Comparison of Ultrasound Corticomedullary Strain with Doppler Parameters in Assessment of Renal Allograft Interstitial Fibrosis/Tubular Atrophy

Advances in imaging techniques to assess kidney fibrosis

As a sign of chronic kidney disease (CKD) progression, renal fibrosis is an irreversible and alarming pathological change. The accurate diagnosis of renal fibrosis depends on the widely used renal biopsy, but this diagnostic modality is invasive and can easily lead to sampling error. With the development of imaging techniques, an increasing number of noninvasive imaging techniques, such as multipara meter magnetic resonance imaging (MRI) and ultrasound elastography, have gained attention in assessing kidney fibrosis. Depending on their ability to detect changes in tissue stiffness and diffusion of water molecules, ultrasound elastography and some MRI techniques can indirectly assess the degree of fibrosis. The worsening of renal tissue oxygenation and perfusion measured by blood oxygenation level-dependent MRI and arterial spin labeling MRI separately is also an indirect reflection of renal fibrosis. Objective and quantitative indices of fibrosis may be available in the future by using novel techniques, such as photoacoustic imaging and fluorescence microscopy. However, these imaging techniques are susceptible to interference or may not be convenient. Due to the lack of sufficient specificity and sensitivity, these imaging techniques are neither widely accepted nor proposed by clinicians. These obstructions must be overcome by conducting technology research and more prospective studies. In this review, we emphasize the recent advancement of these noninvasive imaging techniques and provide clinicians a continuously updated perspective on the assessment of kidney fibrosis.

Ultrasound elastography in chronic kidney disease: a systematic review and meta-analysis

Ultrasound elastography (USE) is a noninvasive technique for assessing tissue elasticity, and its application in nephrology has aroused growing interest in recent years. The purpose of this article is to systematically review the clinical application of USE in patients with chronic kidney disease (CKD), including native and transplanted kidneys, and quantitatively investigate differences in elasticity values between healthy individuals and CKD patients. Furthermore, we provide a qualitative analysis of the studies included, discussing the potential interplay between renal stiffness, estimated glomerular filtration rate, and fibrosis. In January 2022, a systematic search was carried out on the MEDLINE (PubMed) database, concerning studies on the application of USE in patients with CKD, including patients with transplanted kidneys. The results of the included studies were extracted by two independent researchers and presented mainly through a formal narrative summary. A meta-analysis of nine study parts from six studies was performed. A total of 647 studies were screened for eligibility and, after applying the exclusion and inclusion criteria, 69 studies were included, for a total of 6728 patients. The studies proved very heterogeneous in terms of design and results. The shear wave velocity difference of - 0.82 m/s (95% CI: - 1.72-0.07) between CKD patients and controls was not significant. This result agrees with the qualitative evaluation of included studies that found controversial results for the relationship between renal stiffness and glomerular filtration rate. On the contrary, a clear relationship seems to emerge between USE values and the degree of fibrosis. At present, due to the heterogeneity of results and technical challenges, large-scale application in the monitoring of CKD patients remains controversial.

Imaging of renal fibrosis

PURPOSE OF REVIEW

Fibrosis is an important biomarker of chronic kidney injury, and a powerful predictor of renal outcome. Currently, the only method for measuring fibrotic burden is histologic analysis, which requires a kidney biopsy in humans, or kidney removal in animal models. These requirements have not only hindered our ability to manage patients effectively, but have also prevented a full understanding of renal fibrosis pathogenesis, and slowed the translation of new antifibrotic agents. The development of noninvasive fibrosis imaging tools could thus transform both clinical care and renal fibrosis research.

RECENT FINDINGS

Conventional imaging modalities have historically failed to image fibrosis successfully. However, recent exciting technological advances have greatly enhanced their capabilities. New techniques, for example, may allow imaging of the physical consequences of scarring, as surrogate measures of renal fibrosis. Similarly, other groups have developed ways to directly image extracellular matrix, either with the use of contrast-enhanced probes, or using matrix components as endogenous contrast agents.

SUMMARY

New developments in imaging technology have the potential to transform our ability to visualize renal fibrosis and to monitor its progression. In doing so, these advances could have major implications for kidney disease care, the development of new antiscarring agents, and our understanding of renal fibrosis in general.

Value of [68Ga]Ga-FAPI-04 imaging in the diagnosis of renal fibrosis

PURPOSE

Renal fibrosis is a pathological state in the progression of chronic kidney disease. Early detection and treatment are vital to prolonging patient survival. Renal puncture examination is the gold standard for renal fibrosis, but it has several limitations. This study aims to evaluate the diagnostic performance of a novel PET radiotracer, [⁶⁸Ga]Ga-fibroblast activation protein inhibitor (FAPI)-04, which specifically images fibroblast activation protein (FAP) expression for renal fibrosis.

METHODS

All patients underwent renal puncture before receiving [⁶⁸Ga]Ga-FAPI-04 PET/CT imaging. They then underwent [⁶⁸Ga]Ga-FAPI-04 PET/CT and immunochemistry examinations. The data obtained were analyzed.

RESULTS

The [⁶⁸Ga]Ga-FAPI-04 PET/CT examination results demonstrated that almost all patients (12/13) exhibited increased radiotracer uptake. The maximum standardized uptake value (SUVmax) in patients with mild, moderate, and severe fibrosis was 3.92 ± 1.50, 5.98 ± 1.6, and 7.67 ± 2.23, respectively.

CONCLUSION

Compared with renal puncture examination, non-invasive imaging of FAP expression through [⁶⁸Ga]Ga-FAPI-04 PET/CT quickly demonstrates bilateral kidney conditions with high sensitivity. [⁶⁸Ga]Ga-FAPI-04 PET/CT can facilitate the evaluation of disease progression, diagnosis, and the development of a treatment plan.

Recent advances in medical image processing for the evaluation of chronic kidney disease

Assessment of renal function and structure accurately remains essential in the diagnosis and prognosis of Chronic Kidney Disease (CKD). Advanced imaging, including Magnetic Resonance Imaging (MRI), Ultrasound Elastography (UE), Computed Tomography (CT) and scintigraphy (PET, SPECT) offers the opportunity to non-invasively retrieve structural, functional and molecular information that could detect changes in renal tissue properties and functionality. Currently, the ability of artificial intelligence to turn conventional medical imaging into a full-automated diagnostic tool is widely investigated. In addition to the qualitative analysis performed on renal medical imaging, texture analysis was integrated with machine learning techniques as a quantification of renal tissue heterogeneity, providing a promising complementary tool in renal function decline prediction. Interestingly, deep learning holds the ability to be a novel approach of renal function diagnosis. This paper proposes a survey that covers both qualitative and quantitative analysis applied to novel medical imaging techniques to monitor the decline of renal function. First, we summarize the use of different medical imaging modalities to monitor CKD and then, we show the ability of Artificial Intelligence (AI) to guide renal function evaluation from segmentation to disease prediction, discussing how texture analysis and machine learning techniques have emerged in recent clinical researches in order to improve renal dysfunction monitoring and prediction. The paper gives a summary about the role of AI in renal segmentation.

Correlation between Kidney Function and Sonographic Texture Features after Allograft Transplantation with Corresponding to Serum Creatinine: A Long Term Follow-Up Study

Background:

The ability to monitor kidney function after transplantation is one of the major factors to improve care of patients.

Objective:

Authors recommend a computerized texture analysis using run-length matrix features for detection of changes in kidney tissue after allograft in ultrasound imaging.

Material and Methods:

A total of 40 kidney allograft recipients (28 male, 12 female) were used in this longitudinal study. Of the 40 patients, 23 and 17 patients showed increased serum creatinine (sCr) (increased group) and decreased sCr (decreased group), respectively. Twenty run-length matrix features were used for texture analysis in three normalizations. Correlations of texture features with serum creatinine (sCr) level and differences between before and after follow-up for each group were analyzed. An area under the receiver operating characteristic curve (Az) was measured to evaluate potential of proposed method.

Results:

The features under default and 3sigma normalization schemes via linear discriminant analysis (LDA) showed high performance in classifying decreased group with an A_z of 1. In classification of the increased group, the best performance gains were determined in the 3sigma normalization schemes via LDA with an A_z of 0.974 corresponding to 95.65% sensitivity, 91.30% specificity, 93.47% accuracy, 91.67% PPV, and 95.45% NPV.

Conclusion:

Run-length matrix features not only have high potential for characterization but also can help physicians to diagnose kidney failure after transplantation.

Noninvasive assessment of renal fibrosis by magnetic resonance imaging and ultrasound techniques

Renal fibrosis is a useful biomarker for diagnosis and guidance of therapeutic interventions of chronic kidney disease (CKD), a worldwide disease that affects more than 10% of the population and is one of the major causes of death. Currently, tissue biopsy is the gold standard for assessment of renal fibrosis. However, it is invasive, and prone to sampling error and observer variability, and may also result in complications. Recent advances in diagnostic imaging techniques, including magnetic resonance imaging (MRI) and ultrasonography, have shown promise for noninvasive assessment of renal fibrosis. These imaging techniques measure renal fibrosis by evaluating its impacts on the functional, mechanical, and molecular properties of the kidney, such as water mobility by diffusion MRI, tissue hypoxia by blood oxygenation level dependent MRI, renal stiffness by MR and ultrasound elastography, and macromolecule content by magnetization transfer imaging. Other MR techniques, such as T1/T2 mapping and susceptibility-weighted imaging have also been explored for measuring renal fibrosis. Promising findings have been reported in both preclinical and clinical studies using these techniques. Nevertheless, limited specificity, sensitivity, and practicality in these techniques may hinder their immediate application in clinical routine. In this review, we will introduce methodologies of these techniques, outline their applications in fibrosis imaging, and discuss their limitations and pitfalls.

Contrast-enhanced ultrasonography for assessment of tubular atrophy/interstitial fibrosis in immunoglobulin A nephropathy: a preliminary clinical study

PURPOSE

To investigate the potential of contrast-enhanced ultrasonography (CEUS) for evaluating the severity of tubular atrophy/interstitial fibrosis (TA/IF) in immunoglobulin A nephropathy (IgAN) patients.

MATERIALS AND METHODS

A total of 80 patients with IgAN and 33 healthy adults were investigated. Patients were divided into three groups according to the TA/IF (T) grade of the Oxford classification: T0 (n = 28), T1 (n = 35), and T2 (n = 17). Patients and control subjects underwent conventional ultrasound (US) and CEUS. Time-intensity curves of CEUS were drawn for regions of interest located in the renal cortex and medulla using QLab software. Conventional US and CEUS quantitative parameters were analyzed. One-way analysis of variance (ANOVA), binary logistic regression, and receiver operating characteristic (ROC) curves were used.

RESULTS

There were no significant differences in renal size, cortical thickness, and medullary perfusion parameters (P > 0.05), whereas the differences in peak intensity (PI), area under the time-intensity curve (AUC) and wash-in slope (WIS) of cortical perfusion parameters between the control subjects and patients were significant (P < 0.05). PI was significantly lower with the increasing degree of T (P < 0.05). PI was associated independently with the degree of T in IgAN patients (P < 0.05). ROC analysis revealed that using the optimal cutoff values of 15.38 dB for diagnosis of T0-T1 (sensitivity 83.30% and specificity 63.00%) and 14.69 dB for diagnosis of T2 (sensitivity 100.00% and specificity 66.70%), the corresponding areas under the ROC curve were found to be 0.782 and 0.952, respectively.

CONCLUSIONS

CEUS can potentially be used as a noninvasive imaging marker to evaluate the severity of TA/IF in IgAN patients.

Scintigraphic texture analysis for assessment of renal allograft function

Purpose

Early detection and monitoring of kidney function during the post-transplantation period is one of the most important issues for improving the accuracy of an initial diagnosis. The aim of this study was to evaluate texture analysis (TA) in scintigraphic imaging to detect changes in kidney status after transplantation.

Material and methods

Scintigraphic images were used for TA from a total of 94 kidney allografts (39 rejected and 55 non-rejected). Images corresponding to the frames at the 2^nd, 5^th, and 20^th minute of the study were used to determine the optimum time point for analysis of differences in texture features between the rejected and non-rejected allografts.

Results

Linear discriminant analysis indicated the best performance at the fifth minute frame for classification of the rejected and non-rejected allografts with receiver operating characteristic curve (A_z) of 0.982, corresponding to 91.89% sensitivity, 96.49% specificity, and 94.68% accuracy. Also, TA can differentiate acute tubular necrosis from acute rejection with A_z of 0.953 corresponding to 88% sensitivity, 92.31% specificity, and 90.62% accuracy at the 5^th minute frame. The best correlation between texture feature and kidney function was achieved at the 20^th minute frame (r = -0.396) for glomerular filtration rate.

Conclusions

TA has good potential for the characterisation of kidney failure after transplantation and can improve clinical diagnosis.