Continuous bed motion on clinical scanner: design, data correction, and reconstruction.

With the addition of variable bed speed capabilities, continuous bed motion (CBM) becomes an acquisition generalization for axial sensitivity modeling and therefore a flexible tool in axial local image quality adjustment. In this paper, we describe the principles behind CBM mode planning and its influence on image reconstruction. The data correction method underwent the most changes compared to the commonly used step and shoot (S&S) mode. The CBM normalization array accommodates for activity decay, dead time correction, and the fact that various detector pairs acquire the same data for different durations. The normalization array is computed by simulating the movement of an object through the scanner, assisted by the monitoring of basic scanner acquisition parameters such as the singles rate. The sensitivity, which is the number of counts acquired per image plane, is an intrinsic part of normalization computing. Basic equations to estimate acquisition time at matched sensitivity between single speed CBM and S&S mode are presented. The CBM feature was implemented on a Siemens clinical scanner and initial studies of phantoms and patients are presented. The equivalence of single speed CBM and S&S image quality is demonstrated.

Motivation effects in a dichotic listening task as evident from functional magnetic resonance imaging in human subjects.

The present study addresses the effect of motivation on cerebral activity using functional magnetic resonance imaging. Five healthy volunteers performed a dichotic listening task in two sets of three trials during which high or low levels of achievement motivation were introduced. They were told that the first set would be used for calculation of intellectual capacity (high achievement motivation) and the second set for scanner calibration (neutral motivation). In three volunteers, high compared with neutral motivation produced activation in the right prefrontal cortex and the dorsal cingulate. We conclude that motivational effects may lead to significant activations and should be controlled in future cognitive imaging studies. We present preliminary evidence that right prefrontal and dorsal cingulate regions might be involved in motivational processes.

Left-right asymmetry of striatal dopamine D2 receptors.

Brain functions may be lateralized to the right or the left hemisphere. However, the biochemical characteristics accompanying these functions are largely unknown. To test possible lateralization of striatal dopamine D2 receptors, we examined 18 volunteers using 123I-iodobenzamide and single photon emission tomography. The striatum-to-cerebellum D2 binding ratio was 1.93 +/- 0.22 (mean +/- S.D.) on the right side and 1.85 +/- 0.19 on the left side. In 14 subjects, D2 binding was higher in the right compared to the left striatum (P < 0.05). These results are supported by a meta-analysis performed on 15 studies reported in the literature. We conclude that side differences of striatal dopamine D2 receptors exist. We propose that motor activity could be responsible for our findings.