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

Prospective quantitative study: Doppler ultrasound in the evaluation of chronic renal allograft disease and correlation with histopathological finding

Background and Objectives

Renal allograft biopsy is the gold standard for diagnosing chronic allograft nephropathy, but noninvasive methods are needed to avoid unnecessary biopsies. Doppler ultrasonography, particularly the resistive index (RI), correlates with renal allograft dysfunction. This study aims to assess the relationship between renal sonographic parameters and biochemical parameters in diagnosing graft interstitial fibrosis.

Methods

The study evaluated 60 renal allograft recipients for sonographic renal morphological features and Doppler indices. The estimated glomerular filtration rate (eGFR) was calculated, and cortical fibrosis after the biopsy was determined using the Banff score. Continuous variables like mean and SD were calculated, and categorical variables were reported using frequencies and proportions. Associations were examined using independent sample t-tests, χ 2tests, and multivariate regression analysis.

Results

The mean eGFR was 75.23±25.45 ml/min/1.73 m2. A significant correlation of eGFR with RI (r=0.341, P=0.008) was seen. A significant difference in mean RI (F=10.167; df=2,57; P<0.001) was seen among the histological grades of fibrosis. Among the histological grades of fibrosis, significant differences in RI among mild and moderate (S.E. 0.033, P=0.043), mild and severe (S.E. 0.026, P=0.001) as well as moderate and severe (S.E. 0.036, P=0.029) was seen.

Conclusion

Doppler was able to noninvasively predict allograft fibrosis and could be used as a complementary imaging tool during the follow-up of renal allograft patients. Future research is needed to improve evidence, diagnostic criteria, guidelines, and long-term impact.

Diagnostic and predictive value of resistive / pulsatility indices of ophthalmic artery and common carotid artery for the development of diabetic retinopathy

Background

Ophthalmic artery resistive index (OA RI) was a controversial parameter to show hemodynamic changes due to diabetic retinopathy (DRP).

Purpose

To investigate the diagnostic and predictive value of resistive and pulsatility index (RI and PI, respectively) of OA and common carotid artery (CCA) for the development of DRP.

Material and Methods

A total of 60 patients with diabetes mellitus (DM) type 2 (study group) and 30 healthy participants (control group) were evaluated between January and June 2021 by Doppler ultrasonography (DUS). RI and PI values were compared between groups with a Student’s t-test. Cutoff value, sensitivity, and specificity were calculated for the significant variables with receiver operating characteristic (ROC) analysis.

Results

In total, there were 20 (22.2%) patients with DM without DRP (DMwoRP), 20 (22.2%) patients in the non-proliferative diabetic retinopathy group (NPDRP), and 20 (22.2%) patients in the proliferative diabetic retinopathy group (PDRP). The mean of CCA RI and OA RI in the PDRP group was significantly higher than in the other three groups ( P < 0.001). The mean of CCA RI and OA RI was significantly higher in the PDRP group than in the NPDRP group, and in the NPDRP group compared to the DMwoRP group. CCA RI and OA RI showed a significantly high correlation (r = 0.849; P < 0.001). Sensitivity was 95% and specificity was 100% for the diagnosis of PDRP for the 0.82 cutoff value of OA RI (AUR = 0.999, 95% confidence interval for AUC = 0.997–0.1000; P < 0.001).

Conclusion

The OA RI accurately reflects DRP-induced orbital blood flow changes and is a predictive index for DRP prognosis.

RADIOLOGICAL IMAGING IN RENAL TRANSPLANTATION

SUMMARY – Radiological diagnostic methods have a significant role in the preoperative and postoperative care of patients after kidney transplantation. Improvement and innovations in technology, but also the growing experience of the radiologists who deal with kidney transplant patients as part of the transplant team lead to earlier detection of complications in the postoperative period, which are the leading cause of transplant failure. In this article, we describe, through diagnostic imaging examples, detailed evaluation of all possible complications that can occur after kidney transplantation, with evaluation of different possible diagnostic methods that can be used in the preoperative assessment and postoperative follow up and care of the transplanted patient. The goal of this article is to demonstrate and summarize in detail the possible complications of renal transplantation and how to best diagnostically approach them, with special reference to ultrasound which is the main imaging method for this group of conditions.

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.

Imaging in pediatric renal transplantation

Renal transplantation is the therapy of choice in children with ESKD. Radiological investigations are required in both pre- and post-transplant assessment, although there is paucity of both consensus-based statements and evidence-based imaging guidelines in pediatric renal transplantation. The phases of pediatric ESKD management that require imaging are pretransplantation recipient assessment and post-transplantation surveillance for detection of potential complications. We present suggestions for imaging algorithms for both pre- and post-transplant assessment in pediatric renal transplant recipients.

Evaluation of Kidney Allograft in the Early Posttransplant Period Using Ultrasonography

OBJECTIVES

The aim of this study was to evaluate the kidney allograft after transplant to assess restoration of blood flow, the time required to functionally recovery after surgery, and the ability to differentiate normal from pathologic grafts using color Doppler ultrasonography in the early posttransplant period.

MATERIALS AND METHODS

Sixteen kidney recipients underwent renal color Doppler ultrasonography examinations 1, 2, 3, 7, 15, and 30 days after transplant. We evaluated the clinical and biochemical test results of recipients and the functioning allografts and evaluated the acute pathology. Results of resistive index in color Doppler ultrasonography were compared with blood test results.

RESULTS

During the early postoperative period after kidney transplant, the average size of the kidney was 10.7 × 5.1 cm, with parenchyma at 1.7 cm. The structure of the parenchyma was nonhomogeneous in 14 patients and homogeneous in 2 patients. The medullary pyramid layer was prominent in 6 patients, moderately prominent in 7 patients, and not prominent in 3 patients. The pyelocaliceal system was condensed in 1 patient. Hematoma in the perinephrium was found in 5 patients, and free fluid was found in 5 patients. Satisfactory vascularization of allografts occurred in 14 patients, with resistive index sensitivity of 93% and specificity of 83%.

CONCLUSIONS

Color Doppler ultrasonography and resistive index results were useful in evaluating kidney allografts during the early postoperative period and in confirming their condition despite excessive blood parameter values.

Non-invasive approaches in the diagnosis of acute rejection in kidney transplant recipients, part II: omics analyses of urine and blood samples

Kidney transplantation (KTx) represents the best available treatment for patients with end-stage renal disease. Still, the 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, such as 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 leucocytes may be detectable by 18F-fluorodeoxyglucose positron emission tomography. In parallel, urine biomarkers, including CXCL9/CXCL10 or a three-gene signature of CD3ε, CXCL10 and 18S RNA levels, have been identified. None of these approaches has yet been adopted in the clinical follow-up of KTRs, but standardization of analysis procedures may help assess reproducibility and comparative diagnostic yield in large, prospective, multicentre trials.

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.

Tissue elasticity quantification by acoustic radiation force impulse for the assessment of renal allograft function

Acoustic radiation force impulse (ARFI) quantification, a novel ultrasound-based elastography method, has been used to measure liver fibrosis. However, few studies have been performed on the use of ARFI quantification in kidney examinations. We evaluated renal allograft stiffness using ARFI quantification in patients with stable renal function (n = 52) and those with biopsy-proven allograft dysfunction (n = 50). ARFI quantification, given as shear wave velocity (SWV), was performed. The resistance index (RI) was calculated by pulsed-wave Doppler ultrasound, and clinical and laboratory data were collected. Morphologic changes in transplanted kidneys were diagnosed by an independent pathologist. Mean SWV was more significantly negatively correlated with estimated glomerular filtration rate (eGFR) (r = -0.657, p < 0.0001) than was RI (r = -0.429, p = 0.0004) in transplanted kidneys. Receiver operating characteristic curve analysis revealed that the sensitivity and specificity of quantitative ultrasound in the diagnosis of renal allograft dysfunction were 72.0% and 86.5% (cutoff value = 2.625), respectively. The latter values were better than those of RI, which were 62.0% and 69.2% (cutoff value = 0.625), respectively. The coefficient of variation for repeat SWV measurements of the middle part of transplanted kidney was 8.64%, and inter-observer agreement on SWV was good (Bland-Altman method, ICC = 0.890). In conclusion, tissue elasticity quantification by ARFI is more accurate than the RI in diagnosing renal allograft function.

Renal transplant imaging and complications

The management of end stage renal disease has been revolutionised with the advent of renal transplantation, which offers good quality of life with low morbidity. Imaging plays an important role in the diagnosis and management of complications arising in renal transplant recipients. Ultrasound, Doppler and nuclear medicine are the main imaging modalities. CT scan, MRI and angiography are used in indeterminate cases. Interventional radiology plays a vital role in the management of complications. The aim of this pictorial review is to illustrate the role and limitations of imaging in renal transplant. The normal appearances, the spectrum of pathological conditions affecting the transplant and the complications of immunosuppression are discussed and illustrated.

Diagnosis of renal allograft rejection and acute tubular necrosis by 99mTc-mononuclear leukocyte imaging

One hundred kidney transplant recipients were evaluated on the first and fifth days after transplantation by Tc-99m mononuclear cell scintigraphy. We have developed a quantitative method to diagnose rejection and acute tubular necrosis (ATN) by comparing regions of interest drawn on allograft scintigraphs at different times after endovenous administration of the labeled cells. We suggest that the use of Tc-99m-WBC may be useful for the early diagnosis of rejection and the differential diagnosis of ATN.

Preliminary results of [99mTc]OKT3 scintigraphy to evaluate acute rejection in renal transplants

Allograft rejection can be classified as humoral or cellular mechanisms. Accurate diagnosis of acute rejection remains a formidable challenge in renal transplantation. The need to avoid unnecessary immunosuppressive therapy to treat this complication has led to a continued search for improved diagnostic methods to evaluate and identify postoperative episodes. Here we evaluated the use of [(99m)Tc]OKT3 scintigraphy to diagnose acute rejection in renal transplants. Among 22 patients undergoing renal transplant, we observed an increased [(99m)Tc]OKT3 kidney uptake with the passage of time in patients with rejecting allografts. These findings agreed with those of biopsies. We suggest the [(99m)Tc]OKT3 scans may be useful for the monitoring of renal transplants to detect acute rejection.

Avaliação de transplantes renais utilizando-se 99mTc-leucócitos mononucleares

A rejeição aguda do enxerto renal deve ser diagnosticada precocemente, uma vez que a reversibilidade da rejeição está relacionada com a rapidez na qual o tratamento é iniciado. Os objetivos deste estudo foram: 1) estabelecer um método quantitativo para avaliação da rejeição e necrose tubular aguda (NTA) do rim transplantado; 2) determinar o papel em potencial da cintilografia com leucócitos mononucleares marcados com tecnécio-99m no diagnóstico precoce da rejeição do rim transplantado e no diagnóstico diferencial da NTA. Cento e sessenta estudos cintilográficos foram realizados no primeiro e no quinto dia pós-operatório em 80 pacientes transplantados. Células autólogas foram utilizadas para marcação. Imagens foram obtidas 30 minutos, 3 horas e 24 horas após injeção de 444 MBq (12 mCi) das células marcadas. Houve captação anormal das células marcadas em 27 de 31 casos de rejeição e em seis de oito casos de NTA. Os resultados foram comparados com a clínica de cada paciente. Ultra-sonografias com Doppler detectaram 18 de 31 casos de rejeição. A sensibilidade e a especificidade para rejeição foram, respectivamente, de 87,1% e 100% para a cintilografia e 58,1% e 100% para a ultra-sonografia. Foram realizadas biópsias em oito pacientes, que mostraram sete rejeições e uma NTA. Os resultados sugerem que a cintilografia com leucócitos mononucleares marcados com tecnécio-99m pode ser útil no diagnóstico de rejeição e diagnóstico diferencial de NTA.

New imaging applications in the evaluation of pediatric renal disease

Continued improvements in imaging technology have changed many of the traditional diagnostic algorithms for evaluating pediatric renal disease. Newer imaging modalities offer more accurate, specific, and early diagnoses, but can be time consuming and costly. Less invasive modalities, such as ultrasound, computed tomography, and magnetic resonance imaging have widespread applications in pediatric practice. The risks of radiation exposure, contrast toxicity, and sedation or anesthesia versus the potential benefits of obtaining precise diagnostic information should always be considerations before electing any imaging procedure in children.