Comparison of two ultrashort echo time sequences for the quantification of T(1) within phantom and human Achilles tendon at 3 T

Ultrashort echo time (UTE) techniques enable direct imaging of musculoskeletal tissues with short T₂ allowing measurement of T₁ relaxation times. This article presents comparison of optimized 3D variable flip angle UTE (VFA‐UTE) and 2D saturation recovery UTE (SR‐UTE) sequences to quantify T₁ in agar phantoms and human Achilles tendon. Achilles tendon T₁ values for asymptomatic volunteers were compared to Achilles tendon T₁ values calculated from patients with clinical diagnoses of spondyloarthritis (SpA) and Achilles tendinopathy using an optimized VFA‐UTE sequence. T₁ values from phantom data for VFA‐ and SR‐UTE compare well against calculated T₁ values from an assumed gold standard inversion recovery spin echo sequence. Mean T₁ values in asymptomatic Achilles tendon were found to be 725 ± 42 ms and 698 ± 54 ms for SR‐ and VFA‐UTE, respectively. The patient group mean T₁ value for Achilles tendon was found to be 957 ± 173 ms (P < 0.05) using an optimized VFA‐UTE sequence with pulse repetition time of 6 ms and flip angles 4, 19, and 24°, taking a total 9 min acquisition time. The VFA‐UTE technique appears clinically feasible for quantifying T₁ in Achilles tendon. T₁ measurements offer potential for detecting changes in Achilles tendon due to SpA without need for intravenous contrast agents. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.     

Ultrashort TE T1ρ magic angle imaging

An ultrashort TE T₁ρ sequence was used to measure T₁ρ of the goat posterior cruciate ligament (n = 1) and human Achilles tendon specimens (n = 6) at a series of angles relative to the B₀ field and spin‐lock field strengths to investigate the contribution of dipole–dipole interaction to T₁ρ relaxation. Preliminary results showed a significant magic angle effect. T₁ρ of the posterior cruciate ligament increased from 6.9 ± 1.3 ms at 0° to 36 ± 5 ms at 55° and then gradually reduced to 12 ± 3 ms at 90°. Mean T₁ρ of the Achilles tendon increased from 5.5 ± 2.2 ms at 0° to 40 ± 5 ms at 55°. T₁ρ dispersion study showed a significant T₁ρ increase from 2.3 ± 0.9 ms to 11 ± 3 ms at 0° as the spin‐lock field strength increased from 150 Hz to 1 kHz, and from 30 ± 3 ms to 42 ± 4 ms at 55° as the spin‐lock field strength increased from 100 to 500 Hz. These results suggest that dipolar interaction is the dominant T₁ρ relaxation mechanism in tendons and ligaments. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

Dual inversion recovery,ultrashort echo time (DIR UTE) imaging: Creating high contrast for short‐T2 species

Imaging of short‐T₂ species requires not only a short echo time but also efficient suppression of long‐T₂ species in order to maximize the short‐T₂ contrast and dynamic range. This paper introduces a method of long‐T₂ suppression using two long adiabatic inversion pulses. The first adiabatic inversion pulse inverts the magnetization of long‐T₂ water and the second one inverts that of fat. Short‐T₂ species experience a significant transverse relaxation during the long adiabatic inversion process and are minimally affected by the inversion pulses. Data acquisition with a short echo time of 8 μs starts following a time delay of inversion time (TI1) for the inverted water magnetization to reach a null point and a time delay of TI2 for the inverted fat magnetization to reach a null point. The suppression of long‐T₂ species depends on proper combination of TI1, TI2, and pulse repetition time. It is insensitive to radiofrequency inhomogeneities because of the adiabatic inversion pulses. The feasibility of this dual inversion recovery ultrashort echo time technique was demonstrated on phantoms, cadaveric specimens, and healthy volunteers, using a clinical 3‐T scanner. High image contrast was achieved for the deep radial and calcified layers of articular cartilage, cortical bone, and the Achilles tendon. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

In vivo measurement of T1rho dispersion in the human brain at 1.5 tesla

Purpose

To measure T_1ρ relaxation times and T_1ρ dispersion in the human brain in vivo.

Materials and Methods

Magnetic resonance imaging (MRI) was performed on a 1.5‐T GE Signa clinical scanner using the standard GE head coil. A fast spin‐echo (FSE)‐based T_1ρ‐weighted MR pulse sequence was employed to obtain images from five healthy male volunteers. Optimal imaging parameters were determined while considering both the objective of the study and the guarantee that radio‐frequency (RF) power deposition during MR did not exceed Food and Drug Administration (FDA)‐mandated safety levels.

Results

T_1ρ‐weighted MR images showed excellent contrast between different brain tissues. These images were less blurred than corresponding T₂‐weighted images obtained with similar contrast, especially in regions between brain parenchyma and cerebrospinal fluid (CSF). Average T_1ρ values for white matter (WM), gray matter (GM), and CSF were 85 ± 3, 99 ± 1, and 637 ± 78 msec, respectively, at a spin‐locking field of 500 Hz. T_1ρ is 30% higher in the parenchyma and 78% higher in CSF compared to the corresponding T₂ values. T_1ρ dispersion was observed between spin‐locking frequencies 0 and 500 Hz.

Conclusion

T_1ρ‐weighted MRI provides images of the brain with superb contrast and detail. T_1ρ values measured in the different brain tissues will serve as useful baseline values for analysis of T_1ρ changes associated with pathology. J. Magn. Reson. Imaging 2004;19:403–409. © 2004 Wiley‐Liss, Inc.

     

Quantitative magnetization transfer ultrashort echo time imaging of the Achilles tendon

Ultrashort echo time imaging allows the short T₂ Achilles tendon to be directly visualized with MRI. Radiofrequency saturation 1 kHz or less off‐resonance has been used previously to improve image contrast. In this study, magnetization transfer was investigated in the Achilles tendon of eight normal volunteers and one patient with psoriatic arthritis. 2D Ultrashort echo time images were acquired using saturation pulses 2–100 kHz off‐resonance at 4 pulse powers. On‐resonance saturation recovery images were also obtained to estimate T₁. The results were fitted to a two compartment quantitative magnetization transfer model. The estimated bound proton fraction for the eight healthy volunteers was 21.0 ± 1.2% (mean ± standard deviation) compared to 16.4% in the patient with psoriatic arthritis (P < 0.05). The T₂ of the bound protons was measured as 6.1 ± 0.3 μsec in the healthy volunteers and 6.0 μsec in the patient. This technique appears clinically feasible and may be useful for assessing the collagen and water changes which occur in Achilles tendinopathy. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

k‐space water‐fat decomposition with T2* estimation and multifrequency fat spectrum modeling for ultrashort echo time imaging

Purpose:

To demonstrate the feasibility of combining a chemical shift‐based water‐fat separation method (IDEAL) with a 2D ultrashort echo time (UTE) sequence for imaging and quantification of the short T₂ tissues with robust fat suppression.

Materials and Methods:

A 2D multislice UTE data acquisition scheme was combined with IDEAL processing, including T₂* estimation, chemical shift artifacts correction, and multifrequency modeling of the fat spectrum to image short T₂ tissues such as the Achilles tendon and meniscus both in vitro and in vivo. The integration of an advanced field map estimation technique into this combined method, such as region growing (RG), is also investigated.

Results:

The combination of IDEAL with UTE imaging is feasible and excellent water‐fat separation can be achieved for the Achilles tendon and meniscus with simultaneous T₂* estimation and chemical shift artifact correction. Multifrequency modeling of the fat spectrum yields more complete water‐fat separation with more accurate correction for chemical shift artifacts. The RG scheme helps to avoid water‐fat swapping.

Conclusion:

The combination of UTE data acquisition with IDEAL has potential applications in imaging and quantifying short T₂ tissues, eliminating the necessity for fat suppression pulses that may directly suppress the short T₂ signals. J. Magn. Reson. Imaging 2010;31:1027–1034. ©2010 Wiley‐Liss, Inc.     

Comparison of lung T2* during free‐breathing at 1.5 T and 3.0 T with ultrashort echo time imaging

Assessment of lung effective transverse relaxation time (T₂*) may play an important role in the detection of structural and functional changes caused by lung diseases such as emphysema and chronic bronchitis. While T₂* measurements have been conducted in both animals and humans at 1.5 T, studies on human lung at 3.0 T have not yet been reported. In this work, ultrashort echo time imaging technique was applied for the measurement and comparison of T₂* values in normal human lungs at 1.5 T and 3.0 T. A 2D ultrashort echo time pulse sequence was implemented and evaluated in phantom experiments, in which an eraser served as a homogeneous short T₂* sample. For the in vivo study, five normal human subjects were imaged at both field strengths and the results compared. The average T₂* values measured during free‐breathing were 2.11(±0.27) ms at 1.5 T and 0.74(±0.1) ms at 3.0 T, respectively, resulting in a 3.0 T/1.5 T ratio of 2.9. Furthermore, comparison of the relaxation values at end‐expiration and end‐inspiration, accomplished through self‐gating, showed that during normal breathing, differences in T₂* between the two phases may be negligible. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Synchronized inversion recovery-spin echo sequences for precise in vivo T1 measurement of human myocardium: A pilot study on 22 healthy subjects

An ECG-triggered, two-sequence MRI technique is proposed for the precise measurement of proton T₁ relaxation times of the human myocardium at a field strength of 0.5 T. The combination of an inversion recovery (IR) sequence and a spin echo (SE) sequence is not new. It is, however, rarely used in quantitative in vivo cardiac studies. Our approach employs a synchronization of the 90° read pulse to the systolic period. In a study of 22 healthy volunteers, the globally measured T₁ value was estimated to be 714 ± 23 ms. Four of the volunteers also underwent additional imaging scans for the purposes of reproducibility assessment. The T₁ precision was found to be 3.9 ± 1.1% for the IR/SE combination and 16.9 ± 5.3% for a combination of SE sequences. Total imaging time for the IR and SE sequences was 19.2 ± 3.0 mins. The relative rapidity of this classic technique and the T₁ precision obtained give this technique an obvious application in the discrimination of normal and diseased myocardium. In the same study, valuable supplementary tissue characterization is provided by T₂, calculated from the SE sequence. T₂ was evaluated to be 50 ± 3 ms.     

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.     

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.     

Ultrashort echo time MR imaging with off‐resonance saturation for characterization of pathologically altered Achilles tendons at 3 T

Off‐resonance radiofrequency saturation pulses applied prior to regular excitation in MR sequences can be used to modify signal contrast based on magnetization transfer and direct saturation effects. Clinical applicability and value of ultrashort echo time sequences combined with off‐resonance saturation pulses was tested in 16 healthy and 14 tendinopathic as well as paratendinopathic Achilles tendons in vivo at 3 T. A 3D ultrashort echo time sequence in combination with a gaussian off‐resonance saturation pulse (frequency offset: 1000–5000 Hz) was used to modify the detectable MR signal intensity from the Achilles tendon. Off‐resonance saturation ratio was calculated as the relative reduction in signal intensity under selective off‐resonance saturation in relation to a reference measurement without any saturation pulse. Off‐resonance saturation ratio in tendons of healthy volunteers ranged from 0.52 ± 0.06 (1000 Hz) to 0.24 ± 0.02 (5000 Hz), whereas symptomatic tendinopathic tendons (0.35 ± 0.04 to 0.17 ± 0.02) and asymptomatic tendinopathic tendons (0.41 ± 0.06 to 0.21 ± 0.02) showed significantly lower mean off‐resonance saturation ratio values. Off‐resonance saturation ratio values might provide a sensitive and quantitative marker for assessment of pathological microstructure alterations of the Achilles tendon. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

Ultrashort TE MR imaging of bovine cortical bone: The effect of water loss on the T1 and T2* relaxation times

The effects of water loss on the T₁ and T₂* of bovine cortical bone were investigated using ultrashort echo time sequences with signals excited either by a short hard pulse or by two longer half pulses. Nine bovine femur samples were prepared and sequentially air‐ and oven‐dried. On average 3.42% of bone by weight was lost after air‐drying for 3 days, with another 5.98% of bone weight loss after oven‐drying at 100°C for 24 h. T₁ and T₂* were measured after every 1% decrease in weight, with 9–10% bone weight loss at the termination of the drying process. After both forms of drying, the overall T₁ decreased 33% from 153 ± 18 ms to 102 ± 17 ms when measured using the hard pulse and from 186 ± 25 ms to 122 ± 23 ms when using the half pulses. T₂* decreased by 45–50% from 368 ± 29 μs to 201 ± 19 μs using the hard pulse and from 379 ± 35 μs to 191 ± 17 μs using the half pulses. A steady decrease of 26–31% was observed in both T₁ and T₂* with the first 3–4% bone water loss after air‐drying. Oven‐drying at 100°C for 24 h resulted on an additional 4% T₁ reduction but 25% T₂* reduction. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Radiofrequency pulses for simultaneous short T2 excitation and long T2 suppression

Magnetic resonance imaging of short T₂ musculoskeletal tissues such as ligaments, tendon, and cortical bone often requires specialized pulse sequences to detect sufficiently high levels of signal, as well as additional techniques to suppress unwanted long T₂ signals. We describe a specialized radiofrequency technique for imaging short T₂ tissues based on applying hard 180° radiofrequency excitation pulses to achieve simultaneous short T₂ tissue excitation and long T₂ tissue signal suppression for three‐dimensional ultrashort echo time applications. A criterion for the pulse duration of the 180° radiofrequency pulses is derived that allows simultaneous water and fat suppression. This opens up possibilities for direct imaging of short T₂ tissues, without the need for additional suppression techniques. Bloch simulations and experimental studies on short T₂ phantoms and specimen were used to test the sequence performance. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc.     

Imaging with positive T(1) -contrast using superstimulated echoes

This article presents the basic principles of the superstimulated echo mechanism and shows preliminary results of its application to T₁‐weighted imaging with positive T₁‐contrast. A superstimulated echo scheme uses a preparation of square‐wave modulated, periodically inverted z‐magnetization, which after signal evolution during the mixing time TM is fully converted into transverse magnetization. This avoids the 50% signal loss of a conventional stimulated echo. Furthermore, its implementation as a preparation module for standard turbo spin echo (TSE) imaging allows producing images with positive T₁‐contrast. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.     

Prostate T(1) quantification using a magnetization-prepared spiral technique

Purpose

To adapt a magnetization‐prepared spiral imaging technique, termed T1prep, for time‐efficient radiofrequency (RF)‐insensitive prostate T₁ quantification at 1.5 T and evaluate signal‐to‐noise ratio (SNR) limits to voxel‐based versus subregion analysis.

Materials and Methods

A magnetization‐prepared spiral imaging technique was adapted for robust T₁ contrast development, multislice imaging within 5 minutes, and data regression to a monoexponential decay. In vitro testing evaluated RF insensitivity of the multislice acquisition plus method accuracy. A pilot study was performed in 15 patients with low or intermediate risk localized prostate cancer.

Results

The multislice design displayed excellent RF insensitivity (<1% error for RF mistunings to ± 20%) and accuracy (within 3% of gold standard for T₁ values between 140 and 2100 msec). A clinical pilot study reported significantly reduced T₁ from PZ to CG to tumor subregions (PZ: 1421 ± 168 msec, n = 11; CG: 1314 ± 49 msec, n = 13; 1246 ± 68 msec, n = 8). SNR measurements identified an inappropriateness of voxel‐based analysis.

Conclusion

T1prep can quantify prostate T₁ as an adjunct measure for quantitative perfusion measurements and longitudinal treatment response monitoring. Intrapatient heterogeneities support T₁ assessment within individual patients. SNR calculations will support a transition to voxel‐based analysis in future trials. J. Magn. Reson. Imaging 2011. © 2011 Wiley‐Liss, Inc.     

Multicomponent T2* mapping of knee cartilage: Technical feasibility ex vivo

Disorganization of collagen fibers is a sign of early‐stage cartilage degeneration in osteoarthritic knees. Water molecules trapped within well‐organized collagen fibrils would be sensitive to collagen alterations. Multicomponent effective transverse relaxation (T₂*) mapping with ultrashort echo time acquisitions is here proposed to probe short T₂ relaxations in those trapped water molecules. Six human tibial plateau explants were scanned on a 3T MRI scanner using a home‐developed ultrashort echo time sequence with echo times optimized via Monte Carlo simulations. Time constants and component intensities of T₂* decays were calculated at individual pixels, using the nonnegative least squares algorithm. Four T₂*‐decay types were found: 99% of cartilage pixels having mono‐, bi‐, or nonexponential decay, and 1% showing triexponential decay. Short T₂* was mainly in 1‐6 ms, while long T₂* was ～22 ms. A map of decay types presented spatial distribution of these T₂* decays. These results showed the technical feasibility of multicomponent T₂* mapping on human knee cartilage explants. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Fast measurement of blood T1 in the human jugular vein at 3 Tesla

Current T₁ values for blood at 3T largely came from in vitro studies on animal blood or freshly drawn human blood. Measurement of blood T₁ in vivo could provide more specific information, e.g., for individuals with abnormal blood composition. Here, blood T₁ at 3T was measured rapidly (<1 min) in the internal jugular vein using a fast inversion‐recovery technique in which multiple inversion time can be acquired rapidly due to constant refreshing of blood. Multishot EPI acquisition with flow compensation yielded high resolution images with minimum partial volume effect. Results showed T₁ = 1852 ± 104 msec among 24 healthy adults, a value higher than for bovine blood phantoms (1584 msec at Hct of 42%). A second finding was that of a significant difference (P < 0.01) between men and women, namely T₁ = 1780 ± 89 msec (n = 12) and T₁ = 1924 ± 58 msec (n = 12), respectively. This difference in normal subjects is tentatively explained by the difference in Hct between genders. Interestingly, however, studies done on sickle cell anemia patients with much lower Hct (23 ± 3%, n = 10) revealed similar venous blood T₁ = 1924 ± 82 msec, indicating other possible physical influences affecting blood T₁. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc.     

A simple approach for three‐dimensional mapping of baseline cerebrospinal fluid volume fraction

A simple method of measuring baseline cerebrospinal fluid volume fraction (V_CSF) in three‐dimensional is proposed that used the characteristic of cerebrospinal fluid with very long T₂. It is based on the fitting of monoexponential decay of only cerebrospinal fluid signal, using a nonselective T₂ preparation scheme. Three‐dimensional gradient‐ and spin‐echo acquisition also improves signal‐to‐noise ratio efficiency and brain coverage. Both V_CSF and T_2,CSF are fitted voxel by voxel and analyzed in different cortical areas across subjects. V_CSF is largely regionally dependent (occipital: 8.9 ± 1.7%, temporal: 11.4 ± 2.4%, and frontal: 21.4 ± 6.9%). Measured T_2,CSF was 1573 ± 146 msec within cortical lobes as compared with 2062 ± 37 msec from ventricle regions. Different parameter set were compared, and the robustness of the new method is demonstrated. Conversely, when comparing with the proposed approach, large overestimation of segmentation based method using T₁‐weighted images is found, and the underlying causes are suggested. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc.     

Modified PROPELLER approach for T2‐mapping of the abdomen

Quantitative abdominal T₂ measurements may be useful for lesion differentiation and functional tissue characterization. However, T₂ mapping of the abdomen with conventional spin‐echo (SE) and turbo‐spin‐echo (TSE) approaches can be challenging due to physiologic motion artifacts. Multishot TSE‐based PROPELLER (Periodically Rotated Overlapping ParallEL Lines with Enhanced Reconstruction) can provide superior image quality due to reduced sensitivity to motion artifacts. With echo‐reordering to accurately estimate effective echo times and an extended slice thickness ratio to reduce stimulated echo effects, a modified PROPELLER approach may permit accurate, robust abdominal T₂ measurements. We validated the accuracy of our modified PROPELLER T₂‐mapping approach by comparison to conventional SE measurements in a phantom model and demonstrated the feasibility of acquiring accurate, high‐quality abdominal T₂ maps in normal volunteers. Magn Reson Med 61:1269–1278, 2009. © 2009 Wiley‐Liss, Inc.     

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.