Improved myocardial arterial spin labeled perfusion imaging

2019-05-11Coronary artery disease (CAD) affects more than 15.5 million Americans and causes approximately 310,000 deaths per year. One of the most common diagnostic tests is perfusion stress testing, primarily performed using single photon emission computed tomography (SPECT) or first-pass cardiovascular magnetic resonance (CMR). These methods require the use of ionizing radiation or exogenous contrast agents that carry associated risks to patients, especially those who require frequent assessment or have kidney dysfunction. Myocardial arterial spin labeling (ASL) is a promising MRI-based perfusion imaging method that can quantitatively measure myocardial tissue perfusion without the use of ionizing radiation or exogenous contrast agents. Feasibility of CAD detection using ASL has been previously demonstrated, however, several challenges remain, including low sensitivity, coarse spatial resolution, and limited spatial coverage. The contributions of this dissertation are (1) improving sensitivity, (2) exploring clinical applications, and (3) developing a new and advantageous labeling method for myocardial ASL. ❧ Low sensitivity is one of the major limitations of current myocardial ASL methods. I found that cardiac motion is one of the dominant sources of measurement variability and that shortening the acquisition window from 300 ms to 150 ms using parallel imaging significantly reduces measurement variability, i.e. improves sensitivity. I also implemented double-gating which further improves sensitivity of myocardial ASL method. Furthermore, I demonstrated that double-gating is robust to heart rate variation. ❧ I demonstrated a potential application of myocardial ASL in assessment of microvascular obstruction (MVO) in a pig model of acute myocardial infarction (AMI). This study also demonstrated that myocardial ASL is able to assess clinically relevant increase in blood flow during vasodilation. That potentially allows myocardial ASL to assess microvascular dysfunction as studies have shown that microvascular function is impaired not only in the infarcted but also in the remote territories. ❧ Myocardial T₁ mapping with appropriate flow-sensitive preparation is able to assess myocardial blood flow, myocardial blood flow change, and myocardial blood volume change under vasodilation. I demonstrated the feasibility of using myocardial T₁ mapping for assessment of MBF in human subjects. I also explored potential application of T₁-based myocardial blood volume change mapping in heart transplant recipients using myocardial T₁ mapping. ❧ I developed a new and more efficient labeling method named physiologically synchronized multi-module pulsed ASL (SymPASL), which may enable myocardial ASL with volumetric coverage. SymPASL utilizes several labeling pulses that are synchronized with blood flow and image acquisitions are synchronized with motion of the target organ. From simulation and in vivo experiment in human kidneys, SymPASL provides superior ASL signal and signal-to-noise ratio (SNR) efficiency compared to the pulsed ASL method with 1 heart beat post-labeling-delay and has similar ASL signal and SNR efficiency to pseudo-continuous ASL (PCASL) with 1.5-second labeling duration and 1.0-second post-labeling-delay