Blood Flow Maps Research Articles

NIMG-24HIGH SPATIOTEMPORAL DYNAMIC SUSCEPTIBILITY CONTRAST (DSC) PERFUSION MRI USING MULTIBAND ECHOPLANAR IMAGING (MB-EPI)

NIMG-24. HIGH SPATIOTEMPORAL DYNAMIC SUSCEPTIBILITY CONTRAST (DSC) PERFUSION MRI USING MULTIBAND ECHOPLANAR IMAGING (MB-EPI) Benjamin Ellingson, Kevin Leu, Whitney Pope, Albert Lai, Phioanh Nghiemphu, Linda Liau, and Timothy Cloughesy; University of California Los Angeles, Los Angeles, CA, USA BACKGROUND: Dynamic susceptibility contrast (DSC)-MRI is a commonlyusedperfusion imaging techniqueused toassessbrain tumorvascularity and angiogenesis by estimation of relative cerebral blood volume (rCBV). Despite widespread use, technical limitations lead to compromises in terms of resolution, slice coverage, and temporal resolution when acquiring dynamic data using the current single-shot echoplanar (EPI) imaging approach. In the current study we demonstrate the use of a new “multiband” (MB)-EPI sequence for multislice excitation, originally developed for fMRI as part of the Human Connectome Project, to obtain DSC perfusion MRI with whole brain coverage, higher spatial resolution, and twice the temporal resolution of current strategies. METHODS: DSC data collected using standard EPI were compared with DSC obtained using MB-EPI in 20 prospective GBM patients. Standard DSC-MRI were collected on conventional 1.5T or 3T MR scanners using a temporal resolution of 1250-1900ms, matrix size 1⁄4 96x96–128x128, and 5-20 slices with 5mm slice thickness. High spatiotemporalDSC-MRI datawere collectedona3TSiemensPrismawith temporal resolution of 600-750ms, matrix size 1⁄4 100x100–200x200, and 30-32 slices with 4mm slice thickness. Both DSC-MRI datasets were post-processed using standard leakage correction and deconvolution techniques to calculate rCBV and rCBF. RESULTS: Data collected using standard and MB-EPI showed similar dynamic contrast-to-noise, although MB-EPI showed more T1-weighting and leakage effects. RCBV maps obtained using both techniques provided similar information regarding the extent of hypervascularity within the tumor after leakage correction; however, rCBV maps calculated from MB-EPI data had more brain coverage and higher spatial resolution. Parametric maps of blood flow differed slightly due to higher temporal resolution MB-EPI data. CONCLUSION: High spatiotemporal DSC perfusion MRI is desirable and clinically feasible using MB-EPI. DSC using MB-EPI provides comparablequantitativedataand dataqualitywith betteraccuracyandspatial resolution. Neuro-Oncology 17:v153–v171, 2015. doi:10.1093/neuonc/nov225.24 Published by Oxford University Press on behalf of the Society for Neuro-Oncology 2015.

Inter-Slice Blood Flow and Magnetization Transfer Effects as A New Simultaneous Imaging Strategy.

The recent blood flow and magnetization transfer (MT) technique termed alternate ascending/descending directional navigation (ALADDIN) achieves the contrast using interslice blood flow and MT effects with no separate preparation RF pulse, thereby potentially overcoming limitations of conventional methods. In this study, we examined the signal characteristics of ALADDIN as a simultaneous blood flow and MT imaging strategy, by comparing it with pseudo-continuous ASL (pCASL) and conventional MT asymmetry (MTA) methods, all of which had the same bSSFP readout. Bloch-equation simulations and experiments showed ALADDIN perfusion signals increased with flip angle, whereas MTA signals peaked at flip angle around 45°−60°. ALADDIN provided signals comparable to those of pCASL and conventional MTA methods emulating the first, second, and third prior slices of ALADDIN under the same scan conditions, suggesting ALADDIN signals to be superposition of signals from multiple labeling planes. The quantitative cerebral blood flow signals from a modified continuous ASL model overestimated the perfusion signals compared to those measured with a pulsed ASL method. Simultaneous mapping of blood flow, MTA, and MT ratio in the whole brain is feasible with ALADDIN within a clinically reasonable time, which can potentially help diagnosis of various diseases.

Quantitative Assessment of Foot Blood Flow by Using Dynamic Volume Perfusion CT Technique: A Feasibility Study.

To demonstrate the feasibility of foot blood flow measurement by using dynamic volume perfusion computed tomographic (CT) technique with the upslope method in an animal experiment and a human study. The human study was approved by the institutional review board, and written informed consent was obtained from all patients. The animal study was approved by the research animal care and use committee. A perfusion CT experiment was first performed by using rabbits. A color-coded perfusion map was reconstructed by using in-house perfusion analysis software based on the upslope method, and the measured blood flow on the map was compared with the reference standard microsphere method by using correlation analysis. A total of 17 perfusion CT sessions were then performed (a) once in five human patients and (b) twice (before and after endovascular revascularization) in six human patients. Perfusion maps of blood flow were reconstructed and analyzed. The Wilcoxon signed rank test was used to prove significant differences in blood flow before and after treatment. The animal experiment demonstrated a strong correlation (R(2) = 0.965) in blood flow between perfusion CT and the microsphere method. Perfusion maps were obtained successfully in 16 human clinical sessions (94%) with the use of 32 mL of contrast medium and an effective radiation dose of 0.31 mSv (k factor for the ankle, 0.0002). The plantar dermis showed the highest blood flow among all anatomic structures of the foot, including muscle, subcutaneous tissue, tendon, and bone. After a successful revascularization procedure, the blood flow of the plantar dermis increased by 153% (P = .031). The interpretations of the color-coded perfusion map correlated well with the clinical and angiographic findings. Perfusion CT could be used to measure foot blood flow in both animals and humans. It can be a useful modality for the diagnosis of peripheral arterial disease by providing quantitative information on foot perfusion status.

Epidermal devices for noninvasive, precise, and continuous mapping of macrovascular and microvascular blood flow.

Continuous monitoring of variations in blood flow is vital in assessing the status of microvascular and macrovascular beds for a wide range of clinical and research scenarios. Although a variety of techniques exist, most require complete immobilization of the subject, thereby limiting their utility to hospital or clinical settings. Those that can be rendered in wearable formats suffer from limited accuracy, motion artifacts, and other shortcomings that follow from an inability to achieve intimate, noninvasive mechanical linkage of sensors with the surface of the skin. We introduce an ultrathin, soft, skin-conforming sensor technology that offers advanced capabilities in continuous and precise blood flow mapping. Systematic work establishes a set of experimental procedures and theoretical models for quantitative measurements and guidelines in design and operation. Experimental studies on human subjects, including validation with measurements performed using state-of-the-art clinical techniques, demonstrate sensitive and accurate assessment of both macrovascular and microvascular flow under a range of physiological conditions. Refined operational modes eliminate long-term drifts and reduce power consumption, thereby providing steps toward the use of this technology for continuous monitoring during daily activities.

Accuracy of arterial spin labeling magnetic resonance imaging (MRI) perfusion in detecting the epileptogenic zone in patients with drug‐resistant neocortical epilepsy: comparison with electrophysiological data, structural MRI, SISCOM and FDG‐PET

Locating the epileptogenic zone (EZ) in patients with neocortical epilepsy presents major challenges. Our aim was to assess the accuracy of arterial spin labeling (ASL), an emerging non-invasive magnetic resonance imaging (MRI) perfusion technique, to locate the EZ in patients with drug-resistant neocortical epilepsy. Twenty-five consecutive patients with neocortical epilepsy referred to our epilepsy unit for pre-surgical evaluation underwent a standardized assessment including video-electroencephalography (EEG) monitoring, structural MRI, subtraction ictal single-photon emission computed tomography co-registered to MRI (SISCOM) and fluorodeoxyglucose positron emission tomography (FDG-PET) studies. An ASL sequence was included in the MRI studies. Areas of hypoperfusion or hyperperfusion on ASL were classified into 15 anatomic-functional cortical regions; these regional cerebral blood flow maps were compared with the EZ determined by the other tests and the strength of concordance was assessed with the kappa coefficient. Of the 25 patients [16 (64%) women; mean age 32.4 (±13.8) years], 18 (72%) had lesions on structural MRI. ASL abnormalities were seen in 15 (60%) patients (nine hypoperfusion, six hyperperfusion). ASL had a very good concordance with FDG-PET (k = 0.84), a good concordance with structural MRI (k = 0.76), a moderate concordance with video-EEG monitoring (k = 0.53) and a fair concordance with SISCOM (k = 0.28). Arterial spin labeling might help to confirm the location and extent of the EZ in the pre-surgical workup of patients with drug-resistant neocortical epilepsy.

Early changes in perfusion of glioblastoma during radio- and chemotherapy evaluated by T1-dynamic contrast enhanced magnetic resonance imaging

ABSTRACTBackground. The survival times of patients with glioblastoma differ widely and biomarkers that would enable individualized treatment are needed. The objective of this study was to measure changes in the vascular physiology of tumor using T1-dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) in patients with glioblastoma during early stages of radio- and chemotherapy (Tx) and explore possible correlations with treatment outcomes.Material and methods. An exploratory prospective study was planned. Patients underwent DCE-MRI at baseline, after approximately one and six weeks of Tx and three and six months post-Tx. DCE-MRI at three Tesla generated maps of blood flow (BF), blood volume (BV), permeability (Ki) and volume of distribution (Vd) using a combination of model-free deconvolution and Patlak plots. Regions of interest in contrast enhancing tumor and in normal appearing white matter were contoured. Progression-free survival (PFS) was the primary clinical outcome. Patients with PFS > 6 months were compared with those with PFS < 6 months. Parameters of vascular physiology and changes in these during Tx were compared for these two groups at all time points using non-parametric statistics.Results. Eleven eligible patients were included and 46 DCE-MRI examinations were carried out. BF in tumor increased for all patients early during Tx (p = 0.005) and then fell to a level below baseline at post-Tx examinations (p = 0.016). A similar but non-significant trend was seen for tumor BV. There was no detectable difference between patients with PFS > 6 months versus PFS < 6 months with regards to baseline values or changes during and after Tx.Conclusions. Although no correlations to outcomes were found, the results of this exploratory study may be hypothesis generating and will be examined in a larger patient group.

Influence of Recanalization and Time of Cerebral Ischemia on Tissue Outcome after Endovascular Stroke Treatment on Computed Tomography Perfusion

The Alberta Stroke Program Early Computed Tomography Score (ASPECTS) has been proposed as a straightforward alternative to the less reliable visual estimation of tissue at risk. We evaluated the association between admission ASPECTS on computed tomography perfusion (CTP) parameter maps and final infarct ASPECTS in patients with acute ischemic stroke who were treated by endovascular therapy (eT) and compared the results with thrombolysis candidates treated conservatively. eT was performed in 26 consecutive ischemic stroke patients within 6 hours of symptom onset. The control group was matched for age and admission National Institutes of Health Stroke Scale having the same admission imaging protocol and a transcranial Doppler sonography within 24 hours. ASPECTS determined from CTP maps of cerebral blood flow (CBF), cerebral blood volume (CBV), and time to peak (TTP) were compared with final infarct ASPECTS on day 5 noncontrast CT. Recanalization rate was 73% in treatment and 50% in control group. ASPECTS for all CTP parameters were significantly lower than ASPECTS-CT in both groups (P < .005). In the treatment group, this applied to patients with successful recanalization. Only controls without recanalization showed a strong correlation between ASPECTS-CTP parameters and ASPECTS-CT (CBV: P = .005; CBF and TTP: P = .028). Patients with early recanalization (≤4 hours) had greater differences between ASPECTS-CTP and ASPECTS-CT than patients with late recanalization (>4 hours; CBF: P = .056; CBV: P = .095; TTP: P = .048). The initial ASPECTS-CTP lesion was significantly larger than the final infarct determined by ASPECTS in case of recanalization. Initial perfusion lesion, including CBV, is reversible in case of reperfusion, especially in early reperfusion.

From Time is brain to Physiology is brain: a case for reflection in acute stroke treatment decisions.

This scientific commentary refers to ‘Perfusion computed tomography to assist decision making for stroke thrombolysis’, by Bivard et al. (doi:10.1093/brain/awv071). The ischaemic penumbra, defined as severely hypoperfused, functionally impaired yet salvageable tissue, has been established as the key target for acute stroke therapy for more than three decades (Muir et al. , 2006). However, the penumbra has a limited lifespan and, unless reperfused early, it progresses to become part of the irreversibly damaged tissue referred to as the ‘core’. The core therefore grows over time, incorporating first the most hypoperfused portions of the penumbra, and then progressively less hypoperfused portions, until none remains. How fast this process occurs varies greatly from subject to subject, mainly because of variable pial collaterals and the occurrence of spontaneous reperfusion (Fig. 1). On a mechanistic basis, reperfusion therapy—such as with intravenous thrombolysis using recombinant tissue plasminogen activator (rt-PA)—would be expected to be of no benefit, and potentially harmful, in cases with large core or no penumbra (Marchal et al. , 1993). Figure 1 The three main pathophysiological profiles used by Bivard et al. to categorize acute stroke patients, as originally defined using PET with 15oxygen-labelled compounds to generate quantitative maps of cerebral blood flow (CBF, left column ) and the cerebral oxygen metabolic rate (CMRO2, right ). Validated tissue compartments including penumbra (reduced cerebral blood flow but relatively preserved CMRO2) and core (markedly reduced CMRO2) were used to characterize the three profiles of ‘target mismatch', ‘large core' and ‘no mismatch' (Muir et al. , 2006). Consistent with the strikingly distinct spontaneous outcomes associated with these profiles (Marchal et al. , 1993), Bivard et al. provide evidence from their cohort that the target mismatch group, i.e. patients with significant penumbral tissue and a small core, benefit the most from intravenous …

Editorial: the ischemic penumbra: still the target for stroke therapies?

Editorial: the ischemic penumbra: still the target for stroke therapies?

Arterial Spin-Labeling Parameters Influence Signal Variability and Estimated Regional Relative Cerebral Blood Flow in Normal Aging and Mild Cognitive Impairment: FAIR versus PICORE Techniques.

Arterial spin-labeling is a noninvasive method to map cerebral blood flow, which might be useful for early diagnosis of neurodegenerative diseases. We directly compared 2 arterial spin-labeling techniques in healthy elderly controls and individuals with mild cognitive impairment. This prospective study was approved by the local ethics committee and included 198 consecutive healthy controls (mean age, 73.65 ± 4.02 years) and 43 subjects with mild cognitive impairment (mean age, 73.38 ± 5.85 years). Two pulsed arterial spin-labeling sequences were performed at 3T: proximal inversion with a control for off-resonance effects (PICORE) and flow-sensitive alternating inversion recovery technique (FAIR). Relative cerebral blood flow maps were calculated by using commercial software and standard parameters. Data analysis included spatial normalization of gray matter-corrected relative CBF maps, whole-brain average, and voxelwise comparison of both arterial spin-labeling sequences. Overall, FAIR yielded higher relative CBF values compared with PICORE (controls, 32.7 ± 7.1 versus 30.0 ± 13.1 mL/min/100 g, P = .05; mild cognitive impairment, 29.8 ± 5.4 versus 26.2 ± 8.6 mL/min/100 g, P < .05; all, 32.2 ± 6.8 versus 29.3 ± 12.3 mL/min/100 g, P < .05). FAIR had lower variability (controls, 36.2% versus 68.8%, P < .00001; mild cognitive impairment, 18.9% versus 22.9%, P < .0001; all, 34.4% versus 64.9% P < .00001). The detailed voxelwise analysis revealed a higher signal for FAIR, notably in both convexities, while PICORE had higher signal predominantly in deep cerebral regions. Overall, FAIR had higher estimated relative CBF and lower interindividual variability than PICORE. In more detail, there were regional differences between both arterial spin-labeling sequences. In summary, these results highlight the need to calibrate arterial spin-labeling sequences.

Histogram analysis of laser speckle contrast image for cerebral blood flow monitoring

Laser speckle contrast imaging (LSCI) is a powerful tool for blood flow mapping. In this paper, we described a simple algorithm based on histogram analysis of laser speckle contrast image to provide rapid differentiation between macro- and microcirculations. The algorithm was successfully verified by the study of blood flow in rat cortex under functional activation.

The role of transvaginal power Doppler ultrasound in the differential diagnosis of benign intrauterine focal lesions

The purpose of this prospective study was to assess the role of power Doppler imaging in the differential diagnosis of benign intrauterine focal lesions such as endometrial polyps and submucous myomas using the characteristics of power Doppler flow mapping. A total of 480 premenopausal patients with abnormal uterine bleeding were evaluated by transvaginal ultrasonography (TVS) searching for intrauterine pathology. Sixty-four patients with a suspicious focal endometrial lesion received saline infusion sonography (SIS) after TVS. Fifty-eight patients with focal endometrial lesions underwent power Doppler ultrasound (PDUS). Three different vascular flow patterns were defined: Single vessel pattern, multiple vessel pattern, and circular flow pattern. Finally, hysteroscopic resection was performed in all cases, and Doppler flow characteristics were then compared with the final histopathological findings. Histopathological results were as follows: endometrial polyp: 40 (69 %), submucous myoma: 18 (31 %). Of the cases with endometrial polyps, 80 % demonstrated a single vessel pattern, 7.5 % a multiple vessel pattern, and 0 % a circular pattern. Vascularization was not observed in 12.5 % of patients with polyps. Of the cases with submucousal myomas, 72.2 % demonstrated a circular flow pattern, 27.8 % a multiple vessel pattern, and none of them showed a single vessel pattern. The sensitivity, specificity, and positive and negative predictive values of the single vessel pattern in diagnosing endometrial polyps were 80, 100, 100, and 69.2 %, respectively; and for the circular pattern in diagnosing submucous myoma, these were 72.2, 100, 100, and 88.9 %, respectively. Power Doppler blood flow mapping is a useful, practical, and noninvasive diagnostic method for the differential diagnosis of benign intrauterine focal lesions. Especially in cases of recurrent abnormal uterine bleeding, recurrent abortion, and infertility, PDUS can be preferred as a first-line diagnostic method.

Adaptation of local muscle blood flow and surface electromyography to repeated bouts of eccentric exercise.

The aim of this randomized controlled crossover study was to investigate the effect of a bout of unaccustomed eccentric exercise (ECC) followed by a consecutive bout of the same intensity on local muscle blood flow, amplitude, and frequency of the electromyographic (EMG) signal from the exercised tibialis anterior muscle. Sixteen healthy male participants (age, 25.7 (0.6) years; body mass index 24.8 (1) kg·m(-2) participated in this study. Two identical bouts of high-intensity ECC were performed on the tibialis anterior muscle 7 days apart. Control sessions involving no exercise were performed 4 weeks either before or after the exercise sessions. Changes in local total blood flow [ΔtHb], EMG root mean square, and median power frequency were recorded during isometric maximum voluntary contraction of ankle dorsiflexion. Measurements were performed before, immediately after, and the day after both ECCs (ECC1 and ECC2). The participants rested quietly in a chair in the control session. Eccentric exercise 1 led to a significant decrease in [ΔtHb] on the day after (p ≤ 0.05), whereas ECC2 did not. Median power frequency decreased significantly in ECC2 compared with ECC1 (p < 0.01). Root mean square was unchanged in all the instants. The present study showed that adaptation is depicted in the local muscle blood flow and the frequency contents of the EMG after an unaccustomed ECC inducing muscle soreness. These alterations provide a potential mechanism for a rapid adaptation, which decreases susceptibility of the muscle to develop further soreness in the subsequent ECC bout.

Image‐based Characterization of Functional and Structural Heterogeneity of Tumor Xenografts using Blood Flow modeling, Oxygenation Modeling and Multivariate Analysis

Tumor-associated angiogenesis is an indispensable factor for the progression of solid tumors beyond a minimal size (1-2 mm3). The unprecedented advances in automated microscopic imaging allow the accurate 3D visualization of the morphology of individual vessels in tumors and the description of their function. We have combined high-resolution imaging with blood flow and oxygenation modeling to produce maps of blood flow and oxygen distribution across the vascular and extravascular areas of tumor xenografts. Such development can be crucial to address the complex dynamics of the distribution of hypoxic regions across the tumor, and provide insights for their correlation with tumor vasculature structural properties. Since, many of the metrics we calculate are correlated; we employ a statistical methodology to describe all the metrics variability with respect to a reduced number of factors. The multidimensional analysis we are proposing provides a framework where hypotheses about drug delivery strategies among different tumors can be tested in an efficient and inexpensive manner.

Consider ultrasound first for imaging the female pelvis

Ultrasound technology has evolved dramatically in recent years and now includes applications such as 3-dimensional volume imaging, real-time evaluation of pelvic organs (simultaneous with the physical examination), and Doppler blood flow mapping without the need for contrast, which makes ultrasound imaging unique for imaging the female pelvis. Among the many cross-sectional imaging techniques, we should use the most informative, less invasive, and less expensive modality to avoid radiation when possible. Hence, ultrasound imaging should be the first imaging modality used in women with pelvic symptoms.

Thermal imaging of the skin blood flow oscillations in extremities: modification of the spectral components

Objective. The aim of the study was description of the method of skin blood flow imaging via spectral processing of the dynamic thermograms of extremities. Materials and methods. The method realized by decomposition of the temperature signal into spectral components, modification of the spectral components and inverse transform of the spectral components into a new signal, which is considered as blood flow. Modification of spectral components was accomplished taking into account skin properties, and intended for the compensation of attenuation and time lag of temperature spectral components relative to blood flow components. Results. Blood flow maps of hands during arm cuff test have been demonstrated. Blood flow values calculated from the dynamic thermogram have been validated by photoplethysmography. The technique allows restoring of the blood flow oscillations at any point of the thermogram of the object. Benefits of thermal imaging of blood flow are the following: results are not depended from the ambient light, the method not critical to the camera angle, and blood flow maps can be registered both from the whole body and small areas. The method of blood flow imaging, in a long view, applicable for the monitoring of the skin microcirculation in progression and treatment of diabetic foot syndrome, Raynaud's syndrome, as well as burn, frostbite, mechanical injury, and atherosclerosis.

Simultaneous multi-slice Turbo-FLASH imaging with CAIPIRINHA for whole brain distortion-free pseudo-continuous arterial spin labeling at 3 and 7 T

Simultaneous multi-slice (SMS) or multiband (MB) imaging has recently been attempted for arterial spin labeled (ASL) perfusion MRI in conjunction with echo-planar imaging (EPI) readout. It was found that SMS-EPI can reduce the T1 relaxation effect of the label and improve image coverage and resolution with little penalty in signal-to-noise ratio (SNR). However, EPI still suffers from geometric distortion and signal dropout from field inhomogeneity effects especially at high and ultrahigh magnetic fields. Here we present a novel scheme for achieving high fidelity distortion-free quantitative perfusion imaging by combining pseudo-continuous ASL (pCASL) with SMS Turbo-FLASH (TFL) readout at both 3 and 7T. Bloch equation simulation was performed to characterize and optimize the TFL-based pCASL perfusion signal. Two MB factors (3 and 5) were implemented in SMS-TFL pCASL and compared with standard 2D TFL and EPI pCASL sequences. The temporal SNR of SMS-TFL pCASL relative to that of standard TFL pCASL was 0.76±0.10 and 0.74±0.11 at 7T and 0.70±0.05 and 0.65±0.05 at 3T for MB factor of 3 and 5, respectively. By implementing background suppression in conjunction with SMS-TFL at 3T, the relative temporal SNR improved to 0.84±0.09 and 0.79±0.10 for MB factor of 3 and 5, respectively. Compared to EPI pCASL, significantly increased temporal SNR (p<0.001) and improved visualization of orbitofrontal cortex were achieved using SMS-TFL pCASL. By combining SMS acceleration with TFL pCASL, we demonstrated the feasibility for whole brain distortion-free quantitative mapping of cerebral blood flow at high and ultrahigh magnetic fields.

Validation of high temporal resolution spiral phase velocity mapping of coronary artery blood flow against Doppler flow wire

Background The temporal pattern of coronary artery flow velocity through the cardiac cycle provides important information about coronary haemodynamics. The ‘gold standard’ for coronary artery velocity assessment is the Doppler flow wire which is inserted directly into the coronary artery under X-ray fluoroscopic guidance, which is invasive, uses ionising radiation and has a small but significant risk of serious complication. In this study, we perform an in vivo comparison of coronary blood flow velocities measured with breath-hold high temporal resolution spiral phase velocity mapping and Doppler flow wire measurements. Methods Breath-hold proximal coronary artery velocity maps were acquired in 5 left anterior descending (LAD) and 3 right coronary arteries (RCAs) in patients who had undergone invasive Doppler flow wire assessment as part of a clinical assessment. Acquisition parameters were: pixel size 1.4 × 1.4 mm (reconstructed to 0.7 ×0 .7 mm) ×8m m, true temporal resolution 19 ms, 1-1 water excitation (WE), 17 cardiac cycle breath-hold, velocity sensitivity 30-50cm/s, retrospective ECG gating (reconstructed 50 phases). Extraction of MR coronary artery blood flow velocitytime curves was performed using a custom MATLAB program which tracked the motion of the vessel over the cardiac cycle and corrected for the through-plane motion of the vessel using a region of adjacent tracked myocardium (LAD) or a region of surrounding epicardial fat (RCA) from a separately acquired fat-excitation acquisition. For each vessel, the mean through-plane motioncorrected MR velocities at all timepoints were plotted against the equivalent flow wire velocities. If necessary, the profiles were first time-shifted to take into account small differences in data triggering between the two techniques. The correlation between the two profiles was assessed using simple linear regression analysis. Results Figures 1 and 2 show example LAD and RCA studies. On average, the MR measured velocities were 66% less than the Flowire velocities (SD 9%, range: 50% - 78%). The correlation between the MR and flow wire data, however, was high, with R 2 values ranging from 0.6 - 0.95 in the 8 vessels studied (mean R 2 = .80).

Abstract 21: Infarct Distributions Differ in Pediatric Sickle Cell Patients With or Without Large Vessel Vasculopathy

Introduction: Children with sickle cell disease (SCD) have a high risk of ischemic strokes in diverse spatial distributions, but mechanisms responsible for these different patterns are unclear. Methods: MRIs and MRAs from 2006-2014 were retrospectively collected on SCD children with an overt stroke history. Hemispheres were categorized based on presence or absence of large vessel vasculopathy (Vsc) on MRA. Manually delineated infarcts on FLAIR were individually co-registered to the corresponding T1 MPRAGE maps, and then co-registered onto a common space. Left and right hemispheres were separated with a mask in the common space. Hemispheres were flipped so all with Vsc were oriented as right hemispheres, and those without Vsc as left. Co-registered infarct maps were warped into the final anatomic space and averaged to create a lesion density map. A cerebral blood flow (CBF) map was created from average pseudocontinuous arterial spin labeled measurements prospectively collected on 7 children with SCD and no Vsc. Results: Of 22 children with SCD and overt stroke history (median 15.5y, 41% male), 14 had Vsc (median 16 y, 50% male) in 19/44 hemispheres. Both non-Vsc and Vsc hemispheres had infarct hot-spots in a predominantly deep white matter watershed distribution, but Vsc hemisphere infarcts were more numerous, more extensive and encompassed more gray matter (Figure). Hot-spots overlapped with regions of lowest flow within the deep white matter on the CBF map. Vsc hemispheres also had infarcts in classic large artery territories, not seen in non-Vsc hemispheres. Conclusions: The etiology of ischemia in SCD is likely multifactorial, involving reduced oxygen delivery (anemia), impaired CBF (Vsc), and possible associated thrombosis (Vsc with low/turbulent flow distal to stenosis). Differential patterns of infarction reflect these different layers of compromise.

Limitations of the use of the MP-RAGE to identify neural changes in the brain: recent cigarette smoking alters gray matter indices in the striatum.

Limitations of the use of the MP-RAGE to identify neural changes in the brain: recent cigarette smoking alters gray matter indices in the striatum.