<unk>  makes use of plain X-ray images. These are very poor at resolving soft tissues, such as the brain. Moreover, all the structures captured in the image are superimposed on top of each other, which makes it difficult to pick out individual items of interest (unlike modern scanners which are able to produce fine virtual slices of the body, including of soft tissues). Therefore,<unk>  did not usually image abnormalities directly, rather their secondary effects. The overall structure of the brain contains crevices and cavities which are filled by the CSF. Both the brain and the CSF produce similar signals on an X-ray image. However, draining the CSF allows for greater contrast between the brain matter and the (now drained) crevices in and around it, which then show up as dark shadows on the X-ray image. The aim of<unk>  is to outline these shadow-forming air-filled structures so that their shape and anatomical location can be examined. Following the procedure, an experienced radiologist reviews the X-ray films to see if the shape or location of these structures have been distorted or shifted by the presence of certain kinds of lesions. This also means that in order to show up on the images, lesions have to either be located right on the edge of the structures or if located elsewhere in the brain, be large enough to push on surrounding healthy tissues to an extent necessary to cause a distortion in the shape of the more distant air-filled cavities (and hence more-distant tumors detected this way tended to be fairly large). Despite its overall usefulness, there were major portions of the brain and other structures of the head that<unk>  was unable to image. This was partially compensated by increased use of angiography as a complementary diagnostic tool, often in an attempt to infer the condition of non-neurovascular pathology from its secondary vascular characteristics. This additional testing was not without risk though, particularly due to the rudimentary catheterization techniques and deleterious radiocontrast agents of the day. Another drawback of<unk>  was that the risk and discomfort it carried meant that repeat studies were generally avoided, thus making it difficult to assess disease progression over time.
Pneumoencephalography
Brain biopsy
Hemoencephalography
Cranioscopy
Cranio-corpography
Meningeal biopsy
CSF tap test
Lumbar puncture