Radiology of the Bony Thorax

Medical Imaging Procedure: Chest, Bony Thorax, and Abdomen

• The bony thorax consists of the sternum, ribs, and sternocostal joints
• Radiographic positioning of the bony thorax involves various projections for different anatomical structures
• Sternum projections (basic) involve RAO and lateral views
• Sternoclavicular joint projections (basic) involve PA and anterior oblique views
• Ribs projections (basic) include AP, PA, and anterior/posterior oblique views of posterior and anterior ribs
• Unilateral rib studies use AP/PA projections
• Bony thorax anatomy includes a sternum located anteriorly, thoracic vertebrae posteriorly, and 12 pairs of ribs
• The sternum is a thin, narrow, flat bone with a manubrium, body, and xiphoid process
• Palpable landmarks include the jugular notch (T2/T3), sternal angle (T4/T5), xiphoid tip (T9/T10), and inferior rib angle/lower coastal margin (L2/L3)
• Sternoclavicular articulation is a bony connection between the shoulder girdle and bony thorax
• Sternal rib articulations include costocartilages connecting anterior ribs to the sternum
• Ribs are numbered according to the thoracic vertebrae (1-12)
• Ribs 1-7 are true ribs, directly attached to the sternum by their own costocartilages
• Ribs 8-10 are false ribs, attached to the 7th costocartilage
• Ribs 11 and 12 are floating ribs, with no costocartilage
• On radiographs, the posterior end of a rib is always superior to the anterior end
• Typical ribs' key anatomical features (as seen on radiographs) include: vertebral end, head, neck, tubercle, angle, shaft (and body), sternal end, articular facets, neck, and grooves for blood vessels/nerve
• Rib cage structure involves the downward angulation of the ribs; the short, broad, vertical 1st rib, gradually lengthening ribs (2nd-7th), and gradually shortening ribs (8th onwards). The 12th rib is short, and the widest diameter is along the 8th and 9th ribs, laterally
• Articulations of the bony thorax include costochondral union/junction, sternoclavicular joint, sternocostal joint of the first rib (synarthrodial joint), sternocostal joint of the fourth rib (diarthrodial joint allowing gliding motion), and interchondral joints (diarthrodial)
• Clinical indications related to the bony thorax include fractures (of ribs or sternum), congenital anomalies (pectus carinatum/excavatum), metastases (osteolytic/osteoblastic or mixed), osteomyelitis (infection), osteopetrosis (increased density), osteoporosis (bone loss), Paget's disease (thick, soft bone with bowing), and tumors (chondrosarcoma, multiple myeloma)

Summary of Clinical Indications

• Clinical indications include fractures, congenital anomalies, metastases, osteomyelitis, osteopetrosis, osteoporosis, Paget's disease, and tumors
• Possible radiographic appearances vary based on the specific condition
• Exposure factors may need adjustment depending on the condition and type of lesion

Considerations

• The sternum is often problematic to visualize due to overlapping anatomy (spine, heart)
• The cartilaginous nature of the sternum may affect the image's appearance
• Rotation of the patient and angulations of the tube, along with technical factors like the size of the thoracic cavity, are important considerations for obtaining high-quality radiographs
• Important clinical history, such as the nature of trauma or patient complaint, location of rib pain, and whether blood is being coughed up, should be considered.
• Determine if the patient can stand or not

Why RAO View?

• The RAO view superimposes the heart shadow onto the sternum, allowing for better visualization of the sternum.
• Air in the lungs is more radiodense than the heart shadow, making the sternum appear darker.
• This is one of several ways of reducing the overlap seen with other radiographic projections.

Exposure Factors

• 70kV is recommended for sthenic patients
• Breathing technique, shallow breathing, is needed to minimize vascular lung markings
• Low kV (65 ± 5) range
• Low mA
• Exposure time is 3–4 seconds
• SID minimum is 40 inches (100 cm)
• Technical factors such as minimum SID, IR size (lengthwise), grid, kV range, and digital system kV range are also important

Sternum Radiographic Techniques - RAO

• Minimum SID is 40 inches (102 cm)
• IR size is 24 x 30 cm (10 x 12 inches), lengthwise
• Grid used
• 2–3-second exposure time (if breathing technique is used)
• Analog systems use 65–75 kV range
• Digital systems use 70–80 kV range

Sternum Radiographic Techniques - LPO

• Patient's position is erect (preferred)/semiprone, with slight rotation, right arm downward by side, and left arm up.
• Position patient oblique, 15-20° toward the right side (RAO).
• Align the long axis of the sternum to CR and to the midline of the table/upright Bucky.
• Place the top of the IR about 1 ½ inches (4 cm) above the jugular notch.
• CR is perpendicular to IR, is centered on the sternum (1 inch [2.5 cm] to the left of the midline and midway between the jugular notch and the xiphoid process)

Sternum Radiographic Techniques-Lateral

• Patient position is erect/lateral recumbent for erect and recumbent for recumbent.
• Patient should be standing or seated, with arms drawn back and shoulder drawn back (erect); supine (recumbent)
• Position the top of the IR 1.5 inches (4 cm) above the jugular notch.
• The long axis of the sternum aligns with the midline of the grid.
• There is no rotation.

Sternoclavicular Joint - PA Projection

• Patient is prone.
• MSP aligns with CR.
• No rotation of shoulders.
• Center IR to CR (3" distal to the vertebral prominence).
• CR is perpendicular, centered at the level of T2/3 (or 3" below the vertebral prominence).
• SID is 100cm.

Sternoclavicular Joint - RAO/LAO

• Patient is prone, slightly rotated (10–15 degrees).
• Rotate the patient 10–15 degrees, aligning and centering the spinous process 3–5 cm lateral to the mid-IR on the affected (upside or downside) side.
• CR is perpendicular to the level of T2/3 (7.5 cm distal to the vertebra prominence and 3 to 5 cm lateral towards the upside to the MSP). SID is 100cm.
• Respiration is suspended on expiration.
• IR and Exposure Factor: 18x24 cm, 60–70 kV.
• Use a moving/stationary grid.

Ribs - AP Projection

• The patient is erect (above diaphragm) or supine (below diaphragm).
• Aligned MSP to CR & midline of IR.
• Rotate shoulder anteriorly & raise chin.
• No rotation of pelvis or thorax.
• CR is perpendicular to IR, centered to T7(7-8 inch/18cm-20 cm below vertebra prominence)
• Top of IR 1.5" above shoulders. SID 100cm
• Respiration is suspended on inspiration
• IR and Exposure Factor: 35x43 cm; 65-75 kV.
• Use a moving/stationary grid.

Unilateral Rib Images

• Patient position, erect (above diaphragm)/supine (below diaphragm)
• Align left or right side of thorax to CR and midline.
• Raise chin to prevent superimposition.
• No rotation of thorax or pelvis.
• Above Diaphragm, CR is perpendicular to IR, centered midway between midsagittal plane and outer margin of thorax.
• Below Diaphragm, top (top) of IR should be [about 4cm above the shoulders].
• Position the IR as CR so bottom is at iliac crest.
• Respiration, suspend.
• Collimate to region of interest.

Posterior or Anterior Oblique Positions of Ribs

• Posterior-lateral injury: posterior oblique position (affected side is towards the IR)
• Anterior-lateral injury: anterior oblique position (affected side away from the IR)
• Erect (Above Diaphragm), supine (below diaphragm)
• Rotate patient position 45-degrees, affected side towards IR (posterior oblique); affected side away from IR (anterior oblique).
• Elevate arm above the head and behind the patient.
• Use support block.
• Align a plane of thorax midway between the spine and the lateral margin of the thorax, toward CR and midline of grid.
• CR perpendicular to IR, centered midway between spine lateral margin of the thorax.
• If it's above the diaphragm, it should be 3-4" below jugular notch, top of IR 1.5" above the shoulder. It's below the diaphragm, it should be to the level of midway between the xiphoid process and lower rib cage (bottom of IR at iliac crest).