From then on, 5-ALA was widely applied into the resection of brain and spinal tumour, such as gliomas , glioblastoma , meningioma etc., especially for the tumours of high WHO grade . The low grade gliomas can't be visualized and diagnosed very exactly, though the 5-ALA induced PpIX do accumulate on them, but with the fluorescence emissions below the detection threshold of current visual fluorescence imaging techniques . So researchers proposed the combination of intraoperative confocal microscopy into the 5-ALA fluorescence guided surgery for better detection . On June 2017, FDA approved ALA HCl as "an optical imaging agent indicated in patients with gliomas as an adjunct for the visualization of malignant tissue during surgery" .