Data sampling in MR relaxation

Labadie, Christian; Gounot, Daniel; Mauss, Y.; Dumitresco, B.

doi:10.1007/bf01705278

Cited by 8 publications

(5 citation statements)

References 8 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The saturation effect of linear Look‐Locker sampling was reduced by using geometrically sampled TIs and slice‐selective excitations with low flip angle of 5°, which generates a time series approaching that of the true IR at the cost of a low signal‐to‐noise ratio (SNR) . Following magnetization inversion with a nonselective hyperbolic‐secant adiabatic pulse, a train of 2‐ms sinc excitation pulses were applied at n geometrically increasing TIs :

T I_{k = 1.. n} = T I_{1} + a (1 - r^{k - 1}) / (1 - r),

where a is the nominal initial spacing, ( TI 2 – TI 1 ), and r the nominal common ratio, ( TI 3 – TI 2 ) /a . Accommodation of the readout bandwidth limits a strict geometric sampling at early TIs , and the geometric sampling is reported with the values of TI 1 , TI 2 , TI n /2 , and TI n used during measurements.…”

Section: Methodsmentioning

confidence: 99%

Myelin water mapping by spatially regularized longitudinal relaxographic imaging at high magnetic fields

Labadie

Lee

Rooney

et al. 2013

Magnetic Resonance in Med

Self Cite

116

154

View full text Add to dashboard Cite

show abstract

T I_{k = 1.. n} = T I_{1} + a (1 - r^{k - 1}) / (1 - r),

Section: Methodsmentioning

confidence: 99%

Myelin water mapping by spatially regularized longitudinal relaxographic imaging at high magnetic fields

Labadie

Lee

Rooney

et al. 2013

Magnetic Resonance in Med

Self Cite

116

154

View full text Add to dashboard Cite

show abstract

“…Using a non-linear pulse interval can be considered, in order to reduce the number of pulses and heat deposition required for such analyses. 22 Applied to 'H spectroscopy, the method allows precise measurements of transverse relaxation times, almost free of diffusion or perfusion effects. Long T, values such as those encountered in an oedematous area, can therefore be assessed, which simply is not possible with imaging techniques which use field gradients.…”

Section: Discussionmentioning

confidence: 99%

Localized T₂ measurements using an OSIRIS–CPMG method. Application to measurements of blood oxygenation and transverse relaxation free of diffusion effect

et al. 1994

View full text Add to dashboard Cite

This work presents a new method allowing localized T2 measurements, based upon the OSIRIS scheme. A train of 180 degrees pulses is applied after the OSIRIS preparation cycle, recording directly the transverse magnetization decay. The method was verified for two nuclei, 1H and 19F, with phantoms and in vivo on rats. The accuracy of the T2 values is discussed, as well as possible applications of the OSIRIS-CPMG method to proton transverse spin relaxation measurements, free of diffusion effects, and to non-invasive in vivo blood oxygenation measurements, through the use of an emulsion of perfluorooctylbromide, a blood substitute containing fluorine.

show abstract

“…The minimum TI for measurements was always 50 ms and the maximum TI was TR – 100 ms (Signa data) or TR – 175 ms (Vision data) (18). The remaining TI times were chosen with linear, quadratic (3), or geometric (7) spacing between these extremes (Table 1), with values as described for the PAIR technique (20), or with values determined by numerical optimization of Eq. [3] (see below).…”

Section: Methodsmentioning

confidence: 99%

“…The optimization of T 1 relaxation measurements is a long‐standing problem and numerous articles have addressed the subject (1–11). For a given application, the optimization of T 1 measurement depends on a number of factors, including the range of T 1 times of interest, the measurement technique used to estimate the relaxation time, and the acquisition time available for the measurements.…”

mentioning

confidence: 99%

Optimized precision of inversion‐recovery T₁ measurements for constrained scan time

Ogg

Kingsley

2004

Magnetic Resonance in Med

View full text Add to dashboard Cite

The optimization of T 1 relaxation measurements is a longstanding problem and numerous articles have addressed the subject (1-11). For a given application, the optimization of T 1 measurement depends on a number of factors, including the range of T 1 times of interest, the measurement technique used to estimate the relaxation time, and the acquisition time available for the measurements. Most work on T 1 optimization to date has focused on the efficiency of T 1 estimation (precision per unit time), trading off the number and distribution of inversion times against the number of acquisitions (signal averaging) to maximize the efficiency without consideration of explicit limits on the total length of the experiment (1-4,12). In this article we investigate optimization of the precision of brain T 1 measurements when time constraints preclude optimal efficiency of T 1 estimation. In particular, we are interested in the choice of the number of TI times and their values to optimize the precision of T 1 measurements in the human brain in a fixed acquisition time that limits two important parameters of T 1 measurement. First, the number of acquisitions is fixed and the number of inversion times must be traded off with the range of inversion times that can be sampled. Second, the total acquisition time is limited such that all TI Յ 3 ϫ T 1 max. For this application, the range of T 1 times is moderate (500 -1500 ms in healthy brain, 300 -2000 in pathology) (13). We consider modified fast inversion-recovery (MFIR) (14) with segmented k-space acquisition in the MFIR pulse sequence (15,16) and nonlinear least-squares curve-fitting to estimate T 1 (17). MATERIALS AND METHODS NumericalCurve-fitting to estimate T 1 from the inversion-recovery images was based on the Levenburg-Marquardt method (17). With the MFIR method, the repetition time (TR) is constant for all TI times and the total measurement time is proportional to the product of TR and the number of TI times, N. The 3-parameter signal model for the MFIR experiment is given by Eq. [1] (14,16,18):

show abstract

Data sampling in MR relaxation

Cited by 8 publications

References 8 publications

Myelin water mapping by spatially regularized longitudinal relaxographic imaging at high magnetic fields

Myelin water mapping by spatially regularized longitudinal relaxographic imaging at high magnetic fields

Localized T₂ measurements using an OSIRIS–CPMG method. Application to measurements of blood oxygenation and transverse relaxation free of diffusion effect

Optimized precision of inversion‐recovery T₁ measurements for constrained scan time

Contact Info

Product

Resources

About

Data sampling in MR relaxation

Cited by 8 publications

References 8 publications

Myelin water mapping by spatially regularized longitudinal relaxographic imaging at high magnetic fields

Myelin water mapping by spatially regularized longitudinal relaxographic imaging at high magnetic fields

Localized T2 measurements using an OSIRIS–CPMG method. Application to measurements of blood oxygenation and transverse relaxation free of diffusion effect

Optimized precision of inversion‐recovery T1 measurements for constrained scan time

Contact Info

Product

Resources

About

Localized T₂ measurements using an OSIRIS–CPMG method. Application to measurements of blood oxygenation and transverse relaxation free of diffusion effect

Optimized precision of inversion‐recovery T₁ measurements for constrained scan time