def test_im2ksp_noncart(self):
# Image to k-space transformation for non-Cartesian data
nufft_obj = nufft_init(kt=ktraj, params=acq_params)
ksp = im2ksp(
M=ph, cartesian_opt=0, NufftObj=nufft_obj,
params=acq_params) # Sample the image along the trajectory
self.assertEqual(ksp.shape, ktraj.shape) # Dimensions match
def test_ksp2im_noncart(self):
# K-space to image transformation for non-Cartesian
nufft_obj = nufft_init(kt=ktraj, params=acq_params)
im = ksp2im(ksp=noncart_ksp,
cartesian_opt=0,
NufftObj=nufft_obj,
params=acq_params) # reconstructed image
self.assertEqual(im.shape, ph.shape) # dimensions match
im = (im - np.min(im)) / (np.max(im) - np.min(im)) # normalize image
diff = np.round(im - ph)
diff_percent = np.nonzero(diff)[0].shape[0] / N**2 * 100
self.assertLess(
diff_percent, 5
) # Less than 5% of voxels should be different between original and reconstructed image
def add_or(M, kt, df, nonCart=None, params=None):
'''Forward model for off-resonance simulation
Parameters
----------
M : numpy.ndarray
Image data
kt : numpy.ndarray
k-space trajectory
df : numpy.ndarray
Field map
nonCart : int , optional
Cartesian/Non-Cartesian trajectory option. Default is None.
params : dict , optional
Sequence parameters. Default is None.
Returns
-------
M_or : numpy.ndarray
Off-resonance corrupted image data
'''
'''Create a phase matrix - 2*pi*df*t for every df and every t'''
if nonCart is not None:
cartesian_opt = 0
NufftObj = nufft_init(kt, params)
else:
cartesian_opt = 1
NufftObj = None
params = None
kspace = im2ksp(M, cartesian_opt, NufftObj, params)
M_or = np.zeros(M.shape, dtype=complex)
for x in range(M.shape[0]):
for y in range(M.shape[1]):
phi = 2 * pi * df[x, y] * kt
kspace_orc = kspace * np.exp(-1j * phi)
M_corr = ksp2im(kspace_orc, cartesian_opt, NufftObj, params)
M_or[x, y] = M_corr[x, y]
return M_or
def test_missing_params_N(self):
# NUFFT for non-cartesian data will fail if a required parameter is missing from the paramters dictionary (e.g. N)
params = acq_params.copy()
del params['N']
with self.assertRaises(ValueError):
nufft_init(kt=ktraj, params=params)
def MFI(dataIn, dataInType, kt, df, Lx, nonCart=None, params=None):
'''Off-resonance Correction by Multi-Frequency Interpolation
Man, L., Pauly, J. M. and Macovski, A. (1997), Multifrequency interpolation for fast off‐resonance correction. Magn. Reson. Med., 37: 785-792. doi:10.1002/mrm.1910370523
Parameters
----------
dataIn : numpy.ndarray
k-space raw data or image data
dataInType : str
Can be either 'raw' or 'im'
kt : numpy.ndarray
k-space trajectory
df : numpy.ndarray
Field map
Lx : int
L (frequency bins) factor
nonCart : int
Non-cartesian trajectory option. Default is None (Cartesian).
params : dict
Sequence parameters. Default is None.
Returns
-------
M_hat : numpy.ndarray
Corrected image data.
'''
if nonCart is not None and nonCart == 1:
check_inputs_noncartesian(dataIn.shape, dataInType, kt.shape, df.shape,
params)
cartesian_opt = 0
NufftObj = nufft_init(kt, params)
t_vector = params['t_vector']
T = np.tile(params['t_vector'], (1, kt.shape[1]))
t_ro = T[-1, 0] - T[0, 0] # T[end] - TE
N = params['N']
elif nonCart == 'EPI':
# check_inputs_cartesian(dataIn.shape, dataInType, kt.shape, df.shape)
cartesian_opt = 1
NufftObj = None
T = np.flipud(params['t_vector']).reshape(params['N'], params['N'])
T[1:params['N']:2, :] = np.fliplr(T[1:params['N']:2, :])
N = dataIn.shape[0]
t_ro = params['t_readout']
t_vector = params['t_vector']
else:
check_inputs_cartesian(dataIn.shape, dataInType, kt.shape, df.shape)
cartesian_opt = 1
NufftObj = None
N = dataIn.shape[0]
t_vector = kt[0].reshape(kt.shape[1], 1)
T = kt
t_ro = T[0, -1] - T[0, 0]
if dataInType == 'im':
rawData = im2ksp(dataIn, cartesian_opt, NufftObj, params)
elif dataInType == 'raw':
rawData = dataIn
df = np.round(df, 1)
idx, idy = np.where(df == -0.0)
df[idx, idy] = 0.0
# Number of frequency segments
df_max = max(np.abs([df.max(), df.min()])) # Hz
df_range = (df.min(), df.max())
L = ceil(df_max * 2 * pi * t_ro / pi)
L = L * Lx
if len(np.unique(df)) == 1:
L = 1
f_L = np.linspace(df.min(), df.max(), L + 1) # Hz
#T = np.tile(params['t_vector'], (1, kt.shape[1]))
# reconstruct the L basic images
M_MFI = np.zeros((N, N, L + 1), dtype=complex)
for l in range(L + 1):
phi = 2 * pi * f_L[l] * T
kspace_L = rawData * np.exp(1j * phi)
M_MFI[:, :, l] = ksp2im(kspace_L, cartesian_opt, NufftObj, params)
# calculate MFI coefficients
coeffs_LUT = coeffs_MFI_lsq(kt, f_L, df_range, t_vector)
# final image reconstruction
M_hat = np.zeros((N, N), dtype=complex)
for i in range(M_hat.shape[0]):
for j in range(M_hat.shape[1]):
fieldmap_val = df[i, j]
val_coeffs = coeffs_LUT[str(fieldmap_val)]
M_hat[i, j] = sum(val_coeffs * M_MFI[i, j, :])
return M_hat
def fs_CPR(dataIn, dataInType, kt, df, Lx, nonCart=None, params=None):
'''Off-resonance Correction by frequency-segmented Conjugate Phase Reconstruction
Noll, D. C., Pauly, J. M., Meyer, C. H., Nishimura, D. G. and Macovskj, A. (1992), Deblurring for non‐2D fourier transform magnetic resonance imaging. Magn. Reson. Med., 25: 319-333. doi:10.1002/mrm.1910250210
Parameters
----------
dataIn : numpy.ndarray
k-space raw data or image data
dataInType : str
Can be either 'raw' or 'im'
kt : numpy.ndarray
k-space trajectory
df : numpy.ndarray
Field map
Lx : int
L (frequency bins) factor
nonCart : int
Non-cartesian trajectory option. Default is None (Cartesian).
params : dict
Sequence parameters. Default is None (Cartesian).
Returns
-------
M_hat : numpy.ndarray
Corrected image data.
'''
if nonCart is not None and nonCart == 1:
check_inputs_noncartesian(dataIn.shape, dataInType, kt.shape, df.shape,
params)
cartesian_opt = 0
NufftObj = nufft_init(kt, params)
T = np.tile(params['t_vector'], (1, kt.shape[1]))
N = params['N']
t_ro = T[-1, 0] - T[0, 0] # T[end] - TE
elif nonCart == 'EPI':
# check_inputs_cartesian(dataIn.shape, dataInType, kt.shape, df.shape)
cartesian_opt = 1
NufftObj = None
T = np.flipud(params['t_vector']).reshape(params['N'], params['N'])
T[1:params['N']:2, :] = np.fliplr(T[1:params['N']:2, :])
N = dataIn.shape[0]
t_ro = params['t_readout']
else:
check_inputs_cartesian(dataIn.shape, dataInType, kt.shape, df.shape)
cartesian_opt = 1
NufftObj = None
N = dataIn.shape[0]
t_vector = kt[0].reshape(kt.shape[1], 1)
T = kt
t_ro = T[0, -1] - T[0, 0]
if dataInType == 'im':
rawData = im2ksp(dataIn, cartesian_opt, NufftObj, params)
elif dataInType == 'raw':
rawData = dataIn
# Number of frequency segments
df_max = max(np.abs([df.max(), df.min()])) # Hz
L = ceil(4 * df_max * 2 * pi * t_ro / pi)
L = L * Lx
if len(np.unique(df)) == 1:
L = 1
f_L = np.linspace(df.min(), df.max(), L + 1) # Hz
# T = np.tile(params['t_vector'], (1, kt.shape[1]))
# reconstruct the L basic images
M_fsCPR = np.zeros((N, N, L + 1), dtype=complex)
for l in range(L + 1):
phi = 2 * pi * f_L[l] * T
kspace_L = rawData * np.exp(1j * phi)
M_fsCPR[:, :, l] = ksp2im(kspace_L, cartesian_opt, NufftObj, params)
# final image reconstruction
M_hat = np.zeros((N, N), dtype=complex)
for i in range(M_hat.shape[0]):
for j in range(M_hat.shape[1]):
fieldmap_val = df[i, j]
closest_fL_idx = find_nearest(f_L, fieldmap_val)
if fieldmap_val == f_L[closest_fL_idx]:
pixel_val = M_fsCPR[i, j, closest_fL_idx]
else:
if fieldmap_val < f_L[closest_fL_idx]:
f_vals = [f_L[closest_fL_idx - 1], f_L[closest_fL_idx]]
im_vals = [
M_fsCPR[i, j, closest_fL_idx - 1],
M_fsCPR[i, j, closest_fL_idx]
]
else:
f_vals = [f_L[closest_fL_idx], f_L[closest_fL_idx + 1]]
im_vals = [
M_fsCPR[i, j, closest_fL_idx],
M_fsCPR[i, j, closest_fL_idx + 1]
]
pixel_val = np.interp(fieldmap_val, f_vals, im_vals)
M_hat[i, j] = pixel_val
return M_hat
def CPR(dataIn, dataInType, kt, df, nonCart=None, params=None):
'''Off-resonance Correction by Conjugate Phase Reconstruction
Maeda, A., Sano, K. and Yokoyama, T. (1988), Reconstruction by weighted correlation for MRI with time-varying gradients. IEEE Transactions on Medical Imaging, 7(1): 26-31. doi: 10.1109/42.3926
Parameters
----------
dataIn : numpy.ndarray
k-space raw data or image data
dataInType : str
Can be either 'raw' or 'im'
kt : numpy.ndarray
k-space trajectory.
df : numpy.ndarray
Field map
nonCart : int
Non-cartesian trajectory option. Default is None (Cartesian).
params : dict
Sequence parameters. Default is None (Cartesian).
Returns
-------
M_hat : numpy.ndarray
Corrected image data.
'''
if nonCart is not None and nonCart == 1:
check_inputs_noncartesian(dataIn.shape, dataInType, kt.shape, df.shape,
params)
cartesian_opt = 0
NufftObj = nufft_init(kt, params)
T = np.tile(params['t_vector'], (1, kt.shape[1]))
N = params['N']
elif nonCart == 'EPI':
# check_inputs_cartesian(dataIn.shape, dataInType, kt.shape, df.shape)
cartesian_opt = 1
NufftObj = None
T = np.flipud(params['t_vector']).reshape(params['N'], params['N'])
T[1:params['N']:2, :] = np.fliplr(T[1:params['N']:2, :])
N = dataIn.shape[0]
else:
check_inputs_cartesian(dataIn.shape, dataInType, kt.shape, df.shape)
cartesian_opt = 1
NufftObj = None
T = kt
N = dataIn.shape[0]
if dataInType == 'im':
rawData = im2ksp(dataIn, cartesian_opt, NufftObj, params)
elif dataInType == 'raw':
rawData = dataIn
df_values = np.unique(df)
M_CPR = np.zeros((N, N, len(df_values)), dtype=complex)
for i in range(len(df_values)):
phi = 2 * pi * df_values[i] * T
kspace_orc = rawData * np.exp(1j * phi)
M_corr = ksp2im(kspace_orc, cartesian_opt, NufftObj, params)
M_CPR[:, :, i] = M_corr
M_hat = np.zeros((N, N), dtype=complex)
for x in range(df.shape[0]):
for y in range(df.shape[1]):
fieldmap_val = df[x, y]
idx = np.where(df_values == fieldmap_val)
M_hat[x, y] = M_CPR[x, y, idx]
return M_hat
def add_or_CPR(M, kt, df, nonCart=None, params=None):
'''Forward model for off-resonance simulation. The number of fourier transforms = number of unique values in the field map.
Parameters
----------
M : numpy.ndarray
Image data
kt : numpy.ndarray
k-space trajectory
df : numpy.ndarray
Field map
nonCart : int , optional
Cartesian/Non-Cartesian trajectory option. Default is None.
params : dict , optional
Sequence parameters. Default is None.
Returns
-------
M_or : numpy.ndarray
Off-resonance corrupted image data
'''
# Create a phase matrix - 2*pi*df*t for every df and every t
if nonCart is not None and nonCart == 1:
cartesian_opt = 0
NufftObj = nufft_init(kt, params)
T = np.tile(params['t_vector'], (1, kt.shape[1]))
elif nonCart == 'EPI':
cartesian_opt = 1
NufftObj = None
T = np.flipud(params['t_vector']).reshape(params['N'], params['N'])
T[1:params['N']:2, :] = np.fliplr(T[1:params['N']:2, :])
else:
cartesian_opt = 1
NufftObj = None
params = None
T = kt
kspace = im2ksp(M, cartesian_opt, NufftObj, params)
df_values = np.unique(df)
M_or_CPR = np.zeros((M.shape[0], M.shape[1], len(df_values)),
dtype=complex)
kspsave = np.zeros((kspace.shape[0], kspace.shape[1], len(df_values)),
dtype=complex)
for i in range(len(df_values)):
phi = -2 * pi * df_values[i] * T
kspace_or = kspace * np.exp(1j * phi)
kspsave[:, :, i] = kspace_or
M_corr = ksp2im(kspace_or, cartesian_opt, NufftObj, params)
M_or_CPR[:, :, i] = M_corr
M_or = np.zeros(M.shape, dtype=complex)
for x in range(M.shape[0]):
for y in range(M.shape[1]):
fieldmap_val = df[x, y]
idx = np.where(df_values == fieldmap_val)
M_or[x, y] = M_or_CPR[x, y, idx]
'''plt.imshow(abs(M_or))
plt.show()'''
return M_or, kspsave
def spiral_recon(data, ktraj, N, plot=0, save=0, dst_folder=None):
'''
Spiral image reconstruction from raw data
Parameters
----------
data : str or np.ndarray
Path containing the raw data file of array containing the raw data
ktraj : np.ndarray
k-space trajectory coordinates with dimensions [Npoints, Nshots]
N : int
Matrix size of the reconstructed image
plot : bool, Optional
Plotting a slice of the reconstructed image option. Default is 0 (not plot).
save : bool, Optional
Saving the data in a .npy file option. Default is 0 (not save).
dst_folder : str, Optional
Path to the folder where the reconstructed image is saved. Default is None.
'''
##
# Load the raw data
##
if isinstance(data, str):
dat = get_data_from_file(data)
elif isinstance(data, np.ndarray):
dat = data
##
# Acq parameters
##
Npoints = ktraj.shape[0]
Nshots = ktraj.shape[1]
Nchannels = dat.shape[-1]
if len(dat.shape) < 4:
Nslices = 1
dat = dat.reshape(Npoints, Nshots, 1, Nchannels)
else:
Nslices = dat.shape[-2]
if dat.shape[0] != ktraj.shape[0] or dat.shape[1] != ktraj.shape[1]:
raise ValueError('Raw data and k-space trajectory do not match!')
##
# Recon
##
NUFFT_object = nufft_init(ktraj, {
'N': N,
'Npoints': Npoints,
'Nshots': Nshots
})
im = np.zeros((N, N, Nslices, Nchannels), dtype=complex)
for ch in range(Nchannels):
for sl in range(Nslices):
im[:, :, sl, ch] = ksp2im(
dat[:, :, sl, ch], 0, NUFFT_object, {
'N': N,
'Npoints': Npoints,
'Nshots': Nshots
}
) #NufftObj.solve(dat[:,:,sl,ch].flatten(), solver='cg', maxiter=50)
#sos = np.sum(np.abs(im), -1)
sos = np.sqrt(np.sum(np.abs(im)**2, -1))
sos = np.divide(sos, np.max(sos))
if plot:
#plt.imshow(np.rot90(np.abs(sos[:,:,0]),-1), cmap='gray')
plt.imshow(sos[:, :, 0], cmap='gray')
plt.axis('off')
plt.title('Uncorrected Image')
plt.show()
if save:
if dst_folder is None:
raise ValueError('Please specify destination folder')
np.save(dst_folder + 'uncorrected_spiral.npy', sos)
return sos
