Whole-body Studies

Whole-body scintigraphy is especially useful for searching for metastases of tumours. It would be very expensive (at present it is actually impossible) to produce a gamma camera that can take an image of the whole body all at once, instead, ‘regular’ cameras are used in these examinations. These tests are performed using a radiopharmaceutical that accumulates in cancerous tissue and displays an unchanging distribution for a relatively long time.

It is clear that the relative position of the patient and the camera needs to change during the examination. It is easier to move the patient instead of the camera, so the examination is performed on a moving bed.

In theory there are two ways of performing the examination. In the first case, the bed is immobile for a longer period of time, then it is moved to the next position; in the second case the bed moves continuously. The first case results in changes in the patient’s position because the movement of the bed starts, then stops; this makes attaching together the individual images taken in the different positions very difficult. In the second case the image may become blurry because of the constant movement of the bed.

In practice the second method is applied. The bed – together with the patient – is moved by a motor. The imaging software and the speed of the bed are precisely synchronized: as the bed shifts away so that the image would move a pixel away, the imaging software modifies the place of data acquisition by one line. It is also possible to eliminate blurring within a pixel. In order to achieve this, a similar technique needs to be applied as in case of the linearity correction. Before digitalizing the coordinates of the incoming pulse, the coordinates of the pulse need to be corrected by the displacement of the bed at the moment of the arrival of the pulse.

Figure 1. Whole-body examination. Patient Images are acquired from „Anterior” and „Posterior” direction. The interested areas are enlarged.