Improved in vivo magnetic resonance imaging of acute myocardial infarction after intravenous paramagnetic contrast agent administration

Advances in Contrast Agents for Contrast-Enhanced Magnetic Resonance Imaging

INTRODUCTION

Magnetic resonance imaging (MRI) is a well-established medical invention in modern medical technology diagnosis. It is a nondestructive, versatile, and sensitive technique with a high spatial resolution for medical diagnosis. However, MRI has some limitations in differentiating certain tissues, particularly tiny blood vessels, pathological to healthy tissues, specific tumors, and inflammatory conditions such as arthritis, atherosclerosis, and multiple sclerosis. The contrast agent (CA) assisted imaging is the best possible solution to resolve the limitations of MRI.

METHOD

The literature review was carried out using the keywords, "MRI, T1&T2 relaxation, MRI CAs, delivery and adverse effects, classification of CAs." The tools used for the literature search were PubMed, Scopus, and Google Scholar.

RESULT AND DISCUSSION

The literature findings focus on MRI technique, limitations, and possible solutions. Primarily, the review focuses on the mechanism of CAs in image formation with detailed explanations of T1 and T2 relaxations, the mechanism of the MRI-CA image formations. This review presents the adverse effects of CA as well as available marketed formulations and recent patents to extent complete information about the MRI-CA.

CONCLUSION

MRI generates detailed visual information of various tissues with high resolution and contrast. The proton present in the biological fluid plays a crucial role in MR image formation, and it is unable to distinguish pathological conditions in many cases. The CAs are the best solution to resolve the limitation by interacting with native protons. The present review discusses the mechanism of CAs in contrast enhancement and its broad classification with the latest literature. Furthermore, the article presents information about CA biodistribution and adverse effects. The review concludes with an appropriate solution for adverse effects and presents the future prospective for researchers to develop advanced formulations.

Clinical predictors for the manifestation of late gadolinium enhancement after acute myocardial infarction

Despite prompt revascularization, some patients with acute myocardial infarction (AMI) develop myocardial scars, which can be visualized by late gadolinium enhancement (LGE) in cardiovascular magnetic resonance imaging (CMR). Our goal was to identify angiographic findings that were predictive for scar development in patients after reperfused AMI.We examined 136 patients after first ST-elevated myocardial infarction by CMR after a median of 4 days (range: 2-7). Patients with manifestation of LGE were matched to patients without LGE by means of age and gender. Clinical follow-up with a combined primary endpoint including myocardial reinfarction, congestive heart failure, stroke, death and development of left ventricular thrombus was reported after 24 months.Patients with manifestation of LGE had a significant longer time of symptom-to-intervention, a higher prevalence of anterior AMI, and more proximal culprit lesions. Furthermore, left ventricular ejection fraction was significantly decreased, and peak values of infarct markers were significantly higher in these patients. Preinterventional thrombolysis in myocardial infarction-0-flow was significantly more frequent in patients with LGE manifestation. The presence of 3-vessel disease (odds ratio 53.99, 95% confidence interval 8.22-354.63, P <.001), a proximal culprit lesion, and high creatine kinase myocardial band (CK-MB) values were identified as independent predictors of LGE. Follow-up demonstrated a higher incidence of clinical events in the group with LGE, with the most common cause of heart failure (38.2% vs 7.4%, P <.001).The extent of angiographic findings in AMI plays a major role in the manifestation of LGE. The presence of a multivessel disease, a proximal culprit lesion, and high values of CK-MB are strong independent predictors for LGE manifestation.

Magnetic Resonance Imaging of Acute Myocardial Infarction in Pigs Using Gd-Dtpa

Six pigs with coronary artery occlusion were investigated with MR imaging before and subsequently for about 2.5 hours at repeated intervals after the intravenous administration of Gd-DTPA (0.4 mmol/kg). The animals were sacrificed after a total occlusion time of 6 hours and the hearts were excised. The excised hearts were then reexamined in the MR equipment and stained with TTC (triphenyl tetrazolium) in order to define areas of infarction. Four control hearts with 6-hour-old infarctions were only imaged ex vivo without any previous administration of contrast media. In vivo, there was no clear demarcation of infarction with or without Gd-DTPA. Ex vivo, without any contrast media, the infarctions were poorly discriminated with a discretely increased signal intensity relative to normal myocardium in the T2 weighted images. Gd-DTPA was found to accumulate in the infarctions, which caused an elevated signal intensity most pronounced in the T1 weighted images. This considerably improved the delineation of the infarcted area.

Double-Contrast Enhanced Mr Imaging of Myocardial Infarction in the Pig

Myocardial infarction was induced by ligating a diagonal branch of the left anterior descending artery in 18 pigs. All pigs were sacrificed 6 h after the occlusion. Dysprosium diethylenetriaminepentaacetic acid bismethylamide (Dy-DTPA-BMA, 1.0 mmol/kg) was administered i.v. to 6 pigs, starting 3 min before sacrifice (injection time approximately 1 min). In a second group of 6 pigs, a double-contrast technique was used, consisting of an i.v. injection of gadolinium-DTPA-BMA (0.4 mmol/kg) 2 h before sacrifice, followed by an i.v. injection of Dy-DTPA-BMA (1.0 mmol/kg) 3 min before sacrifice. Six additional pigs, subjected to 6 h of coronary artery occlusion without administration of contrast medium, served as controls. The hearts were excised and imaged with MR. In the control animals, the infarctions demonstrated an increased signal intensity in the proton density- and T2-weighted images. Administration of Dy-DTPA-BMA primarily improved infarct visualization in the proton density- and T2-weighted images, due to reduction of signal intensity in nonischemic myocardium. The double-contrast technique further improved infarct visualization in all sequences.

Mr Imaging of Acute Myocardial Infarction in Pigs Using GD-Dtpa-Labeled Dextran

Myocardial infarctions were induced in 12 pigs. In 6 pigs, dextran-(Gd-DTPA)15 (≈0.1 mmol Gd/kg b.w.) was injected i.v. 4 to 4.5 hours after coronary artery occlusion. ECG gated MR images were obtained repeatedly before (n = 4) and after (n = 6) contrast medium injection. Relaxation times in blood samples were measured repeatedly. The animals were sacrificed 2 hours after contrast medium administration. The hearts were excised, reexamined in the MR equipment and stained with triphenyltetrazolium chloride (TTC) in order to define areas of infarction. The remaining 6 pigs were sacrificed 6 hours after occlusion without administration of contrast medium. These hearts were only imaged ex vivo. In vivo, the infarctions could not be identified with or without dextran-(Gd-DTPA)15. Ex vivo, without contrast medium, the infarctions had an increased signal intensity, most pronounced in the T2-weighted images. Dextran-(Gd-DTPA)15 caused a prolonged, pronounced shortening of T1 and T2 in blood samples. The infarct demarcation improved in the T1-weighted images after injection of dextran-(Gd-DTPA)15, due to a moderate enhancement in normal myocardium and a stronger enhancement at the periphery of the infarctions, while the central parts of the infarctions were only weakly enhanced.

Role of Cardiac MR Imaging in Cardiomyopathies

Cardiac MR imaging has made major inroads in the new millennium in the diagnosis and assessment of prognosis for patients with cardiomyopathies. Imaging of left and right ventricular structure and function and tissue characterization with late gadolinium enhancement (LGE) as well as T1 and T2 mapping enable accurate diagnosis of the underlying etiology. In the setting of coronary artery disease, either transmurality of LGE or contractile reserve in response to dobutamine can assess the likelihood of recovery of function after revascularization. The presence of scar reduces the likelihood of a response to medical therapy and to cardiac resynchronization therapy in heart failure. The presence and extent of LGE relate to overall cardiovascular outcome in cardiomyopathies. A major role for cardiac MR imaging in cardiomyopathies is to identify myocardial scar for diagnostic and prognostic purposes.

Multiacquisition T1-mapping MRI during tidal respiration for quantification of myocardial T1 in swine with heart failure

OBJECTIVE

The purpose of this article is to evaluate a free-breathing pulse sequence to quantify myocardial T1 changes in a swine model of tachycardia-induced heart failure.

MATERIALS AND METHODS

Yorkshire swine were implanted with pacemakers and were ventricularly paced at 200 beats/min to induce heart failure. Animals were scanned twice with a 1.5-T MRI scanner, once at baseline and once at heart failure. A T1-mapping sequence was performed during tidal respiration before and 5 minutes after the administration of a gadolinium-chelate contrast agent. T1-mapping values were compared between the baseline and heart failure scans. The percentage of fibrosis of heart failure myocardial tissue was compared with similar left ventricular tissue from control animals using trichrome blue histologic analysis.

RESULTS

In the study cohort, differences were found between the baseline and heart failure T1-mapping values before the administration of contrast agent (960 ± 96 and 726 ± 94 ms, respectively; p = 0.02) and after contrast agent administration (546 ± 180 and 300 ± 171 ms, respectively; p = 0.005). The animals with heart failure also had a difference histologically in the percentage of myocardial collagen compared with tissue from healthy control animals (control, 5.4% ± 1.0%; heart failure, 9.4% ± 1.6%; p < 0.001).

CONCLUSION

The proposed T1-mapping technique can quantify diffuse myocardial changes associated with heart failure without the use of a contrast agent and without breath-holding. These T1 changes appear to be associated with increases in the percentage of myocardial collagen that in this study were not detected by traditional myocardial delayed enhancement imaging. T1 mapping may be a useful technique for detecting early but clinically significant myocardial fibrosis.

MRI for acute chest pain: current state of the art

This article reviews the magnetic resonance imaging (MRI) and angiography (MRA) techniques, imaging findings, and evidence for evaluating patients with acute chest pain due to acute pulmonary embolus (PE), aortic dissection (AD), and myocardial infarction (MI). When computed tomographic angiography (CTA) is contraindicated, MRI and MRA are important alternative imaging modalities for diagnosis and management of patients with acute PE, AD, and MI. Familiarity with the techniques, imaging findings, and evidence is critical to safely and appropriately managing patients presenting with acute chest pain.

An improved real-time cine Late Gadolinium Enhancement (LGE) imaging method at 3T

A real-time Late Gadolinium Enhancement (LGE) MRI technique (free breathing and non-gated) is presented for detection of myocardial scars. Conventional LGE imaging methods currently in use are applied in conjunction with breath-hold and, thus, are difficult to use in patients with cardiac disease and may lead to motion artifacts. Additionally, conventional techniques involve ECG gating, which is problematic in patients with arrhythmias requiring multiple breath holds and use of arrhythmia rejection techniques. Finally, conventional LGE techniques require accurate estimates for the inversion time in order to null the normal myocardium, revealing the location of the scar with high contrast. Real-time LGE imaging obviates these difficulties and can, in principle, acquire cine images to assess wall motion over several heart phases as part of the same scan. To date, the main limitation of real-time LGE imaging has been long acquisition window and low temporal resolution. These limitations lead to temporal blurring of wall motion and possible overestimation of infarct size. The goal of this study was to increase the temporal resolution of real-time, cine LGE imaging, providing the possibility for better visualization of the wall motion and more accurate assessment of myocardial viability.

Improved detection of subendocardial hyperenhancement in myocardial infarction using dark blood-pool delayed enhancement MRI

OBJECTIVE

Delayed enhancement MRI using fast segmented k-space inversion recovery (IR) gradient-echo imaging is a well established "bright-blood" technique for identifying myocardial infarction and is used as the reference standard sequence in this study. The purpose of this study was to validate a recently developed dark blood-pool delayed enhancement technique in a porcine animal model, evaluate its performance in human patients, and quantify its performance compared with the reference standard in both.

SUBJECTS AND METHODS

In an animal study, the reference standard and dark blood-pool delayed enhancement were assessed in three pigs with induced myocardial infarction. In a human study, 26 patients, 31-81 years old (19 men and seven women), with a known history of myocardial infarction were imaged using the reference standard and dark blood-pool delayed enhancement. Contrast-to-noise ratio (CNR), signal intensity ratio, signal-to-noise ratio (SNR), and qualitative scores of hyperenhancement were recorded. Measurements were compared using paired samples t test and Wilcoxon's signed rank test.

RESULTS

In the animal study, the mean CNR of infarct to blood pool was 11 times higher for dark blood-pool delayed enhancement than for the reference standard. The mean SNR was 4.4 times higher for the reference standard. In the human study, the mean CNR and signal intensity ratio of hyperenhancing myocardium to the blood pool were 1.9 (p = 0.04) and 5.5 (p < 0.01) times higher, respectively, for dark blood-pool delayed enhancement compared with reference standard. The mean CNR and signal intensity ratio of hyperenhancing myocardium to normal myocardium and SNR were 2.8 (p < 0.01), 1.3 (p = 0.07), and 2.8 (p < 0.01) higher, respectively, for the reference standard. Qualitative analysis identified seven extra segments with grade 1 scars using dark blood-pool delayed enhancement (p < 0.01).

CONCLUSION

Dark blood-pool delayed enhancement is complementary to the reference standard. It can detect more subendocardial foci of hyperenhancement, thus potentially identifying more infarcts and changing patient management.

Diagnostic and prognostic value of cardiac magnetic resonance imaging in assessing myocardial viability

Assessment of viability is pivotal to the prognosis of patients with chronic coronary artery disease (CAD) and left ventricular dysfunction. Patients with viable myocardium have a better prognosis with revascularization; however, patients with nonviable myocardium have worse outcomes with higher perioperative morbidity and mortality subsequent to revascularization. Cardiac magnetic resonance (CMR) imaging not only is the current reference standard technique in measuring cardiac chamber size and function and myocardial mass and volume but also provides spatially registered 2- or 3-dimensional data sets in myocardial perfusion and myocardial contrast enhancement in the same imaging session. Late gadolinium enhancement by CMR is the best current technique in discriminating myocardial scar versus viable myocardium. An extensive body of preclinical evidence has validated the detection and characterization of the morphology of infarcted tissue. In clinical studies, infarct characteristics by CMR has demonstrated a strong clinical utility in the prediction of left ventricular functional recovery and patient prognosis. In this paper, we aim to review the current CMR techniques in characterizing the spectrum of myocardial changes because of CAD, in the prediction of myocardial viability, and the current evidence of CMR's role in patient prognosis. In addition, we will also review the current literature comparing the clinical utility of CMR with other established imaging modalities in the assessment of CAD.

MRI for the assessment of myocardial viability

Accurate distinction between viable and infarcted myocardium is important for assessment of patients who have cardiac dysfunction. Through the technique of delayed-enhancement MRI (DE-MRI), viable and infarcted myocardium can be simultaneously identified in a manner that closely correlates with histopathology findings. This article provides an overview of experimental data establishing the physiologic basis of DE-MRI-evidenced hyperenhancement as a tissue-specific marker of myocardial infarction. Clinical data concerning the utility of transmural extent of hyperenhancement for predicting response to medical and revascularization therapy are reviewed. Studies directly comparing DE-MRI to other viability imaging techniques are presented, and emerging applications for DE-MRI are discussed.

Contrast-enhanced magnetic resonance imaging in the assessment of myocardial infarction and viability

Contrast-enhanced magnetic resonance imaging (MRI) can be used to visualize the transmural extent of myocardial infarction with high spatial resolution. The aim of this review is to provide an overview of the use of contrast-enhanced MRI for characterization of ischemic myocardial injury in comparison to other imaging methods and its relevance in clinical syndromes related to coronary artery disease. Infarcted myocardium appears hyperenhanced compared with normal myocardium when imaged by a delayed-enhancement MRI technique with the use of an inversion-prepared T(1)-weighted sequence after injection of gadolinium chelates, such as gadolinium-diethylenetriamine pentaacetic acid. Experimental and clinical studies indicate that the extent of delayed enhancement is reproducible and closely correlates with the size of myocardial necrosis or infarct scar as determined by established in vitro and in vivo methods. Furthermore, MRI appears to be more sensitive than other imaging methods in detecting small subendocardial infarctions. The transmural extent of delayed enhancement potentially predicts functional outcome after revascularization in acute myocardial infarction and chronic ischemic heart disease, indicating that it can accurately discriminate between infarction and dysfunctional but viable myocardium. Further experience from clinical trials is needed to understand the association of delayed enhancement with clinical outcomes.

In vivo myocardial tissue kinetics of Gd(ABE-DTTA), a tissue-persistent contrast agent

The phenomenological tissue kinetics of Gd(ABE-DTTA) was investigated in myocardial infarction (MI). Reperfused infarction was generated by balloon catheter in closed-chest canines (N=11). Forty-eight hours thereafter, inversion-recovery (IR)-prepared fast gradient-echo control images were acquired with varying inversion times (TIs). Precontrast R(1) maps were calculated from the TI dependence of signal intensity (SI) using nonlinear curve fitting. Then 0.05 mmol/kg Gd(ABE-DTTA) was administered I.V. In 11 dogs postcontrast R(1) maps were generated at 24 hr and 48 hr postcontrast. In five dogs measurements were also repeated at 108 hr and 12 days. In one dog early measurement was carried out at 4 hr. Delta R(1) values for blood and viable and infarcted myocardium were calculated at each time point by subtracting the precontrast R(1) from the postcontrast R(1). Gd(ABE-DTTA) showed significant, progressive accumulation into infarcts during the first 2 days (k(in)=0.39 hr(-1)) and a delayed clearance (k(out) = 0.005 hr(-1)). Among the time points sampled, the maximum infarct Delta R(1) was detected at 48 hr (1.72 s(-1)). Contrast agent (CA) in infarcted tissue was detectable for 12 days. Clearance from blood and viable myocardium occurred in parallel and was completed by 108 hr. Gd(ABE-DTTA) displays slow, tissue-persistent kinetics and partly intravascular, partly extravascular characteristics. It demonstrates high affinity for infarcted myocardium and induces highlighting of infarcts between 4 hr and 12 days following administration.

Comparison of delayed myocardial enhancement in the early and late phase after contrast injection: is it possible to reduce the examination time for myocardial viability study?

OBJECTIVES

We studied whether we can obtain a myocardial viability study immediately after contrast injection to reduce the whole cardiac MR examination time.

MATERIALS AND METHODS

We examined 36 patients with cardiovascular abnormality on comprehensive cardiac MRI. T1-weighted images with inversion recovery (IR) were obtained 5 min after stress perfusion with 0.05 mmol/kg of gadodiamide and 15 min after the resting perfusion with the same dose. (The latter images were obtained 25 min after the initial administration.) We evaluated the existence, the number of sectors, and the degree of enhancement at each time. The contrast ratio was also calculated. The number of the enhanced sectors and the contrast ratio were statistically compared using Student's t test.

RESULTS

All 17 cases of delayed myocardial enhancement at 25 min after contrast injection showed some enhancement at 5 min after contrast injection. However, the number of enhanced sectors was larger at 25 min after the initial injection in 11 cases, and it was statistically significant (P=.017). The degree of enhancement was stronger at 25 min in 14 cases. However, the contrast ratio at 5 and 25 min after contrast injection was not significantly different (P=.245).

CONCLUSION

Myocardial viability study immediately after contrast injection is too early to evaluate the extent of myocardial injury.

MRI for the Assessment of Myocardial Viability

Accurate distinction between viable and infarcted myocardium is important for assessment of patients who have cardiac dysfunction. Through the technique of delayed-enhancement MRI (DE-MRI), viable and infarcted myocardium can be simultaneously identified in a manner that closely correlates with histopathology findings. This article provides an overview of experimental data establishing the physiologic basis of DE-MRI-evidenced hyperenhancement as a tissue-specific marker of myocardial infarction. Clinical data concerning the utility of transmural extent of hyperenhancement for predicting response to medical and revascularization therapy are reviewed. Studies directly comparing DE-MRI to other viability imaging techniques are presented, and emerging applications for DE-MRI are discussed.

Phase-Sensitive Inversion-Recovery MR Imaging in the Detection of Myocardial Infarction

PURPOSE

To prospectively determine if phase-sensitive inversion-recovery (IR) magnetic resonance (MR) imaging eliminates the need to find the precise inversion time (TI) to null the signal of normal myocardium to achieve high contrast between infarcted and normal myocardium.

MATERIALS AND METHODS

Informed consent was obtained from each patient for this prospective MR imaging research study, which was approved by the institutional review board. Twenty patients (16 men; four women; mean age, 56 years +/- 12.3) who experienced Q-wave myocardial infarction 2 weeks earlier were examined with a 1.5-T MR system 10 minutes after administration of 0.1 mmol per kilogram of body weight gadobenate dimeglumine. To determine the optimal TI, a TI scout sequence was used. A segmented two-dimensional IR turbo fast low-angle shot (FLASH) sequence and a segmented two-dimensional IR true fast imaging with steady-state precession (FISP) sequence that produces both phase-sensitive and magnitude-reconstructed images were used at TI values of 200-600 msec (TI values were varied in 100-msec steps) and at optimal TI (mean value, 330 msec). Contrast-to-noise ratios (CNRs) of normal and infarcted myocardium and the area of infarcted myocardium were determined. Magnitude-reconstructed IR turbo FLASH images were compared with magnitude-reconstructed and phase-sensitive IR true FISP images. Two-tailed unpaired sample Student t test was used to compare CNRs, and two-tailed paired-sample Student t test was used to compare area of infarction.

RESULTS

Mean CNR of images acquired with IR turbo FLASH and IR true FISP (phase-sensitive and magnitude-reconstructed images) at optimal TI (mean value, 330 msec) were 6.6, 6.2, and 6.1, respectively. For a TI of 200 msec, CNR values were -4.3, -4.0, and 7.2, respectively; for TI of 600 msec, CNR values were 3.1, 3.3, and 4.3, respectively. Area of infarcted myocardium was underestimated on magnitude-reconstruction images (P = .002-.03) for short TI values (ie, 200 msec) for both sequences and for a TI of 300 msec for IR true FISP but not on phase-sensitive reconstructed IR true FISP images when compared with IR turbo FLASH images obtained at optimal TI.

CONCLUSION

Phase-sensitive image reconstruction results in reduced need for precise choice of TI and more consistent image quality.

Technology insight: assessment of myocardial viability by delayed-enhancement magnetic resonance imaging

Myocardial viability is of established importance to the management of cardiac patients being considered for revascularization. Existing noninvasive imaging tests to examine myocardial viability, such as stress echocardiography and nuclear scintigraphy, are of recognized utility but are subject to intrinsic limitations. Over the past few years delayed-enhancement MRI (DE-MRI) has emerged as an alternative to traditional tests and for the first time allows direct visualization of the transmural extent of myocardial viability. In this paper we review the scientific data that underlie the use of DE-MRI in patients with ischemic heart disease. Progress in this area is largely the result of the development of a new MRI pulse sequence in the late 1990s, which improved the detection of necrotic and scarred myocardial tissue. Following this technical development, a series of detailed histologic comparisons in large animal models revealed that both acute and healed myocardial infarcts appeared as brighter (hyperenhanced) areas than viable regions, and that the effect is independent of contractile function. The resulting 'bright is dead' hypothesis has thus far proven of significant use in patients with ischemic heart disease. Data are now emerging which suggest that the DE-MRI technique also has important implications for patients with nonischemic forms of cardiomyopathy.

Assessment of Myocardial Viability by Cardiovascular Magnetic Resonance

Patients with ischemic heart disease may have left ventricular (LV) dysfunction due to reversible or irreversible causes. The ability to distinguish viable myocardium with dysfunction due to a reversible etiology (hibernation, stunning) from nonviable scar is critical for determining proper management of the patient. Cardiovascular magnetic resonance (CMR) is a technique that has been established to be useful for the detection of myocardial viability and advancements in the field promise to further increase its utility. In this review we describe the features of CMR that make it suited for this purpose and outline promising developments that may soon make CMR the reference standard for viability assessment.

Magnetic resonance imaging for the assessment of myocardial viability

The identification of myocardial viability in the setting of left ventricular (LV) dysfunction is crucial for the prediction of functional recovery following revascularization. Although echocardiography, positron emission tomography (PET), and nuclear imaging have validated roles, recent advances in cardiac magnetic resonance (CMR) technology and availability have led to increased experience in CMR for identification of myocardial viability. CMR has unique advantages in the ability of magnetic resonance spectroscopy (MRS) to measure subcellular components of myocardium, and in the image resolution of magnetic resonance proton imaging. As a result of excellent image resolution and advances in pulse sequences and coil technology, magnetic resonance imaging (MRI) can be used to identify the transmural extent of myocardial infarction (MI) in vivo for the first time. This review of the role of CMR in myocardial viability imaging describes the acute and chronic settings of ventricular dysfunction and concepts regarding the underlying pathophysiology. Recent advances in MRS and MRI are discussed, including the potential for dobutamine MRI to identify viable myocardium and a detailed review of the technique of delayed gadolinium (Gd) contrast hyperenhancement for visualization of viable and nonviable myocardium.

Cardiovascular magnetic resonance of acute myocardial infarction at a very early stage

OBJECTIVES

Very early changes in myocardial tissue composition during acute myocardial infarction (AMI) are difficult to assess in vivo. Cardiovascular magnetic resonance (CMR) imaging provides techniques for visualizing tissue pathology.

BACKGROUND

The diagnostic role of CMR in very acute stages of myocardial infarction is uncertain. We investigated signal intensity changes beginning within 60 min after acute coronary occlusion in patients undergoing therapeutic septal artery embolization.

METHODS

We investigated eight patients with hypertrophic obstructive cardiomyopathy undergoing interventional septal artery embolization by applying microparticles to reduce left ventricular outflow tract obstruction. In a clinical 1.5-tesla (T) CMR system, we visualized infarct-related myocardial signal by T(1)-weighted sequences before and 20 min after administration of contrast media (delayed enhancement) and edema-related signal by T(2)-weighted spin-echo sequences before and 58 +/- 14 min after the intervention as well as on days 1, 3, 7, 14, 28, 90, and 180 during follow-up.

RESULTS

Infarct-related changes as defined by contrast enhancement were observed as early as 1 h after the intervention and during six months of follow-up. In contrast, infarct-related myocardial edema, as visualized by high signal intensity in T(2)-weighted spin-echo sequences, was not consistently detectable 1 h after acute arterial occlusion; this was possible in all subsequent studies until day 28.

CONCLUSIONS

Contrast-enhanced magnetic resonance imaging detected infarct-related signal changes as early as 1 h after AMI in humans, whereas the sensitivity of edema-related signal changes was not sufficient during this very early stage.

Gadobenate dimeglumine in MRI of acute myocardial infarction: results of a phase III study comparing dynamic and delayed contrast enhanced magnetic resonance imaging with EKG, (201)Tl SPECT, and echocardiography

RATIONALE AND OBJECTIVES

To evaluate the safety and utility of gadobenate dimeglumine as a magnetic resonance (MR) contrast agent in patients with acute myocardial infarction (MI).

METHODS

One hundred three patients with acute MI received intravenous bolus gadobenate dimeglumine (0.05 mmol/kg) during MR examination. Dynamic and delayed T1-weighted spin-echo postcontrast images were compared with precontrast images, EKG, resting (201)Tl SPECT and echocardiography.

RESULTS

Gadobenate dimeglumine was well tolerated. Dynamic imaging with gadobenate dimeglumine was more sensitive (72% vs 56%) than delayed spin echo imaging (P < 0.001). No difference in specificity was seen (98% vs 99%). (201)Tl SPECT was a sensitive (96%) test, but was not specific (63%). Echocardiography was not sensitive (32%), but was specific (92%).

CONCLUSION

The intravenous use of gadobenate dimeglumine, at a bolus dose of 0.05 mmol/kg, is safe in patients with an acute MI. Dynamic contrast enhanced MR imaging has moderate sensitivity and high specificity for demonstrating infarct.

Myocardial magnetic resonance imaging contrast agent concentrations after reversible and irreversible ischemic injury

BACKGROUND

Discrepant reports have been published recently regarding the relationship of contrast-enhanced magnetic resonance image intensities to reversible and irreversible ischemic injury. Unlike image intensities, contrast agent concentrations provide data independent of the MRI technique. We used electron probe x-ray microanalysis (EPXMA) to simultaneously examine concentrations of Gd, Na, P, S, Cl, K, and Ca over a range of myocardial injuries. Methods and Results- Reversible and irreversible injury were studied in 38 rabbits divided into 4 groups defined by occlusion and reperfusion time, as well as time the animals were euthanized. Gd-DTPA was administered, and the hearts were excised and rapidly frozen, cryosectioned, freeze-dried, and examined by EPXMA in up to 3 regions: remote, infarcted, and at risk but not infarcted. Infarcted regions were defined by anti-myoglobin antibody or triphenyltetrazolium chloride staining. Regions at risk were defined by fluorescent microparticles administered during occlusion. Compared with remote regions, in acutely infarcted regions, Gd was increased (235+/-24%, P<0.005) in the same 50 x 100-microm areas in which Na was increased (154+/-5%, P<0.001) and K was decreased (52+/-8%, P<0.001). Similarly, in chronically infarcted regions, Gd was increased (472+/-78%, P<0.001) in areas in which Na was increased (332+/-28%, P<0.001) and K was decreased (47+/-5%, P<0.001). Also compared with remote regions, however, concentrations of Gd, Na, and K were not elevated after reperfusion in regions that were at risk but not infarcted (P=NS).

CONCLUSIONS

Regional elevations in myocardial MRI contrast agent concentrations are exclusively associated with irreversible ischemic injury defined histologically and by regional electrolyte concentrations.

An improved MR imaging technique for the visualization of myocardial infarction

PURPOSE

To design a segmented inversion-recovery turbo fast low-angle shot (turboFLASH) magnetic resonance (MR) imaging pulse sequence for the visualization of myocardial infarction, compare this technique with other MR imaging approaches in a canine model of ischemic injury, and evaluate its utility in patients with coronary artery disease.

MATERIALS AND METHODS

Six dogs and 18 patients were examined. In dogs, infarction was produced and images were acquired by using 10 different pulse sequences. In patients, the segmented turboFLASH technique was used to acquire contrast material-enhanced images 19 days +/- 7 (SD) after myocardial infarction.

RESULTS

Myocardial regions of increased signal intensity were observed in all animals and patients at imaging. With the postcontrast segmented turboFLASH sequence, the signal intensity of the infarcted myocardium was 1,080% +/- 214 higher than that of the normal myocardium in dogs-nearly twice that of the next best sequence tested and approximately 10-fold greater than that in previous reports. All 18 patients with myocardial infarction demonstrated high signal intensity at imaging. On average, the signal intensity of the high-signal-intensity regions in patients was 485% +/- 43 higher than that of the normal myocardium.

CONCLUSION

The segmented inversion-recovery turboFLASH sequence produced the greatest differences in regional myocardial signal intensity in animals. Application of this technique in patients with infarction substantially improved differentiation between injured and normal regions.

Magnetic resonance imaging of myocardial infarct

Magnetic resonance imaging offers the unique opportunity to directly visualize the size and location of myocardial infarcts (MIs) with excellent spatial resolution. Because infarct size is the most important determinant of postinfarct outcome, precise determination of infarct size may be valuable to risk stratify patients after acute MI. In addition, infarct imaging may provide direct information on the amount of irreversibly injured myocardium and thus can be used to identify myocardial viability in dysfunctional regions. Acute infarcts can be recognized as hyperintense signal on T2-weighted spin-echo images. This technique, however, does not identify chronic infarcts and may overestimate infarct size by including area at risk. Also, T2-weighted images often have a low signal-to-noise ratio. Contrast-enhanced perfusion imaging provides better-quality images. Extravascular contrast agents such as (Gd-DTPA) gadolinium diethyletriamine-pentaacetic acid identify infarcts as hyperenhanced regions on images acquired late after contrast injection. In addition, these tracers can examine the integrity and permeability of infarct microvasculature on first-pass perfusion images. Necrosis avid tracers and 23Na imaging are other new exciting approaches to identify infarcted myocardium acutely after MI. These techniques, are still investigational, and their value for clinical imaging remains to be established.

Contrast-enhanced magnetic resonance imaging of myocardium at risk: distinction between reversible and irreversible injury throughout infarct healing

OBJECTIVES

We sought to determine the relationship of delayed hyperenhancement by contrast magnetic resonance imaging (MRI) to viable and nonviable myocardium within the region at risk throughout infarct healing.

BACKGROUND

The relationship of delayed MRI contrast enhancement patterns to injured but viable myocardium within the ischemic bed at risk has not been established.

METHODS

We compared in vivo and ex vivo MRI contrast enhancement to histopathologic tissue sections encompassing the entire left ventricle in dogs (n = 24) subjected to infarction with (n = 12) and without (n = 12) reperfusion at 4 h, 1 day, 3 days, 10 days, 4 weeks and 8 weeks. In vivo MR imaging was performed 30 min after contrast injection.

RESULTS

The sizes and shapes of in vivo myocardial regions of elevated image intensity (828+/-132% of remote) were the same as those observed ex vivo (241 slices, r = 0.99, bias = 0.05+/-1.6% of left ventricle [LV]). Comparison of ex vivo MRI to triphenyltetrazolim chloride-stained sections demonstrated that the spatial extent of hyperenhancement was the same as the spatial extent ofinfarction at every stage of healing (510 slices, lowest r = 0.95, largest bias = 1.7+/-2.9% of LV). Conversely, hyperenhanced regions were smaller than the ischemic bed at risk defined by fluorescent microparticles at every stage of healing (239 slices, 35+/-24% of risk region, p<0.001). Image intensities of viable myocardium within the risk region were the same as those of remote, normal myocardium (102+/-9% of remote, p = NS).

CONCLUSIONS

Delayed contrast enhancement by MRI distinguishes between viable and nonviable regions within the myocardium at risk throughout infarct healing.

The role of cardiovascular magnetic resonance in heart failure

Cardiovascular Magnetic Resonance (CMR) is an accepted gold standard for non-invasive, accurate, and reproducible assessment of cardiac mass and function. The interest in its use for viability, myocardial perfusion and coronary artery imaging is also widespread and growing rapidly as the hardware and expertise becomes available in more centres, and the scans themselves become more cost effective. In patients with heart failure, accurate and reproducible serial assessment of remodelling is of prognostic importance and the lack of exposure to ionizing radiation is helpful. The concept of an integrated approach to heart failure and its complications using CMR is fast becoming a reality, and this will be tested widely in the coming few years, with the new generation of dedicated CMR scanners.

Relationship of MRI delayed contrast enhancement to irreversible injury, infarct age, and contractile function

BACKGROUND

Contrast MRI enhancement patterns in several pathophysiologies resulting from ischemic myocardial injury are controversial or have not been investigated. We compared contrast enhancement in acute infarction (AI), after severe but reversible ischemic injury (RII), and in chronic infarction.

METHODS AND RESULTS

In dogs, a large coronary artery was occluded to study AI and/or chronic infarction (n = 18), and a second coronary artery was chronically instrumented with a reversible hydraulic occluder and Doppler flowmeter to study RII (n = 8). At 3 days after surgery, cine MRI revealed reduced wall thickening in AI (5+/-6% versus 33+/-6% in normal, P<0.001). In RII, wall thickening before, during, and after inflation of the occluder for 15 minutes was 35+/-5%, 1+/-8%, and 21+/-10% and Doppler flow was 19.8+/-5.3, 0.2+/-0.5, and 56.3+/-17.7 (peak hyperemia) cm/s, respectively, confirming occlusion, transient ischemia, and reperfusion. Gd-DTPA-enhanced MR images acquired 30 minutes after contrast revealed hyperenhancement of AI (294+/-96% of normal, P<0.001) but not of RII (98+/-6% of normal, P = NS). Eight weeks later, the chronically infarcted region again hyperenhanced (253+/-54% of normal, n = 8, P<0.001). High-resolution (0.5 x 0.5 x 0.5 mm) ex vivo MRI demonstrated that the spatial extent of hyperenhancement was the same as the spatial extent of myocyte necrosis with and without reperfusion at 1 day (R = 0.99, P<0.001) and 3 days (R = 0.99, P<0.001) and collagenous scar at 8 weeks (R = 0.97, P<0.001).

CONCLUSIONS

In the pathophysiologies investigated, contrast MRI distinguishes between reversible and irreversible ischemic injury independent of wall motion and infarct age.

Gadolinium-DTPA-enhanced magnetic resonance imaging and functional outcome in patients with acute myocardial infarction

This study was designed to test the hypothesis that Gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA)-enhanced magnetic resonance images (MRI) reflect the severity of ischemic injury during the acute and chronic phases of myocardial infarction (MI). Twenty-nine patients with their first acute MI underwent Gd-DTPA-enhanced MRI in the first week (4.2+/-0.3 days) and at 1 month after onset. Pairs of left ventriculograms were compared with Gd-DTPA-enhanced magnetic resonance images, classified into 3 pattern groups: hyper-enhancement, with and without a central hypo-enhanced region (P1 and P2, respectively), and non-enhancement (P3). In the acute phase of MI, P1 was found in 10, P2 in 11, and P3 in 8 patients. One month later, the image pattern had changed from P1 to P2 in a single patient, from P2 to P3 in 4 patients, and had remained identical in the others. Patients with P3 showed improvement of anterior wall motion in the 1-month follow-up study, and had higher TIMI flow grades and lower peak creatine kinase values than those without recovery. Thus, Gd-DTPA-enhanced magnetic resonance images, closely reflecting the severity of myocardial injury, are useful in predicting myocardial functional recovery after MI.

Three-dimensional echocardiographic assessment of the extension of dysfunctional mass in patients with coronary artery disease

Two-dimensional (2D) echocardiographic estimation of infarcted mass is limited by having only a few selected nonparallel views for data analysis. Volume-rendered three-dimensional (3D) echocardiography may be able to overcome the above limitations, because it uses multiple, parallel 2D images to derive quantitative data. Previous experimental studies demonstrated that 3D echocardiography is an accurate and reproducible method to assess dysfunctional mass. To estimate the accuracy of 3D echocardiography in humans, we evaluated 10 patients who had a single myocardial infarction. All patients underwent 2D and 3D echocardiography using the transesophageal approach, and contrast (gadolinium) magnetic resonance imaging (MRI), considered a reference standard for infarcted tissue detection. The mean extent of dysfunctional mass by MRI was 28 +/- 13 g and by 3D echocardiography was 30 +/- 12 g; the mean difference was 1.9 +/- 2.3 g (p = not significant). Linear regression analysis between the 2 measurements was y = 0.97x - 1.12, r = 0.98. Dysfunctional mass derived from 3D echocardiography reflects the real site and extension of damaged myocardium.

Contrast media-enhanced magnetic resonance imaging visualizes myocardial changes in the course of viral myocarditis

BACKGROUND

The course of tissue changes in acute myocarditis in humans is not well understood. Diagnostic tools currently available are unsatisfactory. We tested the hypothesis that inflammation is reflected by signal changes in contrast-enhanced magnetic resonance imaging (MRI).

METHODS AND RESULTS

We assessed 44 consecutive patients with symptoms of acute myocarditis. Nineteen patients met the inclusion criteria revealing ECG changes, reduced myocardial function, elevated creatine kinase, positive troponin T, serological evidence for acute viral infection, exclusion of coronary heart disease, and positive antimyosin scintigraphy. We studied these patients on days 2, 7, 14, 28, and 84 after the onset of symptoms. We obtained ECG-triggered, T1-weighted images before and after application of 0.1 mmol/kg gadolinium. We measured the global relative signal enhancement of the left ventricular myocardium related to skeletal muscle and compared it with measurements in 18 volunteers. The global relative enhancement was higher in patients on days 2 (4.8+/-0.3 [mean+/-SE] versus 2.5+/-0.2; P<.0001); 7 (4.7+/-0.5, P<.0001); 14 (4.6+/-0.5, P<.0002); and 28 (3.9+/-0.4, P=.009) but not on day 84 (3.1+/-0.3; P=NS). On day 2, the enhancement was focal, whereas at later time points, the enhancement was diffuse. In patients with evidence of ongoing disease, the values remained elevated.

CONCLUSIONS

Acute myocarditis evolves from a focal to a disseminated process during the first 2 weeks after onset of symptoms. Contrast media-enhanced MRI visualizes the localization, activity, and extent of inflammation and may serve as a powerful noninvasive diagnostic tool in acute myocarditis.

First-pass evaluation of myocardial output during dipyridamole stress using turbo-FLASH magnetic resonance imaging

RATIONALE AND OBJECTIVES

This study evaluated the value of dynamically enhanced fast low-angle shot (FLASH) magnetic resonance (MR) imaging in measuring cardiac output with and without dipyridamole pharmacological stress.

METHODS

Ten subjects underwent rest and stress MR imaging. Rest images were acquired using electrocardiogram gated MR (turbo-FLASH: repetition time = 6 mseconds; echo time = 12 mseconds; flip angle = 12 degrees, inversion time = 100) 10 to 45 seconds after intravenous bolus of 0.04 mmol/kg gadolinium (Gd)-DTPA using a Siemens 1.0-tesla Magnetom SP. Stress was induced within the MR imaging scanner with 0.56 mg/kg dipyridamole over 4 minutes with stress MR images obtained after a second bolus of Gd-DTPA in exactly the same position and time intervals. Cardiac output was calculated with a least squares error analysis before and after dipyridamole stress for the left and right ventricles in all 10 patients, and comparison was made with cardiac output by Fick dilution technique during cardiac catheterization in seven patients.

RESULTS

This MR analysis methodology shows reasonable correlation (r = 0.953) between left ventricular and right ventricular cardiac output with no effect on cardiac output during immediate dipyridamole stress. Fick dilution studies demonstrated a correlation of 0.96.

CONCLUSIONS

Turbo-FLASH MR can demonstrate time-activity curves and cardiac output calculations consistent with theoretical predictions.

Magnetic resonance imaging in ischemic heart disease

The clinical use of MR imaging in ischemic heart disease is still limited, although this is the major cardiac disease afflicting populations of many countries. However, with the recent development of faster MR techniques, MR imaging provides multiple capabilities for the evaluation of most aspects of ischemic heart disease. We described the potential application of MR imaging for identifying and quantifying morphologic and functional alterations caused by myocardial infarction and ischemia; the contribution of MR contrast media to improve tissue characterization and to identify ischemic myocardium; and the application of fast MR imaging techniques for assessing anatomy and blood flow in the native coronary arteries and bypass conduits. With continued development of these capabilities, MR imaging has the potential to be a comprehensive noninvasive imaging modality in ischemic heart disease.

Assessment of acute myocardial infarction in man with magnetic resonance imaging and the use of a new paramagnetic contrast agent gadolinium-BOPTA

To assess the feasibility of and characterize the new paramagnetic contrast agent gadolinium-BOPTA/dimeglumine (Gd-BOPTA) to detect acute myocardial infarctions with MR imaging, 24 patients (53.3 +/- 8.3 yr) were examined 9.3 +/- 3.6 days after a first myocardial infarction. Short-axis T1-weighted and T2-weighted MR imaging was performed at three slice levels. T1-weighted images were obtained before, immediately after, 15, 30, and 45 min after injection. Patients received either 0.05 or 0.1 mmol/kg body weight Gd-BOPTA. Images were qualitatively and quantitatively analyzed. Two patients showed no signs of infarction on T2-weighted images as opposed to contrast-enhanced T1-weighted images. Contrast-to-noise ratio was not affected by the dosage level. Signal intensity (SI) of normal to infarcted myocardium was significantly improved by both dosages (p < .0005) but a dosage of 0.05 mmol/kg produced significantly higher SI inf/norm (1.42 +/- 0.07 vs. 1.34 +/- 0.06, respectively, p = .015). SI of normal and infarcted myocardium enhanced immediately after administration of 0.05 mmol/kg (29.3 +/- 5.1% and 53.8 +/- 9.6% respectively), which decreased thereafter to 5.3 +/- 4.8% and 40.2 +/- 8.5% respectively, at 45 min (p < .002 for normal myocardium). SI enhancement immediately after 0.1 mmol/kg Gd-BOPTA showed no decrease within the first 45 min. Gd-BOPTA enables the detection of myocardial infarction. Optimal infarct delineation is achieved from 15 to 45 min after administration of 0.05 mmol/kg body weight Gd-BOPTA. Gd-BOPTA at 0.05 mmol/kg does improve image quality as measured by contrast-to-noise ratio and SI enhancement as compared to 0.10 mmol/kg.

Reperfused myocardial infarctions on T1- and susceptibility-enhanced MRI: evidence for loss of compartmentalization of contrast media

The purpose of this study was to characterize the contrast caused by a susceptibility MRI contrast agents, on spin echo T2-weighted imaging of reperfused myocardial infarction. Our interest in this model focused on the expected requirement that such agents be compartmentalized in the tissue to cause signal loss on spin echo images, a condition which may not be present in reperfused infarcted myocardium. Accordingly, nine rats were subjected to 2 h of left coronary artery occlusion followed by 3 +/- 0.5 h of reperfusion prior to administration of contrast media. Three sets of MR images were acquired: (a) baseline axial images at the midventricle, both T1-weighted (TR/TE = 300/20) and T2-weighted (TR/TE = 1500/60); (b) T1-weighted images after administering a T1-enhancing agent, Gd-DTPA-BMA (0.2 mmol/kg), to document that contrast media is delivered to the reperfused infarction; and (c) T2-weighted images after administering the susceptibility agent, Dy-DTPA-BMA (1.0 mmol/kg). Gadolinium-enhanced T1 images depicted reperfused infarction as regions with greatly enhanced signal intensity compared with uninfarcted myocardium, indicating that contrast agent was delivered to the infarcted zone. Dysprosium-enhanced T2 images depicted the injury as a region of persistent signal intensity relative to depletion of signal in normal myocardium, consistent with failure of the contrast agent to cause signal loss. Similar infarction sizes were observed for unenhanced T2-weighted images (33 +/- 5%), gadolinium-enhanced T1-weighted images (36 +/- 5%) and postmortem staining (30 +/- 6%); strong correlations (r > 0.9) were noted in comparisons of these data.(ABSTRACT TRUNCATED AT 250 WORDS)

Magnetic resonance imaging of heterotaxia in infants

OBJECTIVES

This study assessed the usefulness and safety of magnetic resonance imaging (MRI) for systematically diagnosing heterotaxia in infants.

BACKGROUND

Although it is important to diagnose and treat infants with heterotaxia, which is associated with viscerobronchial cardiovascular anomalies, systematic diagnosis of these anomalies by a single imaging technique is difficult.

METHODS

Twenty patients with heterotaxia were evaluated. The infants ranged in age from 21 days to 12 months (average 5.2 months, average body weight 4.3 kg). Electrocardiographically gated MRI was performed by spin echo imaging techniques operating at 0.5 tesla.

RESULTS

In all 20 patients, MRI results were sufficient to evaluate these anomalies without serious complications. In 17 patients, neither a spleen nor splenules were detected, but in 3 patients, a polymorphous spleen was visualized. In all 20 patients, bronchial anatomies were clearly visualized (bilateral eparterial bronchi in 14 patients, bilateral hyparterial bronchi in 2 and normal bronchial patterns in 4). Additionally, in a comparison of 149 observations of cardiovascular anatomy by MRI with those by angiography, discrepancies were found in only 10 observations (6.7%).

CONCLUSIONS

Magnetic resonance imaging was found to be safe and very useful for the systematic diagnosis of heterotaxia in infants.

Contrast induced myocardial signal reduction: effect of lanthanide chelates on ultra high speed MR images

The myocardial MR signal reduction associated with an intravenous bolus of Gd-DTPA and Dy-DTPA was studied in a canine model. Imaging was performed with a high speed echo-planar type imaging system (Instascan, Advanced NMR Systems, Inc.). Gated spin-echo images were obtained with TE of 30 ms, which permits image acquisition in approximately 40 ms. The gated TR was dependent on the heart rate, with an average TR of 2.4 s. After 0.1 mmol/kg of contrast was injected, 70 images were acquired, which showed in an 80-image data set a reduction in myocardial signal with a gradual return to normal. After dipyridamole infusion, the signal loss was significantly more pronounced, and earlier than in the control data set. There was no significant difference between Gd-DTPA and Dy-DTPA in these imaging studies despite the theoretical prediction of better Dy signal reduction, possibly due to physiological variability during the course of a study or between studies. The cause of enhanced contrast effect after dipyridamole infusion is discussed, as is the basis for dipyridamole enhancement, and the possible role of contrast enhanced MR imaging in the detection of cardiac disease.

Precise assessment of myocardial damage associated with secondary cardiomyopathies by use of Gd-DTPA-enhanced magnetic resonance imaging

To evaluate the myocardial damage in patients with secondary cardiomyopathies, the authors examined gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA)-enhanced magnetic resonance imaging (MRI) in 5 patients (2 with cardiac amyloidosis, 2 with acute myocarditis, 1 with cardiac thyrotoxicosis). MR images were performed at 1.5-T by using a spin echo pulse sequence before and after intravenous administration of Gd-DTPA (0.2 mmol/kg). All patients revealed distinct high-intensity areas on postcontrast images. Moreover, MRI with Gd-DTPA could determine the severity and precise regions of myocardial damage associated with secondary cardiomyopathies. It is suggested that gated cardiac MRI with Gd-DTPA enhancement is useful for detecting the myocardial damage in secondary cardiomyopathies.

Quantification of occlusive and reperfused myocardial infarct size with Gd-DTPA-enhanced MR imaging

The potential of Gd-DTPA-enhanced magnetic resonance imaging (MRI) for measuring infarct size was assessed in canine hearts. Twelve dogs underwent pre- and post-contrast MR imaging before and after recanalization. Infarct area was identified by triphenyltetrazolium chloride (TTC) staining of postmortal specimens in each case. Recanalization was complete in 10 dogs. High SI area was seen after reperfusion in nine of them; and it showed low signal intensity before reperfusion in seven of them. Two dogs were killed during reperfusion period: neither of them showed a low SI area before reperfusion. Necrotic regions were confirmed by TTC staining in seven of 12 dogs. Both the visual and quantitative assessment (n = 7) indicated that the extent of the low SI area before reperfusion was approximately the same as that of the necrotic region shown by TTC staining, while the high SI area seen after reperfusion was obviously larger than both the necrotic region and the low SI area on pre-reperfusion images. The correlation coefficient between low SI area and necrotic area was 0.98, and between high SI area and necrotic area was 0.80. These results suggest that Gd-DTPA-enhanced MRI may be useful for quantification of infarct size in occlusive myocardial infarction but it may overestimate in reperfused one.