An index system for comparative parameter weighting in MR imaging

An analytic method for comparative parameter weighting in magnetic resonance (MR) imaging has been developed using the concept of "fractional sensitivity." This new approach results in easily calculated indexes for T1, T2, and hydrogen weighting. This index system enables quantitative comparisons to be made between MR studies that have been performed at various field strengths, using different pulse sequences and pulse timing intervals.     

A template-free approach for determining the latency of single events of auditory evoked M100

The phase of the complex output of a narrow band Gaussian filter is taken to define the latency of the auditory evoked response M100 recorded by magnetoencephalography. It is demonstrated that this definition is consistent with the conventional peak latency. Moreover, it provides a tool for reducing the number of averages needed for a reliable estimation of the latency. Single-event latencies obtained by this procedure can be used to improve the signal quality of the conventional average by latency adjusted averaging.     

Pseudolayering of Gd-DTPA in the urinary bladder

When excreted gadolinium diethylenetriaminepentaacetic acid (DTPA) collects in the bladder of a supine patient during magnetic resonance (MR) imaging, a puzzling pattern of signal intensities is noted. A gradual change in urine signal intensity with progressive addition of Gd-DTPA does not occur; instead, three sharply defined "layers" are seen both on T1- and T2-weighted images within the urine-Gd-DTPA mixture. The physical basis for this triple-layering phenomenon was investigated. A bladder phantom was constructed to reproduce the phenomenon. T1 and T2 relaxivities of urine doped with varying concentrations of Gd-DTPA were measured in vitro; measured signal intensities corresponded closely to predicted intensities. Early urine concentrations of excreted Gd-DTPA may be relatively high (10-40 mmol/L), resulting in extremely short T1 and T2 values (less than 30 msec). These extremely short relaxation times cause an artifactual pseudolayering of signal within the urine-Gd-DTPA mixture.     

Simultaneous measurement of human joint force, surface electromyograms, and functional MRI-measured brain activation

Functional magnetic resonance imaging (fMRI) has been increasingly used in studying human brain function given its non-invasive feature and good spatial resolution. However, difficulties in acquiring data from peripheral (e.g. information from muscle) during fMRI studies of motor function hinder interpretation of fMRI data and designing more sophisticated investigations. Here we describe a system that was designed to concurrently measure handgrip force, surface electromyograms (EMG) of finger flexor and extensor muscles, and fMRI of human brain. The system included a pressure transducer built in a hydraulic environment, a heavily shielded EMG recording element, and a visual feedback structure for online monitoring of force and/or EMG signal, by the subject positioned in the scanner during an fMRI experiment. System evaluation and subsequent fMRI motor function studies have indicated that by using this system, high quality force and EMG signals can be recorded without sacrificing the quality of the fMRI data.     

Latency analysis of single auditory evoked M100 responses by spatio-temporal filtering

Appropriate spatial filtering followed by temporal filtering is well suited for the single-trial analysis of multi-channel magnetoencephalogram or electroencephalogram recordings. This is demonstrated by the results of a single-trial latency analysis obtained for auditory evoked M100 responses from nine subjects using two different stimulation frequencies. Spatial filters were derived automatically from the data via noise-adjusted principle component analysis, and single-trial latencies were estimated from the signal phase after complex bandpass filtering. For each of the two stimulation frequencies, estimated single-trial latencies were consistent with results obtained from a standard approach using averaged evoked responses. The quality of the estimated single-trial latencies was additionally assessed by their ability to separate between the two different stimulation frequencies. As a result, more than 80% of the single trials can be classified correctly by their estimated latencies.