FileReadOption.ReadAll is used.

Controllers/SCUController.cs

@@ -31,7 +31,7 @@ namespace SendFileWebapi.Controllers
                 .Select(fileName => Observable.FromAsync(async () =>
             {
                 var stream = fileName.OpenReadStream();
-                var request = new Dicom.Network.DicomCStoreRequest(await DicomFile.OpenAsync(stream));
+                var request = new Dicom.Network.DicomCStoreRequest(await DicomFile.OpenAsync(stream, FileReadOption.ReadAll));
                 await client.AddRequestAsync(request);
                 await client.SendAsync();
                 stream.Dispose();