Application of Diffusion Kurtosis Imaging and Blood Oxygen Level-Dependent Magnetic Resonance Imaging in Kidney Injury Associated with ANCA-Associated Vasculitis

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study elegantly describes that functional magnetic resonance imaging is a non-ivansive tecnique that seems to be useful in identifying chronic lesions in the renal parenchyma of patients with ANCA-associated vasculitis. Although the number of patients is small, the authors have used appropriate statistical methods to identify correlations between imaging and clinicopathological parameters. The aforementioned results as well as the results of the ROC curve analysis are of great interest. However we must point out that these results may prove to be different in a larger group of patients.

A future evaluation of these imaging parameters in individuals with AAV and various CKD stages may enhance our knowledge of the severity of kidney injury and the prognosis of the disease.

Author Response

1. Summary

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions changes in the resubmitted files. 

2.Point-by-point response to Comments and Suggestions for Authors

This study elegantly describes that functional magnetic resonance imaging is a non-ivansive tecnique that seems to be useful in identifying chronic lesions in the renal parenchyma of patients with ANCA-associated vasculitis. Although the number of patients is small, the authors have used appropriate statistical methods to identify correlations between imaging and clinicopathological parameters. The aforementioned results as well as the results of the ROC curve analysis are of great interest. However we must point out that these results may prove to be different in a larger group of patients.

A future evaluation of these imaging parameters in individuals with AAV and various CKD stages may enhance our knowledge of the severity of kidney injury and the prognosis of the disease.

Answer：Thank you very much for the comments. It is true that the small sample size was the limitation of the present study, which was described in the limitation section. It is a great idea to evaluate the imaging parameters in individuals with AAV and various CKD stages in the future. We highly appreciate the suggestion of future research direction.

Reviewer 2 Report

Comments and Suggestions for Authors

Your study applied DKI and BOLD MRI to detect kidney lesions in patients with AAV and found that some parameters of DKI and BOLD imaging have the potential to become non-invasive imaging markers for patients with AAV and kidney injury. Indeed this study has certain limitations. This was a single-center study with a small sample size, and no adjustments were made for age or blood pressure. No measurement or estimation of blood volume and blood flow was performed, but these are the crucial parameters for BOLD! Please comment on this. It might be possible that in a small sample size only random bold deviations appear.

You should shortly introduce DKI and BOLD as methods before using the acronyms.

DKI ist not that new, while the application on renal imaging has some novelty aspects. Please rephrase.

Example: Lu H, Jensen JH, Ramani A et-al. Three-dimensional characterization of non-gaussian water diffusion in humans using diffusion kurtosis imaging. NMR Biomed. 2006;19 (2): 236-47. doi:10.1002/nbm.1020

Diffusion kurtosis imaging (DKI) is an extension of diffusion tensor imaging by estimating the skewed distribution (kurtosis) of water diffusion based on a probability distribution function. It provides a high order diffusion of water distribution and analyzes and also quantifies the diffusion restriction.  Can you show or how do you know how good DKI on a 3T scanner does perform with only 3 b-values and 3 different diffusion directions? Most of the time more b-values are used for fitting the kurtosis.

In preclinical studies lower pH-values were found in kurtosis lesions in neural tissues. This would also be of relevance in the kidney. Please comment on this.

 

Comments on the Quality of English Language

Please check for some inexactly descriptions and some typos like on line 185 Comparison

Author Response

1.Summary

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions changes in the resubmitted files.

2.Point-by-point response to Comments and Suggestions for Authors

(1)Your study applied DKI and BOLD MRI to detect kidney lesions in patients with AAV and found that some parameters of DKI and BOLD imaging have the potential to become non-invasive imaging markers for patients with AAV and kidney injury. Indeed this study has certain limitations. This was a single-center study with a small sample size, and no adjustments were made for age or blood pressure. No measurement or estimation of blood volume and blood flow was performed, but these are the crucial parameters for BOLD! Please comment on this. It might be possible that in a small sample size only random bold deviations appear.

Answer：Thank you very much for your comments. It is true that the single-center study with a small sample size was the limitation of our study. Due to AAV being a rare disease, there were very few patients included with the strict inclusion and exclusion criteria, resulting in a small sample size. The above limitation was described in the limitation section of the manuscript. Larger cohort is welcomed to verify the results in the future. Correcting for age and blood pressure is particularly challenging in our study. Our method involves obtaining R2* values using classical BOLD software in conjunction with non-invasive vascular magnetic resonance imaging tools. Regions of interest (ROIs) were delineated in the corresponding areas of the renal cortex and medulla. The average R2* or T2* values for the cortex and medulla were determined for each scan slice. The focus of our study is to preliminarily validate the effectiveness of BOLD MRI in assessing renal damage in patients with AAV. Therefore, measurements of blood volume and blood flow were not included. We fully agree that blood volume and blood flow are critical parameters influencing BOLD signals. However, their measurement requires additional imaging techniques and complex post-processing algorithms, which are beyond the scope of our study's resources and technical capabilities. Despite these limitations, existing literature indicates that BOLD MRI can reflect renal oxygenation and function to a certain extent (Yin WJ et al, Eur J Radiol. 2012;81(7):1426-1431.；Pruijm M et al, Front Physiol. 2017;7:667. Published 2017 Jan 5.).

(2)You should shortly introduce DKI and BOLD as methods before using the acronyms.

Answer: Thank you very much for your suggestions. We have added the full names of DKI and BOLD to the abstract. And we have introduced DKI and BOLD as methods in the revised manuscript. (Line94-102)

(3)DKI is not that new, while the application on renal imaging has some novelty aspects. Please rephrase.

Example: Lu H, Jensen JH, Ramani A et-al. Three-dimensional characterization of non-gaussian water diffusion in humans using diffusion kurtosis imaging. NMR Biomed. 2006;19 (2): 236-47. doi:10.1002/nbm.1020

Answer: Thank you very much for the suggestion. We've revised the statement of the introduction in the revised manuscript. And the mentioned manuscript has been cited.

(4)Diffusion kurtosis imaging (DKI) is an extension of diffusion tensor imaging by estimating the skewed distribution (kurtosis) of water diffusion based on a probability distribution function. It provides a high order diffusion of water distribution and analyzes and also quantifies the diffusion restriction. Can you show or how do you know how good DKI on a 3T scanner does perform with only 3 b-values and 3 different diffusion directions? Most of the time more b-values are used for fitting the kurtosis.

Answer: Thank you very much. The present study aimedto assess the severity of renal damage using multiple MRI parameters. The selection of three b-values and three different diffusion directions was based on experimental design and existing literature. The literature indicated that although a scheme with three b-values and three diffusion directions was relatively simplified, it could still provide effective information under specific research conditions. For instance, studies by Afzali et al. and Khan et al. suggested that at higher magnetic field strengths (such as 3T), this simplified scheme was feasible for evaluating tissue microstructure (Afzali M et al, J Neurosci Methods. 2021;347:108951. ; Khan AR et al, Neuroimage. 2016; 142:421-430.). Similar simplified schemes had also been used in the field of renal disease, where studies had utilized three b-values for DKI scans, comparing results between patients with primary aldosteronism and chronic kidney disease (Wen D et al, Abdom Radiol (NY). 2023;48(4):1340-1349.; Mao W et al, J Magn Reson Imaging. 2021;54(2):508-517. ). We acknowledge that the scheme with three b-values and three diffusion directions may have certain limitations. However, our preliminary results indicated that this scheme, based on a 3T scanner, holds significant potential for clinical evaluation of renal damage. In future research, we plan to adopt more b-values and diffusion directions to improve the accuracy and reliability of DKI parameters.

(5)In preclinical studies lower pH-values were found in kurtosis lesions in neural tissues. This would also be of relevance in the kidney. Please comment on this.

Answer：We appreciate the great comments. In neural tissue, the finding that low pH was associated with skewed lesions suggested the importance of cellular metabolism and microenvironmental changes. This phenomenon is also worth exploring in the context of renal tissue. In renal lesions, particularly in ischemia-reperfusion injury or chronic kidney disease, local metabolic abnormalities may lead to localized acidosis. Similar to the situation in neural tissue, this may reflect the metabolic response of the tissue to injury. Low pH may be associated with increased apoptosis and necrosis, which are also common in renal injuries. Apoptosis and necrosis can lead to changes in tissue structure, thereby affecting magnetic resonance imaging (MRI) parameters. The inflammatory response in renal lesions may also contribute to the decrease in local pH. The infiltration of inflammatory cells and the accumulation of metabolic byproducts can alter the local microenvironment, thereby impacting MRI parameters. However, up to now, with noninvasive methods, it is hard to detect the pH of the local renal lesions. The urine pH mainly reflects the acidizing function of renal tubules.

 

Reviewer 3 Report

Comments and Suggestions for Authors

Recently, there is a keen interest regarding the role of functional MRI in kidney diseases diagnosis and evaluation, especially in patients diagnosed with glomerular diseases to whom for various reasons, renal biopsy is contraindicated. Therefore, the present study could highlight valuable insights related to this new form of assessment. The methodology and results were clearly explained, and the conclusions were supported by the findings. I congratulate you for your comprehensive research, but it would be nice if you could provide the following information regarding this procedure focused on the kidney assessment - for example: how many centres in Asia, Europe and USA are performing it?; the associated costs; if there are any exclusion criteria?

Author Response

1.Summary

Thank you very much for taking the time to review this manuscript. Please find the detailed responses below and the corresponding revisions changes in the resubmitted files.

2.Point-by-point response to Comments and Suggestions for Authors

Recently, there is a keen interest regarding the role of functional MRI in kidney diseases diagnosis and evaluation, especially in patients diagnosed with glomerular diseases to whom for various reasons, renal biopsy is contraindicated. Therefore, the present study could highlight valuable insights related to this new form of assessment. The methodology and results were clearly explained, and the conclusions were supported by the findings. I congratulate you for your comprehensive research, but it would be nice if you could provide the following information regarding this procedure focused on the kidney assessment - for example: how many centres in Asia, Europe and USA are performing it?; the associated costs; if there are any exclusion criteria?

Answer：In Asia, fMRI studies on renal injury are primarily conducted at medical research institutions and university-affiliated hospitals in countries such as China, Japan, South Korea, and India. However, we do not have accurate figures on the use of MRI for evaluating renal injury in Asia, Europe, or the United States. The costs associated with these studies may vary depending on the geographical location of the center, the usage of equipment, and the scale of the research. For instance, in China, the cost of using these functional magnetic resonance imaging scans for each region ranges from 650 to 1350 RMB. This cost includes the use of fMRI machines, specialized software for image processing, and professional fees for radiologists and technologists.

Exclusion criteria include:

Patients with severe comorbidities, such as significant cardiopulmonary disease or uncontrolled hypertension. Patients with metal implants or other contraindications for MRI. Pregnant or lactating women. Patients with psychiatric disorders or cognitive impairments who are unable to comply with the study procedures. Other exclusion criteria as defined by the specific study design.