155 Automated Quantitative Perfusion CMR With Simplified Dual-Bolus Contrast Protocol enhancement in regard to the injection rate, where the rate of 2 ml/s was associated with a significantly lower myocardial enhancement in comparison with 4 ml/s at a GBCA dose of 0.05 mmol/kg.35 The authors concluded, that administration of GBCA in a prolonged injection with very low injection rates results in substantial dispersion that it cannot achieve an enhancement comparable to a more concentrated bolus at higher injection rates35. Similarly, myocardial SI curves showed lower upslope when the GBCA was injected at a rate of 2 ml/s compared to 3 and 4 ml/s. However, with faster injection rates the amount of inter-individual dispersion increases.35 Therefore, it has been suggested, that perfusion examinations should be performed with injection rates of 3–4 ml/s.35 In this study, imaging was performed using a 3 T scanner, what is beneficial for image quality and diagnostic performance of first-pass perfusion imaging for ischemia detection13. The proposed simplified dual-bolus protocol applied at 3 T indeed demonstrated relatively good image quality, as assessed by two independent level 3 CMR experts. Although the assessment using 5-point Likert scale is highly subjective and therefore may substantially differ between the expert readers, the majority of cases were assessed having at least moderate overall image quality with good-to-excellent diagnostic confidence. Most importantly for QP CMR analysis, this workflow obtained excellent quality of acquired AIF curves in the absence of substantial T2* effects, which allows absolute quantification of MBF. Studies have shown, that quantitative estimation of myocardial perfusion may increase the diagnostic performance of CMR in evaluation of presence and severity of obstructive CAD.23, 32 QP CMR may be also a promising non-invasive imaging method for detection of myocardial ischemia in symptomatic patients with suspected coronary microvascular dysfunction (CMD).6, 23, 31 Absolute quantification of MBF may also provide better risk stratification and prognostic value, and may serve as a robust and reproducible endpoint in clinical trials.6 In accordance with other studies, in the current study a significantly lower stress MBF values in ischemic than non-ischemic myocardium have been observed. Moreover, the values of rest and stress MBF in ischemic and nonischemic myocardium are consistent with those reported in the literature. In the studied cohort, in the non-ischemic myocardium the mean rest MBF was 1.00 ± 0.17 ml/g/min, whereas the stress MBF was 2.41 ± 0.57 ml/g/min. Recently, the largest QP analysis of healthy volunteers reported mean values of rest and stress MBF of 0.62 ± 0.13 ml/g/min and 2.24 ± 0.53 ml/g/min, respectively.36 Other studies have shown, that in patients the mean rest and stress MBF in non-ischemic myocardium ranges between 0.9 ± 0.3 to 1.4 ± 0.4 ml/g/min and 2.3 ± 0.5 to 3.0 ± 0.8 ml/g/min, respectively.19, 24, 37, 38 Therefore, the proposed simplified dual-bolus protocol provides quantitative measures of rest and stress MBF in non-ischemic myocardium comparable to the dual-sequence performance. The values of rest (1.13 ± 0.18 ml/g/min) and stress (1.9 ± 0.4 ml/g/min) MBF within ischemic myocardium in the current study were also in accordance with other reports. 7
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