Scintigraphy is a type of nuclear medicine imaging study. It is based on the ability of gamma probe cameras to detects radioactively labeled molecules within the body. Usually, a patient is asked to inhale radionucleatide labeled molecules and a picture is taken with special cameras which visualize the lungs while the radioisotopes are distributed within the lungs. If there is an area of the lung where inhaled air is not getting to then the most of the lung will "enhance," however the area that did not get the inhaled substance will not. This can help localize a shunt or an area of the lung that is considered "dead space" which is to say it is not being ventilated. Depending on the reasoning behind why the test is being ordered, a special IV fluid labeled with another radio-labeled substance (for example, radiolabeled albumin) may also be used.
Because lung scintigraphy is used for different things (e.g. detection of PE scans vs pre-operative evaluation for lung transplant), the way in which the test is done may differ slightly as well with respect to how much and through which route the radio-labeled material is administered into the body.
I recommend discussing the test and its indications with your physician or radiologist