7: Radiology

Basic Concepts

  • X-rays

    • Defined as a form of short wavelength, high-frequency ionizing radiation capable of penetrating matter at the molecular level.
    • Uses:
    • Provide images of internal structures.
    • Can damage cellular components (RNA, DNA).
    • Creation of reactive oxidative species.
    • Potential predisposition to cancer upon exposure.
    • Maximum exposure limits:
    • Yearly maximum radiation exposure for adults: 5 rem.
    • Yearly maximum exposure for a fetus of a pregnant worker: 0.5 rem per year or 0.05 rem/month.

  • Sensitivity to Radiation

    • Human tissues vary in sensitivity to radiation:
    • Very High Sensitivity:
      • Bone marrow.
      • Intestinal epithelium.
      • Reproductive cells.
    • High Sensitivity:
      • Optic lens.
      • Thyroid epithelium.
      • Mucus membranes.

  • Exposure Risks and Safety Precautions

    • Any anesthetizing location requiring X-rays or fluoroscopic guidance poses exposure risks to scatter radiation.
    • Safety precautions include:
    • Maintain a distance of at least 6 feet from the X-ray source.
    • Use lead shielding (apron, thyroid shield, goggles).

  • Occupational Exposure Measurement

    • Units of measurement for electromagnetic radiation include:
    • Curie
    • Rad
    • Rem (effective dose).
    • Roentgen (total dose administered).

Our Analysis for the NCE and SEE

  • Educational Gap
    • Many students receive little to no radiology instruction in their curriculum; the goal is to cover essentials in a clinically relevant manner.
    • Anticipation of 1-2 radiology questions on the NCE, focusing on:
    • Image interpretation (e.g., CIED, ETT, CVL).
    • Patient safety aspects (e.g., exposure limits, risk minimization).
    • Structure of the tutorial:
    • Basics of radiology and radiation safety.
    • Step-wise approach to reading chest X-rays (CXR).
    • CXR interpretation concerning devices and pathophysiology.

Basic Science

  • Types of Electromagnetic Waves

    • Electromagnetic spectrum includes:
    • Gamma Rays
    • X-rays
    • Ultraviolet
    • Visible Light
    • Infrared Waves
    • Radio Waves
    • Microwaves
    • Short wavelength indicates:
    • Higher frequency.
    • Higher energy.
    • X-rays and gamma rays are classified as high-energy electromagnetic radiation (ionizing radiation).

  • Production of Radiographs

    • X-rays penetrate structures producing images on photographic film/digitally.
    • Effective barriers against X-rays and gamma rays:
    • Only lead or concrete.

  • Units of Radiation

    • Roentgen (R): Total radiation dose administered.
    • Radiation Absorbed Dose (Rad): Total dose received at the tissue level.
    • Radiation Equivalent Man (Rem): Effective dose.
    • Yearly maximum limits are 5 rem for adults and 0.5 rem for fetuses (0.05 rem/month).
    • Dosimeter Badge: Measures Rad and Rem.

Clinical Application

  • X-ray Beam Features

    • Determined by:
    1. Patient's body weight and habitus.
    2. Density of the body part examined.
    3. Orientation of the X-ray beam relative to the patient.
    • Increased EMR scatter occurs with a stronger beam, increasing radiation exposure risk for bystanders.

  • Human Tissue Sensitivity

    • Varies significantly:
    • Very High Sensitivity:
      • Bone marrow.
      • Intestinal epithelium.
      • Reproductive cells.
      • Fetal tissue.
    • High Sensitivity:
      • Optic lens.
      • Glial cells.
      • Thyroid epithelium.
    • Medium Sensitivity:
      • Liver.
      • Mature RBCs, cartilage, pancreas.
    • Low Sensitivity:
      • Mature bone, lung tissues.

  • Examples of Exposure

    • Intraoperative procedures:
    • Intraoperative cholangiograms.
    • Retrograde pyelograms.
    • Open- and closed-fracture reductions.
    • Endovascular aneurysm repairs.
    • Pain management procedures.
    • Off-site anesthetizing locations include:
    • CT scans.
    • Cath labs.
    • Interventional radiology.
    • ERCP labs.

Radiation Protection Strategies

  • Limiting Radiation Exposure
    • Three strategies:
    1. Distance: Minimum safe distance from radiation source is 6 feet; six feet of air has equivalent protection to 9 inches of concrete or 2.5 mm of lead.
    2. Duration: Minimizing the time spent near the radiation source reduces exposure.
    3. Shielding: Measures to protect against radiation vary (e.g., protective gear made of lead).
  • Inverse Square Law
    • States exposure is inversely proportional to the square of the distance from the source:
    • ext{Intensity} = rac{1}{ ext{Distance}^2}
    • Quantifying exposure:
    • extIntensity<em>1=extDistance</em>22,extIntensity<em>2=extDistance</em>12ext{Intensity}<em>1 = ext{Distance}</em>2^2, ext{Intensity}<em>2 = ext{Distance}</em>1^2

Systematic Approach to Reading Chest X-Rays

  • Mnemonic for CXR Review: ABCDEFGHI

    1. A: Assess film quality and airway.
    2. B: Bones and soft tissue.
    3. C: Cardiac.
    4. D: Diaphragm.
    5. E: Effusion.
    6. F: Fields, fissures, and foreign bodies.
    7. G: Great vessels and gastric bubble.
    8. H: Hila and mediastinum.
    9. I: Impression.

  • Normal Features of a Chest X-ray:

    • Select features include:
    • Domed diaphragm.
    • Heart borders < 60% of chest width.
    • Crisp costophrenic angles.
    • Balanced hilum heights.

Four Roentgen Densities

  • X-ray Passage:

    • X-rays pass more easily through lower density structures and less easily through higher density structures.
    • Densities from least to most dense:
    1. Gas (air).
    2. Fat.
    3. Water (soft tissue).
    4. Bone (metal).

  • CXR Structure Identification:

    • Identify structures:
    • Clavicles.
    • Posterior ribs.
    • Trachea at T3-T4.
    • Bronchi and heart shadows.
    • Costophrenic angles.
    • Gastric bubble under the diaphragm.

Systematic Evaluation: The ABCDEFGHI Approach

  • Comprehensive Evaluation

    • A systematic approach assists in evaluating significant pathology on a CXR, acknowledging its 2-D representation of a 3-D structure.

  • First Step: Quality assessment integrates:

    • Position: Best image quality achieved in an upright patient position, with common views such as:
      • Posterior-anterior (PA): X-rays from back to front.
      • Anterior-posterior (AP): X-rays from front to back, good for immobile patients.
      • Lateral projection: Side-to-side X-ray passage.
    • Inspiration: Adequate inspiration indicated by right hemidiaphragm at the 9th/10th rib.
    • Exposure: Proper exposure integrates visibility of the 4 basic densities.
    • Rotation: Patient shouldn't be rotated upon exposure for accurate symmetry (clavicles aligned with vertebrae).

  • Airway Assessment:

    • Consider trachea, carina, and mainstem bronchi; ideal position of endotracheal tube (ETT) noted at the correct depth.

Evaluation of Structures: Bones & Soft Tissues

  • Bone Assessment: Check for symmetry and fractures through the ribcage.
  • Soft Tissue Analysis: Focus on neck, shoulders, axilla, and abdomen for:
    • Foreign bodies.
    • Swelling or subcutaneous air which may indicate barotrauma.
    • Significant finding regarding subcutaneous emphysema could be caused by lengthy laparoscopic operations.

Evaluation of Cardiac Structures

  • Cardiac Borders Assessment:
    • Key to determining heart size through the cardiothoracic ratio, calculated as the width of the heart compared to the thorax's width.
    • Normal Ratios:
    • PA view: Heart width < 50% thorax width.
    • AP view: Heart width < 60% thorax width, but less accurate.
  • Normal Orientations of Cardiac Chambers:
    • Right atrium forms the heart's right convex border.
    • Check for prosthetic valves, assessing their integrity and positioning.

Evaluation of the Diaphragm

  • Diaphragm Position: Note the usual height difference of the right (higher due to liver) compared to the left.
  • Shape Evaluation:
    • Flat or depressed hemidiaphragm indicates potential tension pneumothorax.
    • Bilateral flattening relates to Chronic Obstructive Pulmonary Disease (COPD).
  • Free air detection: Most common causes of free air include hollow viscus perforation leading to significant diagnostic findings.

Evaluation of Pleural Effusions

  • Costophrenic Angles: Blunted angles may indicate pleural effusions; this is where chest wall meets diaphragm.
  • Fluid Positioning: Pleural fluid follows gravity, creating a U shaped meniscus along edges observed better in lateral views.
  • Differentiating from Atelectasis: Look for air bronchograms to confirm atelectasis, missing them may lead to mistaken pleural effusion diagnosis.

Evaluation of Lung Fields, Fissures & Foreign Bodies

  • Lung Field Examination: Look for:

    • Infiltrates or masses.
    • Consolidation and vascular markings.

  • Vascular Branching: Vessels should taper toward periphery.

  • Interstitial Edema: Indications include the peribronchial cuffing and lines described as Kerley A and B lines.

  • Fissures Assessment:

    • Normal anatomical variations include:
    • Major fissures (right oblique, left separating upper and lower lobes).
    • Minor fissures (right lung only).
    • Recognizing their alterations indicates localized lung issues, like pneumonia or atelectasis.

  • Foreign Bodies: Check for intrathoracic equipment placement (e.g., NGT, ETT).

Evaluation of Great Vessels & Gastric Bubble

  • Pulmonary Vessel Review: Observe size and shape of the aorta and pulmonary vessels, including the aortic knob.
  • Signs of Aortic issues: Widening of aortic knob can indicate conditions like dissections or valvular insufficiency.
  • Gastric Bubble Appearance: Gas causing a radiolucent region beneath the left hemidiaphragm is a regular finding.

Evaluation of Hila & Mediastinum

  • Hilum Analysis: Observe pulmonary vessels and major bronchi noting that the left hilum is typically higher than the right.

  • Mediastinal Width Assessment: Checks for widening indicating potential dissection; also watch for tracheal deviation due to mass effects.

  • Etiological Note:

    • Volume loss results in shifts towards affected areas; increased volume shifts away.
    • Mediastinal air: could signify pneumopericardium due to laceration.

Final Impression

  • Conclude with your overall assessment, considering clinical implications of any abnormalities noted.

Appliances Overview

  • Endotracheal Tubes Assessment: An ETT should be positioned 2-5 cm above the carina, typically located at T4-T5 interspace.
  • Central Venous Line Positioning: Ideal tip should lie in the distal 1/3 of the SVC near junction with right atrium; mispositioning can result in thrombosis or perforation.
  • Pulmonary Artery Catheter (PAC) Guidance: Should track from SVC to RA to RV to the pulmonary artery, with ideal placement in West's zone 3.
  • Cardiac Implanted Electronic Devices (CIED) Evaluation: Look for lead integrity and placement. Utilize two views (PA and lateral) for comprehensive diagnostics.
  • Significance in Chest Films: Unlike other situations, post-intubation and line placement checks are not always mandatory if performed in anesthesia.

Evaluation of Chest X-ray for Conditions

  1. Atelectasis:
    • Manifests as opacities indicating poor lung expansion, often associated with underlying conditions like aspiration.
  2. Pneumothorax Types:
    • Recognize signs for both simple and tension pneumothoraces by symptoms like collapsed lung appearance and mediastinal shifts.
  3. Pulmonary Edema Staging:
    • Cardiac-induced edema resulting from LV failure will show stages progressing through hilar haziness to complete consolidation.
  4. ARDS:
    • Defined by patterns of alveolar infiltrates on CXR correlating to severity of the condition over time.
  5. Fracture Consequences:
    • Traumatic rib fractures can lead to lung contusions and other associated risks involving lung expansion and integrity.
  • First Radiographic Sign of Pulmonary Edema:
    • Identify cephalization or Kerley B lines.