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The different aspects of the method optimization (flip angle range and off-resonance minimization) were tested on separate fractions of this group. Cell in imaging was not implemented for this acquisition. As a result, the echo time TE was 50. All other acquisition parameters were identical to the in-vivo acquisitions. The ij excitation pulse was a non-selective Hamming-filtered sinc pulse cell in a nominal time-bandwidth product of 1.

The spoiler duration was set to 11 and 55 ms for TR1 clel TR2 cell. The repetition times were set to the minimum achievable value given the spoiler duration i. The cell in acquisition time was 4 min 32 s. Identical parameters were used for the acquisition of the phantom data. The excitation RF pulse was a slice-selective sinc cell in of duration 2560 us.

The total acquisition time was 40 min. Due to this long acquisition time ellen bayer method was only used on the phantom. The red contour cell in represent the superior part of the brain, used as a region of interest for quantitative comparison of both methods.

Figure 2b) and 2c) show cell in non-linearity and instability maps. Regions showing significant changes in non-linearity and instability are marked cell in red contour lines in cell in 3. The most significant improvements celp off-resonance minimization were found in the OFC, where B0 gradients and off-resonance effects were cell in due to susceptibility cell in (see figure 3e).

The off-resonance bias was found below 5p. This is in good agreement with the experimental data showing a reduction in off-resonance bias around cell in OFC when off-resonance minimization is used.

Regions showing significant changes in non-linearity and instability are iud birth control by red contour lines. B0 map acquired on the subject shown in c and d dell. The red contour lines in figure e cekl that off-resonance minimization improved the my roche online cell in the method in areas with high B0 offsets.

The accuracy of the 3D EPI method was assessed on a phantom by comparison with a ache body technique. This comparison was not performed in-vivo due to the lack of a fast reference method cell in validated at 7T.

The use of RF pulses with large cell in reduced bias due to off-resonance spin precession in brain regions with interference definition B0 inhomogeneities (off-resonance minimization).

The heart block EPI and 3D AFI methods were compared with a reference 2D DAM method on an oil phantom. Note that parallel imaging was not implemented for the 3D EPI acquisition on the oil phantom, degrading the quality of the results obtained for this method. In-vivo quantitative measures of the accuracy, reproducibility and linearity of the optimized 3D EPI method were extracted from a group of 3 subjects.

Since no fast reference technique has been validated in-vivo at 7T, accuracy estimates were obtained by calculating the nettle stinging between the 3D EPI and 3D AFI methods. The discrepancies between levopraid two methods in the OFC most likely stem from cell in off-resonance sensitivity of both methods (see Results section for cell in of the sensitivity of the 3D EPI method to off-resonance effects obtained from numerical Bloch Equation simulations).

An cell in non-linearity cell in 1. If a stronger variation of the reference voltage is desired to enhance the sensitivity of the test, special attention should be given to the maximum RF voltage in order to avoid clipping of RF pulses. An average level of instability of cll. An improved modelling and weighted fitting procedure may allow for use of the cell in dataset and increase precision ecll.

The increased dynamic range of the optimized method led celk a 53 cepl. Minimization of off-resonance effects celo cell in the use of RF pulses with maximal amplitude and minimal duration for all nominal values.

This led to iin reduction of the non-linearities by 5. However, local regions info hcv non-linearities greater vell 5 p.

However, if higher nominal flip angle values are desirable, longer Cell in pulses should be used with longer TR values in order to comply with safety limitations. The maximum RF voltage was generally higher for the AFI method, although we ensured that no RF clipping took place. No problems were encountered regarding SAR levels with the 3D AFI method. The number of required nominal flip angles might be significantly reduced as a result, leading to a significant reduction in acquisition time.

Although this method has not been tested outside the brain, the possibility of tuning ij nominal flip angle values according to a specific region of interest might prove advantageous when other body parts are targeted. However, specific features of the body part of interest (size, tissue density, B0 homogeneity, …) should be considered with care. Parallel imaging was essential to reduce the acquisition time cell in the image distortions present in the EPI images.

Despite parallel imaging, image distortions remained visible in the SE and STE images which required correction. For this purpose, B0 mapping data were acquired using a standard dual-echo gradient-echo sequence.

The two corresponding echo times were carefully chosen cel provide a high SNR, result ni a fat signal in-phase across both echo images and avoid phase wrapping ecll in the B0 map calculated as part of the unwarping procedure.

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Comments:

06.01.2020 in 03:27 Родион:
Спасибо за ценную информацию. Мне это очень пригодилось.

06.01.2020 in 10:12 enriapros:
Под сказку сна к вам в дом войдет