Biomedical subjects

James Macfall

Publications and source records attributed to James Macfall.

3 recordsLinked to original sources

PubMed2005

Reliability in multi-site structural MRI studies: effects of gradient non-linearity correction on phantom and human data.

Longitudinal and multi-site clinical studies create the imperative to characterize and correct technological sources of variance that limit image reproducibility in high-resolution structural MRI studies, thus facilitating precise, quantitative, platform-independent, multi-site evaluation. In this work, we investigated the effects that imaging gradient non-linearity have on reproducibility of multi-site human MRI. We applied an image distortion correction method based on spherical harmonics description of the gradients and verified the accuracy of the method using phantom data. The correction method was then applied to the brain image data from a group of subjects scanned twice at multiple sites having different 1.5 T platforms. Within-site and across-site variability of the image data was assessed by evaluating voxel-based image intensity reproducibility. The image intensity reproducibility of the human brain data was significantly improved with distortion correction, suggesting that this method may offer improved reproducibility in morphometry studies. We provide the source code for the gradient distortion algorithm together with the phantom data.

Calibration↗

PubMed2005

Improved magnetic resonance thermal imaging by combining proton resonance frequency shift (PRFS) and apparent diffusion coefficient (ADC) data.

Effective thermal therapy for cancer is dependent on adequate tumor heating. Adequate heating, in turn, is dependent on reliable volumetric measurement of temperature to guide heating. Proton resonance frequency shift (PRFS) magnetic resonance imaging is frequently used for the purpose of three-dimensional temperature imaging. However, this method is susceptible to drift in the imaging magnetic field, leading to a corresponding drift in the measured temperature. A new approach to correcting for this drift is presented. It combines PRFS imaging alternated with water apparent diffusion coefficient (ADC) imaging to yield resulting thermal images that are drift corrected and possess the complementary strengths of the two methods. The drift-corrected PRFS images retain the high resolution and relatively noise-free characteristic of PRFS imaging while adding on the drift-free stability of ADC imaging. This technique is successfully demonstrated in a phantom experiment. This technique is also applicable to correcting motion-induced sudden large discontinuities in PRFS imaging, although not explicitly demonstrated in this work.

Body Temperature↗

PubMedDate not supplied

Hippocampal volume measurement in older adults with bipolar disorder.

OBJECTIVE: Decreased hippocampal volumes have been noted in unipolar depressed subjects, especially in elderly patients and those with cognitive impairment. Initial studies of mixed-aged bipolar subjects and controls have had conflicting findings, with most noting no difference; however this region has not been examined in older bipolar subjects. METHODS: The authors examined the hippocampal volumes of 36 older bipolar subjects (mean age: 58 years) and 29 older normal-comparison (NC) subjects (mean age: 61), using logistic-regression analyses to control for age and gender. Differences between late- and early-onset (before age 45) bipolar subjects were also examined. RESULTS: The left hippocampus was noted to be enlarged in older bipolar subjects, compared with the older NC group (sex and age controlled). No differences were noted in hippocampal volumes by age at onset nor number of previous episodes. The increase in hippocampal volume may be associated with the use of lithium, but not valproic acid. CONCLUSIONS: Left-hippocampal volume is increased in older bipolar subjects compared with NC subjects. The differences were not explained by age at onset, current mood state, or cognitive status, but may be associated with exposure to lithium. This finding would support previous observations about the neural-plasticity effect of lithium.

Aged↗