The conventional phase difference method for MR thermometry suffers from disturbances caused by the presence of lipid protons, motion-induced error, and field drift. A signal model is presented with multi-echo gradient echo (GRE) sequence using a fat signal as an internal reference to overcome these problems. The internal reference signal model is fit to the water and fat signals by the extended Prony algorithm and the LevenbergMarquardt algorithm to estimate the chemical shifts between water and fat which contain temperature information. A noise analysis of the signal model was conducted using the CramerRao lower bound to evaluate the noise performance of various algorithms, the effects of imaging parameters, and the influence of the water:fat signal ratio in a sample on the temperature estimate. Comparison of the calculated temperature map and thermocouple temperature measurements shows that the maximum temperature estimation error is 0.614°C, with a standard deviation of 0.06°C, confirming the feasibility of this modelbased temperature mapping method. The influence of sample water:fat signal ratio on the accuracy of the temperature estimate is evaluated in a water-fat mixed phantom experiment with an optimal ratio of approximately 0. Quantitative MRI thermometry has become an attractive method to noninvasively monitor the evolution of tissue temperatures and to guide tumor ablation based on local thermal therapy, such as high-intensity focused ultrasound surgery (1,2). Temperature imaging based on the temperature dependence of the water proton resonance frequency (PRF) (3,4) is currently the main choice for many applications, especially for high magnetic fields above 1 T, because there exists a linear relationship between PRF and temperature that is independent of the physiologic effects of hyperthermia (5). Typically, a temperature map from PRF is generated using phase-difference images from a single long gradient echo sequence (4,6). Despite many advantages, the conventional phasedifference method still has several problems that may influence the precision of the quantitative temperature mapping, such as the presence of lipid protons (7,8), inter-and intrascan motion (9), and frequency drift due to an unstable magnetic field (10). The presence of lipids modifies the phase difference because the lipid resonance frequencies are not temperature dependent, which leads to temperature estimation errors. Fat-suppressed slice-selective excitation or spectral-spatial pulses (7,11) have been proposed by several research groups to overcome this problem. However, these techniques are sensitive to field inhomogeneities and typically yield nonuniform suppression over the field of view (12,13).The motion artifacts and field drift associated with the traditional phase-difference approach have been reduced using an internal frequency reference that has a temperature-insensitive resonance. Magnetic resonance spectroscopic imaging (14) can trace the changes in the water resonance frequency, using a non-temperature-dependent c...

Toe fringe is the most typical morphological feature of lizards adapted to sandy environments, and it is simple in shape, can evolve repeatedly, and has a high degree of repetition; therefore, this feature is suitable for testing the adaptive convergence suggested by form-environment correlations. Phrynocephalus mystaceus mainly lives in dune habitats, has a developed bilateral toe fringe, and exhibits fast sand-burying behavior for predator avoidance. We tested the effects of resecting the medial and bilateral toe fringes on the locomotor performance and sand-burying performance of P. mystaceus. The results showed that the maximum sprint speed and acceleration on sand substrate did not significantly differ under different conditions (P > 0.05). Sand-burying performance scores of the unresected individuals were significantly greater than those of the resected individuals (P < 0.05). A partial least squares (PLS) regression analysis showed that the relative area of toe fringe was the main factor affecting the sand-burying performance of unresected P. mystaceus. For lizards without fringe, the PLS regression showed that the swinging index of the hind-limb was the main factor affecting the sand-burying performance of the lizard. A comparison of the swinging indexes of the hind-limb of the lizard under three states revealed that under the unresected states, the frequency of the swinging of the hind-limb was significantly higher than those of lizards with resected bilateral fringes, further indicating that the lizards compensated for the loss of fringe by increasing the time and frequency of swinging of the hind-limb. A path analysis also showed that the fringe affected the sand-burying performance of P. mystaceus not only directly but also indirectly by affecting the frequency of the swinging of the hind-limb. After the bilateral toe fringe was removed, a significant negative correlation between locomotor and sand-burying performance was observed (P < 0.05). Taken together, these results provide experimental evidence that toe fringe is positively associated with the sand-burying performance of P. mystaceus.