| 1. |
- Ahlgren, André, et al.
(författare)
-
A linear mixed perfusion model for tissue partial volume correction of perfusion estimates in dynamic susceptibility contrast MRI: : Impact on absolute quantification, repeatability, and agreement with pseudo-continuous arterial spin labeling
- 2017
-
Ingår i: Magnetic Resonance in Medicine. - : Wiley. - 1522-2594 .- 0740-3194. ; 77:6, s. 2203-2214
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: The partial volume effect (PVE) is an important source of bias in brain perfusion measurements. The impact of tissue PVEs in perfusion measurements with dynamic susceptibility contrast MRI (DSC-MRI) has not yet been well established. The purpose of this study was to suggest a partial volume correction (PVC) approach for DSC-MRI and to study how PVC affects DSC-MRI perfusion results.METHODS: A linear mixed perfusion model for DSC-MRI was derived and evaluated by way of simulations. Twenty healthy volunteers were scanned twice, including DSC-MRI, arterial spin labeling (ASL), and partial volume measurements. Two different algorithms for PVC were employed and assessed.RESULTS: Simulations showed that the derived model had a tendency to overestimate perfusion values in voxels with high fractions of cerebrospinal fluid. PVC reduced the tissue volume dependence of DSC-MRI perfusion values from 44.4% to 4.2% in gray matter and from 55.3% to 14.2% in white matter. One PVC method significantly improved the voxel-wise repeatability, but PVC did not improve the spatial agreement between DSC-MRI and ASL perfusion maps.CONCLUSION: Significant PVEs were found for DSC-MRI perfusion estimates, and PVC successfully reduced those effects. The findings suggest that PVC might be an important consideration for DSC-MRI applications. Magn Reson Med, 2016. © 2016 Wiley Periodicals, Inc.
|
|
| 2. |
|
|
| 3. |
- Ahlgren, André, et al.
(författare)
-
Partial volume correction of brain perfusion estimates using the inherent signal data of time-resolved arterial spin labeling.
- 2014
-
Ingår i: NMR in Biomedicine. - : Wiley. - 0952-3480. ; 27:9, s. 1112-1122
-
Tidskriftsartikel (refereegranskat)abstract
- Quantitative perfusion MRI based on arterial spin labeling (ASL) is hampered by partial volume effects (PVEs), arising due to voxel signal cross-contamination between different compartments. To address this issue, several partial volume correction (PVC) methods have been presented. Most previous methods rely on segmentation of a high-resolution T1 -weighted morphological image volume that is coregistered to the low-resolution ASL data, making the result sensitive to errors in the segmentation and coregistration. In this work, we present a methodology for partial volume estimation and correction, using only low-resolution ASL data acquired with the QUASAR sequence. The methodology consists of a T1 -based segmentation method, with no spatial priors, and a modified PVC method based on linear regression. The presented approach thus avoids prior assumptions about the spatial distribution of brain compartments, while also avoiding coregistration between different image volumes. Simulations based on a digital phantom as well as in vivo measurements in 10 volunteers were used to assess the performance of the proposed segmentation approach. The simulation results indicated that QUASAR data can be used for robust partial volume estimation, and this was confirmed by the in vivo experiments. The proposed PVC method yielded probable perfusion maps, comparable to a reference method based on segmentation of a high-resolution morphological scan. Corrected gray matter (GM) perfusion was 47% higher than uncorrected values, suggesting a significant amount of PVEs in the data. Whereas the reference method failed to completely eliminate the dependence of perfusion estimates on the volume fraction, the novel approach produced GM perfusion values independent of GM volume fraction. The intra-subject coefficient of variation of corrected perfusion values was lowest for the proposed PVC method. As shown in this work, low-resolution partial volume estimation in connection with ASL perfusion estimation is feasible, and provides a promising tool for decoupling perfusion and tissue volume. Copyright © 2014 John Wiley & Sons, Ltd.
|
|
| 4. |
- Ahlgren, André, et al.
(författare)
-
Perfusion quantification by model-free arterial spin labeling using nonlinear stochastic regularization deconvolution.
- 2013
-
Ingår i: Magnetic Resonance in Medicine. - : Wiley. - 1522-2594 .- 0740-3194. ; 70:5, s. 1470-1480
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose: Quantification of cerebral blood flow can be accomplished by model-free arterial spin labeling using the quantitative STAR labeling of arterial regions (QUASAR) sequence. The required deconvolution is normally based on block-circulant singular value decomposition (cSVD)/oscillation SVD (oSVD), an algorithm associated with nonphysiological residue functions and potential effects of arterial dispersion. The aim of this work was to amend this by implementing nonlinear stochastic regularization (NSR) deconvolution, previously used to retrieve realistic residue functions in dynamic susceptibility contrast MRI. METHODS: To characterize the residue function in model-free arterial spin labeling, and possibly to improve absolute cerebral blood flow quantification, NSR was applied to deconvolution of QUASAR data. For comparison, SVD-based deconvolution was also employed. Residue function characteristics and cerebral blood flow values from 10 volunteers were obtained. Simulations were performed to support the in vivo results. RESULTS: NSR was able to resolve realistic residue functions in contrast to the SVD-based methods. Mean cerebral blood flow estimates in gray matter were 36.6 ± 2.6, 28.6 ± 3.3, 40.9 ± 3.6, and 42.9 ± 3.9 mL/100 g/min for cSVD, oSVD, NSR, and NSR with correction for arterial dispersion, respectively. In simulations, the NSR-based perfusion estimates showed better accuracy than the SVD-based approaches. CONCLUSION: Perfusion quantification by model-free arterial spin labeling is evidently dependent on the selected deconvolution method, and NSR is a feasible alternative to SVD-based methods. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.
|
|
| 5. |
- Ahlgren, André, et al.
(författare)
-
Quantification of microcirculatory parameters by joint analysis of flow-compensated and non-flow-compensated intravoxel incoherent motion (IVIM) data.
- 2016
-
Ingår i: NMR in Biomedicine. - : Wiley. - 0952-3480 .- 1099-1492. ; 29:5, s. 640-649
-
Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to improve the accuracy and precision of perfusion fraction and blood velocity dispersion estimates in intravoxel incoherent motion (IVIM) imaging, using joint analysis of flow-compensated and non-flow-compensated motion-encoded MRI data. A double diffusion encoding sequence capable of switching between flow-compensated and non-flow-compensated encoding modes was implemented. In vivo brain data were collected in eight healthy volunteers and processed using the joint analysis. Simulations were used to compare the performance of the proposed analysis method with conventional IVIM analysis. With flow compensation, strong rephasing was observed for the in vivo data, approximately cancelling the IVIM effect. The joint analysis yielded physiologically reasonable perfusion fraction maps. Estimated perfusion fractions were 2.43 ± 0.81% in gray matter, 1.81 ± 0.90% in deep gray matter, and 1.64 ± 0.72% in white matter (mean ± SD, n = 8). Simulations showed improved accuracy and precision when using joint analysis of flow-compensated and non-flow-compensated data, compared with conventional IVIM analysis. Double diffusion encoding with flow compensation was feasible for in vivo imaging of the perfusion fraction in the brain. The strong rephasing implied that blood flowing through the cerebral microvascular system was closer to the ballistic limit than the diffusive limit. © 2016 The Authors NMR in Biomedicine published by John Wiley & Sons Ltd.
|
|
| 6. |
- Arheden, Håkan, et al.
(författare)
-
Blood flow measurements
- 2006
-
Ingår i: MRI and CT of the Cardiovascular System. - 0781762715 ; , s. 71-90
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)
|
|
| 7. |
|
|
| 8. |
- Bibic, Adnan, et al.
(författare)
-
Denoising of arterial spin labeling data: wavelet-domain filtering compared with Gaussian smoothing.
- 2010
-
Ingår i: Magma. - : Springer Science and Business Media LLC. - 1352-8661. ; 23:3, s. 125-137
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To investigate a wavelet-based filtering scheme for denoising of arterial spin labeling (ASL) data, potentially enabling reduction of the required number of averages and the acquisition time. METHODS: ASL magnetic resonance imaging (MRI) provides quantitative perfusion maps by using arterial water as an endogenous tracer. The signal difference between a labeled image, where inflowing arterial spins are inverted, and a control image is proportional to blood perfusion. ASL perfusion maps suffer from low SNR, and the experiment must be repeated a number of times (typically more than 40) to achieve adequate image quality. In this study, systematic errors introduced by the proposed wavelet-domain filtering approach were investigated in simulated and experimental image datasets and compared with conventional Gaussian smoothing. RESULTS: Application of the proposed method enabled a reduction of the number of averages and the acquisition time by at least 50% with retained standard deviation, but with effects on absolute CBF values close to borders and edges. CONCLUSIONS: When the ASL perfusion maps showed moderate-to-high SNRs, wavelet-domain filtering was superior to Gaussian smoothing in the vicinity of borders between gray and white matter, while Gaussian smoothing was a better choice for larger homogeneous areas, irrespective of SNR.
|
|
| 9. |
- Bibic, Adnan, et al.
(författare)
-
Effects of red blood cells with reduced deformability on cerebral blood flow and vascular water transport: measurements in rats using time-resolved pulsed arterial spin labelling at 9.4 T
- 2021
-
Ingår i: European Radiology Experimental. - : Springer Science and Business Media LLC. - 2509-9280. ; 5, s. 1-12
-
Tidskriftsartikel (refereegranskat)abstract
- BackgroundOur aim was to introduce damaged red blood cells (RBCs) as a tool for haemodynamic provocation in rats, hypothesised to cause decreased cerebral blood flow (CBF) and prolonged water capillary transfer time (CTT), and to investigate whether expected changes in CBF could be observed and if haemodynamic alterations were reflected by the CTT metric.MethodsDamaged RBCs exhibiting a mildly reduced deformability were injected to cause aggregation of RBCs. Arterial spin labelling (ASL) magnetic resonance imaging experiments were performed at 9.4 T. Six datasets (baseline plus five datasets after injection) were acquired for each animal in a study group and a control group (13 and 10 female adult Wistar rats, respectively). For each dataset, ASL images at ten different inversion times were acquired. The CTT model was adapted to the use of a measured arterial input function, implying the use of a realistic labelling profile. Repeated measures ANOVA was used (alpha error = 0.05).ResultsAfter injection, significant differences between the study group and control group were observed for relative CBF in white matter (up to 20 percentage points) and putamen (up to 18–20 percentage points) and for relative CTT in putamen (up to 35–40 percentage points).ConclusionsHaemodynamic changes caused by injection of damaged RBCs were observed by ASL-based CBF and CTT measurements. Damaged RBCs can be used as a tool for test and validation of perfusion imaging modalities. CTT model fitting was challenging to stabilise at experimental signal-to-noise ratio levels, and the number of free parameters was minimised.
|
|
| 10. |
- Bibic, Adnan, et al.
(författare)
-
Measurement of vascular water transport in human subjects using time-resolved pulsed arterial spin labelling.
- 2015
-
Ingår i: NMR in Biomedicine. - : Wiley. - 0952-3480. ; 28:8, s. 1059-1068
-
Tidskriftsartikel (refereegranskat)abstract
- Most approaches to arterial spin labelling (ASL) data analysis aim to provide a quantitative measure of the cerebral blood flow (CBF). This study, however, focuses on the measurement of the transfer time of blood water through the capillaries to the parenchyma (referred to as the capillary transfer time, CTT) as an alternative parameter to characterise the haemodynamics of the system. The method employed is based on a non-compartmental model, and no measurements need to be added to a common time-resolved ASL experiment. Brownian motion of labelled spins in a potential was described by a one-dimensional general Langevin equation as the starting point, and as a Fokker-Planck differential equation for the averaged distribution of labelled spins at the end point, which takes into account the effects of flow and dispersion of labelled water by the pseudorandom nature of the microvasculature and the transcapillary permeability. Multi-inversion time (multi-TI) ASL data were acquired in 14 healthy subjects on two occasions in a test-retest design, using a pulsed ASL sequence and three-dimensional gradient and spin echo (3D-GRASE) readout. Based on an error analysis to predict the size of a region of interest (ROI) required to obtain reasonably precise parameter estimates, data were analysed in two relatively large ROIs, i.e. the occipital lobe (OC) and the insular cortex (IC). The average values of CTT in OC were 260 ± 60 ms in the first experiment and 270 ± 60 ms in the second experiment. The corresponding IC values were 460 ± 130 ms and 420 ± 139 ms, respectively. Information related to the water transfer time may be important for diagnostics and follow-up of cerebral conditions or diseases characterised by a disrupted blood-brain barrier or disturbed capillary blood flow. Copyright © 2015 John Wiley & Sons, Ltd.
|
|
| 11. |
- Björkman-Burtscher, Isabella, et al.
(författare)
-
Aneurysm clip MR artifacts. Titanium versus stainless steel and influence of imaging parameters
- 1998
-
Ingår i: Acta Radiologica. - 1600-0455. ; 39:1, s. 70-76
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: The aim of this study was to evaluate the extent to which titanium aneurysm clips could improve the quality of MR imaging compared with stainless steel clips, and to determine whether the clip artifacts could be reduced by controlling certain MR imaging parameters in frequently used pulse sequences. MATERIAL AND METHODS: The metal artifacts induced by 3 aneurysm clips were compared in 3 pulse sequences. The clips were: a Yasargil titanium aneurysm clip FT 752 T; a Yasargil standard aneurysm clip FE 752 K; and, for comparison, a ferromagnetic Scoville aneurysm clip En-58J. The pulse sequences were: spin echo (SE); gradient echo (GE); and fast SE. An evaluation was made of 3 imaging parameters with regard to their influence on the size of the metal artifacts. The parameters were: bandwidth; echo time (TE); and echo-train length. RESULTS: The titanium clip showed artifacts that were about 60% smaller than those from the stainless steel clip. The only parameter that influenced artifact size to any major degree was bandwidth in the SE sequences but not in the GE sequences. GE sequences induced larger artifacts than SE sequences and showed larger artifacts with longer TE. CONCLUSION: Titanium aneurysm clips reduced MR artifacts by approximately 60% compared to stainless steel clips. Artifacts were further reduced by using SE-based sequences with a high bandwidth or, if necessary, GE sequences with a low TE.
|
|
| 12. |
- Björkman-Burtscher, Isabella, et al.
(författare)
-
Proton (1H) MR spectroscopy for routine diagnostic evaluation of brain lesions
- 1997
-
Ingår i: Acta Radiologica. - 1600-0455. ; 38:6, s. 953-960
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To describe the introduction and performance of proton MR spectroscopy (1H-MRS) in the daily routine of a modern standard MR unit. MATERIAL AND METHODS: Over an 8-month period, 52 patients with brain lesions were studied with 1H-MRS, using SE and STEAM sequences for chemical-shift imaging and single-volume spectroscopy. The quality of the spectra was graded from 1 (best) to 3, and the main factors influencing the quality of the spectra were evaluated. RESULTS: Of the measurements: 85% were graded as 1; 12% as 2; and 3% as 3. The main reasons for poor spectral quality were: the unfortunate positioning of the VOI; hemorrhage; and/or postoperative changes within the VOI. Of 40 patients with a final diagnosis: MRS provided an increased confidence in MR diagnosis in 18 cases; MRS contributed significantly to preoperative diagnosis in 3 cases; and the spectra were not specific (n = 10) or were difficult to evaluate (n = 9) owing to reduced quality (grade 2 or 3) in 19 cases. CONCLUSION: MRS of the brain can provide a high percentage of interpretable spectra and frequently can increase confidence in the MR diagnosis of brain lesions in clinical routine.
|
|
| 13. |
- Björkman-Burtscher, Isabella, et al.
(författare)
-
Proton MR spectroscopy and preoperative diagnostic accuracy: an evaluation of intracranial mass lesions characterized by stereotactic biopsy findings
- 2000
-
Ingår i: AJNR. - 1936-959X. ; 21:1, s. 84-93
-
Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND AND PURPOSE: MR imaging has made it easier to distinguish among the different types of intracranial mass lesions. Nevertheless, it is sometimes impossible to base a diagnosis solely on clinical and neuroradiologic findings, and, in these cases, biopsy must be performed. The purpose of this study was to evaluate the hypothesis that proton MR spectroscopy is able to improve preoperative diagnostic accuracy in cases of intracranial tumors and may therefore obviate stereotactic biopsy. METHODS: Twenty-six patients with intracranial tumors underwent MR imaging, proton MR spectroscopy, and stereotactic biopsy. MR spectroscopic findings were evaluated for the distribution pattern of pathologic spectra (NAA/Cho ratio < 1) across the lesion and neighboring tissue, for signal ratios in different tumor types, and for their potential to improve preoperative diagnostic accuracy. RESULTS: Gliomas and lymphomas showed pathologic spectra outside the area of contrast enhancement while four nonastrocytic circumscribed tumors (meningioma, pineocytoma, metastasis, and germinoma) showed no pathologic spectra outside the region of enhancement. No significant correlation was found between different tumor types and signal ratios. MR spectroscopy improved diagnostic accuracy by differentiating infiltrative from circumscribed tumors; however, diagnostic accuracy was not improved in terms of differentiating the types of infiltrative or circumscribed lesions. CONCLUSION: MR spectroscopy can improve diagnostic accuracy by differentiating circumscribed brain lesions from histologically infiltrating processes, which may be difficult or impossible solely on the basis of clinical or neuroradiologic findings.
|
|
| 14. |
- Björkman-Burtscher, Isabella, et al.
(författare)
-
Quality assessment of localization technique performance in small volume in vivo 1H MR spectroscopy
- 1999
-
Ingår i: Magnetic Resonance Imaging. - 1873-5894. ; 17:10, s. 1511-1519
-
Tidskriftsartikel (refereegranskat)abstract
- A new phantom and evaluation method for experimental evaluation of 1H-magnetic resonance spectroscopy single volume localization techniques regarding signal contamination (C), defined as the part of the signal originating outside the volume of interest, is presented. The quality assessment method is based on a spherical phantom with an oil/water interface in order to reduce susceptibility effects, and applied for stimulated-echo acquisition method (STEAM) and spin-echo (SE) sequences, echo times of 270, 135, and 10 ms, and cubic volumes of interest (VOI) of 1(3), 1.5(3), 2(3), 2.5(3), and 3(3) cm3. To be able to mimic measurements of the contamination in three dimensions the physical gradients representing the three orthogonal directions for slice selection were shifted in the pulse sequences. Contamination values in one dimension differed between 6.5% and 8.4% in SE sequences, and between 0.7% and 13.8% in STEAM sequences. In STEAM sequences a decrease of C with increasing VOI size was observed while SE sequences showed comparable C values for the different VOI sizes tested. The total contamination in three dimensions were 19% and 18% in SE and STEAM sequences with a TE of 270 ms, and 7% in a STEAM sequence with a TE of 10 ms, respectively. The presented evaluation method is easily applied to the new phantom and showed high reproducibility.
|
|
| 15. |
- Brockstedt, Sara, et al.
(författare)
-
High-resolution diffusion imaging using phase-corrected segmented echo-planar imaging
- 2000
-
Ingår i: Magnetic Resonance Imaging. - 1873-5894. ; 18:6, s. 649-657
-
Tidskriftsartikel (refereegranskat)abstract
- Diffusion magnetic resonance imaging (MRI) was performed with a high-resolution segmented echo-planar imaging technique, which provided images with substantially less susceptibility artifacts than images obtained with single-shot echo-planar imaging (EPI). Diffusion imaging performed with any multishot pulse sequence is inherently sensitive to motion artifacts and in order to reduce motion artifacts, the presented method utilizes navigator echo phase corrections, performed after a one-dimensional Fourier transform along the frequency-encoding direction. Navigator echo phases were fitted to a straight line prior to phase correction to avoid errors from internal motion. In vivo imaging was performed using electro cardiographic (ECG) triggering. Apparent diffusion coefficient (ADC) maps were calculated on a pixel-by-pixel basis using up to seven diffusion sensitivities, ranging from b = 0 to 1129 x 10(6) s/m(2).
|
|
| 16. |
- Brockstedt, Sara, et al.
(författare)
-
Quantitative diffusion coefficient maps using fast spin-echo MRI
- 1998
-
Ingår i: Magnetic Resonance Imaging. - 1873-5894. ; 16:8, s. 877-886
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, we have evaluated the performance of a diffusion-sensitive fast spin-echo (FSE) pulse sequence. The proposed pulse sequence utilises velocity-compensating diffusion-encoding gradients and includes the collection of navigator echoes. Spoiler gradients were inserted in the slice-selecting direction to minimise effects from stimulated echoes. Calculations of the b values showed that cross-terms between imaging gradients and diffusion gradients only led to a marginal increase of b values. Pixel-wise calculation of apparent diffusion coefficient (ADC) maps was performed numerically, considering cross-terms between diffusion-encoding and imaging gradients. The sequences investigated used echo train lengths of 16, 8 and 4 echoes and were encoded in either the slice-, frequency- or phase-encoding direction. In order to allow for higher b values a pulse-sequence version using non-motion compensating diffusion-encoding gradients was written. Phantom measurements were performed and the diffusion coefficients of water and acetone were reasonable. Seven healthy volunteers (age 28-50 years) were examined and apparent diffusion coefficient values agreed well with expected values. Diffusion-weighted images, apparent diffusion coefficient maps and images corresponding to the trace of the diffusion tensor of good quality were retrieved in vivo.
|
|
| 17. |
- Brockstedt, Sara, et al.
(författare)
-
Triggering in quantitative diffusion imaging with single-shot EPI
- 1999
-
Ingår i: Acta Radiologica. - 1600-0455. ; 40:3, s. 263-269
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: The aim of this study was to evaluate any possible effects of brain motion, CSF pulsations and other possible sources of physiological motion in electrocardiographic (ECG) triggered and non-triggered single-shot echo-planar imaging (EPI) measurements of diffusion. MATERIAL AND METHODS: Three different triggering protocols were evaluated in 6 healthy volunteers: 1) ECG triggering with time delay (TD) 100 ms; 2) ECG triggering with TD 400 ms; and 3) no triggering at all. RESULTS: The results obtained showed that white matter mean apparent diffusion coefficient (ADC) values were similar for all triggering protocols and that the reproducibility in ADC measurements using diffusion-weighted (DW) EPI was good. The average standard deviation of the ADC values was, however, higher for ADC maps obtained without ECG triggering. CONCLUSION: The use of prospective diastolic ECG triggering significantly improves the accuracy of quantitative diffusion measurements but for routine clinical diffusion imaging, where quantitative data is of less importance, the accuracy obtained without ECG triggering can be considered adequate.
|
|
| 18. |
- Brockstedt, Sara, et al.
(författare)
-
Use of an enhanced gradient system for diffusion MR imaging with motion-artifact reduction
- 1995
-
Ingår i: Acta Radiologica. - 1600-0455. ; 36:6, s. 662-670
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: A spin-echo diffusion-sensitized pulse sequence using high gradients (23 mT/m) is introduced. MATERIAL AND METHODS: In order to minimize motion artefacts, velocity-compensating gradients, ECG-triggering and post-processing with phase correction and raw data averaging using navigator echoes was performed. The in vitro ratio of diffusion coefficients for water and acetone was determined and the water self-diffusion coefficient at different temperatures was evaluated. The pulse sequence was tested in 7 healthy volunteers and in 2 tumour patients with astrocytomas of grades I-II and III-IV. Both single-slice and multi-slice techniques were used. RESULTS: The incorporation of phase correction clearly improved the quality of both diffusion-encoded images and the calculated diffusion maps. Mean values of the diffusion coefficients in vivo were for CSF 2.66 x 10(-9) m2/s and for white and grey matter 0.69 x 10(-9) m2/s and 0.87 x 10(-9) m2/s, respectively. CONCLUSION: Velocity-compensating gradients in combination with a high gradient strength were shown to be useful for in vivo diffusion MR imaging.
|
|
| 19. |
- Brockstedt, Sara, et al.
(författare)
-
Vertical field MR imaging of upper thorax and spine in small children. Evaluation of a new surface coil
- 1993
-
Ingår i: Acta Radiologica. - 1600-0455. ; 34:6, s. 549-553
-
Tidskriftsartikel (refereegranskat)abstract
- To improve image quality in a vertical field MR imaging unit, operating at low field strength (0.3 T), we have designed a half-elliptical coil for use in the upper thoracic region of small children. Our intention was also to shorten the examination time, which until now has been long, because several scans with different coils have been necessary to cover the thoracic region. The experimental coil is designed so that a child's shoulders fit into the central region. The coil consists of 2 serially connected cable-loops, mounted on a foam rubber vest. The coil performance was tested in a phantom and improvements relative to standard coils were demonstrated in in vivo studies. The results indicate that by using the half-elliptical coil, the signal-to-noise (S/N) ratio can be improved by a factor of 2 to 3 in the thoracic region of a child.
|
|
| 20. |
- Carlsson, Marcus, et al.
(författare)
-
Cardiac output and cardiac index measured with cardiovascular magnetic resonance in healthy subjects, elite athletes and patients with congestive heart failure
- 2012
-
Ingår i: Journal of Cardiovascular Magnetic Resonance. - 1097-6647. ; 14
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 21. |
- Carlsson, Marcus, et al.
(författare)
-
Effects of caffeine abstinence on adenosine induced coronary flow reserve quantified on phase contrast velocity encoded MRI of the coronary sinus
- 2010
-
Ingår i: Journal of Cardiovascular Magnetic Resonance. - 1097-6647. ; 12, s. 253-254
-
Konferensbidrag (refereegranskat)abstract
- Introduction: Adenosine is a common pharmacological vasodilator agent used in first pass perfusion MRI as well as nuclear cardiology and echocardiography. Coronary flow reserve (CFR) by adenosine is inhibited by caffeine and therefore caffeine abstinence is routinely proscribed in patients. However, the guidelines differ regarding how long abstinence is needed from 12 to 24 hours. Purpose: This study was performed to investigate if 12 h caffeine abstinence is enough to provide maximal coronary flow reserve (CFR). Methods: 12 healthy individuals (5 females, 39 ± 14 years) were imaged using a 1.5 T Philips Intera CV at rest and during adenosine infusion (140 μg/kg/min) at two occasions, after 12 and 24 h caffeine abstinence respectively. Coronary sinus flow was measured during breath hold with a phase contrast velocity encoded (PC) TFE sequence with 20 phases per cardiac cycle. Typical imaging parameters were: SENSE factor 2, TE/TR/flip: 3.1/4.8 ms/15°, turbo factor 5, spatial resolution 1.2 × 1.2 × 7 mm and VENC 80 cm/s. CFR was calculated as the ratio between coronary sinus flow/min at adenosine and rest. Cardiac output was measured using PC-MRI of the ascending aorta. Results: CFR was higher (5.4 ± 1.0) at 24 h caffeine abstinence compared to 12 h (4.6 ± 0.8, p = 0.03). In most patients the difference was minimal but in three patients (25%) the increase in CFR at 12 h was less than 30% of that at 24 h caffeine abstinence. The increase in HR did not differ at 24 h (40 ± 7%) and 12 h abstinence (39 ± 5%, p = 0.62) nor did the increase in cardiac output (55 ± 8% vs. 48 ± 8%, p = 0.68). Reported symptoms and the blood pressure reaction did not differ between 24 h and 12 h abstinence, Figure 1. Conclusion: Twelve hours caffeine abstinence results in a lower coronary flow reserve compared to 24 hours and there is a large inter-individual difference to caffeine abstinence. This needs to be taken into consideration when performing adenosine perfusion imaging studies. (Figure Presented).
|
|
| 22. |
- Carlsson, Marcus, et al.
(författare)
-
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
-
Ingår i: Journal of Cardiovascular Magnetic Resonance. - 1097-6647. ; 13:55
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 23. |
- Carlsson, Marcus, et al.
(författare)
-
Submaximal adenosine-induced coronary hyperaemia with 12 h caffeine abstinence: implications for clinical adenosine perfusion imaging tests.
- 2015
-
Ingår i: Clinical Physiology and Functional Imaging. - : Wiley. - 1475-0961 .- 1475-097X. ; 35:1, s. 49-56
-
Tidskriftsartikel (refereegranskat)abstract
- Adenosine is widely used as a vasodilator agent in myocardial perfusion imaging. Caffeine inhibits the effect, but the time of caffeine abstinence needed is under discussion and varies from 12 to 24 h. Therefore, our aim was to examine whether the time of caffeine abstinence affects the hyperaemic response using quantification of coronary sinus flow (CS F) with cardiac magnetic resonance (CMR) during adenosine infusion.
|
|
| 24. |
- Carlsson, Marcus, et al.
(författare)
-
Total heart volume variation throughout the cardiac cycle in man.
- 2004
-
Ingår i: American Journal of Physiology: Heart and Circulatory Physiology. - : American Physiological Society. - 1522-1539 .- 0363-6135. ; 287:1, s. 243-250
-
Tidskriftsartikel (refereegranskat)abstract
- Variations in total heart volume (atria plus ventricles) during a cardiac cycle affect efficiency of cardiac pumping. The goals of this study were to confirm the presence, extent, and contributors of total heart volume variation during the cardiac cycle in healthy volunteers with the use of MRI. Eight healthy volunteers were examined by MRI at rest. Changes in total cardiac volume throughout the cardiac cycle were calculated using the following methods: 1) planimetry derived from gradient-echo cine images and 2) flow-sensitive sequences to quantify flow in all vessels leading to and from the heart. The maximum total heart volume diminished during systole by 8.2 +/- 0.8% (SEM, range 4.8-10.6%) measured by method 1 and 8.8 +/- 1.0% (SEM, range 5.6-11.8%) by method 2 with good agreement between the methods [difference according to Bland-Altman analysis -0.6% +/- 1.0% (SD), intraclass correlation coefficient = 0.999]. This decrease in volume is predominantly explained by variation at the midcardiac level at the widest diameter of the heart with a left-sided predominance. In the short axis of the heart, the change of slice volume was proportional to the end-diastolic slice volume. The present study has confirmed the presence of total heart volume variation that predominantly occurs in the region of atrioventricular plane movement and on the left side. The total heart volume variation may relate to the efficiency of energy use by the heart to minimize displacement of surrounding tissue while accounting for the energy required to draw blood into the atria during ventricular systole.
|
|
| 25. |
- Cronqvist, Mats, et al.
(författare)
-
Evaluation of time-of-flight and phase-contrast MRA sequences at 1.0 T for diagnosis of carotid artery disease. I. A phantom and volunteer study
- 1996
-
Ingår i: Acta Radiologica. - 1600-0455. ; 37:3 Pt 1, s. 267-277
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE AND MATERIAL: The aim of this work was, firstly, to compare different manufacturer-provided MRA sequences in a 1.0 T MR unit, with respect to the visibility of an artificial stenosis in a flow phantom and, secondly, to evaluate the same sequences in healthy volunteers with respect to S/N ratio levels and practical in vivo implementation routines. METHODS: The studied sequences were 2D and 3D TOF and sequences with an acquisition time of approximately 10 min. Quantitative signal evaluation was made using single transverse partitions in all phantom experiments. MIP angiograms and MPR reconstructions were made for visual inspection of image quality. In vivo, the images were individually evaluated by visual inspection by experienced neuroradiologists. RESULTS: In the evaluation of the grade and length of a stenosis, a combination of MIP and MPR was seen to be the optimal and necessary procedure. A shortening of TE played an important and significant role in the visualization of the poststenotic flow in the phantom using TOF MRA. However, the shortest TE values gave poor S/N ratio in vivo. The good results achieved in the phantom studies for 3D phase-contrast were somewhat reversed in the volunteer studies, whereas 3D TOF sequences showed good results in both the phantom and the volunteer studies.
|
|
| 26. |
- Engellau, Lena, et al.
(författare)
-
MR evaluation ex vivo and in vivo of a covered stent-graft for abdominal aortic aneurysms: ferromagnetism, heating, artifacts, and velocity mapping
- 2000
-
Ingår i: Journal of Magnetic Resonance Imaging. - 1522-2586. ; 12:1, s. 112-121
-
Tidskriftsartikel (refereegranskat)abstract
- Magnetic resonance imaging (MRI) safety was evaluated at 1.5 T in a covered nickel titanium stent-graft (Vanguard) used for endovascular treatment of abdominal aortic aneurysms (AAAs). Imaging artifacts were assessed on MRI with contrast-enhanced (CE) three-dimensional (3D) MR angiography (MRA) and spiral computed tomography (CT) in 10 patients as well as ex vivo. Velocity mapping was performed in the suprarenal aorta and femoral arteries in 14 patients before and after stent-graft placement. For comparison it was also performed in six healthy volunteers. No ferromagnetism or heating was detected. Metal artifacts caused minimal image distortion on MRI/MRA. The artifacts disturbed image evaluation on CT at the graft bifurcation and graft limb junction. No significant differences in mean flow were found in patients before and after stent-graft placement. Our study indicates that MRI at 1.5 T may be performed safely in patients with the (Vanguard) stent-graft. MRI/MRA provides diagnostic image information. Velocity mapping is not included in our routine protocol.
|
|
| 27. |
- Eriksson, Joakim, et al.
(författare)
-
Measurements of Kinematic Properties of the Cervical Spine Using Magnetic Resonance Imaging
- 1998
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents kinematic data on the cervical and upper thoracic spine, based on measurements made on 20 Scandinavian healthy, female volunteers, aged 22-58 years (mean age 40.4). The aim was to provide anatomical in vivo data, primarily intended as data for biomechanical modelling of the upper spine. Together with the measurements of standard anthropometric body dimensions, magnetic resonance imaging (MRI) was used to capture the inner anatomy for each subject. A rigid linkage system is described for the vertebrae C1 –Tvi, with one link per vertebra. Measurements include link lengths, link rotations, and antero-posterior endpoints of the spinous process. Furthermore, correlation coefficients are calculated between link lengths and anthropometric measurements. Also presented are regression equations for each link length, with stature as a predictor. Using additional images of lower accuracy, a sub-study (N=15) investigated possible differences in link length and link rotation between non-flexion and maximum-flexion of the neck. The differences in link lengths were significant (p>0.05) for only 1 of 16 measured links (Cii-Tx). Regarding link rotation, differences were significant for 4 links (Cv–T1). Finally, the precision of the results was evaluated using two methods: by using a phantom for determining the geometrical uncertainties caused by the scanner; and by comparing results between two repeated measurement rounds. The phantom test revealed that the pixel resolution and magnetic field inhomogenities had only a minor influence on the results. The comparisons of repeated measurements revealed a significant difference for the links Ci and Cii, indicating that the landmarks for determining the occipital and Ci/Cii joints were the most difficult to identify on the images.
|
|
| 28. |
|
|
| 29. |
- Geijer, Bo, et al.
(författare)
-
Persistent high signal on diffusion-weighted MRI in the late stages of small cortical and lacunar ischaemic lesions
- 2001
-
Ingår i: Neuroradiology. - : Springer Science and Business Media LLC. - 1432-1920 .- 0028-3940. ; 43:2, s. 115-122
-
Tidskriftsartikel (refereegranskat)abstract
- Diffusion-weighted imaging (DWI) is very sensitive to early brain infarcts. However, the late stages have been insufficiently studied. Infarcts in small vessel disease are often multiple and of different ages, and differentiation between new and old lesions might be difficult. We have therefore studied the change with time in DWI of small (< 3 ml) ischaemic lesions. We imaged 21 patients with an acute lacunar syndrome and a lesion visible on early DWI. They all had three MRI examinations 12-58 h (early), 7-16 and 54-144 days after the onset of stroke; 10 patients with high DWI signal on the third examination had a fourth examination 12-28 months after the stroke. MRI was performed at 1.5 T, using echo-planar DWI with 7 b-values from 0 to 1200 x 10(6) s/m2 and conventional T2-weighted imaging. After 7-16 days 18 of 21 lesions gave high signal on DWI, and 12/16 measurable lesions had a decreased apparent diffusion coefficient (ADC). After 54-144 days ten lesions still gave high DWI signal and two still had an ADC below normal. On the fourth examination there was no remaining high DWI signal and all ADC were higher than normal.
|
|
| 30. |
- Geijer, Bo, et al.
(författare)
-
Radiological diagnosis of acute stroke. Comparison of conventional MR imaging, echo-planar diffusion-weighted imaging, and spin-echo diffusion-weighted imaging
- 1999
-
Ingår i: Acta Radiologica. - : SAGE Publications. - 1600-0455 .- 0284-1851. ; 40:3, s. 255-262
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To compare conventional MR imaging, echo-planar diffusion-weighted imaging (EP-DWI) and spin-echo diffusion-weighted imaging (SE)-DWI at radiological diagnosis of acute stroke. MATERIAL AND METHODS: Twenty-seven patients (30-85 years old) were examined. Clinical examination was performed before MR imaging. All MR examinations were assessed by an experienced neuroradiologist blinded to clinical findings. RESULTS: In EP-DWI, every patient had a lesion corresponding to the clinical findings. EP-DWI was used as the gold standard. In conventional PD+T2 imaging, 23/59 focal lesions were interpreted as acute, which was false in 11 lesions, and 36/59 lesions were considered to be old, 6 were in fact acute. Nine acute lesions were only detected retrospectively and 12 acute lesions were not detected at all on PD+T2. SE-DWI including the apparent diffusion coefficient correlated fairly well with EP-DWI but the procedure was impractical. CONCLUSION: EP-DWI is reliable for diagnosis of early ischemic stroke, while SE-DWI performs reasonably well. Conventional PD+T2 imaging is not reliable for diagnosis of early ischemia.
|
|
| 31. |
- Geijer, Bo, et al.
(författare)
-
The value of b required to avoid T2 shine-through from old lucunar infarcts in diffusion-weighted imaging
- 2001
-
Ingår i: Neuroradiology. - : Springer Science and Business Media LLC. - 1432-1920 .- 0028-3940. ; 43:7, s. 511-517
-
Tidskriftsartikel (refereegranskat)abstract
- Multiple small infarcts of different ages are common in small-vessel disease. Diffusion-weighted imaging (DWI) is a powerful method for discriminating new from chronic lesions. This can be done on the diffusion-weighted images provided that b is sufficiently high. Our purpose was to determine that critical value of b. We reviewed DWI from a previous study of acute, mainly lacunar strokes, and selected 18 old lacunar infarcts, well defined on uncoded images with b 0 s/m2 (i. e., T2-weighted images) but invisible on DWI with b 1,200 x 10(6) s/m2. We used a 1.5 tesla imager and single-shot echo-planar technique. We had seven separate acquisitions with echo time 123 ms and b in steps between 0 and 1,200 x 10(6) s/m2. Two neuroradiologists blinded to the selection of lesions carried out two different lesion-detection procedures, thereby testing each lesion four times, giving a total of 72 tests of b values. The results were consistent, indicating a level for detection of 800 x 10(6) s/m2 in two tests, 400-600 x 10(6) s/m2 in 65 tests and at lower values in the remainder. For imagers up to 1.5 tesla, at long repetition times and an echo time up to 120 ms T2-shine through of old lacunar infarcts can be avoided using b of 1,000 x 10(6) s/m2.
|
|
| 32. |
|
|
| 33. |
|
|
| 34. |
- Hedström, Erik, et al.
(författare)
-
Effects of gadolinium contrast agent on aortic blood flow and myocardial strain measurements by phase-contrast cardiovascular magnetic resonance
- 2010
-
Ingår i: Journal of Cardiovascular Magnetic Resonance. - 1097-6647. ; 12
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 35. |
- Holmqvist, Catarina, et al.
(författare)
-
Collateral flow in coarctation of the aorta with magnetic resonance velocity mapping: correlation to morphological imaging of collateral vessels.
- 2002
-
Ingår i: Journal of Magnetic Resonance Imaging. - : Wiley. - 1522-2586 .- 1053-1807. ; 15:1, s. 39-46
-
Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To correlate quantification of collateral flow in aortic coarctation with the morphological visualization of the collateral vessels and to compare different approaches to measurement of collateral flow. MATERIALS AND METHODS: Thirteen children with coarctation were examined with T1-weighted spin-echo (T1-W SE) imaging and 3D contrast-enhanced magnetic resonance angiography (MRA). MR velocity mapping was performed at four levels in the descending aorta. RESULTS: The flow immediately above and below the coarctation did not differ significantly. Measuring within the coarctation resulted in flow overestimation. The increase of flow from proximal to distal aorta was 12 +/- 21% in patients with no or uncertain collaterals and 69 +/- 55% in patients with pronounced collaterals. Spin-echo images and MRA were comparable in visualizing collateral vessels. The visual estimation of collaterals correlated reasonably well with flow quantification MR velocity mapping. CONCLUSION: Collateral flow assessment with MR velocity mapping is an accurate technique for evaluating the hemodynamic importance of a coarctation and is recommended if abundant collaterals are not visualized with spin echo or MRA.
|
|
| 36. |
|
|
| 37. |
|
|
| 38. |
|
|
| 39. |
|
|
| 40. |
- Juul-Kristensen, Birgit, et al.
(författare)
-
Muscle Sizes and Moment Arms of Rotator Cuff Muscles Determined by Magnetic Resonance Imaging
- 2000
-
Ingår i: Cells Tissues Organs. - : S. Karger AG. - 1422-6405 .- 1422-6421. ; 167, s. 214-222
-
Tidskriftsartikel (refereegranskat)abstract
- Biomechanical models which require information on, e.g., joint torque and muscle force are useful in the estimation of when and how mechanical overload of the musculoskeletal system may lead to disorders. The aim was to study the reliability and validity of magnetic resonance imaging (MRI) to quantify muscle sizes and moment arms by MRI and to test selected anthropometric measures as predictors of muscle sizes and moment arms. A total of 20 healthy Scandinavian women (age 22–58 years) participated in an MRI scanning of their dominant shoulder. With a PC-based program the reliability and the validity of the MRI measurements was estimated to be high, and mean anatomical cross-sectional areas (ACSA) and muscle lengths were measured to be 4.0, 9.8 and 12.1 cm2 and 12.0, 12.6 and 12.8 cm for m. supraspinatus, m. infraspinatus and m. subscapularis, respectively. Volumes were calculated to be 48.8, 125.1 and 153.6 cm3. Moment arms were measured with the upper arm in a neutral position and in a functional position of 34° abduction for m. supraspinatus only, and were 2.4 and 2.6 cm. Physiological cross-sectional area (PCSA) and its fiber force component were estimated from dissected fiber length and pennation angle. MRI volume and PCSA were 1.4–1.7 times higher than dissection data, primarily because of age differences. No external anthropometric measures were found to be predictors of volumes or moment arms.
|
|
| 41. |
- Jönsson, Bo-Anders, et al.
(författare)
-
EMERALD & EMIT – worldwide computer aided education and training packages in medical physics
- 2005
-
Ingår i: CAL-laborate. - 1443-4482. ; 13:June, s. 10-15
-
Tidskriftsartikel (refereegranskat)abstract
- This paper describes the development of two web based education and training packages EMERALD and EMIT designed to meet the training needs of professional medical physicists. The programme has been developed over a number of years by collaboration between hospitals and universities across Europe. The programme concentrates on assisting competence development in five initial areas; diagnostic radiology, nuclear medicine, magnetic resonance tomography, ultrasound and radiotherapy. Each of the topic areas includes around 50 training tasks in 5 hypertext workbooks, which are supplemented by an image database relevant to each topic. The training materials have been extensively refereed during their development and are now in use in 65 countries across the globe. Initial evaluation has shown that the material enhances the training experience and produces a more consistent output.
|
|
| 42. |
- Kahlon, Babar, et al.
(författare)
-
Is aqueductal stroke volume, measured with cine phase-contrast magnetic resonance imaging scans useful in predicting outcome of shunt surgery in suspected normal pressure hydrocephalus?
- 2007
-
Ingår i: Neurosurgery. - 0148-396X. ; 60:1, s. 124-129
-
Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: To evaluate clinical usefulness of cerebrospinal fluid stroke volume (SV) assessed in the cerebral aqueduct, via cine phase-contrast magnetic resonance imaging, for predicting outcome after shunt surgery in suspected normal pressure hydrocephalus. METHODS: Thirty-eight patients with suspected normal pressure hydrocephalus were included. SV was assessed using cine phase-contrast magnetic resonance imaging, and kept blinded until postoperative follow-up after 7 +/- 5.8 months (mean the results were standard deviation). Selection to surgery was based on a positive lumbar infusion test or cerebrospinal fluid tap test, and outcome was evaluated with objective tests. RESULTS: Six patients were excluded from SV measurements because of technical difficulties. Eight patients were not operated (negative lumbar infusion test and cerebrospinal fluid tap test). SV in the not operated patients (mean, 66 +/- 53 mu l) did not differ from the operated patients (95 +/- 78 mu l; P = 0.335). Operated patients showed statistically significant improvements in walk (P = 0.020), reaction time (P = 0.006), and memory (P = 0.001) tests. Patients were divided into three groups according to SV range: low (0-50 mu l), middle (51 - 100 mu l), and high (> 100 mu l). No statistically significant (P > 0.05) improvements in any of the objective tests were found in any of the SV the different SV ranges. The numbers of individually improved patients were similar in ranges: six out of seven in the low, nine out of nine in the middle, and five out of eight in the high range. Weak correlations were found between SV and the initial pulse,amplitude (R-s = 0.043; P = 0.014) as well as the plateau pulse amplitude (R-s = 0.043; P = 4) as measured with the lumbar infusion test. CONCLUSION: The data from this Study show no evidence that cine phase-contrast magnetic resonance imaging measurements of SV in the cerebral aqueduct are useful for selecting patients with normal pressure hydrocephalus symptoms to shunt surgery.
|
|
| 43. |
- Knutsson, Linda, et al.
(författare)
-
Absolute quantification of cerebral blood flow: correlation between dynamic susceptibility contrast MRI and model-free arterial spin labeling.
- 2010
-
Ingår i: Magnetic Resonance Imaging. - : Elsevier BV. - 1873-5894 .- 0730-725X. ; 28:1, s. 1-7
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 44. |
- Knutsson, Linda, et al.
(författare)
-
Absolute quantification of cerebral blood flow in normal volunteers: Correlation between Xe-133SPECT and dynamic susceptibility contrast MRI
- 2007
-
Ingår i: Journal of Magnetic Resonance Imaging. - : Wiley. - 1522-2586 .- 1053-1807. ; 26:4, s. 913-920
-
Tidskriftsartikel (refereegranskat)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).
|
|
| 45. |
- Knutsson, Linda, et al.
(författare)
-
Absolute quantification of perfusion using dynamic susceptibility contrast MRI: pitfalls and possibilities.
- 2010
-
Ingår i: Magma. - : Springer Science and Business Media LLC. - 1352-8661. ; 23, s. 1-21
-
Forskningsöversikt (refereegranskat)abstract
- Absolute quantification of cerebral blood flow, cerebral blood volume and mean transit time is desirable in the determination of tissue viability thresholds and tissue at risk in acute ischaemic stroke, as well as in cases where a global reduction in cerebral blood flow is expected, for example, in patients with dementia or depressive disorders. Absolute values are also useful when comparing sequential examinations of tissue perfusion parameters, for example, in the monitoring and follow-up of various kinds of therapy. Regardless of the method employed, a number of assumptions and approximations must be made to obtain absolute measures of perfusion. Furthermore, the different stages of data acquisition and processing are associated with various degrees of uncertainty. In this review, the problems of particular relevance to absolute quantification of cerebral perfusion parameters using dynamic susceptibility contrast magnetic resonance imaging are discussed, and possible solutions are outlined.
|
|
| 46. |
|
|
| 47. |
|
|
| 48. |
- Knutsson, Linda, et al.
(författare)
-
Combined diffusion weighting and CSF suppression in functional MRI.
- 2002
-
Ingår i: NMR in Biomedicine. - : Wiley. - 0952-3480. ; 15:3, s. 235-240
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, EPI pulse sequences with diffusion weighting for reduction of contributions from large vessels and inversion pulses in order to minimize the effects of CSF pulsations and CSF partial volume effects were developed for BOLD contrast investigations in functional MR imaging. One inversion recovery echo-planar imaging (IR-EPI) pulse sequence and one IR-EPI with additional diffusion weighting (DW-IR-EPI) were developed and compared to a standard gradient-echo EPI sequence in a cortical stimulation experiment in nine healthy volunteers. Stimulation of motor cortex was performed using a semi-complex finger-tapping paradigm in seven periods of alternating rest and stimulation. Comparison between the three pulse sequences was made by measuring the activated volume in each subject, as well as by calculating the relative signal increase during stimulation. Due to different baseline signal-to-noise levels in the images generated by the three pulse sequences, artificial noise was added so that the comparative investigation could be performed independently of the noise level. The activated volume was 128 +/- 73 pixels (mean +/- SD) using the standard EPI pulse sequence, 31 +/- 12 pixels using IR-EPI and 15 +/- 13 pixels when DW-IR-EPI was employed. The relative signal increase was 5.7 +/- 1.1% using standard EPI, 11.5 +/- 3.1% using IR-EPI and 9.9 +/- 2.4% using DW-IR-EPI. The activated volume obtained with the addition of extra noise, i.e. at equal S/N, was 70 +/- 50 pixels using the standard EPI, and when using IR-EPI, the activated volume was 28 +/- 13 pixels. At equal S/N, the signal increase was 7.3 +/- 1.4% using standard EPI and 12.0 +/- 3.6% using IR-EPI. In BOLD contrast imaging, a combination of diffusion weighting and inversion recovery appeared to reduce false activation caused by CSF pulsation and blood flow in large vessels.
|
|
| 49. |
- Knutsson, Linda, et al.
(författare)
-
Dynamic Susceptibility Contrast MRI at 7 T:Tail-Scaling Analysis and Inferences About Field Strength Dependence
- 2017
-
Ingår i: Tomography : a journal for imaging research. - : MDPI AG. - 2379-1381. ; 3:2, s. 8-74
-
Tidskriftsartikel (refereegranskat)abstract
- Dynamic susceptibility contrast magnetic resonance imaging (DSC-MRI) following bolus injection of gadolinium contrast agent (CA) is widely used for the estimation of brain perfusion parameters such as cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT) for both clinical and research purposes. Although it is predicted that DSC-MRI will have superior performance at high magnetic field strengths, to the best of our knowledge, there are no reports of 7 T DSC-MRI in the literature. It is plausible that the transfer of DSC-MRI to 7 T may be accompanied by increased R2* relaxivity in tissue and a larger difference in ΔR2*-versus-concentration relationships between tissue and large vessels. If not accounted for, this will subsequently result in apparent CBV and CBF estimates that are higher than those reported previously at lower field strengths. The aims of this study were therefore to assess the feasibility of 7 T DSC-MRI and to investigate the apparent field-strength dependence of CBV and CBF estimates. In total, 8 healthy volunteers were examined using DSC-MRI at 7 T. A reduced CA dose of 0.05 mmol/kg was administered to decrease susceptibility artifacts. CBV, CBF, and MTT maps were calculated using standard DSC-MRI tracer-kinetic theory. Subject-specific arterial partial volume correction factors were obtained using a tail-scaling approach. Compared with literature values obtained using the tail-scaling approach at 1.5 T and 3 T, the CBV and CBF values of the present study were found to be further overestimated. This observation is potentially related to an inferred field-strength dependence of transverse relaxivities, although issues related to the CA dose must also be considered.
|
|
| 50. |
- Knutsson, Linda, et al.
(författare)
-
Dynamic susceptibility contrast MRI with a prebolus contrast agent administration design for improved absolute quantification of perfusion.
- 2014
-
Ingår i: Magnetic Resonance in Medicine. - : Wiley. - 1522-2594 .- 0740-3194. ; 72:4, s. 996-1006
-
Tidskriftsartikel (refereegranskat)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.
|
|
