speed up DICOM slice previews

web_backend.py

@@ -12,7 +12,7 @@ from email.policy import default
 from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
 from io import BytesIO
 from pathlib import Path
-from urllib.parse import parse_qs, unquote, urlparse
+from urllib.parse import parse_qs, quote, unquote, urlparse
 
 os.environ.setdefault("MPLCONFIGDIR", "/tmp/head_ct_morph_matplotlib")
 
@@ -37,9 +37,11 @@ HOST = "0.0.0.0"
 PORT = 8787
 JOBS = {}
 JOBS_LOCK = threading.Lock()
+DICOM_FILE_CACHE = {}
 LIBRARY_DIR = APP_DIR / "web_library"
 LIBRARY_META = LIBRARY_DIR / "library.json"
 RESULT_DIR = APP_DIR / "web_results"
+PREVIEW_CACHE_DIR = LIBRARY_DIR / "_preview_cache"
 
 
 def json_default(value):
@@ -124,7 +126,23 @@ def sort_key_for_dicom(path):
 
 
 def sorted_dicom_files(dicom_dir):
-    return sorted(Path(dicom_dir).glob("*.dcm"), key=sort_key_for_dicom)
+    dicom_dir = Path(dicom_dir).resolve()
+    files = list(dicom_dir.glob("*.dcm"))
+    signature = (
+        str(dicom_dir),
+        len(files),
+        max((file_path.stat().st_mtime for file_path in files), default=0),
+    )
+    cached = DICOM_FILE_CACHE.get(str(dicom_dir))
+    if cached and cached["signature"] == signature:
+        return cached["files"]
+
+    sorted_files = sorted(files, key=sort_key_for_dicom)
+    DICOM_FILE_CACHE[str(dicom_dir)] = {
+        "signature": signature,
+        "files": sorted_files,
+    }
+    return sorted_files
 
 
 def find_library_item(item_id):
@@ -142,22 +160,30 @@ def make_library_slice_preview(item_id, index):
 
     count = len(dicom_files)
     index = max(0, min(int(index), count - 1))
-    ds = pydicom.dcmread(str(dicom_files[index]), force=True)
-    image = ds.pixel_array.astype("float32")
-    image = image * float(getattr(ds, "RescaleSlope", 1))
-    image = image + float(getattr(ds, "RescaleIntercept", 0))
+    cache_dir = PREVIEW_CACHE_DIR / item_id
+    safe_mkdir(cache_dir)
+    preview_path = cache_dir / f"slice_{index:04d}.png"
+    if not preview_path.exists():
+        ds = pydicom.dcmread(str(dicom_files[index]), force=True)
+        image = ds.pixel_array.astype("float32")
+        image = image * float(getattr(ds, "RescaleSlope", 1))
+        image = image + float(getattr(ds, "RescaleIntercept", 0))
 
-    preview = Image.fromarray(ct_window(image)).convert("RGB")
-    preview = fit_image(preview, 720, 520)
-    canvas = BytesIO()
-    preview.save(canvas, format="PNG")
-    encoded = base64.b64encode(canvas.getvalue()).decode("ascii")
+        preview = Image.fromarray(ct_window(image)).convert("RGB")
+        preview = fit_image(preview, 720, 520)
+        preview.save(preview_path, format="PNG")
+
+    neighbors = [value for value in [index - 1, index + 1] if 0 <= value < count]
     return {
-        "image": f"data:image/png;base64,{encoded}",
+        "imageUrl": f"/api/file?path={quote(str(preview_path.resolve()), safe='')}",
         "index": index,
         "count": count,
         "file": dicom_files[index].name,
         "patientId": item["patientId"],
+        "neighbors": [
+            f"/api/library/preview?id={item_id}&index={neighbor}"
+            for neighbor in neighbors
+        ],
     }
 
 
@@ -522,7 +548,11 @@ class Handler(BaseHTTPRequestHandler):
         write_library_meta(remaining)
         upload_root = Path(target["dicomPath"]).resolve().parent
         if upload_root.exists() and upload_root.is_relative_to(LIBRARY_DIR.resolve()):
+            DICOM_FILE_CACHE.pop(str(Path(target["dicomPath"]).resolve()), None)
             shutil.rmtree(upload_root)
+        preview_cache = PREVIEW_CACHE_DIR / item_id
+        if preview_cache.exists():
+            shutil.rmtree(preview_cache)
         self.send_json({"ok": True, "items": remaining})
 
     def read_bytes(self):