Siemens MULTI-ECHO EPI 4A21 Скачать руководство пользователя страница 7

Multi-Echo EPI 

Page 7 of 9 

Numaris/4 VA21B 

3  Sequences and Protocols 

 

3.1 General Remarks 

 
Since the sequence is derived from the standard EPI sequence, most of the user 
interface and features are identical to this method. Due to the large number of images 
created in a short time, the images are saved to the database in the mosaic format. 
One mosaic-image contains all slices of one echo time for one repetition. Repetitions 
can be saved in multiple series if desired (Contrast card or BOLD card). 
Prior to the first run of the sequence, the 3D standard shim procedure is performed to 
ensure best field homogeneity. As with standard EPI this option cannot be disabled. 
Due to the high switching rates used in EPI imaging, the peripheral nerve stimulation 
monitor will sometimes not allow the measurement to be performed with the 
parameters selected. In general, a lower bandwidth will decrease the stimulation and 
a different selection of the readout gradient may also help (read direction along L/R-
axis shows generally the lowest stimulation). 
 
 

3.2 New Parameters 

 

 

 

Number of echoes

: The number of echo-images per excitation can be set on the 

sequence card (part1) as the parameter contrasts. The number of echo-images can 
be selected between 1 and 8. The number of TE-times is changes accordingly. 
Please note that only the first echo time can be changed by the user. All other echo 
times are set to the minimum value according to the remaining selected parameters. 
!!Attention!!: Even echo time 1 is adjusted to longer times without warning if required 
by another parameter! It is not set back to minimum if the parameter is changed back! 
Please check echo time 1 after changing other timing relevant parameters of the 
sequence. 
 

 

Содержание MULTI-ECHO EPI 4A21

Страница 1: ...etom under VA21B Installation and User s Guide NUMARIS 4A21 April 4th 2003 Section of Medical Physics University Hospital Freiburg Germany Contact Oliver Speck PhD Hugstetterstr 55 D 79106 Freiburg email oliver speck uniklinik freiburg de phone 49 761 2703832 ...

Страница 2: ...ciple of Multi Echo EPI 3 1 2 Image contrast of Multi Echo EPI 4 1 3 Processing options 4 1 4 References 4 2 Software Installation Procedure 5 2 1 Installation 5 3 Sequences and Protocols 7 3 1 General Remarks 7 3 2 New Parameters 7 3 3 Remarks on reconstruction performance 9 3 4 Protocols 9 ...

Страница 3: ...se gradient is rewound to the original starting position after each echo image to ensure identical k space trajectories for all echo images 2 GP RF GS GR echo image loop n Figure 1 Basic timing of the Multi Echo EPI sequence The shaded gradient in phase encoding direction ensures identical k space trajectories for all echo images The resulting echo images have different increasing echo times and t...

Страница 4: ...ifferent echo times 3 Please see the processing options described below Figure 2 Head images acquired on Magnetom TRIO with the Multi Echo EPI sequence with 4 different echo times in a single shot 1 3 Processing options Several processing options are given in the method The different echo images are always saved separately as the original images and optionally parametric maps can be calculated in ...

Страница 5: ...mepi2d_VA21 m750 n4 ppc750 prod bin Attention This is only correct for systems with Reco PC and m750 MPCU Otherwise copy the relevant MPCU file to the corresponding directory Software does not run on Alpha reconstruction machines CoilSelectManipulator h ist ein noch fehlendes File in C idea n4 comp Measurement CCSpuSer CoilInterface Copy the EVA program dll files to the customer EVA directory copy...

Страница 6: ...Multi Echo EPI Page 6 of 9 Numaris 4 VA21B ...

Страница 7: ...tor will sometimes not allow the measurement to be performed with the parameters selected In general a lower bandwidth will decrease the stimulation and a different selection of the readout gradient may also help read direction along L R axis shows generally the lowest stimulation 3 2 New Parameters Number of echoes The number of echo images per excitation can be set on the sequence card part1 as ...

Страница 8: ... set to 334ms to avoid very large signal intensity differences in case of fitting errors and allow a T2 resolution of 0 1ms without overflows Therefore T2 maps of phantoms with very long T2 and good homogeneity may be calculated falsely The T2 fit is only performed when Mosaic images are created for more than 1 slice Motion Correction Similar to the motion correction in the a_ep2d_mosaic sequence ...

Страница 9: ...re long reconstruction times after the scan are possible The scan is not aborted However no new scan can be started during reconstruction Do not move the patient table to the home position during reconstruction otherwise the reconstruction will stop and data is lost The number of images that can be processed online depends on the reconstruction hardware Up to 20 slices with 4 echoes and a TR of 3s...

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