Towards reliable myocardial blood-oxygen-level-dependent (BOLD) CMR using late effects of regadenoson with simultaneous 13n-ammonia pet validation in a whole-body hybrid PET/MR system
Journal of Cardiovascular Magnetic Resonance volume 18, Article number: O19 (2016)
BOLD CMR is a non-contrast approach for examining myocardial perfusion but despite major technical advancements to date, its reliability remains weak. A key reason for this is the unpredictable cardiac motion during stress, which can lead to pronounced artifacts that confound/mask the true BOLD signal changes during hyperemia. Recently, regadenoson has become the vasodilator of choice owing to greater patient tolerability and ease of use. We hypothesized that at 10-mins post regadenoson administration (p.r.a), (a) BOLD CMR artifacts at stress are markedly reduced compared to those conventionally acquired at 2-mins p.r.a; and (b) that myocardial perfusion reserve (MPR) remains greater than 2.0 and is highly correlated with the BOLD effects estimated from T2 maps.
Canines (n = 7) were studied in a PET/MR system. MR acquisitions were used to generate short-axis 2D T2 maps; and the PET acquisitions following 13N-ammonia infusion were used to quantify myocardial blood flow (MBF). Initially, 2D T2 maps and PET signals were acquired at rest. Subsequently, regadenoson (2.5 μg/kg) was administrated. T2 maps were acquired at 2- and 10-mins p.r.a and PET signals were acquired at 10-mins p.r.a. Standard deviation (s) of myocardial T2 values was measured at rest, 2- and 10-mins p.r.a from T2 maps and were used to determine Myocardial BOLD Variability (MBV, defined as sT2(stress)/sT2(rest)) at 2- and 10-min p.r.a. Similarly, using the mean T2 values, Myocardial BOLD Response (MBR, defined as T2(stress)/T2(rest)) was computed at 10-mins p.r.a. PET images were analyzed with qPET software to determine MBF and MPR at rest and 10-mins p.r.a and were regressed against MBR
A box-plot of observed MBV at 2- and 10-mins p.r.a (and at rest, for reference), along with representative T2 maps are shown in Fig. 1. Note the extensive artifacts present in the T2 map at 2 min, which are absent in the T2 maps acquired at rest and 10-mins p.r.a. MBV was significantly larger at 2-mins p.r.a (1.6 ± 0.9) compared to 10-mins p.r.a (1.0 ± 0.3) and rest (1.0); p < 0.05 for both. Representative MBF at rest and 10-mins p.r.a are shown in Fig. 2A. MBF at 10-min p.r.a (1.8 ± 0.9 ml/g/min) was significantly higher than at rest (0.6 ± 0.3 ml/g/min), p < 0.05 (Fig. 2B). Mean MPR at 10-min p.r.a was 3.0. Corresponding BOLD images (T2 maps) are shown in Fig. 2C. Myocardial T2 at 10-min p.r.a (40.4 ± 1.7 ms) was significantly higher than at rest (37.1 ± 2.0 ms), p < 0.05 (Fig. 2D). MBR was strongly correlated with MPR (R = 0.7, p < 0.05, Fig. 2E)
Myocardial BOLD images acquired at 10-min p.r.a (compared to 2-min p.r.a) can be free of image artifacts. MPR at 10-mins p.r.a can be consistently higher than 2.0 and is strongly correlated with MBR. These data support that delayed acquisition of BOLD CMR post regadenoson administration is a viable means for increasing the reliability of cardiac BOLD. The clinical utility of this approach remains to be evaluated in human subjects.
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Yang, HJ., Dey, D., Sykes, J.M. et al. Towards reliable myocardial blood-oxygen-level-dependent (BOLD) CMR using late effects of regadenoson with simultaneous 13n-ammonia pet validation in a whole-body hybrid PET/MR system. J Cardiovasc Magn Reson 18 (Suppl 1), O19 (2016). https://doi.org/10.1186/1532-429X-18-S1-O19