Dear Diederick, others:
A paper from last year by Schmitter et al. introduced a new sequence
which significantly reduces the amount of acoustic noise through a
combination of modifications (several of which have been mentioned in
this discussion):
Schmitter S, Diesch E, Amann M, Kroll A, Moayer M, Schad LR (2008)
Silent echo-planar imaging for auditory FMRI. Magnetic Resonance
Materials in Physics, Biology and Medicine 21, 317-325.
http://dx.doi.org/10.1007/s10334-008-0132-4
In our experience this sequence is noticeably quieter than our
standard EPI sequence, and in a speech task resulted in significantly
greater acoustic-related activity in primary auditory regions.
However, as you would expect due to the use of a longer TE, there is
greater signal dropout in regions typically associated with
susceptibility effects.
One other comment: reducing scanner noise using headphones/earplugs
can only do so much, as there is a considerable amount of sound
transmitted via bone conduction, which any hearing protection won't be
able to reduce.
That being said, I suspect in terms of people falling asleep, as long
as the sound is continuous you won't have any problems...at least,
given how hard it is to get subjects NOT to fall asleep sometimes,
even with standard sequences! ;-)
Hope this helps,
Jonathan
On Mon, Dec 21, 2009 at 9:03 AM, Torben Ellegaard Lund
<[log in to unmask]> wrote:
> Dear Diederick,
>
>
> In Figure 2 of Foerster et al. 2005 there is actually a plot of vibration
> amplitude as a function of EPI-readout bandwidth. As you can se there can be
> a 12 dB difference in vibrational amplitude between loud and quiet EPI
> protocols. The plot is for a Sonata gradient coil on a 4T varian system, so
> you should make your own investigations specific to the GE and Philips.
>
> Best
> Torben
>
>
>
>
> Foerster et al. Magnetic field shift due to mechanical vibration in
> functional magnetic resonance imaging. Magnetic resonance in medicine :
> official journal of the Society of Magnetic Resonance in Medicine / Society
> of Magnetic Resonance in Medicine (2005) vol. 54 (5) pp. 1261-7
> http://dx.doi.org/10.1002/mrm.20695
>
>
>
>
> Den 20/12/2009 kl. 22.41 skrev David Carmichael:
>
>> Dear Diederick,
>>
>> I remember previously that running with sinusoidal rather than trapezoidal
>> wave forms for the EPI readout can be benificial it can reduce the noise
>> level and make it narrower in frequency so then changing the echospacing can
>> be used to find the gradients vibrational minimum for your particular
>> systems in addition to the steps below.
>>
>> Best regards
>> David Carmichael
>>
>> ps hi helmut!!
>>
>>
>> Quoting Helmut Laufs <[log in to unmask]>:
>>
>>>
>>> Dear Diederick,
>>>
>>> According to our experience, the actual dB are not as relevant as e.g. a
>>> really contiuous and hence monotonous sound (i.e. inter-slice and
>>> inter-volume gap should be identical), proper sound protection and bedding
>>> of the patient, time of day and anxiety level of the subject.
>>>
>>> Hope this helps,
>>>
>>> Bw,
>>>
>>> Helmut
>>>
>>> -------------
>>>
>>>
>>> Hi all,
>>> A question not relating to software, but perhaps someone would be wiling
>>> to help us out.
>>> We
>>> are trying to heave subjects fall asleep during fMRI acq, we would like
>>> to have a more "silent" EPI sequence. There are quite some publications
>>> from groups that have a relatively silent EPI sequence running on a
>>> Siemens machine. We have a 3T GE Signa HD and a 3T Philips Intera
>>> available. We have been playing around with the factory provided silent
>>> mode options on both, but are not particularly happy with the results
>>> (high TR/TE/slice thickness, not much noise reduction). Does anyone
>>> have a reasonably performing "silent" EPI on a GE or Philips system
>>> running? Can anyone recommend what settings to use?
>>> Thanks,
>>> Diederick
>>>
>>>
|