technique in posterior circulation stroke[2]. is study aimed to investigate the effect of a high-resolution perfusion imaging (PI) sequence on posterior circulation ...
MRI methology
Fig 2 shows physiologic regional distribution in the occipital lobe, less pronounced with statistic thresholding.
Discussion/Conclusion: Converting the ASL perfusion maps to statistical maps of label vs. control response using GLM can provide a useful method of visual assessment of perfusion. The underlying hypothesis is that only areas that promptly respond to the labeling contrast are relevant for the assessment of perfusion. Areas with ambiguous response or poor statistical response certainty are toned down. The t statistic thresholding seems less sensitive to some artefacts, and blood vessels with high signal are less dominating. Due to the general unit of t values, a large control group could provide a database to which patients could be compared in a diagnostic situation. References: 1. Aslan et al. Magn Reson Med. 2010;63(3):765-71. 2. Henriksen et al. J Magn Reson Imaging. 2012;35(6):1290-9. 3. Deibler et al. AJNR Am J Neuroradiol. 2008;29(7):1228-34.
575 1.5 T Arterial Spin Labeling (ASL) regional cerebral blood flow (rCBF) mapping. 1, 2
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A. Pavilla , L. Ciobanu , A. Arrigo , M. Mejdoubi DSV, I2BM, NeuroSpin, LRMN, CEA, Gif sur Yvette/FRANCE, 2La Meynard, CHU PZQ, Fort-de-France/MARTINIQUE
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Purpose/Introduction: Establishing normal rCBF (regional cerebral blood flow) maps is a crucial source of knowledge for accurate interpretation in neurologic pathologies such as stroke and neurodegenerative diseases including Alzheimer’s dementia. This study aims to establish 1.5T PASL (Pulsed ASL) rCBF map in human brain. Only two studies proposed rCBF mapping ([1],[2]). Subjects and Methods: Twenty healthy volunteers were studied (10 women, 10 men). Mean age was 44 ± 13. All data were acquired with a 1.5T GE MR450w (GE, Milwaukee, WI). We used a 3D Spiral PASL sequence with the following parameters: 155° flip angle, TR/TE: 4554/ 10.76 ms; Post- labeling delay=1525 ms, FOV 24 x 24 cm, matrix size 512 x 8, slice thickness 4mm (without gap). Ten equal bilaterally volumes of interest (VOIs) in cortical and subcortical grey matter (GM), white matter (WM) and cerebellum were drawn by visual inspection of anatomical MR images. Single VOIs were drawn in protuberance and vermis. Results: No significant lateral asymmetry was observed in any region. Frontal cortical GM had the highest mean CBF: 69.6 ± 0.3 mL/100g/min. Occipital, parietal and temporal cortical GM CBF were 64.8 ± 2.4, 62.6± 0.6 and 56.7 ± 1.3 mL/100g/min, respectively. Subcortical mean CBF values were 57.6 ±
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1.7, 53.0 ± 0.5 and 53.4 ± 1.5 mL/100g/min for thalamus, caudate nucleus and hippocampus, respectively. Putamen had the lowest subcortical GM CBF (44.7±0.4 mL/100g/min). Cerebellum mean CBF was 57.9±0.2 mL/100 g/min. Vermis had high perfusion value with 67.9±12.0 mL/100 g/min and protuberance mean CBF was 45±6.7 mL/100g/min. WM CBF was the lowest of all regions (23.73± 0.3 mL/100 g/min). Discussion/Conclusion: Our results are similar with those obtained with 3T pCASL (pseudo continuous ASL) [2] except that we didn’t find any lateral significant asymmetries. Our results differ significantly from those obtained throught 1.5 T CASL (Continuous ASL) study that used another approach by vascular territories and not anatomical structures for CBF assessment [1]. We also found as in [2] rCBF variability across the brain with higher values in frontal cortical GM. This finding may be explained by the role of the frontal areas in attention control and maintenance. Lowest GM perfusion was found in putamen, likely due to the close pallidum which contains a high concentration of iron shortening the local T1. Quantitative knowledge of these normal physiological rCBF will be useful for proper neurologic physiology and pathology interpretation. References: [1] Floyd ,T, 2003, J.Magn.Reson.Med ,18:649–655 [2] Pfefferbaum,A,2010,Psychiat.Res-Neuroim,182 :266–273.
(0.37ml with StrokeTool and 2.86ml with PMA). The standard sequence had a significantly higher SNR (mean=89.77, SD=16.6 versus mean=55.01, SD=7.56).
Tridecane (mm²/sec)
Table 1: Alkane ADC values [1] [2] ADC measurements were performed either with our double loop endorectal coil prototype (60 mm length, 6 mm width) was successively taped on each bottle (fig 1) or an 8-channel torso array coil. Acquisition sequence: DW-EPI with FOV = 9 cm, matrix = 64×64, 3 in 1 gradients and 6 b-values: 0, 100, 300,500,800, 1100 s/mm2. Data Processing:For a given alkane, a ROI was defined and kept the same for all measurements (fig 2, 3,4).Inside the ROI, for each pixel, we performed a monoexponential fit with Levenberg-marquardt algorithm in order to estimate the ADC. Since the solution is homogeneous, the ADC final value was computed as the average value over the ROI we defined. The routine was developed under MATLAB (Mathworks). 10 consecutives measurements were performed (test-retest) on the same ROI. The coefficient of variation CV (ADC standard deviation / ADC mean) in the ROI was computed for reproducibility assessment. Results:
A.A. Khalil1,3, I. Galinovic2, P. Brunecker2, K. Villringer2, J.B. Fiebach2 International Graduate Program Medical Neurosciences, Charité Universitätsmedizin Berlin, Berlin/GERMANY, 2Centre for Stroke Research Berlin, Charité Universitätsmedizin Berlin, Berlin/GERMANY, 3ERASMUS MONDUS Joint Master Programme in Neuroscience, Bordeaux/FRANCE 1
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Hexadecane (mm²/sec)
Brugières 2004
The effect of slice thickness on perfusion imaging in posterior circulation stroke
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Pentadecane (mm²/sec)
Luciani 2008
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Purpose/Introduction: Perfusion MR imaging, which has been used to reveal potentially salvageable tissue after cerebral ischemia and to guide treatment strategies[1], is challenging in the infratentorial compartment. Partial volume effects and susceptibility artefacts hinder the clinical application of this technique in posterior circulation stroke[2]. This study aimed to investigate the effect of a high-resolution perfusion imaging (PI) sequence on posterior circulation stroke lesion volumes compared to the standard PI sequence using two commercially available perfusion analysis softwares. Subjects and Methods: Thirteen patients with a clinical diagnosis of posterior circulation stroke admitted to the Charité Universitätsmedizin Berlin received a standard MRI stroke protocol on the day of admission (including diffusion weighted imaging, FLAIR, standard 5mm slice-thickness PI and an MR angiography) and a modified protocol with a 2.5mm slice-thickness PI sequence on day 2. A diffusion weighted image (DWI) done on day 6 was used to assess final infarct size. The perfusion data was analyzed using Perfusion Mismatch Analyzer (PMA) version 3.4.0.6 and StrokeTool version 2.3 to generate quantitative cerebral blood flow (CBF) maps. Arterial input functions were automatically selected, manually optimized and a threshold (20ml/100g/ min) was set to generate volumes-of-interest corresponding to the perfusion deficits. Signal-to-noise ratios (SNR) were calculated for both sequences using Analyze version 11.0. Results: The mean perfusion lesion volumes for the standard sequence were 3.43ml and 5.92ml for StrokeTool and PMA respectively. For the high-resolution sequence the lesion volumes were 3.14ml and 3.51ml for StrokeTool and PMA respectively. Agreements between the softwares (limits of agreement = 15.56ml to -18.50ml) and the slice-thicknesses (limits of agreement = 19.8ml to -17.11ml) were poor. Differences between initial perfusion lesion volumes and final DWI volumes were smaller with the high-resolution sequence (0.09ml with StrokeTool and 0.45ml with PMA) compared to the standard sequence
assessing the accuracy and reproducibility of Apparent Diffusion Coefficient (ADC) measurements with distance. Subjects and Methods: Acquisition: Experiments were performed on a GE DVMR750 3T system (General Electric Medical Systems), on bottles of tridecane (8 cm long, 3.3 cm diameter), pentadecane (9.5 cm long, 4 cm diameter) and hexadecane(15 cm long, 6.5 cm diameter) solutions whose ADC values are known (Table 1).
Tridecane ADC (mm²/sec)
Discussion/Conclusion: There is currently little knowledge on whether noise or contrast has a greater influence on the accuracy of perfusion imaging. In this study, despite being associated with a higher level of noise, the high-resolution imaging sequence was relatively accurate in predicting final DWI outcomes in posterior circulation stroke compared to the standard sequence. References: t [1] Albers, G.W., et al., 2006, Ann Neurol, 508-517 t [2] Alvarez-Linera, J., 2010, Semin Ultrasound CT MR, 230-245
Pentadecane ADC Hexadecane ADC (mm²/sec) (mm²/sec)
8-channel torso array coil Endorectal coil Table 2: Measured Tridecane, Pentadecane and Hexadecane solutions ADC-values
577 ADC measurements with an endorectal coil: an in vitro study J.-M. Verret1, 2, F. Pilleul3, C. Rabrait1, O. Beuf2 1 Clinical Science Development Group, General Electric Healthcare, Buc/ FRANCE, 2CNRS UMR 5220, Inserm U630, Université de Lyon, CREATIS, Villeurbanne/FRANCE, 3HEH, Gastroenterology, Hospices Civils de Lyon, Lyon/FRANCE Purpose/Introduction: Diffusion Weighted Imaging (DWI) of the rectal cancer is a promising modality both for the detection of the rectal cancer and assessment of the response to chemotherapy treatment [1]. Because sensitivity of endorectal coil decreases rapidly with distance (fig 1) thus we aimed at
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