| 1. |
- Carlsson, Marcus, et al.
(author)
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Cardiac output and cardiac index measured with cardiovascular magnetic resonance in healthy subjects, elite athletes and patients with congestive heart failure
- 2012
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In: Journal of Cardiovascular Magnetic Resonance. - 1097-6647. ; 14
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Journal article (peer-reviewed)abstract
- Background: Cardiovascular Magnetic Resonance (CMR) enables non-invasive quantification of cardiac output (CO) and thereby cardiac index (CI, CO indexed to body surface area). The aim of this study was to establish if CI decreases with age and compare the values to CI for athletes and for patients with congestive heart failure (CHF). Methods: CI was measured in 144 healthy volunteers (39 +/- 16 years, range 21-81 years, 68 females), in 60 athletes (29 +/- 6 years, 30 females) and in 157 CHF patients with ejection fraction (EF) below 40% (60 +/- 13 years, 33 females). CI was calculated using aortic flow by velocity-encoded CMR and is presented as mean +/- SD. Flow was validated in vitro using a flow phantom and in 25 subjects with aorta and pulmonary flow measurements. Results: There was a slight decrease of CI with age in healthy subjects (8 ml/min/m(2) per year, r(2) = 0.07, p = 0.001). CI in males (3.2 +/- 0.5 l/min/m(2)) and females (3.1 +/- 0.4 l/min/m(2)) did not differ (p = 0.64). The mean +/- SD of CI in healthy subjects in the age range of 20-29 was 3.3 +/- 0.4 l/min/m(2), in 30-39 years 3.3 +/- 0.5 l/min/m(2), in 40-49 years 3.1 +/- 0.5 l/min/m(2), 50-59 years 3.0 +/- 0.4 l/min/m(2) and >60 years 3.0 +/- 0.4 l/min/m(2). There was no difference in CI between athletes and age-controlled healthy subjects but HR was lower and indexed SV higher in athletes. CI in CHF patients (2.3 +/- 0.6 l/min/m(2)) was lower compared to the healthy population (p < 0.001). There was a weak correlation between CI and EF in CHF patients (r(2) = 0.07, p < 0.001) but CI did not differ between patients with NYHA-classes I-II compared to III-IV (n = 97, p = 0.16) or patients with or without hospitalization in the previous year (n = 100, p = 0.72). In vitro phantom validation showed low bias (-0.8 +/- 19.8 ml/s) and in vivo validation in 25 subjects also showed low bias (0.26 +/- 0.61 l/min, QP/QS 1.04 +/- 0.09) between pulmonary and aortic flow. Conclusions: CI decreases in healthy subjects with age but does not differ between males and females. We found no difference in CI between athletes and healthy subjects at rest but CI was lower in patients with congestive heart failure. The presented values can be used as reference values for flow velocity mapping CMR.
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| 2. |
- Carlsson, Marcus, et al.
(author)
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Quantification and visualization of cardiovascular 4D velocity mapping accelerated with parallel imaging or k-t BLAST: head to head comparison and validation at 1.5 T and 3 T
- 2011
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In: Journal of Cardiovascular Magnetic Resonance. - 1097-6647. ; 13:55
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Journal article (peer-reviewed)abstract
- Background: Three-dimensional time-resolved (4D) phase-contrast (PC) CMR can visualize and quantify cardiovascular flow but is hampered by long acquisition times. Acceleration with SENSE or k-t BLAST are two possibilities but results on validation are lacking, especially at 3 T. The aim of this study was therefore to validate quantitative in vivo cardiac 4D-acquisitions accelerated with parallel imaging and k-t BLAST at 1.5 T and 3 T with 2D-flow as the reference and to investigate if field strengths and type of acceleration have major effects on intracardiac flow visualization. Methods: The local ethical committee approved the study. 13 healthy volunteers were scanned at both 1.5 T and 3 T in random order with 2D-flow of the aorta and main pulmonary artery and two 4D-flow sequences of the heart accelerated with SENSE and k-t BLAST respectively. 2D-image planes were reconstructed at the aortic and pulmonary outflow. Flow curves were calculated and peak flows and stroke volumes (SV) compared to the results from 2D-flow acquisitions. Intra-cardiac flow was visualized using particle tracing and image quality based on the flow patterns of the particles was graded using a four-point scale. Results: Good accuracy of SV quantification was found using 3 T 4D-SENSE (r(2) = 0.86, -0.7 +/- 7.6%) and although a larger bias was found on 1.5 T (r(2) = 0.71, -3.6 +/- 14.8%), the difference was not significant (p = 0.46). Accuracy of 4D k-t BLAST for SV was lower (p < 0.01) on 1.5 T (r(2) = 0.65, -15.6 +/- 13.7%) compared to 3 T (r(2) = 0.64, -4.6 +/- 10.0%). Peak flow was lower with 4D-SENSE at both 3 T and 1.5 T compared to 2D-flow (p < 0.01) and even lower with 4D k-t BLAST at both scanners (p < 0.01). Intracardiac flow visualization did not differ between 1.5 T and 3 T (p = 0.09) or between 4D-SENSE or 4D k-t BLAST (p = 0.85). Conclusions: The present study showed that quantitative 4D flow accelerated with SENSE has good accuracy at 3 T and compares favourably to 1.5 T. 4D flow accelerated with k-t BLAST underestimate flow velocities and thereby yield too high bias for intra-cardiac quantitative in vivo use at the present time. For intra-cardiac 4D-flow visualization, however, 1.5 T and 3 T as well as SENSE or k-t BLAST can be used with similar quality.
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| 3. |
- Gatehouse, Peter D., et al.
(author)
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A multi-center inter-manufacturer study of the temporal stability of phase-contrast velocity mapping background offset errors
- 2012
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In: Journal of Cardiovascular Magnetic Resonance. - 1097-6647. ; 14:72
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Journal article (peer-reviewed)abstract
- Background: Phase-contrast velocity images often contain a background or baseline offset error, which adds an unknown offset to the measured velocities. For accurate flow measurements, this offset must be shown negligible or corrected. Some correction techniques depend on replicating the clinical flow acquisition using a uniform stationary phantom, in order to measure the baseline offset at the region of interest and subtract it from the clinical study. Such techniques assume that the background offset is stable over the time of a patient scan, or even longer if the phantom scans are acquired later, or derived from pre-stored background correction images. There is no published evidence regarding temporal stability of the background offset. Methods: This study assessed the temporal stability of the background offset on 3 different manufacturers' scanners over 8 weeks, using a retrospectively-gated phase-contrast cine acquisition with fixed parameters and at a fixed location, repeated 5 times in rapid succession each week. A significant offset was defined as 0.6 cm/s within 50 mm of isocenter, based upon an accuracy of 10% in a typical cardiac shunt measurement. Results: Over the 5 repeated cine acquisitions, temporal drift in the baseline offset was insignificant on two machines (0.3 cm/s, 0.2 cm/s), and marginally insignificant on the third machine (0.5 cm/s) due to an apparent heating effect. Over a longer timescale of 8 weeks, insignificant drift (0.4 cm/s) occurred on one, with larger drifts (0.9 cm/s, 0.6 cm/s) on the other machines. Conclusions: During a typical patient study, background drift was insignificant. Extended high gradient power scanning with work requires care to avoid drift on some machines. Over the longer term of 8 weeks, significant drift is likely, preventing accurate correction by delayed phantom corrections or derivation from pre-stored background offset data.
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| 4. |
- Hedström, Erik, et al.
(author)
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Effects of gadolinium contrast agent on aortic blood flow and myocardial strain measurements by phase-contrast cardiovascular magnetic resonance
- 2010
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In: Journal of Cardiovascular Magnetic Resonance. - 1097-6647. ; 12
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Journal article (peer-reviewed)abstract
- Background: Quantitative blood flow and aspects of regional myocardial function such as myocardial displacement and strain can be measured using phase-contrast cardiovascular magnetic resonance (PC-CMR). Since a gadolinium-based contrast agent is often used to measure myocardial infarct size, we sought to determine whether the contrast agent affects measurements of aortic flow and myocardial displacement and strain. Phase-contrast data pre and post contrast agent was acquired during free breathing using 1.5T PC-CMR. Results: For aortic flow and regional myocardial function 12 and 17 patients were analysed, respectively. The difference pre and post contrast agent was 0.03 +/- 0.16 l/min for cardiac output, and 0.1 +/- 0.5 mm for myocardial displacement. Linear regression for myocardial displacement (MD) after and before contrast agent (CA) showed MDpostCA = 0.95MD(preCA)+0.05 (r = 0.95, p < 0.001). For regional myocardial function, the contrast-to-noise ratios for left ventricular myocardial wall versus left ventricular lumen were pre and post contrast agent administration 7.4 +/- 3.3 and 4.4 +/- 8.9, respectively (p < 0.001). The contrast-to-noise ratios for left ventricular myocardial wall versus surrounding tissue were pre and post contrast agent administration -16.9 +/- 22 and -0.2 +/- 6.3, respectively (p < 0.0001). Conclusions: Quantitative measurements of aortic flow yield equal results both in the absence and presence of gadolinium contrast agent. The total examination time may thereby be reduced when assessing both viability and quantitative flow using PC-CMR, by assessing aortic flow post contrast agent administration. Phase-contrast information for myocardial displacement is also assessable both in the absence and presence of contrast agent. However, delineation of the myocardium may be difficult or impossible post contrast agent due to the lower image contrast. Acquisition of myocardial displacement should therefore be performed pre contrast agent using current PC-CMR sequences.
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| 5. |
- Knutsson, Linda, et al.
(author)
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Absolute quantification of cerebral blood flow: correlation between dynamic susceptibility contrast MRI and model-free arterial spin labeling.
- 2010
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In: Magnetic Resonance Imaging. - : Elsevier BV. - 1873-5894 .- 0730-725X. ; 28:1, s. 1-7
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Journal article (peer-reviewed)abstract
- PURPOSE: To compare absolute cerebral blood flow (CBF) estimates obtained by model-free arterial spin labeling (ASL) and dynamic susceptibility contrast MRI (DSC-MRI), corrected for partial volume effects (PVEs). METHODS: CBF was measured using DSC-MRI and model-free ASL (quantitative signal targeting with alternating radiofrequency labeling of arterial regions) at 3 T in 15 subjects with brain tumor, and the two modalities were compared with regard to CBF estimates in normal gray matter (GM) and DSC-to-ASL CBF ratios in selected tumor regions. The DSC-MRI CBF maps were calculated using a global arterial input function (AIF) from the sylvian-fissure region, but, in order to minimize PVEs, the AIF time integral was rescaled by a venous output function time integral obtained from the sagittal sinus. RESULTS: In GM, the average DSC-MRI CBF estimate was 150+/-45 ml/(min 100 g) (mean+/-SD) while the corresponding ASL CBF was 44+/-10 ml/(min 100 g). The linear correlation between GM CBF estimates obtained by DSC-MRI and ASL was r=.89, and observed DSC-to-ASL CBF ratios differed by less than 3% between GM and tumor regions. CONCLUSIONS: A satisfactory positive linear correlation between the CBF estimates obtained by model-free ASL and DSC-MRI was observed, and DSC-to-ASL CBF ratios showed no obvious tissue dependence.
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| 6. |
- Knutsson, Linda, et al.
(author)
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Dynamic susceptibility contrast MRI with a prebolus contrast agent administration design for improved absolute quantification of perfusion.
- 2014
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In: Magnetic Resonance in Medicine. - : Wiley. - 1522-2594 .- 0740-3194. ; 72:4, s. 996-1006
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Journal article (peer-reviewed)abstract
- Arterial partial-volume effects (PVEs) often hamper reproducible absolute quantification of cerebral blood flow (CBF) and cerebral blood volume (CBV) obtained by dynamic susceptibility contrast MRI (DSC-MRI). The aim of this study was to examine whether arterial PVEs in DSC-MRI data can be minimized by rescaling the arterial input function (AIF) using a sagittal-sinus venous output function obtained following a prebolus administration of a low dose of contrast agent.
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| 7. |
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| 8. |
- Markenroth Bloch, Karin, et al.
(author)
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Magnetisk Resonanstomografi
- 2011. - 3
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In: Klinisk fysiologi. - 9789147103638 ; , s. 133-142
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Book chapter (pop. science, debate, etc.)
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| 9. |
- Nilsson, Anders, et al.
(author)
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Accuracy of four-dimensional phase-contrast velocity mapping for blood flow visualizations: a phantom study.
- 2013
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In: Acta Radiologica. - : SAGE Publications. - 1600-0455 .- 0284-1851. ; 54:6, s. 663-671
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Journal article (peer-reviewed)abstract
- BackgroundTime-resolved three-dimensional, three-directional phase-contrast magnetic resonance velocity mapping (4D PC-MRI) is a powerful technique to depict dynamic blood flow patterns in the human body. However, the impact of phase background effects on flow visualizations has not been thoroughly studied previously, and it has not yet been experimentally demonstrated to what degree phase offsets affect flow visualizations and create errors such as inaccurate particle traces.PurposeTo quantify background phase offsets and their subsequent impact on particle trace visualizations in a 4D PC-MRI sequence. Additionally, we sought to investigate to what degree visualization errors are reduced by background phase correction.Material and MethodsA rotating phantom with a known velocity field was used to quantify background phase of 4D PC-MRI sequences accelerated with SENSE as well as different k-t BLAST speed-up factors. The deviation in end positions between particle traces in the measured velocity fields were compared before and after the application of two different phase correction methods.ResultsPhantom measurements revealed background velocity offsets up to 7 cm/s (7% of velocity encoding sensitivity) in the central slice, increasing with distance from the center. Background offsets remained constant with increasing k-t BLAST speed-up factors. End deviations of up to 5.3 mm (1.8 voxels) in the direction perpendicular to the rotating disc were found between particle traces and the seeding plane of the traces. Phase correction by subtraction of the data from the stationary phantom reduced the average deviation by up to 56%, while correcting the data-set with a first-order polynomial fit to stationary regions decreased average deviation up to 78%.ConclusionPathline visualizations can be significantly affected by background phase errors, highlighting the importance of dedicated and robust phase correction methods. Our results show that pathline deviation can be substantial if adequate phase background errors are not minimized.
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| 10. |
- Nilsson, Anders, et al.
(author)
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Variable velocity encoding in a three-dimensional, three-directional phase contrast sequence: Evaluation in phantom and volunteers.
- 2012
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In: Journal of Magnetic Resonance Imaging. - : Wiley. - 1522-2586 .- 1053-1807.
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Journal article (peer-reviewed)abstract
- PURPOSE: To evaluate accuracy and noise properties of a novel time-resolved, three-dimensional, three-directional phase contrast sequence with variable velocity encoding (denoted 4D-vPC) on a 3 Tesla MR system, and to investigate potential benefits and limitations of variable velocity encoding with respect to depicting blood flow patterns. MATERIALS AND METHODS: A 4D PC-MRI sequence was modified to allow variable velocity encoding (VENC) over the cardiac cycle in all three velocity directions independently. 4D-PC sequences with constant and variable VENC were compared in a rotating phantom with respect to measured velocities and noise levels. Additionally, comparison of flow patterns in the ascending aorta was performed in six healthy volunteers. RESULTS: Phantom measurements showed a linear relationship between velocity noise and velocity encoding. 4D-vPC MRI presented lower noise levels than 4D-PC both in phantom and in volunteer measurements, in agreement with theory. Volunteer comparisons revealed more consistent and detailed flow patterns in early diastole for the variable VENC sequences. CONCLUSION: Variable velocity encoding offers reduced noise levels compared with sequences with constant velocity encoding by optimizing the velocity-to-noise ratio (VNR) to the hemodynamic properties of the imaged area. Increased VNR ratios could be beneficial for blood flow visualizations of pathology in the cardiac cycle. J. Magn. Reson. Imaging 2012. © 2012 Wiley Periodicals, Inc.
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| 11. |
- Rolf, Marijn P, et al.
(author)
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Sequence optimization to reduce velocity offsets in cardiovascular magnetic resonance volume flow quantification - A multi-vendor study
- 2011
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In: JOURNAL OF CARDIOVASCULAR MAGNETIC RESONANCE. - : Taylor and Francis / BioMed Central. - 1097-6647. ; 13
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Journal article (peer-reviewed)abstract
- Purpose: Eddy current induced velocity offsets are of concern for accuracy in cardiovascular magnetic resonance (CMR) volume flow quantification. However, currently known theoretical aspects of eddy current behavior have not led to effective guidelines for the optimization of flow quantification sequences. This study is aimed at identifying correlations between protocol parameters and the resulting velocity error in clinical CMR flow measurements in a multi-vendor study. Methods: Nine 1.5T scanners of three different types/vendors were studied. Measurements were performed on a large stationary phantom. Starting from a clinical breath-hold flow protocol, several protocol parameters were varied. Acquisitions were made in three clinically relevant orientations. Additionally, a time delay between the bipolar gradient and read-out, asymmetric versus symmetric velocity encoding, and gradient amplitude and slew rate were studied in adapted sequences as exploratory measurements beyond the protocol. Image analysis determined the worst-case offset for a typical great-vessel flow measurement. Results: The results showed a great variation in offset behavior among scanners (standard deviation among samples of 0.3, 0.4, and 0.9 cm/s for the three different scanner types), even for small changes in the protocol. Considering the absolute values, none of the tested protocol settings consistently reduced the velocity offsets below the critical level of 0.6 cm/s neither for all three orientations nor for all three scanner types. Using multilevel linear model analysis, oblique aortic and pulmonary slices showed systematic higher offsets than the transverse aortic slices (oblique aortic 0.6 cm/s, and pulmonary 1.8 cm/s higher than transverse aortic). The exploratory measurements beyond the protocol yielded some new leads for further sequence development towards reduction of velocity offsets; however those protocols were not always compatible with the time-constraints of breath-hold imaging and flow-related artefacts. Conclusions: This study showed that with current systems there was no generic protocol which resulted into acceptable flow offset values. Protocol optimization would have to be performed on a per scanner and per protocol basis. Proper optimization might make accurate (transverse) aortic flow quantification possible for most scanners. Pulmonary flow quantification would still need further (offline) correction.
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| 12. |
- van Westen, Danielle, et al.
(author)
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Correlation between arterial blood volume obtained by arterial spin labelling and cerebral blood volume in intracranial tumours.
- 2011
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In: Magma. - : Springer Science and Business Media LLC. - 1352-8661. ; 24, s. 211-223
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Journal article (peer-reviewed)abstract
- OBJECTIVE: To compare measurements of the arterial blood volume (aBV), a perfusion parameter calculated from arterial spin labelling (ASL), and cerebral blood volume (CBV), calculated from dynamic susceptibility contrast (DSC) MRI. In the clinic, CBV is used for grading of intracranial tumours. MATERIALS AND METHODS: Estimates of aBV from the model-free ASL technique quantitative STAR labelling of arterial regions (QUASAR) experiment and of DSC-CBV were obtained at 3T in ten patients with eleven tumours (three grade III gliomas, four glioblastomas and four meningiomas, two in one patient). Parametric values of aBV and CBV were determined in the tumour as well as in normal grey matter (GM), and tumour-to-GM aBV and CBV ratios were calculated. RESULTS: In a 4-pixel ROI representing maximal tumour values, the coefficient of determination R (2) was 0.61 for the comparison of ASL-based aBV tumour-to-GM ratios and DSC-MRI-based CBV tumour-to-GM ratios and 0.29 for the comparison of parametric values of ASL-aBV and DSC-CBV, under the assumption of proportionality. Both aBV and CBV showed a non-significant tendency to increase when going from grade III gliomas to glioblastomas to meningiomas. CONCLUSION: These results suggest that measurement of aBV is a potential tool for non-invasive assessment of blood volume in intracranial tumours.
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| 13. |
- Wirestam, Ronnie, et al.
(author)
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Cerebral perfusion information obtained by dynamic contrast-enhanced phase-shift magnetic resonance imaging: comparison with model-free arterial spin labelling.
- 2010
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In: Clinical Physiology and Functional Imaging. - 1475-0961. ; 30:5, s. 375-379
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Journal article (peer-reviewed)abstract
- Summary Phase-shift time curves following a bolus injection of gadolinium contrast agent were registered for grey-matter regions and large vessels in 14 subjects. Deconvolving a tissue phase-shift curve with a phase-based arterial input function resulted in a tissue residue function R(t). The peak value of R(t) provided a relative cerebral blood flow (CBF) index, while the area-to-height ratio of R(t) provided quantitative mean transit time (MTT). For comparison, quantitative CBF values in grey matter were acquired using model-free arterial spin labelling (ASL). The phase-based relative CBF estimates showed good linear correlation with ASL-based CBF (r = 0.82). Grey-matter MTT was 4.9 +/- 1.1 s (mean +/- SD).
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