Age-independent myocardial infarct quantification by signal intensity percent infarct mapping in swine

Abstract

Purpose To test whether signal intensity percent infarct mapping (SI-PIM) accurately determines the size of myocardial infarct (MI) regardless of its age. Materials and methods Forty-five swine with reperfused MI underwent 1.5T late gadolinium enhancement (LGE) MRI after bolus injection of 0.2mmol/kg Gd(DTPA) on days 2-62 following MI. Animals were classified into acute, healing, and healed groups by pathology. Infarct volume (IV) and infarct fraction (IF) were determined using binary techniques (including 2-5 standard deviations (SD) above the remote, and full-width at half-maximum) and the SI-PIM method by two readers. Triphenyl-tetrazolium-chloride staining (TTC) was performed as reference. Bias (percent under/overestimation of IV relative to TTC) of each quantification method was calculated. Bland-Altman analysis was done to test the accuracy of the quantification methods, while intraclass correlation coefficient (ICC) analysis was done to assess intra-and interobserver agreement. Results Bias of the MRI quantification methods do not depend on the age of the MI. FWHM and SI-PIM gave the best estimate of MI volume determined by the reference TTC (p-values for the FWHM and SI-PIM methods were 0.183, 0.26, 0.95 and 0.073, 0.091, 0.73 in Group 1, Group 2 and Group 3, respectively), while using any of the binary thresholds of 2-4SD above the remote myocardium showed significant overestimation. The 5SD method, however, provided similar IV compared to TTC and was shown to be independent of the size and age of MI. ICC analysis showed excellent inter- and intraobserver agreement between the readers. Conclusions Our results indicate that the SI-PIM method can accurately determine MI volume regardless of the pathological stage of MI. Once tested, it may prove to be useful for the clinic.

Nonbinary quantification technique accounting for myocardial infarct heterogeneity: Feasibility of applying percent infarct mapping in patients

“…4,10,12 While lower binary thresholds (2, 3, and 4SD) have been found to be inaccurate for MI quantification in previous investigations with pathologic validation, higher cutoffs (5 and 6SD, and FWHM) are generally considered more accurate when compared to the binary TTC method. 4,10,12 While lower binary thresholds (2, 3, and 4SD) have been found to be inaccurate for MI quantification in previous investigations with pathologic validation, higher cutoffs (5 and 6SD, and FWHM) are generally considered more accurate when compared to the binary TTC method.…”

“…Our findings showed that MI quantification with nonbinary PIM LGE and PIM T1 leads to significantly lower IV and IF values compared to binary techniques, which is in line with previous animal studies. 4,10,12 While lower binary thresholds (2, 3, and 4SD) have been found to be inaccurate for MI quantification in previous investigations with pathologic validation, higher cutoffs (5 and 6SD, and FWHM) are generally considered more accurate when compared to the binary TTC method. [17][18][19][20] However, it is important to emphasize that the lower IV and IF by PIM LGE and PIM T1 was an expected finding.…”

“…4,10,12 Our study design included manual MI segmentation as a reference method, simply because it is considered accurate and has been the most commonly used method to quantify MI. In our investigation, IF and IV values showed a strong correlation for both measures between the two techniques, and no significant differences were observed between PIM LGE and PIM T1 .…”

“…4,9,10 Previous in vivo and ex vivo swine studies have validated PIM for the quantification of MI when using histopathologic triphenyl tetrazolium chloride (TTC) staining as the reference standard. 4,12 Such studies are appropriate to establish the comparisons among the different techniques. 4,12 Such studies are appropriate to establish the comparisons among the different techniques.…”

“…4,10,11 The noninferiority of the SI-PIM technique compared to the T 1 -mapping-based evaluation has also been demonstrated in porcine models of acute and chronic MI. 4,12 Such studies are appropriate to establish the comparisons among the different techniques. However, these studies are inherently limited, as they are typically performed in a well-controlled environment under general anesthesia with pharmacological heart rate control and mechanical ventilation, allowing for breathholds with perfectly reproducible depth and length.…”