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This study was performed to evaluate the dynamics of an arterial first pass gadolinium (Gd) contrast medium (CM) bolus at the descending aorta (DAo), depending on various saline flush and Gd volumes. Using an ultra-fast twodimensional GE-sequence (Siemens Vision®, 1.5-T), 200 sequential cross-sectional images of the addressed vessel (1 slice/s) were obtained. Several saline flush volumes (15 mL, 30 mL, and 60 mL) were applied following the administration of 10 mL Gd (single dose) to a group of 4 normal volunteers (body weight 50 -55 kg) using a mechanical MR injector (injection rate ‫؍‬ 3.0 mL/s). Additionally, when performing a second test series, the saline volume remained constant, while the Gd volumes were varied from half doses to triple doses (5, 10, 20, and 30 mL Gd were given to every volunteer of the group). The signal intensity versus time (SI/T) curve at a measured region of interest (ROI) within the DAo was calculated. The bolus arrival time (BAT), the maximal signal-to-noise ratio (SNR max ), the bolus time length (BL; 75% and 80% maximum intensity duration), the slope of the SI/T curve, and the areas below the SI/T curve for both the 80% and 75% maximum intensity duration level ( Index terms: arterial first pass; saline flush; gadolinium dose; contrast-enhanced MRA VASCULAR CONTRAST AND RESOLUTION of contrast enhanced (CE) magnetic resonance angiography (MRA) images depend on the relaxivity of the contrast medium (CM), the intravascular CM concentration, and the sequence parameters. Most of the refinements have been applied to increase the speed of pulse sequence and to find intelligent ways of running through the k-space in order to achieve perfect timing during the acquisition of the central k-lines (1). As known from other studies, the optimization of three-dimensional CE MRA quality gains not only in the improvement of acquisition parameters (resolution, acquisition time), but also by increasing image contrast depending on CM application strategies (2,3). The arterial contrast relies on the distribution and concentration of Gd during the acquisition of low frequencies of k-space (4,5). The concentration and the bolus time length (BTL) of Gd during the first pass at the site of the region of interest (ROI) depend on several factors, as well as on pathophysiological parameters (distribution into peripheral vessels and interstitial tissue, blood volume, cardiac output) and the intravenous (IV) CM injection parameters (Gd volume and injection rate) (6,7). A further parameter for IV CM injection is the volume of saline that has to be administered in order to flush the IV line and the cubital vein after Gd bolus application. As Hany et al described, the saline flush is most important (2). Without this flush, the bolus is significantly delayed and the bolus arrival time (BAT) is prolonged. Hany et al also reported that the saline flush had a significant effect on the maximum signal intensity (SI max ) and on the slope of the SI increase. In their study, however, the test bolus was performed only with ...

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To examine possible metabolic frontal lobe alterations in i.v. heroin-dependent patients with different histories of concomitant substance use, N-acetylaspartate (NAA), a putative marker of neuronal viability, was measured by (1)H-MRS. Compared with controls, NAA levels in patients were reduced by 7% in gray matter (p = 0.015) but not in white matter. To what extent comorbid conditions or substance use, including alcohol, contributed to these frontocortical metabolic changes remains to be elucidated.