154 Chapter 7 93% [95% CI 68% to 100%], PPV of 88% [95% CI 47% to 100%] and NPV of 82% [95% CI 57% to 96%]. DISCUSSION This study clinically implemented a ready-to-use QP CMR workflow with a simplified dualbolus GBCA administration scheme and fully automated QP image post-processing. The results demonstrated, that this workflow provides good image quality and holds promise for high diagnostic accuracy for detecting obstructive CAD. The proposed approach is obtainable, easy to implement and only requires a commercially available MRI pulsesequence and post-processing software. Therefore, it may facilitate the introduction of QP CMR in general CMR centers and offers potential to improve the clinical performance of centers already performing qualitative CMR perfusion imaging.23, 31, 32 This easy-toimplement strategy may contribute to a more widespread adoption of non-invasive accurate and quantitative assessment of ischemia by CMR. As described by Ishida et al., a standard dual-bolus GBCA injection scheme for QP CMR requires dilution of pre-bolus to an equal volume as the main bolus of neat GBCA.7 However, this approach requires additional pre-scan preparation, where the pre-bolus has to be diluted to 10% solution which should be preloaded to the infusion line. This impairs the time efficiency of the CMR laboratory workflow. Several studies successfully used the simplified dual-bolus GBCA administration scheme, where the pre-bolus is in fact a small volume bolus of contrast.8-10 Such a simplified dual-bolus approach introduced by Köstler et al. used fixed high doses of GBCA (1 ml pre-bolus of Magnevist 0.5 mmol/ml, Schering, Germany, followed by 8 or 12 ml main bolus at an infusion rate 4 ml/s followed by a flush of 20 ml saline)9. Others used dual-bolus protocols with a fixed dose of prebolus (1 ml of Magnevist 0.5 mmol/ml, Schering, Germany followed by 15 ml saline) and main bolus at a dose of 0.1 mmol/kg followed by 15 ml saline injected at infusion rate 3 ml/s.8 The strength of approach proposed in the current study, however, is administration of a (relatively) higher dose of pre-bolus GBCA (0.0075 mmol/kg), adjusted to patient weight. As previously shown, higher GBCA dosages increase both signal-to-noise ratio and contrast-to-noise ratio and improve the diagnostic performance of stress perfusion CMR in detection of obstructive CAD, but may be related to the substantial saturation effect which limits the accuracy of QP.4, 33, 34 As the proposed approach uses a non-diluted pre-bolus, the moderate infusion rate at 3 ml/s was chosen as a compromise between the risk of temporary GBCA accumulation at the level of LV cavity and associated T1 and T2* saturation effect, and the risk of possible contrast dispersion within the bloodstream. In QP CMR a crucial factor affecting the accuracy of measurements is the linearity between the SI and the amount of administered GBCA.3, 35 Gebker et al. have shown significant differences in myocardial
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