Click
the zoom tool 
and click
on the thumbnail
Define the default size in the Thumbnail Size setting.
The viewer includes a panel showing thumbnail images and headers of each original series, post-processed images, presentation state groups, and key images.
By default, the thumbnail panel appears on the primary monitor. To enable the thumbnail panel on other monitors, activate it on each monitor as follows:
From the View menu, select Customize Settings.
Click the View tab.
In the Monitors section, select the monitor on which you want the thumbnail panel to appear.
Check the Thumbnail Panel checkbox.
Click OK
By default, the thumbnail panel appears on the left image area border. The panel’s location is the same on all enabled monitors. Change the location as follows:
From the View menu, select Customize Settings.
Click the View tab.
In the General section, select the location from the Thumbnail Panel Location menu. Hide will remove the thumbnail panel from all enabled monitors. Left and Top position the thumbnail panel along the respective image frame border.
To display the thumbnail panel, do one of the following:
Click the Thumbnail Panel item in the View menu.
Press Alt + T.
Place the cursor over the leftmost border of the viewing area to change the cursor to a bi-directional arrow, press the left mouse button and drag the border to the left until the thumbnail panel is the desired size.
To set the thumbnail image size, do one of the following:
Click
the zoom tool and click
on the thumbnail
Define the default size in the Thumbnail Size setting.
Thumbnail panel images are for reference only. Load thumbnail images into image frames to display full resolution images and apply the image manipulation tools.
Presentation
state thumbnail images appear in the thumbnail panel after the Presentation
Group header and have a presentation state icon, 
,
on top. One thumbnail series exists for each series containing an image
with a defined presentation state. Load
the thumbnail into an image frame to render the series.
Key images
appear in the thumbnail panel after the Presentation Group header and
have a key image icon, 
, on top.
One thumbnail series exists for each report component containing key images.
Load the thumbnail
into an image frame to render the series like other images.
The thumbnail panel's header and series headers can be customized. Their content is defined in the DICOM Fields section of the Customize Settings panel.