# Quantitative assessment of renal and perirenal adipose tissue distribution at 5 T: a feasibility study

## TL;DR

This study shows that a new MRI technique called FACT can accurately measure fat around the kidneys at 5 T, offering a non-invasive alternative to biopsies.

## Contribution

The study demonstrates the feasibility and accuracy of the FACT technique for quantifying renal and perirenal fat at ultra-high field strength (5 T).

## Key findings

- FACT-PDFF showed excellent agreement with MRS-PDFF in phantom and clinical studies.
- FACT images achieved high quality and excellent repeatability in volunteers.
- Renal fat distribution varied significantly between kidneys, genders, and anatomical regions.

## Abstract

To evaluate the feasibility and accuracy of Fat Analysis Calculation Technique (FACT), a multi-echo Dixon-like sequence, for quantifying renal and perirenal adipose distribution at 5 T.

Accuracy of FACT-based Proton density fat fraction (FACT-PDFF) was assessed by comparing with magnetic resonance spectroscopy-based PDFF (MRS-PDFF) in phantom study. In vivo FACT images from 24 volunteers (13 males and 11 females) without kidney-related diseases were acquired at 5 T and evaluated independently by two readers. Repeatability of FACT-PDFF was assessed through three consecutive scans. Spearman correlation examined associations between averaged FACT-PDFF and clinical characteristics. Linear regression, intraclass correlation coefficients (ICCs), and Bland-Altman plots assessed consistency and deviations between fat quantification methods and field strengths. The Wilcoxon signed-rank test compared image quality scores between radiologists. The paired t test compared FACT-PDFF differences across all regions of interest between bilateral kidneys and between renal cortex and medulla. Analysis of covariance compared gender-related renal fat differences.

In phantom study, FACT-PDFF showed excellent agreement with MRS-PDFF at both fields (ICCs ≥ 0.995). Linear regression revealed strong correlations (R² ≥ 0.998), and Bland-Altman plots indicated minimal bias. In clinical study, FACT images achieved high quality. Repeatability was excellent (ICCs: 0.837–0.991; CVs: 0.78–4.49%). Significant PDFF differences existed between bilateral kidneys (cortex/medulla: P < 0.001; sinus fat: P = 0.003), cortex vs. medulla (P < 0.001), and genders (right cortex, left medulla, and left perirenal fat: P ≤ 0.044). PDFF was correlated positively with age, weight, body mass index, waist/hip circumference, and waist-to-height ratio (r = 0.412–0.797, P ≤ 0.046).

FACT at 5 T reliably quantifies renal and perirenal adipose distribution. It can offer a non-invasive alternative to biopsy, and may facilitate the understanding of renal adipose distribution and its clinical associations.

The online version contains supplementary material available at 10.1186/s12880-025-02136-8.