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Myocardial Infarct: Depiction with Contrast-enhanced MR Imaging—Comparison of Gadopentetate and Gadobenate¹

¹ From the Departments of Diagnostic and Interventional Radiology (T.S., P.H., C.U.H., H.L., S.M., J.B.) and Cardiology (A.L.), University Hospital Essen, Hufelandstrasse 55, 45122 Essen, Germany. Received February 5, 2004; revision requested April 13; final revision received October 3; accepted October 22. Address correspondence to J.B. (e-mail: joerg.barkhausen{at}uni-essen.de).

	ABSTRACT

TOP ABSTRACT INTRODUCTION Materials and Methods Results Discussion References

 
Institutional review board approval and patient written informed consent were obtained. On two separate occasions, 24 hours apart, contrast-enhanced cardiac magnetic resonance (MR) imaging was performed prospectively at 1, 3, 5, 10, and 20 minutes after injection of gadopentetate dimeglumine and gadobenate dimeglumine in 15 patients (11 men, four women) with history of myocardial infarction. Both agents allowed detection of infarcted myocardium. T1 values at all times were significantly (P < .05) lower for gadobenate, compared with values for gadopentetate, in both infarcted and noninfarcted myocardium. At 1 minute after administration of both agents, T1 values in left ventricular cavity (LVC) were not different; at 3–20 minutes after injection, values were significantly (P < .05) lower for gadobenate. Differences between contrast-to-noise ratio (CNR) values of infarcted and noninfarcted myocardium were significantly higher on gadobenate-enhanced images (P < .05). CNR values between infarcted myocardium and LVC were significantly higher on gadopentetate-enhanced images (P < .05). Gadopentetate might permit better delineation of infarcts, especially subendocardial infarcts.

© RSNA, 2005

	INTRODUCTION

TOP ABSTRACT INTRODUCTION Materials and Methods Results Discussion References

 
The accurate assessment of extent and degree of myocardial injury is crucial in patients with acute or chronic myocardial infarction for individual risk stratification and therapy design (1–3). The differentiation of viable from nonviable myocardium aids in the prediction of the success of revascularization, as determined with recovery of regional function, and allows the prognosis of overall survival (4–6).

Magnetic resonance (MR) imaging permits proper evaluation of regional myocardial viability. After injection of gadolinium-based extracellular contrast agents, MR imaging allows one to distinguish between reversible myocardial dysfunction and scar tissue, independent of wall motion and infarct age (7,8). Because of the loss of membrane integrity in necrotic myocardium and the increased interstitial space in scars, extracellular gadolinium-based compounds accumulate in these tissues, whereas they are rapidly washed out of normal myocardium. Therefore, 5–20 minutes after contrast agent injection, marked enhancement can be detected in damaged myocardium, compared with the enhancement in viable myocardium, because of prolonged deposition of gadolinium-based contrast agent. The contrast between damaged and viable myocardium is maximized by using inversion-recovery gradient-echo sequences, with adjusted inversion times to null the signal intensity (SI) of viable myocardium (9).

Much effort has been spent in finding the optimum dose of contrast material, the optimum time for data acquisition after injection, and the optimum inversion times (10,11). The effect of different contrast agents on accumulation in infarcted myocardium, however, has not been assessed yet, to our knowledge.

Compared with gadopentetate dimeglumine, which has been used predominantly in animal and clinical studies for the assessment of myocardial viability (12–15), gadobenate dimeglumine has a weak reversible binding to albumin. This binding results in a considerable increase in the relaxation rate, compared with that of gadopentetate, at a magnetic field strength of 2 T (16). Separate injections of gadopentetate and gadobenate in an animal model for myocardial infarction resulted in significantly greater differences between T1 values of infarcted myocardium and T1 values of noninfarcted myocardium for the latter agent. Hence, gadobenate might be advantageous for late-enhancement imaging in humans (17). The aim of this study, therefore, was to prospectively compare gadopentetate with gadobenate for the assessment of myocardial viability in patients with a history of myocardial infarction.

	Materials and Methods

TOP ABSTRACT INTRODUCTION Materials and Methods Results Discussion References

 
Patients
The study protocol was performed in accordance with the regulations of the institutional review board, which approved our study, and written informed consent was obtained from all patients prior to enrollment.

Fifteen patients (11 men, four women; mean age, 62.6 years ± 11.2 [standard deviation]; range, 49–83 years) with angiographically proved coronary artery disease and a history of myocardial infarction (>3 months old) were examined from June to July of 2003. Ages of the men ranged from 49 to 83 years, with a mean age of 61.3 years ± 12.1, and those of the women ranged from 52 to 79 years, with a mean age of 64.0 years ± 11.1. Only patients with a sinus rhythm were included in the study. Patients with a pacemaker, metal implants, vascular clips in the thorax, arrhythmia, and claustrophobia were excluded from the study.

MR Imaging Protocol
MR imaging was performed with a 1.5-T system (Magnetom Sonata; Siemens, Erlangen, Germany) equipped with a high-performance gradient system, characterized with an amplitude of 40 mT/m, a rise time of 200 µsec, and a slew rate of 200 mT/m/msec, and a phased-array surface coil. All examinations were performed on two separate occasions by using either a dose of 0.2 mmol per kilogram body weight of gadopentetate dimeglumine (Magnevist; Schering, Berlin, Germany) or an equal dose of gadobenate dimeglumine (MultiHance; Bracco, Milan, Italy) in random order. The time between both examinations was at least 24 hours (mean, 26.7 hours ± 1.2).

After the acquisition of cine MR images with the segmented steady-state free precession sequence (repetition time msec/echo time msec, 3.0/1.5; flip angle, 60°) to assess myocardial function, injection of contrast material was performed with an automatic injector (MR Spectris; Medrad, Pittsburgh, Pa) at an injection rate of 2 mL/sec; all injections were followed by a 20-mL saline flush with the same injection rate. T1 values of the noninfarcted myocardium, the infarcted myocardium, and the left ventricular cavity (LVC) were estimated on the basis of the images acquired with steady-state free precession sequence with incrementally increased inversion times (TI Scout; Siemens Medical Solutions, Forchheim, Germany) during a single breath hold (18) (2.4/1.0; flip angle, 50°; inversion time, increased in steps of 20 msec). This sequence for optimization of the inversion time and calculation of T1 values was performed 1, 3, 5, 10, and 20 minutes after contrast material injection. T1 values were obtained by using the following equation: T1 = TI_(min)/ln2, where TI_(min) is the inversion time of the image with the minimum SI of the tissue.

At 15 minutes after the injection of the contrast agent, late-enhancement MR imaging was performed by using an electrocardiographically triggered segmented inversion-recovery gradient-echo sequence (8/4.3; flip angle, 25°). The inversion time for all measurements was individually set to minimize the signal of the noninfarcted myocardium, and both contrast agents were compared with regard to the inversion time. All MR imaging examinations were feasible and were performed without complications or technical failure. No side effects were noted in any of the 15 subjects.

MR Image Analysis
Contrast-to-noise ratio (CNR) values were assessed with measurement of the SI of the inversion-recovery gradient-echo images in manually drawn regions of interest (minimum size, 10 pixels; maximum size, 50 pixels). The regions of interest were placed by two authors (T.S. and P.H.) in consensus; both had 4 years of experience with cardiac MR imaging. The regions of interest were placed in the noninfarcted myocardium of the left ventricle (area depending on the location of the infarction zone), the infarcted myocardium, the LVC, and outside the body (air in the field of view, anterior to the chest wall). Noise was defined as the standard deviation of the mean SI outside the body. CNR values were calculated with the following equations: CNR_inf-noninf = (SI_inf – SI_noninf)/N and CNR_inf-LVC = (SI_inf – SI_LVC)/N, where CNR_inf-noninf is the CNR between infarcted myocardium and noninfarcted myocardium, SI_inf is the SI in infarcted myocardium, SI_noninf is the SI in noninfarcted myocardium, N is noise, CNR_inf-LVC is the CNR between infarcted myocardium and the LVC, and SI_LVC is the SI in the LVC.

Moreover, by using freehandedly drawn regions, the size of the infarction zone was measured (T.S., P.H., J.B., in consensus) on the gadopentetate- and gadobenate-enhanced MR images and was expressed as the percentage of the entire left ventricular myocardium.

Statistical Analysis
For both contrast agents, the T1 values of the noninfarcted myocardium, the infarcted myocardium, and the LVC, as well as the SI, the CNR, and the size of the infarction zone, were expressed as the mean ± standard deviation by using a descriptive statistics tool (SPSS 10.0.7, June 2000; SPSS, Chicago, Ill). Furthermore, the significance of differences between group mean values was determined by using the Wilcoxon signed rank test, and differences were deemed to be significant with P < .05 (19).

	Results

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There were no statistically significant differences between the age distributions according to sex (P > .05). Analysis of T1 values at 1, 3, 5, 10, and 20 minutes after contrast material injection showed that values were significantly lower in the infarcted myocardium and noninfarcted myocardium for gadobenate-enhanced images compared with values for gadopentetate-enhanced images. These data are displayed in box plots (Figs 1, 2) (20). In the LVC, the T1 values were not significantly different between the two agents after 1 minute; however, after 3, 5, 10, and 20 minutes, T1 values were significantly lower for gadobenate (Fig 3).

View larger version (16K): [in this window] [in a new window] [Download PPT slide]   Figure 1. Box plots show T1 values in milliseconds in the infarcted myocardium after administration of gadopentetate (Gd-DTPA) and gadobenate (Gd-BOPTA) at different times over 20 minutes. The horizontal line is the median, the center point marks the mean value, the ends of the box are the upper and lower quartiles, and the upper and lower points of each vertical line mark the full range of values in the data. Results of analysis of T1 values at 1, 3, 5, 10, and 20 minutes after contrast agent injection showed significantly (*) lower values in the infarcted myocardium for gadobenate data sets, compared with those for gadopentetate data sets.

View larger version (19K): [in this window] [in a new window] [Download PPT slide]   Figure 2. Box plots show T1 values in milliseconds in the noninfarcted myocardium after administration of gadopentetate (Gd-DTPA) and gadobenate (Gd-BOPTA) at different times over 20 minutes. Results of analysis of T1 values at 1, 3, 5, 10, and 20 minutes after contrast agent injection showed significantly lower values for gadobenate data sets in the noninfarcted myocardium, compared with those for gadopentetate data sets. Explanatory information is the same as that for Figure 1.

View larger version (17K): [in this window] [in a new window] [Download PPT slide]   Figure 3. Box plots show mean T1 values in the LVC after administration of gadopentetate (Gd-DTPA) and gadobenate (Gd-BOPTA) at different times over 20 minutes. In the LVC, results of analysis of T1 values showed that they were not significantly different for both agents after 1 minute; however, after 3, 5, 10, and 20 minutes, T1 values were significantly lower for gadobenate than they were for gadopentetate. Explanatory information is the same as that for Figure 1.

View larger version (153K): [in this window] [in a new window] [Download PPT slide]   Figure 4a. Transmural anterior chronic myocardial infarction in 59-year-old man. (a, b) Electrocardiographically triggered segmented inversion-recovery gradient-echo MR images (8/4.3; flip angle, 25°) obtained in two-chamber view. (a) Gadobenate-enhanced image. At 15 minutes after contrast agent injection, SI values in the infarcted myocardium (arrow) and the LVC (*) were significantly higher than they were for gadopentetate. (b) Gadopentetate-enhanced image.

View larger version (136K): [in this window] [in a new window] [Download PPT slide]   Figure 4b. Transmural anterior chronic myocardial infarction in 59-year-old man. (a, b) Electrocardiographically triggered segmented inversion-recovery gradient-echo MR images (8/4.3; flip angle, 25°) obtained in two-chamber view. (a) Gadobenate-enhanced image. At 15 minutes after contrast agent injection, SI values in the infarcted myocardium (arrow) and the LVC (*) were significantly higher than they were for gadopentetate. (b) Gadopentetate-enhanced image.

View larger version (158K): [in this window] [in a new window] [Download PPT slide]   Figure 5a. Transmural myocardial infarction in inferoapical segment (arrow in b) in 64-year-old man. (a, b) Electrocardiographically triggered segmented inversion-recovery gradient-echo MR images (8/4.3; flip angle, 25°) obtained in two-chamber view. (a) Gadobenate-enhanced image. Values for CNR between infarcted myocardium and noninfarcted myocardium were significantly higher than they were for gadopentetate. (b) Gadopentetate-enhanced image. Lower SI in the LVC and increased values for CNR between infarcted myocardium and the LVC resulted in better delineation of myocardial infarction.

View larger version (153K): [in this window] [in a new window] [Download PPT slide]   Figure 5b. Transmural myocardial infarction in inferoapical segment (arrow in b) in 64-year-old man. (a, b) Electrocardiographically triggered segmented inversion-recovery gradient-echo MR images (8/4.3; flip angle, 25°) obtained in two-chamber view. (a) Gadobenate-enhanced image. Values for CNR between infarcted myocardium and noninfarcted myocardium were significantly higher than they were for gadopentetate. (b) Gadopentetate-enhanced image. Lower SI in the LVC and increased values for CNR between infarcted myocardium and the LVC resulted in better delineation of myocardial infarction.

View larger version (149K): [in this window] [in a new window] [Download PPT slide]   Figure 6a. Subendocardial infarction of anterior, anteroseptal, inferoseptal, and inferior wall in 65-year-old man. (a, b) Electrocardiographically triggered segmented inversion-recovery gradient-echo MR images (8/4.3; flip angle, 25°) obtained in short-axis view. (a) Gadopentetate-enhanced image obtained at 15 minutes after injection of contrast agent. Infarction (arrows) is clearly visible. (b) Gadobenate-enhanced image obtained at same time as a shows that the subendocardial infarction is masked by the prolonged enhancement of the LVC.

View larger version (143K): [in this window] [in a new window] [Download PPT slide]   Figure 6b. Subendocardial infarction of anterior, anteroseptal, inferoseptal, and inferior wall in 65-year-old man. (a, b) Electrocardiographically triggered segmented inversion-recovery gradient-echo MR images (8/4.3; flip angle, 25°) obtained in short-axis view. (a) Gadopentetate-enhanced image obtained at 15 minutes after injection of contrast agent. Infarction (arrows) is clearly visible. (b) Gadobenate-enhanced image obtained at same time as a shows that the subendocardial infarction is masked by the prolonged enhancement of the LVC.

	Discussion

TOP ABSTRACT INTRODUCTION Materials and Methods Results Discussion References

 
In the present study, we compared two extracellular contrast agents, gadopentetate and gadobenate, for the assessment of chronic myocardial infarction by using MR imaging in conjunction with the late-enhancement technique. This study resulted in three findings we believe to be important: (a) T1 values of the infarcted myocardium, the noninfarcted myocardium, and the LVC were significantly lower for gadobenate compared with those for gadopentetate. (b) With gadobenate, there was a prolonged reduction of the T1 values, compared with those with gadopentetate. (c) At 15 minutes after injection, the values for CNR between infarcted myocardium and noninfarcted myocardium were significantly higher on the gadobenate-enhanced images, compared with those on the gadopentetate-enhanced images, whereas the value for CNR between infarcted myocardium and the LVC was significantly higher on gadopentetate-enhanced images.

Contrast-enhanced MR imaging for the detection and characterization of infarcted myocardium has been a field with active research for nearly 20 years (21,22). Most recent developments in MR imaging hardware and software have dramatically improved image quality; consequently, the technique is now ready for clinical use. In this context, Kim et al (7) demonstrated that gadolinium-based contrast-enhanced MR imaging allows safe distinction between reversible and irreversible ischemic injury, independent of myocardial wall motion irregularities and infarct age. Recently, Hunold et al (23) demonstrated that results with contrast-enhanced MR imaging and with positron emission tomography (PET) show close agreement for the detection of transmural myocardial scars. Because of inherently superior spatial resolution, however, MR imaging permitted the detection and quantification of subendocardial scars that were missed by using PET examinations.

Most of the studies with contrast-enhanced MR imaging for the detection of myocardial injury were performed with gadopentetate. Within the past decade, however, additional MR imaging contrast agents have been approved for use at imaging for different indications in the clinical routine (24–27). Among others, gadobenate is an extracellular gadolinium chelate with a concentration of 0.5 mol/L, which was initially developed for liver imaging due to partial biliary excretion (28). In contrast to gadopentetate, gadobenate has a higher relaxivity and a weak reversible binding to albumin, which result in prolonged enhancement of blood (16). Therefore, gadobenate holds promise for use with MR angiography and was successfully assessed for this purpose in several studies (29–31). With regard to cardiac MR imaging indications, Wendland et al (17) demonstrated, in an animal model for myocardial infarction, that gadobenate, compared with gadopentetate, appears to be better suited for detection of acute myocardial infarction, because of a greater decrease in T1 values and, thus, an improved delineation of infarcted tissue.

Several research groups investigated the optimal time point for late-enhancement imaging. Oshinski et al (10) demonstrated that, in acute myocardial infarction, the area of late enhancement at 21 minutes after administration of gadopentetate, at best, matched the true infarct size defined by using triphenyltetrazolium chloride staining. In acute myocardial infarction, however, early image acquisition after contrast material injection is recommended by Sandstede et al (11) to detect midwall hypoenhancement indicative of microvascular obstruction. In chronic myocardial infarction, the correct selection of the inversion time seems to be more critical than the delay after contrast material injection for the measurement of the infarct size (9,32,33).

In our study, late-enhancement imaging was performed 15 minutes after the injection of the contrast agent, a protocol that is commonly used in the clinical routine at our hospital. At this time, gadobenate demonstrated significantly higher SI values in the infarcted myocardium and the LVC. The SI values in the noninfarcted myocardium were not significantly different for either contrast agent because of the precise determination of nulling of the signal by using a scout sequence for determining optimal inversion times (18).

Values for CNR between infarcted myocardium and noninfarcted myocardium were significantly higher on the gadobenate-enhanced images compared with those calculated for gadopentetate-enhanced images. In principle, higher CNR_inf-noninf values may result in improved differentiation between infarcted and noninfarcted myocardium and, therefore, in improved detection of particularly small myocardial infarctions. A potential drawback in the assessment of myocardial infarction with gadobenate, however, is a rather low CNR value of the infarcted area to the LVC (–10.9 ± 17.9 for gadobenate vs 5.2 ± 8.5 for gadopentetate), caused by prolonged enhancement of blood in the LVC from reversible albumin binding of the compound. Thus, the delineation, particularly of small subendocardial infarctions from the LVC, might be restricted.

To overcome this limitation, the late-enhancement measurements with gadobenate may well be performed later than 15 minutes after contrast material injection, when the agent has cleared the blood pool and still is detectable in the infarcted myocardium. This results in a prolonged duration of the examination, however, and must be considered an important limitation in the clinical routine.

Clearly, the data provided in this study need to be interpreted critically. First and foremost, only a small group of patients with chronic myocardial infarction were examined. Despite the ability to perform intraindividual comparisons within the present study, the data need to be validated with larger patient cohorts and also in patients with acute myocardial infarction. Furthermore, inclusion of consecutive patients would have reflected the clinical routine and, thus, might have elucidated further differences between the contrast agents. Future work will focus on a comparison of extracellular agents with different blood pool contrast agents, such as MS-325 or SH L 643A, which hold promise for MR angiography of coronary arteries (34,35). Use of these agents might allow a comprehensive cardiac MR imaging examination that combines arterial morphology and late-enhancement imaging.

In conclusion, at 15 minutes after contrast agent injection, a comparison of the CNR values of the infarcted myocardium with those of the normal myocardium showed that the CNR values were significantly higher on the gadobenate-enhanced images than they were on the gadopentetate-enhanced images; however, myocardial infarcts were better delineated on the gadopentetate-enhanced images than they were on the gadobenate-enhanced images because of improved contrast between the infarcted myocardium and the LVC. To distinguish between the infarcted tissue and the LVC, late-enhancement studies with gadobenate might benefit from a longer delay after contrast agent injection. To improve work flow in cardiac MR imaging, however, a contrast agent that clears more rapidly appears advantageous.

	FOOTNOTES

 

Abbreviations: CNR = contrast-to-noise ratio • LVC = left ventricular cavity • SI = signal intensity

Authors stated no financial relationship to disclose

Author contributions: Guarantors of integrity of entire study, T.S., J.B.; study concepts, T.S., P.H., C.U.H., H.L.; study design, T.S., A.L., S.M., J.B.; literature research, T.S., P.H., J.B.; clinical studies, T.S., S.M., P.H.; data acquisition, T.S., S.M., H.L., P.H., A.L.; data analysis/interpretation, T.S., P.H., J.B., H.L., C.U.H.; statistical analysis, T.S., J.B., C.U.H.; manuscript preparation, T.S., P.H., J.B., C.U.H.; manuscript definition of intellectual content, revision/review, and final version approval, all authors; manuscript editing, T.S., H.L., S.M., J.B., P.H.

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This Article Abstract Figures Only Full Text (PDF) All Versions of this Article: 2363040220v1 236/3/1041    most recent Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Schlosser, T. Articles by Barkhausen, J. Search for Related Content PubMed PubMed Citation Articles by Schlosser, T. Articles by Barkhausen, J.