large, multicenter study reported that the incidence of unintentional failure to hospitalize patients presenting at the emergency department with acute myocardial infarction (AMI) or unstable angina pectoris (UA) was low, although possibly associated with a poor outcome, and it was suggested that the incidence of missed diagnoses of acute cardiac ischemia in the emergency department could be reduced by using a new imaging modality.Recently, the clinical usefulness of a perfusion tracer in the diagnosis of acute coronary syndromes (ACS) was reported. [1][2][3][4] Rest myocardial perfusion imaging with 99m Tc sestamibi had a high sensitivity for identifying patients with ACS 1 and the sensitivity of 99m Tc perfusion tracer and 201 TlCl imaging for detecting coronary artery lesions ranged from 82% to 95% and from 80% to 84%, respecCirculation Journal Vol. 68, November 2004 tively, with a specificity of 75-100% and 75-82%. [2][3][4] 123 I--methyl-p-iodephenyl-pentadecanoic acid (BMIPP) single photon emission computed tomography (SPECT) imaging is considered suitable for patients with UA or severe coronary artery disease because it does not require a provocative test and thus would be useful for detecting the culprit lesion in patients with ACS. 5,6 This imaging modality represents the lesions as ischemic memory. 7 99m Tc-pyrophosphate (PYP) also uses a flow tracer to assess the severity and extent of ischemia, and that of myocardial viability. In UA the uptake of PYP is visualized as diffuse, slightly positive findings 8-10 and others have suggested that there is uptake of this agent by injured myocardial cells in the absence of infarction. 11,12 Preliminary clinical results suggest that breath-held, black blood turbo short-inversion-time inversion recovery (STIR) imaging may be sensitive to focal changes of contrast between edematous and normal myocardium. 13 In the present study we investigated the clinical significance of PYP, BMIPP, 201 TlCl and T2-weighted inversion -recovery magnetic resonance imaging (MRI) for detecting the culprit lesions in patients with ACS. Katumi Matumoto, MD*; Youhei Yamakawa, MD*; Satosi Umemura, MD* Background The incidence of missed diagnoses of acute cardiac ischemia in the emergency department could be reduced by a new imaging modality. In the present study, the clinical significance of 99m Tc-pyrophosphate (PYP), 123 I--methyl-p-iodephenyl-pentadecanoic acid (BMIPP), 201 TlCl scintigraphy (imaging) and T2-weighted inversion -recovery magnetic resonance imaging (MRI) for the detection of culprit lesion in patients with acute coronary syndromes (ACS) was compared. Methods and ResultsThe study group comprised 18 patients with ACS: 12 patients with acute myocardial infarction (AMI) (11 males; mean age, 63±11 years) and 6 patients with unstable angina (UA) (3 males, mean age, 67±5 years). Of the 12 patients with AMI, 10 underwent 201 TlCl and PYP single photon emission computed tomography (SPECT) studies as a dual-energy acquisition ( 201 TlCl/PYP) and 8 underwent 201 TlCl SPECT w...