Inversion-recovery Fast Low-angle Shot Research Articles

Post‐Myocardial Infarction Remodeling and Hyperkinetic Remote Myocardium in Sheep Measured by Cardiac MRI Feature Tracking

BackgroundCardiac MRI feature tracking (FT) allows objective assessment of segmental left ventricular (LV) function following a myocardial infarction (MI), but its utilization in sheep, where interventions can be tested, is lacking.PurposeTo apply and validate FT in a sheep model of MI and describe post‐MI LV remodeling.Study TypeAnimal model, longitudinal.Animal ModelEighteen lambs (6 months, male, n = 14; female, n = 4; 25.2 ± 4.5 kg).Field Strength/SequenceTwo‐dimensional balanced steady‐state free precession (bSSFP) and 3D inversion recovery fast low angle shot (IR‐FLASH) sequences at 3 T.AssessmentSeven lambs underwent test–retest imaging to assess FT interstudy reproducibility. MI was induced in the remaining 11 by coronary ligation with MRI being undertaken before and 15 days post‐MI. Injury size was measured by late gadolinium enhancement (LGE) and LV volumes, LV mass, ejection fraction (LVEF), and wall thickness (LVWT) were measured, with FT measures of global and segmental radial, circumferential, and longitudinal strain.Statistical TestsSampling variability, inter‐study, intra and interobserver reproducibility were assessed using Pearson's correlation, Bland–Altman analyses, and intra‐class correlation coefficients (ICC). Diagnostic performance of segmental strain to predict LGE was assessed using receiver operating characteristic curve analysis. Significant differences were considered P < 0.05.ResultsInter‐study reproducibility of FT was overall good to excellent, with global strain being more reproducible than segmental strain (ICC = 0.89–0.98 vs. 0.77–0.96). MI (4.0 ± 3.7% LV mass) led to LV remodeling, as evident by significantly increased LV volumes and LV mass, and significantly decreased LVWT in injured regions, while LVEF was preserved (54.9 ± 6.9% vs. 55.6 ± 5.7%; P = 0.778). Segmental circumferential strain (CS) correlated most strongly with LGE. Basal and mid‐ CS increased significantly, while apical CS significantly decreased post‐MI.Data ConclusionFT is reproducible and compensation by hyperkinetic remote myocardium may manifest as overall preserved global LV function.Evidence LevelN/ATechnical EfficacyStage 2

Regional Left Ventricular Myocardial Injury and Function Characterisation by Cardiac Magnetic Resonance Imaging in a Sheep Model of Myocardial Infarction

Left ventricular (LV) remodelling following a myocardial infarction(MI) elicits different responses in infarct and remote LV, with prior studies reporting increased contractility in the latter. We explored the relationship between myocardial injury and its functional consequences using a combination of 3D late gadolinium enhancement (LGE), feature tracking (FT) cardiac magnetic resonance (CMR) and autopsy findings in a sheep model of MI. MI was induced in sheep (n=11) by coronary artery ligation under general anaesthesia. Baseline (pre-MI) and follow-up (15d post-MI) CMR exams were performed for cine imaging. LGE imaging was performed using a 3D inversion recovery fast low angle shot (IR-FLASH) sequence in the follow-up examination. MI size was confirmed at post-mortem. Regions of MI identified by imaging were compared with post-mortem findings using AHA LV segmentation. The sensitivity and specificity of the LGE imaging was calculated and compared to post-mortem using McNemar’s test. FT was applied to the cine imaging to quantify regional circumferential strain (CS). The percentage change in regional CS was calculated for each segment (Data: mean±SD; *p<0.05). LGE detected MI with a sensitivity of 90.6% and specificity of 96.4% (p=0.7). LV ejection fraction (EF) was 55.7±5.6% post-MI. Percentage changes in regional CS were -34.3±13.8% and -17.4±30.7% in AHA segments 13 and 16, respectively, while other segments exhibited increased CS (range=+0.1% to +28.7%). Our novel application of 3D IR-FLASH and FT provided comprehensive visualisation of LV injury and function in the setting of MI. Our data reproduces prior descriptions of compensatory increases in myocardial contractility in remote regions in STEMI patients with ≥50% EF [[1]Leung S.W. Ratajczak T.M. Abo-Aly M. Shokri E. Abdel-Latif A. Wenk J.F. Regional end-systolic circumferential strain demonstrates compensatory segmental contractile function in patients with ST-segment elevation myocardial infarction.J Biomech. 2021; 129 (110794)Crossref PubMed Scopus (1) Google Scholar] and a canine model of MI [[2]Lew W.Y. Chen Z.Y. Guth B. Covell J.W. Mechanisms of augmented segment shortening in nonischemic areas during acute ischemia of the canine left ventricle.Circ Res. 1985; 56: 351-358Crossref PubMed Scopus (112) Google Scholar].

Real-time cardiovascular magnetic resonance tissue characterisation in patients undergoing transcatheter aortic valve replacement

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): German Research Foundation (DFG, CRC 1002, D1) Background Myocardial fibrosis is a major determinant of outcome in aortic stenosis (AS). Novel fast real-time (RT) cardiac magnetic resonance (CMR) mapping techniques allow comprehensive quantification of fibrosis but have not yet been compared against standard techniques and histology. Methods Patients with severe AS underwent CMR before (n = 110) and left ventricular (LV) endomyocardial biopsy (n = 46) at transcatheter aortic valve replacement (TAVR). Midventricular short axis (SAX) native, post-contrast T1 and extracellular volume fraction (ECV) maps were generated using commercially available MOLLI (native: 5(3)3, post-contrast: 4(1)3(1)2) and RT single-shot inversion recovery fast low-angle shot (FLASH) with radial undersampling. Focal late gadolinium enhancement was excluded from T1 and ECV regions of interest. ECV and LV mass were used to calculate LV matrix volumes. Variability and agreements were assessed between RT, MOLLI and histology using intraclass correlation coefficients, coefficients of variation and Bland Altman analyses. Results RT and MOLLI derived ECV were similar for midventricular SAX slice coverage (26.2 vs. 26.5, p = 0.073) and septal region of interest (26.2 vs. 26.5, p = 0.216). MOLLI native T1 time was in median 20 ms longer compared to RT (p &amp;lt; 0.001). Agreement between RT and MOLLI was best for ECV (ICC &amp;gt;0.91), excellent for post-contrast T1 times (ICC &amp;gt;0.81) and good for native T1 times (ICC &amp;gt;0.62). Diffuse collagen volume fraction by biopsies was in median 7.8%. ECV (RT r = 0.345, p = 0.039; MOLLI r = 0.40, p = 0.010) and LV matrix volumes (RT r = 0.45, p = 0.005; MOLLI r = 0.43, p = 0.007) were the only parameters associated with histology. Conclusions RT mapping offers fast and sufficient ECV and LV matrix volume calculation in AS. ECV and LV matrix volume represent robust and universally comparable parameters with associations to histologically assessed fibrosis and may emerge as potential targets for clinical decision making.

Real-time cardiac magnetic resonance tissue characterisation for fibrosis assessment in aortic stenosis

Abstract Background Myocardial fibrosis is a major determinant of outcome in aortic stenosis (AS). Novel fast real-time (RT) cardiac magnetic resonance (CMR) mapping techniques allow comprehensive quantification of fibrosis but have not yet been adequately validated against standard techniques and histology. Methods Patients with severe AS underwent CMR before (n=110) and left ventricular (LV) endomyocardial biopsy (n=46) at transcatheter aortic valve replacement (TAVR). Midventricular short axis native, post-contrast T1 and extracellular volume fraction (ECV) maps were generated using commercially available 5(3)3 MOLLI and RT single-shot inversion recovery fast low-angle shot (FLASH) with radial undersampling. ECV and LV mass were used to calculate LV matrix volumes. Variability and agreements were assessed between RT, MOLLI and histology using intraclass correlation coefficients, coefficients of variation and Bland Altman analyses. Results RT and MOLLI derived ECV were similar for myocardium (26.2 vs. 26.5, p=0.073) and inter-ventricular septum (26.2 vs. 26.5, p=0.216). MOLLI native T1 time was in median 20 ms longer compared to RT (p&amp;lt;0.001). Agreement between RT and MOLLI was best for ECV (ICC &amp;gt;0.91), excellent for post-contrast T1 times (ICC &amp;gt;0.81) and good for native T1 times (ICC &amp;gt;0.62). Diffuse collagen volume fraction by biopsies was in median 7.8%. ECV (RT r=0.345, p=0.039; MOLLI r=0.40, p=0.010) and LV matrix volumes (RT r=0.45, p=0.005; MOLLI r=0.43, p=0.007) were the only parameters associated with histology. Conclusions RT mapping offers precise T1 and ECV assessments with similar agreement with histology as compared to conventional MOLLI techniques. Single-shot real time techniques may be advantageous in sicker patients prone to dyspnoea or arrhythmia. Funding Acknowledgement Type of funding source: Foundation. Main funding source(s): German Research Foundation

Real-time cardiovascular magnetic resonance T1 and extracellular volume fraction mapping for tissue characterisation in aortic stenosis

BackgroundMyocardial fibrosis is a major determinant of outcome in aortic stenosis (AS). Novel fast real-time (RT) cardiovascular magnetic resonance (CMR) mapping techniques allow comprehensive quantification of fibrosis but have not yet been compared against standard techniques and histology.MethodsPatients with severe AS underwent CMR before (n = 110) and left ventricular (LV) endomyocardial biopsy (n = 46) at transcatheter aortic valve replacement (TAVR). Midventricular short axis (SAX) native, post-contrast T1 and extracellular volume fraction (ECV) maps were generated using commercially available modified Look-Locker Inversion recovery (MOLLI) (native: 5(3)3, post-contrast: 4(1)3(1)2) and RT single-shot inversion recovery Fast Low-Angle Shot (FLASH) with radial undersampling. Focal late gadolinium enhancement was excluded from T1 and ECV regions of interest. ECV and LV mass were used to calculate LV matrix volumes. Variability and agreements were assessed between RT, MOLLI and histology using intraclass correlation coefficients, coefficients of variation and Bland Altman analyses.ResultsRT and MOLLI derived ECV were similar for midventricular SAX slice coverage (26.2 vs. 26.5, p = 0.073) and septal region of interest (26.2 vs. 26.5, p = 0.216). MOLLI native T1 time was in median 20 ms longer compared to RT (p < 0.001). Agreement between RT and MOLLI was best for ECV (ICC > 0.91), excellent for post-contrast T1 times (ICC > 0.81) and good for native T1 times (ICC > 0.62). Diffuse collagen volume fraction by biopsies was in median 7.8%. ECV (RT r = 0.345, p = 0.039; MOLLI r = 0.40, p = 0.010) and LV matrix volumes (RT r = 0.45, p = 0.005; MOLLI r = 0.43, p = 0.007) were the only parameters associated with histology.ConclusionsRT mapping offers fast and sufficient ECV and LV matrix volume calculation in AS patients. ECV and LV matrix volume represent robust and universally comparable parameters with associations to histologically assessed fibrosis and may emerge as potential targets for clinical decision making.

Noninvasive Monitoring of the Response of Human Lungs to Low-Dose Lipopolysaccharide Inhalation Challenge Using MRI: A Feasibility Study.

Development of antiinflammatory drugs for lung diseases demands novel methods for noninvasive assessment of inflammatory processes in the lung. To investigate the feasibility of hyperpolarized 129 Xe MRI, 1 H T1 time mapping, and dynamic contrast-enhanced (DCE) perfusion MRI for monitoring the response of human lungs to low-dose inhaled lipopolysaccharide (LPS) challenge compared to inflammatory cell counts from induced-sputum analysis. Prospective feasibility study. Ten healthy volunteers underwent MRI before and 6 hours after inhaled LPS challenge with subsequent induced-sputum collection. 1.5T/hyperpolarized 129 Xe MRI: Interleaved multiecho imaging of dissolved and gas phase, ventilation imaging, dissolved-phase spectroscopy, and chemical shift saturation recovery spectroscopy. 1 H MRI: Inversion recovery fast low-angle shot imaging for T1 mapping, time-resolved angiography with stochastic trajectories for DCE MRI. Dissolved-phase ratios of 129 Xe in red blood cells (RBC), tissue/plasma (TP) and gas phase (GP), ventilation defect percentage, septal wall thickness, surface-to-volume ratio, capillary transit time, lineshape parameters in dissolved-phase spectroscopy, 1 H T1 time, blood volume, flow, and mean transit time were determined and compared to cell counts. Wilcoxon signed-rank test, Pearson correlation. The percentage of neutrophils in sputum was markedly increased after LPS inhalation compared to baseline, P = 0.002. The group median RBC-TP ratio was significantly reduced from 0.40 to 0.31, P = 0.004, and 1 H T1 was significantly elevated from 1157.6 msec to 1187.8 msec after LPS challenge, P = 0.027. DCE MRI exhibited no significant changes in blood volume, P = 0.64, flow, P = 0.17, and mean transit time, P = 0.11. Hyperpolarized 129 Xe dissolved-phase MRI and 1 H T1 mapping may provide biomarkers for noninvasive assessment of the response of human lungs to LPS inhalation. By its specificity to the alveolar region, hyperpolarized 129 Xe MRI together with 1 H T1 mapping adds value to sputum analysis. 1 Technical Efficacy Stage: 2 J. Magn. Reson. Imaging 2020;51:1669-1676.

Model-based T1 mapping with sparsity constraints using single-shot inversion-recovery radial FLASH.

To develop a model-based reconstruction technique for single-shot T1 mapping with high spatial resolution, accuracy, and precision using an inversion-recovery (IR) fast low-angle shot (FLASH) acquisition with radial encoding. The proposed model-based reconstruction jointly estimates all model parameters, that is, the equilibrium magnetization, steady-state magnetization, 1/ T1*, and all coil sensitivities from the data of a single-shot IR FLASH acquisition with a small golden-angle radial trajectory. Joint sparsity constraints on the parameter maps are exploited to improve the performance of the iteratively regularized Gauss-Newton method chosen for solving the nonlinear inverse problem. Validations include both a numerical and experimental T1 phantom, as well as in vivo studies of the human brain and liver at 3 T. In comparison to previous reconstruction methods for single-shot T1 mapping, which are based on real-time MRI with pixel-wise fitting and a model-based approach with a predetermination of coil sensitivities, the proposed method presents with improved robustness against phase errors and numerical precision in both phantom and in vivo studies. The comprehensive model-based reconstruction with L1 regularization offers rapid and robust T1 mapping with high accuracy and precision. The method warrants accelerated computing and online implementation for extended clinical trials. Magn Reson Med 79:730-740, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

High-resolution myocardial T1 mapping using single-shot inversion recovery fast low-angle shot MRI with radial undersampling and iterative reconstruction.

Objective:To develop a novel method for rapid myocardial T1 mapping at high spatial resolution.Methods:The proposed strategy represents a single-shot inversion recovery experiment triggered to early diastole during a brief breath-hold. The measurement combines an adiabatic inversion pulse with a real-time readout by highly undersampled radial FLASH, iterative image reconstruction and T1 fitting with automatic deletion of systolic frames. The method was implemented on a 3-T MRI system using a graphics processing unit-equipped bypass computer for online application. Validations employed a T1 reference phantom including analyses at simulated heart rates from 40 to 100 beats per minute. In vivo applications involved myocardial T1 mapping in short-axis views of healthy young volunteers.Results:At 1-mm in-plane resolution and 6-mm section thickness, the inversion recovery measurement could be shortened to 3 s without compromising T1 quantitation. Phantom studies demonstrated T1 accuracy and high precision for values ranging from 300 to 1500 ms and up to a heart rate of 100 beats per minute. Similar results were obtained in vivo yielding septal T1 values of 1246 ± 24 ms (base), 1256 ± 33 ms (mid-ventricular) and 1288 ± 30 ms (apex), respectively (mean ± standard deviation, n = 6).Conclusion:Diastolic myocardial T1 mapping with use of single-shot inversion recovery FLASH offers high spatial resolution, T1 accuracy and precision, and practical robustness and speed.Advances in knowledge:The proposed method will be beneficial for clinical applications relying on native and post-contrast T1 quantitation.

Investigation of the Longitudinal Relaxation Rate of Blood After Gadobenate Dimeglumine Administration

To optimize the image acquisition parameters for improved steady-state (SS) contrast-enhanced magnetic resonance angiography (CE-MRA) of the carotid arteries with gadobenate dimeglumine. An inversion recovery fast low-angle shot (IR-FLASH) sequence for ultrafast determination of the longitudinal relaxation rate R1 was first optimized on phantoms and tested against a routine variable repetition time (TR) spin echo sequence used as reference standard. Different combinations of flip angle (FA, between 6 and 14 degrees) and inversion time (between 134 and 9000 milliseconds) were evaluated to achieve the best trade off between speed and accuracy. The optimized sequence was thereafter used in vivo in 5 subjects to determine the time evolution of blood R1 at 1.5 T after administration of gadobenate dimeglumine at 0.1 mmol/kg bodyweight. An optimal FA for angiographic measurement was thereafter derived from the Ernst equation based on experimental values of R1 previously determined in vivo. Finally, steady-state CE-MRA examinations were performed in 20 subjects to evaluate the improved contrast achieved after optimization of the FA for maximal blood signal enhancement. An ultrafast IR-FLASH sequence with a flip angle of 8 degrees and a properly defined set of inversion time values was shown to give in vitro R1 determinations that were in good agreement with those obtained using a routine, time consuming, variable-TR spin echo sequence. The use of this ultrafast IR-FLASH sequence in vivo allowed the blood signal behavior in the carotid arteries after gadobenate dimeglumine administration to be monitored. Using this sequence, the R1 decreased from 8.7±0.96 s⁻¹ at 30 seconds after injection to 3.8±0.24 s⁻¹ at 10 minutes after injection. Based on these data for R1, the optimal FA for SS CE-MRA was calculated to be 18 degrees for a gradient echo acquisition protocol with TR=7.5 milliseconds, when gadobenate dimeglumine is used. Significantly higher blood signal to noise ratio was achieved on SS images acquired using a three-dimensional spoiled gradient echo sequence with a FA of 18 degrees than on corresponding images acquired with a FA of 35 degrees as used typically for intravascular blood pool contrast agents (52.5±8.3 vs. 29.5±6.0; P<0.05, Mann-Whitney U test). Detailed experimental knowledge of the in vivo R1 behavior of blood after gadobenate dimeglumine injection and appropriate modification of the acquisition parameters enables improved signal intensity enhancement on steady-state CE-MRA of the carotid arteries.

Comparison study of three-dimensional and two-dimensional delayed enhancement MR imaging for myocardial infarction

Objective To prospectively evaluate the correlation between a single breath-hold three-dimensional (3 D) and several breath-hold two-dimensional (2D) delayed enhancement MR imaging sequences in the assessment of myocardial infarction size and the differences on image quality. Methods Fifteen patients with myocardial infarction underwent MR scan by using a single breath-hold 3D inversion-recovery fast low-angle shot (FLASH) sequence and several breath-hold 2D turbo-FLASH as the reference standard. Paired-samples t test was used to compare the ratio of the infarction areas in two sequences. Two-way ANOVA was used to assess the contrast-to-noise ratio (CNR) on 3D,2D magnitude-reconstructed and 2D phase-sensitive (PS) images. P value less than 0.05 was considered to indicate a significant difference. Meanwhile subjective visual evaluation was also performed to compare the image quality. Results The infarction ratio determined by 3D MR imaging 31.28% was no significant difference with that of 2D MR imaging 30.91% and had a good correlation (t = -0.505,P =0.621,r =0.990). The CNR was significantly higher in 3D and 2D magnitude-reconstructed groups than in 2D-PS group (3D and 2D magnitude-reconstructed images, 2D P5 image, 43.43±20.67 and 34.10±14.29, 7.59±2.59, respectively) (F = 24.376, P < 0.01). However, the contrast between normal and infracted myocardium was the highest in 2D-PS group with subjective visual evaluation (scores of 3D, 2D magnitude-reconstructed and 2D-PS images, 2.33, 2.13 and 2.73, respectively). On the other hand, the background noise on 2D-PS images was the highest in 3 groups (scores of 3 D, 2 D magnitude-reconstructed and 2 D-PS images, 2.67, 2.53 and 1.20, respectively). Conclusion The myocardial infarction ratio obtained with 3D MR imaging sequence is accurate, and the image quality is good. Key words: Magnetic resonance imaging; Myocardial infarction

A simple MR algorithm for estimation of myocardial salvage following acute ST segment elevation myocardial infarction

To assess myocardial salvage in acute ST segment elevation myocardial infarction (STEMI) by using contrast-enhanced CMR. Forty-four consecutive patients (38 male; mean age 59 +/- 10 years) with a first acute STEMI underwent acute percutaneous coronary intervention with successful restoration of TIMI grade 3 flow. CMR was performed 2 +/- 1 days after reperfusion on a standard 1.5 T MR Scanner that included a steady-state free precession cine imaging for LV function and an inversion-recovery fast low angle shot (TR 8 ms, TE 4 ms, FA 25 degrees ) sequences for late gadolinium enhancement (LGE) following the injection of 0.2 mmol/kg BW gadodiamide. The myocardium at risk (MR) was approximated by the volume of myocardium exhibiting LGE and/or impaired wall motion. The myocardial salvage index (MSI) was calculated as the volume of the MR minus the volume of LGE divided by the volume of the MR. Reperfusion therapy was rated successful with an ST elevation resolution (STR) > or =70% and was considered inadequate below 70%. Infarct size (LGE) was 17 +/- 13% of LV mass, the mean STR was 53.4 +/- 28.3%, and the MSI was 10.9 +/- 6.2%. There was a good correlation between the MSI and the STR (r = 0.695, P < 0.0001). Thirty patients had an STR below 70%, and 14 patients had an STR greater than 70%. The MSI was greater in patients with a STE resolution of more than 70% (12 +/- 11 vs. 6 +/- 3%, P < 0.0001). A simple MR algorithm based upon the relationship of functional impairment, which includes myocardial stunning, to the extent of LGE (infarct necrosis) is in accordance with STR as a clinical marker of successful reperfusion in acute myocardial infarction.

3D and 2D Delayed-Enhancement Magnetic Resonance Imaging for Detection of Myocardial Infarction: Preclinical and Clinical Results

The purpose was to verify whether myocardial viability can be detected by a delayed enhancement magnetic resonance imaging (MRI) approach using a rapid three-dimensional inversion-recovery fast low-angle shot (3D IR-FLASH) sequence in a preclinical and clinical setting. Nonreperfused myocardial infarctions were induced in eight minipigs. Both the pigs and 15 patients with suspected myocardial infarction underwent MRI using a rapid 3D IR-FLASH sequence and a two-dimensional IR-FLASH sequence as the reference standard. In the pigs, a total of 52 segments with myocardial infarction were identified with both sequences and there was good agreement in transmurality of 99.5%. The infarction volume determined with the 3D IR-FLASH in the animal study (2.4 +/- 1.5 cm(3)) showed a good correlation with the histomorphometrically determined volume using triphenyltetrazolium chloride (2.3 +/- 1.2 cm(3), r = 0.98, P < .001) and the two-dimensional IR-FLASH sequence (2.3 +/- 1.4 cm(3), r = 0.99, P < .001). Eleven of 15 patients were found to have myocardial infarction in 37 myocardial segments with both sequences and there was a good agreement in transmurality of 98.8%. There was also a good correlation in the clinical study between the 3D and 2D sequences (6.9 +/- 6.7 cm(3) vs. 6.8 +/- 6.5 cm(3), r = 0.98, P < .001). In Bland-Altman analysis there was no significant under- or overestimation of the myocardial infarction volume using the 3D IR-FLASH sequence in comparison to the two-dimensional reference standard in both the preclinical and clinical study. The contrast-to-noise ratios were not significantly different between 3D and 2D sequences in the animal (34.7 +/- 1.5 vs. 33.8 +/- 2.6; P = .51) and clinical study (31.4 +/- 12.5 vs. 36.7 +/- 11.5; P = .31). The breathhold time for the 3D IR-FLASH sequence in the clinical study (20.4 +/- 2.2 s) was significantly shorter than that of the 2D IR-FLASH sequence (190.1 +/- 20.8 s, P < .001). The rapid 3D IR-FLASH sequence detects myocardial infarction with high accuracy and allows a relevant reduction in acquisition time.

Improved Evaluation of Myocardial Perfusion and Viability With the Magnetic Resonance Blood Pool Contrast Agent P792 in a Nonreperfused Porcine Infarction Model

To investigate whether a magnetic resonance (MR) blood pool contrast agent enables both evaluation of myocardial perfusion and viability in nonreperfused infarction in pigs. An optimized MR protocol using the blood pool contrast agent P792 (0.026 mmol/kg, twice the clinical dose, Guerbet, France) was investigated to evaluate nonreperfused myocardial infarction in an animal model. P792 was compared with the extracellular contrast agent Gd-DOTA (0.1 mmol/kg). The MRI findings were compared with histomorphometry performed with microspheres to evaluate perfusion and triphenyltetrazolium chloride (TTC) to evaluate viability. Contrast-enhanced MR imaging of the heart was performed on a 1.5-Tesla scanner 2 days after instrumentation in 6 minipigs. A saturation recovery steady-state free precession sequence was used for perfusion imaging and an inversion recovery fast low-angle shot sequence for evaluation of myocardial viability. P792 tended to depict areas of reduced perfusion more accurately than Gd-DOTA (17.2% +/- 11.1% versus 13.7% +/- 8.0%) in comparison to the gold standard of histomorphometry with microspheres (18.2% +/- 9.8%). Moreover, P792, but not Gd-DOTA, depicted ischemic areas for 30 minutes after intravenous injection. The change in myocardial signal intensity during first pass was not significantly different after P792 compared with Gd-DOTA (140.3% +/- 64.4% versus 123.3% +/- 22.5%, P = 0.56). P792 was highly accurate in depicting infarcted areas (11.1% +/- 7.1%) compared with Gd-DOTA (12.1% +/- 8.2%, r = 0.98, P < 0.001) and histomorphometry with TTC (12.2% +/- 8.0%, r = 0.99, P < 0.001). Unlike Gd-DOTA, the blood pool contrast agent P792 allows evaluation of myocardial perfusion for a period of 30 minutes and shows good agreement with histomorphometry. P792 must be examined in further studies to evaluate its potential in evaluating early myocardial lesions and reperfusion. In addition, P792 also allows for evaluation of myocardial viability.

Myocardial Viability: Assessment with Three-dimensional MR Imaging in Pigs and Patients

To prospectively evaluate the correlation between a three-dimensional (3D) delayed enhancement magnetic resonance (MR) imaging sequence and a two-dimensional (2D) delayed enhancement MR imaging sequence for noninvasive assessment of myocardial viability in pigs and patients. The pig and patient studies were approved by the responsible authorities, and patients gave written informed consent. MR imaging was performed by using a rapid 3D inversion-recovery balanced steady-state free precession sequence and a 2D segmented inversion-recovery fast low-angle shot sequence as the reference standard. Fourteen pigs with reperfused (n=7) or nonreperfused (n=7) myocardial infarction and 17 patients (13 men, four women; mean age, 64.9 years+/-8.6 [standard deviation]) suspected of having myocardial infarction were included. Linear regression analysis and Bland-Altman analysis were used to compare the infarction volumes. In 10 of the 14 pigs the induction of myocardial infarction was successful. In these pigs, altogether 81 segments with myocardial infarction were demonstrated by both MR sequences, and agreement between the two sequences for classification of transmural extent of myocardial infarction was 99.7%. The infarction volume determined by using 3D MR imaging (4.64 cm3+/-2.48) in the pigs highly correlated with that of 2D MR imaging (4.65 cm3+/-2.39, r=0.989, P<.001) and that of staining by using triphenyltetrazolium chloride (4.67 cm3+/-2.44, r=0.996, P<.001). Thirteen of the 17 patients examined showed myocardial infarction in 34 myocardial segments with both sequences, and agreement between the two sequences for classification of transmural extent of myocardial infarction was 98.6%. In the patients, the infarction volume determined with both sequences highly correlated (9.71 cm3+/-7.47 for the 3D sequence vs 10.01 cm3+/-8.04 for the 2D sequence, r=0.982, P<.001). The breath-hold time necessary for the 3D MR imaging (21.0+/-2.3 seconds) was significantly shorter than that for 2D MR imaging (188.3+/-20.2 seconds, P<.001). Myocardial infarction volumes obtained with the 3D MR imaging sequence are highly correlated and in good agreement with volumes obtained with the 2D MR imaging standard approach and reduced the acquisition time by a factor of nine.

MR-Koronarangiographie mit MS-325, einem Blood-Pool-Kontrastmittel: Vergleich einer Inversion Recovery Steady-State Free Precession und einer Inversion Recovery Fast Low Angle Shot Sequenz in Probanden

To compare the signal-to-noise and contrast-to-noise ratio as well as the image quality of 3D inversion recovery steady-state free precession (IR-SSFP) and 3D inversion recovery fast low angle shot (IR-FLASH) sequences for contrast-enhanced breath-hold MRCA. 24 healthy volunteers (10 female, 14 male, mean age 29.8 +/- 6.1 years) were involved in this study. All examinations were performed on a 1.5 T MR scanner (Magnetom Sonata, Siemens, Germany) after injection of 0.05 mmol/kg body weight MS-325 (EPIX Pharmaceuticals, Cambridge, MA and Schering AG, Berlin, Germany). MRCA was performed using IR-SSFP (TR 3.8 ms, TE 1.6 ms, FA 65 degrees , 35 phase encoded steps, bandwidth 540 Hz/pixel, slice thickness 1.5 mm, in-plane resolution 1.2 x 0.9 - 1.4 x 1.0 mm) and IR-FLASH (TR 3.8 ms, TE 1.6 ms, FA 25 degrees , bandwidth 490 Hz/pixel, slice thickness 1.5 mm, in-plane resolution 1.2 x 0.9 - 1.4 x 1.0 mm) sequences. For all scans the inversion time was set to null the signal intensity of the myocardium. Signal-to-noise ratio (SNR) as well as contrast-to-noise ratio (CNR) measurements (blood versus myocardium) were performed. The image quality was assessed based on a 5-point scale ranging from 1 (excellent) to 5 (non-diagnostic) by two radiologists in consensus. The mean signal-to-noise ratio of blood (27.7 +/- 4.7 vs. 22.6 +/- 4.9, P < 0.0001) and the contrast-to-noise ratio (21.0 +/- 4.3 vs. 15.8 +/- 4.3, P < 0.0001) showed significantly higher values for IR-SSFP sequences. The mean image quality scores were significantly higher for SSFP (3.6 +/- 0.7) than FLASH (2.8 +/- 0.9) sequences (P < 0.05). IR-SSFP sequences show a considerable overall improvement in image quality compared to IR-FLASH sequences for MRCA after injection of a gadolinium-based blood pool contrast agent.

Magnetic resonance imaging of myocardial perfusion and viability using a blood pool contrast agent.

A comprehensive cardiac magnetic resonance (MR) examination should comprise imaging of myocardial perfusion, viability, and the coronary arteries. Blood pool contrast agents (BPCAs) improve coronary MR angiography, whereas their potential for imaging of perfusion and viability is unknown. The abilities to noninvasively image myocardial perfusion and viability using the BPCA P792 (Guerbet, France) were tested in a closed-chest model of nonreperfused myocardial infarction in 5 pigs. Two to 3 days after instrumentation, myocardial perfusion imaging with a saturation-recovery steady-state free precession technique and viability imaging with an inversion-recovery fast low-angle shot sequence were conducted on a 1.5-T MR scanner using the extracellular contrast agents (ECCA) Gd-DOTA (0.1 mmol Gd/kg) and blood pool contrast agent (BPCA) P792 (0.013 mmol Gd/kg). Perfusion defects were visualized in all pigs with good correlation between the ECCA and the BPCA (1.77 +/- 1.16 cm2 vs. 1.80 +/- 1.19 cm2, r = 0.959, P < 0.01). Reduced myocardial perfusion was detected using the ECCA up to 80 seconds after injection. In contrast, BPCA administration enabled visualization of perfusion defects on equilibrium perfusion imaging in all cases for 10 minutes. The size of myocardial infarction detected with viability MR imaging correlated well between the standard method (ECCA) and delayed-enhancement imaging with the BPCA (5.40 +/- 3.16 versus 5.52 +/- 3.13 cm3, r = 0.994, P < 0.002). The BPCA investigated in this study allows both reliable detection of perfusion defects on first pass and equilibrium perfusion imaging and characterization of viability after myocardial infarction. Thus, this contrast agent is suitable for a comprehensive cardiac MR examination.

Combined first-pass perfusion and viability study at MR imaging in patients with non-ST segment-elevation acute coronary syndromes: feasibility study.

To assess the feasibility of combined perfusion and viability testing by using magnetic resonance (MR) imaging in one setting in patients with non-ST segment-elevation acute coronary syndromes. The data of 13 patients (mean age, 68 years; range, 40-85 years) at high risk for myocardial infarction who underwent MR imaging at 1.5 T were reviewed. Risk factors were increased troponin T levels in seven, reversible ST depression on an electrocardiogram in four, history of myocardial infarction in two, and presence of heart failure in four. Cine imaging of the left ventricle was performed with a true-fast imaging with steady-state precession (FISP) sequence to assess the regional myocardial contraction and ejection fraction. After injection of 0.1 mmol per kilogram of body weight of gadopentetate dimeglumine, first-pass MR images were obtained by using an inversion-recovery true-FISP sequence at rest and during infusion of adenosine (140 microg/kg/min). Resting and stress images were assessed qualitatively for abnormal regional perfusion (hypoenhancement). The myocardium was divided into three radial segments corresponding to the three coronary artery territories. Delayed (after 15 minutes) contrast material-enhanced images were acquired with use of a segmented inversion-recovery fast low-angle shot sequence. Conventional coronary angiograms were compared with the first-pass images. A more than 50% stenosis in diameter in any coronary artery was considered substantial. Mann-Whitney test was used to assess any significant difference between the left ventricular ejection fraction (LVEF) in patients with and those without myocardial infarct. Mean LVEF was 51.5% (range, 30%-77%). First-pass stress perfusion studies depicted 25 segments of hypoenhancement in 11 patients. Comparison of first-pass perfusion defects with findings on coronary angiograms indicated an overall sensitivity of 92% (24 of 26) and specificity of 92% (12 of 13) in detection of substantial coronary artery disease. Infarcts detected from hyperenhancement on delayed contrast-enhanced images were present in eight segments (four were transmural) in five patients. No significant difference was noted in the LVEF between patients with and those without infarct (P =.724). Combined stress perfusion and viability MR imaging was feasible in patients with acute coronary syndromes. First-pass MR perfusion defects compare well with the presence of substantial coronary artery stenosis on conventional angiograms.

A magnetization-driven gradient echo pulse sequence for the study of myocardial perfusion.

A T1-weighted imaging pulse sequence for contrast-based studies of myocardial perfusion is presented and evaluated in phantoms and in vivo. The sequence is similar to spoiled gradient-recalled echo sequences except that nonselective preparatory RF pulses drive magnetization to steady state prior to image acquisition. Steady state is thus obtained in both tissue and blood resulting in a stable, homogeneous, and dark pre-contrast baseline. Tip angles and timings are chosen so that pixel intensity approximates a linear relation to 1/T1. The dynamic range of signal response to contrast agent concentration is greater than that of an inversion-recovery fast low angle shot sequence. The sequence proposed should be useful for myocardial perfusion studies.