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Basis of magnetic resonance imaging (MRI) Imaging Directions

Samples during magnetic resonance imaging (MRI) experiments, the first question to consider is to determine the direction of three related imaging: selected layer direction (G Slice I), phase encoding direction (G Phase I) and the frequency-encoding direction (G Read I)
In Fig 1, we can see relationship between orthogonal coordinates and the direction of the magnetic field. In the coordinates, Z direction is defined as up and down according to the NMR instrumentation. Y direction is defined as front and back. X direction is defined as left and right. Usually, we make the NMR imaging directions coincide the orthogonal coordinates, i.e. we use X/Y/Z to be slice/phase/read direction. However, we can also make the imaging direction not coincide the orthogonal coordinates. For example, we can choose Z as the slice direction, Y as the phase direction and X as the read direction.
In NMR imaging software, we have three sets of parameters for setting the imaging directions. They are sagittal ,coronal and axial directions.
 the main direction of magnetic field

Fig 1 the main direction of magnetic field

1. Sagittal Imaging

Select the sagittal imaging .As shown in Fig 2.

Sagittal

 

G Slice G Phase G Read
X 0 0 1
Y 0 1 0
Z 1 0 0

 

 

 

 

We choose Z as the slice direction, Y as the phase direction and X as the read direction, and the image we get will be a sagittal image of the sample. The following is a selection value for each parameter of a sagittal image.

2. Coronal Imaging
Select the coronal imaging .As shown in Fig 3, we choose X as the slice direction, Z as the phase direction and Y as the read direction, and the image we get will be a coronal image of the sample. The following is a selection value for each parameter of a coronal image.

Coronal

 

G Slice G Phase G Read
 X 1 0

0

Y 0 1 0
Z 0 0 1

 

 

 

3. Transverse Imaging

 

Transverse

 

 

G Slice G Phase G Read
X 0 0 1
Y 1 0 0
Z 0 1 0

Select the transverse imaging .As shown in Fig 4, we choose Y as the slice direction, Z as the phase direction and X as the read direction and the image we gets will be a transverse image of the sample. The following is a selection value for each parameter of a transverse image.