Defining the optimal temporal and spatial resolution for cardiovascular magnetic resonance imaging feature tracking

Feasibility of left atrial strain assessment using cardiac computed tomography in patients with paroxysmal atrial fibrillation

PURPOSE

To evaluate the feasibility of left atrial strain (LAS) assessment using cardiac computed tomography (CT) in patients with paroxysmal atrial fibrillation (PAF).

METHODS

This retrospective single-center study included 98 patients with PAF who underwent cardiac CT and echocardiography before the first catheter ablation. LAS was analyzed using cardiac CT (CT-LAS) and speckle-tracking echocardiography (STE; STE-LAS). LA reservoir (LASr), conduit (LASc), and pump strain (LASp) were calculated by averaging LAS measured in 4- and 2-chamber views. The results were compared using Pearson's correlation coefficients, paired t-tests, and Bland-Altman analysis. Intraclass correlation coefficients (ICCs) were used to evaluate reproducibility.

RESULTS

CT-LAS could be analyzed in all patients, while STE-LAS could be analyzed in 53 (54%) patients. LASr, LASc, and LASp showed significant correlations between CT- and STE-LAS: LASr, r = 0.68, p < 0.001; LASc, r = 0.47, p < 0.001; LASp, r = 0.67, p < 0.001. LASr, LASc, and LASp of CT- and STE-LAS were 23.7 ± 6.0% and 22.1 ± 6.7%, 11.1 ± 3.6% and 11.1 ± 4.1%, and 12.6 ± 4.6% and 11.0 ± 4.1%, respectively. LASr and LASp were significantly higher in CT-LAS than that in STE-LAS (p = 0.023 for LASr and p = 0.001 for LASp). CT-LAS showed excellent reproducibility. The intra- and interobserver ICCs were 0.96 to 0.99 and 0.89 to 0.90, respectively.

CONCLUSION

CT-LAS was successfully analyzed in more patients than STE-LAS and was highly reproducible. The findings suggest that CT-LAS is feasible for patients with PAF.

Reproducibility assessment of rapid strains in cardiac MRI: Insights and recommendations for clinical application

PURPOSE

Studies have shown the incremental value of strain imaging in various cardiac diseases. However, reproducibility and generalizability has remained an issue of concern. To overcome this, simplified algorithms such as rapid atrioventricular strains have been proposed. This multicenter study aimed to assess the reproducibility of rapid strains in a real-world setting and identify potential predictors for higher interobserver variation.

METHODS

A total of 4 sites retrospectively identified 80 patients and 80 healthy controls who had undergone cardiac magnetic resonance imaging (CMR) at their respective centers using locally available scanners with respective field strengths and imaging protocols. Strain and volumetric parameters were measured at each site and then independently re-evaluated by a blinded core lab. Intraclass correlation coefficients (ICC) and Bland-Altman plots were used to assess inter-observer agreement. In addition, backward multiple linear regression analysis was performed to identify predictors for higher inter-observer variation.

RESULTS

There was excellent agreement between sites in feature-tracking and rapid strain values (ICC ≥ 0.96). Bland-Altman plots showed no significant bias. Bi-atrial feature-tracking and rapid strains showed equally excellent agreement (ICC ≥ 0.96) but broader limits of agreement (≤18.0 % vs. ≤3.5 %). Regression analysis showed that higher field strength and lower temporal resolution (>30 ms) independently predicted reduced interobserver agreement for bi-atrial strain parameters (ß = 0.38, p = 0.02 for field strength and ß = 0.34, p = 0.02 for temporal resolution).

CONCLUSION

Simplified rapid left ventricular and bi-atrial strain parameters can be reliably applied in a real-world multicenter setting. Due to the results of the regression analysis, a minimum temporal resolution of 30 ms is recommended when assessing atrial deformation.

Characterization of pulmonary arterial stiffness using cardiac MRI

Pulmonary arterial stiffness (PAS) is a pathologic hallmark of all types of pulmonary hypertension (PH). Cardiac MRI (CMR), a gold-standard imaging modality for the evaluation of pulmonary flow, biventricular morphology and function has been historically reserved for the longitudinal clinical follow-up, PH phenotyping purposes, right ventricular evaluation, and research purposes. Over the last two decades, numerous indices combining invasive catheterization and non-invasive CMR have been utilized to phenotype the character and severity of PAS in different types of PH and to assess its clinically prognostic potential with encouraging results. Many recent studies have demonstrated a strong role of CMR derived PAS markers in predicting long-term clinical outcomes and improving currently gold standard risk assessment provided by the REVEAL calculator. With the utilization of a machine learning strategies, strong diagnostic and prognostic performance of CMR reported in multicenter studies, and ability to detect PH at early stages, the non-invasive assessment of PAS is on verge of routine clinical utilization. In this review, we focus on appraising important CMR studies interrogating PAS over the last 20 years, describing the benefits and limitations of different PAS indices, and their pathophysiologic relevance to pulmonary vascular remodeling. We also discuss the role of CMR and PAS in clinical surveillance and phenotyping of PH, and the long-term future goal to utilize PAS as a biomarker to aid with more targeted therapeutic management.

Impact of temporal and spatial resolution on atrial feature tracking cardiovascular magnetic resonance imaging

BACKGROUND

Myocardial deformation assessment by cardiovascular magnetic resonance-feature tracking (CMR-FT) has incremental prognostic value over volumetric analyses. Recently, atrial functional analyses have come to the fore. However, to date recommendations for optimal resolution parameters for accurate atrial functional analyses are still lacking.

METHODS

CMR-FT was performed in 12 healthy volunteers and 9 ischemic heart failure (HF) patients. Cine sequences were acquired using different temporal (20, 30, 40 and 50 frames/cardiac cycle) and spatial resolution parameters (high 1.5 × 1.5 mm in plane and 5 mm slice thickness, standard 1.8 × 1.8 × 8 mm and low 3.0 × 3.0 × 10 mm). Inter- and intra-observer reproducibility were calculated.

RESULTS

Increasing temporal resolution is associated with higher absolute strain and strain rate (SR) values. Significant changes in strain assessment for left atrial (LA) total strain occurred between 20 and 30 frames/cycle amounting to 2,5-4,4% in absolute changes depending on spatial resolution settings. From 30 frames/cycle onward, absolute strain values remained unchanged. Significant changes of LA strain rate assessment were observed up to the highest temporal resolution of 50 frames/cycle. Effects of spatial resolution on strain assessment were smaller. For LA total strain a general trend emerged for a mild decrease in strain values obtained comparing the lowest to the highest spatial resolution at temporal resolutions of 20, 40 and 50 frames/cycle (p = 0.006-0.046) but not at 30 frames/cycle (p = 0.140).

CONCLUSION

Temporal and to a smaller extent spatial resolution affect atrial functional assessment. Consistent strain assessment requires a standard spatial resolution and a temporal resolution of 30 frames/cycle, whilst SR assessment requires even higher settings of at least 50 frames/cycle.

The effects of flip angle and gadolinium contrast agent on single breath-hold compressed sensing cardiac magnetic resonance cine for biventricular global strain assessment

Background

Due to its potential to significantly reduce scanning time while delivering accurate results for cardiac volume function, compressed sensing (CS) has gained traction in cardiovascular magnetic resonance (CMR) cine. However, further investigation is necessary to explore its feasibility and impact on myocardial strain results.

Materials and methods

A total of 102 participants [75 men, 46.5 ± 17.1 (SD) years] were included in this study. Each patient underwent four consecutive cine sequences with the same slice localization, including the reference multi-breath-hold balanced steady-state free precession (bSSFPref) cine, the CS cine with the same flip angle as bSSFPref before (CS45) and after (eCS45) contrast enhancement, and the CS cine (eCS70) with a 70-degree flip angle after contrast enhancement. Biventricular strain parameters were derived from cine images. Two-tailed paired t-tests were used for data analysis.

Results

Global radial strain (GRS), global circumferential strain (GCS), and global longitudinal strain (GLS) were observed to be significantly lower in comparison to those obtained from bSSFPref sequences for both the right and left ventricles (all p < 0.001). No significant difference was observed on biventricular GRS-LAX (long-axis) and GLS values derived from enhanced and unenhanced CS cine sequences with the same flip angle, but remarkable reductions were noted in GRS-SAX (short-axis) and GCS values (p < 0.001). After contrast injection, a larger flip angle caused a significant elevation in left ventricular strain results (p < 0.001) but did not affect the right ventricle. The increase in flip angle appeared to compensate for contrast agent affection on left ventricular GRS-SAX, GCS values, and right ventricular GRS-LAX, GLS values.

Conclusion

Despite incorporating gadolinium contrast agents and applying larger flip angles, single breath-hold CS cine sequences consistently yielded diminished strain values for both ventricles when compared with conventional cine sequences. Prior to employing this single breath-hold CS cine sequence to refine the clinical CMR examination procedure, it is crucial to consider its impact on myocardial strain results.

Inter-study reproducibility of cardiovascular magnetic resonance-derived hemodynamic force assessments

Cardiovascular magnetic resonance (CMR)-derived hemodynamic force (HDF) analyses have been introduced recently enabling more in-depth cardiac function evaluation. Inter-study reproducibility is important for a widespread clinical use but has not been quantified for this novel CMR post-processing tool yet. Serial CMR imaging was performed in 11 healthy participants in a median interval of 63 days (range 49-87). HDF assessment included left ventricular (LV) longitudinal, systolic peak and impulse, systolic/diastolic transition, diastolic deceleration as well as atrial thrust acceleration forces. Inter-study reproducibility and study sample sizes required to demonstrate 10%, 15% or 20% relative changes of HDF measurements were calculated. In addition, intra- and inter-observer analyses were performed. Intra- and inter-observer reproducibility was excellent for all HDF parameters according to intraclass correlation coefficient (ICC) values (> 0.80 for all). Inter-study reproducibility of all HDF parameters was excellent (ICC ≥ 0.80 for all) with systolic parameters showing lower coeffients of variation (CoV) than diastolic measurements (CoV 15.2% for systolic impulse vs. CoV 30.9% for atrial thrust). Calculated sample sizes to detect relative changes ranged from n = 12 for the detection of a 20% relative change in systolic impulse to n = 200 for the detection of 10% relative change in atrial thrust. Overall inter-study reproducibility of CMR-derived HDF assessments was sufficient with systolic HDF measurements showing lower inter-study variation than diastolic HDF analyses.

Compressed sensing cine imaging with higher temporal resolution for analysis of left atrial strain and strain rate by cardiac magnetic resonance feature tracking

PURPOSE

Cardiac magnetic resonance (CMR) feature tracking (FT) is more widely used in the measurement of left atrial (LA) strain and strain rate (SR). However, in recent years, researchers have attempted to improve the low temporal resolution of CMR-FT to better capture the subtle deformations of the myocardium. The technique of compressed sensing (CS) has been applied clinically, reducing scan time while increasing temporal resolution. The purpose of this study was to explore the effect of the increased temporal resolution of CS cine sequences on the analysis of LA longitudinal strain and SR.

MATERIALS AND METHODS

Twenty-nine healthy subjects were included in the study. They underwent CMR with a reference steady-state free precession cine sequence of conventional temporal resolution (standard SSFP sequence), a cine sequence of higher temporal resolution (HT sequence), and an HT cine sequence with CS (CS HT sequence) (temporal resolution: 22.1-44.3/24.9-47.1 ms, 11.1-19.4 ms, and 8.3-19.4 ms, respectively). The standard SSFP sequence, HT sequence, and CS HT sequence were acquired in all subjects during the same scanning session. LA longitudinal strain and SR, reflecting LA reservoir, conduit, and contraction booster-pump function, were measured by CMR-FT and compared among the three sequences.

RESULTS

The measurements of LASR reservoir, conduit, and booster-pump were significantly higher on the HT and CS HT sequences than on the standard SSFP sequence. The standard SSFP sequence was correlated significantly with the HT and CS HT sequences in terms of LA strain and SR analysis, respectively. The LA strain and SR measurements also showed excellent agreement between the HT and CS HT sequences.

CONCLUSION

Higher temporal resolution led to significantly higher measured LASR values in CMR-FT. Furthermore, the addition of CS reduced scan time and did not affect LA longitudinal strain or SR analysis.

Accelerating GRAPPA reconstruction using SoC design for real-time cardiac MRI

Real-time cardiac MRI is a rapidly developing area of research that has the potential to improve the diagnosis and treatment of cardiovascular diseases. However, the acquisition of high-quality real-time cardiac MR (CMR) images is challenging as it requires a high frame rate and temporal resolution. To overcome this challenge, there have been recent efforts on several approaches including hardware-based improvements and image reconstruction techniques such as compressed sensing and parallel MRI. The use of parallel MRI techniques such as GRAPPA (Generalized Autocalibrating Partial Parallel Acquisition) is a promising approach for improving the temporal resolution of MRI and expanding its applications in clinical practice. However, the GRAPPA algorithm involves a significant amount of computation, particularly for high acceleration factors and large datasets. This can result in long reconstruction times, which can limit the ability to achieve real-time imaging or high frame rates. One solution to this challenge is to use specialized hardware i.e. field-programmable gate arrays (FPGAs). In this work, a novel 32-bit floating-point FPGA-based GRAPPA accelerator is proposed with an aim to reconstruct high-quality cardiac MR images at higher frame rates, making it well suited for real-time clinical applications. The proposed FPGA-based accelerator consists of custom-designed data processing units named as dedicated computational engines (DCEs) that allow for a continuous flow of data between the calibration and synthesis stages of GRAPPA reconstruction process. This greatly increases the throughput and reduces the latency of the overall proposed system. Moreover, a high-speed memory module (DDR4-SDRAM) is integrated with the proposed architecture to store the multi-coil MR data. An on-chip quad-core ARM Cortex-A53 processor is used to manage access control information required for data transfer between the DCEs and DDR4-SDRAM. The proposed accelerator is implemented on Xilinx Zynq UltraScale + MPSoC using high-level synthesis (HLS) and hardware descriptive language (HDL) with an aim to explore the trade-offs between the reconstruction time, resource utilization and design effort. Several experiments have been performed using in-vivo cardiac datasets i.e. 18-receiver coil and 30-receiver coil to evaluate the performance of the proposed accelerator. A comparison is performed with the contemporary CPU and GPU-based GRAPPA reconstruction methods in terms of reconstruction time, frames-per-second and reconstruction accuracy (RMSE and SNR). The results show that the proposed accelerator achieves speed-up factors up to 121× and 9× as compared to the contemporary CPU-based and GPU-based GRAPPA reconstruction methods, respectively. Moreover, it has been demonstrated that the proposed accelerator can achieve reconstruction rates of up to ∼27 frames-per-second while maintaining the visual quality of the reconstructed images.

Optical micro-elastography with magnetic excitation for high frequency rheological characterization of soft media

The propagation of shear waves in elastography at high frequency (>3 kHz) in viscoelastic media has not been extensively studied due to the high attenuation and technical limitations of current techniques. An optical micro-elastography (OME) technique using magnetic excitation for generating and tracking high frequency shear waves with enough spatial and temporal resolution was proposed. Ultrasonics shear waves (above 20 kHz) were generated and observed in polyacrylamide samples. A cutoff frequency, from where the waves no longer propagate, was observed to vary depending on the mechanical properties of the samples. The ability of the Kelvin-Voigt (KV) model to explain the high cutoff frequency was investigated. Two alternative measurement techniques, Dynamic Mechanical Analysis (DMA) and Shear Wave Elastography (SWE), were used to complete the whole frequency range of the velocity dispersion curve while avoid capturing guided waves in the low frequency range (<3 kHz). The combination of the three measurement techniques provided rheology information from quasi-static to ultrasonic frequency range. A key observation was that the full frequency range of the dispersion curve was necessary if one wanted to infer accurate physical parameters from the rheological model. By comparing the low frequency range with the high frequency range, the relative errors for the viscosity parameter could reach 60 % and they could be higher with higher dispersive behavior. The high cutoff frequency may be predicted in materials that follow a KV model over their entire measurable frequency range. The mechanical characterization of cell culture media could benefit from the proposed OME technique.

Cardiovascular magnetic resonance-derived left atrioventricular coupling index and major adverse cardiac events in patients following acute myocardial infarction

BACKGROUND

Recently, a novel left atrioventricular coupling index (LACI) has been introduced providing prognostic value to predict cardiovascular events beyond common risk factors in patients without cardiovascular disease. Since data on cardiovascular magnetic resonance (CMR)-derived LACI in patients following acute myocardial infarction (AMI) are scarce, we aimed to assess the diagnostic and prognostic implications of LACI in a large AMI patient cohort.

METHODS

In total, 1046 patients following AMI were included. After primary percutaneous coronary intervention CMR imaging and subsequent functional analyses were performed. LACI was defined by the ratio of the left atrial end-diastolic volume divided by the left ventricular (LV) end-diastolic volume. Major adverse cardiac events (MACE) including death, reinfarction or heart failure within 12 months after the index event were defined as primary clinical endpoint.

RESULTS

LACI was significantly higher in patients with MACE compared to those without MACE (p < 0.001). Youden Index identified an optimal LACI cut-off at 34.7% to classify patients at high-risk (p < 0.001 on log-rank testing). Greater LACI was associated with MACE on univariate regression modeling (HR 8.1, 95% CI 3.4-14.9, p < 0.001) and after adjusting for baseline confounders and LV ejection fraction (LVEF) on multivariate regression analyses (HR 3.1 95% CI 1.0-9, p = 0.049). Furthermore, LACI assessment enabled further risk stratification in high-risk patients with impaired LV systolic function (LVEF ≤ 35%; p < 0.001 on log-rank testing).

CONCLUSION

Atrial-ventricular interaction using CMR-derived LACI is a superior measure of outcome beyond LVEF especially in high-risk patients following AMI. Trial registration ClinicalTrials.gov, NCT00712101 and NCT01612312.

Effects of spatial and temporal resolution on cardiovascular magnetic resonance feature tracking measurements using a simple realistic numerical phantom

OBJECTIVES

To develop a single-slice numerical phantom with known myocardial motion, at several temporal and in-plane spatial resolutions, for testing and comparison of Cardiovascular Magnetic Resonance (CMR) feature tracking (FT) software.

METHODS

The phantom was developed based on CMR acquisitions of one volunteer (acquired cine, tagging cine, T1 map, T2 map, proton density weighted image). The numerical MRI simulator JEMRIS was used, and the phantom was generated at several in-plane spatial resolutions (1.4 × 1.4 mm2 to 3.0 × 3.0 mm2) and temporal resolutions (20 to 40 cardiac phases). Two feature tracking software packages were tested: Medical Image Tracking Toolbox (MITT) and two versions of cvi42 (v5.3.8 and v5.13.7). The effect of resolution on strain results was investigated with reference to ground-truth radial and circumferential strain.

RESULTS

Peak radial strain was consistently undermeasured more for cvi42 v5.13.7 than for v5.3.8. Increased pixel size produced a trend of increased difference from ground-truth peak strain, with the largest changes for cvi42 obtained using v5.13.7 between 1.4 × 1.4 mm2 and 3.0 × 3.0 mm2, at 9.17 percentage points (radial) and 8.42 percentage points (circumferential).

CONCLUSIONS

The results corroborate the presence of intervendor differences in feature tracking results and show the magnitude of strain differences between software versions.

ADVANCES IN KNOWLEDGE

This study shows how temporal and in-plane spatial resolution can affect feature tracking with reference to the ground-truth strain of a numerical phantom. Results reaffirm the need for numerical phantom development for the validation and testing of FT software.

Cardiac Magnetic Resonance Strain in Beta Thalassemia Major Correlates with Cardiac Iron Overload

BACKGROUND

Beta thalassemia major (Beta-TM) is an inherited condition which presents at around two years of life. Patients with Beta-;TM may develop cardiac iron toxicity secondary to transfusion dependence. Cardiovascular magnetic resonance (CMR) T2*, a technique designed to quantify myocardial iron deposition, is a driving component of disease management. A decreased T2* value represents increasing cardiac iron overload. The clinical manifestation is a decline in ejection fraction (EF). However, there may be early subclinical changes in cardiac function that are not detected by changes in EF. CMR-derived strain assesses myocardial dysfunction prior to decline in EF. Our primary aim was to assess the correlation between CMR strain and T2* in the Beta-TM population.

METHODS

Circumferential and longitudinal strain was analyzed. Pearson's correlation was calculated for T2* values and strain in the Beta-TM population.

RESULTS

We identified 49 patients and 18 controls. Patients with severe disease (low T2*) were found to have decreased global circumferential strain (GCS) in comparison to other T2* groups. A correlation was identified between GCS and T2* (r = 0.5; p < 0.01).

CONCLUSION

CMR-derived strain can be a clinically useful tool to predict early myocardial dysfunction in Beta-TM.

Influence of temporal resolution on computed tomography feature-tracking strain measurements

PURPOSE

Temporal resolution significantly affects strain values demonstrated by Magnetic resonance feature-tracking and speckle-tracking echocardiography. We investigated the influence of R-R interval reconstruction increments on left ventricular (LV) and left atrial (LA) strain measurements of Computed tomography feature-tracking (CT-FT).

METHODS

Subjects who underwent retrospective electrocardiogram-gated coronary CT angiography (CCTA) were retrospectively included, and CCTA images were reconstructed in 5% and 10% steps throughout the entire cardiac cycle (0-100% R-R interval). LV global longitudinal strain (GLS), circumferential strain (GCS), radial strain (GRS), LA GLS, ejection fraction (EF), and left atrioventricular coupling indices were computed. We evaluated the consistency and variability of continuous variables between the two reconstruction increment groups, the demarcation between the LA conduit and contraction phases, and observer reproducibility in 20 randomly selected participants.

RESULTS

Eighty-one participants with or without cardiac disease were included. The reconstruction increment of the R-R interval significantly affected the CT-FT-derived strain values. The 5% R-R increment resulted in significantly larger absolute strain values. LV GRS had the greatest difference between the two groups. In the subgroups with heart rates greater than 80 beats per minute or impaired cardiac function, group differences were attenuated, especially for LV GLS, LV GRS, and LA GLS. The prevalence of definite demarcation between the LA conduit and contraction phases was significantly higher in the 5% R-R reconstruction increment group than in the 10% R-R reconstruction increment group. The average heart rate during CCTA scanning was a strong risk factor for indefinite demarcation, which is independent of LVEF. As average heart rate increased, so did the incidence of indefinite demarcation between the LA conduit and contraction phases. The observer reproducibility of LV and LA strain values was independent of the R-R reconstruction increment.

CONCLUSION

Reconstruction increment of the R-R interval is an important source of variation in LV and LA CT-FT strain values, especially with low heart rate and preserved cardiac function. It is essential to control the heart rate and apply a narrow R-R reconstruction increment to quantify phasic LA strain.

Left Ventricular Responses during Exercise in Highly Trained Youth Athletes: Echocardiographic Insights on Function and Adaptation

There is an increase in the prevalence of elite youth sports academies, whose sole aim is to develop future elite athletes. This involves the exposure of the child and adolescent athlete to high-volume training during a period of volatile growth. The large amount of data in this area has been garnered from the resting echocardiographic left ventricular (LV) evaluation of the youth athlete; while this can provide some insight on the functional adaptations to training, it is unable to elucidate a comprehensive overview of the function of the youth athletes' LV during exercise. Consequently, there is a need to interrogate the LV responses in-exercise. This review outlines the feasibility and functional insight of capturing global indices of LV function (Stroke Index-SVIndex and Cardiac Index-QIndex), systolic and diastolic markers, and cardiac strain during submaximal and maximal exercise. Larger SVI and QI were noted in these highly trained young athletes compared to recreationally active peers during submaximal and maximal exercise. The mechanistic insights suggest that there are minimal functional systolic adaptions during exercise compared to their recreationally active peers. Diastolic function was superior during exercise in these young athletes, and this appears to be underpinned by enhanced determinants of pre-load.

Artificial intelligence fully automated myocardial strain quantification for risk stratification following acute myocardial infarction

Feasibility of automated volume-derived cardiac functional evaluation has successfully been demonstrated using cardiovascular magnetic resonance (CMR) imaging. Notwithstanding, strain assessment has proven incremental value for cardiovascular risk stratification. Since introduction of deformation imaging to clinical practice has been complicated by time-consuming post-processing, we sought to investigate automation respectively. CMR data (n = 1095 patients) from two prospectively recruited acute myocardial infarction (AMI) populations with ST-elevation (STEMI) (AIDA STEMI n = 759) and non-STEMI (TATORT-NSTEMI n = 336) were analysed fully automated and manually on conventional cine sequences. LV function assessment included global longitudinal, circumferential, and radial strains (GLS/GCS/GRS). Agreements were assessed between automated and manual strain assessments. The former were assessed for major adverse cardiac event (MACE) prediction within 12 months following AMI. Manually and automated derived GLS showed the best and excellent agreement with an intraclass correlation coefficient (ICC) of 0.81. Agreement was good for GCS and poor for GRS. Amongst automated analyses, GLS (HR 1.12, 95% CI 1.08-1.16, p < 0.001) and GCS (HR 1.07, 95% CI 1.05-1.10, p < 0.001) best predicted MACE with similar diagnostic accuracy compared to manual analyses; area under the curve (AUC) for GLS (auto 0.691 vs. manual 0.693, p = 0.801) and GCS (auto 0.668 vs. manual 0.686, p = 0.425). Amongst automated functional analyses, GLS was the only independent predictor of MACE in multivariate analyses (HR 1.10, 95% CI 1.04-1.15, p < 0.001). Considering high agreement of automated GLS and equally high accuracy for risk prediction compared to the reference standard of manual analyses, automation may improve efficiency and aid in clinical routine implementation.Trial registration: ClinicalTrials.gov, NCT00712101 and NCT01612312.

Left Ventricular Strain Measurements Derived from MR Feature Tracking: A Head-to-Head Comparison of a Higher Temporal Resolution Method With a Conventional Method

BACKGROUND

Magnetic resonance feature tracking (MR-FT) is an imaging technique that quantifies both global and regional myocardial strain. Currently, conventional MR-FT provides a superior signal and contrast-to-noise ratio but has a relatively low temporal resolution. A higher temporal resolution MR-FT technique may provide improved results.

PURPOSE

To explore the impact of higher temporal resolution on left ventricular (LV) myocardial strain measurements using MR-FT.

STUDY TYPE

Prospective.

POPULATION

One hundred and fifty-three participants including five healthy subjects and patients with various cardiac diseases referred to MR for cardiac assessment.

FIELD STRENGTH

3 T, balanced steady-state free precession sequence with and without compressed sensing (temporal resolution: 10 msec and 40 msec, respectively).

ASSESSMENT

Conventional (40 msec) and higher (10 msec) temporal resolution data were acquired in all subjects during the same scanning session. Global circumferential strain (GCS), global longitudinal strain (GLS), and global radial strain (GRS) as well as peak systolic and diastolic strain rates (SRs) were measured by MR-FT and compared between the two temporal resolutions. We also performed subgroup analyses according to heart rates (HRs) and LV ejection fraction (LVEF).

STATISTICAL TESTS

Paired t-test, Wilcoxon signed-rank test, linear regression analyses, Bland-Altman plots. A P value <0.05 was considered to be statistically significant.

RESULTS

GCS and GRS were significantly higher in the 10-msec temporal resolution studies compared to the 40-msec temporal resolution studies (GCS: -13.00 ± 6.58% vs. -12.51 ± 5.76%; GRS: 21.97 ± 14.54% vs. 20.62 ± 12.52%). In the subgroup analyses, significantly higher GLS, GCS, and GRS values were obtained in subjects with LVEF ≥50%, and significantly higher GCS and GRS values were obtained in subjects with HRs <70 bpm when assessed with the 10-msec vs. the 40-msec temporal resolutions. All the peak systolic and diastolic SRs were significantly higher in the higher temporal resolution acquisitions. This was also true for all subgroups.

DATA CONCLUSIONS

Higher temporal resolution resulted in significantly higher cardiac strain and SR values using MR-FT and could be beneficial, particularly in patients with LVEF ≥50% and HR <70 bpm.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY: Stage 1.

Left atrial evaluation by cardiovascular magnetic resonance: sensitive and unique biomarkers

Left atrial (LA) imaging is still not routinely used for diagnosis and risk stratification, although recent studies have emphasized its importance as an imaging biomarker. Cardiovascular magnetic resonance is able to evaluate LA structure and function, metrics that serve as early indicators of disease, and provide prognostic information, e.g. regarding diastolic dysfunction, and atrial fibrillation (AF). MR angiography defines atrial anatomy, useful for planning ablation procedures, and also for characterizing atrial shapes and sizes that might predict cardiovascular events, e.g. stroke. Long-axis cine images can be evaluated to define minimum, maximum, and pre-atrial contraction LA volumes, and ejection fractions (EFs). More modern feature tracking of these cine images provides longitudinal LA strain through the cardiac cycle, and strain rates. Strain may be a more sensitive marker than EF and can predict post-operative AF, AF recurrence after ablation, outcomes in hypertrophic cardiomyopathy, stratification of diastolic dysfunction, and strain correlates with atrial fibrosis. Using high-resolution late gadolinium enhancement (LGE), the extent of fibrosis in the LA can be estimated and post-ablation scar can be evaluated. The LA LGE method is widely available, its reproducibility is good, and validations with voltage-mapping exist, although further scan-rescan studies are needed, and consensus regarding atrial segmentation is lacking. Using LGE, scar patterns after ablation in AF subjects can be reproducibly defined. Evaluation of 'pre-existent' atrial fibrosis may have roles in predicting AF recurrence after ablation, predicting new-onset AF and diastolic dysfunction in patients without AF. LA imaging biomarkers are ready to enter into diagnostic clinical practice.

Anterior STEMI associated with decreased strain in remote cardiac myocardium

To assess (1) global longitudinal strain (GLS) by feature tracking cardiac magnetic resonance (CMR) in the sub-acute and chronic phases after ST-elevation infarction (STEMI) and compare to GLS in healthy controls, and (2) the evolution of GLS and regional longitudinal strain (RLS) over time, and their relationship to infarct location and size. Seventy-seven patients from the CHILL-MI-trial (NCT01379261) who underwent CMR 2–6 days and 6 months after STEMI and 27 healthy controls were included for comparison. Steady state free precession (SSFP) long-axis cine images were obtained for GLS and RLS, and late gadolinium enhancement (LGE) images were obtained for infarct size quantifications. GLS was impaired in the sub-acute (− 11.8 ± 3.0%) and chronic phases (− 14.3 ± 2.9%) compared to normal GLS in controls (− 18.4 ± 2.4%; p < 0.001 for both). GLS improved from sub-acute to chronic phase (p < 0.001). GLS was to some extent determined by infarct size (sub-acute: r² = 0.2; chronic: r² = 0.2, p < 0.001). RLS was impaired in all 6 wall-regions in LAD infarctions in both the sub-acute and chronic phase, while LCx and RCA infarctions had preserved RLS in remote myocardium at both time points. Global longitudinal strain is impaired sub-acutely after STEMI and improvement is seen in the chronic phase, although not reaching normal levels. Global longitudinal strain is only moderately determined by infarct size. Regional longitudinal strain is most impaired in the infarcted region, and LAD infarctions have effects on the whole heart. This could explain why LAD infarcts are more serious than the other culprit vessel infarctions and more often cause heart failure.