Fast, interleaved, Look‐Locker‐based T ₁ mapping with a variable averaging approach: towards temperature mapping at low magnetic field

Proton resonance frequency shift (PRFS) is currently the gold standard method for magnetic resonance thermometry. However, the linearity between the temperature-dependent phase accumulation and the static magnetic field B-0 confines its use to rather high-field scanners. Applications such as thermal therapies could naturally benefit from lower field MRI settings through leveraging increased accessibility, a lower physical and economical footprint, and further consideration of the technical challenges associated with the integration of heating systems into conventional clinical scanners. T1$$ {T}_1 $$-based thermometry has been proposed as an alternative to the gold standard; however, because of longer acquisition times, it has found clinical use solely with adipose tissue where PRFS fails. At low field, the enhanced T1$$ {T}_1 $$ dispersion, combined with reduced relaxation times, make T1$$ {T}_1 $$ mapping an appealing candidate. Here, an interleaved Look-Locker-based T1$$ {T}_1 $$ mapping sequence was proposed for temperature quantification at 0.1 T. A variable averaging scheme was introduced, to maximize the signal-to-noise ratio throughout T1$$ {T}_1 $$ recovery. In calibrated samples, an average T1$$ {T}_1 $$ accuracy of 85% +/- 4% was achieved in 10 min, compared with the 77% +/- 7% obtained using a standard averaging scheme. Temperature maps between 29.0 and 41.7 degrees C were eventually reconstructed, with a precision of 3.0 +/- 1.1 degrees C and an accuracy of 1.5 +/- 1.0 degrees C. Accounting for longer thermal treatments and less strict temperature constraints, applications such as MR-guided mild hyperthermia treatments at low field could be envisioned.