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 Magnetic Resonance Materials in Physics, Biology and Medicine   [SJR: 0.787]   [H-I: 46]   [2 followers]  Follow         Hybrid journal (It can contain Open Access articles)    ISSN (Print) 0968-5243 - ISSN (Online) 1352-8661    Published by Springer-Verlag  [2345 journals]
• Respiratory optimized data selection for more resilient self-navigated
whole-heart coronary MR angiography
• Authors: Jerome Chaptinel; Davide Piccini; Gabriele Bonanno; Simone Coppo; Pierre Monney; Matthias Stuber; Juerg Schwitter
Pages: 215 - 225
Abstract: Objectives Our objective was to test a data-exclusion strategy for respiratory motion suppression by retrospectively eliminating data acquired at extreme respiratory positions for improved coronary vessel sharpness (VS) of 1-D self-navigated 3-D radial whole-heart coronary angiography acquisitions. Materials and methods 3-D radial self-navigated acquisitions were performed on a 1.5T scanner in volunteers during free-breathing (n = 8), in coached volunteers (n = 13) who were asked to breathe in a controlled manner to mimic cardiovascular patients presenting with Cheyne-Stokes breathing, and in free-breathing patients (n = 20). Data collected during large respiratory excursions were gradually excluded retrospectively from the reconstruction yielding 14 data sets per subject on average. The impact on VS, blood and myocardium signal-to-noise and contrast-to-noise was measured. From these results, two retrospective gating strategies were defined for the k-line elimination procedure and tested in all groups. Results Maximum right coronary artery VS improvement was +7.4 and +2.7% in coached volunteers and patients (P < 0.0001 for both), respectively, and 1.6% for the free-breathing volunteers (P = 0.13). The first gating strategy was defined as a fixed undersampling factor of 5 compared to a fully sampled 3-D radial acquisition, yielding significant VS improvement in coached volunteers and patients while myocardial signal-to-noise decreased in these. The second strategy was defined as a fixed gating window of 5.7 mm, leading to similar improvements. Conclusion The presented strategies improve image quality of self-navigated acquisitions by retrospectively excluding data collected during end-inspiration.
PubDate: 2017-06-01
DOI: 10.1007/s10334-016-0598-4
Issue No: Vol. 30, No. 3 (2017)

• Reproducible segmentation of white matter hyperintensities using a new
statistical definition
• Authors: Soheil Damangir; Eric Westman; Andrew Simmons; Hugo Vrenken; Lars-Olof Wahlund; Gabriela Spulber
Pages: 227 - 237
Abstract: Objectives We present a method based on a proposed statistical definition of white matter hyperintensities (WMH), which can work with any combination of conventional magnetic resonance (MR) sequences without depending on manually delineated samples. Materials and methods T1-weighted, T2-weighted, FLAIR, and PD sequences acquired at 1.5 Tesla from 119 subjects from the Kings Health Partners-Dementia Case Register (healthy controls, mild cognitive impairment, Alzheimer’s disease) were used. The segmentation was performed using a proposed definition for WMH based on the one-tailed Kolmogorov–Smirnov test. Results The presented method was verified, given all possible combinations of input sequences, against manual segmentations and a high similarity (Dice 0.85–0.91) was observed. Comparing segmentations with different input sequences to one another also yielded a high similarity (Dice 0.83–0.94) that exceeded intra-rater similarity (Dice 0.75–0.91). We compared the results with those of other available methods and showed that the segmentation based on the proposed definition has better accuracy and reproducibility in the test dataset used. Conclusion Overall, the presented definition is shown to produce accurate results with higher reproducibility than manual delineation. This approach can be an alternative to other manual or automatic methods not only because of its accuracy, but also due to its good reproducibility.
PubDate: 2017-06-01
DOI: 10.1007/s10334-016-0599-3
Issue No: Vol. 30, No. 3 (2017)

• Semi-automated myocardial segmentation of bright blood multi-gradient
echo images improves reproducibility of myocardial contours and T2*
determination
• Authors: Pandji Triadyaksa; Niek H. J. Prakken; Jelle Overbosch; Robin B. Peters; J. Martijn van Swieten; Matthijs Oudkerk; Paul E. Sijens
Pages: 239 - 254
Abstract: Objectives Early detection of iron loading is affected by the reproducibility of myocardial contour assessment. A novel semi-automatic myocardial segmentation method is presented on contrast-optimized composite images and compared to the results of manual drawing. Materials and methods Fifty-one short-axis slices at basal, mid-ventricular and apical locations from 17 patients were acquired by bright blood multi-gradient echo MRI. Four observers produced semi-automatic and manual myocardial contours on contrast-optimized composite images. The semi-automatic segmentation method relies on vector field convolution active contours to generate the endocardial contour. After creating radial pixel clusters on the myocardial wall, a combination of pixel-wise coefficient of variance (CoV) assessment and k-means clustering establishes the epicardial contour for each segment. Results Compared to manual drawing, semi-automatic myocardial segmentation lowers the variability of T2* quantification within and between observers (CoV of 12.05 vs. 13.86% and 14.43 vs. 16.01%) by improving contour reproducibility (P < 0.001). In the presence of iron loading, semi-automatic segmentation also lowers the T2* variability within and between observers (CoV of 13.14 vs. 15.19% and 15.91 vs. 17.28%). Conclusion Application of semi-automatic myocardial segmentation on contrast-optimized composite images improves the reproducibility of T2* quantification.
PubDate: 2017-06-01
DOI: 10.1007/s10334-016-0601-0
Issue No: Vol. 30, No. 3 (2017)

• Evaluation of exposure to (ultra) high static magnetic fields during
activities around human MRI scanners
• Authors: Mahsa Fatahi; Jolanta Karpowicz; Krzysztof Gryz; Amirmohammad Fattahi; Georg Rose; Oliver Speck
Pages: 255 - 264
Abstract: Objective To assess the individual exposure to the static magnetic field (SMF) and the motion-induced time-varying magnetic field (TVMF) generated by activities in an inhomogeneous SMF near high and ultra-high field magnetic resonance imaging (MRI) scanners. The study provides information on the level of exposure to high and ultra-high field MRI scanners during research activities. Materials and methods A three-axis Hall magnetometer was used to determine the SMF and TVMF around human 3- and 7-Tesla (T) MRI systems. The 7-T MRI scanner used in this study was passively shielded and the 3-T scanner was actively shielded and both were from the same manufacturer. The results were compared with the exposure restrictions given by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). Results The recorded exposure was highly variable between individuals, although they followed the same instructions for moving near the scanners. Maximum exposure values of B = 2057 mT and dB/dt = 4347 mT/s for the 3-T scanner and B = 2890 mT, dB/dt = 3900 mT/s for 7 T were recorded. No correlation was found between reporting the MRI-related sensory effects and exceeding the reference values. Conclusions According to the results of our single-center study with five subjects, violation of the ICNIRP restrictions for max B in MRI research environments was quite unlikely at 3 and 7 T. Occasions of exceeding the dB/dt limit at 3 and 7 T were almost similar (30% of 60 exposure scenarios) and highly variable among the individuals.
PubDate: 2017-06-01
DOI: 10.1007/s10334-016-0602-z
Issue No: Vol. 30, No. 3 (2017)

• The effect of diffusion gradient direction number on corticospinal
tractography in the human brain: an along-tract analysis
• Authors: Claudia Testa; Stefania Evangelisti; Mariagrazia Popeo; Stefano Zanigni; Laura Ludovica Gramegna; Paola Fantazzini; Caterina Tonon; David Neil Manners; Raffaele Lodi
Pages: 265 - 280
Abstract: Objectives We evaluated diffusion imaging measures of the corticospinal tract obtained with a probabilistic tractography algorithm applied to data of two acquisition protocols based on different numbers of diffusion gradient directions (NDGDs). Materials and methods The corticospinal tracts (CST) of 18 healthy subjects were delineated using 22 and 66-NDGD data. An along-tract analysis of diffusion metrics was performed to detect possible local differences due to NDGD. Results FA values at 22-NDGD showed an increase along the central portion of the CST. The mean of partial volume fraction of the orientation of the second fiber (f2) was higher at 66-NDGD bilaterally, because for 66-NDGD data the algorithm more readily detects dominant fiber directions beyond the first, thus the increase in FA at 22-NDGD is due to a substantially reduced detection of crossing fiber volume. However, the good spatial correlation between the tracts drawn at 22 and 66 NDGD shows that the extent of the tract can be successfully defined even at lower NDGD. Conclusions Given the spatial tract localization obtained even at 22-NDGD, local analysis of CST can be performed using a NDGD compatible with clinical protocols. The probabilistic approach was particularly powerful in evaluating crossing fibers when present.
PubDate: 2017-06-01
DOI: 10.1007/s10334-016-0600-1
Issue No: Vol. 30, No. 3 (2017)

• A low-cost Mr compatible ergometer to assess post-exercise phosphocreatine
recovery kinetics
• Authors: Niels D. Naimon; Jerzy Walczyk; James S. Babb; Oleksandr Khegai; Xuejiao Che; Leeor Alon; Ravinder R. Regatte; Ryan Brown; Prodromos Parasoglou
Pages: 281 - 289
Abstract: Objective To develop a low-cost pedal ergometer compatible with ultrahigh (7 T) field MR systems to reliably quantify metabolic parameters in human lower leg muscle using phosphorus magnetic resonance spectroscopy. Materials and methods We constructed an MR compatible ergometer using commercially available materials and elastic bands that provide resistance to movement. We recruited ten healthy subjects (eight men and two women, mean age ± standard deviation: 32.8 ± 6.0 years, BMI: 24.1 ± 3.9 kg/m2). All subjects were scanned on a 7 T whole-body magnet. Each subject was scanned on two visits and performed a 90 s plantar flexion exercise at 40% maximum voluntary contraction during each scan. During the first visit, each subject performed the exercise twice in order for us to estimate the intra-exam repeatability, and once during the second visit in order to estimate the inter-exam repeatability of the time constant of phosphocreatine recovery kinetics. We assessed the intra and inter-exam reliability in terms of the within-subject coefficient of variation (CV). Results We acquired reliable measurements of PCr recovery kinetics with an intra- and inter-exam CV of 7.9% and 5.7%, respectively. Conclusion We constructed a low-cost pedal ergometer compatible with ultrahigh (7 T) field MR systems, which allowed us to quantify reliably PCr recovery kinetics in lower leg muscle using 31P-MRS.
PubDate: 2017-06-01
DOI: 10.1007/s10334-016-0605-9
Issue No: Vol. 30, No. 3 (2017)

• Feasibility of in vivo three-dimensional T 2 * mapping using
dicarboxy-PROXYL and CW-EPR-based single-point imaging
• Authors: Harue Kubota; Denis A. Komarov; Hironobu Yasui; Shingo Matsumoto; Osamu Inanami; Igor A. Kirilyuk; Valery V. Khramtsov; Hiroshi Hirata
Pages: 291 - 298
Abstract: Objectives The aim of this study was to demonstrate the feasibility of in vivo three-dimensional (3D) relaxation time T 2 * mapping of a dicarboxy-PROXYL radical using continuous-wave electron paramagnetic resonance (CW-EPR) imaging. Materials and methods Isotopically substituted dicarboxy-PROXYL radicals, 3,4-dicarboxy-2,2,5,5-tetra(2H3)methylpyrrolidin-(3,4-2H2)-(1-15N)-1-oxyl (2H,15N-DCP) and 3,4-dicarboxy-2,2,5,5-tetra(2H3)methylpyrrolidin-(3,4-2H2)-1-oxyl (2H-DCP), were used in the study. A clonogenic cell survival assay was performed with the 2H-DCP radical using squamous cell carcinoma (SCC VII) cells. The time course of EPR signal intensities of intravenously injected 2H,15N-DCP and 2H-DCP radicals were determined in tumor-bearing hind legs of mice (C3H/HeJ, male, n = 5). CW-EPR-based single-point imaging (SPI) was performed for 3D T 2 * mapping. Results 2H-DCP radical did not exhibit cytotoxicity at concentrations below 10 mM. The in vivo half-life of 2H,15N-DCP in tumor tissues was 24.7 ± 2.9 min (mean ± standard deviation [SD], n = 5). The in vivo time course of the EPR signal intensity of the 2H,15N-DCP radical showed a plateau of 10.2 ± 1.2 min (mean ± SD) where the EPR signal intensity remained at more than 90% of the maximum intensity. During the plateau, in vivo 3D T 2 * maps with 2H,15N-DCP were obtained from tumor-bearing hind legs, with a total acquisition time of 7.5 min. Conclusion EPR signals of 2H,15N-DCP persisted long enough after bolus intravenous injection to conduct in vivo 3D T 2 * mapping with CW-EPR-based SPI.
PubDate: 2017-06-01
DOI: 10.1007/s10334-016-0606-8
Issue No: Vol. 30, No. 3 (2017)

• Fast T1 and T2 mapping methods: the zoomed U-FLARE sequence compared with
EPI and snapshot-FLASH for abdominal imaging at 11.7 Tesla
• Authors: Géraldine Pastor; María Jiménez-González; Sandra Plaza-García; Marta Beraza; Torsten Reese
Pages: 299 - 307
Abstract: Objective A newly adapted zoomed ultrafast low-angle RARE (U-FLARE) sequence is described for abdominal imaging applications at 11.7 Tesla and compared with the standard echo-plannar imaging (EPI) and snapshot fast low angle shot (FLASH) methods. Materials and methods Ultrafast EPI and snapshot-FLASH protocols were evaluated to determine relaxation times in phantoms and in the mouse kidney in vivo. Owing to their apparent shortcomings, imaging artefacts, signal-to-noise ratio (SNR), and variability in the determination of relaxation times, these methods are compared with the newly implemented zoomed U-FLARE sequence. Results Snapshot-FLASH has a lower SNR when compared with the zoomed U-FLARE sequence and EPI. The variability in the measurement of relaxation times is higher in the Look–Locker sequences than in inversion recovery experiments. Respectively, the average T1 and T2 values at 11.7 Tesla are as follows: kidney cortex, 1810 and 29 ms; kidney medulla, 2100 and 25 ms; subcutaneous tumour, 2365 and 28 ms. Conclusion This study demonstrates that the zoomed U-FLARE sequence yields single-shot single-slice images with good anatomical resolution and high SNR at 11.7 Tesla. Thus, it offers a viable alternative to standard protocols for mapping very fast parameters, such as T1 and T2, or dynamic processes in vivo at high field.
PubDate: 2017-06-01
DOI: 10.1007/s10334-016-0604-x
Issue No: Vol. 30, No. 3 (2017)

• Assessment of edema using STIR+ via 3D cardiovascular magnetic resonance
imaging in patients with suspected myocarditis
• Authors: Michael Jeserich; Bela Merkely; Pascal Schlosser; Simone Kimmel; Gabor Pavlik; Stephan Achenbach
Pages: 309 - 316
Abstract: Objective To evaluate three-dimensional T2-weighted fast spin echo triple inversion recovery sequences (STIR+) for the diagnosis of myocardial edema in patients with suspected early myocarditis after respiratory or gastrointestinal tract viral infection and at follow-up. Materials and methods We prospectively examined 28 patients with suspected myocarditis and 37 controls matched for gender and age. An ECG-triggered STIR+ was used to cover the entire left ventricle in short-axis images with 10-mm slice thickness and no interslice gap. The global signal intensity ratio (heart muscle in relation to skeletal muscle) was calculated (global STIR+ ratio) to evaluate edema. All patients had repeat examinations at follow-up (mean interval 4.9 months, 1–12 months). Results The mean global STIR+ ratio was 2.15 ± 0.4 in the initial examination of patients as compared to 1.78 ± 0.3 in controls (p < 0.0001) and 1.89 ± 0.3 in patients at follow-up (p = 0.0001 vs. first visit). Left ventricular ejection fraction did not differ between patients and controls at baseline and at follow-up. Conclusion We could identify a significantly higher global STIR+ ratio in patients with suspected myocarditis compared to controls, and a dynamic change during follow-up. The global STIR+ ratio may, therefore, be useful for the diagnosis of myocarditis and should be further explored.
PubDate: 2017-06-01
DOI: 10.1007/s10334-016-0603-y
Issue No: Vol. 30, No. 3 (2017)

• Assessment of MRI contrast agent concentration by quantitative
susceptibility mapping (QSM): application to estimation of cerebral blood
• Authors: Emelie Lind; Linda Knutsson; Robin Kämpe; Freddy Ståhlberg; Ronnie Wirestam
Abstract: Objective One major issue in dynamic susceptibility contrast MRI (DSC-MRI) is to accurately determine contrast agent (CA) concentration, since T2* relaxivity in vivo is generally unknown and varies between blood and tissue. In this study, quantitative susceptibility mapping (QSM) was used for quantification of CA concentration. Materials and methods A DSC-MRI protocol, including phase data acquisition, was applied to 20 healthy volunteers in a test–retest study. By selecting a CSF reference region of interest (ROI), the values of all QSM images were shifted to show no CA-induced change in CSF. CA concentration and cerebral blood volume (CBV) were estimated using shifted QSM data. CSF reference ROI optimization was evaluated by investigation of CBV repeatability. The CBV age dependence was analysed and tissue T2* relaxivity was estimated. Results The best repeatability of CBV, using an optimal CSF reference ROI, showed test-versus-retest correlations of r = 0.81 and r = 0.91 for white and grey matter, respectively. A slight CBV decrease with age was observed, and the estimated in vivo T2* relaxivity was 85 mM−1s−1. Conclusion Provided that a carefully selected CSF reference ROI is used to shift QSM image values, susceptibility information can be used to estimate concentration of contrast agent and to calculate CBV.
PubDate: 2017-06-19
DOI: 10.1007/s10334-017-0637-9

• Adaptive step size LMS improves ECG detection during MRI at 1.5 and
3 T
• Authors: André Guillou; Jean-Marc Sellal; Sarah Ménétré; Grégory Petitmangin; Jacques Felblinger; Laurent Bonnemains
Abstract: Objective We describe a new real-time filter to reduce artefacts on electrocardiogram (ECG) due to magnetic field gradients during MRI. The proposed filter is a least mean square (LMS) filter able to continuously adapt its step size according to the gradient signal of the ongoing MRI acquisition. Materials and methods We implemented this filter and compared it, within two databases (at 1.5 and 3 T) with over 6000 QRS complexes, to five real-time filtering strategies (no filter, low pass filter, standard LMS, and two other filters optimized within the databases: optimized LMS, and optimized Kalman filter). Results The energy of the remaining noise was significantly reduced (26 vs. 68%, p < 0.001) with the new filter vs. standard LMS. The detection error of our ventricular complex (QRS) detector was: 11% with our method vs. 25% with raw ECG, 35% with low pass filter, 17% with standard LMS, 12% with optimized Kalman filter, and 11% with optimized LMS filter. Conclusion The adaptive step size LMS improves ECG denoising during MRI. QRS detection has the same F1 score with this filter than with filters optimized within the database.
PubDate: 2017-06-19
DOI: 10.1007/s10334-017-0638-8

• Fatty metaplasia quantification and impact on regional myocardial function
as assessed by advanced cardiac MR imaging
• Authors: Tomas Lapinskas; Bernhard Schnackenburg; Marc Kouwenhoven; Rolf Gebker; Alexander Berger; Remigijus Zaliunas; Burkert Pieske; Sebastian Kelle
Abstract: Objective This study aimed to investigate the advantages of recently developed cardiac imaging techniques of fat–water separation and feature tracking to characterize better individuals with chronic myocardial infarction (MI). Materials and methods Twenty patients who had a previous MI underwent CMR imaging. The study protocol included routine cine and late gadolinium enhancement (LGE) technique. In addition, mDixon LGE imaging was performed in every patient. Left ventricular (LV) circumferential (EccLV) and radial (ErrLV) strain were calculated using dedicated software (CMR42, Circle, Calgary, Canada). The extent of global scar was measured in LGE and fat–water separated images to compare conventional and recent CMR imaging techniques. Results The infarct size derived from conventional LGE and fat–water separated images was similar. However, detection of lipomatous metaplasia was only possible with mDixon imaging. Subjects with fat deposition demonstrated a significantly smaller percentage of fibrosis than those without fat (10.68 ± 5.07% vs. 13.83 ± 6.30%; p = 0.005). There was no significant difference in EccLV or ErrLV between myocardial segments containing fibrosis only and fibrosis with fat. However, EccLV and ErrLV values were significantly higher in myocardial segments adjacent to fibrosis with fat deposition than in those adjacent to LGE only. Conclusions Advanced CMR imaging ensures more detailed tissue characterization in patients with chronic MI without a relevant increase in imaging and post-processing time. Fatty metaplasia may influence regional myocardial deformation especially in the myocardial segments adjacent to scar tissue. A simplified and shortened myocardial viability CMR protocol might be useful to better characterize and stratify patients with chronic MI.
PubDate: 2017-06-15
DOI: 10.1007/s10334-017-0639-7

• Towards accurate and precise T 1 and extracellular volume mapping in the
myocardium: a guide to current pitfalls and their solutions
• Authors: Donnie Cameron; Vassilios S. Vassiliou; David M. Higgins; Peter D. Gatehouse
Abstract: Mapping of the longitudinal relaxation time (T 1) and extracellular volume (ECV) offers a means of identifying pathological changes in myocardial tissue, including diffuse changes that may be invisible to existing T 1-weighted methods. This technique has recently shown strong clinical utility for pathologies such as Anderson-Fabry disease and amyloidosis and has generated clinical interest as a possible means of detecting small changes in diffuse fibrosis; however, scatter in T 1 and ECV estimates offers challenges for detecting these changes, and bias limits comparisons between sites and vendors. There are several technical and physiological pitfalls that influence the accuracy (bias) and precision (repeatability) of T 1 and ECV mapping methods. The goal of this review is to describe the most significant of these, and detail current solutions, in order to aid scientists and clinicians to maximise the utility of T 1 mapping in their clinical or research setting. A detailed summary of technical and physiological factors, issues relating to contrast agents, and specific disease-related issues is provided, along with some considerations on the future directions of the field.
PubDate: 2017-06-12
DOI: 10.1007/s10334-017-0631-2

• Diffusional kurtosis imaging (DKI) incorporation into an intravoxel
incoherent motion (IVIM) MR model to measure cerebral hypoperfusion
induced by hyperventilation challenge in healthy subjects
• Authors: Aude Pavilla; Giulio Gambarota; Alessandro Arrigo; Mehdi Mejdoubi; Régis Duvauferrier; Hervé Saint-Jalmes
Abstract: Objectives The objectives were to investigate the diffusional kurtosis imaging (DKI) incorporation into the intravoxel incoherent motion (IVIM) model for measurements of cerebral hypoperfusion in healthy subjects. Materials and methods Eight healthy subjects underwent a hyperventilation challenge with a 4-min diffusion weighted imaging protocol, using 8 b values chosen with the Cramer-Rao Lower Bound optimization approach. Four regions of interest in gray matter (GM) were analyzed with the DKI–IVIM model and the bi-exponential IVIM model, for normoventilation and hyperventilation conditions. Results A significant reduction in the perfusion fraction (f) and in the product fD* of the perfusion fraction with the pseudodiffusion coefficient (D*) was found with the DKI–IVIM model, during the hyperventilation challenge. In the cerebellum GM, the percentage changes were f: −43.7 ± 40.1, p = 0.011 and fD*: −50.6 ± 32.1, p = 0.011; in thalamus GM, f: −47.7 ± 34.7, p = 0.012 and fD*: −47.2 ± 48.7, p = 0.040. In comparison, using the bi-exponential IVIM model, only a significant decrease in the parameter fD* was observed for the same regions of interest. In frontal-GM and posterior-GM, the reduction in f and fD* did not reach statistical significance, either with DKI–IVIM or the bi-exponential IVIM model. Conclusion When compared to the bi-exponential IVIM model, the DKI–IVIM model displays a higher sensitivity to detect changes in perfusion induced by the hyperventilation condition.
PubDate: 2017-06-12
DOI: 10.1007/s10334-017-0629-9

• Identification of myocardial diffuse fibrosis by 11 heartbeat MOLLI T 1
mapping: averaging to improve precision and correlation with collagen
volume fraction
• Authors: Vassilios S. Vassiliou; Katharina Wassilew; Donnie Cameron; Ee Ling Heng; Evangelia Nyktari; George Asimakopoulos; Anthony de Souza; Shivraman Giri; Iain Pierce; Andrew Jabbour; David Firmin; Michael Frenneaux; Peter Gatehouse; Dudley J. Pennell; Sanjay K. Prasad
Abstract: Objectives Our objectives involved identifying whether repeated averaging in basal and mid left ventricular myocardial levels improves precision and correlation with collagen volume fraction for 11 heartbeat MOLLI T 1 mapping versus assessment at a single ventricular level. Materials and methods For assessment of T 1 mapping precision, a cohort of 15 healthy volunteers underwent two CMR scans on separate days using an 11 heartbeat MOLLI with a 5(3)3 beat scheme to measure native T 1 and a 4(1)3(1)2 beat post-contrast scheme to measure post-contrast T 1, allowing calculation of partition coefficient and ECV. To assess correlation of T 1 mapping with collagen volume fraction, a separate cohort of ten aortic stenosis patients scheduled to undergo surgery underwent one CMR scan with this 11 heartbeat MOLLI scheme, followed by intraoperative tru-cut myocardial biopsy. Six models of myocardial diffuse fibrosis assessment were established with incremental inclusion of imaging by averaging of the basal and mid-myocardial left ventricular levels, and each model was assessed for precision and correlation with collagen volume fraction. Results A model using 11 heart beat MOLLI imaging of two basal and two mid ventricular level averaged T 1 maps provided improved precision (Intraclass correlation 0.93 vs 0.84) and correlation with histology (R 2 = 0.83 vs 0.36) for diffuse fibrosis compared to a single mid-ventricular level alone. ECV was more precise and correlated better than native T 1 mapping. Conclusion T 1 mapping sequences with repeated averaging could be considered for applications of 11 heartbeat MOLLI, especially when small changes in native T 1/ECV might affect clinical management.
PubDate: 2017-06-12
DOI: 10.1007/s10334-017-0630-3

• Automatic frequency and phase alignment of in vivo J-difference-edited MR
spectra by frequency domain correlation
• Authors: Evita C. Wiegers; Bart W. J. Philips; Arend Heerschap; Marinette van der Graaf
Abstract: Objective J-difference editing is often used to select resonances of compounds with coupled spins in 1H-MR spectra. Accurate phase and frequency alignment prior to subtracting J-difference-edited MR spectra is important to avoid artefactual contributions to the edited resonance. Materials and methods In-vivo J-difference-edited MR spectra were aligned by maximizing the normalized scalar product between two spectra (i.e., the correlation over a spectral region). The performance of our correlation method was compared with alignment by spectral registration and by alignment of the highest point in two spectra. The correlation method was tested at different SNR levels and for a broad range of phase and frequency shifts. Results In-vivo application of the proposed correlation method showed reduced subtraction errors and increased fit reliability in difference spectra as compared with conventional peak alignment. The correlation method and the spectral registration method generally performed equally well. However, better alignment using the correlation method was obtained for spectra with a low SNR (down to ~2) and for relatively large frequency shifts. Conclusion Our correlation method for simultaneously phase and frequency alignment is able to correct both small and large phase and frequency drifts and also performs well at low SNR levels.
PubDate: 2017-06-01
DOI: 10.1007/s10334-017-0627-y

• Sex, body mass index, and blood pressure are related to aortic
characteristics in healthy, young adults using magnetic resonance vessel
wall imaging: the AMBITYON study
• Authors: Anouk L. M. Eikendal; Hester M. den Ruijter; Cees Haaring; Tobias Saam; Rob J. van der Geest; Jos J. M. Westenberg; Michiel L. Bots; Imo E. Hoefer; Tim Leiner
Abstract: Objectives More detailed evaluation of atherosclerosis and its key determinants in young individuals is warranted to improve knowledge on the pathophysiology of its development and progression. This study evaluated associations of magnetic resonance imaging (MRI)-derived aortic wall area, wall thickness, and pulse wave velocity (PWV) with cardiovascular risk factors in asymptomatic, young adults. Materials and methods In 124 adults (age: 25–35 years) from the general population-based Atherosclerosis Monitoring and Biomarker Measurements in the Young study, demography, anthropometry, and blood samples were collected. The studied MRI-parameters were measured using a 3.0T MRI system. Relations between cardiovascular risk factors and aortic characteristics were assessed using multivariable linear regression analyses. Results Mean age was 31.8 years, 47.6% was male. Aortic wall area was positively associated with age [β = 0.01, (95% confidence interval (CI) 2.00 × 10−3, 0.02), p = 0.01] and BMI [β = 0.01, (0.01, 0.02), p = 0.003] and negatively associated with sex (reference: men) [β = −0.06, (−0.11, −0.01), p = 0.02]. Natural logarithm transformed (ln) aortic wall thickness was positively associated with BMI [β = 0.01, (1.00 × 10−3, 0.02), p = 0.02]. Ln aortic PWV was positively associated with 10 mmHg increment of SBP [β = 0.06, (0.03, 0.09), p < 0.001] and DBP [β = 0.06, (0.02, 0.09), p = 0.006]. No relations were observed for smoking and lipids. Conclusions Already in early adulthood, aortic wall geometry and stiffness vary by age, sex, BMI, and blood pressure.
PubDate: 2017-05-31
DOI: 10.1007/s10334-017-0626-z

• Quantitative pulsed CEST-MRI at a clinical 3T MRI system
• Authors: Julia Stabinska; Tom Cronenberg; Hans-Jörg Wittsack; Rotem Shlomo Lanzman; Anja Müller-Lutz
Abstract: Objectives The goal of this study was to quantify CEST related parameters such as chemical exchange rate and fractional concentration of exchanging protons at a clinical 3T scanner. For this purpose, two CEST quantification approaches—the AREX metric (for ‘apparent exchange dependent relaxation’), and the AREX-based Ω-plot method were used. In addition, two different pulsed RF irradiation schemes, using Gaussian-shaped and spin-lock pulses, were compared. Materials and methods Numerical simulations as well as MRI measurements in phantoms were performed. For simulations, the Bloch–McConnell equations were solved using a two-pool exchange model. MR experiments were performed on a clinical 3T MRI scanner using a cylindrical phantom filled with creatine solution at different pH values and different concentrations. Results The validity of the Ω-plot method and the AREX approach using spin-lock preparation for determination of the quantitative CEST parameters was demonstrated. Especially promising results were achieved for the Ω-plot method when the spin-lock preparation was employed. Conclusion Pulsed CEST at 3T could be used to quantify parameters such as exchange rate constants and concentrations of protons exchanging with free water. In the future this technique might be used to estimate the exchange rates and concentrations of biochemical substances in human tissues in vivo.
PubDate: 2017-05-31
DOI: 10.1007/s10334-017-0625-0

• Motion-compensated data decomposition algorithm to accelerate dynamic
cardiac MRI
• Authors: Azar Tolouee; Javad Alirezaie; Paul Babyn
Abstract: Objectives In dynamic cardiac magnetic resonance imaging (MRI), the spatiotemporal resolution is often limited by low imaging speed. Compressed sensing (CS) theory can be applied to improve imaging speed and spatiotemporal resolution. The combination of compressed sensing and low-rank matrix completion represents an attractive means to further increase imaging speed. By extending prior work, a Motion-Compensated Data Decomposition (MCDD) algorithm is proposed to improve the performance of CS for accelerated dynamic cardiac MRI. Materials and methods The process of MCDD can be described as follows: first, we decompose the dynamic images into a low-rank (L) and a sparse component (S). The L component includes periodic motion in the background, since it is highly correlated among frames, and the S component corresponds to respiratory motion. A motion-estimation/motion-compensation (ME-MC) algorithm is then applied to the low-rank component to reconstruct a cardiac motion compensated dynamic cardiac MRI. Results With validations on the numerical phantom and in vivo cardiac MRI data, we demonstrate the utility of the proposed scheme in significantly improving compressed sensing reconstructions by minimizing motion artifacts. The proposed method achieves higher PSNR and lower MSE and HFEN for medium to high acceleration factors. Conclusion The proposed method is observed to yield reconstructions with minimal spatiotemporal blurring and motion artifacts in comparison to the existing state-of-the-art methods.
PubDate: 2017-05-31
DOI: 10.1007/s10334-017-0628-x

• Single-breath-hold 3-D CINE imaging of the left ventricle using Cartesian
sampling
• Authors: Jens Wetzl; Michaela Schmidt; François Pontana; Benjamin Longère; Felix Lugauer; Andreas Maier; Joachim Hornegger; Christoph Forman
Abstract: Objectives Our objectives were to evaluate a single-breath-hold approach for Cartesian 3-D CINE imaging of the left ventricle with a nearly isotropic resolution of $$1.9 \times 1.9 \times 2.5\,{\text {mm}^3}$$ and a breath-hold duration of $$\sim$$ 19 s against a standard stack of 2-D CINE slices acquired in multiple breath-holds. Validation is performed with data sets from ten healthy volunteers. Materials and methods A Cartesian sampling pattern based on the spiral phyllotaxis and a compressed sensing reconstruction method are proposed to allow 3-D CINE imaging with high acceleration factors. The fully integrated reconstruction uses multiple graphics processing units to speed up the reconstruction. The 2-D CINE and 3-D CINE are compared based on ventricular function parameters, contrast-to-noise ratio and edge sharpness measurements. Results Visual comparisons of corresponding short-axis slices of 2-D and 3-D CINE show an excellent match, while 3-D CINE also allows reformatting to other orientations. Ventricular function parameters do not significantly differ from values based on 2-D CINE imaging. Reconstruction times are below 4 min. Conclusion We demonstrate single-breath-hold 3-D CINE imaging in volunteers and three example patient cases, which features fast reconstruction and allows reformatting to arbitrary orientations.
PubDate: 2017-05-26
DOI: 10.1007/s10334-017-0624-1

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