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newSchoolWorks.com › VoTechWorks › Health & Personal Services › Limited X-Ray / Radiologic Technology › Anatomy & Positioning for Radiographic Practice › Lesson 8
HLT-RADI64-03 · Lesson 8 · 28 clock hours · lab

Positioning the Spine — Cervical Through Sacrum/Coccyx

Objective. Students will position a cooperative partner for standard AP, lateral, and oblique projections of each spinal region, applying correct CR angles, centering points, and breathing techniques for each.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed clinician in the field or by a certification or approval body. It is a study draft and may contain errors. Do not use it to make decisions about any patient or medication. Always follow your instructor, your supervising professional, and current official references and regulations.

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Positioning the Spine — Cervical Through Sacrum/Coccyx

The vertebral column is divided into five regions: cervical (C1–C7), thoracic (T1–T12), lumbar (L1–L5), sacral, and coccygeal. Each region requires specific projections, central ray (CR) angles, centering landmarks, and source-to-image distance (SID) settings to demonstrate bony anatomy clearly and safely. Mastering these details is essential for the ARRT Limited Scope and RT(R) examinations and for daily clinical practice.

Cervical Spine Series

AP Projection (C3–C7): Position the patient supine or upright with the midsagittal plane perpendicular to the image receptor (IR). Tuck the chin slightly so the occlusal plane is perpendicular to the IR. Direct the CR 15 degrees cephalad to the level of C4 (thyroid cartilage). SID is typically 72 inches (180 cm) for upright cervical work to reduce magnification. The cephalad angle opens the intervertebral disc spaces, which lie at an angle to the IR in the cervical region.

Open-Mouth Odontoid (AP Dens): This projection shows C1 (atlas) and C2 (axis), including the dens (odontoid process). Have the patient open the mouth as wide as possible. Align the CR perpendicular (0 degrees) through the open mouth to the midpoint of the oral opening. On a properly positioned image, the upper incisors and the base of the skull should be superimposed, and the dens should be visible between the lateral masses of C1 without superimposition of the teeth or occiput.

Lateral Cervical: Use a 72-inch SID to minimize magnification of the structure farthest from the IR. The patient's shoulders should be depressed (have the patient hold weights or pull arms downward) to visualize C7–T1. CR is directed horizontally to C4. Collimate to the cervical spine.

Oblique Cervical (Posterior Obliques — RPO/LPO or Anterior Obliques — RAO/LAO): Obliques demonstrate the intervertebral foramina. For posterior obliques (patient facing the tube), rotate 45 degrees; the foramina closest to the IR are demonstrated. CR is angled 15 degrees cephalad to C4. For anterior obliques, rotate 45 degrees with the patient facing the IR; CR is angled 15 degrees caudad to C4. Both bilateral sides are obtained for comparison.

Thoracic Spine Series

AP Thoracic: Patient is supine or upright. CR is perpendicular to T7 (approximately 3–4 inches below the jugular notch, or at the level of the inferior angle of the scapula). SID is 40 inches (100 cm). The upper thoracic vertebrae are often difficult to see due to overlying shoulder structures; breathing technique (patient breathes slowly during a long exposure) blurs the ribs and lung markings, improving vertebral visibility on the lateral projection.

Lateral Thoracic: Patient lateral, knees flexed for stability. CR perpendicular to T7. Use a breathing technique (slow, shallow breathing during exposure) to blur overlying rib and lung detail. A compensating filter placed at the upper thoracic region helps balance density between the thicker lower thoracic and thinner upper thoracic areas.

Lumbar Spine Series

AP Lumbar: Patient supine, knees flexed over a pillow to reduce lordotic curve and bring the spine closer to parallel with the IR. CR perpendicular to L3 (approximately 1–1.5 inches above the iliac crest at the midsagittal plane). SID 40 inches.

Oblique Lumbar (RPO/LPO): Rotate the patient 45 degrees. This demonstrates the zygapophyseal (facet) joints of the elevated side and produces the classic "Scottie dog" sign on the radiograph. The eye of the dog is the pedicle, the ear is the superior articular process, the nose is the transverse process, the neck is the pars interarticularis, and the front leg is the inferior articular process. CR is perpendicular to L3.

Lateral Lumbar: Patient lateral. CR perpendicular to L3–L4 (iliac crest level). A radiolucent support sponge under the waist maintains the spine parallel to the IR for patients with a prominent iliac crest.

L5–S1 Lateral Spot: A dedicated lateral of the lumbosacral junction. CR is angled 5–8 degrees caudad (varies with patient habitus) directed to a point 1.5 inches inferior and posterior to the ASIS, to open the L5–S1 disc space.

Sacrum and Coccyx

AP Sacrum: CR angled 15 degrees cephalad to the midpoint between the pubic symphysis and ASIS. This opens the sacral foramina.

AP Coccyx: CR angled 10 degrees caudad to a point 2 inches superior to the pubic symphysis. Gonadal shielding must be used whenever it does not obscure clinically relevant anatomy — this is especially important in the sacrum/coccyx region.

Safety and Scope-of-Practice Reminders

Key terms9

Central ray (CR)The center of the x-ray beam, directed to the specific anatomical point to open joint spaces and reduce distortion; expressed as perpendicular (0°) or at a named angle.
Cephalad angleA CR angulation directed toward the patient's head, used (for example) 15° cephalad for the AP cervical and AP sacrum projections to open joint spaces that are angled relative to the IR.
Caudad angleA CR angulation directed toward the patient's feet, used (for example) for the AP coccyx and the L5–S1 lateral spot to align the beam with angled structures.
Odontoid process (dens)The tooth-like superior projection of C2 (axis) that pivots within C1 (atlas); visualized on the open-mouth AP projection; critical in trauma assessment.
Scottie dog signThe appearance of the lumbar vertebra on a 45° oblique image where bony structures form the outline of a dog; the neck of the dog (pars interarticularis) is the key area assessed for spondylolysis.
Breathing techniqueHaving the patient breathe slowly and shallowly during a longer exposure to blur overlying structures (ribs, lung markings) and improve visualization of thoracic vertebrae on lateral projections.
Zygapophyseal (facet) jointsThe paired posterior joints between adjacent vertebrae; demonstrated on oblique projections of the lumbar spine and visible as the neck of the Scottie dog.
Source-to-image distance (SID)The measured distance from the x-ray tube focal spot to the image receptor; 40 inches is standard for most spinal projections, while 72 inches is used for upright cervical and chest imaging to reduce magnification.
Pars interarticularisThe segment of bone between the superior and inferior articular processes of a lumbar vertebra; corresponds to the neck of the Scottie dog on oblique images; a stress fracture here causes spondylolysis.

Worked examples4

1. You are performing an AP cervical spine projection. The CR must be angled 15° cephalad. The base of the x-ray tube protractor reads 0° (perpendicular). How many degrees do you rotate the tube toward the patient's head, and in which direction?
  1. Identify the required angle: 15° cephalad (toward the head).
  2. The tube starts at 0° (perpendicular to the IR).
  3. Rotate the tube angle indicator 15° in the cephalad direction.
  4. Verify the angle on the tube protractor reads 15° cephalad before making the exposure.
Answer: Rotate the tube 15° toward the patient's head (cephalad). The protractor should read 15° cephalad.
2. For a lateral thoracic spine projection, you plan to use a breathing technique. The radiologist requests a long exposure time to blur the ribs. Your technique chart suggests 80 kVp and 40 mAs at 40-inch SID. If you keep kVp and SID the same but change the exposure time from 0.5 s to 2.0 s, what mA must you select to maintain 40 mAs?
  1. Recall: mAs = mA × time (in seconds).
  2. Required mAs = 40 mAs; new time = 2.0 s.
  3. Rearrange: mA = mAs ÷ time = 40 ÷ 2.0.
  4. Calculate: mA = 20 mA.
Answer: Set the mA to 20. At 20 mA × 2.0 s = 40 mAs, maintaining the same total exposure while using a longer time to blur overlying structures.
3. For an L5–S1 lateral spot, the protocol calls for a 5° caudad CR angle. The tube is currently set at 0° (perpendicular). Your centering point is 1.5 inches inferior to the ASIS on the lateral surface. You measure and find the ASIS is at the level of the IR center. Where does the CR exit relative to the IR center, and in which direction must you angle the tube?
  1. The required angle is 5° caudad (toward the feet).
  2. The tube must be rotated 5° away from the patient's head (caudad direction).
  3. Because of the caudad angle, the CR will exit slightly superior to where it enters, but the centering point (entry point) is placed 1.5 inches inferior to the ASIS.
  4. Verify the protractor reads 5° caudad before exposure.
Answer: Angle the tube 5° toward the feet (caudad). Center the CR entry point 1.5 inches inferior to the ASIS to direct the beam through the L5–S1 disc space.
4. A patient is 72 inches tall. For the AP lumbar spine, the centering landmark is 1 inch above the iliac crest at the midsagittal plane. You measure the iliac crest at 38 inches from the tabletop (patient supine). Where, in inches from the tabletop surface, should you center the CR?
  1. Iliac crest is at 38 inches from the tabletop.
  2. Center point is 1 inch superior to the iliac crest.
  3. 38 inches + 1 inch = 39 inches from the tabletop.
Answer: Center the CR at 39 inches from the tabletop, which corresponds to approximately L3 for this patient.

The math in this lesson2

Learners set central-ray tube angles such as 15° cephalad on the tube protractor.
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Brush up in the math halls at newSchoolWorks.com:
In class: Set up the complete cervical spine series (AP, bilateral obliques, lateral, open-mouth odontoid) on a partner, verbalizing CR angle (including the 15-degree cephalad for AP cervical), centering landmark, and SID before the instructor approves; repeat for thoracic (AP, lateral) and lumbar (AP, bilateral obliques, lateral, L5-S1 spot) series. · Perform supervised exposures on the energized unit for at least one cervical and one lumbar series projection; complete image critique forms focusing on correct open-mouth odontoid visualization and lumbar oblique demonstration of the 'Scottie dog' sign. · Role-play a patient scenario in which the 'patient' reports neck pain after a minor fall: students discuss which projections are appropriate within limited-scope scope of practice, positioning considerations for a trauma patient, and when to stop and consult the supervising physician.
Materials: Radiographic positioning unit (energized), positioning sponges, head band/Velcro, Merrill's Atlas, image critique forms, protective aprons, lead markers
Check: Instructor-observed competency check: student positions for any four spinal projections (one from each major region) called at random; correct CR angle (within 2 degrees), centering, collimation, and marker required on all four — all must pass.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Radiographic Procedures
1. For an AP cervical spine projection, the central ray is directed 15 degrees cephalad. What is the primary purpose of this angulation?
Radiographic Procedures
2. On a properly positioned open-mouth odontoid radiograph, which structures should be superimposed at the top of the image?
Image Analysis / Radiographic Procedures
3. A student is evaluating a lumbar oblique radiograph. The 'Scottie dog' sign is present. Which structure corresponds to the neck of the Scottie dog?
Radiation Physics / Image Production
4. Why is a 72-inch SID preferred over 40 inches for upright lateral cervical spine radiography?
Patient Care / Safety
5. A patient arrives after a minor fall and reports significant neck pain. Which action is most appropriate before positioning this patient for a cervical spine series?
Radiographic Procedures / Image Production
6. For a lateral thoracic spine projection, a breathing technique is used. This technique improves image quality by:
Radiographic Procedures
7. For an AP sacrum projection, the CR is angled 15 degrees cephalad. What would most likely result if the technologist accidentally used a 15-degree caudad angle instead?
Radiation Protection / Professional Standards
8. Which of the following lead marker practices is required for all spinal radiographs?
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