Consensus-based technical recommendations for clinical translation of renal Dynamic Contrast-Enhanced (DCE) MRI

This paper presents expert consensus-based technical recommendations for the clinical translation of renal Dynamic Contrast-Enhanced (DCE) MRI, aiming to standardize protocols and improve cross-site comparability through a modified Delphi process involving an international panel of experts.

The Gist

Imagine the kidneys as a highly efficient, two-lane highway system that filters your blood. Doctors want to watch how traffic (blood) flows through this system and how quickly it gets cleaned, but they can't just open up the patient to look inside.

For years, they've tried to use a special camera called an MRI to take a movie of this process using a "traffic dye" (a contrast agent). However, every doctor and scientist was driving a different car, using different maps, and taking different routes. Some used high-speed cameras, others used slow ones; some injected the dye fast, others slow. Because everyone did it differently, it was impossible to compare results from one hospital to another. It was like trying to compare the speed of two cars when one is driving in the rain and the other is on a sunny day.

The Big Meeting: Building a Rulebook
To fix this mess, a group of 22 international experts (the "traffic controllers") got together. They didn't just guess; they played a structured game called the "Delphi method." Think of it like a group of chefs trying to agree on the perfect recipe for a soup.

1. They wrote down a list of questions about how to cook the soup (scan the kidneys).
2. They voted on the answers.
3. If they didn't agree, they tweaked the recipe and voted again.
4. They kept doing this until they reached a "green light" (75% agreement) on the most important steps.

The Final Recipe: What They Agreed On
After several rounds of voting, they created a "minimum standard" recipe for kidney MRI scans. Here is the simple breakdown of their new rulebook:

• The Camera (The Scanner): You can use a standard 1.5 Tesla or 3 Tesla MRI machine. It's like saying you can use a standard digital camera or a high-end one, as long as it's a good camera.
• The Dye (The Contrast Agent): Instead of using the full "clinical dose" of the dye (which is like using a whole bottle of food coloring), they agreed to use a smaller, "lighter" amount. Why? Because for this specific movie, a little bit of dye is actually clearer and safer than a lot. It's like using a drop of ink to draw a line rather than pouring a cup of it.
• The Injection: The dye must be injected by a machine (a power injector), not by hand. This ensures the dye arrives at the kidney at the exact same speed every time, like a train arriving on a strict schedule.
• The Movie Settings:
  • Position: The patient lies on their back (supine).
  • Breathing: They should breathe normally (free breathing), not hold their breath, because holding breath is hard for some people and makes the movie shaky.
  • Speed: The camera needs to take pictures very fast (every 3 seconds or less) to catch the dye moving quickly through the kidneys.
  • Duration: The movie should run for up to 7 minutes to see the dye go in and come out.
• The Math (Analysis): To figure out how well the kidneys are working, they agreed to use a specific "two-step" math model. Imagine the kidney as having two rooms: one where the blood enters (the glomerulus) and one where the filtered liquid goes (the tubule). You need to measure the flow in both rooms to get the full picture. Using a model with just one room is too simple, and using three or more is too complicated and might trick the math.

What They Didn't Agree On (The "Red Lights")
Not everything was settled. The experts couldn't agree on:

• Exact pixel size: How tiny the individual picture dots should be.
• Specific software: Which computer program to use to do the math.
• Isotropic voxels: Whether the 3D blocks of data must be perfectly cube-shaped (some said yes, others said it's too hard to do in practice).

A Special Note on Children
The paper notes that while this rulebook is for adults, it's very useful for children too. However, children are like smaller, faster cars on the highway. They have smaller kidneys, faster heartbeats, and move around more. The experts who specialize in kids added a side note: you need even faster cameras and special tricks to stop the motion blur when scanning little ones, but the basic idea of the "two-room" math model still applies.

The Bottom Line
This paper didn't invent a new machine or a new drug. Instead, it built a universal instruction manual. Before, if Hospital A said "Kidney X is working at 50%" and Hospital B said "Kidney X is working at 60%," no one knew who was right because they used different rules. Now, if both hospitals follow this new "Green Light" recipe, their numbers will be comparable. It's the first step toward making kidney MRI a standard, reliable tool that doctors can trust anywhere in the world.

Technical Summary

Technical Summary: Consensus-Based Technical Recommendations for Clinical Translation of Renal DCE-MRI

Problem Statement
Dynamic Contrast-Enhanced (DCE) MRI holds significant potential for the non-invasive assessment of renal haemodynamics and function, offering detailed structural and functional data without ionizing radiation. However, the clinical translation of renal DCE-MRI has been hindered by insufficient standardization and difficulties in post-processing. Unlike other renal MRI techniques (e.g., ASL, BOLD, DWI) which have previously benefited from consensus initiatives, renal DCE-MRI research remains limited. This is partly due to the operational and regulatory complexities associated with gadolinium-based contrast agents (GBCAs), including safety concerns regarding Nephrogenic Systemic Fibrosis (NSF) and contrast-induced acute kidney injury (CI-AKI), as well as the lack of harmonized protocols for acquisition and analysis. Consequently, methodologies vary widely across centers, limiting cross-site comparability and the development of robust clinical biomarkers.

Methodology
To address these challenges, an international panel of 22 experts was recruited to develop consensus-based technical recommendations. The study employed a systematic consensus process approximating a two-step modified Delphi method.

• Panel Composition: The panel included experts from clinical radiology, physics, computing, and engineering across multiple countries, with experience in both adult and paediatric renal DCE-MRI.
• Process: The initiative involved five iterative survey rounds conducted between 2023 and 2024.
  • Round 1: An initial survey of open- and closed-ended questions identified key topics and areas of disagreement.
  • Rounds 2–5: Proposed consensus statements were formulated, refined, and re-circulated. Panellists responded using a "traffic light" system: "Green light" (≥75% agreement) indicated consensus; "Orange light" (60–74% agreement) indicated clear preference; "Red light" (50–59% agreement) indicated open issues. Statements with ≥40% abstentions were either excluded or modified for subsequent rounds.
• Scope: The recommendations cover patient preparation, MRI hardware, acquisition parameters, GBCA administration, data analysis, and reporting standards.

Key Contributions and Results
The process resulted in 37 consensus statements (out of 46 initial proposals) and one statement showing clear preference. Seven statements were excluded due to high abstention rates or lack of consensus. The final recommendations provide a practical minimum technical dataset for renal DCE-MRI, summarized as follows:

1. Patient Preparation: Experts agreed that dietary intake, hydration status, and medication use should be recorded prior to scanning. While specific dietary or hydration protocols (e.g., fasting vs. hydration) varied by population, recording these variables is essential for interpreting functional measurements.
2. Hardware and Field Strength: Both 1.5 T and 3 T scanners are acceptable. A body transmitter and multi-channel receiver coil are recommended, with the coil adjusted to match the patient's size.
3. Contrast Agent Administration:
   • GBCA doses should be body-weight dependent and generally lower than the standard clinical dose (<0.1 mmol/kg) to maintain linearity and reduce T2* effects.
   • Injection must be performed using a power injector followed by a saline flush at the same rate.
   • Administration should occur after recording a sufficient number of baseline volumes (≥5).
4. Acquisition Parameters:
   • Sequence: 3D gradient echo-based (GRE) sequences (cartesian or radial) combined with a T1-mapping preparatory sequence.
   • Orientation: Coronal or coronal oblique, with a field of view (FOV) including both kidneys and major vessels, centered to minimize aortic inflow artifacts.
   • Resolution: Slice thickness of 1–3 mm and in-plane pixel size ≤3 mm.
   • Temporal Resolution: Shortest possible, ideally ≤3 seconds.
   • Duration: Up to 7 minutes, though longer durations may be necessary for specific pathologies (e.g., obstruction).
   • Breathing: Free breathing is recommended, with post-processing image registration for motion correction.
5. Analysis and Modelling:
   • Arterial Input Function (AIF): The abdominal aorta is the preferred source if data quality is sufficient; otherwise, population- or model-based AIFs should be used.
   • Kinetic Modelling: A two-compartment model (glomerular plasma and tubular fluid) is recommended for estimating Renal Blood Flow (RBF) and Glomerular Filtration Rate (GFR). Models with >3 compartments were deemed to risk overfitting.
   • Reporting: GFR should be reported in [mL/min/1.73 m²], while Tubular Flow (Ft) and Plasma Flow (Fp) in [mL/min/100 mL]. Mean and standard deviation should be reported for pixel-based parameters.

Significance
The paper positions these recommendations as a "starting point" for MRI centers worldwide wishing to perform renal DCE-MRI. The primary significance lies in contributing to the harmonization of scan protocols and facilitating clinical translation. By defining a practical minimum technical dataset, the authors aim to improve cross-site comparability and support responsible clinical translation. The authors explicitly note that these recommendations are intended to be reviewed and revised every five years as the field progresses.

The study also highlights specific considerations for paediatric imaging, noting that while the consensus statements are primarily for adults, paediatric applications require higher temporal resolution and motion-robust strategies due to smaller anatomy and faster contrast transit. Furthermore, the paper underscores the unmet need for dedicated, automated, open-access post-processing software to support the quantitative analysis of these standardized protocols.

Limitations
The authors acknowledge that the panel size (n=15 for final rounds) was limited, and not all experts possessed confidence in every technical domain, leading to the exclusion of certain topics (e.g., specific reconstruction methods, isotropic voxel requirements) where consensus could not be reached. Additionally, the recommendations are based on the current state of the field and may require future updates as new technologies and safety data emerge.