| 1. |
- Järnum, Hanna, et al.
(author)
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Diffusion and perfusion MRI of the brain in comatose patients treated with mild hypothermia after cardiac arrest: A prospective observational study.
- 2009
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In: Resuscitation. - : Elsevier BV. - 1873-1570 .- 0300-9572. ; 80, s. 425-430
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Journal article (peer-reviewed)abstract
- BACKGROUND: Outcome for resuscitated cardiac arrest (CA) patients is poor. The 1-year survival rate with favourable neurological outcome (CPC 1-2) after out-of-hospital CA is reported to be 4%. Among resuscitated patients treated within an ICU, approximately 50% regain consciousness, whereas the other 50% remain comatose before they die. Induced hypothermia significantly improves the neurological outcome and survival in patients with primary CA who remain comatose after return of spontaneous circulation. AIM: To evaluate magnetic resonance imaging (MRI) changes in resuscitated CA patients remaining in coma after treatment with hypothermia. METHODS: This prospective, observational study comprised 20 resuscitated CA patients who remained in coma 3 days after being treated with mild hypothermia (32-34 degrees C during 24h). Diffusion and perfusion MRI of the entire brain was performed approximately 5 days after CA. Autopsy was done on two patients. RESULTS: The largest number of diffusion changes on MRI was found in the 16 patients who died. The parietal lobe showed the largest difference in number of acute ischaemic MRI lesions in deceased compared with surviving patients. Perfusion changes, >/=+/-2 SD compared with healthy volunteers from a previously published cerebral perfusion study, were found in seven out of eight patients. The autopsies showed lesions corresponding to the pathologic changes seen on MRI. CONCLUSION: Diffusion and perfusion MRI are potentially helpful tools for the evaluation of ischaemic brain damage in resuscitated comatose patients treated with hypothermia after CA.
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| 2. |
- Knutsson, Linda, et al.
(author)
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Absolute quantification of cerebral blood flow in normal volunteers: Correlation between Xe-133SPECT and dynamic susceptibility contrast MRI
- 2007
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In: Journal of Magnetic Resonance Imaging. - : Wiley. - 1522-2586 .- 1053-1807. ; 26:4, s. 913-920
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Journal article (peer-reviewed)abstract
- Purpose: To compare, absolute cerebral blood flow (CBF) estimates obtained by dynamic susceptibility contrast MRI (DSC-MRI) and Xe-133 SPECT. Materials and Methods: CBF was measured in 20 healthy volunteers using DSC-MRI at 3T and Xe-133 SPECT. DSC- MRI was accomplished by gradient-echo EPI and CBF was calculated using a time-shift-insenisitive deconvolution algorithm and regional arterial input functions (AIFs). To improve the reproducibility of AIF registration the time integral was rescaled by use, of a venous output function. In the Xe-133 SPECT experiment, Xe-133 gas was inhaled over 8 minutes and CBF was calculated using a biexponential analysis. Results: The average whole-brain CBF estimates obtained by DSC-MRI and Xe- 133 SPECT were 85 +/- 23 mL/(min 100 g) and 40 +/- 8 mL/(min 100 g), respectively (mean +/- SD, n = 20). The linear CBF relationship between the two modalities showed a correlation coefficient of r = 0.76 and was described by the equation CBF(MRI) = 2.4 CBF(Xe) - 7.9 (CBF in units of mL/(min 100 g)). Conclusion: A reasonable positive linear correlation between MRI-based and SPECT-based CBF estimates was observed after AIF time-integral correction. The use of DSC-MRI typically results in overestimated absolute perfusion estimates and the present study indicates that this trend is further enhanced by the use of high magnetic field strength (3T).
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| 3. |
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| 4. |
- Knutsson, Linda, et al.
(author)
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Model-free arterial spin labelling for cerebral blood flow quantification: introduction of regional arterial input functions identified by factor analysis.
- 2008
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In: Magnetic Resonance Imaging. - : Elsevier BV. - 1873-5894 .- 0730-725X. ; 26:4, s. 554-559
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Journal article (peer-reviewed)abstract
- PURPOSE: To identify regional arterial input functions (AIFs) using factor analysis of dynamic studies (FADS) when quantification of perfusion is performed using model-free arterial spin labelling. MATERIAL AND METHODS: Five healthy volunteers and one patient were examined on a 3-T Philips unit using quantitative STAR labelling of arterial regions (QUASAR). Two sets of images were retrieved, one where the arterial signal had been crushed and another where it was retained. FADS was applied to the arterial signal curves to acquire the AIFs. Perfusion maps were obtained using block-circulant SVD deconvolution and regional AIFs obtained by FADS. In the volunteers, the ASL experiment was repeated within 24 h. The patient was also examined using dynamic susceptibility contrast MRI. RESULTS: In the healthy volunteers, CBF was 64+/-10 ml/[min 100 g] (mean+/-S.D.) in GM and 24+/-4 ml/[min 100 g] in WM, while the mean aBV was 0.94% in GM and 0.25% in WM. DISCUSSION: Good CBF image quality and reasonable quantitative CBF values were obtained using the combined QUASAR/FADS technique. We conclude that FADS may be a useful supplement in the evaluation of ASL data using QUASAR.
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| 5. |
- Knutsson, Linda
(author)
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Optimisation and Validation of Dynamic Susceptibility Contrast MRI Perfusion Measurements
- 2006
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Doctoral thesis (other academic/artistic)abstract
- The studies presented in this thesis concern the optimisation and evaluation of the dynamic susceptibility contrast magnetic resonance imaging (DSC-MRI) technique for the assessment of perfusion-related parameters of the brain, such as cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT). Several methodological factors influence these measurements, for example, contrast-agent administration, arterial input function (AIF) registration, choice of deconvolution algorithm and the choice of pulse-sequence parameters. In the first study, a comparison of two different deconvolution techniques was made, i.e., one based on the fast Fourier transform (FT) and the other on singular value decomposition (SVD). The primary result of this study was that CBF estimates obtained by FT-based deconvolution were lower than the CBF values resulting from SVD-based deconvolution. This is in agreement with the results presented in previous publications, demonstrating that the use of FT-based deconvolution underestimates high blood-flow rates (at short MTT). In the second study, perfusion parameters were calculated from simulated data corresponding to different experimental conditions. For example, variations in signal-to-noise ratio (SNR), temporal resolution, AIF shape, signal drop and cut-off level in the truncated SVD deconvolution were investigated. The main conclusions were that the echo time requires optimisation to ensure sufficient signal drop in combination with reasonable baseline SNR, and that a broad input function can lead to underestimation of the CBF. Regional AIFs (rAIFs) were the subject of the third investigation. By using factor analysis of dynamic studies in combination with principal component analysis, rAIFs were obtained and the CBF was calculated by using the rAIF located closest to each tissue voxel. The conclusions drawn from the study were that the use of rAIFs reduced dispersion effects which can lead to CBF underestimation. In the fourth study, CBF was measured in absolute terms in 20 volunteers using Xe-133 SPECT and DSC-MRI. An AIF time-integral correction was introduced in order to improve the absolute CBF quantification in DSC-MRI. Average whole-brain estimates as well as regional CBF values in grey matter (GM) and white matter (WM) were obtained, and the results from the two modalities were compared. For the whole-brain average, the linear relationship was found to be CBF(MRI)=2.4?CBF(Xe)-7.9 [CBF given in units of ml/(min 100 g)], with a correlation coefficient of r=0.76.
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| 6. |
- Siemund, Roger, et al.
(author)
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Cerebral perfusion imaging in hemodynamic stroke: be aware of the pattern.
- 2009
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In: Interventional Neuroradiology. - 1591-0199. ; 15:4, s. 385-394
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Journal article (peer-reviewed)abstract
- Summary: Reduction of the cerebral perfusion pressure caused by vessel occlusion or stenosis is a cause of neurological symptoms and border-zone infarctions. The aim of this article is to describe perfusion patterns in hemodynamic stroke, to give a practical approach for the assessment of colour encoded CT- and MR-perfusion maps and to demonstrate the clinical use of comprehensive imaging in the workup of patients with hemodynamic stroke. Five patients with different duration cause and degree of hemodynamic stroke were selected. The patients shared the typical presentation with fluctuating and transient symptoms. All were examined by MR or CT angiography and MR or CT perfusion in the symptomatic phase. All patients were examined with diffusion weighted imaging. All five cases showed the altered perfusion patterns of hemodynamic insufficiency with a slight or marked increase in CBV in the supply area of the affected vessel and only slightly reduced or maintained CBF. The perfusion disturbances were most easily detected on the MTT maps. Border-zone infarctions were seen in all cases. The typical pattern for hemodynamic insufficiency is characterized by increased CBV, normal or decreased CBF and prolonged MTT in the affected areas. The increased CBV is the hallmark of stressed autoregulation. Reading the color-encoded perfusion maps enables a quick and robust assessment of the cerebral perfusion and its characteristic patterns. Internal border-zone infarctions can be regarded as a marker for hemodynamic insufficiency. Finding of the typical rosary-like pattern of DWI lesions should call for further work up.
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| 7. |
- Wirestam, Ronnie, et al.
(author)
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Attempts to improve absolute quantification of cerebral blood flow in dynamic susceptibility contrast magnetic resonance imaging: a simplified t1-weighted steady-state cerebral blood volume approach.
- 2007
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In: Acta Radiologica. - : SAGE Publications. - 1600-0455 .- 0284-1851. ; 48:5, s. 550-556
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Journal article (peer-reviewed)abstract
- Background: Attempts to retrieve absolute values of cerebral blood flow (CBF) by dynamic susceptibility contrast magnetic resonance imaging (DSC-MRI) have typically resulted in overestimations. Purpose: To improve DSC-MRI CBF estimates by calibrating the DSC-MRI-based cerebral blood volume (CBV) with a corresponding T1-weighted (T1W) steady-state ( ss) CBV estimate. Material and Methods: 17 volunteers were investigated by DSC-MRI and Xe-133 SPECT. Steady-state CBV calculation, assuming no water exchange, was accomplished using signal values from blood and tissue, before and after contrast agent, obtained by T1W spin-echo imaging. Using steady-state and DSC-MRI CBV estimates, a calibration factor K=CBV(ss)/CBV(DSC) was obtained for each individual. Average whole-brain CBF( DSC) was calculated, and the corrected MRI-based CBF estimate was given by CBF(ss)=KxCBF(DSC). Results: Average whole-brain SPECT CBF was 40.1 +/- 6.9 ml/min . 100 g, while the corresponding uncorrected DSC-MRI- based value was 69.2 +/- 13.8 ml/min . 100 g. After correction with the calibration factor, a CBF( ss) of 42.7 +/- 14.0 ml/min . 100 g was obtained. The linear fit to CBF( ss)-versus-CBF( SPECT) data was close to proportionality (R=0.52). Conclusion: Calibration by steady-state CBV reduced the population average CBF to a reasonable level, and a modest linear correlation with the reference Xe-133 SPECT technique was observed. Possible explanations for the limited accuracy are, for example, large-vessel partial-volume effects, low post-contrast signal enhancement in T1W images, and water-exchange effects.
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| 8. |
- Ziegelitz, Doerthe, et al.
(author)
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Absolute quantification of cerebral blood flow in neurologically normal volunteers: dynamic-susceptibility contrast MRI-perfusion compared with computed tomography (CT)-perfusion.
- 2009
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In: Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine / Society of Magnetic Resonance in Medicine. - : Wiley. - 1522-2594 .- 0740-3194. ; 62:1, s. 56-65
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Journal article (peer-reviewed)abstract
- To improve the reproducibility of arterial input function (AIF) registration and absolute cerebral blood flow (CBF) quantification in dynamic-susceptibility MRI-perfusion (MRP) at 1.5T, we rescaled the AIF by use of a venous output function (VOF). We compared CBF estimates of 20 healthy, elderly volunteers, obtained by computed tomography (CT)-perfusion (CTP) and MRP on two consecutive days. MRP, calculated without the AIF correction, did not result in any significant correlation with CTP. The rescaled MRP showed fair to moderate correlation with CTP for the central gray matter (GM) and the whole brain. Our results indicate that the method used for correction of partial volume effects (PVEs) improves MRP experiments by reducing AIF-introduced variance at 1.5T.
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