Short‐ and long‐term reproducibility of BOLD signal change induced by breath‐holding at 1.5 and 3 T

Cerebrovascular reactivity (CVR) can give insight into the cerebrovascular function. CVR can be estimated by measuring a blood‐oxygen‐level‐dependent (BOLD) response combined with breath‐holding (BH). The reproducibility of this technique has been addressed and existing studies have focused on short‐term reproducibility using a 3 T magnetic resonance imaging (MRI) system. However, little is known about the long‐term reproducibility of this procedure and the corresponding reproducibility using a 1.5 T MRI system. Here, we systematically examined the short‐ and long‐term reproducibility of BOLD responses to BH across field strengths. Nine subjects participated in three MRI sessions separated by 30 minutes (sessions 1 and 2: short term) and 68–92 days (sessions 1 and 3, long term) at both 1.5 and 3 T MRI. Our findings revealed that significant differences between field strengths were detected in the activated gray matter volume and BOLD signal change (both P < 0.001), with smaller magnitudes at 1.5 T. However, activation patterns were reproducible, independent of the time interval, brain region or field strength. All interscan coefficient of variation values were below the 33% fiducial limit, and the intraclass correlation coefficient values were above 0.4, which is usually considered the acceptability limit in functional studies. These findings suggest that the response of BOLD signal to BH for assessing CVR is reproducible over time at 1.5 and 3 T. This technique can be considered a tool for monitoring longitudinal changes in patients with cerebrovascular diseases, and its use should be encouraged for clinical 1.5 T MRI systems.     

Motion‐compensated b‐tensor encoding for in vivo cardiac diffusion‐weighted imaging

Motion is a major confound in diffusion‐weighted imaging (DWI) in the body, and it is a common cause of image artefacts. The effects are particularly severe in cardiac applications, due to the nonrigid cyclical deformation of the myocardium. Spin echo‐based DWI commonly employs gradient moment‐nulling techniques to desensitise the acquisition to velocity and acceleration, ie, nulling gradient moments up to the 2nd order (M2‐nulled). However, current M2‐nulled DWI scans are limited to encode diffusion along a single direction at a time. We propose a method for designing b‐tensors of arbitrary shapes, including planar, spherical, prolate and oblate tensors, while nulling gradient moments up to the 2nd order and beyond. The design strategy comprises initialising the diffusion encoding gradients in two encoding blocks about the refocusing pulse, followed by appropriate scaling and rotation, which further enables nulling undesired effects of concomitant gradients. Proof‐of‐concept assessment of in vivo mean diffusivity (MD) was performed using linear and spherical tensor encoding (LTE and STE, respectively) in the hearts of five healthy volunteers. The results of the M2‐nulled STE showed that (a) the sequence was robust to cardiac motion, and (b) MD was higher than that acquired using standard M2‐nulled LTE, where diffusion‐weighting was applied in three orthogonal directions, which may be attributed to the presence of restricted diffusion and microscopic diffusion anisotropy. Provided adequate signal‐to‐noise ratio, STE could significantly shorten estimation of MD compared with the conventional LTE approach. Importantly, our theoretical analysis and the proposed gradient waveform design may be useful in microstructure imaging beyond diffusion tensor imaging where the effects of motion must be suppressed.     

Awareness of major cardiovascular risk factors and its relationship with markers of vascular aging: Data from the Brisighella Heart Study

Background and aimGeneral population awareness about cardiovascular risk factors is usually low. The aim of the present study was to evaluate the vascular aging of subjects aware and not aware to be hypertensive, hypercholesterolemic, hypertriglyceridemic or diabetics in a general population sample.Methods and resultsWe interviewed 1652 subjects without atherosclerotic cardiovascular diseases (M: 46.6%, F: 53.4%) about their awareness of hypertension, hypercholesterolemia, hypertriglyceridemia or type 2 diabetes. Then we compared the augmentation index and pulse wave velocity of subjects aware and not aware of the investigated cardiovascular risk factors. 1049 participants declared not to be hypertensive, while 32 were not sure. Among them, respectively, 23.5% and 50% were hypertensive. Subjects not aware of their hypertension had significantly higher aortic blood pressure than aware ones (p < 0.001). 841 participants declared not to be hypercholesterolemic, while 60 were not sure. Among them, respectively, 18.1% and 40% were hypercholesterolemic. Subjects not aware of their hypercholesterolemia had significantly higher augmentation index than the aware ones (p < 0.05). 1226 participants declared not to be hypertriglyceridemic, while 200 were not sure. Among them, respectively, 19.2% and 44% were hypertriglyceridemic. Subjects not aware of their hypertriglyceridemia had significantly higher TG levels aware ones (p < 0.05), although this seemed to not related to increased arterial stiffness. 1472 participants declared not to be diabetic, while 20 were not sure. Among them, respectively, 2.0% and 25.0% were diabetics. Subjects not aware of their diabetes had significantly higher augmentation index than the aware ones (p < 0.05).ConclusionsIn conclusion, the lack of awareness of hypertension and hypercholesterolemia is relatively frequent in the general population and is associated to significantly higher arterial stiffness.     

床旁多普勒超声引导下经皮气管切开术在重症脑出血患者中的应用

目的探讨床旁多普勒超声引导下经皮气管切开术（PDT）在重症脑出血患者中的应用价值。方法选取2014年1月—2019年4月南方医科大学附属小榄医院重症医学科监护治疗的重症脑出血患者126例，在ICU床旁采用超声引导下行PDT。术前采用超声进行检查，明确气管位置、周围组织及血管情况，确定穿刺部位及深度，指导术前气管导管退管。术中实时超声引导，确保手术安全。术后超声确认气管切开套管位置，筛查排除气胸等相关并发症。观察操作时间（从皮肤穿刺到成功置入气管套管时间）、一针穿刺成功率、置管成功率、气管插管意外脱管率；观察术中及术后并发症：出血量、血管/甲状腺损伤、气管后壁损伤、皮下气肿、气胸、低氧血症发生率等。结果126例患者手术均一次操作成功，一针穿刺成功率及置管成功率均为100%，未发生气管插管意外脱管。操作时间5~12 min，平均操作时间7.5 min。术中及术后未发生难以控制的大出血、严重低氧血症、血管/甲状腺损伤、气管后壁损伤、皮下气肿及气胸等并发症。结论对重症脑出血患者行床旁实时超声引导下行PDT，提高了手术的可视性、操作性和安全性，提高PDT成功率，降低相关并发症，具有良好的临床价值。