deepmr.b1field#
- deepmr.b1field(shape, nmodes=1, b1range=(0.5, 2.0), shift=None, dphi=0.0, coil_width=1.1, ncoils=8, nrings=None, mask=None)[source]#
Simulate inhomogeneous B1+ fields.
Adapted from SigPy [1].
- Parameters:
shape (Iterable[int]) – Size of the matrix
(ny, nx)
(2D) or(nz, ny, nx)
(3D) for the B1+ field.nmodes (int, optional) – Number of B1+ modes. First mode is
CP
mode, second isgradient
mode, and so on. The default is1
.b1range (Iterable[float]) – Range of B1+ magnitude. The default is
(0.5, 2.0)
.shift (Iterable[int], optional) – Displacement of the coil center with respect to matrix center. The default is
(0, 0)
/(0, 0, 0)
.dphi (float) – Bulk coil angle in
[deg]
. The default is0.0°
.coil_width (float, optional) – Width of the coil, with respect to image dimension. The default is
1.1
.ncoils (int, optional) – Number of transmit coil elements. Standard coils have
2
channels operating in quadrature. To support multiple modes (i.e., PTX), increase this number. The default is8
.nrings (int, optional) – Number of rings for a cylindrical hardware set-up. The default is
ncoils // 4
.mask (np.ndarray | torch.Tensor, optional) – Region of support of the object of shape
(ny, nx)
(2D) or(nz, ny, nx)
(3D). The default isNone
.
- Returns:
smap – Complex spatially varying b1+ maps of shape
(nmodes, ny, nx)
(2D) or(nmodes, nz, ny, nx)
(3D). Magnitude of the map represents the relative flip angle scaling (wrt to the nominal).- Return type:
Example
>>> import deepmr
We can generate a 2D B1+ field map of shape
(ny=128, nx=128)
by:>>> b1map = deepmr.b1field((128, 128))
Field center and rotation can be modified by
shift
anddphi
arguments:>>> b1map = deepmr.b1field((8, 128, 128), shift=(-3, 5), dphi=30.0) # center shifted by (dy, dx) = (-3, 5) pixels and rotated by 30.0 degrees.
B1+ values range and steepness of variation can be specified using
b1range
andcoil_width
arguments:>>> # transmit coil is 4 times bigger than FOV (e.g., body coil) and >>> # B1+ scalings are between (0.8, 1.2) the nominal flip angle (e.g., 3T scanner) >>> b1map3T = deepmr.b1field((128, 128), b1range=(0.8, 1.2), coil_width=4.0) >>> >>> # transmit coil is 1.1 times bigger than FOV (e.g., head coil) and >>> # B1+ scalings are between (0.5, 2.0) the nominal flip angle (e.g., 7T scanner) >>> b1map7T = deepmr.b1field((128, 128), b1range=(0.5, 2.0), coil_width=1.1)
Multiple orthogonal modes can be simulated by
nmodes
argument. For example,CP
mode andgradient
mode can be obtained as:>>> b1map = deepmr.b1field((128, 128), nmodes=2) # b1map[0] is CP, b1map[1] is gradient mode.
Three dimensional B1+ maps of shape
(nz, ny, nx)
can be obtained as:>>> b1map = deepmr.b1field((128, 128, 128))
Beware that this will require more memory.
References
[1] mikgroup/sigpy