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1.
Figure 5

Figure 5. From: Self-Refocused Adiabatic Pulse for Spin Echo Imaging at 7T.

RF, phase and gradient waveforms for the pulse sequence which utilizes the self-refocused adiabatic pulse to produce a spin echo.

Priti Balchandani, et al. Magn Reson Med. ;67(4):1077-1085.
2.
Figure 4

Figure 4. From: Self-Refocused Adiabatic Pulse for Spin Echo Imaging at 7T.

Simulated values of the magnitude of the magnetization produced by a 16 ms SRA pulse with TE=12 ms for a range of B1 amplitudes.

Priti Balchandani, et al. Magn Reson Med. ;67(4):1077-1085.
3.
Figure 2

Figure 2. From: Self-Refocused Adiabatic Pulse for Spin Echo Imaging at 7T.

(A) Amplitude and (B) phase waveforms for the self-refocused adiabatic 90°-180° pulse. The effective TE for the pulse is 12 ms.

Priti Balchandani, et al. Magn Reson Med. ;67(4):1077-1085.
4.
Figure 1

Figure 1. From: Self-Refocused Adiabatic Pulse for Spin Echo Imaging at 7T.

Amplitude and phase waveforms for the matched-phase 90° pulse (A,B) corresponding to the adiabatic SLR 180° pulse(C,D). Nonlinear phase across the spectral profile is refocused by the 90°-180° pulse pair.

Priti Balchandani, et al. Magn Reson Med. ;67(4):1077-1085.
5.
Figure 7

Figure 7. From: Self-Refocused Adiabatic Pulse for Spin Echo Imaging at 7T.

In vivo axial brain images from a normal volunteer obtained using a standard birdcage head coil at 3T. Image obtained using (A) a conventional SE sequence and (B) the SRA pulse sequence. Acquisition parameters for both sequences were: TE/TR=16.5/200 ms, slice thickness=4 mm and matrix size=256×256, nex=3, FOV=22×22 cm and scan time=2:38 min. Some differences in contrast between tissue types, particularly fluids, exist between the two spin echo acquisitions.

Priti Balchandani, et al. Magn Reson Med. ;67(4):1077-1085.
6.
Figure 3

Figure 3. From: Self-Refocused Adiabatic Pulse for Spin Echo Imaging at 7T.

Simulated (A) magnitude and (B) phase of the spectral profile of the SRA pulse for B1 values at and above the adiabatic threshold by 20% and 30%. The profiles in (A) and (B) are obtained by taking the difference of two acquisitions produced by SRA pulses with a 180° difference in echo phase in order to remove unrefocused components of the magnetization. The magnitude of the associated matched-phase 90° pulse driven to the same B1 values is shown in (C). Except for some high-frequency distortions in the passband for the SRA profiles in (A), profile behavior for the SRA pulse is similar to that for the matched-phase 90° pulse. Magnitude, real and imaginary components of the spectral profile of the spin echo produced by a single SRA pulse with amplitude set to the adiabatic threshold is shown in (D). Due to the absense of crushers, the single acquisition scheme results in some unrefocused components within the transition bands which mostly integrate to zero. For adiabatic 180° pulses, a single acquisition is su cient to produce a reasonably selective spectral profile.

Priti Balchandani, et al. Magn Reson Med. ;67(4):1077-1085.
7.
Figure 6

Figure 6. From: Self-Refocused Adiabatic Pulse for Spin Echo Imaging at 7T.

Image of a slice through a spherical agar phantom obtained at 7T using (A) a standard SE sequence and (B) the SRA pulse sequence shown in . The SE and SRA images after compensation by the receive B1 profile are shown in (C) and (D), respectively. The compensated images in (C) and (D), after division by the sine of the transmit B1 profile of the 90° pulse, are shown in (E) and (F). Vertical cross sections through (E) and (F) are plotted in (I) to show the difference in refocusing e ciency between the two different sequences. Scan parameters for both sequences were: TE/TR: 12/400ms, 256×256 grid, 5 mm slice, 20×20cm FOV. The SRA pulse achieves a more uniform transmit profile when compared to the conventional SE sequence due to the B1 insensitivity of the adiabatic 180° pulse. (G) and (H) Show the measured transmit B1 profile and calculated receive sensitivity profile for the same slice.

Priti Balchandani, et al. Magn Reson Med. ;67(4):1077-1085.
8.
Figure 8

Figure 8. From: Self-Refocused Adiabatic Pulse for Spin Echo Imaging at 7T.

In vivo axial brain images from a normal volunteer obtained using a quadrature head coil at 7T. Image obtained using (A) a conventional SE sequence and (B) the SRA pulse sequence. Acquisition parameters for both sequences were: TE/TR=13.5/300 ms, slice thickness=5 mm and matrix size=256×256, nex=2, FOV=24×24 cm and scan time=2:38 min. A transmit B1 map of the same slice obtained using a BS B1 mapping sequence is shown in (E). The calculated receive sensitivity map is shown in (F). (C) and (D) show the original images in (A) and (B) after compensation by the receive map. The SLR 180° pulse in the conventional spin echo sequence becomes overdriven at the center of the brain and underdriven at the edges of the brain where transmit B1 is at its highest and lowest value, respectively. This results in signal loss and contrast differences. Horizontal cross sections indicated by the dashed lines on (E) and (F) are plotted in (G). Comparatively, the adiabatic SLR pulse achieves greater transmit B1 uniformity, particularly at the center of the brain.

Priti Balchandani, et al. Magn Reson Med. ;67(4):1077-1085.

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