[Mristudio-users] Acquisition with slightly overlapping slice (i.e. negative gap between slices)

[Seongjin]

Dr. Mori

Thanks for the reply.

-SC

On Sat, May 22, 2010 at 4:07 PM, susumu mori <susumu at mri.jhu.edu> wrote:

> Typically, the overlapping slice excitation (or even no-gap) leads to
> leakage of excitation to the adjacent slices and causes signal loss. So you
> pay a penalty of SNR.
>
> Usually, within one TR, which is typically around 6-8 seconds, even number
> slices are excited consecutively and then odd number slices. So, it take
> about 3-4 seconds before an adjacent slice is excited.
>
> Suppose you hit slice #1. If you have an overlap, you excite a part of
> slice #2. About 3-4 seconds later, you excite slice #2 but the spins of
> slice #2 has not been fully recovered and thus you loose signal.
>
> In your case, because it is just 1.5% overlap, you may not see much impact.
> Note that the slice excitation profile is not a step function, but has much
> broader shoulder. So, this SNR penalty by excitation leakage is always there
> even with gap = 0.
>
> When you reconstruct 3D volume, you have to make the slice thickness 0.03mm
> thinner (1.97mm).
>
> If you make sure that the scans are under steady-state (enough prescans), I
> think you don't have to worry about the effect on DTI calculation, except
> for SNR.
>
> On Thu, May 20, 2010 at 11:21 AM, [Seongjin] <choisj70 at gmail.com> wrote:
>
>> This might be a stupid question.
>> However, I would like ask your opinions in the community.
>> Is there anyone tried DTI acquisition with a bit of overlapping adjacent
>> slices (i.e. negative gap between slices: e.g. 2 mm slice thickness with
>> -0.03 gap).
>> What would be consequence of this acquisition and adverse influence on the
>> DTI metrics?
>>
>> -SC
>>
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