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Magnetic Resonance Materials in Physics, Biology and Medicine    [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  [2187 journals]   [SJR: 0.821]   [H-I: 36]
  • Multi-parametric (ADC/PWI/T2-w) image fusion approach for accurate
           semi-automatic segmentation of tumorous regions in glioblastoma multiforme
           
    • Abstract: Object Glioblastoma multiforme (GBM) brain tumor is heterogeneous in nature, so its quantification depends on how to accurately segment different parts of the tumor, i.e. viable tumor, edema and necrosis. This procedure becomes more effective when metabolic and functional information, provided by physiological magnetic resonance (MR) imaging modalities, like diffusion-weighted-imaging (DWI) and perfusion-weighted-imaging (PWI), is incorporated with the anatomical magnetic resonance imaging (MRI). In this preliminary tumor quantification work, the idea is to characterize different regions of GBM tumors in an MRI-based semi-automatic multi-parametric approach to achieve more accurate characterization of pathogenic regions. Materials and methods For this purpose, three MR sequences, namely T2-weighted imaging (anatomical MR imaging), PWI and DWI of thirteen GBM patients, were acquired. To enhance the delineation of the boundaries of each pathogenic region (peri-tumoral edema, viable tumor and necrosis), the spatial fuzzy C-means algorithm is combined with the region growing method. Results The results show that exploiting the multi-parametric approach along with the proposed semi-automatic segmentation method can differentiate various tumorous regions with over 80 % sensitivity, specificity and dice score. Conclusion The proposed MRI-based multi-parametric segmentation approach has the potential to accurately segment tumorous regions, leading to an efficient design of the pre-surgical treatment planning.
      PubDate: 2014-04-02
       
  • Direct 17O MRI with
           partial volume correction: first experiences in a glioblastoma patient
    • Abstract: Object In tumor cells the energy production is shifted from aerobic to anaerobic metabolization of glucose, which makes the cerebral metabolic rate of oxygen consumption (CMRO2) a diagnostic parameter for tissue viability. Direct oxygen-17 (17O) MRI during inhalation of 17O gas allows for a non-invasive determination of the CMRO2. However, the low spatial resolution and the fast transverse relaxation of 17O lead to partial volume effects that severely bias the quantification of signal intensities. The aim of this work was to determine the CMRO2 in a tumor patient by 17O MRI in combination with a partial volume correction (PVC) scheme. Materials and methods Direct 17O MRI was performed in a glioblastoma patient (F, 51 years) prior to surgery at 7 T. The ‘geometric transfer matrix’ algorithm for volume of interest based PVC was adapted to 17O MRI to recover the true signal intensities. We determined the CMRO2 values of gray matter (GM), white matter (WM), cerebrospinal fluid (CSF) and the tumor areas of the contrast enhancing rim (CE), the necrotic center (NE), and the perifocal edema (PE) using a three-phase metabolic model. Results Large differences in the signal increase during 17O2 inhalation were obtained ranging from less than 2 % in the tumor center up to more than 20 % in GM areas. After PVC of the signal time curves, we determined CMRO2 values of 0.67 ± 0.08 μmol/g/min (WM), 3.57 ± 0.67 μmol/g/min (GM), 0.35 ± 0.09 μmol/g/min (CE), and 0.42 ± 0.05 μmol/g/min (PE). In CSF and NE no oxygen uptake (i.e. CMRO2 = 0) was determined from the corrected signals, well in accordance with the underlying physiology in these regions. Conclusion The results show that PVC has a strong effect on the resulting CMRO2 values obtained by 17O MRI. We found substantial differences—especially in GM tissue—between corrected and non-corrected CMRO2 values. Additionally, we demonstrated the feasibility of CMRO2 assessment in a glioblastoma patient by 17O MRI.
      PubDate: 2014-04-01
       
  • Effect of voluntary repetitive long-lasting muscle contraction activity on
           the BOLD signal as assessed by optimal hemodynamic response function
    • Abstract: Objective Among other neuroimaging techniques, functional magnetic resonance imaging (fMRI) can be useful for studying the development of motor fatigue. The aim of this study was to identify differences in cortical neuronal activation in nine subjects on three motor tasks: right-hand movement with minimum, maximum, and post-fatigue maximum finger flexion. Materials and methods fMRI activation maps for each subject and during each condition were obtained by estimating the optimal model of the hemodynamic response function (HRF) out of four standard HRF models and an individual-based HRF model (ibHRF). Results ibHRF was selected as the optimal model in six out of nine subjects for minimum movement, in five out of nine for maximum movement, and in eight out of nine for post-fatigue maximum movement. As compared to maximum movement, a large reduction in the total number of active voxels (primary sensorimotor area, supplementary motor area and cerebellum) was observed in post-fatigue maximum movement. Conclusion This is the first approach to the evaluation of long-lasting contraction effort in healthy subjects by means of the fMRI paradigm with the use of an individual-based hemodynamic response. The results may be relevant for defining a baseline in future studies on central fatigue in patients with neuropathological disorders.
      PubDate: 2014-04-01
       
  • Water exchange-minimizing DCE-MRI protocol to detect changes in tumor
           
    • Abstract: Objective The purpose of this study was to assess changes in the tumor microvasculature induced by combination antiangiogenic therapy in MCF-7 breast tumor mouse models, using a noninvasive DCE-MRI method that minimizes the effect of water exchange. Materials and methods 3D quantitative DCE-MRI images were acquired with a heavily T 1-weighted saturation recovery gradient echo sequence with a recovery delay of 20 ms. Tumor vascular volume (VV) and vascular permeability-surface area product (PS) were obtained through a linear regression of the albumin-Gd-DTPA-enhanced dynamic image intensity on MCF-7 breast tumor mouse models treated with combination bevacizumab/paclitaxel therapy. Results Measured tumor VV values were significantly higher than the values that have been reported previously using quantitative T 1 mapping, and are in good agreement with micro-CT (computed tomography) results reported earlier from other tumor models. A trend of decreasing tumor PS was detected in the group of MCF-7 tumor bearing mice treated with the bevacizumab/paclitaxel combination regimen. Conclusion VV and PS maps obtained by a heavily T 1-weighted acquisition protocol revealed the large peripheral blood vessels as well as the permeable areas within the tumor. A 12-day/three-dose combination treatment of bevacizumab and paclitaxel resulted in delayed tumor growth and a trend of decreasing tumor vascular permeability surface area product.
      PubDate: 2014-04-01
       
  • Quantification in magnetic resonance spectroscopy based on semi-parametric
           approaches
    • Abstract: Abstract Magnetic resonance spectroscopy (MRS) is a value-added modality to magnetic resonance imaging (MRI) that is often used in diagnosis, treatment and progression monitoring, as well as in non-destructive, non-invasive studies of disease states in humans and model systems in animals. The availability of high magnetic field strengths and use of hyperpolarized nuclei, combined with the possibility of acquiring spectra at very short echo-time, have dramatically increased the potential of MRS. For the last two decades, a challenge has been to quantify short echo-time proton spectra that exhibit many metabolites, and to estimate their concentrations. Quantification of such spectra is challenging. Because the model function describing the acquired MRS signal is incomplete, semi-parametric techniques are required for estimation of the wanted metabolite concentrations. The semi-parametric approaches, QUEST, AQSES, TARQUIN, LCModel and SiToolsFITT, are reviewed and discussed according to handling of macromolecule signal and unknown decay of the metabolite signal (lineshape). Estimation of noise-related errors on model parameters and compromise used in real-world applications are detailed, with emphasis on the bias-variance trade-off. Applications of the semi-parametric methods QUEST and AQSES to quantification of MRS, HRMAS and MRSI data are also provided.
      PubDate: 2014-04-01
       
  • FID modulus: a simple and efficient technique to phase and align MR
           spectra
    • Abstract: Object The post-processing of MR spectroscopic data requires several steps more or less easy to automate, including the phase correction and the chemical shift assignment. First, since the absolute phase is unknown, one of the difficulties the MR spectroscopist has to face is the determination of the correct phase correction. When only a few spectra have to be processed, this is usually performed manually. However, this correction needs to be automated as soon as a large number of spectra is involved, like in the case of phase coherent averaging or when the signals collected with phased array coils have to be combined. A second post-processing requirement is the frequency axis assignment. In standard mono-voxel MR spectroscopy, this can also be easily performed manually, by simply assigning a frequency value to a well-known resonance (e.g. the water or NAA resonance in the case of brain spectroscopy). However, when the correction of a frequency shift is required before averaging a large amount of spectra (due to B 0 spatial inhomogeneities in chemical shift imaging, or resulting from motion for example), this post-processing definitely needs to be performed automatically. Materials and methods Zero-order phase and frequency shift of a MR spectrum are linked respectively to zero-order and first-order phase variations in the corresponding free induction decay (FID) signal. One of the simplest ways to remove the phase component of a signal is to calculate the modulus of this signal: this approach is the basis of the correction technique presented here. Results We show that selecting the modulus of the FID allows, under certain conditions that are detailed, to automatically phase correct and frequency align the spectra. This correction technique can be for example applied to the summation of signals acquired from combined phased array coils, to phase coherent averaging and to B 0 shift correction. Conclusion We demonstrate that working on the modulus of the FID signal is a simple and efficient way to both phase correct and frequency align MR spectra automatically. This approach is particularly well suited to brain proton MR spectroscopy.
      PubDate: 2014-04-01
       
  • Quantitative breast MRI: 2D histogram analysis of diffusion tensor
           parameters in normal tissue
    • Abstract: Object Diffusion tensor imaging (DTI) of the breast may provide a powerful new approach for the detection of intraductal processes. The aim of this investigation was to characterize the relation between diffusion tensor parameters [fractional anisotropy (FA), mean diffusivity (MD)] in normal breast tissue to obtain information on the microenvironment of the diffusing water molecules and to provide a systematic approach for DTI analysis. Materials and methods Seven female, healthy volunteers underwent prospective double-spin-echo prepared echo-planar diffusion-weighted sequence (TR/TE 8,250 ms/74 ms, b values 0 and 500 s/mm (2), six encoding directions, 12 averages, 35 slices) in 4 consecutive weeks (3.0 T). Quantitative maps of diffusion tensor parameters were computed offline with custom routines. The interdependence of MD and FA in different voxels was analysed by linear and exponential regression. Results All MD and FA maps were of excellent quality. A consistent pattern was observed in that lower fractional anisotropy values were more likely associated with higher mean diffusivity values. The dependence exhibited an exponential behavior with a correlation coefficient R = 0.60 (R linear = 0.57). Conclusion The likelihood with which FA and MD values are observed in a voxel within normal breast tissue is characterized by a specific pattern, which can be described by an exponential model. Moreover, we could show that the proposed technique does not depend on the menstrual cycle.
      PubDate: 2014-04-01
       
  • Characterization of the impact to PET quantification and image quality of
           an anterior array surface coil for PET/MR imaging
    • Abstract: Object The aim of this study was to determine the impact to PET quantification, image quality and possible diagnostic impact of an anterior surface array used in a combined PET/MR imaging system. Materials and methods An extended oval phantom and 15 whole-body FDG PET/CT subjects were re-imaged for one bed position following placement of an anterior array coil at a clinically realistic position. The CT scan, used for PET attenuation correction, did not include the coil. Comparison, including liver SUVmean, was performed between the coil present and absent images using two methods of PET reconstruction. Due to the time delay between PET scans, a model was used to account for average physiologic time change of SUV. Results On phantom data, neglecting the coil caused a mean bias of −8.2 % for non-TOF/PSF reconstruction, and −7.3 % with TOF/PSF. On clinical data, the liver SUV neglecting the coil presence fell by −6.1 % (±6.5 %) for non-TOF/PSF reconstruction; respectively −5.2 % (±5.3 %) with TOF/PSF. All FDG-avid features seen with TOF/PSF were also seen with non-TOF/PSF reconstruction. Conclusion Neglecting coil attenuation for this anterior array coil results in a small but significant reduction in liver SUVmean but was not found to change the clinical interpretation of the PET images.
      PubDate: 2014-04-01
       
  • Motion correction of multi-contrast images applied to T       class="a-plus-plus">1 and T       class="a-plus-plus">2 quantification in cardiac
           MRI
    • Abstract: Object The ability to manipulate image contrast and thus to obtain complementary information is one of the main advantages of MRI. Motion consistency within the whole data set is a key point in the context of multi contrast imaging. In cardiac and abdominal MRI, the acquisition strategy uses multiple breath-holds and often relies on acceleration methods that inherently suffer from a signal-to-noise ratio loss. The aim of this work is to propose a free-breathing multi-contrast acquisition and reconstruction workflow to improve image quality and the subsequent data analysis. Materials and methods We extended a previously proposed motion-compensated image reconstruction method for multi-contrast imaging. Shared information throughout the imaging protocol is now exploited by the image reconstruction in the form of an additional constraint based on image gradient sparsity. This constraint helps to minimize the amount of data needed for efficient non-rigid motion correction. T1 and T2 weighted images were reconstructed from free-breathing acquisitions in 4 healthy volunteers and in a phantom. The impact of multi-contrast motion correction was evaluated in a phantom in terms of precision and accuracy of T1 and T2 quantification. Results In the phantom, the proposed method achieved an accuracy of 97.5 % on the quantified parameters against 88.0 % before motion correction. In volunteers, motion inconsistency in T1 and T2 quantification were noticeably reduced within 5 min of free-breathing acquisition. Conclusion An efficient, free-breathing, multi-contrast imaging method has been demonstrated that does not require prior assumptions about contrast and that is applicable to a wide range of examinations.
      PubDate: 2014-03-22
       
  • Simple recipe for accurate        class="a-plus-plus">T        class="a-plus-plus">2 quantification with multi
           spin-echo acquisitions
    • Abstract: Objective The quantification of magnetic resonance relaxation parameters T 1 and T 2 have the potential for improved disease detection and classification over standard clinical weighted imaging. Performing a mono-exponential fit on multi spin-echo (MSE) data provides quantitative T 2 values in a clinically acceptable scan-time. However, due to technical imperfections of refocusing pulses, stimulated echo contributions to the signals lead to significant deviations in the resulting T 2 values. In this work, a simple auto-calibrating correction procedure is presented, allowing the accurate estimation of T 2 from MSE acquisitions. Materials and methods Correction factors for T 2 values obtained from MSE acquisitions with a mono-exponential fit are derived from simulations following the extended phase graph formulation. A closed formula is given for the calculation of the required correction factors directly from the measured data itself. Results Simulations and phantom experiments show high accuracy of corrected T 2 values for a wide range of clinically relevant T 2 values and for different nominal refocusing flip angles. In addition, corrected T 2 maps of the human brain are presented. Conclusion A simple recipe is provided to correct T 2 values obtained from MSE acquisitions via a mono-exponential fit for the influence of stimulated echoes. Since all required parameters are extracted from the data themselves, no additional acquisitions are required.
      PubDate: 2014-03-19
       
  • Automatic brain segmentation using fractional signal modeling of a
           multiple flip angle, spoiled gradient-recalled echo acquisition
    • Abstract: Object The aim of this study was to demonstrate a new automatic brain segmentation method in magnetic resonance imaging (MRI). Materials and methods The signal of a spoiled gradient-recalled echo (SPGR) sequence acquired with multiple flip angles was used to map T1, and a subsequent fit of a multi-compartment model yielded parametric maps of partial volume estimates of the different compartments. The performance of the proposed method was assessed through simulations as well as in-vivo experiments in five healthy volunteers. Results Simulations indicated that the proposed method was capable of producing robust segmentation maps with good reliability. Mean bias was below 3 % for all tissue types, and the corresponding similarity index (Dice’s coefficient) was over 95 % (SNR = 100). In-vivo experiments yielded realistic segmentation maps, with comparable quality to results obtained with an established segmentation method. Relative whole-brain cerebrospinal fluid, grey matter, and white matter volumes were (mean ± SE) respectively 6.8 ± 0.5, 47.3 ± 1.1, and 45.9 ± 1.3 % for the proposed method, and 7.5 ± 0.6, 46.2 ± 1.2, and 46.3 ± 0.9 % for the reference method. Conclusion The proposed approach is promising for brain segmentation and partial volume estimation. The straightforward implementation of the method is attractive, and protocols that already rely on SPGR-based T1 mapping may employ this method without additional scans.
      PubDate: 2014-03-18
       
  • An RF-induced voltage sensor for investigating pacemaker safety in MRI
    • Abstract: Object Magnetic resonance imaging (MRI) is inadvisable for patients with pacemakers, as radiofrequency (RF) voltages induced in the pacemaker leads may cause the device to malfunction. Our goal is to develop a sensor to measure such RF-induced voltages during MRI safety tests. Materials and methods A sensor was designed (16.6 cm2) for measuring voltages at the connection between the pacemaker lead and its case. The induced voltage is demodulated, digitized, and transferred by optical fibres. The sensor was calibrated on the bench using RF pulses of known amplitude and duration. Then the sensor was tested during MRI scanning at 1.5 T in a saline gel filled phantom. Results Bench tests showed measurement errors below 5 % with a (−40 V; +40 V) range, a precision of 0.06 V, and a temporal resolution of 24.2 μs. In MRI tests, variability in the measured voltages was below 3.7 % for 996 measurements with different sensors and RF exposure. Coupling between the sensor and the MRI electromagnetic environment was estimated with a second sensor connected and was below 6.2 %. For a typical clinical MRI sequence, voltages around ten Vp were detected. Conclusion We have built an accurate and reproducible tool for measuring RF-induced voltages in pacemaker leads during MR safety investigations. The sensor might also be used with other conducting cables including those used for electrocardiography and neurostimulation .
      PubDate: 2014-03-15
       
  • Endometrial cancer: diagnostic value of quantitative measurements of
           microvascular changes with DCE-MR imaging
    • Abstract: Object To assess the diagnostic value of dynamic contrast-enhanced (DCE) perfusion-magnetic resonance imaging (MRI) in detection, characterization and grading of endometrial cancer, using histopathological analysis as the standard of reference. Materials and methods Eighty patients with histologically proven endometrial carcinoma who underwent MRI (1.5 T magnet) of the pelvis for staging purposes were enrolled in the study. Each MR examination consisted of multiplanar T2 and T1-weighted turbo spin echo (TSE) sequences and T1-weighted gradient echo sequences before, during and after the administration of contrast medium. For each patient colour perfusion maps were derived from the dynamic sequences using a dedicated workstation. On the maps a region of interest was manually drawn both on normal myometrium and on the endometrial lesion. Then the following perfusion parameters were automatically calculated: relative enhancement (RE, %), maximum enhancement (ME, %), maximum relative enhancement (MRE, %) and time to peak (TTP, s). Results All patients underwent total hysterectomy. Histopathological analysis documented: G1 tumour in 21 patients, G2 tumour in 44 patients, G3 tumour in 14 patients and one squamous cell carcinoma. The following mean value perfusion parameters, with corresponding mean standard deviation, were obtained for endometrial cancer: RE (%) = 59.3 ± 36.3; ME (%) = 862.7 ± 475.9; MRE (%) = 75.3 ± 37.6 and TTP (s) = 164.7 ± 78. RE, ME and MRE were lower in tumour lesions than in normal myometrium (p < 0.001) and significantly higher values (p < 0.001) of perfusion parameters were obtained for G1 (well-differentiated) tumours as compared to those in G2 and G3 (moderately and poorly differentiated) lesions. Conclusion DCE perfusion-MRI can provide quantitative information on tissue vascularity, which may be of help in detecting endometrial cancer and in the assessment of tumour grading.
      PubDate: 2014-03-15
       
  • Spatio-temporal wavelet regularization for parallel MRI reconstruction:
           application to functional MRI
    • Abstract: Background Parallel magnetic resonance imaging (MRI) is a fast imaging technique that helps acquiring highly resolved images in space/time. Its performance depends on the reconstruction algorithm, which can proceed either in the k-space or in the image domain. Objective and methods To improve the performance of the widely used SENSE algorithm, 2D regularization in the wavelet domain has been investigated. In this paper, we first extend this approach to 3D-wavelet representations and the 3D sparsity-promoting regularization term, in order to address reconstruction artifacts that propagate across adjacent slices. The resulting optimality criterion is convex but nonsmooth, and we resort to the parallel proximal algorithm to minimize it. Second, to account for temporal correlation between successive scans in functional MRI (fMRI), we extend our first contribution to 3D +  $t$ acquisition schemes by incorporating a prior along the time axis into the objective function. Results Our first method (3D-UWR-SENSE) is validated on T1-MRI anatomical data for gray/white matter segmentation. The second method (4D-UWR-SENSE) is validated for detecting evoked activity during a fast event-related functional MRI protocol. Conclusion We show that our algorithm outperforms the SENSE reconstruction at the subject and group levels (15 subjects) for different contrasts of interest (motor or computation tasks) and two parallel acceleration factors ( $R=2$ and $R=4$ ) on $2\times 2\times 3\,\hbox{mm}^3$ echo planar imaging (EPI) images.
      PubDate: 2014-03-12
       
  • Absolute quantification of perfusion by dynamic susceptibility contrast
           MRI using Bookend and VASO steady-state CBV calibration: a comparison with
           pseudo-continuous ASL
    • Abstract: Objective Dynamic susceptibility contrast MRI (DSC-MRI) tends to return elevated estimates of cerebral blood flow (CBF) and cerebral blood volume (CBV). In this study, subject-specific calibration factors (CFs), based on steady-state CBV measurements, were applied to rescale the absolute level of DSC-MRI CBF. Materials and methods Twenty healthy volunteers were scanned in a test–retest approach. Independent CBV measurements for calibration were accomplished using a T1-based contrast agent steady-state method (referred to as Bookend), as well as a blood-nulling vascular space occupancy (VASO) approach. Calibrated DSC-MRI was compared with pseudo-continuous arterial spin labeling (pCASL). Results For segmented grey matter (GM) regions of interests (ROIs), pCASL-based CBF was 63 ± 11 ml/(min 100 g) (mean ± SD). Nominal CBF from non-calibrated DSC-MRI was 277 ± 61 ml/(min 100 g), while calibrations resulted in 56 ± 23 ml/(min 100 g) (Bookend) and 52 ± 16 ml/(min 100 g) (VASO). Calibration tended to eliminate the overestimation, although the repeatability was generally moderate and the correlation between calibrated DSC-MRI and pCASL was low (r < 0.25). However, using GM instead of WM ROIs for extraction of CFs resulted in improved repeatability. Conclusion Both calibration approaches provided reasonable absolute levels of GM CBF, although the calibration methods suffered from low signal-to-noise ratio, resulting in weak repeatability and difficulties in showing high degrees of correlation with pCASL measurements.
      PubDate: 2014-02-26
       
  • Delayed hepatic signal recovery on ferucarbotran-enhanced magnetic
           resonance images in a rat model with regional liver irradiation
    • Abstract: Object To determine whether superparamagnetic iron oxide (SPIO)-enhanced magnetic resonance (MR) imaging could demonstrate signal recovery delay in irradiated areas of rat livers. We also investigated the relationship between MR imaging and histological findings. Materials and methods Twelve rats received 20 μmol iron/kg of SPIO followed by X-irradiation to the right upper abdomen 4 h later. Radiation doses were 0, 50 and 70 Gy. Hepatic signals were assessed on unenhanced T 2 * -weighted images for up to 7 days using a 9.4-Tesla scanner. The livers were excised on day 7 and examined histologically. Results Normalized relative signal intensity of 70 Gy-irradiated right liver lobe (2.36 ± 0.22) and 50 Gy-irradiated right liver lobe (2.37 ± 0.46) was significantly lower than that of the non-irradiated right liver lobe (4.04 ± 0.28) on day 7, respectively (p < 0.05). Pearson product-moment correlation coefficient between relative intensity of the liver and the number of hepatic iron deposits was −0.588 (p < 0.01). Conclusion Superparamagnetic iron oxide-enhanced MR imaging could demonstrate signal recovery delay in irradiated areas of rat livers. It seems that the signal recovery delay in irradiated areas was due to SPIO-derived iron deposition. Hepatic signal recovery could be a novel diagnostic marker for delineation of irradiated areas.
      PubDate: 2014-02-26
       
  • Pilot study of Iopamidol-based quantitative pH imaging on a clinical 3T MR
           scanner
    • Abstract: Objective The objective of this study was to show the feasibility to perform Iopamidol-based pH imaging via clinical 3T magnetic resonance imaging (MRI) using chemical exchange saturation transfer (CEST) imaging with pulse train presaturation. Materials and methods The pulse train presaturation scheme of a CEST sequence was investigated for Iopamidol-based pH measurements using a 3T magnetic resonance (MR) scanner. The CEST sequence was applied to eight tubes filled with 100-mM Iopamidol solutions with pH values ranging from 5.6 to 7.0. Calibration curves for pH quantification were determined. The dependence of pH values on the concentration of Iopamidol was investigated. An in vivo measurement was performed in one patient who had undergone a previous contrast-enhanced computed tomography (CT) scan with Iopamidol. The pH values of urine measured with CEST MRI and with a pH meter were compared. Results In the measured pH range, pH imaging using CEST imaging with pulse train presaturation was possible. Dependence between the pH value and the concentration of Iopamidol was not observed. In the in vivo investigation, the pH values in the human bladder measured by the Iopamidol CEST sequence and in urine were consistent. Conclusion Our study shows the feasibility of using CEST imaging with Iopamidol for quantitative pH mapping in vitro and in vivo on a 3T MR scanner.
      PubDate: 2014-02-26
       
  • Quantitative lung ventilation using Fourier decomposition MRI; comparison
           and initial study
    • Abstract: Objective The Fourier decomposition (FD) method is a noninvasive method for assessing ventilation and perfusion-related information in the lungs, but the lack of quantifiable values is a drawback. We demonstrate a novel technique for quantification of the FD ventilation maps, compare it to two published methods, and show results from both healthy volunteers and patients diagnosed with lung cancer. Materials and methods We quantified the standard FD ventilation images by utilizing additional information, i.e., the zero-frequency component image, which is also obtained from the Fourier analysis. This image acts as a baseline for the changes recorded in the FD ventilation image and can therefore be used to calculate the ventilation. Using this technique, we compared the ventilation values from ten healthy volunteers and ten patients to two previously published methods for quantitative ventilation assessment. Results All methods showed good overall agreement (mean difference between the methods was 14–38 ml/min). The mean minute ventilation for the FD method was calculated to be 693 ml/min for a 2D slice, which is in the expected range. Conclusion The zero-frequency component image can be used as a baseline to quantify the FD ventilation maps. Our initial study showed good agreement with published methods in healthy volunteers, but less so in patients with lung cancer.
      PubDate: 2014-02-12
       
  • Two-dimensional accelerated MP-RAGE imaging with flexible linear
           reordering
    • Abstract: Object Implementation of an accelerated Magnetization Prepared RApid Gradient Echo (MP-RAGE) sequence for T1 weighted neuroimaging; exploiting modern MRI technologies to minimize scan time while preserving the image quality. Materials and methods A custom MP-RAGE sequence was implemented on a state-of-the-art 3T MR scanner equipped with a 32-channel receiver array head coil. The sequence utilized a shifted CAIPIRINHA k y –k z under-sampling pattern combined with elliptical scanning and a two-dimensional view ordering scheme to achieve high parallel imaging acceleration factors at maintained image contrast. Results It could be shown that MP-RAGE accelerated in two k-space directions outperforms single direction acceleration, which is the common practice with standard view ordering. Applying the CAIPIRINHA technique in conjunction with elliptical scanning further increased this benefit. Conclusion By combining MP-RAGE with CAIPIRINHA sampling and elliptical scanning, the scan time can be reduced from 4–5 min to 2–3 min with insignificant reduction in image quality.
      PubDate: 2014-02-08
       
  • Measurement of anesthetic uptake kinetics in the brain using        class="a-plus-plus">19F MRI and cross-correlation
           analysis after pulsed application
    • Abstract: Object We present a pilot study based on 19F-MRI to measure fast and slow wash-in and wash-out kinetics of volatile anesthetics in pig brain. Method The periodic administration of anesthetics in pulsed mode is used to enhance the sensitivity of the anesthetic concentration detection by 19F-MRI signal. Temporal correlation analysis allows mapping the kinetics time constants. Results The clear correlation response to anesthetics concentration changes was found in the brain region in comparison with fatty tissues. Conclusion The methodology may yield important pharmacological findings on regional effect of the anesthetics in brain and be a step towards human studies.
      PubDate: 2014-02-01
       
 
 
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