Cardiac magnetic resonance imaging

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Systematic use of cardiac Magnetic Resonance Imaging in myocardial infarction with nonobstructive coronary arteries increases the incidence of myocarditis

Systematic use of cardiac Magnetic Resonance Imaging in myocardial infarction with nonobstructive coronary arteries increases the incidence of myocarditis

1. Berg J., Kottwitz J., Baltensperger N., Kissel C., Lovrinovic M., Scherff F., Schmied C., Templin C., Lüscher T., Heidecker B.*, and Manka R.* Cardiac Magnetic Resonance Imaging in Myocarditis Reveals Persistent Disease Activity Despite Normalization of Cardiac Enzymes and Inflammatory Parameters at 3 Months Follow-up, published online in Circulation Heart Failure November 2017 With editorial: The Changing Face of Cardiac Inflammation, New Opportunities in the Management of Myocarditis by Cooper L.T.; impact factor: 6.4
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Quantification of diffuse myocardial fibrosis by cardiac magnetic resonance imaging / submitted by Andreas A. Kammerlander

Quantification of diffuse myocardial fibrosis by cardiac magnetic resonance imaging / submitted by Andreas A. Kammerlander

Interstitial Fibrosis, Functional Status, and Outcomes in Heart Failure With Preserved Ejection Fraction: Insights From a Prospective Cardiac Magnetic Resonance Imaging Study.. American [r]

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Multiparametric cardiac magnetic resonance imaging with motion compensation

Multiparametric cardiac magnetic resonance imaging with motion compensation

In principle, cardiac T1 mapping using both approaches is not restricted to radial trajectories and gradient echo read out. The approach would gain clinical relevance by acquisition with bSSFP read out because higher SNR that is needed for lower field strength, since nowadays most clinical MRI examinations are performed on a 1.5 Tesla scanner. However, this implementation comes with challenges, such as magnetization transfer effect and T2 dependencies [ 14 ]. These effects have to be included into the model function and preliminary results can be found in [ C1 ]. Other trajectories that provide frequent coverage of low frequencies would be suitable for multiparametric imaging, such as spiral trajectories with golden radial ratio between two consecutive read outs, providing more information per read out line than radial spokes. Another option would be pseudo-random sampling along phase encoding, where compressed sensing with higher sampling rate of low frequencies for a good determination of the longitudinal magnetization during magnetization recovery and motion of the heart could be used instead of iterative SENSE reconstruction for faster image reconstruction.
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Extracellular volume quantification by cardiac magnetic resonance imaging without hematocrit sampling: Ready for prime time?

Extracellular volume quantification by cardiac magnetic resonance imaging without hematocrit sampling: Ready for prime time?

11. Mascherbauer J, Marzluf BA, Tufaro C, et al. Cardiac magnetic resonance postcontrast T1 time is associated with outcome in patients with heart failure and preserved ejection fraction. CircCardiovascImaging. 2013;6:1056–65. 12. Miller CA, Naish JH, Bishop P, et al. Comprehensive valida- tion of cardiovascular magnetic resonance techniques for the assessment of myocardial extracellular volume. Circ Cardiovasc Imaging. 2013;6:373–83.

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Reproducibility of small animal cine and scar cardiac magnetic resonance imaging using a clinical 3.0 tesla system

Reproducibility of small animal cine and scar cardiac magnetic resonance imaging using a clinical 3.0 tesla system

ischemia-reperfusion model and showed similar inter- study (3.3% vs. 4.8%) and intra-study (1.6% vs. 1.0%) repro- ducibility for the assessment of LVEF. Accurate depiction of myocardial infarct size in animal models of cardiac diseases is crucial; hence, late en- hancement imaging was incorporated in the current study protocol. Recently, Voelkl et al. [12] showed that widely available clinical 1.5 Tesla scanners enable high quality and accurate assessment of infarct size and func- tional parameters in mice. In our study quantitative analysis of myocardial infarct size demonstrated high inter-study, inter-reader and intra-reader reproducibility. The overall high reproducibility of quantitative CMR measurements may allow for the reliable and accurate assessment of even small treatment effects during serial examinations with the additional benefit of reducing sample size. In general, CMR imaging has been proposed the imaging method of choice to assess treatment effects in clinical and animal studies due to its high accuracy and low inter-study variability [6,16]. Based on the re- sults of the present study conducted with the use of a conventional clinical 3.0 Tesla MR system a more wide- spread use of CMR imaging in small animal studies can be encouraged. In particular, the combined protocol of functional and morphological imaging of the rat heart is advantageous and can be integrated in pharmacological or interventional treatment studies in small animals. Limitations
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Reproducibility of small animal cine and scar cardiac magnetic resonance imaging using a clinical 3.0 tesla system

Reproducibility of small animal cine and scar cardiac magnetic resonance imaging using a clinical 3.0 tesla system

beyond that, require expensive investments. To overcome these restrictions, clinical MR systems may have the poten- tial to represent a valuable alternative for accurate assess- ment of cardiovascular anatomy and function in small rodents. However, several key items need to be considered when performing CMR examinations in small animals: First, robust ECG monitoring is essential to ensure reliably triggered image data acquisition. Second, anaesthesia and animal temperature have to be monitored and maintained throughout the complete CMR examination in particular when aiming at serial examinations. Finally, in order to achieve an optimal signal-to-noise ratio resulting in high quality CMR images, high magnetic field strengths need to be combined with dedicated small animal radiofrequency receiver coils. In the present study, a clinically employed 3.0 Tesla system was introduced for the purpose of small animal imaging. In order to increase image SNR and minimize breathing artefacts, signal averaging was mandatory thereby accepting an increased total scan dur- ation. In addition, for cine imaging a segmented gradient echo sequence was chosen over the commonly used steady-state free precession (SSFP) sequence type since the latter resulted in poor image quality mainly due to flow-/ bloodpool-related artifacts with impairment of endocardial visibility (e.g. in the region of mitral inflow/aortic root). However, small animal CMR imaging at 3.0 Tesla proved to be feasible with a success rate of >97%. Recently, Saleh et al. [10] proved that long-term left ventricular remodel- ling in rat hearts after myocardial infarction can be rapidly and accurately assessed using a clinical 3.0 Tesla System with a dedicated small animal coil and a gradient echo se- quence. In addition, quantitative assessment of cardiac vol- umes, mass and infarct size provided robust results with high inter-study, inter-reader and intra-reader reproduci- bility. The high reproducibility for the quantification of left-ventricular volumes and mass was in accordance to previously published data by Montet-Abou et al. [17] who investigated nine normal rats with four standard MR fast gradient- echo sequences using a 1.5 Tesla MR system. However, inter-, and intra-reader reproducibility was lim- ited to four rats. Jones et al. [18] investigated 11 rats in an
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Impact of Systemic Volume Status on Cardiac Magnetic Resonance T1 Mapping

Impact of Systemic Volume Status on Cardiac Magnetic Resonance T1 Mapping

Cardiac magnetic resonance imaging (CMR) including T1 mapping is increasingly used to characterize myocar- dial disease 1,2 . Native T1 values are a composite signal from myocytes and extracellular volume (ECV). The two most important determinants of an increase in native T1 are edema and fibrosis or amyloid. Native T1 time has been studied as a surrogate marker of diffuse myocardial fibrosis in heart failure with preserved and reduced ejec- tion fraction (HFpEF and HFrEF) 3,4 , and also in myocardial inflammation and subsequent edema 5,6 . Especially in heart failure, fluid overload is a frequently encountered clinical problem. However, it currently remains unclear to what extent systemic fluid overload influences CMR T1 times and whether a differentiation between fibrosis and overhydration is possible in affected patients. Patients with end-stage renal disease on maintenance hemodialysis (HD), who are closely followed with regard to their fluid status, frequently develop left ventricular hypertrophy and diastolic dysfunction 7 . This has been linked to a high prevalence of risk factors such as hypertension, coro- nary artery disease, chronic inflammation and diabetes 8 . Chronic kidney disease patients frequently develop left ventricular hypertrophy as well as diastolic dysfunction with the most extreme forms typically found in dialy- sis patients 9 . The combined effects of pre-existing comorbidities, the continuous strain put on the myocardium through hemodialysis and ultrafiltration and the effects of chronic fluid overload, which remain even after ultra- filtration, lead to a particularly high HFpEF prevalence in HD patients 10 .
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Robust segmentation of human cardiac contours from spatial magnetic resonance images

Robust segmentation of human cardiac contours from spatial magnetic resonance images

In Chapter 1 we introduced the field of medical imaging, and how the role of medical imaging has expanded beyond the simple visualization and inspection of anatomic structures, through the rapid development and proliferation of medical imaging technologies such as CT, Ultrasound, MR, and other modalities. We then motivated and defined the challenging problem, the robust segmentation of the left ventricular endocardial boundary of the human heart, which has received a great deal of attention in recent years. Finally, at the end of this chapter, we outline the segmentation model (described in details in the followed chapters) with a diagram description of all of its process, and summarized the contributions given by the thesis.
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Functional connectivity of the rat brain in magnetic resonance imaging

Functional connectivity of the rat brain in magnetic resonance imaging

Processing of respiratory waveforms was implemented in IDL (ITT Visual Information Solutions, Boulder, USA) and involved detection of peak inspiration and subsequent baseline correction using the median values (representing expiration) within the respective respiratory cycle. The resulting waveforms were smoothed using a sliding window of 50 ms. Based on this, the respiratory derivative was calculated and smoothed likewise. Processing of the cardiac waveform is less complex due to its more regular shape. Cardiac waveforms were temporally filtered (band-pass filter, 2.5 – 10.0 Hz) and smoothed (sliding window, 50 ms). Based on this, the cardiac derivative was calculated. Peak detection was used to calculate the cardiac and respiratory rates that were median filtered (3 s window) to remove outliers or detection errors. Based on the temporal information stored with the waveforms, corresponding values of body temperature and oxygen saturation were extracted from the session recordings. All these data were merged into a multichannel file covering the entire scan duration with a temporal resolution of 10 ms including trigger information.
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Evaluation of aortic root for definition of prosthesis size by magnetic resonance imaging and cardiac computed tomography: Implications for transcatheter aortic valve implantation

Evaluation of aortic root for definition of prosthesis size by magnetic resonance imaging and cardiac computed tomography: Implications for transcatheter aortic valve implantation

Conclusions In patients referred for TAVI, CMR measurements of aortic root dimensions show a good correlation with DSCT measurements and thus CMR may be an alterna- tive 3D-imaging modality without the need for radiation or contrast-agent exposure. Aortic annulus measure- ments using TEE, CMR and DSCT were close but not identical and the method used has important potential implications on TAVI strategy.

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Evaluation of aortic root for definition of prosthesis size by magnetic resonance imaging and cardiac computed tomography: Implications for transcatheter aortic valve implantation

Evaluation of aortic root for definition of prosthesis size by magnetic resonance imaging and cardiac computed tomography: Implications for transcatheter aortic valve implantation

Conclusions In patients referred for TAVI, CMR measurements of aortic root dimensions show a good correlation with DSCT measurements and thus CMR may be an alterna- tive 3D-imaging modality without the need for radiation or contrast-agent exposure. Aortic annulus measure- ments using TEE, CMR and DSCT were close but not identical and the method used has important potential implications on TAVI strategy.

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Analysis of functional magnetic resonance imaging time series by independent component analysis

Analysis of functional magnetic resonance imaging time series by independent component analysis

should be applied to the data is discussed in Calhoun et al., 2001, Stone, 1999a, Stone et al., 2002. So far the sICA dominated in the application of ICA to fMRI data sets. TICA was rather applied to EEG or MEG data, which have a high temporal resolution (in the milliseconds domain) [Makeig et al., 1997]. The electrical signals originating from the brain are quire weak at the scalp, in the microvolt range, and there are larger artificial components arising from eye movements and muscles. Makeig et al., 1997 applied the Infomax algorithm to EEG data showing that the algorithm can extract EEG activations and isolate artifacts. Jung et al., 2000 show that the extended Infomax algorithm is able to linearly decompose EEG artifacts such as line noise, eye blinks, and cardiac noise into independent components with sub- and supergaussian distributions. In Seifritz et al., 2002, they used an initial sICA to reduce the spatial dimensionality of the data by locating a region of interest in which they performed a tICA to study the structure of the nontrivial temporal response in the human auditory cortex in more detail.
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Improvements of Magnetic Resonance Imaging techniques for clinical diagnosis
in cerebrovascular disease

Improvements of Magnetic Resonance Imaging techniques for clinical diagnosis in cerebrovascular disease

For Subproject 3 (Publications II and VII), patients were included in a prospective imaging study (7.0 Tesla Ultra-High Field Project, “7UP-Study”, WHO International Clinical Trials Registry No. DRKS00003193, http://apps.who.int/trialsearch/Trial.aspx?TrialID=DRKS00003193). Inclusion criteria were: (1) subacute/chronic ischemia or transitory ischemic attack (TIA), (2) age 18–80 years, (3) ability to give informed consent and (4) legal competence. Exclusion criteria were: (1) cardiac pacemakers or any other electronic implants, (2) any metallic implant, (3) pregnancy or breast feeding period, (4) claustrophobia, (5) chronic or episodic vertigo, (6) retinal diseases and (7) dental bridges and more than two metallic dental crowns in a row. Neurological status was assessed using the National Institute of Health Stroke Scale (NIHSS) at time of admission for index stroke and before MR imaging. Imaging was performed first at 3.0 T, immediately followed by 7.0 T. A neurologist specialized in stroke supervised the patients during MRI. In total, 18 patients were eligible for Publication II and 6 patients for Publication VII, which was performed on the subset of Moya-Moya-patients (n=6).
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Improved cardiac gating and patient monitoring in high field magnetic resonance imaging by means of electrocardiogram signal processing

Improved cardiac gating and patient monitoring in high field magnetic resonance imaging by means of electrocardiogram signal processing

The MHD effect is not the only effect that can lead to false or missed R-peak detections. Morphological variations of the QRS complex can also lead to such misclassifications. Such variations can occur in patients suffering from congenital heart disease (CHD). CHDs such as Ebstein’s anomaly of the tricuspid valve or the Tetralogy of Fallot cause variations of the ECG signal [ Kastor 75 , Gatzoulis 97 ]. Patients suffering from the Ebstein anomaly partially show altered QRS patterns [ Kastor 75 ]. Due to these altered QRS patterns, gating based on the ECG can cause incorrect results, e. g. during MRI- based flow quantifications, or it can make cardiac gating impossible [ Fratz 08 ]. To cope with gating problems in CHD patients, a matched filter, a template matching algorithm and a modified version of the VCG-based method were used for R-peak detection [ Knesewitsch 13 ]. No further details were given about the implementation and combination of these techniques. The method was also partly described in [ Frank 11 , Frank 13 ]. No further details were provided about how the templates and the matched filter were designed. Although this method achieved a high R-peak detection quality for ECG signals recorded in a 1.5 T MR scanner in terms of specificity (99.76 %) and sensitivity (100 %), results for the mean delay and jitter of the detected R-peaks were not reported quantitatively. Besides, the proposed method was not tested in MR scanners with higher magnetic field strengths.
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Magnetic Resonance Imaging on Patients with Implanted Cardiac Pacemakers

Magnetic Resonance Imaging on Patients with Implanted Cardiac Pacemakers

The set of tested objects comprised several different types. Besides isolated straight wires, leads with helix shaped wires and detailed representations of the electrodes at the tip were evaluated. Furthermore, models of the pacemakers/lead system containing electronic components to reproduce the dielectric properties of those systems were de- veloped. It became clear that due to the skin depth in the order of 0.1 mm the grid size near to the tip of the electrode had to be about 0.1mm leading to a significant increase in demands on storage capacity and calculation time. In addition averaging current den- sities and SAR over 10 g (corresponding to voxels of several millimeter side length) as recommended in the MRI guidelines is not adequate to describe the phenomena at the tip of the catheter properly. The resulting electromagnetic field and SAR distributions were significantly influenced by a several aspects. The most prominent impact had the orientation of the objects in relation to the RF fields. The higher the dB 1 /dt along the course of the objects – e.g. at positions further from the center of the coils – the higher the observed induced currents and SAR values. For objects placed close to the body’s center, the currents were substantially lower. Another property leading to lower SAR distributions was the encapsulation of the electrodes with fibrotic tissue. The reduced conductivity of this low-perfused tissue inhibited the transgression of induced currents into the cardiac tissue.
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Optimisation of Phase Data Processing for Susceptibility Reconstruction in Magnetic Resonance Imaging

Optimisation of Phase Data Processing for Susceptibility Reconstruction in Magnetic Resonance Imaging

11.5. SUSCEPTIBILITY RECONSTRUCTION FOR A STUDY OF PARKINSON’S DISEASE This suggests, that physiological noise such as body movement is an unlikely source. The as- sumption is that the artefacts result either in an inappropriate recombination of the channels or in a problem with the scanner imaging acceleration system, GRAPPA [ Griswold et al. , 2002 ]. Accel- eration was used for acquisition, so it is indeed a potential source for the encountered artefacts. Nevertheless, compensation could not easily be accomplished. In case of a channel-recombination issue, it could be solved by post-processed channel recombination. Unfortunately, within this study the data were acquired only in combined mode, so this improvement is not applicable. However, the information collected potentially provides a novel insight into the structure of various brain tumour types. The susceptibility contrast shows very distinct properties for the illustrated examples. Susceptibility reconstruction might evolve as an additional aid in diagnosing tumour tissue, haemorrhages and oedemas. The fact that despite the adverse measurement parameters the developed workflow for phase imaging leads to meaningful field and susceptibility maps con- firms the robustness of the employed methods. Future studies on susceptibility contrast in brain tumours, e.g. on analysing its use for tumour classification, are a valuable perspective.
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Optimisation of Phase Data Processing for Susceptibility Reconstruction in Magnetic Resonance Imaging

Optimisation of Phase Data Processing for Susceptibility Reconstruction in Magnetic Resonance Imaging

7.4. RECONSTRUCTING SUSCEPTIBILITY DISTRIBUTIONS 7.4 Reconstructing Susceptibility Distributions All strategies for estimating susceptibility distributions in soft tissue are based on the a priori estimation of fieldmaps, and thus on phase imaging. Single-echo GRE measurements are not useful for this aim, since fieldmaps derived of such data may contain deviations from the true field due to unconsidered phase offsets (see Section 6.1). Fieldmaps used for susceptibility recon- struction should at least rely on double-echo, or offset-corrected phase data. Furthermore it is evident, that the estimation of susceptibility requires knowledge of the magnetic field in all spatial dimensions. Ideally, an isotropic sampling of space should be attempted. This is best achieved using an isotropically sampled, full 3D GRE sequence with slab- or non-selective excitation. Sev- eral strategies for the reconstruction of tissue magnetic susceptibility were introduced during the last years. Two main categories can be defined, single and multiple orientation measurements. Furthermore, reconstruction can be performed directly or by using a minimisation approach. All methods presented below use the model of scalar susceptibility (Section 7.3.1), and will be shown in application examples using optimised parametrisation. Parameter optimisation will be discussed later on in Section 7.6. A comprehensive discussion of the current reconstruction techniques and applications for susceptibility imaging in MRI can be found in Reichenbach [ 2012 ].
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Development and application of electrical conductivity mapping using magnetic resonance imaging

Development and application of electrical conductivity mapping using magnetic resonance imaging

88 Abstract To develop an imaging modality for the quantification of brain tissue sodium concentration (TSC) calculated from magnetic resonance electrical properties tomography (MR-EPT) based on the correlations between conductivity and sodium concentration in saline solutions. Conductivity maps were reconstructed using the transceive phase of the combined signal at 3T while sodium concentration scans were acquired at 4T both in phantom and in 8 healthy subjects. The brain conductivity and sodium concentration maps were co-registered and normalised to 1mm 152 MNI brain atlas. So-called pseudo tissue sodium maps (pTSC) were generated by performing a linear transform of conductivity maps based on saline solution model at 37°C. Statistical analysis was performed to investigate the discrepancy between pTSC and TSC. A strong linear correlation between pTSC and TSC was found when all brain regions were included (r=0.60, p<0.001). The same trend was found in gray matter (r=0.58, p<0.001) and in white matter (r=0.43, p<0.05), respectively. The slope of the overall linear regression was 0.72, which indicates that pseudo- sodium concentration tends to underestimate TSC values obtained by sodium MRI. Moreover, Bland-Altman analysis revealed that the mean difference between the two methods was ~4mMol/L. The underestimation of pTSC is likely due to the lower water content of brain tissue relative to the saline solution. Despite an overall underestimation compared to sodium MRI, pseudo sodium concentration correlated well with sodium MRI measurement. This provides evidence that sodium ion concentration is the dominant source of electrical conductivity, the latter being accessible with MR-EPT.
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A navigator based rigid body motion correction for magnetic Resonance imaging

A navigator based rigid body motion correction for magnetic Resonance imaging

tion of a sequence, where the abscissa is the time axis of a sequence diagram. Along the ordinate, multiple axes are arranged: one for each event type of the sequence (RF pulses, gradients, readout, sig- nal). The sequence diagram of a gradient echo sequence is shown in Figure 2.6. After the echo readout as shown in Figure 2.6, residual magnetisation can be removed from the imaging process by applying additional gradients or modifying the phase of the subsequent RF pulses. This process is known as spoiling. GRE sequences are dif- ferentiated depending on the spoiling applied after the readout. The Fast Low Angle Shot (FLASH) sequence [20] is a spoiled gradient echo, whereas steady state free precession (SSFP) sequences refocus the available magnetisation in the transverse plane. This leads to higher signal–to–noise but may lead to a reduced T 1 contrast [21].
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Quantitative fetal magnetic resonance imaging assessment of cystic posterior fossa malformations

Quantitative fetal magnetic resonance imaging assessment of cystic posterior fossa malformations

Recent advances in fetal imaging and, specifically, fetal MRI, allow for accurate and reliable delineation of the vermian lobules 11 . Characterization and quantification of vermian structures are relevant for the diagnosis of morphologically different subgroups of cPFM, as these subgroups may explain the well-known heterogeneity in the neurodevelopmental outcomes of affected cases. The findings of this retrospective fetal MRI study, in which a variety of posterior fossa structures were assessed quantitatively, show that detailed analysis of the fetal vermis is possible and allows further classification of cPFM into subgroups.
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