<p>I will focus on question #1:</p>

<p>Analysis of MRI scans is typically done using <strong>voxels</strong> (Fig. 1). Voxels have a volume defined by three dimensions (length, width and depth).</p>

<p><img src="https://i.sstatic.net/xbRwv.jpg" alt="voxel"><br>
<sup>Voxel analysis. Source: <a href="https://www.google.com.au/url?sa=t&amp;rct=j&amp;q=&amp;esrc=s&amp;source=web&amp;cd=4&amp;cad=rja&amp;uact=8&amp;ved=0CDUQFjAD&amp;url=http%3A%2F%2Fincenter.medical.philips.com%2Fdoclib%2Fgetdoc.aspx%3Ffunc%3Dll%26objid%3D5529294%26objaction%3Dopen&amp;ei=xR5XVf-MCojp8gWF4oPwAg&amp;usg=AFQjCNHEL418AlYm9zC7BEnj2n-BJr-5Cw&amp;sig2=MyJ5dI2-HpEsb8HsJzalVw" rel="nofollow noreferrer">Philips</a></sup></p>

<p>The slice thickness plus the 2D in-plane resolution (pixel size) yields the voxel size. The time to scan a slice can be regarded to be negligible. Making a scan consisting of multiple slices takes time. Hence, the time dimension is not directly relevant for voxel size. Practically, voxel size depends mostly on slice size, as well as the capacity of the scanner. More Tesla's makes smaller voxels possible.   </p>

CC BY-SA 3.0
2015-05-16T11:26:52.503Z
Thank you for the explanation. So a voxel is a 3D pixel and a whole fMRI volume consists of voxels + time which makes it 4D. But does your answer imply that a slice is also 3D because a slice consists of voxels or is it indeed 4D with considering time?
machinery
CC BY-SA 3.0
2015-05-16T11:28:30.777Z
A slice can be considered to be made at once. Multiple slices takes time. in the end making one slice also takes time, but negligibly so. i have adapted my answer
AliceD
CC BY-SA 3.0
2015-05-16T11:41:48.307Z
I mean the time in a timeseries, i.e. imaging different volumes in sequences. Nevertheless, a slice is in 3D, right?
machinery
CC BY-SA 3.0
2015-05-16T11:42:39.877Z
Yes, slice is 3D
AliceD
CC BY-SA 3.0
2015-05-16T10:55:02.360Z
2015-05-16T11:30:33.107Z
2015-05-16T11:30:33.107Z
AliceD
<p>Is a slice obtained with functional MRI (fMRI) always 3-dimensional, i.e., x-y-z? I thought that a typical fMRI scan's total imaged volume would be 4D, i.e., made up of 3D slices plus time.</p>

CC BY-SA 3.0
2015-05-16T10:38:44.073Z
The sub-question 2 has just been answered on Bio.SE (http://biology.stackexchange.com/questions/34269/oxygenated-hemoglobin-in-mri - coincidence or what!) and I think it should not be cross-posted here. Could you perhaps elaborate more on subquestion #1 (i.e., remove subquestion 2 and focus on #1?)?
AliceD
<neuroimaging><fmri>
Slices and aquisition of fMRI
machinery
# Slices and aquisition of fMRI

(Asked by: username_0 on 2015-05-16)

Is a slice obtained with functional MRI (fMRI) always 3-dimensional, i.e., x-y-z? I thought that a typical fMRI scan's total imaged volume would be 4D, i.e., made up of 3D slices plus time.

**Tags:** neuroimaging, fmri

> **Comments:**
> **username_1**: The sub-question 2 has just been answered on Bio.SE (http://biology.stackexchange.com/questions/34269/oxygenated-hemoglobin-in-mri - coincidence or what!) and I think it should not be cross-posted here. Could you perhaps elaborate more on subquestion #1 (i.e., remove subquestion 2 and focus on #1?)?  

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## 1 answers

### Answer by username_1 on 2015-05-16. Score: 3 | Accepted answer

I will focus on question #1:

Analysis of MRI scans is typically done using **voxels** (Fig. 1). Voxels have a volume defined by three dimensions (length, width and depth).

![voxel](https://i.sstatic.net/xbRwv.jpg)  
Voxel analysis. Source: [Philips](https://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&cad=rja&uact=8&ved=0CDUQFjAD&url=http%3A%2F%2Fincenter.medical.philips.com%2Fdoclib%2Fgetdoc.aspx%3Ffunc%3Dll%26objid%3D5529294%26objaction%3Dopen&ei=xR5XVf-MCojp8gWF4oPwAg&usg=AFQjCNHEL418AlYm9zC7BEnj2n-BJr-5Cw&sig2=MyJ5dI2-HpEsb8HsJzalVw)

The slice thickness plus the 2D in-plane resolution (pixel size) yields the voxel size. The time to scan a slice can be regarded to be negligible. Making a scan consisting of multiple slices takes time. Hence, the time dimension is not directly relevant for voxel size. Practically, voxel size depends mostly on slice size, as well as the capacity of the scanner. More Tesla's makes smaller voxels possible.

> **Comments:**
> **username_0**: Thank you for the explanation. So a voxel is a 3D pixel and a whole fMRI volume consists of voxels + time which makes it 4D. But does your answer imply that a slice is also 3D because a slice consists of voxels or is it indeed 4D with considering time?  
> **username_1**: A slice can be considered to be made at once. Multiple slices takes time. in the end making one slice also takes time, but negligibly so. i have adapted my answer  
> **username_0**: I mean the time in a timeseries, i.e. imaging different volumes in sequences. Nevertheless, a slice is in 3D, right?  
> **username_1**: Yes, slice is 3D  

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