Imaging Modalities Lecture Notes

Radiographic Anatomy

  • Radiology questions will be included in the anatomy exam, specifically exam one.
  • Upper extremities imaging will be covered in the written portion of exam one.

Benefits of Radiographic Anatomy

  • Different Perspective: Provides an alternative viewpoint for anatomical structures.
  • Abnormality Detection: Facilitates the identification of abnormal conditions.
  • Diagnostic Aid: Imaging techniques like X-rays, CT scans, ultrasounds, and MRIs are crucial for diagnosis.
  • Learning Facilitation: Integrates with books, lectures, cadaver labs, and topographical anatomy to enhance understanding.

Course Objectives

  • Modality Comparison: Compare and contrast radiographs, ultrasound, fluoroscopy, CT scans, and MRI.
  • Projectional vs. Sectional Imaging: Discuss the differences between projectional radiography and sectional imaging.
  • Anatomical Planes: Identify axial, coronal, and sagittal planes.
  • Modality Indications: Understand the indications for different imaging modalities.
  • Clinical Image Recognition: Distinguish clinical images produced by various diagnostic imaging modalities.
  • Advantages and Disadvantages: Know the advantages and disadvantages of each modality.

Importance of Imaging in Diagnosis

  • Facilitating Diagnosis: Imaging helps confirm or clarify suspected diagnoses.
  • Comprehensive Patient Care: Consider the patient as a whole, not just the test results.
  • Integrating Information: Combine imaging findings with clinical symptoms and other diagnostic data.

Overview of Imaging Modalities

  • Modalities Covered: X-ray, fluoroscopy, CT, MRI, ultrasound.
  • Key Aspects: How each modality works, typical uses, advantages, and disadvantages.
  • Image Recognition: Ability to differentiate between images from different modalities.

X-Rays

  • Projection Imaging: X-rays provide a two-dimensional image.

  • Electromagnetic Radiation: Uses high-energy electromagnetic radiation similar to light.

  • Ionizing Radiation: X-rays are a form of ionizing radiation, which can be harmful.

    • Ionizing radiation can remove electrons from atoms, potentially damaging DNA and causing mutations.

  • Millisieverts (mSv): Unit used to measure radiation exposure.

  • Image Production: Photons pass through the body and are detected on a plate; denser materials block more photons.

    • The amount of radiation exposure varies, but is significantly lower than early X-ray techniques.

  • Radiation Exposure: Background radiation is approximately 3 mSv3 \text{ mSv} per year.

    • Chest X-ray: 0.1 mSv0.1 \text{ mSv} (10 days of ambient radiation).
    • Extremity X-ray: 0.001 mSv0.001 \text{ mSv} (3 hours of ambient radiation).

  • Image Interpretation: The degree of energy that passes through tissues determines the image's appearance.

    • Air: Appears black due to minimal obstruction.
    • Fat and Water: Appear gray.
    • Bone and Metal: Appear white due to higher absorption.

Examples of X-Ray Interpretation

  • Lumbar Spine: Look for vertebrae and spaces between them.

    • Absence of space may indicate bone-on-bone contact due to cartilage or disc destruction.
    • Bowel gas appears as black areas.
    • Soft tissue and edema can also be observed.

  • Hand X-Ray: Observe bone contours for disruptions indicating fractures.

    • Sesamoid bones are normal findings often found in areas of friction such as the thumb or big toe; the largest sesamoid is the patella.

  • Image Orientation: Always check the right/left indicator to ensure correct orientation.

  • Knee X-Ray: Follow contours, look for smooth lines and appropriate spacing, and identify the patella shadow.

  • Scapula X-Ray: Check alignment of the AC joint; look for gaps indicating separation.

  • Elbow Dislocation: Get an X-ray before attempting manipulation to avoid further injury.

  • Large Intestine: Identify the ascending, transverse, and descending colon.

  • Small Bowel Obstruction: Look for curly cues and valvulae conniventes; gas overlap appears darker.

  • Chest X-Ray: Assess lung fields, heart silhouette, and look for abnormalities.

    • Patchy or cloudy areas may indicate fluid buildup (effusion) or pneumonia.
    • Compare left and right sides for symmetry.

Technical Aspects of X-Rays

  • Two-Dimensional Image: A limitation of X-rays; requires multiple views for comprehensive assessment.

  • Digital X-Rays: Most offices now use digital X-ray machines.

    • Digital X-rays reduce radiation exposure, allow zooming, measuring, and contrast adjustment.

Chest X-Ray Views

  • AP (Anterior-Posterior) View: X-ray beam passes from front to back.

    • Heart appears magnified because it is further from the plate.
    • Often used for patients who are not mobile (portable view).

  • PA (Posterior-Anterior) View: X-ray beam passes from back to front.

    • Heart appears clearer and less magnified because it is closer to the plate.
    • Preferred view for accurate assessment of heart and lung conditions.

  • Lateral View: Provides a side view of the chest, useful for detecting subtle abnormalities.

Reading a Chest X-Ray

  • Systematic Approach: Develop a consistent method to avoid missing critical details.
  • Key Structures: Identify heart outline, diaphragm, ribs, trachea, and bronchi.
  • Rib Identification: Use imagination to follow the curves of the ribs, recognizing their overlapping arrangement.
  • Costophrenic Angles: Sharp angles are normal; cupping shapes may indicate fluid buildup.
  • Tube View: May reveal subtleties not visible on PA view.

Clinical Uses of X-Rays

  • Trauma: Assessing bone abnormalities and fractures.
  • Chest X-Rays: Diagnosing pneumonia and other pulmonary infections.
  • Abdominal X-Rays: Identifying bowel obstructions.
  • KUB (Kidney, Ureter, Bladder): Detecting kidney stones.
  • Warm Bodies: Assessing retained foreign objects (e.g. bullet fragments)

Fluoroscopy

  • Live X-Ray: Provides real-time video imaging.
  • Radiopaque Substances: Uses dye to visualize structures better.
  • Applications: Barium swallows, GI studies, angiograms.
  • C-Arm: A mobile X-ray machine used for live video imaging.
  • Image Inversion: Fluoroscopy images are often inverted, with dense structures appearing dark.

Clinical Uses of Fluoroscopy

  • Angiograms: Visualizing blood flow and identifying blockages.
  • Fracture Reduction: Guiding manipulation and alignment during fracture repair.

Advantages of X-Rays and Fluoroscopy

  • Quick and Accessible: Widely available and can be performed rapidly.
  • Affordable: Relatively inexpensive compared to other imaging modalities.
  • Informative: Provides significant information about bones and chest conditions.

Disadvantages of X-Rays and Fluoroscopy

  • Radiation Exposure: Higher with fluoroscopy but generally low for individual X-rays.
  • Limited Visualization: Cannot visualize all structures (e.g., soft tissues, MI, pulmonary embolisms).
  • Nonspecific Findings: May yield ambiguous results requiring further investigation.

Sectional Imaging

  • Image Acquisition: Images are acquired in slices to create a three-dimensional representation.
  • Digital Breast Tomosynthesis: Creates a model of breast tissue for detailed viewing following an abnormal screening mammogram.

CT (Computed Tomography) Scans

  • Image Acquisition: A tube emits radiation as it spins around the patient, with detectors collecting data.
  • The CT scans collect images in axial, but the computer can manipulate the data in coronal and sagittal planes.

Anatomical Planes

  • Axial (Transverse): Divides the body into top and bottom.
  • Coronal: Divides the body into front and back.
  • Sagittal: Divides the body into right and left.

Image Orientation in Sectional Imaging

  • Perspective: Images are viewed as if looking at the patient's feet.
  • Side Assignment: The patient's right side is on the left side of the image, and vice versa.

CT Scan Process

  • Axial Cuts: CT scans take thin slices (0.6 to 1.5 mm) in the axial plane.
  • Computer Reconstruction: The computer reconstructs the images into different planes (coronal and sagittal).
  • Density Display: Dense objects appear white, and less dense objects appear dark.

Key Characteristics of CT Scans

  • Bone Appearance: Bones appear very bright white.
  • Metal Artifact: Metal objects can create artifacts on CT scans.
  • Hemorrhage Detection: Excellent for visualizing blood or acute hemorrhage.
  • Windowing: Different windows (bone, soft tissue, lung) can be used to optimize visualization of specific tissues.

Clinical Examples of CT Scans

  • Brain CT: Brain windows display brain structures Gray and white matter, while bone windows enhance skull visualization.

  • Spine CT: Assesses spinal alignment and fractures, using contrast to highlight structures.

  • Kidney Imaging (CT Urogram): Special test using contrast.

    • Three phases: no contrast (check for stones), contrast in kidney (check for masses), and contrast excreted into ureters (check for ureteral abnormalities).

Role of Contrast in CT Scans

  • Enhanced Visualization: Helps visualize blood vessels and potential tumors.
  • Pulmonary Embolism: Blood clots don't absorb contrast, allowing them to be identified.
  • Tumor Margin Definition: Highlights tumor margins for better delineation.

Clinical Indications for CT Scans

  • Complex Fractures: Useful when plain X-rays are insufficient.
  • GI Issues: Diagnosing appendicitis and kidney stones.
  • Suspected Stroke: Assessing brain bleeding, swelling, and clots.

Advantages of CT Scans

  • Quick: Fast image acquisition.
  • Accessible: Commonly available in emergency rooms.
  • Good for Bone and Blood: Excellent visualization of bones and blood.
  • High Sensitivity and Specificity: Reliable diagnostic tool.

Disadvantages of CT Scans

  • High Radiation Exposure: Significantly higher than X-rays.
  • High Cost: Can be expensive, depending on location and services.

MRI (Magnetic Resonance Imaging)

  • Image Production: Uses a strong magnetic field to align protons and detect signals.
  • No Radiation: A significant advantage over CT scans.
  • Image Planes: Can obtain images in any plane (axial, coronal, sagittal).
  • Contrast: Uses gagnolium, but it can be hard on the kidneys