diff --git a/optuna_dashboard/preferential/_study.py b/optuna_dashboard/preferential/_study.py
index 585db64d..71c00882 100644
--- a/optuna_dashboard/preferential/_study.py
+++ b/optuna_dashboard/preferential/_study.py
@@ -79,7 +79,7 @@ class PreferentialStudy:
 
     def get_preferences(self, *, deepcopy: bool = True) -> list[tuple[FrozenTrial, FrozenTrial]]:
         trials = self._study.get_trials(deepcopy=deepcopy)
-        preferences = get_preferences(self._study, trials)
+        preferences = get_preferences(self._study._study_id, self._study._storage)
         return [(trials[better], trials[worse]) for (better, worse) in preferences]
 
     def set_user_attr(self, key: str, value: Any) -> None:
diff --git a/optuna_dashboard/preferential/_system_attrs.py b/optuna_dashboard/preferential/_system_attrs.py
index 2be921da..3b73c12b 100644
--- a/optuna_dashboard/preferential/_system_attrs.py
+++ b/optuna_dashboard/preferential/_system_attrs.py
@@ -2,9 +2,7 @@ from __future__ import annotations
 
 import uuid
 
-import optuna
 from optuna.storages import BaseStorage
-from optuna.trial import FrozenTrial
 from optuna.trial import TrialState
 
 from .._storage import get_study_summary