Detection of scarred and viable myocardium using a new magnetic resonance imaging technique: blood oxygen level dependent (BOLD) MRI

Myocardial involvement in end-stage renal disease patients with anemia as assessed by cardiovascular magnetic resonance native T1 mapping: An observational study

Cardiovascular disease has become to the main cause of death in the patients with end-stage renal disease (ESRD), and anemia is associated with increased cardiovascular morbidity and mortality in these patients. This study aimed to explore the impact of anemia on myocardial fibrosis using T1 mapping technique in patients with ESRD. A total of 128 subjects including 98 ESRD patients (65 with anemia, 33 without anemia) and 30 normal controls were enrolled. All subjects were underwent cardiovascular magnetic resonance to obtain cardiac cine and T1 mapping images. As potential markers of fibrosis, native T1 values and global longitudinal strain derived by feature-tracking technique were compared. Differences between 3 groups were analyzed using one-way analysis of variance. Associations between variables were assessed by Pearson and Spearman correlation coefficient appropriately. An independent association was identified by the multiple stepwise linear regression analysis. Intraclass correlation was applied to assess observer variability. In all ESRD patients, native T1 values were significantly longer than those of normal controls (global T1, 1357 ± 42 ms vs 1275 ± 48 ms, P < .001). Global T1 value in ESRD patients with anemia was significantly higher (1375 ± 36 ms) compared to that in ESRD patients without anemia (1322 ± 25 ms) and normal controls (1275 ± 48 ms), respectively (all P < .001). Global T1 correlated with hemoglobin negatively (R= -0.499, P < .001). Multiple stepwise linear regression analysis presented the anemia is independently associated with global T1 (R = 0.607, P < .001). Global longitudinal strain was remarkably reduced in ESRD patients with anemia in comparison to those without anemia (P < .001). Diffuse myocardial fibrosis could be detected by native T1 mapping in ESRD patients with long-term anemia. Anemia is an important factor in myocardial fibrosis in ESRD patients, and the evaluation of myocardial involvement is worth considering for clinical management.

[Oxygenation-sensitive cardiac magnetic resonance imaging]

BACKGROUND

Oxygenation-sensitive cardiac magnetic resonance imaging (OS-CMR) is an evolving cardiac imaging technique offering new perspectives to understand, predict, and diagnose cardiac pathologies.

OBJECTIVES

To provide an overview of the basic principles of OS-CMR, the current diagnostic applications and how it may aid in future diagnostic challenges.

MATERIALS AND METHODS

Description, analysis, and interpretation of the current literature on basic research and applicational studies in both humans and animals assessing OS-CMR.

RESULTS

OS-CMR is based on the paramagnetic properties of deoxygenated hemoglobin, which is visualized by a T2*-sensitive sequence. The measured signal correlates with the oxygenation of the myocardium and can analyze vascular function during pharmacological vasodilation or vasoactive breathing exercises (hyperventilation, apnea). The herewith triggered changes in myocardial oxygenation and oxygenation reserve can be used to identify relevant stenoses in coronary artery disease. Other areas of application involve myocardial hypertrophy, microvascular dysfunction, and pulmonary hypertension.

CONCLUSION

A broad number of applications for the clinical use of OS-CMR exist so far, especially in combination with breathing exercises. OS-CMR can be conducted medication- and needle-free. Limitations involve the current lack of clinically approved, automated evaluation tools and the unavailability of vendor- and site-independent normal values.

Myocardial Tissue Oxygenation and Microvascular Blood Volume Measurement Using a Contrast Blood Oxygenation Level-Dependent Imaging Model

OBJECTIVES

We propose a method of quantitatively measuring drug-induced microvascular volume changes, as well as drug-induced changes in blood oxygenation using calibrated blood oxygen level-dependent magnetic resonance imaging (MRI). We postulate that for MRI signals there is a contribution to R2* relaxation rates from static susceptibility effects of the intravascular blood that scales with the blood volume/magnetic field and depends on the oxygenation state of the blood. These may be compared with the effects of an intravascular contrast agent. With 4 R2* measurements, microvascular blood volume (MBV) and tissue oxygenation changes can be quantified with the administration of a vasoactive drug.

MATERIALS AND METHODS

The protocol examined 12 healthy rats in a prospective observational study. R2* maps were acquired with and without infusion of adenosine, which increases microvascular blood flow, or dobutamine, which increases myocardial oxygen consumption. In addition, R2* maps were acquired after the intravenous administration of a monocrystalline iron oxide nanoparticle, with and without adenosine or dobutamine.

RESULTS

Total microvascular volume was shown to increase by 10.8% with adenosine and by 25.6% with dobutamine ( P < 0.05). When comparing endocardium versus epicardium, both adenosine and dobutamine demonstrated significant differences between endocardial and epicardial MBV changes ( P < 0.05). Total myocardial oxygenation saturation increased by 6.59% with adenosine and by 1.64% with dobutamine ( P = 0.27). The difference between epicardial and endocardial oxygenation changes were significant with each drug (adenosine P < 0.05, dobutamine P < 0.05).

CONCLUSIONS

Our results demonstrate the ability to quantify microvascular volume and oxygenation changes using calibrated blood oxygen level-dependent MRI, and we demonstrate different responses of adenosine and dobutamine. This method has clinical potential in examining microvascular disease in various disease states without the administration of radiopharmaceuticals or gadolinium-based contrast agents.

Gated metabolic myocardial imaging, a surrogate for dual perfusion-metabolism imaging by positron emission tomography

Objective

Perfusion-metabolism mismatch pattern on positron emission tomography (PET) predicts hibernating myocardium. We assess the ECG-gated metabolic PET as a surrogate for the perfusion-metabolism mismatch pattern on PET imaging.

Methods

¹³N-Ammonia (NH₃) and ¹⁸F-fluorodeoxyglucose (FDG) are respectively perfusion and metabolism PET tracers. We used ECG gating to acquire FDG-PET to collect wall thickening (mechanical) data. These allow detection of metabolic activity in regions with reduced contraction (metabolism-mechanical mismatch pattern). We had two data sets on each patient: perfusion-metabolism and metabolism-mechanical data sets. We tested the hypothesis that metabolism-mechanical pattern on PET could predict perfusion-metabolism mismatch pattern.

Results

We studied 55 patients (48 males), mean age 62 years. All were in sinus rhythm, and had impaired left ventricular contraction. Perfusion-metabolism mismatch pattern was found in 26 patients. Metabolism-mechanical mismatch pattern was found in 25 patients. The results were concordant in 52 patients (95%). As a surrogate for perfusion-metabolism mismatch pattern, demonstration of metabolism-mechanical mismatch pattern is highly sensitive (92%) and specific (97%). In this cohort, the positive and negative predictive accuracy of the new method are 96% and 93%, respectively.

Conclusion

Metabolism-mechanical mismatch pattern could predict perfusion-metabolism mismatch pattern in patients with myocardial viability criteria on PET. Prospective validation against the gold standard of improved myocardial contraction after revascularisation is needed.

Hypoxia-induced expression of cellular prion protein improves the therapeutic potential of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are ‘adult' multipotent cells that promote regeneration of injured tissues in vivo. However, differences in oxygenation levels between normoxic culture conditions (21% oxygen) and both the MSC niche (2–8% oxygen) and ischemic injury-induced oxidative stress conditions in vivo have resulted in low efficacy of MSC therapies in both pre-clinical and clinical studies. To address this issue, we examined the effectiveness of hypoxia preconditioning (2% oxygen) for enhancing the bioactivity and tissue-regenerative potential of adipose-derived MSCs. Hypoxia preconditioning enhanced the proliferative potential of MSCs by promoting the expression of normal cellular prion protein (PrP^C). In particular, hypoxia preconditioning-mediated MSC proliferation was regulated by PrP^C-dependent JAK2 and STAT3 activation. In addition, hypoxia preconditioning-induced PrP^C regulated superoxide dismutase and catalase activity, and inhibited oxidative stress-induced apoptosis via inactivation of cleaved caspase-3. In a murine hindlimb ischemia model, hypoxia preconditioning enhanced the survival and proliferation of transplanted MSCs, ultimately resulting in improved functional recovery of the ischemic tissue, including the ratio of blood flow perfusion, limb salvage, and neovascularization. These results suggest that Hypo-MSC offer a therapeutic strategy for accelerated neovasculogenesis in ischemic diseases, and that PrP^C comprises a potential target for MSC-based therapies.

Improving Cell Engraftment in Cardiac Stem Cell Therapy

Myocardial infarction (MI) affects millions of people worldwide. MI causes massive cardiac cell death and heart function decrease. However, heart tissue cannot effectively regenerate by itself. While stem cell therapy has been considered an effective approach for regeneration, the efficacy of cardiac stem cell therapy remains low due to inferior cell engraftment in the infarcted region. This is mainly a result of low cell retention in the tissue and poor cell survival under ischemic, immune rejection and inflammatory conditions. Various approaches have been explored to improve cell engraftment: increase of cell retention using biomaterials as cell carriers; augmentation of cell survival under ischemic conditions by preconditioning cells, genetic modification of cells, and controlled release of growth factors and oxygen; and enhancement of cell survival by protecting cells from excessive inflammation and immune surveillance. In this paper, we review current progress, advantages, disadvantages, and potential solutions of these approaches.

Impaired Myocardial Oxygenation Response to Stress in Patients With Chronic Kidney Disease

BACKGROUND

Coronary artery disease and left ventricular hypertrophy are prevalent in the chronic kidney disease (CKD) and renal transplant (RT) population. Advances in cardiovascular magnetic resonance (CMR) with blood oxygen level-dependent (BOLD) technique provides capability to assess myocardial oxygenation as a measure of ischemia. We hypothesized that the myocardial oxygenation response to stress would be impaired in CKD and RT patients.

METHODS AND RESULTS

Fifty-three subjects (23 subjects with CKD, 10 RT recipients, 10 hypertensive (HT) controls, and 10 normal controls without known coronary artery disease) underwent CMR scanning. All groups had cine and BOLD CMR at 3 T. The RT and HT groups also had late gadolinium CMR to assess infarction/replacement fibrosis. The CKD group underwent 2-dimensional echocardiography strain to assess fibrosis. Myocardial oxygenation was measured at rest and under stress with adenosine (140 μg/kg per minute) using BOLD signal intensity. A total of 2898 myocardial segments (1200 segments in CKD patients, 552 segments in RT, 480 segments in HT, and 666 segments in normal controls) were compared using linear mixed modeling. Diabetes mellitus (P=0.47) and hypertension (P=0.57) were similar between CKD, RT, and HT groups. The mean BOLD signal intensity change was significantly lower in the CKD and RT groups compared to HT controls and normal controls (-0.89±10.63% in CKD versus 5.66±7.87% in RT versus 15.54±9.58% in HT controls versus 16.19±11.11% in normal controls, P<0.0001). BOLD signal intensity change was associated with estimated glomerular filtration rate (β=0.16, 95% CI=0.10 to 0.22, P<0.0001). Left ventricular mass index and left ventricular septal wall diameter were similar between the CKD predialysis, RT, and HT groups. None of the CKD patients had impaired global longitudinal strain and none of the RT group had late gadolinium hyperenhancement.

CONCLUSIONS

Myocardial oxygenation response to stress is impaired in CKD patients and RT recipients without known coronary artery disease, and unlikely to be solely accounted for by the presence of diabetes mellitus, left ventricular hypertrophy, or myocardial scarring. The impaired myocardial oxygenation in CKD patients may be associated with declining renal function. Noncontrast BOLD CMR is a promising tool for detecting myocardial ischemia in the CKD population.

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

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

Contrast-enhanced cardiac magnetic resonance imaging

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

CMR for characterization of the myocardium in acute coronary syndromes

The utility of cardiac magnetic resonance imaging (CMR) as a diagnostic technique is well established. CMR enables tissue characterization, distinction between myocardial scar tissue and viable tissue, and evaluation of myocardial perfusion and contractile function. To date, CMR has been mostly applied in the assessment of stable disease; however, a role for CMR in the acute setting is also emerging. An accurate appraisal of the myocardium with CMR in the first hours after the onset of chest pain could provide supporting information to standard diagnostic tools, such as electrocardiography and measurement of blood biomarkers, which could help guide the selection of appropriate treatment. The aims of this integrated approach include positive identification of an ischemic syndrome, estimation of downstream areas at risk of damage, evaluation of epicardial artery patency and small vessel integrity, quantification of infarct size, and determination of myocardial function. This Review critically evaluates both established and emerging CMR techniques, and relates the imaging findings to the underlying pathophysiological processes in acute coronary syndromes. A more thorough understanding of CMR techniques will clarify their potential clinical applications and limitations, and assess the practicality of CMR in the setting of acute coronary syndromes, where early intervention is crucial to save myocardium at risk of irreversible injury.

Carbogen gas-challenge BOLD MR imaging in a rat model of diethylnitrosamine-induced liver fibrosis

PURPOSE

To investigate the relationship between gas-challenge blood oxygen level-dependent (BOLD) magnetic resonance (MR) imaging measurements and hepatic disease progression in a rat model of diethylnitrosamine (DEN)-induced liver fibrosis.

MATERIALS AND METHODS

The institutional animal care and use committee approved all experiments. Liver fibrosis was induced in 27 male Wistar rats by means of weekly oral gavage with 5 mL of 1.5% DEN solution per kilogram of body weight for 3-11 weeks, which produced varying degrees of liver fibrosis. Eight rats developed nonsubstantial fibrosis; eight rats, substantial fibrosis; and 15 rats, cirrhosis. Four nontreated healthy rats served as controls. Multiple-gradient-echo MR images were acquired in the rats at steady-state normoxia and hyperoxia and then during dynamic gas challenges. The change in R2* (DeltaR2*) during the gas challenge and the ratio of number of activated voxels to total number of voxels in the liver were quantified. Masson trichrome staining of liver tissue was used to identify collagen tissue. Liver fibrosis was assessed by using a semiquantitative METAVIR scoring system and quantitative analysis of the percentage of liver fibrosis. Hepatic hemodynamic responses at BOLD MR imaging were compared across the fibrosis stages at independent-sample t test and linear regression analyses.

RESULTS

DeltaR2* was well correlated with gas-challenge interval. Mean DeltaR2* decreased during liver fibrosis progression, from 19.60 sec(-1) +/- 4.47 (standard deviation) in animals without substantial fibrosis to 14.02 sec(-1) +/- 2.88 and 6.26 sec(-1) +/- 7.40 in animals with substantial fibrosis and cirrhosis, respectively (P = .006 for rats without vs rats with substantial fibrosis, P = .001 for rats with substantial fibrosis vs rats with cirrhosis, P < .001 for rats without substantial fibrosis vs rats with cirrhosis). Mean DeltaR2* (r = -0.773) and liver activation (r = -0.691) were inversely correlated with liver fibrosis (P < .001).

CONCLUSION

Carbogen gas-challenge BOLD MR imaging can depict hepatic hemodynamic alterations during the progression of fibrosis and has the potential to serve as a noninvasive, nonenhanced imaging method for liver fibrosis diagnosis and staging.

Remodeling of the ischemia-reperfused murine heart: 11.7-T cardiac magnetic resonance imaging of contrast-enhanced infarct patches and transmurality

Our laboratory has published the first evidence obtained from fast low-angle-shot cine magnetic resonance imaging (11.7 T) studies demonstrating secondary myocyte death after ischemia/reperfusion (IR) of the murine heart. This work provides the first evidence from 11.7-T magnet-assisted pixel-level analysis of the post-IR murine myocardial infarct patches. Changes in function of the remodeling heart were examined in tandem. IR compromised cardiac function and induced LV hypertrophy. During recovery, the IR-induced increase in LV mass was partly offset. IR-induced wall thinning was noted in the anterior aspect of LV and at the diametrically opposite end. Infarct size was observed to be largest on post-IR days 3 and 7. With time (day 28), however, the infarct size was significantly reduced. IR-induced absolute signal-intensity enhancement was highest on post-IR days 3 and 7. As a function of post-IR time, signal-intensity enhancement was attenuated. The threshold of hyperenhanced tissue resulted in delineation of contours that identified necrotic (bona fide infarct) and reversibly injured infarct patches. The study of infarct transmurality indicated that whereas the permanently injured tissue volume remained unchanged, part of the reversibly injured infarct patch recovered in 4 weeks after IR. The approach validated in the current study is powerful in noninvasively monitoring remodeling of the post-IR beating murine myocardium.

Blood oxygen level-dependent (BOLD) MRI: A novel technique for the assessment of myocardial ischemia as identified by nuclear imaging SPECT

BACKGROUND

The different levels of deoxyhemoglobin in the ischemic myocardium, induced by stressors such as dipyridamole, can be detected by blood oxygen level-dependent (BOLD) MRI and may be used to diagnose myocardial ischemia. The aim of this study was to assess the signal change in the myocardium on BOLD MRI as well as wall thickening between rest and dipyridamole stress images in ischemic and non-ischemic myocardium as identified on SPECT imaging.

METHODS

Twelve patients with stress-induced myocardial ischemia on SPECT underwent rest and dipyridamole stress MRI using a double breath-hold, T2()-weighted, ECG-gated sequence to produce BOLD contrast images as well as cine-MRI for wall thickening assessment in 10 of the 12 patients. Signal change on BOLD MRI and wall thickening were compared between rest and stress images in ischemic and non-ischemic myocardial segments as identified on SPECT. In each patient, two MRI slices containing 16 segments per slice were analysed.

RESULTS

In total, there were 384 segments for BOLD analysis and 320 for wall thickening. For BOLD signal 137 segments correlated to segments with reversible ischemia on SPECT and 247 to normal segments, while for wall thickening 112 segments correlated to segments with reversible ischemia and 208 to normal segments. The average BOLD MRI signal intensity change was -13.8 (+/-16.3)% in the ischemic segments compared to -10.3 (+/-14.7)% in the non-ischemic segments (p=0.05). The average wall thickening was 6.4 (+/-3.4) mm in the ischemic segments compared to 8.7 (+/-3.8) mm in the non-ischemic segments (p<0.0001).

CONCLUSION

Stress-induced ischemic myocardium has a different signal change and wall thickening than non-ischemic myocardium and may be differentiated on BOLD MRI. Larger studies are needed to define a threshold for detection and to determine the sensitivity and specificity of this technique.

Understanding the Heart

Methods of noninvasive evaluation of coronary artery disease-including multidetector row computed tomography, electron beam computed tomography, magnetic resonance imaging, and nuclear studies (single photon emission computed tomography, positron emission tomography)-are reviewed.

T2 measurement of the human myocardium using aT2-prepared transient-state trueFISP sequence

A fast and motion-insensitive technique suitable for myocardial BOLD contrast imaging is presented. The method, termed T2-TrueFISP, combines T2 magnetization preparation with steady-state free precession (SSFP) imaging for T2 relaxation mapping of the myocardium in healthy volunteers. The T2 contrast-to-noise ratio (CNR) was optimized with the use of transient-state TrueFISP readout and half-Fourier readout with linear phase encoding. Single-slice myocardial T2-weighted image was obtained within one heartbeat, and a single slice T2 map of the myocardium was obtained in under 5-7 s. A respiratory navigator-gating method was incorporated for serial measurements and signal averaging, with the subjects breathing freely. The mean myocardial T2 relaxation time measured in 12 healthy volunteers was 54 +/- 5.7 ms. Regional variations of T2 values across the myocardium were 7%. Temporal variations across serial T2 measurements in a transmural region covering approximately 0.5 cc of the left ventricular (LV) wall were 3.6% without signal averaging (number of excitations (NEX) = 1) and 1.7% with signal averaging (NEX = 10). According to our preliminary results, the T2-TrueFISP method is expected to provide a robust and sensitive tool for clinical application of myocardial BOLD contrast imaging.

Blood oxygen level-dependent (BOLD) magnetic resonance imaging in patients with dypiridamole induced ischaemia; a PET comparative study

BACKGROUND

Blood oxygen level-dependent (BOLD) MRI relies on changes in deoxyhaemoglobin level in tissues under stress for signal variation and may be used for detection of ischaemic myocardium.

METHODS

15 patients with stress induced myocardial ischaemia on PET scanning underwent rest and dypiridamole stress MRI using a double breath-hold T2-weighted, ECG gated sequence to produce BOLD contrast images and cine-MRI for wall thickening assessment. Signal change on BOLD MRI and wall thickening were compared between rest and stress images in ischaemic and non-ischaemic myocardial segments.

RESULTS

Using PET, 156 segments were identified with reversible ischaemia and 324 as non-ischaemic. The ischaemic segments were found on BOLD MRI to have an average signal change between rest and stress of -16.7% compared to -14% in the non-ischaemic segments (p=0.04). The average wall thickening was 7.8 mm in the ischaemic segments compared with 9.5 mm in the non-ischaemic segments (p<0.0001).

CONCLUSION

BOLD MRI with wall thickening assessment may differentiate ischaemic from non-ischaemic myocardium in patients with stress induced myocardial ischaemia. Larger studies with improved spatial resolution would help define a threshold for detection of ischaemia as well as determine this technique's sensitivity and specificity.

Discrimination of Myocardial Acute and Chronic (Scar) Infarctions on Delayed Contrast Enhanced Magnetic Resonance Imaging With Intravascular Magnetic Resonance Contrast Media

OBJECTIVES

The purpose of this study was to examine the potential of intravascular gadolinium (Gd)-chelates in discriminating acute from chronic myocardial infarctions (MIs).

BACKGROUND

A potential limitation of delayed contrast enhanced magnetic resonance imaging with standard extracellular Gd-chelates is its inability to distinguish acute from chronic MIs.

METHODS

Eight pigs with MIs were studied at 3 days and 8 weeks. Inversion recovery gradient echo (IR-GRE), T(1)-turbo spin echo (TSE), and T(2)-TSE images were acquired before and after administration of intravascular and extracellular Gd-chelates. Triphenyltetrazolium chloride (TTC) was used to delineate infarctions at postmortem. Masson's trichrome and Biotinylated Bandeiria simplicifolia Isolectin B4 stains were used to characterize scarred myocardium. Analysis of variance was used to compare signal intensity (SI) ratios and determine differences in infarct extent.

RESULTS

The intravascular agent produced differential enhancement of acute infarctions at 3 days (SI ratio 5.8 +/- 1.3) but not at 8 weeks (1.6 +/- 0.4, p < 0.01). The extracellular agent provided differential enhancement of both acute (SI ratio 7.7 +/- 1.4) and chronic (7.5 +/- 0.9) infarctions. The extents of enhanced regions in acute infarctions were not different after intravascular (16.0 +/- 1.3%) or extracellular (17.1 +/- 1.7%) agents; at 8 weeks the extent of extracellular enhanced and TTC regions were smaller (13.2 +/- 1.4% and 12.0 +/- 1.5%, respectively). Masson's trichrome stain demonstrated dense scar tissue, signaling the complete healing of infarction. The vascular stain showed that scar tissue contained fewer microvessels oriented in a haphazard array.

CONCLUSIONS

The combination of intravascular and extracellular Gd-chelates discriminates acute from chronic infarctions on delayed images. This double contrast agent approach can be used to determine the age and extent of infarctions.

Long-term stability of cardiac function in normal and chronically failing mouse hearts in a vertical-bore MR system

We previously demonstrated stability of ventricular volumes and cardiac function in normal and in chronically failing mouse hearts in MR systems with a vertical-bore magnet for up to 1 h. However, in order to exploit the benefits of an increased magnetic field strength of these MR systems in more time-consuming studies required by, for example MR spectroscopy, we investigated whether cardiac function and ventricular volumes of healthy and infarcted mice would be affected in vertical position over a prolonged period. We applied high-resolution MR cine imaging on an 11.7 T vertical MR system to monitor cardiac functional parameters of normal and chronically failing mouse hearts over a period of 3 h in an upright position, with a temporal resolution of < or =15 min. We monitored left-ventricular volumes and cardiac functional parameters in both groups. In normal mice, we detected a decrease of left-ventricular end-systolic volumes by 8 microl and an approximately 23% increase of ejection fraction over time indicating a small but detectable degree of orthostatic dysregulation. Observed changes were more pronounced in mice with heart failure. Despite significant changes in left-ventricular volumes and function, absolute values measured for all functional cardiac parameters are consistent with near-physiological conditions. Thus, mice can be studied in high-field MR systems positioned vertically for 3 h.

Contrast-enhanced MR imaging of the heart: overview of the literature

The use of magnetic resonance (MR) imaging for cardiac diagnosis is expanding, aided by the administration of paramagnetic contrast agents for a growing number of clinical applications. This overview of the literature considers the principles and applications of cardiac MR imaging with an emphasis on the use of contrast media. Clinical applications of contrast material-enhanced MR imaging include the detection and characterization of intracardiac masses, thrombi, myocarditis, and sarcoidosis. Suspected myocardial ischemia and infarction, respectively, are diagnosed by using dynamic first-pass and delayed contrast enhancement. Promising new developments include blood pool contrast media, labeling of myocardial precursor cells, and contrast-enhanced imaging at very high fields.

Future prospects in magnetic resonance imaging

Cardiovascular magnetic resonance (CMR) is widely regarded as capable of providing a cornucopia of detailed diagnostic information. However, of that information, very little is truly unique, and can be obtained by a combination of alternate diagnostic modalities. Given this, it is anticipated that in the short term (1-5 years) CMR will find use primarily as a modality to service patients whose diagnosis is inaccessible to established technologies such as ultrasound and radionuclide imaging. Due to the evolving emphasis on finding new and more efficient approaches to disease detection and prevention, as outlined in a policy-setting speech given by the director of the National Institutes of Health, it is anticipated that the scientific and clinical trial communities will adopt CMR at a more rapid pace due to its inherent dimensional accuracy and comprehensive nature. CMR is particularly well suited to participate in the approaching explosion of nanoparticle technologies, as they are applied to diagnostic and therapeutic approaches. In the longer term (5-10 years), as paradigms of disease detection likely expand beyond evaluation of symptoms and risk factors, the comprehensive nature of information provided by CMR will drive the increase of its use as a primary, first-tier, diagnostic modality. In summary, the use of CMR will become increasingly common, and as understanding of disease processes expand, it will emerge as a diagnostic modality that provides an abundance of unique information.