Dark Blood MRI Sequences in Myocardial Tissue Characterization: A Comprehensive Review

Background: Myocardial tissue characterization is crucial in diagnosing and treating cardiovascular diseases (CVDs) such as myocardial infarction (MI), myocarditis, and cardiomyopathies. Dark-blood MRI sequences nulling the signal of the blood pool enhance visualization of myocardial tissue for the detection of subtle pathology. Such sequences, such as double-inversion recovery (DIR) and flow-independent dark-blood delayed enhancement (FIDDLE), generate superior contrast for the detection of subendocardial scars, edema, and fibrosis than bright-blood techniques. Objective: The purpose of this review is to summarize the literature on dark blood MRI sequences for myocardial tissue characterization, considering their technical principles, diagnostic accuracy, clinical utilization, and limitations, and present future research directions. Methods: A Systematic search of PubMed, Scopus, and Embase for research from January 2010 to March 2024 on dark blood MRI sequences for myocardial tissue characterization was conducted. Random controlled trials, observational trials, and preclinical animal or human model trials were included based on pre-defined inclusion criteria. Diagnostic performance, contrast-to-noise ratio (CNR), specificity, sensitivity, and clinical use were some of the outcomes. Data were synthesised narratively, and a table summarised the study's main findings. Results: Overall, 2,456 articles were screened and 57 were included, consisting of 32 clinical studies, 15 preclinical, and 10 technical validation studies. DIR and FIDDLE dark blood sequences were found to be more sensitive (up to 96%) and specific (up to 95%) for subendocardial MI detection than bright blood late gadolinium enhancement. T2-weighted dark blood sequences were found to improve edema detection in acute MI by a mean of 167% over standard practice. Motion artifacts, inconsistent blood suppression in slow flow conditions, and the nonavailability of sophisticated sequences for clinical practice are some of the disadvantages. Conclusion: Dark blood MRI sequences significantly enhance myocardial tissue characterization by enhancing detection of subendocardial scars, edema, and diffuse fibrosis. Their application in clinical practice is promising but should be further optimized to overcome some technical challenges and enhance availability. Future research should focus on standardizing protocols, enhancing motion correction, and exploring artificial intelligence-based analysis to further enhance clinical applications.