Integrated TOF-PET/MR is a multimodal imaging system which can acquire high-quality magnetic resonance (MR) and positron emission tomography (PET) images at the same time, and it has time of flight (TOF) function. The TOF-PET system usually features better image quality compared to traditional PET because it is capable of localizing the lesion on the line of response where annihilation takes place. TOF technology measures the time difference between the detectors on which the two 180-degrees-seperated photons generated from positron annihilation are received. Since every individual crystal might be prone to its timing bias, timing calibration is needed for a TOF-PET system to work properly. Three approaches of timing calibration are introduced in this article. The first one named as fan-beam method is an iterative method that measures the bias of the Gaussian distribution of timing offset created from a fan-beam area constructed using geometric techniques. The second one is to find solutions of the overdetermination equations set using L1 norm minimization and is called L1-norm method. The last one called L2-norm method is to build histogram of the TOF and find the peak, and uses L2 norm minimization to get the result. This article focuses on the comparison of the amount of the data and the calculation time needed by each of the three methods. To avoid location error of the cylinder radioactive source during data collection, we developed a location calibration algorithm which could calculate accurate position of the source and reduce image artifacts. The experiment results indicate that the three approaches introduced in this article could enhance the qualities of PET images and standardized uptake values of cancer regions, so the timing calibration of integrated TOF-PET/MR system was realized. The fan-beam method has the best image quality, especially in small lesions. In integrated TOF-PET/MR timing calibration, we recommend using fan-beam method.
Objective To evaluate short-term effectiveness of staged management for complex tibial plateau fracture with severe soft tissue injury. Methods A clinical data of 12 patients with complex tibial plateau fractures and severe soft tissue injuries between July 2017 and March 2021 and met the selection criteria was retrospectively analyzed. There were 7 males and 5 females with an average age of 43.1 years (range, 33-58 years). All patients were traffic accident injuries and admitted to hospital within 24 hours after injury. The tibial plateau fractures were closed fractures. According to the Schatzker classification standard, the fractures were rated as type Ⅳ in 3 cases, type Ⅴ in 4 cases, and type Ⅵ in 5 cases. According to the Tscherne classification standard, the soft tissue injuries were rated as grade Ⅱ in 4 cases and grade Ⅲ in 8 cases. The treatment of all patients was divided into 3 stages. In the first stage, emergency trans-articular fracture fixation with external fixator was performed; in the second stage, the fracture reduction and internal fixation were performed and bone cement was implanted to fill the bone defect; in the third stage, the bone cement was removed and the bone graft was performed to repair defect. All patients performed joint function exercise after operation as early as possible. Results There was no neurological symptom after all staged managements, the incisions healed by first intention, and no complications such as incision infection or necrosis occurred. All patients were followed up 6-32 months (mean, 16.9 months). The fractures were all anatomical reduction confirmed by the X-ray films after operation. During follow-up, there was no obvious loss of reduction, loosening and rupture of internal fixator, or collapse of the articular surface. All fractures healed after 14-20 weeks (mean, 17.6 weeks). The posterior slope angle of the tibial plateau was (9.7±2.3)° and the varus angle was (3.9±1.9)° immediately after bone grafting, and were (8.5±2.9)° and (4.3±1.9)° respectively at 6 months after operation. There was no significant difference between the two time points (t=0.658, P=0.514; t=−1.167, P=0.103). At last follow-up, the Hospital for Special Surgery (HSS) score was 85-96 (mean, 91.2), and the range of motion of knee was 110°-135° (mean, 120.9°). Conclusion The staged management for complex tibial plateau fracture with severe soft tissue injury can obtain good short-term effectiveness, but the long-term effectiveness needs to be further followed up.