diff --git a/tox.ini b/tox.ini
index 3b6d49c..be330a9 100644
--- a/tox.ini
+++ b/tox.ini
@@ -23,7 +23,9 @@ BACKEND =
 
 [testenv]
 description = Run unit-testing
-passenv = DISPLAY XAUTHORITY
+passenv =
+    DISPLAY
+    XAUTHORITY
 deps =
     pytest
     coverage
diff --git a/ultrack/cli/_test/test_cli.py b/ultrack/cli/_test/test_cli.py
index 7220371..995c885 100644
--- a/ultrack/cli/_test/test_cli.py
+++ b/ultrack/cli/_test/test_cli.py
@@ -90,6 +90,8 @@ def test_ctc_export(self, instance_config_path: str, tmp_path: Path) -> None:
                 "0.5,1,1",
                 "-ma",
                 "5",
+                "-di",
+                "1",
                 "-o",
                 str(tmp_path / "01_RES"),
             ]
diff --git a/ultrack/cli/export.py b/ultrack/cli/export.py
index 87408d2..22264cd 100644
--- a/ultrack/cli/export.py
+++ b/ultrack/cli/export.py
@@ -47,6 +47,14 @@
     show_default=True,
     help="Optional first frame path used to select a subset of lineages connected to this reference annotations.",
 )
+@click.option(
+    "--dilation-iters",
+    "-di",
+    default=0,
+    type=int,
+    show_default=True,
+    help="Iterations of radius 1 morphological dilations on labels, applied after scaling.",
+)
 @click.option(
     "--stitch-tracks",
     default=False,
@@ -60,6 +68,7 @@ def ctc_cli(
     margin: int,
     scale: Optional[Tuple[float]],
     first_frame_path: Optional[Path],
+    dilation_iters: int,
     stitch_tracks: bool,
     overwrite: bool,
 ) -> None:
@@ -73,11 +82,12 @@ def ctc_cli(
     to_ctc(
         output_directory,
         config.data_config,
-        margin,
-        scale,
-        first_frame,
-        stitch_tracks,
-        overwrite,
+        margin=margin,
+        scale=scale,
+        first_frame=first_frame,
+        dilation_iters=dilation_iters,
+        stitch_tracks=stitch_tracks,
+        overwrite=overwrite,
     )
 
 
diff --git a/ultrack/core/export/ctc.py b/ultrack/core/export/ctc.py
index 14106a2..70281fc 100644
--- a/ultrack/core/export/ctc.py
+++ b/ultrack/core/export/ctc.py
@@ -6,8 +6,10 @@
 import pandas as pd
 import sqlalchemy as sqla
 from numpy.typing import ArrayLike
-from scipy.ndimage import zoom
+from scipy.ndimage import generate_binary_structure, grey_dilation, zoom
+from scipy.optimize import linear_sum_assignment
 from scipy.spatial import KDTree
+from scipy.spatial.distance import cdist
 from skimage.measure import regionprops
 from skimage.segmentation import relabel_sequential
 from sqlalchemy.orm import Session
@@ -211,19 +213,20 @@ def select_tracks_from_first_frame(
         query = session.query(NodeDB.pickle).where(NodeDB.t == 0, NodeDB.selected)
         starting_nodes = [n for n, in query]
 
-    selected_track_ids = set()
-    centroids = np.asarray([n.centroid for n in starting_nodes])
+    root_centroids = np.asarray([n.centroid for n in starting_nodes])
+    marker_centroids = np.asarray(
+        [n.centroid for n in regionprops(first_frame, cache=False)]
+    )
+    D = cdist(marker_centroids, root_centroids)
+
+    _, root_ids = linear_sum_assignment(D)
 
+    selected_track_ids = set()
     graph = tracks_forest(df)
 
-    for det in tqdm(regionprops(first_frame), "Selecting tracks from first trame"):
-        # select nearest node that contains the reference detection.
-        dist = np.square(centroids - det.centroid).sum(axis=1)
-        node = starting_nodes[np.argmin(dist)]
-        if node.contains(det.centroid):
-            # add the whole tree to the selection
-            track_id = df.loc[node.id, "track_id"]
-            selected_track_ids.update(connected_component(graph, track_id))
+    for root in tqdm(root_ids, "Selecting tracks from first trame"):
+        track_id = df.loc[starting_nodes[root].id, "track_id"]
+        selected_track_ids.update(connected_component(graph, track_id))
 
     if stitch_tracks:
         selected_df = stitch_tracks_df(graph, df, selected_track_ids)
@@ -252,6 +255,7 @@ def _write_tiff_buffer(
     buffer: np.ndarray,
     output_dir: Path,
     scale: Optional[ArrayLike] = None,
+    dilation_iters: int = 0,
 ) -> None:
     """Writes a single tiff stack into `output_dir` / "mask%03d.tif"
 
@@ -265,12 +269,19 @@ def _write_tiff_buffer(
         Output directory.
     scale : Optional[ArrayLike], optional
         Mask rescaling factor, by default None
+    dilation_iters: int
+        Iterations of radius 1 morphological dilations on labels, applied after scaling, by default 0.
     """
     if scale is not None:
         buffer = zoom(
             buffer, scale[-buffer.ndim :], order=0, grid_mode=True, mode="grid-constant"
         )
 
+    footprint = generate_binary_structure(buffer.ndim, 1)
+    for _ in range(dilation_iters):
+        dilated = grey_dilation(buffer, footprint=footprint)
+        np.putmask(buffer, buffer == 0, dilated)
+
     imwrite(output_dir / f"mask{t:03}.tif", buffer)
 
 
@@ -280,6 +291,7 @@ def to_ctc(
     margin: int = 0,
     scale: Optional[Tuple[float]] = None,
     first_frame: Optional[ArrayLike] = None,
+    dilation_iters: int = 0,
     stitch_tracks: bool = False,
     overwrite: bool = False,
 ) -> None:
@@ -298,6 +310,8 @@ def to_ctc(
         Margin used to filter out nodes and splitting their tracklets
     first_frame : Optional[ArrayLike], optional
         Optional first frame detection mask to select a subset of tracks (e.g. Fluo-N3DL-DRO), by default None
+    dilation_iters: int
+        Iterations of radius 1 morphological dilations on labels, applied after scaling, by default 0.
     stitch_tracks: bool, optional
         Stitches (connects) incomplete tracks nearby tracks on subsequent time point, by default False
     overwrite : bool, optional
@@ -372,7 +386,9 @@ def condition(node: Node) -> bool:
     export_segmentation_generic(
         data_config,
         df,
-        _write_tiff_buffer(scale=scale, output_dir=output_dir),
+        _write_tiff_buffer(
+            output_dir=output_dir, scale=scale, dilation_iters=dilation_iters
+        ),
     )