Rationale and Objectives
The purpose was to verify whether myocardial viability can be detected by a delayed enhancement magnetic resonance imaging (MRI) approach using a rapid three-dimensional inversion-recovery fast low-angle shot (3D IR-FLASH) sequence in a preclinical and clinical setting.
Materials and Methods
Nonreperfused myocardial infarctions were induced in eight minipigs. Both the pigs and 15 patients with suspected myocardial infarction underwent MRI using a rapid 3D IR-FLASH sequence and a two-dimensional IR-FLASH sequence as the reference standard.
Results
In the pigs, a total of 52 segments with myocardial infarction were identified with both sequences and there was good agreement in transmurality of 99.5%. The infarction volume determined with the 3D IR-FLASH in the animal study (2.4 ± 1.5 cm 3 ) showed a good correlation with the histomorphometrically determined volume using triphenyltetrazolium chloride (2.3 ± 1.2 cm 3 , r = 0.98, P < .001) and the two-dimensional IR-FLASH sequence (2.3 ± 1.4 cm 3 , r = 0.99, P < .001). Eleven of 15 patients were found to have myocardial infarction in 37 myocardial segments with both sequences and there was a good agreement in transmurality of 98.8%. There was also a good correlation in the clinical study between the 3D and 2D sequences (6.9 ± 6.7 cm 3 vs. 6.8 ± 6.5 cm 3 , r = 0.98, P < .001). In Bland-Altman analysis there was no significant under- or overestimation of the myocardial infarction volume using the 3D IR-FLASH sequence in comparison to the two-dimensional reference standard in both the preclinical and clinical study. The contrast-to-noise ratios were not significantly different between 3D and 2D sequences in the animal (34.7 ± 1.5 vs. 33.8 ± 2.6; P = .51) and clinical study (31.4 ± 12.5 vs. 36.7 ± 11.5; P = .31). The breathhold time for the 3D IR-FLASH sequence in the clinical study (20.4 ± 2.2 s) was significantly shorter than that of the 2D IR-FLASH sequence (190.1 ± 20.8 s, P < .001).
Conclusions
The rapid 3D IR-FLASH sequence detects myocardial infarction with high accuracy and allows a relevant reduction in acquisition time.
The demonstration of myocardial viability is important for the diagnosis, therapeutic decision, and evaluation of the outcome of medical and surgical treatment. In the last few years, magnetic resonance imaging (MRI) has become more important in analyzing left ventricular myocardial viability ( ). An accurate assessment of the transmurality of myocardial infarction is only possible with the high spatial resolution of delayed-enhancement MRI ( ). The transmurality of myocardial infarction is crucial for the prognosis and the reconstitution of contractile function of the left ventricle ( ). The reference standard for delayed-enhancement MRI is a two-dimensional (2D) inversion-recovery fast low-angle shot sequence (IR-FLASH) ( ). The main drawback of this technique is the long acquisition time of 10–14 heartbeats for one single slice ( ). As a consequence, 10–16 breathholds each lasting at least 10 heartbeats are necessary to cover the entire left ventricle on short-axis orientation using this 2D approach. Therefore the purpose of our study to evaluate the correlation and accuracy of a rapid three-dimensional (3D) IR-FLASH sequence in comparison to the reference standard sequence (2D IR-FLASH) for noninvasive assessment of myocardial viability in pigs (with histopathologic correlation) and patients.
Materials and methods
Experimental Study and Instrumentation
In eight minipigs (weighing 22.6 ± 3.1 kg), anesthesia was induced using 15 mg/kg ketamine hydrochloride IM (Ketamine 500 mg, Curamed Pharma GmbH, Karlsruhe, Germany), 0.2 mg/kg droperidol IM (Dehydrobenzperidol, Janssen-Cilag GmbH, Neuss, Germany), and 0.2 mg/kg midazolam hydrochloride IM (Dormicum, Hoffmann-La Roche AG, Grenzach-Whylen, Germany) followed by 5–7 mg/kg/h propofol IV (Disoprivan 1%, AstraZeneca, Wedel, Germany) and maintained by ventilation for the entire instrumentation period (approximately 60 min) with 2–5% isoflurane (Forene, Abbott GmbH, Wiesbaden, Germany). Nonreperfused myocardial infarction was induced with a closed-chest model ( ): with a multipurpose catheter (Multipurpose, 6F, XBR 2, Vistabrite Tip, 80 cm, Miami, FL) tungsten spirals with a length of 4–6 cm (Spirale n detachable en tungstene, Balt Extrusion, Montmorency, France) were flushed with saline into the left circumflex coronary artery to induce nonreperfused myocardial infarction. Immediately after MRI, the animals were euthanized under deep anesthesia with intravenous injection of 5 mL of a commercially available mixture of tetracaine hydrochloride (5 mg/mL), mebezonium iodide (50 mg/mL), and embutramide (200 mg/mL) (T61; Intervet Deutschland, Unterschleissheim, Germany). Subsequently, the hearts were removed and stiffened by repetitive immersion in 95% ethanol precooled to −80°C and sliced from base to apex into 5-mm thick sections. These sections were incubated in 2% triphenyltetrazolium chloride (TTC) for 20 minutes at 37°C to define the infarcted areas (= regions that failed to stain brick-red). These slices were scanned with a flat bed scanner. An observer measured infarction sizes (in cm 3 ) in the TTC-stained slices. The care and treatment of animals was according to legal requirements and all experiments performed were approved by the responsible state authority.
Clinical Study
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MRI Protocol
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Data Analysis
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Statistical Analysis
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Results
Experimental Study
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Table 1
Comparison of Contrast-to-Noise Ratios using the Two Sequences
Contrast-to-Noise Ratios 2D IR-FLASH 3D IR-FLASH_P_ Experimental study 33.8 ± 2.6 34.7 ± 1.5 .51 Clinical study 36.7 ± 11.5 31.4 ± 12.5 .31
2D: two-dimensional; 3D: three-dimensional; IR-FLASH: inversion-recovery fast low-angle shot.
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Clinical Study
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Discussion
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