# RF phase modulation improves quantitative transient state sequences under constrained conditions

## TL;DR

This paper shows that using RF phase modulation in MRI improves the accuracy of tissue relaxation maps, especially under strict safety limits.

## Contribution

The study introduces optimized RF phase modulation to enhance precision in quantitative MRI under constrained conditions.

## Key findings

- Amplitude+phase modulation reduced noise by 34% compared to amplitude-only modulation.
- RF phase modulation decreased the need for inversion pulses and pauses in MRI sequences.
- Improved accuracy was observed under SAR restrictions using phase modulation.

## Abstract

Within gradient-spoiled transient-state MR sequences like Magnetic Resonance Fingerprinting or Magnetic Resonance Spin TomogrAphy in Time-domain (MR-STAT), it is examined whether an optimized RF phase modulation can help to improve the precision of the resulting relaxometry maps.

Using a Cramer-Rao based method called BLAKJac, optimized sequences of RF pulses have been generated for two scenarios (amplitude-only modulation and amplitude + phase modulation) and for several conditions. These sequences have been tested on a phantom, a healthy human brain and a healthy human leg, to reconstruct parametric maps (\documentclass[12pt]{minimal}
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The amplitude + phase modulation scenario systematically resulted in lower noise levels than the amplitude-only modulation scenario. On average, the difference was around 34%, but it was substantially larger for scans acquired under SAR restrictions. Compared to amplitude-only, in the amplitude + phase modulation scenario, the relevance of an inversion pulse and of a pause were greatly reduced, at least considering overall precision and in-phantom accuracy.

The application of an optimized RF phase modulation in quantitative transient-states MRI is beneficial for almost all tested scenarios and conditions, in particular under SAR restrictions Furthermore, RF phase modulation reduces the need for inversions pulses and pauses.

The online version contains supplementary material available at 10.1007/s10334-025-01293-9.