Inverse transformation

monai/transforms/__init__.py

@@ -138,7 +138,7 @@
     ThresholdIntensityD,
     ThresholdIntensityDict,
 )
-from .inverse import InvertibleTransform
+from .inverse import InvertibleTransform, NonRigidTransform
 from .io.array import LoadImage, SaveImage
 from .io.dictionary import LoadImaged, LoadImageD, LoadImageDict, SaveImaged, SaveImageD, SaveImageDict
 from .post.array import (

monai/transforms/inverse.py

@@ -9,13 +9,19 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import warnings
 from typing import Dict, Hashable, Optional, Tuple
 
 import numpy as np
 import torch
 
 from monai.transforms.transform import RandomizableTransform, Transform
 from monai.utils.enums import InverseKeys
+from monai.utils.module import optional_import
+
+sitk, has_sitk = optional_import("SimpleITK")
+vtk, has_vtk = optional_import("vtk")
+vtk_numpy_support, _ = optional_import("vtk.util.numpy_support")
 
 __all__ = ["InvertibleTransform"]
 
@@ -119,3 +125,127 @@ def inverse(self, data: dict) -> Dict[Hashable, np.ndarray]:
 
         """
         raise NotImplementedError(f"Subclass {self.__class__.__name__} must implement this method.")
+
+
+class NonRigidTransform(Transform):
+    @staticmethod
+    def _get_disp_to_def_arr(shape, spacing):
+        def_to_disp = np.mgrid[[slice(0, i) for i in shape]].astype(np.float64)
+        for idx, i in enumerate(shape):
+            # shift for origin (in MONAI, center of image)
+            def_to_disp[idx] -= (i - 1) / 2
+            # if supplied, account for spacing (e.g., for control point grids)
+            if spacing is not None:
+                def_to_disp[idx] *= spacing[idx]
+        return def_to_disp
+
+    @staticmethod
+    def _inv_disp_w_sitk(fwd_disp, num_iters):
+        fwd_disp_sitk = sitk.GetImageFromArray(fwd_disp, isVector=True)
+        inv_disp_sitk = sitk.InvertDisplacementField(fwd_disp_sitk, num_iters)
+        inv_disp = sitk.GetArrayFromImage(inv_disp_sitk)
+        return inv_disp
+
+    @staticmethod
+    def _inv_disp_w_vtk(fwd_disp):
+        orig_shape = fwd_disp.shape
+        required_num_tensor_components = 3
+        # VTK requires 3 tensor components, so if shape was (H, W, 2), make it
+        # (H, W, 1, 3) (i.e., depth 1 with a 3rd tensor component of 0s)
+        while fwd_disp.shape[-1] < required_num_tensor_components:
+            fwd_disp = np.append(fwd_disp, np.zeros(fwd_disp.shape[:-1] + (1,)), axis=-1)
+            fwd_disp = fwd_disp[..., None, :]
+
+        # Create VTKDoubleArray. Shape needs to be (H*W*D, 3)
+        fwd_disp_flattened = fwd_disp.reshape(-1, required_num_tensor_components)  # need to keep this in memory
+        vtk_data_array = vtk_numpy_support.numpy_to_vtk(fwd_disp_flattened)
+
+        # Generating the vtkImageData
+        fwd_disp_vtk = vtk.vtkImageData()
+        fwd_disp_vtk.SetOrigin(0, 0, 0)
+        fwd_disp_vtk.SetSpacing(1, 1, 1)
+        fwd_disp_vtk.SetDimensions(*fwd_disp.shape[:-1][::-1])  # VTK spacing opposite order to numpy
+        fwd_disp_vtk.GetPointData().SetScalars(vtk_data_array)
+
+        if __debug__:
+            fwd_disp_vtk_np = vtk_numpy_support.vtk_to_numpy(fwd_disp_vtk.GetPointData().GetArray(0))
+            assert fwd_disp_vtk_np.size == fwd_disp.size
+            assert fwd_disp_vtk_np.min() == fwd_disp.min()
+            assert fwd_disp_vtk_np.max() == fwd_disp.max()
+            assert fwd_disp_vtk.GetNumberOfScalarComponents() == required_num_tensor_components
+
+        # create b-spline coefficients for the displacement grid
+        bspline_filter = vtk.vtkImageBSplineCoefficients()
+        bspline_filter.SetInputData(fwd_disp_vtk)
+        bspline_filter.Update()
+
+        # use these b-spline coefficients to create a transform
+        bspline_transform = vtk.vtkBSplineTransform()
+        bspline_transform.SetCoefficientData(bspline_filter.GetOutput())
+        bspline_transform.Update()
+
+        # invert the b-spline transform onto a new grid
+        grid_maker = vtk.vtkTransformToGrid()
+        grid_maker.SetInput(bspline_transform.GetInverse())
+        grid_maker.SetGridOrigin(fwd_disp_vtk.GetOrigin())
+        grid_maker.SetGridSpacing(fwd_disp_vtk.GetSpacing())
+        grid_maker.SetGridExtent(fwd_disp_vtk.GetExtent())
+        grid_maker.SetGridScalarTypeToFloat()
+        grid_maker.Update()
+
+        # Get inverse displacement as an image
+        inv_disp_vtk = grid_maker.GetOutput()
+
+        # Convert back to numpy and reshape
+        inv_disp = vtk_numpy_support.vtk_to_numpy(inv_disp_vtk.GetPointData().GetArray(0))
+        # if there were originally < 3 tensor components, remove the zeros we added at the start
+        inv_disp = inv_disp[..., : orig_shape[-1]]
+        # reshape to original
+        inv_disp = inv_disp.reshape(orig_shape)
+
+        return inv_disp
+
+    @staticmethod
+    def compute_inverse_deformation(
+        num_spatial_dims, fwd_def_orig, spacing=None, num_iters: int = 100, use_package: str = "vtk"
+    ):
+        """Package can be vtk or sitk."""
+        if use_package.lower() == "vtk" and not has_vtk:
+            warnings.warn("Please install VTK to estimate inverse of non-rigid transforms. Data has not been modified")
+            return None
+        if use_package.lower() == "sitk" and not has_sitk:
+            warnings.warn(
+                "Please install SimpleITK to estimate inverse of non-rigid transforms. Data has not been modified"
+            )
+            return None
+
+        # Convert to numpy if necessary
+        if isinstance(fwd_def_orig, torch.Tensor):
+            fwd_def_orig = fwd_def_orig.cpu().numpy()
+        # Remove any extra dimensions (we'll add them back in at the end)
+        fwd_def = fwd_def_orig[:num_spatial_dims]
+        # Def -> disp
+        def_to_disp = NonRigidTransform._get_disp_to_def_arr(fwd_def.shape[1:], spacing)
+        fwd_disp = fwd_def - def_to_disp
+        # move tensor component to end (T,H,W,[D])->(H,W,[D],T)
+        fwd_disp = np.moveaxis(fwd_disp, 0, -1)
+
+        # If using vtk...
+        if use_package.lower() == "vtk":
+            inv_disp = NonRigidTransform._inv_disp_w_vtk(fwd_disp)
+        # If using sitk...
+        elif use_package.lower() == "sitk":
+            inv_disp = NonRigidTransform._inv_disp_w_sitk(fwd_disp, num_iters)
+        else:
+            raise RuntimeError("Enter vtk or sitk for inverse calculation")
+
+        # move tensor component back to beginning
+        inv_disp = np.moveaxis(inv_disp, -1, 0)
+        # Disp -> def
+        inv_def = inv_disp + def_to_disp
+        # Add back in any removed dimensions
+        ndim_in = fwd_def_orig.shape[0]
+        ndim_out = inv_def.shape[0]
+        inv_def = np.concatenate([inv_def, fwd_def_orig[ndim_out:ndim_in]])
+
+        return inv_def

monai/transforms/spatial/array.py

@@ -430,7 +430,8 @@ def __call__(
         padding_mode: Optional[Union[GridSamplePadMode, str]] = None,
         align_corners: Optional[bool] = None,
         dtype: DtypeLike = None,
-    ) -> np.ndarray:
+        return_rotation_matrix: bool = False,
+    ) -> Union[np.ndarray, Tuple[np.ndarray, np.ndarray]]:
         """
         Args:
             img: channel first array, must have shape: [chns, H, W] or [chns, H, W, D].
@@ -447,6 +448,7 @@ def __call__(
             dtype: data type for resampling computation. Defaults to ``self.dtype``.
                 If None, use the data type of input data. To be compatible with other modules,
                 the output data type is always ``np.float32``.
+            return_rotation_matrix: whether or not to return the applied rotation matrix.
 
         Raises:
             ValueError: When ``img`` spatially is not one of [2D, 3D].

monai/transforms/spatial/dictionary.py

@@ -25,7 +25,7 @@
 from monai.networks.layers import AffineTransform
 from monai.networks.layers.simplelayers import GaussianFilter
 from monai.transforms.croppad.array import CenterSpatialCrop, SpatialPad
-from monai.transforms.inverse import InvertibleTransform
+from monai.transforms.inverse import InvertibleTransform, NonRigidTransform
 from monai.transforms.spatial.array import (
     Affine,
     AffineGrid,
@@ -50,9 +50,9 @@
     ensure_tuple,
     ensure_tuple_rep,
     fall_back_tuple,
+    optional_import,
 )
 from monai.utils.enums import InverseKeys
-from monai.utils.module import optional_import
 
 nib, _ = optional_import("nibabel")
 
@@ -730,7 +730,7 @@ def inverse(self, data: Mapping[Hashable, np.ndarray]) -> Dict[Hashable, np.ndar
         return d
 
 
-class Rand2DElasticd(RandomizableTransform, MapTransform):
+class Rand2DElasticd(RandomizableTransform, MapTransform, InvertibleTransform, NonRigidTransform):
     """
     Dictionary-based wrapper of :py:class:`monai.transforms.Rand2DElastic`.
     """
@@ -822,6 +822,17 @@ def randomize(self, spatial_size: Sequence[int]) -> None:
         super().randomize(None)
         self.rand_2d_elastic.randomize(spatial_size)
 
+    @staticmethod
+    def cpg_to_dvf(cpg, spacing, output_shape):
+        grid = torch.nn.functional.interpolate(
+            recompute_scale_factor=True,
+            input=cpg.unsqueeze(0),
+            scale_factor=ensure_tuple_rep(spacing, 2),
+            mode=InterpolateMode.BICUBIC.value,
+            align_corners=False,
+        )
+        return CenterSpatialCrop(roi_size=output_shape)(grid[0])
+
     def __call__(
         self, data: Mapping[Hashable, Union[np.ndarray, torch.Tensor]]
     ) -> Dict[Hashable, Union[np.ndarray, torch.Tensor]]:
@@ -831,25 +842,63 @@ def __call__(
         self.randomize(spatial_size=sp_size)
 
         if self._do_transform:
-            grid = self.rand_2d_elastic.deform_grid(spatial_size=sp_size)
-            grid = self.rand_2d_elastic.rand_affine_grid(grid=grid)
-            grid = torch.nn.functional.interpolate(  # type: ignore
-                recompute_scale_factor=True,
-                input=grid.unsqueeze(0),
-                scale_factor=ensure_tuple_rep(self.rand_2d_elastic.deform_grid.spacing, 2),
-                mode=InterpolateMode.BICUBIC.value,
-                align_corners=False,
-            )
-            grid = CenterSpatialCrop(roi_size=sp_size)(grid[0])
+            cpg = self.rand_2d_elastic.deform_grid(spatial_size=sp_size)
+            cpg_w_affine, affine = self.rand_2d_elastic.rand_affine_grid(grid=cpg, return_affine=True)
+            grid = self.cpg_to_dvf(cpg_w_affine, self.rand_2d_elastic.deform_grid.spacing, sp_size)
+            extra_info: Optional[Dict] = {"cpg": deepcopy(cpg), "affine": deepcopy(affine)}
         else:
             grid = create_grid(spatial_size=sp_size)
+            extra_info = None
 
         for key, mode, padding_mode in self.key_iterator(d, self.mode, self.padding_mode):
+            self.push_transform(d, key, extra_info=extra_info)
             d[key] = self.rand_2d_elastic.resampler(d[key], grid, mode=mode, padding_mode=padding_mode)
         return d
 
+    def inverse(self, data: Mapping[Hashable, np.ndarray]) -> Dict[Hashable, np.ndarray]:
+        d = deepcopy(dict(data))
+        # This variable will be `not None` if vtk or sitk is present
+        inv_def_no_affine = None
+
+        for idx, (key, mode, padding_mode) in enumerate(self.key_iterator(d, self.mode, self.padding_mode)):
+            transform = self.get_most_recent_transform(d, key)
+            # Create inverse transform
+            if transform[InverseKeys.DO_TRANSFORM.value]:
+                orig_size = transform[InverseKeys.ORIG_SIZE.value]
+                # Only need to calculate inverse deformation once as it is the same for all keys
+                if idx == 0:
+                    # If magnitude == 0, then non-rigid component is identity -- so just create blank
+                    if self.rand_2d_elastic.deform_grid.magnitude == (0.0, 0.0):
+                        inv_def_no_affine = create_grid(spatial_size=orig_size)
+                    else:
+                        fwd_cpg_no_affine = transform[InverseKeys.EXTRA_INFO.value]["cpg"]
+                        fwd_def_no_affine = self.cpg_to_dvf(
+                            fwd_cpg_no_affine, self.rand_2d_elastic.deform_grid.spacing, orig_size
+                        )
+                        inv_def_no_affine = self.compute_inverse_deformation(len(orig_size), fwd_def_no_affine)
+                    # if inverse did not succeed (sitk or vtk present), data will not be changed.
+                    if inv_def_no_affine is not None:
+                        fwd_affine = transform[InverseKeys.EXTRA_INFO.value]["affine"]
+                        inv_affine = np.linalg.inv(fwd_affine)
+                        inv_def_w_affine_wrong_size = AffineGrid(affine=inv_affine, as_tensor_output=False)(
+                            grid=inv_def_no_affine
+                        )
+                        # Back to original size
+                        inv_def_w_affine = CenterSpatialCrop(roi_size=orig_size)(inv_def_w_affine_wrong_size)  # type: ignore
+                # Apply inverse transform
+                if inv_def_no_affine is not None:
+                    out = self.rand_2d_elastic.resampler(d[key], inv_def_w_affine, mode, padding_mode)
+                    d[key] = out.cpu().numpy() if isinstance(out, torch.Tensor) else out
+
+            else:
+                d[key] = CenterSpatialCrop(roi_size=orig_size)(d[key])
+            # Remove the applied transform
+            self.pop_transform(d, key)
+
+        return d
+
 
-class Rand3DElasticd(RandomizableTransform, MapTransform):
+class Rand3DElasticd(RandomizableTransform, MapTransform, InvertibleTransform, NonRigidTransform):
     """
     Dictionary-based wrapper of :py:class:`monai.transforms.Rand3DElastic`.
     """
@@ -949,17 +998,54 @@ def __call__(
         sp_size = fall_back_tuple(self.rand_3d_elastic.spatial_size, data[self.keys[0]].shape[1:])
 
         self.randomize(grid_size=sp_size)
-        grid = create_grid(spatial_size=sp_size)
+        grid_no_affine = create_grid(spatial_size=sp_size)
+        affine = np.eye(4)
         if self._do_transform:
             device = self.rand_3d_elastic.device
-            grid = torch.tensor(grid).to(device)
+            grid_no_affine = torch.tensor(grid_no_affine).to(device)
             gaussian = GaussianFilter(spatial_dims=3, sigma=self.rand_3d_elastic.sigma, truncated=3.0).to(device)
             offset = torch.tensor(self.rand_3d_elastic.rand_offset, device=device).unsqueeze(0)
-            grid[:3] += gaussian(offset)[0] * self.rand_3d_elastic.magnitude
-            grid = self.rand_3d_elastic.rand_affine_grid(grid=grid)
+            grid_no_affine[:3] += gaussian(offset)[0] * self.rand_3d_elastic.magnitude
+            grid_w_affine, affine = self.rand_3d_elastic.rand_affine_grid(grid=grid_no_affine, return_affine=True)
+        else:
+            grid_w_affine = grid_no_affine
+            affine = np.eye(len(sp_size) + 1)
 
         for key, mode, padding_mode in self.key_iterator(d, self.mode, self.padding_mode):
-            d[key] = self.rand_3d_elastic.resampler(d[key], grid, mode=mode, padding_mode=padding_mode)
+            self.push_transform(d, key, extra_info={"grid_no_affine": grid_no_affine, "affine": affine})
+            d[key] = self.rand_3d_elastic.resampler(d[key], grid_w_affine, mode=mode, padding_mode=padding_mode)
+        return d
+
+    def inverse(self, data: Mapping[Hashable, np.ndarray]) -> Dict[Hashable, np.ndarray]:
+        d = deepcopy(dict(data))
+
+        for idx, (key, mode, padding_mode) in enumerate(self.key_iterator(d, self.mode, self.padding_mode)):
+            transform = self.get_most_recent_transform(d, key)
+            # Create inverse transform
+            if transform[InverseKeys.DO_TRANSFORM.value]:
+                orig_size = transform[InverseKeys.ORIG_SIZE.value]
+                # Only need to calculate inverse deformation once as it is the same for all keys
+                if idx == 0:
+                    fwd_def_no_affine = transform[InverseKeys.EXTRA_INFO.value]["grid_no_affine"]
+                    inv_def_no_affine = self.compute_inverse_deformation(len(orig_size), fwd_def_no_affine)
+                    # if inverse did not succeed (sitk or vtk present), data will not be changed.
+                    if inv_def_no_affine is not None:
+                        fwd_affine = transform[InverseKeys.EXTRA_INFO.value]["affine"]
+                        inv_affine = np.linalg.inv(fwd_affine)
+                        inv_def_w_affine_wrong_size = AffineGrid(affine=inv_affine, as_tensor_output=False)(
+                            grid=inv_def_no_affine
+                        )
+                        # Back to original size
+                        inv_def_w_affine = CenterSpatialCrop(roi_size=orig_size)(inv_def_w_affine_wrong_size)  # type: ignore
+                # Apply inverse transform
+                if inv_def_w_affine is not None:
+                    out = self.rand_3d_elastic.resampler(d[key], inv_def_w_affine, mode, padding_mode)
+                    d[key] = out.cpu().numpy() if isinstance(out, torch.Tensor) else out
+            else:
+                d[key] = CenterSpatialCrop(roi_size=orig_size)(d[key])
+            # Remove the applied transform
+            self.pop_transform(d, key)
+
         return d
 
 
@@ -1169,6 +1255,7 @@ def __call__(self, data: Mapping[Hashable, np.ndarray]) -> Dict[Hashable, np.nda
                 padding_mode=padding_mode,
                 align_corners=align_corners,
                 dtype=dtype,
+                return_rotation_matrix=True,
             )
             rot_mat = self.rotator.get_rotation_matrix()
             self.push_transform(d, key, orig_size=orig_size, extra_info={"rot_mat": rot_mat})
@@ -1302,6 +1389,7 @@ def __call__(self, data: Mapping[Hashable, np.ndarray]) -> Dict[Hashable, np.nda
                 padding_mode=padding_mode,
                 align_corners=align_corners,
                 dtype=dtype,
+                return_rotation_matrix=True,
             )
             rot_mat = rotator.get_rotation_matrix()
             self.push_transform(d, key, orig_size=orig_size, extra_info={"rot_mat": rot_mat})

requirements-dev.txt

@@ -32,3 +32,4 @@ sphinx-autodoc-typehints==1.11.1
 sphinx-rtd-theme==0.5.0
 cucim==0.18.1
 openslide-python==1.1.2
+vtk