Monitoring of renal allografts by duplex ultrasound

Deterioration of renal transplant function due to rejection is accompanied by changes in renal blood flow that can be measured by duplex ultrasound (DU). In the present study, 60 transplanted patients were followed up. A total of 233 duplex examinations, 68 percutaneous biopsies, 44 renal scintigraphies, and 6 transplant nephrectomies were performed on these patients. Diagnoses were made on the basis of clinical and histological data. Renal perfusion was calculated by means of DU. In addition, the arterial Doppler signals were quantified using a pulsatility index (PI). Mean perfusion of normal renal allografts was 0.47 l/min. A decrease in blood flow could be found in acute vascular and chronic rejection but not in acute cellular rejection. A lack of renal perfusion due to acute vascular rejection was observed in four patients. Mean PI, used as a parameter of DU, rose significantly in all forms of rejection, which could be diagnosed with a sensitivity of 93% and a specificity of 86%. Cyclosporin overdosage did not alter the Doppler flow shape.     

Renal transplant blood flow evaluation by ultrasonic duplex scanning

The transplant blood flow was measured renal transplantation by ultrasonic duplex scanner composed of pulsed Doppler flowmeter and real-time B-mode linear scanner in 32 patients. The blood flow information could be obtained from anywhere of interest within the renal transplant. Then blood flow in 3 regions including renal hilum, central echoes and renal parenchyma were measured. The parenchymal peripheral blood flow was not always similar to the hilar central blood flow. Parenchymal blood flow was the most correlated with graft function and decreased remarkably during acute rejection episode. This method enabled detection of occurrence of acute rejection in the course of post-cadaver transplant ATN. Prolongation of delta t (acceleration time) in Doppler spectrogram from parenchyma was also reliable evidence for the deterioration of graft function. Ultrasonic duplex scanning is a useful method in managing post-transplantation patients because intrarenal hemodynamics can be evaluated by this method.     

Evaluation of renal allograft function by Doppler spectrum analysis

A decreased renal function is rather common after renal transplantation. The causes of this decreased function are diverse and difficult to differentiate. Yet, duplex examination, and especially quantitative Doppler spectrum analysis of the blood velocities in the renal artery, may be an effective method for differentiating between some of these causes. Forty-five renal transplant recipients were included in this preliminary study. Doppler spectra were recorded from the renal artery to the allograft. Parameters were derived from every Doppler spectrum in order to characterize each spectrum. Renal allograft function was evaluated on the basis of a number of clinical parameters. A significant correlation was found between the clinical parameters and the Doppler spectrum parameters indicative for changes in the peripheral resistance. Patients with a normal renal allograft function showed Doppler spectra with a high diastolic flow, typical of a vascular bed with a low peripheral resistance. Patients with a decreased renal allograft function caused by a stenosis in the renal artery could be distinguished by a low peak velocity and a low pulsatility index. A decreased allograft function caused by allograft rejection or cyclosporin nephrotoxicity also led to characteristic arterial flow disturbances. In these cases, the peripheral resistance was increased, and this was primarily reflected in a decrease in the diastolic blood velocity. We conclude that quantitative analysis of the blood velocities in the renal artery by Doppler spectrum analysis seems to be a useful, noninvasive diagnostic tool that discriminates between some of the causes of a decreased renal allograft function.     

Evaluation of canine renal transplants with pulsed Doppler duplex sonography

Preliminary studies of human renal transplants suggested that pulsed Doppler sonography may complement other studies of renal transplant dysfunction. To further evaluate the Doppler technique, 11 dogs who received renal transplants were examined a total of 50 times. No antirejection chemotherapy was used, and following rejection the kidneys were removed and examined histologically. The canine transplants underwent accelerated acute or hyperacute rejection. A pulsed Doppler index (PDI) was derived to quantitate patterns of renal blood flow and peripheral vascular resistance. Arterial Doppler signals were obtained from renal transplant branch vessels in vivo and the PDI consistently fell as rejection occurred. No arterial signals were obtained from one kidney which was subsequently proven to have arterial thrombosis. Pulsed Doppler analysis provides new information about renal transplant blood flow patterns and may demonstrate evidence of rejection and renal arterial occlusion.     

彩色多普勒超声在肾移植后排斥反应诊断中的应用

目的 探讨彩色多普勒超声在移植肾排斥反应监测中的应用价值。方法 对68例肾移植患者采用彩色多普勒超声进行监测，观察移植肾的结构及体积、肾皮质厚度、肾动脉内径、血流灌注情况、血流动力学参数。结果术后随访最长者达4年，45例移植肾功能正常，未发生排斥反应者，其移植肾在彩色多普勒超声下表现为边界清晰，肾内结构清楚，皮、髓质界限分明，血流丰富。13例发生急性排斥反应者，彩色多普勒超声下可见移植肾明显肿大，肾实质血流信号稀少，叶间动脉呈断续闪烁状，弓形动脉几乎无血流信号。10例发生慢性排斥反应者，彩色多普勒超声下可见移植肾体积缩小，皮质变薄，肾皮质与肾髓质界限不清，肾内血管分枝稀疏，血管树不连续，弓形动脉及小叶间动脉往往不显示，为低速高阻血流。血流动力学参数显示，发生急性排斥反应者的肾动脉阻力指数及搏动指数明显增高，舒张期峰值流速减低；发生慢性排斥反应者的肾动脉内径明显缩小，收缩期峰值流速及舒张期峰值流速明显减低，血流灌注量明显减少，阻力指数及搏动指数明显升高，与肾功能正常者比较，差异均有统计学意义。结论对于肾移植患者的术后监测，彩色多普勒超声具有独特的优点，无创、便捷，其所测得的移植肾形态学数据和血流动力学参数对排斥反应的判断具有重要参考价值，可作为肾移植术后的常规峪测手段。     

Evaluation of renal transplant dysfunction by duplex Doppler sonography: a prospective study and review of the literature

A disconcertingly wide variation exists in the literature as to the accuracy of duplex Doppler sonography in the detection of acute renal transplant rejection. Sensitivities range from 9% to 76%. In an attempt to explain the disparity of results, we undertook a double-blind prospective study of the accuracy of duplex Doppler ultrasound in the detection of acute rejection in renal transplants. We scanned 49 consecutive patients with a total of 65 biopsies; 46 biopsies in 33 consecutive patients were included in our study. In our population, the prevalence of acute rejection was 61% (28/46). Using a resistive index (RI) cutoff of greater than 0.90 based on the main renal artery flow pattern, the sensitivity of our test was 43%, with a 67% specificity. The positive predictive value was 67%. Our results are contrasted and compared with the published data from other groups in a critical survey of the literature. We conclude that duplex Doppler sonography alone is inadequate to evaluate acute rejection in renal transplants.     

彩色多普勒血流显像及多普勒能量图在移植肾排斥反应中的应用

目的探讨彩色多普勒血流显像及多普勒能量图在检测移植肾排斥反应中的应用价值。方法对46例肾移植受者术后进行了彩色多普勒血流显像及多普勒能量图检查。根据检测结果将46例肾移植术后受者分为3组,移植肾正常组(30例)、急性排斥组(9例)和慢性排斥组(7例),并与超声引导下肾组织穿刺的病理检查结果进行比较。结果16例急、慢性排斥反应的患者移植肾动脉搏动指数及阻力指数均高于移植肾正常组;急性排斥组肾脏长径及肾皮质厚度明显大于移植肾正常组;慢性排斥反应时肾皮质厚度、肾脏长径、宽径均小于移植肾正常组。结论彩色多普勒血流显像及多普勒能量图对移植肾血流灌注及排斥反应判断有独特的优点,搏动指数、阻力指数以及肾皮质厚度可作为有无移植肾排斥的指标之一。     

Evaluation of cortical perfusion in renal transplants: application of quantified power Doppler ultrasonography

Perfusion of renal transplants may be altered by various pathological conditions. This study assessed cortical perfusion of renal transplants during acute rejection episodes using power Doppler quantification. Forty-eight renal transplant patients with clinical indications for biopsy were included in this study. Power Doppler ultrasonography (US) of these renal transplants was performed prior to biopsy. Power Doppler image intensity in the proximal outer cortex of renal transplants was quantified by image analysis software. The results of power Doppler quantification were compared with the clinical data and histological findings. Biopsies were classified into three groups based on Banff diagnostic categories: group 1 (no acute rejection; 26 patients), group 2 (acute cell-mediated rejection alone; 12 patients), and group 3 (acute antibody-mediated rejection with/or without acute cell-mediated rejection; 10 patients). The power Doppler intensity of the outer renal cortex was 1.98 +/- 1.50 dB for group 1, 1.38 +/- 0.86 dB for group 2, and 0.81 +/- 0.66 dB for group 3. Statistically, there was a significant difference between group 1 and group 3 (1.98 vs 0.81 dB, P = .01) but not between group 1 and group 2 (1.98 vs 1.38 dB, P = .34). In conclusion, the status of cortical perfusion of renal transplants can be determined noninvasively by quantified power Doppler US. Accordingly, acute antibody-mediated rejection is associated with significantly decreased cortical perfusion, which, we propose, is due to this distinct pathological process.     

彩色多普勒超声诊断早期移植肾急性排斥

目的探讨彩色多普勒超声图像数据分析在诊断早期移植肾急性排斥中的作用及临床价值.方法总结203例肾移植术后6～30d内行彩色多普勒超声检查,结合临床症状、生化检查并参照病理诊断,对二维灰阶图像、彩色血流图、血流频谱及阻力指数(RI)、搏动指数(PI)、收缩期与舒张期血流速度比(S/D)等参数进行回顾性分析.结果以彩色多普勒RI>0.78、PI>1.82、S/D>4.1为标准,结合彩色血流图及血流频谱形态,早期移植肾急性排斥正确诊断率可达85.7%.结论应用彩色多普勒超声诊断移植肾早期急性排斥并监测其功能恢复,具有快速、准确、无创等优点,可提早发现病情变化并指导治疗,提高移植肾存活率.     

Role of duplex Doppler sonography in diagnosis of acute allograft dysfunction—time to stop measuring the resistive index?

Measurement of vascular resistive index (RI) by duplex Doppler sonography (DDS) has been proposed as a non-invasive technique to detect the presence of acute rejection in renal allograft recipients. Our aim was to evaluate the clinical utility of this technique. From 107 patients we reviewed 159 biopsies that were performed from 1993 to 2001 for the investigation of acute allograft dysfunction. Histological findings were correlated with RI measurements by contemporaneously performed DDS. The majority of biopsies were carried out within the first 3 months post-transplantation (111/159). Sixty-eight biopsies showed acute rejection, 91 biopsies had findings other than rejection (acute tubular necrosis, CyA toxicity, recurrent GN). Using a threshold mean RI value of 0.9, the test had a specificity for acute rejection of 89%, but a sensitivity of just 6%. If the threshold was lowered the sensitivity rose, but specificity declined sharply. Average RI in the rejection group was not higher than in controls (0.73+/-0.11 vs 0.74+/-0.11, respectively). We conclude that measurement of RI by DDS does not contribute to the diagnosis of acute allograft dysfunction.     

Careful clinical monitoring in comparison to sequential Doppler sonography for the detection of acute rejection in the early phase after renal transplantation

Abstract Acute rejection is the most frequent cause of early graft failure. There is unanimity that Doppler sonography is a helpful method for the detection of complications after kidney transplantation. In the past, the indication for renal biopsy relied mainly on clinical assessment, although this assessment has not been standardised. Therefore, we conducted this prospective study to compare the value of sequential Doppler measurements with a standardised clinical rejection score, based on renal function, weight gain, graft swelling and tenderness. Fifty‐eight patients (37 males, 21 females, mean age 46 ± 12 years) after kidney transplantation were consecutively enrolled into the study. Doppler investigations were obtained within the first 24 h after transplantation, followed by an interval of 48‐72 h. At the same time, a clinical examination was scored by a transplant physician blinded to the Doppler results. Clinical score and Doppler results, both were referred to the histological results of renal biopsy. In 24 out of 58 patients 25 acute rejections occurred. In seven patients, acute rejection was superimposed on primary graft failure. The cut‐off levels for rejection were set at RI ≥ 0.80 and PI ≥ 1.70 based on receiver‐operator curves using data from 663 Doppler examinations. Sensitivity and specificity was 72 % for RI, and 72 % and 74 % for PI, respectively. The calculation of the intraindividual increase (ΔRI ≥ 3 %, ΔPI ≥ 10 %) did not improve these values. The clinical score revealed a sensitivity and specificity of 82% and 87 %, respectively. The combined analysis of Doppler indices and clinical score showed a sensitivity of 96 % with a specificity of 66%. Careful clinical monitoring alone using a clinical score is an appropriate procedure with which to decide about renal biopsy. Our data show that Doppler sonography should be performed within the first 24 h after transplantation to evaluate graft perfusion and baseline values. Afterwards, it should be used when clinical signs of rejection occur to underline the decision for renal biopsy even in borderline cases.     

Role of duplex imaging and fine needle aspiration cytology of renal allografts in monitoring response to anti-rejection therapy

The role of duplex imaging and fine-needle aspiration cytology (FNAC) in monitoring the response to anti-rejection therapy was investigated in 14 of the 22 rejection episodes which occurred in 30 renal allografts recipients. In 9 of these 14 episodes of rejection, with good resolution, both resistive (RI) and pulsatility (PI) indices decreased by significant proportions (p less than 0.05). The FNAC scores also fell significantly with anti-rejection therapy. In 5 other episodes of rejection where the graft continued to deteriorate there was no significant fall of RI and PI (p greater than or equal to 0.2). In a small group of patients, both FNAC and Doppler predicted rejection. In conclusion, both duplex imaging and FNAC have a role in selection and optimal modulation of drugs in the treatment of acute renal allograft rejection.     

Utility of serial Doppler ultrasound scans for the diagnosis of acute rejection in renal allografts

This study aims to explore the utility of serial duplex scanning and to compare its results with those of single time-point scans of renal allografts in the diagnosis of acute rejection (AR). A retrospective analysis of 6017 serial duplex scans (mean: 9.8 scans per patient, 5.7 of which were done during the first 10 days) was performed in 614 patients with 462 episodes of AR from 1992–2000. Even in the absence of AR (n=278), there were day-to-day fluctuations in pulsatility index (PI) and resistive index (RI). An increase of >10% in intra-renal indices was noted 0.95 days (mean) before the commencement of treatment for AR (SD 1.3, range 1–6 days). In patients with acute tubular necrosis (ATN), who have high base line indices, sensitivity of single value of PI and RI was 58% (cut-off level 1.8) and 68% (cut-off level 0.8), with specificity of 66% and 56%, respectively. By contrast, a >10% increase over the previous best in PI and RI had a sensitivity of 78% and 60% respectively, and a specificity of 78% and 90%, respectively. Reversal of flow during diastole (n=50) was found to be associated with 22% graft loss within 3 months of transplantation. We can conclude that a considerable overlap between the indices of patients with AR and those with ATN greatly limits the diagnostic yield of duplex scanning. Nonetheless, serial scanning of renal allografts is more likely to herald the need for biopsy in the diagnosis of AR than one-time scanning.     

Duplex-Doppler ultrasonography in monitoring clinical pancreas transplantation

Abstract. The findings are reported that were obtained with duplex-Doppler ultrasonography (US) in seven diabetic patients who underwent pancreatic grafting with pancreaticocystostomy. Five normal functioning grafts showed homogenous echostructure and pulsed Doppler spectrum characteristics of low impedance vascular beds. Four of these patients developed graft rejection (five episodes). The remaining two grafts had pulsed Doppler evidence of venous thrombosis. It was not possible to differentiate graft rejection from venous thrombosis using real-time US. In both circumstances a heterogeneous pancreatic echostructure with a small amount of peripancreatic fluid and an increase in pancreas size were observed. Pulsed Doppler, however, showed absence of venous flow in both cases of venous thrombosis whereas all rejection episodes were characterized by an increase in arterial impedance. We conclude that duplex-Doppler US is a promising noninvasive method of detecting surgical complications and graft rejection in pancreatic transplant recipients.     

Monitoring of renal allografts by Doppler ultrasound.

Cyclosporin (CyA) associated renal dysfunction may be due to an arteriolopathy which reduces graft perfusion. We have prospectively monitored 27 renal allograft recipients, within 30 days of transplantation, by continuous wave Doppler ultrasound. Changes in the frequency shift waveform should indicate alterations in renal blood flow. Objective analysis was made in 112 waveforms by determining the ratio of the area under the frequency shift/time curve of the first half and the second half of the cardiac cycle (AUC 1/2 ratio). The AUC of the first half of the cycle indicates systolic blood flow plus the first part of diastolic flow, whereas the AUC of the second half indicates the remainder of diastolic flow. The AUC 1/2 ratio during ATN was not significantly different from that during stable renal function. However the ratio was significantly higher during acute rejection episodes and CyA nephrotoxicity. Although a statistical difference was demonstrated between acute rejection and CyA nephrotoxicity, the AUC 1/2 ratio alone does not differentiate these 2 conditions. These preliminary findings suggest CyA nephrotoxicity does reduce renal allograft blood flow and that this non-invasive technique may have a useful role to play in monitoring of patients immunosuppressed with CyA.     

Eine neue Methode zur standardisierten Diagnostik nach Nierentransplantation

Ultrasound (US) imaging is an important diagnostic tool following renal transplantation. Unfortunately, due to the heterogeneity of the recipients and their multimorbidity, imaging procedures in the early phase after kidney transplantation are difficult and of limited use. We performed a study to evaluate the use of a contrast enhancer for US examination as a standardized method in the follow-up of kidney transplant recipients.The study included 40 recipients: 32 were examined on the 5th to 7th day following transplantation and 8 patients at the time when clinically suspicious findings occurred (acute rejection, tumor, acute tubular necrosis). Following the intravenous application of the contrast medium, pictures were taken during the arterial and parenchymatous phase and compared with conventional B-mode and power Doppler pictures of the same visual plane. Three examiners assessed different parameters of the transplant organ (max. vascularized area, suspected hematomas, tumors, rejection, acute tubular necrosis). Findings were confirmed by histological results of a biopsy if rejection, tumor, or acute tubular necrosis were suspected.Application of ultrasound contrast medium significantly increased visualization of the vascularized kidney area. Also, US findings in the follow-up after acute rejection therapy corresponded with the clinical course; 19 hematomas could be detected with contrast medium compared to only 9 without. With contrast medium a perfusion deficit was detectable in three patients compared to one patient with power Doppler US. Also, US contrast medium helped to detect tumor vascularization in two patients in whom conventional sonography suspected no abnormality.Ultrasound contrast medium enhancement is a reproducible, reliable, and easy to apply method which is superior to conventional sonography in the follow-up after kidney transplantation. This method is also helpful to detect and control acute rejections and to better visualize hematomas, deficits of perfusion, and tumors.     

A comparison of duplex Doppler ultrasonography and intrarenal manometry in the diagnosis of acute renal transplant rejection

Renal transplant rejection is frequently difficult to differentiate from other causes of renal dysfunction. This study examined the use of duplex Doppler ultrasound and intrarenal manometry in a consecutive series of 73 patients who underwent renal transplantation. Altogether 327 duplex scans were analyzed and, for each, a resistive index (RI) was calculated. A raised RI predicted rejection in patients with grafts that functioned immediately, but not in those that had delayed function. A rise in intrarenal pressure ( greater than or equal to 40 mmHg) indicated the presence of rejection in both groups. However, neither test had a sensitivity of more than 71% and this was not improved by combining the results of the two tests for each patient. Although both tests have a place in transplantation, renal biopsies may still be required to confirm rejection.     

Diagnostic techniques in the work-up of renal allograft dysfunction--an update

After renal transplantation, acute allograft dysfunction secondary to acute rejection occurs in around 30-40% of patients. Although in the majority of patients these episodes are reversible, acute rejection remains a major risk factor for the development of chronic rejection. Remarkably, prior episodes of acute allograft rejection are associated with decreased allograft survival. Histologic examination of the percutaneous core needle transplant biopsy remains the gold standard for the diagnosis of acute rejection. It does, however, have a number of shortcomings, and less invasive procedures that could diagnose incipient rejection and simultaneously provide mechanistic information on the rejection process (allowing delivery of more tailored therapy) are being sought. To address these problems a number of alternative diagnostic procedures have been suggested, including duplex Doppler ultrasound assessment, fine-needle aspiration biopsy, urine cytology, urine cytokine analysis, serum cytokine analysis, and cytokine analysis of biopsy material.     

The evaluation of paediatric renal transplants using resistive index and renal blood flow

Six children (aged 1.3–6.9 years) were examined with serial duplex Doppler sonography and diethylenetriaminepenta-acetic acid (DTPA) isotope renography in the post-renal transplant period. The resistive index (RI) was derived from sonographic studies and the renal blood flow (RBF) calculated from the isotope scans. The clinical status of the child and the corresponding plasma creatinine level were assessed together with these two parameters. The RIs ranged from 40% to 100% and the RBF from 0% to 16.8%. There were six rejection episodes in four patients. A significant fall in RBF mirrored a rise in plasma creatinine on each occasion, but there was no significant change in RI recorded. There were two graft losses, both associated with renal venous thrombosis. In both cases no significant RBF could be detected on DTPA renography. In one patient, the RBF remained low throughout a period of primary non-function associated with acute tubular necrosis, and increased as primary function was established and the plasma creatinine fell. Throughout this period there was no significant change in the RI. From our preliminary data RBF reflects graft dysfunction more accurately than does the RI.     

Transitory peaked waveforms with elevated velocities in Doppler sonography after renal transplant

Vascular complications after a renal transplant are rare and critical. Duplex Doppler evaluation constitutes the primary imaging modality in renal transplant. Early diagnosis and appropriate intervention to address potential complications are crucial in graft survival. This report describes a 25-year-old woman who underwent a live-donor renal transplant. During a routine study 4 hours after surgery, she was found to have high peak flow velocities suggestive of stenosis. An angiogram obtained as a result of this finding showed no abnormalities. A repeat duplex Doppler sonogram performed 12 hours later revealed normal waveforms and velocities. Postrenal transplant vascular complications are rare but may represent a significant morbidity factor for patients and grafts. Peak wave forms, elevated velocities, and a tardus-parvus configuration are suggestive of vascular disorders that require aggressive evaluation. In our patient, the Doppler ultrasound, angiogram, and lack of clinical signs were compatible with a renal artery vasospasm. This entity, despite its reversibility in the majority of instances, may cause severe graft injury if it does not regress promptly.