Biomedical subjects

P Ledden

Publications and source records attributed to P Ledden.

2 recordsLinked to original sources

PubMed1999

Measurement of human myocardial perfusion by double-gated flow alternating inversion recovery EPI.

This paper presents a flow-sensitive alternating inversion recovery (FAIR) method for measuring human myocardial perfusion at 1.5 T. Slice-selective/non-selective IR images were collected using a double-gated IR echoplanar imaging sequence. Myocardial perfusion was calculated after T1 fitting and extrapolation of the mean signal difference SI(Sel - SI(NSel). The accuracy of the method was tested in a porcine model using graded intravenous adenosine dose challenge. Comparison with radiolabeled microsphere measurements showed a good correlation (r = 0.84; mean error = 20%, n = 6) over the range of flows tested (0.9-7 ml/g/min). Applied in humans, this method allowed for the measurement of resting myocardial flow (1.04+/-0.37 ml/g/min, n = 11). The noise in our human measurements (SE(flow) = 0.2 ml/g/min) appears to come primarily from residual respiratory motion. Although the current signal-to-noise ratio limits our ability to measure small fluctuations in resting flow accurately, the results indicate that this noninvasive method has great promise for the quantitative assessment of myocardial flow reserve in humans.

Adult↗

PubMed1998

Imaging subcortical auditory activity in humans.

There is a lack of physiological data pertaining to how listening humans process auditory information. Functional magnetic resonance imaging (fMRI) has provided some data for the auditory cortex in awake humans, but there is still a paucity of comparable data for subcortical auditory areas where the early stages of processing take place, as amply demonstrated by single-unit studies in animals. It is unclear why fMRI has been unsuccessful in imaging auditory brain-stem activity, but one problem may be cardiac-related, pulsatile brain-stem motion. To examine this, a method eliminating such motion (using cardiac gating) was applied to map sound-related activity in the auditory cortices and inferior colliculi in the brain stem. Activation in both the colliculi and cortex became more discernible when gating was used. In contrast with the cortex, the improvement in the colliculi resulted from a reduction in signal variability, rather than from an increase in percent signal change. This reduction is consistent with the hypothesis that motion or pulsatile flow is a major factor in brain-stem imaging. The way now seems clear to studying activity throughout the human auditory pathway in listening humans.

Auditory Cortex↗