GENERAL ANATOMY AND RADIOGRAPHIC POSITIONING TERMINOLOGY

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GENERAL ANATOMY AND RADIOGRAPHIC POSITIONING TERMINOLOGY




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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 PLANES


The full dimension of the human body as viewed in the anatomic position (see Chapter 1) can be effectively subdivided through the use of imaginary body planes. These planes slice through the body at designated levels from all directions. The following four fundamental body planes referred to regularly in radiography are illustrated in Fig. 3-1, A:





Sagittal plane


A sagittal plane divides the entire body or a body part into right and left segments. The plane passes vertically through the body from front to back (see Fig. 3-1, A and B). The midsagittal plane is a specific sagittal plane that passes through the midline of the body and divides it into equal right and left halves (Fig. 3-1, C).



Coronal plane


A coronal plane divides the entire body or a body part into anterior and posterior segments. The plane passes through the body vertically from one side to the other (see Fig. 3-1, A and B). The midcoronal plane is a specific coronal plane that passes through the midline of the body, dividing it into equal anterior and posterior halves (see Fig. 3-1, C). This plane is sometimes referred to as the midaxillary plane.




Oblique plane


An oblique plane can pass through a body part at any angle among the three previously described planes (see Fig. 3-1, A and B). Planes are used in radiographic positioning to center a body part to the image receptor (IR) or central ray and to ensure that the body part is properly oriented and aligned with the IR. The midsagittal plane may be centered and perpendicular to the IR with the long axis of the IR parallel to the same plane. Planes can also be used to guide projections of the central ray. The central ray for an anteroposterior (AP) projection passes through the body part parallel to the sagittal plane and perpendicular to the coronal plane. Quality imaging requires attention to all relationships among body planes, the IR, and the central ray.


Body planes are used in computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound (US) to identify the orientation of anatomic cuts or slices shown in the procedure (Fig. 3-2). Imaging in several planes is often used to show large sections of anatomy (Fig. 3-3).






BODY CAVITIES


The two great cavities of the torso are the thoracic and abdominal cavities (Fig. 3-5). The thoracic cavity is subdivided into a pericardial segment and two pleural portions. Although the abdominal cavity has no intervening partition, the lower portion is called the pelvic cavity. Some anatomists combine the abdominal and pelvic cavities and refer to them as the abdominopelvic cavity. The principal structures located in the cavities are listed on the following page.






DIVISIONS OF THE ABDOMEN


The abdomen is the portion of the trunk that is bordered superiorly by the diaphragm and inferiorly by the superior pelvic aperture (pelvic inlet). The location of organs or an anatomic area can be described by dividing the abdomen according to one of two methods: four quadrants or nine regions.





SURFACE LANDMARKS


Most anatomic structures cannot be visualized directly; the radiographer must use various protuberances, tuberosities, and other external indicators to position the patient accurately. These surface landmarks enable the radiographer to obtain radiographs of optimal quality consistently for a wide variety of body types. If surface landmarks are not used for radiographic positioning or if they are used incorrectly, the chance of having to repeat the radiograph greatly increases.


Many commonly used landmarks are listed in Table 3-1 and diagrammed in Fig. 3-8. These landmarks are accepted averages for most patients and should be used only as guidelines. Variations in anatomic build or pathologic conditions may warrant positioning compensation on an individual basis. The ability to compensate is gained through experience.





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.






GENERAL BONE FEATURES


The general features of most bones are shown in Fig. 3-12. All bones are composed of a strong, dense outer layer called the compact bone and an inner portion of less dense spongy bone. The hard outer compact bone protects the bone and gives it strength for supporting the body. The softer spongy bone contains a spiculated network of interconnecting spaces called the trabeculae (Fig. 3-13). The trabeculae are filled with red and yellow marrow. Red marrow produces red and white blood cells, and yellow marrow stores adipose (fat) cells. Long bones have a central cavity called the medullary cavity, which contains trabeculae filled with yellow marrow. In long bones, the red marrow is concentrated at the ends of the bone and not in the medullary cavity.




A tough, fibrous connective tissue called the periosteum covers all bony surfaces except the articular surfaces, which are covered by the articular cartilage. The tissue lining the medullary cavity of bones is called the endosteum. Bones contain various knoblike projections called tubercles and tuberosities, which are covered by the periosteum. Muscles, tendons, and ligaments attach to the periosteum at these projections. Blood vessels and nerves enter and exit the bone through the periosteum.



BONE VESSELS AND NERVES


Bones are live organs and must receive a blood supply for nourishment or they die. Bones also contain a supply of nerves. Blood vessels and nerves enter and exit the bone at the same point, through openings called the foramina. Near the center of all long bones is an opening in the periosteum called the nutrient foramen. The nutrient artery of the bone passes into this opening and supplies the cancellous bone and marrow. The epiphyseal artery separately enters the ends of long bones to supply the area, and periosteal arteries enter at numerous points to supply the compact bone. Veins exiting the bones carry blood cells to the body (Fig. 3-14).




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).



Mar 4, 2016 | Posted by in GENERAL RADIOLOGY | Comments Off on GENERAL ANATOMY AND RADIOGRAPHIC POSITIONING TERMINOLOGY
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