| T1 relaxation time constant |
As temperature increases, the motion rate increases, resulting in a greater exchange rate between water molecules. Relative temperature is measured using: ∆T = c∆T1
|
Readily available imaging sequences |
Low temperature sensitivity (1%/°C); other factors can change T1; the apparent T1 relaxation time constant is the weighted average of T1s of water molecules in tissue microstructures. This could cause a nonlinear dependence of T1 on temperature |
(63) |
| T2 relaxation time constant |
A linear relationship between T2 and temperature (T) exists for the free water model |
Can be used for adipose tissues; higher sensitivity than T1 (10%/°C) |
More difficult to measure than T1 due to shorter T2 values; irreversible T2w signal change at high tissue temperature due to tissue damage. |
(17,63,64) |
| Diffusion coefficient (D) |
The diffusion coefficient (D) is linearly related to the temperature through a Strokes-Einstein equation |
Readily available imaging sequences |
Low temperature sensitivity (2%/°C); other factors can change diffusion coefficient (D) |
(19,65) |
| Proton density (PD) |
Water proton density is inversely proportional to the tissue temperature |
Independent of tissue type; readily available imaging sequences |
Very low temperature sensitivity (0.29%/°C) |
(66) |
| Magnetization transfer (MT) |
The signal intensity, magnetization transfer ratio ((M0-MT)/M0) correlates non-linearly with tissue temperature |
Can be used together with other MT applications |
Quantitative relationship between MT signal intensity and the chemical exchange rate as a function of temperature has not been reported; non-linear function of tissue temperature; Tissue-type dependent. |
(67-69) |
| Proton resonance frequency shift (PRFS) |
Water hydrogen bond disruption at elevated temperature results in increased shielding constant, and thus decreased chemical shift (frequency) for water protons |
Fast temperature mapping techniques readily available; linear function of tissue temperature; independent of tissue type (non-fat tissue) |
Cannot be applied for fat tissue; relatively low temperature sensitivity (0.01 ppm/°C) |
(13,22,60) |
