Optimization of Improved Motion-sensitized Driven-equilibrium (iMSDE) blood suppression for carotid artery wall imaging

Background

Improved motion-sensitized driven-equilibrium (iMSDE) preparations have been successfully used in carotid artery wall imaging to achieve blood suppression, but it causes notable signal loss, mostly due to inherent T₂ decay, eddy current effects and B₁⁺ inhomogeneity. In this study, we investigate the signal to noise ratio (SNR) and blood suppression performance of iMSDE using composite RF pulses and sinusoidal gradients. Optimized first moment (m₁) values for iMSDE prepared T₁- and T₂- weighted (T₁- and T₂-w) imaging are presented.

Methods

Twelve healthy volunteers and six patients with carotid artery disease underwent iMSDE and double inversion recovery (DIR) prepared T₁- and T₂-w fast spin echo (FSE) MRI of the carotid arteries. Modified iMSDE module using composite RF pulses and sinusoidal gradients were evaluated with a range of m₁. SNR of adjacent muscle, vessel wall and the lumen were reported. The optimized iMSDE module was also tested in a 3D variable flip angle FSE (CUBE) acquisition.

Results

The SNR of muscle was highest using sinusoidal gradients, and the relative improvement over the trapezoidal gradient increased with higher m₁ (p<0.001). Optimal SNR was observed using an iMSDE preparation scheme containing two 180° composite pulses and standard 90° and -90° pulses (p=0.151). iMSDE produced better blood suppression relative to DIR preparations even with a small m₁ of 487 mT*ms²/m (p<0.001). In T₁-w iMSDE, there was a SNR decrease and an increased T₂ weighting with increasing m_1. In T₂-w iMSDE, by matching the effective echo time (TE), the SNR was equivalent when m₁ was <= 1518 mT*ms²/m, however, higher m₁ values (2278 – 3108 mT*ms²/m) reduced the SNR. In the patient study, iMSDE improved blood suppression but reduced vessel wall CNR efficiency in both T₁-w and T₂-w imaging. iMSDE also effectively suppressed residual flow artifacts in the CUBE acquisition.

Conclusions

iMSDE preparation achieved better blood suppression than DIR preparation with reduced vessel wall CNR efficiency in T_1-w and T₂-w images. The optimized m₁s are 487 mT*ms²/m for T₁-w imaging and 1518 mT*ms²/m for T₂-w imaging. Composite 180° refocusing pulses and sinusoidal gradients improve SNR performance. iMSDE further improves the inherent blood suppression of CUBE.     

Predicting nurses' turnover intentions by demographic characteristics,perception of health,quality of work attitudes

The purpose of this paper is to examine the impact of demographic variables, organizational commitment levels, perception of health and quality of work on turnover intentions. A self‐reported cross‐sectional survey design was used to collect data from Jordanian registered nurses who were working between June 2011 and November 2011. The findings showed strong effects of the quality of work, perception of health and normative organizational commitments on turnover intentions. This study sheds the light on the important work outcomes in health‐care organizations. Increasing nursing quality of work and normative organizational commitment are good strategies for reducing turnover intentions.     

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