Update release_notes.md

release_notes.md

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 # Release notes
 
-## OMEGA v2.0.0
-
-### New features
-
-- Added two new projectors for CT data
-  - Projector type 4 is an interpolation-based GPU-only projector
-  - Projector type 5 is the branchless distance-driven projector (GPU only)
-
-- Added support for SPECT reconstruction
-  - Supports also GATE projection data
-  - Collimator-detector response is only supported with implementation 2
-
-- Added support for direction-vector based reconstruction in CT
-  - Added support for pitch/roll/yaw for cone-beam CT
-
-- Added subset selection based on projection images/sinograms
-  - I.e. every Nth projection image/sinogram is selected
-  - Alternatively the projections can be selected randomly
-
-- Added support for dual-layer PET reconstruction
-  - Supports both with and without detector offset
-  - Automatic GATE data import only supports dual-layer without detector offset
-
-- Added ROOT support for Windows
-  - This uses "legacy" load that causes crashes on Linux systems, but works on Windows
-  - Requires 64-bit version of ROOT and thus at least Visual Studio 2022
-
-- RDP and total variation is now faster to compute on implementation 2 and uses much less memory
-  - Does not apply to TV when using anatomical reference image
-
-- Orthogonal distance-based and volume of intersection based projectors are faster to compute with implementation 2
-
-- Removed MLEM as a separate algorithm
-  - MLEM can still be computed by selecting OSEM with 1 subset
-  - Any subset-based algorithm can now be run without subsets
-
-- Only one algorithm/prior can be selected at a time with any implementation
-  - Previously implementation 2 allowed multiple different algorithms/priors
-
-- Added five different image-based preconditioners and two measurement-based preconditioners
-  - For image-based these include diagonal, EM, IEM, momentum, normalized gradient and filtering based preconditioners
-  - For measuremented-based, only diagonal and filtering-based preconditioners are available
-  - Support is limited to only a few algorithms (MBSREM, PKMA, PDHG, FISTA)
-
-- Added several new algorithms
-  - These include primal-dual hybrid gradient (PDHG), FISTA, LSQR, CGLS
-  - PDHG contains several different variations with and without regularization
-  - Works with any input data (PET, CT, SPECT)
-  - For CT, these use linearized data (this is done automatically)
-
-- Added ramp-filtering with several different windowing functions
-  - Window functions include Hamming, Hann, Blackman, Nuttal, Parzen, cosine, Gaussian, and Shepp-Logan
-
-- Added the ability to use mask images to limit LORs/measurements and/or voxels to take into account during reconstructions
-  - It is possible, for example, to only reconstruct a cylindrical region instead of the whole rectangular volume
-  - Alternatively, it is possible to take into account only measurements from a certain region
-  - Improves computation speed
-
-- Added support for hybrid projectors
-  - Works with only a limited number of combinations, such as projector types 1 and 4
-  - Forward projector can thus be different from backprojection (this is already default with projector type 4)
-  - Projector type 4 can be used as a forward projector with PET data (setting `options.projector_type = 41`)
-  - The first value is the forward projector, while the second one is backprojection, i.e. 41 uses type 4 for forward and type 1 for backward
-
-- For non-Poisson-based algorithms, positivity can be enforced with `options.enforcePositivity = true`
-
-- Added support for object offset
-  - I.e. FOV does not need to be in the origin
-
-- Combined all regularization parameters into one variable
-  - Rather than have separate regularization parameters for ALL function and prior combinations, only one `options.beta` is now used
-  - The change, however, is backwards compatible, i.e. you can keep using the old ones as well
-  - All new algorithms, however, only use the `options.beta` alue
-  - Should reduce clutter in the main-files
-
-- The above change was also done for relaxation parameter lambda
-
-- Removed support for PKMA sigma value
-  - Code still remains, although commented
-
 ## OMEGA v1.2.1
 
 ### Bug fixes and enhancements