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Journal Cover Magnetic Resonance Materials in Physics, Biology and Medicine
  [SJR: 0.787]   [H-I: 46]   [3 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0968-5243 - ISSN (Online) 1352-8661
   Published by Springer-Verlag Homepage  [2353 journals]
  • Track-weighted imaging methods: extracting information from a streamlines
           tractogram
    • Authors: Fernando Calamante
      Pages: 317 - 335
      Abstract: Abstract A whole-brain streamlines data-set (so-called tractogram) generated from diffusion MRI provides a wealth of information regarding structural connectivity in the brain. Besides visualisation strategies, a number of post-processing approaches have been proposed to extract more detailed information from the tractogram. One such approach is based on exploiting the information contained in the tractogram to generate track-weighted (TW) images. In the track-weighted imaging (TWI) approach, a very large number of streamlines are often generated throughout the brain, and an image is then computed based on properties of the streamlines themselves (e.g. based on the number of streamlines in each voxel, or their average length), or based on the values of an associated image (e.g. a diffusion anisotropy map, a T2 map) measured at the coordinates of the streamlines. This review article describes various approaches used to generate TW images and discusses the flexible formalism that TWI provides to generate a range of images with very different contrast, as well as the super-resolution properties of the resulting images. It also explains how this approach provides a powerful means to study structural and functional connectivity simultaneously. Finally, a number of key issues for its practical implementation are discussed.
      PubDate: 2017-08-01
      DOI: 10.1007/s10334-017-0608-1
      Issue No: Vol. 30, No. 4 (2017)
       
  • Highly-accelerated self-gated free-breathing 3D cardiac cine MRI:
           validation in assessment of left ventricular function
    • Authors: Jing Liu; Li Feng; Hsin-Wei Shen; Chengcheng Zhu; Yan Wang; Kanae Mukai; Gabriel C. Brooks; Karen Ordovas; David Saloner
      Pages: 337 - 346
      Abstract: Objective This work presents a highly-accelerated, self-gated, free-breathing 3D cardiac cine MRI method for cardiac function assessment. Materials and methods A golden-ratio profile based variable-density, pseudo-random, Cartesian undersampling scheme was implemented for continuous 3D data acquisition. Respiratory self-gating was achieved by deriving motion signal from the acquired MRI data. A multi-coil compressed sensing technique was employed to reconstruct 4D images (3D+time). 3D cardiac cine imaging with self-gating was compared to bellows gating and the clinical standard breath-held 2D cine imaging for evaluation of self-gating accuracy, image quality, and cardiac function in eight volunteers. Reproducibility of 3D imaging was assessed. Results Self-gated 3D imaging provided an image quality score of 3.4 ± 0.7 vs 4.0 ± 0 with the 2D method (p = 0.06). It determined left ventricular end-systolic volume as 42.4 ± 11.5 mL, end-diastolic volume as 111.1 ± 24.7 mL, and ejection fraction as 62.0 ± 3.1%, which were comparable to the 2D method, with bias ± 1.96 × SD of −0.8 ± 7.5 mL (p = 0.90), 2.6 ± 3.3 mL (p = 0.84) and 1.4 ± 6.4% (p = 0.45), respectively. Conclusion The proposed 3D cardiac cine imaging method enables reliable respiratory self-gating performance with good reproducibility, and provides comparable image quality and functional measurements to 2D imaging, suggesting that self-gated, free-breathing 3D cardiac cine MRI framework is promising for improved patient comfort and cardiac MRI scan efficiency.
      PubDate: 2017-08-01
      DOI: 10.1007/s10334-017-0607-2
      Issue No: Vol. 30, No. 4 (2017)
       
  • Interpretation of cardiac wall motion from cine-MRI combined with
           parametric imaging based on the Hilbert transform
    • Authors: Narjes Benameur; Enrico Gianluca Caiani; Younes Arous; Nejmeddine ben Abdallah; Tarek Kraiem
      Pages: 347 - 357
      Abstract: Object The aim of this study was to test and validate the clinical impact of parametric amplitude images obtained using the Hilbert transform on the regional interpretation of cardiac wall motion abnormalities from cine-MR images by non-expert radiologists compared with expert consensus. Materials and methods Cine-MRI short-axis images obtained in 20 patients (10 with myocardial infarction, 5 with myocarditis and 5 with normal function) were processed to compute a parametric amplitude image for each using the Hilbert transform. Two expert radiologists blindly reviewed the cine-MR images to define a gold standard for wall motion interpretation for each left ventricular sector. Two non-expert radiologists reviewed and graded the same images without and in combination with parametric images. Grades assigned to each segment in the two separate sessions were compared with the gold standard. Results According to expert interpretation, 264/320 (82.5%) segments were classified as normal and 56/320 (17.5%) were considered abnormal. The accuracy of the non-expert radiologists’ grades compared to the gold standard was significantly improved by adding parametric images (from 87.2 to 94.6%) together with sensitivity (from 64.29 to 84.4%) and specificity (from 92 to 96.9%), also resulting in reduced interobserver variability (from 12.8 to 5.6%). Conclusion The use of parametric amplitude images based on the Hilbert transform in conjunction with cine-MRI was shown to be a promising technique for improvement of the detection of left ventricular wall motion abnormalities in less expert radiologists.
      PubDate: 2017-08-01
      DOI: 10.1007/s10334-017-0609-0
      Issue No: Vol. 30, No. 4 (2017)
       
  • Biomarkers from in vivo molecular imaging of breast cancer: pretreatment
           18 F-FDG PET predicts patient prognosis, and pretreatment DWI-MR predicts
           response to neoadjuvant chemotherapy
    • Authors: Francesca Gallivanone; Marta Maria Panzeri; Carla Canevari; Claudio Losio; Luigi Gianolli; Francesco De Cobelli; Isabella Castiglioni
      Pages: 359 - 373
      Abstract: Objective Human cancers display intra-tumor phenotypic heterogeneity and recent research has focused on developing image processing methods extracting imaging descriptors to characterize this heterogeneity. This work assesses the role of pretreatment 18F-FDG PET and DWI-MR with respect to the prognosis and prediction of neoadjuvant chemotherapy (NAC) outcomes when image features are used to characterize primitive lesions from breast cancer (BC). Materials and methods A retrospective protocol included 38 adult women with biopsy-proven BC. Patients underwent a pre-therapy 18F-FDG PET/CT whole-body study and a pre-therapy breast multi-parametric MR study. Patients were then referred for NAC treatment and then for surgical resection, with an evaluation of the therapy response. Segmentation methods were developed in order to identify functional volumes both on 18F-FDG PET images and ADC maps. Macroscopic and histogram features were extracted from the defined functional volumes. Results Our work demonstrates that macroscopic and histogram features from 18F-FDG PET are able to biologically characterize primitive BC, and define the prognosis. In addition, histogram features from ADC maps are able to predict the response to NAC. Conclusion Our work suggests that pre-treatment 18F-FDG PET and pre-treatment DWI-MR provide useful complementary information for biological characterization and NAC response prediction in BC.
      PubDate: 2017-08-01
      DOI: 10.1007/s10334-017-0610-7
      Issue No: Vol. 30, No. 4 (2017)
       
  • A comparative study of the sensitivity of diffusion-related parameters
           obtained from diffusion tensor imaging, diffusional kurtosis imaging,
           q-space analysis and bi-exponential modelling in the early disease course
           (24 h) of hyperacute (6 h) ischemic stroke patients
    • Authors: Gaëtan Duchêne; Frank Peeters; André Peeters; Thierry Duprez
      Pages: 375 - 385
      Abstract: Objectives To compare the sensitivity and early temporal changes of diffusion parameters obtained from diffusion tensor imaging (DTI), diffusional kurtosis imaging (DKI), q-space analysis (QSA) and bi-exponential modelling in hyperacute stroke patients. Materials and methods A single investigational acquisition allowing the four diffusion analyses was performed on seven hyperacute stroke patients with a 3T system. The percentage change between ipsi- and contralateral regions were compared at admission and 24 h later. Two out of the seven patients were imaged every 6 h during this period. Results Kurtoses from both DKI and QSA were the most sensitive of the tested diffusion parameters in the few hours following ischemia. An early increase–maximum–decrease pattern of evolution was highlighted during the 24-h period for all parameters proportional to diffusion coefficients. A similar pattern was observed for both kurtoses in only one of two patients. Conclusion Our comparison was performed using identical diffusion encoding timings and on patients in the same stage of their condition. Although preliminary, our findings confirm those of previous studies that showed enhanced sensitivity of kurtosis. A fine time mapping of diffusion metrics in hyperacute stroke patients was presented which advocates for further investigations on larger animal or human cohorts.
      PubDate: 2017-08-01
      DOI: 10.1007/s10334-017-0612-5
      Issue No: Vol. 30, No. 4 (2017)
       
  • Long T2 suppression in native lung 3-D imaging using k-space reordered
           inversion recovery dual-echo ultrashort echo time MRI
    • Authors: Neville D. Gai; Ashkan A. Malayeri; David A. Bluemke
      Pages: 387 - 395
      Abstract: Objective Long T2 species can interfere with visualization of short T2 tissue imaging. For example, visualization of lung parenchyma can be hindered by breathing artifacts primarily from fat in the chest wall. The purpose of this work was to design and evaluate a scheme for long T2 species suppression in lung parenchyma imaging using 3-D inversion recovery double-echo ultrashort echo time imaging with a k-space reordering scheme for artifact suppression. Materials and methods A hyperbolic secant (HS) pulse was evaluated for different tissues (T1/T2). Bloch simulations were performed with the inversion pulse followed by segmented UTE acquisition. Point spread function (PSF) was simulated for a standard interleaved acquisition order and a modulo 2 forward-reverse acquisition order. Phantom and in vivo images (eight volunteers) were acquired with both acquisition orders. Contrast to noise ratio (CNR) was evaluated in in vivo images prior to and after introduction of the long T2 suppression scheme. Results The PSF as well as phantom and in vivo images demonstrated reduction in artifacts arising from k-space modulation after using the reordering scheme. CNR measured between lung and fat and lung and muscle increased from −114 and −148.5 to +12.5 and 2.8 after use of the IR-DUTE sequence. Paired t test between the CNRs obtained from UTE and IR-DUTE showed significant positive change (p < 0.001 for lung-fat CNR and p = 0.03 for lung-muscle CNR). Conclusion Full 3-D lung parenchyma imaging with improved positive contrast between lung and other long T2 tissue types can be achieved robustly in a clinically feasible time using IR-DUTE with image subtraction when segmented radial acquisition with k-space reordering is employed.
      PubDate: 2017-08-01
      DOI: 10.1007/s10334-017-0613-4
      Issue No: Vol. 30, No. 4 (2017)
       
  • What are the true volumes of SEGA tumors' Reliability of planimetric
           and popular semi-automated image segmentation methods
    • Authors: Konrad Stawiski; Joanna Trelińska; Dobromiła Baranska; Iwona Dachowska; Katarzyna Kotulska; Sergiusz Jóźwiak; Wojciech Fendler; Wojciech Młynarski
      Pages: 397 - 405
      Abstract: Objective To evaluate the reliability of the standard planimetric methodology of volumetric analysis and three different open-source semi-automated approaches of brain tumor segmentation. Materials and methods The volumes of subependymal giant cell astrocytomas (SEGA) examined by 30 MRI studies of 10 patients from a previous everolimus-related trial (EMINENTS study) were estimated using four methods: planimetric method (modified MacDonald ellipsoid method), ITK-Snap (pixel clustering, geodesic active contours, region competition methods), 3D Slicer (level-set thresholding), and NIRFast (k-means clustering, Markov random fields). The methods were compared, and a trial simulation was performed to determine how the choice of approach could influence the final decision about progression or response. Results Intraclass correlation coefficient was high (0.95; 95% CI 0.91–0.98). The planimetric method always overestimated the size of the tumor, while virtually no mean difference was found between ITK-Snap and 3D Slicer (P = 0.99). NIRFast underestimated the volume and presented a proportional bias. During the trial simulation, a moderate level of agreement between all the methods (kappa 0.57–0.71, P < 0.002) was noted. Conclusion Semi-automated segmentation can ease oncological follow-up but the moderate level of agreement between segmentation methods suggests that the reference standard volumetric method for SEGA tumors should be revised and chosen carefully, as the selection of volumetry tool may influence the conclusion about tumor progression or response.
      PubDate: 2017-08-01
      DOI: 10.1007/s10334-017-0614-3
      Issue No: Vol. 30, No. 4 (2017)
       
  • Combined quantification of fatty infiltration, T 1 -relaxation times and T
           2 *-relaxation times in normal-appearing skeletal muscle of controls and
           dystrophic patients
    • Authors: Benjamin Leporq; Arnaud Le Troter; Yann Le Fur; Emmanuelle Salort-Campana; Maxime Guye; Olivier Beuf; Shahram Attarian; David Bendahan
      Pages: 407 - 415
      Abstract: Objectives To evaluate the combination of a fat–water separation method with an automated segmentation algorithm to quantify the intermuscular fatty-infiltrated fraction, the relaxation times, and the microscopic fatty infiltration in the normal-appearing muscle. Materials and methods MR acquisitions were performed at 1.5T in seven patients with facio-scapulo-humeral dystrophy and eight controls. Disease severity was assessed using commonly used scales for the upper and lower limbs. The fat–water separation method provided proton density fat fraction (PDFF) and relaxation times maps (T 2* and T 1). The segmentation algorithm distinguished adipose tissue and normal-appearing muscle from the T 2* map and combined active contours, a clustering analysis, and a morphological closing process to calculate the index of fatty infiltration (IFI) in the muscle compartment defined as the relative amount of pixels with the ratio between the number of pixels within IMAT and the total number of pixels (IMAT + normal appearing muscle). Results In patients, relaxation times were longer and a larger fatty infiltration has been quantified in the normal-appearing muscle. T 2* and PDFF distributions were broader. The relaxation times were correlated to the Vignos scale whereas the microscopic fatty infiltration was linked to the Medwin-Gardner-Walton scale. The IFI was linked to a composite clinical severity scale gathering the whole set of scales. Conclusion The MRI indices quantified within the normal-appearing muscle could be considered as potential biomarkers of dystrophies and quantitatively illustrate tissue alterations such as inflammation and fatty infiltration.
      PubDate: 2017-08-01
      DOI: 10.1007/s10334-017-0616-1
      Issue No: Vol. 30, No. 4 (2017)
       
  • Vessel wall characterization using quantitative MRI: what’s in a
           number'
    • Abstract: Abstract The past decade has witnessed the rapid development of new MRI technology for vessel wall imaging. Today, with advances in MRI hardware and pulse sequences, quantitative MRI of the vessel wall represents a real alternative to conventional qualitative imaging, which is hindered by significant intra- and inter-observer variability. Quantitative MRI can measure several important morphological and functional characteristics of the vessel wall. This review provides a detailed introduction to novel quantitative MRI methods for measuring vessel wall dimensions, plaque composition and permeability, endothelial shear stress and wall stiffness. Together, these methods show the versatility of non-invasive quantitative MRI for probing vascular disease at several stages. These quantitative MRI biomarkers can play an important role in the context of both treatment response monitoring and risk prediction. Given the rapid developments in scan acceleration techniques and novel image reconstruction, we foresee the possibility of integrating the acquisition of multiple quantitative vessel wall parameters within a single scan session.
      PubDate: 2017-08-14
       
  • Highly accelerated intracranial 4D flow MRI: evaluation of healthy
           volunteers and patients with intracranial aneurysms
    • Authors: Jing Liu; Louise Koskas; Farshid Faraji; Evan Kao; Yan Wang; Henrik Haraldsson; Sarah Kefayati; Chengcheng Zhu; Sinyeob Ahn; Gerhard Laub; David Saloner
      Abstract: Objectives To evaluate an accelerated 4D flow MRI method that provides high temporal resolution in a clinically feasible acquisition time for intracranial velocity imaging. Materials and methods Accelerated 4D flow MRI was developed by using a pseudo-random variable-density Cartesian undersampling strategy (CIRCUS) with the combination of k-t, parallel imaging and compressed sensing image reconstruction techniques (k-t SPARSE-SENSE). Four-dimensional flow data were acquired on five healthy volunteers and eight patients with intracranial aneurysms using CIRCUS (acceleration factor of R = 4, termed CIRCUS4) and GRAPPA (R = 2, termed GRAPPA2) as the reference method. Images with three times higher temporal resolution (R = 12, CIRCUS12) were also reconstructed from the same acquisition as CIRCUS4. Qualitative and quantitative image assessment was performed on the images acquired with different methods, and complex flow patterns in the aneurysms were identified and compared. Results Four-dimensional flow MRI with CIRCUS was achieved in 5 min and allowed further improved temporal resolution of <30 ms. Volunteer studies showed similar qualitative and quantitative evaluation obtained with the proposed approach compared to the reference (overall image scores: GRAPPA2 3.2 ± 0.6; CIRCUS4 3.1 ± 0.7; CIRCUS12 3.3 ± 0.4; difference of the peak velocities: −3.83 ± 7.72 cm/s between CIRCUS4 and GRAPPA2, −1.72 ± 8.41 cm/s between CIRCUS12 and GRAPPA2). In patients with intracranial aneurysms, the higher temporal resolution improved capturing of the flow features in intracranial aneurysms (pathline visualization scores: GRAPPA2 2.2 ± 0.2; CIRCUS4 2.5 ± 0.5; CIRCUS12 2.7 ± 0.6). Conclusion The proposed rapid 4D flow MRI with a high temporal resolution is a promising tool for evaluating intracranial aneurysms in a clinically feasible acquisition time.
      PubDate: 2017-08-07
      DOI: 10.1007/s10334-017-0646-8
       
  • Radial MRI with variable echo times: reducing the orientation dependency
           of susceptibility artifacts of an MR-safe guidewire
    • Authors: Katharina E. Schleicher; Michael Bock; Klaus Düring; Stefan Kroboth; Axel J. Krafft
      Abstract: Objectives Guidewires are indispensable tools for intravascular MR-guided interventions. Recently, an MR-safe guidewire made from a glass-fiber/epoxy compound material with embedded iron particles was developed. The size of the induced susceptibility artifact, and thus the guidewire’s visibility, depends on its orientation against B 0. We present a radial acquisition scheme with variable echo times that aims to reduce the artifact’s orientation dependency. Materials and methods The radial acquisition scheme uses sine-squared modulated echo times depending on the physical direction of the spoke to balance the susceptibility artifact of the guidewire. The acquisition scheme was studied in simulations based on dipole fields and in phantom experiments for different orientations of the guidewire against B 0. The simulated and measured artifact widths were quantitatively compared. Results Compared to acquisitions with non-variable echo times, the proposed acquisition scheme shows a reduced angular variability. For the two main orientations (i.e., parallel and perpendicular to B 0), the ratio of the artifact widths was reduced from about 2.2 (perpendicular vs. parallel) to about 1.2 with the variable echo time approach. Conclusion The reduction of the orientation dependency of the guidewire’s artifact via sine-squared varying echo times could be verified in simulations and measurements. The more balanced artifact allows for a better overall visibility of the guidewire.
      PubDate: 2017-08-02
      DOI: 10.1007/s10334-017-0645-9
       
  • Utilization of MR angiography in perfusion imaging for identifying
           arterial input function
    • Authors: Bora Buyuksarac; Mehmed Ozkan
      Abstract: Objective This research utilizes magnetic resonance angiography (MRA) to identify arterial locations during the parametric evaluation of concentration time curves (CTCs), and to prevent shape distortions in arterial input function (AIF). Materials and methods We carried out cluster analysis with the CTC parameters of voxels located within and around the middle cerebral artery (MCA). Through MRA, we located voxels that meet the AIF criteria and those with distorted CTCs. To minimize partial volume effect, we re-scaled the time integral of CTCs by the time integral of venous output function (VOF). We calculated the steady-state value to area under curve ratio (SS:AUC) of VOF and used it as a reference in selecting AIF. CTCs close to this reference value (selected AIF) and those far from it were used (eliminated AIF) to compute cerebral blood flow (CBF). Results Eliminated AIFs were found to be either on or anterior to MCA, whereas selected AIFs were located superior, inferior, posterior, or anterior to MCA. If the SS:AUC of AIF was far from the reference value, CBF was either under- or over-estimated by a maximum of 41.1 ± 14.3 and 36.6 ± 19.2%, respectively. Conclusion MRA enables excluding voxels on the MCA during cluster analysis, and avoiding the risk of shape distortions.
      PubDate: 2017-07-25
      DOI: 10.1007/s10334-017-0643-y
       
  • Variable slice thickness (VAST) EPI for the reduction of susceptibility
           artifacts in whole-brain GE-EPI at 7 Tesla
    • Authors: Sascha Brunheim; Sören Johst; Viktor Pfaffenrot; Stefan Maderwald; Harald H. Quick; Benedikt A. Poser
      Abstract: Objective A new technique for 2D gradient-recalled echo echo-planar imaging (GE-EPI) termed ‘variable slice thickness’ (VAST) is proposed, which reduces signal losses caused by through-slice susceptibility artifacts, while keeping the volume repetition time (TR) manageable. The slice thickness is varied across the brain, with thinner slices being used in the inferior brain regions where signal voids are most severe. Materials and methods Various axial slice thickness schemes with identical whole-brain coverage were compared to regular EPI, which may either suffer from unfeasibly long TR if appropriately thin slices are used throughout, or signal loss if no counter-measures are taken. Evaluation is based on time-course signal-to-noise (tSNR) maps from resting state data and a statistical group-level region of interest (ROI) analysis on breath-hold fMRI measurements. Results The inferior brain region signal voids with static B0 inhomogeneities could be markedly reduced with VAST GE-EPI in contrast to regular GE-EPI. ROI-averaged event-related signal changes showed 48% increase in VAST compared to GE-EPI with regular “thick” slices. tSNR measurements proved the comparable signal robustness of VAST in comparison to regular GE-EPI with thin slices. Conclusion A novel acquisition strategy for functional 2D GE-EPI at ultrahigh magnetic field is presented to reduce susceptibility-induced signal voids and keep TR sufficiently short for whole-brain coverage.
      PubDate: 2017-07-10
      DOI: 10.1007/s10334-017-0641-0
       
  • Temperature dependence of 1 H NMR chemical shifts and its influence on
           estimated metabolite concentrations
    • Authors: Felizitas C. Wermter; Nico Mitschke; Christian Bock; Wolfgang Dreher
      Abstract: Objectives Temperature dependent chemical shifts of important brain metabolites measured by localised 1H MRS were investigated to test how the use of incorrect prior knowledge on chemical shifts impairs the quantification of metabolite concentrations. Materials and methods Phantom measurements on solutions containing 11 metabolites were performed on a 7 T scanner between 1 and 43 °C. The temperature dependence of the chemical shift differences was fitted by a linear model. Spectra were simulated for different temperatures and analysed by the AQSES program (jMRUI 5.2) using model functions with chemical shift values for 37 °C. Results Large differences in the temperature dependence of the chemical shift differences were determined with a maximum slope of about ±7.5 × 10−4 ppm/K. For 32–40 °C, only minor quantification errors resulted from using incorrect chemical shifts, with the exception of Cr and PCr. For 1–10 °C considerable quantification errors occurred if the temperature dependence of the chemical shifts was neglected. Conclusion If 1H MRS measurements are not performed at 37 °C, for which the published chemical shift values have been determined, the temperature dependence of chemical shifts should be considered to avoid systematic quantification errors, particularly for measurements on animal models at lower temperatures.
      PubDate: 2017-07-06
      DOI: 10.1007/s10334-017-0642-z
       
  • Three-dimensional black-blood multi-contrast carotid imaging using
           compressed sensing: a repeatability study
    • Authors: Jianmin Yuan; Ammara Usman; Scott A. Reid; Kevin F. King; Andrew J. Patterson; Jonathan H. Gillard; Martin J. Graves
      Abstract: Objective The purpose of this work is to evaluate the repeatability of a compressed sensing (CS) accelerated multi-contrast carotid protocol at 3 T. Materials and methods Twelve volunteers and eight patients with carotid disease were scanned on a 3 T MRI scanner using a CS accelerated 3-D black-blood multi-contrast protocol which comprises T 1w, T 2w and PDw without CS, and with a CS factor of 1.5 and 2.0. The volunteers were scanned twice, the lumen/wall area and wall thickness were measured for each scan. Eight patients were scanned once, the inter/intra-observer reproducibility of the measurements was calculated. Results In the repeated volunteer scans, the interclass correlation coefficient (ICC) for the wall area measurement using a CS factor of 1.5 in PDw, T 1w and T 2w were 0.95, 0.81, and 0.97, respectively. The ICC for lumen area measurement using a CS factor of 1.5 in PDw, T 1w and T 2w were 0.96, 0.92, and 0.96, respectively. In patients, the ICC for inter/intra-observer measurements of lumen/wall area, and wall thickness were all above 0.81 in all sequences. Conclusion The results show a CS accelerated 3-D black-blood multi-contrast protocol is a robust and reproducible method for carotid imaging. Future protocol design could use CS to reduce the scanning time.
      PubDate: 2017-06-26
      DOI: 10.1007/s10334-017-0640-1
       
  • Assessment of MRI contrast agent concentration by quantitative
           susceptibility mapping (QSM): application to estimation of cerebral blood
           volume during steady state
    • 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: 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
       
 
 
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