[Gate-users] Material image dose scoring

Fri Jun 15 03:25:19 CEST 2018

Hello Sir,

Thanks for your reply. I will go through and let you know of any further assistance. I really appreciate it.

Best regards,

Emmanuel

________________________________
From: Maikol Salas Ramirez <mmsalas at gmail.com>
Sent: Friday, 15 June 2018 12:03:46 AM
To: Emmanuel Marfo
Subject: Re: [Gate-users] Material image dose scoring

Hi Emmanuel,

I am not an expect, but I will recommend some possible steps:

1- You sum the fat and water images and than transform the image in a mask, I mean all the voxel with a value higher than zero, yo set them to 1.

2- Segment the bone image, for example you can use a threshold, which all the voxels with a value higher than 0.1 (this value you have to decided) in the bone image will assigned a value of 1, then you will have a bone mask, then you subtract it from the first mask (step 1). At same time you use the bone mask to create a mesh volume, you can do this procedure in 3DSlicer or in ImageJ (using 3d viewer).

3- in this point you have a three masks (water + fat, bone, water + fat - bone ) and one mesh volume (bone)

4- You take the fat image, and you make a mask of this image (again you have to chose a threshold value). Also you can make a mesh volume of this mask.

5- Now you substract from the  water + fat - bone mask the fat image, then you will have a mask of pure water. Then you can create a new mesh for water.

You can do all of this steps with ImageJ, and it is very important that each time that you create a new mask, you have to apply some filter to smooth the mask and avoid holes (please see the effect over the image of the imageJ funtion in Process->Binary and Process->filter), also go through all the images to check the mask. Only after this fine tune you have to do mask subtractions.

At end you will have three mesh files and thre masks. The water-mesh in the mother volume and the fat an bone are child volumes.

Let me now if it works. I hope, It will help you.

Best regards
Maikol.

2018-06-14 11:48 GMT+02:00 Emmanuel Marfo <emmanuel.marfo at postgrad.otago.ac.nz<mailto:emmanuel.marfo at postgrad.otago.ac.nz>>:

Dear Sir,

Please, I followed your procedure and was able to convert my images to mass density fraction for lipid, water and HA. I was also able to correct the NaN too.

Now I am wondering what the next step will be. Please, can I adopt your method for the MRI image(lipid/water) and see if it can work for me. The procedure you talk about by creating a mask of each material or creating mesh volumes for each material is not quite clear to me. Can you help me with that? I have attached an interface of a plugin in ImageJ called morphological segmentation showing one of my images. I was hoping this could help me create the mask of each material. I am not sure if is the right method. I am not an expert in Imaging. I seek your guidance.

>>I think, it is not possible to use the material decomposed images directly in GATE without a table,

  1.  one option is to create a mask of each material and
  2.  A second is to create mesh volumes of each material and used them like a child volume of the contour of the normal ct image.

thanks.

Best regards,

Emmanuel

________________________________
From: Maikol Salas Ramirez <mmsalas at gmail.com<mailto:mmsalas at gmail.com>>
Sent: Wednesday, 13 June 2018 12:47:57 PM
To: Emmanuel Marfo
Subject: Re: [Gate-users] Material image dose scoring

Hi Emmanuel,

I think, it is not possible to use the material decomposed images directly in GATE without a table, one option is to create mask of each material and a second is to create mesh volumes of each material and used them like  a child volumes of the contour of the normal ct image.

One option to start is create fraction images:

When you use material decomposed images, you have mass conservation (it depend of your spectral method, but normally is like that, you have to check it), it means Mass_Fraction(HA) + Mass(Lipid) _Fraction + Mass(Water)_Fraction = 1.

The problem here is how to transform your images in fraction images, I had a previous experience but with Water/Fat images but from MRI. For my MRI experiment I calculated the fat fraction and the water fraction (1-fat fraction).

In your case you can do the same:
1- HA_Fraction = HA_Voxel_Value / ( HA_Voxel_Value +  Lipid_Voxel_Value +  Water_Voxel_Value).
2- Lipid_Fraction = Lipid_Voxel_Value / ( HA_Voxel_Value +  Lipid_Voxel_Value +  Water_Voxel_Value).
3- Water_Fraction = Water_Voxel_Value / ( HA_Voxel_Value +  Lipid_Voxel_Value +  Water_Voxel_Value).

I did this calculation with your images using ImageJ and it works pretty easy, you just need to sum all the three images and divide each one by the sum, if you chose one voxel you will see that the sum is 1. The attached image shows the three images.

The only artifact here is in voxel with air or with a zero value you will have NaN value, you have to fix them (given the zero value), ImageJ has an option to do that.

--------------
This is what I can see, the main point is that a normal voxel in a CT images has a composition of material and what you have in each voxel is a effective atomic number and effective density, with spectral CT you separate the material and you have to take care to use the individual images because you lost anatomical information information.

Sorry I think, I could not help you to much.

Best regards
Maikol

2018-06-12 10:50 GMT+02:00 Emmanuel Marfo <emmanuel.marfo at postgrad.otago.ac.nz<mailto:emmanuel.marfo at postgrad.otago.ac.nz>>:

Hello

Thanks for the quick response. Please, the images are density images obtained by dividing linear attenuation(energy information) values by mass attenuation(material basis).

Attached is a dropbox link of a folder containing the material decomposed images for your assessment. thanks

https://www.dropbox.com/sh/zxfio5azk4q6osb/AADw0a1BMYQiPnqFjMgwdCnYa?dl=0

[https://cfl.dropboxstatic.com/static/images/icons128/folder_dropbox.png]<https://www.dropbox.com/sh/zxfio5azk4q6osb/AADw0a1BMYQiPnqFjMgwdCnYa?dl=0>

material images from spectral CT<https://www.dropbox.com/sh/zxfio5azk4q6osb/AADw0a1BMYQiPnqFjMgwdCnYa?dl=0>
www.dropbox.com<http://www.dropbox.com>
Shared with Dropbox

Best regards,

Emmanuel

________________________________
From: Maikol Salas Ramirez <mmsalas at gmail.com<mailto:mmsalas at gmail.com>>
Sent: Tuesday, 12 June 2018 5:45:25 PM
To: Emmanuel Marfo
Cc: gate-users at lists.opengatecollaboration.org<mailto:gate-users at lists.opengatecollaboration.org>
Subject: Re: [Gate-users] Material image dose scoring

Hi Emmanuel,

When you said material decomposed image, are you talking about Rho/Z image (effective density and atomic number - image)?
What info do you have in your image?

Best regards
Maikol

El El mar, 12 jun 2018 a las 0:34, Emmanuel Marfo <emmanuel.marfo at postgrad.otago.ac.nz<mailto:emmanuel.marfo at postgrad.otago.ac.nz>> escribió:

Hello Gate Users,

Please, I need help on this or if anyone has the knowledge of how it can be done I would be grateful. I am using a spectral CT system to obtained material decomposed image based on mass attenuation and energy information. I want to do dose deposition on the material decomposed images without the use of Schneider material converter employed in GATE.  My problem is I want to know if GATE architecture supports it and second I can not import the material decomposed image into GATE because is always requesting for a conversion text file. Can I bypass it? Can someone help me, please? Thanks

Best regards,

Emmanuel Marfo

Student

University of Otago

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