General Techniques Final Parts PDF

C H A P T E R 1 Terminology, Positioning, and Imaging Principles CO N T R I B U T I O N S BY Andrew Woodward, MA, RT(R)(CT)(QM) R A D I AT IO N P ROT E C TI O N CON T R I B...

C H A P T E R 1 Terminology, Positioning, and Imaging Principles CO N T R I B U T I O N S BY Andrew Woodward, MA, RT(R)(CT)(QM) R A D I AT IO N P ROT E C TI O N CON T R I B UTOR Frank Goerner, PhD, DABR W. R. Hedrick, PhD, FACR, Cindy Murphy, BHSc, RT(R), ACR, CO N T R I B U TO R S TO PA ST E D I T IO N S Joseph Popovitch, RT(R), ACR, DHSA, Kathy M. Martensen, BS, RT(R), Barry T. Anthony, RT(R), Katrina Lynn Steinsultz, BS, RT(R)(M) R A D I AT IO N P ROT E C TI O N PA ST CO NT R I B UTO R S Richard Geise, PhD, FACR, FAAPM, E. Russel Ritenour, PhD CONTENTS PA R T O N E : T E R M I N O L O G Y A N D PA R T T W O : I M A G I N G POSITIONING PRINCIPLES General, Systemic, and Skeletal Anatomy Image Quality in Film-Screen (Analog) and Arthrology, 3 Radiography, 38 General Anatomy, 3 Analog Images, 38 Systemic Anatomy, 4 Exposure Factors for Analog (Film-Screen) Skeletal Anatomy, 7 Imaging, 38 Arthrology (Joints), 11 Image Quality Factors, 39 Body Habitus, 15 Density, 39 Contrast, 42 Positioning Terminology, 16 Spatial Resolution, 44 General Terms, 16 Distortion, 46 Body Planes, Sections, and Lines, 17 Image Quality in Digital Radiography, 49 Body Surfaces and Parts, 18 Radiographic Projections, 19 Digital Images, 49 Body Positions, 20 Exposure Factors for Digital Imaging, 49 Additional Special Use Projection Terms, 23 Image Quality Factors, 50 Relationship Terms, 25 Brightness, 50 Terms Related to Movements, 26 Contrast Resolution, 50 Summary of Potentially Misused Positioning Terms, 29 Spatial Resolution, 51 Distortion, 51 Positioning Principles, 31 Exposure Indicator, 51 Evaluation Criteria, 31 Noise, 52 Image Markers and Patient Identification, 32 Postprocessing, 53 Professional Ethics and Patient Care, 33 Applications of Digital Technology, 54 Essential Projections, 34 General Principles for Determining Positioning Digital Imaging Systems, 54 Routines, 34 Image Receptor Sizes and Orientation, 57 Palpation of Topographic Positioning Landmarks, 35 Picture Archiving and Communication System Image Receptor (IR) Alignment, 36 (PACS), 58 Viewing Radiographic Images, 36 Digital Imaging Glossary of Terms, 59 Viewing CT or MRI Images, 37 1  2 C HA PTE R 1 TERMINOLOGY, POSITIONING, AND IMAGING PRINCIPLES PA R T T H R E E : R A D I AT I O N Accurate Collimation, 64 PROTECTION Specific Area Shielding, 65 Pregnant Patient, 66 Radiation Units, 60 1 Optimum Speed, 67 Traditional and SI Units, 60 Minimize Patient Dose by Selecting Projections and Dose Limits, 60 Exposure Factors With Least Patient Dose, 67 Personnel Monitoring, 61 ALARA, 61 Radiation Safety Practices, 68 Pregnant Technologists, 62 Fluoroscopic Patient Dose, 68 Radiographic Patient Dose, 62 Dose Reduction Techniques During Fluoroscopy, 68 Scattered Radiation, 69 Patient Protection in Radiography, 63 Radiation Protection Practices During Fluoroscopy, 69 Minimum Repeat Radiographs, 63 Image Wisely, 70 Correct Filtration, 63  16 C HA PTE R 1 TERMINOLOGY, POSITIONING, AND IMAGING PRINCIPLES POSITIONING TERMINOLOGY 1 Radiographic positioning refers to the study of patient positioning L performed for radiographic demonstration or visualization of specific body parts on image receptors (IRs). The radiologic technologist must clearly understand the correct use of positioning terminology. This section lists, describes, and illustrates the com- monly used terms consistent with the positioning and projection terminology as approved and published by the American Registry of Radiologic Technologists (ARRT).4 Throughout this text, named positions (i.e., with the proper name of the person who first described a specific position or procedure) are referred to as methods, such as the Towne, Waters, and Caldwell methods. The ARRT concurs regarding the use of the named method in parentheses after the projection or position term. The description of radiographic positions by the proper name method is becoming less common. General Terms Radiograph (ra′-de-o-graf): An image of a patient’s anatomic part(s), as produced by the action of x-rays on an image receptor (Fig. 1.36). If the radiograph is produced with the use of tradi- Fig. 1.36 Chest radiograph. tional film-screen (analog) technology, the image is captured and displayed on film; if the radiograph is produced via digital technology, the image is viewed and stored on display monitors. Radiography (ra″-de-og′-rah-fe): The process and procedures of producing a radiograph. Radiograph versus x-ray film: In practice, the terms radiograph and x-ray film (or just film) are often used interchangeably. However, x-ray film specifically refers to the physical piece of material on which a latent (nonprocessed) radiographic image is stored. The term radiograph includes the recording medium and the image. Image receptor (IR): The device that captures the radiographic image that exits the patient; refers to both film-screen cassettes and digital acquisition devices. Central ray (CR): Refers to the centermost portion of the x-ray beam emitted from the x-ray tube—the portion of the x-ray beam that has the least divergence. Fig. 1.37 Radiographic examination. Radiographic Examination or Procedure A radiologic technolo- gist is shown positioning a patient for a routine chest examination or procedure (Fig. 1.37). A radiographic examination involves five general functions: 1. Positioning of body part and alignment with the IR and CR 2. Application of radiation protection measures and devices 3. Selection of exposure factors (radiographic technique). 4. Instructions to the patient related to respiration (breathing) and initiation of the x-ray exposure 5. Processing of the IR (film-based [chemical processing] or com- puted radiography image receptor [digital processing] systems) Anatomic Position The anatomic (an″-ah-tom′-ik) position is a reference position that defines specific surfaces and planes of the body. The anatomic position is an upright position with arms abducted slightly (down), hands by side with palms forward, and head and feet together and directed straight ahead (Fig. 1.38). Viewing Radiographs A general rule in viewing radiographs is to display them so that the patient is facing the viewer, with the patient in the anatomic position. Fig. 1.38 Anatomic position.  TERMINOLOGY, POSITIONING, AND IMAGING PRINCIPLES C H A P TE R 1 17 Body Planes, Sections, and Lines (Fig. 1.39) Positioning terms that describe CR angles or relationships between Sagittal (midsagittal body parts often are related to imaginary planes that pass through or median) plane the body in the anatomic position. The study of CT, MRI (magnetic resonance imaging), and sonography (diagnostic medical ultra- 1 sound) emphasizes sectional anatomy, which also involves the Oblique plane primary body planes and sections as described subsequently. PLANE: STRAIGHT LINE SURFACE CONNECTING TWO POINTS Horizontal (axial) Four common planes as used in medical imaging are as follows: plane Sagittal Plane A sagittal (saj′-i-tal) plane is any longitudinal plane that divides the body into right and left parts. The midsagittal plane, sometimes called the median plane, is a midline sagittal plane that divides the body into equal right and Coronal (frontal or left parts. It passes approximately through the sagittal suture of the midcoronal) plane skull. Any plane parallel to the midsagittal or median plane is called a sagittal plane. Fig. 1.39 Sagittal, coronal, oblique, and horizontal body planes. Coronal Plane A coronal (ko-ro′-nal) plane is any longitudinal plane that divides the body into anterior and posterior parts. The midcoronal plane divides the body into approximately equal anterior and posterior parts. It is called a coronal plane because it passes approximately through the coronal suture of the skull. Any plane parallel to the midcoronal or frontal plane is called a coronal plane. Horizontal (Axial) Plane A horizontal (axial) plane is any transverse plane that passes through the body at right angles to a longitudinal plane, dividing the body into superior and inferior portions. Oblique Plane Oblique transverse Transverse (axial or cross-sectional) plane or section of leg plane or section of arm An oblique plane is a longitudinal or transverse plane that is at an angle or slant and is not parallel to the sagittal, coronal, or Fig. 1.40 Transverse and oblique sections of body parts. horizontal plane. SECTIONAL IMAGE OF BODY PART Longitudinal Sections—Sagittal, Coronal, and Oblique These sections or images run lengthwise in the direction of the long axis of the body or any of its parts, regardless of the position of the body (erect or recumbent). L Longitudinal sections or images may be taken in the sagittal, coronal, or oblique plane. Transverse or Axial Sections (Cross-Sections) Sectional images are at right angles along any point of the longitu- dinal axis of the body or its parts (Fig. 1.40) Sagittal, Coronal, and Axial Images Fig. 1.41 Sagittal image. Fig. 1.42 Coronal image. CT, MRI, and sonography images are obtained in these three common orientations or views. These common orientations are sagittal, coronal, and transverse (axial). (MRI sectional images are shown in Figs. 1.41 through 1.43.) L Fig. 1.43 Transverse (axial) image.  18 C HA PTE R 1 TERMINOLOGY, POSITIONING, AND IMAGING PRINCIPLES PLANES OF THE SKULL (FIG. 1.44) Base Plane of Skull This precise transverse plane is formed by connecting the lines from the infraorbital margins (inferior edge of bony orbits) to the superior 1 margin of the external auditory meatus (EAM), the external opening of the ear. This sometimes is called the Frankfort horizontal plane,1 as used in orthodontics and cranial topography to measure Base plane and locate specific cranial points or structures. Occlusal Plane Occlusal plane This horizontal plane is formed by the biting surfaces of the upper and lower teeth with jaws closed (used as a reference plane of the head for cervical spine and skull radiography). Fig. 1.44 Planes of skull. Body Surfaces and Parts TERMS FOR THE BACK AND FRONT PORTIONS OF THE BODY (FIG. 1.45) Posterior or Dorsal Posterior (pos-te′-re-or) or dorsal (dor′-sal) refers to the back half of the patient, or the part of the body seen when the person is viewed from the back; includes the bottoms of the feet and the Anterior surface backs of the hands as demonstrated in the anatomic position. (ventral) Posterior surface (dorsal) Anterior or Ventral Anterior (an-te′-re-or) or ventral (ven′-tral) refers to front half of the patient, or the part seen when viewed from the front; includes the tops of the feet and the fronts or palms of the hands in the anatomic position. Midsagittal plane TERMS FOR SURFACES OF THE HANDS AND FEET Three terms are used in radiography to describe specific surfaces of the upper and lower limbs. Dorsum (dorsum Plantar pedis) Plantar (plan′-tar) refers to the sole or posterior surface of the foot. Plantar surface of foot Fig. 1.45 Posterior vs. anterior. Dorsal Foot Dorsal (dor′-sal) refers to the top or anterior surface of the foot (dorsum pedis). Hand Dorsal also refers to the back or posterior aspect of the hand (dorsum manus) (Fig. 1.46). NOTE: The term dorsum (or dorsal) in general refers to the vertebral or Dorsal Palmar posterior part of the body. However, when used in relationship with the (posterior, (anterior) foot, dorsum (dorsum pedis) specifically refers to the upper surface, or dorsal anterior aspect, of the foot opposite the sole, whereas for the hand manus) (dorsum manus), it refers to the back or posterior surface opposite the palm.1 Fig. 1.46 Dorsal and palmar surfaces of hand. Palmar Palmar (pal′-mar) refers to the palm of the hand; in the anatomic position, the same as the anterior or ventral surface of the hand.1  TERMINOLOGY, POSITIONING, AND IMAGING PRINCIPLES C H A P TE R 1 19 Radiographic Projections Projection is a positioning term that describes the direction or path of the CR of the x-ray beam as it passes through the patient, projecting an image onto the IR. Although the term position is used in the clinical setting, the term projection is considered to be the 1 most accurate term for describing how the procedure is performed. Therefore, the term projection is used most frequently throughout this text. COMMON PROJECTION TERMS Posteroanterior (PA) Projection Posteroanterior (pos″-ter-o-an-te′-re-or) (PA) projection refers to a projection of the CR from posterior to anterior. Combines these two terms, posterior and anterior, into one Fig. 1.47 PA projection. word, abbreviated as PA. The CR enters at the posterior surface and exits at the anterior surface (PA projection) (Fig. 1.47). Assumes a true PA without intentional rotation, which requires the CR to be perpendicular to the coronal body plane and parallel to the sagittal plane, unless some qualifying oblique or rotational term is used to indicate otherwise. Anteroposterior (AP) Projection Anteroposterior (an″-ter-o-pos-te′-re-or) (AP) projection refers to a projection of CR from anterior to posterior, the opposite of PA. Combines these two terms, anterior and posterior, into one word. Describes the direction of travel of the CR, which enters at an anterior surface and exits at a posterior surface (AP projection) (Fig. 1.48). Assumes a true AP without rotation unless a qualifier term also Fig. 1.48 AP projection. is used, indicating it to be an oblique projection. AP Oblique Projection An AP projection of the upper or lower limb that is rotated is called “oblique.” This is not a true AP projection and must also include a qualifying term that indicates which way it is rotated, such as medial or lateral rotation (Fig. 1.49). (For oblique of the whole body, see oblique position descriptions later in this chapter.) With an AP oblique projection, the CR enters the anterior surface and exits the posterior surface of the body or body part. PA Oblique Projection A PA projection of the upper limb with lateral rotation (from PA) is shown in Fig. 1.50. (This is applicable to both upper and lower limbs.) This projection is described as a PA oblique. It must also Fig. 1.49 AP oblique projection— Fig. 1.50 PA oblique include a qualifying term that indicates which way it is rotated. medial rotation (from AP). projection—lateral With a PA oblique projection, the CR enters the posterior surface rotation (from PA). and exits the anterior surface of the body or body part. Mediolateral and Lateromedial Projections A lateral projection is described by the path of the CR. Two examples are the mediolateral projection of the ankle (Fig. 1.51) and the lateromedial projection of the wrist (Fig. 1.52). The medial and lateral sides are determined with the patient in the anatomic position. In the case of the mediolateral ankle projection, the CR enters the medial aspect and exits the lateral aspect of the ankle. Fig. 1.51 Mediolateral projection Fig. 1.52 (ankle). Lateromedial projection (wrist).  20 C HA PTE R 1 TERMINOLOGY, POSITIONING, AND IMAGING PRINCIPLES Body Positions In radiography, the term position is used in two ways, first as general body positions, as described next, and second as specific body positions, which are described in the pages that follow. 1 GENERAL BODY POSITIONS The eight most commonly used general body positions in medical imaging are as follows: 1. Supine (soo′-pine) Lying on back, facing upward (Fig. 1.53). 2. Prone (prohn) Lying on abdomen, facing downward (head may be turned to one side) (Fig. 1.54). 3. Erect (e-reckt′) (upright) An upright position, to stand or sit erect. Fig. 1.55 Trendelenburg position—head lower than feet. 4. Recumbent (re-kum′-bent) (reclining) Lying down in any position (prone, supine, or on side). Dorsal recumbent: Lying on back (supine). Ventral recumbent: Lying face down (prone). Lateral recumbent: Lying on side (right or left lateral). 5. Trendelenburg5 (tren-del′-en-berg) position A recumbent position with the body tilted with the head lower than the feet (Fig. 1.55). 6. Fowler6 (fow′-ler) position A recumbent position with the body tilted with the head higher than the feet (Fig. 1.56). 7. Sims position (semiprone position) A recumbent oblique position with the patient lying on the left anterior side, with the right knee and thigh flexed and the left arm extended down behind the back. A modified Sims position as used for insertion of the rectal tube for barium enema is shown in Fig. 1.57 (demonstrated in Chapter 13). 8. Lithotomy (li-thot′-o-me) position A recumbent (supine) position with knees and hip flexed and Fig. 1.56 Fowler position—feet lower than head. thighs abducted and rotated externally, supported by ankle supports (Fig. 1.58). This position is seen frequently in the surgical suite for certain urinary studies. Fig. 1.57 Modified Sims position. Fig. 1.53 Supine position. Fig. 1.54 Prone position. Fig. 1.58 Lithotomy position. (From Chitlik A: Safe positioning for robotic-assisted laparoscopic prostatectomy, AORN J 90:39, 2011.)  TERMINOLOGY, POSITIONING, AND IMAGING PRINCIPLES C H A P TE R 1 21 SPECIFIC BODY POSITIONS NOTE: These also can be described as PA oblique projections if a position In addition to a general body position, the second way the term clarifier is added, such as an RAO or LAO position. position is used in radiography is to refer to a specific body position It is not correct to use these oblique terms or the abbreviations described by the body part closest to the IR (oblique and lateral) LPO, RPO, RAO, or LAO as projections because they do not describe or by the surface on which the patient is lying (decubitus). the direction or path of the CR; rather, these are positions. 1 Lateral Position Lateral (lat′-er-al) position refers to the side of, or a side view. Specific lateral positions described by the part closest to the IR or the body part from which the CR exits. A right lateral position is shown with the right side of the body closest to the image receptor (IR) in the erect position (Fig. 1.59). Fig. 1.60 demonstrates a recumbent left lateral position. A true lateral position is always 90°, or perpendicular, or at a right angle, to a true AP or PA projection. If it is not a true lateral, it is an oblique position. Oblique Position5 Oblique (ob-lek′, or ob-lik′)7 (oh bleek′, or oh blike′) position refers to an angled position in which neither the sagittal nor the coronal Fig. 1.61 Erect LPO position. body plane is perpendicular or at a right angle to the IR. Oblique body positions of the thorax, abdomen, or pelvis are described by the part closest to the IR or the body part from which the CR exits. Left and Right Posterior Oblique (LPO and RPO) Positions Describe the specific oblique positions in which the left or right posterior aspect of the body is closest to the IR. A left posterior oblique (LPO) is demonstrated in both the erect (Fig. 1.61) and recumbent (Fig. 1.62) positions. The CR exits from the left or right posterior aspect of the body. NOTE: These also can be referred to as AP oblique projections because the CR enters an anterior surface and exits posteriorly. However, this is not a complete description and requires a specific position clarifier such as LPO or RPO position. Therefore, throughout this text, these body obliques are referred to as positions and not projections. Fig. 1.62 Recumbent LPO position. Obliques of upper and lower limbs are described correctly as AP and PA oblique, but require the use of either medial or lateral rotation as a qualifier (see Figs. 1.49 and 1.50). Right and Left Anterior Oblique (RAO and LAO) Positions Refer to oblique positions in which the right or left anterior aspect of the body is closest to the IR and can be erect or recumbent general body positions. (A right anterior oblique [RAO] is shown in both examples (Figs. 1.63 and 1.64). Fig. 1.63 Erect RAO position. Fig. 1.59 Erect R lateral Fig. 1.60 Recumbent L lateral position. position. Fig. 1.64 Recumbent RAO position.  22 C HA PTE R 1 TERMINOLOGY, POSITIONING, AND IMAGING PRINCIPLES Decubitus (Decub) Position The word decubitus (de-ku′bi-tus) literally means to “lie down,” or the position assumed in “lying down.” This body position, meaning to lie on a horizontal surface, is 1 designated according to the surface on which the body is resting. This term describes a patient who is lying on one of the following body surfaces: back (dorsal), front (ventral), or side (right or left lateral). In radiographic positioning, decubitus is always performed with the central ray horizontal. Decubitus positions are essential for detecting air-fluid levels or free air in a body cavity such as the chest or abdomen, where the air rises to the uppermost part of the body cavity. Decubitus posi- tions are often performed if the patient cannot assume erect position. Fig. 1.66 Right lateral decubitus position (PA projection). Right or Left Lateral Decubitus Position—AP or PA Projection In this position, the patient lies on the side, and the x-ray beam is directed horizontally from anterior to posterior (AP) (Fig. 1.65) or from posterior to anterior (PA) (Fig. 1.66). The AP or PA projection is important as a qualifying term with decubitus positions to denote the direction of the CR. This position is either a left lateral decubitus (see Fig. 1.65) or a right lateral decubitus (see Fig. 1.66). NOTE: The decubitus position is identified according to the dependent side (side down) and the AP or PA projection indication. Example: Left lateral decubitus (PA projection) is with the patient lying on left side facing the image receptor. The CR enters the posterior side and exits the anterior side. Dorsal Decubitus Position—Left or Right Lateral In this position, the patient is lying on the dorsal (posterior) surface with the x-ray beam directed horizontally, exiting from the side closest to the IR (Fig. 1.67). The position is named according to the surface on which the patient is lying (dorsal or ventral) and by the side closest to the IR (right or left). Fig. 1.67 Dorsal decubitus position (L lateral). Ventral Decubitus Position—Right or Left Lateral In this position, the patient is lying on the ventral (anterior) surface with the x-ray beam directed horizontally, exiting from the side closest to the IR (Fig. 1.68). Fig. 1.65 Left lateral decubitus position (AP projection). Fig. 1.68 Ventral decubitus position (R lateral).  TERMINOLOGY, POSITIONING, AND IMAGING PRINCIPLES C H A P TE R 1 23 Additional Special Use Projection Terms CR Following are some additional terms that are commonly used to describe projections. These terms, as shown by their definitions, 37! also refer to the path or projection of the CR and are projections rather than positions. 1 Axial Projection Axial (ak′-se-al) refers to the long axis of a structure or part (around which a rotating body turns or is arranged). Special application—AP or PA axial: In radiographic positioning, the term axial is used to describe any angle of the CR of 10° or more along the long axis of the body or body part.8 However, in a true sense, an axial projection would be directed along, or parallel to, the long axis of the body or part. The term semiaxial, or “partly” axial, more accurately describes any angle along the axis that is not truly perpendicular or parallel to the long axis. However, Fig. 1.70 AP axial (semiaxial) projection (CR 37° caudal). for the sake of consistency with other references, the term axial projection is used throughout this text to describe both axial and semiaxial projections, as defined earlier and as illustrated in Figs. 1.69 through 1.71. Inferosuperior and Superoinferior Axial Projections Inferosu- perior axial projections are frequently performed for the shoulder and hip, where the CR enters below or inferiorly and exits above or superiorly (see Fig. 1.71). The opposite of this is the superoinferior axial projection, such as a special nasal bone projection (see Fig. 1.69). Tangential Projection Tangential (ta″-jen′-shal) means touching a curve or surface at only one point. This is a special use of the term projection to describe the central ray that skims a body part to project the anatomy into profile and free of superimposition of surrounding body structures. Fig. 1.71 Inferosuperior axial projection. Examples Following are two examples or applications of the term tangential projection: CR CR Tangential projection of zygomatic arch (Fig. 1.72) Tangential projection of patella (Fig. 1.73) AP Axial Projection—Lordotic Position This is a specific AP axial chest projection for demonstrating the apices of the lungs. It also is called the AP lordotic position. In this case, the long axis of the body rather than the CR is angled. The term lordotic comes from lordosis, a term that denotes curvature of the cervical and lumbar spine (see Chapters 8 and 9). As the patient assumes this position (Fig. 1.74), the lumbar lordotic curvature is exaggerated, making this a descriptive term for this Fig. 1.72 Tangential Fig. 1.73 Tangential projection special chest projection. projection (zygomatic (patella). arch). Fig. 1.69 Superoinferior (axial) projection. Fig. 1.74 AP lordotic chest position.  24 C HA PTE R 1 TERMINOLOGY, POSITIONING, AND IMAGING PRINCIPLES Transthoracic Lateral Projection (Right Lateral Position) A lateral projection through the thorax. Requires a qualifying positioning term (right or left lateral posi- tion) to indicate which shoulder is closest to the IR and is being 1 examined (Fig. 1.75). NOTE: This is a special adaptation of the projection term, indicating that the CR passes through the thorax even though it does not include an entrance or exit site. In practice, this is a common lateral shoulder projection and is referred to as a right or left transthoracic lateral shoulder. Dorsoplantar and Plantodorsal Projections These are secondary terms for AP or PA projections of the foot. Dorsoplantar (DP) describes the path of the CR from the dorsal (anterior) surface to the plantar (posterior) surface of the foot (Fig. 1.76). Fig. 1.77 Axial plantodorsal Fig. 1.78 Parietoacanthial A special plantodorsal projection of the heel bone (calcaneus) (PD) projection of calcaneus. projection (PA Waters position). is called an axial plantodorsal projection (PD) because the angled CR enters the plantar surface of the foot and exits the dorsal surface (Fig. 1.77). NOTE: The term dorsum for the foot refers to the anterior surface, dorsum pedis (see Fig. 1.45). Parietoacanthial and Acanthioparietal Projections The CR enters at the cranial parietal bone and exits at the acan- thion (junction of nose and upper lip) for the parietoacanthial projection (Fig. 1.78). The opposite CR direction would describe the acanthioparietal projection (Fig. 1.79). These are also known as PA Waters and AP reverse Waters methods and are used to visualize the facial bones. Submentovertical (SMV) and Verticosubmental (VSM) Projections These projections are used for the skull and mandible. CR enters below the chin, or mentum, and exits at the vertex or top of the skull for the submentovertical (SMV) projection Fig. 1.79 Acanthioparietal projection. (Fig. 1.80). The less common, opposite projection of this would be the verticosubmental (VSM) projection, entering at the top of the skull and exiting below the mandible (not shown). Fig. 1.75 Transthoracic lateral Fig. 1.76 AP or dorsoplantar Fig. 1.80 Submentovertical (SMV) projection. shoulder projection (R lateral (DP) projection of foot. shoulder position).  TERMINOLOGY, POSITIONING, AND IMAGING PRINCIPLES C H A P TE R 1 25 Relationship Terms Following are paired positioning or anatomic terms that are used to describe relationships to parts of the body with opposite meanings. Medial Versus Lateral 1 Proximal Medial (me′-de-al) versus lateral refers to toward versus away Medial plane from the center, or median plane. In the anatomic position, the medial aspect of any body part is Lateral the “inside” part closest to the median plane, and the lateral part abdomen is away from the center, or away from the median plane or midline of the body (Fig. 1.81). Lateral arm Medial arm Examples In the anatomic position, the thumb is on the lateral aspect of the hand. The lateral part of the abdomen and thorax is Lateral hand the part away from the median plane. Distal Proximal Versus Distal Fig. 1.81 Medial vs. lateral, proximal vs. distal. Proximal (prok′-si-mal) is near the source or beginning, and distal (dis′-tal) is away from. In regard to the upper and lower limbs, proximal and distal would be the part closest to or away from the trunk, the source or beginning of that limb (see Fig. 1.81). Examples The elbow is proximal to the wrist. The finger joint closest to the palm of the hand is called the proximal interphalan- geal (PIP) joint, and the joint near the distal end of the finger is the distal interphalangeal (DIP) joint (see Chapter 4). Cephalad Versus Caudad Cephalad (sef′-ah-lad) means toward the head end of the body; caudad (kaw′-dad) means away from the head end of the body. A cephalad angle is any angle toward the head end of the Fig. 1.82 Cephalad CR angle Fig. 1.83 Caudad CR angle body (Figs. 1.82 and 1.84). (Cephalad, or cephalic, literally means (toward head). (away from head). “head” or “toward the head.”) A caudad angle is any angle toward the feet or away from the head end (Fig. 1.83). (Caudad or caudal comes from cauda, liter- ally meaning “tail.”) In human anatomy, cephalad and caudad also can be described as superior (toward the head) or inferior (toward the feet). NOTE: As is shown in Figs. 1.82, 1.83, and 1.84, these terms are correctly used to describe the direction of the CR angle for axial projections along the entire length of the body, not just projections of the head. Interior (Internal, Inside) Versus Exterior (External, Outer) Interior is inside of something, nearer to the center, and exterior is situated on or near the outside. Cephalad Caudad The prefix intra- means within or inside (e.g., intravenous: (superior) (inferior) inside a vein). The prefix inter- means situated between things (e.g., intercos- tal: located between the ribs). The prefix exo- means outside or outward (e.g., exocardial: Fig. 1.84 Cephalic angle (AP axial projection of sacrum). something that develops or is situated outside the heart). Superficial Versus Deep Superficial is nearer the skin surface; deep is farther away. Example The cross-sectional drawing in Fig. 1.85 shows that the Skin (superficial) humerus is deep compared with the skin of the arm, which is superficial. Another example would be a superficial tumor or lesion, which Humerus is located near the surface, compared with a deep tumor or lesion, (deep) which is located deeper within the body or part. Ipsilateral Versus Contralateral Ipsilateral (ip″-si-lat′-er-al) is on the same side of the body or part; contralateral (kon″-trah-lat′-er-al) is on the opposite side. Fig. 1.85 Cross-section of arm. Example The right thumb and the right great toe are ipsilateral; the right knee and the left hand are contralateral.  26 C HA PTE R 1 TERMINOLOGY, POSITIONING, AND IMAGING PRINCIPLES Terms Related to Movement Flexion The final group of positioning and related terms that every technolo- gist should know relates to various movements. Most of these are listed as paired terms that describe movements in opposite 1 directions. Flexion Flexion Versus Extension When a joint is flexed or extended, the angle between parts is Extension decreased or increased. Flexion decreases the angle of the joint (see examples of knee, elbow, and wrist flexions in Fig. 1.86). Extension Extension increases the angle as the body part moves from a flexed to a straightened position. This is true for the knee, elbow, and wrist joints, as is shown. Fig. 1.86 Flexion vs. extension. Hyperextension Extension Extending a joint beyond the straight or neutral position. Hyperextension (neutral) Flexion Abnormal Hyperextension A hyperextended elbow or knee results when the joint is extended beyond the straightened or neutral position. This is not a natural movement for these two joints and results in injury or trauma. Normal Flexion and Hyperextension of Spine Flexion is bending forward, and extension is returning to the straight or neutral position. A backward bending beyond the neutral posi- tion is hyperextension. In practice, however, the terms flexion and extension are commonly used for these two extreme flexion and Fig. 1.87 Hyperextension, extension, and flexion of spine. hyperextension projections of the spine (Fig. 1.87). Normal Hyperextension of Wrist A second example of a special use of the term hyperextension concerns the wrist, where the carpal canal (tangential, inferosupe- rior) projection of the carpals is visualized by a special hyperex- tended wrist movement in which the wrist is extended beyond the neutral position. This specific wrist movement is also called dorsiflexion (backward or posterior flexion) (Fig. 1.88A). Acute Flexion of Wrist An acute or full flexion of the wrist is required for a special tangential projection for a carpal bridge projection of the posterior aspect of the wrist (see Fig. 1.88B). Ulnar Deviation Versus Radial Deviation of Wrist A Hyperextension or dorsiflexion B Acute flexion Deviation literally means “to turn aside” or “to turn away from the Fig. 1.88 Wrist extension and flexion movements. A, Hyperextension. standard or course.”9 B, Acute flexion. Ulnar deviation (Fig. 1.89A) is to turn or bend the hand and wrist from the natural position toward the ulnar side, and radial deviation (Fig. 1.89B) is toward the radial side of the wrist. NOTE: Earlier editions of this textbook and other positioning references have defined these wrist movements as ulnar and radial flexion movements because they describe specific flexion movements toward either the ulna or the radius.10 However, because practitioners in the medical community, including orthopedic physicians, commonly use the terms ulnar and radial deviation for these wrist movements, this text also has changed this termi- nology to ulnar and radial deviation movements to prevent confusion and to ensure consistency with other medical references. Ulna Radius A Ulnar deviation B Radial deviation Fig. 1.89 Deviation wrist movements. A, Ulnar deviation. B, Radial deviation.  TERMINOLOGY, POSITIONING, AND IMAGING PRINCIPLES C H A P TE R 1 27 Dorsiflexion Versus Plantar Flexion of Foot and Ankle Dorsiflexion of Foot To decrease the angle (flex) between the dorsum (top of foot) and the lower leg, moving foot and toes upward (Fig. 1.90A). 1 Plantar Flexion of Foot Extending the ankle joint, moving foot and toes downward from the normal position; flexing or decreasing the angle toward the plantar (posterior) surface of the foot (Fig. 1.90B). NOTE: See preceding page for dorsiflexion of the wrist (see Fig. 1.88A) A Dorsiflexion B Plantar flexion compared with dorsiflexion of the foot (Fig. 1.90A). Fig. 1.90 Movements of ankle and foot. A, Dorsiflexion. B, Plantar flexion. Eversion Versus Inversion Eversion (e-ver′-zhun) is an outward stress movement of the foot at the ankle joint (Fig. 1.91). Inversion (in-ver′-zhun) is inward stress movement of the foot as applied to the foot without rotation of the leg (Fig. 1.92). The plantar surface (sole) of the foot is turned or rotated away from the median plane of the body (the sole faces in a more lateral direction) for eversion and toward the median plane for inversion. The leg does not rotate, and stress is applied to the medial and Fig. 1.91 Eversion (valgus stress). lateral aspects of the ankle joint for evaluation of possible widening of the joint space (ankle mortise). Valgus Versus Varus1 Valgus (val′-gus) describes an abnormal position in which a part or limb is forced outward from the midline of the body. Valgus sometimes is used to describe eversion stress of the ankle joint. Varus (va′-rus) describes an abnormal position in which a part or limb is forced inward toward the midline of the body. The term varus stress sometimes is used to describe inversion stress applied at the ankle joint. NOTE: The terms valgus and varus are also used to describe the loss of normal alignment of bones due to fracture (see Chapter 15). Fig. 1.92 Inversion (varus stress). Medial (Internal) Rotation Versus Lateral (External) Rotation Medial rotation is a rotation or turning of a body part with move- ment of the anterior aspect of the part toward the inside, or median, plane (Fig. 1.93A). Lateral rotation is a rotation of an anterior body part toward the outside, or away from the median plane (Fig. 1.93B). NOTE: In radiographic positioning, these terms describe movement of the anterior aspect of the part that is being rotated. In the forearm movements (see Fig. 1.93A and B), the anterior aspect of the forearm moves medially or internally on medial rotation and laterally or externally on lateral rotation. Another example is the medial and lateral oblique projections of the knee, in which the anterior part of the knee is rotated medially and laterally in either the AP or PA projections (see Chapter 6). A Medial rotation B Lateral rotation Fig. 1.93 Rotational movements of upper limb. A, Medial (internal) rotation. B, Lateral (external) rotation.  28 C HA PTE R 1 TERMINOLOGY, POSITIONING, AND IMAGING PRINCIPLES Abduction Versus Adduction Abduction (ab-duk′-shun) is the lateral movement of the arm or leg away from the body. Another application of this term is the abduction of the fingers 1 or toes, which means spreading them apart (Fig. 1.94A). Adduction (ah-duk′-shun) is a movement of arm or leg toward the body, to draw toward a center or medial line (Fig. 1.94B). Adduction of the fingers or toes means moving them together or toward each other. Supination Versus Pronation Supination (su″-pi-na′-shun) is a rotational movement of the hand into the anatomic position (palm up in supine position or forward in erect position) (Fig. 1.95A). This movement rotates the radius of the forearm laterally along its long axis. Pronation (pro-na′-shun) is a rotation of the hand into the Abduction Adduction A (away from) B (toward) opposite of the anatomic position (palm down or back) (Fig. 1.95B). Fig. 1.94 Movements of upper limbs. A, Abduction. B, Adduction. NOTE: To help remember these terms, relate them to the body positions of supine and prone. Supine or supination means face up or palm up, and prone or pronation means face down or palm down. Protraction Versus Retraction Protraction (pro-trak′-shun) is a movement forward from a normal position (Fig. 1.96A). Retraction (re-trak′-shun) is a movement backward or the condition of being drawn back (Fig. 1.96B). Example Protraction is moving the jaw forward (sticking the chin out) or drawing the shoulders forward. Retraction is the opposite of this—that is, moving the jaw backward or squaring the shoulders, A Supination B Pronation as in a military stance. Fig. 1.95 Movements of hand. A, Supination. B, Pronation. A Protraction B Retraction Fig. 1.96 Movements of mandible. A, Protraction. B, Retraction.  TERMINOLOGY, POSITIONING, AND IMAGING PRINCIPLES C H A P TE R 1 29 Elevation Versus Depression Elevation Depression Elevation is a lifting, raising, or moving of a part superiorly (Fig. 1.97A). Depression is a letting down, lowering, or moving of a part inferiorly (Fig. 1.97B). 1 Example Shoulders are elevated when they are raised, as when shrugging the shoulders. Depressing the shoulders is lowering them. Circumduction Circumduction (ser″-kum-duk′-shun) means to move around in the form of a circle (Fig. 1.98). This term describes sequential movements of flexion, abduction, extension, and adduction, result- ing in a cone-type movement at any joint where the four move- ments are possible (e.g., fingers, wrist, arm, leg). A B Rotation Versus Tilt Fig. 1.97 Movements of shoulders. A, Elevation. B, Depression. Rotate is to turn or rotate a body part on its axis. In Fig. 1.99, the midsagittal plane of the entire body, including the head, is rotated. Tilt is a slanting or tilting movement with respect to the long axis. Fig. 1.100 demonstrates no rotation of the head but a tilting (slanting) of the midsagittal plane of the head, which therefore is not parallel to the tabletop. Understanding the difference between these two terms is important in cranial and facial bone positioning (see Chapter 11). See Table 1.4 for a summary of positioning-related terminology. Summary of Potentially Misused Positioning Terms The three terms position, projection, and view are sometimes confusing and may be used incorrectly in practice. These terms should be understood and used correctly (Table 1.5). Position Fig. 1.98 Circumduction movements. Position is a term that is used to indicate the patient’s general physical position, such as supine, prone, recumbent, or erect. TABLE 1.4 SUMMARY OF POSITIONING-RELATED TERMS Fig. 1.99 Rotation—midsagittal Fig. 1.100 Tilt—midsagittal plane Body Planes, Sections, and Lines Relationship Terms plane rotated. of head tilted. Longitudinal planes or sections Medial vs. lateral Sagittal Proximal vs. distal TABLE 1.5 SUMMARY OF PROJECTIONS AND POSITIONS Coronal Cephalad vs. caudad Oblique Ipsilateral vs. contralateral GENERAL BODY SPECIFIC BODY PROJECTIONS (PATH OF CR) POSITIONS POSITIONS Transverse planes or sections Internal vs. external Horizontal, axial, or cross-section Superficial vs. deep Posteroanterior (PA) Anatomic R or L lateral Oblique Lordosis vs. kyphosis (scoliosis) Anteroposterior (AP) Supine Oblique Base plane Mediolateral Prone Left posterior oblique Movement Terms Lateromedial Erect (upright) (LPO) Occlusal plane Infraorbitomeatal line (IOML) Flexion vs. extension (acute AP or PA oblique Recumbent Right posterior flexion vs. hyperextension) AP or PA axial Trendelenburg oblique (RPO) Body Surfaces Ulnar vs. radial deviation Tangential Sims Left anterior oblique Posterior Dorsiflexion vs. plantar flexion Transthoracic Fowler (LAO) Anterior Eversion vs. inversion Dorsoplantar (DP) Lithotomy Right anterior oblique Plantar Valgus vs. varus Plantodorsal (PD) (RAO) Dorsum Medial vs. lateral rotation Inferosuperior axial Decubitus Palmar Abduction vs. adduction Superoinferior axial Left lateral decubitus Supination vs. pronation Axiolateral Right lateral decubitus Protraction vs. retraction Submentovertex (SMV) Ventral decubitus Elevation vs. depression Verticosubmental (VSM) Dorsal decubitus Tilt vs. rotation Parietoacanthial Lordotic Circumduction Acanthioparietal Cephalad vs. caudad Craniocaudal  30 C HA PTE R 1 TERMINOLOGY, POSITIONING, AND IMAGING PRINCIPLES Position also is used to describe specific body positions by the The term projection should be “restricted to discussion of the body part closest to the IR, such as lateral and oblique. path of the central ray.”11 The term position should be “restricted to discussion of the patient’s physical position.”11 View 1 View is not a correct positioning term in the United States. Projection View describes the body part as seen by the IR or other record- Projection is a correct positioning term that describes or refers to ing medium, such as a fluoroscopic screen. In the United States, the path or direction of the central ray (CR), projecting an image the term view should be “restricted to discussion of a radiograph onto an image receptor (IR). or image.”11  40 C HA PTE R 1 TERMINOLOGY, POSITIONING, AND IMAGING PRINCIPLES Density and Anode Heel Effect The intensity of radiation emitted from the cathode end of the x-ray tube is greater than that emitted at the anode end; this phenomenon is known as the anode heel effect. Greater attenua- 1 tion or absorption of x-rays occurs at the anode end because of the angle of the anode; x-rays emitted from deeper within the anode must travel through more anode material before exiting; thus, they are attenuated more. Studies show that the difference in intensity from the cathode to the anode end of the x-ray field when a 17-inch (43-cm) IR is Heel used at 40-inch (102-cm) SID can vary by 45%, depending on the anode angle12 (Fig. 1.128). The anode heel effect is more pro- Central axis Collimator nounced when a short SID and a large field size are used. Applying the anode heel effect to clinical practice assists the technologist in obtaining quality images of body parts that exhibit significant variation in thickness along the longitudinal axis of the Anode side Cathode side x-ray field. The patient should be positioned so that the thicker portion of the part is at the cathode end of the x-ray tube and 75 80 90 100 105 110 120 the thinner part is under the anode (the cathode and anode Percent intensity of x-ray beam ends of the x-ray tube usually are marked on the protective housing). (more pronounced at shorter SID and larger IR) The abdomen, thoracic spine, and long bones of the limbs (e.g., Fig. 1.128 Anode heel effect. the femur and tibia/fibula) are examples of structures that vary enough in thickness to warrant correct use of the anode heel effect. A summary chart of body parts and projections for which the TABLE 1.6 SUMMARY OF ANODE HEEL EFFECT anode heel effect can be applied is provided in Table 1.6; this APPLICATIONS information is also noted in the positioning pages for each of these PROJECTION ANODE END CATHODE END projections throughout the text. In practice, the most common application of the anode heel effect is for anteroposterior (AP) Thoracic Spine projections of the thoracic spine. AP Head Feet It may not always be practical or even possible to take advantage Femur of the anode heel effect; this depends on the patient’s condition or the arrangement of specific x-ray equipment within a room. AP and lateral (see Fig. 1.123) Feet Head Humerus AP and lateral Elbow Shoulder Leg (Tibia/Fibula) AP and lateral Ankle Knee Forearm AP and lateral Wrist Elbow  C H A P T E R 2 Chest CO N T R I B U T I O N S BY Nancy Johnson, MEd, RT(R)(CV)(CT)(QM)(ARRT), FASRT CO N T R I B U TO R S TO PA ST E D I T IO N S Karen Brown, RT(R), Kathy M. Martensen, BS, RT(R) CONTENTS Radiographic Anatomy, 72 Routine and Special Projections, 91 Bony Thorax, 72 Chest, 92 Respiratory System, 73 PA, 92 Mediastinum, 79 Lateral, 94 Alternative Lateral, 95 Radiographic Positioning, 80 AP, 96 Body Habitus, 80 Lateral Decubitus, 97 Breathing Movements, 80 AP Lordotic, 98 Degree of Inspiration, 80 Anterior Oblique, 99 Positioning Considerations, 81 Posterior Oblique, 101 Breathing Instructions, 82 Upper Airway, 102 Evaluation Criteria, 83 Lateral, 102 Digital Imaging Considerations, 88 AP, 103 Alternative Modalities and Procedures, 88 Radiographs for Critique, 104 Clinical Indications, 88 71  80 C HA PTE R 2 CHEST RADIOGRAPHIC POSITIONING Body Habitus L Body habitus requires special consideration in chest radiography. There are four different styles of body build or habitus (Fig. 2.25). The four types of body habitus were explained in Chapter 1. A massively built hypersthenic patient has a thorax that is very broad and very deep from front to back but is shallow in vertical dimen- sion, as is shown in the PA radiograph in Fig. 2.26. Therefore, care must be taken that the sides or the costophrenic angles are not cut off on a PA chest radiograph, which must be taken with the IR placed landscape. Careful centering is also required on the lateral projection to ensure that the anterior or posterior margins are included on the radiograph. Hypersthenic (5%) Sthenic (50%) Fig. 2.26 PA (hypersthenic). The other extreme is a slender asthenic patient. With this build, the thorax is narrow in width and shallow from front to back but is L very long in its vertical dimension. Therefore, in positioning for a 2 chest radiograph, the technologist must ensure that the IR is long enough to include both the upper apex areas, which extend well above the clavicles, and the lower costophrenic angles. A chest PA radiograph in a nearer average hyposthenic patient is shown in Fig. 2.27. Care in vertical collimation for such patients must be exercised so that the costophrenic angles are not cut off on the lower margin. Breathing Movements Movements of the bony thorax during inspiration (taking air in) and expiration (expelling air) greatly change the dimensions of the Hyposthenic (35%) Asthenic (10%) thorax and the thoracic volume. To increase the volume of the chest Fig. 2.25 Body habitus. Fig. 2.27 PA (hyposthenic). during inspiration (Fig. 2.28), the thoracic cavity increases in diam- eter in three dimensions. The first of these is the vertical diameter, which is increased primarily by contraction and moving downward of the diaphragm, Increases in 3 increasing the thoracic volume. dimensions: The transverse diameter is the second dimension that is - Vertical increased during inspiration. The ribs swing outward and upward, (diaphragm and this increases the transverse diameter of the thorax. downward) The third dimension is the anteroposterior diameter, which is also increased during inspiration by the raising of the ribs, especially - Transverse the second through sixth ribs. - AP dimension During expiration, the elastic recoil of the lungs, along with the weight of the thoracic walls, causes the three diameters of the thorax to return to normal (Fig. 2.29). Degree of Inspiration To determine the degree of inspiration in chest radiography, one Fig. 2.28 Inspiration. Fig. 2.29 Expiration. should be able to identify and count the rib pairs on a chest radio- 1 L graph. The first and second pairs are the most difficult to locate. When a chest radiograph is taken, the patient should take as deep a breath as possible and then hold it to aerate the lungs fully. Taking a second 2 3 deep breath before holding it allows for a deeper inspiration. 4 The best method that can be used to determine the degree of 5 inspiration is to observe how far down the diaphragm has moved by counting the pairs of posterior ribs in the lung area above the dia- 6 phragm. A general rule for average adult patients is to “show” a 7 minimum of 10 on a good PA chest radiograph. To determine this, 8 start at the top with the first rib and count down to the tenth or 9 eleventh rib posteriorly. The posterior part of each rib, where it joins a thoracic vertebra, is the most superior part of the rib. The diaphragm 10 should always be checked to see that it is below the level of at least 11 the tenth posterior rib (see following Note). (Fig. 2.30 shows 11 posterior ribs, which can be expected in many healthy patients.) NOTE: Patients with pulmonary diseases and trauma may be unable to inspire deeply. Therefore, it may be impossible to demonstrate 10 ribs above the diaphragm for these chest projections. Fig. 2.30 Posterior ribs.  CHEST C H A P TE R 2 81 Positioning Considerations TECHNICAL FACTORS Patient preparation for chest radiography includes the removal of Kilovoltage all opaque objects from the chest and neck regions, including Kilovoltage (kV) should be high enough to result in sufficient clothes with buttons, snaps, hooks, or any objects that would be contrast to demonstrate the many shades of gray needed to visual- visualized on the radiograph as a shadow (radiopaque artifact). To ize finer lung markings. In general, chest radiography uses low ensure that all opaque objects are removed from the chest region, contrast, described as long-scale contrast, with more shades of the usual procedure is to ask the patient to remove all clothing, gray. This requires a high kV of 110 to 125. This kV range typically including bras, necklaces, or other objects around the neck. The is used for both analog and digital imaging systems. patient then puts on a hospital gown, which commonly has the Lower kV, yielding high contrast, would not provide sufficient opening in the back. penetration to allow clear visualization of the fine lung markings in Long hair may be visible as an artifact on chest radiographs taken the areas behind the heart and lung bases. Too high contrast is evident with digital imaging systems. Long hair should be drawn up or when the heart and other mediastinal structures appear underex- draped across the shoulder to eliminate superimposition within the posed, even though the lung fields are sufficiently penetrated. chest anatomy. Hair that is braided or tied together in bunches with As a general rule, in chest radiography, the use of high kV (>100) rubber bands or other fasteners may also cause suspicious shadows requires the use of grids. Moving grids or fine-line focused fixed on the radiograph if left superimposing the chest area. Oxygen lines grids can be used. Exceptions are mobile chest projections taken or electrocardiogram (ECG) monitor leads should be moved care- with equipment that is limited to 90 kV, for which IRs without grids fully to the side of the chest if possible. All radiopaque objects may be used, but this is not recommended. 2 should be moved carefully from the radiographic field of interest to prevent artifacts from interfering with the quality of the diagnostic Exposure Time and Milliamperage image. (mAs–Milliampere Seconds) Generally, chest radiography requires the use of high mA and RADIATION PROTECTION short exposure time to minimize the chance of motion and Patients should be protected from unnecessary radiation for all resultant loss of sharpness. diagnostic radiographic examinations, especially for chest radio- Sufficient mAs should be used to provide for optimum density graphs because these are the most common of all radiographic (brightness) of lungs and mediastinal structures. A determining examinations. factor for this on PA chest radiographs is to be able to see faint outlines of at least the mid and upper vertebrae and posterior Repeat Exposures ribs through the heart and other mediastinal structures. Although the chest radiographic examination often is considered the simplest of all radiographic procedures, it also is the examina- Placement of Image Markers tion with the highest number of repeats in many radiology depart- Throughout the positioning sections of this text, the correct or best ments. Therefore, unnecessary radiation exposure from repeat placement of patient identification (ID) information and image exposures should be minimized by taking extra care in position- markers is indicated. The top portion of each positioning page ing, CR centering, and selecting correct exposure factors if auto- includes a drawing that demonstrates the correct IR size and place- matic exposure control (AEC) systems are not used. Reduce ment (portrait or landscape) and indicates the best location for the patient dose as much as possible through the use of correct radia- patient ID blocker (analog systems) and the location and type of tion protection practices by close collimation and protective image marker used for that specific projection or position. shielding. Although there is an assumption that the heart is located in the left thorax, there are conditions such as situs inversus (also known Collimation as visceral inversion)2 in which the major organs of the body are Careful collimation is important in chest radiography. Restricting the on the opposite side. With this condition, the heart is located in the primary x-ray beam by collimation not only reduces patient dose right thorax. An anatomic side marker (left or right) must be placed by reducing the volume of tissue irradiated but also improves image on the image receptor prior to exposure. If not seen radiographi- quality by reducing scatter radiation. cally, the exposure should be retaken to ensure the correct side of the thorax is identified. Lead Shielding In addition to careful collimation, a lead shield should be used to PEDIATRIC APPLICATIONS protect the abdominal area below the lungs. This shielding Supine Versus Erect is especially important for children, pregnant women, and all Generally, with newborns and small infants, for whom head support individuals of childbearing age. However, many departments have is required, chest radiographs are taken AP supine. Laterals also a general policy of shielding for all patients undergoing chest may be taken supine with a horizontal beam to demonstrate fluid radiography. levels (dorsal decubitus). However, erect PA and laterals are pre- A common type of shield for chest radiography is a type of ferred whenever possible, with the use of immobilization devices freestanding, adjustable mobile shield placed between the patient such as the Pigg-O-Stat (Modern Way Immobilizers, Inc, Clifton, and the x-ray tube. A vinyl-covered lead shield that ties around the Tennessee) (described in Chapter 16). waist can also be used. Both of these types of shields should provide shielding from the level of the iliac crests, or slightly higher, Technical Factors to the mid-thigh area. Lower kV (70 to 85) and less mAs are required for pediatric patients with the shortest exposure time possible (to prevent Backscatter Protection motion). Higher speed imaging systems or receptors generally are To protect the gonads from scatter and secondary radiation from used with pediatric patients for two reasons: (1) to reduce the the IR holder device and the wall behind it, some references chance of motion and (2) to reduce the patient exposure dose suggest that a freestanding shield or a wraparound shield also (important because of the sensitivity of young tissue to radiation should be placed over the radiosensitive structures outside the exposure). See Chapter 16 for more detailed information on special anatomy of interest between the patient and the IR. positioning considerations required with pediatric patients.  82 C HA PTE R 2 CHEST Note the number of ribs demonstrated above the diaphragm on GERIATRIC APPLICATIONS the expiration projection. There are a greater number of ribs dem- CR Centering onstrated above the diaphragm in the full inspiration radiograph. Frequently, older patients have less inhalation capability with resul- Also note the position of the two opacities in the right lung between tant “more shallow” lung fields, and a higher CR location is inspiration and expiration projections. They shift position, which required (CR to T6-7, p. 86). indicates they are within the lungs or pleura. Note also the number of ribs visible above the diaphragm, indicating the degree of inspira- Technical Factors tion (10 posterior ribs) and expiration (8 posterior ribs). Certain pathologic conditions are more common in geriatric patients, such as pneumonia and emphysema, which may require different exposure factor adjustments, as described under Clinical L Indications. Instructions and Patient Handling More care, time, and patience frequently are required when breath- ing and positioning requirements are explained to geriatric patients. Help and support provided to these patients during the positioning process are important. Arm supports for keeping the arms raised high for the lateral position are essential for many older patients. 2 OBESE PATIENT CONSIDERATIONS An obese patient may present positioning and centering challenges. Because of a larger body girth, the technologist may place the top of the image receptor (IR) 1 to 2 inches (2.5 to 5.0 cm) above the shoulder. Because the lung apices may not reach as high as perceived, center the CR and IR to level of T7 rather than base centering on the levels of the shoulders. T7 remains your centering Fig. 2.31 Inspiration chest. point for most chest projections. T7 is generally located at the level of the inferior angle of the scapula. If it cannot be located, the vertebra prominens may serve as a landmark to assist in locating the T7 level. See p. 86 for information on CR centering based on the vertebra prominens. L For the AP chest projection, the jugular notch is a palpable landmark on the obese patient. T7 is approximately 3 to 4 inches (8 to 10 cm) inferior to the jugular notch. Breathing Instructions Breathing instructions are very important in chest radiography because any chest or lung movement that occurs during the exposure results in “blurring” of the radiographic image. Chest radiographs must be taken on full inspiration to show the lungs as they appear fully expanded. HOLD BREATH ON SECOND INSPIRATION More air can be inhaled without too much strain on the second breath compared with the first. Therefore, the patient should be asked to hold the second full inspiration rather than the first. However, the full inspiration should not be forced to the point of Fig. 2.32 Expiration chest. strain that causes unsteadiness; this should be explained to the patient before the exposure as the patient is being positioned. INSPIRATION AND EXPIRATION Occasional exceptions have been noted to taking chest radiographs on full inspiration only. For certain conditions, comparison radio- graphs are taken on both full inspiration (Fig. 2.31) and full expiration (Fig. 2.32). Indicators for this include a possible small pneumothorax (air or gas in the pleural cavity), fixation or lack of normal movement of the diaphragm, the presence of a foreign body, and the need to distinguish between an opacity in the rib and one in the lung. When such comparison radiographs are taken, they should be labeled “inspiration” and “expiration.”  CHEST C H A P TE R 2 83 ERECT CHEST RADIOGRAPHS Rotation on PA chest radiographs can be determined by exami- All chest radiographs should be taken in an erect position if the nation of both sternal ends of the clavicles for a symmetric appear- patient’s condition allows. Three reasons for this are as follows: ance in relationship to the spine. On a true PA chest without 1. The diaphragm is allowed to move down farther. An erect rotation, both the right and the left sternal ends of the clavicles position causes the liver and other abdominal organs to drop, are the same distance from the center line of the spine. Note allowing the diaphragm to move farther down (inferior) on full the rotation evident in Fig. 2.36 by the difference in distance inspiration and allowing the lungs to aerate fully. between the center of the spinal column and the sternal end of 2. Air and fluid levels in the chest may be visualized. If both air the right clavicle compared with the left. and fluid are present within a lung or within the pleural space, The direction of rotation can be determined by noting which the heavier fluid, such as blood or pleural fluid resulting from sternal end of the clavicle is closest to the spine. For example, in infection or trauma, gravitates to the lowest position, whereas Fig. 2.36, the left side of the thorax is rotated toward the IR (right the air rises. In the recumbent position, a pleural effusion spreads side moved away from IR), which creates a slight left anterior out over the posterior surface of the lung, producing a hazy oblique (LAO) that decreases the distance of the left clavicle from appearance of the entire lung. In the upright position, free fluid the spine. is located near the base of the lung. The PA erect chest radio- graph (Fig. 2.33) shows some fluid in the left lower thoracic L cavity near the base of the lung. The supine radiograph taken on a different patient (Fig. 2.34) demonstrates a generalized hazy appearance of the entire right lung, resulting from the 2 presence of fluid now spread throughout the right thorax. 3. Engorgement and hyperemia of pulmonary vessels may be prevented. The term engorgement literally means “distended or swollen with fluid.” Hyperemia (hy″-per-e′-me-ah) is an excess of blood that results in part from relaxation of the distal small blood vessels or arterioles.3,4 An erect position tends to minimize engorgement and hyper- emia of pulmonary vessels, whereas a supine position increases Fig. 2.33 PA erect, some fluid evident in left lower lung. (Note flat these, which can change the radiographic appearance of these line appearance near left hemidiaphragm.) vessels and the lungs in general. PA 72-inch (183-cm) source image receptor distance Chest radiographs taken AP rather than PA at 72 inches (183 cm) result in increased magnification of the heart shadow, which complicates the diagnosis of possible cardiac enlargement. The reason for this increased magnification is the anterior location of the heart within the mediastinum; placing it closer to the IR on the PA results in less magnification. A longer source to image receptor distance (SID), such as 72 inches [183 cm], magnifies less because the x-ray beam has less divergence. Evaluation Criteria The description for each chest projection or position in this chapter Fig. 2.34 Supine AP chest (fluid in right lung). includes an evaluation criteria section. This section lists and describes specific criteria by which one can evaluate the resultant radiograph. The goal of every technologist should be to take the “optimal” L radiograph. These criteria provide a definable standard by which every chest radiographic image can be evaluated to determine where improvements can be made. Important evaluation criteria for all routine PA and lateral chest radiographs are described in the following sections. PA CHEST POSITIONING True PA, No Rotation Even a slight amount of rotation on a PA chest projection results in distortion of size and shape of the heart shadow because the heart is located anteriorly in the thorax. Therefore, it is important that there be no rotation (Fig. 2.35). To prevent rotation, ensure that the patient is standing evenly on both feet with both shoulders rolled forward and downward. Also, check the posterior aspect of Fig. 2.35 Without rotation. Fig. 2.36 With rotation (slight the shoulders and the lower posterior rib cage and the pelvis to LAO). ensure no rotation. Scoliosis and excessive kyphosis make it more difficult to prevent rotation. Scoliosis is lateral, or side-to-side, cur- vature of the spine, which frequently is combined with excessive kyphosis, a humpback curvature. Together, these spinal curvatures frequently result in “twisting” deformity of the bony thorax, making a true PA without some rotation more difficult or impossible.  84 C HA PTE R 2 CHEST Extending the Chin L L Sufficient extension of the patient’s neck ensures that the chin and neck are not superimposing the uppermost lung regions, the apices of the lungs. This is demonstrated by the two radiographs in Figs. 2.37 and 2.38. Also, ensure that the upper collimation border is high enough so that the apices are not cut off. Minimizing Breast Shadows A patient with large pendulous breasts should be asked to lift them up and outward and then to remove her hands as she leans against the chest board (IR) to keep them in this position. This position lessens the effect of breast shadows over the lower lung fields. However, depending on the size and density of the breasts, breast Fig. 2.37 Chin up. Fig. 2.38 Chin down. shadows over the lower lateral lung fields cannot be totally elimi- nated (Fig. 2.39). LATERAL CHEST POSITIONING Side Closest to IR The patient’s side closest to the IR is best demonstrated on the 2 finished radiograph. A left lateral (Fig. 2.40) should be performed unless departmental protocol indicates otherwise, or unless certain pathology in the right lung indicates the need for a right lateral. A left lateral more accurately demonstrates the heart region (without as much magnification) because the heart is located primarily in the left thoracic cavity. True Lateral, No Rotation or Tilt Ensure that the patient is standing straight with weight evenly dis- tributed on both feet and arms raised. As a check against rotation, confirm that the posterior surfaces of the shoulder and the pelvis are directly superimposed and perpendicular to the IR. Because of Fig. 2.39 Breast shadows evident—patient has pneumonia. the divergent x-ray beam, the posterior ribs on the side farthest away from the IR are magnified slightly and projected slightly posterior compared with the side closest to the IR on a true lateral chest; this is more noticeable on a broad-shouldered patient. However, this separation of posterior ribs resulting from divergence of the x-ray beam at the commonly used 72-inch (183-cm) SID should be only 14 to 12 inch, or about 1 cm. Any greater separa- tion than this indicates rotation of the thorax from a true lateral position.4 NOTE: Some references recommend an intentional slight anterior rotation of the side away from the IR so that the posterior ribs are directly super- imposed. This rotation may be preferred in some departments, but because the heart and most lung structures are near-midline structures and are not affected by the beam divergence, a straight lateral with respect to the IR is more common; this causes slight separation of the posterior ribs and costophrenic angles, as described earlier. Fig. 2.41 shows a lateral chest with excessive rotation, as indicated by the amount of separation of the right and left posterior ribs and separation of the two costophrenic angles. Fig. 2.40 Without excessive Fig. 2.41 Excessive rotation— This represents a positioning error and generally would require a rotation (ribs superimposed). positioning error (ribs not repeat radiograph. superimposed).  CHEST C H A P TE R 2 85 Direction of Rotation The direction of rotation on a lateral chest is sometimes difficult to determine. Frequently, however, this can be done by identifying the left hemidiaphragm by the gastric air bubble in the stomach or by the inferior border of the heart shadow, both of which are associ- ated with the left hemidiaphragm.3 No Tilt There also should be no tilt, or leaning “sideways.” The midsagittal plane must be parallel to the IR. If the patient’s shoulders are placed firmly against the chest board (IR) on a lateral chest, the lower lateral thorax or hips or both may be 1 or 2 inches away. This is especially true on broad-shouldered patients. Tilt, if present, may be evident by closed disk spaces in the thoracic vertebra. Arms Raised High Ensure that the patient raises both arms sufficiently high to prevent superimposition on the upper chest field. Patients who are weak or unstable may need to grasp a support (Fig. 2.42). 2 When the patient’s arms are not raised sufficiently, the soft tissues of the upper arm superimpose portions of the lung field, as Fig. 2.43 Arms not raised—positioning error. is demonstrated in Fig. 2.43. Arrows show margins of soft tissues of the arms overlying upper lung fields. This would require a repeat and should be avoided. CR Location The top of the shoulder traditionally has been used for chest positioning. This method includes placing the top of the image receptor (IR) 112 to 2 inches (4 to 5 cm) above the shoulders and centering the CR to the center of the IR. However, this positioning method is inconsistent, given variations in lung field dimensions owing to differences in body habitus, as demonstrated by a com- X parison of Figs. 2.44 and 2.45. The small circle indicates where the CR was placed on these two patients. The center of the lungs (indicated by X) is shown to be near the center of the IR for the male patient in Fig. 2.44 but is above center on the small and older female patient in Fig. 2.45. This centering error unnecessarily exposes a large portion of the upper abdomen. These variations demonstrate the importance of a chest posi- tioning method that consistently centers the CR to the center of the lung fields on all types of patients with accurate collimation on both top and bottom. Fig. 2.44 Average sthenic/hyposthenic male patient (correct CR and collimation). X CR Center of lungs Fig. 2.45 Small and older female patient (incorrect CR and Fig. 2.42 Arms raised high. collimation and tilt).  86 C HA PTE R 2 CHEST CR CHEST-POSITIONING METHOD Bony landmarks are consistent and reliable as a means of determin- ing CR locations. Landmarks for locating the center of the lung fields are as follows. Vertebra Prominens (PA Chest) The vertebra prominens corresponds to the level of T1 and the uppermost margin of the apex of the lungs. This landmark, which can be palpated at the base of the neck, is the preferred landmark for locating the CR on a PA chest (Figs. 2.46 and 2.47). For an average adult female patient, this is down about 7 inches (18 cm); for an average adult male patient, this is down about 8 inches (20 cm). One method of determining this distance is by using an average hand spread as shown. Most hands can reach 7 inches (18 cm) (Fig. 2.48). The 8-inch (20-cm) distance can be determined by estimating an additional inch. If the hand spread method is used, practice with a ruler to determine these distances consistently. These differences between male and female are true for near- 2 average body types in the general population, with crossover Fig. 2.47 Correct CR using vertebra prominens. Distance on an exceptions in which certain larger athletic women may have longer average female is 7 inches (18 cm). lung fields and some men may have shorter lungs. However, for purposes of chest positioning for the general population, the average measurements of 7 inches (18 cm) for a woman and 8 inches (20 cm) for a man can be used as reliable guidelines (Fig. 2.49). Exceptions Other noteworthy exceptions in centering involve variations in body type. For example, the author found that 15% to 20% of the general male population consisted of the well-developed athletic sthenic/hyposthenic type, which requires centering nearer to T8, or 9 inches (23 cm) down from the vertebra prominens. The hyper- sthenic type describes about 5% to 10% of the population, which requires centering only from 6 to 7 inches (15 to 18 cm) down. Fig. 2.48 Hand spread method—7 to 8 inches (18 to 20 cm). NOTE: For most patients, this CR level for PA chests is near the level of the inferior angle of the scapula, which corresponds to the level of T7 on an average patient. 5