Conventional magnetic resonance (MR) pulse sequences typically have an echo time (TE) of 1 ms or longer, providing an excellent contrast between different soft tissues. However, some short T2 tissues appear dark in conventional MR images because the signal from these tissues has decayed to nearly zero before the center of k-space is acquired. Because of the ability of directly imaging short T2 tissues, ultrashort echo time technique has been widely studied in recent years. An overwhelming majority of the studies were carried out at high fields, while many low-field scanner systems are still used in developing countries. To investigate the effects of the delay between analog-to-digital converter sampling and the readout gradient, the TE of the second echo used to calculate the R2* map, and the undersampling ratio on the results of three-dimensional (3D) ultrashort echo time imaging at a low field, we implemented a 3D ultrashort echo time sequence on a 0.35T scanner. Different parameters were used and the reconstructed images and R2* maps were compared. Images reconstructed with slightly varying delays appeared quite different. Different contrast between short and long T2 tissues were found in R2* maps calculated with different echoes. The result of undersampling study indicated that excessive undersampling could cause unwanted blurring, making it difficult to better visualize the short T2 tissues in the R2* map. The results suggested that cautions should be taken in the choice of these parameters in 3D ultrashort echo time imaging. Short T2 tissues can be visualized with appropriate imaging parameters at this low field.
Abdominal imaging is one of the important clinical applications of magnetic resonance imagining, but image degradation due to respiratory motion remains a major problem. Retrospective respiratory navigator gating technique is an effective approach to alleviate such degradation but is subject to long scan time and low signal-to-noise ratio (SNR) efficiency. In this study, a modified retrospective navigator gating technique with variable over-sampling ratio acquisition and weighted average reconstruction algorithm is presented. Experiments in phantom and the imaging results of seven volunteers demonstrated that the proposed method provided an enhanced SNR and reduced ghost-to-image ratio compared to the conventional method. The proposed method can also be used to reduce imaging time while maintaining comparable image quality.
Objective To analyse the clinical features of Peutz-Jeghers syndrome and its canceration, and to summarize the management and the follow-up strategy for patients with Peutz-Jeghers syndrome. Methods Clinical data of 30 patients with Peutz-Jeghers syndrome dating from October 1985 to September 2005 in West China Hospital of Sichuan University were analyzed retrospectively. Results Fourteen (46.67%) definite family histories of Peutz-Jeghers syndrome were found. Pigmentation of skin and mucosa, abdominalgia and hematochezia were major clinical manifestations of the syndrome. There were 18 patients (60.00%) complicated with intussusception and acute intestinal obstructions, 16 patients (53.33%) with gastrointestinal bleeding, and 6 patients (20.00%) developed malignancy. The frequent types of malignancy were carcinoma of small intestine (3 cases), colon carcinoma (2 cases) and gastric carcinoma (1 case) in order. The mean age of the canceration-diagnosed patients was 32 years old. The type of pathohistology of all the malignancy was poorly differentiated mucus adenocarcinoma. High-frequency endoscopic electroresection, orthdox polypectomy and enterectomy were the major means of treatment. Conclusion Patients with Peutz-Jeghers syndrome are at high risk of canceration at relatively early ages and usually the differentiation of the tumor is poor. Endoscopy should be performed regularly and the high-frequency electroresection is an effective therapy in disposing intestinal polyp. Screening can also improve the efficacy of Peutz-Jeghers syndrome.
目的 探讨妊娠期并发急性胰腺炎(APIP)的病因、发病机理、临床特点及防治措施. 方法 对四川省宜宾市第二人民医院和四川大学华西医院1995年1月至2006年12月期间收治的72例APIP患者的临床资料进行回顾性分析. 结果 本组72例中,属轻型急性胰腺炎(MAP)者49例(68.06%),重症急性胰腺炎(SAP)者23例(31.94%); 有胆囊炎合并胆囊结石病史者43例(59.72%),伴高脂血症者21例(29.17%).采用非手术治疗56例,手术治疗16例,孕妇治愈66例(91.67%),死亡6例(8.33%),死因为多器官功能障碍综合征、急性呼吸窘迫综合征及严重复腔感染; 终止妊娠16例(均为32～38周妊娠),56例继续妊娠; 72例中双胎2例,胎儿死亡共15例(20.27%); 漏诊、误诊6例.结论 APIP的发生与胆结石和高脂血症有关,并于妊娠中晚期发病率高; 其临床表现复杂,易误诊,对孕妇及胎儿威胁极大; 把握该疾病的特点,提高对APIP的认识和警惕性,及时准确的诊断与"个体化"的治疗原则,适时终止妊娠,可以提高其治愈率,降低母婴死亡率.