Continuous Arterial Spin Labeling MRI Research Articles

Lower cerebral vasoreactivity as a predictor of gait speed decline in type 2 diabetes mellitus.

Gait speed is an indicator of overall functional health and is correlated with survival in older adults. We prospectively evaluated the long-term association between cerebral vasoreactivity and gait speed during normal walking (NW) and dual-task walking (DTW) in older adults with and without type 2 diabetes mellitus (T2DM). 40 participants (aged 67.3 ± 8.8 years, 20 with T2DM) completed a 2-year prospective study consisting of MRI, blood sampling, and gait assessments. The whole brain vasoreactivity was quantified using continuous arterial spin labeling MRI. Gait speed during DTW was assessed by subtracting serial sevens. Dual-task cost was calculated as the percent change in gait speed from NW to DTW. In the entire cohort, higher glycemic profiles were associated with a slower gait speed. In the diabetic group, lower vasoreactivity was associated with a slower gait speed during NW ([Formula: see text] = 0.30, p = 0.019) and DTW ([Formula: see text] = 0.35, p = 0.01) and a higher dual-task cost ([Formula: see text] = 0.69, p = 0.009) at 2-year follow-up. The participants with T2DM and lower cerebral vasoreactivity had a greater decrease in gait speed during NW and DTW after the 2-year follow-up ([Formula: see text] = 0.17, p = 0.04 and [Formula: see text] = 0.28, p = 0.03, respectively). Longer diabetes duration was associated with a higher dual-task cost ([Formula: see text] = 0.19, p = 0.04) and a greater decrease in gait speed during NW ([Formula: see text] = 0.17, p = 0.02). These findings indicate that in older adults with type 2 diabetes, gait performance is highly dependent on the integrity of cerebrovascular regulation.

Evaluation of retained products of conception using pulsed continuous arterial spin-labeling MRI: clinical feasibility and initial results.

We evaluated the vascularity of retained products of conception (RPOC) using arterial spin-labeling magnetic resonance imaging (ASL-MRI) to clarify the clinical feasibility of this approach. A pulsed-continuous ASL sequence with echo-planar imaging (EPI) acquisitions was used. Ten consecutive patients with RPOC were enrolled. All ASL images were evaluated visually and semiquantitatively and compared with the findings of Doppler ultrasound (US) and dynamic contrast-enhanced MRI (DCE-MRI). The technical success rate was 93.7% (15/16 scans). One failed case was excluded from the analysis. Six patients showed quite high signals over RPOC, while three patients showed no abnormal signals. Doppler US alone failed to detect the hypervascular area in two cases, and ASL-MRI alone failed in three. A significant linear correlation was found between semiquantitative values of ASL-MRI and DCE-MRI. All six patients showing high signals on ASL-MRI underwent follow-up MRI after therapy. High signals in five patients decreased visually and semiquantitatively, while one patient showed signal increases. Evaluation of RPOC using ASL-MRI was clinically feasible and response to therapy could be evaluated. However, the clinical advantages over conventional imaging remain unclear and need to be evaluated.

Pseudo continuous arterial spin labeling quantification in anemic subjects with hyperemic cerebral blood flow

PurposeTo investigate possible sources of quantification errors in global cerebral blood flow (CBF) measurements by comparing pseudo continuous arterial spin labeling (PCASL) and phase contrast (PC) MRI in anemic, hyperemic subjects. MethodsAll studies were performed on a Philips 3T Achieva MRI scanner. PC and PCASL CBF examinations were performed in 10 healthy, young adult subjects and 18 young adults with chronic anemia syndromes including sickle cell disease and thalassemia. CBF estimates from single and two compartment ASL kinetic models were compared. Numerical simulation and flow phantom experiments were used to explore the effects of blood velocity and B1+ on CBF quantification and labeling efficiency. ResultsPCASL CBF underestimated PC in both populations using a single compartment model (30.1±9.2% control, 45.2±17.2% anemia). Agreement substantially improved using a two-compartment model (−8.0±6.0% control, 11.7±12.3% anemia). Four of the anemic subjects exhibited venous outflow of ASL signal, suggestive of cerebrovascular shunt, possibly confounding PC-PCASL comparisons. Additionally, sub-study experiments demonstrated that B1+ was diminished at the labeling plane (82.9±5.1%), resulting in suboptimal labeling efficiency. Correcting labeling efficiency for diminished B1+, PCASL slightly overestimated PC CBF in controls (−15.4±6.8%) and resulted in better matching of CBF estimates in anemic subjects (0.7±10.0% without outflow, 10.5±9.4% with outflow). ConclusionsThis work demonstrates that a two-compartment model is critical for PCASL quantification in hyperemic subjects. Venous outflow and B1+ under-excitation may also contribute to flow underestimation, but further study of these effects is required.

A comparison study between the saturation-recovery-T1 and CASL MRI methods for quantitative CBF imaging

The saturation-recovery (SR)-T1 MRI method for quantitatively imaging cerebral blood flow (CBF) change (ΔCBF) concurrently with the blood oxygenation level dependence (BOLD) alteration has been recently developed and validated by simultaneous measurement of relative CBF change using laser Doppler flowmetry (LDF) in rats at 9.4T. In this study, ΔCBF induced by mildly transient hypercapnia and measured by the SR-T1 MRI method was rigorously compared with an established perfusion MRI method—continuous arterial spin labeling (CASL) approach in normal and preclinical middle cerebral artery occlusion (MCAo) rat models. The results show an excellent agreement between ΔCBF values measured with these two imaging methods. Moreover, the intrinsic longitudinal relaxation rate (R1int) was experimentally determined in vivo in normal rat brains at 9.4T by comparing two independent measures of the apparent longitudinal relaxation rate (R1app) and CBF measured by the CSAL approach across a wide range of perfusion. In turn, the R1int constant can be employed to calculate the CBF value based on the R1app measurement in healthy brain. This comparison study validates the fundamental relationship for linking brain tissue water R1app and cerebral perfusion, demonstrates the feasibility of imaging and quantifying both CBF and its change using the SR-T1 MRI method in vivo.

Arterial Transit Time-corrected Renal Blood Flow Measurement with Pulsed Continuous Arterial Spin Labeling MR Imaging.

Purpose:The importance of arterial transit time (ATT) correction for arterial spin labeling MRI has been well debated in neuroimaging, but it has not been well evaluated in renal imaging. The purpose of this study was to evaluate the feasibility of pulsed continuous arterial spin labeling (pcASL) MRI with multiple post-labeling delay (PLD) acquisition for measuring ATT-corrected renal blood flow (ATC-RBF).Materials and Methods:A total of 14 volunteers were categorized into younger (n = 8; mean age, 27.0 years) and older groups (n = 6; 64.8 years). Images of pcASL were obtained at three different PLDs (0.5, 1.0, and 1.5 s), and ATC-RBF and ATT were calculated using a single-compartment model. To validate ATC-RBF, a comparative study of effective renal plasma flow (ERPF) measured by 99mTc-MAG3 scintigraphy was performed. ATC-RBF was corrected by kidney volume (ATC-cRBF) for comparison with ERPF.Results:The younger group showed significantly higher ATC-RBF (157.68 ± 38.37 mL/min/100 g) and shorter ATT (961.33 ± 260.87 ms) than the older group (117.42 ± 24.03 mL/min/100 g and 1227.94 ± 226.51 ms, respectively; P < 0.05). A significant correlation was evident between ATC-cRBF and ERPF (P < 0.05, r = 0.47). With suboptimal single PLD (1.5 s) settings, there was no significant correlation between ERPF and kidney volume-corrected RBF calculated from single PLD data.Conclusion:Calculation of ATT and ATC-RBF by pcASL with multiple PLD was feasible in healthy volunteers, and differences in ATT and ATC-RBF were seen between the younger and older groups. Although ATT correction by multiple PLD acquisitions may not always be necessary for RBF quantification in the healthy subjects, the effect of ATT should be taken into account in renal ASL–MRI as debated in brain imaging.

Abstract TP446: Independent Measures of Cerebral Blood Flow in Asymptomatic Carotid Artery Disease.

Background: Cerebral blood flow (CBF) regulation is a critical element in cerebrovascular pathophysiology, particularly in large vessel disease. Different methods to assess hemodynamics may represent different aspects of blood flow regulation, however, uniquely affecting outcomes and management. We examined 4 different blood-flow related measures in patients with high-grade unilateral carotid disease, assessing asymmetry between the occluded vs non-occluded side, and the correlations among the measures. Methods: Thirty-three patients (age 50-93, 19M) with unilateral 80-100% ICA occlusion but no stroke underwent: 1) quantitative resting CBF using continuous arterial spin labeling (CASL) MRI, 2) mean flow velocity (MFV) in both middle cerebral arteries (MCAs) by transcranial Doppler, 3). Vasomotor reactivity (VMR) in response to 2 minutes of 5% CO2 inhalation, and 4) Dynamic cerebral autoregulation (DCA) using continuous insonation of both MCAs for 10 minutes at depth 56mm with a standard head frame. Phase shift (PS) between spontaneous oscillations in blood pressure (measured with finger photoplethysmography) and MCA MFV at frequencies .06-.12 Hz was calculated for each hemisphere using transfer function analysis. Lower PS indicated worse autoregulation. Paired T-tests and Pearson correlations were used to look for side-to-side differences within each measure, and correlations between measures (SPSS v.22). Results: CASL CBF (p=.001), MFV (p&lt;.001), VMR (p=.008), and DCA (p=.047) all showed significantly lower values on the occluded side. The 4 measures were independent of each other on correlation analysis, even when controlling for age and anterior circle of Willis collateral (correlation coefficients all &lt;0.40, p-values &gt;0.09). Conclusions: These 4 measures showed high sensitivity to the occluded carotid artery, but appear to represent independent aspects of cerebral blood flow (CASL: resting gray matter CBF; MFV: whole-hemisphere CBF; VMR: cerebrovascular reserve, and DCA: homeostatic blood flow regulation) suggesting that any given measure only partially characterizes hemodynamic state. Further investigation will use these 4 measures to predict outcomes including vascular cognitive impairment.

Attenuation of functional hyperemia to visual stimulation in mild Alzheimer's disease and its sensitivity to cholinesterase inhibition

Despite the growing recognition of the significance of cerebrovascular impairment in the etiology and progression of Alzheimer's disease (AD), the early stage brain vascular dysfunction and its sensitivity to pharmacological interventions is still not fully characterized. Due to the early and aggressive treatment of probable AD with cholinesterase inhibitors (ChEI), which in and of themselves have direct effects on brain vasculature, the vast majority of hemodynamic measurements in early AD subjects reported hitherto have consequently been made only after the start of treatment, complicating the disentanglement of disease- vs. treatment-related effects on the cerebral vasculature. To address this gap, we used pseudo continuous arterial spin labeling MRI to measure resting perfusion and visual stimulation elicited changes in cerebral blood flow (CBF) and blood oxygenation dependent (BOLD) fMRI signal in a cohort of mild AD patients immediately prior to, 6months post, and 12months post commencement of open label cholinesterase inhibitor treatment. Although patients exhibited no gray matter atrophy prior to treatment and their resting perfusion was not distinguishable from that in age, education and gender-matched controls, the patients' visual stimulation-elicited changes in BOLD fMRI and blood flow were decreased by 10±4% (BOLD) and 23±2% (CBF), relative to those in controls. Induction of cholinesterase inhibition treatment was associated with a further, 7±2% reduction in patients' CBF response to visual stimulation, but it stabilized, at this new lower level, over the follow-up period. Likewise, MMSE scores remained stable during the treatment; furthermore, higher MMSE scores were associated with higher perfusion responses to visual stimulation. This study represents the initial step in disentangling the effects of AD pathology from those of the first line treatment with cholinesterase inhibitors on cerebral hemodynamics and supports the use of arterial spin labeling MRI for quantitative evaluation of the brain vascular function in mild Alzheimer's disease. The findings provide evidence of a pronounced deficit in the visual cortex hyperemia despite the relative sparing of visual function in early stage AD, its reduction with ChEI treatment induction, and its stabilization in the first year of cholinesterase inhibition treatment. This article is part of a Special Issue entitled: Vascular Contributions to Cognitive Impairment and Dementia edited by M. Paul Murphy, Roderick A. Corriveau and Donna M. Wilcock.

Abstract T P181: Static And Dynamic Cerebral Autoregulation Dissociate In Asymptomatic Carotid Artery Disease

Background: High grade internal carotid artery (ICA) disease can alter cerebral autoregulation and thus increase risk for ischemia. We aimed to differentiate two types of autoregulation - dynamic cerebral autoregulation (DCA), thought to be a homeostatic process, and vasomotor reactivity (VMR), which determines cerebrovascular reserve - in patients with asymptomatic ICA stenosis. Methods: Twenty-two patients (age 50-93, 16M) with unilateral 80-100% ICA occlusion but no stroke underwent quantitative CBF measurements using continuous arterial spin labeling (CASL) MRI. DCA was performed by continuous insonation of both middle cerebral arteries with transcranial Doppler for 10 minutes at depth 56mm using a standard head frame. Phase shift (PS) between spontaneous oscillations in blood pressure (measured with finger photoplethysmography (Finapres)) and MCA mean flow velocities (MFV) at frequencies .06-.12 Hz was calculated for each hemisphere using transfer function analysis. Lower degree of PS indicated worse autoregulation (abnormal &lt;24deg1). VMR was determined as a response to 2 minutes of 5% CO2 inhalation (abnormal &lt;2% rise in MCA MFV per mmHg PCO2 by Doppler-integrated inline capnometer (Spencer Technologies)). T-test Chi-square, and multivariable linear regression were used to look for associations between VMR, DCA, and hemispheral CBF (SPSS v.22). Results: MCA MFV (p&lt;.001), VMR (p=.002), and CBF (p&lt;.003), were lower in the ICA occlusion hemisphere. DCA difference approached significance (p=0.064). Controlling for age and anterior circle of Willis collateral cross-filling, DCA (p=0.024), but not VMR (p=0.079) on the occluded side was associated with greater hemispheral CBF asymmetry (F=6.87, p=0.024). VMR and DCA were not correlated (Fisher exact =.61). Conclusions: DCA but not VMR correlated with a low flow state produced by high grade ICA disease in asymptomatic patients. Our results suggest that in ICA stenosis dynamic/homeostatic mechanisms may be affected without substantially altering the static/protective mechanism of cerebrovascular reserve. Ongoing studies will investigate the effect of these two autoregulatory mechanisms on vascular cognitive impairment. 1 Ortega-Gutierrez S, et al. J Neuroimaging. 2014 24:379-86

Slow gait speed - an indicator of lower cerebral vasoreactivity in type 2 diabetes mellitus.

Objective: Gait speed is an important predictor of health that is negatively affected by aging and type 2 diabetes. Diabetes has been linked to reduced vasoreactivity, i.e., the capacity to regulate cerebral blood flow in response to CO2 challenges. This study aimed to determine the relationship between cerebral vasoreactivity and gait speed in older adults with and without diabetes.Research design and methods: We studied 61 adults with diabetes (65 ± 8 years) and 67 without diabetes (67 ± 9 years) but with similar distribution of cardiovascular risk factors. Preferred gait speed was calculated from a 75 m walk. Global and regional perfusion, vasoreactivity and vasodilation reserve were measured using 3-D continuous arterial spin labeling MRI at 3 Tesla during normo-, hyper- and hypocapnia and normalized for end-tidal CO2.Results: Diabetic participants had slower gait speed as compared to non-diabetic participants (1.05 ± 0.15 m/s vs. 1.14 ± 0.14 m/s, p < 0.001). Lower global vasoreactivity (r2adj = 0.13, p = 0.007), or lower global vasodilation reserve (r2adj = 0.33, p < 0.001), was associated with slower walking in the diabetic group independently of age, BMI and hematocrit concentration. For every 1 mL/100 g/min/mmHg less vasodilation reserve, for example, gait speed was 0.05 m/s slower. Similar relationships between vasodilation reserve and gait speed were also observed regionally within the cerebellum, frontal, temporal, parietal, and occipital lobes (r2adj = 0.27–0.33, p < 0.0001). In contrast, vasoreactivity outcomes were not associated with walking speed in non-diabetic participants, despite similar vasoreactivity ranges across groups.Conclusion: In the diabetic group only, lower global vasoreactivity was associated with slower walking speed. Slower walking in older diabetic adults may thus hallmark reduced vasomotor reserve and thus the inability to increase perfusion in response to greater metabolic demands during walking.

Abstract W P170: Hemodynamic Effects in Carotid Occlusion Using Arterial Spin Labeling and Transcranial Doppler

Background: High grade carotid stenosis produces hemodynamic effects on the brain, but the relationship between cerebral autoregulation, absolute CBF and neurovascular coupling has not been well-delineated. Methods: Twelve subjects (age 74±9, 3F) with unilateral ICA stenosis (80-100% occluded) but no infarct (asymptomatic or TIA only) underwent dynamic cerebral autoregulation (DCA) testing with transcranial Doppler by comparing phase shift (PS) of spontaneous oscillations in blood pressure (measured with finger photoplethysmography (Finapres)) versus MCA flow velocities at frequencies .06-.12 Hz using transfer function analysis, lower degree of PS indicating worse autoregulation.Neurovascular coupling was assessed by amplitude of absolute increase in CBF in bilateral Brodman area (BA) 4 during a bilateral repetitive hand closure task using continuous arterial spin labeling (CASL) MRI. Four activation (ON) periods were averaged and subtracted from 4 rest (OFF) periods. Resting CBF for each hemisphere’s motor cortex was determined by averaging the OFF periods. Results: All subjects showed: 1) hemispheric asymmetry in baseline CBF with the occluded side being on average 25mL/100g*min (+/- 14 mL/100g*min) lower than the unoccluded hemisphere. 2) hemispheric asymmetry in motor activation: unoccluded hemisphere average activation (mean_CBF_ON - mean_CBF_OFF) in BA4 was 23.7mL/100g*min, representing a 21% increase in local CBF due to activation; occluded hemisphere mean activation was 14 mL/100g*min, representing 18% percent increase in local CBF. 3) Hemispheric asymmetry in DCA, PS=33.1 deg ± 31 on the occluded side vs. 43.5 deg±23 on the non-occluded side. Both the hemispheral difference in baseline CBF (impaired flow) and the difference in DCA measurement (impaired autoregulation) were good predictors of the lower activation (neurovascular coupling) on the occluded hemisphere: R 2 = 0.85 and 0.80, respectively. Conclusion: Both impaired resting CBF and impaired cerebral autoregulation appear to contribute to decreased neurovascular coupling in carotid artery occlusive disease, representing a potential mechanism for occult neuronal dysfunction such as mild cognitive impairment in this patient population.

Comparison of retinal and cerebral blood flow between continuous arterial spin labeling MRI and fluorescent microsphere techniques

To compare basal retinal and cerebral blood flow (BF) values using continuous arterial spin labeling (CASL) MRI and fluorescent microspheres. A total of 41 animals were used. BF was measured using an established microsphere technique (a mixture of 2.5 million 8 μm green and 0.5 million 10 μm blue fluorescent microspheres) and CASL MRI blood flow measurement in the rat retina and brain at 7 Tesla (T) and 11.7T, respectively. Retinal BF by MRI was 1.18 ± 0.57 mL/g/min and choroidal BF was 8.14 ± 1.8 mL/g/min (n = 6). Microsphere retinal BF was 9.12 ± 2.8 μL/min per tissue and choroidal BF was 73.38 ± 44 μL/min per tissue (n = 18), corresponding to a retinal BF value of 1.22 ± 0.36 mL/g/min by means of a wet weight conversion. The wet-weight of the choroid could not be determined. To corroborate our findings, cerebral BF (CBF) by MRI was also analyzed. In the cerebral cortices, CBF was 0.91 ± 0.29 mL/g/min (n = 14) by CASL MRI and 1.09 ± 0.37 mL/g/min (n = 6) by microspheres. There were no significant differences found between MRI and microsphere blood flow in the retina and brain. BF values in the rat retina and cerebral cortex by MRI are in agreement with those obtained by the microsphere technique.

Sickle cell anemia: reference values of cerebral blood flow determined by continuous arterial spin labeling MRI.

Sickle cell anemia (SCA) is a chronic illness associated with progressive deterioration in patients' quality of life. The major complications of SCA are cerebrovascular accidents (CVA) such as asymptomatic cerebral infarct or overt stroke. The risk of CVA may be related to chronic disturbances in cerebral blood flow (CBF), but the thresholds of "normal" steady-state CBF are not well established. The reference tolerance limits of CBF can be useful to estimate the risk of CVA in asymptomatic children with SCA, who are negative for hyperemia or evidence of arterial narrowing. Continuous arterial spin labeling (CASL) MR perfusion allows for non-invasive quantification of global and regional CBF. To establish such reference tolerance limits we performed CASL MR examinations on a 3-Tesla MR scanner in a carefully selected cohort of 42 children with SCA (mean age, 8.1±3.3 years; range limits, 2.3-14.4 years; 24 females), who were not on chronic transfusion therapy, had no history of overt stroke or transient ischemic attack, were free of signs and symptoms of focal vascular territory ischemic brain injury, did not have intracranial arterial narrowing on MR angiography and were at low risk for stroke as determined by transcranial Doppler ultrasonography.

Hemodynamic effects of cholinesterase inhibition in mild Alzheimer's disease

To evaluate the spatiotemporal progression of perfusion changes in early stages of Alzheimer's disease (AD), we imaged the perfusion response to pharmacological treatment in a group of mild AD patients and contrasted it to the perfusion of age-, sex-, and education-matched healthy volunteers over the same time interval. We used pseudo continuous arterial spin labeling (PCASL) MRI for quantitative three-dimensional mapping of perfusion immediately before and 6 months after cholinesterase inhibitor treatment. Before treatment, patients were found hypoperfused relative to their healthy counterparts in the gray matter of lateral temporal lobe, posterior cingulate, and anterior cingulate as well as in the white matter of the posterior cingulate. Most of the cortical regions investigated and the white matter of posterior cingulate and prefrontal regions showed treatment-elicited increases in perfusion, which were not secondary to changes in regional tissue volume nor were they associated with improvement in either MMSE or ADAS-Cog scores, although lack of deterioration suggested a cognitive benefit. This study provides a hemodynamic profile of mild AD and sheds light on the perfusion changes related to prolonged cholinesterase inhibition in this early disease stage.

Hypertension and Cerebral Vasoreactivity

Hypertension is associated with microvascular and macrovascular brain injury but its direct influence on the cerebral circulation is not fully clear. Our objective was to investigate the association of hypertension with global and regional cerebral vasoreactivity to CO 2 using continuous arterial spin labeling MRI, independent of stroke and white matter hyperintensities. Participants (n=62; mean age: 66.7±1.0 years, 55% women, 84% white, 65% hypertension, 47% stroke) underwent arterial spin labeling perfusion MRI during normal breathing, 5% CO 2 rebreathing, and hyperventilation, as well as 24-hour ambulatory blood pressure monitoring. Vasoreactivity was the slope of the regression between cerebral perfusion and end-tidal CO 2 . White matter hyperintensity volumes were quantified. Nighttime dipping was calculated as the percentage decline in nighttime/daytime blood pressure. After accounting for stroke and white matter hyperintensity volume, hypertensive participants had lower global vasoreactivity (1.11±0.13 versus 0.43±0.1 mL/100 g per minute per millimeter of mercury; P =0.0012). Regionally, this was significant in the frontal, temporal, and parietal lobes. Higher mean systolic blood pressure was associated with lower vasoreactivity (decreased by 0.11 U/10-mm Hg increase in systolic blood pressure; P =0.04), but nighttime dipping was not ( P =0.2). The magnitude of decrease in vasoreactivity in hypertension without stroke was comparable to the magnitude of decrease in vasoreactivity in stroke without hypertension. Hypertension has a direct negative effect on the cerebrovascular circulation independent of white matter hyperintensities and stroke that is comparable to that seen with stroke. Because lower vasoreactivity is associated with poor outcomes, studies of the impact of antihypertensive on vasoreactivity are important.

Corrigendum

CORRIGENDACorrigendumPublished Online:01 Mar 2009https://doi.org/10.1152/ajpheart.zh4-8713-corr.2009MoreSectionsPDF (25 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat Volume 63, May 2008 Wu WC, Wang J, Detre JA, Wehrli FW, Mohler E 3rd, Ratcliffe SJ, Floyd TF. Hyperemic flow heterogeneity within the calf, foot, and forearm measured with continuous arterial spin labeling MRI. Am J Physiol Heart Circ Physiol 294: H2129–H2136, 2008. First published February 29, 2008; doi:10.1152/ajpheart.01399.2007 ( http://ajpheart.physiology.org/cgi/content/full/294/5/H2129).—Due to a spreadsheet layout error, the time-to-peak values shown in Tables 1 and 3 (on p. H2131–H2132) had an offset of one effective repetition time (16 s). The corrected tables are shown below (corrected data displayed in boldface). The correction has no effects on any of the statistical results and text description within the article. Table 1.Calf Muscle GroupnPeak Flow, ml·100 g−1·min−1Mean Hyperemic Flow, ml·100 g−1·min−1Hyperemic Flow Volume, ml/100 gHyperemic Period, sTime To Peak, sDPC19127±4969±2096±3377±2753±11Sol18116±5767±39106±6684±2950±9Gstrc-L1887±3249±2075±4087±2352±13Gstrc-M1985±4349±2575±4880±2952±12AC1986±3353±2272±3376±2550±12LC1775±4743±2564±4979±3250±11Values are means ± SD; n, number of subjects. Flow measurements in the midcalf. Six regions of interest were analyzed: deep posterior compartment (DPC), soleus (Sol), lateral (Gstrc-L) and medial (Gstrc-M) gastrocnemius, and anterior (AC) and lateral (LC) component. Table 3.Muscle GroupnPeak Flow, ml·100 g−1·min−1Mean Hyperemic Flow, ml·100 g−1·min−1Hyperemic Flow Volume, ml/100 gHyperemic Period, sTime To Peak, sFoot D-Ext9117±4466±2394±3985±1546±13 P-Flx9105±46 (0.31)57±20 (0.17)79±49 (0.34)78±23 (0.43)62±5 (0.0085)Forearm F-Flx1572±2246±3356±4175±1033±11 F-Ext15103±37 (0.0013)81±43 (0.0020)91±58 (0.020)66±12 (0.015)33±17 (1.000)Values are means ± SD; n, number of subjects. Values in parentheses are P values from repeated-measures ANOVA. Flow measurements in the foot and forearm. D-Ext, dorsal group; P-Flx, plantar flexor group; F-Flx, forearm flexors; F-Ext, forearm extensors.This article has no references to display. Download PDF Previous Back to Top FiguresReferencesRelatedInformation More from this issue > Volume 296Issue 3March 2009Pages H902-H902 Copyright & PermissionsCopyright © 2009 the American Physiological Societyhttps://doi.org/10.1152/ajpheart.zh4-8713-corr.2009History Published online 1 March 2009 Published in print 1 March 2009 Metrics

Separating function from structure in perfusion imaging of the aging brain

The accuracy of cerebral blood flow (CBF) imaging in humans has been impeded by the partial volume effects (PVE), which are a consequence of the limited spatial resolution. Because of brain atrophy, PVE can be particularly problematic in imaging the elderly and can considerably overestimate the CBF difference with the young. The primary goal of this study was to separate the structural decline from the true CBF reduction in elderly. To this end, a PVE-correction algorithm was applied on the CBF images acquired with spin-echo EPI continuous arterial spin labeling MRI (voxel size = 3.4 x 3.4 x 8 mm(3)). Tissue-specific CBF images that were independent of voxels' tissue fractional volume were obtained in elderly (N = 30) and young (N = 26); mean age difference was 43 years. Globally, PVE-corrected gray matter CBF was 88.2 +/- 16.1 and 107.3 +/- 17.5 mL/100 g min(-1) in elderly and young, respectively. The largest PVE contribution was found in the frontal lobe and accounted for an additional 10% and 12% increase in the age-related CBF difference between men and women, respectively. The GM-to-WM CBF ratios were found to be on average 3.5 in elderly and 3.9 in young. Whole brain voxelwise comparisons showed marked CBF decrease in anterior cingulate (bilateral), caudate (bilateral), cingulate gyrus (bilateral), cuneus (left), inferior frontal gyrus (left), insula (left), middle frontal gyrus (left), precuneus (bilateral), prefrontal cortex (bilateral), and superior frontal gyrus (bilateral) in men and amygdala (bilateral), hypothalamus (left), hippocampus (bilateral), and middle frontal gyrus (right) in women.

Cerebral Blood Flow Measurement in Children With Sickle Cell Disease Using Continuous Arterial Spin Labeling at 3.0-Tesla MRI

Cerebral infarction is an important complication of sickle cell disease (SCD) and occurs in one third of the patients with SCD. The risk of infarction is commonly attributed to the hyperemia that is associated with anemia and reduces the cerebral vascular reserve. We measured regional cerebral blood flow (rCBF) by continuous arterial spin labeling MRI, which is a noninvasive method that does not require ionizing radiation. The purpose of this study was to examine rCBF in children with SCD and compare it with rCBF in healthy children. rCBF was measured at 3-T continuous arterial spin labeling MRI in 24 neurological normal patients with SCD and in 12 healthy children matched for ethnicity and age (mean age in both groups 13 years). rCBF was calculated for 6 vascular territories (left and right anterior, middle and posterior cerebral artery). Asymmetry in rCBF was evaluated by measuring differences in flow between left and right hemispheres. The definition of asymmetry (>11.7 mL/100 g/min) was based on a repeatability study performed in 6 healthy adults. The rCBF was of similar magnitude in patients with SCD and control subjects in the frontal, middle, and posterior territories. The majority of patients with SCD (58%) demonstrated a left-right asymmetry of rCBF in one or more vascular territories, whereas none of the control subjects did. In contrast to previous studies, we found no difference in cerebral blood flow between patients and control subjects. We did observe an asymmetry in rCBF in the majority of patients with SCD that was not present in healthy control subjects.

Cerebral Blood Flow Measurement in Children with Sickle Cell Disease Using CASL at 3.0 Tesla MRI

One of the most devastating complications of SCD is cerebral infarction. Cerebral infarcts are present on MRI scans in one third of SCD patients at the age of 18 years, although most of them are not accompanied by overt, focal neurological deficits. These so-called silent infarcts appear to be associated with diminished neurocognitive functioning and an increased risk of new infarcts. The risk of infarction is commonly attributed to the hyperemia that is associated with anemia and reduces the cerebral vascular reserve. In patients with anemia, adequate oxygenation of the brain tissue is presumably preserved by vasodilatation of the cerebral vasculature. In this hyperemic state there is limited reserve for further vasodilatation to assure adequate oxygen supply to the brain if the arterial pressure falls or metabolic demands increase. The lack of reserve capacity and ensuing ischemia is thought to predispose to cerebral infarction. The regional cerebral blood flow (rCBF) can be measured non-invasively by continuous arterial spin labeling (CASL) MRI. Proximal to entry in the brain, protons in the arterial blood are labeled using a radiofrequency pulse and quantified in terms of tissue perfusion on distal images in the brain. We performed a study to evaluate whether CASL MRI could detect differences in rCBF when these regions appear unaffected on conventional 3T MRI. The purpose of this study was to examine rCBF in children with SCD and compare it to rCBF in healthy children. Neurologically normal patients with sickle cell disease (HbSS or HbS-β0-thalassemia) and normal flow on Transcranial Doppler Ultrasonography (TCD) and healthy children (HbAA, matched for ethnicity and age) underwent 3T MRI examination in a stable clinical situation between August 2006 and June 2007. Conventional MRI and MRA images were assessed by a standardized evaluation protocol by two independent observers (MW and CM), blinded to the clinical data. Cerebral infarcts, leukoareosis and vasculopathy were scored. From CASL MRI the rCBF was calculated for 6 vascular territories (left and right anterior, middle and posterior cerebral artery, respectively ACA, MCA and PCA). Left-right asymmetry in rCBF for the vascular territories within each patient was evaluated by calculating differences in flow between both hemispheres. Asymmetry was defined as > 11.7 ml/100g/min between the two hemispheres. Mean differences between patients and controls and 95% confidence intervals were calculated. The Chi-square test was performed to test the hypothesis that left-right asymmetry was equally distributed among the patients and controls. We enrolled 24 SCD patients (mean age 13.4 yr, SD 3.0) and 12 controls (mean age 13.4 yr, SD 3.5). The rCBF was of similar magnitude in SCD patients and controls in the frontal, middle and posterior territories (Table 1). A left-right asymmetry of rCBF in one or more vascular territories was present in the majority of SCD patients (58%), whereas this was absent in all controls. The difference in proportions of patients and controls with left-right asymmetry was statistically significant for the MCA and PCA territory (Chi-square test respectively p=0.005 and p=0.037). In contrast to previous studies we found no difference in CBF between patients and controls. We did observe an asymmetry in rCBF in the majority of patients with SCD that was not present in healthy controls.Table 1. rCBF (ml/100g/min) values of patients and healthy controls.Patients n=24Healthy controls n=12Mean difference95% CITerritoriesMeanSDMeanSDACA73.217.471.514.4−1.7(−13.6–10.1)MCA77.119.976.116.4−1.0(−14.5–12.5)PCA89.616.484.516.6−5.1(−17.0–6.7)Right hemisphere77.619.276.315.3−1.3(−14.3–11.5)Left hemisphere77.517.776.616.1−0.9(−13.3–11.4)Total77.617.476.415.6−1.2(−13.4–11.0)

Blood Flow Magnetic Resonance Imaging of Retinal Degeneration

This study aims to investigate quantitative basal blood flow as well as hypercapnia- and hyperoxia-induced blood flow changes in the retinas of the Royal College of Surgeons (RCS) rats with spontaneous retinal degeneration, and to compare with those of normal rat retinas. Experiments were performed on male RCS rats at post-natal days P90 (n=4) and P220 (n=5), and on age-matched controls at P90 (n=7) and P220 (n=6). Hyperoxic (100% O(2)) and hypercapnic (5% CO(2), 21% O(2), balance N(2)) challenges were used to modulate blood flow. Quantitative baseline blood flow, and hypercapnia- and hyperoxia-induced blood flow changes in the retinas were imaged using continuous arterial spin labeling MRI at 90 x 90 x 1500 microm. In the normal rat retinas, basal blood flow of the whole-retina was 5.5 mL/gram per min, significantly higher than those reported in the brain (approximately 1 mL/gram per min). Hyperoxia decreased blood flow due to vasoconstriction and hypercapnia increased blood flow due to vasodilation in the normal retinas. In the RCS rat retinas, basal blood flow was diminished significantly (P<0.05). Interestingly, absolute hyperoxia- and hypercapnia-induced blood flow changes in the RCS retinas were not statistically different from those in the normal retinas (P>0.05). However, blood flow percent changes in RCS retinas were significantly larger than in normal retinas due to lower basal blood flow in the RCS retinas. Retinal degeneration markedly reduces basal blood flow but does not appear to impair vascular reactivity. These data also suggest caution when interpreting relative stimulus-evoked functional MRI changes in diseased states where basal parameters are significantly perturbed. Quantitative blood flow MRI may serve as a valuable tool to study the retina without depth limitation.

Cerebral blood flow MRI in mice using the cardiac‐spin‐labeling technique

Continuous arterial spin labeling MRI with a separate neck labeling coil provides a highly sensitive method to image cerebral blood flow (CBF). In mice, however, this has not been possible because the proximity of the neck coil to the brain uses the neck coil to significantly saturate the brain signal. To overcome this limitation the cardiac spin labeling (CSL) technique is introduced in which the labeling coil is placed at the heart position. To demonstrate its utility, CSL CBF was applied to image quantitative basal CBF and hypercapnia-induced CBF changes. This approach provides a practical means to image CBF with high sensitivity in small animals, compares favorably to existing mouse CBF imaging techniques, and could broaden CBF applications in mice where many brain disease and transgenic models are widely available.