Color Doppler sonography in early renal transplantation follow-up: resistive index measurements versus power Doppler sonography

Predictive performance of renal resistive index, semiquantitative power Doppler ultrasound score and renal venous Doppler waveform pattern for acute kidney injury in critically ill patients and prediction model establishment: a prospective observational study

BACKGROUND

This study aimed to explore the performance of renal resistive index (RRI), semiquantitative power Doppler ultrasound (PDU) score and renal venous Doppler waveform (RVDW) pattern in predicting acute kidney injury (AKI) in critically ill patients and establish prediction models.

METHODS

This prospective observational study included 234 critically ill patients. Renal ultrasound was measured within 24 h after intensive care unit admission. The main outcome was the highest AKI stage within 5 days after admission according to the Kidney Disease Improving Global Outcomes criteria.

RESULTS

Patients in the AKI stage 3 group had significantly higher RRI, RVDW pattern and lower PDU score (p < 0.05). Only lactate, urine volume, serum creatinine (SCr) on admission, PDU score and RVDW pattern were statistically significant predictors (p < 0.05). Model 1 based on these five variables (area under the curve [AUC] = 0.938, 95% confidence interval [CI] 0.899-0.965, p < 0.05) showed the best performance in predicting AKI stage 3, and difference in AUC between it and the clinical model including lactate, urine volume and SCr (AUC = 0.901, 95% CI 0.855-0.936, p < 0.05) was statistically significant (z statistic = 2.224, p = 0.0261). The optimal cut-off point for a nomogram based on Model 1 was ≤127.67 (sensitivity: 95.8%, specificity: 82.3%, Youden's index: 0.781).

CONCLUSIONS

The nomogram model including SCr, urine volume, lactate, PDU score and RVDW pattern upon admission exhibited a significantly stronger capability for AKI stage 3 than each single indicator and clinical model including SCr, urine volume and lactate.

The Resistive Index by Doppler Ultrasonography as a Predictor of the Long-Term Outcomes After Kidney Transplantation

BACKGROUND

Doppler ultrasonography (US) is a noninvasive examination for assessing graft function after kidney transplantation. Although Doppler US is routinely performed, only a few reports have investigated whether a high resistive index (RI) detected by Doppler US affects graft function and survival. We hypothesized that there is a relationship between a high RI and inferior outcomes after kidney transplantation.

METHODS

We included 164 living kidney transplant patients treated between April 2011 and July 2019. We divided the patients into 2 groups according to RI (cut-off, 0.7) 1 year after transplantation.

RESULTS

The recipient was significantly older in the high RI (≥0.7) group. Moreover, there were significant differences in the prevalence of pretransplant diabetes mellitus and the value of pretransplant hemoglobin A1c. Regarding long-term outcome, there was no significant difference in overall graft survival (5 years, 92.6% vs 91.8%; 10 years, 85.0% vs 67.9%; P = .64). On the other hand, the mortality was significantly worse in the high RI group (5 years, 99.1% vs 93.9%; 10 years, 96.4% vs 70.0%, P = .013).

CONCLUSIONS

A high RI might predict mortality after kidney transplantation.

Predictive value of the renal resistive index in the immediate postoperative period after kidney transplantation on short- and long-term graft and patient outcomes

INTRODUCTION

During the postoperative stay in the intensive care unit after kidney transplantation, the renal resistive index (RI) is routinely measured. An increased RI, measured months posttransplant, is associated with a higher mortality. We wanted to investigate the value of the RI immediately posttransplant in predicting both short- and long-term outcome.

METHODS

We performed a retrospective single-center study. The RI was collected <48 h posttransplant in patients undergoing kidney transplantations between 2005 and 2014. Short-term outcome was evaluated by delayed graft function (DGF). The long-term endpoints were kidney function and mortality at 30 days, 1 year and 5 years.

RESULTS

We included 478 recipients, 91.4% of whom reached the end of the 5-year follow-up. A higher RI < 48 h posttransplant was significantly associated with DGF. This association was particularly strong in patients receiving grafts from donors after brain death and expanded criteria donors. A higher RI also correlated with mortality and death with functioning graft but not with graft failure. After adjustment for confounders, we found an association between increased RI and DGF, but not with long-term kidney function or mortality.

CONCLUSION

The RI routinely measured <48 h posttransplant is an independent predictor of short-term kidney function.

B-Flow Sonography vs. Color Doppler Sonography for the Assessment of Vascularity in Pediatric Kidney Transplantation

OBJECTIVE

 To compare B-flow sonography (BFS) with color Doppler sonography (CDS) for imaging of kidney transplant vascularization in children.

PATIENTS AND METHODS

 All children receiving a kidney transplantation who underwent a protocol-based ultrasound examination (Loqiq 9, GE Medical Systems, Milwaukee, WI, USA) using the BFS and CDS technique with equal settings and probe position between January 2013 and January 2016 were retrospectively assessed (n = 40). The obtained datasets were visually graded according to the following criteria: (I) delineation of the renal vascular tree (Grade 1 - clear demarcation of interlobar, together with arcuate and interlobular vessels; Grade 2 - clear demarcation of interlobar and cortical vessels, but no distinction of interlobular from arcuate vessels; Grade 3 - only clear demarcation of interlobar vessels, Grade 4 - insufficient demarcation) (II) delineation of cortical vessel density in ventral, lateral, and dorsal part of the transplant, (III) smallest vessel-capsule distance, and (IV) maximum cortical vessel count. Comparison between methods was performed using Fisher's exact and paired sample t-tests.

RESULTS

 Applying a curved transducer (C1-6), BFS showed superior delineation of the renal vascular tree (p < 0.001), a lower vessel-capsule distance (p < 0.001), a higher cortical vessel count (p < 0.001), and a higher cortical vessel density in the superficial cortex (p = 0.01) than CDS. In the dorsal and lateral aspects of the transplant, cortical vessel density was lower with BFS (both p < 0.001). Using a linear high-resolution transducer (ML 6-15), no significant differences between the methods were found.

CONCLUSION

 Improved imaging of kidney transplant vascularization can be achieved in children by adding BFS to a standard protocol. The BFS technique is especially beneficial for overall assessment of the renal vascular tree together with the extent of cortical vascularization on curved array images.

KEY POINTS

  · Depiction of vascular tree and ventral cortical vessels is improved by BFS.. · The dorso-lateral cortex was better represented with CDS because of higher penetration.. · Additional monitoring with BFS improves the monitoring of transplant viability..

CITATION FORMAT

· Dammann E, Groth M, Schild R et al. B-Flow Sonography vs. Color Doppler Sonography for the Assessment of Vascularity in Pediatric Kidney Transplantation. Fortschr Röntgenstr 2021; 193: 49 - 60.

Quantitative evaluation of renal parenchymal perfusion using contrast-enhanced ultrasonography in renal ischemia-reperfusion injury in dogs

This study evaluated whether renal perfusion changes can be noninvasively estimated by using contrast-enhanced ultrasonography (CEUS) in renal ischemia-reperfusion injury and investigated the correlation between renal perfusion measured by CEUS and necrosis and apoptosis of renal tubular epithelial cells. In six dogs with experimentally induced renal ischemia-reperfusion injury, changes in time to peak intensity, peak intensity, and area under the curve were measured on CEUS. Peak intensity and area under the curve of the renal cortex began to decrease on day 1 (about 20% lower than baseline) and reached the lowest levels (about 50% of baseline) on day 4. They then gradually increased until day 10, at which time peak intensity was about 87% and area under the curve was about 95% of baseline; neither fully recovered. Both parameters were strongly correlated with the necrosis scores on histopathologic examination on day 4 (r = −0.810 of peak intensity and r = −0.886 of area under the curve). CEUS allowed quantitative evaluation of perfusion changes in acute renal ischemia-reperfusion injury, and CEUS results were correlated with renal tubular damage on histopathologic examination. Thus, CEUS could be a noninvasive, quantitative diagnostic method for determining progress of renal ischemia-reperfusion injury.

Diffusion-weighted imaging of the kidneys in haemolytic uraemic syndrome

OBJECTIVES

To evaluate the kidneys of patients with haemolytic uraemic syndrome (HUS) using diffusion-weighted imaging (DWI) and Doppler ultrasound (US) compared with healthy controls.

MATERIALS AND METHODS

Fifteen patients (mean age 33.3 years; three male; 12 female) with diarrhoea-positive HUS and 15 healthy volunteers were prospectively evaluated with DWI and Doppler US. A total apparent diffusion coefficient (ADC_TOT), and ADCs predominantly reflecting microperfusion (ADC_LOW) and diffusion (ADC_HIGH) were calculated. Doppler US evaluated renal vascularity and flow.

RESULTS

When compared with controls, kidneys affected by HUS showed reduced cortical ADC values (ADC_TOT 1.79±0.22 vs. 2.04±0.1x10^-3 mm²/s, P 0.001), resulting in either low corticomedullary differences (11/15 patients) or an inverted corticomedullary pattern (4/15 patients). Reduction of cortical ADC values was associated with a decrease of cortical vascularity on Doppler US (ADC_TOT, P<0.001; ADC_LOW, P 0.047). Kidneys with complete absence of the cortical vasculature on Doppler US (four patients) also demonstrated limited diffusion (ADC_HIGH, P 0.002). Low glomerular filtration rate, requirement for haemodialysis during hospitalization, and longer duration of haemodialysis were associated with decreased cortical diffusivity (ADC_TOT: P 0.04, 0.007, and <0.001, respectively).

CONCLUSION

DWI shows qualitative and quantitative abnormalities in kidneys affected by HUS, thereby extending the non-invasive assessment of renal parenchymal damage.

KEY POINTS

• In HUS, DWI is feasible for functional characterization of kidney involvement. • Kidneys affected by HUS showed reduced cortical diffusivity. • Decreased cortical diffusivity was associated with lower kidney function. • Requirement and duration of haemodialysis was linked to degree of cortical alterations.

The predictive value of resistive index obtained by Doppler ultrasonography early after renal transplantation on long-term allograft function

DUSG is a useful diagnostic tool for the follow-up of renal transplant recipients. The measurement of intrarenal arterial RI by DUSG has been proven to predict short-term AF. The aim of the study was to evaluate the predictive value of DUSG performed during the early after RTx on long-term AF. Seventy patients were enrolled into study. DUSG was performed at third and seventh days after RTx. Patients were divided into two groups according to rate of recovery of graft function as patients with normal graft function and abnormal graft function. Although the RI values were correlated with the AF early after transplantation, they were not correlated with long-term AF. However, the rate of recovery of graft function at early period after RTx was correlated with creatinine level at first year and with glomerular filtration rate at first year and last visit. Although the RI has no predictive value for long-term AF, the rate of recovery of graft function at early post-transplantation period has predictive value for long-term AF; patients with higher RI values early after RTx should be followed carefully for the development of chronic allograft injury.

The inability of an early post-transplantation intrarenal resistive index to predict renal allograft function at 12 weeks after engraftment in young adults

Background The intrarenal resistive index (RI) is a promising tool for predicting renal graft outcomes. Due to the complexity of graft function and the presence of diverse contributing factors, however, the available data are inconclusive. Purpose To examine the performance of the RI 1 week after transplant in predicting allograft function at week 12, with an emphasis on the type of intrarenal artery used in the examination. Material and Methods A total of 58 first-time living-donor kidney-allograft-transplantation patients aged less than 50 years underwent Doppler ultrasonography (US) of the intrarenal arteries 1 week after engraftment. The RI was calculated for both the segmental (RI-C) and interlobar-arcuate (RI-P) arteries. Serum creatinine level and the creatinine reduction ratio (CRR) were determined at weeks 1 and 12 post transplantation. Results While the RI did not correlate with serum creatinine level and CRR at week 1, significant correlations were present between the RI and serum creatinine level (r = 0.28, P = 0.03 for both RI-C and RI-P) and CRR (r = -0.25, P = 0.05 for both RI-C and RI-P) at week 12. The sensitivity, specificity, positive predictive value, and negative predictive value of using RI-C in predicting abnormal 12-week serum creatinine level were 51.2%, 52.9%, 72.4%, and 31.3%, respectively; and 53.7%, 47.1%, 70.9%, and 29.6% for RI-P, respectively ( P > 0.99 for all comparisons). Conclusion Early post-transplantation RI correlates significantly with both serum creatinine level and creatinine reduction ratio 12 weeks after engraftment with intermediate predictive accuracy.

Non-invasive approaches in the diagnosis of acute rejection in kidney transplant recipients. Part I. In vivo imaging methods

Kidney transplantation (KTx) represents the best available treatment for patients with end-stage renal disease. Still, full benefits of KTx are undermined by acute rejection (AR). The diagnosis of AR ultimately relies on transplant needle biopsy. However, such an invasive procedure is associated with a significant risk of complications and is limited by sampling error and interobserver variability. In the present review, we summarize the current literature about non-invasive approaches for the diagnosis of AR in kidney transplant recipients (KTRs), including in vivo imaging, gene expression profiling and omics analyses of blood and urine samples. Most imaging techniques, like contrast-enhanced ultrasound and magnetic resonance, exploit the fact that blood flow is significantly lowered in case of AR-induced inflammation. In addition, AR-associated recruitment of activated leukocytes may be detectable by ¹⁸F-fluoro-deoxy-glucose positron emission tomography. In parallel, urine biomarkers, including CXCL9/CXCL10 or a three-gene signature of CD3ε, IP-10 and 18S RNA levels, have been identified. None of these approaches has been adopted yet in the clinical follow-up of KTRs, but standardization of procedures may help assess reproducibility and compare diagnostic yields in large prospective multicentric trials.

Correlation of histopathologic and dynamic tissue perfusion measurement findings in transplanted kidneys

Background

Cortical perfusion of the renal transplant can be non-invasively assessed by color Doppler ultrasonography. We performed the Dynamic Tissue Perfusion Measurement (DTPM) of the transplant’s renal cortex using color Doppler ultrasonography (PixelFlux technique), and compared the results with the histopathological findings of transplant biopsies.

Methods

Ninety-six DTPM studies of the renal transplant’s cortex followed by transplant biopsies were performed in 78 patients. The cortical perfusion data were compared with the parameter of peritubular inflammatory cell accumulation (PTC 0 to 3) based on Banff-classification system.

Results

A significant decrease of cortical perfusion could be demonstrated as the inflammatory cells accumulation in peritubular capillaries increased. Increasing peritubulitis caused a perfusion loss from central to distal layers of 79% in PTC 0, of 85% in PTC 1, of 94% in PTC 2, and of 94% in PTC 3. Furthermore, the perfusion loss due to peritubular inflammation was more prominent in the distal cortical layer. The extent of perfusion decline with increasing peritubulitis (from PTC 0 to PTC 3) was 64% in proximal 20% cortical layer (p20), 63% in proximal 50% cortical layer (p50), increased to 76% in distal 50% cortical layer (d50), and peaked at 90% in the distal 20% cortical layer (d20). For those without peritubulitis (PTC 0), the increase in the the Interstitial Fibrosis/Tubular Atrophy (IF/TA) score was accompanied by a significantly increased cortical perfusion. A Polyomavirus infection was associated with an increased cortical perfusion.

Conclusions

Our study demonstrated that the perfusion of the renal transplant is associated with certain pathological changes within the graft. DTPM showed a significant reduction of cortical perfusion in the transplant renal cortex related to peritubular capillary inflammation.

Relation of resistive and pulsatility indices with graft function after renal transplant

OBJECTIVES

There are conflicting data regarding the use of some measured indices by Doppler ultrasound such as the resistive index and the pulsatility index in predicting renal allograft dysfunction. This study sought to evaluate the association of early postoperative Doppler indices and 3-month serum creatinine levels in renal transplant recipients.

MATERIALS AND METHODS

During a 1-year period, all patients who underwent renal transplant at our hospital were recruited into a prospective study. Doppler ultrasound was performed on all patients 6 days and 3 months after the transplant and the resistive index and the pulsatility index were calculated for each patient. Then, the association between these indices and 3-month outcomes of patients were investigated.

RESULTS

Thirty-eight patients including 21 men (mean age, 36.6 ± 13.1 y) were evaluated. There was a positive correlation between the resistive index and the pulsatility index at 6 days after transplant and the serum creatinine measured at the same day (P < .001 and r=0.570 for resistive index; P < .001 and r=0.547 for pulsatility index). There was also a positive correlation between the pulsatility index and the resistive index at 6 days after transplant and 3-month serum creatinine level (P = .009 and r=0.420 for resistive index; P = .009 and r=0.417 for pulsatility index). There were negative correlations between the resistive index and the pulsatility index on the sixth day after surgery and creatinine clearance measured at 6 days and 3 months after transplant.

CONCLUSIONS

This study reveals a strong-to-medium correlation between the resistive index and the pulsatility index, serum creatinine level, measured 6 days after transplant.

Color Doppler indexes in early phase after kidney transplantation and their association with kidney function on six month follow up

BACKGROUND

Doppler ultrasonography (DU) and measurement of its indexes, resistive index (RI) and pulsatility index (PI), is used to investigate transplanted kidney hemodynamic status and function. The aim of this study was to determine the correlation between Doppler indexes in the early phase after transplantation with long-term transplanted kidney function.

MATERIALS AND METHODS

In this cross-sectional study on 38 newly kidney transplant patients, we performed DU with assessment of its indexes within 48 hours, 1 week, and 6 months after kidney transplantation. Serum creatinine after stability and 6 months after kidney transplantation were assessed. Cyclosporine level was measured 1 week after kidney transplantation and compared with DU indexes.

RESULTS

About 71% of kidney transplanted patients reached their normal initial creatinine level(cr<1.5 mg/ dl) and 28% of all patients were involved in kidney dysfunction after 6 months (increase in basic creatinine level more than 25%).There was no significant difference between mean RI and PI in patients with normal and disturbed kidney function based on creatinine level in early posttransplantation period but there was linear correlation between mean RI and PI within 48 hours and 1 week with kidney function after 6 months. Also no association between cyclosporine level and RI and PI was shown. There was a direct association between age and the levels of RI and PI 6 months after transplantation.

CONCLUSION

This study suggests assessment of RI and PI in early period after transplantation and can be used as predictive parameters for long-term function of transplanted kidney and RI more than 0.80 in early phase after transplantation has an acceptable sensitivity and specificity to predict long-term kidney dysfunction.

Prognostic impact of renal arterial resistance index upon renal allograft survival: the time point matters

BACKGROUND

The renal arterial resistance index (RI) is reported to be a significant predictive parameter for renal allograft failure or death. The influence of the time point after renal transplantation on its predictive power has not been sufficiently evaluated. We performed a retrospective analysis of RI and its power to predict renal allograft failure or death with special emphasis on the time point of RI measurement.

METHODS

The present analysis is based on ultrasonographically recorded intrarenal arterial RI measurements, routinely obtained in our outpatient department, over a period of 13 years. Altogether, 88 patients with an RI measurement 0-3, 3-6 and 12-18 months after transplantation were included and retrospectively stratified into two groups according to the RI: those with an index >0.75 and those with an index of ≤0.75.

RESULTS

Twenty patients (23%) reached the combined end point, i.e. allograft failure with a return to dialysis or death. The RI measured early after transplantation (0-3 and 3-6 months) did not predict the end point, whereas the RI obtained between 12 and 18 months showed a significant predictive value for renal transplant failure or death in a univariate approach [Wald test, P = 0.0013, hazard ratio (HR) 4.787, 95% confidence interval (CI) 1.846-12.411]. At 12-18 months after transplantation, 14% (12 patients) of the study population had an RI >0.75. Seven (58%) of these patients reached the end point versus 13 of 76 patients (17%) with an RI ≤0.75. In a multivariate Cox model, the RI measured between 12 and 18 months after transplantation exhibited the highest hazard ratio (HR 6.191, 95% CI 2.288-16.756, P = 0.0003) for transplant failure or death.

CONCLUSION

In our hands, the RI obtained during the first 6 months after transplantation failed to predict renal allograft failure or death, whereas the RI measured 12-18 months after transplantation appeared useful to predict long-term allograft outcomes.

Complications of renal transplantation: ultrasonographic evaluation

OBJECTIVE

The purpose of this presentation is to show the ultrasonographic findings of complications of renal transplantation.

METHODS

We reviewed the ultrasonographic findings of complications of renal transplantation, including urologic complications, fluid collections, graft dysfunction, vascular complications, neoplasms, and recurrent native renal disease.

RESULTS

Specific ultrasonographic features of complications of renal transplantation have been illustrated.

CONCLUSIONS

Familiarity with the clinical setting and the appearance of potential renal transplant complications as depicted with the most commonly used modality, ultrasonography, will facilitate prompt, accurate diagnosis and treatment.

Color Doppler Findings in Transplanted Kidneys and Remnant Kidneys of Donors 6 to 12 Months After Kidney Transplantation

OBJECTIVES

Ultrasonography and color Doppler have been used extensively in the evaluation of transplanted kidney. The aim of this study was evaluation and comparison of color Doppler sonography findings in the remnant kidney of living donors and the transplanted kidney at 6 to 12 months after kidney transplantation.

METHODS

In a cross-sectional study we evaluated ultrasonographic (US) and color Doppler findings in 20 kidney allograft recipient and donors. Group 1 were unrelated and related kidney donors, and group 2, allograft recipients. Color Doppler US was performed by one sonologist on the remnant kidney of the living donor and the transplanted kidney of the recipient at 6 to 12 months after kidney donation and transplantation. We recorded, kidney size (including length and anteroposterior diameter), cortical thickness, resistive index (RI), and pulsatile index (PI). Statistical analysis was performed using SPSS 13 win (t test) for comparison of the results in donors and recipients. All data are presented as mean values +/- SD with P values less than .05 considered significant.

RESULTS

In group 1, mean age of kidney allograft recipients was 39.92 +/- 11.95 years with male-to-female ratio of 1/2. Mean length, width, and cortical thickness of the transplanted kidney were 120.15 +/- 11.95 mL, 53.65 +/- 7.50 mL, and 8.53 +/- 1.00 mL, respectively. Mean RI and PI were 0.60 +/- 0.08 and 1.02 +/- 0.23, respectively. Mean serum creatinine was 1.23 +/- 0.24 mg/dL. Mean duration of renal transplantation was 7.27 +/- 1.10 months. In group 2, mean age of recipients was 25.63 +/- 3.50 years with male-to-female ratio of 1/10. Mean length, anteroposterior diameter, and cortical thickness were 120.77 +/- 9.28 mL, 53.36 +/- 4.52 mL, and 9.04 +/- 1.27 mL, respectively. Mean RI and PI were 0.60 +/- 0.02 and 1.07 +/- 0.13, respectively. There was no significant difference in the length, anteroposterior diameter, cortical thickness, RI, and PI of donors and transplanted kidneys at 6 to 12 months after transplantation (P>.05). There was a significant increase in both donor and recipient kidney size at 6 to 12 months after transplantation (P<.05).

CONCLUSION

It seems that renal US and Doppler parameters remain stable in the recipient and donor at least upon short-term evaluation. Long-term study with more patients is recommended.

Avaliação da perfusão renal pelo Power Doppler em pacientes transplantados renais

OBJETIVOS: O objetivo deste estudo é testar a aplicabilidade do estudo ultra-sonográfico com Power Doppler na identificação das alterações da perfusão dos rins transplantados e sua correlação com a reserva funcional renal e microalbuminúria antes e após a infusão de solução de aminoácidos intravenosos. MÉTODOS: Vinte e três pacientes transplantados renais foram avaliados pelo Power Doppler antes (fase basal), após 120 minutos (fase 1) e após 240 minutos (fase 2) da infusão intravenosa de aminoácidos. Concomitantemente, foram realizadas, nas três fases, dosagem de creatinina, avaliação do índice de filtração glomerular, da reserva funcional renal e de microalbuminúria. RESULTADOS: De acordo com os padrões de perfusão na fase basal pelo Power Doppler, descritos por Hoyer et al. em 1999, os pacientes foram divididos em três grupos: 12 pacientes com escore I, seis com escore II e cinco com escore III de perfusão renal. Nos enxertos renais com excelente perfusão renal (escore I), observou-se variação significativa das variáveis estudadas, tanto na fase 1 como na 2 (P CONCLUSÕES: Os achados sugerem que os transplantes com escore I de perfusão apresentam reserva funcional renal quando submetidos a estímulo com aminoácidos. No entanto, com a progressiva diminuição no grau de perfusão renal pelo Power Doppler, observa-se perda da capacidade dos rins transplantados em aumentar o índice de filtração glomerular como resposta a estímulos externos, com seqüente ausência de reserva funcional renal. A partir deste estudo, será possível criar novos horizontes para o entendimento da evolução dinâmica do processo de perda da função renal nos transplantados renais.

Role of duplex Doppler and power Doppler sonography in transplanted kidneys with acute renal parenchymal dysfunction

The limited work published on the comparison of power Doppler sonography (PDS) and duplex Doppler sonography (DDS) in the assessment of acute renal allograft dysfunction has shown contradictory results. We compared the role of DDS and PDS in renal transplant recipients developing acute renal parenchymal dysfunction and correlated these findings with kidney biopsy, which was taken as the gold standard. Thirty post-renal transplant patients with acute graft dysfunction underwent Doppler sonography, DDS and PDS using an HDI 5000 ATL machine. Patients who developed graft dysfunction as a result of vascular, obstructive or other non-parenchymal causes were excluded. All patients underwent an allograft biopsy within 72 h of the sonography. Based on the biopsy findings, 24 patients were categorized as having acute rejection, and six patients as having no rejection. The overall sensitivity, specificity and accuracy of DDS for evaluation of graft dysfunction were 54.17, 33.33, and 50.00%, respectively, and that for PDS were superior with 87.50, 33.30, and 76.67%, respectively. The low specificity can be partially attributed to the small number of cases without rejection in our study population. We conclude that PDS is superior to DDS in screening patients with acute parenchymal renal dysfunction post-transplant. However, a normal PDS examination does not exclude the presence of acute rejection. Power Doppler sonography is a useful screening test for diagnosing acute rejection but a renal allograft biopsy remains the gold standard for diagnosis of this condition.

Color Doppler Ultrasound in Renal Transplant: Role of Resistive Index versus Renal Cortical Ratio in the Evaluation of Renal Transplant Diseases

BACKGROUND/AIMS

Ultrasound (US) and color Doppler are not sensitive enough to detect anomalies in cortical perfusion, which is affected in most graft dysfunctions. The renal cortical ratio (RCR) is a variation in the resistive index (RI) values from the renal artery to cortical vessels, expressed in percent. The aim of this study was to compare the RI and RCR in the differentiation of normal and pathological grafts, to assess the positive predictive value of RCR and show that RCR enables earlier diagnosis than RI.

METHODS

Based on clinical, biochemical and histological examinations, 494 renal allografts were divided into 3 groups (normal grafts, acute and chronic pathologies). All patients underwent US color Doppler. RI was measured and RCR calculated. Follow-up confirmed the initial division in groups. Statistical significance was calculated using the two-tailed Student's t test. The positive predictive value was calculated for each group.

RESULTS

24 h after transplant, RCR differentiated normal grafts from acute dysfunctions despite confusing biochemical values and clinical symptoms. In chronic patients, RCR variations occurred later but always before the serum creatinine level increased.

CONCLUSION

RCR presented a higher positive predictive value than RI. RCR curves were already altered in the early stages of transplant pathologies. RCR calculation is easy and makes a significant contribution towards a correct early diagnosis.

Prediction of renal allograft function with early Doppler ultrasonography

INTRODUCTION

Doppler ultrasonography (USG) is an useful, noninvasive diagnostic tool for the management and follow-up of the transplanted kidney. However, it is believed that the value of Doppler USG is limited to discrimination of acute rejection episodes. We tested whether early Doppler USG findings were predictive of 1-month and 1-year allograft functions in noncomplicated renal transplant recipients (RTRs).

PATIENTS AND METHODS

Resistive index (RI) and pulsatile index (PI) values obtained by doppler USG within the first week of transplantation were correlated with allograft function at 1 month and 1 year in 45 (10 women, 35 men, mean age: 27 years) noncomplicated cases. Patients with complications during the first posttransplant year were not included.

RESULTS

There was a negative correlation between both RI and PI with creatinine clearance values at 1 month and at 1 year posttransplant. There was a significant decline in allograft function among cases with either RI > or = 0.7 or PI > or = 1.1. Patients with impaired allograft function have higher RI and PI values.

CONCLUSION

Renal allograft survival is influenced by many factors. However, no reliable simple parameter has been identified to predict long-term outcome. Doppler USG performed during the early transplantation period with calculation of RI and PI may have a predictive value to forecast early and long-term outcomes of noncomplicated kidney transplants.

The renal arterial resistance index and renal allograft survival

BACKGROUND

Most renal transplants fail because of chronic allograft nephropathy or because the recipient dies, but no reliable factor predicting long-term outcome has been identified. We tested whether a renal arterial resistance index of less than 80 was predictive of long-term allograft survival.

METHODS

The renal segmental arterial resistance index (the percentage reduction of the end-diastolic flow as compared with the systolic flow) was measured by Doppler ultrasonography in 601 patients at least three months after transplantation between August 1997 and November 1998. All patients were followed for three or more years. The combined end point was a decrease of 50 percent or more in the creatinine clearance rate, allograft failure (indicated by the need for dialysis), or death.

RESULTS

A total of 122 patients (20 percent) had a resistance index of 80 or higher. Eighty-four of these patients (69 percent) had a decrease of 50 percent or more in creatinine clearance, as compared with 56 of the 479 patients with a resistance index of less than 80 (12 percent); 57 patients with a higher resistance index (47 percent) required dialysis, as compared with 43 patients with a lower resistance index (9 percent); and 36 patients with a higher resistance index (30 percent) died, as compared with 33 patients with a lower resistance index (7 percent) (P<0.001 for all comparisons). A total of 107 patients with a higher resistance index (88 percent) reached the combined end point, as compared with 83 of those with a lower resistance index (17 percent, P<0.001). The multivariate relative risk of graft loss among patients with a higher resistance index was 9.1 (95 percent confidence interval, 6.6 to 12.7). Proteinuria (protein excretion, 1 g per day or more), symptomatic cytomegalovirus infection, and a creatinine clearance rate of less than 30 ml per minute per 1.73 m2 of body-surface area after transplantation also increased the risk.

CONCLUSIONS

A renal arterial resistance index of 80 or higher measured at least three months after transplantation is associated with poor subsequent allograft performance and death.

[Ultrasonography in urology]

After its introduction more than twenty years ago, ultrasound has continually increased in importance in urology diagnostics and is currently one of the most frequent exploratory techniques used. It corresponds to one out of every four imaging techniques carried out in medicine. The possibility of intervention under echographic control, for either diagnostic or therapeutic purposes, has been studied ever since ultrasound first appeared. Nowadays, interventionist echography is a commonly used technique in urology and is applied in a wide range of procedures carried out on the prostate gland, bladder and kidney that require echography-guided puncture techniques. Timely modifications of ultrasound for control and monitoring of treatments such as shock wave extracorporeal lithotripsy or transperineal brachitherapy has increased even more its day-to-day use by urologists. New technologies currently under development such as high-energy ultrasound in the management of kidney and prostate cancer, 3-dimensional ultrasound, Doppler-energy and contrast ultrasound have also increased the importance of this procedure in urology.

A straightforward algorithm for the quantification of power Doppler signals

RATIONALE AND OBJECTIVES

To document a simple algorithm that quantifies power Doppler signals by computer-based statistical image analysis.

METHODS

Personal computer-based software was developed. Color pixels representing power Doppler signals were separated from the background gray pixels in power Doppler images converted in BMP format. To avoid misregistration during this segmentation, a threshold value is required to adequately distinguish between gray and color pixels. Equating the intensity of each color pixel to a Power Value (PV), a histogram of Power Values in power Doppler images was obtained.

RESULTS

The software was designed to allow users to adjust two thresholds (Difference Threshold and Intensity Threshold) by observing the segmentation results in real time. The software calculates the following indexes within any region of interest as defined by the operator: mean PV, peak PV, standard deviation of PV, percentage power Doppler area, and integrated PV per unit area.

CONCLUSIONS

Power Doppler signals can be objectively quantified using this straightforward algorithm. This simple and practical method can be applied to comparative or longitudinal studies upon vascularity or blood flow.

Power Doppler imaging and resistance index measurement in the evaluation of acute renal transplant rejection

PURPOSE

This study was designed to test the hypotheses that power Doppler imaging has a predictive value in the assessment of acute renal allograft rejection and that the information garnered from the combination of resistance index (RI) determination and power Doppler imaging has an even greater predictive value in this assessment.

METHODS

Power Doppler images obtained prior to 96 sequential renal allograft biopsies in 92 patients with suspected renal transplant rejection were retrospectively graded for parenchymal vascularity on a scale of 1 to 4: 1, normal, uniform cortical flow; 2, mild peripheral cortical hypoperfusion; 3, vascular pruning in cortex and medulla; and 4, no visible parenchymal flow, with flow seen only in central vessels. Power Doppler grades and RIs for these cases were compared to graft biopsy results.

RESULTS

No statistically significant association was observed between parenchymal vascularity as graded by power Doppler imaging, RI, and the presence of acute transplant rejection.

CONCLUSIONS

Neither grading of vascularity on power Doppler images, RI measurement, nor the combination of these methods is an accurate means of detecting renal allograft rejection.

Contribution of power Doppler sonography to the detection of renal allograft rejection in the cynomolgus monkey

RATIONALE AND OBJECTIVES

To evaluate whether a change in the power Doppler (PD) flow signals produced by the renal cortical interlobular vasculature of allografts in cynomolgus monkey transplant models is useful for the detection of cellular rejection and vasculopathies.

METHODS

Seventy-three monkeys with life-supporting allografts (bilateral native kidney nephrectomy) and 20 monkeys with allografts implanted with only unilateral native kidney nephrectomy were examined with ultrasound that included an examination with PD. Each graft received a PD score of 3 (normal cortical blush), 2 (reduced flow, no blush), or 1 (absence of cortical flow), and the results were compared with histology either from ultrasound-guided biopsy or at necropsy.

RESULTS

One hundred seventy-one allograft examinations (histological and PD) were compared. Histologically normal grafts were statistically more likely to have normal PD findings than were those with reduced flow or absent flow. Allografts with reduced flow had statistically more severe cellular rejection than those with normal flow. Also, vasculopathies were present in all three PD groups.

CONCLUSIONS

Reduced renal cortical flow in the cynomolgus monkey renal allograft indicates that more severe degrees of cellular rejection are present compared with allografts with normal flow. Overlap in the histological diagnoses of allografts with normal and reduced flow exists, and the finding of reduced flow with PD may be prognostically important and indicates the need for tissue sampling.

Ultrasound contrast agents: a promising future

The emerging field of contrast ultrasound has great and untapped potential. Improved vascular enhancement may increase the number and type of diagnostic vascular examinations. Improved vessel depiction may increase examination speed and improve patient throughput. New gray-scale contrast imaging techniques may substantially increase the sonographic detection and characterization of liver, kidney, and other focal parenchymal masses. Contrast ultrasound examinations may increase diagnostic confidence, decrease nondiagnostic studies, and decrease the requirement for additional imaging studies. Further investigation is needed, however, to determine the diagnostic use and cost-effectiveness of this new approach relative to CT, MR imaging, angiography, and conventional ultrasound imaging.

Renal allograft vasculopathy: ultrasound findings in a non-human primate model of chronic rejection

The purpose was to determine whether decreased cortical flow detected with power Doppler (PD) ultrasound in renal allografts in cynomolgus monkeys marks the presence or onset of chronic renal allograft vasculopathy. The 2D grey scale and PD ultrasound findings of 24 consecutively implanted non-life-supporting renal allografts in cynomolgus monkeys that underwent either 24 h (n=15) or 48 h (n=9) cold ischaemia times were recorded and compared with the results of histology performed every 2 weeks post-operatively. 13 allografts developed vasculopathies, 10 of which had PD scores equal to 1 (severe reduction of cortical flow). A PD score of 1 occurred in only one instance in the group of allografts without vasculopathies and this was due to necrosis. Allografts without vasculopathies otherwise had either PD scores of 3 (normal flow; n=2) or 2 (reduced flow; n=4). Allografts subjected to 48 h cold ischaemia times were smaller than those with 24 h cold ischaemia times (significant at weeks 5-11, p<0.05), but a reduction in graft size associated with vasculopathies occurred infrequently. In conclusion, the finding of reduced renal cortical flow detected by PD ultrasound during serial examination of non-life-supporting renal allografts is highly supportive of a diagnosis of graft vasculopathy due to arteriolar intimal proliferation, and illustrates an excellent method of monitoring changes in cortical perfusion in allografts in animal models. The combination of findings of reduced or absent cortical flow together with severe graft enlargement is highly suggestive of the presence of not only vasculopathies but also tissue damage and degeneration.

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.