Performance and safety assessment of an integrated transmit array for body imaging at 7 T under consideration of specific absorption rate,tissue temperature,and thermal dose

In this study, the performance of an integrated body-imaging array for 7 T with 32 radiofrequency (RF) channels under consideration of local specific absorption rate (SAR), tissue temperature, and thermal dose limits was evaluated and the imaging performance was compared with a clinical 3 T body coil. Thirty-two transmit elements were placed in three rings between the bore liner and RF shield of the gradient coil. Slice-selective RF pulse optimizations for B₁ shimming and spokes were performed for differently oriented slices in the body under consideration of realistic constraints for power and local SAR. To improve the B₁⁺ homogeneity, safety assessments based on temperature and thermal dose were performed to possibly allow for higher input power for the pulse optimization than permissible with SAR limits. The results showed that using two spokes, the 7 T array outperformed the 3 T birdcage in all the considered regions of interest. However, a significantly higher SAR or lower duty cycle at 7 T is necessary in some cases to achieve similar B₁⁺ homogeneity as at 3 T. The homogeneity in up to 50 cm-long coronal slices can particularly benefit from the high RF shim performance provided by the 32 RF channels. The thermal dose approach increases the allowable input power and the corresponding local SAR, in one example up to 100 W/kg, without limiting the exposure time necessary for an MR examination. In conclusion, the integrated antenna array at 7 T enables a clinical workflow for body imaging and comparable imaging performance to a conventional 3 T clinical body coil.     

尼莫地平对烫伤大鼠脑内ZO-1 mRNA及血脑屏障通透性的影响

目的:观察尼莫地平对严重烫伤大鼠脑内紧密连接相关蛋白ZO-1mRNA及血脑屏障通透性的影响。方法:实验于2005-04/10在南昌大学基础医学院应用解剖实验室完成。①取健康SD大鼠132只分为正常对照组12只、烫伤组60只,尼莫地平组60只,后两组又设烫伤后1,3,6,12,24h5个时间点,每个时间点12只,其中6只用于脑组织伊文思蓝含量的测定,剩余6只用于ZO-1mRNA的检测。②烫伤组和尼莫地平组大鼠100℃开水烫伤15s,造成背部30%体表总面积Ⅲ度烧伤。尼莫地平组大鼠于烫伤后即刻腹腔注射尼莫地平(0.5mg/kg),其他2组不给药。③各组大鼠于相应的时间点麻醉并处死动物取材,应用化学定量方法检测大鼠脑组织内伊文思蓝含量,运用RT-PCR方法检测大鼠脑内ZO-1mRNA的表达变化。结果:经补充后132只大鼠进入结果分析。①大脑伊文思蓝含量:正常对照组为(10.18±1.79)μg/g,烫伤组伤后1,3,6,12h均高于正常对照组(P<0.05),其高峰在烫伤后6h,为(20.00±0.58)μg/g;尼莫地平组伤后1,6,12h均低于烫伤组(P<0.01),烫伤后6h时为(16.74±0.78)μg/g。②小脑伊文思蓝含量:正常对照组为(12.90±1.32)μg/g,烫伤组伤后1,3,6,12h均高于正常对照组(P<0.05),其高峰在烫伤后6h,为(31.3±1.47)μg/g;尼莫地平组伤后1,3,6,12h均低于烫伤组(P<0.01),烫伤后6h时为(21.05±2.36)μg/g。③脑组织ZO-1mRNA的表达:烫伤组烫伤后3,6,12,24h分别为正常对照组的(0.1235±0.0158),(0.1890±0.0531),(0.2014±0.0412),(0.1555±0.0163)倍(P<0.01);尼莫地平组较烫伤组高,以烫伤后3,6h最为明显,分别为烫伤组的3.96及1.81倍(P<0.01).结论:①严重烫伤后血脑屏障通透性增高,脑内ZO-1mRNA表达下降。②烫伤后早期应用尼莫地平能防止脑内ZO-1mRNA表达下降,并能起到保护血脑屏障功能的作用。     

Prevalence of cytomegalovirus antibody in hemophiliacs and homosexuals infected with human immunodeficiency virus type 1

We determined the prevalence of antibody to cytomegalovirus (CMV) in the sera of non-homosexual hemophilia patients and homosexual men infected with the human immunodeficiency virus type 1 (HIV-1). CMV antibody testing by latex agglutination revealed 33 of 58 HIV-1 infected hemophiliacs (57%) were antibody-positive compared with 54 of 54 HIV-1 infected asymptomatic non-hemophiliac homosexuals (100%) (p less than .001). Nine of 15 hemophiliacs (60%) with symptomatic HIV-1 infection were CMV antibody-positive. We also tested 22 HIV-1 antibody-negative hemophiliacs who had received non-heat treated factor concentrates. 14 of these 22 (64%) were CMV antibody-positive compared with 57% of HIV-1 antibody-positive hemophiliacs. We conclude 1) there is little correlation between transmission of HIV-1 and CMV by factor concentrates, 2) the presence of CMV antibody does not appear to be associated with clinical stage of HIV-1 infection in hemophiliacs, and 3) there may be a significant number of CMV antibody-negative hemophiliacs with HIV-1 infection at risk for primary infection and subsequent disease if CMV seronegative blood products are not provided for future transfusions.     

Hernia en masse

Described is the case of a patient who developed symptoms compatible with small bowel obstruction approximately 16 hours after a difficult self-performed left inguinal hernia reduction. Exploratory laparotomy was performed, and release of an incarcerated loop of ileum was performed. A large inguinal hernia defect also was found, and this was repaired with a Cooper's ligament repair. The patient recovered uneventfully.     

In vitro evaluation of current thoracic aortic stent-grafts for real-time MR-guided placement.

PURPOSE: To systematically evaluate the magnetic resonance imaging (MRI) characteristics of current thoracic aortic stent-graft devices before, during, and after in vitro deployment as a step toward real-time MRI-guided stent placement. METHODS: Six stent-graft devices used for thoracic aortic repair were examined in a dedicated phantom model using a 1.5-T MRI scanner. First, the delivery systems with the mounted stent-graft were examined using real-time fast imaging with steady-state precession (TrueFISP) with Cartesian and radial k-space filling. TrueFISP imaging was subsequently used for real-time monitoring of stent-graft expansion. The deployed stent-grafts were then examined in a water bath containing gadolinium (1:40) with high-resolution T1-weighted 3D fast low-angle shot (FLASH) sequences. The images were analyzed for artifacts, radiofrequency caging effects, and device visualization quality. RESULTS: Three delivery systems with mounted stent-grafts did not contain ferromagnetic elements and were well visualized. Imaging with radial k-space filling showed fewer artifacts than Cartesian imaging. Movement of the delivery system and stent-graft expansion of these devices were successfully demonstrated at a rate of up to 6 frames per second. Evaluation of the expanded stent-grafts revealed only minor susceptibility artifacts without relevant signal attenuation in the stent-graft lumen for 5 nitinol-based stent-grafts. Only a stainless steel-based stent-graft was associated with severe artifacts, thwarting visualization of its lumen or surroundings. CONCLUSION: The present study shows that 3 nitinol-based thoracic stent-graft devices are potentially suited for real-time MRI-guided placement with respect to both the delivery system and the stent-graft itself. These observations provide the basis for the evaluation of MRI-guided stent-graft placement in vivo.     

Real-time vascular interventional magnetic resonance imaging

Endovascular stent-graft placement is emerging as a promising alternative to medical and surgical treatment of patients with diseases of the descending thoracic and abdominal aorta. Precise placement of the stentgraft, which is currently performed under x-ray control, remains, however, challenging as there are several shortcomings to fluoroscopic guidance beyond that related to the harmful effect of radiation exposure and nephrotoxic contrast media. While transesophageal echocardiography and intravascular ultrasound have been used as adjunct imaging modalities during endovascular stent-graft procedures to overcome the limitations of angiography, these techniques have not mitigated the need for fluoroscopy.Magnetic resonance imaging (MRI) guidance of vascular interventional procedures offers several potential advantages over fluoroscopy-guided techniques, including image acquisition in any desired orientation, superior 3D soft-tissue contrast with simultaneous visualization of the interventional device, absence of ionizing radiation, and avoidance of nephrotoxic contrast media. Magnetic resonance imaging is often used for pre-operative diagnosis of aortic disease and can provide all relevant information for the planning of endovascular stent-graft procedures as well as for accurate and immediate post-interventional evaluation. However, visualization of interventional instruments by MRI has proven to be the chief obstacle. This article will review current approaches that have been developed for depicting vascular instruments by MRI and will also discuss the first experimental experiences with MRI-guided endovascular stent-graft placement in a swine model of aortic dissection.