Biomedical subjects

M E Bastin

Publications and source records attributed to M E Bastin.

At least 19 recordsLinked to original sources

PubMed2006

MR diffusion-weighted imaging and outcome prediction after ischemic stroke.

BACKGROUND: MR diffusion-weighted imaging (DWI) shows acute ischemic lesions early after stroke so it might improve outcome prediction and reduce sample sizes in stroke treatment trials. Previous studies of DWI and outcome produced conflicting results. OBJECTIVE: To determine whether DWI lesion characteristics independently predict outcome in a broad range of patients with acute stroke. METHODS: The authors recruited hospital-admitted patients with all severities of suspected stroke, assessed stroke severity on the NIH Stroke Scale (NIHSS), performed early brain DWI, and assessed outcome at 3 months (modified Rankin Scale). Clinical data and DWI lesion parameters were evaluated in a logistic regression model to identify independent predictors of outcome at 3 months and a previously described "Three-Item Scale" (including DWI) was tested for outcome prediction. RESULTS: Among 82 patients (mean NIHSS 7.1 [+/-6.3 SD]), the only independent outcome predictors were age and stroke severity. Neither DWI lesion volume nor apparent diffusion coefficient nor the previously described Three-Item Scale predicted outcome independently. Comparison with previous studies suggested that DWI may predict outcome only in patients with more severe cortical ischemic strokes. CONCLUSIONS: Across a broad range of stroke severities, diffusion-weighted imaging (DWI) did not predict outcome beyond that of key clinical variables. Thus, DWI is unlikely to reduce sample sizes in acute stroke trials assessing functional outcome, especially where estimated treatment effects are modest.

Acute Disease↗

PubMed2006

White matter integrity and cognition in childhood and old age.

OBJECTIVE: To test the hypothesis that white matter integrity, as measured by diffusion tensor and magnetization transfer MRI is significantly associated with cognitive ability measured in youth and old age. METHODS: Forty, nondemented, surviving participants of the Scottish Mental Survey of 1932 underwent brain MRI and a battery of psychometric tests covering major cognitive domains and tests of information processing efficiency. IQ scores were available from age 11. Mean diffusivity, fractional anisotropy (FA), and magnetization transfer ratio (MTR) were measured in frontal and parieto-occipital white matter and centrum semiovale. RESULTS: Centrum semiovale FA correlated (r = 0.36 to 0.56; p < 0.02) with contemporaneous (age 83) scores on psychometric tests of nonverbal reasoning, working memory, executive function, and information processing efficiency. Centrum semiovale FA also correlated with IQ at age 11 (r = 0.37; p = 0.02). Controlling for IQ at age 11 and information processing at age 83 attenuated the association between centrum semiovale FA and general cognitive ability by approximately 85%. MTR, largely, did not show significant correlations with cognitive test scores. CONCLUSIONS: These data support the information processing efficiency hypothesis of cognitive aging and suggest one foundation for individual differences in processing efficiency. They also suggest that studies of imaging and cognition in the elderly should take into account prior mental ability rather than assuming that any associations between imaging parameters and cognitive test scores are the result of age-related changes.

Aged, 80 and over↗

PubMed2006

Effects of dexamethasone on cerebral perfusion and water diffusion in patients with high-grade glioma.

BACKGROUND AND PURPOSE: The mechanisms by which the glucocorticoid dexamethasone produces its therapeutic action in patients with intracranial tumors still remain unclear. The purpose of this study was to investigate whether dexamethasone affects cerebral perfusion and water molecule diffusion by using quantitative dynamic susceptibility contrast perfusion MR imaging (DSC-MR imaging) and diffusion tensor MR imaging (DT-MR imaging). METHODS: Ten consecutive patients with glioblastoma multiforme underwent DSC-MR imaging and DT-MR imaging before and 48-72 hours after dexamethasone treatment (16 mg/day). Cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT), and water mean diffusivity ( ) were measured for enhancing tumor, nonenhancing peritumoral edematous brain, and normal-appearing contralateral white matter before and after steroid therapy. The percentage change in CBF, CBV, MTT, and for the 3 tissue types was calculated for each patient, a mean value obtained for the population, and the statistical significance determined by using a paired-samples Student t test. RESULTS: After dexamethasone treatment, there was no significant change in tumor CBF, CBV, or MTT. Edematous brain CBV and MTT were also unchanged. There was, however, an increase in edematous brain CBF (11.6%; P = .05). was reduced in both enhancing tumor (-5.8%; P = .001) and edematous brain (-6.0%; P < .001). There was no significant change in CBF, CBV, MTT, or for normal-appearing contralateral white matter after treatment. CONCLUSION: These data suggest that dexamethasone does not significantly affect tumor blood flow but may, by reducing peritumoral water content and local tissue pressure, subtly increase perfusion in the edematous brain.

Adult↗

PubMed2005

Do acute diffusion- and perfusion-weighted MRI lesions identify final infarct volume in ischemic stroke?

BACKGROUND AND PURPOSE: An acute mismatch on diffusion-weighted MRI (DWI) and perfusion-weighted MRI (PWI) may represent the "tissue-at-risk." It is unclear which "semiquantitative" perfusion parameter most closely identifies final infarct volume. METHODS: Acute stroke patients underwent DWI and PWI (dynamic-susceptibility contrast imaging) on admission (baseline), and T2-weighted imaging (T2WI) at 1 or 3 months after stroke. "Semiquantitative" mean transit time (MTTsq=first moment of concentration/time curve), cerebral blood volume (CBVsq=area under concentration/time curve), and cerebral blood flow (CBFsq=CBVsq/MTTsq) were calculated. DWI and PWI lesions were measured at baseline and final infarct volume on T2WI acquired > or =1 month after stroke. Baseline DWI, CBFsq, and MTTsq lesion volumes were compared with final T2WI lesion volume. RESULTS: Among 46 patients, baseline DWI and CBFsq lesions were not significantly different from final T2WI lesion volume, but baseline MTTsq lesions were significantly larger. The correlation with final T2WI lesion volume was strongest for DWI (Spearman rank correlation coefficient rho=0.68), intermediate for CBFsq (rho=0.55), and weakest for MTTsq (rho=0.49) baseline lesion volumes. Neither DWI/CBFsq nor DWI/MTTsq mismatch predicted lesion growth; lesion growth was equally common in those with and without mismatch. CONCLUSIONS: Of the 2 PWI parameters, CBFsq lesions most closely identifies, and MTTsq overestimates, final T2WI lesion volume. "DWI/PWI mismatch" does not identify lesion growth. Patients without "DWI/PWI mismatch" are equally likely to have lesion growth as those with mismatch and should not be excluded from acute stroke treatment.

Adult↗

PubMed2005

Cognitive correlates of cerebral white matter lesions and water diffusion tensor parameters in community-dwelling older people.

BACKGROUND: The biological basis of cognitive ageing is unknown. One underlying process might be disruption of white matter tracts connecting cortical regions. White matter lesions (WML) seen on structural MRI may disrupt cortical connections, but diffusion tensor MRI (DT-MRI) parameters - mean diffusivity ( ) and fractional anisotropy (FA) - may reflect more subtle changes in white matter integrity. Here the relationships between WML load, DT-MRI parameters and cognition in a large cohort of elderly subjects with a very narrow age range were investigated. METHODS: 105 community-dwelling volunteers underwent MRI and neuropsychological assessment. Seventy-two (68.6%) were female, and their mean age was 78.4 (SD 1.5) years. Scans were rated for WML load. and FA were measured from regions of interest in normal-appearing frontal and occipital white matter, and centrum semiovale. RESULTS: and FA differed significantly among the three brain regions studied (p << 0.01). increased with age (r = 0.22 to 0.35, p < 0.03), and was negatively correlated with FA (r = -0.20 to -0.51, p < 0.05) in all three regions. There was a trend towards increased WML load correlating with poorer cognitive function, and this was statistically significant for the Mini-Mental State Examination (rho = -0.23, p = 0.02). was generally negatively correlated with cognitive test score, and FA was positively correlated. This pattern was more consistent for than for FA, and particularly for verbal fluency ( : r = -0.22 to -0.27, p < 0.03), which measures executive function. CONCLUSIONS: DT-MRI parameters, in particular , are sensitive to early ultrastructural changes underlying cognitive ageing. Executive function may be the cognitive domain most sensitive to age-related decline in white matter tract integrity.

Aged↗

PubMed2005

Possible structural abnormality of the brainstem in unipolar depressive illness: a transcranial ultrasound and diffusion tensor magnetic resonance imaging study.

BACKGROUND: Most empirically derived antidepressants increase monoamine levels. The nuclei of cells synthesising these monoamines are located in the brainstem, and projection tracts such as the medial forebrain bundle reach virtually all other brain areas. Two studies of unipolar depressive illness using transcranial ultrasound have reported reduced echogenicity of the brainstem midline in unipolar depressed patients. This may be consistent with disruption of white matter tracts, including the medial forebrain bundle, and it has been suggested that the effect of such disruption could be reversed by antidepressants. OBJECTIVE: To replicate these findings in a group of unipolar depressed patients and controls. METHODS: Fifteen unipolar depressed patients and 15 controls were studied using transcranial ultrasound imaging and diffusion tensor magnetic resonance imaging (DT-MRI). RESULTS: No difference in echogenicity of the brainstem midline of unipolar depressed patients was found. A possible trend (Cohen's d = 0.39) in the direction of previous studies was found. Although the echogenicity of the brainstem midline of the control group was found to be similar to previous reports, there was no reduction in the patient group. Additionally, no structural abnormality of the brainstem was identified using DT-MRI. CONCLUSIONS: While these data do not replicate the findings of previous studies reporting a significant reduction in the echogenicity of the brainstem midline in unipolar depressed patients, the ultrasound investigation indicated that there may be a trend in this direction. Given the importance of identifying the causes of depressive illness, it is important that other groups attempt similar studies.

Adult↗

PubMed2004

Effects of dexamethasone on peritumoural oedematous brain: a DT-MRI study.

OBJECTIVES: Glucocorticoids (dexamethasone) are thought to reduce peritumoural brain oedema by decreasing the permeability of neoplastic capillaries and/or enhancing the clearance of extracellular water. Diffusion tensor magnetic resonance imaging (DT-MRI) was used to measure the water diffusion parameters of oedematous and normal brain in a group of patients with intracranial tumours before and after steroid treatment. METHODS: Fifteen patients with intracranial tumours (seven with high-grade glioma, four with metastatic carcinoma and four with meningioma) were examined before and 48-72 h after dexamethasone treatment (16 mg/day). The mean diffusivity ( ) and fractional anisotropy (FA) were measured for oedematous brain and apparently normal contralateral white matter before and after steroid therapy. RESULTS: In all three patient groups there was a significant decrease in of oedematous brain after steroid treatment (p<0.01). There was no significant change in FA of oedematous brain after treatment in any of the three groups. There was also no significant change in either or FA of apparently normal contralateral white matter after treatment. CONCLUSION: These data indicate that dexamethasone produces a localised reduction in the magnitude of extracellular water molecule mobility, and hence water content, in peritumoural oedematous brain. Furthermore, the magnitude of these changes is similar for both intra- and extra-axial tumours.

Adult↗

PubMed2004

Temporal evolution of water diffusion parameters is different in grey and white matter in human ischaemic stroke.

OBJECTIVES: Our purpose was to investigate whether differences exist in the values and temporal evolution of mean diffusivity ( ) and fractional anisotropy (FA) of grey and white matter after human ischaemic stroke. METHODS: Thirty two patients with lesions affecting both grey and white matter underwent serial diffusion tensor magnetic resonance imaging (DT-MRI) within 24 hours, and at 4-7 days, 10-14 days, 1 month, and 3 months after stroke. Multiple small circular regions of interest (ROI) were placed in the grey and white matter within the lesion and in the contralateral hemisphere. Values of [grey], [white], FA[grey] and FA[white] were measured in these ROI at each time point and the ratios of ischaemic to normal contralateral values ( R and FAR) calculated. RESULTS: and FA showed different patterns of evolution after stroke. After an initial decline, the rate of increase of [grey] was faster than [white] from 4-7 to 10-14 days. FA[white] decreased more rapidly than FA[grey] during the first week, thereafter for both tissue types the FA decreased gradually. However, FA[white] was still higher than FA[grey] at three months indicating that some organised axonal structure remained. This effect was more marked in some patients than in others. R[grey] was significantly higher than R[white] within 24 hours and at 10-14 days (p<0.05), and FAR[white] was significantly more reduced than FAR[grey] at all time points (p<0.001). CONCLUSIONS: The values and temporal evolution of and FA are different for grey and white matter after human ischaemic stroke. The observation that there is patient-to-patient variability in the degree of white matter structure remaining within the infarct at three months may have implications for predicting patient outcome.

Aged↗

PubMed2004

In which patients is diffusion-weighted magnetic resonance imaging most useful in routine stroke care?

BACKGROUND AND PURPOSE: Magnetic resonance (MR) diffusion-weighted imaging (DWI) has been used extensively in hyperacute cortical ischemic stroke, but its broader role in the assessment of patients presenting at later times after a wider variety of strokes has been less widely studied. METHODS: The authors assessed the clinical usefulness of DWI across a range of patients referred prospectively as either inpatients or outpatients. Detailed clinical information was collected. Diffusion (DWI) and T2-weighted images were read separately and blindly to clinical details. The presence of any infarct and its type were noted. RESULTS: In 153 stroke patients, imaged at a median of 2 days (range, 6 hours to 77 days) after stroke, recent infarcts were identified more often on DWI (70%) than on T2-weighted MRI (32%) in all severities of stroke. The proportion of scans on which relevant lesions were only seen on DWI was greatest among milder strokes due to small cortical or lacunar infarcts and among patients imaged later rather than earlier after the stroke. CONCLUSIONS: DWI is clinically useful up to several weeks after stroke, not just within the first few hours, and especially in patients with minor strokes.

Adult↗

PubMed2003

Rapid clinical deterioration in a patient with multi-focal glioma despite corticosteroid therapy: a quantitative MRI study.

A patient with high-grade multi-focal glioma deteriorated rapidly despite high dose corticosteroid therapy (dexamethasone: 16 mg/day). MRI was used to measure diffusion tensor parameters and longitudinal relaxation time (T1) values of peritumoural oedematous brain before and after commencing steroid treatment. Forty-eight hours after steroid treatment there was no evidence of brain oedema reduction. Specifically, regions of oedematous brain showed a significant increase in mean diffusivity ( ) with a significant decrease in diffusion anisotropy (p < 0.05), but without any change in T1 values. These quantitative MRI data were mirrored by the rapid deterioration seen when assessing the patient clinically. This case shows that quantitative MRI can not only measure steroid treatment response but also failure in patients with malignant gliomas.

Brain Neoplasms↗

PubMed2003

Diffuse brain oedema in idiopathic intracranial hypertension: a quantitative magnetic resonance imaging study.

OBJECTIVES: To investigate the hypothesis that idiopathic intracranial hypertension is associated with diffuse brain oedema, using quantitative magnetic resonance imaging. METHODS: Values for the mean diffusivity of water ( ) and the proton longitudinal relaxation time (T1) were measured for various brain regions in 10 patients with idiopathic intracranial hypertension and 10 age, sex, and weight matched controls. RESULTS: No significant differences in and T1 values were found between patient and control groups in any of the brain regions investigated. CONCLUSIONS: The results suggest that idiopathic intracranial hypertension is not associated with abnormalities of convective transependymal water flow leading to diffuse brain oedema.

Adolescent↗

PubMed2003

Structural disconnectivity in schizophrenia: a diffusion tensor magnetic resonance imaging study.

BACKGROUND: There is growing evidence that schizophrenia is a disorder of cortical connectivity. Specifically, frontotemporal and frontoparietal connections are thought to be functionally impaired. Diffusion tensor magnetic resonance imaging (DT-MRI) is a technique that has the potential to demonstrate structural disconnectivity in schizophrenia. AIMS: To investigate the structural integrity of frontotemporal and frontoparietal white matter tracts in schizophrenia. METHOD: Thirty patients with DSM-IV schizophrenia and thirty matched control subjects underwent DT-MRI and structural MRI. Fractional anisotropy - an index of the integrity of white matter tracts - was determined in the uncinate fasciculus, the anterior cingulum and the arcuate fasciculus and analysed using voxel-based morphometry. RESULTS: There was reduced fractional anisotropy in the left uncinate fasciculus and left arcuate fasciculus in patients with schizophrenia compared with controls. CONCLUSIONS: The findings of reduced white matter tract integrity in the left uncinate fasciculus and left arcuate fasciculus suggest that there is frontotemporal and frontoparietal structural disconnectivity in schizophrenia.

Anisotropy↗

PubMed2002

Is diffusion imaging appearance an independent predictor of outcome after ischemic stroke?

BACKGROUND: MR diffusion-weighted imaging (DWI) in ischemic stroke can be quantified by calculating the apparent diffusion coefficient (ADC) or measuring lesion volume. OBJECTIVE: To clarify the association between DWI lesion parameters, clinical stroke severity at baseline, and the relationship with functional outcome. METHODS: Consecutive patients with stroke were categorized for stroke type (Oxford Community Stroke Project Classification [OCSP]) and severity (Canadian Neurologic Scale [CN Scale]) before DWI. The ratio of the trace of the apparent diffusion tensor in the ischemic lesion to the mirror image area in the contralateral hemisphere was calculated ( r). The volume of the visible lesion on DWI was measured. Any visible lesion on T2-weighted imaging (T2WI) was noted. All assessments were blind to all other information. A blinded observer obtained a 6-month Rankin score. Univariate and multivariate analyses were performed to test for independent associations with outcome. RESULTS: In 108 patients, those with lower (i.e., more abnormal) r values had more severe strokes according to the CN Scale (p = 0.01) and the OCSP stroke type (p = 0.002), a large lesion on DWI (p = 0.05), a visible lesion on T2WI (p = 0.001), and poor 6-month functional outcome (p = 0.009). However, on logistic regression, neither r nor DWI lesion volume were independent predictors of 6-month outcome over and above age and stroke severity. CONCLUSION: The r is associated with functional outcome, but that is because it and DWI lesion volume are also associated with stroke severity. Although DWI lesion features are univariate surrogate outcome predictors, the authors were unable to show that they were independent outcome predictors in the current study. Differences between these and other results may be due to differences in study design, sample size, and case mix.

Adult↗

PubMed2001

Diffusion tensor imaging (DTI) and proton magnetic resonance spectroscopy (1H MRS) in schizophrenic subjects and normal controls.

Several proton magnetic resonance spectroscopy (1H MRS) studies in schizophrenia have found reduced N-acetyl aspartate (NAA) concentrations in pre-frontal and temporal regions of the brain. Reductions in NAA may reflect abnormalities of neuronal structure (e.g. reduced neuronal density or viability) or abnormalities of neuronal function. Diffusion tensor imaging (DTI) measures diffusion anisotropy, an indicator of the structural integrity of a neuronal tract. Both techniques were used to examine the anatomical basis of pre-frontal dysfunction in schizophrenia. Ten patients with DSM-IV schizophrenia were compared with 10 healthy controls. 1H MRS and DTI were performed on a clinical MR system and analysed with a region of interest approach. NAA concentrations and diffusion anisotropy were measured in the same pre-frontal white matter region. Diffusion anisotropy was also measured in a control region (occipital white matter). 1H MRS revealed non-significant but consistently reduced NAA concentrations (by 10-15%) in the pre-frontal white matter in schizophrenic subjects. Diffusion anisotropy measures revealed no such differences between schizophrenics and controls. It is concluded that the abnormalities of 'connectivity' reported in brain-imaging studies of schizophrenia may not be attributable to structural abnormalities of white matter and that reduced NAA in the pre-frontal white matter may reflect abnormal function of structurally intact neurons.

Adult↗

PubMed2001

Utilizing the diffusion-to-noise ratio to optimize magnetic resonance diffusion tensor acquisition strategies for improving measurements of diffusion anisotropy.

It is well known that quantitative anisotropy measurements derived from the diffusion tensor are extremely sensitive to noise contamination. The level of noise in the diffusion tensor imaging (DTI) experiment is usually measured from some estimate of the signal-to-noise ratio (SNR) in the component diffusion-weighted (DW) images. This measure is, however, highly dependent on experimental parameters, such as the diffusion attenuation b-value and the diffusion coefficient of the subject. Conversely, the diffusion-to-noise ratio (DNR), defined as the SNR of the calculated diffusion tensor trace map, provides a reliable estimate of noise contamination, which is largely independent of such parameters. In this work it is demonstrated how reliable anisotropy measurements can be obtained using an image acquisition strategy that optimizes the DNR of the DTI experiment. This acquisition scheme is shown to provide noise-independent measurements of typical diffusion anisotropy values found in the human brain.

Anisotropy↗

PubMed2001

On the use of the FLAIR technique to improve the correction of eddy current induced artefacts in MR diffusion tensor imaging.

Eddy current induced geometric distortions can only be accurately corrected in brain diffusion-weighted echo-planar (DW-EP) images for b-values less than approximately 300 s mm(-2) using the iterative cross-correlation (ICC) algorithm. This is due to the difference in signal intensity of the cerebrospinal fluid (CSF) compartment in the diffusion-weighted and baseline T(2)-weighted echo-planar (T2W-EP) images. At larger values of b, image misalignment artefacts can, however, be removed by directly correlating CSF-suppressed T2W-EP images with non-CSF-suppressed and CSF-suppressed DW-EP images. Separate phantom experiments can also be performed to provide eddy current calibration data. Here the ability of these methods to remove eddy current induced artefacts from DW-EP images collected in volunteer diffusion tensor imaging (DTI) experiments is investigated. Monte Carlo simulations show that in order for the ICC algorithm to produce accurate estimates of the eddy current induced distortions at b-values greater than 1000 s mm(-2), the degree of CSF suppression should be greater than approximately 80%. This condition is typically met for FLAIR inversion times between 0.5 and 0.8 of the spin-lattice relaxation time of CSF. In volunteer studies the most complete image realignment was provided by direct correlation of CSF-suppressed T2W-EP and DW-EP images acquired in the FLAIR DTI experiment. These results indicate that although calibration data obtained from brain or phantom images can significantly reduce eddy current induced distortions, the optimum image realignment achievable using post-processing methods is likely to be that obtained by direct image warping techniques.

Algorithms↗

PubMed2000

A study of the apparent diffusion coefficient of grey and white matter in human ischaemic stroke.

We examined whether there was any difference in the value, and temporal evolution, of the apparent diffusion tensor trace (ADC) in acute and subacute grey and white matter lesions. Thirty-seven patients underwent diffusion imaging once (up to 3 days), 15 patients were scanned twice (up to 7 days), and seven patients were scanned three times (up to 14 days) after stroke. Values of the ratio of ischaemic to contralateral ADC (ADCr) were reduced on average by 30% (p<0.001) in the whole hyperintense region up to 7 days post-ictus. No difference was seen between ADCr values of grey and white matter in individual subjects within the patient groups scanned up to 7 days. However, in the subgroup of patients scanned beyond 7 days, ADCr for grey matter rose significantly (p=0.02) from ADCr approximately 0.7 (< 7 days) to 0.95 (> or = 10 days). This increase did not occur in white matter whose ADCr remained fairly constant (ADCr approximately 0.7) over the time course of the study.

Acute Disease↗

PubMed2000

Selecting an appropriate anisotropy index for displaying diffusion tensor imaging data with improved contrast and sensitivity.

A review of the behavior of different diffusion anisotropy indices (DAIs) to changes in diffusion anisotropy was undertaken and the limitations of several previously proposed DAIs are discussed. A mathematical representation of anisotropy sensitivity was used to enable image contrast and sensitivity to noise to be predicted. This technique was utilized to devise a new DAI, the gamma-variate anisotropy, which has a low sensitivity to noise and an improved contrast range for human brain imaging. This index can be easily modified for other applications, in that the range of anisotropy values to which it is highly sensitive can be altered. Magn Reson Med 44:117-121, 2000.

Anisotropy↗