Keywords:
MR physics, Molecular imaging, Ultrasound physics, MR, CT, Ultrasound, Experimental investigations, Physics, Imaging sequences, Biological effects, Image verification, Image registration
Authors:
J. Blackwell, W. van der Putten, B. Tuohy, N. Colgan; Galway/IE
DOI:
10.1594/ecr2018/C-1382
Methods and materials
As there is a negligible contribution from thermal conduction in our SAR assessment and our phantom is a nonperfused material,
physiological changes can be ignored.
The SAR at discreet points in the observation plane the can be determined
Table 1: specific absorption rate
Where Cagar is 4200J/kg,
ΔT is the change in temprature and Δt is the change in time.
Proton Resonance Frequency Shift (PRF) thermometry was utilised to find the change in temperature.
Table 2: Proton Resonance Frequency Shift (PRF) thermometry
Where α is the temprature coefficanet 0.01ppm/C,
γ is the gyromatnetic ratio (MHz/T),
B0 is the field strength (T),
TE is the echotime (ms) and φ-φ0 is the phase shift in degrees.
A 3L volume,T1 doped MR phantom was created by dissolving 60g/L agar,
10g/L NaCl,
1g/L NaCl in distilled water.
The solution was autoclaved at 121C for 15min to ensure the solution was homogeneous and to remove air bubbles.
Phase maps were created pre and post heating.
These were then used to create a phase difference map and a heat map could then be created using PRF.
A FLAIR sequence was used over the whole volume to heat the phantom.
The calculated SAR was compared to the scanner readout.