Quantification of arterial wall inhomogeneity size,distribution, and modulus contrast using FSI numerical pulse wave propagation

Changes in aortic wall material properties, such as stiffness, have been shown to accompany onset and progression of various cardiovascular pathologies. Pulse Wave velocity (PWV) and propagation along the aortic wall have been shown to depend on the wall stiffness (i.e. stiffer the wall, higher the PWV), and can potentially enhance the noninvasive diagnostic techniques. Conventional clinical methods involve a global examination of the pulse traveling between femoral and carotid arteries, to provide an average PWV estimate. Such methods may not prove effective in detecting focal wall changes as entailed by a range of cardiovascular diseases. A two-way-coupled fluid-structure interaction (FSI) simulation study of pulse wave propagation along inhomogeneous aortas with focal stiffening and softening has previously proved the model reliable. In this study, simulations are performed in inhomogeneous aortic walls with hard inclusions of different numbers, size and modulus in order to further characterize the effects of focal hardening on pulse wave propagation. Spatio-temporal maps of the wall displacement were used to analyze the regional pulse wave propagations and velocities. The findings showed that the quantitative markers – such as PWVs and r²s on the pre-inclusion forward, reflected and post-inclusion waves, and the width of the standing wave – as well as qualitative markers – such as diffracted reflection zone versus single reflection wave – allow the successful and reliable distinction between the changes in inclusion numbers, size and modulus. Future studies are needed to incorporate the wall softening and physiologically-relevant wall inhomogeneities such as those seen in calcifications or aneurysms.     

Role of neuroimaging before reperfusion therapy. Part 1 – IV thrombolysis – Review

This review paper summarises the yield of the different imaging modalities in the evaluation of patients for IV thrombolysis. Non-contrast CT and CTA or brain MRI combined with MRA are the recommended sequences for the evaluation of patients within the 4.5 hours time window. Multimodal MRI (DWI/PWI), and more recently, CT perfusion, offer reliable surrogate of salvageable penumbra, the target mismatch, which is now currently used as selection criteria for revascularisation treatment in an extended time window. Those sequences may also help the physician for the management of other limited cases when the diagnosis of acute ischemic stroke is difficult. Another approach the DWI/FLAIR mismatch has been proposed to identify among wake-up stroke patients those who have been experiencing an acute ischemic stroke evolving from less than 4.5 hrs. Other biomarkers, such as the clot imaging on MRI and CT, help to predict the recanalisation rate after IVT, while the impact of the presence microbleeds on MRI remains to be determined.     

大鼠放射性脑损伤的MRS、PWI研究

目的研究大鼠放射性脑损伤不同时期的MRS、PWI表现,为其早期诊断提供依据。方法将成年大鼠30只随机分为对照组和照射组,照射前均行MRI、MRS及PWI检查。照射组分别于照射后1、3、6、9及12个月行MRI、MRS及PWI检查,计算NAA/Cr和Cho/Cr比值,测量灌注后大鼠双侧侧脑室周围的rCBV值。结果 1各照射组大鼠的NAA/Cr比值与对照组相比逐渐下降,差异均有统计学意义(P0.05);照射后Cho/Cr比值先上升,3个月时达峰值,随后逐渐下降,6个月内各组的Cho/Cr与对照组相比有统计学意义(P0.05);2照射1个月后各组的rCBV值均明显低于对照组,差异有统计学意义(P0.05)。结论 MRS及PWI能在放射性脑损伤发生形态学改变之前检测出脑组织代谢及灌注异常,为放射性脑损伤的早期诊断提供依据。     

Magnetic resonance imaging in neonatal encephalopathy

Magnetic resonance imaging may provide invaluable information in the term born neonate with encephalopathy. However, both hardware and sequences may need adaptation from normal adult protocols. Sedation is often required to obtain good quality imaging, but anaesthesia is not necessary in this population. The perinatal history may predict the pattern of brain lesions, which, in turn, may be used to predict the neurodevelopmental outcome. Image interpretation is not easy and requires a full clinical history in addition to experience of both normal and abnormal neonatal brain appearances. Lesions evolve rapidly, and perinatally acquired leasions are at the most obvious 1-2 weeks from delivery. Early imaging in the first few days from presentation should always include diffusion-weighted sequences to identify early ischaemic change. Advanced techniques such as venography, angiography and perfusion-weighted imaging may be useful in certain situations, and serial imaging may help differentiate perinatal-acquired lesions from other pathologies.     

实验性脑出血血肿灶周脑血流量变化与细胞凋亡的相关性研究

目的　探讨脑出血 (ICH)后血肿灶周脑血流量变化与细胞凋亡的相互关系。方法　健康家犬 2 7只 ,随机分为对照组和ICH组 (3h、6h、12h、2 4h、4 8h、72h、7d和 15d)。ICH模型采用立体定向自体血额叶皮层注射法建立。应用磁共振灌注加权成像 (PWI)和流式细胞术 (FCM ) ,动态检测不同时间点血肿灶周相对脑血流量 (rCBF)与凋亡峰 /凋亡率的变化。结果　①脑血流量变化 :PWI显示血肿灶周 12h之内rCBF明显降低 ,呈低灌注状态 ,12～ 2 4hrCBF回升 ,出现血流再灌注 ,或高灌注现象 ,4 8h以后接近对侧 ,呈持续稍低灌注状态。②细胞凋亡变化 :FCM显示血肿灶周区凋亡峰 /凋亡率 6h开始出现 ,72h最高 ,7d下降。③血肿灶周凋亡峰值与凋亡率的变化呈正相关 (r =0 84 6 ,P <0 0 5 )。结论　ICH后血肿灶周脑血流量呈中 -轻度降低 ,细胞凋亡主要存在于血肿灶周区 ,72h是血肿灶周细胞凋亡的时间窗。     

Combined Intravenous and Intraarterial Revascularization Therapy Using MRI Perfusion/Diffusion Mismatch Selection for Acute Ischemic Stroke at 3–6 h After Symptom Onset

Background and Purpose  Intravenous (IV) thrombolysis with recombinant tissue plasminogen activator (rt-PA) has demonstrated favorable clinical outcomes in a 3–6 h window in patients selected with perfusion/diffusion mismatch. However, the advantages of combined IV and intraarterial (IA) thrombolysis after 3 h of stroke onset are unexplored. Methods  Acute ischemic stroke patients with persistent occlusion of intracranial large arteries were screened prospectively for thrombolysis by evaluating perfusion/diffusion mismatch on MRI. The IV rt-PA was initiated within 3–6 h, and additional urokinase (UK) was then administered via the IA route after angiography. Results  Four patients had middle cerebral artery occlusion and one patient had an internal carotid artery occlusion. The median time from the symptom onset to the initiation of IV therapy and to the initiation of IA treatment was 215 ± 30 min and 292 ± 41 min, respectively. The median National Institutes of Health Stroke Scale (NIHSS) scores were as follows: initial, 13; immediately after IA treatment, 8; at 24 h, 5; and at 7 days, 3. The Thrombolysis in Myocardial Infarction (TIMI) score after the completion of thrombolysis was 2–3. Four patients without intracerebral hemorrhage recovered completely or exhibited mild disability and one patient with hemorrhage also demonstrated a favorable outcome. Conclusion  This preliminary result suggests that if a significant perfusion/diffusion mismatch on MRI is identified, a sequential combination thrombolysis of IV rt-PA and IA UK is potentially beneficial in moderate to severe acute ischemic stroke patients who are treated within 3–6 h after symptom onset.     

磁共振成像在评价脑转移瘤伽玛刀治疗效果中的应用

目前,伽玛刀治疗被认为是脑转移瘤局部治疗的有效方法.磁共振成像在其治疗效果及并发症的评估方面起着重要作用.以肿瘤的形态学改变为基础的传统磁共振成像及以脑组织的生理为基础的功能磁共振成像均为伽玛刀治疗效果的评价及进一步治疗方法 的制定提供了大量信息.就磁共振成像在评价脑转移瘤伽玛刀治疗效果中的应用予以综述.     

短暂性脑缺血发作的脑电地形图与功能磁共振及血管病变的相关研究

目的观察短暂性脑缺血发作（TIA）患者间期脑电地形图（BEAM）变化情况,并与磁共振、血管病变对比,深入探讨TIA的病变机制。方法 18例颈内动脉系统TIA患者均行常规头MRI（T1WI、T2WI）、功能磁共振（DWI、PWI）,BEAM检查,综合磁共振血管成像（MRA）、数字减影脑血管造影（DSA）及颈动脉超声联合经颅多普勒超声（TCD,简称超声）检测判定血管病变并对上述结果进行分析。结果 BEAM病灶检出率94.4%,灌注加权成像（PWI）异常率70.6%,TCD异常率50%,DWI异常率16.7%。TIA间期BEAM广泛异常77.8%,责任病变部位集中于中央、顶部、前颞,主要表现为α频段较对侧功率降低,δ和θ频段较对侧功率增高。结论将BEAM和TCD/PWI相结合,可为TIA提供可靠的辅助检查。临床医生应重视TIA患者的神经保护治疗。     

Cortical calcification in sturge–weber syndrome on MRI‐SWI: Relation to brain perfusion status and seizure severity

Purpose:

To determine the relationship between calcified cortex and perfusion status of white matter and seizure severity in patients with Sturge–Weber Syndrome (SWS), a sporadic neurocutaneous disorder characterized by a leptomeningeal angioma, progressive brain ischemia, and a high incidence of seizures using susceptibility weighted imaging (SWI) and dynamic susceptibility contrast‐enhanced perfusion weighted imaging (DSC‐PWI).

Materials and Methods:

Fifteen children (ages: 0.9–10 years) with unilateral SWS prospectively underwent magnetic resonance imaging (MRI). The degree of cortical calcification was assessed using SWI while perfusion status was quantified using DSC‐PWI images (asymmetries of various perfusion parameters). Comparisons between calcification, perfusion status, and seizure variables were performed.

Results:

Patients with severely calcified cortex demonstrated significantly lower perfusion in the ipsilateral white matter (mean asymmetry: ?0.52 ± 0.22) as compared to patients with only mildly calcified cortex or no calcification (mean asymmetry: 0.08 ± 0.25). Patients with severely calcified cortex also suffered from a higher seizure burden (a composite measure of seizure frequency and epilepsy duration; P = 0.01) and a trend for earlier seizure onset and longer epilepsy duration.

Conclusion:

Severe calcification in the affected hemisphere is related to severely decreased perfusion in underlying white matter and is associated with more severe epilepsy in SWS patients. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.