MRI Evaluation Of Acute Cardiovascular Disease

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The overall aim of the National Heart, Lung and Blood Institute (NHLBI)/Suburban Hospital Cardiovascular MRI Research Project is to develop new approaches in assessing patients with cardiovascular disease with MRI technology. 1) Detection and characterization of acute coronary syndrome with MRI. We found that a rest MRI scan had higher sensitivity and specificity for diagnosing non-ST elevation acute coronary syndrome than cardiac risk factors, ECG, and troponin Kwong RY, Schussheim AE, Rekhraj S, Aletras AH, Geller N, Davis J, Christian TF, Balaban RS, Arai AE. Detecting acute coronary syndrome in the emergency department with cardiac magnetic resonance imaging. Circulation 2003; 107:538-544. The sensitivity and specificity for detecting acute coronary syndrome was 84% and 85% by MRI, 80% and 61% by an abnormal ECG, 16% and 95% for ST depression or T-wave inversion, 40% and 97% for peak troponin-I, and 48% and 85% for a TIMI risk score >3. The MRI was more sensitive than strict ECG criteria for ischemia (p< 0.001), peak troponin-I (p< 0.001), and the TIMI Risk Score (p=0.004). The MRI was more specific than an abnormal ECG (p< 0.001). Multivariate logistic regression analysis showed an abnormal MRI was the strongest predictor of acute coronary syndrome and added statistically significant diagnostic value over clinical parameters (p< 0.001). We concluded that the resting MRI scan exhibited diagnostic operating characteristics suitable for triage of patients with chest pain in the emergency department. We have extended this work in a second protocol that used adenosine stress MRI to evaluate 141 consecutive patients with troponin-negative acute coronary syndrome. The overall sensitivity and specificity for detecting ischemic heart disease were both greater than 90%. An abnormal adenosine stress MRI had significant 1 year prognostic value. (Ingkanisorn et al. JACC 2006; 47: 1427). We have determined that gadolinium delayed enhancement cardiovascular magnetic resonance corrrelates with clinical measures of myocardial infarction. Ingkanisorn et al. J Am Coll Cardiol 43:2253-9. This study imaged patients with acute myocardial infarction an average of 2 days post-MI. The transmural extent of delayed enhancement predicted the recovery of regional myocardial function. We completed a project that aims to characterize recently ischemic myocardium and demonstrated that we can image the ischemic area at risk after myocardial perfusion has been restored Natanzon A, Aletras AH, Hsu L, Arai AE. Determining Myocardial Area at Risk with Contrast Enhanced Manganese MRI. Radiology. 2005 Sep;236(3):859-66. This can be described as a form of "ischemic memory imaging." We found that T2-weighted MRI can determine the area at risk in acute MI and is thus complementary to delayed enhancement imaging (Aletras et al. Circulation 2006; 113: 1865). This methodology also works in non-reperfused myocardial infarction (Tilak et al. Investigative Radiology in press). Despite the promise of using T2-weighted images in diagnosing the ischemic area at risk associated with acute coronary syndrome, commercial software used to obtain these images is limited by artifacts and other technical factors that reduce the diagnostic accuracy to about 70%, an unacceptable level of performance. We developed 2 new methods for imaging myocardial edema associated with acute coronary syndrome (Kellman et al Magn Resonance Med 2007; 57: 891) and a second method that may offer better signal to noise ratio but is more difficult to implement (Aletras AH et al Magn Reson Med 2008; 59: 229). The steady state free precession methodology markedly improved the diagnostic accuracy of determining the coronary territory associated with an acute myocardial infarction. 2) Characterizing myocardial infarction and viability with MRI. We also developed a phase sensitive reconstruction method which improves the quality of heart attack images and minimizes the influence of user selected parameters on the apparent size of the heart attack Kellman P, Arai AE, McVeigh ER, Aletras AH. Phase-sensitive inversion recovery for detecting myocardial infarction using gadolinium-delayed hyperenhancement. Magnetic Resonance in Medicine 2002 47(2):372-383. Our histopathological validation of the phase sensitive reconstruction method and a validation study showing that a computer algorithm can accurately measure infarct size on in vivo and ex vivo images is now in press. We have also extended this work to characterize IL-2 myocarditis and community acquired myocarditis. We have extended our validations of the phase sensitive inverson recovery methods for imaging myocardial infarction with another study: Artifact suppression in imaging of myocardial infarction using B1-weighted phased-array combined phase-sensitive inversion recovery (Kellman et al. Magn Reson Med 2004; 51:408-12). We developed comuter algorithms with advanced image processing logic to improve the accuracy of measuring the size of myocardial infarction (Hsu et al. J Magn Resonance Imaging 2006; 23: 298-308 and Hsu et al. J Magn Resonance Imaging 2006; 23: 309-314). We developed a method to improve the contrast between myocardial infarction and the blood in the left ventricular cavity (Kellman et al. J Magn Resonance Imaging 2005; 22: 605-613) and a method that allows imaging myocardial infarction without resorting to breatholds that are not feasible in all patients (Kellman et al. 2005; 53: 194-200). We recently completed analysis of the ICELAND MI study of the prevalence of myocardial infarction in 978 participants in the AGES-Reykjavik study. Preliminary results indicate a much higher than expected prevalence for unrecognized myocardial infarction than suggested by prior epidemiological studies relying on ECG methods. 3) Improving first pass myocardial perfusion imaging. We have extended our first pass perfusion methods to provide quantitative analysis methods. We have shown that the MRI can measure myocardial perfusion as accurately as microsphere injections (a gold standard method only usable in animal models) Christian TF, Rettmann D, Aletras AH, Liao S, Taylor JL, Balaban RS, Arai AE. Absolute Myocardial Perfusion by MRI Using a Dual-Bolus First-Pass Method: Benefits Over Qualitative and Semi-Quantitative Analysis. Radiology 2004; 232:677-84. We confirmed that most of the conclusions derived from Dr. Christian's work applies to humans (Hsu et al. JMRI 2006; 23: 315). We completed a study in humnas comparing the diagnostic accuracy of quantitative stress perfusion with quantiative coronary angiography. This work, which is in review, indicates that the fully objective quantitative stress perfusion methods can diagnose patients with significant coronary stenosis without needing additional input from delayed enhancement images or cine MRI. We also developed methods for accelerating perfusion image acquisition (Kellman et al. Mag Resonance Med 2004; 52: 200-204) and used a variant of these methods to measure T2* during the first pass of contrast through the heart (Kellman et al. Mag Resonace Med 2006; 56: 1132-4). This later paper is important since T2* is thought to be a major source of image artifacts and false positive findings on MRI perfusion studies. In fact, T2* does not appear affected severely enough to explain the endocardial artifacts seen on many patients.