Types of Tests

Different isotope-diagnostic tests can be performed with a gamma camera. Studies can be categorized as static, dynamic or gated based on the manner in which temporal functional processes are imaged. In a static study the equilibrium distribution of the injected isotope is of interest, so this is a time-integrated imaging technique. In these studies both hot spots – places where the isotope accumulates – and cold spots – parts of the areas of high activity where there are no isotopes – can be sought. In contrast, in dynamic studies a series of images is taken, which can provide information about the temporal and spatial behaviour of the infiltration and excretion of the radiopharmaceutical. In a gated study the images are taken after a trigger signal, which can be a well defined phase of the cardiac cycle.

In view of the area that is being imaged we distinguish between examinations with one field of view (e.g. thyroid or cardiac studies) and whole-body studies, in which case static images need to be attached together (e.g. bone studies). According to the type of imaging we can distinguish between planar, i.e. not moving (or moving only in a given plane) imaging performed with a gamma camera head and tomographic studies (in other words SPECT, Single Photon Emission Tomography). In case of tomography the gamma camera head rotates around the patient and a 3D image can be created from the images taken this way.

Figure 1.: Bone scintigraphy: detection of bone metastases

In diagnostic applications the post-processing of images is also required. The aim in this case is to highlight the diagnostic information of the planar images. In order to achieve this, different filtering techniques are used which sharpen the image. To be able to sharpen the image, the point response function of the imaging needs to be known, by the help of which, even if the duration of the study or the dose are reduced, an image of the same quality can be acquired as without a filter and by a longer duration or higher dose. Furthermore, filtering can also be performed by using the grain map, the Poisson noise of the collection matrix and as a result, an image with better characteristics can be obtained.