Chapter 3: Chest

Detailed Chapter Overview

Chest radiography is the most commonly performed radiographic examination, providing a wealth of information about the heart, lungs, and surrounding thoracic structures. This chapter provides a comprehensive exploration of the anatomy and procedures essential for producing high-quality, diagnostic chest images. A thorough understanding of the bony thorax, respiratory system, and mediastinum is critical for accurate positioning and image evaluation. The chapter emphasizes the importance of specific patient preparation, including the removal of artifacts and clear breathing instructions, to ensure image clarity. Technical factors are examined in detail, explaining why high kVp and a long SID are standard protocol. The preference for the PA projection over AP is explained in the context of minimizing heart magnification. A significant portion of the chapter is dedicated to the precise positioning for routine and special projections, including PA, lateral, AP (supine and erect), decubitus, and apical lordotic views. For each projection, the evaluation criteria for a diagnostic image are meticulously outlined, enabling the student to develop a critical eye for details such as inspiration level, rotation, and penetration. Mastering the content of this chapter is fundamental for any radiographer, as the skills learned here are applied daily in clinical practice.

In-Depth Study Guide

Anatomy of the Chest

The chest, or thoracic cavity, contains vital organs of the respiratory and circulatory systems. Its anatomy is divided into three main sections.

1. Bony Thorax:

Provides a protective framework for the parts of the chest involved with breathing and blood circulation.

• Sternum (Breastbone): Consists of the manubrium (superior), the body (center), and the xiphoid process (inferior).
• Clavicles (Collarbones): Connect the sternum to the scapulae.
• Scapulae (Shoulder Blades): Large, triangular bones in the upper back.
• Ribs: 12 pairs that enclose the thoracic cavity.
• Thoracic Vertebrae: 12 vertebrae that articulate with the ribs posteriorly.

2. Respiratory System:

The primary function is the exchange of gaseous substances between the air and blood.

• Pharynx, Larynx, Trachea, Bronchi: The four main divisions of the respiratory system that form a continuous, tubular structure for air to pass from the nose and mouth into the lungs.
• Trachea (Windpipe): A fibrous, muscular tube that bifurcates at the **carina** into the right and left main bronchi.
• Right and Left Main Bronchi: The right bronchus is wider, shorter, and more vertical than the left, making it a more common site for foreign bodies to lodge.
• Lungs: The main organs of respiration. The right lung has three lobes (superior, middle, inferior), while the left lung has two lobes (superior, inferior) to accommodate the heart. The lungs are composed of a light, spongy, elastic substance called **parenchyma**.
• Pleura: A delicate double-walled sac that encloses each lung. The inner layer is the **visceral pleura**, and the outer layer is the **parietal pleura**. The space between them, the **pleural cavity**, contains lubricating fluid.

3. Mediastinum:

The medial portion of the thoracic cavity between the lungs.

• Thymus Gland: A key gland of the immune system. Prominent in infants, it gradually decreases in size in adulthood.
• Heart and Great Vessels: The heart and the roots of the great vessels (aorta, venae cavae, pulmonary arteries and veins) are located in the mediastinum.
• Trachea and Esophagus: The trachea is located anterior to the esophagus within the mediastinum.

Positioning Considerations & Topography

Breathing Instructions:

• Inspiration: For a standard chest x-ray, exposures are made on the **second full inspiration**. This ensures maximum aeration of the lungs. The goal is to visualize a minimum of **10 posterior ribs** above the diaphragm.
• Expiration: An exposure on full expiration may be requested to check for a small pneumothorax (air in the pleural space) or to demonstrate the movement of the diaphragm.

Topographic Landmarks for Positioning:

• Vertebra Prominens (C7): The most prominent spinous process at the base of the neck. A key landmark for centering PA chest projections.
• Jugular Notch (Manubrial Notch): The deep notch at the superior aspect of the sternum. Used for centering AP chest projections.
• Xiphoid Process: The inferior tip of the sternum. Not a reliable landmark for positioning as its position varies greatly.

Technical Factors for Chest Radiography

• Kilovoltage (kVp): A high kVp (110-125 kV) is used. This produces low-contrast, long-scale images, allowing visualization of the fine lung markings through the heart and other mediastinal structures.
• Source-to-Image Receptor Distance (SID): A minimum SID of **72 inches (183 cm)** is required. This long distance minimizes magnification of the heart and increases recorded detail (spatial resolution).
• Patient Position: Erect position is preferred whenever possible. This allows the diaphragm to move to its lowest position, prevents engorgement of the great vessels, and allows for the visualization of air-fluid levels.
• Grids: Generally used for chest radiography due to the high kVp, which produces significant scatter.

Routine and Special Projections

PA Chest

• Why PA?: The Posteroanterior projection is the gold standard. Placing the anterior chest (heart) closer to the image receptor significantly reduces heart magnification compared to an AP projection.
• Positioning: Patient is erect, facing the IR. Shoulders are rolled forward and depressed to move the scapulae out of the lung fields. CR is perpendicular to the IR, centered to the midsagittal plane at the level of T7 (vertebra prominens).
• Evaluation Criteria: Entire lungs included (apices to costophrenic angles), no rotation (evidenced by symmetric sternoclavicular joints), scapulae outside the lung fields, full inspiration (10 posterior ribs visible), and sufficient penetration to see thoracic vertebrae through the heart shadow.

Lateral Chest

• Positioning: Patient is erect, turned 90 degrees from PA, with the side of interest against the IR (typically a left lateral is performed unless pathology is suspected on the right). Arms are raised above the head. CR is perpendicular, centered to the mid-thorax at the level of T7.
• Evaluation Criteria: Superimposition of the posterior ribs, arm soft tissues not obscuring the apices, and an open thoracic intervertebral joint spaces.

AP Chest (Supine or Semi-Erect)

• Use: For patients who are too ill or injured to stand. Often performed portably.
• Limitations: Causes significant heart magnification, and air-fluid levels are not well-defined.
• Positioning: CR is angled caudad to be perpendicular to the long axis of the sternum to prevent clavicles from obscuring the apices. Centering is to the level of T7 (3-4 inches below the jugular notch).

AP Lordotic Chest

• Purpose: To visualize the pulmonary apices without superimposition of the clavicles, often to rule out tumors or tuberculosis.
• Positioning: Patient stands about 1 foot away from the IR and leans back. Alternatively, the patient can be erect and the CR angled 15-20 degrees cephalad.

Decubitus Positions

• Purpose: To demonstrate air-fluid levels (pleural effusions) or free air (pneumothorax). The patient must be on their side for at least 5 minutes before exposure to allow fluid/air to settle. The CR is always horizontal.
• Lateral Decubitus (AP or PA): Patient lies on their right or left side. Used to see air-fluid levels. A right lateral decubitus shows fluid in the right pleural space and air in the left.
• Dorsal/Ventral Decubitus: Patient lies supine (dorsal) or prone (ventral) and the CR is directed horizontally. Less common but can demonstrate fluid levels in specific locations.