Dear all,
One guess would be the stimulated echos in the b=0 image that are not
properly crushed. Have you tried increasing the crusher gradients?
Good luck!
Fer
---------------
> Mark,
>
> John Thornton at the NHNN emailed the EPIC mailing list
> about this. There was no solution to it (only a comment from Roddy
> McColl, see below), but you may like to get in touch with JT
> ([log in to unmask])...
>
> Cheers,
>
> Phil
> **********************************************************************
> Phil Boulby, Ph.D - MRI Physicist
>
> MRI Unit Tel: +44 (0)1494 874646
> National Society for Epilepsy Fax: +44 (0)1494 875666
> Chalfont Center for Epilepsy
> Chalfont St. Peter Email:[log in to unmask]
> Gerrards Cross http://www.epilepsynse.org.uk/
> Buckinghamshire http://www.erg.ion.ucl.ac.uk/
> SL9 0RJ, UK http://www.nmr.ion.ucl.ac.uk/
> **********************************************************************
>
> ----------------************************----------------
>
>>Dear EPIC mailing list,
>>
>>We have recently upgraded our operating system to 9.1.
>>
>>We now have serious problems with our diffusion-weighted imaging: ADC
>>values appear 20% too high in brain, and there appear to be diffusion
>>hypo-intense areas on some ADC maps. Similar errors are seen in phantom
>>data.
>>
>>The issue appears to be related to the "dual echo" option in the
>> diffusion
>>psd. I am wondering if this is specific to our system (short term eddy
>>currents ?) or more general.
>>
>>Does anyone else have experience of this problem, either at 9.1 or 9.0 ?
>>
>>Many thanks,
>>
>>
>>John Thornton
>>
>>Clinical Scientist (Magnetic Resonance Physics)
>>Lysholm Department of Neuroradiology,
>>National Hospital for Neurology and Neurosurgery,
>>Queen Square, London, UK
>>
> --
> epic Mailing list - Message sent by Roddy McColl
> <[log in to unmask]>
> --
> We are also running 9.1 on a NV/i system. I have been running DTI scans on
> 8.3
> and 9.1 software and didn't notice a (big) difference but I ran a phantom
> today
> in case there was an effect caused by the dual echo. Note: if you can put
> your
> scanner in RESEARCH MODE you can turn off the dual echo mode and check for
> differences. I ran a few scans using the phantom that GE supplies with its
> NVARRAY coil (copper sulphate-doped distilled water), and didn't find any
> large
> differences with or without the dual echo:
>
> B=1000 FOV=24 128x128 4mm thick/ 4mm gap, NEX=4, 3 T2 images
>
> NDrns Single Echo Mean D (S.D) Dual Echo Mean D (S.D.)
> ----------------------------------------------------------------
> 6 200 (31) 199 (5)
> 15 201 (14) 197 (5)
> 25 201 (13) 198 (4)
>
> TE for Single-Echo was 71.7, and for Dual-Echo was 79.3. TR=3000.
>
> (You may expect MD to be more in the region of 2000 than 200, I use x10-5
> rather
> than x10-6).
>
> Looks like on our scanner there is no difference between SE and DE.
>
> -roddy
>
> Roddy McColl
> UT Southwestern
>
> ----------------************************----------------
>>
>> Hi Folks,
>> This is a question for those of you who have a GE Signa.
>> We are currently assessing the dual spin-echo acquisition on our
>> system (9.1M4), which is supposed to reduce eddy current artefacts,
>> but find that the <D> values are radically inaccurate compared with
>> results from our standard acquisition. I seem to remember reading
>> something about this on the EPIC users group e-mail list, but cannot
>> recall what the answer was. Do any of you use this option, and if
>> so what have been your experiences?
>>
>> Of course it could just be that there is a bug in GE's software that
>> means it doesn't work as it should. It's happened before ...
>>
>> Cheers,
>>
>> Mark
>>
>> Dr. Mark E. Bastin
>> Medical and Radiological Sciences (Medical Physics)
>> University of Edinburgh
>> Western General Hospital
>> Crewe Road
>> Edinburgh, EH4 2XU
>> UK.
>>
>> TEL: ++44 (0)131 537 2511
>> FAX: ++44 (0)131 537 1026
>>
>
|
