Practical Implementation and Optimization of One‐shot <i>T</i><sub>1</sub> imaging

Kay, Ian; Henkelman, R. Mark

doi:10.1002/mrm.1910220249

Cited by 88 publications

(71 citation statements)

References 22 publications

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“…MT data were acquired as described in Sled and Pike (5), consisting of two protocols with different pulse repetition times and saturation pulse durations, for a total of 60 measurements. The observed T 1 (T 1obs ), required for QMTI, was measured using a Look-Locker pulse sequence (33), with published acquisition parameters (5). To improve the accuracy and reproducibility of T 1 and QMTI parameters, the static and transmit (amplitude of radiofrequency) fields were mapped in each subject.…”

Section: Scanning Protocolmentioning

confidence: 99%

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Quantitative magnetization transfer and myelin water imaging of the evolution of acute multiple sclerosis lesions

et al. 2010

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Quantitative magnetization transfer imaging provides in vivo estimates of liquid and semisolid constituents of tissue, while estimates of the liquid subpopulations, including myelin water, can be obtained from multicomponent T 2 analysis. Both methods have been suggested to provide improved myelin specificity compared to conventional MRI. The goal of this study was to investigate the sensitivity of each technique to the progression of acute, gadolinium-enhancing regions of multiple sclerosis. Magnetization transfer and T 2 relaxometry data were acquired longitudinally over the course of 1 year in five relapsing-remitting multiple sclerosis patients and in five healthy controls. Parametric maps were analyzed in enhancing lesions and normal-appearing white matter regions. Quantitative magnetization transfer parameters in lesions were most abnormal at the time of enhancement and followed a pattern of recovery over subsequent months. Lesion myelin water fraction was abnormal but did not show a significant trend over time. Quantitative magnetization transfer was able to track the degree and timing of the partial recovery in enhancing multiple sclerosis lesions in a small group of patients, while the recovery was not detected in myelin water estimates, possibly due to their large variability. Our data suggest the recovery is characterized by quick resolution of inflammation and a slower remyelination process. Key words: quantitative; magnetization transfer; multicomponent T 2 ; multiple sclerosis; acute lesions A few MRI methods have been suggested to provide improved pathologic specificity in human white matter (WM) over conventional MRI sequences. Two techniques proposed to be more specific for myelin are quantitative magnetization transfer imaging (QMTI) and multicomponent T 2 analysis of spin echo data (QT2). In this longitudinal study, both techniques were used to follow the progression of the gadolinium (Gd)-enhancing region of acute lesions of multiple sclerosis (MS).The magnetization transfer (MT) effect can be exploited to produce contrast in MRI (for a review see Henkelman et al. (1) and Tofts (2)) and is sensitive to the principal constituents of myelin in human WM (3). MT can be described using a two-component model, grouping spins into the free (or liquid) pool, consisting of water hydrogen nuclei with long T 2 (T 2f > 10 ms), and the restricted (or semisolid) pool, consisting of hydrogen nuclei of large lipids with T 2 too short to be imaged directly using MRI (T 2r < 100 ls). Detailed information about these spin populations can be mapped using offresonance QMTI techniques, with an appropriate twopool model of MT in tissue (4). QMTI yields the relative size of the restricted proton pool (F), the first-order forward magnetization exchange rate (k f ), and most relaxation parameters of the free and restricted pools (R 1f , T 2f , and T 2r ) (5).While QMTI measurements do not provide absolute specificity to the molecular constituents of tissue, there is convergent evidence that MT changes in WM reflect cha...

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Section: Scanning Protocolmentioning

confidence: 99%

“…Separate amplitude of static field maps were also acquired for each MT sequence without the saturation pulse to account for eddy currents due to the large crushing gradients in the MT sequence. A twopoint method with nonselective preparation (flip angles 33 and 66 ) was used to map the relative amplitude of radiofrequency field (35).…”

Section: Scanning Protocolmentioning

confidence: 99%

Quantitative magnetization transfer and myelin water imaging of the evolution of acute multiple sclerosis lesions

et al. 2010

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“…To calculate the tissue concentration of Gd-DTPA from the T 1 -weighted FSPGR signal intensity, the native T 1 of the tissue must be measured (31). This was achieved by acquiring a preinjection T 1 -map using a Look-Locker sequence (32,33) with the following parameters (TR/TE ϭ 3000/ 225 msec, one echo, ϭ 20°, BW ϭ 125 kHz, FOV ϭ 16 cm, matrix ϭ 4096 readout points ϫ 8 spiral interleaves, spatial resolution ϭ 0.85 mm, slice thickness ϭ 3 mm, four averages). Conventional T 2 -weighted images were also acquired using a fast spin-echo sequence (TR/TE ϭ 2000/75 msec, echo train length (ETL) ϭ 8, FOV ϭ 16 cm, matrix ϭ 256 ϫ 192, slice thickness ϭ 3 mm, two averages).…”

Section: Mri Evaluation Of Therapymentioning

confidence: 99%

Prediction of subtle thermal histopathological change using a novel analysis of Gd‐DTPA kinetics

Cheng

Purcell

Bilbao

et al. 2003

Magnetic Resonance Imaging

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Purpose: To investigate Gd-DTPA kinetics as predictors of histopathological changes following focused ultrasound (FUS) thermal ablation for improved planning and assessment. Materials and Methods:Twenty-nine FUS lesions were created in the thigh muscle of eight rabbits under MRguidance at 1.5 Tesla. Three rabbits were killed at four hours; and 11 lesions were analyzed with histopathology. Temperature-sensitive MRI using proton-resonant frequency-shift was used for time-dependent temperature measurements. Analysis of the uptake kinetics of Gd-DTPA was performed after Gd-DTPA injection, within 20 minutes after heating and again at two hours after heating. The resulting kinetic maps, permeability (K trans ) and leakage space (v e ), were correlated to peak temperatures, T 2 -weighted MR, and histopathology.Results: Images of K trans and v e reveal regions of histopathological change not visible on conventional posttherapy MR. At early times after heating, v e predicts the area of injury more accurately than T 2 (7 Ϯ 2% vs. 25 Ϯ 6% underestimation). A circular region of extensive structural/ vascular disruption is indicated only on K trans maps. The sharp decrease in K trans at the boundary of this region occurs at 47.5 Ϯ 0.5°C, and may be a better estimate of cell death than the conventional method of temperature threshold (55°C for coagulation) used in therapy planning. Conclusion:Our results suggest Gd-DTPA kinetics can predict different histopathological changes following FUS ablation and may be valuable for early prediction.

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“…[5] then needs to be adjusted to account for the influence of the RF-pulses on the magnetization curve (21). In order to establish the correlation between R 1 in blood and myocardium, the myocardial IR curve obtained at each value of R 1,i is fitted to the monoexponential expression given in Eq.…”

Section: Water Exchange Rate and Blood Volume Analysismentioning

confidence: 99%

Assessment of myocardial blood volume and water exchange: Theoretical considerations and in vivo results

Bjørnerud

Bjerner

Johansson

et al. 2003

Magnetic Resonance in Med

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The measured signal response in contrast-enhanced myocardial perfusion imaging has been shown to be affected by the rate of water exchange between the intravascular and extravascular compartments, the effect being particularly significant when intravascular contrast agents are used. In the present study, the T 1 relaxation rates were measured in eight pigs in blood and myocardium using a Look-Locker sequence after repeated injections of the intravascular contrast agent NC100150. The selection of myocardial region of interest was automated based on a minimum chi-square method. The intraand extravascular water exchange rates and the myocardial blood volume were calculated from the measured relaxation rates by applying a two-compartment water exchange limited model that accounts for biexponential longitudinal relaxation. Key words: cardiac imaging; T 1 quantification; iron oxide nanoparticle; water exchange dependent relaxation; myocardial water exchange; NC100150 Injection; Clariscan™The influence of water exchange between the different tissue compartments of the MR signal response following administration of a T 1 -shortening contrast agent is well known (1-7). Water exchange effects are of particular importance when the MR signal needs to be related to the contrast agent concentration in tissue, as is the case in T 1 -based contrast-enhanced perfusion imaging. The effect of water exchange on the signal response depends on the peak difference in 1/T 1 relaxation rate between the different tissue compartments relative to the rate of water exchange between the compartments. As long as the difference in 1/T 1 between the compartments in the presence of the contrast agent is significantly less than the rate of water exchange between the compartments, the measured tissue signal response is unaffected by water exchange. This condition is referred to as fast exchange. When the difference in 1/T 1 is comparable to or larger than the water exchange rate the signal response is significantly affected by water exchange and a linear relationship between 1/T 1 and contrast agent concentration can no longer be assumed (3). There is a consensus in the literature that water exchange between the intravascular and extravascular compartments is the rate-limiting factor determining maximum achievable tissue enhancement following injection of a T 1 -enhancing agent. This is because the intra-and extracellular water exchange rate is at least an order of magnitude higher than the intra-and extravascular rate (2,4,8).Contrast-enhanced myocardial perfusion imaging is possibly the one method where water exchange effects have been most comprehensively addressed (4,5,7,9,10). In a recent study, Larsson et al. (5) concluded, based on comprehensive simulations as well as clinical data, that water exchange effects do not introduce significant errors in the estimation of myocardial perfusion-related parameters when extracellular fluid (ECF) agents are used. However, when intravascular agents are used they concluded that water exchange limitation...

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Practical Implementation and Optimization of One‐shot T₁ imaging

Cited by 88 publications

References 22 publications

Quantitative magnetization transfer and myelin water imaging of the evolution of acute multiple sclerosis lesions

Quantitative magnetization transfer and myelin water imaging of the evolution of acute multiple sclerosis lesions

Prediction of subtle thermal histopathological change using a novel analysis of Gd‐DTPA kinetics

Assessment of myocardial blood volume and water exchange: Theoretical considerations and in vivo results

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Practical Implementation and Optimization of One‐shot T1 imaging

Cited by 88 publications

References 22 publications

Quantitative magnetization transfer and myelin water imaging of the evolution of acute multiple sclerosis lesions

Quantitative magnetization transfer and myelin water imaging of the evolution of acute multiple sclerosis lesions

Prediction of subtle thermal histopathological change using a novel analysis of Gd‐DTPA kinetics

Assessment of myocardial blood volume and water exchange: Theoretical considerations and in vivo results

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Practical Implementation and Optimization of One‐shot T₁ imaging