Haosen Zhang

Fast mapping of myocardial blood flow with MR first-pass perfusion imaging.

Accurate and fast quantification of myocardial blood flow (MBF) with MR first‐pass perfusion imaging techniques on a pixel‐by‐pixel basis remains difficult due to relatively long calculation times and noise‐sensitive algorithms. In this study, Zierlers central volume principle was used to develop an algorithm for the calculation of MBF with few assumptions on the shapes of residue curves. Simulation was performed to evaluate the accuracy of this algorithm in the determination of MBF. To examine our algorithm in vivo, studies were performed in nine normal dogs. Two first‐pass perfusion imaging sessions were performed with the administration of the intravascular contrast agent Gadomer at rest and during dipyridamole‐induced vasodilation. Radiolabeled microspheres were injected to measure MBF at the same time. MBF measurements in dogs using MR methods correlated well with the microsphere measurements (R2 = 0.96, slope = 0.9), demonstrating a fair accuracy in the perfusion measurements at rest and during the vasodilation stress. In addition to its accuracy, this method can also be optimized to run relatively fast, providing potential for fast and accurate myocardial perfusion mapping in a clinical setting. Magn Reson Med, 2008.

Accurate myocardial T1 measurements: Toward quantification of myocardial blood flow with arterial spin labeling

In this study, we investigated a method for accurately measuring myocardial T1 for the quantification of myocardial blood flow (MBF) with arterial spin labeling (ASL). A single‐shot gradient‐echo (GE)‐based ASL sequence with an adiabatic hyperbolic secant inversion recovery pulse was modified to acquire a pair of myocardial T1s within a breath‐hold. A multivariable regression algorithm that accounted for the magnetization saturation effects was developed to calculate T1. The MBF was then determined with a well‐developed model. The accuracy of our T1 calculation was first evaluated in a phantom, and then in six dogs for the MBF calculation, with (N = 4) and without (N = 2) coronary artery stenosis. In the phantom study, the accuracy of T1 measured with a slice‐selective inversion prepared pulse was within 2.5% of error. In healthy dogs, the MBF increased 2–5 times during vasodilation. In contrast, regional differences of MBF were well visualized in the stenotic dogs during vasodilation (perfusion reserve of 2.75 ± 0.83 in normal myocardium, and 1.46 ± 0.75 in the stenotic area). A correlation analysis revealed a close agreement in MBF between the ASL and microsphere (MS) in both healthy and stenotic dogs. In summary, the modified ASL technique and T1 regression algorithm proposed here provide an accurate measurement of myocardial T1 and demonstrate potential for reliably assessing MBF at steady state. Magn Reson Med 53:1135–1142, 2005.

Improvement of quantification of myocardial first-pass perfusion mapping: A temporal and spatial wavelet denoising method

Mapping of myocardial blood flow (MBF) with first‐pass perfusion imaging is becoming an important tool in the study of coronary artery disease. In this study a wavelet‐based denoising method was developed to improve the accuracy of pixel‐by‐pixel MBF maps. We performed an in vivo study in five stenotic dogs with 70% stenosis in the left coronary arteries. First‐pass perfusion imaging sessions were performed by administering the intravascular contrast agent Gadomer at rest and during dipyridamole‐induced vasodilation. Color microspheres (MS) were injected into the dogs to measure MBF at the same time. After denoising was performed, the signal‐to‐noise ratio (SNR) of the first‐pass perfusion image improved by approximately 180%, whereas spatial variation of MBF maps decreased 38%. It was also found that the correlation of MBFs measured by MRI with the MS method indicates a significant improvement with the denoising method (R2 increased from 0.24 to 0.78, P < .001). This suggests that the wavelet denoising method may be an effective way to increase the accuracy of pixel‐by‐pixel MBF quantification and reduce spatial variation, and may be applicable to other forms of noise‐sensitive image analysis. Magn Reson Med, 2006.

Resting myocardial perfusion quantification with CMR arterial spin labeling at 1.5 T and 3.0 T

BackgroundThe magnetic resonance technique of arterial spin labeling (ASL) allows myocardial perfusion to be quantified without the use of a contrast agent. This study aimed to use a modified ASL technique and T1 regression algorithm, previously validated in canine models, to calculate myocardial blood flow (MBF) in normal human subjects and to compare the accuracy and repeatability of this calculation at 1.5 T and 3.0 T. A computer simulation was performed and compared with experimental findings.ResultsEight subjects were imaged, with scans at 3.0 T showing significantly higher T1 values (P < 0.001) and signal-to-noise ratios (SNR) (P < 0.002) than scans at 1.5 T. The average MBF was found to be 0.990 ± 0.302 mL/g/min at 1.5 T and 1.058 ± 0.187 mL/g/min at 3.0 T. The repeatability at 3.0 T was improved 43% over that at 1.5 T, although no statistically significant difference was found between the two field strengths. In the simulation, the accuracy and the repeatability of the MBF calculations were 61% and 38% higher, respectively, at 3.0 T than at 1.5 T, but no statistically significant differences were observed. There were no significant differences between the myocardial perfusion data sets obtained from the two independent observers. Additionally, there was a trend toward less variation in the perfusion data from the two observers at 3.0 T as compared to 1.5 T.ConclusionThis suggests that this ASL technique can be used, preferably at 3.0 T, to quantify myocardial perfusion in humans and with further development could be useful in the clinical setting as an alternative method of perfusion analysis.

Myocardial Blood Volume Is Associated With Myocardial Oxygen Consumption : An Experimental Study With Cardiac Magnetic Resonance in a Canine Model

Understanding the oxygen consumption of the left ventricular myocardium provides important insight into the relationship between myocardial oxygen supply and demand. In other territories, cardiac magnetic resonance has been utilized to measure myocardial oxygen consumption with a blood level oxygen dependent (BOLD) technique. The BOLD technology requires repetitive sampling of stationary tissues and is frequently implemented in areas such as the brain. A limitation to utilizing BOLD cardiac magnetic resonance techniques in the heart has been cardiac motion. In this study, we document a methodology for acquiring BOLD images in the heart and demonstrate the utility of the technique for identifying associations between myocardial oxygen consumption and blood flow.

Quantification of myocardial blood volume during dipyridamole and doubtamine stress: a perfusion CMR study.

PURPOSE Myocardial blood volume (MBV) may provide complementary information about myocardial oxygen needs and viability. The aim of this study is to examine a Cardiovascular Magnetic Resonance (CMR) perfusion method to quantify the changes in MBV, in comparison with the radiolabeled 99mTc-Red-Blood-Cell (RBC) method. METHODS Normal mongrel dogs (n=12) were used in this study. Eight dogs were injected intravenously with dipyridamole, and 4 dogs were given dobutamine during the MR scans. CMR first-pass perfusion imaging was performed at rest and during the pharmacological stress. An intravascular contrast agent, Gadomer (Schering AG, Berlin, Germany), was injected (0.015 mmol/kg) as a bolus during the scans. A perfusion quantification method was applied to obtain MBV maps. Radiolabeled-RBCs were injected at the end of the study to measure reference MBV at rest (n=4), during dipyridamole vasodilation (n=4), and during dobutamine stress (n=4). RESULTS Myocardial blood flow (MBF) increased approximately 3-fold with both dipyridamole and dobutamine injections. Transmural MBV values measured by CMR were closely correlated with those measured by 99mTc method (CMR:MBV=6.2+/-1.3, 7.2+/-0.8, and 8.3+/-0.5 mL/100 g, at rest, with dipyridamole, and with dobutamine, respectively. 99mTc-RBC: MBV=6.1+/-0.5, 7.0+/-0.9, and 8.6+/-0.7 mL/100 g). Dobutamine stress significantly increased MBV by CMR (33%) and 99mTc methods (35%). During dipyridamole induced vasodilation, MBV increased non-significantly by 14% with the 99mTc method and 1% with CMR method, which agreed well with other reports. CONCLUSION First-pass perfusion CMR with the injection of intravascular contrast agents is a promising non-invasive approach for the assessment of MBV both at rest and pharmacologically induced stress.

Assessment of myocardial oxygen extraction fraction and perfusion reserve with BOLD imaging in a canine model with coronary artery stenosis

To determine the feasibility of T2‐weighted BOLD imaging for estimating regional myocardial oxygen extraction fraction (OEF) and approximating perfusion reserve (MPR) simultaneously in a canine model with moderate coronary artery stenosis.

Myocardial Blood Volume Is Associated with Myocardial Oxygen Consumption: An Experimental Study with CMR in a Canine Model

Understanding the oxygen consumption of the left ventricular myocardium provides important insight into the relationship between myocardial oxygen supply and demand. In other territories, cardiac magnetic resonance has been utilized to measure myocardial oxygen consumption with a blood level oxygen dependent (BOLD) technique. The BOLD technology requires repetitive sampling of stationary tissues and is frequently implemented in areas such as the brain. A limitation to utilizing BOLD cardiac magnetic resonance techniques in the heart has been cardiac motion. In this study, we document a methodology for acquiring BOLD images in the heart and demonstrate the utility of the technique for identifying associations between myocardial oxygen consumption and blood flow.

Improvement of hyperemic myocardial oxygen extraction fraction estimation by a diffusion-prepared sequence

Myocardial oxygen extraction fraction (OEF) during hyperemia can be estimated using a double‐inversion‐recovery‐prepared T2‐weighted black‐blood sequence. Severe irregular electrocardiogram (ECG) triggering due to elevated heart rate and/or arrhythmias may render it difficult to adequately suppress the flowing left ventricle blood signal and thus potentially cause errors in the estimates of myocardial OEF. Thus, the goal of this study was to evaluate another black‐blood technique, a diffusion‐weighted‐prepared turbo spin echo sequence for its ability to determine regional myocardial OEF during hyperemia. Control dogs and dogs with acute coronary artery stenosis were imaged with both the double‐inversion‐recovery‐ and diffusion‐weighted‐prepared turbo spin echo sequences at rest and during either dipyridamole or dobutamine hyperemia. Validation of MRI OEF estimates was performed using blood sampling from the artery and coronary sinus in control dogs. The two methods showed comparable correlations with blood sampling results (R2 = 0.9). Similar OEF estimations for all dogs were observed, except for the group of dogs with severe coronary stenosis during dobutamine stress. In these dogs, the diffusion‐weighted method provided more physiologically reasonable OEF (hyperemic OEF = 0.75 ± 0.08 versus resting OEF of 0.6) than the double‐inversion‐recovery method (hyperemic OEF = 0.56 ± 0.10). Diffusion‐weighted preparation may be a valuable alternative for more accurate oxygenation measurements during irregular ECG‐triggering. Magn Reson Med, 2010.

Myocardial Blood Volume Is Associated With Myocardial Oxygen Consumption

Understanding the oxygen consumption of the left ventricular myocardium provides important insight into the relationship between myocardial oxygen supply and demand. In other territories, cardiac magnetic resonance has been utilized to measure myocardial oxygen consumption with a blood level oxygen dependent (BOLD) technique. The BOLD technology requires repetitive sampling of stationary tissues and is frequently implemented in areas such as the brain. A limitation to utilizing BOLD cardiac magnetic resonance techniques in the heart has been cardiac motion. In this study, we document a methodology for acquiring BOLD images in the heart and demonstrate the utility of the technique for identifying associations between myocardial oxygen consumption and blood flow.