A multi-vendor, multi-center study on reproducibility and comparability of fast strain-encoded cardiovascular magnetic resonance imaging

Myocardial strain is a convenient parameter to quantify left ventricular (LV) function. Fast strain-encoding (fSENC) enables the acquisition of cardiovascular magnetic resonance images for strain-measurement within a few heartbeats during free-breathing. It is necessary to analyze inter-vendor agreement of techniques to determine strain, such as fSENC, in order to compare existing studies and plan multi-center studies. Therefore, the aim of this study was to investigate inter-vendor agreement and test-retest reproducibility of fSENC for three major MRI-vendors. fSENC-images were acquired three times in the same group of 15 healthy volunteers using 3 Tesla scanners from three different vendors: at the German Heart Institute Berlin, the Charité University Medicine Berlin-Campus Buch and the Theresien-Hospital Mannheim. Volunteers were scanned using the same imaging protocol composed of two fSENC-acquisitions, a 15-min break and another two fSENC-acquisitions. LV global longitudinal and circumferential strain (GLS, GCS) were analyzed by a trained observer (Myostrain 5.0, Myocardial Solutions) and for nine volunteers repeatedly by another observer. Inter-vendor agreement was determined using Bland-Altman analysis. Test-retest reproducibility and intra- and inter-observer reproducibility were analyzed using intraclass correlation coefficient (ICC) and coefficients of variation (CoV). Inter-vendor agreement between all three sites was good for GLS and GCS, with biases of 0.01–1.88%. Test-retest reproducibility of scans before and after the break was high, shown by ICC- and CoV values of 0.63–0.97 and 3–9% for GLS and 0.69–0.82 and 4–7% for GCS, respectively. Intra- and inter-observer reproducibility were excellent for both parameters (ICC of 0.77–0.99, CoV of 2–5%). This trial demonstrates good inter-vendor agreement and test–retest reproducibility of GLS and GCS measurements, acquired at three different scanners from three different vendors using fSENC. The results indicate that it is necessary to account for a possible bias (< 2%) when comparing strain measurements of different scanners. Technical differences between scanners, which impact inter-vendor agreement, should be further analyzed and minimized.

DRKS Registration Number: 00013253.

Universal Trial Number (UTN): U1111-1207-5874.

Spectrally-Presaturated Modulation (SPM): An efficient fat suppression technique for STEAM-based cardiac imaging sequences

Stimulated-echo acquisition mode (STEAM) is a key pulse sequences in MRI in general, and in cardiac imaging in particular. Fat suppression is an important feature in cardiac imaging to improve visualization and eliminate off-resonance and chemical-shift artifacts. Nevertheless, fat suppression comes at the expense of reduced temporal resolution and signal-to-noise ratio (SNR). The purpose of this study is to develop an efficient fat suppression method (Spectrally-Presaturated Modulation) for STEAM-based sequences to enable imaging with high temporal-resolution, high SNR, and no increase in scan time. The developed method is based on saturating the fat magnetization prior to applying STEAM modulation; therefore, only the water-content of the tissues is modulated by the sequence, resulting in fat-suppressed images without the need to run the fat suppression module during image acquisition. The potential significance of the proposed method is presented in two STEAM-based cardiac MRI applications: complementary spatial-modulation of magnetization (CSPAMM), and black-blood cine imaging. Phantom and in vivo experiments are conducted to evaluate the developed technique and compare it to the commonly implemented chemical-shift selective (CHESS) and water-excitation using spectral-spatial selective pulses (SSSP) fat suppression techniques. The results from the phantom and in vivo experiments show superior performance of the proposed method compared to the CHESS and SSSP techniques in terms of temporal resolution and SNR. In conclusion, the developed fat suppression technique results in enhanced image quality of STEAM-based images, especially in cardiac applications, where high temporal-resolution is imperative for accurate measurement of functional parameters and improved performance of image analysis algorithms.

Assessment of liver fibrosis using fast strain-encoded MRI driven by inherent cardiac motion

PURPOSE

An external driver-free MRI method for assessment of liver fibrosis offers a promising noninvasive tool for diagnosis and monitoring of liver disease. Lately, the heart's intrinsic motion and MR tagging have been utilized for the quantification of liver strain. However, MR tagging requires multiple breath-hold acquisitions and substantial postprocessing. In this study, we propose the use of a fast strain-encoded (FSENC) MRI method to measure the peak strain (Sp ) in the liver's left lobe, which is in close proximity and caudal to the heart. Additionally, we introduce a new method of measuring heart-induced shear wave velocity (SWV) inside the liver.

METHODS

Phantom and in vivo experiments (11 healthy subjects and 11 patients with liver fibrosis) were conducted. Reproducibility experiments were performed in seven healthy subjects.

RESULTS

Peak liver strain, Sp , decreased significantly in fibrotic liver compared with healthy liver (6.46% ± 2.27% vs 12.49% ± 1.76%; P < 0.05). Heart-induced SWV increased significantly in patients compared with healthy subjects (0.15 ± 0.04 m/s vs 0.63 ± 0.32 m/s; P < 0.05). Reproducibility analysis yielded no significant difference in Sp (P = 0.47) or SWV (P = 0.56).

CONCLUSION

Accelerated external driver-free noninvasive assessment of left liver lobe strain and SWV is feasible using strain-encoded MRI. The two measures significantly separate healthy subjects from patients with fibrotic liver. Magn Reson Med 74:106-114, 2015. © 2014 Wiley Periodicals, Inc.

Strain-encoded breast MRI in phantom and ex vivo specimens with histological validation: preliminary results

PURPOSE

To evaluate the feasibility of using strain-encoded (SENC) breast magnetic resonance images (MRI) for breast cancer detection by examining the compression and relaxation response properties in phantoms and ex vivo breast samples.

METHODS

A tissue phantom was constructed to mimic different sizes of breast masses and tissue stiffness. In addition, five human ex vivo whole breast specimens with and without masses were studied. MR data was acquired on a 3T scanner consisting of T(1)-weighted, fat suppressed spin echo T(2)-weighted, and SENC breast images. Mechanical tissue characteristics (strain) of the phantoms and breast tissue samples were measured using SENC imaging in both compression and relaxation modes. The breast tissue specimens were sectioned and stained in the same plane as the MRI for histological evaluation.

RESULTS

For the phantom, SENC images showed soft masses with quantitative strain values between 35% and 50%, while harder masses had strain values between 0% and 20%. Combined compression (CMP) and relaxation (REX) breast SENC images separately categorized all masses into three different groups. For breast SENC, the signal intensities between ex vivo breast mass and breast glandular tissue were significantly different (-7.6 ± 2.6 verses -20.6 ± 5.4 for SENC-CMP, and 4.2 ± 1.5 verses 22.6 ± 5 for SENC-REX, p < 0.05).

CONCLUSIONS

We have demonstrated that SENC breast MRI can be used to obtain mechanical tissue properties and give quantitative estimates of strain in tumors. This feasibility study provides the basis for future clinical studies.

Regional and global biventricular function in pulmonary arterial hypertension: a cardiac MR imaging study

PURPOSE

To determine whether chronic pulmonary arterial pressure (PAP) elevation affects regional biventricular function and whether regional myocardial function may be reduced in pulmonary arterial hypertension (PAH) patients with preserved global right ventricular (RV) function.

MATERIALS AND METHODS

After informed consent, 35 PAH patients were evaluated with right heart catheterization and cardiac magnetic resonance (MR) imaging and compared with 13 healthy control subjects. Biventricular segmental, section, and mean ventricular peak systolic longitudinal strain (E(LL)), as well as left ventricular (LV) circumferential and RV tangential strains were compared between PAH patients and control subjects and correlated with global function and catheterization of the right heart indexes. Spearman ρ correlation with Bonferroni correction was used. Multiple linear regression analysis was performed to determine predictors for regional myocardial function.

RESULTS

In the RV of PAH patients, longitudinal contractility was reduced at the basal, mid, and apical levels, and tangential contractility was reduced at the midventricular level. Mean RV E(LL) positively correlated with mean PAP (r = 0.62, P < .0014) and pulmonary vascular resistance index (PVRI) (r = 0.77, P < .0014). Mean PAP was a predictor of mean RV E(LL) (β = .19, P = .005) in a multiple linear regression analysis. In the LV, reduced LV longitudinal and circumferential contractility were noted at the base. LV anteroseptal E(LL) positively correlated with increased mean PAP (r = 0.5, P = .03) and septal eccentricity index (r = 0.5, P = .01). In a subgroup of PAH patients with normal global RV function, significantly reduced RV longitudinal contractility was noted at basal and mid anterior septal insertions, as well as the mid anterior RV wall (P < .05 for all).

CONCLUSION

In PAH patients, reduced biventricular regional function is associated with increased RV afterload (mean PAP and PVRI). Cardiac MR imaging helps identify regional RV dysfunction in PAH patients with normal global RV function.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12111599/-/DC1.

The strain-encoded (SENC) MR imaging for detection of global right ventricular dysfunction in pulmonary hypertension

The aim of this study was to explore whether the regional peak longitudinal (LS) and circumferential strains (CS) at the right ventricular (RV) free wall could be used to identify global RV dysfunction in relation to RV ejection fraction (RVEF) and plasma concentration of brain natriuretic peptide (BNP) in pulmonary hypertension (PH). A total of 37 consecutive patients diagnosed with PH and 13 healthy control subjects were included. Fast strain encoded and routine cine MRI was performed. The LS and CS at three RV levels were quantified and their relations with RVEF and BNP were investigated. Receiver operating characteristic (ROC) analysis was employed to assess the diagnostic utility of strain encoded MRI for the detection of low RVEF. Significant correlations with LS were observed for RVEF and BNP. Compared to CS, LS showed better correlation with RVEF. The mid-ventricular level of RV was the most sensitive site for evaluation of RV dysfunction. According to our ROC analysis, LS showed higher sensitivity and specificity to detect low RVEF. Compared to CS, LS showed stronger correlations with RVEF and BNP and could be a good detector of RV dysfunction in PH.

Left ventricular diastolic function in type 2 diabetes mellitus is associated with myocardial triglyceride content but not with impaired myocardial perfusion reserve

PURPOSE

To study myocardial perfusion reserve and myocellular metabolic alterations indicated by triglyceride content as possible causes of diastolic dysfunction in patients with type 2 diabetes mellitus, preserved systolic function, and without clinically evident coronary artery disease.

MATERIALS AND METHODS

Patients with type 2 diabetes mellitus (n = 42) underwent cardiac magnetic resonance (CMR) for quantification of 1) myocardial contractility by strain-encoded MR (SENC); 2) myocardial triglyceride content by proton magnetic resonance spectroscopy ((1) H-MRS); and 3) myocardial perfusion reserve during pharmacologic hyperemia. Age-matched healthy volunteers (n = 16) also underwent CMR to acquire normal values for myocardial strain and perfusion reserve.

RESULTS

Stress CMR procedures were successfully performed in all subjects, and no regional inducible perfusion defects were observed in type 2 diabetes mellitus patients. Diastolic strain rate and myocardial perfusion reserve were significantly impaired in patients with type 2 diabetes mellitus compared to control subjects (P < 0.001 for both). Interestingly, impaired diastolic function in type 2 diabetes mellitus was not associated with impaired myocardial perfusion reserve (r = 0.12, P = NS). Conversely a significant association was observed between diastolic dysfunction and myocardial triglyceride content (r = -0.71, P < 0.001), which proved to be independent of age, gender, diabetes duration, blood pressure, and fasting blood glucose.

CONCLUSION

Myocardial steatosis may represent an early marker of diabetic heart disease, triggering subclinical myocardial dysfunction irrespective of myocardial perfusion reserve.

Improved hardware for higher spatial resolution strain-encoded (SENC) breast MRI for strain measurements

RATIONALE AND OBJECTIVES

Early detection of breast lesions using mammography has resulted in lower mortality rates. However, some breast lesions are mammography occult, and magnetic resonance imaging (MRI) is recommended, but it has lower specificity. It is possible to achieve higher specificity by using strain-encoded (SENC) MRI and/or magnetic resonance elastography. SENC breast MRI can measure the strain properties of breast tissue. Similarly, magnetic resonance elastography is used to measure the elasticity (ie, shear stiffness) of different tissue compositions interrogating the tissue mechanical properties. Reports have shown that malignant tumors are three to 13 times stiffer than normal tissue and benign tumors.

MATERIALS AND METHODS

The investigators have developed a SENC breast hardware device capable of periodically compressing the breast, thus allowing for longer scanning time and measuring the strain characteristics of breast tissue. This hardware enables the use of SENC MRI with high spatial resolution (1 × 1 × 5 mm(3)) instead of fast SENC imaging. Simple controls and multiple safety measures were added to ensure accurate, repeatable, and safe in vivo experiments.

RESULTS

Phantom experiments showed that SENC breast MRI has higher signal-to-noise ratio and contrast-to-noise ratio than fast SENC imaging under different scanning resolutions. Finally, the SENC breast device reproducibility measurements resulted in a difference of <1 mm with a 1% strain difference.

CONCLUSIONS

SENC breast magnetic resonance images have higher signal-to-noise ratio and contrast-to-noise ratios than fast SENC images. Thus, combining SENC breast strain measurements with diagnostic breast MRI to differentiate benign from malignant lesions could potentially increase the specificity of diagnosis in the clinical setting.

Real-time single-heartbeat fast strain-encoded imaging of right ventricular regional function: normal versus chronic pulmonary hypertension

Patients with pulmonary hypertension and suspected right ventricular (RV) dysfunction often have dyspnea at rest, making reliable assessment of RV function using traditional breath-holding methods difficult to perform. Using single-heartbeat fast strain encoding (Fast-SENC) imaging, peak systolic RV circumferential and longitudinal strains were measured in 11 healthy volunteers and 11 pulmonary hypertension patients. Fast-SENC RV longitudinal strain and circumferential strain measurements were compared to conventional SENC and MR tagging, respectively. Fast-SENC circumferential and longitudinal RV shortening correlated closely with SENC measurements (r = 0.86, r = 0.90, P < 0.001 for all). Circumferential strain, by conventional tagging, showed moderate correlation with Fast-SENC in pulmonary hypertension patients only (r = 0.5, P = 0.003). A nonuniform pattern of RV circumferential shortening was depicted in both groups. Peak systolic circumferential strain was significantly reduced at the basal RV in pulmonary hypertension patients (-18.06 +/- 3.3 versus -21.9 +/- 1.9, P < 0.01) compared to normal individuals, while peak systolic longitudinal strain was significantly reduced at all levels (P < 0.01 for all). Fast-SENC is a feasible and reliable technique for rapid quantification of RV regional function in a single-heartbeat acquisition. Information derived from Fast-SENC allows characterization of RV regional function in normal individuals and in pulmonary hypertension patients.

Myocardial tissue tagging with cardiovascular magnetic resonance

Cardiovascular magnetic resonance (CMR) is currently the gold standard for assessing both global and regional myocardial function. New tools for quantifying regional function have been recently developed to characterize early myocardial dysfunction in order to improve the identification and management of individuals at risk for heart failure. Of particular interest is CMR myocardial tagging, a non-invasive technique for assessing regional function that provides a detailed and comprehensive examination of intra-myocardial motion and deformation. Given the current advances in gradient technology, image reconstruction techniques, and data analysis algorithms, CMR myocardial tagging has become the reference modality for evaluating multidimensional strain evolution in the human heart. This review presents an in depth discussion on the current clinical applications of CMR myocardial tagging and the increasingly important role of this technique for assessing subclinical myocardial dysfunction in the setting of a wide variety of myocardial disease processes.

Strain-encoded cardiac magnetic resonance for the evaluation of chronic allograft vasculopathy in transplant recipients

The aim of our study was to investigate the ability of Strain-Encoded magnetic resonance imaging (MRI) to detect cardiac allograft vasculopathy (CAV) in heart transplantation (HTx)-recipients. In consecutive subjects (n = 69), who underwent cardiac catheterization, MRI was performed for quantification of myocardial strain and perfusion reserve. Based on angiographic findings subjects were classified: group A including patients with normal vessels; group B, patients with stenosis <50%; and group C, patients with severe CAV (stenosis >or= 50%). Significant correlations were observed between myocardial perfusion reserve with peak systolic strain (r =-0.53, p < 0.001) and with mean diastolic strain rate (r = 0.82, p < 0.001). Peak systolic strain and strain rate were significantly reduced only in group C, while mean diastolic strain rate and myocardial perfusion reserve were already reduced in group B and A. Myocardial perfusion reserve and mean diastolic strain rate had higher accuracy for the detection of CAV (AUC = 0.95, 95% CI = 0.87-0.99 and AUC = 0.93, 95% CI = 0.84-0.98, respectively) and followed peak systolic strain and strain rate (AUC = 0.80, 95% CI = 0.69-0.89 and AUC = 0.78, 95% CI = 0.67-0.87, respectively). Besides the quantification of myocardial perfusion, the estimation of the diastolic strain rate is a useful parameter for CAV assessment. In combination with the clinical evaluation, these parameters may be effective tools for the routine surveillance of HTx-recipients.

Cine cardiac imaging using black-blood steady-state free precession (BB-SSFP) at 3T

PURPOSE

To propose a new black-blood (BB) pulse sequence that provides BB cine cardiac images with high blood-myocardium contrast. The proposed technique is based on the conventional steady-state free precession (SSFP) sequence.

MATERIALS AND METHODS

Numerical simulations of the Bloch equation were conducted to compare the resulting signal-to-noise ratio (SNR) to that of conventional BB imaging, including the effects of changing the imaging flip angle and heart rates. Simulation results were verified using a gel phantom experiment and five normal volunteers were scanned using the proposed technique.

RESULTS

The new sequence showed higher SNR and contrast-to-noise ratio (CNR) (approximately 100%) compared to the conventional BB imaging. Also, the borders of the left ventricle (LV) and right ventricle (RV) appear more distinguishable than the conventional SSFP. We were also able to cover about 80% of the cardiac cycle with short breath-hold time (approximately 10 cardiac cycles) and with reasonable SNR and CNR.

CONCLUSION

Based on an SSFP conventional sequence, the new sequence provides BB cines that cover most of the cardiac cycle and with higher SNR and CNR than the conventional BB sequences.

Clinical assessment of left ventricular rotation and strain: a novel approach for quantification of function in infarcted myocardium and its border zones

Left ventricular (LV) circumferential strain and rotation have been introduced as clinical markers of myocardial function. This study investigates how regional LV apical rotation and strain can be used in combination to assess function in the infarcted ventricle. In healthy subjects ( n = 15) and patients with myocardial infarction ( n = 23), LV apical segmental rotation and strain were measured from apical short-axis recordings by speckle tracking echocardiography (STE) and MRI tagging. Infarct extent was determined by late gadolinium enhancement MRI. To investigate mechanisms of changes in strain and rotation, we used a mathematical finite element simulation model of the LV. Mean apical rotation and strain by STE were lower in patients than in healthy subjects (9.0 ± 4.9 vs. 12.9 ± 3.5° and −13.9 ± 10.7 vs. −23.8 ± 2.3%, respectively, P < 0.05). In patients, regional strain was reduced in proportion to segmental infarct extent ( r = 0.80, P < 0.0001). Regional rotation, however, was similar in the center of the infarct and in remote viable myocardium. Minimum and maximum rotations were found at the infarct borders: minimum rotation at the border zone opposite to the direction of apical rotation, and maximum rotation at the border zone in the direction of rotation. The simulation model reproduced the clinical findings and indicated that the dissociation between rotation and strain was caused by mechanical interactions between infarcted and viable myocardium. Systolic strain reflects regional myocardial function and infarct extent, whereas systolic rotation defines infarct borders in the LV apical region. Regional rotation, however, has limited ability to quantify regional myocardial dysfunction.

Strain-encoded cardiac MR during high-dose dobutamine stress testing: comparison to cine imaging and to myocardial tagging

PURPOSE

To investigate regional strain response during high-dose dobutamine stress cardiac magnetic resonance imaging (DS-CMR) using myocardial tagging and Strain-Encoded MR (SENC).

MATERIALS AND METHODS

Stress induced ischemia was assessed by wall motion analysis, by tagged CMR and by SENC in 65 patients with suspected or known CAD who underwent DS-CMR in a clinical 1.5 Tesla scanner. Coronary angiography deemed as the standard reference for the presence or absence of CAD (> or =50% diameter stenosis) in all patients.

RESULTS

SENC and conventional tagging detected abnormal strain response in six and five additional patients, respectively, who were missed by cine images and proved to have CAD by angiography (P < 0.05 for SENC versus cine, P = 0.06 for tagging versus cine and p = NS for SENC versus tagging). On a per-vessel level, wall motion analysis on cine images showed high specificity (95%) but moderate sensitivity (70%) for the detection of CAD. Tagging and SENC yielded significantly higher sensitivity of 81% and 89%, respectively (P < 0.05 for tagging and P < 0.01 for SENC versus wall motion analysis, and p = NS for SENC versus tagging), while specificity was equally high (96% and 94%, respectively, P = NS for all).

CONCLUSION

Both the direct color-coded visualization of strain on CMR images and the generation of additional visual markers within the myocardium with tagged CMR represent useful adjuncts for DS-CMR, which may provide incremental value for the detection of CAD in humans. J. Magn. Reson.

Strain-encoded MRI to evaluate normal left ventricular function and timing of contraction at 3.0 Tesla

PURPOSE

To define the reproducibility of strain-encoded (SENC) magnetic resonance imaging (MRI) for assessment of regional left ventricular myocardial strain and timing of contraction in a 3T MRI system.

MATERIALS AND METHODS

The study population consisted of 16 healthy subjects. SENC measurements were performed in three short-axis (SA) slices (apical, mid, and basal) and three long-axis (LA) views (two-, three-, and four-chamber) for assessment of maximal transmural systolic strain and time to peak strain. To assess the interobserver and interstudy reproducibility, analysis of SENC MRI was performed by two independent observers who were blinded to each other's results and four studies were repeated on a different day.

RESULTS

Maximal longitudinal strain was highest at the apex, as was maximal circumferential strain. Peak longitudinal strain occurred earliest at the base, as did peak circumferential strain. Interclass correlation coefficient between observers and repeated studies ranged from 0.92 to 0.98 (P < 0.001 for all).

CONCLUSION

The present study demonstrates the ability of SENC MRI to define regional left ventricular strain and the time sequence of regional strain. SENC MRI may represent a highly objective method for quantifying regional left ventricular function.

Strain-encoded (SENC) magnetic resonance imaging to evaluate regional heterogeneity of myocardial strain in healthy volunteers: Comparison with conventional tagging

PURPOSE

To evaluate the ability of strain-encoded (SENC) magnetic resonance imaging (MRI) for regional systolic and diastolic strain analysis of the myocardium in healthy volunteers.

MATERIALS AND METHODS

Circumferential and longitudinal peak systolic strain values of 75 healthy volunteers (35 women and 40 men, mean age 44 +/- 12 years) were measured using SENC at 1.5T. MR tagging was used as the reference standard for measuring regional function. Diastolic function was assessed in the 10 youngest (24 +/- 8 years) and 10 oldest (62 +/- 5 years) subjects.

RESULTS

Peak strain values assessed with SENC were comparable to those obtained by MR tagging, showing narrow limits of agreement (limits of agreement -5.6% to 8.1%). Regional heterogeneity was observed between different segments of the left ventricle (LV) by both techniques (P < 0.001). Longitudinal strain obtained by SENC was also heterogenous (P < 0.001). Interestingly, no age- or gender-specific differences in peak systolic strain were observed, whereas the peak rate of relaxation of circumferential strain rate was decreased in the older group.

CONCLUSION

SENC is a reliable tool for accurate and objective quantification of regional myocardial systolic as well as diastolic function. In agreement with tagged MRI, SENC detected slightly heterogeneous myocardial strain within LV segments.

Regional right ventricular function and timing of contraction in healthy volunteers evaluated by strain-encoded MRI

PURPOSE

To prospectively determine the feasibility and accuracy of strain-encoded (SENC) magnetic resonance imaging (MRI) for the characterization of the right ventricular free wall (RVFW) strain and timing of contraction at 3.0 Tesla (3T) MRI.

MATERIALS AND METHODS

In 12 healthy volunteers the RVFW was divided into three segments (anterior, lateral, and inferior) in each of three short-axis (SA) slices (apical, mid, and basal) and into three segments (apical, mid, and basal) in a four-chamber view. The study was repeated on a different day and interobserver and interstudy agreements were evaluated.

RESULTS

Maximal systolic longitudinal strain values were highest at the apex and base, with a pronounced decrease in the medial segments (apex: -19.1% +/- 1.4; mid: -17.4% +/- 2; base: -19.4% +/- 2.4, P < 0.001), and maximal systolic circumferential strain showed the highest values at the apex (apex: -18.1% +/- 1.7; mid: -17.6% +/- 1.2; base: -16.6% +/- 0.9, P < 0.001). Peak systolic longitudinal and circumferential shortening occurred earliest at the apex compared to the mid-ventricle and base. Excellent interobserver and interstudy correlation and agreement were observed.

CONCLUSION

The use of SENC MRI for the assessment of normal RV contraction pattern is feasible and accurate in 3T MRI.

Strain-encoded cardiac MRI as an adjunct for dobutamine stress testing: incremental value to conventional wall motion analysis

BACKGROUND

High-dose dobutamine stress MRI is safe and feasible for the diagnosis of coronary artery disease (CAD) in humans. However, the assessment of cine scans relies on the visual interpretation of regional wall motion, which is subjective. Recently, strain-encoded MRI (SENC) has been proposed for the direct color-coded visualization of myocardial strain. The purpose of our study was to compare the diagnostic value of SENC with that provided by conventional wall motion analysis for the detection of inducible ischemia during dobutamine stress MRI.

METHODS AND RESULTS

Stress-induced ischemia was assessed by wall motion analysis and by SENC in 101 patients with suspected or known CAD and in 17 healthy volunteers who underwent dobutamine stress MRI in a clinical 1.5-T scanner. Quantitative coronary angiography deemed as the standard reference for the presence or absence of significant CAD (> or =50% diameter stenosis). On a coronary vessel level, SENC detected inducible ischemia in 86 of 101 versus 71 of 101 diseased coronary vessels (P<0.01 versus cine) and showed normal strain response in 189 of 202 versus 194 of 202 vessels with <50% stenosis (P=NS versus cine). On a patient level, SENC detected inducible ischemia in 63 of 64 versus 55 of 64 patients with CAD (P<0.05 versus cine) and showed normal strain response in 32 of 37 versus 34 of 37 patients without CAD (P=NS versus cine). Quantification analysis demonstrated a significant correlation between strain rate reserve and coronary artery stenosis severity (r(2)=0.56, P<0.001), and a cutoff value of strain rate reserve of 1.64 was deemed as a highly accurate marker for the detection of > or =50% stenosis (area under the curve, 0.96; SE, 0.01; 95% CI, 0.94 to 0.98; P<0.001).

CONCLUSIONS

The direct color-coded visualization of strain on MR images is a useful adjunct for dobutamine stress MRI, which provides incremental value for the detection of CAD compared with conventional wall motion readings on cine images.

Strain-encoded MRI for evaluation of left ventricular function and transmurality in acute myocardial infarction

BACKGROUND

Strain-encoded imaging (SENC) is a new technique for myocardial deformation analysis in cardiac MRI. The aim of the study was, therefore, to evaluate whether myocardial deformation imaging performed by SENC allows for quantification of regional left ventricular function and is related to transmurality states of infarcted tissue in patients with acute myocardial infarction.

METHODS AND RESULTS

Cardiac MRI was performed in 38 patients with acute myocardial infarction 3+/-1 days after successful reperfusion using a clinical 1.5-T MRI scanner. Ten healthy volunteers served as controls. SENC is a technique that directly measures peak circumferential strain from long-axis views and peak longitudinal strain from short-axis views. Measurements were obtained for each segment in a modified 17-segment model. Wall motion and infarcted tissue were evaluated semiquantitatively from steady-state free-precession cine sequences and contrast-enhanced MR images and were then related to myocardial strain. Comparison of peak circumferential strain assessed by SENC and MR tagging was performed. In total, 456 segments were analyzed. Peak circumferential and longitudinal strain calculated from SENC images was significantly different in regions defined as normokinetic, hypokinetic, or akinetic (P<0.001). A cutoff peak systolic circumferential strain value of -10% differentiated nontransmural from transmural infarcted myocardium, with a sensitivity of 97% and a specificity of 94%. Strain analysis of SENC and MR tagging correlated well (r=0.76) with narrow limits of agreement (-9.9% to 8.5%).

CONCLUSIONS

SENC provides rapid and objective quantification of regional myocardial function and allows discrimination between different transmurality states in patients with acute myocardial infarction.

A combined harmonic phase and strain-encoded pulse sequence for measuring three-dimensional strain

Measurement of myocardial strain provides direct information about heart function that can be correlated with disease. We present an MRI pulse sequence that acquires in just six heartbeats both harmonic phase (HARP) and strain-encoded (SENC) images and provides dense measurements of radial, circumferential and longitudinal strains within a single short-axis slice. Normal volunteer data confirm the feasibility of this pulse sequence, and acquired data demonstrate the strain measurement reliability.

Identification of different heart tissues from MRI C-SENC images using an unsupervised multi-stage fuzzy clustering technique

PURPOSE

To objectively characterize different heart tissues from functional and viability images provided by composite-strain-encoding (C-SENC) MRI.

MATERIALS AND METHODS

C-SENC is a new MRI technique for simultaneously acquiring cardiac functional and viability images. In this work, an unsupervised multi-stage fuzzy clustering method is proposed to identify different heart tissues in the C-SENC images. The method is based on sequential application of the fuzzy c-means (FCM) and iterative self-organizing data (ISODATA) clustering algorithms. The proposed method is tested on simulated heart images and on images from nine patients with and without myocardial infarction (MI). The resulting clustered images are compared with MRI delayed-enhancement (DE) viability images for determining MI. Also, Bland-Altman analysis is conducted between the two methods.

RESULTS

Normal myocardium, infarcted myocardium, and blood are correctly identified using the proposed method. The clustered images correctly identified 90 +/- 4% of the pixels defined as infarct in the DE images. In addition, 89 +/- 5% of the pixels defined as infarct in the clustered images were also defined as infarct in DE images. The Bland-Altman results show no bias between the two methods in identifying MI.

CONCLUSION

The proposed technique allows for objectively identifying divergent heart tissues, which would be potentially important for clinical decision-making in patients with MI.

Strain-encoding cardiovascular magnetic resonance for assessment of right-ventricular regional function

BACKGROUND

Tissue tagging by cardiovascular magnetic resonance (CMR) is a comprehensive method for the assessment of cardiac regional function. However, imaging the right ventricle (RV) using this technique is problematic due to the thin wall of the RV relative to tag spacing which limits assessment of regional function using conventional in-plane tagging.

HYPOTHESIS

We hypothesize that the use of through-plane tags in the strain-encoding (SENC) CMR technique would result in reproducible measurements of the RV regional function due to the high image quality and spatial resolution possible with SENC.

AIM

To test the intra- and inter-observer variabilities of RV peak systolic strain measurements with SENC CMR for assessment of RV regional function (systolic strain) in healthy volunteers.

METHODS

Healthy volunteers (n = 21) were imaged using SENC. A four-chamber view was acquired in a single breath-hold. Circumferential strain was measured during systole at six equidistant points along the RV free wall. Peak contraction is defined as the maximum value of circumferential strain averaged from the six points, and regional function is defined as the strain value at each point at the time of peak contraction.

RESULTS

Mean values for peak circumferential strain (+/- standard deviation) of the basal, mid, and apical regions of the RV free wall were -20.4 +/- 2.9%, -18.8 +/- 3.9%, and -16.5 +/- 5.7%, Altman plots showed good intra- and inter-observer agreements with mean difference of 0.11% and 0.32% and limits of agreement of -4.038 to 4.174 and -4.903 to 5.836, respectively.

CONCLUSION

SENC CMR allows for rapid quantification of RV regional function with low intra- and inter-observer variabilities, which could permit accurate quantification of regional strain in patients with RV dysfunction.

Quantitative MR measurements of regional and global left ventricular function and strain after intramyocardial transfer of VM202 into infarcted swine myocardium

Previous studies have shown the beneficial effects of the hepatocyte growth factor (HGF) gene on myocardial perfusion and infarction size but not on the regional strain in relationship to global left ventricular function. A noninvasive magnetic resonance (MR) study was performed to determine the effect of a new HGF gene, VM202, expressing two isoforms of HGF, on regional and global left ventricular function. Pigs (8/group) were divided into three groups: 1) controls without infarction; 2) reperfused, infarcted controls; and 3) infarcted, treated (1 h after reperfusion) with VM202 injected at eight sites. Cine, tagging, and delayed enhancement MR images were acquired at 3 and 50 +/- 3 days after infarction. At 50 days, ejection fraction in infarcted, treated animals increased (38 +/- 1% to 47 +/- 2%, P < 0.01) to the level of controls without infarction (52 +/- 1%, P = 0.16) but decreased in infarcted controls (41 +/- 1% to 37 +/- 1%, P < 0.05). Two-dimensional strain improved in remote, peri-infarcted, and infarcted myocardium. Furthermore, the infarction size was smaller in infarcted, treated animals (7.0 +/- 0.5%) compared with infarcted controls (13.2 +/- 1.6%, P < 0.05). Histopathology showed a lack of hypertrophy in myocytes in peri-infarcted and remote myocardium and the formation of islands/peninsulas of myocytes in infarcted, treated animals but not in infarcted controls. In conclusion, the plasmid HGF gene caused a near complete recovery of ejection fraction and improved the radial and circumferential strain of remote, peri-infarcted, and infarcted regions within 50 days. These beneficial effects may be explained by the combined effects of a speedy and significant infarct resorption and island/peninsulas of hypertrophied myocytes within the infarcted territory but not by compensatory hypertrophy. The combined use of cine and tagging MR imaging provides valuable information on the efficacy of gene therapy.

Combined functional and viability cardiac MR imaging in a single breathhold

The combination of cardiac viability and functional information enhances the identification of different heart tissues in the setting of ischemic heart disease. A method has recently been proposed for obtaining black-blood delayed-enhancement (DE) viability images using the stimulated-echo acquisition mode (STEAM) MRI pulse sequence in a single short breathhold. The method was validated against conventional inversion-recovery (IR) DE images for identifying regions of myocardial infarction (MI). The method was based on the acquisition of three consecutive images of the same anatomical slice. One image has T(1)-weighted contrast in which infarction appears bright. The two other images are used to construct an anatomical image of the heart, which is combined with the first image to produce a black-blood viability image. However, using appropriate modulation and demodulation frequencies, the latter two images bear useful information about myocardial deformation that results in a cardiac strain-encoding (SENC) functional image. In this work, a method is proposed for obtaining three consecutive SENC images in a single acquisition that can be combined to produce a composite image of the heart, which shows both functional and viability information. The proposed technique reduces scan time by one-half, compared with separate acquisitions of functional and viability images, and alleviates misregistration problems caused by separate breathholds.

Real-time monitoring of cardiac regional function using fastHARP MRI and region-of-interest reconstruction

Cardiovascular stress test imaging assists in the diagnosis and monitoring of cardiovascular disease. The procedure can be carried out in a magnetic resonance (MR) scanner using pharmacological agents that mimic the effects of natural exercise. In order to provide real time indication of ischemia, thereby assisting in diagnosis and helping to assure patient safety, it is desirable to have real time monitoring of the myocardial regional function. This paper presents an algorithm for the real time myocardium region-of-interest reconstruction and myocardial strain computation using data acquired from a real time pulse sequence that has been previously reported. The chirp Fourier transform is used for efficient computation, enabling a real-time continuous strain map at a rate of 25 frames/s. Coupled with a real time data path from the scanner to a laptop computer, this algorithm enables real time continuous monitoring of cardiac strain and is targeted for use in the early detection and quantification of ischemia during MR stress tests.

Diminished left ventricular dyssynchrony and impact of resynchronization in failing hearts with right versus left bundle branch block

OBJECTIVES

We compared mechanical dyssynchrony and the impact of cardiac resynchronization therapy (CRT) in failing hearts with a pure right (RBBB) versus left bundle branch block (LBBB).

BACKGROUND

Cardiac resynchronization therapy is effective for treating failing hearts with conduction delay and discoordinate contraction. Most data pertain to LBBB delays. With RBBB, the lateral wall contracts early so that biventricular (BiV) pre-excitation may not be needed. Furthermore, the magnitude of dyssynchrony and impact of CRT in pure RBBB versus LBBB remains largely unknown.

METHODS

Dogs with tachypacing-induced heart failure combined with right or left bundle branch radiofrequency ablation were studied. Basal dyssynchrony and effects of single and BiV CRT on left ventricular (LV) function were assessed by pressure-volume catheter and tagged magnetic resonance imaging, respectively.

RESULTS

Left bundle branch block and RBBB induced similar QRS widening, and LV function (ejection fraction, maximum time derivative of LV pressure [dP/dt(max)]) was similarly depressed in failing hearts with both conduction delays. Despite this, mechanical dyssynchrony was less in RBBB (circumferential uniformity ratio estimate [CURE] index: 0.80 +/- 0.03 vs. 0.58 +/- 0.09 for LBBB, p < 0.04; CURE 0-->1 is dyssynchronous-->synchronous). Cardiac resynchronization therapy had correspondingly less effect on hearts with RBBB than those with LBBB (i.e., 5.5 +/- 1.1% vs. 29.5 +/- 5.0% increase in dP/dt(max), p < 0.005), despite similar baselines. Furthermore, right ventricular-only pacing enhanced function and synchrony in RBBB as well or better than did BiV, whereas LV-only pacing worsened function.

CONCLUSIONS

Less mechanical dyssynchrony is induced by RBBB than LBBB in failing hearts, and the corresponding impact of CRT on the former is reduced. Right ventricular-only pacing may be equally efficacious as BiV CRT in hearts with pure right bundle branch conduction delay.

Three-dimensional magnetic resonance myocardial motion tracking from a single image plane

Three-dimensional imaging for the quantification of myocardial motion is a key step in the evaluation of cardiac disease. A tagged magnetic resonance imaging method that automatically tracks myocardial displacement in three dimensions is presented. Unlike other techniques, this method tracks both in-plane and through-plane motion from a single image plane without affecting the duration of image acquisition. A small z-encoding gradient is subsequently added to the refocusing lobe of the slice-selection gradient pulse in a slice following CSPAMM acquisition. An opposite polarity z-encoding gradient is added to the orthogonal tag direction. The additional z-gradients encode the instantaneous through plane position of the slice. The vertical and horizontal tags are used to resolve in-plane motion, while the added z-gradients is used to resolve through-plane motion. Postprocessing automatically decodes the acquired data and tracks the three-dimensional displacement of every material point within the image plane for each cine frame. Experiments include both a phantom and in vivo human validation. These studies demonstrate that the simultaneous extraction of both in-plane and through-plane displacements and pathlines from tagged images is achievable. This capability should open up new avenues for the automatic quantification of cardiac motion and strain for scientific and clinical purposes.

ZHARP: three-dimensional motion tracking from a single image plane

Three-dimensional imaging and quantification of myocardial function are essential steps in the evaluation of cardiac disease. We propose a tagged magnetic resonance imaging methodology called zHARP that encodes and automatically tracks myocardial displacement in three dimensions. Unlike other motion encoding techniques, zHARP encodes both in-plane and through-plane motion in a single image plane without affecting the acquisition speed. Postprocessing unravels this encoding in order to directly track the 3-D displacement of every point within the image plane throughout an entire image sequence. Experimental results include a phantom validation experiment, which compares zHARP to phase contrast imaging, and an in vivo study of a normal human volunteer. Results demonstrate that the simultaneous extraction of in-plane and through-plane displacements from tagged images is feasible.

Three-Dimensional Mapping of Optimal Left Ventricular Pacing Site for Cardiac Resynchronization

BACKGROUND

The efficacy of cardiac resynchronization therapy (CRT) depends on placement of the left ventricular lead within the late-activated territory. The geographic extent and 3-dimensional distribution of left ventricular (LV) locations yielding optimal CRT remain unknown.

METHODS AND RESULTS

Normal or tachypacing-induced failing canine hearts made dyssynchronous by right ventricular free wall pacing or chronic left bundle-branch ablation were acutely instrumented with a nonconstraining epicardial elastic sock containing 128 electrodes interfaced with a computer-controlled stimulation/recording system. Biventricular CRT was performed using a fixed right ventricular site and randomly selected LV sites covering the entire free wall. For each LV site, global cardiac function (conductance catheter) and mechanical synchrony (magnetic resonance imaging tagging) were determined to yield 3-dimensional maps reflecting CRT impact. Optimal CRT was achieved from LV lateral wall sites, slightly more anterior than posterior and more apical than basal. LV sites yielding > or = 70% of the maximal dP/dtmax increase covered approximately 43% of the LV free wall. This distribution and size were similar in both normal and failing hearts. The region was similar for various systolic and diastolic parameters and correlated with 3-dimensional maps based on mechanical synchrony from magnetic resonance imaging strain analysis.

CONCLUSIONS

In hearts with delayed lateral contraction, optimized CRT is achieved over a fairly broad area of LV lateral wall in both nonfailing and failing hearts, with modest anterior or posterior deviation still capable of providing effective CRT. Sites selected to achieve the most mechanical synchrony are generally similar to those that most improve global function, confirming a key assumption underlying the use of wall motion analysis to optimize CRT.

Improved myocardial tagging contrast in cine balanced SSFP images

PURPOSE

To improve the tag persistence throughout the whole cardiac cycle by providing a constant tag-contrast throughout all the cardiac phases when using balanced steady-state free precession (bSSFP) imaging.

MATERIALS AND METHODS

The flip angles of the imaging radiofrequency pulses were optimized to compensate for the tagging contrast-to-noise ratio (Tag-CNR) fading at later cardiac phases in bSSFP imaging. Complementary spatial modulation of magnetization (CSPAMM) tagging was implemented to improve the Tag-CNR. Numerical simulations were performed to examine the behavior of the Tag-CNR with the proposed method, and to compare the resulting Tag-CNR with that obtained from the more commonly used spoiled gradient echo (SPGR) imaging. A gel phantom, as well as five healthy human volunteers, were scanned on a 1.5T scanner using bSSFP imaging with and without the proposed technique. The phantom was also scanned with SPGR imaging.

RESULTS

With the proposed technique, the Tag-CNR remained almost constant during the whole cardiac cycle. Using bSSFP imaging, the Tag-CNR was about double that of SPGR.

CONCLUSION

The tag persistence was significantly improved when the proposed method was applied, with better Tag-CNR during the diastolic cardiac phase. The improved Tag-CNR will support automated tagging analysis and quantification methods.