| 1. |
- Björkman-Burtscher, Isabella, et al.
(author)
-
Aneurysm clip MR artifacts. Titanium versus stainless steel and influence of imaging parameters
- 1998
-
In: Acta Radiologica. - 1600-0455. ; 39:1, s. 70-76
-
Journal article (peer-reviewed)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.
|
|
| 2. |
- Björkman-Burtscher, Isabella, et al.
(author)
-
Proton (1H) MR spectroscopy for routine diagnostic evaluation of brain lesions
- 1997
-
In: Acta Radiologica. - 1600-0455. ; 38:6, s. 953-960
-
Journal article (peer-reviewed)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.
|
|
| 3. |
- Björkman-Burtscher, Isabella, et al.
(author)
-
Quality assessment of localization technique performance in small volume in vivo 1H MR spectroscopy
- 1999
-
In: Magnetic Resonance Imaging. - 1873-5894. ; 17:10, s. 1511-1519
-
Journal article (peer-reviewed)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.
|
|
| 4. |
- Brockstedt, Sara, et al.
(author)
-
Quantitative diffusion coefficient maps using fast spin-echo MRI
- 1998
-
In: Magnetic Resonance Imaging. - 1873-5894. ; 16:8, s. 877-886
-
Journal article (peer-reviewed)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.
|
|
| 5. |
- Brockstedt, Sara, et al.
(author)
-
Triggering in quantitative diffusion imaging with single-shot EPI
- 1999
-
In: Acta Radiologica. - 1600-0455. ; 40:3, s. 263-269
-
Journal article (peer-reviewed)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.
|
|
| 6. |
- Brockstedt, Sara, et al.
(author)
-
Use of an enhanced gradient system for diffusion MR imaging with motion-artifact reduction
- 1995
-
In: Acta Radiologica. - 1600-0455. ; 36:6, s. 662-670
-
Journal article (peer-reviewed)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.
|
|
| 7. |
- Cronqvist, Mats, et al.
(author)
-
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
-
In: Acta Radiologica. - 1600-0455. ; 37:3 Pt 1, s. 267-277
-
Journal article (peer-reviewed)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.
|
|
| 8. |
- Eriksson, Joakim, et al.
(author)
-
Measurements of Kinematic Properties of the Cervical Spine Using Magnetic Resonance Imaging
- 1998
-
Other publication (other academic/artistic)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.
|
|
| 9. |
- Geijer, Bo, et al.
(author)
-
Radiological diagnosis of acute stroke. Comparison of conventional MR imaging, echo-planar diffusion-weighted imaging, and spin-echo diffusion-weighted imaging
- 1999
-
In: Acta Radiologica. - : SAGE Publications. - 1600-0455 .- 0284-1851. ; 40:3, s. 255-262
-
Journal article (peer-reviewed)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.
|
|
| 10. |
|
|
