T1 mapping of the ischemic myocardium: Review of potential clinical use

Native T1 Mapping for the Diagnosis of Myocardial Fibrosis in Patients With Chronic Myocardial Infarction

BACKGROUND

Myocardial fibrosis is a fundamental process in cardiac injury. Cardiac magnetic resonance native T1 mapping has been proposed for diagnosing myocardial fibrosis without the need for gadolinium contrast. However, recent studies suggest that T1 measurements can be erroneous in the presence of intramyocardial fat.

OBJECTIVES

The purpose of this study was to investigate whether the presence of fatty metaplasia affects the accuracy of native T1 maps for the diagnosis of myocardial replacement fibrosis in patients with chronic myocardial infarction (MI).

METHODS

Consecutive patients (n = 312) with documented chronic MI (>6 months old) and controls without MI (n = 50) were prospectively enrolled. Presence and size of regions with elevated native T1 and infarction were quantitatively determined (mean + 5SD) on modified look-locker inversion-recovery and delayed-enhancement images, respectively, at 3.0-T. The presence of fatty metaplasia was determined using an out-of-phase steady-state free-precession cine technique and further verified with standard fat-water Dixon methods.

RESULTS

Native T1 mapping detected chronic MI with markedly higher sensitivity in patients with fatty metaplasia than those without fatty metaplasia (85.6% vs 13.3%) with similar specificity (100% vs 98.9%). In patients with fatty metaplasia, the size of regions with elevated T1 significantly underestimated infarct size and there was a better correlation with fatty metaplasia size than infarct size (r = 0.76 vs r = 0.49). In patients without fatty metaplasia, most of the modest elevation in T1 appeared to be secondary to subchronic infarcts that were 6 to 12 months old; the T1 of infarcts >12 months old was not different from noninfarcted myocardium.

CONCLUSIONS

Native T1 mapping is poor at detecting replacement fibrosis but may indirectly detect chronic MI if there is associated fatty metaplasia. Native T1 mapping for the diagnosis and characterization of myocardial fibrosis is unreliable.

Cardiovascular magnetic resonance imaging in the UK Biobank: a major international health research resource

The UK Biobank (UKB) is a health research resource of major international importance, incorporating comprehensive characterization of >500 000 men and women recruited between 2006 and 2010 from across the UK. There is prospective tracking of health outcomes for all participants through linkages with national cohorts (death registers, cancer registers, electronic hospital records, and primary care records). The dataset has been enhanced with the UKB imaging study, which aims to scan a subset of 100 000 participants. The imaging protocol includes magnetic resonance imaging of the brain, heart, and abdomen, carotid ultrasound, and whole-body dual X-ray absorptiometry. Since its launch in 2015, over 48 000 participants have completed the imaging study with scheduled completion in 2023. Repeat imaging of 10 000 participants has been approved and commenced in 2019. The cardiovascular magnetic resonance (CMR) scan provides detailed assessment of cardiac structure and function comprising bright blood anatomic assessment (sagittal, coronal, and axial), left and right ventricular cine images (long and short axes), myocardial tagging, native T1 mapping, aortic flow, and imaging of the thoracic aorta. The UKB is an open access resource available to health researchers across all scientific disciplines from both academia and industry with no preferential access or exclusivity. In this paper, we consider how we may best utilize the UKB CMR data to advance cardiovascular research and review notable achievements to date.

Clinical assessment of adenosine stress and rest cardiac magnetic resonance T1 mapping for detecting ischemic and infarcted myocardium

Cardiac magnetic resonance (CMR) spin-lattice relaxation time (T1) may be influenced by pathologic conditions due to changes in myocardial water content. We aimed to validate the principle and investigate T1 mapping at rest and adenosine stress to differentiate ischemic and infarcted myocardium from controls. Patients with suspected coronary artery disease who underwent CMR were prospectively recruited. Native rest and adenosine stress T1 maps were obtained using standard modified Look-Locker Inversion-Recovery technique. Among 181 patients included, T1 values were measured from three groups. In the control group, 72 patients showed myocardium with a T1 profile of 1,039 ± 75 ms at rest and a significant increase during stress (4.79 ± 3.14%, p < 0.001). While the ischemic (51 patients) and infarcted (58 patients) groups showed elevated resting T1 compared to controls (1,040 ± 90 ms for ischemic; 1,239 ± 121 ms for infarcted, p < 0.001), neither of which presented significant T1 reactivity (1.38 ± 3.02% for ischemic; 1.55 ± 5.25% for infarcted). We concluded that adenosine stress and rest T1 mapping may be useful to differentiate normal, ischemic and infarcted myocardium.

Practical Guide to Evaluating Myocardial Disease by Cardiac MRI

OBJECTIVE. A spectrum of pathophysiologic mechanisms can lead to the development of myocardial disorders including ischemia, genetic abnormalities, and systemic disorders. Cardiac MRI identifies different myocardial disorders, provides prognostic information, and directs therapy. In comparison with other imaging modalities, cardiac MRI has the advantage of allowing both functional assessment and tissues characterization in a single examination without the use of ionizing radiation. Newer cardiac MRI techniques including mapping can provide additional information about myocardial disease that may not be detected using conventional techniques. Emerging techniques including MR spectroscopy and finger printing will likely change the way we understand the pathophysiology mechanisms of the wide array of myocardial disorders. CONCLUSION. Imaging of myocardial disorders encompasses a large variety of conditions including both ischemic and nonischemic diseases. Cardiac MRI sequences, such as balanced steady-state free precession and late gadolinium enhancement, play a critical role in establishing diagnosis, determining prognosis, and guiding therapeutic management. Additional sequences-including perfusion imaging, T2*, real-time cine, and T2-weighted sequences-should be performed in specific clinical scenarios. There is emerging evidence for the use of mapping in imaging of myocardial disease. Multiple other new techniques are currently being studied. These novel techniques will likely change the way myocardial disorders are understood and diagnosed in the near future.

The Value of T1 Mapping Techniques in the Assessment of Myocardial Interstitial Fibrosis

Cardiac fibrosis, characterized by net accumulation of extracellular matrix in the myocardium, is a common final pathway of heart failure. This myocardial fibrosis (MF) is not necessarily the primary cause of dysfunction; it often results from a reparative process activated in response to cardiomyocyte injury. In light of currently available treatments, late-identified MF could be definitive or irreversible, associated with worsening ventricular systolic function, abnormal cardiac remodeling, and increased ventricular stiffness and arrhythmia. T1 mapping should be used to detect incipient changes leading to myocardial damage in several clinical conditions and also in subclinical disease. This article reviews available techniques for MF detection, focusing on noninvasive quantification of diffuse fibrosis and clinical applications.

Cardiac magnetic resonance T1 mapping. Part 2: Diagnostic potential and applications

Non-invasive identification and differentiation of myocardial diseases represents the primary objectives of cardiac magnetic resonance (CMR) longitudinal relaxation time (T1) and extracellular volume (ECV) mapping. Given the fact that myocardial T1 and ECV values overlap throughout and within left ventricular phenotypes, a central issue to be addressed is whether and to what extent myocardial T1 and ECV mapping provides additional or superior diagnostic information to standard CMR imaging, and whether native T1 mapping could be employed as a non-contrast alternative to late gadolinium enhancement (LE) imaging. The present review aims to summarize physiological and pathophysiological alterations in native T1 and ECV values and summarized myocardial T1 and ECV alterations associated with cardiac diseases to support the translation of research findings into routine CMR imaging.

Molecular imaging of myocardial infarction with Gadofluorine P - A combined magnetic resonance and mass spectrometry imaging approach

Background

Molecular MRI is becoming increasingly important for preclinical research. Validation of targeted gadolinium probes in tissue however has been cumbersome up to now. Novel methodology to assess gadolinium distribution in tissue after in vivo application is therefore needed.

Purpose

To establish combined Magnetic Resonance Imaging (MRI) and Mass Spectrometry Imaging (MSI) for improved detection and quantification of Gadofluorine P deposition in scar formation and myocardial remodeling.

Materials and methods

Animal studies were performed according to institutionally approved protocols. Myocardial infarction was induced by permanent ligation of the left ascending artery (LAD) in C57BL/6J mice. MRI was performed at 7T at 1 week and 6 weeks after myocardial infarction. Gadofluorine P was used for dynamic T₁ mapping of extracellular matrix synthesis during myocardial healing and compared to Gd-DTPA. After in vivo imaging contrast agent concentration as well as distribution in tissue were validated and quantified by spatially resolved Matrix-Assisted Laser Desorption Ionization (MALDI) MSI and Laser Ablation – Inductively Coupled Plasma – Mass Spectrometry (LA-ICP-MS) imaging.

Results

Both Gadofluorine P enhancement as well as local tissue content in the myocardial scar were highest at 15 minutes post injection. R₁ values increased from 1 to 6 weeks after MI (1.62 s⁻¹ vs 2.68 s⁻¹, p = 0.059) paralleled by an increase in Gadofluorine P concentration in the infarct from 0.019 mM at 1 week to 0.028 mM at 6 weeks (p = 0.048), whereas Gd-DTPA enhancement showed no differences (3.95 s⁻¹ vs 3.47 s⁻¹, p = 0.701). MALDI-MSI results were corroborated by elemental LA-ICP-MS of Gadolinium in healthy and infarcted myocardium. Histology confirmed increased extracellular matrix synthesis at 6 weeks compared to 1 week.

Conclusion

Adding quantitative MSI to MR imaging enables a quantitative validation of Gadofluorine P distribution in the heart after MI for molecular imaging.