Unit 5: Medical Imaging Techniques

Medical imaging provides visual representations of the interior of the body for diagnostic and therapeutic purposes.

1. X-Ray

• Basic Principle: X-rays are a form of high-energy ionizing radiation. An X-ray machine sends beams of radiation through the body. These beams are absorbed differently by different tissues.
  • Dense Tissues (like bone): Absorb most of the X-rays and appear bright white.
  • Soft Tissues (like organs, muscle): Absorb less and appear in shades of grey.
  • Air (like in lungs): Absorbs almost no X-rays and appears black.
  The resulting "shadows" are captured on a detector or film to create a 2D image.
• Applications:
  • Bones & Joints: Detecting broken bones (fractures) and dislocated joints.
  • Chest: Diagnosing lung infections (like pneumonia or tuberculosis) and checking for an enlarged heart.
  • Abdomen: Detecting kidney stones or swallowed foreign objects.
  • Dentistry: Finding cavities.

2. CT Scan (Computed Tomography)

• Basic Principle: A CT scan is essentially a sophisticated, 3D X-ray. The X-ray source rotates around the patient's body, taking many cross-sectional X-ray images (or "slices") from different angles. A computer then processes all these slices and assembles them into a detailed 3D image, eliminating the superimposition of organs seen in a plain X-ray.
• Types: Can be done with or without "contrast dye" (iodine-based), which is injected to make blood vessels, tumors, and organs stand out more clearly.
• Applications:
  • Trauma: The fastest and best method for diagnosing internal injuries in emergency situations (e.g., organ injury, internal bleeding).
  • Oncology (Cancer): Used to detect and stage tumors, guide biopsies, and monitor treatment response.
  • Neurology: Detecting brain tumors, blood clots, or bleeding after a stroke.
  • Vascular: Visualizing complex bone fractures.

3. MRI (Magnetic Resonance Imaging)

• Basic Principle: MRI uses NO ionizing radiation. Instead, it uses a powerful magnetic field and radio waves.
  1. The strong magnet forces the protons (mostly in the body's water molecules) to align with the field.
  2. A radio wave pulse is then applied, "knocking" the protons out of alignment.
  3. When the pulse is turned off, the protons "relax" back into alignment, releasing a small energy signal.
  4. Sensors detect these signals, which vary depending on the tissue type (e.g., water in fat relaxes at a different speed than water in muscle). A computer uses this information to build a highly detailed 3D image.
• Applications:
  • Excellent for Soft Tissues: MRI provides much better detail of soft tissues than a CT scan.
  • Neurology: The best tool for imaging the brain and spinal cord (e.g., detecting tumors, multiple sclerosis plaques).
  • Musculoskeletal: Ideal for joint injuries, such as imaging ligaments (e.g., ACL tear in the knee) and tendons (e.g., shoulder injuries).
• CT vs. MRI: Use CT for speed, bones, and emergencies (trauma, stroke). Use MRI for high-detail soft tissue (brains, spines, joints, ligaments).

4. Sonography (Ultrasound)

• Basic Principle: Sonography uses high-frequency sound waves (not radiation).
  1. A handheld probe called a transducer emits sound waves into the body.
  2. These waves travel through the tissue and "echo" (reflect) back when they hit a boundary between different tissue types (e.g., fluid and soft tissue, or soft tissue and bone).
  3. The same transducer detects these returning echoes.
  4. A computer measures the time and strength of the echoes to create a real-time, 2D image (a sonogram).
• Applications:
  • Obstetrics: The most common use is monitoring the growth and development of a foetus during pregnancy.
  • Abdominal Organs: Excellent for imaging solid organs like the liver, kidneys, and spleen, and fluid-filled structures like the gallbladder (for gallstones).
  • Cardiology (Echocardiogram): Used to see the heart beating in real-time and assess valve function.
  • Vascular (Doppler Ultrasound): A special type that can measure the speed and direction of blood flow, used to detect blockages in arteries (like the carotid) or veins (DVT).
  • Guided Procedures: Used to guide needles during biopsies.

Practical Component: Rh Factor Determination

Principle: To determine the presence or absence of the Rh antigen (also called D antigen) on the surface of red blood cells. This is a critical part of blood typing for transfusions and pregnancy.

The test relies on the principle of agglutination. If the Rh antigen is present on the RBCs (Rh-positive), they will clump together when mixed with Anti-D serum.

Slide Test Procedure (Practical):

1. Materials: Clean glass slide, lancet, alcohol swab, mixing sticks (toothpicks), and Anti-D serum.
2. Prepare: Clean the ring finger with an alcohol swab and let it dry. Prick the finger with a sterile lancet.
3. Place Drops: Place one drop of blood onto a clean glass slide. (Often, this is done alongside ABO typing, so 3 drops are placed in total).
4. Add Antiserum: Add one drop of Anti-D serum to the drop of blood.
5. Mix: Using a clean, separate mixing stick, mix the blood and antiserum over an area of about 1 inch.
6. Observe: Gently rock the slide for 1-2 minutes and observe for agglutination (clumping).

Interpretation of Results:

• Agglutination (Clumping) Present: The blood is Rh-Positive (+).
• No Agglutination (Remains Smooth): The blood is Rh-Negative (-).