Mo - Physics of MRI in cancer (contrast enhancement, DWI) Flashcards
Why is there restricted diffusion in stroke? Explain
Because there’s hypoxia, leading to cell swelling, leading to restricted diffusion.
Why is the ischaemic area bright in DWI?
Because there’s less signal loss
Why is the ischaemic area dark in ADC?
Because there’s less diffusion.
The (smaller/larger) the b, the larger the sensitivity for diffusion.
Larger the b, the larger the sensitivity for diffusion.
ADC is a (technical/tissue) property.
Tissue property.
Why is there a high signal in DWI for tumors?
Because there’s less diffusion because the cells are more compact together than in normal tissue.
Past exam question:
DWI MRI is a tool to diagnose cancer. Is the DW-MRI intensity in tumors increased or decreased, as compared with healthy tissues.
Explain your answer.
Increased. Because tumors have high cellularity, and because there’s a restricted diffusion.
Why is there a higher uptake of gadolinium in the tumor?
Because the vessels are leaking, so the MRI contrast agent (Gd) leaks through the interstitial space through tumor vessel walls due to greater permeability, into extravascular space.
Why is the tumor signal intensity higher due to the gadolinium uptake?
Because Gd shortens the T1 of hydrogen nuclei.
Another exam question:
Imaging in oncology is used for assessment of treatment effects. Name a CT criterion, and another MRI (with contrast agent) criterion for a positive tumor response to therapy. Explain the MRI criterion.
CT: tumor smaller because tumor tissue disappears
MRI with contrast agent: less contrast enhancement
Explanation of the MRI criterion:
Because less blood supply to the tumor, and less leaky vessels.
Tumors have high cellularity, restricted diffusion and thus high MRI signal, low ADC. If tumor responds to therapy: (less/more) diffusion, MRI signal (brighter/darker), ADC (lower/higher)
If tumor responds to therapy: more diffusion, MRI signal darker, ADC higher
