Improved MRI Thermometry with Multiple-Echo Spirals.

PurposeLow‐bandwidth PRF shift thermometry is used to guide HIFU ablation treatments. Low sampling bandwidth is needed for high signal‐to‐noise ratio with short acquisition times, but can lead to off‐resonance artifacts. In this work, improved multiple‐echo thermometry is presented that allows for high bandwidth and reduced artifacts. It is also demonstrated with spiral sampling, to improve the trade‐off between resolution, speed, and measurement precision.MethodsFour multiple‐echo thermometry sequences were tested in vivo, one using two‐dimensional Fourier transform (2DFT) sampling and three using spirals. The spiral sequences were individually optimized for resolution, for speed, and for precision. Multifrequency reconstruction was used to correct for off‐resonance spiral artifacts. Additionally, two different multiecho temperature reconstructions were compared.ResultsWeighted combination of per‐echo phase differences gave significantly better precision than least squares off‐resonance estimation. Multiple‐echo 2DFT sequence obtained precision similar to single‐echo 2DFT, while greatly increasing sampling bandwidth. The multiecho spiral acquisitions achieved 2× better resolution, 2.9× better uncertainty, or 3.4× faster acquisition time, without negatively impacting the other two design parameters as compared to single‐echo 2DFT.ConclusionMultiecho spiral thermometry greatly improves the capabilities of temperature monitoring, and could improve transcranial treatment monitoring capabilities. Magn Reson Med 76:747–756, 2016. © 2015 Wiley Periodicals, Inc.