Contrast-enhanced Steady-state Free Precession Research Articles

Unravelling the mechanisms of CE-SSFP in imaging myocardium at risk: The effect of relaxation times on myocardial contrast

PurposeThe aim of this study was to investigate the contrast mechanisms of Contrast-enhanced steady-state free-precession (CE-SSFP) through the utilization of Bloch simulations in an experimental porcine model and in patients with acute myocardial infarction. MethodsSix pigs and ten patients with myocardial infarction underwent CMR and tissue characterization at 1.5 T whereas a Bloch simulation framework was utilized to simulate the CE-SSFP signal formation and compare it against the actual CE-SSFP signal acquired from the experimental porcine model and the patient population. The relaxation times of remote, salvaged, and infarcted myocardium were calculated after the injection of gadolinium, at the time of CE-SSFP acquisition. Simulations were performed using the same CE-SSFP pulse sequence as used on the scanner on a set of spins with the calculated relaxation times from the CMR scans. ResultsThe normalized signal intensities of salvaged and infarcted myocardium obtained with simulations were lower than the corresponding normalized signal intensities obtained in vivo in pigs (p < 0.05, 134% vs 153%) and in patients (p < 0.05, 126% vs 145%). The results from simulations showed a linear relationship to the results obtained in the experimental porcine model (r2 = 0.61) and in patients (r2 = 0.69). ConclusionThe T1 and T2 values of remote, salvaged, and infarcted myocardium only partly explain the signal intensities in CE-SSFP images. Bloch simulations suggest that there may be more elements that contribute to the CE-SSFP contrast. Integration of other aspects of the MR experiment into the simulation model could further help to fully unravel the mechanisms of CE-SSFP.

Non-invasive pressure volume loops derived by cardiovascular magnetic resonance: association between area at risk or infarct size and cardiac hemodynamics at 2-6 days after myocardial infarction

Abstract Background A novel non-invasive method for generation of pressure volume loops (PV-loops) using brachial blood pressure and cardiovascular magnetic resonance (CMR) imaging has recently been presented and validated (1). The non-invasive nature of this method enables calculation of PV-loops in large patient cohorts previously not feasible due to the need of invasive measurements. Purpose The purpose of the present study was to investigate how cardiac hemodynamics assessed by PV-loop variables such as stroke work, potential energy, contractility and ventriculoarterial coupling is related to myocardium at risk and infarct size in a cohort of patients with acute myocardial infarction (MI). Method A total of 100 patients with ST-elevation MI (STEMI) were included from the SOCCER, MITOCARE and CHILL-MI trials (2-4). The CHILL-MI cohort (n = 11) was prone to a stricter selection criterion than the SOCCER cohort, including first-time myocardial infarction and no comorbidities. All patients underwent a CMR examination at 2-6 days after MI. Non-invasive PV-loops were generated by combining volumetric CMR data and brachial sphygmomanometric pressure measurements using a recently validated method (1). Maximal elastance (Emax, translated to contractility), stroke work, potential energy and ventriculoarterial coupling (Ea/Emax) were measured from the PV-loops. Myocardium at risk and infarct size were assessed using contrast-enhanced steady state free precession and late gadolinium enhancement images, respectively. Results Contractility, ventriculoarterial coupling, stroke work and potential energy all correlated to myocardium at risk (Emax: r²=0.25, Ea/Emax: r²=0.36, stroke work: r²=0.21, potential energy: r²=0.10) and infarct size (Emax: r²=0.29, Ea/Emax: r²=0.41, stroke work: r²=0.25, potential energy: r²=0.15) as shown in Figure 1. Furthermore, contractility showed a stronger correlation to myocardium at risk (Emax: r²=0.77) than to infarct size (Emax: r²=0.37) for the CHILL-MI patients as shown in Figure 2. Conclusion Non-invasive CMR derived PV-loop parameters can be used to assess cardiac hemodynamics early after STEMI showing that increased myocardium at risk and infarct size are both associated with an increased ventriculoarterial coupling and potential energy, and a decreased contractility and stroke work. To what extent these hemodynamic parameters provide incremental prognostic information compared to conventional parameters such as ejection fraction and left ventricular dimensions after STEMI remains to be determined.Figure 1Figure 2

Longitudinal assessment of myocardial edema following experimental acute myocardial infarction using a comprehensive CMR protocol

Abstract Background Preclinical and clinical data following acute myocardial infarction (MI) and reperfusion have shown a bimodal pattern of edematous myocardium at risk (MaR) on cardiovascular magnetic resonance (CMR) imaging during the first week [1,2]. In contrary, there have also been data demonstrating that MaR is stable during the first week in patients using contrast-enhanced steady-state free precession (CE-SSFP) imaging [3]. Purpose To use a comprehensive CMR protocol to assess the dynamics of edematous MaR during the first week following acute experimental MI. Methods Acute myocardial ischemia was induced in seven pigs by endovascular balloon occlusion in the left anterior descending artery with reperfusion after 40 minutes. CMR was performed at baseline, at 120 minutes, 24 hours and seven days post-reperfusion on a 1.5T scanner. The CMR protocol comprised of a prototype T2-SSFP sequence where two experiments with 16 echo times (T2 mapping16) and with 10 echo times (T2 mapping10) [1] were performed. After contrast administration, a short-axis CE-SSFP stack and late gadolinium enhancement (LGE) images were acquired. T2-maps were acquired in a mid-apical ventricular short-axis slice corresponding to the same anatomical level at all time points. All image analysis was performed using designated software. Severity of MaR was measured by placing a region of interest in the ischemic area on T2 maps and extent of MaR was assessed by delineating hyperintense areas in CE-SSFP short-axis stacks. Data is presented as mean ± SD and one-way ANOVA was used followed by Tukey's multiple comparison test. Results An example of all acquired CMR sequences is shown in Figure 1, with red arrows depicting the extent of edematous MaR. Figure 2 shows the severity of MaR by T2 values from T2 mapping16 where T2 values were significantly lower at 24 hours compared to 120 minutes post-reperfusion (P&amp;lt;0.05). However, no significant difference was seen at 120 minutes or at 24 hours compared to T2 values at seven days (P=0.46 and P=0.35). No difference at baseline (47±3 ms vs 49±3 ms, P=0.10) was observed when comparing T2 mapping16 against T2 mapping10 but a significant difference between the time points 120 min (80±8 ms vs 69±7 ms, P=0.02), 24 h, (69±9 ms vs 54±4 ms, P=0.03), and seven days (76±10 ms vs 67±5 ms, P=0.04) post-reperfusion. There was no statistically significant difference between T2 values post-reperfusion using T2 mapping10 (P=ns). The extent of myocardium at risk assessed by CE-SSFP did not show a bimodal pattern of edema, but rather a significantly lower extent at seven days compared to the extent at 120 minutes and 24 hours (P&amp;lt;0.05). Conclusion The severity and extent of edematous myocardium at risk does not follow a bimodal pattern over the course of one week. However, absolute T2 values differ between T2 mapping sequences and therefore a standardization of a CMR protocol for the assessment of MaR is of importance. Funding Acknowledgement Type of funding sources: Foundation. Main funding source(s): The Swedish Heart-Lung Foundation and The Medical Faculty of Lund University (ALF)

Value of Fast MVO Identification From Contrast-Enhanced Cine (CE-SSFP) Combined With Myocardial Strain in Predicting Adverse Events in Patients After ST-Elevation Myocardial Infarction.

ObjectivesCardiac magnetic resonance imaging (CMR) can be used for a one-step evaluation of myocardial function and pathological features after acute ST-elevation myocardial infarction (STEMI). We aimed to evaluate the value of fast microvascular occlusion (MVO) identification from contrast-enhanced steady-state free precession (CE-SSFP) combined with myocardial strain in predicting major cardiovascular adverse events (MACEs) in primary percutaneous coronary intervention (pPCI) patients with STEMI.MethodsIn total, 237 patients with STEMI who received pPCI and completed CMR scans within the following week were enrolled, MVO identification and the myocardial strain analysis were performed in CE-SSFP images without an additional method. The primary endpoint was the presence of MACE, which is defined as a composite of death, reinfarction, and congestive heart failure (HF).ResultsAfter 13 months of follow-up [interquartile range (IQR): 11–24], 30 patients (14%) developed MACE; the MVO (hazard ratio (HR) was 3.10; 95% CI: 1.14–8.99, p = 0.028), and the infarct size (IS) (HR: 1.03; 95% CI: 1.0–1.06, p = 0.042) and global longitudinal strain (GLS) (HR: 1.08; 95% CI: 1.01–1.17, p = 0.029) were finally associated with MACE. Receiver operating characteristic (ROC) analyses show that the area under the curve (AUC) of GLS was large (0.73 [95% CI, 0.63–0.82], p = 0.001), and the best cut-off was −11.8%, with 76.7% sensitivity and 58.9% specificity, which are greater than those of IS (0.70, 95% CI, 0.60–0.81, p < 0.001) and MVO (0.68, 95% CI, 0.58–0.78, p < 0.001). However, combining MVO and GLS resulted in a much greater finding (AUC = 0.775, 95% CI: 0.727–0.824, p < 0.001) and better sensitivity and specificity (83.3%, 66.5%).ConclusionMicrovascular occlusion identification from contrast-enhanced cine combined with myocardial strain could be a quick and reliable option for patients with STEMI who underwent pPCI; it correlates well with the prognosis of patients with STEMI in terms of MACE.

Three-Dimensional Free-Breathing Whole-Heart Coronary Magnetic Resonance Angiography at 1.5 T: Gadobutrol-Enhanced Gradient-Echo Acquisition Sequence Versus Non-Contrast-Enhanced Steady-State Free Precession Sequence.

The objective of this study was to compare gadobutrol-enhanced gradient-echo sequence (GRE) acquisition with T2-prepared non-contrast-enhanced steady-state free precession (SSFP) in coronary magnetic resonance angiography at 1.5 T. Twenty-one subjects successfully completed GRE and SSFP acquisition. Signal-to-noise ratio (SNR), contrast-to-noise ratio, image quality, sharpness, visibility, length, and lumen diameter of vessels were analyzed by 2 experienced radiologists. The SNR at whole left circumflex artery, left main artery, and proximal left descending artery (LAD) was significantly higher in SSFP acquisition (P < 0.05). The SNR of distal LAD was slightly higher in GRE acquisition (P < 0.05). The contrast-to-noise ratio at distal LAD, proximal and distal RCA were significantly higher with GRE acquisition (P < 0.05). Double-dose gadobutrol-enhanced GRE and unenhanced SSFP coronary magnetic resonance angiography at 1.5 T have their own characteristics, and the combined use of the 2 methods may be taken into consideration.

Validation of contrast enhanced cine steady-state free precession and T2-weighted CMR for assessment of ischemic myocardial area-at-risk in the presence of reperfusion injury.

The purpose of the study was to validate by histopathology, contrast enhanced cine steady-state free precession and T2-weighted CMR for the assessment of ischemic myocardial area-at-risk (AAR) in the presence of microvascular obstruction (MVO). Eleven anesthetized pigs underwent CMR 7 to 10 days post infarction. The area-at-risk was measured from T2-weighted fast spin echo (T2-STIR) and contrast-enhanced steady-state free precession magnetic resonance imaging (CE-SSFP) images using semi-automated algorithms based on a priori knowledge of perfusion territory. Also, late gadolinium enhancement (LGE) was performed to measure final infarct size (FIS). Histopathological comparison with Evans blue dye to define AAR and triphenyltetrazolium chloride to define FIS served as the reference. All infarcts demonstrated MVO on LGE images. Bland-Altman analysis showed no significant bias in AAR or myocardial salvage between T2-STIR and CE-SSFP or between CMR and histopathology. The mean differences ± 2SD from Bland-Altman analysis were: AAR: Evans Blue vs. T2-STIR [0.7%; +13.5%; -12.1%]; AAR: Evans Blue vs. CE-SSFP [0.1%; +13.8%; -13.7%]; AAR: T2-STIR vs. CE-SSFP [0.7%; +6.2%; -4.9%]; Salvage: Evans Blue-TTC vs. T2-STIR-LGE [0.8%; +11.1%; -9.6%]; Salvage: Evans Blue-TTC vs. CE-SSFP-LGE [0.1%; +9.9%; -9.6%]; Salvage: CE-SSFP-LGE vs. T2-STIR-LGE [0.7%; +6.2%; -4.9%]. Both T2-STIR and CE-SSFP sequences allow for unbiased quantification of AAR in the presence of ischemia/reperfusion injury when analysed by semi-automated algorithms. These experimental data, which was validated by histopathology, supports the use of CMR for the assessment of myocardial salvage during the subacute phase.

Quantification of myocardium at risk in ST- elevation myocardial infarction: a comparison of contrast-enhanced steady-state free precession cine cardiovascular magnetic resonance with coronary angiographic jeopardy scores

BackgroundClinical outcome following acute myocardial infarction is predicted by final infarct size evaluated in relation to left ventricular myocardium at risk (MaR). Contrast-enhanced steady-state free precession (CE-SSFP) cardiovascular magnetic resonance imaging (CMR) is not widely used for assessing MaR. Evidence of its utility compared to traditional assessment methods and as a surrogate for clinical outcome is needed.MethodsRetrospective analysis within a study evaluating post-conditioning during ST elevation myocardial infarction (STEMI) treated with coronary intervention (n = 78). CE-SSFP post-infarction was compared with angiographic jeopardy methods. Differences and variability between CMR and angiographic methods using Bland-Altman analyses were evaluated. Clinical outcomes were compared to MaR and extent of infarction.ResultsMaR showed correlation between CE-SSFP, and both BARI and APPROACH scores of 0.83 (p < 0.0001) and 0.84 (p < 0.0001) respectively. Bias between CE-SSFP and BARI was 1.1% (agreement limits -11.4 to +9.1). Bias between CE-SSFP and APPROACH was 1.2% (agreement limits -13 to +10.5). Inter-observer variability for the BARI score was 0.56 ± 2.9; 0.42 ± 2.1 for the APPROACH score; -1.4 ± 3.1% for CE-SSFP. Intra-observer variability was 0.15 ± 1.85 for the BARI score; for the APPROACH score 0.19 ± 1.6; and for CE-SSFP -0.58 ± 2.9%.ConclusionQuantification of MaR with CE-SSFP imaging following STEMI shows high correlation and low bias compared with angiographic scoring and supports its use as a reliable and practical method to determine myocardial salvage in this patient population.Trial registrationClinical trial registration information for the parent clinical trial:Karolinska Clinical Trial Registration (2008)Unique identifier: CT20080014. Registered 04th January 2008

Experimental validation of contrast-enhanced SSFP cine CMR for quantification of myocardium at risk in acute myocardial infarction

BackgroundAccurate assessment of myocardium at risk (MaR) after acute myocardial infarction (AMI) is necessary when assessing myocardial salvage. Contrast-enhanced steady-state free precession (CE-SSFP) is a recently developed cardiovascular magnetic resonance (CMR) method for assessment of MaR up to 1 week after AMI. Our aim was to validate CE-SSFP for determination of MaR in an experimental porcine model using myocardial perfusion single-photon emission computed tomography (MPS) as a reference standard and to test the stability of MaR-quantification over time after injecting gadolinium-based contrast.MethodsEleven pigs were subjected to either 35 or 40 min occlusion of the left anterior descending artery followed by six hours of reperfusion. A technetium-based perfusion tracer was administered intravenously ten minutes before reperfusion. In-vivo and ex-vivo CE-SSFP CMR was performed followed by ex-vivo MPS imaging. MaR was expressed as % of left ventricular mass (LVM).ResultsThere was good agreement between MaR by ex-vivo CMR and MaR by MPS (bias: 1 ± 3% LVM, r2 = 0.92, p < 0.001), between ex-vivo and in-vivo CMR (bias 0 ± 2% LVM, r2 = 0.94, p < 0.001) and between in-vivo CMR and MPS (bias -2 ± 3% LVM, r2 = 0.87, p < 0.001. No change in MaR was seen over the first 30 min after contrast injection (p = 0.95).ConclusionsContrast-enhanced SSFP cine CMR can be used to measure MaR, both in vivo and ex vivo, in a porcine model with good accuracy and precision over the first 30 min after contrast injection. This offers the option to use the less complex ex-vivo imaging when determining myocardial salvage in experimental studies.

Myocardium at risk quantified by contrast enhanced steady-state free precession does not differ in extent or severity when comparing patients with ST-elevation myocardial infarction treated with standard reperfusion or postconditioning

Background Accurate quantification of the ischemic myocardium at risk (MaR) in patients with STelevation myocardial infarction (STEMI) is paramount in studies of therapies seeking to reduce infarct size expressed as percent of MaR. Cardiac magnetic resonance (CMR) is an important clinical research tool for determination of MaR and infarct size in the same examination within one week after STEMI. Recent data suggest that cardioprotective interventions such as ischemic postconditioning or remote conditioning reduce infarct size, but may also reduce the extent and severity of edema detected with T2-weighted imaging. Such an effect might limit the value of determining MaR using T2-weighted sequences. Contrast enhanced steady-state free precession (CESSFP) imaging for quantifying MaR in STEMI has previously been validated compared to single photon emission computed tomography following radiotracer injection prior to reperfusion. The aim of the current study was to compare extent and severity of signal intensity changes in MaR determined from CE-SSFP in patients with STEMI randomized to postconditioning or standard percutaneous coronary intervention (PCI). Methods Patients (n=76, age 37-87 years) eligible for primary PCI due to STEMI were randomized to standard PCI (controls, n=38) or postconditioning (n=38) consisting of four cycles of 60 sec reperfusion and 60 sec of re-occlusion before permanent reperfusion. CMR (1.5T Signa Excite Twin Speed, General Electric Healthcare, Waukesha, Wisconsin, USA) was performed 7.8±1.2 days after myocardial infarction using a protocol in which the contrast agent (0.2 mmol/kg; Omniscan, GE Healthcare) was administered before acquisition of short-axis CE-SSFP images. MaR was determined by manual delineation, in end-diastole and end-systole, as the contrast-enhanced myocardial volume in relation to left ventricular mass (Figure 1). A subgroup of patients underwent quantification of the signal intensity ratio of the contrast enhanced MaR region divided by a remote region.

Myocardium at risk by magnetic resonance imaging: head-to-head comparison of T2-weighted imaging and contrast-enhanced steady-state free precession

AimsTo determine the myocardial salvage index, the extent of infarction needs to be related to the myocardium at risk (MaR). Thus, the ability to assess both infarct size and MaR is of central clinical and scientific importance. The aim of the present study was to explore the relationship between T2-weighted cardiac magnetic resonance (CMR) and contrast-enhanced steady-state free precession (CE-SSFP) CMR for the determination of MaR in patients with acute myocardial infarction.Methods and resultsTwenty-one prospectively included patients with first-time ST-elevation myocardial infarction underwent CMR 1 week after primary percutaneous coronary intervention. For the assessment of MaR, T2-weighted images were acquired before and CE-SSFP images were acquired after the injection of a gadolinium-based contrast agent. For the assessment of infarct size, late gadolinium enhancement images were acquired. The MaR by T2-weighted imaging and CE-SSFP was 29 ± 11 and 32 ± 12% of the left ventricle, respectively. Thus, the MaR with T2-weighted imaging was slightly smaller than that by CE-SSFP (−3.0 ± 4.0%; P < 0.01). There was a significant correlation between the two MaR measures (r2= 0.89, P < 0.01), independent of the time after contrast agent administration at which the CE-SSFP was commenced (2–8 min).ConclusionThere is a good agreement between the MaR assessed by T2-weighted imaging and that assessed by CE-SSFP in patients with reperfused acute myocardial infarction 1 week after the acute event. Thus, both methods can be used to determine MaR and myocardial salvage at this point in time.

Projection imaging of the right coronary artery with an intravenous injection of contrast agent.

Contrast-enhanced (CE) MR angiography of the right coronary artery (RCA) was performed using 2D thick-slice projection imaging with a small (8 mL) intravenous injection of contrast agent in six volunteers. With a tight contrast bolus injection, the RCA was enhanced for a few seconds after the contrast bolus was washed out of the right ventricle. This allowed data to be acquired when only the RCA was enhanced. Using 2D thick-slice magnetization prepared steady-state free precession (SSFP) imaging, background signal was suppressed and a complete data set was acquired in three heartbeats. A mean vessel length of 7.1 +/- 0.9 cm was depicted with a signal-to-noise ratio of 11.8 +/- 0.7 and contrast-to-noise ratio of 6.1 +/- 0.6. Thick-slice 2D projection CE SSFP is a promising method to depict the RCA.