Portable Brain Scanner Technology for Use in Emergency Medicine

Wald, Lawrence L.; Cooley, Clarissa Zimmerman

doi:10.1002/9783527827244.ch3

Cited by 1 publication

(4 citation statements)

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“…Although it is not practically feasible with clinical MRI systems because of the limitations on SAR and/or the RF amplifier's capability, the optimal flip angle without the SAR constraint (i.e., λ = 0) was also computed (Table 2). The optimal flip angle required more than 150 for the two RF pulses right before the data acquisition/missing RF pulse timing, regardless of N MP (3)(4)(5)(6). The optimal RF pulse phase was even (Equation 5), but with an odd number of N MP (= 3, 5), the same performance can be achieved with odd RF phase (Equation 6) by changing the flip angles of the even-numbered RF pulses from α n to 360 Àα n (n = 2, 4).…”

Section: Optimization Of Rf Flip Angle and Phase In Mp-ssfpmentioning

confidence: 99%

“…Considerable research efforts have been devoted to the development of such compact MRI systems. [1][2][3] However, because standard pulse sequences used in standard clinical MRI systems are designed to work with highly homogeneous magnetic fields, most pulse sequences reach the limits of their functionality in the inhomogeneous field MRI systems. Therefore, dedicated imaging techniques are required for MRI with inhomogeneous magnetic fields.…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, dedicated imaging techniques are required for MRI with inhomogeneous magnetic fields. [1][2][3][4][5][6] Steady-state free precession (SSFP) is a widely used MRI technique in clinical diagnosis and research. [7][8][9][10][11][12] SSFP-based pulse sequences generate a steady state by repeatedly applying excitation radiofrequency (RF) pulses with a constant interval.…”

Section: Introductionmentioning

confidence: 99%

“…Mitigating the magnetic field homogeneity requirement may allow the construction of compact and lightweight MRI systems. Considerable research efforts have been devoted to the development of such compact MRI systems 1–3 . However, because standard pulse sequences used in standard clinical MRI systems are designed to work with highly homogeneous magnetic fields, most pulse sequences reach the limits of their functionality in the inhomogeneous field MRI systems.…”

Section: Introductionmentioning

confidence: 99%

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Optimization of flip angle and radiofrequency pulse phase to maximize steady‐state magnetization in three‐dimensional missing pulse steady‐state free precession

Kobayashi

2024

NMR in Biomedicine

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Missing pulse (MP) steady‐state free precession (SSFP) is a magnetic resonance imaging (MRI) pulse sequence that is highly tolerant to the magnetic field inhomogeneity. In this study, optimal flip angle and radiofrequency (RF) phase scheduling in three‐dimensional (3D) MP‐SSFP is introduced to maximize the steady‐state magnetization while keeping broadband excitation to cover widely distributed frequencies generated by inhomogeneous magnetic fields. Numerical optimization based on extended phase graph (EPG) simulation was performed to maximize the MP‐SSFP steady‐state magnetization. To limit the specific absorption rate (SAR) associated with the broadband excitation in 3D MP‐SSFP, SAR constraint was introduced in the numerical optimization. Optimized flip angle and RF phase settings were experimentally tested by introducing a linear inhomogeneous magnetic field in a range of 10–20 mT/m and using a phantom with known T1/T2 relaxation and diffusion parameters at 3 T. The experimental results were validated through comparisons with EPG simulation. Image contrasts and molecular diffusion effects were investigated in in vivo human brain imaging with 3D MP‐SSFP with the optimal flip angle and RF phase settings. In the phantom measurements, the optimal flip angle and RF phase settings improved the MP‐SSFP steady‐state magnetization/signal‐to‐noise ratio by up to 41% under the fixed SAR conditions, which matched well with EPG simulation results. In vivo brain imaging with the optimal RF pulse settings provided T2‐like image contrasts. Diffusion effects were relatively minor with the linear inhomogeneous field of 10–20 mT/m for white and gray matter, but cerebrospinal fluid showed conspicuous signal intensity attenuation as the linear inhomogeneous field increased. Numerical optimization achieved significant improvement in the steady‐state magnetization in MP‐SSFP compared with the RF pulse settings used in previous studies. The proposed flip angle and RF phase optimization is promising to improve 3D MP‐SSFP image quality for MRI in inhomogeneous magnetic fields.

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Section: Optimization Of Rf Flip Angle and Phase In Mp-ssfpmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%