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David K B Li

Publications and source records attributed to David K B Li.

8 recordsLinked to original sources
PubMed2006

Reproducibility and reliability of MR measurements in white matter: clinical implications.

The purpose of this study was to determine the reproducibility and reliability of five MRI-derived measurements, namely, total water content (WC), myelin water content (MWC), mean T2 relaxation time (GMT2), T1 relaxation time (T1) and magnetization transfer ratio (MTR). Five controls were scanned 5 times over 1 year. The five MR measurements were made for 5 white matter regions. All measurements were found to be highly reproducible. MTR had a low reliability coefficient because all individual values were similar. Therefore, MTR would be most sensitive in detecting changes from normal. WC had a high reliability coefficient in all regions. For MWC, GMT2 and T1, the overall reliability coefficients were high but for some individual regions were low. The high coefficients suggest that these measurements, although different between normal subjects, are consistent over time. They could be used to explore natural differences in the normal population, but due to the large spread in normal values, larger sample sizes are needed to detect pathological changes.

Adult↗
PubMed2006

The role of MRI in the diagnosis of multiple sclerosis.

There is no single test that is diagnostic of MS, including MRI. The lesions detected with MRI are pathologically nonspecific. The principles of MS diagnosis are based on showing dissemination of white matter lesions in space and time. MRI is the most sensitive method for revealing asymptomatic dissemination of lesions in space and time. The pattern and evolution of MRI lesions, in the appropriate clinical setting, has made MRI abnormalities invaluable criteria for the early diagnosis of MS. The first important role for MRI in the diagnosis of MS allows for an early diagnosis of MS for CIS patients using the IP diagnostic criteria, including MRI for dissemination in space (DIS) and time (DIT). The sensitivity of diagnosing MS within the first year after a single attack is 94%, with a specificity of 83%. The MRI evidence required to support the diagnosis varies, depending on the strength of the clinical findings. Allowing a new MRI lesion to substitute for a clinical attack doubles the number of CIS patients who can be diagnosed as having MS within 1 year of symptom onset. Increasing the sensitivity of the test with more lenient criteria, as recommended by the AAN subcommittee, can result in decreased specificity. The second important role for MRI in the diagnostic work-up of suspected MS patients is to rule out alternative diagnoses obvious on MRI, such as spinal stenosis and most brain tumors. Characteristic lesions that favor MS include Dawson Fingers, ovoid lesions, corpus callosum lesions, and asymptomatic spinal cord lesions. However, other white matter diseases can have similar appearances on MRI. Persistent gadolinium enhancement greater than three months, lesions with mass effect, and meningeal enhancement suggest other disorders. A standardized MRI protocol for brain and spinal cord is crucial for comparing across studies or between centers. T2W MRI cannot distinguish between acute and chronic lesions. Gadolinium provides useful information about new lesion activity and is helpful in ruling out alternative diagnoses such as neoplasm, vascular malformations, and leptomeningeal disease. A single gadolinium-enhanced MRI can potentially provide evidence for dissemination in space and time. Spinal cord imaging is equally valuable to rule out spinal stenosis or tumor, and for detecting asymptomatic lesions when brain imaging is nondiagnostic in patients suspected of having MS. Precise criteria may be too suggestive that MS can be diagnosed by MRI and a negative MRI at the time of CIS does not rule out MS. MRI evidence plays a supportive role in what is ultimately a clinical diagnosis of MS, in the appropriate clinical situation, and always at the exclusion of alternative diagnoses.

Central Nervous System↗
PubMed2006

The use of MRI as an outcome measure in clinical trials.

Because the changes on MRI likely reflect various aspects of the underlying pathology of multiple sclerosis, MRI outcome measures have become an important component of most MS clinical trials, providing objective, supportive evidence for the clinical endpoints. Although there is currently insufficient evidence to support any single or combination of MRI measures as a fully validated surrogate, it is now generally accepted that if the aim of a new therapy is to prevent relapses, new Gd-enhancing and T2 lesions can be considered an appropriate surrogate outcome measure of relapses, and MRI activity outcomes can be recommended as the primary measure of treatment efficacy.

Biomarkers↗
PubMed2003

Evolution of focal and diffuse magnetisation transfer abnormalities in multiple sclerosis.

Magnetisation transfer (MT) imaging provides indirect information on tissue structure abnormalities in areas that otherwise may appear normal on conventional MRI. We determined the evolution of MT changes in normal appearing white matter (NAWM) and lesion on serial examination of 9 multiple sclerosis (MS) patients and age matched controls. The mean NAWM MT ratio (MTR) was found to correlate strongly (R = 0.93) with the length of time since the patient's first clinical presentation and was well characterized by a linear decrease of -0.16%/year (p < 0.0001). The time zero intercept of the NAWM MTR regression was 30.7 +/- 0.2%, not different from the average MTR of white matter from controls (30.4 +/- 0.2 %). An additional gradual decrease in NAWM MTR was observed 6 to 12 months before the appearance of a new lesion on conventional MRI, while a more precipitous decrease in MTR was seen 2 to 6 months before the lesion appeared. Those lesions that exhibited pre-lesion MTR decreases showed less MTR recovery than lesions which had no pre-lesion MTR decrease. The data suggest that the MTR of NAWM in MS undergoes a slow progressive decrease that starts at disease onset and accelerates rapidly in focal areas just prior to lesion appearance on conventional MRI.

Adult↗
PubMed2003

MRI contributes to the differentiation between MS and HTLV-I associated myelopathy in British Columbian coastal natives.

BACKGROUND: Human T-cell lymphotropic virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) in British Columbian Coastal Natives has, to date, been a clinical and laboratory diagnosis. However, magnetic resonance imaging (MRI) abnormalities have been well-described in other populations in which HAM/TSP is endemic. METHODS: In order to assess the usefulness of MRI as a diagnostic tool in this population, we compared scans of HAM/TSP patients with those of HTLV-I positive non-HAM/TSP British Columbian Coastal Natives (carriers) and multiple sclerosis patients presenting with progressive paraparesis. RESULTS: The typical nonspecific findings of thoracic cord atrophy and increased signal in the periventricular and subcortical white matter on T2-weighted images were confirmed in the HAM/TSP patients. Despite a lack of specificity of the MRI findings between HAM/TSP patients and HTLV-I carriers, criteria that could effectively differentiate HAM/TSP patients from multiple sclerosis patients with similar clinical presentations were determined. CONCLUSIONS: Clinical and radiological correlations suggest that longitudinal MRI investigations charting the course of HAM/TSP may reveal the clinical significance of these lesions and further define the role of MRI in the diagnosis of this entity. Magnetic resonance imaging is an important supplement to immunological and clinical data in differentiating multiple sclerosis from HAM/TSP.

Brain↗
PubMed2002

Normal-appearing white matter in multiple sclerosis has heterogeneous, diffusely prolonged T(2).

T(2) relaxation in normal-appearing white matter (NAWM) of multiple sclerosis (MS) patients was reexamined using more complete sampling and analysis of decay curves, and to assess focal vs. diffuse abnormalities. Nine MS patients and 10 controls were scanned using a single-slice 32-echo pulse sequence with a 10-ms echo spacing. Decay curves from outlined white and gray matter structures were analyzed using non-negative least-squares (NNLS). Resulting T(2) distributions were each summarized by the geometric mean T(2), T(2). Different white matter structures had different mean (over the subjects in a group) T(2). Mean T(2) in NAWM was always greater than that of controls. Differences were not caused by a few voxels with extreme T(2) (i.e., focal lesions), but rather by shifts of the entire T(2) distribution (diffuse prolongation). This T(2) increase suggests diffuse myelin or axonal pathology.

Adult↗