Biomedical subjects

Kenneth P Whittall

Publications and source records attributed to Kenneth P Whittall.

4 recordsLinked to original sources

PubMed2004

Linear combination of multiecho data: short T2 component selection.

The myelin sheath, which is wrapped around the axons in the brain, can be affected by many diseases, resulting in cognitive and physical disability. Other work showed water in the myelin sheath has a T2 approximately 15 ms. The current standard technique to estimate the fraction of myelin water in vivo is to collect multiecho data and fit the decay curves using a nonnegative least-squares (NNLS) algorithm. A new algorithm was developed to calculate optimized coefficients which were used to linearly combine multiecho data to estimate the myelin water signal. A set of simulations showed the new technique was accurate over a broad range of myelin water signal. The myelin water fraction from brain regions in scans from five volunteers, estimated by the linear combination method, agreed with the myelin water fraction estimated by the standard technique. The strength of the new technique is that the linear combination does not assume an underlying T2 model and is 20,000 times faster than NNLS.

Algorithms↗

PubMed2003

Robust myelin water quantification: averaging vs. spatial filtering.

The myelin water fraction is calculated, voxel-by-voxel, by fitting decay curves from a multi-echo data acquisition. Curve-fitting algorithms require a high signal-to-noise ratio to separate T(2) components in the T(2) distribution. This work compared the effect of averaging, during acquisition, to data postprocessed with a noise reduction filter. Forty regions, from five volunteers, were analyzed. A consistent decrease in the myelin water fraction variability with no bias in the mean was found for all 40 regions. Images of the myelin water fraction of white matter were more contiguous and had fewer "holes" than images of myelin water fractions from unfiltered echoes. Spatial filtering was effective for decreasing the variability in myelin water fraction calculated from 4-average multi-echo data.

Algorithms↗

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↗

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↗