Cervical and Thoracic Vertebrae

• Visibility of cervical and thoracic vertebral details. An optimal kilovoltage peak (kVp) technique, as shown in Table 8-1, sufficiently penetrates the cervical and thoracic vertebral structures and provides the contrast scale necessary to visualize the vertebral details. To obtain optimal density, set a manual milliampere-seconds (mAs) level based on the patient's thickness or choose the appropriate automatic exposure control (AEC) chamber. Table 8-1 lists the technical data for the most common projections.

• An AP axial projection of the cervical vertebrae is obtained by placing the patient supine or upright, with the shoulders positioned at equal distances from the imaging table or upright image receptor (IR; Figure 8-2). The patient's face should be positioned so it is forward, placing the mandibular angles and mastoid tips at equal distances from the imaging table or upright grid holder.

• Effect of cervical rotation. When the patient and cervical vertebrae are rotated away from the AP axial projection, the vertebral bodies move toward the side positioned closer to the IR, and the spinous processes move toward the side positioned farther from the IR. The upper (C1 to C4) and lower (C5 to C7) cervical vertebrae can demonstrate rotation independently or simultaneously, depending on which part of the body is rotated. If the head is rotated but the thorax remains in an AP axial projection, the upper cervical vertebrae demonstrate rotation as C1 rotates on C2, and the lower cervical vertebrae remain in an AP axial projection. If the thorax is rotated but the head remains in a forward position to match, the lower cervical vertebrae demonstrate rotation and the upper cervical vertebrae remain in an AP axial projection. If the patient's head and thorax are rotated simultaneously, the entire cervical column demonstrates rotation (see Image 1).

• Detecting rotation. Rotation is present on an AP axial projection in the following situations: (1) if the mandibular angles and mastoid tips are not demonstrated at equal distances from the cervical vertebrae; (2) if the spinous processes are not demonstrated in the midline of the cervical bodies; (3) if the pedicles and articular pillars are not symmetrically demonstrated lateral to the vertebral bodies; and (4) if the medial ends of the clavicles are not demonstrated at equal distances from the vertebral column (see Image 1). The side of the patient positioned closer to the imaging table or upright IR is the side toward which the mandible is rotated and also the side that demonstrates less of the articular pillars and less clavicular and vertebral column superimposition.

• Positioning for trauma. When cervical vertebral projections are exposed on a trauma patient with suspected subluxation or fracture, obtain the AP axial projection with the patient positioned as is. Do not attempt to remove the cervical collar or adjust the head or body rotation, mandible position, or cervical column tilting. This might result in greater injury to the vertebrae or spinal cord. Spinal cord injuries may occur from mishandling the patient after the initial injury has taken place.

• The cervical vertebral column demonstrates a lordotic curvature. This curvature and the shape of the vertebral bodies cause the disk-articulating surfaces of the vertebral bodies to slant upward anteriorly to posteriorly.

• Importance of central ray angulation. To obtain open intervertebral disk spaces and undistorted vertebral bodies, the central ray must be angled in the same direction as the slope of the vertebral bodies. This can be easily discerned by viewing the lateral cervical projection in Figure 8-3. Studying this lateral cervical projection, you can see that when the correct central ray angulation is used, each vertebra's spinous process is located within its inferior intervertebral disk space. The degree of central ray angulation needed to obtain open intervertebral disk spaces and to align the spinous processes within them accurately depends on the degree of cervical lordotic curvature.

• Upright versus supine position. If the AP axial cervical vertebrae projection is performed with the patient in an upright position, the cervical vertebrae demonstrate more lordotic curvature than if the examination is performed with the patient supine. In a supine position, the gravitational pull placed on the middle cervical vertebrae results in straightening of the cervical curvature. Figure 8-3 demonstrates a lateral cervical projection taken with the patient in an upright position and Figure 8-4 demonstrates a lateral cervical projection taken with the patient supine. Note the difference in lordotic curvature between these two images. Because of this difference, the central ray angulation should be varied when an AP axial cervical vertebrae projection is taken with the patient erect rather than supine. In the erect position, a 20-degree cephalad central ray angulation is needed to align the central ray parallel with the intervertebral disk spaces. In the supine position, a 15-degree cephalad central ray angulation sufficiently aligns the central ray parallel with the intervertebral disk spaces.

• Kyphotic patient. The kyphotic patient demonstrates an exaggerated kyphotic curvature of the thoracic vertebrae that will cause excessive lordotic curvature of the cervical vertebrae (Figure 8-5). To demonstrate the upper and lower cervical vertebrae with open intervertebral spaces for an upright AP axial cervical vertebrae projection, it will be necessary to increase the degree of central ray angulation above that routinely needed for a patient without kyphosis. If the AP axial projection is taken with the kyphotic patient in a supine position, a radiolucent sponge should be placed beneath the patient's head to prevent the upper cervical vertebrae from extending toward the imaging table and from superimposing the posterior occiput on the image (see Image 2).

• Effect of central ray misalignment. Misalignment of the central ray and intervertebral disk spaces results in closed disk spaces, distorted vertebral bodies, and projection of the spinous processes into the vertebral bodies. If the central ray angulation is not used or is insufficient, the resulting image demonstrates closed intervertebral disk spaces, and each vertebra's spinous process is demonstrated within its vertebral body (see Images 3 and 4). This anatomic relationship also results if the patient's head is tilted toward the x-ray tube for the examination, causing the cervical vertebrae to tilt anteriorly. If the central ray is angled more than needed to align the central ray parallel with the intervertebral disk spaces, or if the patient's cervical vertebral column was extended posteriorly for the examination, the resulting image demonstrates closed intervertebral disk spaces, each vertebra's spinous process is demonstrated within the inferior adjoining vertebral body, and the uncinate processes are elongated (see Image 5).

• Accurate positioning of the occiput and mandibular mentum is achieved when an imaginary line connecting the upper occlusal plane (chewing surface of maxillary teeth) and the base of the skull is aligned perpendicular to the imaging table or upright IR. This positioning also aligns the acanthiomeatal line (an imaginary line connecting the point at which the upper lip and nose meet with the external ear opening) perpendicular to the imaging table or upright IR (see Figure 8-2). With this position, you might expect the patient's mandible to be superimposed over the upper cervical vertebrae but this will not be the case because the cephalad central ray angulation used will project the mandible superiorly.

• Effect of occiput-mentum mispositioning. Mispositioning of the posterior occiput and the upper occlusal plane results in an obstructed image of the upper cervical vertebrae. If the occlusal plane is positioned superior to the base of the skull (head tilted too far backward), the upper cervical vertebrae are superimposed over the occiput (see Image 6). If the upper occlusal plane is positioned inferior to the base of the skull (chin tucked too far downward), the mandibular mentum is superimposed over the superior cervical vertebrae (see Image 7).

• Aligning the long axis of the cervical column with the long axis of the collimated field ensures that no lateral flexion of the cervical column is present (see Image 8) and allows for tight collimation (see Image 7). This alignment is obtained by aligning the midline of the patient's neck with the collimator's longitudinal light line.

• Center the central ray to the patient's midsagittal plane at a level halfway between the external auditory meatus (EAM) and the jugular notch to center C4 to the collimated field.

• Open the longitudinal collimation to the EAM and the jugular notch. Transverse collimation should be to within 0.5 inch (1.25 cm) of the lateral neck skin line.

• An 8- × 10-inch (18- × 24-cm) IR placed lengthwise should be adequate to include all the required anatomic structures.

Anteroposterior Axial Cervical Vertebrae Projection Analysis

• An AP projection of the atlas and axis is obtained by placing the patient in a supine or upright position, with the shoulders, mandibular angles, and mastoid tips positioned at equal distances from the imaging table or upright IR (Figure 8-7).

• Effect of rotation. Rotation of the atlas and axis occurs when the head is turned away from an AP projection. On head rotation, the atlas pivots around the dens so that the lateral mass located on the side the face is rotated toward is displaced posteriorly and the mass toe side the face is rotated away from is displaced anteriorly. This displacement causes the space between the lateral mass and dens to narrow on the side the face is rotated away from and to enlarge on the side the face is rotated toward (see Image 9). As the amount of head rotation increases, the axis rotates in the same direction as the atlas, resulting in a shift in the position of its spinous process in the direction opposite that in which the patient's face is turned.

• Detecting direction of rotation. To determine how the patient's face was turned, judge the distance between the mandibular rami and lateral masses. The side that demonstrates the greater distance is the side toward which the face was rotated.

• Positioning for trauma. When cervical vertebrae projections are taken on a trauma patient with suspected subluxation or fractures, obtain the AP cervical atlas and axis projection with the patient's position left as is. Do not attempt to remove the cervical collar or adjust head or body rotation, mandible position, or cervical vertebral column tilting. To do so might result in increased injury to the vertebrae or spinal cord.

• The dens and the atlantoaxial joint are located at the midsagittal plane, at a level 0.5 inch (1.25 cm) inferior to an imaginary line connecting the mastoid tips. To demonstrate them without upper incisor (front teeth) or posterior occiput superimposition, instruct the patient to open the mouth as widely as possible. Then have the patient tuck the chin until an imaginary line connecting the upper occlusal plane (chewing surface of maxillary teeth) and the base of the skull is aligned perpendicular to the imaging table or upright grid holder. If the patient does not have upper teeth, one should imagine where the occlusal plane would be if the patient had teeth. This positioning also aligns the acanthiomeatal line (an imaginary line drawn between the point where the upper lip and nose meet the external ear opening) perpendicular with the imaging table or upright grid holder. It may be necessary to position a small angled sponge beneath the patient's head to maintain accurate head positioning, especially if the patient's chin has to be tucked so much that it is difficult to open the mouth adequately. The sponge causes the upper occlusal plane and base of the skull to align perpendicularly without requiring as much chin tucking.

• Relationship of central ray angulation and patient position. The lateral cervical projection in Figure 8-8 demonstrates how the occlusal plane and the base of the skull should be aligned for an accurate open-mouth AP projection. After studying this image, you might conclude that the atlantoaxial joint will be free of upper incisor or occiput superimposition if the patient maintains this head position and simply drops the jaw. Because the upper incisors are positioned at a long object–image receptor distance (OID), however, they are greatly magnified, causing them to be projected onto the dens and atlantoaxial joint. In most patients, when the upper occlusal plane and base of the skull are superimposed, magnification causes the upper incisors to be projected approximately 1 inch (2.5 cm) inferior to the base of the skull (see Image 10). For these incisors to be projected superiorly, a 5-degree cephalic angle should be placed on the central ray. The upper incisors will be projected approximately 1 inch (2.5 cm) for every 5 degrees of angulation. This angle adjustment is based on a 40-inch (102-cm) SID; if a longer SID is used, the required angle adjustment would be less, whereas if a shorter SID is used, the angulation adjustment would be greater. If, instead of an angle adjustment, the patient's chin were tilted upward in an attempt to shift the upper incisors superiorly, the posterior occiput would simultaneously be shifted inferiorly.

• This inferior shift of the occiput would obscure the dens and possibly the atlantoaxial joint. The dens and atlantoaxial joint space may also be obscured if a 5-degree cephalad central ray angle was used but the occlusal plane and base of the skull were not superimposed. When the base of the skull is positioned inferior to the upper occlusal plane, the image demonstrates the dens and, depending on the degree of mispositioning, the atlantoaxial joint space superimposed onto the posterior occiput (see Image 11). When the occlusal plane is positioned inferior to the base of the skull, the posterior occiput is demonstrated superior to the dens, and the upper incisors are superimposed over a portion of the superior dens (see Image 12).

• Positioning for trauma. For the dens and atlantoaxial joint to be demonstrated without incisor or occiput superimposition in a trauma patient, the direction of the central ray must be changed from the standard position. A trauma patient's head and neck cannot be adjusted, so you must angle the central ray until it is aligned parallel with the infraorbitomeatal line (IOML) (imaginary line connecting the inferior orbital rim and the external ear opening). This line is easily accessible in a patient wearing a cervical collar. The exact degree of angulation needed depends on the amount of chin elevation. Most patients in a cervical collar require approximately a 10-degree caudal angle. Once the angle is set, attempt to get the patient to drop the lower jaw. Do not adjust head rotation or tilting. If the cervical collar allows the lower jaw to move without elevating the upper jaw, instruct the patient to drop the lower jaw. If the cervical collar prevents lower jaw movement without elevating the upper jaw, instruct the patient about the importance of holding the head and neck perfectly still; then have the ordering physician remove the front of the cervical collar so that the patient can drop the jaw without adjusting the head or neck position (Figure 8-9). After the patient's jaw is dropped, align the central ray to the midsagittal plane at a level 0.5 inch (1.25 cm) inferior to the occlusal plane. Immediately after the image is taken, the physician should return the front of the cervical collar to its proper position. For trauma positioning, insufficient caudal angulation causes the upper incisors to be demonstrated superior to the dens and the dens to be superimposed over the posterior occiput (see Image 13). If the central ray was angled too caudally, the posterior occiput is demonstrated superior to the dens and the upper incisors are superimposed over the dens (see Image 14).

• AP neck extension and flexion determine the alignment of the atlantoaxial joint with the imaging table and the position of the axis's spinous process to the dens. When the occlusal plane and base of the skull are aligned perpendicular to the imaging table, the atlantoaxial joint should be open.

• Effect of cervical column flexion and extension. If the cervical column is flexed, the atlantoaxial joint is closed and the spinous process of the axis is demonstrated closer to the dens (see Image 15). If the cervical column is extended, the atlantoaxial joint is closed and the spinous process of the axis is demonstrated more inferiorly to the dens.

• Center the central ray through the open mouth to the midsagittal plane to center the dens to the center of the exposure field.

• Open the longitudinally collimated field to the patient's external ear opening. Transverse collimation should be to a 5-inch (12.5-cm) field size.

• An 8- × 10-inch (18- × 24-cm) IR placed lengthwise should be adequate to include all the required anatomic structures.

Anteroposterior Cervical Atlas and Axis Projection Analysis

• Prevertebral fat stripe. The soft tissue structure of interest on a lateral cervical projection is the prevertebral fat stripe. It is located anterior to the cervical vertebrae and is visible on correctly exposed lateral cervical projections with accurate positioning (Figure 8-11). The reviewer evaluates the distance between the anterior surface of the cervical vertebrae and the prevertebral fat stripe. Abnormal widening of this space is used for the detection and localization of fractures, masses, and inflammation.

• A lateral cervical vertebral projection is obtained by placing the patient in an upright position with the midcoronal plane positioned perpendicular to the IR (Figure 8-12). In this position the right and left sides of each cervical vertebra are superimposed, demonstrating the spinous processes and vertebral bodies in profile. To prevent rotation, superimpose the patient's shoulders, mastoid tips, and mandibular rami.

• Effect of rotation. The upper and lower cervical vertebrae can demonstrate rotation simultaneously or separately, depending on which part of the body is rotated. If the head was rotated and the thorax remained in a lateral projection, the upper cervical vertebrae demonstrate rotation. If the thorax was rotated and the head remained in a lateral projection, the lower cervical vertebrae demonstrate rotation. If the patient's head and thorax were rotated simultaneously, the entire cervical column demonstrates rotation.

• Detecting rotation. Rotation can be detected on a lateral cervical projection by evaluating each vertebra for anterior and posterior pillar superimposition and for zygapophyseal joint superimposition. When the patient is rotated, the pillars and zygapophyseal joints on one side of the vertebra move anterior to those on the other side (see Images 16 and 17). Because the two sides of the vertebrae are mirror images, it is very difficult to determine from a rotated lateral cervical projection which side of the patient is rotated anteriorly and which is rotated posteriorly. The magnification of the side situated farther from the IR may provide a moderately reliable clue at the articular pillar regions.

• Positioning for trauma. When cervical vertebral projections are taken of a trauma patient with suspected subluxation or fracture, take the lateral projection with the patient's position left as is. Do not attempt to remove the cervical collar or adjust head or body rotation, mandible position, or vertebral tilting. This might result in increased injury to the vertebrae or spinal cord. A trauma lateral cervical vertebral projection is obtained by placing a lengthwise IR against the patient's shoulder and directing a horizontal beam to the cervical vertebrae (Figure 8-13). Such an image should meet as many of the analysis requirements listed for a nontrauma lateral projection as possible without moving the patient. A 10- × 12-inch (24- × 30-cm) IR may be needed to include all the required structures.

• When the patient is positioned for a lateral cervical projection, place the head in a lateral projection with the midsagittal plane aligned parallel with the IR and the chin is elevated until the acanthiomeatal line is aligned parallel with the floor and the interpupillary line is aligned perpendicular to the IR. This positioning accomplishes five goals: alignment of the cervical vertebral column parallel with the IR; demonstration of C1 and C2 without occiput or mandibular superimposition; superimposition of the anterior and posterior and superior and inferior aspects of the cranial and mandibular cortices, and of the superior and inferior aspects of the right and left articular pillars and zygapophyseal joints.

• Effect of mandibular rotation and elevation on C1 and C2 visualization. The position of the mandible and demonstration of C1 and C2 on a lateral cervical vertebrae projection are affected by head positioning. The posterior cortices of the mandibular rami are superimposed when the head's midsagittal plane was aligned parallel with the IR. If the posterior cortices of the mandibular rami are not superimposed on a lateral cervical vertebrae projection, one mandibular ramus is superimposed over the bodies of C1 and/or C2 and the other is situated anteriorly (see Image 18).

    If the chin was elevated adequately to place the acanthiomeatal line parallel with the floor, the mandibular rami are demonstrated anterior to the vertebral column. If the patient's chin was not adequately elevated, the mandibular rami are superimposed over the bodies of C1 and/or C2 (see Image 19).

• Detecting head and shoulder tilting that causes lateral cervical flexion. If the patient's head is tilted toward or away from the IR enough to flex the upper cervical column laterally, or if the shoulders are not placed on the same plane but are tilted enough to flex the lower cervical column laterally, the lateral cervical projection will demonstrate a superoinferior separation between the right and left articular pillars and zygapophyseal joints of the flexed vertebrae (see Images 18 and 20). Head tilting will also result in a superoinferior separation between the cranial cortices and between the mandibular rami; this can be avoided by positioning the interpupillary line (imaginary line connecting the outer corners of the eyelids) parallel with the floor. If the head was tilted toward the IR, neither the superior or the inferior cortices of the cranium nor the mandibular rami are superimposed, and the vertebral foramen of C1 is demonstrated (see Image 20). If the head and upper cervical vertebral column were tilted away from the IR, neither the inferior cortices of the cranium nor the mandibular rami are superimposed, and the posterior arch of C1 remains in profile (see Image 18).

• Aligning the long axis of the cervical vertebral column with the long axis of the exposure field ensures against flexion or extension of the cervical column and allows for tight collimation. This alignment is obtained by positioning the patient's neck vertically and aligning the midline of the patient's neck with the collimator's longitudinal light line; it places the cervical column in a neutral position.

• Hyperflexion and hyperextension positioning to evaluate AP mobility of cervical vertebrae. Hyperflexion and hyperextension lateral cervical vertebrae projections are obtained to evaluate AP vertebral mobility. For hyperflexion, instruct the patient to tuck the chin into the chest as far as possible (Figure 8-14). For patients who demonstrate extreme degrees of flexion, it may be necessary to place the IR crosswise to include the entire cervical column on the same image. Such an image should meet all the analysis requirements listed for a neutral lateral projection, except that the long axis demonstrates forward bending (see Image 21). For hyperextension, instruct the patient to extend the chin up and backward as far as possible (Figure 8-15). Such an image should meet all the analysis requirements listed for a neutral lateral projection, except that the long axis demonstrates backward bending (see Image 22). If the lateral projection is used with the patient in hyperflexion or hyperextension, an arrow pointing in the direction the neck is moving or a flexion or extension marker should be included to indicate the direction of neck movement.

• Center a perpendicular central ray to the midcoronal plane at a level halfway between the EAM and the jugular notch to center C4 to the exposure field.

• Open the longitudinally and transversely collimated field enough to include the clivus and sella turcica, which is at a level 0.75 inch (2 cm) anterosuperior to the EAM. (The clivus, a slanted structure that extends posteriorly off the sella turcica, and the dens are used to determine cervical injury. A line drawn along the clivus should point to the tip of the dens on the normal upper lateral cervical vertebrae projection.)

• An 8- × 10-inch (18- × 24-cm) IR placed lengthwise should be adequate to include all the required anatomic structures.

• Demonstration of C7 and T1 vertebrae. The seventh cervical vertebra and first thoracic vertebra are located between the patient's shoulders. This location makes it difficult to demonstrate them because of the great difference in lateral thickness between the neck and the shoulders. The best method to demonstrate C7 is to have the patient hold 5- or 10-lb weights on each arm to depress the shoulders and attempt to move them inferior to C7. Weights are best placed on each arm rather than in each hand, because sometimes the patient's shoulders will elevate when weights are placed in the hands. Without weights, it is often difficult to demonstrate more than six cervical vertebrae (see Image 23). Taking the image on expiration also aids in lowering the shoulders.

• Visualization of C7 and T1 in trauma or recumbency. For trauma or recumbent patients who do not have upper extremity or shoulder injuries, depress the shoulders by having a qualified assistant, with the consent of a physician, pull down on the patient's arms while the image is taken. To accomplish this, instruct an assistant to wear a protection apron and stand at the end of the imaging table or stretcher, with the patient's feet resting against the assistant's abdomen and the assistant's hands wrapped around the patient's wrists. The assistant should slowly pull on the patient's arms until the shoulders are moved inferiorly as much as possible.

• Demonstration C7. If even after using weights to depress the patient's shoulders C7 cannot be demonstrated in its entirety, a special image known as the lateral cervicothoracic projection (Twining method, Swimmer's technique) should be taken. Refer to page 449 for specifics.

Lateral Cervical Vertebrae Projection Analysis

• To position the intervertebral foramina and pedicles of interest in profile, begin by placing the patient in a recumbent or upright PA-AP axial oblique projection. Rotate the patient from this position until the midcoronal plane is at a 45-degree angle to the imaging table or upright IR. To demonstrate the foramina and pedicles on both sides of the cervical vertebrae, right and left oblique projections must be taken. When PA axial oblique projections (Figure 8-18) are obtained, the foramina and pedicles situated closer to the IR are demonstrated, whereas AP axial oblique projections (Figure 8-19) demonstrate the foramina and pedicles situated farther from the IR.

• Effect of incorrect rotation. If the cervical vertebral rotation is insufficient, the intervertebral foramina are narrowed or obscured, the pedicles are foreshortened, and a portion of the sternum, one sternoclavicular joint, and the vertebral column are superimposed (see Image 24). If the cervical vertebrae are rotated more than 45 degrees, one side of the pedicles is partially foreshortened but the other side is aligned with the midline of the vertebral bodies, and the zygapophyseal joints—demonstrated without vertebral body superimposition—are open (see Image 25). Because it is possible for the upper and lower cervical vertebrae to be rotated to different degrees on the same image, one needs to evaluate the entire cervical vertebrae for proper rotation (see Image 26).

• Positioning for trauma. When imaging the cervical vertebrae of a trauma patient with suspected subluxation or fracture, obtain the trauma AP axial and lateral projections and have them evaluated before the patient is moved for the AP axial oblique projection. The trauma AP axial oblique projection of the cervical vertebrae is accomplished by elevating the supine patient's head, neck, and thorax enough to place a lengthwise IR beneath the neck. If the right vertebral foramina and pedicles are of interest, the IR should be shifted to the left enough to align the right mastoid tip with the longitudinal axis of the IR and inferior enough to position the right gonion (C3) with the transverse axis of the IR. Direct the central ray 45 degrees medially to the right side of the patient's neck and 15 degrees cephalically, and then center it halfway between the AP surfaces of the neck at the level of the thyroid cartilage (C4) (Figure 8-20). If the left vertebral foramina and pedicles are of interest, shift the IR to the right enough to align the right mastoid tip with the longitudinal axis of the IR and inferior enough to position the left gonion with the transverse axis of the IR. The central ray should be angled and centered as described earlier, except that it should be directed to the left side of the patient's neck. A trauma AP axial oblique cervical projection should meet all the analysis requirements listed for a regular AP axial oblique cervical projection; the cranium will be in an AP oblique projection (Figure 8-21).

• The cervical vertebral column demonstrates a lordotic curvature. This curvature, along with the shape of the cervical bodies, causes the disk-articulating surfaces of the vertebral bodies to slant downward posteriorly to anteriorly.

• Importance of central ray angulation. To obtain open intervertebral disk spaces and undistorted, uniformly shaped vertebral bodies, the central ray must be angled in the same direction as the slope of the vertebral bodies. This is accomplished by angling the central ray 15 to 20 degrees caudally for PA axial oblique projections and 15 to 20 degrees cephalically for AP axial oblique projections. This angle will also result in demonstration of the atlas's vertebral foramen on the projections.

• Effect of inaccurate central ray angulation. If the central ray is not accurately angled with the intervertebral disk spaces, they are closed and the cervical bodies are not demonstrated as individual structures (see Images 27 and 28). Because this examination can be performed using AP or PA axial oblique projections that require differing central ray angulations, and the typical cervical vertebral series requires the radiographer to change angle directions several times, radiographers should be able to identify an image that was taken with an incorrect angle. Image 27 was taken using a perpendicular central ray, and Image 28 was taken with the central ray angled in the wrong direction. Note the closed intervertebral disk spaces, distorted cervical bodies, and demonstration of the posterior tubercles within the intervertebral foramina.

• Positioning for kyphosis. In patients with severe kyphosis, the lower cervical vertebrae are angled toward the IR because of the greater lordotic curvature of this area. To demonstrate the lower cervical vertebrae with open intervertebral disk spaces and undistorted cervical bodies, the central ray will need to be angled more than the suggested 15 to 20 degrees for the AP-PA oblique projection. The patient in Image 29 had kyphosis. Note the decrease in intervertebral disk space openness and vertebral body distortion and the demonstration of the zygapophyseal joints through the cervical bodies between the upper and lower cervical regions.

• Mandibular rami and cranial demonstration. The distances demonstrated between the inferior cortical outlines of the cranium and the mandibular rami are a result of the angulation placed on the central ray. On PA axial oblique cervical projections, the caudal angle projects the cranial cortex situated farther from the IR approximately 0.25 inch (0.6 cm) inferiorly and the mandibular ramus situated farther from the IR approximately 0.5 inch (1.25 cm) inferiorly. The ramus is projected farther inferiorly because it is located at a larger OID than the cranial cortex. On AP axial oblique projections, the cephalic angle projects the cranial cortex and mandibular rami situated farther from the IR superiorly.

    The distance between these two cortical outlines will be increased or decreased if the patient's head is allowed to tilt toward or away from the IR. Such tilting also causes the upper cervical vertebrae to lean toward or away from the IR. To avoid head and cervical column tilting, position the interpupillary line parallel with the floor.

• Detecting head tilting. On PA axial oblique projections, if the head and upper cervical column are allowed to tilt, the atlas and its posterior arch are distorted. From such an image, one can determine whether the head and upper cervical vertebrae were tilted toward or away from the IR by evaluating the distance demonstrated between the inferior cranial cortices and the inferior mandibular rami. If these distances are increased, the head and upper cervical vertebrae were tilted away from the IR (see Image 30). If these distances are decreased, the head and upper cervical vertebrae were tilted toward the IR.

• The desired position of the patient's head for an AP axial oblique cervical projection varies among facilities. If an AP oblique cranium projection is desired, rotate the patient's head 45 degrees with the body. If a lateral cranium projection is desired, turn the patient's face away from the side of interest until the head's midsagittal plane is aligned parallel with the IR.

• To demonstrate the upper cervical vertebrae without mandibular superimposition and aligned right and left cranial and mandibular cortices on an AP axial oblique cervical projection, place the patient's cranium in a lateral projection and adjust chin elevation until the acanthiomeatal line is aligned parallel with the floor. If the patient's chin is not properly elevated and/or the patient's head is rotated, the mandibular rami are superimposed over C1 and C2 (see Image 31).

• Center a 15- to 20-degree cephalically angled central ray for the AP axial oblique or a 15- to 20-degree caudally angled central ray for the PA axial oblique to the patient's midsagittal plane at a level halfway between the EAM and the jugular notch to center C4 to the exposure field.

• Open the longitudinal collimation to the EAM and the jugular notch. Transverse collimation should be to within 0.5 inch (1.25 cm) of the neck skin line.

• An 8- × 10-inch (18- × 24-cm) IR placed lengthwise should be adequate to include all the required anatomic structures.

Posteroanterior Axial Oblique Cervical Vertebrae Projection Analysis

CERVICOTHORACIC VERTEBRAE: LATERAL PROJECTION (TWINING METHOD; SWIMMER's TECHNIQUE)

This examination is performed when the routine lateral cervical projection does not adequately demonstrate the seventh cervical vertebra or when the routine lateral thoracic projection does not demonstrate the first through third thoracic vertebrae. See Figure 8-22 and Box 8-6.

The cervicothoracic vertebrae are demonstrated in a lateral projection. The humerus elevated above the patient's head is aligned with the vertebral column, the right and left cervical zygapophyseal joints and articular pillars are superimposed, and the posterior ribs are superimposed.

The intervertebral disk spaces are open, and the vertebral bodies are demonstrated without distortion.

The first thoracic vertebra is centered within the exposure field. The fifth through seventh cervical vertebrae and the first through fourth thoracic vertebrae are included within the collimated field.

THORACIC VERTEBRAE: ANTEROPOSTERIOR PROJECTION

See Figure 8-25 and Box 8-7.

There should be uniform density across the thoracic vertebrae.

The thoracic vertebral column demonstrates an AP projection. The spinous processes are aligned with the midline of the vertebral bodies, the distances from the vertebral column to the medial (sternal) ends of the clavicles are equal, and the distances from the pedicles to the spinous processes are equal on the two sides.

The intervertebral disk spaces are open, and the vertebral bodies are demonstrated without distortion.

The seventh thoracic vertebra is centered within the exposure field. The seventh cervical vertebra, first through twelfth thoracic vertebrae, first lumbar vertebra, and 2.5 inches (6.25 cm) of the posterior ribs and mediastinum on each side of the vertebral column are included within the collimated field.

• Breathing technique. The thoracic vertebrae have many overlying structures, including the axillary ribs and lungs. Using a long exposure time (3 to 4 seconds) and requiring the patient to breathe shallowly (costal breathing) during the exposure forces a slow and steady, upward and outward movement of the ribs and lungs. This technique is often referred to as breathing technique. This movement causes blurring of the ribs and lung markings on the image, providing greater thoracic vertebral demonstration. Deep breathing, which requires movement (elevation) of the sternum and a faster and expanded upward and outward movement of the ribs and lungs, should be avoided during the breathing technique, because deep breathing results in motion of the thoracic cavity and vertebrae (see Image 39).

• NOTE: If patient motion cannot be avoided when using the extended 3 to 4 seconds for breathing technique, take the image on suspended expiration to reduce the air volume within the thoracic cavity.

• To obtain a lateral thoracic vertebrae projection, place the patient on the imaging table in a lateral recumbent projection. Whether the patient is lying on the right or left side is not significant, although left-side positioning is easier for the technologist (Figure 8-31). One exception to this guideline is the scoliotic patient, who should be placed on the imaging table so the central ray is directed into the spinal curve. Abduct the patient's arms to a 90-degree angle with the body to prevent the humeri or their soft tissue from obscuring the thoracic vertebrae. Flex the patient's knees and hips for support, and position a pillow or sponge between the knees. The thickness of the pillow or sponge should be enough to prevent the side of the pelvis situated farther from the IR from rotating anteriorly but not so thick as to cause posterior rotation. To avoid vertebral rotation, align the shoulders, the posterior ribs, and the posterior pelvic wings perpendicular to the imaging table and IR by resting an extended flat palm against each, respectively, and then adjusting patient rotation until the hand is positioned perpendicular to the IR.

• Effect of rotation. The upper and lower thoracic vertebrae can demonstrate rotation independently or simultaneously, depending on which section of the torso was rotated. If the shoulders and the superoposterior ribs were not placed on top of each other but the posterior pelvic wings and inferoposterior ribs were aligned, the upper thoracic vertebrae demonstrate rotation and the lower thoracic vertebrae demonstrate a true lateral projection. If the posterior pelvic wings and inferoposterior ribs were rotated but the shoulders and superoposterior ribs were placed on top of each other, the lower thoracic vertebrae demonstrate rotation and the upper vertebrae demonstrate a lateral projection.

• Detecting rotation. Rotation can be detected on a lateral thoracic vertebrae projection by evaluating the superimposition of the right and left posterior surfaces of the vertebral bodies and the amount of posterior rib superimposition. On a nonrotated lateral thoracic projection, the posterior surfaces are superimposed and the posterior ribs are almost superimposed. Because the posterior ribs positioned farther from the IR were placed at a greater OID than the other side, they demonstrate more magnification. This magnification prevents the posterior ribs from being directly superimposed but positions them approximately 0.5 inch (1.25 cm) apart. This distance is based on a 40-inch (102-cm) SID. If a longer SID is used, the distance between the posterior ribs is decreased and, if a shorter SID is used, the distance is increased. On rotation, the right and left posterior surfaces of the vertebral bodies are demonstrated one anterior to the other on a lateral projection.

    Because the two sides of the thorax and vertebrae are mirror images, it is very difficult to determine from a rotated lateral thoracic projection which side of the patient was rotated anteriorly and which posteriorly. If the patient was only slightly rotated, one way of determining which way the patient was rotated is to evaluate the amount of posterior rib superimposition. If the patient's elevated side was rotated posteriorly, the posterior ribs demonstrate more than 0.5 inch (1.25 cm) of space between them (see Image 40). If the patient's elevated side was rotated anteriorly, the posterior ribs are superimposed on slight rotation (see Image 41) and demonstrate greater separation as rotation of the patient increases. Another method is to view the scapulae and humeral heads when visible. The scapula and humeral head demonstrating the greatest magnification will be the ones situated farthest from the IR (see Image 42).

• Distinguishing rotation from scoliosis: On the image of a patient with spinal scoliosis, the lung field may appear rotated because of the lateral deviation of the vertebral column (see Image 12, Chapter 3). On such an image, the posterior ribs demonstrate differing degrees of separation depending on the severity of the scoliosis. View the accompanying AP thoracic projection (see Image 3, Chapter 3) to confirm this patient condition.

• The thoracic vertebral column is capable of lateral flexion. When the patient is placed in a recumbent lateral projection, the vertebral column may not be aligned parallel with the imaging table and IR but may sag at the level of the lower thoracic vertebrae, especially in a patient who has wide hips and a narrow waist (Figure 8-32). If the patient's thoracic column is allowed to sag, the diverging x-ray beams are not aligned parallel with the intervertebral disk spaces and perpendicular with the vertebral bodies. Lateral flexion on a lateral thoracic vertebrae projection is most evident at the lower thoracic vertebral bodies, where closed disk spaces and distorted vertebral bodies are present (see Image 43). For a patient who has a sagging thoracic column, it may be necessary to tuck an immobilization device between the lateral body surface and imaging table just superior to the iliac crest, elevating the sagging area. The radiolucent sponge should be thick enough to bring the thoracic vertebral column parallel with the imaging table and IR (see Figure 8-31)

• An alternative method of obtaining open disk spaces and undistorted vertebral bodies in a patient whose thoracic column is sagging is to angle the central ray 10 degrees cephalically for female patients and 15 degrees for male patients. The degree of cephalic angulation used should align the central ray perpendicular to the thoracic vertebral column.

• Center a perpendicular central ray to the inferior scapular angle. With the patient's arm positioned at a 90-degree angle with the body, the inferior scapular angle is placed over the seventh thoracic vertebra.

• Open the longitudinal collimation the full 17-inch (43-cm) IR length for adult patients. Transverse collimation should be to an 8-inch (20-cm) field.

• A 14- × 17-inch (35- × 43-cm) IR placed lengthwise should be adequate to include all the required anatomic structures.

• Verifying inclusion of all thoracic vertebrae. When viewing a lateral thoracic projection, you can be sure that the twelfth thoracic vertebra has been included by locating the vertebra that has the last rib attached to it; this is the twelfth vertebra. To confirm this finding, follow the posterior vertebral bodies of the lower thoracic and upper lumbar vertebrae, watching for the subtle change in curvature from kyphotic to lordotic. The twelfth thoracic vertebra is located just above it. The first thoracic vertebra can be identified on a lateral thoracic projection by counting up from the twelfth thoracic vertebra or by locating the seventh cervical vertebral prominens. The first thoracic vertebra is at the same level as this prominens.

• Lateral cervicothoracic projection (Twining method). Because of shoulder thickness and the superimposition of the shoulders over the first through third thoracic vertebrae, it may be necessary to take a supplementary image of this area to demonstrate the thoracic vertebrae. Refer to page 449 for details.

Lateral Thoracic Vertebrae Projection Analysis