Background: Delayed enhanced (DE) multidetector computed tomography (MDCT) can identify acute and chronic myocardial infarct. To our knowledge, automated techniques for infarct quantification on DE-MDCT have not been used. Objective: We evaluated an automated signal intensity (SI) threshold method for quantification of subacute myocardial infarct and identified and quantified microvascular obstruction (MO) in subacute infarct. Methods: DE-MDCT imaging was performed on 5 pigs 6-7 days after mid left anterior descending artery occlusion-reperfusion. DE-MDCT images were compared with triphenyl tetrazolium chloride (TTC) staining for infarct quantification and with hematoxylin and eosin (H&E) staining for MO quantification. Pixels with SI more than the mean SI of a remote normal myocardial region (SIremote) plus 2 times the standard deviation (SIremote + 2 SD) value were considered infarct pixels. The ratio of infarct to total area of a given slice, the percentage of infarct area per slice (PIS), was calculated. MO as a percentage of total infarct area was also calculated. Results: The average density values on DE-MDCT (5 minutes after contrast injection) were remote normal myocardium of 93 ± 19 Hounsfield units (HU), infarct myocardium of 159 ± 40 HU, blood of 140 ± 26 HU, and MO of 85 ± 30 HU. PISMDCT showed substantial agreement with PISTTC (y = 1.003x + 4.12; R = 0.90, P < 0.05). A relation was also shown between MO determined by MDCT compared with H&E staining (y = 0.74x + 3.4). Conclusions: We show the feasibility of using a semiautomated SI threshold technique for quantification of subacute myocardial infarct. We also show the persistent MO in subacute myocardial infarct on DE-MDCT images. © 2008 Society of Cardiovascular Computed Tomography.