The total movement of the diaphragm will be less for which type of body habitus

3

GENERAL ANATOMY AND RADIOGRAPHIC POSITIONING TERMINOLOGY

General Anatomy

Radiographers must possess a thorough knowledge of anatomy, physiology, and osteology to obtain radiographs that show the desired body part. Anatomy is the term applied to the science of the structure of the body. Physiology is the study of the function of the body organs. Osteology is the detailed study of the body of knowledge relating to the bones of the body.

Radiographers also must have a general understanding of all body systems and their functions. Particular attention must be given to gaining a thorough understanding of the skeletal system and the surface landmarks used to locate different body parts. The radiographer must be able to visualize mentally the internal structures that are to be radiographed. By using external landmarks, the radiographer should properly position body parts to obtain the best diagnostic radiographs possible.

BODY HABITUS

Common variations in the shape of the human body are termed the body habitus. 1 determined the primary classifications of body habitus based on his study of 1000 patients. The specific type of body habitus is important in radiography because it determines the size, shape, and position of the organs of the thoracic and abdominal cavities.

Body habitus directly affects the location of the following:

An organ such as the gallbladder may vary in position by 8 inches, depending on the body habitus. The stomach may be positioned horizontally, high, and in the center of the abdomen for one type of habitus and positioned vertically, low, and to the side of the midline in another type. Fig. 3-9 shows an example of the placement, shape, and size of the lungs, heart, and diaphragm in patients with four different body habitus types.

Body habitus and the placement of the thoracic and abdominal organs are also important in the determination of technical and exposure factors for the appropriate radiographic density and contrast and the radiation doses. Contrast medium in the gallbladder may affect the automatic exposure control detector. For one type of habitus, the gallbladder may lie directly over the detector (which is undesirable); for another, it may not even be near the detector. The standard placement and size of the IR may have to be changed because of body habitus. The selection of kilovolt (peak) and milliampere-second exposure factors may also be affected by the type of habitus because of wide variations in physical tissue density. These technical considerations are described in greater detail in radiography physics and imaging texts.

Box 3-1 describes specific characteristics of the four types of body habitus and outlines their general shapes and variations. The four major types of body habitus and their approximate frequency in the population are identified as follows:

More than 85% of the population has either a sthenic or hyposthenic body habitus. The sthenic type is considered the dominant type of habitus. The relative shape of patients with a sthenic or hyposthenic body habitus and the position of their organs are referred to in clinical practice as ordinary or average. All standard radiographic positioning and exposure techniques are based on these two groups. Radiographers must become thoroughly familiar with the characteristics and organ placements of these two body types.

Radiographers must also become familiar with the two extreme habitus types: asthenic and hypersthenic. In these two small groups (15% of the population), the placement and size of the organs significantly affect positioning and the selection of exposure factors. Consequently, radiography of these patients can be challenging. Experience and professional judgment enable the radiographer to determine the correct body habitus and to judge the specific location of the organs.

Body habitus is not an indication of disease or other abnormality, and it is not determined by the body fat or physical condition of the patient. Habitus is simply a classification of the four general shapes of the trunk of the human body. When positioning patients, the radiographer should be conscious that habitus is not associated with height or weight. Four patients of equal height could have four different trunk shapes (Fig. 3-10).

Osteology

The adult human skeleton is composed of 206 primary bones. Ligaments unite the bones of the skeleton. Bones provide the following:

The 206 bones of the body are divided into two main groups:

The axial skeleton supports and protects the head and trunk with 80 bones (Table 3-2). The appendicular skeleton allows the body to move in various positions and from place to place with its 126 bones (Table 3-3). Fig. 3-11 identifies these two skeletal areas.

BONE DEVELOPMENT

Ossification is the term given to the development and formation of bones. Bones begin to develop in the 2nd month of embryonic life. Ossification occurs separately by two distinct processes: intermembranous ossification and endochondral ossification.

Secondary ossification

Secondary ossification occurs after birth when a separate bone begins to develop at both ends of each long bone. Each end is called the epiphysis (Fig. 3-15, B). At first, the diaphysis and epiphysis are distinctly separate. As growth occurs, a plate of cartilage called the epiphyseal plate develops between the two areas (Fig. 3-15, C). This plate is seen on long bone radiographs of all pediatric patients (Fig. 3-16, A). The epiphyseal plate is important radiographically because it is a common site of fractures in pediatric patients. Near age 21 years, full ossification occurs, and the two areas become completely joined; only a moderately visible epiphyseal line appears on the bone (Fig. 3-16, B).

Fig. 3-16 A, Radiograph of a 6-year-old child. Epiphysis and epiphyseal plate shown on knee radiograph (arrows). B, Radiograph of same area in a 21-year-old adult. Full ossification has occurred, and only subtle epiphyseal lines are seen (arrows). C, PA radiograph of hand of a 2½-year-old child. Note early stages of ossification in epiphyses at proximal ends of phalanges and first metacarpal, distal ends of other metacarpals, and radius. (C, From Standring S: Gray’s anatomy, ed 40, New York, 2009, Churchill Livingstone.) Churchill Livingstone

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