Ultrasound (US)-based thermal imaging is very sensitive to tissue motion, which is a major obstacle to apply US temperature monitoring to noninvasive thermal therapies of in vivo subjects. In this study, we aim to develop a motion compensation method for stable US thermal imaging in in vivo subjects. Based on the assumption that the major tissue motion is approximately periodic caused by respiration, we propose a motion compensation method for change in backscattered energy (CBE) with multiple reference frames. Among the reference frames, the most similar reference to the current frame is selected to subtract the respiratory-induced motions. Since exhaustive reference searching in all stored reference frames can impede real-time thermal imaging, we improve the reference searching by using a motion-mapped reference model. We tested our method in six tumor-bearing mice with high intensity focused ultrasound (HIFU) sonication in the tumor volume until the temperature had increased by 7°C. The proposed motion compensation was evaluated by root-mean-square-error (RMSE) analysis between the estimated temperature by CBE and the measured temperature by thermocouple. As a result, the mean ±SD RMSE in the heating range was 1.1±0.1°C with the proposed method, while the corresponding result without motion compensation was 4.3±2.6°C. In addition, with the idea of motion-mapped reference frame, total processing time to produce a frame of thermal image was reduced in comparison with the exhaustive reference searching, which enabled the motion-compensated thermal imaging in 15 frames per second with 150 reference frames under 50% HIFU duty ratio.
RR outperformed both RA and RNFLT of the Cirrus OCT, especially at areas with diagnostic importance. This suggests that combinations of RA and RNFLT by sector-based analysis of Cirrus OCT would be promising to determine early glaucoma.
We present a method to enhance depth quality of a time-of-flight (ToF) camera without additional devices or hardware modifications. By controlling the turn-off patterns of the LEDs of the camera, we obtain depth and normal maps simultaneously. Sixteen subphase images are acquired with variations in gate-pulse timing and light emission pattern of the camera. The subphase images allow us to obtain a normal map, which are combined with depth maps for improved depth details. These details typically cannot be captured by conventional ToF cameras. By the proposed method, the average of absolute differences between the measured and laser-scanned depth maps has decreased from 4.57 to 3.77 mm.
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