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M Jenkinson

Publications and source records attributed to M Jenkinson.

12 recordsLinked to original sources
PubMed2005

A consistent relationship between local white matter architecture and functional specialisation in medial frontal cortex.

Functionally significant landmarks in the brain do not necessarily align with local sulcal and gyral architecture in a manner that is consistent across individuals. However, the functional specialisation underlying these landmarks is strongly constrained by the connectional architecture of the region. Here, we explore this relationship in the supplementary motor area (SMA) and pre-SMA in the medial frontal cortex of the human brain. Using diffusion tensor, conventional and functional MR imaging, we find that the location of the functional boundary between SMA and preSMA is more consistent with respect to specific features of the local white matter as it approaches neocortex than with respect to the local gyral and sulcal anatomy in the region.

Adult↗
PubMed2003

Characterization and propagation of uncertainty in diffusion-weighted MR imaging.

A fully probabilistic framework is presented for estimating local probability density functions on parameters of interest in a model of diffusion. This technique is applied to the estimation of parameters in the diffusion tensor model, and also to a simple partial volume model of diffusion. In both cases the parameters of interest include parameters defining local fiber direction. A technique is then presented for using these density functions to estimate global connectivity (i.e., the probability of the existence of a connection through the data field, between any two distant points), allowing for the quantification of belief in tractography results. This technique is then applied to the estimation of the cortical connectivity of the human thalamus. The resulting connectivity distributions correspond well with predictions from invasive tracer methods in nonhuman primate.

Algorithms↗
PubMed2003

MRI brain T1 relaxation time changes in MS patients increase over time in both the white matter and the cortex.

OBJECTIVE: To test the sensitivity of whole-brain T1 relaxometry to the evolution of pathological changes in multiple sclerosis (MS). BACKGROUND: T1-weighted hypointense lesion load in the brains of patients with MS is associated with axonal loss. Other work has shown that T1 measurements may provide information complementary to existing imaging techniques, such as magnetization transfer imaging. METHODS: The authors studied 14 MS patients twice over a median time interval of 19.5 months (range, 14-22 months). Structural images and whole-brain T1 maps using a novel rapid-scanning technique (3 min/study) were performed at 3 T. Analysis focused on defining changes separately in the lesional and normal-appearing white matter (NAWM) and in the cortical gray matter. RESULTS: At baseline, there was an inverse relationship between disease duration and the NAWM T1 histogram peak height (r = -0.75, P = .03). The total white matter T1 histogram peak height decreased over time (P < .001). This could be accounted for by changes in the NAWM (P < .03). There also was a decrease (6%) in the mean (11 of 14 patients, P = .004) and in the median (7%) (13 of 14 patients, P < .001) neocortical gray matter T1 over the follow-up period. CONCLUSIONS: Brain T1 maps can be generated quickly and are sensitive to pathological changes over time. T1 values in both the gray and the white matter at the baseline visit were related to disease duration, suggesting that the T1 changes are clinically relevant. Although the absolute values will be different, it is likely that similar changes will be able to be detected at 1.5 T. The role of T1 measurement as a magnetic resonance imaging outcome measure in clinical trials now should be explored.

Adult↗
PubMed2002

White matter and lesion T1 relaxation times increase in parallel and correlate with disability in multiple sclerosis.

Previous studies have established the clinical relevance of hypointense lesions ("black holes") on T1-weighted MRI as a surrogate marker for pathological change [36]. In contrast to measuring the volume of "black holes", the direct measurement of T1 values allows an objective assessment of the changes contributing to hypointensity both in the focal lesions and in the normal appearing white matter (NAWM). The aims of this study were first, to determine the relationship between T1 values in the NAWM and in discrete lesions, second, to test the relationship between white matter T1 changes and measures of disability and third, to determine whether pathology leading to T1 change occurred in thalamic grey matter of patients with multiple sclerosis. 24 patients with clinically definite multiple sclerosis (13 with relapsing-remitting multiple sclerosis and 11 with secondary progressive multiple sclerosis) and 11 controls participated. White matter T1 histograms and mean T1 values for the thalamus were generated from whole brain T1 relaxation time maps measured using a novel echo-planar imaging based MRI sequence at 3Tesla. Tissue segmentation based on T2- and T1-weighted images allowed independent study of changes in lesions and NAWM. White matter T1 histograms from the patient group showed a reduced peak height and a shift towards higher T1 values (p = 0.028) relative to controls. The mean thalamic T1 was greater for secondary progressive patients than for healthy controls (p = 0.03). Mean white matter T1 values correlated significantly with disability (r = 0.48, p = 0.02). The mean T1 value in the T1-hypointense lesions correlated strongly with the mean T1 value in the NAWM (r = 0.80, p < 0.001). No significant relationship was found between mean white matter T1 value and cerebral volume (r = -0.23, p = 0.31). The T1 measurements extend previous observations suggesting that changes in the NAWM occur in parallel with pathology in lesions of MS. T1 measurements of either the total or NAWM therefore may provide a potentially observer- and scanner- independent marker of pathology relevant to disability in MS.

Adult↗
PubMed2001

A global optimisation method for robust affine registration of brain images.

Registration is an important component of medical image analysis and for analysing large amounts of data it is desirable to have fully automatic registration methods. Many different automatic registration methods have been proposed to date, and almost all share a common mathematical framework - one of optimising a cost function. To date little attention has been focused on the optimisation method itself, even though the success of most registration methods hinges on the quality of this optimisation. This paper examines the assumptions underlying the problem of registration for brain images using inter-modal voxel similarity measures. It is demonstrated that the use of local optimisation methods together with the standard multi-resolution approach is not sufficient to reliably find the global minimum. To address this problem, a global optimisation method is proposed that is specifically tailored to this form of registration. A full discussion of all the necessary implementation details is included as this is an important part of any practical method. Furthermore, results are presented for inter-modal, inter-subject registration experiments that show that the proposed method is more reliable at finding the global minimum than several of the currently available registration packages in common usage.

Brain Mapping↗
PubMed2000

Evidence for adaptive functional changes in the cerebral cortex with axonal injury from multiple sclerosis.

Axonal injury occurs even in the earliest stages of multiple sclerosis. Magnetic resonance spectroscopic imaging (MRSI) measurements of brain N:-acetylaspartate (NAA), a marker of axonal integrity, show that this axonal injury can occur even in the absence of clinically evident functional impairments. To test whether cortical adaptive responses contribute to the maintenance of normal motor function in patients with multiple sclerosis, we performed MRSI and functional MRI (fMRI) examinations of nine multiple sclerosis patients who had unimpaired hand function. We found that activation of the ipsilateral sensorimotor cortex with simple hand movements was increased by a mean of fivefold relative to normal controls (n = 8) and that the extent of this increase was strongly correlated (sigma = -0.93, P = 0.001) with decreases in brain NAA. These results suggest that compensatory cortical adaptive responses may help to account for the limited relationship between conventional MRI measures of lesion burden and clinical measures of disability, and that therapies directed towards promoting cortical reorganization in response to brain injury could enhance recovery from relapses of multiple sclerosis.

Aspartic Acid↗
PubMed2000

The motor cortex shows adaptive functional changes to brain injury from multiple sclerosis.

Although multiple sclerosis (MS) is an inflammatory demyelinating disease, there can be substantial axonal injury and loss. We therefore hypothesized that adaptive cortical changes may contribute to limiting functional impairment, particularly in the early stages of the disease. To test our hypothesis, we used functional magnetic resonance imaging (MRI) to characterize the localization and volumes of activation in the motor cortex during simple flexion-extension finger movements. There were differences in the patterns of cortical activation with movement between the 12 MS patients and the 12 normal controls. All patients showed greater relative supplementary motor area activation than did the normal controls. The relative hemispheric lateralization of sensorimotor cortex (SMC) activation decreased in direct proportion to the total cerebral T2-weighted MRI hyperintense lesion load. This appeared to be due primarily to increases in ipsilateral SMC activation with increasing lesion load in white matter of the hemisphere contralateral to the limb moved. The center of activation in the contralateral SMC was shifted a mean of 8.8 mm posterior in patients relative to controls, providing additional evidence for cortical adaptive responses to injury. The magnitude of this posterior shift in the SMC activation increased with greater T2 lesion loads. These observations demonstrate that cortical recruitment for simple finger movements can change both quantitatively and qualitatively in the SMCs of MS patients, suggesting that cortical reorganization or "unmasking" of latent pathways can contribute to functional recovery. These adaptive changes are another factor potentially limiting the strength of the relationship between MRI measures of pathology and clinical measures of disability.

Adaptation, Physiological↗
PubMed1997

Synaesthesia in the normal limb.

We explored the degree to which vision may alter kinaesthetic perception by asking participants to view their hand through a prism, introducing different horizontal deviations, while trying to align their fingers above and below a thin table. When the visual image of one hand was displaced this overwhelmed kinaesthetic judgements and participants reliably reported that they felt their limbs were aligned, even when they were laterally mis-aligned by as much as 10 cm. This effect, however, was mediated by 'visual capture' and when the task was attempted in a darkened room with limb position indicated by an LED taped to the finger, kinaesthesis dominated and participants reported that the LED seemed to become detached from their finger tip. In both light and dark conditions the finger was clearly visible and only the background detail was extinguished. Hence, in perceiving limb position, it appears that we believe in what we see, rather than in what we feel, when the visual background is rich, and in what we feel when the visual background is sparse.

Arm↗
PubMed1986

Efficacy of mevinolin as adjuvant therapy for refractory familial hypercholesterolaemia.

Mevinolin, a potent inhibitor of cholesterol synthesis, was used as a therapeutic adjuvant in patients with refractory familial hypercholesterolaemia for an average period of 13 months. Sustained decreases in serum cholesterol of 23 and 31 per cent were achieved by doses of 20 mg and 40 mg/day respectively in 13 heterozygotes already on cholestyramine or after partial ileal bypass. Administration of 80 mg/day to three patients undergoing plasma exchange reduced peak serum cholesterol levels by 11.5 per cent in two homozygotes and by 17 per cent in a double heterozygote for familial hypercholesterolaemia and type III hyperlipoproteinaemia. The decrease in cholesterol was largely confined to low-density lipoprotein and no significant changes occurred in serum triglyceride or high-density lipoprotein cholesterol. Mevinolin was well-tolerated except in one patient who developed myositic symptoms; asymptomatic, transient elevations of serum enzymes were observed in five others. Short and long Synacthen tests showed no evidence that the drug impaired adrenocortical response to ACTH. These results indicate that mevinolin provides a safe and highly effective means of reducing LDL levels in patients with heterozygous familial hypercholesterolaemia refractory to conventional treatment but is less useful in homozygotes.

Adult↗
PubMedDate not supplied

Normalized accurate measurement of longitudinal brain change.

PURPOSE: Quantitative measurement of change in brain size and shape (e.g., to estimate atrophy) is an important current area of research. New methods of change analysis attempt to improve robustness, accuracy, and extent of automation. A fully automated method has been developed that achieves high estimation accuracy. METHOD: A fully automated method of longitudinal change analysis is presented here, which automatically segments brain from nonbrain in each image, registers the two brain images while using estimated skull images to constrain scaling and skew, and finally estimates brain surface motion by tracking surface points to subvoxel accuracy. RESULTS AND CONCLUSION: The method described has been shown to be accurate ( approximately 0.2% brain volume change error) and to achieve high robustness (no failures in several hundred analyses over a range of different data sets).

Adult↗