Quantifying temperature-dependent T₁changes in cortical bone using ultrashort echo-time MRI

Abstract

Purpose To demonstrate the feasibility of using ultrashort echo-time (UTE) MRI to quantify T1 changes in cortical bone due to heating. Methods Variable flip-angle T1 mapping combined with 3D UTE imaging was used to measure T1 in cortical bone. A calibration experiment was performed to detect T1 changes with temperature in ex vivo cortical bone samples from a bovine femur. Ultrasound heating experiments were performed using an interstitial applicator in ex vivo bovine femur specimens, and heat-induced T1 changes were quantified. Results The calibration experiment demonstrated that T1 increases with temperature in cortical bone. We observed a linear relationship between temperature and T1 with a linear coefficient of 0.67–0.84 ms/°C over a range of 25–70°C. The ultrasound heating experiments showed increased T1 changes in the heated regions, and the relationship between the temperature changes and T1 changes was similar to that of the calibration. Conclusion We demonstrated a temperature dependence of T1 in ex vivo cortical bone using a variable flip-angle UTE T1 mapping method.

Rotator cuff tendon assessment using magic‐angle insensitive 3D ultrashort echo time cones magnetization transfer (UTE‐Cones‐MT) imaging and modeling with histological correlation

“…Our study attempted to overcome this by utilizing ROIs that were more histologically homogenous, but this was not standardized. Third, relaxation times are temperature‐dependent and the RCTs in our experiments were imaged at room temperature. In particular, T 1 would be expected to increase from room temperature to body temperature.…”

Feasibility of using an inversion-recovery ultrashort echo time (UTE) sequence for quantification of glenoid bone loss

“…The following parameters were used: FOV of 16 cm, matrix of 192 × 192, slice thickness of 3-4 mm, and TE of 0.03 ms. TI, TR, and flip angle (FA) for cadaveric imaging was 55 ms, 134 ms, and 18° whereas it was 45 ms, 106 ms, and 16° for in vivo imaging. Selection of TI, TR, and FA varied between cadaveric and in vivo imaging largely due to temperature, which affects T1 relaxation [13]. The 3D IR-UTE-Cones technique was performed in the same imaging planes as the conventional sequences, including axial and sagittal oblique, with imaging time of approximately 3 to 4.5 minutes per sequence, depending on number of slices required to cover the anatomy.…”

MR techniques for guiding high‐intensity focused ultrasound (HIFU) treatments

“…The other important progress in thermometry is cortical bone thermometry for monitoring HIFU treatment of bone metastasis . Han et al quantified previous changes in T 1 with temperature in cortical bone ex vivo. Using 3D radial acquisition with ultrashort echo time (UTE) and variable flip‐angle T 1 mapping, they demonstrated the feasibility of T 1 ‐based thermometry.…”

“…They also used double‐echo 2D fast spin echo (2D FSE) for measuring T 2 in bone marrow for temperature measurement . The primary drawback of using UTE is that most existing UTE sequences are 3D acquisitions with long acquisition times (1.4‐min scan time for one timepoint in the reported setup) . Ramsey et al used an alternative image acquisition scheme, dual echo gradient echo sequence, to demonstrate the feasibility of simultaneous cortical bone and soft‐tissue thermometry in vitro.…”