Brain: perfitsion and diffusion The recognition of the regulatory mechanisms underlying fMRI is an important topic for neurophysiological research as a fundamental issue for the understanding of the working of the human brain as well as for the assessment of fMRl-examinations of the pathological brain, where the normal BOLD effect cannot be always expected to exist.
References [1] Kuschinsky W, Wahl M. Physiol Rev 1978;58:656-689. [2] Grinvald A, Lieke EE, et al. Nature 1986;324:361-364. [3] Ernst T. et al. Magn Reson Med 1994;32:146-149; Hennig J, et al. Int J Syst Technol 1995;6:203; Menon RS, et al. Magn Resort Med 1995;33(3):453; Hu X, et al. Magn Reson Med 1997; 37(6):877; Yacoub E. et al. Magn Reson Med 1997:41(3):436. [4] Fox PT, Raichle ME. Proc Natl Acad Sci USA 1986;83:1140-1144. [5] Janz C, Schmitt C, et al. Proc 6th Ann Meeting ISMRM, Sydney, 1998, p. 4. 2-6-] W i l l i a m s
MRI Imaging Protocol: Imaging was performed on a 1.0 T GE imager. Multi-slice spin-echo EPI was performed with diffusion gradients applied in three orthogonal directions (b = 1000 s/rnm2), in addition to one unweighted image (b = 0), from which an isotropic diffusion-weighted image was calculated. PWI was performed by dynamic gradient echo EPI (TR/TE = 1500/45) tracking a bolus injection of 0.2 mmot/kg gadodiamide (Omniscan| Nycomed, Norway) at a rate of 5 ml/se. Data analysis: Maps of cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT) were calculated using a non-invasively determined arterial input function and SVD deconvolution [5]. The areas of hyperintensity on the DWl and MTT images were measured and volumes were calculated. Statistics: Pearson's correlation coefficient determined the correlation between the DWl or MTT lesion volume, and the SSS score. Results: In ten patients the lesion on DWI was a lacunar infarct, and eight of these were located in the basal ganglia (Fig. 1). In three patients the location was the cortical grey matter, and in one the cerebellum. A logarithmic transformation of the volumes on the DWl and PWl maps showed the best correlation with the SSS scores. Pearson correlation coefficient and P-values are shown in the table below. The lacunar infarcts in the basal ganglia we re also analysed separately (see Table). Volume DWI (log values) (n = 14)
-] Functional MRI: current status and f u t u r e perspectives Lucie Herk-Pannier. Brain functional mapping studies have tremendous implications for both the description of normal functional anatomy of neuronal networks, and the understanding of brain plasticity in patients with focal brain disorders. In normal subjects, inter-individual variability of both sulco-gyral anatomy and functional organization of cortical regions makes it impossible to infer on functional networks from the anatomy only. In patients, plasticity adds to this variability, and precise invasive cortical mapping may be required in cases of lesions located in or near critical regions that must be spared during surgery. Therefore, advances in non-invasive functional mapping are potentially revolutionary for both cognitive research and patient care. Among the numerous methods that are being developed to map non invasively functional networks, perfusion techniques such as 150-Positron Emission Tomography (PET) and BOLD functional MRI (f'MRI), provide an indirect reflection of neuronal activity, with lower temporal resolution, but with better spatial resolution, than electrophysiological techniques. BOLD functional MRI combines a number of advantages over tSO-PET for non invasive cortical mapping. Using examples of language block and event-related paradigms, we will illustrate the achievements of current functional MRI in research and clinical fields. Language fMRI individual studies have confirmed and largely extended the main hypotheses drawn from observations of brain-lesioned patients at the turn of the XXth century, and from the results of PET group studies, fMRI is now increasingly being accepted as a reference method for the assessment of hemispheric language dominance in patients, but further work is needed regarding precise presurgical localization of critical language areas. The perspectives include the need for combining various techniques (electrophysiology, diffusion, perfusion, and fMRI), along with sophisticated anatomical analysis, to gain better understanding of neuronal networks, connectivity, plasticity and cognitive development, in health and in disease.
r Acute SSS Subacute SSS Chronic SSS
MTT (n = I2) P
r
P
DWI (BG) (n = 8)
MTT (BG) (n = 8)
r
r
P
P
- 0 . 5 5 0.043* - 0 . 3 3 0.288 - 0 . 9 2 0.00t** - 0 . 6 0 0.024* - 0 . 6 6 0.019" - 0 . 8 3 0.011"
- 0 . 7 7 0.024* - 0 . 7 3 0.040*
- 0 . 5 2 0.060
-0.41
-0.I0
0.747
- 0 . 4 4 0.271
0.314
* Correlation sign at 0.05 level, or ** at 0.01 level. BG, lacunar infarct in the basal ganglia. Discussionand Conclusion:DWl was moderately correlated with the acute SSS score, and both DWI and PWI were highly correlated with the SSS score after 12-24 h, in agreement with previous reports [2,3]. When the infarctions in the basal ganglia were analyzed separately there was an even stronger correlation, probably because white matter lesions involving major tracts create more homogenous neurologic deficit. In contrast to previous studies, no significant .correlation was found between acute DWl or PWI and chronic neurologic deficit, probably due to our very early acute MRI (mean 5.5 h) where the size of the infarct was still in progress, and the long follow-up period (30 days). In conclusion, our result suggests that it is not possible to predict long term neurologic deficit from very early DWE/PWI.
Fig. 2. MRI 6 h after onset of symptoms. Hyperintensity in the left thalamus is seen on DWI (left), however, MTT is prolonged in the total MCA area (right).
Brain: perfusion and diffusion
Acknowledgements: Dr LeBihan for kind assistance; Nycomed Imaging for providing contrast agent.
' ~ ] Correlation between diffusion- and peffusion-weighted MRI and neurological deficit measured by Scandinavian Stroke Scale in acute stroke ( < 8 h) L. Rohl I, J. Geday~, L. Ostergaardz, C.Z. Simonsen2, P. Vestergaard-Poulsen3, G. Andersen2, C. Gyldensted t. tDepartment of Neuroradiology; "-Department of
Neurology; 3Department of Biomedical Engineering, Aarhus University Hospital, Aarhus, Denmark
Introduction: Diffusion- and perfusion-weighted MRI (DWI and PWI) has recently become a strong diagnostic method in the early assessment of cerebral ischaemia in humans [1]. However, reports on the relationship between neurologic deficit and DWI and PWI lesion volumes in humans in early ischaemia are scarce [2,3]. The purpose of this study was to evaluate the correlation between DWI/PWI and neurological deficit determined by Scandinavian Neurological Stroke Scale (SSS) [4]. Subject and Methods: DWI was performed in 14 patients within 8 h (mean 5,4 h) after onset of symptoms, but PWI failed in two patients due to patient movement. Neurological deficits were measured by SSS score acute (time of admission), subacute (12-24 h) and chronic (after 30 days).
References [1] Warach S, et al. Neurology 1992;42:1717-1723. [2] Lovblad KO, et al. Ann Neorol 1975;42: 164-170. [3] Tong DC, et al. Neorology 1998;50:864-870. [4] SSSG. Stroke 1985;16:885-890. [5] Ostergaard L, et al. MRM 1996;36:715-735.
~]
The identification of at-risk tissue in children with sickle cell disease using MR diffusion and perfusion imaging
F. Calamante ~, M. Bynevelt2, D.A. Porter l, C.L. Johnson ~, E. Strehle 2, M. Prengler2, W.K. Chongz, F.J. Kirkham 2, D.G. Gadian l, A. Connelly I.
1Radiology and Physics Unit, Institute of Child Health, UCL Medical School; -'Great Ormond St Hospital for Children, London, UK
Introduction:Although stroke is primarily a disease of adulthood, it occurs in children with a similar incidence to that of brain tumours. Aetiology is uncertain in many cases, and about 85% have eerebrovascular disease. Certain groups of children are at particular risk, such as those with sickle cell disease
Brain: perfusion and diffusion (SCDt, who have a stroke incidence similar to adults (285/105l: 11% have a stroke by the age of 20. The primary preventive treatment in SCD is by means of blood exchange transfusion [1]. Due to the long term adverse effects of this treatment, it is highly desirable to have a robust method for optimal patient selection and transfusion timing. The aim of this work was the evaluation of the role of diffusion and perfusion MRI in the investgation of children with SCD. Methods: MRI was performed on a Siemensl.5T Vision. Diffusion imaging was obtained using a FLAIR SE-EPI sequence, with a pair of diffusion gradients (TE/TR/TI = 86/8700/2100 ms; 128 • 128; 24 cm FOV: 5 mm slice thickness). Diffusion parameters: 6/A = 15/40.2 ms. b-values = 0 and 617 s/ mm2. A reference scan was acquired for the on-line correction of Bo-eddy-current effects [2]. ADC maps were calculated in three orthogonal directions, which were combined to calculate trace maps. Perfusion MRI was performed using a SE-EPI sequence (TE/TR = 0.1/1.5 s) during the passage of a bolus of Gd-DTPA through the brain [3]. A singular value decomposition method was used to obtain maps of CBF, CBV and MTT [3]. Results and Discussion: Diffusion studies were performed in over 60 patients with SCD, both symptomatic and asymptomatic The trace of the diffusion tensor was found to be not statistically significantly different in normal (noninfarcted) regions between the groups of patients with and without lesions. However, new lesions were observed in later scans in regions that had normal diffusion in the acute scan (as shown in Fig, l). Therefore, diffusion alone is not an adequate technique for the identification of tissue at risk in SCD patients. Combined diffusion and perfusion imaging was performed in 12 further children. These studies suggested that this combined analysis can be of great help to identify patients ~vho may benefit from blood transfusion (see Fig. 2). The techniques described can be performed on very young children and should contribute significantly to the management of children with SCD.
~]
Measurement of cerebral perfusion in patients with stenoses of the internal carotid artery by optimized EPI-sequences
S. Friese, U. Klose, T. N~igele, H. Krapf, K. Voigt. Department of Neuroradi-
ology, University Tubingen, Germany
Purpose: Patients
with high-grade stenoses of the internal carotid artery (ICA) may have a different perfusion in the cerebral hemispheres [1]. Dynamic susceptibility contrast (DSC) imaging [2] with an optimized EPl-sequence was performed to examine whether patients with different degrees of stenoses have a different cerebral perfusion and whether the perfusion would change after thrombendarterieetomy (TEA). Subjects and Methods: A total of 17 patients (mean age 72 years, 11 male, 2 female) with high-degree stenoses ( > 80%) on one ( N = 13) or both ( N = 4 ) sides were examined before and after TEA. The applied EPI-sequence (TE 83 ms; sl 4 ram; 1.5 T) generates three slices with 96 repetitions in 65 s achieving a high temporal resolution (0.68 s) for every slice with high spatial resolution (1.8 x 1.8 ram; matrix 128 • 128). A bolus of Gd-DTPA (0.1 mmol/kg KG) was administered during the measurement. Following parameter maps were calculated: a reference image and maps representing the time of contrast arrival (t~), and the time of the maximum signal reduction (to). In the reference images regions of interest (ROI) were located in the centrum semiovale and in the basal ganglia in both hemispheres. For the selected, anatomically nonpathologic regions the relative regional cerebral blood volume (rrCBV) and the rrCBF were estimated. Results: In 8/13 patients with unilateral stenoses a difference of the tp (mean 1.92 s) was measured. In 5/13 patients there was no difference. In these five patients and in three patients with a preoperatively existing difference between the hemispheres operation did not change the status. In the four patients with high-grade stenoses on both sides and/or occlusion on one side two had an improvement on the operated hemisphere (difference 2.5 s) and two did not show any changes. The improving patients had an elevated rrCBV before surgery and no hemispherical difference after operation. Discussion: Comparing the hemipheres, all patients with a unilateral delayed perfusion and elevated rrCBV have improved values (/p, rrCBV) after operation. It is suggested that patients with larger rCBV are at higher risk for ischemia [3] and therefore may profit from surgery.
References
Fig. 1. Trace maps from an SCD child (12 years) with severe headaches and
left hemiparesis. The scan l day after symptom onset showed a haemorrhagic infarct in the left hemisphere, without any abnormality in ADC or T 2 on the right. The follow-up scan (3 days later) showed a new ischaemic lesion in watershed areas on the right. Perfusion MRI was not available at the time, but left sided symptoms suggest it is likely there was a perfusion deficit on the right side at the time of the first scan, stressing the importance of combined perfusion/diffusion evaluation.
[1] Nighoghossian N. Berthezene Y, Philippon B, Adeieine P, Froment JC, Trouillas P. Stroke 1996:27:474-479. [2] Guckel F J, Brix G, Schmiedek P, Piepgras A, Becker G, K6pke J, Gross H, Georgi M. Radiology 1996:201:405-412.[3] Kluytmans M, van der Grnnd J, Klijn CJM, Kapelle LJ. Folkers PJM. Mali WPThM, Viergever MA. ISMRM 1997;5:1773.
~
Effect of occlusive carotid artery disease on cerebral perfusion parameters demonstrated by dynamic susceptibility contrast - - enhanced MR imaging
A. Jackson, A. Kassner, H. Chant, A. Farooq, C. McCollum. University of
Manchester, Philips Medical Systems, and South Manchester University Hospitals Trust, UK
Fig. 2. Perfusion MRI on an SCD child (11 years) with severe headaches but normal neurology. No abnormalities were seen on conventional MRI and DWI, but there was an extensive perfusion deficit on the right side and in a posterior region on the left. This was consistent with the transcranial Doppler findings - - R MCA velocity (V) 200 cm/s consistent with a 40% risk of stroke in the next 40 months [1]; L MCA V 185 cm/s. This tissue is probably at risk of stroke, which may be preventable with transfusion.
References [1] Adams RJ, et al. New Engl J Med 1998;339:339. [2] Calamante F, et al. MRM 1999;41:95. [3] Ostergaard L, et al. MRM 1996;36:715.
Introduction: Patients with stenotic or occlusive disease of the carotid arteries may suffer hypoperfusion induced infarction as a result of reduced cerebral blood flow (CBF), Assessing this risk is difficult, since hypoperfusional stroke occurs principally in patients with impaired collateral flow. It is therefore of clinical importance to assess the regional changes in CBF which result from arterial occlusive disease in individual patients. Dynamic susceptibility contrast-enhanced MR imaging (DSCI) has been used to measure regional distribution of relative cerebral blood volume (rCBV), mean transit time (MTT) and relative cerebral blood flow (rCBF). However, measurements of rCBV and rCBF produced by this technique are unscaled and do not allow inter-patient comparison. Previous workers have attempted to reference these measurements to apparently 'normal' areas such as the contra-lateral cerebral hemisphere or cerebellum [1]. The aim of this study was to examine the correlation between rCBF changes and true flow changes measured using flow quantification MR angiography (QF). Patients and Methods: Imaging was performed on 16 patients with unilateral or bilateral carotid stenosis greater than 70% on one side. Blood flow (BF) in the carotid, basilar and middle cerebral arteries was measured using QF. DSCI was performed using an axial 2D fast field echo multi-shot EPI sequence (TR 249 ms, TE 30 ms, FOV 230 • 158 mm, 128 • 92 matrix, 6 m m slices, EPI factor 9, 50 acquisitions). Contrast (Gadolinium DTPA-BMA, 0.1 mmol/kg) was administered by fast intravenous injection after ten acquisitions. Data was analysed using a gamma variate fitting technique to derive parametric maps of rCBV. rCBF, MTT and contrast arrival time TO [2]. Regions of interest
Brain: perfusion and diffusion corresponding to the middle cerebral artery and adjacent anterior and posterior watershed areas were identified using an affine transform. Hemispheric asymmetry measures of rCBV, rCBF, MTT and TO were correlated to CBF measurements from carotid, basilar and middle cerebral arteries. Simple mathematical normalisation of rCBF values (nCBF) was performed using the true CBF, calculated from QF images and the analysis repeated. Results: CBF measaured by QF ranged from 308 to 791 mt, min. Middle cerebral artery flow was consistenly lower on the side of the stenosis but these differences were not statistically significant and did not correlate to overall CBF. Asymmetry of rCBV and rCBF did not reach significance although significant elevations of MTT and TO were seen on the side of the worst stenosis. Asymmetry of MTT showed weak correlation with overall CBF, and middle cerebral artery CBF and TO also showed similar, stronger correlations. After data normalisation, nCBF measures from the watershed areas showed a strong correlation with CBF (Fig. 1). This change in nCBF was bilateral, worst ipsilateral to the stenosis but progressed more rapidly on the contralateral side. Asymmetry of nCBF therefore decreased with decreases in CBF. Discussion: Our results demonstrate that collateral flow mechanisms minimise asymmetry between cerebral hemispheres resulting from carotid stenosis. In the most severely affected watershed areas asymmetry of rCBF actually decreases as hypoperfusional insult worsens. This invalidates the concept of using 'normal' areas of the brain as reference measurements. As a result, true inter-patient comparison is not possible using this technique unless some alternative normalisation method is developed. The use of QF provides a first approximation normalisation measure and is superior to other currently used methods. 30o
lo0
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/.,
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en
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GRE-EPI by about a factor of two (see Table). Although the peak heights of the SE-EPI and GRE-EPI tissue curves were similar, the peak height of the AIF was about 2 times lower with SE-EPI compared to GRE-EPI. Average and standard deviation of the MTT. CBV, CBF and max from the ROIs drawn on the cortex, the thalamus (Thal) and the white matter (WM) and of the max of the AIF curves GRE-EPI
SE-EPI
ORE/ SE
7.9 + 2.5 8.2 • 0.7 68 + 20 0.32 + 0.08
7.5 + 1.6 14.8 _ 2.8 121 + 24 0.28 + 0.06
0.95 1.80 1.78 0.88
7.3_+3.1 9.0 _+ 1.2 81 _+22 0.35 _+0.06
7.1 _+ 1.6 18.5 _+ 5.0 156_+21 0.36 _+0.07
0.97 2.05 1.92 1.02
8.5 _+2.5 3.7 _+0.4 28 _+8 0.12 -+ 0.03
8.7 _+2.1 7.6 _+ 1.5 54 -+ 8 0.13 -+ 0.02
1.02 2.05 1.93 1.08
5.19 + 0.53
2.68 + 0.25
0.52
Cortex MTT (s) CBV(%) CBF (ml/min per t00 g Max (raw curves) (AU)
Thal MTT (s) CBV (%) CBF (mI/min per 100 g) Max (raw curves) (AU)
WM MTT (s) CBV(%) CBF (ml/min per 100 gl Max (raw curves) (AU)
AIF Max (AU)
Discussion and Conclusion: The acquisition technique had a big influence on the quantification of perfusion parameters. With SE techniques, the susceptibiltyinduced relaxivity is dependent on the vessel diameter and therefore a SE-EPI sequence is less sensitive than GRE-EPI to the susceptibility effect created by large vessels compared to small vessels and capillaries while a GRE-EPI sequence is not dependent on the vessel diameter [2]. We postulate that this leads to an underestimation of the AIF and therefore to an overestimation of CBV and CBF with SE-EPI. References
0 g
[1] Rempp KA, Brix G. Wenz F, et al. Radiology 1994;193:637-641. [2] Weiskoff RM, Zuo CZ, Boxerman JL, Rosen BR. MRM 1994;31:601-610. CBF mls/min
'] W h o l e b r a i n q u a n t i t a t i v e C B F and C B V using M R bolus
Fig. l. Correlations between CBF measured from QF data (x axis) and nCBF in the anterior watershed ipsilaeral (O, R-'=0.506) and contralateral (11, R e = 0.636) to the worst carotid stenosis. Note the decreasing asymmetry at low levels of CBF.
AM Smith, CB Grandin, F Mataigne. T Duprez, G Cosnard. Department oJ
References
Medical lmaging, Cliniques Universitaires Saint Luc, Universitb Catholique de Louvam, Brussels. Belgium
[1] Kluytmans M, van der Grond J, Folkers PJM. et al. JRMI 1998:8:767-774. [2] Boxerman JL, Rosen BR, Weisskoff RM. JMRI 1997:7:528-537.
Introduction: Although all methods for quantitatively calculating CBF and CBV
-32-~ Q u a n t i f i c a t i o n of brain perfusion with bolus t r a c k i n g M R I :
comparison of G R E - E P I and S E - E P I C.B. Grandin, A.M. Smith, F. Mataigne, T.P. Duprez. G. Cosnard. Department of Radiology, St. Luc University Hospital, Universit~ Catholique de Louvain. Brussels, Belgium
Introduction: Although methods based on indicator-dilution theory have been proposed for evaluating brain perfusion [1], absolute quantification of CBV and CBF remains challenging and may depend on numerous factors. In this study, we compared the influence of the acquisition technique on the quantification of perfusion parameters. Methods: Ten patients with unremarquable MR exam were enrolled for a perfusion study with either a GRE-EPI (n = 5, 64 _+ I0 years) or a SE-EPI (n = 5. 61 _+ 15 years) sequence acquired at 1.5 T. The GRE-EPI protocol was: TR/TE (ms) 2300/30, FOV 24 cm, slice thickness 5 ram, matrix 128 x 96, 24 axial slices and the SE-EPI protocol was: TR/TE (ms) 2000/79, FOV 20 cm, slice thickness 6 mm. matrix 96 x 96, 15 coronal slices. A bolus of Gd-DTPA was injected at a rate of 10 cc/s using a dose of 0.l mmol/kg for GRE-EPI and 0.2 mmol/kg for SE-EPI. For each study, an arterial input function (AIF) was calculated using an interactive program whereby the user selected 8-12 voxels with concentration versus time curves that showed an early, narrow and high peak. Quantitative CBV and CBF values were obtained by deconvolving the AIF from the tissue curves fitted to a gamma variate function and the MTI' was equal to CBV/CBF. Results: The MTT values did not differ between the two techniques but the CBV and CBF values were consistently higher with SE-EPI compared to
tracking: comparison of methodologies
in the brain using Gd-DTPA bolus tracking are based on indicator-dilution theory, differences in their implementation may cause significant differences in the CBF and CBV values. We compared two different implementations that have been described in the literature [1.2]. Methods: Twenty single-shot serial gradient echo EPI volumes (TE 30 ms, FOV 24 cm, slice thickness 5 mm, 128 x 96 matrix, 24 slices) were acquired every 2.3 s on a 1.5 T scanner (GE Milwaukee, WI) from 38 stroke patients. The bolus of Gd-DTPA was either injected at the same time or a few seconds before the start of image acquisition. The voxels used to calculate the arterial input function (AIF) were selected using an interactive program whereby the user selected those concentration versus time curves that showed an early and large peak, and 8-12 voxels were usually selected from the entire volume. In order for quantitative measures to be calculated, the AIF had to be deconvolved from the tissue curves. To perform this deconvolution, we used either the technique in [1] whereby the Gd-DTPA concentration versus time curves were fit to a gamma variate function and then the deconvolution was performed using the Fourier transform (called the FT technique) or the technique in [2] where the concentration versus time curves were deconvolved directly (i.e. no fitting was performed) using single value decomposition (called the NP-SVD technique). The CBF and CBV were calculated and compared for each technique in 210 regions using the same AIF for both techniques. The regions covered a wide range of possible flow values: thalamus, WM, infarct, penumbra, and mirror infarct and penumbra. Results: Figure IA shows the comparison between the FT CBF values and the NP-SVD CBF values for all 210 regions. Note the data show two distinct groups. When a subset of the regions was made by selecting regions with minimal truncation in the concentration versus time curves, the correlation between the two methods improved greatly (see Fig. IB). When a similar analysis was performed for the calculated CBV values using the two methods from the subset of regions, the result was y = 1.00x, r z = 0.84, whereas the result was y = l.fllx, r-' = 0.67 for all 210 regions.
Brain: perfusion ant/difjusion
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Fig. 1. A F T calculated CBF compared to NP-SVD CBF for all 210 regions. B. Same as A except only a subset of the regions were plotted (see text),
Fig. I. (A) CBF for the thalamus (upper curves) and WM (lower curves) regions calculated using the four different AIFs selected by the different radiologists (C. TD: + , GC: A. CG; [], FM). (B) CBV for the thalamus and WM regions using the same symbols as in A.
Conclusion: If enough time volumes were acquired to avoid truncation in concentration time curves, the two different techniques [1,2] for calculating CBF and CBV agreed very well. References [I] Rempp KA. Brix G, Wenz F, Becker CR, Giickel F, Lorenz WJ Radiology 1994;193:637-641. [2] ~stergaard L. Weisskoff RM, Chesler DA, Gyldensted C, Rosen BR, MRM, 1996;36:715-725.
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9
Whole brain quantitative CBF, CBV and MTT using MR bolus tracking: implementation
Thalamus
tN= 38)
WM (N = 38)
Infarct (N = 22)
Mir infarct Penum (N = 22) (N = 24)
Mir penum (N ~ 24)
CBF(ml/ 70,1_+22.8 283_+6.98 41.5-+23.9 62.3_+24.6 51.2_+16.3 66.1_+16.5 min per 100 g) CBV(%) 9.44_.3.0 4.03_+1.17 7.85_+2.67 8.19+__2.89 11,5+_2.74 1(},0-+252 MTT(s} 8.43_+2.61 8.90_+2.97 14.1_+6.97 8.38+2.40 14.1-+3.23 9.43-+2.60
Conclusion: A user independent whole brain bolus tracking technique t'or calculating CBF, CBV and MTT has been developed and the calculated CBF and CBV values matched well with those reported using single slice techniques [ 1,21. References
A.M. Smith, C.B. Grandin, F. Mataigne, T. Duprez, G~ Cosnard. Department
of Medical lmaghtg, Cliniques Universitaires Saint Luc. Universitb Catholique de Louvain, Brussels, Belgium Introduction: Single-slice MRI bolus tracking techniques of Gd-DTPA have been used to quantify CBF and CBV in the brain [1,2]. In this study, we implemented these techniques on whole brain T*-weighted volume acquisitions. Methods: Twenty single-shot serial gradient echo EPI volumes (TE 30 ms, FOV 24 cm, slice thickness 5 mm, 128 • 96 matrix, 24 slices) were acquired every 2.3 s on a 1.5 T scanner (GE Milwaukee, WI). The bolus of Gd-DTPA was either injected at the same time or a few seconds before the start of image acquisition, User interaction was necessary to calculate the arterial input function (AIF) voxels by selecting an early and narrow time window for the peak of the Gd-DTPA concentration versus time curves (we used a window width of a single volume acquisition or 2.3 s), and the user also had to select a minimum threshold (relative to the maximum value of those voxels contained in the time window) to include those voxels with large peaks. To test for inter-observer differences, four radiologists calculated the AIFs independently for 38 stroke patients. The CBF, CBV and MTT were calculated for six different regions: thalamus, centrum semiovale (WM), infarct, penumbra, and the mirror infarct and penumbra. Results: Figure 1 shows the excellent agreement between the radiologists when calculating the CBF and CBV for the thalamus and WM regions. The quantitative analysis from the six regions are reported in Table 1. Average and standard deviations of the CBF, CBV and MTT from all the patients for the 6 ROIs drawn in this study
[1] Rempp KA. Brix G, Wenz F, Becker CR, G/ickel F, Lorenz WJ. Radiology 1994:193:637-641. [2] Hagen T, Bartylla K, Piepgras U. JCAT 1999;23:257-264.
~-'] Quantitative diffusion imaging studies in a child with SturgeWeber Syndrome A. Connelly *, F. Calamante ~. D.A, Porter ~, W.K. Chonga, D.G. Gadian ], F.J. Kirkham3. 1Radiology and Physics, b*stitute of Child Health, University
College London Medical School; "-Department of Radiology; 3Department of Neurology, Great Ormond Street Hospital Jbr Children, London, UK Introduction: Sturge-Weber syndrome is a disease characterised by seizures, impaired psychomotor development, facial naevus, and leptomeningeal angiomatosis with perifocal calcification. In some patients, there is progressive cognitive impairment, while in others almost normal development takes place. The contributory factors to neurological deterioration associated with neurological deterioration are not yet clearly defined. However, it has been suggested that seizures may play a major role in such progression. In addition, investigations of cerebral blood flow and metabolism have suggested that cerebral ischaemia may contribute significantly. The aim of the present work was to investigate longitudinally a SWS patient with onset seizures using quantitative
10
Contrast agents: methodology
Fig. 1. ADCAv map and T2-weighted EPI 12 days after initial onset. Regions of reduced diffusion and low T z can be seen throughout the ipsilateral (left) hemisphere. MR diffusion imaging to determine if there is evidence of ischaemia following a period of repeated seizures. Methods: Patient: The patient was a 4 month old girl with a capillary haemangioma since birth. She presented at age 4 months with a seizure lasting 40 min, treated with diazepam. Despite further treatment, she continued over a period of 6 days to have further seizures, including one of 2 h and one of 30 min. The child was loaded with phenobarbitone, and no further clinical seizures or abnormal EEG were observed. MR: MR investigations were performed on a Siemens 1.5T Magnetom Vision system. T_~ weighted imaging and diffusion imaging were performed 6, 12 and 19 days after initial presentation. A FLAIR diffusion weighted EPI sequence was used. Imaging parameters were: TE = 86 ms, 128 x 128 matrix, 240 mm FOV, 5 mm slice thickness. The diffusion parameters were: ,~/A = 15/40.2 ms, and b-values of 0 and 617 s/mm 2. The effects of eddy currents were corrected as previously described [1]. ADC maps were calculated in three orthogonal directions, which were combined to calculate the trace of the diffusion tensor. Results: The ADC maps obtained at 6 days after initial onset of seizures show evidence of restricted diffusion throughout a substantial part of the abnormal left hemisphere. Representative regions show an ipsi/contralateral ADC ratio of 0.77 (cf typically of the order of 0.5 in stroke and 1.0 in controls). The ADC remains low in the affected areas of 12 and 19 days (ipsi/contralaterat ADC ratio 0.83 and 0.8, respectively). Throughout this period, the T2-weighted images show hypointensity in corresponding regions. Figure 1 shows examples of an ADC map and a T2-weighted image at 12 days post seizure onset. Discussion: Progressive hypoperfusion is associated with neurological deterioration in SWS [2]. In addition, patients with progressive symptoms show a reduced response in the contralateral hemisphere and in remote regions of the ipsilateral hemisphere to the administration of acetazolamide (a vasodilatory agent), suggesting haemodynamic compromise [3]. Also, the haemodynamic response to seizures is compromised ipsi- and contralaterally to the haemangioma [4], which may result in post-seizure hypoxia. The diffusion data presented in this work suggest that, not only is tissue compromised following prolonged seizure activity, but also that such a state can persist over a period of weeks. Moreover, the continued T,-weighted hypointensity is consistent with an increase in local deoxyhaemoglobin. The combined diffusion/T2 data are suggestive of tissue that is compromised, with an increased oxygen extraction fraction, but which has not proceeded to infarction. Further diffusion studies, in combination with MR perfusion studies, should provide important information regarding the mechanism of deficit progression in SWS.
Methods: Male SD rats (n = 18) were anesthetized. MnCI 2 (Sigma) was dissolved in normal saline (0.8 M). Three models used to study axonal transports in sciatic nerve: intra-neural injection (3 ~1), local application around sciatic nerve (10 I~1), injection in the junction of Gastrocnemius muscle-Achilles tendon (10 ~tl). Three-dimensional FISP with fat and MT suppression (50-58/ 10/60~ were acquired in coronal and axial plane (75-50 mm in FOV/128 • 128 in matrix size) with a small loop surface coil in 1.5T MRI (Vision, Siemens, Erlangen, Germany). In order to remove the contamination of flow signal in gradient echo sequence, the parallel saturation were applied in axial acquisition. Results: The contrast enhancement of sciatic nerve was well depicted in all of three models. The intra-neural injection showed the strongest enhancement. The speed of axonal transport was about 2 mm/h. The contrast enhancement can persist for at least 2 days. All of animals were well tolerated in local application and intra-muscular models, except two animals in intra-neural model had sciatic nerve injury with leg dysfunction which might be due to trauma induced by surgery and/or injection. Acute compression cannot block the transport of MnCI 2 (Fig. 1) Discussion: Two kinds of axonal transport have been demonstrated by MRI. Pautler et al. demonstrated the tracing fast axonal transport in CNS, such as olfactory nerve and optic nerve [1]. The intraneural injection of MION showed the slow axonal transport in sciatic nerve but it is relative invasive and traumatic to nerve itself [2]. Intra-muscular injection of CE-MRN can provide not only morphological but also functional abnormalities in peripheral nerve, by using the minimal invasive way.
Fig. 1. (A) lntra-neural injection. (B) Local application. (C) Intra-muscular injection.
References
References
[1] Calamante F, et al. MRM 1999;41:95. [2] Maria BL, et al. J Child Neurol 1998;13:1. [3] Okudaira Y, et al. Child Nerv Syst 1997;13:214. [4] Aylett SE, et al. Dev Med Child Neurol (in press).
[1] Pautler RG, Silva AC, Koretsky AP. Magn Reson Med 1998;40:740-748. [2] Van Everdingen KJ, Enochs WS, Weissleder, et al. Radiology 1994; 193:485 -491.
Contrast agents: methodology
F • - ]
~
Contrast-enhanced MR neurography ( C E - M R N )
H.C. Cheng 1'3, Henich H. Cheng 2. T.C. Yeh 1"3, J.C. Hsieh l, Larryy T. Ho l, C.Y. Chang3. 1Department of Medical Research and Education; 2Department of
Neurosurgery; 3Department of Radiology, VGH, Taipei
Introduction: MRI has been widely applied in clinical practice, especially in CNS. However, the peripheral nerve system is limited by the low contrast between nerves and surrounding soft tissue. So far, the imaging diagnosis of peripheral neuropathy is based on the anatomic abnormality or tumor invasion, not related to functional deficit of nerve itself. Here, we reported contrast-enhaneed MR neurography to demonstrate the sciatic nerve by the administration of MnCI_, in three different ways.
Manganese dipyridoxyl diphosphate: MRI contrast agent with antioxidant and cardioprotective properties?
H. Brurok 1, J.O.G. Karlsson 2, I. Laursen3, P. Jynge 1. 1Department of Physiology Biomed. Engineering, NTNU, Trondheirn, Norway; "-Department of Pharmacology, Linkoping University, Linkoping, Sweden; 3Deparonent of Automation, University of Technology, Lyngby, Denmark
Introduction: Recently, the liver MRI contrast agent manganese dipyridoxyl diphosphate (MnDPDP) was shown to attenuate cardiotoxicity of anthracyclines [1], probably by mimicking the action of superoxide dismutase (MTSOD) [2], which converts superoxide (.02-) to hydrogen-peroxide (H202) and oxygen. MnDPDP is metabolised [3] to Mn or zink (Zn) liganded pyridoxyl ethylenediamine diacetate (PLED). We wanted to examine whether MnDPDP, MnPLED and ZnPLED possess SOD-mimetic activity in vitro and whether MnDPDP protects the rat heart in oxidative stress.
