Extracellular volume fractions in chronic myocardial infarction.

OBJECTIVES: The aim of this study was to assess and delineate chronic myocardial infarction (CMI) using precontrast and postcontrast T1 mapping techniques including quantification of extracellular volume fractions (ECVs). MATERIALS AND METHODS: A total of 26 patients with CMI were examined at 1.5 T applying a modified Look-Locker Inversion Recovery sequence before and 10 minutes after contrast at 3 short-axis slice positions. An inversion recovery gradient recalled echo sequence (standard of reference) was used for imaging late gadolinium enhancement. Precontrast and postcontrast T1 maps were calculated, and CMI was defined as areas with T1 values more than 3 SDs different compared with normal myocardium (MYO). T1 values of CMI, MYO, and blood pool were measured, and ECVs of CMI and MYO were calculated. Two-tailed Student t test was used for statistical analysis of T1 values and ECVs. Sensitivities and specificities for detection of CMI on precontrast and postcontrast T1 maps were calculated. Receiver operating characteristic (ROC) analysis was performed for postcontrast T1 values and ECV for discrimination of CMI. RESULTS: The comparison of T1 values of CMI and MYO revealed significant differences in precontrast and postcontrast scans (1159 ± 64 vs 1001 ± 47 milliseconds, P < 0.001, and 238 ± 74 vs 379 ± 59 milliseconds, P < 0.001). Sensitivities and specificities for detection of CMI on T1 mapping were 41.7% and 100% in precontrast Look-Locker Inversion Recovery scans and 95.8% and 99.3% in postcontrast images, respectively. Average ECV for MYO and CMI were 28% ± 5% and 53% ± 10% (P < 0.001). ROC analysis revealed nonsignificantly different areas under the curve of 0.937 and 0.997 for T1 values and ECV, respectively (P = 0.137). Sensitivities and specificities were 92.3% and 92.3% for detecting CMI by postcontrast T1 values and 95.5% and 100% for ECV, with cutoff values being 305 milliseconds or less and greater than 42%. Combined criteria did not result in any further improvement of sensitivity for CMI detection. CONCLUSIONS: Postcontrast T1 values and ECV of chronically infarcted MYO are significantly different compared with respective values of normal MYO. Both parameters allow for accurate detection of CMI with ECV showing marginally higher sensitivity and specificity. Precontrast T1 values lack accuracy in delineation of CMI.

Magnetic resonance perfusion of the myocardium: semiquantitative and quantitative evaluation in comparison with coronary angiography and fractional flow reserve.

PURPOSE: The aim of this study was to investigate if a quantitative evaluation of a magnetic resonance (MR) perfusion examination of the myocardium can achieve a comparable diagnostic accuracy as a semiquantitative evaluation. METHODS: A total of 31 patients with suspected coronary artery disease underwent MR imaging and conventional coronary angiography. Stenoses with a diameter reduction between 50% and 75% were evaluated by an intracoronary pressure wire examination (fractional flow reserve) for assessment of their hemodynamic relevance. A 0.05 mmol/kg contrast material bolus (gadopentetate dimeglumine) was applied during adenosine-induced stress (140 µg/kg/min) and at rest with a flow rate of 5 mL/s. Signal intensity time curves of the first-pass MR perfusion images, acquired at rest and under adenosine stress with a Saturation Recovery-turbo Fast Low Angle Shot Magnetic Resonance Imaging sequence, were analyzed by Argus Dynamic Signal Analysis (Siemens Healthcare, Erlangen, Germany). For the semiquantitative evaluation, the upslope value of a linear fit from the foot point to the signal maximum was calculated for 18 segments (signal intensity units per second). For the quantitative evaluation, a model-independent deconvolution was used to calculate coronary blood flow (MBF in mL/100 g/min). For each segment for the stress and rest examination, upslope value and MBF were determined. In addition, the ratio of the stress and rest value for each segment was determined (myocardial perfusion reserve index [MPRI]). The mean value of the 2 segments with the lowest value was calculated for each patient. Coronary artery stenosis greater than 75% or greater than 50% with positive fractional flow reserve less than 0.75 was considered as hemodynamically relevant. Receiver-operator-curves were calculated. RESULTS: The values of the area under the ROC curves were 0.74, 0.66, and 0.92 for the US(Stress), US(Rest), and US(MPRI) evaluations (semiquantitative evaluation). The values for the MBF(Stress), MBF(Rest), and MBF(MPRI) evaluations (quantitative evaluation) were 0.92, 0.68, and 0.84, respectively. Comparing US(MPRI) and MBF(Stress), identical values and no significant difference were found for the area under the ROC curves. CONCLUSION: A quantitative evaluation using a model-free deconvolution provides identical diagnostic performance when only a stress examination is used, much similar to a semiquantitative evaluation, if both stress and rest examinations are used.