# CT reconstruction and blank measurements **URL:** \ **Category:** General Discussions\ **Tags:** ct\ **Created:** [May 17, 2024, 9:38am UTC](https://castor-project.discourse.group/t/ct-reconstruction-and-blank-measurements/779 "2024-05-17T09:38:43Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![savvidis](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@savvidis](https://castor-project.discourse.group/u/savvidis)\ **Post date:** [May 17, 2024, 9:38am UTC](https://castor-project.discourse.group/t/ct-reconstruction-and-blank-measurements/779/1 "2024-05-17T09:38:43Z")
Dear Castor users, I am working on CT reconstruction with Castor using GATE simulations, and I would like to incorporate the blank measurements in my .cdf file. I have the projections for each angle (with my phantom) and the corresponding blank measurement (without the phantom in my scan) and I don’t know how to exploit these blank projections. Should I pre-process my projections dividing the blank measurements with them or there is another way? Any tip would be very helpful! Thank you in advance for your time! Best Giorgos ---
**Author:** ![sstute](https://avatars.discourse-cdn.com/v4/letter/s/8c91f0/32.png) [@sstute](https://castor-project.discourse.group/u/sstute)\ **Post date:** [May 17, 2024, 10:06am UTC](https://castor-project.discourse.group/t/ct-reconstruction-and-blank-measurements/779/2 "2024-05-17T10:06:05Z")
Hi, Have a look at the documentation. The blank values for each projection bin can be incorporated into the castor CT datafile. It will then be automatically taken into account in the reconstruction. Simon > ![](https://global.discourse-cdn.com/free1/uploads/castor_project/original/1X/a3eba7fb43c371fde7fa5ca5ca3befc0b147b723.png "savvidis") | [savvidis](https://castor-project.discourse.group/u/savvidis) > May 17 | > > - | - | Dear Castor users, I am working on CT reconstruction with Castor using GATE simulations, and I would like to incorporate the blank measurements in my .cdf file. I have the projections for each angle (with my phantom) and the corresponding blank measurement (without the phantom in my scan) and I don’t know how to exploit these blank projections. Should I pre-process my projections dividing the blank measurements with them or there is another way? Any tip would be very helpful! Thank you in advance for your time! Best Giorgos ---
**Author:** ![savvidis](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@savvidis](https://castor-project.discourse.group/u/savvidis)\ **Post date:** [May 17, 2024, 12:38pm UTC](https://castor-project.discourse.group/t/ct-reconstruction-and-blank-measurements/779/3 "2024-05-17T12:38:16Z")
Hello Simon! Thank you for your fast reply! Actually, I looked into the documentation and it wasn’t clear for me how to incorporate the blank values to my datafile. I did 360 projection with my object, and 360 projection without the object as I described before, but still is unclear how to merge that results. Is this the way or I miss something? Many thanks once again for your time! GIorgos ---
**Author:** ![sstute](https://avatars.discourse-cdn.com/v4/letter/s/8c91f0/32.png) [@sstute](https://castor-project.discourse.group/u/sstute)\ **Post date:** [May 17, 2024, 1:32pm UTC](https://castor-project.discourse.group/t/ct-reconstruction-and-blank-measurements/779/4 "2024-05-17T13:32:59Z")
Did you succeed in building your cdf file without blank ? If so, then you simply add another float value for each bin corresponding to your blank measurement, according to the table 7 of the documentation. There is nothing to merge, simply add the information into the cdf file. Simon ---
**Author:** ![satyamtiwari](https://avatars.discourse-cdn.com/v4/letter/s/da6949/32.png) [@satyamtiwari](https://castor-project.discourse.group/u/satyamtiwari)\ **Post date:** [August 20, 2025, 1:10pm UTC](https://castor-project.discourse.group/t/ct-reconstruction-and-blank-measurements/779/5 "2025-08-20T13:10:49Z")
Hi, i am facing the same issue. Did u find the solution to this?