MR-Signalverhalten des 4 Wochen alten okklusiven Myokardinfarktes im Tierexperiment

Zusammenfassung.

Ziel: Untersuchung des 4 Wochen alten okklusiven Myokardinfarktes in T₁- und T₂-gewichteten Aufnahmen nach Gd-DTPA im Vergleich zur Histologie. Material und Methoden: Bei 7 Schafen wurde nach Thorakotomie ein Ramus diagonalis ligiert und ein anterolateraler Infarkt induziert. Nach 4 Wochen erfolgte 15 min vor Entnahme des Herzens in 5 Tieren eine Injektion von 0,1 mmol Gd-DTPA/kg. Die in vitro MR-Bildgebung bei 1,5 T umfaßte T₁- und T₂-gewichtete Spin-Echo Aufnahmen. Regionale Myokarddicke und Signalintensität (SI) wurde in jeweils 36 Segmenten pro Kurzachsenschicht gemessen und mit der Histologie verglichen. Ergebnisse: Histologisch fand sich jeweils ein anterolateraler Infarkt, welcher mit der hyperintensen Region im T₁-Bild (195 von insgesamt 1296 Segmenten) nach Gd-DTPA übereinstimmte. Mit 122 Segmenten war die Ausdehnung von Gewebsanteilen mit erhöhter T₂-SI im Infarkt geringer. In diesen Regionen lag histologisch kapillarreiches Granulationsgewebe vor, während eine Erhöhung der T₁-SI nach Gd-Injektion ohne signifikante T₂-SI Erhöhung in bereits fibrotisch organisiertem Infarkt gefunden wurde. Insgesamt bestand bei erhöhter SI eine Abnahme der Wanddicke (3,8 ± 1,2 mm) gegenüber Regionen mit normaler SI (9,8 ± 1,1 mm, p < 0,001). Schlußfolgerung: Anhand von T₂- und T₁-Aufnahmen nach Gd-DTPA kann im Infarkt zwischen Granulations- und Bindegewebe differenziert werden.

MR Signal Behaviour of Four-Week-Old Occlusive Myocardial Infarctions in Sheep.

Purpose: To correlate signal behaviour in T₁- and T₂-weighted images after Gd-DTPA with regional histopathology in occlusive myocardial infarction (MI). Methods: Ligation of a diagonal branch of the LAD was performed in seven sheep. Four weeks later 0.1 mmol Gd-DTPA/kg were injected in five sheep 15 min before cardiac arrest and the sheep were slaughtered. In vitro imaging was performed at 1.5 T included T₁- and T₂-weighted spin echo sequences in long and short axis views. Signal intensities (SI) were determined in 36 myocardial segments per slice and compared to macro- and microscopy. Results: In all animals an antero-lateral infarct region was evident histologically. This region presented with increased T₂ SI and T₁ SI after Gd-DTPA. The number of segments with increased SI in T₁-weighted images was higher (n = 195 segments) compared to segments with increased T₂ SI (n = 122 segments). Granulation tissue could be differentiated from rarely vascularized connective tissue at a high level of significance (p < 0.001) by T₁ and T₂ SI analysis. Wall thickness was significantly decreased in necrotic myocardium (3.8 ± 1.2 mm) compared to normal tissue (9.8 ± 1.1 mm, p < 0.001). Conclusion: In four-week-old occlusive MI the extent of necrosis can be accurately assessed by analysis of post contrast T₁-weighted images. Considering regional T₂ SI, granulation tissue can be differentiated from regions with predominant fibrous organisation.

Schlüsselwörter:

MR Tomographie - Myokardinfarkt - Gadolinium-DTPA

Key words:

Magnetic Resonance Imaging - Myocardium, Infarction - Gadolinium-DTPA

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