Fix eager nvimgcodec plugin import

monai/__init__.py

@@ -86,6 +86,7 @@ def filter(self, record):
 # *.so files and folder "_C" may not exist when the cpp extensions are not compiled
 excludes = "|".join(
     [
+        "(.*(nvimgcodec_pydicom_plugin)$)",
         "(^(monai.handlers))",
         "(^(monai.bundle))",
         "(^(monai.fl))",

monai/data/image_reader.py

@@ -1087,7 +1087,7 @@ class NvImgCodecPydicomReader(PydicomReader):
     Load DICOM images using Pydicom with GPU-accelerated decompression via nvImageCodec.
 
     This reader extends :py:class:`PydicomReader` and registers the nvImageCodec pydicom
-    decoder plugin on initialization. The plugin accelerates decoding of compressed pixel data
+    decoder plugin lazily on first use. The plugin accelerates decoding of compressed pixel data
     for JPEG, JPEG 2000, and HTJ2K transfer syntaxes when CUDA, CuPy and ``nvidia-nvimgcodec`` are available.
 
     If nvImageCodec is not available, a warning is issued and the reader falls back to the
@@ -1117,8 +1117,8 @@ class NvImgCodecPydicomReader(PydicomReader):
 
         This reader only declares ``@require_pkg(pkg_name="pydicom")`` so that :py:class:`monai.transforms.LoadImage`
         can register it without hard-failing when GPU dependencies are missing. ``pydicom`` is required to construct
-        the reader; nvimgcodec, CUDA, and CuPy availability is checked at runtime with a warning issued and fallback to
-        default pydicom decoders if missing.
+        the reader; nvImageCodec, CUDA, and CuPy availability is checked when a DICOM file is verified or read.
+        If the plugin is unavailable or registration fails, the reader falls back to the default pydicom decoders.
 
     Args:
         channel_dim: the channel dimension of the input image, default is None.
@@ -1159,6 +1159,14 @@ def __init__(
             to_gpu=False,
             **kwargs,
         )
+
+        self._nvimgcodec_available = False
+        self._setup_done = False
+
+    def _ensure_setup(self) -> None:
+        """Import and register the nvImageCodec plugin on first use only."""
+        if self._setup_done:
+            return
         from monai.data.nvimgcodec_pydicom_plugin import is_nvimgcodec_available, register_as_decoder_plugin
 
         self._nvimgcodec_available = is_nvimgcodec_available()
@@ -1167,14 +1175,28 @@ def __init__(
                 "NvImgCodecPydicomReader: nvImageCodec decoder plugin did not register successfully. "
                 "Falling back to default pydicom decoders."
             )
+        self._setup_done = True
 
     def verify_suffix(self, filename: Sequence[PathLike] | PathLike) -> bool:
         """
         Verify whether the specified file or files are DICOM and nvImageCodec is available.
         """
-        if not has_pydicom or not self._nvimgcodec_available:
+        if not has_pydicom or not is_dicom_path(filename):
             return False
-        return is_dicom_path(filename)
+        self._ensure_setup()
+        return self._nvimgcodec_available
+
+    def read(self, data: Sequence[PathLike] | PathLike, **kwargs):
+        """Read image data using the configured reader.
+
+        Args:
+            data: Input image data or file path.
+            **kwargs: Additional arguments passed to the underlying reader.
+
+        Returns:
+            The image data returned by the underlying reader."""
+        self._ensure_setup()
+        return super().read(data, **kwargs)
 
 
 @require_pkg(pkg_name="nibabel")

monai/data/nvimgcodec_pydicom_plugin.py

@@ -66,7 +66,7 @@ def is_nvimgcodec_available() -> bool:
 def register_as_decoder_plugin(module_path: str | None = None) -> bool:
     """Register the nvImageCodec pydicom decoder plugin."""
     if not is_nvimgcodec_available():
-        _logger.warning("nvImageCodec is not available; skipping pydicom decoder plugin registration.")
+        _logger.debug("nvImageCodec is not available; skipping pydicom decoder plugin registration.")
         return False
     if not has_pydicom_plugin:
         return False

tests/data/test_init_reader.py

@@ -12,8 +12,11 @@
 from __future__ import annotations
 
 import os
+import subprocess
+import sys
 import tempfile
 import unittest
+from importlib.machinery import PathFinder
 
 import numpy as np
 
@@ -65,6 +68,45 @@ def test_load_image(self):
             inst = LoadImaged("image", reader="NvImgCodecPydicomReader")
             self.assertIsInstance(inst, LoadImaged)
 
+    def test_nvimgcodec_not_imported_on_monai_import(self):
+        """Verify importing MONAI does not eagerly load the optional NVIDIA package."""
+        nvidia_spec = PathFinder.find_spec("nvidia")
+        if nvidia_spec is None or nvidia_spec.submodule_search_locations is None:
+            self.skipTest("nvidia.nvimgcodec is not installed")
+
+        nvimgcodec_spec = PathFinder.find_spec("nvimgcodec", nvidia_spec.submodule_search_locations)
+        if nvimgcodec_spec is None:
+            self.skipTest("nvidia.nvimgcodec is not installed")
+
+        code = "import monai, sys; print('nvidia.nvimgcodec' in sys.modules)"
+        result = subprocess.run([sys.executable, "-c", code], capture_output=True, text=True)
+
+        self.assertEqual(result.returncode, 0, result.stderr)
+        self.assertEqual(result.stdout.strip(), "False")
+        self.assertEqual(result.stderr, "")
+
+    def test_nvimgcodec_not_imported_on_loadimage_init(self):
+        """Verify initializing LoadImage does not eagerly load nvimgcodec."""
+        nvidia_spec = PathFinder.find_spec("nvidia")
+        if nvidia_spec is None or nvidia_spec.submodule_search_locations is None:
+            self.skipTest("nvidia.nvimgcodec is not installed")
+
+        nvimgcodec_spec = PathFinder.find_spec("nvimgcodec", nvidia_spec.submodule_search_locations)
+        if nvimgcodec_spec is None:
+            self.skipTest("nvidia.nvimgcodec is not installed")
+
+        code = (
+            "import monai, sys; "
+            "from monai.transforms import LoadImage; "
+            "LoadImage(); "
+            "print('nvidia.nvimgcodec' in sys.modules)"
+        )
+        result = subprocess.run([sys.executable, "-c", code], capture_output=True, text=True)
+
+        self.assertEqual(result.returncode, 0, result.stderr)
+        self.assertEqual(result.stdout.strip(), "False")
+        self.assertEqual(result.stderr, "")
+
     @SkipIfNoModule("nibabel")
     @SkipIfNoModule("cupy")
     @SkipIfNoModule("kvikio")

tests/data/test_nvimgcodec_pydicom_reader.py

@@ -100,13 +100,28 @@ class TestNvImgCodecPydicomReader(unittest.TestCase):
     @SkipIfNoModule("pydicom")
     @patch("monai.data.nvimgcodec_pydicom_plugin.register_as_decoder_plugin", return_value=True)
     @patch("monai.data.nvimgcodec_pydicom_plugin.is_nvimgcodec_available", return_value=True)
-    def test_reader_init_registers_plugin(self, _mock_available, mock_register):
+    def test_reader_registers_plugin_lazily(self, _mock_available, mock_register):
         from monai.data import NvImgCodecPydicomReader
 
         reader = NvImgCodecPydicomReader()
         self.assertIsInstance(reader, NvImgCodecPydicomReader)
+
+        mock_register.assert_not_called()
+
+        reader.verify_suffix("x.dcm")
+
         mock_register.assert_called_once()
 
+    @SkipIfNoModule("pydicom")
+    @patch("monai.data.nvimgcodec_pydicom_plugin.register_as_decoder_plugin", return_value=True)
+    @patch("monai.data.nvimgcodec_pydicom_plugin.is_nvimgcodec_available", return_value=True)
+    def test_reader_does_not_register_plugin_for_non_dicom(self, _mock_available, mock_register):
+        from monai.data import NvImgCodecPydicomReader
+
+        reader = NvImgCodecPydicomReader()
+        self.assertFalse(reader.verify_suffix("x.png"))
+        mock_register.assert_not_called()
+
     @SkipIfNoModule("pydicom")
     @patch("monai.data.nvimgcodec_pydicom_plugin.is_nvimgcodec_available", return_value=False)
     def test_verify_suffix_without_nvimgcodec(self, _mock_available):