145 Automated Quantitative Perfusion CMR With Simplified Dual-Bolus Contrast Protocol INTRODUCTION Stress perfusion cardiovascular magnetic resonance (CMR) imaging is an established non-invasive method for detection of myocardial ischemia.1 In daily clinical practice, stress perfusion CMR is evaluated by visual assessment of first-pass perfusion images, where the hypo-perfused myocardial segments show delayed gadolinium-based contrast agent (GBCA) wash-in kinetics during first pass, resulting in areas with lower signal intensity (SI; i.e. perfusion defect). Recent technical advances allow absolute quantification of myocardial blood flow (MBF) by applying CMR perfusion imaging (quantitative perfusion CMR; QP CMR).2 A critical step for MBF quantification is the accurate assessment of the arterial input function (AIF), which reflects the proportion of GBCA entering the coronary circulation. Since myocardial contrast enhancement is considered to have a linear response to arterial contrast enhancement, it is crucial to make sure the relation between GBCA concentration and SI in the blood pool is also linear.3 However, high concentrations of a GBCA in the blood pool as a result of a standard single-bolus injection (typically 0.05–0.1 mmol/kg) may exacerbate the T1 and T2* saturation effect, which causes a non-linear relation between SI and GBCA concentration. This non-linearity results in a truncated or dampened AIF curve. As a consequence, the MBF may be wrongly overestimated following the deconvolution process, affecting the overall QP CMR result and interpretation.4 As a solution, two different approaches of AIF saturation correction are available, including the dualsequence and dual-bolus method. The dual-sequence method uses a single dose bolus of contrast medium and combines two different types of image acquisitions within the same cardiac cycle, i.e. short saturation recovery with low spatial resolution and reduced T1weighting for AIF, and long saturation recovery with high spatial resolution for myocardial enhancement.5 In general, the dual-sequence approach is considered more easy to use with a single bolus of GBCA and simultaneous assessment of AIF and myocardial SI. However, its major limitation is the requirement of a specific, dedicated pulse sequence.6 The dual-bolus approach enables the use of high dose of GBCA for myocardial perfusion analysis (typically 0.05–0.1 mmol/kg) combined with measurement of the AIF using an initial low-dose bolus (typically 0.0025–0.005 mmol/kg, ~ 1:10 concentration of the main bolus) of contrast injection, which preserves the linearity of SI to GBCA concentration in the blood pool and maintains high contrast-to-noise ratio. In this manner, the AIF can be accurately determined and is less affected by the substantial T1 and T2* saturation effect.4, 7 In contrast to dual-sequence, the dual-bolus method uses standard, regulatory-approved sequences for first-pass perfusion imaging, which makes it more widely available and easy to implement for general CMR centers. However, in a standard approach, the dual-bolus GBCA administration scheme requires an equal volume of both the main bolus of neat GBCA and the pre-bolus.7 This requires a time-consuming preparation of the pre-bolus which is considered the major limitation of this technique, due to its inconvenience in 7
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