Hi, I would like to ask how to read a big file from disk and maintain the PyQt4 UI responsive (not blocked). I had moved the load of the file to a QThread subclass but my GUI thread get freezed. Any suggestions? I think it must be something with the GIL but I don't know how to sort it? EDIT: I am using vtkGDCMImageReader from the GDCM project to read a multiframe DICOM image and display it with vtk and pyqt4. I do this load in a different thread (QThread) but my app freeze until the image is loaded. here is an example code: class ReadThread(QThread): def __init__(self, file_name): super(ReadThread, self).__init__(self) self.file_name = file_name self.reader.vtkgdcm.vtkGDCMImageReader() def run(self): self.reader.SetFileName(self.file_name) self.reader.Update() self.emit(QtCore.SIGNAL('image_loaded'), self.reader.GetOutput())