島津 敬¹, 松本 正幸¹, 西岡 浩嗣¹, 藤原 誠¹, 松山 泰三¹, 前田 孝男¹, 浜中 康彦¹, 北畠 顕¹, 志村 孚城¹, 三輪 博秀¹, 井上 通敏¹, 鎌田 武信¹

Takashi SHIMAZU¹, Masayuki MATSUMOTO¹, Hirotsugu NISHIOKA¹, Makoto FUJIWARA¹, Taizo MATSUYAMA¹, Takao MAEDA¹, Yasuhiko HAMANAKA¹, Akira KITABATAKE¹, Takaki SHIMURA¹, Hirohide MIWA¹, Michitoshi INOUE¹, Takenobu KAMADA¹

¹大阪大学医学部第一内科, ²金沢医科大学老人病科, ³富士通研究所

¹The First Department of Medicine, Osaka University Medical School, ²The Department of Geriatrics, Kanazawa Medical College, ³Fujitsu Laboratory Ltd.

キーワード : Ultrasonic tissue characterization, Myocardial infarction, Gray level analysis, Hydroxyproline

　To determine the feasibility and limitation of gray level analysis of 2-D echocardiograms in detecting myocardial infarction, sequential changes in gray levels of B-mode images of normal and infarcted canine myocardium were studied in vitro. Myocardial infarction was produced by ligating left anterior descending coronary artery in 21 mongrel dogs. These dogs were subsequently reanesthetized and killed on postoperative days 3(n=6), 7(n=5), 14(n=6) and 28(n=4), and we excised the infarcted myocardium from per fusion area of the ligated artery. Normal myocardium was also excised from the opposite side of left ventricle. We obtained the B-mode images of the specimen in the sample bath filled with physiological saline using 3 different transducers with center frequencies of 2.25, 3.5 and 5.0 MHz. Gray levels of the myocardial images were measured using a lightmeter. Changes in histological findings and hydroxyproline content were also determined. At 3 days after ligation, gray levels of infarcted myocardium showed no significant difference compared with the normal with all ultrasounds used. One week after, however, significant increases in gray level in infarcted myocardium were shown with 3.5 and 5.0 MHz ultrasounds (3.5 MHz: 5.38±1.39 vs 8.83±1.93 cd/m², p2, p2, p=ns). Gray levels in infarcted myocardium were significantly larger than in normal 2 and 4 weeks after coronary ligation with all three ultrasounds. Tissue contents of hydroxyproline increased significantly 2 weeks after ligation, although they showed no significant increases on third day and 7th day. In conclusion, although connective tissue is one of major determinants for echogenecity of infarcted myocardium, high frequency ultrasound such as 3.5 or 5.0 MHz of center frequency is useful for detecting early changes in infarcted myocardium, when collagen content does not still increase.