Christopher A. Hamilton

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PURPOSE To characterize near-resonance saturation pulse MR imaging on a 1.5-T scanner in order to gain insight into underlying mechanisms that alter tissue contrast and to optimize the technique for neuroimaging. METHODS Off-resonance saturation pulses were applied to T1-weighted, spin-density-weighted, and T2-weighted sequences at frequency offsets(More)
Functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS) are noninvasive techniques recently used to investigate cortical motor physiology. However, these modalities measure different phenomena, and in studies of human motor control they have given inconsistent results. We have developed a reproducible technique which(More)
The phase-mapping method of phase-contrast magnetic resonance angiography is shown to be based on an implicit assumption that the intravoxel velocity distribution is symmetric about its mean velocity. The effect of asymmetric distributions on the accuracy of quantitative average velocity measurements is determined analytically and verified experimentally.(More)
PURPOSE We examined the utility of near-resonance saturation pulse imaging (magnetization transfer [MT] and spin lock) in characterizing microstructural changes occurring in the extraocular muscles of patients with thyroid-related ophthalmopathy (TRO). METHODS Eight healthy volunteers and 10 patients with TRO were imaged using an off-resonance saturation(More)
Magnetization transfer (MT) imaging is a new MR imaging technique in which off-resonance radiofrequency pulses are used to selectively saturate protons in macromolecules. This saturation effect is transferred subsequently (by dipolar and chemical exchange interactions) to protons in free water, thereby altering tissue relaxation times and modulating image(More)
Spin-lock and spin-tip excitations are the two magnetization components created by the preparatory RF pulse of an MRI contrast enhancement sequence. Only spin-lock is inherently adiabatic, preserving spin alignment so that tissue-specific relaxation can generate desired saturation contrasts. Spin-tip is the rotating-frame oscillating excitation, and(More)
Spiders (Order Araneae) are massively abundant generalist arthropod predators that are found in nearly every ecosystem on the planet and have persisted for over 380 million years. Spiders have long served as evolutionary models for studying complex mating and web spinning behaviors, key innovation and adaptive radiation hypotheses, and have been inspiration(More)
At conventional magnetic resonance imaging, the number of phase-encoding steps is often chosen to be less than the number of readout samples, resulting in reduced spatial resolution in the phase-encoding direction. Signal averaging improves the signal-to-noise ratio of the image but does not affect this asymmetry in resolution. By swapping the phase- and(More)
The phase difference method of phase contrast MR angiography provides a means of measuring the average velocity in each voxel of an MR scan. When static tissue is present in a voxel containing flow, the measured velocity is not the average velocity of the flow alone, but is lower due to the partial volume effect of the static tissue. We present a(More)