# Investigation of Endogenous Renal CEST Contrast and the Influence of Respiratory Motion on a Clinical 3 Tesla MRI: An In Vivo and In Vitro Study

## TL;DR

This study shows that timed breathing reduces motion artifacts in kidney MRI scans and reveals distinct chemical signals in different kidney regions.

## Contribution

The study introduces timed breathing as a method to reduce motion artifacts in renal CEST MRI and identifies compartment-specific CEST effects.

## Key findings

- Timed breathing significantly reduces motion artifacts in both phantom and in vivo CEST MRI data.
- CEST effects vary significantly between renal cortex, medulla, and pelvis at different ppm frequencies.
- MTRasym values in a patient with ccRCC differ significantly from those in healthy volunteers.

## Abstract

The aim is to evaluate the effectiveness of timed breathing in reducing respiratory motion artifacts in renal chemical exchange saturation transfer (CEST) MRI and to assess potential differences in CEST effects between renal compartments.

An electro‐pneumatic phantom with a kidney CEST model simulated variable respiratory motion and sequence‐synchronized breathing. Motion‐induced deviations from a static reference were quantified using the mean absolute error (MAE). Ten healthy volunteers (six females, four males; 25.2 ± 1.9 years) and one patient (47 years) with ccRCC (3.0 × 2.2 × 2.2) cm3 were examined on a 3 T MRI system using a multi‐echo gradient echo sequence with 15 Gaussian‐shaped saturation pulses (B1 = 1.5 μT, t
p = t
ipd = 100 ms). CEST effects in cortex, medulla, and pelvis at 1.0, 2.0, and 3.5 ppm were quantified by MTRasym analysis under timed and free‐breathing conditions.

Timed breathing reduced motion artifacts in both phantom and in vivo data. MTRasym analysis exhibits visibly distinguishable and significantly different (p < 0.05) CEST effects in renal compartments, with increased MTRasym values of (0.78% ± 0.41%) at 1.0 ppm in the cortex, (1.43% ± 0.70%) at 2.0 ppm in the medulla, and (−2.02% ± 0.84%) at 3.5 ppm in the pelvis. Significant differences (p < 0.05) in MTRasym values were observed between the patient and the healthy cohort.

Timed breathing improves renal CEST MRI by reducing motion artifacts and enabling detection of compartment‐specific CEST effects, highlighting its potential for biochemical characterization of renal tissue in clinical applications.