gho Zun

CBF measurements using multidelay pseudocontinuous and velocity‐selective arterial spin labeling in patients with long arterial transit delays: Comparison with xenon CT CBF

To test the theory that velocity‐selective arterial spin labeling (VSASL) is insensitive to transit delay.

Comparison of R2′ measurement methods in the normal brain at 3 tesla

R2′, the reversible component of transverse relaxation, is an important susceptibility measurement for studies of brain physiology and pathologies. In existing literature, different R2′ measurement methods are used with assumption of equivalency. This study explores the choice of measurement method in healthy, young subjects at 3T.

Pseudocontinuous arterial spin labeling with prospective motion correction (PCASL-PROMO).

Arterial spin labeling (ASL) perfusion imaging with a segmented three‐dimensional (3D) readout is becoming increasing popular, yet conventional motion correction approaches cannot be applied in segmented imaging. The purpose of this study was to demonstrate the integration of 3D pseudocontinuous ASL (PCASL) and PROMO (PROspective MOtion correction) for cerebral blood flow measurements.

Non-Invasive Placental Perfusion Imaging in Pregnancies Complicated by Fetal Heart Disease Using Velocity-Selective Arterial Spin Labeled MRI.

The placenta is a vital organ for fetal growth and development during pregnancy. Congenital heart disease (CHD) is a leading cause of morbidity and mortality in newborns. Despite the parallel development of the placenta and fetal heart early in pregnancy, very few studies suggested an association between placental dysfunction and fetal CHD. In this study, we report placental perfusion of healthy pregnancies and pregnancies complicated by fetal CHD measured using advanced fetal MRI techniques. We studied forty-eight pregnant women (31 healthy volunteers and 17 with fetal CHD) that underwent fetal MRI during their second or third trimester of pregnancy. Placental perfusion imaging was performed using velocity-selective arterial spin labeling (VSASL) and 3D image acquisition with whole-placenta coverage. In pregnancies with fetal CHD, global placental perfusion significantly decreased and regional variation of placental perfusion significantly increased with advancing gestational age; however, no such correlation was found in healthy pregnancies. Also, global placental perfusion was significantly higher in fetal CHD versus controls, in the lateral side-lying patient position versus supine, and in the posterior placental position versus anterior placental position. This study reports for the first time non-invasive whole-placenta perfusion imaging in utero. These data suggest that placental VSASL may serve as a potential biomarker of placental dysfunction in fetuses diagnosed with CHD.

Near-contiguous spin echo imaging using matched-phase RF and its application in velocity-selective arterial spin labeling

The minimum slice spacing in multislice imaging is limited by inter‐slice crosstalk due to an imperfect slice profile. This study sought to minimize the slice spacing using matched‐phase RF pulses and demonstrate its application in cerebral blood flow imaging using velocity‐selective arterial spin labeling.

Imaging of cerebrovascular reserve and oxygenation in Moyamoya disease

This study aimed to determine whether measurements of cerebrovascular reserve and oxygenation, assessed with spin relaxation rate R2′, yield similar information about pathology in pre-operative Moyamoya disease patients, and to assess whether R2′ is a better measure of oxygenation than other proposed markers, such as R2* and R2. Twenty-five pre-operative Moyamoya disease patients were scanned at 3.0T with acetazolamide challenge. Cerebral blood flow mapping with multi-delay arterial spin labeling, and R2*, R2, and R2′ mapping with Gradient-Echo Sampling of Free Induction Decay and Echo were performed. No baseline cerebral blood flow difference was found between angiographically abnormal and normal regions (49 ± 12 vs. 48 ± 11 mL/100 g/min, p = 0.44). However, baseline R2′ differed between these regions (3.2 ± 0.7 vs. 2.9 ± 0.6 s−1, p < 0.001), indicating reduced oxygenation in abnormal regions. Cerebrovascular reserve was lower in angiographically abnormal regions (21 ± 38 vs. 41 ± 26%, p = 0.001). All regions showed trend toward significantly improved oxygenation post-acetazolamide. Regions with poorer cerebrovascular reserve had lower baseline oxygenation (Kendalls τ = −0.24, p = 0.003). A number of angiographically abnormal regions demonstrated preserved cerebrovascular reserve, likely due to the presence of collaterals. Finally, of the concurrently measured relaxation rates, R2′ was superior for oxygenation assessment.

Robust preprocessing for stimulus-based functional MRI of the moving fetus

Abstract. Fetal motion manifests as signal degradation and image artifact in the acquired time series of blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) studies. We present a robust preprocessing pipeline to specifically address fetal and placental motion-induced artifacts in stimulus-based fMRI with slowly cycled block design in the living fetus. In the proposed pipeline, motion correction is optimized to the experimental paradigm, and it is performed separately in each phase as well as in each region of interest (ROI), recognizing that each phase and organ experiences different types of motion. To obtain the averaged BOLD signals for each ROI, both misaligned volumes and noisy voxels are automatically detected and excluded, and the missing data are then imputed by statistical estimation based on local polynomial smoothing. Our experimental results demonstrate that the proposed pipeline was effective in mitigating the motion-induced artifacts in stimulus-based fMRI data of the fetal brain and placenta.

Improved multislice perfusion imaging with velocity‐selective arterial spin labeling

To improve the multislice performance of velocity‐selective arterial spin labeling (VS‐ASL) imaging for cerebral blood flow (CBF) measurement such that it might be routinely applied for clinical applications with whole brain coverage.

Comparing accuracy and reproducibility of sequential and Hadamard-encoded multidelay pseudocontinuous arterial spin labeling for measuring cerebral blood flow and arterial transit time in healthy subjects: A simulation and in vivo study

To compare performance of sequential and Hadamard‐encoded pseudocontinuous arterial spin labeling (PCASL).

Semi-automatic segmentation of the placenta into fetal and maternal compartments using intravoxel incoherent motion MRI

Intravoxel incoherent motion (IVIM) magnetic resonance imaging is an emerging non-invasive technique that has been recently applied to quantify in vivo global placental perfusion. We propose a robust semi-automated method for segmenting the placenta into fetal and maternal compartments from IVIM data, using a multi-label image segmentation algorithm called ‘GrowCut’. Placental IVIM data were acquired on a 1.5T scanner from 16 healthy pregnant women between 21-37 gestational weeks. The voxel-wise perfusion fraction was then estimated after non-rigid image registration. The seed regions of the fetal and maternal compartments were determined using structural T2-weighted reference images, and improved progressively through an iterative process of the GrowCut algorithm to accurately encompass fetal and maternal compartments. We demonstrated that the placental perfusion fraction decreased in both fetal (-0.010/week) and maternal compartments (-0.013/week) while their relative difference (ffetal-fmaternal) gradually increased with advancing gestational age (+0.003/week, p=0.065). Our preliminary results show that the proposed method was effective in distinguishing placental compartments using IVIM.