MRI Imaging: T1 vs T2

Overview

• MRI utilizes two main sequences: T1-weighted (T1) and T2-weighted (T2).
• T1 MRI: Focuses on anatomy, shows fluids as dark, provides crisp images.
• T2 MRI: Highlights pathology, shows fluids as bright, useful for visualizing inflammation, edema, lesions.
• Understanding T1 and T2 is crucial for accurate medical diagnosis.

T1-Weighted Imaging (T1 MRI)

• Emphasizes differences in longitudinal relaxation times (T1) of tissues.
• Contrast determined by protons' return to equilibrium.
• Uses short repetition time (TR: 400-600ms) and short echo time (TE: 10-20ms).
• Image Characteristics:
  • Fat: Bright (hyperintense).
  • Water/Fluids: Dark (hypointense).
  • High fat content structures (e.g., adipose tissue) appear bright.
  • Fluid-filled structures (e.g., brain ventricles, CSF) appear dark.

T2-Weighted Imaging (T2 MRI)

• Emphasizes differences in transverse relaxation times (T2) of tissues.
• Contrast determined by phase coherence loss of protons.
• Uses long TR (3000-6000ms) and long TE (90-110ms).
• Image Characteristics:
  • Fluids: Bright (hyperintense).
  • Fluid-filled areas (e.g., CSF, joints, bladder) appear bright.

Image Appearance by Structure

Brain

• T2 Appearance:
  • Muscle: Intermediate to dark.
  • Fat: Very bright.
  • CSF: Intermediate to bright.
  • White Matter: Darker than gray matter.
  • Gray Matter: Intermediate to bright.
  • Bone: Dark.
• T1 Appearance:
  • Muscle: Intermediate.
  • Fat: Bright.
  • CSF: Dark.
  • White Matter: Intermediate to bright.
  • Gray Matter: Slightly darker than white matter.

Spine

• T2 Appearance:
  • Muscle: Intermediate to dark.
  • CSF: Bright.
  • Bone: Dark.
• T1 Appearance:
  • Muscle: Intermediate.
  • CSF: Dark.
  • Bone Marrow: Bright.

Neck

• T2 Appearance:
  • Muscle: Intermediate to dark.
  • CSF: Bright.
• T1 Appearance:
  • Muscle: Intermediate.
  • CSF: Dark.

Abdomen

• T2 Appearance:
  • Muscle: Intermediate to dark.
  • CSF: Bright.
• T1 Appearance:
  • Muscle: Intermediate.
  • CSF: Dark.

Pelvis

• T2 Appearance:
  • Muscle: Intermediate to dark.
  • Urinary Bladder: Bright (when filled with urine).
• T1 Appearance:
  • Muscle: Intermediate.
  • Urinary Bladder: Dark (when filled with urine).

Knee & Other Joints

• T2 Appearance:
  • Muscle: Intermediate to dark.
  • Synovial Fluid: Bright.
• T1 Appearance:
  • Muscle: Intermediate.
  • Synovial Fluid: Intermediate to dark.

Pathology Appearance

• T1 Pathology:
  • Edema/Inflammation: Low Signal.
  • Cysts: Low Signal.
• T2 Pathology:
  • Edema/Inflammation: High Signal.
  • Cysts: High Signal.
• Pathological processes often involve increased water content, appearing bright on T2W images and dark on T1W images.

References

• Numerous studies and textbooks provide insights into MRI imaging techniques and applications.