diff --git a/atlas_densities/densities/inhibitory_neuron_densities_optimization.py b/atlas_densities/densities/inhibitory_neuron_densities_optimization.py
index 21be29f..35c7837 100644
--- a/atlas_densities/densities/inhibitory_neuron_densities_optimization.py
+++ b/atlas_densities/densities/inhibitory_neuron_densities_optimization.py
@@ -38,7 +38,6 @@
 """
 from __future__ import annotations
 
-import itertools as it
 import logging
 import warnings
 from typing import Dict, List, Optional, Set, Tuple
@@ -48,7 +47,7 @@
 from atlas_commons.typing import AnnotationT, FloatArray
 from scipy.optimize import linprog
 from tqdm import tqdm
-from voxcell import RegionMap
+from voxcell import RegionMap, voxel_data
 
 from atlas_densities.densities import utils
 from atlas_densities.densities.inhibitory_neuron_densities_helper import (
@@ -171,66 +170,6 @@ def _replace_inf_with_none(bounds: FloatArray) -> List[MinMaxPair]:
     return [(float(min_), None if np.isinf(max_) else float(max_)) for min_, max_ in bounds]
 
 
-class ValueToIndexVoxels:
-    """Faster indexing of annotation style voxel volumes"""
-
-    def __init__(self, values):
-        """Initialize.
-
-        Args:
-            values(np.array): volume with each voxel marked with a value; usually to group regions
-        """
-        self._order = "C" if values.flags["C_CONTIGUOUS"] else "F"
-
-        values = values.ravel(order=self._order)
-        uniques, counts = np.unique(values, return_counts=True)
-
-        offsets = np.empty(len(counts) + 1, dtype=np.uint64)
-        offsets[0] = 0
-        offsets[1:] = np.cumsum(counts)
-
-        self._indices = np.argsort(values, kind="stable")
-        self._offsets = offsets
-        self._mapping = {v: i for i, v in enumerate(uniques)}
-
-    @property
-    def values(self):
-        """List of values that are found in the original volume."""
-        return list(self._mapping)
-
-    def value_to_1d_indices(self, value):
-        """Return the indices array indices corresponding to the 'value'.
-
-        Note: These are 1D indices, so the assumption is they are applied to a volume
-        who has been ValueToIndexVoxels::ravel(volume)
-        """
-        if value not in self._mapping:
-            return np.array([], dtype=np.uint64)
-
-        group_index = self._mapping[value]
-        return self._indices[self._offsets[group_index] : self._offsets[group_index + 1]]
-
-    def ravel(self, voxel_data):
-        """Ensures `voxel_data` matches the layout that the 1D indices can be used."""
-        return voxel_data.ravel(order=self._order)
-
-    def apply(self, values, funcs, voxel_data):
-        """For pairs of `values` and `funcs`, apply the func as if a mask was created from `value`.
-
-        Args:
-            values(iterable of value): values to be found in original values array
-            funcs(iterable of funcs): if only a single function is provided,
-            it is used for all `values`
-            voxel_data(np.array): Array on which to apply function based on desired `values`
-        """
-        flat_data = self.ravel(voxel_data)
-        if hasattr(funcs, "__call__"):
-            funcs = (funcs,)
-        for value, func in zip(values, it.cycle(funcs)):
-            idx = self.value_to_1d_indices(value)
-            yield func(flat_data[idx])
-
-
 def _compute_region_cell_counts(
     annotation: AnnotationT,
     density: FloatArray,
@@ -260,7 +199,7 @@ def _compute_region_cell_counts(
              ...                             ...
         The index is the sorted list of all region identifiers.
     """
-    vtiv = ValueToIndexVoxels(annotation)
+    vtiv = voxel_data.ValueToIndexVoxels(annotation)
     density_copy = vtiv.ravel(density.copy())
 
     id_counts = []
diff --git a/setup.py b/setup.py
index 9fbd57d..308d6ee 100644
--- a/setup.py
+++ b/setup.py
@@ -28,7 +28,7 @@
         # from the HiGHS library. We use the "highs" method in the densities module.
         "scipy>=1.6.0",
         "tqdm>=4.44.1",
-        "voxcell>=3.0.0",
+        "voxcell>=3.1.7",
     ],
     extras_require={
         "tests": [