Modified Look-Locker inversion recovery (MOLLI) for high-resolution T1 mapping of the heart

Flip angle profile correction for T₁ and T₂ quantification with look-locker inversion recovery 2D steady-state free precession imaging

Fast methods using balanced steady-state free precession have been developed to reduce the scan time of T₁ and T₂ mapping. However, flip angle (FA) profiles created by the short radiofrequency pulses used in steady-state free precession deviate substantially from the ideal rectangular profile, causing T₁ and T₂ mapping errors. The purpose of this study was to develop a FA profile correction for T₁ and T₂ mapping with Look-Locker 2D inversion recovery steady-state free precession and to validate this method using 2D spin echo as a reference standard. Phantom studies showed consistent improvement in T₁ and T₂ accuracy using profile correction at multiple FAs. Over six human calves, profile correction provided muscle T₁ estimates with mean error ranging from excellent (-0.6%) at repetition time/FA = 18 ms/60° to acceptable (6.8%) at repetition time/FA = 4.9 ms/30°, while muscle T₂ estimates were less accurate with mean errors of 31.2% and 47.9%, respectively.

Fast T1 mapping determined using incomplete inversion recovery look-locker 3D balanced SSFP acquisition and a simple two-parameter model fit

PURPOSE

To evaluate a fast T1 mapping technique using incomplete inversion recovery 3D balanced steady-state free precession acquisition along with a two-parameter model fit.

MATERIALS AND METHODS

Using Bloch simulations, we explored the two-parameter model fit for data acquired using such an acquisition scheme. The parameter space over which the fit holds good was determined through simulations. A linear correction was derived for the R1* (1/T1*) values so determined. Two phantoms and six volunteers were scanned using the described technique. Comparison scans using full recovery as well as gold standard inversion recovery spin echo were also performed.

RESULTS

The two-parameter fit works exceedingly well over a large parameter space. T1 values in the phantoms showed an error of 4.9% and 39% before correction and 0.9% and 1.6% after correction. For the six volunteers, error in T1 value was 5.3% for white matter (WM) and 2.4% for gray matter (GM) after correction, while it was 11.2% and 18.2% before correction.

CONCLUSION

The work presented here allows for T1 map determination with higher resolution and shorter acquisition time than previously possible. The technique is especially well suited for GM/WM T1 mapping.

The role of cardiovascular magnetic resonance in patients with acute coronary syndromes

Cardiovascular magnetic resonance (CMR) imaging is a recognized technique for characterization of myocardial tissue in stable ischemic heart disease. In addition, CMR is emerging as a noninvasive imaging tool that can provide supporting information to guide treatment in acute coronary syndromes (ACSs). The advantages of using CMR acutely could potentially include triage/differential diagnosis in patients presenting with chest pain and troponin rise but without diagnostic electrocardiogram changes, assessment of severity of myocardial injury (irreversible vs reversible damage) in patients with ST-elevation myocardial infarction and non-ST-elevation myocardial infarction, and risk stratification and assessment of prognosis in patients with ACS. This review evaluates a potential clinical role of CMR in the acute setting, highlighting its advantages and limitations. This critical approach emphasizes areas of uncertainty and ongoing controversies but aims to equip the reader to evaluate the potential clinical application and the practicalities of CMR in patients presenting with ACS.

Myocardial T1 mapping with MRI: comparison of look-locker and MOLLI sequences

PURPOSE

To evaluate the relationship between "Look-Locker" (LL) and modified Look-Locker Inversion recovery (MOLLI) approaches for T1 mapping of the myocardium.

MATERIALS AND METHODS

A total of 168 myocardial T1 maps using MOLLI and 165 maps using LL were obtained in human subjects at 1.5 Tesla. The T1 values of the myocardium were calculated before and at five time points after gadolinium administration. All time and heart rate normalizations were done. The T1 values obtained were compared to determine the absolute and bias agreement.

RESULTS

The precontrast global T1 values were similar when measured by the LL and by MOLLI technique (mean, 1004.9 ms ± 120.3 versus 1034.1 ms ± 53.1, respectively, P = 0.26). Postcontrast myocardial T1 time from LL was significantly longer than MOLLI from 5 to 25 min (mean difference, LL - MOLLI was +61.8 ± 46.4 ms, P < 0.001). No significant differences in T1 values were noted between long and short axis measurements for either MOLLI or LL.

CONCLUSION

Postcontrast LL and MOLLI showed very good agreement, although LL values are higher than MOLLI. Precontrast T1 values showed good agreement, however LL has greater limits of agreement. Short and long axis planes can reliably assess T1 values.

Association of imaging markers of myocardial fibrosis with metabolic and functional disturbances in early diabetic cardiomyopathy

BACKGROUND

Metabolic and vascular disturbances contribute to diabetic cardiomyopathy, but the role of interstitial fibrosis in early disease is unproven. We sought to assess the relationship between imaging markers of diffuse fibrosis and myocardial dysfunction and to link this to possible causes of early diabetic cardiomyopathy.

METHODS AND RESULTS

Hemodynamic and metabolic data were measured in 67 subjects with type 2 diabetes mellitus (age 60±10 years) with no cardiac symptoms. Myocardial function was evaluated with standard echocardiography and myocardial deformation; ischemia was excluded by exercise echocardiography. Calibrated integrated backscatter was calculated from parasternal long-axis views. T1 mapping was performed after contrast with a modified Look-Locker technique using saturation recovery images. Amino-terminal propeptides of procollagens type I and III, as well as the carboxy-terminal propeptide of procollagen type I, were assayed to determine collagen turnover. Subjects with abnormal early diastolic tissue velocity (E(m)) had shorter postcontrast T1 values (P=0.042) and higher calibrated integrated backscatter (P=0.007). They were heavier (P=0.003) and had worse exercise capacity (P<0.001), lower insulin sensitivity (P=0.003), and blunted systolic tissue velocity (P=0.05). Postcontrast T1 was associated with diastolic dysfunction (E(m) r=0.28, P=0.020; E/E(m) r=-0.24, P=0.049), impaired exercise capacity (r=0.30, P=0.016), central adiposity (r=-0.26, P=0.046), blood pressure (systolic r=-0.30, P=0.012; diastolic r=-0.49, P<0.001), and insulin sensitivity (r=0.30, P=0.037). The association of T1 with E/E(m) (β=-0.31, P=0.017) was independent of blood pressure and metabolic disturbance. Amino-terminal propeptide of procollagens type III was linked to diastolic dysfunction (E(m) r=-0.32, P=0.008) and calibrated integrated backscatter (r=0.30, P=0.015) but not T1 values.

CONCLUSIONS

The association between myocardial diastolic dysfunction, postcontrast T1 values, and metabolic disturbance supports that diffuse myocardial fibrosis is an underlying contributor to early diabetic cardiomyopathy.

Motion correction for myocardial T1 mapping using image registration with synthetic image estimation

Quantification of myocardial T1 relaxation has potential value in the diagnosis of both ischemic and nonischemic cardiomyopathies. Image acquisition using the modified Look-Locker inversion recovery technique is clinically feasible for T1 mapping. However, respiratory motion limits its applicability and degrades the accuracy of T1 estimation. The robust registration of acquired inversion recovery images is particularly challenging due to the large changes in image contrast, especially for those images acquired near the signal null point of the inversion recovery and other inversion times for which there is little tissue contrast. In this article, we propose a novel motion correction algorithm. This approach is based on estimating synthetic images presenting contrast changes similar to the acquired images. The estimation of synthetic images is formulated as a variational energy minimization problem. Validation on a consecutive patient data cohort shows that this strategy can perform robust nonrigid registration to align inversion recovery images experiencing significant motion and lead to suppression of motion induced artifacts in the T1 map.

Molecular MRI of acute necrosis with a novel DNA-binding gadolinium chelate: kinetics of cell death and clearance in infarcted myocardium

BACKGROUND

Current techniques to image cell death in the myocardium are largely nonspecific. We report the use of a novel DNA-binding gadolinium chelate (Gd-TO) to specifically detect the exposed DNA in acutely necrotic (ruptured) cells in vivo.

METHODS AND RESULTS

In vivo MRI was performed in 20 mice with myocardial infarction (MI). The mice were injected with Gd-TO or Gd-DTPA at varying time points after MI. MRI was performed 2 hours after probe injection, to avoid nonspecific signal from the late gadolinium enhancement effect. Cell rupture (Gd-TO uptake) was present within 2 hours of infarction but peaked 9 to 18 hours after the onset of injury. A significant increase in the longitudinal relaxation rate (R(1)) in the infarct was seen in mice injected with Gd-TO within 48 hours of MI, but not in those injected more than 72 hours after MI (R(1)=1.24±0.08 and 0.92±0.03 s(-1), respectively, P<0.001). Gd-DTPA, unlike Gd-TO, washed completely out of acute infarcts within 2 hours of injection (P<0.001). The binding of Gd-TO to exposed DNA in acute infarcts was confirmed with fluorescence microscopy.

CONCLUSIONS

Gd-TO specifically binds to acutely necrotic cells and can be used to image the mechanism and chronicity of cell death in injured myocardium. Cell rupture in acute MI begins early but peaks many hours after the onset of injury. The ruptured cells are efficiently cleared by the immune system and are no longer present in the myocardium 72 hours after injury.

Small animal Look-Locker inversion recovery (SALLI) for simultaneous generation of cardiac T1 maps and cine and inversion recovery-prepared images at high heart rates: initial experience

PURPOSE

To develop a single magnetic resonance (MR) imaging approach for comprehensive assessment of cardiac function and tissue properties in small animals with high heart rates.

MATERIALS AND METHODS

All animal studies were approved by the local animal care committee. Small animal Look-Locker inversion recovery (SALLI) was implemented on a clinical 3.0-T MR unit equipped with a 70-mm solenoid coil. SALLI combines a segmented, electrocardiographically gated, inversion recovery-prepared Look-Locker-type pulse sequence with a multimodal reconstruction framework. Temporal undersampling and radial nonbalanced steady-state free precession enabled acceleration of data acquisition and reduction of motion artifacts, respectively. Nine agarose gel phantoms were used to investigate different sequence settings. For in vivo studies, 10 Sprague-Dawley rats were evaluated to establish normal T1 values before and after injection of gadopentetate dimeglumine. Seven rats with surgically induced acute myocardial infarction were examined to test the feasibility of detecting myocardial injury. In vitro T1 behavior was studied with linear regression analysis, and in vivo T1 differences between infarcted and remote areas were tested by using the Wilcoxon signed rank test.

RESULTS

Phantom studies demonstrated systematic behavior of the T1 measurements, and T1 error could be reduced to 1.3% ± 7.4 by using a simple linear correction algorithm. The pre- and postcontrast T1 of myocardium and blood showed narrow normal ranges. In the area of infarction, SALLI demonstrated hypokinesia (on cine images), myocardial edema (on precontrast T1 maps), and myocardial necrosis (on postcontrast T1 maps and late gadolinium enhancement images).

CONCLUSION

An MR imaging method enabling simultaneous generation of cardiac T1 maps and cine and inversion recovery-prepared images at high heart rates is presented. SALLI allows for simultaneous and time-efficient assessment of cardiac T1 behavior, function, and late gadolinium enhancement at high heart rates.

Emerging MRI methods in translational cardiovascular research

Cardiac magnetic resonance imaging (CMR) has become a reference standard modality for imaging of left ventricular (LV) structure and function and, using late gadolinium enhancement, for imaging myocardial infarction. Emerging CMR techniques enable a more comprehensive examination of the heart, making CMR an excellent tool for use in translational cardiovascular research. Specifically, emerging CMR methods have been developed to measure the extent of myocardial edema, changes in ventricular mechanics, changes in tissue composition as a result of fibrosis, and changes in myocardial perfusion as a function of both disease and infarct healing. New CMR techniques also enable the tracking of labeled cells, molecular imaging of biomarkers of disease, and changes in calcium flux in cardiomyocytes. In addition, MRI can quantify blood flow velocity and wall shear stress in large blood vessels. Almost all of these techniques can be applied in both pre-clinical and clinical settings, enabling both the techniques themselves and the knowledge gained using such techniques in pre-clinical research to be translated from the lab bench to the patient bedside.

Evaluation of the effect of myocardial segmentation errors on myocardial blood flow estimates from DCE-MRI

Quantitative analysis of cardiac dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) perfusion datasets is dependent on the drawing (manually or automatically) of myocardial contours. The required accuracy of these contours for myocardial blood flow (MBF) estimation is not well understood. This study investigates the relationship between myocardial contour errors and MBF errors. Myocardial contours were manually drawn on DCE-MRI perfusion datasets of healthy volunteers imaged in systole. Systematic and random contour errors were simulated using spline curves and the resulting errors in MBF were calculated. The degree of contour error was also evaluated by two recognized segmentation metrics. We derived contour error tolerances in terms of the maximum deviation (MD) a contour could deviate radially from the 'true' contour expressed as a fraction of each volunteer's mean myocardial width (MW). Significant MBF errors were avoided by setting tolerances of MD ≤ 0.4 MW, when considering the whole myocardium, MD ≤ 0.3 MW, when considering six radial segments, and MD ≤ 0.2 MW for further subdivision into endo- and epicardial regions, with the exception of the anteroseptal region, which required greater accuracy. None of the considered segmentation metrics correlated with MBF error; thus, both segmentation metrics and MBF errors should be used to evaluate contouring algorithms.

Rapid T1 mapping of mouse myocardium with saturation recovery Look-Locker method

Dynamic contrast-enhanced MRI using gadolinium or manganese provides unique characterization of myocardium and its pathology. In this study, an electrocardiography (ECG) triggered saturation recovery Look-Locker method was developed and validated for fast cardiac T(1) mapping in small animal models. By sampling the initial portion of the longitudinal magnetization recovery curve, high temporal resolution (∼ 3 min) can be achieved at a high spatial resolution (195 × 390 μm2) in mouse heart without the aid of parallel imaging or echo-planar imaging. Validation studies were performed both in vitro on a phantom and in vivo on C57BL/6 mice (n = 6). Our results showed a strong agreement between T(1) measured by saturation recovery Look-Locker and by the standard saturation recovery method in vitro or inversion recovery Look-Locker in vivo. The utility of saturation recovery Look-Locker in dynamic contrast-enhanced MRI studies was demonstrated in manganese-enhanced MRI experiments in mice. Our results suggest that saturation recovery Look-Locker can provide rapid and accurate cardiac T(1) mapping for studies using small animal models.

Assessment of myocardial fibrosis with cardiovascular magnetic resonance

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

Three-dimensional T1 mapping of the mouse heart using variable flip angle steady-state MR imaging

Cardiac MR T(1) mapping is a promising quantitative imaging tool for the diagnosis and evaluation of cardiomyopathy. Here, we present a new preclinical cardiac MRI method enabling three-dimensional T(1) mapping of the mouse heart. The method is based on a variable flip angle analysis of steady-state MR imaging data. A retrospectively triggered three-dimensional FLASH (fast low-angle shot) sequence (3D IntraGate) enables a constant repetition time and maintains steady-state conditions. 3D T(1) mapping of the complete mouse heart could be achieved in 20 min. High-quality, bright-blood T(1) maps were obtained with homogeneous T(1) values (1764 ± 172 ms) throughout the myocardium. The repeatability coefficient of R(1) (1/T(1) ) in a specific region of the mouse heart was between 0.14 and 0.20 s(-1) , depending on the number of flip angles. The feasibility for detecting regional differences in ΔR(1) was shown with pre- and post-contrast T(1) mapping in mice with surgically induced myocardial infarction, for which ΔR(1) values up to 0.83 s(-1) were found in the infarct zone. The sequence was also investigated in black-blood mode, which, interestingly, showed a strong decrease in the apparent mean T(1) of healthy myocardium (905 ± 110 ms). This study shows that 3D T(1) mapping in the mouse heart is feasible and can be used to monitor regional changes in myocardial T(1), particularly in relation to pathology and in contrast-enhanced experiments to estimate local concentrations of (targeted) contrast agent.

Molecular imaging with targeted contrast agents

Molecular imaging with targeted contrast agents by magnetic resonance imaging (MRI) allows for the noninvasive detection and characterization of biological changes on a molecular level. In this article, the principles of molecular MRI and its applications in cardiovascular diseases are reviewed. First, basic properties of positive and negative contrast agents are introduced and their effect on signal generation in a magnetic field is described. In the next part, different types of MRI scanners and the influence of field strength on signal properties of contrast agents for molecular imaging are discussed. Additionally, the assessment, analysis, and quantification of the changes in T1 and T2* relaxation time induced by the different molecular contrast agents are reviewed. Finally, the basic mechanisms of targeting of imaging probes on a molecular level and recent applications of molecular MRI in cardiovascular disease are reviewed.

Shortened Modified Look-Locker Inversion recovery (ShMOLLI) for clinical myocardial T1-mapping at 1.5 and 3 T within a 9 heartbeat breathhold

BACKGROUND

T1 mapping allows direct in-vivo quantitation of microscopic changes in the myocardium, providing new diagnostic insights into cardiac disease. Existing methods require long breath holds that are demanding for many cardiac patients. In this work we propose and validate a novel, clinically applicable, pulse sequence for myocardial T1-mapping that is compatible with typical limits for end-expiration breath-holding in patients.

MATERIALS AND METHODS

The Shortened MOdified Look-Locker Inversion recovery (ShMOLLI) method uses sequential inversion recovery measurements within a single short breath-hold. Full recovery of the longitudinal magnetisation between sequential inversion pulses is not achieved, but conditional interpretation of samples for reconstruction of T1-maps is used to yield accurate measurements, and this algorithm is implemented directly on the scanner. We performed computer simulations for 100 ms

RESULTS

We found good agreement between the average ShMOLLI and MOLLI estimates for T1 < 1200 ms. In contrast to the original method, ShMOLLI showed no dependence on heart rates for long T1 values, with estimates characterized by a constant 4% underestimation for T1 = 800-2700 ms. In-vivo, ShMOLLI measurements required 9.0 ± 1.1 s (MOLLI = 17.6 ± 2.9 s). Average healthy myocardial T1 s by ShMOLLI at 1.5T were 966 ± 48 ms (mean ± SD) and 1166 ± 60 ms at 3T. In MI patients, the T1 in unaffected myocardium (1216 ± 42 ms) was similar to controls at 3T. Ischemically injured myocardium showed increased T1 = 1432 ± 33 ms (p < 0.001). The difference between MI and remote myocardium was estimated 15% larger by ShMOLLI than MOLLI (p < 0.04) which suffers from heart rate dependencies for long T1. The in-vivo variability within ShMOLLI T1-maps was only 14% (1.5T) or 18% (3T) higher than the MOLLI maps, but the MOLLI acquisitions were twice longer than ShMOLLI acquisitions.

CONCLUSION

ShMOLLI is an efficient method that generates immediate, high-resolution myocardial T1-maps in a short breath-hold with high precision. This technique provides a valuable clinically applicable tool for myocardial tissue characterisation.

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Key Words Collapse

MESH Headings

• Adult
• Algorithms
• Cardiac-Gated Imaging Techniques/instrumentation
• Computer Simulation
• Contrast Media
• Electrocardiography
• England
• Female
• Gadolinium DTPA
• Heart Rate
• Humans
• Image Interpretation, Computer-Assisted
• Magnetic Resonance Imaging/instrumentation
• Male
• Middle Aged
• Myocardial Infarction/pathology
• Myocardial Infarction/physiopathology
• Phantoms, Imaging
• Predictive Value of Tests
• Reproducibility of Results
• Respiratory Mechanics
• Time Factors

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Grants

• G0701128 Medical Research Council

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Affiliation(s)

Stefan K Piechnik University of Oxford Centre for Clinical Magnetic Resonance Research (OCMR), Department of Cardiovascular Medicine, John Radcliffe Hospital, Oxford, UK
Vanessa M Ferreira University of Oxford Centre for Clinical Magnetic Resonance Research (OCMR), Department of Cardiovascular Medicine, John Radcliffe Hospital, Oxford, UK Stephenson CMR Centre, Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Canada
Erica Dall'Armellina University of Oxford Centre for Clinical Magnetic Resonance Research (OCMR), Department of Cardiovascular Medicine, John Radcliffe Hospital, Oxford, UK
Lowri E Cochlin Dept. of Physiology, Anatomy and Genetics, University of Oxford, Oxford, UK
Andreas Greiser Siemens AG Healthcare Sector, Erlangen, Germany
Stefan Neubauer University of Oxford Centre for Clinical Magnetic Resonance Research (OCMR), Department of Cardiovascular Medicine, John Radcliffe Hospital, Oxford, UK
Matthew D Robson University of Oxford Centre for Clinical Magnetic Resonance Research (OCMR), Department of Cardiovascular Medicine, John Radcliffe Hospital, Oxford, UK

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Quantification of diffuse myocardial fibrosis and its association with myocardial dysfunction in congenital heart disease

BACKGROUND

the etiology of ventricular dysfunction in adult congenital heart disease (ACHD) is not well understood. Diffuse fibrosis is a likely common final pathway and is quantifiable using MRI.

METHODS AND RESULTS

patients with ACHD (n=50) were studied with cardiac MRI to quantify systemic ventricular volume and function and diffuse fibrosis. The fibrosis index for a single midventricular plane of the systemic ventricle was quantified by measuring T1 values for blood pool and myocardium before and after administration of gadolinium (0.15 mmol/kg) and then adjusted for hematocrit. Results were compared to healthy volunteers (normal controls, n=14) and patients with acquired heart failure (positive controls, n=4). Patients studied (age, 37±12 years; female sex, 40%) included 11 with a systemic right ventricle (RV), 17 with tetralogy of Fallot, 10 with cyanosis, and 12 with other lesions. The fibrosis index was significantly elevated in patients with ACHD compared to normal controls (31.9±4.9% versus 24.8±2.0%; P=0.001). Values were highest in patients with a systemic RV (35.0±5.8%; P<0.001) and those who were cyanotic (33.7±5.6%; P<0.001). The fibrosis index correlated with end-diastolic volume index (r=0.60; P<0.001) and ventricular ejection fraction (r=-0.53; P<0.001) but not with age or oxygen saturation in patients who were cyanotic. Late gadolinium enhancement did not account for the differences seen.

CONCLUSIONS

patients with ACHD have evidence of diffuse, extracellular matrix remodeling similar to patients with acquired heart failure. The fibrosis index may facilitate studies on the mechanisms and treatment of myocardial fibrosis and heart failure in these patients.

An open-source software tool for the generation of relaxation time maps in magnetic resonance imaging

BACKGROUND

In magnetic resonance (MR) imaging, T1, T2 and T2* relaxation times represent characteristic tissue properties that can be quantified with the help of specific imaging strategies. While there are basic software tools for specific pulse sequences, until now there is no universal software program available to automate pixel-wise mapping of relaxation times from various types of images or MR systems. Such a software program would allow researchers to test and compare new imaging strategies and thus would significantly facilitate research in the area of quantitative tissue characterization.

RESULTS

After defining requirements for a universal MR mapping tool, a software program named MRmap was created using a high-level graphics language. Additional features include a manual registration tool for source images with motion artifacts and a tabular DICOM viewer to examine pulse sequence parameters. MRmap was successfully tested on three different computer platforms with image data from three different MR system manufacturers and five different sorts of pulse sequences: multi-image inversion recovery T1; Look-Locker/TOMROP T1; modified Look-Locker (MOLLI) T1; single-echo T2/T2*; and multi-echo T2/T2*. Computing times varied between 2 and 113 seconds. Estimates of relaxation times compared favorably to those obtained from non-automated curve fitting. Completed maps were exported in DICOM format and could be read in standard software packages used for analysis of clinical and research MR data.

CONCLUSIONS

MRmap is a flexible cross-platform research tool that enables accurate mapping of relaxation times from various pulse sequences. The software allows researchers to optimize quantitative MR strategies in a manufacturer-independent fashion. The program and its source code were made available as open-source software on the internet.

Estimation of gadolinium-induced T1-shortening with measurement of simple signal intensity ratio between the cochlea and brain parenchyma on 3D-FLAIR: correlation with T1 measurement by TI scout sequence

PURPOSE

T(1)-shortening of labyrinthine fluid on 3-dimensional fluid-attenuated inversion recovery (3D-FLAIR) has been reported in many inner ear disorders. Although semi-quantitative assessment by simple signal intensity ratio between cochlear fluid and brain tissue has been tried, its feasibility using a multi-channel phased-array head coil with an inherently inhomogenous sensitivity distribution has not been fully evaluated. We evaluated the feasibility of measuring simple signal intensity ratio by correlating rapid T(1) measurements using an inversion time (TI) scout sequence.

MATERIALS AND METHODS

We evaluated 10 patients with Meniere's disease and 4 patients with sudden deafness. Nine of the patients with Meniere's disease received a unilateral intratympanic injection of Gd-DTPA; the tenth patient received bilateral injections. The 4 patients with sudden deafness received a double-dose intravenous injection. Magnetic resonance (MR) images were obtained 24 hours after intratympanic injections and 4 hours after intravenous injections at 3 tesla using a 32-channel head coil. We measured the ratio (CM ratio) between the signal intensity of the perilymph in the cochlea (C) and that of the medulla oblongata (M) and correlated it with the null-point inversion time (TI(null)) obtained with the TI scout sequence. The TI scout consisted of 85 images obtained with TI values between 132.5 and 3087.5 ms at increments of 37.5 ms.

RESULTS

The correlation coefficient between TI(null) and the natural logarithm of the CM ratio was -0.88 (P<0.01). There was significant negative linear correlation.

CONCLUSIONS

Measurement of the simple signal intensity ratio between the cochlea and the medulla can be used for semi-quantitative analysis of 3D-FLAIR. The results of this study may facilitate clinical research of inner-ear disease using 3D-FLAIR.

Hybrid adiabatic-rectangular pulse train for effective saturation of magnetization within the whole heart at 3 T

Uniform T(1)-weighting is a major challenge for first-pass cardiac perfusion MRI at 3 T. Previously proposed adiabatic amplitude of radiofrequency field (B(1))-insensitive rotation (BIR-4) pulse and standard and tailored pulse trains of three nonselective pulses have been important developments but each pulse has limitations at 3 T. As an extension of the tailored pulse train, we developed a hybrid pulse train by synergistically combining two nonselective rectangular radiofrequency pulses and an adiabatic half-passage pulse, in order to achieve effective saturation of magnetization within the heart, while remaining within clinically acceptable specific absorption rate limits. The standard pulse train, tailored pulse train, hybrid pulse train, and BIR-4 pulse train were evaluated through numerical, phantom, and in vivo experiments. Among the four saturation pulses, only the hybrid pulse train yielded residual magnetization <2% of equilibrium magnetization in the heart while remaining within clinically acceptable specific absorption rate limits for multislice first-pass cardiac perfusion MRI at 3 T.

Modulated repetition time look-locker (MORTLL): a method for rapid high resolution three-dimensional T1 mapping

PURPOSE

To demonstrate a modification of the Look-Locker (LL) technique that enables rapid high resolution T1 mapping over the physiologic range of intracranial T1 values, ranging from white matter to cerebrospinal fluid (CSF). This is achieved by use of a three-dimensional (3D) balanced steady-state free precession (b-SSFP) acquisition (for high signal-to-noise and resolution) along with variable repetition time to allow effective full recovery of longitudinal magnetization.

MATERIALS AND METHODS

Two modifications to the Look-Locker technique were made to realize high resolution imaging in a clinically reasonable scan time. The 3D b-SSFP acquisition after an initial inversion pulse was followed by a variable repetition time. This technique makes it possible to image a volume of thin contiguous slices with high resolution and accuracy using a simple fitting procedure and is particularly useful for imaging long T1 species such as CSF. The total scan time is directly proportional to the number of slices to be acquired. The scan time was reduced by almost half when the repetition time was modified using a predesigned smooth function. Phantoms and volunteers were imaged at different resolutions on a 3 Tesla scanner. Results were compared with other accepted techniques.

RESULTS

T1 values in the brain corresponded well with full repetition time imaging as well as inversion recovery spin echo imaging. T1 values for white matter, gray matter, and CSF were measured to be 755 +/- 10 ms, 1202 +/- 9 ms, and 4482 +/- 71 ms, respectively. Scan times were reduced by approximately half over full repetition time measurements.

CONCLUSION

High resolution T1 maps can be obtained rapidly and with a relatively simple postprocessing method. The technique is particularly well suited for long T1 species. For example, changes in the composition of proteins in CSF are linked to various pathologies. The T1 values showed excellent agreement with values obtained from inversion recovery spin-echo imaging.

Cardiac MRI in ischemic heart disease

Considerable progress has been made in cardiac magnetic resonance imaging (MRI). Cine MRI is recognized as the most accurate method for evaluating ventricular function. Late gadolinium-enhanced MRI can clearly delineate subendocardial infarction, and the assessment of transmural extent of infarction on MRI is widely useful for predicting myocardial viability. Stress myocardial perfusion MRI allows for detection of subendocardial myocardial ischemia, and the diagnostic accuracy of stress perfusion MRI is superior to stress perfusion single-photon emission computed tomography in patients with multivessel coronary artery disease (CAD). In recent years, image quality, volume coverage, acquisition speed and arterial contrast of 3-dimensional coronary magnetic resonance angiography (MRA) have been substantially improved with use of steady-state free precession sequences and parallel imaging techniques, permitting the acquisition of high-quality, whole-heart coronary MRA within a reasonably short imaging time. It is now widely recognized that cardiac MRI has tremendous potential for the evaluation of ischemic heart disease. However, cardiac MRI is technically complicated and its use in clinical practice is relatively limited. With further improvements in education and training, as well as standardization of appropriate study protocols, cardiac MRI will play a central role in managing patients with CAD.

Interleaved T(1) and T(2) relaxation time mapping for cardiac applications

PURPOSE

To diagnose acute myocardial infarction (MI) with MRI, T(1)-weighted and T(2)-weighted images are required to detect necrosis and edema. The calculation of both T(1) and T(2) maps can be relevant for quantitative diagnosis. In this work, we present a simultaneous quantification of T(1)-T(2) relaxation times of a short-axis view of the heart in a single scan.

MATERIALS AND METHODS

An electrocardiograph (ECG)-triggered, navigator-gated, interleaved T(1) and T(2) mapping sequence was implemented for the quantification of the T(1) and T(2) values of phantoms, healthy volunteers, and three patients with acute MI. The proposed acquisition scheme consisted of an interleaved two-dimensional (2D) steady-state free precession (SSFP) sequence with three different modules: an inversion-recovery (IR) sequence with multiple time delays, followed by a delay of one cardiac cycle for magnetization recovery and a T(2)-preparation pulse with multiple echo-times for T(2) quantification.

RESULTS

Measurements of in vivo relaxation times were in good agreement with literature values. The interleaved sequence was able to measure T(1) and T(2) relaxation times of the myocardium.

CONCLUSION

The interleaved sequence acquires data for the calculation of T(1) and T(2) maps in only one scan without the need for registration. This technique has the potential to differentiate between acute and chronic MI by estimating the concentration of gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) in the necrotic tissue and to assess the extent of edema from T(2) maps.

Advanced methods for quantification of infarct size in mice using three-dimensional high-field late gadolinium enhancement MRI

Conventional methods to quantify infarct size after myocardial infarction in mice are not ideal, requiring either tissue destruction for histology or relying on nondirect measurements such as wall motion. We therefore implemented a fast, high-resolution method to directly measure infarct size in vivo using three-dimensional (3D) late gadolinium enhancement MRI (3D-LGE). Myocardial T1 relaxation was quantified at 9.4 Tesla in five mice, and reproducibility was tested by repeat imaging after 5 days. In a separate set of healthy and infarcted mice (n = 8 of each), continuous T1 measurements were made following intravenous or intraperitoneal injection of a contrast agent (0.5 micromol/g gadolinium-diethylenetriamine pentaacetic acid). The time course of T1 contrast development between viable and nonviable myocardium was thereby determined, with optimal postinjection imaging windows and inversion times identified. Infarct sizes were quantified using 3D-LGE and compared with triphenyltetrazolium chloride histology on day 1 after infarction (n = 8). Baseline myocardial T1 was highly reproducible: the mean value was 952 +/- 41 ms. T1 contrast peaked earlier after intravenous injection than with intraperitoneal injection; however, contrast between viable and nonviable myocardium was comparable for both routes (P = 0.31), with adequate contrast remaining for at least 60 min postinjection. Excellent correlation was obtained between infarct sizes derived from 3D-LGE and histology (r = 0.91, P = 0.002), and Bland-Altman analysis indicated good agreement free from systematic bias. We have validated an improved 3D MRI method to noninvasively quantify infarct size in mice with unsurpassed spatial resolution and tissue contrast. This method is particularly suited to studies requiring early quantification of initial infarct size, for example, to measure damage before intervention with stem cells.

Uncertainty in T(1) mapping using the variable flip angle method with two flip angles

Propagation of errors, in conjunction with the theoretical signal equation for spoiled gradient echo pulse sequences, is used to derive a theoretical expression for uncertainty in quantitative variable flip angle T(1) mapping using two flip angles. This expression is then minimized to derive a rigorous expression for optimal flip angles that elucidates a commonly used empirical result. The theoretical expressions for uncertainty and optimal flip angles are combined to derive a lower bound on the achievable uncertainty for a given set of pulse sequence parameters and signal-to-noise ratio (SNR). These results provide a means of quantitatively determining the effect of changing acquisition parameters on T(1) uncertainty.

Quantitative molecular magnetic resonance imaging of tumor angiogenesis using cNGR-labeled paramagnetic quantum dots

The objective of this study was to develop and apply cyclic Asn-Gly-Arg (cNGR)-labeled paramagnetic quantum dots (cNGR-pQDs) for the noninvasive assessment of tumor angiogenic activity using quantitative in vivo molecular magnetic resonance imaging (MRI). cNGR was previously shown to colocalize with CD13, an aminopeptidase that is highly overexpressed on angiogenic tumor endothelium. Because angiogenesis is important for tumor growth and metastatization, its in vivo detection and quantification may allow objective diagnosis of tumor status and evaluation of treatment response. I.v. injection of cNGR-pQDs in tumor-bearing mice resulted in increased quantitative contrast, comprising increased longitudinal relaxation rate and decreased proton visibility, in the tumor rim but not in tumor core or muscle tissue. This showed that cNGR-pQDs allow in vivo quantification and accurate localization of angiogenic activity. MRI results were validated using ex vivo two-photon laser scanning microscopy (TPLSM), which showed that cNGR-pQDs were primarily located on the surface of tumor endothelial cells and to a lesser extent in the vessel lumen. In contrast, unlabeled pQDs were not or only sparsely detected with both MRI and TPLSM, supporting a high specificity of cNGR-pQDs for angiogenic tumor vasculature.

Characterisation of peripartum cardiomyopathy by cardiac magnetic resonance imaging

Peripartum cardiomyopathy (PPCM) is a rare cause of heart failure. Only half of the patients recover normal cardiac function. We assessed the usefulness of magnetic resonance imaging (MRI) and late enhancement imaging to detect myocardial fibrosis in order to predict cardiac function recovery in patients with peripartum cardiomyopathy. Among a consecutive series of 1,037 patients referred for heart failure treatment or prognostic evaluation between 1999 and 2006, eight women had confirmed PPCM. They all underwent echocardiography and cardiac MRI for assessment of left ventricular anatomy, systolic function and detection of myocardial fibrosis through late enhancement imaging. Mean (+/- SD) baseline left ventricular ejection fraction (LVEF) was 28 +/- 4%. After a follow-up of 50 +/- 9 months, half the patients recovered normal cardiac function (LVEF = 58 +/- 4%) and four did not (LVEF = 35 +/- 6%). None of the eight patients exhibited abnormal myocardial late enhancement. No difference in MRI characteristics was observed between the two groups. Patients with PPCM do not exhibit a specific cardiac MRI pattern and particularly no myocardial late enhancement. It suggests that myocardial fibrosis does not play a major role in the limitation of cardiac function recovery after PPCM.

Delayed enhancement cardiac magnetic resonance imaging reveals typical patterns of myocardial injury in patients with various forms of non-ischemic heart disease

BACKGROUND

Late gadolinium-hyperenhancement (LHE) on cardiac magnetic resonance imaging (CMR) has been linked to cardiovascular risk in ischemic and non-ischemic heart disease. We aimed to systematically categorize LHE-patterns in a variety of non-ischemic heart diseases (NIHD) and to explore their relationship with left ventricular (LV) function.

METHODS

In a retrospective database search, 156 patients with NIHD who exhibited LHE on CMR were identified. All images were re-analyzed stepwise. LHE was correlated to LV functional parameters. Cardiac magnetic resonance (CMR) was conducted on 1.5 T scanners.

RESULTS

Typically, LHE spared the subendocardium. Consistent LHE-patterns were observed in myocarditis, hypertrophic and dilated cardiomyopathy and systemic vasculitis. No conclusive LHE-patterns were observed in patients with aortic stenosis, arterial hypertension, lupus erythematosus, sarcoidosis, ventricular arrhythmia and in a mixed subgroup of rare NIHDs. There was no significant relationship between LHE and ejection fraction. There was no correlation between enddiastolic volume and LHE in either myocarditis (P = 0.13) or dilated cardiomyopathy (P = 0.62). LHE was unrelated to LV-mass in aortic stenosis (P = 0.13) and hypertrophic cardiomyopathy (P = 0.38).

CONCLUSIONS

Distinct LHE patterns exist in various NIHDs and their visualization may ultimately aid diagnosis. Unlike in ischemic heart disease, the structure-function relationship does not appear to be strong.

Comparison of the effectiveness of saturation pulses in the heart at 3T

Cardiac MRI at 3T provides a means to increase the contrast-to-noise ratio (CNR) for first-pass perfusion MRI. However, both the static magnetic field (B(0)) and radio frequency (RF) field (B(1)) variations within the heart are comparatively higher at 3T than at 1.5T. The increased field variations can degrade the performance of a single rectangular saturation pulse that is conventionally used for magnetization preparation. The accuracy of T(1)-weighted signal measurement depends on the uniformity of the magnetization saturation. The purpose of this study was to assess the relative effectiveness of the rectangular, pulse train, and adiabatic composite (BIR-4) saturation pulses in the human heart at 3T. In volunteers, after nominal saturation, the mean residual magnetization within the left ventricle (LV) was different between all three pulses (0.13 +/- 0.06 vs. 0.03 +/- 0.02 vs. 0.03 +/- 0.01, respectively; P < 0.001). Within paired groups, the mean residual magnetization was significantly higher for the rectangular pulse than for either the pulse train and BIR-4 pulses (P < 0.001), but not different between the pulse train and BIR-4 pulses. The performances of all three saturation pulses were comparatively poorer in the right ventricle (RV) than in the LV, respectively.

Optimization and validation of a fully-integrated pulse sequence for modified look-locker inversion-recovery (MOLLI) T1 mapping of the heart

PURPOSE

To optimize and validate a fully-integrated version of modified Look-Locker inversion-recovery (MOLLI) for clinical single-breathhold cardiac T1 mapping.

MATERIALS AND METHODS

A MOLLI variant allowing direct access to all pulse sequence parameters was implemented on a 1.5T MR system. Varying four critical sequence parameters, MOLLI was performed in eight gadolinium-doped agarose gel phantoms at different simulated heart rates. T1 values were derived for each variant and compared to nominal T1 values. Based on the results, MOLLI was performed in midcavity short-axis views of 20 healthy volunteers pre- and post-Gd-DTPA.

RESULTS

In phantoms, a readout flip angle of 35 degrees , minimum TI of 100 msec, TI increment of 80 msec, and use of three pausing heart cycles allowed for most accurate and least heart rate-dependent T1 measurements. Using this pulse sequence scheme in humans, T1 relaxation times in normal myocardium were comparable to data from previous studies, and showed narrow ranges both pre- and postcontrast without heart rate dependency.

CONCLUSION

We present an optimized implementation of MOLLI for fast T1 mapping with high spatial resolution, which can be integrated into routine imaging protocols. T1 accuracy is superior to the original set of pulse sequence parameters and heart rate dependency is avoided.

Myocardial T1 mapping: application to patients with acute and chronic myocardial infarction

T(1) maps obtained with modified Look-Locker inversion recovery (MOLLI) can be used to measure myocardial T(1). We aimed to evaluate the potential of MOLLI T(1) mapping for the assessment of acute and chronic myocardial infarction (MI). A total of 24 patients with a first MI underwent MRI within 8 days and after 6 months. T(1) mapping was performed at baseline and at selected intervals between 2-20 min following administration of gadopentetate dimeglumine (Gd-DTPA). Delayed-enhancement (DE) imaging served as the reference standard for delineation of the infarct zone. On T(1) maps the myocardial T(1) relaxation time was assessed in hyperenhanced areas, hypoenhanced infarct cores, and remote myocardium. The planimetric size of myocardial areas with standardized T(1) threshold values was measured. Acute and chronic MI exhibited different T(1) changes. Precontrast threshold T(1) maps detected segmental abnormalities caused by acute MI with 96% sensitivity and 91% specificity. Agreement between measurements of infarct size from T(1) mapping and DE imaging was higher in chronic than in acute infarcts. Precontrast T(1) maps enable the detection of acute MI. Acute and chronic MI show different patterns of T(1) changes. Standardized T(1) thresholds provide the potential to dichotomously identify areas of infarction.

Equilibrium signal intensity mapping, an MRI method for fast mapping of longitudinal relaxation rates and for image enhancement

INTRODUCTION

Inhomogeneity of magnetic fields, both B(0) and B(1), has been a major challenge in magnetic resonance imaging (MRI). Field inhomogeneity leads to image artifacts and unreliability of signal intensity (SI) measurements. This work proposes and shows the feasibility of generating equilibrium signal intensity (SI(Eq)) maps that can be utilized either to speed up relaxation-rate measurement or to enhance image quality and relaxation-rate-based weighting in various applications.

METHODS

A 1.5-T MRI scanner was used. In canines (n=4), myocardial infarction was induced, and 48 h after the administration of 0.05 mmol kg(-1) Gd(ABE-DTTA), a contrast agent with slow tissue kinetics, in vivo R(1) mapping was carried out using an inversion recovery (IR)-prepared, fast gradient-echo sequence with varying inversion times (TIs). To test the SI(Eq) mapping method without the confounding effects of motion and blood flow, we carried out ex vivo R(1) mapping after the administration of 0.2 mmol kg(-1) Gd(DTPA) using an IR-prepared, fast spin-echo sequence in another group of dogs (n=2). R(1,full) maps and SI(Eq) maps were generated from the data from both sequences by three-parameter nonlinear curve fitting of the SI versus TI dependence. R(1,full) maps served as the reference standard. Raw IR images were then divided by the SI(Eq) maps, yielding corrected SI maps (COSIMs). Additionally, R(1) values were calculated from each single-TI image separately, using the SI(Eq) value and a one-parameter curve-fitting procedure (R(1,single)). Voxelwise correlation analysis was carried out for the COSIMs and the R(1,single) maps, both versus the standard R(1,full) maps. Deviations of R(1,single) from R(1,full) were statistically evaluated.

RESULTS

In vivo, COSIM versus R(1,full) showed significantly (P<.05) better correlation [correlation coefficient (CC)=0.95] than SI versus R(1,full) with a TI=700-800 ms, which is 200-300 ms longer than the tau(null) (500 ms) of viable myocardium. With such TIs, SI versus R(1,full) yielded CCs of 0.86-0.88. R(1,single) versus R(1,full) yielded a peak CC of 0.96 at TI=700-900 ms. Mean deviations of R(1,single) from R(1,full) were below 5% for TIs between 500 and 1000 ms. Ex vivo, where tau(null) was 300 ms, the advantage of correction with SI(Eq) was not in the improvement of linear correlation but more in the reduction of scatter. Peak CCs for SI versus R(1,full) and COSIM versus R(1,full) at TI=500 ms were 0.96 for both. The ex vivo CC for R(1,single) versus R(1,full) at TI=500 ms was 0.98. Mean deviations of R(1,single) from R(1,full) were below 5% for TIs between 400 and 700 ms.

CONCLUSIONS

Once the corresponding SI(Eq) map is obtained from a control stack, R(1) can be obtained accurately, using only a single IR image and without the need for a stack of TI-varied images. This approach could be applied in various dynamic MRI studies where short measurement time, once the dynamics has started, is of essence. When using this method with IR-prepared T(1)-weighted images, it is essential that the single TI be chosen such that the longitudinal relaxation in all voxels of interest would have passed tau(null). SI(Eq) maps are also useful in eliminating confounders from MR images to allow obtaining SI values that reflect more faithfully the relaxation parameter (R(1)) sought.

Phase-encoding strategies for optimal spatial resolution and T1 accuracy in 3D Look-Locker imaging

The Look-Locker (LL) imaging method provides an accurate and efficient approach for mapping the spin-lattice relaxation time, T(1). However, the same recovery of signal during LL image acquisition required to estimate T(1) also results in unwanted modulation of k-space. This is particularly problematic with 3D LL imaging as the number of phase-encoding steps during the recovery interval (e.g., 16) increases in an effort to reduce imaging times. This modulation of k-space has the effect of introducing a point spread function (PSF), which can lead to either image blurring (if the earlier tip angles are assigned to the centre of k-space) or edge enhancement (if the earlier tip angles are assigned to the edges of k-space), thus corrupting T(1) estimation, particularly for small objects. In this study, the PSF and its effect on the acquired images for four different interleaved phase-encode schemes (centric-in, centric-out, sequential and hybrid-sequential) are simulated for a range of T(1), tip angle and 3D LL acquisition parameters expected in practice. It is shown by simulation and confirmed experimentally in phantoms that a hybrid sequential phase-encoding scheme reduces image blurring while maintaining T(1) accuracy ( approximately 2%) and precision (2%) over a range of object sizes down to 2 pixels (2 mm).

Cardiac MRI is Complementary to Echocardiography in the Assessment of Cardiac Masses

Despite the fact that the incidence of cardiac tumors is low, the prompt evaluation and adequate intervention of these is highly important. Although most tumors of the heart are considered histologically benign, there are significant risks associated with these "benign" tumors. These are associated with significant morbidity and mortality due to obstruction of blood flow, alterations of conduction, propagation of arrhythmias, and thromboembolism, depending on their size, location, and nature. With the advent of noninvasive imaging modalities--traditionally echocardiography; but more recently using cross-sectional imaging with cardiac computed tomography and magnetic resonance imaging--cardiac tumors can be optimally assessed providing a greater opportunity for curative treatments by cardiothoracic surgery.

Characterization of myocardial viability using MR and CT imaging

Cardiovascular magnetic resonance (MR) imaging is of proven clinical value for the noninvasive characterization of myocardial viability. Computed tomography (CT) is also being exploited for this indication. Examples of each of these imaging strategies for the assessment of myocardial viability will be provided in this review. Key MRI concepts and practical considerations such as customized MR imaging techniques and tailored imaging protocols dedicated to viability assessment are outlined with the primary focus on recent developments. Clinical applications of MR-based viability assessment are reviewed, ranging from rapid functional cine imaging to tissue characterization using T2-weighted imaging and T1-weighted late-contrast-enhanced imaging. Next, the merits and limitations of state-of-the-art CT imaging are surveyed, and their implications for viability assessment are considered. The final emphasis is on current trends and future directions in noninvasive viability assessment using MRI and CT.

Manganese dipyridoxyl-diphosphate (MnDPDP) as a viability marker in patients with myocardial infarction

PURPOSE

To evaluate contrast accumulation in left ventricular (LV) myocardium after manganese dipyridoxyl-diphosphate (MnDPDP) administration in patients with recent first time myocardial infarction.

MATERIALS AND METHODS

MnDPDP (5 micromol/kg) was administered to 10 patients with recent myocardial infarction (three to 12 weeks). One slice of interest (SOI) likely to traverse the infarction was chosen, and sectorial pre- and postcontrast longitudinal relaxivity rates (R(1)) and signal changes during infusion were estimated with a fast gradient echo sequence. LV volume and wall thickening were measured in short-axis cine recordings. Infarct localization from R(1) and wall thickening data were compared by vector analyses.

RESULTS

Reduced wall thickening was associated with reduced precontrast R(1) and reduced contrast enhancement. Both remote and infarcted regions showed rapid initial contrast accumulation. In remote regions, this was followed by a continuing slow increase. Mean precontrast R(1) was 0.87 +/- 0.06 second(-1) in infarcted regions and 0.96 +/- 0.03 second(-1) in remote regions (P < 0.001). Mean R(1) change over one hour was 0.24 +/- 0.07 second(-1) in infarcted regions and 0.38 +/- 0.03 second(-1) in remote regions (P < 0.0001).

CONCLUSION

Remote regions showed larger increases in R(1) than infarcted regions. This is most likely due to selective and slow Mn accumulation in viable myocytes.

Magnetic resonance imaging for ischemic heart disease

Cardiac MRI has long been recognized as an accurate and reliable means of evaluating cardiac anatomy and ventricular function. Considerable progress has been made in the field of cardiac MRI, and cardiac MRI can provide accurate evaluation of myocardial ischemia and infarction (MI). Late gadolinium (Gd)-enhanced MRI can clearly delineate subendocardial infarction, and the assessment of transmural extent of infarction on late enhanced MRI has been shown to be useful in predicting functional recovery of dysfunctional myocardium in patients after MI. Stress first-pass contrast-enhanced (CE) myocardial perfusion MRI can be used to detect subendocardial ischemia, and recent studies have demonstrated the high diagnostic accuracy of stress myocardial perfusion MRI for detecting significant coronary artery disease (CAD). Free-breathing, whole-heart coronary MR angiography (MRA) was recently introduced as a method that can provide visualization of all three major coronary arteries within a single three-dimensional (3D) acquisition. With further improvements in MRI techniques and the establishment of a standardized study protocol, cardiac MRI will play a pivotal role in managing patients with ischemic heart disease.