Purpose: To implement and evaluate a pulse sequence for clinical-grade 3T MRI scanners that generates an intermolecular multiple quantum coherence signal to provide contrast between brown adipose tissue (BAT) and surrounding tissues including white adipose tissue (WAT).
Methods: A base pulse sequence available on GE 3T MRI systems, named Contiguous Slice Multi Echo Multiplaner (CSMEMP), was reprogrammed to create a Multiple Spin Echo HOMOGENIZED with Off-resonance Transfer (MSE-HOT) sequence modified to detect BAT. The sequence was modified to allow pairs of water and fat molecules separated by a specific distance (the “correlation distance”) to generate signal, such that most signal would be generated by closely packed intracellular water and fat molecules within BAT rather than the homogeneous fat molecules of WAT. The pulse sequence was tested on water-fat emulsion phantoms at various fat fractions as well as mouse WAT and BAT samples. Pulse sequence tests across a range of correlation distances were evaluated based on BAT-WAT signal contrast.
Results: Signal acquired from water-fat emulsions correlated with correlation distance, but there was no statistically significant difference in signal strength between fat fractions at any correlation distance. Signals were generated from both mouse BAT and WAT samples, but no statistically significant difference in signal strength between the two samples. All testing produced unreliable signals with substantial imaging artifacts.
Conclusion: An MSE-HOT based sequence was able to generate signal from BAT on a clinical grade 3T GE MRI machine. However, the inability to differentiate between BAT and WAT signals also indicates the need for additional corrections to the pulse sequence and more reliable phantoms for testing BAT detection MRI pulse sequences.
Funding Support, Disclosures, and Conflict of Interest: Funding for this project was provided by an Economic Development Assistantship from the LSU Office of Research and Development.
MRI, Pulse Sequences, Multiple-echo Sequence