Acquisition Data

All acquisition data is stored in the a type that looks like this

mutable struct AcquisitionData{S<:AbstractSequence}
  seq::S
  kdata::Vector{ComplexF64}
  numEchoes::Int64
  numCoils::Int64
  numSlices::Int64
  samplePointer::Vector{Int64}
  subsampleIndices::Array{Int64}
  encodingSize::Vector{Int64}
  fov::Vector{Float64}
end

The composite type consists of the imaging sequence, the k-space data, several parameters describing the dimension of the data and some additional index vectors.

The k-space data kdata is flattened into a 1D vector but it represents data from a 4D space with dimensions

1. kspace nodes
2. echo times
3. coils
4. slices / repetitions

The reason to use a flattened 1D data is that the number k-space nodes needs not to be constant for different echo times. The entry point to the data is stored in the index vector samplePointer. It has length

numEchoes * numCoils * numSlices

and gives for each combination of echo, coil and slice the corresponding index, where the k-space data starts. The end-point can be obtained by incrementing the index by one.

In case of undersampled data, the subsampling indices are stored in subsampleIndices. One check if the data is undersampled by checking if isempty(subsampleIndices).

The encoded space is stored in the field encodingSize. It is especially relevant for non-Cartesian trajectories where it is not clear upfront, how large the grid size for reconstruction can be chosen. Finally fov describes the physical lengths of the encoding grid.