Acute myocardial infarction: comparison of T2-weighted and T1-weighted gadolinium-DTPA enhanced MR imaging

The salvaged area at risk in reperfused acute myocardial infarction as visualized by cardiovascular magnetic resonance

OBJECTIVES

We aimed to characterize the tissue changes within the perfusion bed of infarct-related vessels in patients with acutely reperfused myocardial infarction (MI) using cardiovascular magnetic resonance (CMR).

BACKGROUND

Even in successful early revascularization, intermittent coronary artery occlusion affects the entire perfusion bed, also referred to as the area at risk. The extent of the salvaged area at risk contains prognostic information and may serve as a therapeutic target. Cardiovascular magnetic resonance can visualize the area at risk; yet, clinical data have been lacking.

METHODS

We studied 92 patients with acute MI and successful reperfusion 3 +/- 3 days after the event and 18 healthy control subjects. Breath-hold T2-weighted and contrast-enhanced ("late enhancement") CMR were used to visualize the reversible and the irreversible myocardial injury, respectively.

RESULTS

All reperfused infarcts consistently revealed a pattern with both reversibly and irreversibly injured tissue. In contrast to the infarcted area, reversible damage was always transmural, exceeding the infarct in its maximal extent by 16 +/- 11% (absolute difference of the area of maximal infarct expansion 38 +/- 15% vs. 22 +/- 10%; p < 0.0001). None of the controls had significant T2 signal intensity abnormalities.

CONCLUSIONS

In patients with reperfused MI, CMR visualizes both reversible and irreversible injury. This allows for quantifying the extent of the salvaged area after revascularization as an important parameter for clinical decision-making and research.

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.

Three-dimensional magnetic resonance imaging technique for myocardial-delayed hyperenhancement: a comparison with the two-dimensional technique

PURPOSE

To compare two-dimensional and three-dimensional techniques in the detection of myocardial infarction (MI) and in the grading transmural extent (TE).

MATERIALS AND METHODS

Twelve patients with clinically proven MI were examined using two-dimensional and three-dimensional techniques with cardiac-gated, breath-hold, T1-weighted gradient echo sequence with an inversion recovery pulse following gadopentetate dimeglumine (Gd-DTPA) at 0.2 mmol/kg. Contrast-to-noise, signal-to-noise, and signal intensity ratios (CNR, SNR, and SIR, respectively) were derived and compared for each technique.

RESULTS

From two-dimensional to three-dimensional, statistical significant difference was found in the mean CNR (11.65 vs. 56.59; P = 0.002), SNR (18.03 vs. 76.90; P < 0.001), and SIR (3.6 vs. 6.36; P = 0.05). Intraobserver agreement (kappa) between two-dimensional and three-dimensional were R1 = 74% and R2 = 90%. Interobserver agreements between the readers were two-dimensional = 77% and three-dimensional = 79%.

CONCLUSION

Mean CNR, SNR, and SIR are significantly increased in the three-dimensional technique compared to the conventional two-dimensional technique.

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.

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.

Assessment of myocardial infarction in humans with (23)Na MR imaging: comparison with cine MR imaging and delayed contrast enhancement

PURPOSE

To demonstrate the feasibility of sodium 23 ((23)Na) magnetic resonance (MR) imaging for assessment of subacute and chronic myocardial infarction and compare with cine, late enhancement, and T2-weighted imaging.

MATERIALS AND METHODS

Thirty patients underwent MR imaging 8 days +/- 4 (subacute, n = 15) or more than 6 months (chronic, n = 15) after myocardial infarction by using a (23)Na surface coil with a double angulated electrocardiogram-triggered three-dimensional gradient-echo sequence at 1.5 T. In addition, cine, inversion-recovery gradient-echo, and, in the subacute group, T2-weighted images (n = 9) were obtained. Myocardial infarction mass was depicted as elevated signal intensity or wall motion abnormalities and expressed as a percentage of total left ventricular mass for all modalities. Correlations were tested with correlation coefficients.

RESULTS

All patients after subacute infarction and 12 of 15 patients with chronic infarction had an area of elevated (23)Na signal intensity that significantly correlated with wall motion abnormalities (subacute; r = 0.96, P <.001, and chronic; r = 0.9, P <.001); three patients had no wall motion abnormalities or elevated (23)Na signal intensity. Only 10 patients in the subacute and nine in the chronic group revealed late enhancement; significant correlation with (23)Na MR imaging occurred only in subacute group (r = 0.68, P <.05). Myocardial edema in subacute infarction correlated (r = 0.71, P <.05) with areas of elevated (23)Na signal intensity but was extensively larger.

CONCLUSION

(23)Na MR imaging demonstrates dysfunctional myocardium caused by subacute and chronic myocardial infarction.

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.

[Acute myocardial infarct studied by magnetic resonance with gadolinium-DTPA contrast compared to echocardiography]

INTRODUCTION AND OBJECTIVES

Gadolinium-DTPA used as a contrast agent in magnetic resonance imaging allows the detection and quantification of the necrotic area in acute myocardial infarction. The aim of the present study is to assess the value of this method for the diagnosis of myocardial infarction in comparison with clinical and echocardiographic data.

METHODS

Contrast magnetic resonance imaging and echocardiographic studies were performed on 16 patients during the first week after admission for acute myocardial infarction. Necrotic and total myocardial mass were calculated from magnetic resonance images and this was compared to the extension of the myocardial infarction assessed by electrocardiography and the peak level of total creatinine-phosphokinase serum enzyme. The number and localization of myocardial segments showing contrast uptake was related to segments with contractile abnormalities at the echocardiographic exam.

RESULTS

The mean value of the mass of myocardial necrosis calculated from the total area of gadolinium-DTPA uptake in each patient was 25 g (range: 2-67 g), corresponding to 17% of the total myocardial mass (range: 1-45%). This value correlated with the peak serum level of total creatinine-phosphokinase enzyme (r = 0.714; p < 0.003) and with the number of Q waves present at the electrocardiogram (r = 0.69; p < 0.005). A very good agreement between the location of the myocardial infarction by ECG, echocardiography and magnetic resonance was evidenced, and a satisfactory correlation existed between myocardial segments with gadolinium-DTPA uptake and akinetic echocardiographic segments (kappa = 0.65).

CONCLUSIONS

The detection and quantitation of the necrotic area in the acute myocardial infarction with gadolinium-DTPA contrast magnetic resonance shows a good correlation with clinical and echocardiographic data.

Subendocardial enhancement in gadolinium-diethylene-triamine-pentaacetic acid-enhanced magnetic resonance imaging in aortic stenosis

We investigated the usefulness of magnetic resonance imaging (MRI) with gadolinium-diethylene-triamine-pentaacetic acid (Gd-DTPA) in assessing myocardial damage from valvular aortic stenosis (AS). Cardiac catheterization and echocardiography were performed in 17 patients with AS. T1-weighted spin-echo sequence was used to obtain magnetic resonance images of short-axis planes of the left ventricle before and after intravenous Gd-DTPA injection in all patients using a 1.5 Tesla imager. Patients were divided into 2 groups according to the presence or absence of regional myocardial enhancement in the images. The Gd-DTPA-enhanced magnetic resonance images of 7 patients showed circumferential subendocardial enhancement. All patients with enhancement had a history of heart failure and were in New York Heart Association functional class III or IV, whereas patients without enhancement were in New York Heart Association functional class I or II. Patients with enhancement had a smaller aortic valve area (0.28 +/- 0.09 vs 0.38 +/- 0.07 cm2/m2, p <0.05), a higher transvalvular pressure gradient (109 +/- 40 vs 68 +/- 18 mm Hg, p <0.05), greater elevation of left ventricular end-diastolic pressure (22 +/- 11 vs 12 +/- 2 mm Hg, p <0.05), and greater reduction in left ventricular ejection fraction (40 +/- 9 vs 59 +/- 10%, p <0.05). Subendocardial enhancement by Gd-DTPA-enhanced MRI was thus shown to be closely related to the severity of AS. In conclusion, Gd-DTPA-enhanced MRI is a new noninvasive tool that can provide useful information about myocardial damage in AS.

Noninvasive measurements of infarct size after thrombolysis with a necrosis-avid MRI contrast agent

BACKGROUND

Gadophrin-2 is a new MRI contrast agent with high affinity for necrotic myocardium. The aim of the study was to evaluate whether noninvasive measurements of infarct size after thrombolysis are possible with gadophrin-2-enhanced MRI.

METHODS AND RESULTS

Coronary artery thrombosis was induced in 3 groups of dogs by the copper-coil technique. Thrombolytic therapy together with aspirin and heparin was initiated after 90 minutes of occlusion. One day (group A), 2 days (group B), or 6 days (group C) after infarction, gadophrin-2 was injected intravenously (50 micromol. kg-1). In vivo T1-weighted segmented turbo-FLASH, in vivo T2-weighted segmented half-Fourier turbo spin echo (HASTE), and T1- and T2-weighted spin-echo MRI of the excised heart were performed 24 hours after gadophrin-2 injection. Regions of strong enhancement were observed on T1-weighted images. Planimetry of short-axis MR images and of corresponding triphenyltetrazolium chloride (TTC)-stained left ventricular (LV) slices showed a close correlation between the enhanced areas and TTC-negative areas for both in vivo (r2=0.98, P<0.0001; mean difference, 0.9+/-2.0% [SD] of the LV volume [LVV]) and postmortem (r2=0.99, P<0.0001; mean difference, 0.9+/-1.4% of LVV) measurements. T2-weighted images overestimated the infarct size by 8.1+/-5.4% of LVV. The mean infarct size was 10.8+/-11.6% of LVV (group A), 22.4+/-11.7% (group B), and 5.1+/-9.3% (group C).

CONCLUSIONS

In this animal model, in vivo gadophrin-2-enhanced MRI could precisely determine infarct size after thrombolytic therapy. This technique may be very useful for the noninvasive evaluation of infarct size after reperfusion for AMI.

The contributory role of interstitial water in Gd-DTPA-enhanced MRI in myocardial infarction

We studied the mechanism underlying regional enhancement of myocardial infarction using T1-weighted MRI with gadolinium (Gd)-DTPA. Anterior myocardial infarction (MI) was produced by left anterior descending coronary artery ligation in three groups of rats as follows: 60 minutes occlusion (occlusion group, N = 6), 60 minutes occlusion plus 120 minutes reperfusion (reperfusion group, N = 8), and sham-operated (control, N = 6). In Gd-DTPA-enhanced MRI, MI was demarcated as a hypoenhanced region in the occlusion group and as a homogeneous hyperenhanced region in the reperfusion group. Both Gd-DTPA tissue concentration and tissue water content in the anterior wall were highest in the reperfusion group (P<0.05), a finding suggestive of microscopically observed interstitial edema. The data suggest that regional accumulation of Gd-DTPA in the reperfused group can be explained by increased interstitial water content, contributing to the delayed washout of the water-soluble contrast medium.

Measurement of perfusion rate in human melanoma xenografts by contrast-enhanced magnetic resonance imaging

Reliable methods based on MRI for measurement of the perfusion rate in human tumors are highly warranted. Tumors of two amelanotic human melanoma xenograft lines were subjected to dynamic 1H MRI after i.v. administration of gadopentetate dimeglumine (Gd-DTPA). The aim was to investigate to what extent different perfusion parameters determined from the Gd-DTPA kinetics, i.e., the initial uptake rate, the maximal uptake, the decay rate, and the perfusion rate calculated by use of the Kety equation, can be used as a reliable estimate of tumor perfusion rate. Each parameter was calculated in dual; one calculation was based on relative signal intensity increase (RSII) in T1-weighted MR images and the other on Gd-DTPA concentration determined from the images. The perfusion parameters were compared with the perfusion rates determined from measurement of tumor uptake of 86Rb or [14C]iodoantipyrine. The results showed that reliable estimates of tumor perfusion rate can be achieved from analysis of Gd-DTPA kinetics by use of the Kety equation. Gd-DTPA kinetics based on concentration might be used to achieve reliable estimates of absolute tumor perfusion rate, whereas reliable estimates of the relative perfusion rate might also be achieved from Gd-DTPA kinetics based on RSII. The initial uptake rate, the maximal uptake, and the decay rate of Gd-DTPA, however, are not reliable estimates of tumor perfusion rate, mainly because these parameters are highly influenced by the tumor extracellular volume fraction in addition to the perfusion rate.

Contrast enhanced and functional magnetic resonance imaging for the detection of viable myocardium after infarction

PURPOSE

Viable myocardium after acute myocardial infarction may be characterized by magnetic resonance imaging (MRI) either by demonstration of recovery of wall motion under dobutamine stress or by perfusion patterns after contrast medium administration. This study examines the relation between the two techniques.

MATERIALS AND METHODS

Gradient-echo MRI at rest and under low-dose dobutamine stress was performed in 28 patients within the first 2 weeks after acute myocardial infarction. In addition, spin-echo MRI was performed after gadolinium-DOTA administration. Wall motion at rest and under stress was scored to assess the contractile reserve of the infarct regions. Infarct enhancement patterns were classified as subendocardial, transmural, or as a doughnut pattern.

RESULT

Subendocardial or absent infarct enhancement was related to functional recovery under stress in 31 of 37 infarct segments. Transmural infarct enhancement was correlated with the absence of functional recovery in 10 of 17 infarct segments (p < 0.002), indicating nonviability. The doughnut pattern was exclusively associated with the absence of viability (five of five).

CONCLUSION

Contrast enhancement patterns are related to residual myocardial viability.

Localization and determination of infarct size by Gd-Mesoporphyrin enhanced MRI in dogs

BACKGROUND

Accurate localization and sizing of a myocardial infarction are necessary for clinical decision making and even more in research. Gd-Mesoporphyrin enhanced magnetic resonance imaging (MRI) was recently shown to specifically delineate necrosis in liver tumors, renal and muscle necrosis and myocardial infarction in rats. In this study, we investigated this technique's potential to accurately delineate myocardial infarction in a larger animal species, the dog.

METHODS

Myocardial infarction was induced in 8 dogs by ligation of the left anterior descending coronary artery, 4 of which were reperfused after 3 hr Gd-Mesoporphyrin (0.05 mmol/kg) was injected intravenously 210 min after the onset of ischemia (n = 6) or after 24 hr in 2 dogs with non-reperfused infarctions. MRI was performed 10 hr after administration of Gd-Mesoporphyrin. In vivo MRI consisted of EKG-triggered, respiratory gated T1-weighted spin echo and segmented turboFLASH long and short axis measurements. Post-mortem, a spin echo short axis measurement was repeated. Infarct size was determined planimetrically by TTC staining of left ventricular slices.

RESULTS

In all instances, there was a very close qualitative agreement between the MRI and TTC defined myocardial infarction. Quantitatively, the linear regression from post-mortem MRI to TTC determined infarct size yielded a result very close to the line of identity (regression coefficient: 0.980 +/- 0.026, p < 0.000001, adjusted R2 = 0.964).

CONCLUSION

We conclude that Gd-Mesoporphyrin enhanced MRI is a promising tool for the accurate delineation of myocardial infarction.

Myocardial Gd-DTPA kinetics determine MRI contrast enhancement and reflect the extent and severity of myocardial injury after acute reperfused infarction

BACKGROUND

Contrast medium-enhanced magnetic resonance images of acute, reperfused infarcts have shown hypoenhanced and hyperenhanced regions in areas of injured myocardium. The precise mechanisms that lead to these altered enhancement patterns are unknown. This study was designed to evaluate possible mechanisms and to relate altered enhancement patterns to myocardial perfusion and viability.

METHODS AND RESULTS

Thirteen rabbits underwent in situ coronary artery occlusion and reperfusion followed by isolated perfusion with cardioplegic solution. T1-weighted spin-echo images were acquired continuously during step changes in perfusate Gd-DTPA concentration. Regional blood flow was also measured by use of radioactive microspheres in all rabbits. There were marked differences in Gd-DTPA wash-in and washout time constants (wash-in, 0.8 +/- 0.1, 2.1 +/- 02, and 16.3 +/- 2.4 minutes, P < .001; washout, 1.6 +/- 0.1, 4.8 +/- 0.5, and 31.1 +/- 3.3 minutes, P < .001) in normal, infarct rim, and infarct core regions, respectively, resulting in differential enhancement of these regions. Microsphere flows in the infarct rim and core were 42.9 +/- 4.0% and 12.0 +/- 1.6% of normal myocardium and correlated well with washout time constants (r = .86, y = 0.77x - 0.002, P < .001), suggesting that these time constants index the severity of microvascular damage. In addition, spatial maps of washout time constants were produced. The extent of regions with abnormal time constants correlated well with triphenyltetrazolium chloride-determined infarct size (r = .94, y = 0.95x + 4.17, P < .001).

CONCLUSIONS

In contrast-enhanced magnetic resonance images of acute, reperfused rabbit infarcts, differential image intensity is primarily due to regional differences in contrast agent wash-in and washout time constants. These regional differences in time constants also indicate the extent and severity of myocardial injury.

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.

Magnetic resonance techniques for assessment of myocardial viability

In general, the following three standards for myocardial viability can be used: (a) preserved coronary flow (adequate perfusion); (b) preserved wall motion (systolic wall thickening); and (c) preserved metabolism (metabolic integrity). The current magnetic resonance (MR) techniques provide a great potential to measure all three standards of viability. Adequate perfusion can be assessed by spin-echo MR imaging and/or ultrafast MR imaging, systolic wall thickening by cine MR imaging, and the presence of metabolic integrity can be determined by MR spectroscopy. These noninvasive and versatile techniques have led to an increasing interest and research in recent years. Particular strengths of the MR techniques are: the inherent three-dimensional data acquisition without radiation exposure; the intrinsic soft-tissue contrast that allows tissue characterization; the excellent spatial resolution (in the 1- to 2-mm range), which permits the evaluation of regional abnormalities; multitomographic imaging capabilities that allow acquisition of cardiac images in any plane; the inherent sensitivity to blood and wall motion; and the potential for in vivo measurement of myocardial metabolism using MR spectroscopy. This review article demonstrates that MR techniques might play a growing role in the assessment of myocardial viability.

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.

Magnetic resonance imaging in coronary artery disease

The cardiovascular applications of nuclear magnetic resonance (MR) techniques in coronary artery disease have increased considerably in recent years. Technical advantages of MR imaging in comparison with other techniques are the excellent spatial resolution, the characterization of myocardial tissue, and the potential for three-dimensional imaging. This allows the accurate assessment of left ventricular mass and volume, the differentiation of infarcted tissue from normal myocardial tissue, and the determination of systolic wall thickening and regional wall motion abnormalities. Myocardial perfusion, metabolism, and inducible myocardial ischemia with the use of pharmacological stress also can be assessed by MR techniques. Future technical improvements in real-time imaging and development of noninvasive visualization of the coronary arteries and coronary artery bypasses will constitute a tremendous progress in clinical cardiology. Early detection and flow assessment of stenosed coronary arteries by MR angiography with the use of flow velocity measurements may outweigh the cost inherent to the MR imaging procedure. A particular strength of the MR technique is the potential to encompass cardiac anatomy, perfusion, function, metabolism, and coronary angiography in a single test. The replacement of multiple diagnostic tests with one MR test may have major effects on cardiovascular healthcare economics.

Magnetic resonance imaging and spectroscopy of the human heart

Magnetic resonance imaging and spectroscopy have a great potential both for clinical cardiac diagnostics and for research in cardiac physiology, metabolism and disease. At the present time, cardiac MRI already is the method of choice in several clinical conditions, especially in imaging central vasculature and intra- and paracardiac masses. With the recent development of contrast agents and ability to measure both flow velocities and flow volume, the cardiac MRI is likely to have a profound role in evaluating coronary arterial disease as well as valvular heart disease. The limitations due to long imaging times of cardiac MRI-studies are likely to be overcome with the development of ultrafast imaging techniques in the near future. On the other hand, cardiac MRS is still a research tool, which needs technical improvements before it can be widely utilized in clinical work. However, attempts to this aim are highly justified, when the possibility that MRS will provide metabolic information of the heart is considered and bearing in mind, that MR-magnets with sufficient field strength for MRS are increasingly in use in most modern hospitals. The role of magnetic resonance imaging (MRI) and spectroscopy (MRS) in the evaluation of heart diseases is still evolving. Some clear indications for clinical use of cardiac MRI have already become apparent, whereas cardiac MRS is still confined to research applications. The current paper consists of a review of the role of MRI for cardiovascular diagnosis together with a review of the currents status of cardiac MRS.

Phosphonate-modified Gd-DTPA complexes. III: The detection of myocardial infarction by MRI

The potential of a phosphonate-modified-Gd-DTPA for MR image enhancement of myocardial infarction has been demonstrated in imaging experiments on rats. The agent, 1-hydroxy-3-aminopropane-1,1-diphosphonate-modified-Gd-DTPA (Gd-DTPA-HPDP) accumulates in two models of myocardial infarction, (i.e., drug-induced diffusely infarcted whole hearts and in focal acute myocardial infarction from a left coronary artery ligation). The time course of the accumulation of the agent in the focal model of infarction and subsequent washout has also been followed in vitro. Results of this kinetics demonstrate that the agent first perfuses all normal fluid spaces and then slowly diffuses into the occluded zone where it is retained for a prolonged period, in sufficient quantities to be useful as an MRI contrast agent. Wash-out of the agent from normal myocardium is fast and complete with MR signal returning to background in minutes. The specificity of Gd-DTPA-HPDP for soft-tissue calcification and its retention within the infarcts permitted imaging at 1 to 2 h postinjection, (after unbound material has cleared the normal tissues). Infarcted tissue appeared as regions of increased signal intensity in T1-weighted images (> 200% enhancement), and correlated with histopathology. Unmodified Gd-DTPA was not retained under identical conditions. Gd-DTPA-HPDP permits a more accurate infarct delineation than is possible with the unmodified agent.

Sequential analysis of infarcted and normal myocardium in piglets using in vivo gadolinium-enhanced MR images

Gadolinium-enhanced magnetic resonance (MR) imaging was performed before, and 1 and 3 wk after coronary occlusion in domestic piglets. After administration of the contrast agent gadopentetate dimeglumine, two different enhancement patterns within the infarcted region were observed. The first pattern, showing peripheral enhancement of the infarcted region with absence of contrast in the center, was seen at 1 wk after occlusion at 5 min after administration of the contrast agent. The second pattern showed signal enhancement of the center of the infarcted region and was observed at 1 wk after occlusion, 30 min following contrast administration, and at 3 wk after occlusion, both 5 and 30 min following contrast administration. Infarct size and left ventricular (LV) mass by MR imaging, measured 3 wk after infarction, corresponded well with pathologic assessment. LV mass, measured by static and dynamic MR imaging, increased during the period of investigation. It is concluded that gadolinium-enhanced MR imaging clearly identifies infarcted myocardium early and late after coronary occlusion in the piglet. Combined results of infarct size and LV mass can be obtained simultaneously during one imaging procedure.

Magnetic resonance imaging of myocardial infarction: correlation with enzymatic, angiographic, and radionuclide findings

Spin-echo cardiac magnetic resonance imaging studies were performed in 20 patients with a first 7- to 14-day-old (mean 10) myocardial infarction. The magnetic resonance imaging findings were compared with coronary angiography (14 patients), myocardial enzyme release (18 patients), radionuclide angiography (19 patients), and thallium-201 perfusion scintigraphy (19 patients). Regional T2 relaxation times determined from the signal intensities at echo times 30 msec and 90 msec were significantly prolonged in the infarcted areas. Based on abnormal T2 times for every patient, a regional and a total myocardial damage score was determined. The infarct-related artery was correctly identified in 93% of patients by magnetic resonance imaging, in 79% of patients by thallium-201 scintigraphy, and in 62% of patients by radionuclide angiography. The total damage score correlated well with enzymatic infarct size (r = 0.75, p less than 0.001). The correlation between left ventricular end-systolic volume index determined by magnetic resonance imaging and by radionuclide angiography was r = 0.89 (p less than 0.002). The left ventricular end-systolic volume index correlated significantly with enzymatic infarct size (r = 0.72, p less than 0.001), total damage score (r = 0.68, p less than 0.002), and radionuclide left ventricular ejection fraction (r = -0.68, p less than 0.002). Correlations between the magnetic resonance damage score and the thallium-201 perfusion score were r = 0.60 (p less than 0.01) for the exercise images, and r = 0.72 (p less than 0.001) for the redistribution images. This study shows that spin-echo magnetic resonance imaging is quite comparable with the established noninvasive imaging modalities currently used in patients with acute myocardial infarction.