Principles of Medical Imaging Week 6

Hounsfield Units and Biopsies

  • Hounsfield Unit (HU): A measurement based on the density of tissues that helps in identifying tumors when biopsy is unsafe due to comorbidity or other risks.

    • Tumors exhibit specific densities that can be compared using Hounsfield units to assess the likelihood of cancer.

    • Classifications range from "not cancer" to "likely cancer" based on numerical grading systems.

  • Role of Pathologists:

    • Pathologists have the final decision in determining if tissue samples indicate cancer. Ideal practice involves a pathologic assessment before initiating treatment plans.

Exam Preparation

  • Midterm Exam Details:

    • Scheduled for March 5; format discussion is open to students’ preferences regarding the number of questions (100 or 50 questions).

    • Emphasis on past experiences with midterm and exam strategies such as diverse question counts to enhance scores.

  • Study Tips:

    • Utilize study guides and major module content; questions will largely derive from these materials.

    • Expect multiple-choice questions with a mix of matching and other formats.

MRI Technology Overview

  • MRI Principles:

    • History: Based on principles of NMR (nuclear magnetic resonance) developed by early physicists, including Nikola Tesla.

    • Function: MRI detects changes in water density, which is crucial as cancerous tissues often have a different water composition than healthy tissues.

    • Technical Mechanism:

      • Creates strong magnetic fields (1.5 to 3 Tesla often used in practice) that align hydrogen nuclei in the body.

      • Radio frequency pulses disturb alignment, and as they return to baseline, signals create detailed images of internal structures.

  • Functional MRI:

    • Purpose: Assesses tissue function, not just structure, allowing for evaluation of conditions like strokes and tumors-based changes.

    • Importance of Contrast Agents:

      • Helps enhance visibility of structures; however, entails careful consideration regarding safety, especially for patients with potential allergies.

    • Common Contrast Used: Galamine, which adheres to safety measures when administered.

Safety Protocols in MRI

  • Safety Considerations:

    • MRI is non-ionizing radiation and safer than alternatives; yet, screening for metal objects is critical due to risks of projectile incidents in the magnetic field.

    • Screening Protocols:

      • All patients must be screened for metal implants, tattoos (due to potential metal content), piercings, and medication patches.

  • Physical Reactions:

    • Some patients experience side effects such as warmth in areas of injection or feeling anxious/claustrophobic during scans.

    • Awareness of the potential need for sedation or calming techniques for patients is essential.

  • Contrast Safety:

    • Potential side effects of contrast agents include nausea and allergic reactions; therefore, pre-assessment is crucial, particularly for those with kidney issues or prior allergic responses.

Advances in Radiation Therapy using MRI

  • Adaptive Radiation Therapy:

    • Incorporates MRI data for real-time adjustments based on tumor positioning and size to minimize effects on healthy tissues.

    • Advances in imaging allow for further personalized therapy strategies and more effective targeting of treatments.

  • Future Directions:

    • Ongoing developments include MRI-integrated systems for enhanced treatment delivery, vital for the future of cancer therapy.

    • Emphasis on the necessity for radiation therapists to understand the evolving technology related to MRI and its clinical implications.