# Boosting the velocity detection limit of 3D single‐cell tracking time‐lapse MRI by balanced SSFP imaging

## TL;DR

This paper introduces a new MRI technique that improves tracking of fast-moving single cells in the brain, allowing better observation of dynamic cellular processes.

## Contribution

The novel use of balanced SSFP imaging in time-lapse MRI significantly enhances velocity detection limits for single-cell tracking.

## Key findings

- Balanced SSFP imaging achieves a velocity detection limit of 0.8 mm/min in vitro, a fourfold improvement over conventional GRE.
- Interleaved 3D radial sampling with bSSFP enables whole-brain coverage and retrospective reconstruction with high temporal resolution.
- Compressed sensing with fivefold acceleration optimizes cell visibility and image quality in time-lapse MRI.

## Abstract

Time‐lapse MRI allows for the dynamic tracking of single iron‐labeled cells. However, the time required for spatial encoding creates a temporal blur and, therefore, a limited ability to resolve moving cells. To study fast moving cells, such as rolling immune cells along the endothelium during inflammatory processes, advanced accelerated acquisition techniques are required.

Balanced SSFP (bSSFP) imaging is applied to phantom and in vivo murine brain time‐lapse MRI measurements at 9.4 T. Its detection capability of moving iron‐labeled cells is compared with conventional gradient echo imaging (GRE) for 2D Cartesian sampling and evaluated for fully sampled and accelerated reconstructions with compressed sensing for 3D interleaved radial sampling in bSSFP.

Both phantom and in vivo time‐lapse MRI measurements show that single cells can be followed dynamically using bSSFP. High temporal resolution of less than 2 min reduces geometric distortion. The velocity detection limit increases to 0.8 mm/min in vitro and previously hidden fast‐moving cells are recovered. Interleaved 3D radial sampling enables 3D cell tracking and simultaneous imaging at varying acceleration factors. Fivefold acceleration with compressed sensing optimizes cell visibility, image quality, and temporal resolution.

bSSFP time‐lapse MRI improves single‐cell tracking by enhancing temporal resolution. In vitro, the velocity detection limit is increased fourfold compared to conventional GRE. Interleaved 3D radial bSSFP offers whole‐brain coverage at isotropic spatial resolution and retrospective reconstruction of both fully sampled and high temporal resolution images.