Blood Edge Trivia: Understanding MRI Brain Hemorrhage Imaging

Jul 16, 2024

Blood Edge Trivia: Understanding MRI Brain Hemorrhage Imaging

Introduction

  • Blood edge trivia is often perceived as confusing and intimidating.
  • Important to understand it to avoid being tricked on multiple-choice questions.
  • Often shown with brain MRI because aging blood in the brain doesn’t follow the same rules as elsewhere in the body.
  • Focus on two sequences: T1 and T2.

Common Question Terminology

  • Hyperacute, acute, subacute, late subacute, chronic.
  • Can be framed using specific time frames in hours or days, or by changes in red blood cells (e.g., oxyhemoglobin vs. deoxyhemoglobin).
  • Knowledge areas:
    • Color changes of blood stages.
    • Terminology (hyperacute, subacute, etc.).
    • Correlation of stages with hours/days.
    • Changes in red blood cell physiology.
    • Basic physics concepts.

Key Physics Concepts

Susceptibility

  • Measure of how a substance becomes magnetized in an external magnetic field.
    • Diamagnetism: opposes the magnetic field (e.g., water, fat, calcium).
    • Paramagnetism, superparamagnetism, ferrimagnetism: aligns with the field (affects MRI signal).

T2 and T2 Star Effect

  • T2 decay: signal loss due to dephasing of spins over time.
  • T2 star effect: enhanced signal loss due to both tissue spin interactions and field inhomogeneity.
  • Homogeneous tissues retain signal longer (T2 bright), heterogeneous lose signal faster (T2 dark).

T1 Recovery

  • T1 recovery: process of protons in high-energy state returning to low-energy state (gives off heat).
  • Efficient heat transfer = short T1 time (T1 bright), inefficient transfer = long T1 time (T1 dark).
  • Biological tissues' ability to transfer heat affects how they appear on T1-weighted images.

Physiological Changes in Blood

  • Blood consists of plasma (liquid) and cellular components (mainly red blood cells).
  • Hemoglobin in red blood cells carries oxygen, undergoes changes over time:
    • Oxygenated hemoglobin (weakly diamagnetic)
    • Deoxygenated hemoglobin (paramagnetic)
    • Methemoglobin (strongly paramagnetic)
    • Breakdown into fragments (Feridun, hemosiderin – superparamagnetic)

Stages of Hemorrhage on MRI

  1. Hyperacute (first few hours): Oxygenated hemoglobin; T2 bright, T1 slightly dark or isointense.
  2. Acute (within a day): Deoxygenated hemoglobin; T2 dark due to T2 star effect, T1 remains the same.
  3. Early/Subacute (first week): Intracellular methemoglobin; T2 dark, T1 bright due to interaction with water.
  4. Late/Subacute (late first week): Extracellular methemoglobin; T2 brightening again, T1 remains bright.
  5. Chronic (weeks/months): Hemosiderin and Feridun accumulation; T2 star effect revives, T1 dark.

Application on Questions

  • Identifying T1 and T2 on MRI helps determine the stage of hemorrhage.
  • Example Question: Bright on T1, dark on T2 indicates subacute phase due to methemoglobin.

Diagrams and Charts

  • Use visual aids to remember stages (coiled diagram in notes).
  • Memorize key timelines and correlate them with changes.

Conclusion

  • Revisiting and practicing these concepts essential to grasp the aging blood trivia in brain MRI.
  • Avoid mnemonic devices; focus on understanding the changes and their effects on MRI signals.