diff --git a/tissues/femoral_cartilage.py b/tissues/femoral_cartilage.py
index c5ed81f..fdcff32 100644
--- a/tissues/femoral_cartilage.py
+++ b/tissues/femoral_cartilage.py
@@ -208,16 +208,17 @@ def split_regions(self, unrolled_quantitative_map):
 
         assert ml_mask.shape == acp_mask.shape
 
+        # convert backgorund label to NaN
+        ml_mask[ml_mask == self.BACKGROUND_KEY] = np.nan
+        acp_mask[acp_mask == self.BACKGROUND_KEY] = np.nan
+
         ml_mask = ml_mask[..., np.newaxis]
         acp_mask = acp_mask[..., np.newaxis]
 
         self.regions_mask = np.concatenate((ml_mask, acp_mask), axis=2)
 
-        # convert backgorund label to NaN
-        self.regions_mask[self.regions_mask == self.BACKGROUND_KEY] = np.nan
-
-        assert (self.regions_mask[..., 0] == ml_mask[..., 0]).all()
-        assert (self.regions_mask[..., 1] == acp_mask[..., 0]).all()
+        assert np.allclose(self.regions_mask[..., 0], ml_mask[..., 0], equal_nan=True)
+        assert np.allclose(self.regions_mask[..., 1], acp_mask[..., 0], equal_nan=True)
 
     def calc_quant_vals(self, quant_map, map_type):
         """