Keywords: Kidney, DSC & DCE Perfusion, kidney, renal blood flow, standardisation, consensus

Motivation: Clinical translation of renal functional and quantitative MRI is hindered by a lack in standardisation of scan protocols.

Goal(s): To develop expert consensus-based technical recommendations on the acquisition and post-processing of renal DCE-MRI.

Approach: Experts were recruited and surveyed following the Delphi method to create consensus-based technical recommendations in renal DCE-MRI. Preliminary results will be used to construct the second survey round.

Results: 16 experts responded to the preliminary survey. Consensus statements informed by the responses were drafted and will be circulated and refined in the next phase of the project.

Impact: The insights obtained from this work will be invaluable in delivering recommendations that are comprehensive and widely accepted. Consensus-based technical recommendations for renal DCE-MRI aim to contribute to harmonisation of MRI scan protocols across sites, facilitating clinical translation.

Keywords: Kidney, Data Analysis, Layers

Motivation: To provide improved methods to estimate cortical-medullary changes in multiparametric MRI measures of the kidney.

Goal(s): To develop an analysis method for use with 3D data to generate quantitative-depth-based cortical-medullary layers which can be applied to any multiparametric map.

Approach: 3DQLayers segments the kidney into layers based on their distance from the renal surface using the Trimesh Python library.

Results: Generated 3D layers can be applied to multiparametric MRI scans collected in the same session. Here, this is applied to assess cortical layer profiles and contour plots of quantitative T₁-mapping, R₂^*-mapping and perfusion measures, and to estimate renal cortical thickness.

Impact: 3DQLayers provides a layer-based analysis technique for renal multiparametric MRI data, extending traditional ROI-based methods. Layer profiles of any quantitative MRI data can be output and average renal cortical thickness estimated, these are important measures to study in renal disease.

Keywords: Kidney, Kidney

Motivation: ASL-measured perfusion values are assumed to change homogeneously across the kidney. We believe that additional information might be retrieved by analyzing regional perfusion differences. 

Goal(s): Renal perfusion is assumed to decrease with aging but also in renal pathologies.

• Does renal perfusion decrease uniformly?

Approach:

• Retrieve renal ASL images from 27 subjects.
• Create one 2D mesh per subject.
• Pool the results for 3 different groups.
• Analyze the variation of renal perfusion.

Results:

• Patients compared to younger healthy volunteers (HVs) show lower perfusion.
  
• Patients compared to older HVs exhibit a negative variation in the kidney lateral outermost region, while other regions show higher perfusion values.

Impact: Understanding kidney blood flow patterns could aid early disease detection and personalized treatments. Identifying specific regions affected in kidney patients might improve targeted therapies. This knowledge may enhance patient outcomes, potentially leading to a better life quality for kidney patients.

Keywords: Kidney, Kidney

Motivation: Whole-organ renal oxygen metabolism increases by 40-65% during early stages of kidney disease. Current biomarkers are sensitive to later kidney disease stages once tissue damage has already occurred.

Goal(s): Non-invasively quantify renal metabolic rate of oxygen during free-breathing, to be used as a potential biomarker for early diagnosis of kidney disease. 

Approach: A new MRI sequence was tested in healthy adults at the left kidney that simultaneously measures blood water T₂ and blood flow rate, from which metabolic rate of oxygenation is determined from Fick’s Principle. 

Results: Quantification of metabolic parameters show good agreement between free-breathing and breath-hold acquisitions.

Impact: The renal metabolic rate of oxygen was non-invasively quantified at the left kidney during free-breathing in healthy adults. Renal oxygen metabolism can be a valuable physiological biomarker for early diagnosis of kidney disease before irreversible tissue damage occurs.

Keywords: Kidney, Motion Correction

Motivation: Post-contrast T1-weighted imaging is vital for diagnosing renal MRI by assessing vasculature, finding vascular abnormalities, and evaluating kidney function. However, breathing motion degrades image quality, which is problematic since breath-holding is difficult for some patients, especially children. 

Goal(s): There is an urgent need for motion-robust renal imaging for breath-holding challenged patients.

Approach: In this study, we demonstrated the effectiveness of FIDnavs in correcting motion-related artifacts in clinical post-contrast T1w-imaging of kidneys. We evaluated our pipeline on 5 pediatric patients, both retrospectively and prospectively, using FIDnav-based motion correction (MoCo).

Results: Utilizing FIDnavs for MoCo, reduced motion artifacts and blurring in post-contrast T1w-imaging. 

Impact: Use of FID-navigated motion correction for post-contrast T1w-imaging of kidneys can reduce motion artifacts and minimize the scan time by eliminating the need of gating. However, the calibration step required for prospective motion correction should be eased for pediatric patients. 

Keywords: Kidney, Kidney

Motivation: Alterations of renal water transport and exchange may reflect kidney function and disease.

Goal(s): To develop and test a novel sequence for quantitative assessment of intrarenal fluid exchange.

Approach: We developed a T₂ selective labeling sequence for water exchange quantification and tested it on healthy subjects.

Results: Images showed a characteristic spatial distribution of signal with increased signal in the renal medulla, in support of its detection and assessment of fluid exchange.

Impact: Exchange imaging by T₂ selective saturation may open new possibilities for the study of water transport and exchange and the diagnosis of renal disorders.

Keywords: Kidney, MR Fingerprinting

Motivation: A free-breathing renal joint T₁-T₂ MR fingerprinting technique with respiratory navigators would allow kidney function to be mapped non-invasively in patients that cannot hold their breath.

Goal(s): To assess the effect of rejected respiratory navigators on the relaxation times and their precision.

Approach: Joint kidney T₁-T₂ maps with four different navigator acceptance window widths (NAWW, from ±4mm to ±32mm) were acquired in 8 healthy volunteers and compared to clinical routine maps.

Results: Map accuracy and precision were high and did not change as a function of NAWW, suggesting that the NAWW can be chosen as a balance between navigator inefficiency and through-plane motion.

Impact:  This work demonstrates the feasibility of a free-breathing 2D joint T₁-T₂ renal MR fingerprinting in healthy volunteers. The navigator allows a free breathing acquisition with limited through-plane motion.

Keywords: Kidney, Quantitative Imaging

Motivation: Quantitative MRI techniques, such as T₂ and T₂* mapping, have the potential to become important imaging biomarkers for non-invasive renal tissue assessment. However, clinical T₂ and T₂* mapping faces challenges posed by respiratory motion.

Goal(s): This study explores the feasibility of simultaneous T₂ and T₂* mapping of the human kidneys with mitigated respiratory motion artifacts, using the 2in1-RARE-EPI technique.

Approach: We used the distinctive acoustic noise pattern generated by the gradient coil switching during 2in1-RARE-EPI data acquisition to guide the subject to time their respiration during the scan.

Results: This approach facilitates high in-plane resolution (1x1x5mm³) T₂ and T₂* mapping of human kidneys. 

Impact: Our approach for simultaneous and motion-synchronized T₂ and T₂* mapping of the human kidney provides a technical foundation for swift translation into the clinic and for gaining a better mechanistic understanding of renal (patho-)physiology.

Keywords: Kidney, Kidney, Renal blood flow, Perfusion, Phase contrast, Arterial spin labelling

Motivation: Variations in dietary conditions can impact renal blood flow (RBF), but it is currently unknown whether fasting overnight can affect the measurement. A recent consensus for phase contrast (PC) advises against fasting, but similar consensus for arterial spin labelling (ASL) was not reached. Other laboratory tests might require fasting, leading to variability in preparation for MRI. It is therefore critical to understand whether fasting affects the measurement

Goal(s): This study investigates the effect of fasting compared to the recommended MRI preparation.

Approach: ASL and PC acquired in healthy volunteers.

Results: No significant difference between fasting and consensus-preparation was found for RBF and perfusion.

Impact: A strict control for diet may not be required for MRI studies measuring renal blood flow and perfusion using phase contrast and arterial spin labelling. 

Keywords: Kidney, Kidney

Motivation: Magnetic Resonance Elastography (MRE) can determine tissue isotropic stiffness measurements to assess kidney disease and injury. Similarly, Diffusion Tensor Imaging (DTI) in combination with MRE can provide additional information regarding tissue health through anisotropic stiffness.

Goal(s): The goal of this study is to compute tissue isotropic and anisotropic stiffness of the cortex, medulla, and whole kidney to compare against both measurements.

Approach: 9 subjects were imaged for both MRE and DTI scans to estimate isotropic and anisotropic stiffness, respectively.

Results: Preliminary results indicate a good correlation between isotropic stiffness and anisotropic stiffness in all regions.

Impact: The application of MRI diffusion scans in conjunction with MRE shows promise in elucidating hard to detect disease and injury in human kidney.

Keywords: Kidney, Data Analysis, Aging, chronic kidney disease, diagnosis,renal stiffness, intravoxel incoherent motion, shifted apparent diffusion coefficients ,virtual elastography

Motivation: Various b values of shifted apparent diffusion coefficients (sADC) and virtual magnetic resonance elastography (vMRE) were not validated for renal stiffness. Hence, a new method was required for assessing chronic kidney disease (CKD) noninvasively.

Goal(s): To investigate the relationship between sADC and vMRE and the clinical indicators and diagnostic efficacy of CKD.

Approach: The μ_diff generated with sADC was used to quantify renal stiffness. The data were analyzed using Spearman, partial correlation, Mann–Whitney U test, and receiver-operating characteristic curves. 

Results: sADC and vMRE were effective in assessing renal function and diagnosing CKD, but distinctly at various b values.

Impact: This study provides a reference b value for sADC and vMRE and suggests that vMRE could be used as a new noninvasive technique to assess chronic kidney disease. 

Keywords: Kidney, Arterial spin labelling, Magnetic resonance elastography, chronic kidney disease, perfusion assessment, renal stiffness

Motivation:  The impact of renal perfusion on stiffness values is yet to be conclusively validated, which has hindered the diagnostic application of magnetic resonance elastography (MRE) in patients with chronic kidney disease (CKD).

Goal(s): To explore the characteristics of renal perfusion and stiffness values in patients with CKD and their correlation.

Approach:  Renal MRE and arterial spin labeling (ASL) were used to measure renal stiffness and blood flow. The study employed t-test, receiver-operating characteristic curves, and Spearman correlation for data analysis.

Results:  The two techniques were effective in diagnosing CKD, simultaneously confirming the influence of perfusion factors on stiffness.

Impact: This preliminary human study further supported the correlation between renal stiffness and perfusion, supporting the enhanced diagnostic efficacy of combining MRE and ASL for CKD, thus facilitating staging.

Keywords: Kidney, Kidney, CKD, ASL, DWI, BOLD, MRE

Motivation: Multiparametric (mp) MRI can enable functional characterization of entire kidneys for the assessment of patients with chronic kidney disease (CKD).

Goal(s): To evaluate quantitative mpMRI for functional characterization in CKD patients and compare against healthy volunteers.

Approach: Seven CKD patients and 6 healthy volunteers underwent MRI including ASL (perfusion), DWI (cellularity), BOLD (oxygenation), and MRE (fibrosis).

Results: ASL measured perfusion was significantly lower in CKD patients compared to healthy volunteers (P<0.05), while DWI measured ADC was not different (P=0.36). BOLD measurement was statistically different in Medulla (T2*: P=0.009; R2*: P=0.05), but was not different in cortex (T2*: P=0.08; R2*: P=0.32).

Impact: Multi-parametric MRI, particularly using ASL measured perfusion and BOLD measured R2* provides functional characterization of kidneys that could facilitate longitudinal monitoring and therapeutic interventions in CKD patients.

Keywords: Kidney, Transplantation, kidney

Motivation: Although renal biopsy is the gold standard for the diagnosis of renal allograft dysfunction, it is an invasive procedure. Magnetic resonance imaging (MRI) can be used to evaluate renal allograft function in a noninvasive manner.

Goal(s): To investigate the utilities of various diffusion models in evaluating early renal allograft function.

Approach: Follow-up MRI was performed at 14, 30, and 90 days after renal transplantation to evaluate correlations between MRI parameters and estimated glomerular filtration rate, along with their abilities to measure renal function after transplantation.

Results: Various diffusion models can reflect changes in early renal function after transplantation.

Impact: Intravoxel incoherent motion and diffusion kurtosis imaging models may serve as useful tools to investigate early renal function after transplantation.