Room: Room 205
Purpose: Due to short T2 of ice protons conventional MRI pulse sequences are incapable of visualization of frozen volumes. The purpose of this work is to use an ultrashort-Time of Echo (UTE) pulse sequence to image a volume which is rapidly cooled to sub-zero temperatures and to determine the relationship between UTE signal intensity with absolute temperature.
Methods: An IceRodTM cryoneedle (Galil Medical, Yokneam, Israel) was inserted into a phantom made of slab of tofu (9x12x5cm3) along with three fiber optic temperature sensors (Neoptix, Quebec, Canada) positioned near the center of the active region of the cryoneedle. The phantom was then imaged using a 1.5T MRI scanner (Ingenia, Philips Healthcare, Best, Netherlands). First, a high-resolution image was acquired using 3D T1-weighted FSE pulse sequence to identify thermal probe locations. Subsequently, active freezing of 8-minute duration was initiated during which a dynamic 3D UTE acquisition were continually executed (Stack of Stars with a non-selective excitation pulse; TE=0.14ms, TR=5.24ms, Flip=15Â°, Matrix=200x200, BW=946Hz/Pix, Slice Thickness/Interval=2mm, FOV=200mm, Acq Time=54s). Throughout the duration of the freeze, real-time temperatures were continuously recorded at 0.5 second sampling intervals using fiber optic sensors. At each UTE image time point, average signal intensity values were measured in 2.8x2.8x2mm3 volumes corresponding to the locations of the fiber optic sensors in the MR images. UTE signal intensity data were compared with corresponding thermal sensor data.
Results: Average UTE signal intensity values inside the frozen volume continuously decreased throughout the duration of the freeze and correlated linearly with the corresponding temperature measurements obtained with the sensors , ranging from -37 to -16Â°C (R2=0.93).
Conclusion: UTE MRI signal intensity has been shown to vary linearly with absolute temperature. Moreover, UTE could potentially be used to provide rapidly acquired temperature maps inside frozen volumes created during MRI-guided cryoablation procedures.
Not Applicable / None Entered.