冠状動脈疾患における心筋イメージングの有用性

Clinical availability of radio-isotope myocardial imaging in patients with coronary artery disease

　近年，生活様式の変化に伴い冠状動脈疾患は増加している。核医学的手法は非侵襲的な診断法として日常の臨床面へ導入されている^1〜4）。本稿では症例を呈示し，それを中心として臨床的有用性と内科医が実際に利用する際の問題点について述べる。

Recently clinical usefullness of cardiovascular nuclear medicine for detecting and evaluating of coronary artery disease (CAD) was reported. In this paper, we presented various cases of CAD and dis-cussed the availability of myocardial imaging for physicians.

(I) Tc-99m-pyrophosphate (PYP) infarct scintigram : Infarct scintigram by means of 99m-Tc-PYP are more sensitive than the electrograms for diagnosis of acute myocardial infarction, parti-cularly if the electrocardiogram container pre-exist-ing abnormalities such as left bundle branch block. As a mechanism of "positive scintigram", deposition of 99m-Tc-PYP at the hydroxyapatite in the mito-chondria has been thought. Persistent positive scin-tigram over 7 days had prognostic value in patients with myocardial infarction. A doughnut type of 99m-Tc-PYP scintigraphic pattern of myocardium was identified with massive myocardial infarct as-sociated with high mortality rate (80%).

False positive scintigram was noted in the pa-tients with myocarditis, severe unstable angina and valvular calcification.

(II) Tl-201 myocardial perfusion image (Tl- 201MPI) : Thallium-201 is produced by electron capture with a 73-hr half time. Tl-201 is a potas-sium analog and the myocardium contains over 3% of the injected dose of Tl-201.

(a) Rest image : As Tl-201 has a potency for myocardial visualization the infarcted myocardium is detected as "cold spot" of radionuclide uptake. (b) Stress Tl-201 MPI : Stress Tl-201 was performed to evaluate ischemic heart disease. Venous injection of Tl-201 was admistrated at the peak exercise, that is approximately submaximal heart rate, the initial and delayed scintigrams were obtained at the time of 10 minutes and 240 minutes after the stress. Res-pectively in a typical ischemic region, redistribu-tion was observed, although continuous perfusion defect was found the arear of necrotic changes of myocardial cells. Stress Tl-201 MPI was available to evaluate the diseases such as follows : (1) ven-tricular conduction disturbances. (2) severe trip-ple vessel disease, who were unable to be examin-ed by cardiac catheterization. (3) Syndrome X. (4) post operation of A-C bypass.

For the more qualitative and quantitative analy-sis in stress MPI, spatial and temporal analysis by using circumferential profile method were per-formed. In future, emission CT by using positron as a metabolic tracers will be developed.