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

[susumu mori]

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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