Radiographic Anatomy of the Chest

Study Notes

Radiographic Anatomy of the Chest (Respiratory System)

The chest (thorax) is the upper portion of the trunk, between the neck and abdomen.

Bony Thorax

It's part of the skeletal system, providing a framework for structures involved in breathing and blood circulation.
It consists of:
- Sternum (anteriorly)
- Clavicles (superiorly)
- 12 pairs of ribs
- 12 thoracic vertebrae (posteriorly)

Thoracic Viscera

Describes the parts of the chest, including the lungs and other thoracic organs in the mediastinum.

Mediastinum

Contains all thoracic organs except the lungs.
The heart occupies a large portion and its shape varies with age, respiration, and patient position.
Other structures in the mediastinum include the thyroid and thymus glands, as well as nervous and lymphatic tissues.

Topographic Positioning Landmarks

Vertebra prominens: A key landmark for determining the central ray (CR) location on a posteroanterior (PA) chest projection.
Jugular notch: A key landmark for determining the CR placement on an anteroposterior (AP) chest projection.
Midthorax: Located at the level of T7.
Average distance of Vertebra prominens:
- Female: 7 in. (18 cm)
- Male: 8 in. (20 cm)

Respiratory System

Air enters the body through the upper airways: Nasal cavity, Pharynx , Larynx
Air continues through the lower airways: Trachea, Primary Bronchi, Bronchial tree, Bronchioles, Alveoli.

Lungs

Divided into lobes:
- Left lung: Upper lobe, Lower lobe, Lingula
- Right lung: Upper lobe, Middle lobe, Lower lobe
Alveoli are the areas responsible for gaseous exchange, having a large surface area.
Each alveolus is closely associated with a network of capillaries.

Anatomical Divisions of the Mediastinum

Anterior mediastinum: Thyroid and Thymus glands
Middle mediastinum: Heart and great vessels, Esophagus and trachea
Posterior mediastinum: Descending aorta and the spine.

Chest Radiography Considerations

Position and Projection
- Position refers to the body arrangement (e.g., erect, supine, recumbent).
- Projection refers to the path of the X-ray beam (e.g., AP, PA, lateral).
- Standard projections used in chest radiography include erect posteroanterior (PA) and left lateral.
- The erect PA projection positions the heart closer to the film to minimize magnification, mostly to the viewer's left side..
Imaging Considerations -The most frequent examination in radiology is chest radiography. -Additive pathology requires increased technical factors (e.g., pneumonia).
- Subtractive pathology requires decreased technical factors (e.g., emphysema).
Patient Position
- The upright position is best for preventing blood engorgement of the pulmonary vessels and to visualize air and fluid levels in the chest
- Upright PA views are preferred for the diagnosis of pneumoperitoneum (free air in the abdominal cavity).
- Positioning for oblique and/or the apico-lordotic views.
Patient Positioning (Cont'd)
- Ask the patient to move shoulders forward and downward and 2" above the shoulders for superior lung view.
- Position patient's arms overhead; this will position the scapulae away from the lungs to prevent superimposition.
- Position patient in upright projection; this is a common location for obtaining clear views of the entire chest.
Patient Positioning considerations
- Ensuring that the patient stands evenly, both shoulders forward and downward, positioning of the patient for the appropriate central ray location to minimize rotation and ensure that the medial ends of the clavicles are equidistant.
Respiration
- Make exposure on the second deep breath to ensure full inspiration.
- Determine inspiration degree by starting on the top of the rib cage and counting ribs down (e.g., Rib # 1), and counting to the 10th or 11th posterior rib.
Cardiothoracic ratio
- The ratio is calculated using measured dimensions of the chest and heart.
- This value helps to assess the size of the heart
Rotation
- Even slight rotation can distort the mediastinal borders on a chest radiograph and obscure structures or lung regions.