Multi-echo Magnetic Resonance Imaging Research Articles

MRI-based biodistribution assessment of holmium-166 poly(L-lactic acid) microspheres after radioembolisation

ObjectivesTo demonstrate the feasibility of MRI-based assessment of the intrahepatic Ho-PLLA-MS biodistribution after radioembolisation in order to estimate the absorbed radiation dose.MethodsFifteen patients were treated with holmium-166 (166Ho) poly(L-lactic acid)-loaded microspheres (Ho-PLLA-MS, mean 484 mg; range 408–593 mg) in a phase I study. Multi-echo gradient-echo MR images were acquired from which R2* maps were constructed. The amount of Ho-PLLA-MS in the liver was determined by using the relaxivity r2* of the Ho-PLLA-MS and compared with the administered amount. Quantitative single photon emission computed tomography (SPECT) was used for comparison with MRI regarding the whole liver absorbed radiation dose.ResultsR2* maps visualised the deposition of Ho-PLLA-MS with great detail. The mean total amount of Ho-PLLA-MS detected in the liver based on MRI was 431 mg (range 236–666 mg) or 89 ± 19 % of the delivered amount (correlation coefficient r = 0.7; P < 0.01). A good correlation was found between the whole liver mean absorbed radiation dose as assessed by MRI and SPECT (correlation coefficient r = 0.927; P < 0.001).ConclusionMRI-based dosimetry for holmium-166 radioembolisation is feasible. Biodistribution is visualised with great detail and quantitative measurements are possible.Key Points• Radioembolisation is increasingly used for treating unresectable primary or metastatic liver tumours. • MRI-based intrahepatic microsphere biodistribution assessment is feasible after holmium-166 radioembolisation. • MRI enables quantification of holmium-166 microspheres in liver in a short imaging time. • MRI can estimate the whole liver absorbed radiation dose following holmium-166 radioembolisation.

Hepatic Fat Quantification

The aims of this study were to assess the confounding effects of hepatic iron deposition, inflammation, and fibrosis on hepatic steatosis (HS) evaluation by magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) and to assess the accuracies of MRI and MRS for HS evaluation, using histology as the reference standard. In this institutional review board-approved prospective study, 56 patients gave informed consents and underwent chemical-shift MRI and MRS of the liver on a 1.5-T magnetic resonance scanner. To estimate MRI fat fraction (FF), 4 analysis methods were used (dual-echo, triple-echo, multiecho, and multi-interference), and MRS FF was calculated with T2 correction. Degrees of HS, iron deposition, inflammation, and fibrosis were analyzed in liver resection (n = 37) and biopsy (n = 19) specimens. The confounding effects of histology on fat quantification were assessed by multiple linear regression analysis. Using the histologic degree of HS as the reference standard, the accuracies of each method in estimating HS and diagnosing an HS of 5% or greater were determined by linear regression and receiver operating characteristic analyses. Iron deposition significantly confounded estimations of FF by the dual-echo (P < 0.001) and triple-echo (P = 0.033) methods, whereas no histologic feature confounded the multiecho and multi-interference methods or MRS. The MRS (r = 0.95) showed the strongest correlation with histologic degree of HS, followed by the multiecho (r = 0.92), multi-interference (r = 0.91), triple-echo (r = 0.90), and dual-echo (r = 0.85) methods. For diagnosing HS, the areas under the curve tended to be higher for MRS (0.96) and the multiecho (0.95), multi-interference (0.95), and triple-echo (0.95) methods than for the dual-echo method (0.88) (P ≥ 0.13). The multiecho and multi-interference MRI methods and MRS can accurately quantify hepatic fat, with coexisting histologic abnormalities having no confounding effects.

Multicontrast multiecho FLASH MRI for targeting the subthalamic nucleus

The subthalamic nucleus (STN) is one of the most common stimulation targets for treating Parkinson's disease using deep brain stimulation (DBS). This procedure requires precise placement of the stimulating electrode. Common practice of DBS implantation utilizes microelectrode recording to locate the sites with the correct electrical response after an initial location estimate based on a universal human brain atlas that is linearly scaled to the patient's anatomy as seen on the preoperative images. However, this often results in prolonged surgical time and possible surgical complications since the small-sized STN is difficult to visualize on conventional magnetic resonance (MR) images and its intersubject variability is not sufficiently considered in the atlas customization. This paper proposes a multicontrast, multiecho MR imaging (MRI) method that directly delineates the STN and other basal ganglia structures through five co-registered image contrasts (T1-weighted navigation image, R2* map, susceptibility-weighted imaging (phase, magnitude and fusion image)) obtained within a clinically acceptable time. The image protocol was optimized through both simulation and in vivo experiments to obtain the best image quality. Taking advantage of the multiple echoes and high readout bandwidths, no interimage registration is required since all images are produced in one acquisition, and image distortion and chemical shift are reduced. This MRI protocol is expected to mitigate some of the shortcomings of the state-of-the-art DBS implantation methods.

High-quality multiple T2(*) contrast MR images from low-quality multi-echo images using temporal-domain denoising methods

The aim of this study was to develop an effective postprocessing method to increase the signal-to-noise ratio in successive multi-echo magnetic resonance (MR) images acquired at multiple time points and generate high-quality multiple T(2)(*) contrast images from low-quality multi-echo images. Successive multi-echo MR images were acquired at multiple time points using a multigradient-recalled echo sequence at 3T and rearranged so that each pixel in the images had its own decay signal in the temporal-domain. Two different denonising approaches were implemented in the temporal-domain: (1) In a filtering approach, conventional low-pass filter, median filter, and anisotropic diffusion filter were applied to the decay signals to reduce random noise; (2) In a model-based approach, a non-negative least squares algorithm was applied for fitting to MR relaxation model for decay signals. Numerical simulations and in vivo experiments were conducted. The denoised images were compared to each other by visual inspection and analysis of mean square error (MSE) and contrast-to-noise ratio (CNR) on several regions of interest. Our proposed method suppressed noise in each multi-echo images without introducing spatial artifacts. This was a natural consequence of the proposed denoising process, which was performed in the temporal-domain and did not use any cross-pixel operation. MSEs decreased by a factor of 5.4-7.9 and CNRs increased by a factor of 5 in simulation studies. The results were consistent with the in vivo findings. Random noise in the images was effectively reduced and high-quality multiple T(2)(*) contrast images were obtained. This study demonstrated that denoising methods in the temporal-domain can effectively suppress noise in the spatial domain, and increase signal-to-noise ratio (SNR) for each image of different T(2)(*) weights at multiple time points, resulting in multiple high-quality T(2)(*) contrast images.

Joint reconstruction of multiecho MR images using correlated sparsity

This works addresses the problem of reconstructing multiple T1- or T2-weighted images of the same anatomical cross section from partially sampled K-space data. Previous studies in reconstructing magnetic resonance (MR) images from partial samples of the K-space used compressed sensing (CS) techniques to exploit the spatial correlation of the images (leading to sparsity in wavelet domain). Such techniques can be employed to reconstruct the individual T1- or T2-weighted images. However, in the current context, the different images are not really independent; they are images of the same cross section and, hence, are highly correlated. We exploit the correlation between the images, along with the spatial correlation within the images to achieve better reconstruction results than exploiting spatial correlation only. For individual MR images, CS-based techniques lead to a sparsity-promoting optimization problem in the wavelet domain. In this article, we show that the same framework can be extended to incorporate correlation between images leading to group/row sparsity-promoting optimization. Algorithms for solving such optimization problems have already been developed in the CS literature. We show that significant improvement in reconstruction accuracy can be achieved by considering the correlation between different T1- and T2-weighted images. If the reconstruction accuracy is considered to be constant, our proposed group sparse formulation can yield the same result with 33% less K-space samples compared with simple sparsity-promoting reconstruction. Moreover, the reconstruction time by our proposed method is about two to four times less than the previous method.

A novel noise removal using homomorphic normalization for multi-echo knee MRI

This paper presents a novel approach for removing noise from multi-echo knee magnetic resonance images using global intensity normalization and the averaging operation along the echo-time. Firstly, the global mean and standard deviation at the zero echo-time are estimated by applying the mono-exponential spin echo model to the means and standard deviations of multi-echo images. Secondly, the signal and noise levels at multi-echo images are normalized to the estimated mean and standard deviation at the zero echo-time. Then, the normalized multi-echo images are averaged along the echo-time into a noise-removed zero echo-time image. Finally, the multi-echo MR images are reconstructed from the noise-removed zero echo-time image by the inverse normalization. The experiments demonstrate that the proposed method effectively removes not only the noises of each multi-echo image but also noises of the Quantitative T2 image.

Noninvasive MRI-SERS Imaging in Living Mice Using an Innately Bimodal Nanomaterial

We report a novel nanomaterial (AuMN-DTTC) that can be used as a bimodal contrast agent for in vivo magnetic resonance imaging (MRI) and Raman spectroscopy. The probe consists of MRI-active superparamagnetic iron oxide nanoparticles, stably complexed with gold nanostructures. The gold component serves as a substrate for a Raman active dye molecule to generate a surface-enhanced Raman scattering (SERS) effect. The synthesized probe produces T2 weighted contrast and can be used as a SERS active material both in silico (in aqueous solution) and in vivo. A quantitative assessment of T2 relaxation times was obtained using multiecho MRI analysis. The T2 relaxation times of AuMN-DTTC and MN (dextran-coated iron oxide nanoparticles) were 29.23 + 1.45 and 31.58 + 1.7 ms, respectively. The SERS signature of AuMN-DTTC revealed peaks at 508, 629, 782, 844, 1080, 1108, 1135, and 1242 cm(-1). Intramuscular administration of the probe resulted in a decrease of the T2 relaxation time of muscle from 33.4 + 2.5 to 20.3 + 2.2 ms. SERS peaks were observed at 508, 629, 782, 844, 1080, 1108, 1135, and 1242 cm(-1), consistent with the in silico results. Our studies illustrate for the first time the design and in vivo application of a contrast agent, whose component modalities include MRI and SERS. The value of this agent lies in its innately bimodal nature and its application in vivo for molecular imaging applications.

Distribution of abdominal adipose tissue as a predictor of hepatic steatosis assessed by MRI

To evaluate the relationship between the distribution of visceral and subcutaneous adipose tissue and hepatic steatosis assessed using magnetic resonance imaging (MRI). One T1-weighted, in-/out-of-phase, single-section sequence at the L3/L4 level and one multi-echo gradient MRI (MGRE) sequence were performed on 65 patients [19 females and 46 males; age 57+/-9.5 years; body mass index (BMI) 31+/-5.1kg/m(2)]. Visceral adipose tissue (VAT), subcutaneous adipose tissue (SAT) surfaces, and hepatic steatosis were automatically calculated using in-house software. Weight, height, BMI, waist circumference, hip circumference, and waist:hip ratio were recorded. The probability of having a steatosis greater than 10% on MRI was evaluated by receiver operating characteristic (ROC) curves. The anthropometric parameter best correlated to hepatic steatosis was the waist-to-hip ratio (r=0.301). VAT and proportion of VAT were correlated to liver fat content (r=0.307 and r=0.249, respectively). No significant correlations were found for BMI, hip circumference, and SAT. The area under the receiver operating characteristics (AUROCs) for the relationship between liver steatosis and BMI, waist circumference, waist:hip ratio, VAT surface, and proportion of VAT, were respectively 0.52, 0.63, 0.71, 0.73 and 0.75. Adipose tissue distribution is more relevant than total fat mass when assessing the possibility of liver steatosis in overweight patients.

A new approach combining different MRI methods to provide detailed view on swelling dynamics of xanthan tablets influencing drug release at different pH and ionic strength

The key element in drug release from hydrophilic matrix tablets is the gel layer that regulates the penetration of water and controls drug dissolution and diffusion. We have selected magnetic resonance imaging (MRI) as the method of choice for visualizing the dynamic processes occurring during the swelling of xanthan tablets in a variety of media. The aims were (i) to develop a new method using MRI for accurate determination of penetration, swelling and erosion fronts, (ii) to investigate the effects of pH and ionic strength on swelling, and (iii) to study the influence of structural changes in xanthan gel on drug release. Two dimensional (2D) MRI and one dimensional single point imaging (SPI) of swollen xanthan tablets were recorded, together with T 2 mapping. The border between dry and hydrated glassy xanthan—the penetration front—was determined from 1D SPI signal intensity profiles. The erosion front was obtained from signal intensity profiles of 2D MR images. The swelling front, where xanthan is transformed from a glassy to a rubbery state (gel formation), was determined from T 2 profiles. Further, the new combination of MRI methods for swelling front determination enables to explain the appearance of the unusual “bright front” observed on 2D MR images in tablets swollen in HCl pH 1.2 media, which represents the position of swelling front. All six media studied, differing in pH and ionic strength, penetrate through the whole tablet in 4 h ± 0.3 h, but formation of the gel layer is significantly delayed. Unexpectedly, the position of the swelling front was the same, independently of the different xanthan gel structures formed under different conditions of pH and ionic strength. The position of the erosion front, on the other hand, is strongly dependent on pH and ionic strength, as reflected in different thicknesses of the gel layers. The latter are seen to be the consequence of the different hydrodynamic radii of the xanthan molecules, which affect the drug release kinetics. The slowest release of pentoxifylline was observed in water where the thickest gel was formed, whereas the fastest release was observed in HCl pH 1.2, in which the gel layer was thinnest. Moreover, experiments simulating physiological conditions showed that changes of pH and ionic strength influence the xanthan gel structure relatively quickly, and consequently the drug release kinetics. It is therefore concluded that drug release is greatly influenced by changes in the xanthan molecular conformation, as reflected in changed thickness of the gel layer. A new method utilizing combination of SPI, multi-echo MRI and T 2 mapping eliminates the limitations of standard methods used in previous studies for determining moving fronts and improves current understanding of the dynamic processes involved in polymer swelling.

Gadolinium toxicity: epidermis thickness measurement by magnetic resonance imaging at 500 MHz

Regional epidermal thickening and hair follicle width measurement by delayed gadolinium contrast magnetic resonance imaging (MRI) may assess the contrast agent gadolinium toxicity on mice skin. Delayed contrast in vivo MRI was performed in mice. Six mice skin samples were removed and exposed to a gadolinium contrast agent at different times after 2, 4, 6 and 8 h. The relaxation constants of each skin structure were measured. The thickness of the epidermis and hair follicle on follow-up ex vivo delayed-contrast MRI served as an index of gadolinium toxicity on the skin. In vivo MRI by fast low-angle shot imaging technique showed distinct skin layers. High-resolution gradient echo T1-weighted and multislice multiecho proton density-weighted MRI intensities in the epidermis and hair follicle showed a positive correlation with delayed gadolinium-enhanced MRI hyperintensities (Pearson's correlation coefficient r(2)=0.81, P<0.0001) in the excised mice skin tissues. Delayed contrast-enhanced mice skin MRI after 2-4 h showed epidermis swelling and hair follicle regions with a size measurement accuracy of 65%, a sensitivity of 95%, a specificity of 25%, a positive predictive value of 65% and a negative predictive value of 65%. Areas under the receiver operating characteristic curves by MRI were 0.92-0.94 for hair and epidermis as good discriminators. MRI visualized distinct relaxation constants of the epidermis, sebaceous gland, skin papillary and reticular dermis layers and hair follicle. Gadolinium contrast-enhanced MRI may visualize the thickening of the epidermis wall and hair follicle as an index of viable mice skin. Gadolinium enhanced the MRI visibility of skin structures. Gadolinium treatment showed skin toxicity as epidermis thickening the first time due to the undesirable use of high concentrations of gadolinium in microimaging.

Long-Term Chelation Therapy with Deferasirox

We report the long-term effects of deferasirox 10-30 mg/kg/day on cardiac iron overload in a case series of five patients with transfusion-dependent beta-thalassaemia major who underwent up to 5 years of chelation therapy. Iron overload was monitored by multislice multi-echo T2* magnetic resonance imaging (MRI). Overall, T2* MRI showed a decrease from baseline in cardiac iron levels in all patients during treatment with deferasirox (baseline T2* levels 13-24 ms; final T2* levels 21-41 ms). The improvement in T2* values correlated with maintenance of left ventricular ejection fraction (LVEF) [baseline LVEF values 56-61%; final LVEF values 57-70%]. Deferasirox chelation treatment regimen was well tolerated and adherence to the regimen was good. In conclusion, this case series suggests that deferasirox may decrease cardiac iron overload and maintain stable LVEF over the long term. Moreover, it emphasizes the importance of T2* multislice multi-echo MRI in the monitoring of cardiac iron overload.

Synthetic–Echo Time Postprocessing Technique for Generating Images with Variable T2-weighted Contrast: Diagnosis of Meniscal and Cartilage Abnormalities of the Knee

To assess the feasibility and accuracy of a synthetic-echo time (TE) magnetic resonance (MR) postprocessing technique for the diagnostic evaluation of abnormalities of menisci and articular cartilage in the knee. This study was approved by the institutional review board. Twenty-four patients (three women, 21 men; mean age, 44.8 years) gave informed written consent to prospectively undergo evaluation of their knees (10 left and 14 right knees) with standard sagittal intermediate-weighted (repetition time msec/TE msec, 2200/17) and fat-saturated T2-weighted (3600/88) fast spin-echo sequences. In addition, sagittal multiecho fast gradient-echo sequences were performed for the generation of synthetic-TE images with variable T2- or T2(*)-weighted contrast by using a newly developed synthetic-TE analysis tool that was incorporated directly into the picture archiving and communication system. Sensitivity, specificity, and accuracy values for detection of lesions in menisci and articular cartilage were calculated by using findings at surgery as reference standard. The standard intermediate-weighted and fat-suppressed T2-weighted MR sequences had overall sensitivity, specificity, and accuracy values of 100% and 100%, 88% and 93%, and 95% and 95% for the diagnosis of tears of medial and lateral menisci, respectively, as well as sensitivity, specificity, and accuracy values of 82%, 97%, and 95%, respectively, for articular cartilage defects. Corresponding sensitivity, specificity, and accuracy values for multiecho MR imaging with synthetic-TE MR image generation were 92% and 100%, 88% and 87%, and 90% and 90% for the diagnosis of tears of medial and lateral menisci, respectively, as well as sensitivity, specificity, and accuracy values of 70%, 99%, and 95%, respectively, for articular cartilage defects. For the evaluation of menisci and articular cartilage, images generated with the synthetic-TE technique are a potentially viable alternative to standard T2-weighted images obtained at different TEs. Furthermore, the synthetic-TE approach allowed assessment of abnormalities of menisci and articular cartilage with high sensitivity and specificity.

Effects of Magnetic Resonance Image Interpolation on the Results of Texture-Based Pattern Classification

To (1) determine whether magnetic resonance (MR) image interpolation at the pixel or k-space level can improve the results of texture-based pattern classification, and (2) compare the effects of image interpolation on texture features of different categories, with regard to their ability to distinguish between different patterns. We obtained T2-weighted, multislice multiecho MR images of 2 sets of each 3 polystyrene spheres and agar gel (PSAG) phantoms with different nodular patterns (sphere diameter: PSAG-1, 0.8-1.25 mm; PSAG-2, 1.25-2.0 mm; PSAG-3, 2.0-3.15 mm), using a 3.0 Tesla scanner equipped with a dedicated microimaging gradient insert. Image datasets, which consisted of 20 consecutive axial slices each, were obtained with a constant field of view (30 x 30 mm(2)), but with variations of matrix size (MTX): 16 x 16; 32 x 32; 64 x 64; 128 x 128; and 256 x 256. Original images were interpolated to higher matrix sizes (up to 256 x 256) by means of linear and cubic B-spline (pixel level) as well as zero-fill (k-space level) interpolation. For both original and interpolated image datasets, texture features derived from the co-occurrence (COC) and run-length matrix (RUN), absolute gradient (GRA), autoregressive model, and wavelet transform (WAV) were calculated independently. Based on the 3 best texture features of each category, as determined by calculation of Fisher coefficients using images from the first set of PSAG phantoms (training dataset), k-means clustering was performed to separate PSAG-1, PSAG-2, and PSAG-3 images belonging to the second set of phantoms (test dataset). This was done independently for all original and interpolated image datasets. Rates of misclassified data vectors were used as primary outcome measures. For images based on a very low original resolution (MTX = 16 x 16), misclassification rates remained high, despite the use of interpolation. For higher resolution images (MTX = 32 x 32 and 64 x 64), interpolation enhanced the ability of texture features, in all categories except WAV, to discriminate between the 3 phantoms. This positive effect was particularly pronounced for COC and RUN features, and to a lesser degree, also GRA features. No consistent improvements, and even some negative effects, were observed for WAV features, after interpolation. Although there was no clear superiority of any single interpolation techniques at very low resolution (MTX = 16 x 16), zero-fill interpolation outperformed the two pixel interpolation techniques, for images based on higher original resolutions (MTX = 32 x 32 and 64 x 64). We observed the most considerable improvements after interpolation by a factor of 2 or 4. MR image interpolation has the potential to improve the results of pattern classification, based on COC, RUN, and GRA features. Unless spatial resolution is very poor, zero-filling is the interpolation technique of choice, with a recommended maximum interpolation factor of 4.

Quantitative MR imaging of individual muscle involvement in facioscapulohumeral muscular dystrophy

The purpose of this study was to implement a quantitative MR imaging method for the determination of muscular and fat content in individual skeletal muscles of patients with facioscapulohumeral muscular dystrophy (FSHD). Turbo Inversion Recovery Magnitude (TIRM) and multiecho MR images were acquired from seven FSHD patients and healthy volunteers. Signal decay in the multiecho MR images was fitted to a biexponential function with fixed relaxation rates for muscle and fat tissue and used to calculate the degree of fatty infiltration in eight muscles in the lower leg. Considerable differences in fatty infiltration between different muscles were observed in FSHD patients, suggesting that this could be used as a biomarker for disease progression. TIRM imaging indicated an inflammatory component of the disease previously only observed in muscle biopsies. Typically, muscle involvement was non-uniform even within one muscle, indicating that MRI can be used as a valuable tool to study pathophysiology and therapy evaluation in FSHD.

Nonalcoholic Fatty Liver Disease: Diagnostic and Fat-Grading Accuracy of Low-Flip-Angle Multiecho Gradient-Recalled-Echo MR Imaging at 1.5 T

To assess the accuracy of four fat quantification methods at low-flip-angle multiecho gradient-recalled-echo (GRE) magnetic resonance (MR) imaging in nonalcoholic fatty liver disease (NAFLD) by using MR spectroscopy as the reference standard. In this institutional review board-approved, HIPAA-compliant prospective study, 110 subjects (29 with biopsy-confirmed NAFLD, 50 overweight and at risk for NAFLD, and 31 healthy volunteers) (mean age, 32.6 years +/- 15.6 [standard deviation]; range, 8-66 years) gave informed consent and underwent MR spectroscopy and GRE MR imaging of the liver. Spectroscopy involved a long repetition time (to suppress T1 effects) and multiple echo times (to estimate T2 effects); the reference fat fraction (FF) was calculated from T2-corrected fat and water spectral peak areas. Imaging involved a low flip angle (to suppress T1 effects) and multiple echo times (to estimate T2* effects); imaging FF was calculated by using four analysis methods of progressive complexity: dual echo, triple echo, multiecho, and multiinterference. All methods except dual echo corrected for T2* effects. The multiinterference method corrected for multiple spectral interference effects of fat. For each method, the accuracy for diagnosis of fatty liver, as defined with a spectroscopic threshold, was assessed by estimating sensitivity and specificity; fat-grading accuracy was assessed by comparing imaging and spectroscopic FF values by using linear regression. Dual-echo, triple-echo, multiecho, and multiinterference methods had a sensitivity of 0.817, 0.967, 0.950, and 0.983 and a specificity of 1.000, 0.880, 1.000, and 0.880, respectively. On the basis of regression slope and intercept, the multiinterference (slope, 0.98; intercept, 0.91%) method had high fat-grading accuracy without statistically significant error (P > .05). Dual-echo (slope, 0.98; intercept, -2.90%), triple-echo (slope, 0.94; intercept, 1.42%), and multiecho (slope, 0.85; intercept, -0.15%) methods had statistically significant error (P < .05). Relaxation- and interference-corrected fat quantification at low-flip-angle multiecho GRE MR imaging provides high diagnostic and fat-grading accuracy in NAFLD.

Multiecho MR Imaging and Proton MR Spectroscopy for Liver Fat Quantification

HomeRadiologyVol. 249, No. 3 PreviousNext CommunicationsLetters to the EditorMultiecho MR Imaging and Proton MR Spectroscopy for Liver Fat QuantificationBoris Guiu*,†, Romaric Loffroy*, Jean-Pierre Cercueil*, Denis Krause*Boris Guiu*,†, Romaric Loffroy*, Jean-Pierre Cercueil*, Denis Krause*Author Affiliations*Departments of Radiology, Le Bocage University Hospital, Bd Maréchal de Lattre de Tassigny, 21000 Dijon, France e-mail: [email protected]†Clinical Research, Le Bocage University Hospital, Bd Maréchal de Lattre de Tassigny, 21000 Dijon, FranceBoris Guiu*,†Romaric Loffroy*Jean-Pierre Cercueil*Denis Krause*Published Online:Dec 1 2008https://doi.org/10.1148/radiol.2493081034MoreSectionsFull textPDF ToolsImage ViewerAdd to favoritesCiteTrack CitationsPermissionsReprints ShareShare onFacebookTwitterLinked In References1 O'Regan DP, Callaghan MF, Wylezinska-Arridge M, et al. Liver fat content and T2*: simultaneous measurement by using breath-hold multiecho MR imaging at 3.0 T—feasibility. Radiology 2008; 247(2): 550–557. Link, Google Scholar2 Alustiza JM, Castiella A. Liver fat and iron at in-phase and opposed-phase MR imaging. Radiology 2008; 246(2):641. Google Scholar3 Westphalen AC, Qayyum A, Yeh BM, et al. Liver fat: effect of hepatic iron deposition on evaluation with opposed-phase MR imaging. Radiology 2007; 242(2): 450–455. Link, Google Scholar4 Johnson NA, Walton DW, Sachinwalla T, et al. Noninvasive assessment of hepatic lipid composition: advancing understanding and management of fatty liver disorders. Hepatology 2008; 47(5): 1513–1523. Crossref, Medline, Google Scholar5 Jansen JF, Backes WH, Nicolay K, Kooi ME. 1H MR spectroscopy of the brain: absolute quantification of metabolites. Radiology 2006; 240(2): 318–332. Link, Google Scholar6 de Bazelaire CM, Duhamel GD, Rofsky NM, Alsop DC. MR imaging relaxation times of abdominal and pelvic tissues measured in vivo at 3.0 T: preliminary results. Radiology 2004; 230(3): 652–659. Link, Google ScholarArticle HistoryPublished in print: 2008 FiguresReferencesRelatedDetailsCited ByEuropean Radiology, Vol. 30, No. 9Journal of Urology, Vol. 200, No. 4The British Journal of Radiology, Vol. 89, No. 1062European Radiology, Vol. 25, No. 6American Journal of Roentgenology, Vol. 205, No. 6American Journal of Roentgenology, Vol. 202, No. 4Intravoxel Incoherent Motion Diffusion-weighted Imaging in Nonalcoholic Fatty Liver Disease: A 3.0-T MR StudyBoris Guiu, , Jean-Michel Petit, , Violaine Capitan, , Serge Aho, , David Masson, , Pierre-Henri Lefevre, , Sylvain Favelier, , Romaric Loffroy, , Bruno Vergès, , Patrick Hillon, , Denis Krausé, , and Jean-Pierre Cercueil, 1 October 2012 | Radiology, Vol. 265, No. 1European Radiology, Vol. 22, No. 5Journal of Magnetic Resonance Imaging, Vol. 33, No. 1Journal of Magnetic Resonance Imaging, Vol. 34, No. 4IEEE Transactions on Medical Imaging, Vol. 30, No. 1American Journal of Roentgenology, Vol. 194, No. 3European Radiology, Vol. 19, No. 7European Radiology, Vol. 19, No. 11Journal de Radiologie, Vol. 90, No. 11Recommended Articles Proton MR Spectroscopy Measurements of White and Brown Adipose Tissue in Healthy Humans: Relaxation Parameters and Unsaturated Fatty AcidsRadiology2021Volume: 299Issue: 2pp. 396-406Quantitative MRI of Diffuse Liver Disease: Current Applications and Future DirectionsRadiology2018Volume: 290Issue: 1pp. 23-30Quantification of Liver Fat Content with CT and MRI: State of the ArtRadiology2021Volume: 301Issue: 2pp. 250-262MR Fingerprinting for Liver Tissue Characterization: A Histopathologic Correlation StudyRadiology2022Volume: 0Issue: 0Water-Fat Separation in MR Fingerprinting for Quantitative Monitoring of the Skeletal Muscle in Neuromuscular DisordersRadiology2021Volume: 300Issue: 3pp. 652-660See More RSNA Education Exhibits MRI Quantification of Hepatic Fat, Iron, and Fibrosis: A Practical GuideDigital Posters2018Friend or Foe: How to Suppress and Measure fat in Abdominal MRI?Digital Posters2020Conventional and Advanced MRI for Sarcopenia Assessment  Digital Posters2018 RSNA Case Collection Posterior fossa dermoid cyst without a dermal sinusRSNA Case Collection2020Ruptured Spinal Dermoid RSNA Case Collection2021CraniopharyngiomaRSNA Case Collection2020 Vol. 249, No. 3 Metrics Downloaded 324 times Altmetric Score PDF download

Liver Fat Content and T2*: Simultaneous Measurement by Using Breath-hold Multiecho MR Imaging at 3.0 T—Feasibility

Research ethics committee approval was obtained for this study, and written informed consent was obtained from all participants. The purpose was to prospectively evaluate the feasibility of breath-hold multiecho in- and out-of-phase magnetic resonance (MR) imaging for simultaneous lipid quantification and T2* measurement. A spoiled gradient-echo sequence with seven echo times alternately in phase and out of phase was used at 3.0 T. Imaging was performed in a lipid phantom, in five healthy volunteers (all men; mean age, 37 years), and in five obese individuals with hyperlipidemia or diabetes (four men, one woman; mean age, 53 years). A biexponential curve-fitting model was used to derive the relative signal contributions from fat and water, and these results were compared with results of liver proton MR spectroscopy, the reference standard. There was a significant correlation between multiecho and spectroscopic measurements of hepatic lipid concentration (r(2) = 0.99, P < .001). In vivo, the T2* of water was consistently longer than that of fat and reliably enabled the signal components to be correctly assigned. In the lipid phantom, the multiecho method could be used to determine the fat-to-water ratio and the T2* values of fat and water throughout the entire range of fat concentrations. Multiecho imaging shows promise as a method of simultaneous fat and T2* quantification.

High‐field magnetic resonance imaging of the response of human prostate cancer to Pc 4‐based photodynamic therapy in an animal model

High-field magnetic resonance imaging (MRI) is an emerging technique that provides a powerful, non-invasive tool for in vivo studies of cancer therapy in animal models. Photodynamic therapy (PDT) is a relatively new treatment modality for prostate cancer, the second leading cause of cancer mortality in American males. The goal of this study was to evaluate the response of human prostate tumor cells growing as xenografts in athymic nude mice to Pc 4-sensitized PDT. PC-3, a cell line derived from a human prostate malignant tumor, was injected intradermally on the back flanks of athymic nude mice. Two tumors were initiated on each mouse. One was treated and the other served as the control. A second-generation photosensitizing drug Pc 4 (0.6 mg/kg body weight) was delivered to each animal by tail vein injection 48 hours before laser illumination (672 nm, 100 mW/cm(2), 150 J/cm(2)). A dedicated high-field (9.4 T) small-animal MR scanner was used for image acquisitions. A multi-slice multi-echo (MSME) technique, permitting noninvasive in vivo assessment of potential therapeutic effects, was used to measure the T2 values and tumor volumes. Animals were scanned immediately before and after PDT and 24 hours after PDT. T2 values were computed and analyzed for the tumor regions. For the treated tumors, the T2 values significantly increased (P<0.002) 24 hours after PDT (68.2+/- 8.5 milliseconds), compared to the pre-PDT values (55.8+/-6.6 milliseconds). For the control tumors, there was no significant difference (P = 0.53) between the pre-PDT (52.5+/-6.1 milliseconds) and 24-hour post-PDT (54.3+/-6.4 milliseconds) values. Histologic analysis showed that PDT-treated tumors demonstrated necrosis and inflammation that was not seen in the control. Changes in tumor T2 values measured by multi-slice multi-echo MR imaging provide an assay that could be useful for clinical monitoring of photodynamic therapy of prostate tumors.

High resolution MR based polymer dosimetry versus film densitometry: a systematic study based on the modulation transfer function approach

Precise methods of modern radiation therapy such as intensity modulated radiotherapy (IMRT), brachytherapy (BT) and high LET irradiation allow for high dose localization in volumes of a few mm3. However, most dosimetry methods—ionization chambers, TLD arrangements or silicon detectors, for example—are not capable of detecting sub-mm dose variations or do not allow for simple dose imaging. Magnetic resonance based polymer dosimetry (MRPD) appears to be well suited to three-dimensional high resolution relative dosimetry but the spatial resolution based on a systematic modulation transfer function (MTF) approach has not yet been investigated. We offer a theoretical construct for addressing the spatial resolution in different dose imaging systems, i.e. the dose modulation transfer function (DMTF) approach, an experimental realization of this concept with a phantom and quantitative comparisons between two dosimetric systems: polymer gel and film dosimetry. Polymer gel samples were irradiated by Co-60 photons through an absorber grid which is characterized by periodic structures of different spatial period (a), the smallest one at width of a/2 = 280 µm. The modulation in dose under the grid is visualized via calibrated, high resolution, parameter-selective (T2) and dose images based on multi-echo MR imaging. The DMTF is obtained from the modulation depth of the spin–spin relaxation time (T2) after calibration. Voxel sizes below 0.04 mm3 could be achieved, which are significantly smaller than those reported in MR based dose imaging on polymer gels elsewhere, using a powerful gradient system and a highly sensitive small birdcage resonator on a whole-body 3T MR scanner. Dose modulations at 22% of maximum dose amplitude could be observed at about 2 line pairs per mm. The polymer DMTF results are compared to those of a typical clinical film-scanner system. This study demonstrates that MR based gel dosimetry at 200 µm pixel resolution might even be superior, with reference to relative spatial resolution, to the results of a standard film-scanner system offering a nominal scan resolution of 200 µm.

Evidential segmentation scheme of multi-echo MR images for the detection of brain tumors using neighborhood information

In this paper we propose and study an evidential segmentation scheme of multi-echo MR images for the detection of brain tumors. We show that the modeling by means of evidence theory is well suited to the processing of redundant and complementary data as the MR images. Moreover neighborhood relationship between voxels is taken into account via Dempster's combination rule. We show that using this information improves the classification results previously obtained and leads to a real region-based segmentation. Moreover, the combination of spatial information allows to compute a measure of conflict, which reflects the spatial organization of the data: the conflict is higher at the boundaries between different structures. Thus, it provides a new source of evidence that the specialist can aggregate with the segmentation results to soften its own decision.