T1-weighted magnetic resonance imaging shows fatty deposition after myocardial infarction

Noninvasive Assessment of Lipomatous Metaplasia as a Substrate for Ventricular Tachycardia in Chronic Infarct

Myocardial lipomatous metaplasia (LM) has been increasingly reported in patients with prior myocardial infarction. Cardiac magnetic resonance and cardiac contrast-enhanced computed tomography have been used to noninvasively detect and quantify myocardial LM in postinfarct patients, and may provide useful information for understanding cardiac mechanics, arrhythmia susceptibility, and prognosis. This review aims to summarize the advantages and disadvantages, clinical applications, and imaging features of different cardiac magnetic resonance sequences and cardiac contrast-enhanced computed tomography for LM detection and quantification. We also briefly summarize LM prevalence in different cohorts of postinfarct patients and review the clinical utility of cardiac imaging in exploring myocardial LM as an arrhythmogenic substrate in patients with prior myocardial infarction.

Artificial Intelligence for Contrast-Free MRI: Scar Assessment in Myocardial Infarction Using Deep Learning-Based Virtual Native Enhancement

BACKGROUND

Myocardial scars are assessed noninvasively using cardiovascular magnetic resonance late gadolinium enhancement (LGE) as an imaging gold standard. A contrast-free approach would provide many advantages, including a faster and cheaper scan without contrast-associated problems.

METHODS

Virtual native enhancement (VNE) is a novel technology that can produce virtual LGE-like images without the need for contrast. VNE combines cine imaging and native T1 maps to produce LGE-like images using artificial intelligence. VNE was developed for patients with previous myocardial infarction from 4271 data sets (912 patients); each data set comprises slice position-matched cine, T1 maps, and LGE images. After quality control, 3002 data sets (775 patients) were used for development and 291 data sets (68 patients) for testing. The VNE generator was trained using generative adversarial networks, using 2 adversarial discriminators to improve the image quality. The left ventricle was contoured semiautomatically. Myocardial scar volume was quantified using the full width at half maximum method. Scar transmurality was measured using the centerline chord method and visualized on bull's-eye plots. Lesion quantification by VNE and LGE was compared using linear regression, Pearson correlation (R), and intraclass correlation coefficients. Proof-of-principle histopathologic comparison of VNE in a porcine model of myocardial infarction also was performed.

RESULTS

VNE provided significantly better image quality than LGE on blinded analysis by 5 independent operators on 291 data sets (all P<0.001). VNE correlated strongly with LGE in quantifying scar size (R, 0.89; intraclass correlation coefficient, 0.94) and transmurality (R, 0.84; intraclass correlation coefficient, 0.90) in 66 patients (277 test data sets). Two cardiovascular magnetic resonance experts reviewed all test image slices and reported an overall accuracy of 84% for VNE in detecting scars when compared with LGE, with specificity of 100% and sensitivity of 77%. VNE also showed excellent visuospatial agreement with histopathology in 2 cases of a porcine model of myocardial infarction.

CONCLUSIONS

VNE demonstrated high agreement with LGE cardiovascular magnetic resonance for myocardial scar assessment in patients with previous myocardial infarction in visuospatial distribution and lesion quantification with superior image quality. VNE is a potentially transformative artificial intelligence-based technology with promise in reducing scan times and costs, increasing clinical throughput, and improving the accessibility of cardiovascular magnetic resonance in the near future.

Triglyceride-induced cardiac lipotoxicity is mitigated by Silybum marianum

BACKGROUND AND AIMS

Silybum marianum (SM) is an herbal product with cytoprotective and antioxidant properties. We have previously demonstrated that SM ameliorates ventricular remodeling and improves cardiac performance. Here, we evaluated whether SM could exert beneficial effects against cardiac lipotoxicity in a pig model of closed-chest myocardial infarction (MI).

METHODS

Study 1 investigated the effect of SM administration on lipid profile and any potential SM-related adverse effects. Animals received SM or placebo during 10 days and were afterward sacrificed. Study 2 evaluated the effectiveness of SM daily administration in reducing cardiac lipotoxicity in animals subjected to a 1.5h myocardial infarction (MI), who were subsequently reperfused for 2.5h and euthanized or kept under study for three weeks and then sacrificed.

RESULTS

Animals administered a 10-day SM regime presented a sharp decline in plasma triglyceride levels vs. controls, with no other modifications in lipid profile. The decrease in triglyceride concentration was accompanied by a marked reduction in triglyceride intestinal absorption and glycoprotein-P expression. Three weeks post-MI the triglyceride content in the ischemic myocardium of the SM-treated animals was significantly lower than in the ischemic myocardium of placebo-controls. This effect was associated with an enhanced cardiac expression of PPARγ and triglyceride clearance receptors. This long-term SM-administration induced a lower expression of lipid receptors in subcutaneous adipose tissue. No SM-related side-effects were registered.

CONCLUSION

SM administration reduces plasma triglyceride levels through attenuation of triglyceride intestinal absorption and modulates cardiac lipotoxicity in the ischemic myocardium, likely contributing to improve ventricular remodeling.

Multicenter Study on the Diagnostic Performance of Native-T1 Cardiac Magnetic Resonance of Chronic Myocardial Infarctions at 3T

BACKGROUND

Preclinical studies and pilot patient studies have shown that chronic infarctions can be detected and characterized from cardiac magnetic resonance without gadolinium-based contrast agents using native-T1 maps at 3T. We aimed to investigate the diagnostic capacity of this approach for characterizing chronic myocardial infarctions (MIs) in a multi-center setting.

METHODS

Patients with a prior MI (n=105) were recruited at 3 different medical centers and were imaged with native-T1 mapping and late gadolinium enhancement (LGE) at 3T. Infarct location, size, and transmurality were determined from native-T1 maps and LGE. Sensitivity, specificity, receiver-operating characteristic metrics, and inter- and intraobserver variabilities were assessed relative to LGE.

RESULTS

Across all subjects, T1 of MI territory was 1621±110 ms, and remote territory was 1225±75 ms. Sensitivity, specificity, and area under curve for detecting MI location based on native-T1 mapping relative to LGE were 88%, 92%, and 0.93, respectively. Native-T1 maps were not different for measuring infarct size (native-T1 maps: 12.1±7.5%; LGE: 11.8±7.2%, P=0.82) and were in agreement with LGE (R²=0.92, bias, 0.09±2.6%). Corresponding inter- and intraobserver assessments were also highly correlated (interobserver: R²=0.90, bias, 0.18±2.4%; and intraobserver: R²=0.91, bias, 0.28±2.1%). Native T1 maps were not different for measuring MI transmurality (native-T1 maps: 49.1±15.8%; LGE: 47.2±19.0%, P=0.56) and showed agreement (R²=0.71; bias, 1.32±10.2%). Corresponding inter- and intraobserver assessments were also in agreement (interobserver: R²=0.81, bias, 0.1±9.4%; and intraobserver: R²=0.91, bias, 0.28±2.1%, respectively). While the overall accuracy for detecting MI with native-T1 maps at 3T was high, logistic regression analysis showed that MI location was a prominent confounder.

CONCLUSIONS

Native-T1 mapping can be used to image chronic MI with high degree of accuracy, and as such, it is a viable alternative for scar imaging in patients with chronic MI who are contraindicated for LGE. Technical advancements may be needed to overcome the imaging confounders that currently limit native-T1 mapping from reaching equivalent detection levels as LGE.

Effects of supplemental oxygen on cardiovascular magnetic resonance water proton relaxation time constant measurements (T1, T2 and T2*)

OBJECTIVE

To study, the effects of supplemental oxygen on the measurement of native cardiovascular water proton relaxation time constants using commercially available protocols.

METHODS

T₁, T₂ and T₂* relaxation time constant mapping were performed in twelve volunteers at 1.5 T breathing room air and supplemental oxygen supplied by nasal cannula and a non-rebreather mask. Regions-of-interest were drawn for quantitative measurements in the bloodpool of each ventricle and atria as well as septal myocardium. The effects of supplemental oxygen were investigated statistically using a mixed model analysis of variance. Intra- and inter-observer reproducibility were assessed using the Intraclass Correlation Coefficient and Coefficient of Variation.

RESULTS

Blood T₁ relaxation time constants in the left ventricle (T₁ change = -241.0 ms) and left atrium (T₁ change = -247.0 ms) decreased significantly in every subject after oxygen inhalation with a non-rebreather mask (p < 0.001). No significant changes of T₁ in the right side of the heart were detected after oxygen inhalation with the non-rebreather mask (p = 0.345). Oxygen inhalation with nasal cannula did not significantly change blood T₁ in the study (p = 0.497). No significant changes in myocardial T₁ (p = 0.390), T₂ (p = 0.960) or T₂* (p = 0.438) were observed with supplemental oxygen supplied by nasal cannula or the non-rebreather mask. Results were similar in mid-short-axis and horizontal long-axis acquisitions.

CONCLUSION

Supplemental oxygen does not affect myocardial relaxation time constant measurements with current protocols. On the other hand, blood T₁ measurements with the inhalation of supplemental oxygen supplied by a non-rebreather mask change significantly and could affect myocardial tissue characterization if used for the calculation of extracellular volume. Additionally, current relaxation time constant mapping protocols do not reproducibly detect myocardial T₁ changes with supplemental oxygen inhalation.

Imaging sequence for joint myocardial T1 mapping and fat/water separation

Purpose

To develop and evaluate an imaging sequence to simultaneously quantify the epicardial fat volume and myocardial T₁ relaxation time.

Methods

We introduced a novel simultaneous myocardial T₁ mapping and fat/water separation sequence (joint T₁‐fat/water separation). Dixon reconstruction is performed on a dual‐echo data set to generate water/fat images. T₁ maps are computed using the water images, whereas the epicardial fat volume is calculated from the fat images. A phantom experiment using vials with different T₁/T₂ values and a bottle of oil was performed. Additional phantom experiment using vials of mixed fat/water was performed to show the potential of this sequence to mitigate the effect of intravoxel fat on estimated T₁ maps. In vivo evaluation was performed in 17 subjects. Epicardial fat volume, native myocardial T₁ measurements and precision were compared among slice‐interleaved T₁ mapping, Dixon, and the proposed sequence.

Results

In the first phantom, the proposed sequence separated oil from water vials and there were no differences in T₁ of the fat‐free vials (P = .1). In the second phantom, the T₁ error decreased from 22%, 36%, 57%, and 73% to 8%, 9%, 16%, and 26%, respectively. In vivo there was no difference between myocardial T₁ values (1067 ± 17 ms versus 1077 ± 24 ms, P = .6). The epicardial fat volume was similar for both sequences (54.3 ± 33 cm³ versus 52.4 ± 32 cm³, P = .8).

Conclusion

The proposed sequence provides simultaneous quantification of native myocardial T₁ and epicardial fat volume. This will eliminate the need for an additional sequence in the cardiac imaging protocol if both measurements are clinically indicated.

Fatty Images of the Heart: Spectrum of Normal and Pathological Findings by Computed Tomography and Cardiac Magnetic Resonance Imaging

Ectopic cardiac fatty images are not rarely detected incidentally by computed tomography and cardiac magnetic resonance, or by exams focused on the heart as in general thoracic imaging evaluations. A correct interpretation of these findings is essential in order to recognize their normal or pathological meaning, focusing on the eventually associated clinical implications. The development of techniques such as computed tomography and cardiac magnetic resonance allowed a detailed detection and evaluation of adipose tissue within the heart. This pictorial review illustrates the most common characteristics of cardiac fatty images by computed tomography and cardiac magnetic resonance, in a spectrum of normal and pathological conditions ranging from physiological adipose images to diseases presenting with cardiac fatty foci. Physiologic intramyocardial adipose tissue may normally be present in healthy adults, being not related to cardiac affections and without any clinical consequence. However cardiac fatty images may also be the expression of various diseases, comprehending arrhythmogenic right ventricular dysplasia, postmyocardial infarction lipomatous metaplasia, dilated cardiomyopathy, and lipomatous hypertrophy of the interatrial septum. Fatty neoplasms of the heart as lipoma and liposarcoma are also described.

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.

Fat deposition in the left ventricle: descriptive and observacional study in autopsy

BACKGROUND

The human heart contains varying amounts of fat deposits. Cardiac physiological fat occurs predominantly in the right ventricle (RV). The discovery and characterization of adipose tissue along the left ventricle (LV) has been rarely reported. This study aimed to determine the occurrence of fatty deposits in epicardial, pericoronay and myocardial compartments in the LV, and to trace the epidemiological profile and clinical associations with this finding.

METHODS

Epidemiological and morphological data and heart samples were collected from corpses submitted to necropsy. Cardiac samples were fixed, embedded in paraffin and subjected to hematoxylin-eosin for microscopic study.

RESULTS

The research was based on 40 samples of cardiac tissue, 21 male cadavers and 19 female ones with mean age of 68.2 years. 52.2% of the subjects had a history of smoking, 20% of them had alcohol consumption and 43.59% showed cardiac cause as a cause of death (acute myocardial infarction - AMI - was the most frequent immediate cause of death). 82.5% of the subjects showed atherosclerotic disease in the ascending aorta (ADAA). The fat deposition in the left ventricule (FDLV) was observed in 95% of cases. Epicardial fat (EF) and pericoronary adipose tissue (PAT) are the most frequent topographies in fat accumulation in the left heart chamber and the EF deposition is associated with myocardial adiposity (MA) (Fisher test [FT] 0.019; odds ratio [OR] 0.097 [95% CI 0.033 to 0.284]; p < 0.05). FDLV was associated with alcoholism (FT 0.04, OR 0.161 [95% CI 0.072 to 0.36]; p < 0.05); smoking (FT 0.508; OR 0581 [95% CI 0.431 to 0.73]; p < 0.05), presence of Frank's sign (FT 0.502; OR 0.567 [95% CI 0.414 to 0.775]; p < 0.05); ADAA (0.774 OR [95% CI 0.6405 to 0.936]; p < 0.05); AMI (OR 0.730 [95% CI 0.600 to 0.888]; p < 0.05) and macroscopic finding of cardiac hypertrophy (OR 0.700 [95% CI 0.525 to 0.933]; p < 0.05). FDLV is related with the thickness of the abdominal fat cushion.

CONCLUSIONS

FDLV is common and associated with cardiovascular disease risk factors. Cardiac adiposity cannot be considered a random autopsy finding, requiring diagnostic research and more studies to investigate the clinical implications.

Myocardial fat as a part of cardiac visceral adipose tissue: physiological and pathophysiological view

Thoracic fat includes extra-pericardial (outside the visceral pericardium) and intra-pericardial (inside the visceral pericardium) adipose tissue. It is called ectopic adipose tissue although it is a normal anatomical structure. Intra-pericardial adipose tissue, which is predominantly composed of epicardial and pericoronary adipose tissue, has a significant role in cardiovascular system function. It provides metabolic-mechanical support to the heart and blood vessels in physiological conditions, while it represents metabolic-cardiovascular risk in case of qualitative and quantitative structural changes in the tissue: it correlates with coronary atherosclerotic disease, left ventricular mass, left atrium enlargement and atrial fibrillation presence. In the last decade there has been mounting evidence of fat cells presence in the myocardium of healthy (non-diseased) persons as well as in persons with both cardiovascular and non-cardiovascular diseases. Thus, it is necessary to clarify the incidence, aetiology, physiological role of fat cells in the myocardium, as well as the clinical significance of pathological fatty infiltration of the myocardium.

Native T1 Mapping by 3-T CMR Imaging for Characterization of Chronic Myocardial Infarctions

OBJECTIVES

The purpose of this study was to investigate whether native T1 maps at 3-T can reliably characterize chronic myocardial infarctions (MIs) in patients with prior ST-segment elevation myocardial infarction (STEMI) or non-ST-segment elevation myocardial infarction (NSTEMI).

BACKGROUND

Late gadolinium enhancement (LGE) cardiac magnetic resonance is the gold standard for characterizing chronic MIs, but it is contraindicated in patients with end-stage chronic kidney disease.

METHODS

Native T1 and LGE images were acquired at 3-T in patients with prior STEMI (n = 13) and NSTEMI (n = 12) at a median of 13.6 years post-MI. Infarct location, size, and transmurality were measured using mean ± 5 SDs thresholding criterion from LGE images and T1 maps and compared against one another. Independent reviewers assessed visual conspicuity of MIs on LGE images and T1 maps.

RESULTS

Native T1 maps and LGE images were not different for measuring infarct size (STEMI: p = 0.46; NSTEMI: p = 0.27) and transmurality (STEMI: p = 0.13; NSTEMI: p = 0.21) using thresholding criterion. Using thresholding criterion, good agreement was observed between LGE images and T1 maps for measuring infarct size (STEMI: bias = 0.6 ± 3.1%; R(2) = 0.93; NSTEMI: bias = -0.4 ± 4.4%; R(2) = 0.85) and transmurality (STEMI: bias = 2.0 ± 4.2%; R(2) = 0.89; NSTEMI: bias = -2.7 ± 7.9%; R(2) = 0.68). Sensitivity and specificity of T1 maps for detecting chronic MIs based on thresholding criterion were 89% and 98%, respectively (STEMI), and 87% and 95%, respectively (NSTEMI). Relative to LGE images, the mean visual conspicuity score for detecting chronic MIs was significantly lower for T1 maps (p < 0.001 for both cases). Median infarct-to-remote myocardium contrast-to-noise ratio was 2.5-fold higher for LGE images relative to T1 maps (p < 0.001). Sensitivity and specificity of T1 maps for visual detection were 60% and 86%, respectively (STEMI), and 64% and 91% (NSTEMI), respectively.

CONCLUSIONS

Chronic MIs in STEMI and NSTEMI patients can be reliably characterized using threshold-based detection on native T1 maps at 3-T. Visual detection of chronic MIs on native T1 maps in both patient populations has high specificity, but modest sensitivity.

Impact of low signal intensity assessed by cine magnetic resonance imaging on detection of poorly viable myocardium in patients with prior myocardial infarction

Late gadolinium enhancement magnetic resonance imaging (LGE-MRI) has been established as a modality to detect myocardial infarction (MI). However, the use of gadolinium contrast is limited in patients with advanced renal dysfunction. Although the signal intensity (SI) of infarct area assessed by cine MRI is low in some patients with prior MI, the prevalence and clinical significance of low SI has not been evaluated. The aim of this study was to evaluate how low SI assessed by cine MRI may relate to the myocardial viability in patients with prior MI. Fifty patients with prior MI underwent both cine MRI and LGE-MRI. The left ventricle was divided into 17 segments. The presence of low SI and the wall motion score (WMS) of each segment were assessed by cine MRI. The transmural extent of infarction was evaluated by LGE-MRI. LGE was detected in 329 of all 850 segments (39%). The low SI assessed by cine MRI was detected in 105 of 329 segments with LGE (32%). All segments with low SI had LGE. Of all 329 segments with LGE, the segments with low SI showed greater transmural extent of infarction (78 [72 - 84] % versus 53 [38 - 72] %, P < 0.01), thinner wall (4.0[3.1 - 4.8] mm versus 6.5 [5.2 - 8.1] mm, P < 0.01), and higher WMS (4.0 [4.0 - 4.0] versus 2.0 [2.0 - 3.0], P < 0.01). The low SI assessed by cine MRI may be effective for detecting poorly viable myocardium in patients with prior MI.

Characterization of myocardial T1-mapping bias caused by intramyocardial fat in inversion recovery and saturation recovery techniques

BACKGROUND

Quantitative measurement of T1 in the myocardium may be used to detect both focal and diffuse disease processes such as interstitial fibrosis or edema. A partial volume problem exists when a voxel in the myocardium also contains fat. Partial volume with fat occurs at tissue boundaries or within the myocardium in the case of lipomatous metaplasia of replacement fibrosis, which is commonly seen in chronic myocardial infarction. The presence of fat leads to a bias in T1 measurement. The mechanism for this artifact for widely used T1 mapping protocols using balanced steady state free precession readout and the dependence on off-resonance frequency are described in this paper.

METHODS

Simulations were performed to illustrate the behavior of mono-exponential fitting to bi-exponential mixtures of myocardium and fat with varying fat fractions. Both inversion recovery and saturation recovery imaging protocols using balanced steady state free precession are considered. In-vivo imaging with T1-mapping, water/fat separated imaging, and late enhancement imaging was performed on subjects with chronic myocardial infarction.

RESULTS

In n = 17 subjects with chronic myocardial infarction, lipomatous metaplasia is evident in 8 patients (47%). Fat fractions as low as 5% caused approximately 6% T1 elevation for the out-of-phase condition, and approximately 5% reduction of T1 for the in-phase condition. T1 bias in excess of 1000 ms was observed in lipomatous metaplasia with fat fraction of 38% in close agreement with simulation of the specific imaging protocols.

CONCLUSIONS

Measurement of the myocardial T1 by widely used balanced steady state free precession mapping methods is subject to bias when there is a mixture of water and fat in the myocardium. Intramyocardial fat is frequently present in myocardial scar tissue due lipomatous metaplasia, a process affecting myocardial infarction and some non-ischemic cardiomyopathies. In cases of lipomatous metaplasia, the T1 biases will be additive or subtractive depending on whether the center frequency corresponds to the myocardium and fat being in-phase or out-of-phase, respectively. It is important to understand this mechanism, which may otherwise lead to erroneous interpretation.

Imaging of reperfused intramyocardial hemorrhage with cardiovascular magnetic resonance susceptibility weighted imaging (SWI)

Purpose

To report initial experience with TE-averaged susceptibility weighted imaging (SWI) in normal subjects and acute myocardial infarction (AMI) patients for the detection of intramyocardial hemorrhage (IMH).

Materials and Methods

15 healthy control and 11 AMI subjects were studied at 1.5T before contrast agent administration with a dark blood double inversion recovery multiple spoiled gradient-echo sequence. Magnitude, susceptibility weighted and TE-averaged images were reconstructed from raw data. Contrast and signal-difference-to-noise were measured and compared between methods for IMH detection.

Results

There were six patients with microvascular obstruction (MVO) and four patients with IMH detected by TE-averaged SWI imaging. All patients with IMH on SWI scans had MVO on late gadolinium-enhanced (LGE) imaging. There was a three-fold increase in IMH contrast with SWI compared to magnitude images. IMH contrast decreased and signal-to-noise increased with increased TE averages.

Conclusions

TE-averaged SWI imaging is a promising method for myocardial tissue characterization in the setting of AMI for the detection of IMH. Along with gray-scale colormap inversion, it combines not only magnitude and phase information, but also images across TEs to provide a single image sensitive to IMH with characteristics similar to LGE imaging.

Imaging body fat: techniques and cardiometabolic implications

Obesity is a worldwide epidemic and is associated with multiple comorbidities. The mechanisms underlying the relationship between obesity and adverse health outcomes remain poorly understood. This may be because of several factors including the crude measures used to estimate adiposity, the striking heterogeneity between adipose tissue depots, and the influence of fat accumulation in multiple organs. To advance our understanding of fat stores and associated comorbidities in humans, it will be necessary to image adiposity throughout the body and ultimately also assess its functionality. Large clinical studies are demonstrating the prognostic importance of adipose tissue imaging. Newer techniques capable of imaging fat metabolism and other functions of adipose tissue may provide additional prognostic use and may be useful in guiding therapeutic interventions.

Noncontrast myocardial T1 mapping using cardiovascular magnetic resonance for iron overload

PURPOSE

To explore the use and reproducibility of magnetic resonance-derived myocardial T1 mapping in patients with iron overload.

MATERIALS AND METHODS

The research received ethics committee approval and all patients provided written informed consent. This was a prospective study of 88 patients and 67 healthy volunteers. Thirty-five patients underwent repeat scanning for reproducibility. T1 mapping used the shortened modified Look-Locker inversion recovery sequence (ShMOLLI) with a second, confirmatory MOLLI sequence in the reproducibility group. T2 * was performed using a commercially available sequence. The analysis of the T2 * interstudy reproducibility data was performed by two different research groups using two different methods.

RESULTS

Myocardial T1 was lower in patients than healthy volunteers (836 ± 138 msec vs. 968 ± 32 msec, P < 0.0001). Myocardial T1 correlated with T2 * (R = 0.79, P < 0.0001). No patient with low T2 * had normal T1 , but 32% (n = 28) of cases characterized by a normal T2 * had low myocardial T1 . Interstudy reproducibility of either T1 sequence was significantly better than T2 *, with the results suggesting that the use of T1 in clinical trials could decrease potential sample sizes by 7-fold.

CONCLUSION

Myocardial T1 mapping is an alternative method for cardiac iron quantification. T1 mapping shows the potential for improved detection of mild iron loading. The superior reproducibility of T1 has potential implications for clinical trial design and therapeutic monitoring.

Assessment of the myocardium with cardiac computed tomography

The imaging of myocardial disease is of increasing importance for cardiologists from all subspecialties, for diagnosis, risk stratification, or to facilitate therapy. While the gold standard modalities for such assessment are cardiac magnetic resonance and echocardiography, these are not universally suitable. Cardiac computed tomography (CT), well-established for the assessment of coronary artery disease (CAD), can be of value in the assessment of myocardial pathology, due to excellent patient compatibility and tolerability, high spatial resolution, and acceptable tissue characterization. This review considers the value and limitations of CT in the assessment of the myocardial sequelae of CAD, and for patients with a variety of other cardiomyopathic diseases, depicts some of the common findings, and considers current developments in this area.

[Extensive left ventricular myocardial fat deposition detected by cardiac MRI]

Although it is well known from pathological studies that intramyocardial fat deposition frequently occurs after left ventricular myocardial infarction, a left ventricular fat deposition is rarely diagnosed in the clinical routine. We report the case of extensive fat deposition in the left ventricular myocardium which was detected by routine cardiac magnetic resonance imaging.

Left ventricular fat deposition on CT in patients without proven myocardial disease

To analyze computed tomography (CT) characteristics of left ventricle (LV) fat deposition in patients without proven myocardial disease and to correlate these CT findings with electrocardiogram (ECG) and echocardiography data. We retrospectively searched our database of 14,470 consecutive coronary CT scans performed in the past 4 years for LV fat deposition in patients without proven myocardial disease. In total, we identified 25 patients (0.2 %; 10 males, 15 females; mean age 63 years) involving 91 cardiac segments. Pattern and location of LV fat deposition on CT were analyzed and compared to ECG and echocardiographic data. LV fat deposition can be categorized into 3 patterns: fat deposits in an apical cap (pattern I, n = 14), localized fat accumulation (pattern II, n = 12), and diffuse linear accumulation (pattern III, n = 6). Both patterns I and II were seen in 7 patients. The most common locations were apical segments (40 %) and the mid-myocardial layer (70 %). No patients had ECG findings positive for left-dominant arrhythmogenic dysplasia. Regional wall-motion abnormalities and decreased LV function (ejection fraction < 50 %) were only observed in 33 % of pattern III cases. LV fat deposition on CT can be seen in patients without proven myocardial disease. LV fat depositions were most commonly seen in the mid-myocardial location and apical segments. Diffuse linear fat deposition in the LV may correlates with decreased regional and global function.

Myocardial fat at cardiac imaging: how can we differentiate pathologic from physiologic fatty infiltration?

Myocardial fat is often seen at cardiac computed tomography (CT) and magnetic resonance (MR) imaging of healthy adults and patients with myocardial diseases. Physiologic myocardial fat develops with aging and is commonly seen at CT in the anterolateral right ventricular (RV) free wall and RV outflow tract with normal or thickened RV myocardium and a normal-sized RV in elderly patients. Pathologic conditions with myocardial fat include healed myocardial infarction (MI); arrhythmogenic RV cardiomyopathy or dysplasia (ARVC); and others, such as cardiac lipoma, lipomatous hypertrophy of the interatrial septum, tuberous sclerosis complex, dilated cardiomyopathy, and cardiomyopathy with muscular dystrophy. In patients with healed MI, CT and MR imaging show fat in left ventricular myocardium that is of normal thickness or thin and follows the distribution of the coronary artery; CT often depicts fat in mostly subendocardial regions. In patients with ARVC, characteristic CT and MR imaging findings include a thin RV outflow tract and free wall caused by subepicardial fatty infiltration; fat in the RV moderator band, trabeculae, and ventricular septum; and RV enlargement and wall motion abnormality. Recognition of patient age, characteristic locations of myocardial fat, myocardial thickness, and ventricular size helps in differentiating physiologic and pathologic myocardial fat at cardiac imaging; findings of wall motion abnormality and late gadolinium enhancement at MR imaging help narrow the diagnosis.

Non-contrast cardiac computed tomography can accurately detect chronic myocardial infarction: Validation study

BACKGROUND

This study evaluates whether non-contrast cardiac computed tomography (CCT) can detect chronic myocardial infarction (MI) in patients with irreversible perfusion defects on nuclear myocardial perfusion imaging (MPI).

METHODS

One hundred twenty-two symptomatic patients with irreversible perfusion defect (N = 62) or normal MPI (N = 60) underwent coronary artery calcium (CAC) scanning. MI on these non-contrast CCTs was visually detected based on the hypo-attenuation areas (dark) in the myocardium and corresponding Hounsfield units (HU) were measured.

RESULTS

Non-contrast CCT accurately detected MI in 57 patients with irreversible perfusion defect on MPI, yielding a sensitivity of 92%, specificity of 72%, negative predictive value (NPV) of 90%, and a positive predictive value (PPV) of 77%. On a per myocardial region analysis, non-contrast CT showed a sensitivity of 70%, specificity of 85%, NPV of 91%, and a PPV of 57%. The ROC curve showed that the optimal cutoff value of LV myocardium HU to predict MI on non-contrast CCT was 21.7 with a sensitivity of 97.4% and specificity of 99.7%.

CONCLUSION

Non-contrast CCT has an excellent agreement with MPI in detecting chronic MI. This study highlights a novel clinical utility of non-contrast CCT in addition to assessment of overall burden of atherosclerosis measured by CAC.

Dual gradient-echo in-phase and opposed-phase magnetic resonance imaging to evaluate lipomatous metaplasia in patients with old myocardial infarction

We present an alternative method for evaluating cardiac fat tissue-dual gradient-echo in-phase and opposed-phase magnetic resonance imaging (IPOP-MRI) with electrocardiographic (ECG) gating. Conventional IPOP-MRI can be used to evaluate small amounts of fat and is widely used for abdominal imaging, but cardiac motion artifacts make its use difficult for cardiac imaging. Using ECG gating prior to IPOP-MRI, we evaluated lipomatous metaplasia after myocardial infarction. The areas of lipomatous metaplasia measured by IPOP-MRI with ECG gating correlated well with those areas on black-blood T(1)-weighted imaging (r=0.82, P<0.0001, mean bias-0.29 cm(2), limit of agreement+/-2.06 cm(2)).

Magnetic resonance separation imaging using a divided inversion recovery technique (DIRT)

The divided inversion recovery technique is an MRI separation method based on tissue T(1) relaxation differences. When tissue T(1) relaxation times are longer than the time between inversion pulses in a segmented inversion recovery pulse sequence, longitudinal magnetization does not pass through the null point. Prior to additional inversion pulses, longitudinal magnetization may have an opposite polarity. Spatial displacement of tissues in inversion recovery balanced steady-state free-precession imaging has been shown to be due to this magnetization phase change resulting from incomplete magnetization recovery. In this paper, it is shown how this phase change can be used to provide image separation. A pulse sequence parameter, the time between inversion pulses (T180), can be adjusted to provide water-fat or fluid separation. Example water-fat and fluid separation images of the head, heart, and abdomen are presented. The water-fat separation performance was investigated by comparing image intensities in short-axis divided inversion recovery technique images of the heart. Fat, blood, and fluid signal was suppressed to the background noise level. Additionally, the separation performance was not affected by main magnetic field inhomogeneities.

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.

Multiecho dixon fat and water separation method for detecting fibrofatty infiltration in the myocardium

Conventional approaches for fat and water discrimination based on chemical-shift fat suppression have reduced ability to characterize fatty infiltration due to poor contrast of microscopic fat. The multiecho Dixon approach to water and fat separation has advantages over chemical-shift fat suppression: 1) water and fat images can be acquired in a single breathhold, avoiding misregistration; 2) fat has positive contrast; 3) the method is compatible with precontrast and late-enhancement imaging, 4) less susceptible to partial-volume effects, and 5) robust in the presence of background field variation; and 6) for the bandwidth implemented, chemical-shift artifact is decreased. The proposed technique was applied successfully in all 28 patients studied. This included 10 studies with indication of coronary artery disease (CAD), of which four cases with chronic myocardial infarction (MI) exhibited fatty infiltration; 13 studies to rule out arrhythmogenic right ventricular cardiomyopathy (ARVC), of which there were three cases with fibrofatty infiltration and two confirmed with ARVC; and five cases of cardiac masses (two lipomas). The precontrast contrast-to-noise ratio (CNR) of intramyocardial fat was greatly improved, by 240% relative to conventional fat suppression. For the parameters implemented, the signal-to-noise ratio (SNR) was decreased by 30% relative to conventional late enhancement. The multiecho Dixon method for fat and water separation provides a sensitive means of detecting intramyocardial fat with positive signal contrast.

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.

Recent myocardial infarction: assessment with unenhanced T1-weighted MR imaging

The purpose of the study was to prospectively evaluate a T1-weighted technique for detection of myocardial edema resulting from recent myocardial infarction (MI) or intervention. This study was HIPAA compliant and institutional review board approved. Fifteen men and one woman (mean age, 57.8 years+/-11.5 [standard deviation]) were examined with T1-weighted magnetic resonance (MR) imaging and inversion-recovery cine pulse sequence in two groups, recent MI and chronic MI, and gave informed consent. T1 relaxation times of MI and adjacent myocardium were compared (Student t test and correlation analysis). In patients with recent MI, areas of myocardial edema were well depicted with T1-weighted MR imaging. T1 relaxation times of recent infarcts were longer than those of older MIs (925 msec+/-169 vs 551 msec+/-107, P<.001). From local edema, T1 relaxation time of infarcted myocardium is increased, may remain elevated for 2 months, and enables imaging with T1-weighted techniques.