Terminology, Positioning, and Imaging Principles C H A P T E R 1
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Image Receptor Sizes and Orientation As noted previously, image receptor (IR) applies to the device that captures the radiation that exits the patient; IR refers to the film cassette as well as to the digital acquisition device. Use of metric System Internationale (SI) units to describe the size of film-screen cassettes and image plates in CR has primarily replaced use of the English units. See the accompanying table for a list of available IR sizes for film-screen imaging and for CR.
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AVAILABLE IR SIZES IN FILM-SCREEN IMAGING METRIC (SI) SIZE (CM)
18 × 24
ENGLISH UNIT REFERENCE (INCHES)
8 × 10
CLINICAL APPLICATION
General imaging, mammography
24 × 24
9×9
Fluoroscopic spot imaging
18 × 43
7 × 17
General imaging
24 × 30
10 × 12
General imaging, mammography
30 × 35; 35 × 35; 30 × 40
11 × 14
General imaging
NA 35 × 43 NA
14 × 36; 14 × 51 14 × 17 5 × 12; 6 × 12
Full spine/lower limbs General imaging Mandible/ orthopantotomography
AVAILABLE IR SIZES IN PSP-BASED SYSTEMS METRIC (SI) SIZE (CM)
ENGLISH UNIT REFERENCE (INCHES)
CLINICAL APPLICATION
18 × 24
8 × 10
General imaging, mammography
24 × 30
10 × 12
General imaging, mammography
35 × 35
14 × 14
General imaging
35 × 43
14 × 17
General imaging
The selection of IR size depends primarily on the body part that is to be examined. The size and shape of the body part being examined also determines the orientation of the IR. If the IR is positioned with the longer dimension of the IR parallel to the long axis of the body part, the orientation is portrait; if the IR is positioned with the shorter dimension of the IR parallel to the long axis of the body part, the orientation is landscape. A common example applied to clinical practice relates to chest radiography. Patients who are hypersthenic are imaged with the IR in landscape orientation, so the lateral aspects of the chest may be included in the image (Fig. 1-171). Students also may hear the terms lengthwise and crosswise used to describe IR orientation. These correspond to portrait and landscape, respectively.
Fig. 1-171 AP mobile chest landscape (crosswise) IR alignment.
