Keywords: Blood Vessels, Blood vessels

Motivation: While previous research has focused on realistic vessel and flow replication, the background tissue mimicking in 4D flow MRI remains unexplored despite its significant impact on phase correction accuracy.

Goal(s): Aims to identify a suitable material for a Circle of Willis flow phantom that can mimic background static tissue, ensure transparency, and constrain vessel motion.

Approach: Transparent water beads soaked in a Gd-doped solution were used as background static tissue in a flow phantom. A MATLAB tool was used for the post-processing of the 4D-flow data.

Results: Water beads effectively minimized motion artifacts, and increased the number of time-averaged streamlines and their quality.

Impact: This study introduces a practical solution, to enhance the accuracy of in-vitro 4D Flow MRI of complex vessel phantoms by mitigating motion artifacts. The transparent water beads offer a cost-effective and easily exchangeable alternative for mimicking background static tissue.

Keywords: Blood Vessels, Perfusion, ASL

Motivation: The ability to distinguish arterial blood supply above CoW is crucial in the study of collateral circulation, but it is challenging due to the complex positioning of arteries around the CoW.

Goal(s): To achieve a robust vascular territories separation above CoW.

Approach: We propose improvements to the original OES method, optimizing its SNR efficiency while minimizing high spatial frequencies to avoid mislabeling. We have also selected a set of PCASL parameters that facilitate thin-slice labeling and ensure high labeling efficiency to overcome issues related to vascular tortuosity.

Results: Combining optimized parameters and improved OES, the vascular territories separation has significantly improved.

Impact: Our study optimized the fully automatic encoding pattern design above the circle of Willis, and achieved a robust vascular territories separation, combining with optimized PCASL parameters.

Keywords: Blood Vessels, Blood vessels, Velocity & flow; Vessel size

Motivation: To address the gap in MRI techniques for assessing cerebral small vessels with slow flow non-invasively.

Goal(s): To develop a quantitative 2D time-of-flight (qTOF) technique for measuring blood velocity and the size of cerebral small vessels.

Approach: We developed an analytic qTOF framework to generate realistic TOF model images, which are optimized to match the acquired TOF images for extracting blood velocity and vessel size.  

Results: The proposed qTOF framework was validated in simulation and phantom studies, and demonstrated in vivo. Incorporating a second acquisition improved blood velocity and vessel size estimation. Flow velocities were comparable to those measured by phase-contrast MRI.

Impact: A quantitative Time-of-Flight technique was developed to provide insights into blood flow and the size of cerebral small vessels, and dynamically in response to changing brain activity, helping to elucidate the role of cerebral small vessels in healthy brain function.

Keywords: Vessel Wall, Vessels

Motivation: 4D-MR angiography techniques have been developed to visualize both luminal stenosis and collateral circulation.

Goal(s): This study aimed to assess whether 4D-MRA (4D-PACK and 4D-S-PACK) can be used as a noninvasive alternative to intraarterial DSA in internal carotid artery occlusion (ICAO).

Approach: We prospective enrolled patients diagnosed as internal carotid artery occlusion by ultrasound or CTA and scheduled for intra-arterial DSA for this study. All patients underwent carotid multi-contrast MR imaging and DSA.

Results: 4D-PACK and 4D-S-PACK can be used to diagnose ICAO, type of Circle of Willis (CoW), collateral circulation via CoW and blood flow direction of cerebral arteries.

Impact: We offered a noninvasive alternative to intraarterial DSA to diagnose ICAO, type of CoW, collateral circulation via CoW and blood flow direction. By using three durations, we could greatly reduce time cost while ensuring the accuracy of 4D-PACK and 4D-S-PACK.

Keywords: Vessel Wall, Stroke, Aneurysm, vessel wall MRI

Motivation: Unruptured intracranial aneurysm (UIA) with wall enhancement identified on vessel wall MRI was considered at high risk of rupture and growth. But previous longitudinal studies were limited by small sample size (n<130).

Goal(s): To evaluate whether wall enhancement can predict UIA growth or rupture in a large-scale multi-center longitudinal study.

Approach: 709 UIA patients were followed by 2 years. Growth or rupture was recorded as primary outcome. 

Results: Size ratio, aspect ratio, irregular shape and wall enhancement index were identified as factors of UIA instability. The final model has an AUC of 0.89, which was superior to traditional risk models (AUC 0.67-0.70, p<0.001).

Impact: To our best knowledge, this is the largest longitudinal study using vessel wall MRI to predict the natural risk of UIA rupture and growth. The model can potentially help select small but high-risk UIAs for early intervention.

Keywords: Blood Vessels, Blood vessels

Motivation: Vessel size imaging, which provides a measure for the vessel radius, is usually performed by injection of contrast agent. Venous vessel radius imaging is also possible by exploiting hypercapnia and hyperoxia. However, these respiratory challenges need external devices such as special masks and monitors.

Goal(s): The question would be if we could measure vessel size wihtout contrast agent in a simple setup.

Approach: In this study, we employ a breath-hold task that doesn’t need external devices to mimic hypercapnia for the measurement of venous vessel size.

Results: Mean venous vessel radii in GM and WM are 11.5±3 and 8.3±2 µm from initial tests.

Impact: Mean venous vessel radii during hypercapnia were 7.3±0.3 µm in GM and 6.6±0.5 µm in WM, respectively, from a previous study. Our results are close to these parameters. This study presents the feasibility of VSI using a breath-hold task.

Keywords: Blood Vessels, Blood vessels, 5.0-T magnetic resonance angiography

Motivation: Limited studies have scrutinized the capability of MRI in evaluating collateral circulation in Moyamoya Disease (MMD), with 3.0T TOF MRA often lacking the necessary precision.

Goal(s): To systematically compare the effectiveness of 5.0T and 3.0T TOF MRA in depicting the complex vascular networks in MMD patients.

Approach: A retrospective study on 21 MMD patients was performed using both 5.0T and 3.0T MRI systems, focusing on the visibility of moyamoya vessels, leptomeningeal anastomoses, and basal ganglia signal intensity.

Results: The study found that 5.0T MRA significantly outperforms 3.0T in visualizing the fine details of MMD's vascular architecture.

Impact: The introduction of 5.0T MRA into clinical practice could revolutionize the imaging landscape for Moyamoya Disease, offering superior diagnostic clarity and aiding in the precise evaluation of cerebrovascular collateral networks, which is critical for surgical planning and patient prognosis.

Keywords: Vessel Wall, Atherosclerosis

Motivation: Whole brain vessel wall imaging (VWI) of isotropic 0.4 mm³ on 3T can’t utilize higher than 5-fold acceleration to reduce the scan time due to insufficient signal-to-noise.

Goal(s): To achieve 10-fold accelerated whole brain VWI of isotropic 0.4 mm³ on the 5T scanner with a 48-channel transmit receive head coil.

Approach: Deep learning (DL) reconstruction equipped with 3D convolution neural network was developed to alleviate the nonuniform noise amplified by SPIRiT reconstruction and the B1 inhomogeneity of 5T scanner.

Results: The proposed DL SPIRiT reconstruction achieves 10-fold accelerated intracranial VWI scan on 5T in 6 minutes and give better VWI quality than 3T.

Impact: This work develops a 10-fold accelerated whole brain vessel wall imaging of isotropic 0.4 mm³ in 6 minutes using deep learning (DL) unrolled SPIRiT reconstruction on the 5T scanner equipped with a 48-channel transmit receive head coil.

Keywords: Vascular, Cardiovascular, vessel compliance, white matter, laminar, deep white matter

Motivation: Compliance of the cerebral microvasculature is critical for brain hemodynamics but remains challenging to measure due to the complex cerebral vascular architecture and limitations in imaging technology.

Goal(s): This study aims to utilize high-resolution VASO MRI across cardiac cycles to quantify microvascular compliance at 7T.

Approach: Vascular compliance (VC) was defined as the ratio of CBV changes to changes in blood pressure across a cardiac cycle, which was proportional to the change in rCBV.

Results: The middle layer of grey matter exhibits lower VC than superficial and deep layers. While higher VC was observed in the white matter (WM), especially deep WM.

Impact: The proposed high-resolution VASO MRI offers a promising noninvasive method for estimating cerebral microvascular compliance.

Keywords: Blood Vessels, Blood vessels

Motivation: In vivo imaging of intra-cortical vessels of human brain, including penetrating arteries, veins and capillary density are still scarce.

Goal(s): To reconstruct the in vivo intra-cortical vessels of the human brain and estimate the cortical layer-specific changes in susceptibility (χ) in the presence of superparamagnetic iron oxides.

Approach: With aid of Ferumoxytol at 7T, high resolution gradient echo imaging was implemented to reconstruct pre-/post-SWI, R2* and χ maps.

Results: Intra-cortical penetrating arteries and veins can be differentiated by pre- and post-contrast SWI. Changes in R2* and χ revealed variations reflective of capillary density across different layers, which is in agreement with histological findings.

Impact: This study provides in vivo imaging characterization of intra-cortical vessels of human brain using high-resolution Ferumoxytol-enhanced SWI at 7T. Utilizing changes in R2* and χ enables us delve deeper into the laminar distribution of capillary density across various cortical layers.