

CONCLUSION

This study suggests that the flow hemodynamics in retrobulbar circulation has more altered Behçet's disease with ocular involvement than without ocular involvement and healthy control. Additionally, the cerebral hemodynamic might be affected in patients with Behçet's disease compared with healthy controls.

Renal Interlobar Artery Parameters with Duplex Doppler Sonography and Correlations with Age, Plasma Renin, and Aldosterone Levels in Healthy Children

OBJECTIVE

The objectives of this study were to compare and make correlations between age and Doppler parameters of the interlobar arteries, including synchronously obtained plasma renin and aldosterone levels and to obtain new normative data regarding acceleration time in healthy children from neonates to 16 years.

SUBJECTS AND METHODS

One hundred sixty-nine healthy children (72 girls and 97 boys) were classified into four groups: group 1 (< 1 year; n = 34), group 2 (range, 1-6 years; n = 48), group 3 (range, 6-12 years; n = 50), and group 4 (range, 12-16 years; n = 37). Blood samples from the renin and aldosterone were collected in the morning after bed rest and fasting. The resistive index (RI), pulsatility index (PI), and the acceleration time of the renal interlobar arteries with duplex Doppler sonography, including both kidney longitudinal lengths with grayscale sonography, were evaluated. One-way analysis of variance with the least significant difference post-hoc test and Pearson's correlation test were used to compare the differences between groups and to make correlations, respectively. An independent-sample t test was used to evaluate the differences between all parameters based on sex and to compare the left and right kidney longitudinal lengths in each group.

RESULTS

The RI, PI, and acceleration time were statistically significant in between-group comparisons. Only in group 4 was acceleration time not statistically significant compared with groups 2 and 3. Plasma renin levels were significantly higher in group 1 compared with groups 2 (p < 0.03) and 4 (p < 0.0001); in group 2 compared with group 4 (p < 0.05); and in group 3 compared with group 4 (p < 0.01). The plasma aldosterone levels were significantly higher only in group 1 compared with groups 2 (p < 0.001), 3 (p < 0.008), and 4 (p < 0.0001). The RI correlated linearly with the PI, plasma renin levels, and aldosterone levels and correlated inversely with acceleration time. Age had a negative correlation with the RI, PI, plasma renin levels, and aldosterone levels and correlated positively with acceleration time. There were no statistically significant differences between all parameters based on sex and no significant difference found between the right and left kidney longitudinal lengths in each group.

CONCLUSION

The RI in children up to 54 months old is higher than in adults. Therefore, the adult mean renal RI criterion of 0.70 should be applicable to children 54 months old and older. We showed that the age dependency of the RI was directly related to that of plasma renin and aldosterone levels in healthy children in whom Doppler parameters and blood analysis were evaluated synchronously.

New intrarenal echo-Doppler velocimetric indices for the diagnosis of renal artery stenosis

We aimed at comparing the positive and negative predictive values (PPV, NPV) of several intrarenal velocimetric indices for revealing the presence of renal artery stenosis (RAS) among hypertensive patients who underwent a renal angiography for the clinical suspicion of renovascular hypertension. In 106 patients (200 kidneys), the pulsatility index (PI) and resistive index (RI), the acceleration time (AT), and the mean systolic acceleration (ACC(sys)) were evaluated. In addition, the maximal systolic acceleration (ACC(max)), that is, the maximal slope of the acceleration phase, and the maximal acceleration index (AI(max)), that is, the ratio between ACC(max) and the relative peak systolic velocity, were calculated. On angiography, we found that 56 (28%) of the 200 arteries had a greater than 60% RAS. PI and RI had an NPV below 75%, whereas AT, ACC(sys), ACC(max), and AI(max) had an NPV always above 95%. However, ACC(max), and AI(max), at their best cutoff limits, had higher PPV than ACC(sys) and AT (60 and 70% vs 45 and 51%, respectively). Thus, in a cohort of patients with a high prevalence of RAS, PI and RI failed to reach an NPV adequate for a screening test. In contrast, all the acceleration indices we tested had a sufficiently high NPV but AI(max) appears superior to the others because of higher PPV. We propose the evaluation of AI(max) as an additional screening test in patients with hypertension and the clinical suspicion of RAS.

Innominate Artery Occlusive Disease: Sonographic Findings

OBJECTIVE

The objective of this study was to report the sonographic abnormalities in a group of patients with angiographically proven innominate artery stenosis and occlusion.

MATERIALS AND METHODS

A review of all cerebrovascular sonograms at our institutions was undertaken to identify patients with complete or partial flow reversal in the right vertebral artery and reversal or midsystolic deceleration of flow in any one of the three major segments of the right carotid system (common, internal, or external carotid artery). The distribution and appearance of these abnormalities was evaluated, and the presence or absence of tardus-parvus waveforms was noted in any segment of the right carotid artery. Additionally, a left to right common carotid peak systolic velocity ratio (LCCA/RCCA) was calculated and compared to published normal values. All patients had correlative contrast or MR angiography. Correlation was made between the severity of stenosis as determined by angiographic images and waveform aberrations as well as the more objective LCCA/RCCA ratios.

RESULTS

Twelve patients were identified as having the abnormalities described above in the right vertebral and carotid arteries. Doppler waveforms from the right vertebral artery revealed that eight of the 12 patients had complete reversal of flow at rest. Bidirectional flow was found in the remaining four as manifested by the presence of marked midsystolic deceleration. In the carotid arteries, one patient had complete reversal of flow in all segments of the right carotid system. Waveforms with midsystolic deceleration were identified in at least one of the carotid arteries of the remaining 11 patients: common carotid artery (8/11 = 73%), internal carotid artery (10/11 = 91%), external carotid artery (3/11 = 27%). The average LCCA/RCCA was 3.1 with a range of 1.7 to 5.7 (normal = 0.7-1.3). All patients had severe innominate artery disease (from 70% to occlusion) by contrast angiography or MR angiography. There was no correlation between the angiographically determined degree of stenosis and the Doppler findings.

CONCLUSION

A distinctive pattern of hemodynamic alterations occurs in the right vertebral and carotid arteries of patients with severe innominate artery disease. Findings include reversed or bidirectional flow in the right vertebral artery, the presence of midsystolic deceleration in any of the branches of the right carotid system, and elevated LCCA/RCCA ratio.

Pediatric applications of abdominal vascular Doppler: Part II

Ultrasound is a remarkably powerful and versatile modality for pediatric imaging, without requiring exposure to radiation or sedatives. By providing information on blood flow, Doppler sonography can reveal details about normal physiology and disease processes not discernable from gray-scale anatomic images alone. In part I, the basics of hemodynamics and effects on the Doppler waveform were discussed, along with clinical applications in hepatic disease. In part II, the application of Doppler in renal disease and in conditions affecting the deep abdominal vessels are discussed. The role of ultrasound contrast agents in pediatric Doppler imaging is briefly reviewed.

Changes of Renal Blood Flow in Nephroptosis: Assessment by Color Doppler Imaging, Isotope Renography and Correlation with Clinical Outcome after Laparoscopic Nephropexy

OBJECTIVE

Previously, we have detected changes in renal blood flow secondary to nephroptosis by assessing the renal resistive index (RI) using color Doppler imaging (CDI). The aim of the current study was to compare two diagnostic methods, CDI and isotope renography (IRG), for detection of renal blood flow impairment in patients with nephroptosis.

METHODS

26 patients with nephroptosis and flank pain underwent CDI and isotope renography (IRG) before and after laparoscopic nephropexy. The RI was assessed in segmental arteries with the patient in both the supine and erect position. Pre- and postoperative patient symptoms, results of Doppler measurements and IRG findings were assessed.

RESULTS

Preoperatively, 23 of 26 symptomatic patients showed a mean reduction in RI of more than 0.10 on the affected side, while only 7 of 26 patients had abnormal findings on preoperative IRGs. Postoperatively, none of the patients with preoperative changes in Doppler parameters showed any posture-related changes in RI. On postoperative IRG, obtained in 4 of 7 patients, normalization of renal perfusion was documented. Twenty out of 26 patients were asymptomatic postoperatively; in the remaining 6 patients symptoms were markedly improved.

CONCLUSION

Impairment of renal blood flow due to nephroptosis was detected with both CDI and IRG. RI measurement by CDI appears to be significantly more sensitive in detecting renal blood flow impairment. RI should be assessed in patients with nephroptosis and may impact on the decision for laparoscopic nephropexy.

Evaluation of the hypertensive infant

This article reviews the literature and describes a methodologic approach to the diagnosis of hypertension in the young infant. The numerous etiologies of hypertension have been discussed and normative blood pressure data for neonates and infants have been provided. Techniques for accurate blood pressure measurement in the intensive care setting and for routine outpatient settings, are discussed. The lengthy discussion of radiologic approach to imaging can be summarized with the following suggested algorithm. Initial screening should be performed with gray-scale sonography, to identify renal parenchymal or collecting system abnormalities, including mass lesions and congenital anomalies. Further imaging with color and duplex Doppler sonography detects renal arterial or aortic thrombosis, and alterations in the arterial waveform caused by intrinsic or extrinsic renal artery narrowing. The major limitation of Doppler sonography is the recognition that disease in accessory renal arteries or in small segmental intrarenal arteries may frequently be undetected. Functional imaging with ACEI renography should follow renal sonography to detect hemodynamically significant renovascular disease (with a sensitivity and specificity of approximately 90%); intravenous enalaprilat is the preferred ACEI. Angiography should be reserved for older children in whom interventional percutaneous angioplasty may be more feasible. A young infant with hypertension caused by renal artery stenosis should be controlled medically until he or she is large enough to undergo angiography and angioplasty successfully. CT angiography and MR angiography, although promising in the adult population, may not adequately resolve the small intrarenal vessels, which are frequently the culprit in renovascular hypertension of infancy.

Reliability of intrarenal Doppler sonographic parameters of renal artery stenosis

PURPOSE

The goal of this study was to retrospectively evaluate false-negative results of Doppler sonography in the diagnosis of renal artery stenosis (RAS) using intrarenal criteria.

METHODS

We reviewed the clinical data and Doppler sonographic data for all patients in whom a diagnosis of RAS had been confirmed angiographically between November 1992 and January 2001. Mean intrarenal acceleration and acceleration time values-data obtained directly from color Doppler sonography-and findings of angiographic examination of the kidneys and stenotic renal arteries were evaluated.

RESULTS

During the study period, 55 cases of RAS had been angiographically confirmed in 46 patients (25 male and 21 female; mean age, 50 +/- 19 years [+/- standard deviation]). Intrarenal arterial acceleration, acceleration time values, or both were abnormal in 42 kidneys (76%) (group A) and normal in 13 kidneys (24%) (group B). The mean age +/- standard deviation was significantly higher for patients in group B (60 +/- 12 years) than for those in group A (47 +/- 20 years) (p > 0.05). In group B, most of the stenotic lesions were atherosclerotic, and in all kidneys but 1, the lesions were located at the renal ostium or the proximal half of the artery.

CONCLUSIONS

Isolated use of intrarenal Doppler sonographic criteria for RAS may lead to an unacceptably high incidence of false-negative results in the diagnosis of this condition, especially in elderly patients.

Sonography in renovascular hypertension

OBJECTIVE

To familiarize practitioners with different sonographic manifestations of renal artery compromise and the sonographic techniques for renal artery imaging.

METHODS

Approximately 1500 examinations evaluating for renal artery disease are performed in our vascular laboratory every year. Most of the patients have the symptoms of hypertension (possibly related to renovascular etiology) and renal insufficiency. From our cumulative experience, the optimal scanning techniques are defined for each renal artery, for extrarenal versus intrarenal vascular evaluation, and for patients with different body habitus. We have also tabulated our technical success rate. Cases with sonographic evidence of renal artery compromise are identified. The validity, sensitivity, and specificity of different parameters are examined.

RESULTS

We achieve an approximately 75% to 80% success rate in obtaining technically adequate studies. We have not found the tardus-parvus waveform evaluation to be as valuable as direct interrogation of the renal artery.

CONCLUSIONS

Duplex/color Doppler sonography serves a vital role in the diagnosis of renal artery stenosis and occlusion; it has an excellent correlation with contrast-enhanced angiography. It is also used for intraoperative or postrevascularization surveillance to show evidence of recurring stenosis, thrombosis, and other complications.

Interventional Radiology in the Pediatric Liver Transplant Patient

Liver transplantation now plays a major role in the treatment of end-stage liver disease in children. Reduced-size liver transplant surgical techniques have allowed increasing numbers of children to undergo liver transplantation. As more children are undergoing liver transplantation, there is a growing need for radiologic diagnosis of and intervention in post-transplantation complications in these patients.

Utility of intrarenal Doppler ultrasound in the diagnosis of renal artery stenosis

PURPOSE

To determine the utility of intrarenal Doppler parameters and waveform analysis in a hypertensive population screened for renal artery stenosis (RAS).

MATERIALS AND METHODS

Sixty five patients were studied (122 kidneys) with intrarenal Doppler sonography. Doppler waveforms of three different areas from each kidney were obtained (superior, middle and inferior level). Waveform morphology, acceleration time (AT), acceleration (Ac) and resistive index (RI) were evaluated in each kidney, comparing retrospectively the Doppler findings with the angiographic results.

RESULTS

Arteriography demonstrated 33 (27.2%) renal arteries with stenosis (18 with RAS>75%). Statistically significant differences for AT and Ac were found among the patients with RAS>75% and the other groups (P<0.01). An AT>80 ms and an Ac< or =1 m/s(2) showed a sensitivity of 89% and a specificity of 99%, for the diagnosis of RAS>75%. Better results were obtained in patients less than 50 years old (100% of sensitivity and specificity). The morphologic analysis of the Doppler waveform had poor results but the detection of a waveform grade 0 had a high specificity (98%). An additional comparison of both kidneys didn't improve the results.

CONCLUSION

Intrarenal Doppler waveform analysis using quantitative measurements (AT and Ac) is an adequate technique for the diagnosis of severe RAS in previously selected patients, especially in younger patients (<50 years).

[Current methods for diagnosing renal artery stenosis]

PURPOSE

Today, the methods for detecting renal artery stenosis are numerous. They lead to the identification either of anatomic stenosis or functional stenosis (onset of renin-angiotensin system). The purpose of this review is to emphasize the performances, limitations and diagnostic criteria for each technique.

CURRENT KNOWLEDGE AND KEY POINTS

For detection of anatomic stenosis, the feasibility of Doppler examination has been increased by the improvement of US systems and the development of contrast agents. However, the criteria used nowadays still need wider evaluation. Helical CT angiography allows a better detection of accessory arteries and calcifications but MR angiography has a better spatial resolution and uses a non-nephrotoxic contrast agent. The performances of these two techniques have never been compared. The choice between these techniques depends on the operators' experience and the availability of the systems. For functional stenosis, detection is now based on captopril-sensitized scintigraphy.

FUTURE PROSPECTS AND PROJECTS

It would be necessary to better compare performances and cost-effectiveness ratios of these methods and of the two imaging strategies (detection of anatomic stenosis versus functional stenoses). Probably in the future, MR will gain a major place, providing, in the same imaging session, morphologic and functional data.

Sonographic contrast agents in vascular imaging

The use of ultrasound contrast agents for peripheral vascular imaging has not been adapted widely worldwide and remains experimental in the United States. Nevertheless, there is considerable interest in contrast agents, because they potentially might offer substantial benefits for peripheral vascular imaging. This article reviews the status of ultrasound contrast agents. It includes a thorough discussion of the types of agents that are available or are under development and an assessment of the desirable properties of an ideal contrast agent. The interaction of these agents with ultrasound is considered next, including consideration of the advantages of harmonic imaging with contrast. Finally, the potential clinical benefits of contrast, as revealed by the authors experience and published data, are reviewed for a variety of cerebral, peripheral, and abdominal vascular applications. These include the carotid arteries, transcranial Doppler, extremity arteries and veins, the renal arteries, and hepatic vessels.

Detection of segmental branch renal artery stenosis by Doppler US: a case report

In stenosis of a segmental branch or among multiple renal arteries, Doppler sampling of intrarenal arteries in the upper, mid and lower poles demonstrates strikingly different waveform patterns that might otherwise be overlooked. We report a case of segmental branch renal artery stenosis in which a pulsus parvus et tardus waveform was observed in a segmental branch of a renal artery. In this case, systematic analysis of Doppler waveforms of intrarenal arteries at more than three different locations facilitated a rapid and confident diagnosis of segmental branch renal artery stenosis.

Imaging of renovascular hypertension: respective values of renal scintigraphy, renal Doppler US, and MR angiography

Renovascular hypertension affects 15%-30% of patients who have clinical criteria suggestive of renovascular disease. Noninvasive screening is crucial for patient selection prior to conventional angiography and renal revascularization. Renal scintigraphy has been reported to be sensitive for detection of renovascular hypertension, but some of its limitations (eg, in the setting of bilateral renal artery stenosis and renal failure) should be considered. Doppler ultrasonography (US) allows direct evaluation of the renal arteries as well as transrenal Doppler waveform analysis, but it remains operator dependent. Gadolinium-enhanced magnetic resonance (MR) angiography is becoming an excellent alternative to conventional angiography. The main limiting factors of this technique are inadequate visualization of segmental and accessory renal arteries as well as a tendency toward overestimation of stenoses. Given the high cost and low availability of MR angiography, scintigraphy and Doppler US should be considered the primary studies in screening for renovascular hypertension. MR angiography could be reserved for patients with inconclusive scintigraphic and Doppler US results, patients with high clinical suspicion of renovascular hypertension, and patients with a contraindication to conventional angiography.

Effect of acute intravenous ace-inhibition on the intrarenal doppler flow characteristics in hypertensive patients with and without unilateral renal artery stenosis

Assessment of intrarenal doppler signals is of particular importance in screening for renal artery stenosis. We studied the effect of acute ACE-inhibition (1,25 mg enalaprilate i.v.) on intrarenal resistive indices in 10 hypertensive patients with unilateral renal artery stenosis versus 10 patients with essential hypertension. Any changes limited to poststenotic vessels could possibly improve the diagnostic value of duplex sonography. After ACE-inhibition a significant fall of the intrarenal Resistive Index occurred in both patient groups. In cases of unilateral renal artery stenosis we saw a tendency to an increased side difference of the Resistive Index due to a greater fall on the poststenotic side. Therefore a clear advantage of duplex scanning after acute ACE-inhibition due to a limited effect of enalaprilate on poststenotic vessels was not found. The results suggest that the vascular resistance and not only the degree of renal artery stenosis is of significance for the characteristics of the doppler signal.

Angiotensin-converting enzyme inhibitor-enhanced phase-contrast MR imaging to measure renal artery velocity waveforms in patients with suspected renovascular hypertension

OBJECTIVE

We investigated the usefulness of phase-contrast MR imaging to measure renal artery velocity waveforms as an adjunct to renal MR angiography. We also examined whether an angiotensin-converting enzyme (ACE) inhibitor improves the diagnostic accuracy of waveform analysis.

SUBJECTS AND METHODS

Thirty-five patients referred for MR angiography of renal arteries underwent non-breath-hold oblique sagittal velocity-encoded phase-contrast MR imaging through both renal hila (TR/TE, 24/5; flip angle, 30 degrees; signal averages, two; encoding velocity, 75 cm/sec) before and after i.v. administration of an ACE inhibitor (enalaprilat). We analyzed velocity waveforms using established Doppler sonographic criteria. A timing examination with a test bolus of gadolinium contrast material was performed to ensure optimal arterial enhancement during breath-hold gadolinium-enhanced three-dimensional gradient-echo MR angiography.

RESULTS

MR phase-contrast waveform pattern analysis was 50% (9/18) sensitive and 78% (40/51) specific for the detection of renal artery stenosis equal to or greater than 60% as shown on MR angiography. Sensitivity (67%, 12/18) and specificity (84%, 42/50) increased slightly, but not significantly, after i.v. administration of an ACE inhibitor. Also, the accuracy of quantitative criteria such as acceleration time and acceleration index did not improve after the administration of ACE inhibitor.

CONCLUSION

Renal hilar velocity waveforms, measured using non-breath-hold MR phase-contrast techniques with or without an ACE inhibitor, are insufficiently accurate to use in predicting renal artery stenosis.

Pulsed Doppler US findings of renal interlobar arteries in pregnancy-induced hypertension

PURPOSE

To evaluate whether Doppler ultrasonographic (US) velocimetry in renal interlobar arteries is altered in women with pregnancy-induced hypertension (PIH) compared with that in healthy pregnant and nonpregnant women.

MATERIALS AND METHODS

Flow waveform measurements in renal interlobar arteries were obtained in 39 nonpregnant women, 77 healthy pregnant women at 16-40 weeks gestation, and 15 women with PIH at 28-39 weeks gestation by using color and pulsed Doppler US.

RESULTS

In the nonpregnant group, the mean (+/- SD) peak systolic velocity, end-diastolic blood flow velocity, resistive index, and acceleration time were 0.34 m/sec +/- 0.08, 0.14 m/sec +/- 0.03, 0.62 m/sec +/- 0.07, and 52.3 m/sec +/- 13.7, respectively. In the healthy pregnant group, the peak systolic and end-diastolic blood flow velocities at 16 weeks gestation had decreased greatly by 40 weeks gestation. However, the values of other indexes in this group did not change with gestational age. In the PIH group, the acceleration time values were greatly prolonged compared with those in the other groups.

CONCLUSION

Acceleration time is one of the hemodynamic parameters of substantial upstream stenosis. These findings suggest that severe stenosis or continuous vasospasm in the proximal arteries, such as the main renal artery and segmental artery, might be implicated in the pathogenesis of PIH.

Contrast-Enhanced Doppler Ultrasound of Renal Artery Stenosis: Prologue to a Promising Future

Over the past few years, there has been extensive research for a reliable, noninvasive, and nonionizing imaging method to screen for renal artery stenosis (RAS). Doppler ultrasound (US) is one of many modalities that have been evaluated for the detection of RAS. The lack of standardization in examination protocols and diagnostic criteria, as well as the wide differences in reported accuracy among different laboratories, however, have prevented universal acceptance of this technique as a reliable screening test for RAS. Recently, the introduction of US contrast agents has substantially expanded the potentials of color Doppler US. The use of microbubble echo enhancers in combination with harmonic Doppler imaging has been shown to improve diagnostic confidence by improving the operator's ability to visualize the renal arteries, and to significantly reduce the number of equivocal examinations. In addition, contrast-enhanced harmonic Doppler US can currently provide objective functional assessment of RAS through analysis of time-intensity renal enhancement curve. State-of-the-art contrast-enhanced Doppler US seems to have the potential to become a useful screening test for patients at risk from renovascular hypertension and a tool for follow-up of patients who undergo revascularization procedures.

Childhood hypertension. An update on etiology, diagnosis, and treatment

In the general population, an estimated 70% or more of premature morbidity can be attributed to tobacco use, undertreatment of hypertension, and obesity. From a public health perspective, health-related behaviors that reduce the risk for cardiovascular disease should be encouraged for all children and their families. Pediatricians are obligated to accurately and frequently monitor patients' blood pressures. When discovered, elevated blood pressure should be appropriately investigated, with the evaluation being tailored to the age of the child and to the severity of the blood pressure elevation. Investigation should focus on not only a search for a cause but also target organ effects. Timely recognition of abnormal blood pressure and appropriate interventions are necessary to affect the future development of cardiovascular and renal morbidity and mortality.

Comparison of Doppler US and CT angiography for evaluation of renal artery stenosis

RATIONALE AND OBJECTIVES

The authors compared Doppler ultrasound (US) with computed tomographic (CT) angiography in the evaluation of stenosis of the main renal artery.

MATERIALS AND METHODS

Fifty-six patients who had undergone conventional angiography of the renal arteries participated in a prospective comparison of Doppler US (45 patients) and CT angiography (52 patients). US evaluation included both the main renal artery and segmental renal arteries.

RESULTS

There were 27 main renal arteries with at least 50% stenosis in 20 patients. In 36 patients, there was no significant stenosis. All cases of main renal artery stenosis detected with Doppler US of the segmental arteries were also identified with Doppler US of the main renal artery. The by-artery sensitivity (63%) of US of the main renal artery was greater than that (33%) of US of the segmental arteries. CT angiography was more sensitive (96%) than Doppler US (63%) in the detection of stenosis, but the specificity of CT (88%) was similar to that of US (89%). The difference in the area under the receiver operating characteristic curve (AUC) between CT (AUC = 0.94) and US (AUC = 0.82) was statistically significant (P = .038).

CONCLUSION

Doppler US of the main renal artery is more sensitive than Doppler US of segmental arteries in the detection of stenosis. CT angiography is more accurate than Doppler US in the evaluation of renal artery stenosis.

Variations in blood flow waveforms in stenotic renal arteries by 2D phase-contrast cine MRI

Waveform variations in blood flow measurements through stenotic renal arteries have been reported already with echo Doppler studies. We studied these variations with MRI in 14 patients (mean age, 60 years) with suspected renal arterial stenosis (24 patent arteries, four occluded). Flow measurements were successful in 15 arteries and unsuccessful in nine, due to practical limitations. Seven healthy younger volunteers (mean age, 28 years) and five healthy older volunteers (mean age, 58 years) were recruited for comparison purposes. In patients, the severity of stenoses was also assessed by digital subtraction angiography and intraarterially measured transstenotic pressure drops. We found flow patterns to be statistically significantly (P < 0.01) age-related. Younger healthy subjects showed shorter wave duration, higher diastolic flow, and total blood flow per minute. Also, with increasing stenosis severity, the systolic wave became more damped and the systolic wave duration became statistically significantly (P = .03) longer.

Interobserver and interequipment variability of hepatic, splenic, and renal arterial Doppler resistance indices in normal subjects and patients with cirrhosis

BACKGROUND/AIMS

Doppler arterial resistance indices are used to evaluate alterations in arterial hemodynamics in the liver, spleen, and kidney. The purpose of this study was to determine the interobserver and interequipment variability of hepatic, splenic, and renal arterial Doppler resistance indices, and the influence of a cooperative training program of the operators on the reproducibility of the results.

METHODS

In the first part of the study, hepatic (PI-L, RI-L), splenic (PI-S, RI-S), and renal (PI-K, RI-K) pulsatility and resistive indices were measured by echo-color-Doppler in eight control subjects and ten patients with cirrhosis by three operators using three different machines. In the second part of the study, measurements were taken by the three operators in nine controls and nine patients with cirrhosis, after cooperative training, with a single machine.

RESULTS

Significant interobserver variability was present for all parameters except RI-L. Significant interequipment variability was present for all parameters except PI-S and RI-S. Only 0-3% of variance was equipment- or operator-related, while 58-72% was patient-related. Hepatic and renal coefficients of variation were similar in patients with cirrhosis and controls, while splenic coefficients of variation were higher in patients with cirrhosis than in controls. After training, differences among operators disappeared for all variables except RI-K, and the operator-related component of variance nearly disappeared for all parameters.

CONCLUSIONS

Hepatic, splenic, and renal arterial resistance indices show small but significant interobserver and interequipment variability. Interobserver variability can be decreased to non-significant levels by a common training program. Thus, these indices can be widely applied to the study of arterial circulation in these organs.

Color-coded duplex sonography of experimentally induced multilevel stenosis. Evaluation of poststenotic Doppler spectrum

RATIONALE AND OBJECTIVES

The authors evaluated the influence of a proximal arterial stenosis on the poststenotic doppler spectrum of a second, distal stenosis and determined duplex parameters, which permitted description of the severity of the distal stenosis.

METHODS

Moderate (ie, 50%) and severe (ie, 90%) stenoses of the distal aorta and the distal iliac arteries of 10 pigs were created surgically and characterized by angiography. All possible combinations of moderate and severe stenoses were examined. The Doppler spectrum was depicted in the distal iliac and distal femoral arteries of both limbs and analyzed by use of maximum and minimum flow velocity (Vmax, Vmin), acceleration index (modified Handa index), acceleration time, and pulsatility index.

RESULTS

In cases of moderate as well as severe proximal stenosis, acceleration index, acceleration time, and pulsatility index of the poststenotic curve of the distal stenosis were significantly reduced (P < 0.05). Independent of the severity of the proximal stenosis, differentiation of moderate as well as severe distal stenosis was possible (P < 0.05) with these parameters.

CONCLUSIONS

Despite interference of spectral curves in proximal and distal stenosis, duplex sonography enabled the differentiation of experimental aortic iliac multilevel stenosis.

Determination of intervillous flow in early pregnancy

The process of placentation in the macaque has been extensively studied and found to resemble closely that observed in the human. In this model, histopathologically, intervillous flow is anticipated from week 3 post-conception. We set out to document the nature and onset of intervillous flow in the macaque in vivo using colour Doppler imaging (CDI), colour Doppler energy (CDE) and pulsed-wave Doppler (PWD). Pregnant females were assessed between 15-50 days gestation (term = 165 days) with an Acuson 128/XP10 high-resolution ultrasound scanner, using a 7-MHz linear array probe. The placenta, subjacent decidua and myometrium were assessed using CDI and CDE. Specific regions of flow were interrogated using PWD; the resulting flow velocity waveforms were stored and quantified using conventional Doppler indices. B-mode sonography was able to demonstrate the well-defined placental-decidual interface observed in this species; CDI and CDE clearly visualized the uteroplacental vasculature. Spiral arteries were followed to their point of discharge into the intervillous space, and PWD at these sites obtained a characteristic flow velocity waveform. The indices obtained confirmed a flow of low resistance and pulsatility throughout the gestation studied. Flow within the intervillous space was noted from day 20 of gestation.

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.

Doppler ultrasound of the kidney

Conventional ultrasound of the kidney is used commonly to depict structural abnormalities. It is limited, however, by a lack of functional and vascular information. Doppler sonography can reduce this limitation of standard sonography quickly and noninvasively. Doppler examinations, although not difficult, must be done property to obtain useful data. Information regarding the presence and direction of flow in renal vessels can be obtained. Vascular stenosis can be identified by several Doppler criteria, although the role of Doppler as a screening measure remains controversial. Assessment of vascular resistance is possible from Doppler waveform analysis, using parameters such as the resistive index. These data may provide hemodynamic and predictive information regarding a dilated collecting system identified by conventional ultrasound. Analysis of the resistive index also may provide helpful clinical information in nonobstructive renal disease. In certain clinical settings, such analysis provides diagnostic data not readily available with other clinical and laboratory assessment methods. Pharmacologically stimulated renal Doppler examinations may lead to even greater benefits in the future. This article reviews renal Doppler ultrasound, including the physiological basis for Doppler examination, the technical principles of renal Doppler sonography, and the clinical applications of Doppler findings.

Renal impairment after surgical resection of neuroblastoma

Postoperative renal impairment was observed in 6 of 58 patients with neuroblastoma treated between November 1982 and March 1994. To clarify the clinical characteristics of these patients (renal-impairment group), they were compared with 26 patients treated during the same period who did not have renal impairment (no-impairment group). The incidence of primary retroperitoneal tumor and invasion of the hilum renalis was clearly higher in the renal-impairment group than in the group with no impairment. However, no significant difference was observed with respect to age, tumor laterality, or stage of disease. The results of postoperative biochemical examinations showed that the serum concentrations of lactic dehydrogenase were significantly higher in the renal-impairment group. In the group with renal impairment, the mean maximal body temperatures on the first, second, and third postoperative days were 38.7 degrees C, 38.6 degrees C, and 38.1 degrees C, respectively. These were higher than those of the no-impairment group. For patients with these risk factors, intraoperative prophylactic measures and early postoperative renal blood flow evaluation (in anticipation of postoperative renal impairment) are considered necessary.

Colour Doppler ultrasound in renal artery stenosis: intrarenal waveform analysis

Renal artery stenosis (RAS) is the commonest secondary cause of hypertension and may result in renal ischaemia with resultant renal failure. Recent studies hve suggested that colour Doppler ultrasound, with spectral analysis of the intrarenal waveforms, can identify those patients with a significant RAS. A prospective study was performed in which colour Doppler ultrasound was compared with angiography in 73 patients (143 kidneys) presenting for renal angiography. Colour Doppler ultrasound was unsuccessful in 16% of kidneys due to a combination of technical failures and small kidney size. Accessory renal vessels were present in 14% of kidneys on angiography but none was detected by ultrasound. Of the 120 kidneys that had both examinations, no significant difference in intrarenal pulsatility or resistive index was noted between the angiographically stenosed and normal arteries. There were significant differences for intrarenal peak and end diastolic velocities, and acceleration time and index. Of these measurements, acceleration time was the best indicator of RAS. The probability of detecting a high grade RAS in an individual patient did not reach 90% until the acceleration time was prolonged to more than 0.12 s. Intrarenal colour Doppler ultrasound is not a general screening test for RAS and it should be reserved for selected patient groups where the incidence of disease is high. Patients with prolonged acceleration times of more than 0.12 s have a high likelihood of at least 70% RAS and should proceed directly to angiography.

Intra-renal Doppler wave-form analysis as a screening test for renal artery stenosis

A double-blinded trial was performed comparing Doppler interrogation of intra-renal arteries with findings at renal angiography in the assessment of renal artery stenosis. Fifty-three consecutive patients were studied. Previously reported parameters and cut-off values were used for predicting the presence of renal artery stenosis with Doppler. Doppler wave-form analysis proved relatively specific (91%) but insensitive (68%) to the presence of renal artery stenosis (of greater than 60%) if acceleration parameters were used alone. The technique of using a difference in mean resistive indices was found to be both insensitive (61%) and non-specific (54%). Patients with fibromuscular dysplasia, branch vessel stenoses, multiple renal arteries and chronic renal impairment proved to cause the most false negatives. Young patients with normal arteries were the source of the few false positive results. The interrogation of intra-renal arteries does not have appropriate sensitivity to be useful as a screening test for renal artery stenosis.

Assessment of renal resistance index after captopril test by Doppler in essential and renovascular hypertension

Ultrasonic duplex scanning has been validated as a noninvasive method to evaluate the kidney arteries and hemodynamic characteristics of renal blood flow in patients with renal artery stenosis. The purpose of our study was to assess the changes in renal vascular impedance in 22 patients with renovascular hypertension, as compared with 45 essential hypertensives and 15 normotensives, by using the Doppler parameter resistance index (RI) before and after a captopril oral test. After the captopril test the delta RI decreased significantly in the stenotic artery (P < 0.05). Univariate analysis showed that PRA values after captopril correlated inversely with the changes of RI only in the stenotic artery (P < 0.05). Thus, our findings suggest that the application of the captopril test to renal echo-Doppler may represent a feasible, noninvasive, and inexpensively useful tool in the screening studies aimed at diagnosing renovascular hypertension.

Effect of a main renal artery stenosis on the downstream Doppler waveform in dogs

RATIONALE AND OBJECTIVES

We evaluated the changes in the down-stream Doppler waveforms caused by a proximal stenosis in the main renal artery of dogs.

METHODS

Renal parenchymal arterial waveforms downstream from mild (< 50%), moderate (50-75%), and severe (76-95%) stenoses were compared with nonstenotic baseline waveforms in five mongrel dogs. Waveform shapes were categorized as biphasic or monophasic. The percentage of biphasic and monophasic waveforms was determined for each stenosis. The acceleration index (AI) and the acceleration time (AT) were determined using traditional and modified calculations (AI' and AT'). Late systolic deceleration (DS), diastolic deceleration (DD), and the resistive index (RI) also were measured.

RESULTS

AT, AI', and AT' demonstrated significant differences between the severe stenoses and nonstenotic baselines (p < .05); however, there was no difference between the mild and moderate stenoses versus baselines. The percentage distribution of monophasic and biphasic waveforms was highly correlated with the degree of stenosis. Monophasic waveforms increased on average from 22.5% of baseline waveforms to 76.5% of waveforms in the severe stenoses. Biphasic waveforms decreased on average from 69.9% of baseline waveforms to 18.7% of waveforms in the severe stenoses.

CONCLUSION

Quantitative evaluation of the downstream waveform parameters (AI, AT, AI', AT', DS, DD, and RD in the dog kidney is not sufficiently accurate, but calculation of the percentage of the monophasic and biphasic waveforms present may be useful to predict a hemodynamically significant renal artery stenosis (> or = 50%).