Objective To evaluate the impacts of slice thickness and registration frame range on the accuracy of cone-beam computed tomography ( CBCT) image-guided head and neck ( HN) radiotherapy, and to provide a basis for positioning correction in image-guided radiotherapy.Methods A planned CT scan was performed for an anthropomorphic HN phantom with slice thickness of 1 mm and 3 mm and simulated positioning errors in x, y, and z directions on the accelerator.CBCT scan and reconstruction were performed with slice thickness of 1 mm and 3 mm.Two different registration frame ranges were used ( range 1:from C7 to superior orbit;range 2:from C7 to calvaria ) .Automatic bony registration was performed for CBCT and planned CT images with slice thickness of 1 mm and 3 mm.The registration accuracy was evaluated.Results For range 1, the registration errors in x, y, and z directions with a slice thickness of 1 mm were significantly lower than those with a slice thickness of 3 mm (0.5±0.2 mm vs.-0.7±0.2 mm, P=0.00;0.5±0.3 mm vs. 1.0±0.3 mm, P=0.00;-0.1±0.5 mm vs.1.5±0.5 mm, P=0.00).For range 2, the registration errors in x, y, and z directions with a slice thickness of 3 mm were-0.4±0.2 mm, 0.5±0.2 mm, and 0.7±0.4 mm, respectively.Conclusions Engagement of calvaria in registration range can substantially enhance the registration accuracy in CBCT or CT images for HN.The registration error with slice thickness of 1 mm can be controlled within 1 mm.

BACKGROUND: Ultrasonic coupling agent is indispensable in ultrasonic imaging. The service life and change frequency of the ultrasonic probe is determined by the internal coupling agent of the chosen hydrogel material. Due to defects in the existing gel-formula, after a period of time in use it can cause the surface depression of probes and thus influence the ultrasonic imaging quality. OBJECTIVE: To optimize the gel formula of the coupling agent. METHODS: The amplified synthesis process of polyacrylamide hydrogel was optimized by changing the ratio of monomer concentration to N, N-methylenebisacrylamide crosslinker in the synthesis conditions, and the factors influencing its acoustic properties were explored to meet the technical requirements in the clinical use process. RESULTS AND CONCLUSION: When the monomer concentration was set to 70 g/L and the mass ratio of monomer to crosslinker was 7:1, the polyacrylamide hydrogel was in the best state. The obtained polyacrylamide hydrogel had a stable swelling rate, had a strong ability to keep water and make the volume reduce under the influence of the operating temperature of ultrasound, and its relative amplitude changed less with the change of ultrasonic frequency. The sound attenuation coefficient of polyacrylamide hydrogel would be higher when the frequency of ultrasonic sound source was higher. The changes of monomer concentration would have significant impacts on the acoustic properties of polyacrylamide hydrogel. Therefore, by controlling the monomer concentration ratio, we can prepare the coupling agent that exhibits relatively stable acoustic properties at an optimum concentration and achieves an optimal imaging effect.

Objective: To evaluate the response of neoadjuvant chemotherapy on osteosarcoma by semi-quantitative parameters of dynamic contrast-enhancement magnetic resonance imaging (DCE-MRI). Methods: Retrospectively analysis 25 cases of osteosarcoma confirmed by pathology.All cases received DCE-MRI scan before and after 4 cycles of neoadjuvant chemotherapy.The following semi-quantitative parameters were calculated by post-processing software: early dynamic enhancement wash-in slope (Slope), maximum signal intensity (SI_max), time to peak (TTP), signal enhanced extent (SEE), peak percent enhancement (PPE), wash out rate (WOR), enhancement rate (R). All cases were divided into good response group (tumor necrosis rate ≥90%, n=12) and non-response group (tumor necrosis rate <90%, n=13) according to the Huvos grading method. Semi-quantitative parameters of DCE-MRI before and after neoadjuvant chemotherapy between good response group and non-response group were compared by Mann-whitney U test. Receiver operating characteristic curve (ROC) analysis was performed to evaluate the efficacy of different good response group and non-response group after neoadjuvant chemotherapy (NAC). Results: Slope, SI_max, TTP, SEE, PPE, WOR, R, TTP, WOR before and after NAC in good response group were significant different (P<0. 05), but only SI_max, SEE in non-response group. TTP, R were significant different between the above two groups before NAC, and Slope, SI_max, TTP, SEE, WOR, R were significant different after NAC (P<0.05). ROC was used to predict the diagnostic efficiency of various parameters for tumor necrosis rate after osteosarcoma NAC. It was found that the sensitivity and specificity of Slope, TTP and R parameters for predicting the response of osteosarcoma after chemotherapy were 83.3% and 92.3%, 91.7% and 69.2%, 84.6% and 75.0% respectively. The area under the curve (AUC) were 0.872 (95% CI: 0.716 to 1.027), 0.846 (95% CI: 0.685 to 1.007), 0.833 (95% CI: 0.662 to 1.004), the cut-off value were 0.032, 175 s, 5.441, Youden index were 0.756, 0.609, 0.596, respectively. Conclusions Slope, TTP, R were the most valuable semi-quantitative parameter of DCE-MRI to predict the response of NAC in osteosarcoma.