Signal formation in echo-shifted sequences

Chung, Yousun; Duerk, Jeffrey L.

doi:10.1002/(sici)1522-2594(199911)42:5<864::aid-mrm5>3.0.co;2-8

Cited by 17 publications

(31 citation statements)

References 24 publications

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“…In the small flip angle limit, this allows us to give a physical interpretation of the peaks observed in the graph of signal intensity versus precession angle increment. Also, the partition method provides an interpretation of deviations from the ideal spoiling behavior assumed previously for echoshifted sequences (12). In this sense, the present study can be considered as an extension of Ref.…”

mentioning

confidence: 63%

“…[ 12] This shows that, with a large uncompensated gradient area per TR and the detector phase set to k nϪ1 , the collected signal converges to a steady state value given by the product of 3 factors, the second one accounting for permanent off-resonance effects over the effective echo time kTR ϩ TE, and the third one being the k-th Fourier coefficient of M T,pss (). For FLASH imaging (k ϭ 0) this means that, without detector phase modulation, the MR signal converges towards a constant value given by the product of the DC component of M pss () with a factor describing T * 2 decay (T* 2 Ϫ1 ϭ T 2 Ϫ1 ϩ TЈ 2 Ϫ1 ) and dephasing over the time to echo TE.…”

Section: Existence Of a Steady-state Signal Intensity: Integration Mementioning

confidence: 99%

“…[12] and [5], it is possible to derive (see proof in Appendix C) the property that, if ␦ 0 ϭ 0, S k,ss ͑Ϫ͒ ϭ ϪS* k,ss ͑͒. [13] This result means that signal in the y channel is a symmetric function of , while the x component is antisymmetric.…”

Section: Existence Of a Steady-state Signal Intensity: Integration Mementioning

confidence: 99%

“…As a consequence, the analysis of RF spoiled gradient-echo sequences can be restricted to values in the interval [0, ], and at ϭ 0 the x component of S k,ss is zero for any value of k. Since no general analytical expression has been found for M pss (), the integral in Eq. [12] cannot be calculated explicitly for arbitrary values. If ϭ (K/P)(2), with K and P integer, the signal intensity can in principle be obtained by integrating Eq.…”

Section: Existence Of a Steady-state Signal Intensity: Integration Mementioning

confidence: 99%

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New insights into the mechanisms of signal formation in RF‐spoiled gradient echo sequences

Denolin

Azizieh

Metens

2005

Magnetic Resonance in Med

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RF spoiling is a well established method to produce T 1 -weighted images with short repetition-time gradient-echo sequences, by eliminating coherent transverse magnetization with appropriate RF phase modulation. This paper presents 2 novel approaches to describe signal formation in such sequences. Both methods rely on the formulation of RF spoiling as a linear increase of the precession angle between RF pulses, which is an alternative to the commonly used quadratic pulse phase scheme. The first technique demonstrates that a steady state signal can be obtained by integrating over all precession angles within the voxel, in spite of the lack of a genuine steadystate for separate isochromats. This clear mathematical framework allows a straightforward incorporation of off-resonance effects and detector phase settings. Moreover, it naturally introduces the need for a large net gradient area per repetition interval. In the second step, a modified partition method including RF spoiling is developed to obtain explicit expressions for all signal components. This provides a physical interpretation of the deviations from ideal spoiling behavior in FLASH and echo-

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mentioning

confidence: 63%

Section: Existence Of a Steady-state Signal Intensity: Integration Mementioning

confidence: 99%

Section: Existence Of a Steady-state Signal Intensity: Integration Mementioning

confidence: 99%

Section: Existence Of a Steady-state Signal Intensity: Integration Mementioning

confidence: 99%

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New insights into the mechanisms of signal formation in RF‐spoiled gradient echo sequences

Denolin

Azizieh

Metens

2005

Magnetic Resonance in Med

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“…Among the available methods related to MR thermometry, proton-resonance-frequency (PRF) shift mapping is the most popular, due to its linearity, sensitivity, and ability to function independent of tissue type (10,13,14). Shifts in frequency can be detected directly according to the phase of the spoiled gradient echo image as long as the contribution of stimulated echoes can be disregarded (15,16). As a result, the phase change Df is proportional to the change in temperature.…”

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confidence: 99%

Proton resonance frequency shift‐weighted imaging for monitoring MR‐guided high‐intensity focused ultrasound transmissions

Chen

Huang

Peng

et al. 2011

Magnetic Resonance Imaging

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Purpose: To combine temperature-related information of phase images and magnitude images acquired from an MR spoiled gradient echo sequence using a postprocessing method referred to as PRF-shift-weighted imaging (PRFSWI). Materials and Methods:Phase images are capable of detecting shifts in proton resonance frequency (PRF) caused by local changes in temperature. Magnitude images provide anatomical information for treatment planning and positioning as well as temperature-related contrast. We used PRFSWI to produce a phase-mask and performed multiplication on the magnitude image to increase temperature-related contrast.Results: Through MRI-guided focused ultrasound (MRIg-FUS) experiments (both ex vivo and in vivo), we determined that PRFSWI is capable of enhancing the contrast of a heated area even in the initial stages of transmitting high-intensity focused ultrasound energy. Conclusion:The PRFSWI images are sensitive to changes in temperature and display the heated spot directly in the magnitude images. Although the images do not provide quantitative data related to temperature, this method could be used as a complement to the phase temperature mapping method in the real-time monitoring of MRIgFUS experiments.

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