Quantitative myocardial infarction on delayed enhancement MRI. Part II: Clinical application of an automated feature analysis and combined thresholding infarct sizing algorithm

CMRSegTools: An open-source software enabling reproducible research in segmentation of acute myocardial infarct in CMR images

In the last decade, a large number of clinical trials have been deployed using Cardiac Magnetic Resonance (CMR) to evaluate cardioprotective strategies aiming at reducing the irreversible myocardial damage at the time of reperfusion. In these studies, segmentation and quantification of myocardial infarct lesion are often performed with a commercial software or an in-house closed-source code development thus creating a barrier for reproducible research. This paper introduces CMRSegTools: an open-source application software designed for the segmentation and quantification of myocardial infarct lesion enabling full access to state-of-the-art segmentation methods and parameters, easy integration of new algorithms and standardised results sharing. This post-processing tool has been implemented as a plug-in for the OsiriX/Horos DICOM viewer leveraging its database management functionalities and user interaction features to provide a bespoke tool for the analysis of cardiac MR images on large clinical cohorts. CMRSegTools includes, among others, user-assisted segmentation of the left-ventricle, semi- and automatic lesion segmentation methods, advanced statistical analysis and visualisation based on the American Heart Association 17-segment model. New segmentation methods can be integrated into the plug-in by developing components based on image processing and visualisation libraries such as ITK and VTK in C++ programming language. CMRSegTools allows the creation of training and testing data sets (labeled features such as lesion, microvascular obstruction and remote ROI) for supervised Machine Learning methods, and enables the comparative assessment of lesion segmentation methods via a single and integrated platform. The plug-in has been successfully used by several CMR imaging studies.

Histopathological validation of semi-automated myocardial scar quantification techniques for dark-blood late gadolinium enhancement magnetic resonance imaging

AIMS

To evaluate the performance of various semi-automated techniques for quantification of myocardial infarct size on both conventional bright-blood and novel dark-blood late gadolinium enhancement (LGE) images using histopathology as reference standard.

METHODS AND RESULTS

In 13 Yorkshire pigs, reperfused myocardial infarction was experimentally induced. At 7 weeks post-infarction, both bright-blood and dark-blood LGE imaging were performed on a 1.5 T magnetic resonance scanner. Following magnetic resonance imaging (MRI), the animals were sacrificed, and histopathology was obtained. The percentage of infarcted myocardium was assessed per slice using various semi-automated scar quantification techniques, including the signal threshold vs. reference mean (STRM, using 3 to 8 SDs as threshold) and full-width at half-maximum (FWHM) methods, as well as manual contouring, for both LGE methods. Infarct size obtained by histopathology was used as reference. In total, 24 paired LGE MRI slices and histopathology samples were available for analysis. For both bright-blood and dark-blood LGE, the STRM method with a threshold of 5 SDs led to the best agreement to histopathology without significant bias (-0.23%, 95% CI [-2.99, 2.52%], P = 0.862 and -0.20%, 95% CI [-2.12, 1.72%], P = 0.831, respectively). Manual contouring significantly underestimated infarct size on bright-blood LGE (-1.57%, 95% CI [-2.96, -0.18%], P = 0.029), while manual contouring on dark-blood LGE outperformed semi-automated quantification and demonstrated the most accurate quantification in this study (-0.03%, 95% CI [-0.22, 0.16%], P = 0.760).

CONCLUSION

The signal threshold vs. reference mean method with a threshold of 5 SDs demonstrated the most accurate semi-automated quantification of infarcted myocardium, without significant bias compared to histopathology, for both conventional bright-blood and novel dark-blood LGE.

Expression of Hypersensitive Troponin I and Soluble ST2 in Acute Organophosphorus Pesticide Poisoning

The role of soluble growth stimulating gene 2 protein and highly sensitive cardiac troponin in the diagnosis of early myocardial injury caused by acute organophosphorus pesticide poisoning was studied. 171 inpatients with AOPP were divided into three experimental groups according to their mild, moderate, and severe conditions. 20 healthy people were selected as the control group. The levels of cTnI, HS-CTNI, NT proBNP, and ST2 were measured at the 4th and 12th hours after the experiment. The measured data were expressed by mean standard deviation. The independent sample t-test was used for the detection between the two groups, and one-way ANOVA was used for the analysis and comparison between multiple groups. The relevant data were analyzed by Spearman correlation test (P < 0.05). The levels of cTnI and HS cTnI in the experimental group increased with the extension of time and the deepening of poisoning degree; four hours after admission, ST2 and NT proBNP water in the control group and the experimental group increased significantly on average. According to the analysis of the data, there was a positive correlation between HS TnI and ST2 in patients with AOPP (r = 0.938, P < 0.001, r = 0.827, P < 0.001). The more serious the disease, the higher the concentrations of HS TnI and ST2, and the more serious the myocardial injury.

Extracellular volume-guided late gadolinium enhancement analysis for non-ischemic cardiomyopathy: The Women's Interagency HIV Study

BACKGROUND

Quantification of non-ischemic myocardial scar remains a challenge due to the patchy diffuse nature of fibrosis. Extracellular volume (ECV) to guide late gadolinium enhancement (LGE) analysis may achieve a robust scar assessment.

METHODS

Three cohorts of 80 non-ischemic-training, 20 non-ischemic-validation, and 10 ischemic-validation were prospectively enrolled and underwent 3.0 Tesla cardiac MRI. An ECV cutoff to differentiate LGE scar from non-scar was identified in the training cohort from the receiver-operating characteristic curve analysis, by comparing the ECV value against the visually-determined presence/absence of the LGE scar at the highest signal intensity (SI) area of the mid-left ventricle (LV) LGE. Based on the ECV cutoff, an LGE semi-automatic threshold of n-times of standard-deviation (n-SD) above the remote-myocardium SI was optimized in the individual cases ensuring correspondence between LGE and ECV images. The inter-method agreement of scar amount in comparison with manual (for non-ischemic) or full-width half-maximum (FWHM, for ischemic) was assessed. Intra- and inter-observer reproducibility were investigated in a randomly chosen subset of 40 non-ischemic and 10 ischemic cases.

RESULTS

The non-ischemic groups were all female with the HIV positive rate of 73.8% (training) and 80% (validation). The ischemic group was all male with reduced LV function. An ECV cutoff of 31.5% achieved optimum performance (sensitivity: 90%, specificity: 86.7% in training; sensitivity: 100%, specificity: 81.8% in validation dataset). The identified n-SD threshold varied widely (range 3 SD-18 SD), and was independent of scar amount (β = -0.01, p = 0.92). In the non-ischemic cohorts, results suggested that the manual LGE assessment overestimated scar (%) in comparison to ECV-guided analysis [training: 4.5 (3.2-6.4) vs. 0.92 (0.1-2.1); validation: 2.5 (1.2-3.7) vs. 0.2 (0-1.6); P < 0.01 for both]. Intra- and inter-observer analyses of global scar (%) showed higher reproducibility in ECV-guided than manual analysis with CCC = 0.94 and 0.78 versus CCC = 0.86 and 0.73, respectively (P < 0.01 for all). In ischemic validation, the ECV-guided LGE analysis showed a comparable scar amount and reproducibility with the FWHM.

CONCLUSIONS

ECV-guided LGE analysis is a robust scar quantification method for a non-ischemic cohort. Trial registration ClinicalTrials.gov; NCT00000797, retrospectively-registered 2 November 1999; NCT02501811, registered 15 July 2015.

Prevalence and prognosis of ischaemic and non-ischaemic myocardial fibrosis in older adults

Aims

Non-ischaemic cardiomyopathies (NICM) can cause heart failure and death. Cardiac magnetic resonance (CMR) detects myocardial scar/fibrosis associated with myocardial infarction (MI) and NICM with late gadolinium enhancement (LGE). The aim of this study was to determine the prevalence and prognosis of ischaemic and non-ischaemic myocardial fibrosis in a community-based sample of older adults.

Methods and results

The ICELAND-MI cohort, a substudy of the Age, Gene/Environment Susceptibility Reykjavik (AGES-Reykjavik) study, provided a well-characterized population of 900 subjects after excluding subjects with pre-existing heart failure. Late gadolinium enhancement CMR divided subjects into four groups: MI (n = 211), major (n = 54) non-ischaemic fibrosis (well-established, classic patterns, associated with myocarditis, infiltrative cardiomyopathies, or pathological hypertrophy), minor (n = 238) non-ischaemic fibrosis (remaining localized patterns not meeting major criteria), and a no LGE (n = 397) reference group. The primary outcome was time to death or first heart failure hospitalization. During a median follow-up of 5.8 years, 192 composite events occurred (115 deaths and 77 hospitalizations for incident heart failure). After inverse probability weighting, major non-ischaemic fibrosis [hazard ratio (HR) 3.2, P < 0.001] remained independently associated with the primary endpoint, while MI (HR 1.4, P = 0.10) and minor non-ischaemic LGE (HR 1.2, P = 0.39) did not. Major non-ischaemic fibrosis was associated with a poorer outcome than MI (HR = 2.3, P = 0.001) in the adjusted analysis.

Conclusion

Major non-ischaemic patterns of myocardial fibrosis portended worse prognosis than no fibrosis/scar in an older community-based cohort. Traditional risk factors largely accounted for the effect of MI and minor non-ischaemic LGE.

Sources of variability in quantification of cardiovascular magnetic resonance infarct size - reproducibility among three core laboratories

BACKGROUND

Acute myocardial infarct (AMI) size depicted by late gadolinium enhancement cardiovascular magnetic resonance (CMR) is increasingly used as an efficacy endpoint in randomized trials comparing AMI therapies. Infarct size is quantified using manual planimetry (MANUAL), visual scoring (VISUAL), or automated techniques using signal-intensity thresholding (AUTO). Although AUTO is considered the most reproducible, prior studies did not account for the subjective determination of endocardial/epicardial borders, which all methods require. For MANUAL and VISUAL, prior studies did not address how to treat intermediate signal intensities due to partial volume.

METHODS

To assess sources of variability, AMI size was measured in 30 patients and 12 controls by 3 core-laboratories using 8 methods, each separated by more than 2 months time (n = 720 evaluations). The methods were: (1,2) AUTOSegment, AUTOFWHM (using Segment software or the full-width-at-half-maximum algorithm, respectively); (3,4) AUTO-UCSegment, AUTO-UCFWHM (user correction for endocardial border pixels, no-reflow, etc.); (5) MANUAL; (6) MANUAL-ISI (adjustment for intermediate signal-intensities); (7) VISUAL; (8) VISUAL-ISI.

RESULTS

Mean infarct size varied between 16.8% and 27.2% of LV mass depending on method. Even automated techniques with no user interaction for infarct borders resulted in significant within-patient variability given the need to subjectively trace endocardial/epicardial contours. The coefficient-of-variation (CV) was 10.6% and 14.6% for AUTOSegment and AUTOFWHM, respectively. For manual and visual categories, reproducibility was improved when intermediate signal-intensities were considered (MANUAL-ISI vs MANUAL: CV = 8.3% vs 14.4%; p = 0.03; VISUAL-ISI vs VISUAL: CV = 8.4% vs 10.9%; p = 0.01). For AUTO-UCSegment, MANUAL-ISI, and VISUAL-ISI (best technique in each category) within-patient variability due to the quantification method was less than 10% of total variability, and the required sample sizes for detecting a 5% absolute difference in infarct size were 62, 63, and 62 patients, respectively.

CONCLUSION

Among CMR core-laboratories, an important source of variability in infarct size quantification is the subjective delineation of endocardial/epicardial borders. When intermediate signal intensities are considered in manual planimetry and visual scoring, reproducibility and impact on sample size are similar to automated techniques.

Fatty metaplasia quantification and impact on regional myocardial function as assessed by advanced cardiac MR imaging

Objective

This study aimed to investigate the advantages of recently developed cardiac imaging techniques of fat–water separation and feature tracking to characterize better individuals with chronic myocardial infarction (MI).

Materials and methods

Twenty patients who had a previous MI underwent CMR imaging. The study protocol included routine cine and late gadolinium enhancement (LGE) technique. In addition, mDixon LGE imaging was performed in every patient. Left ventricular (LV) circumferential (Ecc_LV) and radial (Err_LV) strain were calculated using dedicated software (CMR⁴², Circle, Calgary, Canada). The extent of global scar was measured in LGE and fat–water separated images to compare conventional and recent CMR imaging techniques.

Results

The infarct size derived from conventional LGE and fat–water separated images was similar. However, detection of lipomatous metaplasia was only possible with mDixon imaging. Subjects with fat deposition demonstrated a significantly smaller percentage of fibrosis than those without fat (10.68 ± 5.07% vs. 13.83 ± 6.30%; p = 0.005). There was no significant difference in Ecc_LV or Err_LV between myocardial segments containing fibrosis only and fibrosis with fat. However, Ecc_LV and Err_LV values were significantly higher in myocardial segments adjacent to fibrosis with fat deposition than in those adjacent to LGE only.

Conclusions

Advanced CMR imaging ensures more detailed tissue characterization in patients with chronic MI without a relevant increase in imaging and post-processing time. Fatty metaplasia may influence regional myocardial deformation especially in the myocardial segments adjacent to scar tissue. A simplified and shortened myocardial viability CMR protocol might be useful to better characterize and stratify patients with chronic MI.

Impact of microvascular obstruction on semiautomated techniques for quantifying acute and chronic myocardial infarction by cardiovascular magnetic resonance

Aims

The four most promising semiautomated techniques (5-SD, 6-SD, Otsu and the full width half maximum (FWHM)) were compared in paired acute and follow-up cardiovascular magnetic resonance (CMR), taking into account the impact of microvascular obstruction (MVO) and using automated extracellular volume fraction (ECV) maps for reference. Furthermore, their performances on the acute scan were compared against manual myocardial infarct (MI) size to predict adverse left ventricular (LV) remodelling (≥20% increase in end-diastolic volume).

Methods

40 patients with reperfused ST segment elevation myocardial infarction (STEMI) with a paired acute (4±2 days) and follow-up CMR scan (5±2 months) were recruited prospectively. All CMR analysis was performed on CVI42.

Results

Using manual MI size as the reference standard, 6-SD accurately quantified acute (24.9±14.0%LV, p=0.81, no bias) and chronic MI size (17.2±9.7%LV, p=0.88, no bias). The performance of FWHM for acute MI size was affected by the acquisition sequence used. Furthermore, FWHM underestimated chronic MI size in those with previous MVO due to the significantly higher ECV in the MI core on the follow-up scans previously occupied by MVO (82 (75–88)% vs 62 (51–68)%, p<0.001). 5-SD and Otsu were precise but overestimated acute and chronic MI size. All techniques were performed with high diagnostic accuracy and equally well to predict adverse LV remodelling.

Conclusions

6-SD was the most accurate for acute and chronic MI size and should be the preferred semiautomatic technique in randomised controlled trials. However, 5-SD, FWHM and Otsu could also be used when precise MI size quantification may be adequate (eg, observational studies).

Relationship between vitamin D level and left atrial fibrosis in patients with lone paroxysmal atrial fibrillation undergoing cryoballoon-based catheter ablation

BACKGROUND

Left atrial (LA) fibrosis is known as the hallmark for arrhythmogenic substrate in atrial fibrillation (AF). Quantification of LA fibrosis by using delayed-enhanced magnetic resonance imaging (DE-MRI) in AF patients is a pioneering noninvasive technique. Vitamin D (vitD) negatively regulates the renin-angiotensin system, binds to vitD receptors on cardiac myocytes, and has antioxidant properties that may ameliorate the inflammation and proarrhythmic substrate formation. However, its role in LA fibrosis is unclear. We aimed to investigate the association of serum 25(OH)D level with the extent of LA fibrosis by using DE-MRI and also predictors for AF recurrence after cryoablation was assessed in patients with paroxysmal AF.

METHODS

A total of 48 patients with lone paroxysmal AF (41.7% female; age: 48.5±8.4 years) who underwent DE-MRI at 1.5T and initial cryoballoon-based catheter ablation along with 48 healthy control subjects were enrolled. Fibrosis degree was categorized according to Utah class defined in the DECAAF study.

RESULTS

Serum 25(OH)D levels were significantly lower in AF group compared to control group (25.8±7.6ng/ml vs. 31.0±9.5ng/ml, p=0.004). Serum 25(OH)D levels were associated with moderate-severe LA fibrosis independent of other measures (OR: 0.72, 95% CI: 0.54-0.97, p=0.028). At a mean 16.5±2.6 months follow-up, late recurrence was observed in 10 (20.8%) patients. In multivariable Cox regression analysis, LA volume index (HR: 1.42, 95% CI: 1.01-2.01, p=0.045) and the extent of LA fibrosis (HR: 1.14, 95% CI: 1.01-1.28, p=0.034) were found as independently associated with late AF recurrence during follow-up.

CONCLUSION

Lower levels of serum 25(OH)D are significantly associated with more extensive LA fibrosis in patients with lone paroxysmal AF and may be implicated in the pathophysiology of AF recurrence after cryoablation. Further large-scale studies are needed to elucidate the exact role of vitD deficiency and replacement on LA fibrosis.

A new automatic algorithm for quantification of myocardial infarction imaged by late gadolinium enhancement cardiovascular magnetic resonance: experimental validation and comparison to expert delineations in multi-center, multi-vendor patient data

BACKGROUND

Late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) using magnitude inversion recovery (IR) or phase sensitive inversion recovery (PSIR) has become clinical standard for assessment of myocardial infarction (MI). However, there is no clinical standard for quantification of MI even though multiple methods have been proposed. Simple thresholds have yielded varying results and advanced algorithms have only been validated in single center studies. Therefore, the aim of this study was to develop an automatic algorithm for MI quantification in IR and PSIR LGE images and to validate the new algorithm experimentally and compare it to expert delineations in multi-center, multi-vendor patient data.

METHODS

The new automatic algorithm, EWA (Expectation Maximization, weighted intensity, a priori information), was implemented using an intensity threshold by Expectation Maximization (EM) and a weighted summation to account for partial volume effects. The EWA algorithm was validated in-vivo against triphenyltetrazolium-chloride (TTC) staining (n = 7 pigs with paired IR and PSIR images) and against ex-vivo high resolution T1-weighted images (n = 23 IR and n = 13 PSIR images). The EWA algorithm was also compared to expert delineation in 124 patients from multi-center, multi-vendor clinical trials 2-6 days following first time ST-elevation myocardial infarction (STEMI) treated with percutaneous coronary intervention (PCI) (n = 124 IR and n = 49 PSIR images).

RESULTS

Infarct size by the EWA algorithm in vivo in pigs showed a bias to ex-vivo TTC of -1 ± 4%LVM (R = 0.84) in IR and -2 ± 3%LVM (R = 0.92) in PSIR images and a bias to ex-vivo T1-weighted images of 0 ± 4%LVM (R = 0.94) in IR and 0 ± 5%LVM (R = 0.79) in PSIR images. In multi-center patient studies, infarct size by the EWA algorithm showed a bias to expert delineation of -2 ± 6 %LVM (R = 0.81) in IR images (n = 124) and 0 ± 5%LVM (R = 0.89) in PSIR images (n = 49).

CONCLUSIONS

The EWA algorithm was validated experimentally and in patient data with a low bias in both IR and PSIR LGE images. Thus, the use of EM and a weighted intensity as in the EWA algorithm, may serve as a clinical standard for the quantification of myocardial infarction in LGE CMR images.

CLINICAL TRIAL REGISTRATION

CHILL-MI: NCT01379261 .

MITOCARE

NCT01374321 .

Myocardial infarct sizing by late gadolinium-enhanced MRI: Comparison of manual, full-width at half-maximum, and n-standard deviation methods

PURPOSE

To compare three widely used methods for myocardial infarct (MI) sizing on late gadolinium-enhanced (LGE) magnetic resonance (MR) images: manual delineation and two semiautomated techniques (full-width at half-maximum [FWHM] and n-standard deviation [SD]).

MATERIALS AND METHODS

3T phase-sensitive inversion-recovery (PSIR) LGE images of 114 patients after an acute MI (2-4 days and 6 months) were analyzed by two independent observers to determine both total and core infarct sizes (TIS/CIS). Manual delineation served as the reference for determination of optimal thresholds for semiautomated methods after thresholding at multiple values. Reproducibility and accuracy were expressed as overall bias ± 95% limits of agreement.

RESULTS

Mean infarct sizes by manual methods were 39.0%/24.4% for the acute MI group (TIS/CIS) and 29.7%/17.3% for the chronic MI group. The optimal thresholds (ie, providing the closest mean value to the manual method) were FWHM30% and 3SD for the TIS measurement and FWHM45% and 6SD for the CIS measurement (paired t-test; all P > 0.05). The best reproducibility was obtained using FWHM. For TIS measurement in the acute MI group, intra-/interobserver agreements, from Bland-Altman analysis, with FWHM30%, 3SD, and manual were -0.02 ± 7.74%/-0.74 ± 5.52%, 0.31 ± 9.78%/2.96 ± 16.62% and -2.12 ± 8.86%/0.18 ± 16.12, respectively; in the chronic MI group, the corresponding values were 0.23 ± 3.5%/-2.28 ± 15.06, -0.29 ± 10.46%/3.12 ± 13.06% and 1.68 ± 6.52%/-2.88 ± 9.62%, respectively. A similar trend for reproducibility was obtained for CIS measurement. However, semiautomated methods produced inconsistent results (variabilities of 24-46%) compared to manual delineation.

CONCLUSION

The FWHM technique was the most reproducible method for infarct sizing both in acute and chronic MI. However, both FWHM and n-SD methods showed limited accuracy compared to manual delineation. J. Magn. Reson. Imaging 2016;44:1206-1217.

The Association of Serum Galectin-3 Levels with Atrial Electrical and Structural Remodeling

INTRODUCTION

Left atrial (LA) interstitial fibrosis is known to have a role in the initiation and maintenance of atrial fibrillation (AF). The role of galectin-3 in the pathogenesis of cardiac fibrosis has been demonstrated in previous studies. We aimed to determine whether serum galectin-3 level is associated with markers of atrial remodeling, including the extent of LA fibrosis detected by delayed enhancement magnetic resonance imaging (DE-MRI) and atrial electromechanical delay (AEMD) in paroxysmal AF patients with preserved left ventricular (LV) functions.

METHODS AND RESULTS

Thirty-three patients (58 [28-74] years, 51.5% male) with paroxysmal AF who underwent DE-MRI prior to cryoballoon-based AF ablation were included in the study. Serum galectin-3 levels were measured with ELISA. LA volume index (B ± SE: 0.424 ± 0.504, 95% CI: 0.560-2.627, P = 0.004) and serum galectin-3 levels (B ± SE: 0.549 ± 7.745, 95% CI: 16.874-47.550, P < 0.001) were found to be independently correlated with extent of LA fibrosis detected with DE-MRI in paroxysmal AF patients with preserved LV function. Correlation analysis between AEMD parameters and baseline characteristics showed that galectin-3 was significantly correlated with intra-left (ρ = 0.432, P = 0.012) and inter-AEMD (ρ = 0.395, P = 0.023). Duration of AF, LAD, and extent of LA fibrosis were also found to be significantly correlated with AEMD parameters.

CONCLUSION

This is a hypothesis-generating study pointing out that serum galectin-3 level is significantly associated with atrial remodeling in paroxysmal AF patients with preserved LV function. Further studies are necessary to provide exact pathophysiological mechanisms.

Comparison of semi-automated methods to quantify infarct size and area at risk by cardiovascular magnetic resonance imaging at 1.5T and 3.0T field strengths

BACKGROUND

There is currently no gold standard technique for quantifying infarct size (IS) and ischaemic area-at-risk (AAR [oedema]) on late gadolinium enhancement imaging (LGE) and T2-weighted short tau inversion recovery imaging (T2w-STIR) respectively. This study aimed to compare the accuracy and reproducibility of IS and AAR quantification on LGE and T2w-STIR imaging using Otsu's Automated Technique (OAT) with currently used methods at 1.5T and 3.0T post acute ST-segment elevation myocardial infarction (STEMI).

METHODS

Ten patients were assessed at 1.5T and 10 at 3.0T. IS was assessed on LGE using 5-8 standard-deviation thresholding (5-8SD), full-width half-maximum (FWHM) quantification and OAT. AAR was assessed on T2w-STIR using 2SD and OAT. Accuracy was assessed by comparison with manual quantification. Interobserver and intraobserver variabilities were assessed using Intraclass Correlation Coefficients and Bland-Altman analysis. IS using each technique was correlated with left ventricular ejection fraction (LVEF).

RESULTS

FWHM and 8SD-derived IS closely correlated with manual assessment at both field strengths (1.5T: 18.3 ± 10.7% LV Mass [LVM] with FWHM, 17.7 ± 14.4% LVM with 8SD, 16.5 ± 10.3% LVM with manual quantification; 3.0T: 10.8 ± 8.2% LVM with FWHM, 11.4 ± 9.0% LVM with 8SD, 11.5 ± 9.0% LVM with manual quantification). 5SD and OAT overestimated IS at both field strengths. OAT, 2SD and manually quantified AAR closely correlated at 1.5T, but OAT overestimated AAR compared with manual assessment at 3.0T. IS and AAR derived by FWHM and OAT respectively had better reproducibility compared with manual and SD-based quantification. FWHM IS correlated strongest with LVEF.

CONCLUSIONS

FWHM quantification of IS is accurate, reproducible and correlates strongly with LVEF, whereas 5SD and OAT overestimate IS. OAT accurately assesses AAR at 1.5T and with excellent reproducibility. OAT overestimated AAR at 3.0T and thus cannot be recommended as the preferred method for AAR quantification at 3.0T.

M2-muscarinic acetylcholine receptor autoantibody levels predict left atrial fibrosis severity in paroxysmal lone atrial fibrillation patients undergoing cryoablation

AIMS

Atrial fibrosis has been found to be associated with recurrent atrial fibrillation (AF) following catheter ablation. Autoantibodies against M2-muscarinic receptors (anti-M2-R) may play a role in the development of AF by inducing left atrial (LA) fibrosis. In this study, we aim to compare anti-M2-R levels between paroxysmal lone AF patients and healthy control subjects and to investigate the relationship between pre-ablation anti-M2-R level, LA fibrosis quantified by delayed enhancement magnetic resonance imaging (DE-MRI), and AF recurrence following cryoablation.

METHODS AND RESULTS

Thirty-one patients with paroxysmal lone AF (53.4 ± 8.0 years, 61% male), who underwent cryoballoon-based ablation, along with 31 healthy control subjects were included. Enzyme-linked immunosorbent assay tests to measure serum anti-M2-R levels were performed in both groups and DE-MRI was done to quantify LA fibrosis prior to the ablation in the patients. Anti-M2-R levels were higher in the study population when compared with control subjects [212.4 (103.2-655.5) vs. 73.0 (39.5-299.1) ng/mL, P < 0.001]. Anti-M2-R level predicted moderate-extensive LA fibrosis independent of other measures [odds ratio: 1.26 (95% confidence interval (CI): 1.04-1.53), P = 0.017]. At a mean follow-up of 35.2 ± 3.5 months, nine patients (29.0%) had AF recurrence. In the Cox regression model including pre-ablation anti-M2-R level, LA diameter, LA volume index, and moderate-extensive LA fibrosis, only moderate-extensive LA fibrosis predicted late AF recurrence independent of other measures [hazard ratio: 29.41 (95% CI: 3.52-250.00), P = 0.002].

CONCLUSION

Serum anti-M2-R levels may be associated with the severity of LA fibrosis and may be implicated in the pathophysiology of AF recurrence following cryoablation. Detection of anti-M2-R levels may help select appropriate patients for the procedure.

Differences in quantitative assessment of myocardial scar and gray zone by LGE-CMR imaging using established gray zone protocols

Late gadolinium enhancement cardiac magnetic resonance (LGE-CMR) imaging is the gold standard for myocardial scar evaluation. Heterogeneous areas of scar ('gray zone'), may serve as arrhythmogenic substrate. Various gray zone protocols have been correlated to clinical outcomes and ventricular tachycardia channels. This study assessed the quantitative differences in gray zone and scar core sizes as defined by previously validated signal intensity (SI) threshold algorithms. High quality LGE-CMR images performed in 41 cardiomyopathy patients [ischemic (33) or non-ischemic (8)] were analyzed using previously validated SI threshold methods [Full Width at Half Maximum (FWHM), n-standard deviation (NSD) and modified-FWHM]. Myocardial scar was defined as scar core and gray zone using SI thresholds based on these methods. Scar core, gray zone and total scar sizes were then computed and compared among these models. The median gray zone mass was 2-3 times larger with FWHM (15 g, IQR: 8-26 g) compared to NSD or modified-FWHM (5 g, IQR: 3-9 g; and 8 g. IQR: 6-12 g respectively, p < 0.001). Conversely, infarct core mass was 2.3 times larger with NSD (30 g, IQR: 17-53 g) versus FWHM and modified-FWHM (13 g, IQR: 7-23 g, p < 0.001). The gray zone extent (percentage of total scar that was gray zone) also varied significantly among the three methods, 51 % (IQR: 42-61 %), 17 % (IQR: 11-21 %) versus 38 % (IQR: 33-43 %) for FWHM, NSD and modified-FWHM respectively (p < 0.001). Considerable variability exists among the current methods for MRI defined gray zone and scar core. Infarct core and total myocardial scar mass also differ using these methods. Further evaluation of the most accurate quantification method is needed.

Cardiac MRI for myocardial ischemia

Proper assessment of the physiologic impact of coronary artery stenosis on the LV myocardium can affect patient prognosis and treatment decisions. Cardiac magnetic resonance imaging (CMR) assesses myocardial perfusion by imaging the myocardium during a first-pass transit of an intravenous gadolinium bolus, with spatial and temporal resolution substantially higher than nuclear myocardial perfusion imaging. Coupled with late gadolinium enhancement (LGE) imaging for infarction during the same imaging session, CMR with vasodilating stress perfusion imaging can qualitatively and quantitatively assess the myocardial extent of hypoperfusion from coronary stenosis independent of infarcted myocardium. This approach has been validated experimentally, and multiple clinical trials have established its diagnostic robustness when compared to stress single-photon emission computed tomography. In specialized centers, dobutamine stress CMR has been shown to have incremental diagnostic value above stress echocardiography due to its high imaging quality and ability to image the heart with no restriction of imaging window. This paper reviews the technical aspects, diagnostic utility, prognostic values, challenges to clinical adaptation, and future developments of stress CMR imaging.

In-vivo T1 cardiovascular magnetic resonance study of diffuse myocardial fibrosis in hypertrophic cardiomyopathy

BACKGROUND

In hypertrophic cardiomyopathy (HCM), autopsy studies revealed both increased focal and diffuse deposition of collagen fibers. Late gadolinium enhancement imaging (LGE) detects focal fibrosis, but is unable to depict interstitial fibrosis. We hypothesized that with T1 mapping, which is employed to determine the myocardial extracellular volume fraction (ECV), can detect diffuse interstitial fibrosis in HCM patients.

METHODS

T1 mapping with a modified Look-Locker Inversion Recovery (MOLLI) pulse sequence was used to calculate ECV in manifest HCM (n = 16) patients and in healthy controls (n = 14). ECV was determined in areas where focal fibrosis was excluded with LGE.

RESULTS

The total group of HCM patients showed no significant changes in mean ECV values with respect to controls (0.26 ± 0.03 vs 0.26 ± 0.02, p = 0.83). Besides, ECV in LGE positive HCM patients was comparable with LGE negative HCM patients (0.27 ± 0.03 vs 0.25 ± 0.03, p = 0.12).

CONCLUSIONS

This study showed that HCM patients have a similar ECV (e.g. interstitial fibrosis) in myocardium without LGE as healthy controls. Therefore, the additional clinical value of T1 mapping in HCM seems limited, but future larger studies are needed to establish the clinical and prognostic potential of this new technique within HCM.

MR imaging of myocardial infarction

Magnetic resonance (MR) imaging plays an important role in evaluation of various aspects of myocardial infarction (MI). MR imaging is useful in establishing the diagnosis of acute MI, particularly in patients who present with symptoms of MI but outside the diagnostic time frame of altered cardiac enzyme levels or with clinical features of acute MI but without an angiographic culprit lesion. MR imaging is valuable in establishing a diagnosis of chronic MI and distinguishing this condition from nonischemic cardiomyopathies, mainly through use of delayed-enhancement patterns. MR imaging also provides clinicians with several prognostic indicators that enable risk stratification, such as scar burden, microvascular obstruction, hemorrhage, and peri-infarct ischemia. The extent and transmurality of scar burden have been shown to have independent and incremental prognostic power over a range of left ventricular function. The extent of scarring at MR imaging is an important predictor of successful outcome after revascularization procedures, and extensive scarring in the lateral wall indicates poor outcome after cardiac resynchronization therapy. Scar size at MR imaging is also a useful surrogate end point in clinical trials. Finally, MR imaging can be used to detect complications of MI, such as aneurysms, pericarditis, ventricular septal defect, thrombus, and mitral regurgitation. Supplemental material available at http://radiographics.rsna.org/lookup/suppl/doi:10.1148/rg.335125722/-/DC1.

Myocardial scar identification based on analysis of Look-Locker and 3D late gadolinium enhanced MRI

The aim of this study is to introduce and evaluate an approach for objective and reproducible scar identification from late gadolinium enhanced (LGE) MR by analysis of LGE data with post-contrast T(1) mapping from a routinely acquired T(1) scout Look-Locker (LL) sequence. In 90 post-infarction patients, a LL sequence was acquired prior to a three-dimensional LGE sequence covering the entire left ventricle. In 60/90 patients (training set), the T(1) relaxation rates of remote myocardium and dense myocardial scar were linearly regressed to that of blood. The learned linear relationship was applied to 30/90 patients (validation set) to identify the remote myocardium and dense scar, and to normalize the LGE signal intensity to a range from 0 to 100 %. A 50 % threshold was applied to identify myocardial scar. In the validation set, two observers independently performed manual scar identification, annotated reference regions for the full-width-half-maxima (FWHM) and standard deviation (SD) method, and analyzed the LL sequence for the proposed method. Compared with the manual, FWHM, and SD methods, the proposed method demonstrated the highest inter-class correlation coefficient (0.997) and Dice overlap index (98.7 ± 1.3 %) between the two observers. The proposed method also showed excellent agreement with the gold-standard manual scar identification, with a Dice index of 89.8 ± 7.5 and 90.2 ± 6.6 % for the two observers, respectively. Combined analysis of LL and LGE sequences leads to objective and reproducible myocardial scar identification in post-infarction patients.

[Cardiac MRI: technology, clinical applications, and future directions]

The field of cardiovascular MRI has evolved rapidly over the past decade, feeding new applications across a broad spectrum of clinical and research areas. Advances in magnet hardware technology, and key developments such as segmented k-space acquisitions, advanced motion encoding techniques, ultra-rapid perfusion imaging and delayed myocardial enhancement imaging have all contributed to a revolution in how patients with ischemic and non-ischemic heart disease are diagnosed and treated. Actually, cardiac MRI is a widely accepted method as the "gold standard" for detection and characterization of many forms of cardiac diseases. The aim of this review is to present an overview of cardiac MRI technology, advances in clinical applications, and future directions.

Assessing myocardial recovery following ST-segment elevation myocardial infarction: short- and long-term perspectives using cardiovascular magnetic resonance

Myocardial recovery after revascularization for ST-segment elevation myocardial infarction (STEMI) remains a significant diagnostic and, despite novel treatment strategies, a therapeutic challenge. Cardiovascular magnetic resonance (CMR) has emerged as a valuable clinical and research tool after acute STEMI. It represents the gold standard for functional and morphological evaluation of the left ventricle. Gadolinium-based perfusion and late-enhancement viability imaging has expanded our knowledge about the underlying pathologies of inadequate myocardial recovery. T2-weighted imaging of myocardial salvage after early reperfusion of the infarct-related artery underlines the effectiveness of current invasive treatment for STEMI. In the last decade, the number of publications on CMR after acute STEMI continued to rise, with no plateau in sight. Currently, CMR research is gathering robust prognostic data on standardized CMR protocols with the aim to substantially improve patient care and prognosis. Beyond established CMR protocols, more specific methods such as magnetic resonance relaxometry, myocardial tagging, 4D phase-contrast imaging and novel superparamagnetic contrast agents are emerging. This review will discuss the currently available data on the use of CMR after acute STEMI and take a brief look at developing new methods currently under investigation.

Fat deposition in dilated cardiomyopathy assessed by CMR

OBJECTIVES

The aim of this study was to prospectively investigate the prevalence of fat deposition in idiopathic dilated cardiomyopathy (DCM) by fat-water separation imaging. An auxiliary aim was to determine the relationship between left ventricular (LV) fat deposition and characteristic myocardial fibrosis, as well as cardiac functional parameters.

BACKGROUND

Idiopathic DCM remains the most common cause of heart failure in young people referred for cardiac transplantation; little is known about the clinical value of fat deposition in DCM.

METHODS

A total of 124 patients with DCM were studied after written informed consent was obtained. The magnetic resonance imaging scan protocols included a series of short-axis LV cine imaging for functional analysis, fat-water separation imaging, and late gadolinium enhancement (LGE) imaging. Fat deposition and fibrosis location were compared to the scar regions on LGE images using a 17-segment model. Statistical comparisons of LV global functional parameters, fibrosis volumes, and fat deposition were carried out using the Pearson correlation, Student t test, and multiple regressions.

RESULTS

The patients had a 41.9% (52 of 124) prevalence of positive LGE, and 12.9% (16 of 124) fat deposition prevalence was found in this DCM cohort. The patients with fat deposition had larger LV end-diastolic volume (LVEDV) index (140.8 ± 20.2 ml/m(2) vs. 123.4 ± 15.8 ml/m(2); p < 0.01), larger LV end-systolic volume (LVESV) index (111.3 ± 19.2 ml/m(2) vs. 87.0 ± 20.3 ml/m(2); p < 0.01), and decreased LV ejection fraction (LVEF) (21.1 ± 7.1% vs. 30.0 ± 10.7%; p < 0.01). Higher volumes of LGE were found in the group with myocardial fat deposition (18.39 ± 9.0 ml vs. 13.40 ± 6.54 ml; p = 0.001), as well as a higher percentage of LGE/LV mass (19.11 ± 7.78% vs. 13.60 ± 4.58%; p = 0.000). The volume of fat deposition was correlated with scar volume, LVEF, LVEDV index, and LVESV index.

CONCLUSIONS

Fat deposition is a common phenomenon in DCM, and it is associated with DCM characteristics such as fibrosis volume and LV function.

Cardiac imaging techniques for physicians: late enhancement

Late enhancement imaging is used to diagnose and characterize a wide range of ischemic and nonischemic cardiomyopathies, and its use has become ubiquitous in the cardiac MR exam. As the use of late enhancement imaging has matured and the span of applications has widened, the demands on image quality have grown. The characterization of subendocardial MI now includes the accurate quantification of scar size, shape, and characterization of borders which have been shown to have prognostic significance. More diverse patterns of late enhancement including patchy, mid-wall, subepicardial, or diffuse enhancement are of interest in diagnosing nonischemic cardiomyopathies. As clinicians are examining late enhancement images for more subtle indication of fibrosis, the demand for lower artifacts has increased. A range of new techniques have emerged to improve the speed and quality of late enhancement imaging including: methods for acquisition during free breathing, and fat water separated imaging for characterizing fibrofatty infiltration and reduction of artifacts related to the presence of fat. Methods for quantification of T1 and extracellular volume fraction are emerging to tackle the issue of discriminating globally diffuse fibrosis from normal healthy tissue which is challenging using conventional late enhancement methods. The aim of this review will be to describe the current state of the art and to provide a guide to various clinical protocols that are commonly used.

Administration of cardiac stem cells in patients with ischemic cardiomyopathy: the SCIPIO trial: surgical aspects and interim analysis of myocardial function and viability by magnetic resonance

BACKGROUND

SCIPIO is a first-in-human, phase 1, randomized, open-label trial of autologous c-kit(+) cardiac stem cells (CSCs) in patients with heart failure of ischemic etiology undergoing coronary artery bypass grafting (CABG). In the present study, we report the surgical aspects and interim cardiac magnetic resonance (CMR) results.

METHODS AND RESULTS

A total of 33 patients (20 CSC-treated and 13 control subjects) met final eligibility criteria and were enrolled in SCIPIO. CSCs were isolated from the right atrial appendage harvested and processed during surgery. Harvesting did not affect cardiopulmonary bypass, cross-clamp, or surgical times. In CSC-treated patients, CMR showed a marked increase in both LVEF (from 27.5 ± 1.6% to 35.1 ± 2.4% [P=0.004, n=8] and 41.2 ± 4.5% [P=0.013, n=5] at 4 and 12 months after CSC infusion, respectively) and regional EF in the CSC-infused territory. Infarct size (late gadolinium enhancement) decreased after CSC infusion (by manual delineation: -6.9 ± 1.5 g [-22.7%] at 4 months [P=0.002, n=9] and -9.8 ± 3.5 g [-30.2%] at 12 months [P=0.039, n=6]). LV nonviable mass decreased even more (-11.9 ± 2.5 g [-49.7%] at 4 months [P=0.001] and -14.7 ± 3.9 g [-58.6%] at 12 months [P=0.013]), whereas LV viable mass increased (+11.6 ± 5.1 g at 4 months after CSC infusion [P=0.055] and +31.5 ± 11.0 g at 12 months [P=0.035]).

CONCLUSIONS

Isolation of CSCs from cardiac tissue obtained in the operating room is feasible and does not alter practices during CABG surgery. CMR shows that CSC infusion produces a striking improvement in both global and regional LV function, a reduction in infarct size, and an increase in viable tissue that persist at least 1 year and are consistent with cardiac regeneration.

CLINICAL TRIAL REGISTRATION

This study is registered with clinicaltrials.gov, trial number NCT00474461.

Different algorithms for quantitative analysis of myocardial infarction with DE MRI: comparison with autopsy specimen measurements

RATIONALE AND OBJECTIVES

To compare two semiautomated methods for measurement of infarcted myocardium area on delayed contrast enhanced magnetic resonance imaging, with histopathology findings as standard of reference.

MATERIALS AND METHODS

Percentage area of myocardial infarction was measured in 10 Yorkshire landrace pigs manually and using two semiautomated methods. The first (standard deviation method) used two operator-selected regions of interest (ROIs) and nine different cutoff values (one to nine times the standard deviation of signal intensity in normal myocardium) to identify infarction. The second (threshold method) used threshold values based on percentages of maximum signal intensity to identify infarction. Results were compared with histopathology findings.

RESULTS

Difference between percentage area of infarction obtained with standard deviation method and autopsy specimens was in the range: -13.5% to +13.2%. With threshold method (thresholds from 30% to 90% of signal intensity), difference was -15% to +23%. Manual contouring underestimated infarcted area by 2% comparing to autopsy results. The best agreement between histopathology and semi-automated software was achieved for 4 standard deviations with standard deviation method: difference -0.45%, and for a percentage threshold of 70% (difference +0.67%) with threshold method. However, with standard deviation method, there was statistically significant difference between ROIs based on their location in viable myocardium: mean difference 1.7 ± 4%, P < .0001.

CONCLUSION

Semiautomated measurement of myocardial infarcted area on delayed enhanced magnetic resonance images performs well compared to autopsy. The threshold method, based on percentages of maximum signal intensity is preferable over standard deviation method, which is more susceptible to variability from location of ROIs within viable myocardium.

Cardiac magnetic resonance imaging parameters as surrogate endpoints in clinical trials of acute myocardial infarction

Cardiac magnetic resonance (CMR) offers a variety of parameters potentially suited as surrogate endpoints in clinical trials of acute myocardial infarction such as infarct size, myocardial salvage, microvascular obstruction or left ventricular volumes and ejection fraction. The present article reviews each of these parameters with regard to the pathophysiological basis, practical aspects, validity, reliability and its relative value (strengths and limitations) as compared to competitive modalities. Randomized controlled trials of acute myocardial infarction which have used CMR parameters as a primary endpoint are presented.

Cardiac magnetic resonance imaging parameters as surrogate endpoints in clinical trials of acute myocardial infarction

Cardiac magnetic resonance (CMR) offers a variety of parameters potentially suited as surrogate endpoints in clinical trials of acute myocardial infarction such as infarct size, myocardial salvage, microvascular obstruction or left ventricular volumes and ejection fraction. The present article reviews each of these parameters with regard to the pathophysiological basis, practical aspects, validity, reliability and its relative value (strengths and limitations) as compared to competitive modalities. Randomized controlled trials of acute myocardial infarction which have used CMR parameters as a primary endpoint are presented.

Bright-blood T2-weighted MRI has higher diagnostic accuracy than dark-blood short tau inversion recovery MRI for detection of acute myocardial infarction and for assessment of the ischemic area at risk and myocardial salvage

BACKGROUND

T2-Weighted MRI reveals myocardial edema and enables estimation of the ischemic area at risk and myocardial salvage in patients with acute myocardial infarction (MI). We compared the diagnostic accuracy of a new bright-blood T2-weighted with a standard black blood T2-weighted MRI in patients with acute MI.

METHODS AND RESULTS

A breath-hold, bright-blood T2-weighted, Acquisition for Cardiac Unified T2 Edema pulse sequence with normalization for coil sensitivity and a breath-hold T2 dark-blood short tau inversion recovery sequence were used to depict the area at risk in 54 consecutive acute MI patients. Infarct size was measured on gadolinium late contrast enhancement images. Compared with dark-blood T2-weighted MRI, consensus agreements between independent observers for identification of myocardial edema were higher with bright-blood T2-weighted MRI when evaluated per patient (P<0.001) and per segment of left ventricle (P<0.001). Compared with bright-blood T2-weighted MRI, dark-blood T2-weighted MRI underestimated the area at risk compared with infarct size (P<0.001). The 95% limits of agreement for interobserver agreements for the ischemic area at risk and myocardial salvage were wider with dark-blood T2-weighted MRI than with bright-blood T2-weighted MRI. Bright blood enabled more accurate identification of the culprit coronary artery with correct identification in 94% of cases compared with 61% for dark blood (P<0.001).

CONCLUSIONS

Bright-blood T2-weighted MRI has higher diagnostic accuracy than dark-blood T2-weighted MRI. Additionally, dark-blood T2-weighted MRI may underestimate area at risk and myocardial salvage.

Assessment of myocardial fibrosis with cardiovascular magnetic resonance

Diffuse interstitial or replacement myocardial fibrosis is a common feature of a broad variety of cardiomyopathies. Myocardial fibrosis leads to impaired cardiac diastolic and systolic function and is related to adverse cardiovascular events. Cardiovascular magnetic resonance (CMR) may uniquely characterize the extent of replacement fibrosis and may have prognostic value in various cardiomyopathies. Myocardial longitudinal relaxation time mapping is an emerging technique that could improve CMR's diagnostic accuracy, especially for interstitial diffuse myocardial fibrosis. As such, CMR could be integrated in the monitoring and therapeutic management of a large number of patients. This review summarizes the advantages and limitations of CMR for the assessment of myocardial fibrosis.

Reliability of myocardial salvage assessment by cardiac magnetic resonance imaging in acute reperfused myocardial infarction

Myocardial salvage assessed by cardiac magnetic resonance imaging (CMRI) holds promise as a surrogate endpoint in studies comparing different treatment strategies for ST-elevation myocardial infarction (STEMI). The aim of this study was to evaluate the reliability of salvaged myocardium measurements by CMRI. Twenty patients underwent CMRI on 2 consecutive days early after reperfused STEMI to assess the area at risk (AAR) on T2-weighted and final infarct size (IS) on delayed enhancement images. Myocardial salvage index (MSI) was calculated (AAR minus IS). Agreement between scans 1 and 2 for the AAR, IS and MSI were analyzed using Bland-Altman analyses. Inter- and intraobserver reliability were assessed. Paired t testing revealed a trend for a significant difference for MSI between scans 1 and 2 (scan 1: 43.8 ± 22.5; scan 2: 45.5 ± 22.0; P = 0.052). The average difference for AAR and IS between scan 1 and scan 2 was -0.5 (upper limit of agreement 5.4% of left ventricular [LV] volume; lower limit of agreement -6.4%LV) and 0.1%LV (upper limit of agreement 2.3%LV; lower limit of agreement -2.1%LV). The corresponding calculated MSI measurements showed a mean bias of -1.7 (upper limit of agreement 5.5; lower limit of agreement -8.9). Coefficients of repeatability for interobserver variability were 3.6%LV for AAR, 2.4%LV for IS and 5.4 for MSI. Likewise, for intraobserver variability, coefficients of repeatability were 5.0%LV (AAR), 2.4%LV (IS) and 4.8 (MSI). Assessment of myocardial salvage by CMRI shows acceptable reliability. Further validation studies and trials showing the prognostic value of myocardial salvage by CMRI are needed before routine implementation as a surrogate endpoint in STEMI trials.

Magnetic resonance imaging delineates the ischemic area at risk and myocardial salvage in patients with acute myocardial infarction

BACKGROUND

The area at risk (AAR) is a key determinant of myocardial infarction (MI) size. We investigated whether magnetic resonance imaging (MRI) measurement of AAR would be correlated with an angiographic AAR risk score in patients with acute MI.

METHODS AND RESULTS

Bright-blood, T2-prepared, steady-state, free-precession MRI was used to depict the AAR in 50 consecutive acute MI patients, whereas infarct size was measured on gadolinium late-contrast-enhancement images. AAR was also estimated by the APPROACH and DUKE angiographic jeopardy scores and ST-segment elevation score. Myocardial salvage was calculated as AAR minus infarct size. Results are mean ± SD unless specified otherwise. Patients were 61 ± 12 years of age, 76% had an ST-segment elevation MI, and 20% had a prior MI. All underwent MRI 4 ± 2 days after initial presentation. The relation between MRI and the APPROACH angiographic estimates of AAR was similar (overall size relative to left ventricular mass was 32 ± 12% vs 30 ± 12%, respectively, P=0.33), correlated well (r = 0.78, P < 0.0001), and had a 2.5% bias on Bland-Altman analysis. The DUKE jeopardy score underestimated AAR relative to infarct size and was correlated less well with MRI (r = 0.39, P = 0.0055). ST-segment elevation score underestimated infarct size in 19 subjects (50%) and was not correlated with MRI (r = 0.27, P = 0.06). Myocardial salvage varied according to Thrombolysis in Myocardial Infarction flow grade at the end of angiography/percutaneous coronary intervention (P = 0.04), and Thrombolysis in Myocardial Infarction flow grade was a univariable predictor of myocardial salvage (P = 0.011). In multivariable analyses, infarct size was predicted by T2-prepared, steady-state, free-precession MRI (P < 0.0001).

CONCLUSIONS

T2-prepared, steady-state, free-precession MRI delineates the AAR and enables estimation of myocardial salvage when coupled with a measurement of infarct size.

An automated quantification of the transmural myocardial infarct extent using cardiac DE-MR images

Evaluating myocardial viability is an important prognostic factor in the follow-up of infarctions. Delayed Enhancement magnetic resonance (DE-MR) imaging allows precise delineation of the infarct transmural extent. Visual interpretation is the most commonly used method to assess the myocardial infarction (MI) transmural extent. This study proposes to automate the segmentation of the (DE) images prior to the estimation of the extent of infarcted tissue. Indeed the segmentation of the myocardium was performed using cine contraction images which present a high contrast between cavity and myocardium. After the segmentation, the segmental transmurality is estimated on a conventional five point scale. A head to head comparison was performed between visual and quantitative analysis of infarct transmurality on DE-MR imaging. Results on 921 sub-segments (9 patients) showed an absolute agreement of 80% and a relative agreement (with one point difference) of 97%.

Cardiovascular magnetic resonance in patients with myocardial infarction: current and emerging applications

In patients with known or suspected myocardial infarction (MI), cardiovascular magnetic resonance (CMR) provides a comprehensive, multifaceted view of the heart. The data, including that from a recent multicenter clinical trial, indicate that delayed-enhancement cardiac magnetic resonance imaging (DE-CMR) is a well-validated, robust technique that can be easily implemented on scanners that are commonly available worldwide, with an effectiveness that clearly rivals the best available imaging techniques for the detection and assessment of acute and chronic MI. When patients present outside the diagnostic window of cardiac troponins, DE-CMR may be especially useful. Moreover, because DE-CMR can uniquely differentiate between ischemic and various nonischemic forms of myocardial injury, it may be helpful in cases of diagnostic uncertainty, such as in patients with classical features of MI in whom coronary angiography does not show a culprit lesion. Even after the diagnosis of MI has been made, CMR provides clinically relevant information by identifying residual viability, microvascular damage, stunning, and right ventricular infarction. In addition, post-MI sequelae, including left ventricular thrombus and pericarditis, are easily identified. Given that quantification of infarct size by DE-CMR is highly reproducible, this technique may provide a useful surrogate end point for clinical trials with appreciable reductions in sample size compared with alternative methods.

Myocardial fat deposition after left ventricular myocardial infarction: assessment by using MR water-fat separation imaging

PURPOSE

To prospectively investigate the prevalence of fat deposition in chronic myocardial infarction (MI) by using magnetic resonance (MR) fat-water separation imaging with sampling of the entire left ventricular (LV) myocardium. A subsidiary aim was to determine the relationship between LV fat deposition and scar characteristics, as well as regional and global cardiac functional parameters.

MATERIALS AND METHODS

Twenty-five patients with LV MI were evaluated in this prospective institutional review board-approved, Health Insurance Portability and Accountability Act-compliant study after they provided written informed consent. A 1.5-T MR system was used to perform volumetric cine, fat-sensitive, and late gadolinium-enhanced (LGE) infarct imaging. Water-fat separation was performed by using a three-point Dixon reconstruction from in- and opposed-phase black-blood gradient-echo images. Fat deposition location was compared with LGE infarct imaging by using a 17-segment model. Global and regional functional variables, LGE volumes, and fat deposition were compared by using the Pearson correlation, Student t test, and multiple regression.

RESULTS

A fat deposition prevalence of 68% was found in areas of chronic MI. The patients with fat deposition had larger infarctions (30.0 mL +/- 15.1 [standard deviation] vs 14.8 mL +/- 6.1; P = .002), decreased wall thickening (2.3% +/- 20.0 vs 37.8% +/- 34.4; P = .003), and impaired endocardial wall motion (2.9 mm +/- 2.0 vs 5.8 mm +/- 2.6; P = .007). The volume of fat deposition was correlated with infarct volume, LV ejection fraction, LV end-diastolic volume index, and LV end-systolic volume index.

CONCLUSION

There is a high prevalence of fat deposition in healed MI. It is associated with post-infarction characteristics including infarct volume, LV mass, wall thickness, wall thickening, and wall motion.

Quantification of late gadolinium enhanced CMR in viability assessment in chronic ischemic heart disease: a comparison to functional outcome

BACKGROUND

Quantification of late gadolinium enhanced cardiovascular magnetic resonance (LGE CMR) by objective window setting increases reproducibility and facilitates multicenter comparison and cooperation. So far, quantification methods or models have only been validated to postmortem animal studies. This study was undertaken to evaluate quantification of LGE in relation to the clinical standard of viability, i.e. functional outcome after revascularization.Thirty-eight patients with chronic ischemic myocardial dysfunction underwent cine and LGE 1 month before and cine CMR 6 months after coronary revascularization. Enhancement was quantified by thresholding window setting at: 2-8 SD above mean signal intensity of a remote normal region, and according to the full width at half maximum method (FWHM). Dysfunctional segments were divided in 5 groups according to segmental extent of enhancement (SEE): SEE 1--no enhancement to SEE 5--76-100% with each quantification method.

RESULTS

Quantification methods had a strong influence on SEE and total infarct size. Multilevel analysis showed that thresholding contrast images at 6 SD best predicted segmental functional outcome after revascularization, but the difference with other methods was small and non-significant.

CONCLUSION

Simple thresholding techniques strongly influence global and segmental extent of LGE, but have relatively little influence on the accuracy to predict segmental functional improvement after revascularization.

Fat-water separated delayed hyperenhanced myocardial infarct imaging

Fat deposition associated with myocardial infarction (MI) has been reported as a commonly occurring phenomenon. Magnetic resonance imaging (MRI) has the ability to efficiently detect MI using T(1)-sensitive contrast-enhanced sequences and fat via its resonant frequency shift. In this work, the feasibility of fat-water separation applied to the conventional delayed hyperenhanced (DHE) MI imaging technique is demonstrated. A three-point Dixon acquisition and reconstruction was combined with an inversion recovery gradient-echo pulse sequence. This allowed fat-water separation along with T(1) sensitive imaging after injection of a gadolinium contrast agent. The technique is demonstrated in phantom experiments and three subjects with chronic MI. Areas of infarction were well defined as conventional hyperenhancement in water images. In two cases, fatty deposition was detected in fat images and confirmed by precontrast opposed-phase imaging.

Reperfusion hemorrhage following acute myocardial infarction: assessment with T2* mapping and effect on measuring the area at risk

Research ethics committee approval and informed consent were obtained. The purpose of this study was to assess the feasibility of multiecho T2* mapping of the heart for detecting reperfusion hemorrhage following percutaneous primary coronary intervention (PPCI) for acute myocardial infarction, and to measure the effect of hemorrhage on quantifying the ischemic area at risk (IAR) on T2-weighted magnetic resonance images. Fifteen patients (mean age, 59 years; 13 men, two women) were imaged a mean of 3.2 days following PPCI. The mean area of hemorrhage, indicated by a T2* decay constant of less than 20 msec, was 5.0% +/- 4.9 (standard deviation) at the level of the infarct and this correlated with the infarct (r(2) = 0.76, P < .01) and microvascular obstruction (r(2) = 0.75, P < .01) volumes. When 5% or less hemorrhage was present, the IAR was underestimated by 50% at a standard deviation threshold level of five, compared with a boundary detection tool (21.8% vs 44.0%, P < .05). T2* mapping is feasible for quantifying post-reperfusion hemorrhage and boundary detection is required to accurately assess the IAR when hemorrhage is present.