Biomedical subjects

Trevor Andrews

Publications and source records attributed to Trevor Andrews.

3 recordsLinked to original sources

PubMed2005

Testing the three-pool white matter model adapted for use with T2 relaxometry.

A three-pool model was used to improve white-matter T2 relaxometry in low signal-to-noise (SNR) data. To verify the model very high SNR T2 relaxometry experiments were performed on myelinated tissue samples and three-pool fractions were consistently found. Relaxation curves based on the in vitro results were simulated with multiple SNRs and fit using the three-pool model and three less constraining nonnegative least squares-based methods. All methods performed well with noiseless data. At lower SNR values the three-pool model was superior, primarily due to the fact that the other methods often could not unambiguously calculate pool fractions.

Algorithms↗

PubMed2005

Myelination in children with partial deletions of chromosome 18q.

BACKGROUND AND PURPOSE: We compared myelin levels in white matter (WM) in typically developing children with those of children with partial deletions of chromosome 18q (18q-). METHODS: Conventional spin-echo MR imaging at 1.9T was used to acquire T1-, T2-, and proton density-weighted images of the brain. From these images, a three-pool model was used to estimate the fraction of water in myelin, myelinated axon, and mixed water compartments (or pools) in six WM regions. A model curve was fit to the pool fractions to model the trend of myelin development by age in each region. Water-pool fractions in children with 18q- aged 5 months to 13 years were compared with those of age-matched, typically developing children. RESULTS: In children with 18q-, the model predicted later onset of myelination (P <.02), lower myelination rates (P <.001), and smaller equilibrium myelin pool fractions (P <.001). Significant differences were seen between the two groups for all three water pool fractions (P <.001). The mixed pool fraction was larger in children with 18q-. Although the myelin pool fraction was significantly smaller, the myelinated axon pool fraction was only slightly smaller, leading to a significantly smaller estimate of myelin per myelinated axon in children with 18q- (P <.001). CONCLUSION: Myelination modeling in 18q- children indicated delayed onset, a lower rate of myelination, and equilibrium myelin levels less than 50% those of age-matched, typically developing children.

Axons↗

PubMed2003

Three-pool model of white matter.

PURPOSE: To investigate the use of a three-pool relaxation model to measure myelin, myelinated-axon, and mixed water-pool fractions in white matter (WM) during myelination. MATERIALS AND METHODS: MRI at 1.9 Tesla, and conventional spin-echo imaging were used to acquire T1 and T2 relaxation data in 15 normal children ranging in age from 3 months to 13 years 4 months. Three equations with three unknowns were solved to calculate three water-pool fractions for each child in a frontal association-fiber area and a frontal-parietal projection-fiber area. The temporal trend of the fractions was compared with a theoretical three-pool myelination model. RESULTS: The myelin level in the projection-fiber area rose earlier than in the association-fiber area following the standard caudal-to-rostral trend. The temporal trend of the three-pool fractions followed that predicted by the theoretical myelination model in both brain areas. The myelinated-axon and mixed pool sizes were significantly different in the two WM areas following early myelination, although their myelin pools were similar. T1 values correlated more highly with the myelinated-axon and mixed pool fractions than with the myelin pool fraction. CONCLUSION: The three-pool relaxation model provides measurements of water-pool fractions in WM that follow values predicted during myelination.

Adolescent↗