| 1. |
- Björnfot, Cecilia, et al.
(författare)
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Assessing cerebral arterial pulse wave velocity using 4D flow MRI
- 2021
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Ingår i: Journal of Cerebral Blood Flow and Metabolism. - : Sage Publications. - 0271-678X .- 1559-7016. ; 41:10, s. 2769-2777
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Tidskriftsartikel (refereegranskat)abstract
- Intracranial arterial stiffening is a potential early marker of emerging cerebrovascular dysfunction and could be mechanistically involved in disease processes detrimental to brain function via several pathways. A prominent consequence of arterial wall stiffening is the increased velocity at which the systolic pressure pulse wave propagates through the vasculature. Previous non-invasive measurements of the pulse wave propagation have been performed on the aorta or extracranial arteries with results linking increased pulse wave velocity to brain pathology. However, there is a lack of intracranial “target-organ” measurements. Here we present a 4D flow MRI method to estimate pulse wave velocity in the intracranial vascular tree. The method utilizes the full detectable branching structure of the cerebral vascular tree in an optimization framework that exploits small temporal shifts that exists between waveforms sampled at varying depths in the vasculature. The method is shown to be stable in an internal consistency test, and of sufficient sensitivity to robustly detect age-related increases in intracranial pulse wave velocity.
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| 2. |
- Holmgren, Madelene, 1992-
(författare)
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4D flow MRI and modelling to assess cerebral arterial hemodynamics : method development and evaluation, with implementation in patients with symptomatic carotid stenosis
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Blood flow measurements are important for understanding the development of cerebrovascular diseases. With 4D flow magnetic resonance imaging (4D flow MRI), simultaneous velocity measurements are obtained in all cerebral arteries in a scan of about ten minutes. However, 4D flow MRI is a relatively new technique. For usefulness in both clinics and research, detailed knowledge is needed about its accuracy and precision for flow quantification. In patients with stroke or transient ischemic attack (TIA) from a symptomatic carotid stenosis, the stenosis may generate a difference in blood pressure and flow between the left and right cerebral hemispheres. Such a hemispheric pressure difference could be an early marker of to what extent a stenosis is affecting cerebral hemodynamics, which could be useful in the planning of carotid surgery. The overall aim of the thesis was to determine the accuracy of 4D flow MRI to measure cerebral arterial blood flow, and to develop and evaluate an approach combining 4D flow MRI and computational fluid dynamics (CFD) to characterize the cerebral arterial hemodynamics, with implementation in patients with symptomatic carotid stenosis. The thesis is based on four papers, investigating two cohorts.The first cohort consisted of 35 elderly volunteers (mean age 79 years) and was studied in paper I-II. Blood flow rates were measured in nine cerebral arteries with 4D flow MRI and 2D phase-contrast MRI as reference. Three different flow quantification methods for 4D flow MRI were evaluated and optimized: one clustering approach and two threshold-based methods. The proposed new method, based on a locally adapted threshold, outperformed the previously suggested methods in flow rate quantification. For the clustering method, flow rates were systematically underestimated. 4D flow MRI was also evaluated to assess different arterial pulsatility measures, and a Windkessel model was used to estimate reference values for cerebrovascular resistance and cerebral arterial compliance in elderly.The second cohort consisted of 28 stroke and TIA patients (mean age 73 years) with symptomatic carotid stenosis and was studied in paper III-IV. With 4D flow MRI and CFD, the preoperative hemispheric pressure laterality was quantified in the patients. The pressure laterality was compared to hemispheric flow lateralities. Estimating the hemispheric pressure laterality was a promising physiological biomarker for grading the cerebral arterial hemodynamic disturbances in patients with symptomatic carotid stenosis. A CFD model was also developed to predict carotid stump pressure, i.e., the important pressure measured in the clamped carotid artery during surgical removal of the stenosis. The predicted stump pressures were correlated with the pressures measured during surgery. Stump pressure prediction was promising and could be a potential tool in the preoperative planning in order to avoid hypoperfusion during surgery. In summary, post-processing methods were successfully developed and evaluated for accurate assessment of mean and pulsatile cerebral blood flow rates with 4D flow MRI. Thereby, this thesis provided knowledge about possibilities and limitations of how 4D flow MRI can be used with respect to cerebral arterial blood flow rate assessment. By contributing with models combining 4D flow MRI and CFD, specifically developed for analysis of pressure distributions in cerebral arteries, novel methods were proposed for assessing patients with symptomatic carotid stenosis in the planning of carotid surgery.
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| 3. |
- Kaipainen, Aku L, et al.
(författare)
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Cerebrospinal fluid dynamics in idiopathic intracranial hypertension : a literature review and validation of contemporary findings
- 2021
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Ingår i: Acta Neurochirurgica. - : Springer. - 0001-6268 .- 0942-0940. ; 163:12, s. 3353-3368
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Tidskriftsartikel (refereegranskat)abstract
- Background: Idiopathic intracranial hypertension (IIH) is a rare disease of unknown aetiology related possibly to disturbed cerebrospinal fluid (CSF) dynamics and characterised by elevated intracranial pressure (ICP) causing optic nerve atrophy if not timely treated. We studied CSF dynamics of the IIH patients based on the available literature and our well-defined cohort.Method: A literature review was performed from PubMed between 1980 and 2020 in compliance with the PRISMA guideline. Our study includes 59 patients with clinical, demographical, neuro-ophthalmological, radiological, outcome data, and lumbar CSF pressure measurements for suspicion of IIH; 39 patients had verified IIH while 20 patients did not according to Friedman’s criteria, hence referred to as symptomatic controls.Results: The literature review yielded 19 suitable studies; 452 IIH patients and 264 controls had undergone intraventricular or lumbar CSF pressure measurements. In our study, the mean CSF pressure, pulse amplitudes, power of respiratory waves (RESP), and the pressure constant (P0) were higher in IIH than symptomatic controls (p < 0.01). The mean CSF pressure was higher in IIH patients with psychiatric comorbidity than without (p < 0.05). In IIH patients without acetazolamide treatment, the RAP index and power of slow waves were also higher (p < 0.05). IIH patients with excess CSF around the optic nerves had lower relative pulse pressure coefficient (RPPC) and RESP than those without (p < 0.05).Conclusions: Our literature review revealed increased CSF pressure, resistance to CSF outflow and sagittal sinus pressure (SSP) as key findings in IIH. Our study confirmed significantly higher lumbar CSF pressure and increased CSF pressure waves and RAP index in IIH when excluding patients with acetazolamide treatment. In overall, the findings reflect decreased craniospinal compliance and potentially depleted cerebral autoregulation resulting from the increased CSF pressure in IIH. The increased slow waves in patients without acetazolamide may indicate issues in autoregulation, while increased P0 could reflect the increased SSP.
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| 4. |
- Kristiansen, Martin, et al.
(författare)
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Feasibility of MRI to assess differences in ophthalmic artery blood flow rate in normal tension glaucoma and healthy controls
- 2021
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Ingår i: Acta Ophthalmologica. - : John Wiley & Sons. - 1755-375X .- 1755-3768. ; 99:5, s. e679-e685
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To examine feasibility of phase-contrast magnetic resonance imaging (PCMRI) and to assess blood flow rate in the ophthalmic artery (OA) in patients with normal tension glaucoma (NTG) compared with healthy controls.Methods: Sixteen patients with treated NTG and 16 age- and sex-matched healthy controls underwent PCMRI using a 3-Tesla scanner and ophthalmological examinations. OA blood flow rate was measured using a 2D PCMRI sequence with a spatial resolution of 0.35 mm(2).Results: The blood flow rate in the NTG group was 9.6 +/- 3.9 ml/min [mean +/- SD] compared with 11.9 +/- 4.8 ml/min in the control group. Resistance Index (RI) and Pulsatility Index (PI) were 0.73 +/- 0.08 and 1.36 +/- 0.29, respectively, in the NTG group and 0.68 +/- 0.13 and 1.22 +/- 0.40, respectively, in the healthy group. The mean visual field index (VFI) was 46% +/- 25 for the worse NTG eyes. The measured differences observed between the NTG group and the control group in blood flow rate (p = 0.12), RI (p = 0.18) and PI (p = 0.27) were non-significant.Conclusions: This case-control study, using PCMRI, showed a slight, but non-significant, reduction in OA blood flow rate in the NTG patients compared with the healthy controls. These results indicate that blood flow may be of importance in the pathogenesis of NTG. Considering that only a limited portion of the total OA blood flow supplies the ocular system and the large inter-individual differences, a larger study or more advanced PCMRI technique might give the answer.
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