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Start horizontally centered in the periphery. Swing the camera head downwards and upwards. Re-
turn back to the middle position. Go to the right. Again swing the camera downwards and up-
wards, etc.
Proceed until you covered the whole area of interest. Stop the acquisition of images by pressing
the 'freeze' button on the control panel. A reasonable value for the number of acquired images for
the composite image is 30 up to 100.
You are not restricted to this moving pattern. After you've got some experience with this kind of
acquisition, you will find the most suitable pattern for your needs.
Important:
To obtain an image series suitable for the mosaic computation, it is important to
avoid any movements of the camera mounting base or any adjustments of the height
of the camera.
6.2.2 Computing Mean Images
To compute a mean image of several single images, select the images as described above and
choose 'Compute Mean Image':
After the averaging procedure, the resulting image is appended at the end of the examination.
Averaging makes sense for images with a low signal to noise ratio, e.g. auto-flourescence images,
late phase images or images of cataract patients. The signal to noise ratio increases by a factor of
n
, where n is the number of images to be averaged (e.g. factor of 2 (for n=2) and factor of 4 (for
n=16)). Because of this mathematical fact, using more then 16 images will only slightly enhance
the resulting mean image quality.
Summary of Contents for HRA 2
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