Diet and adipose tissue distributions: The Multi-Ethnic Study of Atherosclerosis.

BACKGROUND AND AIMS: Dietary quality affects cardiometabolic risk, yet its pathways of influence on regional adipose tissue depots involved in metabolic and diabetes risk are not well established. We aimed to investigate the relationship between dietary quality and regional adiposity. METHODS AND RESULTS: We investigated 5079 individuals in the Multi-Ethnic Study of Atherosclerosis (MESA) who had food-frequency questionnaires and measurement of pericardial fat and hepatic attenuation at the baseline study visit in MESA, as well as a subgroup with imaging for visceral and subcutaneous fat (N = 1390). A dietary quality score (DietQuality) was constructed to include established food group constituents of a Mediterranean-type diet. Linear models estimated associations of dietary score as well as its constituents with regional adiposity. Baseline mean age was 61 (± 10) years, and approximately half of the participants (47%) were male. Those with a higher DietQuality score were generally older, female, with a lower body mass index, C-reactive protein, and markers of insulin resistance. After adjustment, a higher DietQuality score was associated with lower visceral fat (lowest vs. highest dietary score quartile: 523.6 vs. 460.5 cm(2)/m; P < 0.01 for trend), pericardial fat (47.5 vs. 41.3 cm(3)/m; P < 0.01 for trend), lesser hepatic steatosis (by hepatic attenuation; 58.6 vs. 60.7 Hounsfield units; P < 0.01 for trend), but not subcutaneous fat (P = 0.39). Greater fruits, vegetables, whole grains, seeds/nuts and yogurt intake were associated with decreased adiposity, while red/processed meats were associated with greater regional adiposity. CONCLUSION: A higher quality diet pattern is associated with less regional adiposity, suggesting a potential mechanism of beneficial dietary effects on diabetes, metabolic, and cardiovascular risk.

Abdominal fat radiodensity, quantity and cardiometabolic risk: The Multi-Ethnic Study of Atherosclerosis.

BACKGROUND AND AIMS: Fat radiodensity, as measured by fat attenuation on computed tomography (CT), has emerged as a potential biomarker of "fat quality." We sought to characterize the relationship between fat radiodensity and quantity in subcutaneous, visceral, and intermuscular fat depots, and its role in inflammation, insulin resistance, and metabolic syndrome (MetS). METHODS AND RESULTS: We studied 1511 individuals from the Multi-Ethnic Study of Atherosclerosis who underwent CT for measurement of regional fat distribution and radiodensity, along with biomarker assessments and adjudication of incident metabolic syndrome (MetS). Linear, logistic and Cox regression analyses were used to measure association between fat radiodensity and (1) fat quantity, (2) biomarkers of cardiometabolic dysfunction, and (3) both prevalent and incident MetS. In each fat depot, radiodensity was strongly and inversely associated with quantity (e.g., visceral fat radiodensity vs. quantity: ρ = -0.82, P < 0.01). After adjustment for age, sex and race, lower visceral fat radiodensity was associated with greater C-reactive protein, leptin and insulin, but lower adiponectin (P < 0.01 for all). After full adjustment for cardiovascular disease risk factors, visceral (but not subcutaneous or intermuscular) fat radiodensity was associated with prevalent MetS (OR = 0.96, 95% CI = 0.93-0.99, P = 0.01). Moreover, lower visceral fat radiodensity was associated with incident MetS after the same adjustment (HR = 0.95, 95% CI 0.93-0.98, P < 0.01). However, this association became non-significant after further adjustment for visceral fat quantity. CONCLUSION: Fat radiodensity is strongly correlated with fat quantity and relevant inflammatory biomarkers. Fat radiodensity (especially for visceral fat) may be a complementary, easily assessed marker of cardiometabolic risk.

Visceral adiposity and left ventricular remodeling: The Multi-Ethnic Study of Atherosclerosis.

BACKGROUND AND AIMS: Visceral fat (VF) is a source of pro-inflammatory adipokines implicated in cardiac remodeling. We sought to determine the impact of visceral fat and subcutaneous fat (SQ) depots on left ventricular (LV) structure, function, and geometry in the Multi-Ethnic Study of Atherosclerosis (MESA). METHODS AND RESULTS: We performed a post-hoc analysis on 1151 participants from MESA with cardiac magnetic resonance quantification of LV mass and LV mass-to-volume ratio (LVMV, an index of concentricity) and computed tomographic-derived SQ and VF area. Multivariable regression models to estimate association between height-indexed SQ and VF area (per cm(2)/m) with height-indexed LV mass (per height(2.7)) and LVMV were constructed, adjusted for clinical, biochemical, and demographic covariates. We found that both VF and SQ area were associated with height-indexed LV mass (ρ = 0.36 and 0.12, P < 0.0001, respectively), while only VF area was associated with LVMV (ρ = 0.28, P < 0.0001). Individuals with above-median VF had lower LV ejection fraction, greater indexed LV volumes and mass, and higher LVMV (all P < 0.001). In multivariable models adjusted for weight, VF (but not SQ) area was associated with LV concentricity and LV mass index, across both sexes. CONCLUSION: Visceral adiposity is independently associated with LV concentricity, a precursor to heart failure. Further study into the role of VF in LV remodeling as a potential therapeutic target is warranted.

[3 tesla magnetic resonance imaging in children and adults with congenital heart disease]. / 3-Tesla-Magnetresonanztomographie zur Untersuchung von Kindern und Erwachsenen mit angeborenen Herzfehlern.

Cardiovascular magnetic resonance imaging (CMR) has become a routinely used imaging modality for congenital heart disease. A CMR examination allows the assessment of thoracic anatomy, global and regional cardiac function, blood flow in the great vessels and myocardial viability and perfusion. In the clinical routine cardiovascular MRI is mostly performed at field strengths of 1.5 Tesla (T). Recently, magnetic resonance systems operating at a field strengths of 3 T became clinically available and can also be used for cardiovascular MRI. The main advantage of CMR at 3 T is the gain in the signal-to-noise ratio resulting in improved image quality and/or allowing higher acquisition speed. Several further differences compared to MRI systems with lower field strengths have to be considered for practical applications. This article describes the impact of CMR at 3 T in patients with congenital heart disease by meanings of methodical considerations and case studies.

[Cardiovascular magnetic resonance imaging in childhood - clinical indications and case studies]. / Kardiovaskuläre Magnetresonanztomografie im Kindesalter - klinische Indikationen und Beispiele.

In today's clinical practice cardiovascular magnetic resonance (CMR) imaging is increasingly used for assessment of congenital and acquired heart disease in children. CMR complements echocardiography and provides a noninvasive alternative to diagnostic cardiac catheterization. In contrast to echocardiography, CMR is not limited by acoustic windows, and unlike cardiac catheterization, CMR lacks ionizing radiation. Contiguous three and four dimensional data sets allow to display cardiac and thoracic vessel anatomy in any desired imaging plane. These characteristics provide unique images for the complete depiction of the pathological anatomy in particular in congenital heart disease. Furthermore CMR is also used for assessment of cardiac function, blood-flow measurements, tissue characterization, and, more recently, for evaluation of myocardial perfusion and viability. The following article reviews CMR indications in pediatric cardiology by means of clinical examples.

Fully automated registration of first-pass myocardial perfusion MRI using independent component analysis.

This paper presents a novel method for registration of cardiac perfusion MRI. The presented method successfully corrects for breathing motion without any manual interaction using Independent Component Analysis to extract physiologically relevant features together with their time-intensity behavior. A time-varying reference image mimicking intensity changes in the data of interest is computed based on the results of ICA, and used to compute the displacement caused by breathing for each frame. Qualitative and quantitative validation of the method is carried out using 46 clinical quality, short-axis, perfusion MR datasets comprising 100 images each. Validation experiments showed a reduction of the average LV motion from 1.26+/-0.87 to 0.64+/-0.46 pixels. Time-intensity curves are also improved after registration with an average error reduced from 2.65+/-7.89% to 0.87+/-3.88% between registered data and manual gold standard. We conclude that this fully automatic ICA-based method shows an excellent accuracy, robustness and computation speed, adequate for use in a clinical environment.

The delay of contrast arrival in magnetic resonance first-pass perfusion imaging: a novel non-invasive parameter detecting collateral-dependent myocardium.

AIM: To establish the regional delay of contrast arrival in magnetic resonance perfusion imaging (MRPI) for the detection of collateral-dependent myocardium in patients with coronary artery disease. DESIGN AND SETTING: Observational study, case series; single centre, university hospital. PATIENTS: 30 patients with coronary artery disease and collateral-dependent myocardium and 17 healthy volunteers. METHODS: Resting and hyperaemic (adenosine) MRPI was used to determine the delay time (Deltat(d)) of contrast arrival between the left ventricle and collateral-dependent or antegradely perfused myocardium, and myocardial perfusion (MP, ml/min/g). RESULTS: In healthy volunteers, mean (SD) Deltat(d) at rest and during hyperaemia were 0.8 (0.4) and 0.3 (0.3) s, and MP was 1.14 (0.21) and 4.23 (1.12) ml/min/g. In patients Deltat(d) in antegradely perfused vs collateral-dependent myocardium was 0.9 (0.7) vs 1.7 (1.0) s at rest (p<0.001), and 0.4 (0.3) vs 1.1 (0.6) s (p<0.001) during hyperaemia. MP was 1.12 (0.11) and 0.98 (0.28) ml/min/g (p = NS) at rest and 2.46 (0.85) vs 1.86 (0.91) ml/min/g (p<0.01) during hyperaemia. Receiver operating characteristics analysis showed the best sensitivity and specificity of 90% and 83% for hyperaemic Deltat(d) of >0.6 s (area under the curve (AUC) = 0.89) to detect collateral-dependent myocardium, while resting Deltat(d) (AUC = 0.77) and perfusion (AUC = 0.69 at rest or 0.70 during hyperaemia) were less accurate. CONCLUSIONS: MRPI-derived hyperaemic delay of contrast arrival detects collateral-dependent myocardium with high sensitivity and specificity. Perfusion was less sensitive, emphasising the clinical role of Deltat(d) in non-invasive detection of collateral-dependent myocardium.

Magnetic resonance first-pass perfusion imaging: overview and perspectives.

The data from clinical studies with quantitative MR first-pass perfusion imaging suggests that this technique outperforms SPECT--widely available clinical imaging tool--in sensitivity and specificity. Moreover, MRFP imaging may be combined with the assessment of global and segmental function of the heart and regional wall thickening, and in addition, performed with pharmacological stress agents. The inter- and intra-observer reproducibility of quantitative MRFP is comparable with clinically used nuclear medicine techniques. MRFP measurements can discern collateral myocardium and are able to identify small changes in myocardial blood flow and myocardial perfusion reserve (the ratio of stress blood flow over resting). MRFP imaging has been mainly used in context of coronary artery disease but many other exciting areas in clinical cardiology are awaiting of new insights that can be accomplished with this technique. Trials are needed to obtain the approval of the contrast agent (Gd-DTPA) and perfusion sequences by the Food and Drug Administration and to establish reimbursement procedures with the third-party insurance companies and health maintenance organizations.

Variability in the cardiac EIT image as a function of electrode position, lung volume and body position.

A study was conducted using the Sheffield electrical impedance tomography (EIT) portable system DAS-01 P to determine the change in the cardiac image with electrode position, lung volume and body position. Sixteen electrodes were positioned in three transverse planes around the thorax at the level of the second intercostal space, at the level of the xiphisternal joint, and midway between upper and lower locations. Data were collected at each electrode level with the breath held at end expiration and after inspiring 0.5, 1 and 1.5 l of air with the subject in both the supine and sitting position. These data were analysed using a Matlab developed program that calculates the average resistivity change in the cardiac region from automatically determined borders. Results show significant individual variability with electrode position and air volume. The middle electrode most consistently shows an increase in impedance in the region of the heart during systole. In some subjects the change in the ventricular-volume-like curve showed a greater than 50% change as a function of lung volume. The pattern of variability with electrode position was not consistent among subjects. In one subject MRI images were obtained to compare actual structures with those seen in the EIT image. The results suggest that using these electrode locations reliable and consistent data, which could be used in clinical applications, cannot be obtained.

Echo-planar magnetic resonance myocardial perfusion imaging: parametric map analysis and comparison with thallium SPECT.

Magnetic resonance (MR) perfusion FLASH imaging has been used for assessing coronary artery disease (CAD). Echo-planar MR techniques have advantages in speed and in making MR perfusion imaging results more clinically accessible through parametric maps, but have not been previously assessed. We implemented a spin-echo, echo-planar MR technique and applied it at rest and during adenosine stress in 26 patients with CAD and abnormal thallium single-photon-emission computed tomography (SPECT), and analyzed the results by using a newly developed parametric map analysis of time to peak, peak intensity, and slope of contrast washin. The results were compared with the results of conventional visual analysis of the perfusion cine series. For detecting abnormal coronary territories, MR and SPECT were comparable for sensitivity, specificity, and accuracy (thallium, 70%, 78%, and 73%; MR, 79% 83%, and 80%; P = NS). There was good agreement between thallium and MR during stress (kappa = 0.49), but defects were larger by MR (2.4 vs. 3.1 segments for slope; P < 0.01). Additional segments were detected at rest by MR (58 for slope vs. 25 for thallium), which correlated with areas that became abnormal with stress in the thallium (sensitivity, 100%; specificity, 63%). The parametric maps were easier and faster to interpret than review of the original first-pass series of images (chi2 = 10.8; P < 0.04). The diagnostic performance of echo-planar perfusion MR and SPECT was similar, and combining the results with parametric mapping was useful for interpretation and considerably improved data display for clinical interpretation. MR, however, was faster and yielded images of higher resolution with no radiation burden. In multislice mode, these new MR techniques may have clinical value.

Quantitative magnetic resonance first-pass perfusion analysis: inter- and intraobserver agreement.

Magnetic resonance first-pass (MRFP) imaging awaits longitudinal clinical trials for quantification of myocardial perfusion. The purpose of this study was to assess inter- and intraobserver agreement of this method. Seventeen MRFP studies (14 rest and 3 under adenosine-induced hyperemia) from 14 patients were acquired. Two observers visually graded study quality. Each study was subdivided into eight regions. Both observers analyzed all 17 studies (8 x 17 = 136 regions) for interobserver agreement. Each observer then analyzed 10 of the 17 studies a second time (2 x 8 x 10 = 160 regions) for intraobserver agreement. Signal intensity curves were obtained with Argus software (Siemens, Iselin, NJ). The maximum amplitude of the impulse response function (Rmax) and the change of signal intensity (deltaSImax) of the contrast bolus were determined. Intraclass correlation coefficient was used to determine intra- and interobserver agreement. The quality was good or excellent in 14 studies. Intraobserver agreement of Rmax and deltaSImax were good (0.85 and 0.80, n = 160). Interobserver agreement of Rmax was fair (0.55, n = 136) but improved after exclusion of poor-quality studies (0.88, n = 112). Interobserver agreement of deltaSImax was good (0.73) and improved less than Rmax with study quality (0.83). Interobserver agreement for Rmax in individual myocardial regions before and after exclusion of studies with poor quality changed most markedly in lateral and posterior regions (0.69 and 0.65 vs. 0.97 and 0.94), where signal-to-noise ratios were reduced compared with anteroseptal regions (p < 0.01). Analysis of MRFP images provides good intraobserver agreement. Interobserver agreement of the quantitative perfusion analysis is good under the premise of good image quality.

Magnetic resonance imaging of myocardial perfusion in single-vessel coronary artery disease: implications for transmural assessment of myocardial perfusion.

The purpose of the study was to investigate the potential of magnetic resonance imaging (MRI) to assess transmural differences in myocardial perfusion. Contrast-enhanced MRI was performed at rest and during hyperemia in a dog model and in 22 patients with single-vessel coronary artery disease. From MR signal intensity-versus-time curves, three perfusion parameters were derived: maximum myocardial contrast enhancement (MCE), slope, and inverse mean transit time (1/MTT). In dogs, MCE correlated well (r = 0.87, p < 0.00001) with microsphere-assessed myocardial blood flow. In the patients, the subendocardial MCE decreased during hyperemia (0.89 +/- 0.18 vs. 0.74 +/- 0.15, p < 0.003) and was lower in subendocardium than in subepicardium (0.74 +/- 0.15 vs. 0.84 +/- 0.21, p < 0.02). Parameters slope and 1/MTT paralleled MCE. Contrast-enhanced MRI reflects the transmural redistribution of myocardial perfusion during hyperemia. Perfusion abnormalities can be identified most distinctly in subendocardial myocardium.

Magnetic resonance first-pass myocardial perfusion imaging: clinical validation and future applications.

Clinical studies suggest that magnetic resonance first-pass (MRFP) perfusion imaging is comparable to current diagnostic tests that are used clinically for the assessment of myocardial perfusion. In addition, magnetic resonance imaging (MRI) perfusion imaging is a noninvasive method for determining myocardial blood flow. The spatial resolution (in-plane spatial resolution < 3 mm) is sufficient to differentiate between subendocardial perfusion and subepicardial perfusion. The measurement can be repeated regularly without any adverse effects for the patient. MRI perfusion measurements can be combined with the evaluation of global function and regional wall thickening. Currently, there is no other imaging technique that offers similar advantages. The MRI perfusion measurements can be carried out during baseline conditions and during maximal hyperemia induced with either adenosine or dipyridamole. The ratio of the measured myocardial blood flows provides an estimate of the absolute and relative myocardial perfusion reserve. The perfusion reserve determined with MRFP imaging is a quantitative measure for the assessment of the collateral-dependent myocardial flow. Based on the available data using MRFP perfusion imaging, the current clinical first-line perfusion imaging tests are going to be challenged in the near future. J. Magn. Reson. Imaging 1999;10:676-685.

Myocardial viability.

This article reviews various means to assess myocardial viability by imaging, and provides recommendations for current clinical practice. This article also discusses future directions in assessing myocardial viability.

Myocardial oxygenation during high work states in hearts with postinfarction remodeling.

BACKGROUND: Postinfarction left ventricular remodeling (LVR) is associated with reductions in myocardial high-energy phosphate (HEP) levels, which are more severe in animals that develop overt congestive heart failure (CHF). During high work states, further HEP loss occurs, which suggests demand-induced ischemia. This study tested the hypothesis that inadequate myocyte oxygen availability is the basis for these HEP abnormalities. METHODS AND RESULTS: Myocardial infarction was produced by left circumflex coronary artery ligation in swine. Studies were performed in 20 normal animals, 14 animals with compensated LVR, and 9 animals with CHF. Phosphocreatine (PCr)/ATP was determined with 31P NMR and deoxymyoglobin (Mb-delta) with 1H NMR in myocardium remote from the infarct. Basal PCr/ATP tended to be decreased in postinfarct hearts, and this was significant in animals with CHF. Infusion of dobutamine (20 microg x kg-1 x min-1 IV) caused doubling of the rate-pressure product in both normal and LVR hearts and resulted in comparable significant decreases of PCr/ATP in both groups. This decrease in PCr/ATP was not associated with detectable Mb-delta. In CHF hearts, rate-pressure product increased only 40% in response to dobutamine; this attenuated response also was not associated with detectable Mb-delta. CONCLUSIONS: Thus, the decrease of PCr/ATP during dobutamine infusion is not the result of insufficient myocardial oxygen availability. Furthermore, in CHF hearts, the low basal PCr/ATP and the attenuated response to dobutamine occurred in the absence of myocardial hypoxia, indicating that the HEP and contractile abnormalities were not the result of insufficient oxygen availability.

Direct comparison of an intravascular and an extracellular contrast agent for quantification of myocardial perfusion. Cardiac MRI Group.

A direct comparison of extracellular and intravascular contrast agents for the assessment of myocardial perfusion was carried out in a porcine model (N = 5) with a flow-limiting occluder on the left anterior descending coronary artery. Rapid imaging during the first pass of an extracellular or intravascular contrast agent with a saturation-recovery-prepared TurboFLASH sequence showed comparable peak contrast-to-noise enhancements in myocardial tissue regions with flows averaging 1.1 +/- 0.2 at baseline to 4.8 +/- 0.6 ml/min/g during hyperemia. The coefficient of variation between the MR estimates of blood flow with Gadomer-17 and the microsphere blood flow measurements was 11 +/- 11%, while the corresponding co-efficient of variation for blood flow estimates with the extracellular CA was 23 +/- 11%. Blood volume differences between rest and hyperemia observed with the intravascular tracer were significant (Vvasc(rest) = 0.078 +/- 0.013 ml/g, versus Vvasc(hyperemia) = 0.102 +/- 0.019 ml/g; p < 0.05). The effects of water exchange were minimized through the choice of pulse sequence parameters to provide blood volume estimates consistent with the changes expected between rest and hyperemia. This study represents the first application of multiple indicators in first pass imaging studies for the assessment of myocardial perfusion. The use of an intravascular instead of an extracellular contrast agent allows a reduction of the degrees of freedom for modeling tissue residue curves and results in improved accuracy of blood flow estimates.