Multi-echo dipole inversion for magnetic susceptibility mapping.

Purpose: Reconstructing tissue magnetic susceptibility (QSM) from MRI phase data involves solving multiple consecutive ill-posed inverse problems such as phase unwrapping, background field removal, and field-to-source inversion. Multi-echo acquisitions present an additional challenge, as the magnetization field is typically computed from the multiple phase data prior to reconstructing the susceptibility map. Processing the multiple phase data introduces errors during the field estimation, violating assumptions of the subsequent inverse problems, manifesting as streaking artifacts in the susceptibility map.

Orientation dependence of R relaxation in the newborn brain.

In MRI the transverse relaxation rate, R = 1/T shows dependence on the orientation of ordered tissue relative to the main magnetic field. In previous studies, orientation effects of R relaxation in the mature brain's white matter have been found to be described by a susceptibility-based model of diffusion through local magnetic field inhomogeneities created by the diamagnetic myelin sheaths. Orientation effects in human newborn white matter have not yet been investigated.

Recovering SWI-filtered phase data using deep learning.

Purpose: To develop a deep neural network to recover filtered phase from clinical MR phase images to enable the computation of QSMs.

Methods: Eighteen deep learning networks were trained to recover combinations of 13 SWI phase-filtering pipelines. SWI-filtered data were computed offline from five multiorientation, multiecho MRI scans yielding 132 3D volumes (118/7/7 training/validation/testing).

Myelin water imaging depends on white matter fiber orientation in the human brain.

Purpose: The multi-exponential T decay of the MRI signal from cerebral white matter can be separated into short T components related to myelin water and long T components related to intracellular and extracellular water. In this study, we investigated to what degree the apparent myelin water fraction (MWF) depends on the angle between white matter fibers and the main magnetic field.

Methods: Maps of the apparent MWF were acquired using multi-echo Carr-Purcell-Meiboom-Gill and gradient-echo spin-echo sequences.

DECAES - DEcomposition and Component Analysis of Exponential Signals.

Combinations of multiple exponentially decaying signals are found across many disciplines of science. Decomposition of these multi-exponential signals into their individual components provides insight into the various contributors to the signal. Magnetic resonance images, for instance, can be acquired with multiple gradient or spin echoes to provide voxel by voxel multi-exponential T2* or T2 decays, respectively.

The role of iron and myelin in orientation dependent R of white matter.

Brain myelin and iron content are important parameters in neurodegenerative diseases such as multiple sclerosis (MS). Both myelin and iron content influence the brain's R relaxation rate. However, their quantification based on R maps requires a realistic tissue model that can be fitted to the measured data.

Rapid solution of the Bloch-Torrey equation in anisotropic tissue: Application to dynamic susceptibility contrast MRI of cerebral white matter.

Blood vessel related magnetic resonance imaging (MRI) contrast provides a window into the brain's metabolism and function. Here, we show that the spin echo dynamic susceptibility contrast (DSC) MRI signal of the brain's white matter (WM) strongly depends on the angle between WM tracts and the main magnetic field. The apparent cerebral blood flow and volume are 20% larger in fibres perpendicular to the main magnetic field compared to parallel fibres.

Southwick angle measurements and SCFE slip severity classifications are affected by frog-lateral positioning.

Objective: Slipped capital femoral epiphysis (SCFE) is a hip disorder where the femoral head slips relative to the neck at the physis. Appropriate treatment of SCFE depends on the severity of the slip, commonly categorised using the Southwick (SW) angle. The SW angle is measured in the frog-lateral leg position, which can be painful and potentially unattainable for patients.

Relationships Between Severity of Deformity and Impingement in Slipped Capital Femoral Epiphysis.

Background: In situ pinning, a low-risk treatment for slipped capital femoral epiphysis (SCFE), leaves the slipped femoral head in place and may reduce range of motion (ROM) and cause impingement. It is unclear when a more complex surgery should be considered, because the relationships between severity, slip stability, remodeling, impingement, and ROM are unknown.

Research Questions: (1) Do more severe acute SCFE deformities (no bony remodeling) result in a greater loss of flexion ROM?(2) Does the presence or location of impingement on the pelvis vary with severity of acute SCFE deformity?

Methods: We developed a 3D geometric model of acute SCFE deformity from 1 computed tomography scan of a normal adolescent hip.