Introduction to Chest X-rays

Administrative and Grading Information

• Grading Timeline: The instructor has been teaching across various departments (including anatomy for master's students at Allied Health) but plans to grade over the upcoming weekend and into the next week to provide students with an accurate view of their standing.
• Grade Calculations Tool: A "Grade Calculations" worksheet (an Excel file) is available for students to perform "what-if" scenarios.
  • Students can input current grades (e.g., a $65\%$ on the first test and a $60\%$ on the second) to determine the scores required on remaining exams to reach a target (e.g., an $80\%$ average).
  • Assumes a $100\%$ score in attendance and homework completion for students who attend and turn in assignments.
  • The standard Canvas grade display may be intentionally disabled to encourage students to use the provided Excel breakdown for a more accurate understanding of the grade book's weighted setup.

Introduction to Chest X-ray (CXR)

• Educational Context: Chest X-rays will be a recurring topic throughout the semester, including during Respiratory Care Fundamentals (RCF), clinical rotations, and critical care rotations. Each semester adds a layer of complexity to the knowledge.
• Examination Details: The upcoming exam will include approximately $4$ to $6$ questions regarding chest X-ray basics.
• Clinical Role of the Respiratory Therapist (RT):
  • RTs must be proficient in accessing and interpreting chest images because they specialize in cardiopulmonary science (heart and lungs).
  • X-rays are considered a quick and easy diagnostic tool for internal visualization.
  • RTs can suggest X-rays based on patient assessment (e.g., heavy breathing or abnormal breath sounds). While physicians order them, RTs and nurses facilitate the process.
  • Orders for intubated or mechanically ventilated patients are often placed on a $PRN$ (as needed) basis.
• The Learning Process:
  • CXR interpretation is difficult and often compared to learning physics or Latin.
  • Historically, students used "programmatic texts" (fill-in-the-blank paragraphs with images and side-bar answers), but modern proficiency requires consistent practice.
  • The best method for mastery is viewing images daily in a clinical setting, reading the radiologist's official report, and comparing one's own findings with the radiologist's conclusions to identify missed details.

Technical Fundamentals of Radiology

• Terminology: "CXR" is the standard abbreviation. It is also referred to as a "chest radiograph" or "chest roentgenology."
• Mechanism of Action: An X-ray beam is shot through the lungs to expose a film cassette placed behind the patient.
• Image Dimension: A chest X-ray creates a two-dimensional ($2D$) image of a three-dimensional ($3D$) structure, which causes certain anatomical features to overlap or flatten.
• Evolution of Technology:
  • Previously, X-rays were captured on physical film (similar to camera film) that required manual processing.
  • Modern systems are digital, using electronic cassettes and the PACS system (Radiology database).
  • Digital images are clearer and allow for tools like zooming, marking, measuring, and adjusting brightness/contrast.
  • Portable bedside machines provide near-instant results for immediate evaluation of image quality.
• Security and Access:
  • Access to images in the hospital is typically restricted to healthcare team members (RTs, physicians, and sometimes nurses).
  • Remote access from home is restricted to prevent HIPAA violations.
  • Radiologists often work from home offices with high-definition, television-sized monitors to provide quick interpretations.

Physics of Density and Absorption

• Core Principle: X-rays penetrate structures at different degrees based on their relative density.
• Absorption vs. Penetration:
  • High Density: Structures absorb more X-ray beams. Fewer beams reach the cassette. This produces a white or light gray appearance. Termed Radio-opaque.
  • Low Density: Structures absorb fewer beams. More beams reach the cassette. This produces a dark or black appearance. Termed Radiolucent.
• Radiographic Densities (Ordered from Most Dense to Least Dense):
  1. Metal (Most Dense/Brightest White):
     • Includes pacemakers, wires, staples, prosthetics (hip/knee replacements), and surgical gauzes (which contain radio-opaque lines for safety).
     • Indwelling lines and tubes (like $ET$ tubes) have a radio-opaque line so their placement can be tracked.
  2. Bone (White to Light Gray):
     • Includes ribs, clavicles, and scapula.
     • Areas where bones overlap appear brighter white due to increased absorption.
  3. Fluid/Tissue (Grayish):
     • Includes muscles (such as the diaphragm), the heart, great vessels, blood-filled organs, skin, and fat.
  4. Air (Least Dense/Blackest):
     • Includes the lungs (alveoli), the gastric bubble (stomach air), and colon gas.
     • Normal lungs appear dark gray/black due to air, but should still show the "vasculature" (vessel markings). Pure black areas (no tissue markings) are abnormal.

Common Radiographic Views

• PA (Posterior-to-Anterior) View:

  • The preferred standard view for ambulatory patients.
  • Process: The beam hits the patient's back first and travels to the front. The cassette is placed against the anterior chest.
  • Technique: The patient stands, usually "hugging" the machine or placing hands on hips and rotating shoulders forward to move the scapula (shoulder blades) out of the lung field.
  • Distance: The X-ray is shot from exactly $6\,\text{feet}$ away.
  • Benefit: Provides sharp images of the heart and great vessels because the heart is closest to the film.

• AP (Anterior-to-Posterior) View:

  • Standard for portable chest X-rays at the bedside.
  • Process: The beam hits the anterior chest and travels to the back. The cassette is placed behind the patient.
  • Distance: Shot from approximately $3\,\text{feet}$ away.
  • Limitations: Image quality is less sharp because beams scatter more while traveling through anterior structures to reach the posterior cassette.
  • Diagnostic Caveat: The heart often appears larger on an AP film (shadowing/scattering effect). This is not the gold standard for measuring heart size; an echo is preferred for heart failure diagnosis.

• Lateral View:

  • Taken as an adjunct to the PA view (side view).
  • Technique: Patient stands on the side with arms raised above the head to move the humerus out of the image.
  • Preferred Side: Left lateral is preferred because the heart sits toward the left; placing the left side against the cassette minimizes scattering.
  • Benefit: Delineates if a lesion or abnormality is located in the anterior, middle, or posterior part of the chest.

• Lateral Decubitus View:

  • The patient lies on their side with the cassette against the chest and the beam shot $PA$.
  • Naming Convention: Named by the side that is "down" (e.g., lying on the left side is a left lateral decubitus).
  • Use Cases:
    • Pleural Effusion (Fluid): Place the affected side down. Fluid layers out at the bottom of the lung.
    • Pneumothorax (Air): Place the affected side up. Air rises to the top of the pleural space.

Specialized and Uncommon Views

• Apical Lordotic View:
  • The beam is angled upward while the patient stands straight or leans back.
  • Used to visualize the apices (top) of the lungs, which are often obscured by the clavicles and first ribs.
• Anterior Oblique View ($RAO$ or $LAO$):
  • Patient is angled at $45^\circ$ to the cassette.
  • Used to separate the structures in the mediastinum (heart, descending aorta, esophagus, and spine).
• Expiratory Film:
  • Standard X-rays are "Inspiratory" (breathe in and hold).
  • Expiratory films are used to help detect small pneumothoraces. By breathing out, lung tissue becomes more dense (grayer), making the trapped air (black) easier to see.

Anatomical Markers on CXR

• Diaphragm: The right side is typically $2-3\,\text{cm}$ higher than the left because the liver sits beneath it.
• Gastric Bubble: A small pocket of air at the top of the stomach, sometimes jokingly called a "UBF" (unborn fart).
• Trachea: Should be visible and midline.
• Lungs: Upper, middle, and lower lobes are visible. The horizontal fissure separates the right upper and middle lobes (though it is often only visible if it contains fluid or is perfectly perpendicular to the beam).
• Heart: Cardiac borders should be well-defined. In a good quality film, the vertebral discs (spine) should be visible behind the heart shadow.
• Quality Check:
  • Overexposed: The image is too dark.
  • Underexposed: The image is too light/opaque; vertebral discs cannot be seen behind the heart.

Questions & Discussion

• Student Question: Can we access patient charting software in clinicals?
  • Response: Student access varies by hospital. Some give restricted access to see images/info (not for charting), others require students to log in with a preceptor. RTs almost always have image access, while some nurses may not.
• Student Question: Who relays info if the radiologist is at home?
  • Response: The Electronic Health Record (EHR) flags the results. Critical findings require a direct call or text to the physician/nurse under hospital policy.
• Student Question: What if the radiologist misses something?
  • Response: Physicians can message radiologists to request a re-read if they suspect a specific finding (like a hairline rib fracture) was overlooked. Artificial Intelligence (AI) is increasingly used because it can detect subtle gray-scale changes better than humans, though a human check is still required.