Transverse relaxometry with reduced echo train lengths via stimulated echo compensation

Transverse relaxation (T₂) mapping has many applications, including imaging of iron accumulation in grey matter. Using the typical multiecho spin‐echo sequence with long echo trains, stimulated echo compensation can enable T₂ fitting under conditions of variable radio frequency homogeneity arising from slice profile and in‐plane radio frequency variation. Substantial reduction in the number of refocusing pulses could enable use at high magnetic fields where specific absorption rate is a major limitation, and enable multislice use with reduced incidental magnetization transfer at all field strengths. We examine the effect of reduced echo train lengths and multislice imaging on T₂ fitting using stimulated echo compensation applied to iron‐rich subcortical grey matter in human brain at 4.7 T. Our findings indicate that reducing from 20 echoes to as few as four echoes can maintain consistent T₂ values when using stimulated echo compensation in grey and white matter, but not for cerebrospinal fluid. All territories produce marginal results when using standard exponential fitting. Savings from reduced echoes can be used to substantially increase slice coverage. In multislice mode, the resulting incidental magnetization transfer decreased brain signal but had minimal effect on measured T₂ values. Magn Reson Med 70:1340–1346, 2013. © 2013 Wiley Periodicals, Inc.     

An MRI method for measuring T2 in the presence of static and RF magnetic field Inhomogeneities

A magnetic resonance imaging method for measuring the T₂ relaxation time constant is proposed. It is based on the assumption that, under very general conditions, the MR signal near a spin echo has a special symmetry arising from the refocusing nature of the 180° RF pulse. A gradient echo sampling of the spin echo (GESSE) sequence is implemented to evaluate T₂ by collecting multiple gradient echoes before and after the spin echo. This approach is a modification of the GESFIDE sequence proposed by Ma and Wehrli. However, our approach compares images that are not separated by any RF pulses and, as a result, is insensitive to slice profile imperfections. In addition, the calculated T₂ value does not rely on any special assumptions about the MRI signal behavior in the presence of an inhomogeneous static magnetic field and, hence, is insensitive to the presence of static magnetic field inhomogeneities.     

Localized proton spectroscopy of focal brain pathology in humans: Significant effects of edema on spin–spin relaxation time

Localized proton nuclear magnetic resonance (NMR) spectroscopy of human brain in two common focal pathologies producing brain edema (peritumor edema and acute edema–tous ischemic stroke) was performed utilizing point resolved spectroscopy (PRESS). The spectra obtained from the pathological tissues were characterized by a reduced N-acetyl-as–partate (NAA) to total creatine (Cr) ratio (NAA/Cr) and high level of lactate. While the spin lattice relaxation time (T₁) of the main metabolite resonances, namely, those of NAA, Cr, and choline containing compounds (Cho), showed values similar to those of normal brain, the spin-spin relaxation time (T₂) of these metabolites exhibited a dramatic shortening in pathological tissues. Serial postoperative measurements of T₂ in two patients with peritumor edema showed a gradual recovery of the T₂ shortening corresponding to improvement of the edema. The majority of localized spectroscopy studies in humans is performed using a sequence which utilizes spin echo signals with a fixed single echo time. Hence, the signal intensities of the metabolite resonances obtained are inherently T₂ dependent. The current study underscores that cautious interpretation of clinical data with respect to metabolite quantification is warranted.     

Diffusional anisotropy of T2 components in bovine optic nerve

A diffusion-CPMG hybrid experiment was used to analyze the diffusion characteristics of different T₂ relaxation components in bovine optic nerve. Data were collected using a pulsed field gradient (PFG) multi spin echo ( MSE ) CPMG sequence for parallel and perpendicular axon orientation and four diffusion times. The apparent diffusion coefficient (ADC) was evaluated for two observed T₂ components as a function of axonal orientation and diffusion time Δ. The short T₂ component exhibited minor diffusional anisotropy and larger ADC, whereas the long T₂ component showed significant anisotropy effects. This is consistent with the hypothesis that the short T₂ component is associated with water within the myelin sheath, which is less restricted than axonal water that is limited by cell membrane permeability.     

Measurement of transverse relaxation times of J‐coupled metabolites in the human visual cortex at 4 T

Accurate quantification of ¹H NMR spectra often requires knowledge of the relaxation times to correct for signal losses due to relaxation and saturation. In human brain, T₂ values for singlets such as N‐acetylaspartate, creatine, and choline have been reported, but few T₂ values are available for J‐coupled spin systems. The purpose of this study was to measure the T₂ relaxation times of J‐coupled metabolites in the human occipital lobe using the LASER sequence. Spectra were acquired at multiple echo times and were analyzed with an LCModel using basis sets simulated at each echo time. Separate basis spectra were used for resonances of protons belonging to the same molecule but having very different T₂ values (e.g., two separate basis spectra were used for the singlet and multiplet signal in N‐acetylaspartate). The T₂ values for the N‐acetylaspartate multiplet (149 ± 12 ms), glutamate (125 ± 10 ms), myo‐inositol (139 ± 20 ms), and taurine (196 ± 28 ms) were successfully measured in the human visual cortex at 4 T. These measured T₂ relaxation times have enabled the accurate and absolute quantification of cerebral metabolites at longer echo times. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

SWIFT‐CEST: A new MRI method to overcome T2 shortening caused by PARACEST contrast agents

The exchange of water molecules between the inner sphere of a paramagnetic chemical exchange saturation transfer (PARACEST) contrast agent and bulk water can shorten the bulk water T₂ through the T₂‐exchange (T_2ex) mechanism. The line‐broadening T_2ex effect is proportional to the agent concentration, the chemical shift of the exchanging water molecule, and is highly dependent on the water molecule exchange rate. A significant T_2ex contribution to the bulk water linewidth can make the regions of agent uptake appear dark when imaging with conventional sequences like gradient‐echo and fast spin‐echo. The minimum echo times for these sequences (1–10 ms) are not fast enough to capture signal from the regions of shortened T₂. This makes “Off” (saturation at ?Δω) minus “On” (saturation at +Δω) imaging of PARACEST agents difficult, because the regions of uptake are dark in both images. It is shown here that the loss of bulk water signal due to T_2ex can be reclaimed using the ultrashort echo times (<10 μs) achieved with the sweep imaging with Fourier transform pulse sequence. Modification of the sweep imaging with Fourier transform sequence for PARACEST imaging is first discussed, followed by parameter optimization using in vitro experiments. In vivo PARACEST studies comparing fast spin‐echo to sweep imaging with Fourier transform were performed using EuDOTA‐(gly) uptake in healthy mouse kidneys. The results show that the negative contrast caused by T_2ex can be overcome using the ultrashort echo time achieved with sweep imaging with Fourier transform, thereby enabling fast and sensitive in vivo PARACEST imaging. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc.     

Improved fat suppression using multipeak reconstruction for IDEAL chemical shift fat‐water separation: Application with fast spin echo imaging

Purpose

To evaluate and quantify improvements in the quality of fat suppression for fast spin‐echo imaging of the knee using multipeak fat spectral modeling and IDEAL fat‐water separation.

Materials and Methods

T₁‐weighted and T₂‐weighted fast spin‐echo sequences with IDEAL fat‐water separation and two frequency‐selective fat‐saturation methods (fat‐selective saturation and fat‐selective partial inversion) were performed on 10 knees of five asymptomatic volunteers. The IDEAL images were reconstructed using a conventional single‐peak method and precalibrated and self‐calibrated multipeak methods that more accurately model the NMR spectrum of fat. The signal‐to‐noise ratio (SNR) was measured in various tissues for all sequences. Student t‐tests were used to compare SNR values.

Results

Precalibrated and self‐calibrated multipeak IDEAL had significantly greater suppression of signal (P < 0.05) within subcutaneous fat and bone marrow than fat‐selective saturation, fat‐selective partial inversion, and single‐peak IDEAL for both T₁‐weighted and T₂‐weighted fast spin‐echo sequences. For T₁‐weighted fast spin‐echo sequences, the improvement in the suppression of signal within subcutaneous fat and bone marrow for multipeak IDEAL ranged between 65% when compared to fat‐selective partial inversion to 86% when compared to fat‐selectivesaturation. For T2‐weighted fast spin‐echo sequences, the improvement for multipeak IDEAL ranged between 21% when compared to fat‐selective partial inversion to 81% when compared to fat‐selective saturation.

Conclusion

Multipeak IDEAL fat‐water separation provides improved fat suppression for T₁‐weighted and T₂‐weighted fast spin‐echo imaging of the knee when compared to single‐peak IDEAL and two widely used frequency‐selected fat‐saturation methods. J. Magn. Reson. Imaging 2009;29:436–442. © 2009 Wiley‐Liss, Inc.     

Irreversible change in the T1 temperature dependence with thermal dose using the proton resonance frequency‐T1 technique

Denaturation of macromolecules within the tissues is believed to be the major factor contributing to the damage of tissues upon hyperthermia. As a result, the value of the spin‐lattice relaxation time T₁ of the tissue water, which is related to the translational and rotational rates of water, represents an intrinsic probe for investigating structural changes in tissues at high temperature. Therefore, the goal of this work is to investigate whether the simultaneous measurement of temperature and T₁ using a hybrid proton resonance frequency (PRF)‐T₁ measurement technique can be used to detect irreversible changes in T₁ that might be indicative of tissue damage. A new hybrid PRF‐T₁ sequence was implemented based on the variable flip angle driven‐equilibrium single‐pulse observation (DESPOT)₁ method from a standard three dimensional segmented echo‐planar imaging sequence by alternating two flip angles from measurement to measurement. The structural changes of the heated tissue volumes were analyzed based on the derived T₁ values and the corresponding PRF temperatures. Using the hybrid PRF‐T₁ technique, we demonstrate that the change of spin lattice relaxation time T₁ is reversible with temperature for low thermal dose (thermal dose ≤ 240 cumulative equivalent minutes [CEM] 43°C) and irreversible with temperature after significant accumulation of thermal dose in ex vivo chicken breast tissue. These results suggest that the hybrid PRF‐T₁ method may be a potentially powerful tool to investigate the extent and mechanism of heat damage of biological tissues. Magn Reson Med 69:1122–1130, 2013. © 2012 Wiley Periodicals, Inc.     

Rapid three‐dimensional multicomponent relaxation imaging of the cervical spinal cord

Currently, little is known about the pathology of myelin in spinal cord disease due to the technical challenges of specifically measuring myelin content noninvasively. Multicomponent relaxometry allows estimation of the myelin water fraction, which is related to myelin content. However, conventional multiple‐echo spin–echo‐based multicomponent relaxometry techniques require prohibitively long acquisition times, lack spatial coverage, and are sensitive to artifacts common in spinal cord imaging. Multicomponent driven equilibrium single pulse observation of T₁ and T₂ (mcDESPOT) offers a promising alternative to conventional multicomponent relaxometry techniques. The goal of this pilot study was to assess the efficacy of mcDESPOT for obtaining high spatial resolution spinal cord myelin water fraction data covering the entire cervical spinal cord. Myelin water fraction values were found to be highly reproducible between subjects and over time but varied considerably along the length of the cord. Other relaxation characteristics that relate to tissue structure and health were also reliably measured. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc.     

Improved T2 mapping accuracy with dual‐echo turbo spin echo: Effect of phase encoding profile orders

Turbo spin echo (TSE) pulse sequences have been applied to estimate T₂ relaxation times in clinically feasible scan times. However, T₂ estimations using TSE pulse sequences has been shown to differ considerable from reference standard sequences due to several sources of error. The purpose of this work was to apply voxel‐sensitivity formalism to correct for one such source of error introduced by differing phase encoding profile orders with dual‐echo TSE pulse sequences. The American College of Radiology phantom and the brains of two healthy volunteers were imaged using dual‐echo TSE as well as 32‐echo spin‐echo acquisitions and T₂ estimations from uncorrected and voxel‐sensitivity formalism‐corrected dual‐echo TSE and 32‐echo acquisitions were compared. In all regions of the brain and the majority of the analyses of the American College of Radiology phantom, voxel‐sensitivity formalism correction resulted in considerable improvements in dual‐echo TSE T₂ estimation compared with the 32‐echo acquisition, with improvements in T₂ value accuracy ranging from 5.2% to 18.6%. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

T₁-weighted ultrashort echo time method for positive contrast imaging of magnetic nanoparticles and cancer cells bound with the targeted nanoparticles

Purpose

To obtain positive contrast based on T₁ weighting from magnetic iron oxide nanoparticle (IONP) using ultrashort echo time (UTE) imaging and investigate quantitative relationship between positive contrast and the core size and concentration of IONPs.

Materials and Methods

Solutions of IONPs with different core sizes and concentrations were prepared. T₁ and T₂ relaxation times of IONPs were measured using the inversion recovery turbo spin echo (TSE) and multi‐echo spin echo sequences at 3 Tesla. T₁‐weighted UTE gradient echo and T₂‐weighted TSE sequences were used to image IONP samples. U87MG glioblastoma cells bound with arginine‐glycine‐aspartic acid (RGD) peptide and IONP conjugates were scanned using UTE, T₁ and T₂‐weighted sequences.

Results

Positive contrast was obtained by UTE imaging from IONPs with different core sizes and concentrations. The relative‐contrast‐to‐water ratio of UTE images was three to four times higher than those of T₂‐weighted TSE images. The signal intensity increases as the function of the core size and concentration. Positive contrast was also evident in cell samples bound with RGD‐IONPs.

Conclusion

UTE imaging allows for imaging of IONPs and IONP bound tumor cells with positive contrast and provides contrast enhancement and potential quantification of IONPs in molecular imaging applications. J. Magn. Reson. Imaging 2011;33:194–202. © 2010 Wiley‐Liss, Inc.     

Longitudinal and multi-echo transverse relaxation times of normal breast tissue at 3 Tesla

Purpose

To measure longitudinal (T₁) and multi‐echo transverse (T₂) relaxation times of healthy breast tissue at 3 Tesla (T).

Materials and Methods

High‐resolution relaxation time measurements were made in six healthy female subjects. Inversion recovery images were acquired at 10 inversion times between 100 ms and 4000 ms, and multiple spin echo images were acquired at 16 echo times between 10 ms and 160 ms.

Results

Longitudinal relaxation times T₁ were measured as 423 ± 12 ms for adipose tissue and 1680 ± 180 ms for fibroglandular tissue. Multi‐echo transverse relaxation times T₂ were measured as 154 ± 9 ms for adipose tissue and 71 ± 6 ms for fibroglandular tissue. Histograms of the voxel‐wise relaxation times and quantitative relaxation time maps are also presented.

Conclusion

T₁ and multi‐echo T₂ relaxation times in normal human breast tissue are reported. These values are useful for pulse sequence design and optimization for 3T breast MRI. Compared with the literature, T₁ values are significantly longer at 3T, suggesting that longer repetition time and inversion time values should be used for similar image contrast. J. Magn. Reson. Imaging 2010;32:982–987. © 2010 Wiley‐Liss, Inc.     

A technique for rapid single‐echo spin‐echo T2 mapping

A rapid technique for mapping of T₂ relaxation times is presented. The method is based on the conventional single‐echo spin echo approach but uses a much shorter pulse repetition time to accelerate data acquisition. The premise of the new method is the use of a constant difference between the echo time and pulse repetition time, which removes the conventional and restrictive requirement of pulse repetition time ? T₁. Theoretical and simulation investigations were performed to evaluate the criteria for accurate T₂ measurements. Measured T₂s were shown to be within 1% error as long as the key criterion of pulse repetition time/T₂ ≥3 is met. Strictly, a second condition of echo time/T₁ ? 1 is also required. However, violations of this condition were found to have minimal impact in most clinical scenarios. Validation was conducted in phantoms and in vivo T₂ mapping of healthy cartilage and brain. The proposed method offers all the advantages of single‐echo spin echo imaging (e.g., immunity to stimulated echo effects, robustness to static field inhomogeneity, flexibility in the number and choice of echo times) in a considerably reduced amount of time and is readily implemented on any clinical scanner. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Single‐shot T1 mapping using simultaneous acquisitions of spin‐ and stimulated‐echo‐planar imaging (2D ss‐SESTEPI)

The conventional stimulated‐echo NMR sequence only measures the longitudinal component while discarding the transverse component, after tipping up the prepared magnetization. This transverse magnetization can be used to measure a spin echo, in addition to the stimulated echo. Two‐dimensional single‐shot spin‐ and stimulated‐echo‐planar imaging (ss‐SESTEPI) is an echo‐planar‐imaging‐based single‐shot imaging technique that simultaneously acquires a spin‐echo‐planar image and a stimulated‐echo‐planar image after a single radiofrequency excitation. The magnitudes of the spin‐echo‐planar image and stimulated‐echo‐planar image differ by T₁ decay and diffusion weighting for perfect 90° radiofrequency and thus can be used to rapidly measure T₁. However, the spatial variation of amplitude of radiofrequency field induces uneven splitting of the transverse magnetization for the spin‐echo‐planar image and stimulated‐echo‐planar image within the imaging field of view. Correction for amplitude of radiofrequency field inhomogeneity is therefore critical for two‐dimensional ss‐SESTEPI to be used for T₁ measurement. We developed a method for amplitude of radiofrequency field inhomogeneity correction by acquiring an additional stimulated‐echo‐planar image with minimal mixing time, calculating the difference between the spin echo and the stimulated echo and multiplying the stimulated‐echo‐planar image by the inverse functional map. Diffusion‐induced decay is corrected by measuring the average diffusivity during the prescanning. Rapid single‐shot T₁ mapping may be useful for various applications, such as dynamic T₁ mapping for real‐time estimation of the concentration of contrast agent in dynamic contrast enhancement MRI. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Assessment of cortical bone with clinical and ultrashort echo time sequences

We describe the use of ultrashort echo time (UTE) sequences and fast spin echo sequences to assess cortical bone using a clinical 3T scanner. Regular two‐ and three‐dimensional UTE sequences were used to image both bound and free water in cortical bone. Adiabatic inversion recovery prepared UTE sequences were used to image water bound to the organic matrix. Two‐dimensional fast spin echo sequences were used to image free water. Regular UTE sequences were used together with bicomponent analysis to measure T*₂s and relative fractions of bound and free water components in cortical bone. Inversion recovery prepared UTE sequences were used to measure the T*₂ of bound water. Saturation recovery UTE sequences were used to measure the T₁ of bone water. Eight cadaveric human cortical bone samples and a lower leg specimen were studied. Preliminary results show two distinct components in UTE detected signal decay, a single component in inversion recovery prepared UTE detected signal decay, and a single component in saturation recovery UTE detected signal recovery. Regular UTE sequences appear to depict both bound and free water in cortical bone. Inversion recovery prepared UTE sequences appear to depict water bound to the organic matrix. Two‐dimensional fast spin echo sequences appear to depict bone structure corresponding to free water in large pores. Magn Reson Med 70:697–704, 2013. © 2012 Wiley Periodicals, Inc.     

Simultaneous estimation of T(2) and apparent diffusion coefficient in human articular cartilage in vivo with a modified three-dimensional double echo steady state (DESS) sequence at 3 T

T₂ mapping and diffusion‐weighted imaging complement morphological imaging for assessing cartilage disease and injury. The double echo steady state sequence has been used for morphological imaging and generates two echoes with markedly different T₂ and diffusion weighting. Modifying the spoiler gradient area and flip angle of the double echo steady state sequence allows greater control of the diffusion weighting of both echoes. Data from two acquisitions with different spoiler gradient areas and flip angles are used to simultaneously estimate the T₂ and apparent diffusion coefficient of each voxel. This method is verified in phantoms and validated in vivo in the knee; estimates from different regions of interest in the phantoms and cartilage are compared to those obtained using standard spin‐echo methods. The Pearson correlations were 0.984 for T₂ (～2% relative difference between spin‐echo and double echo steady state estimates) and 0.997 for apparent diffusion coefficient (?1% relative difference between spin‐echo and double echo steady state estimates) for the phantom study and 0.989 for T₂ and 0.987 for apparent diffusion coefficient in regions of interest in the human knee in vivo. High accuracy for simultaneous three‐dimensional T₂ and apparent diffusion coefficient measurements are demonstrated, while also providing morphologic three‐dimensional images without blurring or distortion in reasonable scan times. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Ultrashort TE T1rho (UTE T1rho) imaging of the Achilles tendon and meniscus

In this study, we report the use of a novel ultrashort echo time T₁rhoT₁ sequence that combines a spin‐lock preparation pulse with a two‐dimensional ultrashort echo time sequence of a nominal echo time 8 μsec. The ultrashort echo time‐T₁rho sequence was employed to quantify T₁rho in short T₂ tissues including the Achilles tendon and the meniscus. T₁rho dispersion was investigated by varying the spin‐lock field strength. Preliminary results on six cadaveric ankle specimens and five healthy volunteers show that the ultrashort echo time‐T₁rho sequence provides high signal and contrast for both the Achilles tendon and the meniscus. The mean T₁rho of the Achilles tendon ranged from 3.06 ± 0.51 msec for healthy volunteers to 5.22 ± 0.58 msec for cadaveric specimens. T₁rho increased to 8.99 ± 0.24 msec in one specimen with tendon degeneration. A mean T₁rho of 7.98 ± 1.43 msec was observed in the meniscus of the healthy volunteers. There was significant T₁rho dispersion in both the Achilles tendon and the meniscus. Mean T₁rho increased from 2.06 ± 0.23 to 7.85 ± 0.74 msec in normal Achilles tendon and from 7.08 ± 0.64 to 13.42 ± 0.93 msec in normal meniscus when the spin‐lock field was increased from 250 to 1,000 Hz. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Simultaneous T2 and lipid quantitation using IDEAL‐CPMG

Muscle damage, edema, and fat infiltration are hallmarks of a range of neuromuscular diseases. The T₂ of water, T_2,w, in muscle lengthens with both myocellular damage and inflammation and is typically measured using multiple spin‐echo or Carr–Purcell–Meiboom–Gill acquisitions. However, microscopic fat infiltration in neuromuscular diseases prevents accurate T_2,w quantitation as the longer T₂ of fat, T_2,f, masks underlying changes in the water component. Fat saturation can be inconsistent across the imaging volume and removes valuable physiological fat information. A new method is presented that combines iterative decomposition of water and fat with echo asymmetry and least squares estimation with a Carr–Purcell–Meiboom–Gill–sequence. The sequence results in water and fat separated images at each echo time for use in T_2,w and T_2,f quantification. With knowledge of the T_2,w and T_2,f, a T₂‐corrected fat fraction map can also be calculated. Monte‐Carlo simulations and measurements in phantoms, volunteers, and a patient with inclusion body myositis are demonstrated. In healthy volunteers, uniform T_2,w and T₂‐corrected fat fraction maps are present within all muscle groups. However, muscle‐specific patterns of fat infiltration and edema are evident in inclusion body myositis, which demonstrates the power of separating and quantifying the fat and water components. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc.     

Consequences of T2 relaxation during half‐pulse slice selection for ultrashort TE imaging

A “half‐pulse” slice selection approach is used in the ultrashort echo time pulse sequence and is required to give minimal transverse relaxation in a two‐dimensional acquisition. This method splits the normal excitation radiofrequency pulse in half and acquires a pair of images, each using one of these half‐pulses. These half‐pulses are used without a refocusing gradient since summing the pair of images yields images with accurate slice selection. When the radiofrequency pulse duration is similar to the sample T₂, characteristics such as the effective echo time and choice of radiofrequency pulse require careful evaluation as some of the approximations in conventional slice selection do not apply. We derive a theory that includes relaxation during excitation using Pauly's excitation k‐space formalism. Further, this theory is tested on phantoms with a range of values of T₂ demonstrating the effect on the slice profile. We conclude that relaxation during excitation is significant and should be included in our estimate of the T₂ weighting of the sequence. In general, the T₂ weighting should be measured from the time of the centroid of the excitation pulse. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Bayesian algorithm using spatial priors for multiexponential T(2) relaxometry from multiecho spin echo MRI

Multiexponential T₂ relaxometry is a powerful research tool for detecting brain structural changes due to demyelinating diseases such as multiple sclerosis. However, because of unusually high signal‐to‐noise ratio requirement compared with other MR modalities and ill‐posedness of the underlying inverse problem, the T₂ distributions obtained with conventional approaches are frequently prone to noise effects. In this article, a novel multivoxel Bayesian algorithm using spatial prior information is proposed. This prior takes into account the expectation that volume fractions and T₂ relaxation times of tissue compartments change smoothly within coherent brain regions. Three‐dimensional multiecho spin echo MRI data were collected from five healthy volunteers at 1.5 T and myelin water fraction maps were obtained using the conventional and proposed algorithms. Compared with the conventional method, the proposed method provides myelin water fraction maps with improved depiction of brain structures and significantly lower coefficients of variance in white matter. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.