Assessing arterial stiffness and cardiac pulsations in the brain at sub-millimetre resolution using MRI

人类的大脑需要持续顺畅的血液流动来维持良好的神经系统健康。当心脏跳动时，它会导致血液通过大动脉“脉动”，当心脏收缩时加速，当心脏放松时减慢。正是大动脉壁的弹性结构改变了这种脉动流，并且它是重要的，因为它保护大脑微循环免受过度脉动能量的影响。然而，随着年龄的增长，动脉壁的结构发生变化，导致它们膨胀。由于大脑是一个高流量的器官，因此动脉僵硬度增加与脑血管疾病有关并不奇怪。出于这个原因，评估动脉的硬度和脉动性在临床上是非常需要的，然而目前在大脑中这样做的方法很少。在这个项目中，我们建议开发一种新的超高场磁共振成像（MRI）的方法来评估大脑动脉的刚度和脉动。现有的MRI方法将血流速度“编码”到MRI信号中，但这需要扫描仪产生额外的磁场，这需要时间。我们的新方法是基于利用在一定条件下的MRI信号固有的血流速度的强敏感性，从而使我们能够测量脉动流在脑动脉与高时间resolution.The拟议的项目包括MRI序列开发主题和应用主题。对于序列开发主题，我们将开发一种通过测量心脏压力波速度（即脉搏波速度）评估脑大动脉僵硬度的新方法。该测量技术将提供颈内动脉和大脑中动脉段硬度的定量测量。然后，我们将重点测量直接从大脑中动脉分支的小纹状体动脉的搏动。这些新开发的技术将使我们能够探索大脑大动脉的硬度和小动脉下游的相关脉动之间的关系。在应用主题中，我们将在一个广泛年龄范围的健康个体队列和一个脑小血管疾病患者队列中应用这些新的测量技术。这个实验计划将使我们能够了解大脑大动脉僵硬度和下游脉动性如何随着年龄的增长而变化，以及这个过程如何在小血管病变患者中改变。

The human brain requires a constant smooth flow of blood to maintain good neurological health. As the heart beats it causes blood to ‘pulsate’ through the large arteries, speeding up when the heart contracts, and slowing down when it relaxes. It is the elastic structure of the walls of large arteries that modify this pulsatile flow, and it is important as it protects the cerebral microcirculation from excessive pulsatile energy. However, as we age, changes occur in the structure of the artery wall that cause them to stiffen. As the brain is a high-flow organ, it is unsurprising that increased arterial stiffness is associated with cerebrovascular disease. For this reason, assessing the stiffness and pulsatility of arteries is highly clinically desirable, however there are currently very few methods to do this in the brain. In this project we propose to develop a novel ultra-high field magnetic resonance imaging (MRI) method for assessing both stiffness and pulsatility of cerebral arteries. Existing MRI methods ‘encode’ blood flow velocity into the MRI signal, but this requires additional magnetic fields to be generated by the scanner, which takes time. Our new approach is based on exploiting the strong sensitivity to blood flow velocity inherent in the MRI signal under certain conditions, and thus allows us to measure pulsatile flow in cerebral arteries with high temporal resolution.The proposed project includes an MRI sequence development theme and an applications theme. For the sequence development theme, we will develop a new method for assessing cerebral large arterial stiffness by measuring the speed of the cardiac pressure wave (i.e. pulse wave velocity). This measurement technique will provide a quantitative measure of stiffness in the internal carotid and middle cerebral artery segments. Then we will focus on measuring the pulsatility in the small lenticulostriate arteries that branch directly from the middle cerebral artery. These newly developed techniques will allow us to explore the relationship between the stiffness of large cerebral arteries and the associated pulsatility downstream in the small arteries. In the applications theme we will apply these new measurement techniques in a cohort of healthy individuals across a broad age range and in a cohort of patients with cerebral small vessel disease. This programme of experiments will allow us to characterise how cerebral large artery stiffness and downstream pulsatility evolve with age, and how this process is altered in patients with small vessel pathology.