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Biomedical subjects

M R Elliott

Publications and source records attributed to M R Elliott.

11 recordsLinked to original sources
PubMed1999

"Sparse" temporal sampling in auditory fMRI.

The use of functional magnetic resonance imaging (fMRI) to explore central auditory function may be compromised by the intense bursts of stray acoustic noise produced by the scanner whenever the magnetic resonance signal is read out. We present results evaluating the use of one method to reduce the effect of the scanner noise: "sparse" temporal sampling. Using this technique, single volumes of brain images are acquired at the end of stimulus and baseline conditions. To optimize detection of the activation, images are taken near to the maxima and minima of the hemodynamic response during the experimental cycle. Thus, the effective auditory stimulus for the activation is not masked by the scanner noise. In experiment 1, the course of the hemodynamic response to auditory stimulation was mapped during continuous task performance. The mean peak of the response was at 10.5 sec after stimulus onset, with little further change until stimulus offset. In experiment 2, sparse imaging was used to acquire activation images. Despite the fewer samples with sparse imaging, this method successfully delimited broadly the same regions of activation as conventional continuous imaging. However, the mean percentage MR signal change within the region of interest was greater using sparse imaging. Auditory experiments that use continuous imaging methods may measure activation that is a result of an interaction between the stimulus and task factors (e.g., attentive effort) induced by the intense background noise. We suggest that sparse imaging is advantageous in auditory experiments as it ensures that the obtained activation depends on the stimulus alone.

Acoustic Stimulation↗
PubMed1999

The effect of scanner sound in visual, motor, and auditory functional MRI.

The potentially important effect of gradient switching sound on brain function during functional magnetic resonance imaging (fMRI) was studied by comparing experiments with low and high scanner sound levels. To provide a low sound level experiment, a sparse scanning method was used, characterized by long, 9 sec, periods of scanner silence interspersed with 1 sec echoplanar imaging (EPI) bursts. For the condition with high sound levels, extra EPI gradient modules were inserted in the 9 sec inter-image intervals. Visual, motor, or auditory stimuli were presented in the interval between imaging. It was found that with the addition of gradient sounds, auditory activation was significantly decreased while motor and visual activation were not significantly altered. Other general factors relating to fMRI were also examined, such as experimental duration and fatigue. For example, motion of the subjects during the experiments was found to be related to the time spent in the scanner, rather than to the ambient sound level.

Acoustic Stimulation↗
PubMed1997

An evaluation of the potential and limitations of three-dimensional reconstructions from intravascular ultrasound images.

Three-dimensional (3D) reconstructions of arteries can be produced using two-dimensional (2D) intravascular ultrasound (IVUS) images. Any artefact that affects 2D images has the potential to limit the quality of a 3D reconstruction. Using a catheter withdrawal technique, a range of test rigs were used to assess: (i) the effect of rotation of the probe orientation; (ii) the ability to reconstruct the true path of a tortuous vessel; (iii) the effect of image distortion on diameter measurements; (iv) the number of images per unit length used to produce a 3D reconstruction; and (v) the quality of the IVUS 3D reconstruction of a stent. These investigations show that 3D IVUS imaging is prone to artefacts. For 3D IVUS images to be used to quantify the vessel path or to make accurate measurements of vessel dimensions, more information about the catheter tip position and orientation is required than is currently available with the pullback technique.

Humans↗
PubMed1997

Early infant crying: child and family follow-up at three years.

Children who cried excessively at six to eight weeks of age were re-examined at two to four years of age to determine the enduring effects of excessive crying ("colic") on behavioural development, parent-child interaction, and family functioning. The more crying in early infancy, the more family disruptions occurred three years later (r = .29). Analyses showed that early crying had little impact on the children's later behavioural development. No significant major lasting effects on the family related to the infant's early crying behaviour were found. Families with sufficient social and economic resources can be reassured that problems related to early infant crying can be ameliorated over time.

Child Development↗
PubMed1996

Measurement of resolution in intravascular ultrasound images.

Detailed images of arteries can be formed by inserting intravascular ultrasound (IVUS) catheters within them. These catheters contain rotating ultrasound transducers and are capable of displaying disease and features such as the layers of artery walls. There is, however, relatively little information available on IVUS resolution even though this is necessary to interpret the images. Techniques for assessing IVUS resolution in three dimensions are described for a 20 MHz Boston Scientific catheter and a Diasonics IVUS scanner as well as the results obtained. Out-of-plane resolution was measured by finding the ultrasound beam thickness. Axial and lateral resolution were assessed by the minimum separation of two point targets when their images could just be distinguished. The out-of-plane resolution was found to improve slightly with distance from the catheter, varying from 2.0-1.5 mm. Lateral resolution worsened in a linear manner with distance. At a distance of 5 mm from the catheter, lateral resolution was 0.83 mm. The axial resolution was the best of the three resolutions and was actually limited by the screen display scale. With the highest magnification the axial resolution was approximately 0.19 mm and was constant with distance.

Arteries↗
PubMed1996

Subjective appraisal of infant crying.

How families appraise difficult situations contributes to later adaptive functioning. We have observed in both research and practice that when appraising their infants' crying, mothers often compared their own infants' crying to actual or supposed much worse infants. They typically appraised their infants to be crying less than average infants. This phenomenon, defined in the social psychology literature, is called downward comparison. Secondary analysis of an established data set was used to assess the extent of downward comparison and the identification of excessive crying among a sample of 193 primiparous mothers. Mothers appraised their own infants' crying to be less than that of the expected average infant. Mothers who identified their infants as excessive criers made less robust downward comparisons than did mothers who did not identify their infants as excessive criers. Nursing interventions that focus on supporting mothers' positive appraisal and promoting knowledge of infant behaviors, particularly infant crying, are proposed.

Adult↗