Myocardial tagging with steady state free precession techniques and semi-automatic postprocessing--impact on diagnostic value

Myocardial tagging by cardiovascular magnetic resonance: evolution of techniques--pulse sequences, analysis algorithms, and applications

Cardiovascular magnetic resonance (CMR) tagging has been established as an essential technique for measuring regional myocardial function. It allows quantification of local intramyocardial motion measures, e.g. strain and strain rate. The invention of CMR tagging came in the late eighties, where the technique allowed for the first time for visualizing transmural myocardial movement without having to implant physical markers. This new idea opened the door for a series of developments and improvements that continue up to the present time. Different tagging techniques are currently available that are more extensive, improved, and sophisticated than they were twenty years ago. Each of these techniques has different versions for improved resolution, signal-to-noise ratio (SNR), scan time, anatomical coverage, three-dimensional capability, and image quality. The tagging techniques covered in this article can be broadly divided into two main categories: 1) Basic techniques, which include magnetization saturation, spatial modulation of magnetization (SPAMM), delay alternating with nutations for tailored excitation (DANTE), and complementary SPAMM (CSPAMM); and 2) Advanced techniques, which include harmonic phase (HARP), displacement encoding with stimulated echoes (DENSE), and strain encoding (SENC). Although most of these techniques were developed by separate groups and evolved from different backgrounds, they are in fact closely related to each other, and they can be interpreted from more than one perspective. Some of these techniques even followed parallel paths of developments, as illustrated in the article. As each technique has its own advantages, some efforts have been made to combine different techniques together for improved image quality or composite information acquisition. In this review, different developments in pulse sequences and related image processing techniques are described along with the necessities that led to their invention, which makes this article easy to read and the covered techniques easy to follow. Major studies that applied CMR tagging for studying myocardial mechanics are also summarized. Finally, the current article includes a plethora of ideas and techniques with over 300 references that motivate the reader to think about the future of CMR tagging.

[Myocardial MR tagging: analysis of regional and global myocardial function]

Myocardial MR tagging is a powerful method which allows for assessment of myocardial function and may become an important tool for clinical evaluation of cardiac dysfunction, particularly in ischemic heart disease. In addition to visual assessment it allows direct quantification of myocardial deformation and strain to measure contractility. The use of myocardial tagging has provided new insights into the (patho)physiology of regional wall motion, and several parameters have been described as being useful to identify an ischemic response of the myocardium. One challenge encountered with tagging at 1.5 T is the fading of tags at end-diastole, greatly limiting the evaluation of myocardial function during diastole. Due to longer T(1) relaxation times of the myocardium, tagging at 3 T has shown to have a higher CNR(Tag) and better tag persistence when compared to current clinical gradient-echo tagging protocols at 1.5 T. As a consequence, tagging at higher field strengths may be well suited for the characterization of the diastolic portion of the cardiac cycle in future applications.

Balanced left ventricular myocardial SSFP-tagging at 1.5T and 3T

The purpose of the study was to evaluate the performance of steady-state free precession (SSFP)-tagging at 1.5T and 3T and to define the ideal settings with respect to optimized tag contrast throughout the cardiac cycle for both field strengths. To identify optimal imaging parameters data acquisition was repeated for different flip angles. Left ventricular tag-tissue contrast, tag fading times, tag persistence, and myocardial signal-to-noise ratio (SNR) were quantified in basal, mid-ventricular, and apical slice locations. To assess the effect of field strength on image quality and artifact level, additional semiquantitative image grading was performed by two experienced readers. SSFP-tagging at 3T proved superior to 1.5T and provided significantly enhanced tag persistence and myocardial SNR while maintaining overall image quality and artifact level. The definition of a tag quality index demonstrated optimal SSFP-tagging performance for a flip angle of 20 degrees . Diastolic tag visibility was improved at 3T and resulted in enhanced average tag persistence of 789 +/- 128 ms compared to 523 +/- 40 ms at 1.5T. For SSFP-tagging at 3T the combination of T(1) lengthening and superior myocardial SNR is highly promising and has the potential to improve the depiction of tagged myocardial function throughout the entire cardiac cycle.