Improved detection of acute myocardial infarction by magnetic resonance imaging using gadolinium-DTPA

Assessment of cardiac function, blood flow and myocardial tissue relaxation parameters at 0.35 T

A low field strength (B0) system could increase cardiac MRI availability for patients otherwise contraindicated at higher field. Lower equipment costs could also broaden cardiac MR accessibility. The current study investigated the feasibility of cardiac function with steady-state free precession and flow assessment with phase contrast (PC) cine images at 0.35 T, and evaluated differences in myocardial relaxation times using quantitative T1, T2 and T2* maps by comparison with 1.5 and 3 T results in a small cohort of six healthy volunteers. Signal-to-noise ratio (SNR) differences across systems were characterized with proton density-weighted spin echo phantom data. SNR at 0.35 T was lower by factors of 5.5 and 15.0 compared with the 1.5 and 3 T systems used in this study. All cine images at 0.35 T scored 3 or greater on a five-point image quality scale. Normalized blood-myocardium contrast in cine images, left ventricular volumes (end diastolic volume, end systolic volume) and function (ejection fraction and stroke volume) measures at 0.35 T matched 1.5 and 3 T results. Phase-to-noise ratio in 0.35 T PC images (11.7 ± 1.9) was lower than 1.5 T (18.7 ± 5.2) and 3 T (44.9 ± 16.5). Peak velocity and stroke volume determined from PC images were similar across systems. Myocardial T1 increased (564 ± 13 ms at 0.35 T, 955 ± 19 ms at 1.5 T and 1200 ± 35 ms at 3 T) while T2 (59 ± 4 ms at 0.35 T, 49 ± 3 ms at 1.5 T and 40 ± 2 ms at 3 T) and T2* (42 ± 8 ms at 0.35 T, 33 ± 6 ms at 1.5 T and 24 ± 3 ms at 3 T) decreased with increasing B0. Despite SNR deficits, cardiovascular function, flow assessment and myocardial relaxation parameter mapping is feasible at 0.35 T using standard cardiovascular imaging sequences.

Cardiac MR imaging: state of the technology

Recent developments in magnetic resonance (MR) imaging of the heart have refocused attention on the potential of MR and continue to attract intense interest within the radiology and cardiology communities. Improvements in speed, image quality, reliability, and range of applications have evolved to the point where cardiac MR imaging is increasingly seen as a practical clinical tool. As is often the case with MR imaging, not all of the most powerful techniques are necessarily easy to master or understand, and many-nonspecialists and specialists alike-are challenged to stay abreast. This review covers some of the major milestones that have led to the current state of cardiac MR and attempts to put into context some concepts that, although technical, have a real impact on the diagnostic power of cardiac MR imaging. Topics discussed include functional imaging, myocardial viability and perfusion imaging, flow quantification, and coronary artery imaging. A review such as this can only scratch the surface of what is a dynamic interdisciplinary field, but the hope is that sufficient information and insight are provided to stimulate the motivated reader to take his or her interest to the next level.

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.

Magnetic resonance imaging in coronary heart disease

Modern level of cardiac magnetic resonance imaging (MRI) development already allows its routine use (with proper indications) in coronary heart disease patients for studies of heart morphology and functions, performance of stress tests for evaluation of myocardial perfusion and contractile function. Coronary MRA and some other new MR techniques are close to its wide-scale clinical application. It has been shown that cardiac MRI is a valuable tool for detection of postinfarction scars, aneurysms, pseudoaneurysms, septal defects, mural thrombi and valvular regurgitations. Due to intrinsic advantages of the method it is of special value when these pathological conditions cannot be fully confirmed or excluded with echocardiography. MRI is recognized as the best imaging method for quantification of myocardial thickness, myocardial mass, systolic myocardial thickening, chamber volumes, ejection fraction and other parameters of global and regional systolic and diastolic function. MRI is used in studies of cardiac remodeling in postinfarction patients. The most attractive areas for cardiovascular applications of MRI are assessment of myocardial perfusion and non-invasive coronary angiography. Substantial progress has been achieved in these directions. There are some other new developments in studies of coronary artery disease with MRI. High-resolution MR is used for imaging and quantification of atherosclerotic plaque composition in vivo. Intravascular MR devices suitable for performing imaging-guided balloon angioplasty are created. But before MRI will be widely accepted by the medical community as a important cardiovascular imaging modality several important problems have to be solved. Further technical advances are necessary for clinical implementation of all major diagnostic capabilities of cardiac MRI. The subjective obstacles for growth of clinical applications of cardiac MRI are lack of understanding of its possibilities and benefits both by clinicians and radiologists themselves. So proper training of specialists and promotion of this promising modality among the medical community are necessary.

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.

Comparison of T1 estimation techniques in cardiac MRI

We have shown that the use of a simple combination of inversion recovery/spin-echo (IR/SE) sequences provides undeniably superior precision in quantitative in vivo myocardium T1 estimation than the standard multiple spin-echo approach. On a group of 25 healthy subjects, the T1 dispersion was, respectively, 3.8% for the IR/SE combination and 19.6% for the best SE pair combination. Moreover, repeated measurements were carried out on seven of the volunteers in order to assess T1 reproducibility. The mean intra-individual T1 precision was found to be 2.8% for the IR/SE pair and 20.0% for the best SE pair. The in vivo imaging work was supported and corroborated by a thorough treatment of the theoretical T1 errors. We also highlight the importance of quality control in quantitative MRI; a correction being required in the SE sequences to bring measured signal intensities into line with those predicted from simple theory.

Synchronized inversion recovery-spin echo sequences for precise in vivo T1 measurement of human myocardium: a pilot study on 22 healthy subjects

An ECG-triggered, two-sequence MRI technique is proposed for the precise measurement of proton T1 relaxation times of the human myocardium at a field strength of 0.5 T. The combination of an inversion recovery (IR) sequence and a spin echo (SE) sequence is not new. It is, however, rarely used in quantitative in vivo cardiac studies. Our approach employs a synchronization of the 90 degrees read pulse to the systolic period. In a study of 22 healthy volunteers, the globally measured T1 value was estimated to be 714 +/- 23 ms. Four of the volunteers also underwent additional imaging scans for the purposes of reproducibility assessment. The T1 precision was found to be 3.9 +/- 1.1% for the IR/SE combination and 16.9 +/- 5.3% for a combination of SE sequences. Total imaging time for the IR and SE sequences was 19.2 +/- 3.0 mins. The relative rapidity of this classic technique and the T1 precision obtained give this technique an obvious application in the discrimination of normal and diseased myocardium. In the same study, valuable supplementary tissue characterization is provided by T2, calculated from the SE sequence. T2 was evaluated to be 50 +/- 3 ms.

Myocardial infarct sizing and assessment of reperfusion by magnetic resonance imaging: a review

Early thrombolytic therapy restores patency of thrombotic coronary artery occlusion in many patients. Intravenous streptokinase appears to be effective in achieving recanalization of the occluded infarct-related artery, thereby reducing myocardial infarct size. However, it may be difficult to assess non-invasively the relative value of different reperfusion therapies. MR imaging with or without the use of contrast agents may become a reliable non-invasive technique to assess infarct size after reperfusion therapy. There are indications that early MR imaging after administration of Gd-DTPA is able to differentiate reperfused from non-reperfused infarcts. Furthermore, MR infarct sizing using Gd-DTPA can demonstrate infarct size reduction in patients with successful reperfusion. The availability of ultrafast imaging methods and MR contrast agents may allow assessment of myocardial perfusion in the near future. This article reviews the current status of MR imaging for evaluating ischemic myocardial disease.

Gadolinium-enhanced magnetic resonance imaging in acute myocardial infarction

To evaluate the usefulness of the paramagnetic contrast agent Gadolinium-DTPA (diethylenetriaminepentaacetic acid) in Magnetic Resonance Imaging of acute myocardial infarction, we studied a total of 45 patients with a first acute myocardial infarction by ECG-gated magnetic resonance imaging before and after intravenous administration of 0.1 mmol/kg Gadolinium-DTPA. All patients received thrombolytic treatment by intravenous streptokinase. The magnetic resonance imaging studies were performed after a mean of 88 h (range 15-241) after the acute onset of acute myocardial infarction. Five patients without evidence of cardiac disease served as controls. Spin-echo measurements (TE 30 ms) were made using a Philips Gyroscan (0.5 Tesla) or a Teslacon II (0.6 Tesla). The 45 patients were divided into four groups of patients. In Group I (5 patients) Gadolinium-DTPA improved the detection of myocardial infarction by Gadolinium-DTPA. In Group II (20 patients) the magnetic resonance imaging procedure was repeated every 10 min for up to 40 min following administration of Gadolinium-DTPA. Optimal contrast enhancement was obtained 20-25 min after Gadolinium-DTPA. In Group III (27 patients) signal intensities were significantly higher in the patients who underwent the magnetic resonance imaging study more than 72 h (mean 120) after the acute event, suggesting increased accumulation of Gadolinium-DTPA in a more advanced stage of the infarction process. In Group IV (45 patients) Gadolinium-DTPA was administered in an attempt to distinguish between reperfused and nonreperfused myocardial areas after thrombolytic treatment for acute myocardial infarction.(ABSTRACT TRUNCATED AT 250 WORDS)