Myocardial infarction: optimization of inversion times at delayed contrast-enhanced MR imaging

Motion-compensated T1 mapping in cardiovascular magnetic resonance imaging: a technical review

T 1 mapping is becoming a staple magnetic resonance imaging method for diagnosing myocardial diseases such as ischemic cardiomyopathy, hypertrophic cardiomyopathy, myocarditis, and more. Clinically, most T 1 mapping sequences acquire a single slice at a single cardiac phase across a 10 to 15-heartbeat breath-hold, with one to three slices acquired in total. This leaves opportunities for improving patient comfort and information density by acquiring data across multiple cardiac phases in free-running acquisitions and across multiple respiratory phases in free-breathing acquisitions. Scanning in the presence of cardiac and respiratory motion requires more complex motion characterization and compensation. Most clinical mapping sequences use 2D single-slice acquisitions; however newer techniques allow for motion-compensated reconstructions in three dimensions and beyond. To further address confounding factors and improve measurement accuracy, T 1 maps can be acquired jointly with other quantitative parameters such as T 2 , T 2 ∗ , fat fraction, and more. These multiparametric acquisitions allow for constrained reconstruction approaches that isolate contributions to T 1 from other motion and relaxation mechanisms. In this review, we examine the state of the literature in motion-corrected and motion-resolved T 1 mapping, with potential future directions for further technical development and clinical translation.

Coronary Optical Coherence Tomography and Cardiac Magnetic Resonance Imaging to Determine Underlying Causes of Myocardial Infarction With Nonobstructive Coronary Arteries in Women

BACKGROUND

Myocardial infarction with nonobstructive coronary arteries (MINOCA) occurs in 6% to 15% of myocardial infarctions (MIs) and disproportionately affects women. Scientific statements recommend multimodality imaging in MINOCA to define the underlying cause. We performed coronary optical coherence tomography (OCT) and cardiac magnetic resonance (CMR) imaging to assess mechanisms of MINOCA.

METHODS

In this prospective, multicenter, international, observational study, we enrolled women with a clinical diagnosis of myocardial infarction. If invasive coronary angiography revealed <50% stenosis in all major arteries, multivessel OCT was performed, followed by CMR (cine imaging, late gadolinium enhancement, and T2-weighted imaging and T1 mapping). Angiography, OCT, and CMR were evaluated at blinded, independent core laboratories. Culprit lesions identified by OCT were classified as definite or possible. The CMR core laboratory identified ischemia-related and nonischemic myocardial injury. Imaging results were combined to determine the mechanism of MINOCA, when possible.

RESULTS

Among 301 women enrolled at 16 sites, 170 were diagnosed with MINOCA, of whom 145 had adequate OCT image quality for analysis; 116 of these underwent CMR. A definite or possible culprit lesion was identified by OCT in 46.2% (67/145) of participants, most commonly plaque rupture, intraplaque cavity, or layered plaque. CMR was abnormal in 74.1% (86/116) of participants. An ischemic pattern of CMR abnormalities (infarction or myocardial edema in a coronary territory) was present in 53.4% (62/116) of participants undergoing CMR. A nonischemic pattern of CMR abnormalities (myocarditis, takotsubo syndrome, or nonischemic cardiomyopathy) was present in 20.7% (24/116). A cause of MINOCA was identified in 84.5% (98/116) of the women with multimodality imaging, higher than with OCT alone (P<0.001) or CMR alone (P=0.001). An ischemic cause was identified in 63.8% of women with MINOCA (74/116), a nonischemic cause was identified in 20.7% (24/116) of the women, and no mechanism was identified in 15.5% (18/116).

CONCLUSIONS

Multimodality imaging with coronary OCT and CMR identified potential mechanisms in 84.5% of women with a diagnosis of MINOCA, 75.5% of which were ischemic and 24.5% of which were nonischemic, alternate diagnoses to myocardial infarction. Identification of the cause of MINOCA is feasible and has the potential to guide medical therapy for secondary prevention. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT02905357.

Single breath-hold compressed sensing real-time cine imaging to assess left ventricular motion in myocardial infarction

PURPOSE

To evaluate the reliability of a real-time compressed sensing (CS) cine sequence for the detection of left ventricular wall motion disorders after myocardial infarction in comparison with the reference steady-state free precession cine sequence.

MATERIALS AND METHODS

One hundred consecutive adult patients referred for either initial work-up or follow-up by cardiac magnetic resonance (CMR) in the context of myocardial infarction were prospectively included. There were 77 men and 23 women with a mean age of 63.12±11.3 (SD) years (range: 29-89 years). Each patient underwent the reference segmented multi-breath-hold steady-state free precession cine sequence including one short-axis stack and both vertical and horizontal long-axis slices (SSFP_ref) and the CS real-time single-breath-hold evaluated sequence (CS_rt) providing the same slices. Wall motion disorders were independently and blindly assessed with both sequences by two radiologists, using the American Heart Association left ventricle segmentation. Paired Wilcoxon signed-rank test was used to search for differences in wall motion disorders conspicuity between both sequences and receiver operating characteristic curve (ROC) analysis was performed to assess the diagnosis performance of CS_rt sequence using SSFP_ref as the reference method.

RESULTS

Each patient had at least one cardiac segment with wall motion abnormality on SSFP_ref and CS_rt images. The 1700 segments analyzed with SSFP_ref were classified as normokinetic (360/1700; 21.2%), hypokinetic (783/1700; 46.1%), akinetic (526/1700; 30.9%) or dyskinetic (31/1700; 1.8%). Sensitivity and specificity of the CS sequence were 99.6% (95% CI: 99.1-99.9%) and 99.7% (95% CI: 98.5-100%), respectively. Area under ROC of CS_rt diagnosis performance was 0.997 (95% CI: 0.993-0.999).

CONCLUSION

CS real-time cine imaging significantly reduces acquisition time without compromising the conspicuity of left ventricular -wall motion disorders in the context of myocardial infarction.

Validation of black blood late gadolinium enhancement (LGE) for evaluation of myocardial infarction in patients with or without pathological Q-wave on electrocardiogram (ECG)

Background

The pathological Q-wave (QW) is an important indicator of infarcted myocardial volume indicating a worse prognosis compared to non-Q-wave (NQW) infarctions. Traditional classification divides infarcts into transmural and non-transmural based on QW and NQW. This view has been challenged by the advent of late gadolinium enhancement (LGE) MR imaging. Conventional LGE (Conv-LGE) detection of subendocardial MI is limited by bright blood pool. Dark Blood LGE imaging (DB-LGE) nulls the blood pool improving the conspicuity and accuracy of detection of subendocardial infarcts. We hypothesize that improved detection of subendocardial enhancement with DB-LGE will result in improved correlation of electrocardiogram (ECG) and extent of infarction.

Methods

Sixty-four clinically confirmed infarction patients were enrolled in this prospective study. All the participants underwent cardiac MR imaging including conv-LGE and DB-LGE. Twelve-lead ECG were performed on the same day. The patients were divided into QW and NQW groups by one experienced cardiologist. MI quantitation was by MI% (the ratio of MI volume to whole myocardial volume) and transmural grading, compared using paired t-test and Wilcoxon-test, respectively. The image quality obtained by Conv-LGE and DB-LGE were evaluated according to the signal intensity ratio (SIR) and contrast-to-noise ratio (CNR).

Results

Fifty-six subjects were enrolled in the final analysis [23 (41%) QW and 33 (59%) NQW infarcts]. For the QW cohort, both sequences classified infarcts as transmural in 21/23 (91%) subjects and subendocardial in 2/23 (9%). For the NQW cohort, both sequences classified infarcts as transmural in 16/33 (48%) subjects and subendocardial in 17/33 (52%). Using BB-LGE there were significant differences in detecting subendocardial infarcts in QW and NQW cohorts (Z=-5.85, P<0.001). The MI% of QW group was greater than in NQW group (24.2±10.3 vs.15.9±9.8, P=0.003). Compared to Conv-LGE, BB-LGE provided higher CNR and SIR between infarcted myocardium and blood pool (6.3±2.6 vs. 2.1±1.3, P<0.001; 5.4±1.9 vs. 1.3±0.2, P<0.001). BB-LGE detected more subendocardial infarcted segments in the QW group and NQW group (Z=-4.24, P<0.001; Z=-5.57, P<0.001). The larger MI% was displayed in BB-LGE than in Conv-LGE in both QW group and NQW group (24.2±10.3 vs. 22.6±10.3, P<0.001; 15.9±9.8 vs.14.6±9.6, P=0.001).

Conclusions

Compared to conventional LGE, DB-LGE can provide more accurate detection and characterization of infarction in terms of transmurality and subendocardial extent. This is important for evaluating QW and NQW MIs. Due to nulling the high signal of blood pool, DB-LGE can effectively improve the identification of subendocardial MI which may be missed on conventional LGE. Therefore, in both QW and NQW MIs, DB-LGE detects more subendocardial MIs and larger MI% is found. This may facilitate more accurate quantitative MR assessment of both QW and NQW MIs and further empower LGE volume as a predictive biomarker.

Comparison of fast multi-slice and standard segmented techniques for detection of late gadolinium enhancement in ischemic and non-ischemic cardiomyopathy - a prospective clinical cardiovascular magnetic resonance trial

BACKGROUND

Segmented phase-sensitive inversion recovery (PSIR) cardiovascular magnetic resonance (CMR) sequences are reference standard for non-invasive evaluation of myocardial fibrosis using late gadolinium enhancement (LGE). Several multi-slice LGE sequences have been introduced for faster acquisition in patients with arrhythmia and insufficient breathhold capability. The aim of this study was to assess the accuracy of several multi-slice LGE sequences to detect and quantify myocardial fibrosis in patients with ischemic and non-ischemic myocardial disease.

METHODS

Patients with known or suspected LGE due to chronic infarction, inflammatory myocardial disease and hypertrophic cardiomyopathy (HCM) were prospectively recruited. LGE images were acquired 10-20 min after administration of 0.2 mmol/kg gadolinium-based contrast agent. Three different LGE sequences were acquired: a segmented, single-slice/single-breath-hold fast low angle shot PSIR sequence (FLASH-PSIR), a multi-slice balanced steady-state free precession inversion recovery sequence (bSSFP-IR) and a multi-slice bSSFP-PSIR sequence during breathhold and free breathing. Image quality was evaluated with a 4-point scoring system. Contrast-to-noise ratios (CNR) and acquisition time were evaluated. LGE was quantitatively assessed using a semi-automated threshold method. Differences in size of fibrosis were analyzed using Bland-Altman analysis.

RESULTS

Three hundred twelve patients were enrolled (n = 212 chronic infarction, n = 47 inflammatory myocardial disease, n = 53 HCM) Of which 201 patients (67,4%) had detectable LGE (n = 143 with chronic infarction, n = 27 with inflammatory heart disease and n = 31 with HCM). Image quality and CNR were best on multi-slice bSSFP-PSIR. Acquisition times were significantly shorter for all multi-slice sequences (bSSFP-IR: 23.4 ± 7.2 s; bSSFP-PSIR: 21.9 ± 6.4 s) as compared to FLASH-PSIR (361.5 ± 95.33 s). There was no significant difference of mean LGE size for all sequences in all study groups (FLASH-PSIR: 8.96 ± 10.64 g; bSSFP-IR: 8.69 ± 10.75 g; bSSFP-PSIR: 9.05 ± 10.84 g; bSSFP-PSIR free breathing: 8.85 ± 10.71 g, p > 0.05). LGE size was not affected by arrhythmia or absence of breathhold on multi-slice LGE sequences.

CONCLUSIONS

Fast multi-slice and standard segmented LGE sequences are equivalent techniques for the assessment of myocardial fibrosis, independent of an ischemic or non-ischemic etiology. Even in patients with arrhythmia and insufficient breathhold capability, multi-slice sequences yield excellent image quality at significantly reduced scan time and may be used as standard LGE approach.

TRIAL REGISTRATION

ISRCTN48802295 (retrospectively registered).

Magnetic resonance imaging for characterizing myocardial diseases

The National Institute of Health defined cardiomyopathy as diseases of the heart muscle. These myocardial diseases have different etiology, structure and treatment. This review highlights the key imaging features of different myocardial diseases. It provides information on myocardial structure/orientation, perfusion, function and viability in diseases related to cardiomyopathy. The standard cardiac magnetic resonance imaging (MRI) sequences can reveal insight on left ventricular (LV) mass, volumes and regional contractile function in all types of cardiomyopathy diseases. Contrast enhanced MRI sequences allow visualization of different infarct patterns and sizes. Enhancement of myocardial inflammation and infarct (location, transmurality and pattern) on contrast enhanced MRI have been used to highlight the key differences in myocardial diseases, predict recovery of function and healing. The common feature in many forms of cardiomyopathy is the presence of diffuse-fibrosis. Currently, imaging sequences generating the most interest in cardiomyopathy include myocardial strain analysis, tissue mapping (T₁, T_2, T₂*) and extracellular volume (ECV) estimation techniques. MRI sequences have the potential to decode the etiology by showing various patterns of infarct and diffuse fibrosis in myocarditis, amyloidosis, sarcoidosis, hypertrophic cardiomyopathy due to aortic stenosis, restrictive cardiomyopathy, arrythmogenic right ventricular dysplasia and hypertension. Integrated PET/MRI system may add in the future more information for the diagnosis and progression of cardiomyopathy diseases. With the promise of high spatial/temporal resolution and 3D coverage, MRI will be an indispensible tool in diagnosis and monitoring the benefits of new therapies designed to treat myocardial diseases.

Updates on Stress Imaging Testing and Myocardial Viability With Advanced Imaging Modalities

OPINION STATEMENT

Non-invasive stress testing plays a key role in diagnosis and risk stratification in patients with coronary artery disease. Technical advances in CT, MRI, and PET have lead to increased utility of these modalities in myocardial perfusion imaging. The aim of the review is to provide a succinct update on CT, PET, and MRI for myocardial stress perfusion imaging.

Dark blood late enhancement imaging

BACKGROUND

Bright blood late gadolinium enhancement (LGE) imaging typically achieves excellent contrast between infarcted and normal myocardium. However, the contrast between the myocardial infarction (MI) and the blood pool is frequently suboptimal. A large fraction of infarctions caused by coronary artery disease are sub-endocardial and thus adjacent to the blood pool. It is not infrequent that sub-endocardial MIs are difficult to detect or clearly delineate.

METHODS

In this present work, an inversion recovery (IR) T2 preparation was combined with single shot steady state free precession imaging and respiratory motion corrected averaging to achieve dark blood LGE images with good signal to noise ratio while maintaining the desired spatial and temporal resolution. In this manner, imaging was conducted free-breathing, which has benefits for image quality, patient comfort, and clinical workflow in both adults and children. Furthermore, by using a phase sensitive inversion recovery reconstruction the blood signal may be made darker than the myocardium (i.e., negative signal values) thereby providing contrast between the blood and both the MI and remote myocardium. In the proposed approach, a single T1-map scout was used to measure the myocardial and blood T1 using a MOdified Look-Locker Inversion recovery (MOLLI) protocol and all protocol parameters were automatically calculated from these values within the sequence thereby simplifying the user interface.

RESULTS

The contrast to noise ratio (CNR) between MI and remote myocardium was measured in n = 30 subjects with subendocardial MI using both bright blood and dark blood protocols. The CNR for the dark blood protocol had a 13 % loss compared to the bright blood protocol. The CNR between the MI and blood pool was positive for all dark blood cases, and was negative in 63 % of the bright blood cases. The conspicuity of subendocardial fibrosis and MI was greatly improved by dark blood (DB) PSIR as well as the delineation of the subendocardial border.

CONCLUSIONS

Free-breathing, dark blood PSIR LGE imaging was demonstrated to improve the visualization of subendocardial MI and fibrosis in cases with low contrast with adjacent blood pool. The proposed method also improves visualization of thin walled fibrous structures such as atrial walls and valves, as well as papillary muscles.

Noninvasive mapping of endothelial dysfunction in myocardial ischemia by magnetic resonance imaging using an albumin-based contrast agent

Noninvasive preclinical methods for the characterization of myocardial vascular function are crucial to an understanding of the dynamics of ischemic cardiac disease. Ischemic heart disease is associated with myocardial endothelial dysfunction, resulting in leakage of plasma albumin into the extravascular space. These features can be harnessed in a novel noninvasive three-dimensional magnetic resonance imaging method to measure fractional blood volume (fBV) and vascular permeability (permeability-surface area product, PS) using labeled albumin as a blood pool contrast agent. C57BL/6 mice were imaged before and 3 days after myocardial infarction (MI). Following the quantification of endogenous myocardial R₁ , the dynamics of intravenously injected albumin-based contrast agent, extravasating from permeable myocardial blood vessels, were tracked on short-axis magnetic resonance images of the entire heart. This study successfully discriminated between infarcted and remote regions at 3 days post-infarct, based on a reduced fBV and increased PS in the infarcted region. These findings were confirmed using ex vivo fluorescence imaging and histology. We have demonstrated a novel method to quantify blood volume and permeability in the infarcted myocardium, providing an imaging biomarker for the assessment of endothelial dysfunction. This method has the potential to three-dimensionally visualize subtle changes in myocardial permeability and to track endothelial function for longitudinal cardiac studies determining pathophysiological processes during infarct healing.

Imaging cardiac morphology in hypertrophic cardiomyopathy: recent advances

PURPOSE OF REVIEW

To describe new cardiac MRI (CMR) findings on cardiac structure and myocardial composition in hypertrophic cardiomyopathy (HCM).

RECENT FINDINGS

Quantitative CMR assessment of replacement fibrosis and interstitial fibrosis can risk stratify HCM patients for adverse outcomes. Patients with global LVH (increased LV mass index) have more adverse outcomes. The HCM phenotype with a spiral distribution of hypertrophy entails a good prognosis. Myocardial noncompaction can be associated with HCM, as are papillary muscle and mitral apparatus abnormalities. Genotype positive, phenotype negative relatives of HCM probands may be detected by myocardial motion abnormalities. Emerging CMR methods for myocardial fiber disarray and altered myocardial stiffness may shed more light on cardiac structure, function and outcomes in HCM in coming years.

SUMMARY

CMR structural features of HCM, including severity and distribution of hypertrophy and fibrosis, can augment clinical evaluation of HCM. New CMR phenotypes, associated papillary muscle, mitral leaflet and myocardial noncompaction abnormalities, role of left atrial enlargement, findings in genotype positive phenotype negative HCM, and emerging methods for the detection of myocardial fiber disarray and altered myocardial stiffness may shed light in coming years.

CMR Guidance for Recanalization of Coronary Chronic Total Occlusion

OBJECTIVES

This study explored whether cardiac magnetic resonance (CMR) could help select patients who could benefit from revascularization by identifying inducible myocardial ischemia and viability in the perfusion territory of the artery with chronic total occlusion (CTO).

BACKGROUND

The benefit of revascularization using percutaneous coronary intervention (PCI) in CTO is controversial. CMR offers incomparable left ventricular (LV) systolic function assessment in addition to potent ischemic burden quantification and reliable myocardial viability analysis. Whether CMR guided CTO revascularization would be helpful to such patients has not yet been explored fully.

METHODS

A prospective study of 50 consecutive CTO patients was conducted. Of 50 patients undergoing baseline stress CMR, 32 (64%) were selected for recanalization based on the presence of significant inducible perfusion deficit and myocardial viability within the CTO arterial territory. Patients were rescanned 3 months after successful CTO recanalization.

RESULTS

At baseline, myocardial perfusion reserve (MPR) in the CTO territory was significantly reduced compared with the remote region (1.8 ± 0.72 vs. 2.2 ± 0.7; p = 0.01). MPR in the CTO region improved significantly after PCI (to 2.3 ± 0.9; p = 0.02 vs. baseline) with complete or near-complete resolution of CTO related perfusion defect in 90% of patients. Remote territory MPR was unchanged after PCI (2.5 ± 1.2; p = NS vs. baseline). The LV ejection fraction increased from 63 ± 13% to 67 ± 12% (p < 0.0001) and end-systolic volume decreased from 65 ± 38 to 56 ± 38 ml (p < 0.001) 3 months after CTO PCI. Importantly, despite minimal post-procedural infarction due to distal embolization and side branch occlusion in 8 of 32 patients (25%), the total Seattle Angina Questionnaire score improved from a median of 54 (range 45 to 74) at baseline to 89 (range 77 to 98) after CTO recanalization (p < 0.0001).

CONCLUSIONS

In this small group of patients showing CMR evidence of significant myocardial inducible perfusion defect and viability, CTO recanalization reduces ischemic burden, favors reverse remodeling, and ameliorates quality of life.

Improved respiratory efficiency of 3D late gadolinium enhancement imaging using the continuously adaptive windowing strategy (CLAWS)

PURPOSE

Acquisition durations of navigator-gated high-resolution three-dimensional late gadolinium enhancement studies may typically be up to 10 min, depending on the respiratory efficiency and heart rate. Implementation of the continuously adaptive windowing strategy (CLAWS) could increase respiratory efficiency, but the resulting non-smooth k-space acquisition order during gadolinium wash-out could result in increased artifact.

METHODS

Navigator-gated three-dimensional late gadolinium enhancement acquisitions were performed in 18 patients using tracking end-expiratory accept/reject (EE-ARA) and CLAWS algorithms in random order.

RESULTS

Retrospective analysis of the stored navigator data shows that CLAWS scan times are very close to (within 1%) or equal to the fastest achievable scan times while EE-ARA significantly extends the acquisition duration (P < 0.0001). EE-ARA acquisitions are 26% longer than CLAWS acquisitions (378 ± 104 s compared to 301 ± 85 s, P = 0.002). Image quality scores for CLAWS and EE-ARA acquisitions are not significantly different (4.1 ± 0.6 compared to 4.3 ± 0.6, P = ns). Numerical phantom simulations show that the non-uniform k-space ordering introduced by CLAWS results in slight, but not statistically significant, reductions in both blood signal-to-noise ratio (10%) and blood-myocardium contrast-to-noise ratio (12%).

CONCLUSIONS

CLAWS results in markedly reduced acquisition durations compared to EE-ARA without significant detriment to the image quality.

Cardiac MR imaging: current status and future direction

Coronary artery disease is currently a worldwide epidemic with increasing impact on healthcare systems. Magnetic resonance imaging (MRI) sequences give complementary information on LV function, regional perfusion, angiogenesis, myocardial viability and orientations of myocytes. T2-weighted short-tau inversion recovery (T2-STIR), fat suppression and black blood sequences have been frequently used for detecting edematous area at risk (AAR) of infarction. T2 mapping, however, indicated that the edematous reaction in acute myocardial infarct (AMI) is not stable and warranted the use of edematous area in evaluating therapies. On the other hand, cine MRI demonstrated reproducible data on LV function in healthy volunteers and LV remodeling in patients. Noninvasive first pass perfusion, using exogenous tracer (gadolinium-based contrast media) and arterial spin labeling MRI, using endogenous tracer (water), are sensitive and useful techniques for evaluating myocardial perfusion and angiogenesis. Recently, new strategies have been developed to quantify myocardial viability using T1-mapping and equilibrium contrast enhanced MR techniques because existing delayed contrast enhancement MRI (DE-MRI) sequences are limited in detecting patchy microinfarct and diffuse fibrosis. These new techniques were successfully used for characterizing diffuse myocardial fibrosis associated with myocarditis, amyloidosis, sarcoidosis heart failure, aortic hypertrophic cardiomyopathy, congenital heart disease, restrictive cardiomyopathy, arrhythmogenic right ventricular dysplasia and hypertension). Diffusion MRI provides information regarding microscopic tissue structure, while diffusion tensor imaging (DTI) helps to characterize the myocardium and monitor the process of LV remodeling after AMI. Novel trends in hybrid imaging, such as cardiac positron emission tomography (PET)/MRI and optical imaging/MRI, are recently under intensive investigation. With the promise of higher spatial-temporal resolution and 3D coverage in the near future, cardiac MRI will be an indispensible tool in the diagnosis of cardiac diseases, coronary intervention and myocardial therapeutic delivery.

Modified wideband three-dimensional late gadolinium enhancement MRI for patients with implantable cardiac devices

PURPOSE

To study the effects of cardiac devices on three-dimensional (3D) late gadolinium enhancement (LGE) MRI and to develop a 3D LGE protocol for implantable cardioverter defibrillator (ICD) patients with reduced image artifacts.

THEORY AND METHODS

The 3D LGE sequence was modified by implementing a wideband inversion pulse, which reduces hyperintensity artifacts, and by increasing bandwidth of the excitation pulse. The modified wideband 3D LGE sequence was tested in phantoms and evaluated in six volunteers and five patients with ICDs.

RESULTS

Phantom and in vivo studies results demonstrated extended signal void and ripple artifacts in 3D LGE that were associated with ICDs. The reason for these artifacts was slab profile distortion and the subsequent aliasing in the slice-encoding direction. The modified wideband 3D LGE provided significantly reduced ripple artifacts than 3D LGE with wideband inversion only. Comparison of 3D and 2D LGE images demonstrated improved spatial resolution of the heart using 3D LGE.

CONCLUSION

Increased bandwidth of the inversion and excitation pulses can significantly reduce image artifacts associated with ICDs. Our modified wideband 3D LGE protocol can be readily used for imaging patients with ICDs given appropriate safety guidelines are followed.

MOLLI and AIR T1 mapping pulse sequences yield different myocardial T1 and ECV measurements

Both post-contrast myocardial T1 and extracellular volume (ECV) have been reported to be associated with diffuse interstitial fibrosis. Recently, the cardiovascular magnetic resonance (CMR) field is recognizing that post-contrast myocardial T1 is sensitive to several confounders and migrating towards ECV as a measure of collagen volume fraction. Several recent studies using widely available Modified Look-Locker Inversion-recovery (MOLLI) have reported ECV cutoff values to distinguish between normal and diseased myocardium. It is unclear if these cutoff values are translatable to different T1 mapping pulse sequences such as arrhythmia-insensitive-rapid (AIR) cardiac T1 mapping, which was recently developed to rapidly image patients with cardiac rhythm disorders. We sought to evaluate, in well-controlled canine and pig experiments, the relative accuracy and precision, as well as intra- and inter-observer variability in data analysis, of ECV measured with AIR as compared with MOLLI. In 16 dogs, as expected, the mean T1 was significantly different (p < 0.001) between MOLLI (891 ± 373 ms) and AIR (1071 ± 503 ms), but, surprisingly, the mean ECV between MOLLI (21.8 ± 2.1%) and AIR (19.6 ± 2.4%) was also significantly different (p < 0.001). Both intra- and inter-observer agreements in T1 calculations were higher for MOLLI than AIR, but intra- and inter-observer agreements in ECV calculations were similar between MOLLI and AIR. In six pigs, the coefficient of repeatability (CR), as defined by the Bland-Altman analysis, in T1 calculation was considerably lower for MOLLI (32.5 ms) than AIR (82.3 ms), and the CR in ECV calculation was also lower for MOLLI (1.8%) than AIR (4.5%). In conclusion, this study shows that MOLLI and AIR yield significantly different T1 and ECV values in large animals and that MOLLI yields higher precision than AIR. Findings from this study suggest that CMR researchers must consider the specific pulse sequence when translating published ECV cutoff values into their own studies.

Wideband late gadolinium enhanced magnetic resonance imaging for imaging myocardial scar without image artefacts induced by implantable cardioverter-defibrillator: a feasibility study at 3 T

AIM

Late gadolinium enhanced (LGE) magnetic resonance imaging (MRI) is a useful tool for facilitating ventricular tachycardia (VT) ablation. Unfortunately, most VT ablation candidates often have prophylactic implantable cardioverter-defibrillator (ICD) and do not undergo cardiac MRI largely due to image artefacts generated by ICD. A prior study has reported success of 'wideband' LGE MRI for imaging myocardial scar without image artefacts induced by ICD at 1.5T. The purpose of this study was to widen the availability of wideband LGE MRI to 3T, since it has the potential to achieve higher spatial resolution than 1.5T.

METHODS AND RESULTS

We compared the performance of standard and wideband LGE MRI pulse sequences in phantoms and canines with myocardial lesions created by radiofrequency ablation. Standard LGE MRI produced image artefacts induced by ICD and 49% accuracy in detecting 97 myocardial scars examined in this study, whereas wideband LGE MRI produced artefact-free images and 94% accuracy in detecting scars. The mean image quality score (1 = nondiagnostic, 2 = poor, 3 = adequate, 4 = good, 5 = excellent) was significantly (P < 0.001) higher for wideband (3.7 ± 0.8) than for standard LGE MRI (2.1 ± 0.7). The mean artefact level score (1 = minimal, 2 = mild, 3 = moderate, 4 = severe, 5 = nondiagnostic) was significantly (P < 0.001) lower for wideband (2.1 ± 0.8) than for standard LGE MRI (4.0 ± 0.6). Wideband LGE MRI agreed better with gross pathology than standard LGE MRI.

CONCLUSION

This study demonstrates the feasibility of wideband LGE MRI for suppression of image artefacts induced by ICD at 3T.

Late gadolinium enhancement magnetic resonance imaging for the assessment of myocardial infarction: comparison of image quality between single and double doses of contrast agents

To compare the image quality of late gadolinium enhancement (LGE) cardiac magnetic resonance imaging (CMR) using a single dose of gadolinium contrast agent versus the conventional double dose for assessing myocardial infarction. This retrospective study examined 37 patients with chronic myocardial infarction who underwent LGE CMR using both inversion recovery (IR)-turbo fast low-angle shot magnitude-reconstructed and phase-sensitive images with two different dosages of gadolinium contrast agent: a single dose of 0.1 mmol/kg gadolinium-DTPA in 17 patients and a double dose of 0.2 mmol/kg in 20 patients. The contrast-to-noise ratio (CNR) and visual conspicuity between infarct and normal myocardium (CNRinfarct-normal, conspicuityinfarct-normal) and between infarct and left ventricular cavity (CNRinfarct-LVC, conspicuityinfarct-LVC) were compared. Interobserver agreement for the maximal transmural extent of infarction was also evaluated. CNRinfarct-normal was significantly higher with double-dose gadolinium contrast agent (15.5 ± 20.7 vs. 40.4 ± 16.1 in magnitude images and 9.5 ± 2.8 vs. 11.2 ± 2.7 in phase-sensitive images, P < 0.001) while conspicuityinfarct-normal showed no significant difference between the two groups (P > 0.05). Both CNRinfarct-LVC (7.7 ± 10.7 vs. -6.6 ± 19.0 in magnitude images and 4.1 ± 2.3 vs. -0.4 ± 4.1 in phase-sensitive images, P < 0.05) and conspicuityinfarct-LVC were significantly better with single-dose gadolinium contrast. Interobserver agreement for assessing the transmural extent of infarction was moderate in both groups: 0.591 for single-dose and 0.472 for double-dose. LGE CMR using a single dose of gadolinium contrast agent showed significantly better contrast between infarcted myocardium and left ventricular cavity lumen without a significant decrease in visual contrast between infarcted myocardium and normal myocardium, compared to a double dose.

Application of single shot free-breathing fast imaging employing steady state sequence in cardiac magnetic resonance imaging

OBJECTIVE

To investigate the imaging quality of single shot (SS) fast imaging employing steady state (FIESTA) sequence in contrast-enhanced cardiac magnetic resonance (MR) examination, in comparison with the segmented inversion recovery 2D fast gradient echo (IR FGRE) sequence.

MATERIALS AND METHODS

Fifty-two cases with suspected or known heart disease were enrolled in this study, including 24 patients who had enhanced myocardium in myocardial delayed enhancement (MDE). We analyzed the imaging quality of the sequences by measuring the myocardium and blood pool signal-to-noise ratios (SNR) and the contrast-to-noise ratios (CNR) of blood pool relative to normal myocardium and of enhanced myocardium relative to normal myocardium and compared the new sequences with traditional sequence.

RESULTS

The scanning time of SS FIESTA was significantly shortened as compared to IR FGRE. The differences in the image quality scores, enhanced myocardium (EM) mass and percentages, SNR(bp), SNR(myo), CNR(myo/bp) and CNR(l/bg) were not statistically significant between SS FIESTA and IR FGRE (P > 0.05). However, the difference in CNR(em/myo) was statistically significant between SS FIESTA and IR FGRE (P < 0.0001), with CNR(em/myo) of IR FGRE higher than SS FIESTA.

CONCLUSION

Single shot FIESTA speeded up the acquisition time, halving it to (27.6 ± 1.8 s) instead of 146 + 13.8 s (IR FGRE), it had higher SNR and CNR, and its image quality did not differ significantly from IR FGRE. The SS FIESTA is more suitable for patients with severely heart diseases or those unable to hold breath. 3D IR FGRE sequence had higher SNR(myo) than the others and it is suitable for displaying the subendocardial scar. However, it has more artefacts and poor imaging quality than IR FGRE.

Improved late gadolinium enhancement MR imaging for patients with implanted cardiac devices

PURPOSE

To propose and test a modified wideband late gadolinium enhancement (LGE) magnetic resonance (MR) imaging technique to overcome hyperintensity image artifacts caused by implanted cardiac devices.

MATERIALS AND METHODS

Written informed consent was obtained from all participants, and the HIPAA-compliant study protocol was approved by the institutional review board. Studies in phantoms and in a healthy volunteer were performed to test the hypothesis that the hyperintensity artifacts that are typically observed on LGE images in patients with implanted cardiac devices are caused by insufficient inversion of the affected myocardial signal. The conventional LGE MR imaging pulse sequence was modified by replacing the nonselective inversion pulse with a wideband inversion pulse. The modified LGE sequence, along with the conventional LGE sequence, was evaluated in 12 patients with implantable cardioverter defibrillators (ICDs) who were referred for cardiac MR imaging.

RESULTS

The ICD causes 2-6 kHz in frequency shift at locations 5-10 cm away from the device. This off-resonance falls outside the typical spectral bandwidth of the nonselective inversion pulse used in conventional LGE, which results in the hyperintensity artifact. In 10 of the 12 patients, the conventional LGE technique produced severe, uninterpretable hyperintensity artifacts in the anterior and lateral portions of the left ventricular wall. These artifacts were eliminated with use of the wideband LGE sequence, thereby enabling confident evaluation of myocardial viability.

CONCLUSION

The modified wideband LGE MR imaging technique eliminates the hyperintensity artifacts seen in patients with cardiac devices. The technique may enable LGE MR imaging in patients with cardiac devices, in whom LGE MR imaging otherwise could not be used for diagnosis.

Volumetric late gadolinium-enhanced myocardial imaging with retrospective inversion time selection

PURPOSE

To develop and validate a novel free-breathing 3D radial late gadolinium-enhanced magnetic resonance imaging technique (3D LGE-MRI) with isotropic resolution and retrospective inversion time (TI) selection for myocardial viability imaging.

MATERIALS AND METHODS

The 3D radial LGE-MRI method featuring an interleaved and bit-reversed radial k-space trajectory was evaluated in 12 subjects that also had clinical breath-hold Cartesian 2D LGE-MRI. The 3D LGE-MRI acquisition requires a predicted TI and a user-controlled data acquisition window that determines the sampling width around the predicted TI. Sliding window reconstructions with update rates of 1× the repetition time (TR) allow for a user selectable TI to obtain the maximum nulling of the myocardium. The retrospective nature of the acquisition allows the user to choose from a range of possible TI times centered on the expected TI. Those projections most corrupted by respiratory motion, as determined by a respiratory bellows signal, were resampled according to the diminishing variance algorithm. The quality of the left ventricular myocardial nulling on the 3D LGE-MRI and 2D LGE-MRI was assessed using a 4-point Likert scale by two experienced radiologists. Comparison of image quality scores for the two methods was performed using generalized estimating equations.

RESULTS

All 3D LGE-MRI cases produced similar nulling of myocardial signal as the 2D LGE-MRI. The image quality of myocardial nulling was not significantly different between the two acquisitions (mean nulling of 3.4 for 2D vs. 3.1 for 3D, and P = 0.0645). The average absolute deviation from mean scores was also not determined to be statistically significant (1.8 for 2D and 0.4 for 3D and P = 0.1673). Total acquisition time was ∼9 minutes for 3D LGE-MRI with voxel sizes ranging from 1.6(3) to 2.0(3) mm(3) . Conversely, the total imaging time was twice as long for the 2D DCE-MRI (>17 minutes) with an eight times larger voxel size of 1.4 × 2.2 × 7.0 mm.

CONCLUSION

The 3D LGE-MRI technique demonstrated in this study is a promising alternative for the assessment of myocardial viability in patients who have difficulty sustaining breath-holds for the clinical standard 2D LGE-MRI.

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.

Detection of papillary muscle infarction by late gadolinium enhancement: incremental value of short-inversion time vs. standard imaging

AIMS

Late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) imaging can detect myocardial scar in patients with myocardial infarction. The detection of papillary muscle infarction (PMI) may be difficult due to the bright blood signal. The aim of our study was to evaluate the incremental value of LGE CMR imaging using an inversion recovery (IR)-GRE with a short-inversion time (TI) over standard LGE imaging in identifying PMI.

METHODS AND RESULTS

Fifty-six patients with myocardial infarction were studied using a standard IR-GRE LGE sequence with an adjusted TI to null the signal intensity of normal myocardium and with a 3D IR-GRE with a short TI (<180 ms). Signal-to-noise and contrast-to-noise ratios (CNR) and the frequency of PMI were determined. Image quality and infarction sharpness were evaluated. The short-TI LGE sequence detected a higher number of PMI compared with standard LGE sequence (19/54 vs. 15/54) with an increased sharpness of PMI (84.2 vs. 53.3%). The CNR was higher between infarcted myocardium and blood (77.9 ± 60 vs. 19.3 ± 16, P < 0.001) and between PMI and blood (69.4 ± 51 vs. 39.4 ± 26, respectively, P = 0.0157).

CONCLUSIONS

Our data indicate that in patients with myocardial infarction, LGE CMR imaging using a short TI may be more sensitive than standard LGE imaging for the detection of PMI.

Contrast-enhanced cardiac magnetic resonance imaging

Cardiac magnetic resonance (CMR) imaging has significantly evolved in the past decade and is well established in the evaluation of coronary artery disease (CAD). The evaluation of cardiac anatomy and contractility by high-resolution CMR can be improved by using intravenous administration of gadolinium-based contrast agents. Delayed enhancement CMR imaging has become the gold standard for quantification of myocardial viability in CAD. Contrast-enhanced CMR imaging may circumvent the need for endomyocardial biopsy or localize the involved regions, thereby improving the diagnostic yield of this invasive procedure. The application of contrast-enhanced CMR as an advanced imaging technique for ischemic and nonischemic diseases is reviewed.

Evaluation of phase-sensitive versus magnitude reconstructed inversion recovery imaging for the assessment of myocardial infarction in mice with a clinical magnetic resonance scanner

PURPOSE

To evaluate phase-sensitive inversion-recovery (PSIR) imaging at 1.5 T in a mouse model of permanent coronary artery ligation as a potentially rapid and robust alternative for the accurate assessment of myocardial infarction (MI) by cardiac magnetic resonance imaging (MRI).

MATERIALS AND METHODS

PSIR late gadolinium enhancement (LGE) imaging was compared to conventional 2D segmented inversion-recovery imaging for the assessment of murine MI.

RESULTS

PSIR images provided comparable contrast and kinetics of intravenously injected gadopentetate dimeglumine (Gd-DTPA). At the mid-ventricular level there was good agreement between conventional IR and PSIR for infarct size assessment. After intravenous injection a limited time window of ∼6 minutes is available for delayed enhancement imaging in mice. Whole-heart infarct imaging with 1 mm thick slices was only possible in this restricted time frame when the PSIR method is applied, avoiding the need for repetitively adapting the correct inversion time. Infarct size determined by PSIR MRI demonstrated good agreement with postmortem histology. Infarct size determined by PSIR LGE MRI inversely correlates with left-ventricular function on day 7 after MI.

CONCLUSION

The PSIR technique provides stable and consistent contrast between hyperenhanced and remote myocardium independent of the selected inversion time (TI) and proved to be a robust, fast, and accurate tool for the assessment of MI in mice.

Extracellular volume fraction mapping in the myocardium, part 1: evaluation of an automated method

BACKGROUND

Disturbances in the myocardial extracellular volume fraction (ECV), such as diffuse or focal myocardial fibrosis or edema, are hallmarks of heart disease. Diffuse ECV changes are difficult to assess or quantify with cardiovascular magnetic resonance (CMR) using conventional late gadolinium enhancement (LGE), or pre- or post-contrast T1-mapping alone. ECV measurement circumvents factors that confound T1-weighted images or T1-maps, and has been shown to correlate well with diffuse myocardial fibrosis. The goal of this study was to develop and evaluate an automated method for producing a pixel-wise map of ECV that would be adequately robust for clinical work flow.

METHODS

ECV maps were automatically generated from T1-maps acquired pre- and post-contrast calibrated by blood hematocrit. The algorithm incorporates correction of respiratory motion that occurs due to insufficient breath-holding and due to misregistration between breath-holds, as well as automated identification of the blood pool. Images were visually scored on a 5-point scale from non-diagnostic (1) to excellent (5).

RESULTS

The quality score of ECV maps was 4.23 ± 0.83 (m ± SD), scored for n=600 maps from 338 patients with 83% either excellent or good. Co-registration of the pre-and post-contrast images improved the image quality for ECV maps in 81% of the cases. ECV of normal myocardium was 25.4 ± 2.5% (m ± SD) using motion correction and co-registration values and was 31.5 ± 8.7% without motion correction and co-registration.

CONCLUSIONS

Fully automated motion correction and co-registration of breath-holds significantly improve the quality of ECV maps, thus making the generation of ECV-maps feasible for clinical work flow.

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.

Optimization of myocardial nulling in pediatric cardiac MRI

BACKGROUND

Current protocols to determine optimal nulling time in late enhancement imaging using adult techniques may not apply to children.

OBJECTIVE

To determine the optimal nulling time in anesthetised children, with the hypothesis that this occurs earlier than in adults.

MATERIALS AND METHODS

Sedated cardiac MRI was performed in 12 children (median age: 12 months, range: 1-60 months). After gadolinium administration, scout images at 2, 3, 4 and 10 min and phase sensitive inversion recovery (PSIR) images from 5 to 10 min were obtained. Signal-to-noise ratio (SNR) and inversion time (TI) were determined. Quality of nulling was assessed according to a grading score by three observers. Data was analysed using linear regression, Kruskal-Wallis and quadratic-weighted kappa statistics.

RESULTS

One child with a cardiomyopathy had late enhancement. Good agreement in nulling occurred for scout images at 2 (κ = 0.69) and 3 (κ = 0.66) min and moderate agreement at 4 min (κ = 0.57). Agreement of PSIR images was moderate at 7 min (κ = 0.44) and poor-fair at other times. There were significant correlations between TI and scout time (r = 0.61, P < 0.0001), and SNR and kappa (r = 0.22, P = 0.017).

CONCLUSION

Scout images at 2-4 min can be used to determine the TI with little variability. Image quality for PSIR images was highest at 7 min and SNR optimal at 7-9 min. TI increases with time and should be adjusted frequently during imaging. Thus, nulling times in children differ from nulling times in adults when using standard adult techniques.

Cardiac MR imaging of nonischemic cardiomyopathies: imaging protocols and spectra of appearances

Recent technologic advances in cardiac magnetic resonance (MR) imaging have resulted in images with high spatial and temporal resolution and excellent myocardial tissue characterization. Cardiac MR is a valuable imaging technique for detection and assessment of the morphology and functional characteristics of the nonischemic cardiomyopathy. It has gained acceptance as a standalone imaging modality that can provide further information beyond the capabilities of traditional modalities such as echocardiography and angiography. Black-blood fast spin-echo MR images allow morphologic assessment of the heart with high spatial resolution, while T2-weighted MR images can depict acute myocardial edema. Contrast material-enhanced images can depict and be used to quantify myocardial edema, infiltration, and fibrosis. This review presents recommended cardiac MR protocols for and the spectrum of imaging appearances of the nonischemic cardiomyopathies.

Head-to-head comparison of eight late gadolinium-enhanced cardiac MR (LGE CMR) sequences at 1.5 tesla: from bench to bedside

PURPOSE

To compare-theoretically and experimentally-clinically available two-dimensional/three-dimensional (2D/3D), breathhold and non-breathhold, inversion-recovery (IR) gradient-echo (GRE) sequences used to differentiate between nonviable injured and normal myocardium with late gadolinium-enhanced techniques (IR-GRE2D sequence is used as a reference), and to evaluate their respective clinical benefit.

MATERIALS AND METHODS

Six breathhold (2D-IR-GRE, 3D-IR-GRE, balanced steady-state free precession 2D-IR-bSSFP and 3D-IR-bSSFP, phase-sensitive 2D-PSIR-GRE, and 2D-PSIR-bSSFP) and two non-breathhold late gadolinium-enhanced techniques (single-shot 2D-ssbSSFP and 2D-PSIR-ssbSSFP) were consecutively performed in 32 coronary artery disease patients with chronic myocardial infarction. Qualitative assessment and manual planimetry were performed by two independent observers. Quantitative assessment was based on percentage signal intensity elevation between injured and normal myocardium and contrast-to-noise ratio. Theoretical simulations were compared with experimental measurements performed on phantoms with various concentrations of gadolinium.

RESULTS

The 3D-IR-GRE image quality appeared better than the other 2D and 3D sequences, showing better delineation of complex nontransmural lesions, with significantly higher percentage signal intensity and contrast-to-noise ratio. PSIR techniques appeared more limited in differentiating sub-endocardial lesions and intracavity blood pool, but in all other cases were comparable to the other techniques. Single-shot PSIR-ssbSSFP appeared to be a valuable alternative technique when breathhold cannot be achieved.

CONCLUSION

We recommend 3D-IR-GRE as the method of choice for late gadolinium-enhanced cardiac magnetic resonance imaging in clinical practice.

Mechanisms of myocardial infarction in women without angiographically obstructive coronary artery disease

BACKGROUND

There is no angiographically demonstrable obstructive coronary artery disease (CAD) in a significant minority of patients with myocardial infarction, particularly women. We sought to determine the mechanism(s) of myocardial infarction in this setting using multiple imaging techniques.

METHODS AND RESULTS

Women with myocardial infarction were enrolled prospectively, before angiography, if possible. Women with ≥50% angiographic stenosis or use of vasospastic agents were excluded. Intravascular ultrasound was performed during angiography; cardiac magnetic resonance imaging was performed within 1 week. Fifty women (age, 57±13 years) had median peak troponin of 1.60 ng/mL; 11 had ST-segment elevation. Median diameter stenosis of the worst lesion was 20% by angiography; 15 patients (30%) had normal angiograms. Plaque disruption was observed in 16 of 42 patients (38%) undergoing intravascular ultrasound. There were abnormal myocardial cardiac magnetic resonance imaging findings in 26 of 44 patients (59%) undergoing cardiac magnetic resonance imaging, late gadolinium enhancement (LGE) in 17 patients, and T2 signal hyperintensity indicating edema in 9 additional patients. The most common LGE pattern was ischemic (transmural/subendocardial). Nonischemic LGE patterns (midmyocardial/subepicardial) were also observed. Although LGE was infrequent with plaque disruption, T2 signal hyperintensity was common with plaque disruption.

CONCLUSIONS

Plaque rupture and ulceration are common in women with myocardial infarction without angiographically demonstrable obstructive coronary artery disease. In addition, LGE is common in this cohort of women, with an ischemic pattern of injury most evident. Vasospasm and embolism are possible mechanisms of ischemic LGE without plaque disruption. Intravascular ultrasound and cardiac magnetic resonance imaging provide complementary mechanistic insights into female myocardial infarction patients without obstructive coronary artery disease and may be useful in identifying potential causes and therapies. Clinical Trial Registration- URL: http://www.clinicaltrials.gov. Unique identifier: NCT00798122.

Rapid T1 quantification based on 3D phase sensitive inversion recovery

Background

In Contrast Enhanced Magnetic Resonance Imaging fibrotic myocardium can be distinguished from healthy tissue using the difference in the longitudinal T₁ relaxation after administration of Gadolinium, the so-called Late Gd Enhancement. The purpose of this work was to measure the myocardial absolute T₁ post-Gd from a single breath-hold 3D Phase Sensitivity Inversion Recovery sequence (PSIR). Equations were derived to take the acquisition and saturation effects on the magnetization into account.

Methods

The accuracy of the method was investigated on phantoms and using simulations. The method was applied to a group of patients with suspected myocardial infarction where the absolute difference in relaxation of healthy and fibrotic myocardium was measured at about 15 minutes post-contrast. The evolution of the absolute R₁ relaxation rate (1/T₁) over time after contrast injection was followed for one patient and compared to T₁ mapping using Look-Locker. Based on the T₁ maps synthetic LGE images were reconstructed and compared to the conventional LGE images.

Results

The fitting algorithm is robust against variation in acquisition flip angle, the inversion delay time and cardiac arrhythmia. The observed relaxation rate of the myocardium is 1.2 s^-1, increasing to 6 - 7 s^-1 after contrast injection and decreasing to 2 - 2.5 s^-1 for healthy myocardium and to 3.5 - 4 s^-1 for fibrotic myocardium. Synthesized images based on the T₁ maps correspond very well to actual LGE images.

Conclusions

The method provides a robust quantification of post-Gd T₁ relaxation for a complete cardiac volume within a single breath-hold.

Gadolinium pharmacokinetics of chronic myocardial infarcts: Implications for late gadolinium-enhanced infarct imaging

PURPOSE

To monitor gadolinium pharmacokinetics in the hearts of patients with chronic myocardial infarcts and to determine the variability of contrast agent concentrations and accuracy of infarct detection over an hour time period.

MATERIALS AND METHODS

Twenty-five patients with chronic myocardial infarcts were examined. T1 measurements were performed every 2 minutes using an inversion recovery CINE balanced steady-state free precession technique. Paired differences in T1 values over time for the discrimination between the left ventricular (LV) bloodpool, viable, and infarct myocardium were statistically evaluated. The average change per 1, 5, and 10 minutes of the inversion time parameter for optimal nulling of viable myocardium was calculated. Receiver operator characteristic (ROC) curve analysis was performed to compare the performance of late gadolinium-enhanced infarct imaging at increasing delays after contrast agent administration.

RESULTS

Significantly different T1 values were reached after 10 minutes between the LV bloodpool, infarcted, and viable myocardium. The T1 difference between myocardial infarcts and the LV bloodpool increased over time, while the difference between viable myocardium and the LV bloodpool decreased. ROC curve analysis showed a decrease in performance of a fixed T1 value to discriminate between the LV bloodpool and viable myocardium over time, while there was a marked increase in the discrimination between the LV bloodpool and infarcted myocardium.

CONCLUSION

The ability to discriminate between infarcted myocardium and the LV bloodpool improves with an increasing delay after contrast agent administration while discrimination between viable myocardium and the LV bloodpool decreases.

Contrast-enhanced whole-heart MR coronary angiography at 3.0 T using the intravascular contrast agent gadofosveset

OBJECTIVES

The purpose of this study was to compare contrast-enhanced (CE) whole-heart coronary magnetic resonance angiography (MRA) at 3.0 T using gadofosveset to noncontrast-enhanced steady-state free precession (SSFP) coronary MRA at 1.5 T.

MATERIALS AND METHODS

A prospective randomized study was conducted among 20 healthy male volunteers. The same group of subjects underwent CE whole heart MRA at 3.0 T employing a 3D FLASH sequence with IR prepulse after gadofosveset injection as well as noncontrast-enhanced coronary MRA at 1.5 T using a 3D SSFP sequence with T2-preparation. Both techniques were performed using prospective ECG-triggering and adaptive respiratory gating. Acquisition time, signal-to-noise ratio of coronary blood, contrast-to-noise ratio (CNR) between coronaries and adjacent myocardium or epicardial fat, and image quality were evaluated in each case.

RESULTS

A significant increase of the overall CNR between coronary blood and adjacent myocardium was measured on images acquired at 3 T in comparison to 1.5 T. The mean values were 38.9 +/- 19.6 and 26.3 +/- 15.4, respectively (P[r] < 0.005). There was no significant difference in CNR between coronary blood and epicardial fat. The mean image quality for the proximal and mid coronary segments was not statistically different between 1.5 T and 3.0 T (P > 0.05), however, the distal coronary segments were rated significantly higher for the CE MRA at 3.0 T (P = 0.02). The average acquisition time (15.29 +/- 5.73 minutes at 1.5 T vs. 17.29 +/- 5.18 minutes at 3 T) and overall image quality (2.15 +/- 0.49 at 1.5 T vs. 2.35 +/- 0.39 at 3 T) were similar for both methods.

CONCLUSIONS

CE whole-heart coronary MRA at 3.0 T demonstrated higher overall CNR between coronary blood and myocardium and an improved image quality of the distal coronary segments compared with noncontrast-enhanced SSFP coronary MRA at 1.5 T.