def test_unwrap_phase_wrong_shape(self):
"""Input wrong shape."""
# This should return an error
try:
unwrap_phase(np.expand_dims(self.phase, -1), self.affine, mag=self.mag)
except RuntimeError:
# If an exception occurs, this is the desired behaviour
return 0
# If there isn't an error, then there is a problem
print('\nWrong dimensions but does not throw an error.')
assert False
def test_unwrap_phase_wrong_unwrapper(self):
"""Input wrong unwrapper."""
# This should return an error
try:
unwrap_phase(self.phase, self.affine, mag=self.mag, unwrapper='Not yet implemented.')
except NotImplementedError:
# If an exception occurs, this is the desired behaviour
return 0
# If there isn't an error, then there is a problem
print('\nNot supported unwrapper but does not throw an error.')
assert False
def test_unwrap_phase_prelude_2d_mask(self):
"""Test prelude with 2d mask parameter."""
phase = self.phase[..., 0, 0]
mag = self.mag[..., 0, 0]
unwrapped = unwrap_phase(phase, self.affine, unwrapper='prelude', mag=mag, mask=np.ones_like(phase))
assert unwrapped.shape == phase.shape
def test_unwrap_phase_prelude_4d_mask(self):
"""Test prelude with mask parameter."""
unwrapped = unwrap_phase(self.phase, self.affine, unwrapper='prelude', mag=self.mag,
mask=np.ones_like(self.phase))
assert unwrapped.shape == self.phase.shape
def test_unwrap_phase_prelude_threshold(self):
"""Test prelude with threshold parameter."""
unwrapped = unwrap_phase(self.phase, self.affine, unwrapper='prelude', mag=self.mag, threshold=0.1)
assert unwrapped.shape == self.phase.shape
def test_unwrap_phase_prelude_2d(self):
"""Test prelude with 2d input data."""
phase = self.phase[..., 0, 0]
mag = self.mag[..., 0, 0]
unwrapped = unwrap_phase(phase, self.affine, unwrapper='prelude', mag=mag)
assert unwrapped.shape == phase.shape
def test_unwrap_phase_prelude_4d(self):
"""Test prelude with 4d input data."""
unwrapped = unwrap_phase(self.phase, self.affine, unwrapper='prelude', mag=self.mag)
assert unwrapped.shape == self.phase.shape
def prepare_fieldmap(phase,
echo_times,
affine,
unwrapper='prelude',
mag=None,
mask=None,
threshold=None):
""" Creates fieldmap (in Hz) from phase images. This function accommodates multiple echoes (2 or more) and phase
difference. This function also accommodates 4D phase inputs, where the 4th dimension represents the time, in case
multiple field maps are acquired across time for the purpose of real-time shimming experiments.
Args:
phase (list): List of phase values in a numpy.ndarray. The numpy array can be [x, y], [x, y, z] or [x, y, z, t].
The values must range from [-pi to pi].
echo_times (list): List of echo times in seconds for each echo. The number of echotimes must match the number of
echoes. It input is a phasediff (1 phase), input 2 echotimes.
affine (numpy.ndarray): 4x4 affine matrix.
unwrapper (str): Unwrapper to use for phase unwrapping. Supported: prelude.
mag (numpy.ndarray): Array containing magnitude data relevant for ``phase`` input. Shape must match phase[echo].
mask (numpy.ndarray): Mask for masking output fieldmap. Must match shape of phase[echo].
threshold: Prelude parameter used for masking.
Returns
numpy.ndarray: Unwrapped fieldmap in Hz.
"""
# Check inputs
for i_echo in range(len(phase)):
# Check that the output phase is in radian (Note: the test below is not 100% bullet proof)
if (phase[i_echo].max() > math.pi) or (phase[i_echo].min() < -math.pi):
raise RuntimeError("read_nii must range from -pi to pi.")
# Check that the input echotimes are the appropriate size by looking at phase
is_phasediff = (len(phase) == 1 and len(echo_times) == 2)
if not is_phasediff:
if len(phase) != len(echo_times) or (len(phase) == 1
and len(echo_times) == 1):
raise RuntimeError(
"Phasediff must have 2 echotime points. Otherwise the number of echoes must match the"
" number of echo times.")
# Make sure mag is the right shape
if mag is not None:
if mag.shape != phase[0].shape:
raise RuntimeError("mag and phase must have the same dimensions.")
# Make sure mask has the right shape
if mask is not None:
if mask.shape != phase[0].shape:
raise RuntimeError("Shape of mask and phase must match.")
# Get the time between echoes and calculate phase difference depending on number of echoes
if len(phase) == 1:
# phase should be a phasediff
phasediff = phase[0]
echo_time_diff = echo_times[1] - echo_times[0] # [s]
elif len(phase) == 2:
echo_0 = phase[0]
echo_1 = phase[1]
# Calculate phasediff using complex difference
comp_0 = np.ones_like(echo_0) * np.exp(-1j * echo_0)
comp_1 = np.ones_like(echo_1) * np.exp(1j * echo_1)
phasediff = np.angle(comp_0 * comp_1)
# Calculate the echo time difference
echo_time_diff = echo_times[1] - echo_times[0] # [s]
else:
# TODO: More echoes
# TODO: Add method once multiple methods are implemented
raise NotImplementedError(
f"This number of phase input is not supported: {len(phase)}.")
# Run the unwrapper
phasediff_unwrapped = unwrap_phase(phasediff,
affine,
unwrapper=unwrapper,
mag=mag,
mask=mask,
threshold=threshold)
# TODO: correct for potential wraps between time points
# Divide by echo time
fieldmap_rad = phasediff_unwrapped / echo_time_diff # [rad / s]
fieldmap_hz = fieldmap_rad / (2 * math.pi) # [Hz]
return fieldmap_hz
