Clinical cancer imaging Flashcards
Why is cancer imaging important? 3 things
- Early diagnosis through screening
- Staging and location of tumors to guide surgeons and to help plan therapies
- Therapeutic response and recurrence when patients are followed longitudinally
what are 4 problems associated with breast cancer screening
Overdiagnosis, false positives, false negatives, radiation dose causes a small number of breast cancers.
What is a barium swallow
Contrast agent
How could a barium swallow show a tumour in the intestines or esophagus
CT scan following a barium swallow, you can observe the barium going down the esophagus and through the intestines. If there are areas where the flow of barium is interrupted, this may suggest the presence of a tumor at that location.
What is seen in a CT scan during the arterial phase after iodine injection.
Soon after injection, the arterial phase shows iodine in the vessels surrounding the tumour. Shows tumour perfusion.
What is seen in a CT scan during the venous phase after iodine injection
The venous phase is after iodine has passed out the blood and through the interstitial spaces before returning back into venous blood. If you image this at the right time, iodine uptake can be seen within the tumour.
How can imaging of vascularisation of a tumour by CT help a patient
Helps in determining prognosis but also if a treatment has been effective. For example if a highly vascularised tumour loses contrast then the drug has had an effect.
What is a complete response (RECIST)
Disappearance of all lesions
What is a partial response (RECIST)
30% decrease in lesions
What is a progressive disease (RECIST)
20% increase in lesions
What is a stable disease (RECIST)
Small changes that don’t meet any of the other RECIST criteria
True or false - Patients with a pacemaker can’t be given a CT scan?
False
Rephasing of protons due to tissues during an MRI causes them to recover back to their original precessing frequency faster or slower?
Faster
In T1, to protons recover faster in blood or bone, and what is the result of this
T1, protons in the blood take longer to revert back to the original frequency so produce a smaller signal. As a result they are dark in the image, compared to bone which is light.
What is the relationship between T1 and T2?
T1 is the inverse of T2
Is blood light or dark in a T2 MRI
Blood is light in T2, bone and fat are dark.
What is the name of the process used to detect perfusion using an MRI
Arterial spin labeling - Protons are inverted 180 degrees.
Inverted nuclei flow into the imaging slice causing dephasing (darkening of the image)
There is a direct correlation between the amount of darkening and the amount of perfusion.
How is diffusion imaging using an MRI relevant to cancer?
In tumours there are areas of necrotic cells which have perforated cell walls. As a result, these areas will exhibit a higher level of diffusion compared to surrounding normal cells. This can be used to determine if a suspected tumour is in fact cancerous.
How is a signal produced by PET?
It’s the result of an annihilation event when an electron interacts with a positron which is emitted following nuclear decay.
Do positrons used in PET have a short or long half life
Short, often minutes so following production of the positrons, a scan must be completed soon after.
What is the result of the annihilation event in a PET scan
2 gamma ray photons emitted at 180 degrees and at 511keV. A ring of detectors measure coincidence events between 180 degrees to produce a tomographic image.
Outline the way that 18FDG is used in PET imaging
FDG is taken up by normal glut1 transporters where it becomes stuck. This is because the deoxyglucose is not able to be processed further in the Krebs cycle. In cancer there is an upregulation of Glut 1 transporters and uptake of glucose due to a switch in metabolism which favors glycolysis. So in a PET scan, areas with a high uptake of glucose will be seen as a high uptake of 18FDG suggesting these are tumour cells.
What other areas of the body exhibit background 18FDG signalling and why?
Brain and heart as they are highly metabolically active. Bladder and kidneys as this is the route FDG takes to be excreted.
FDG can be used as a contrast agent to investigate brain tumours? true or false
False
How is iodine used as a tracer in SPECT scans?
Used for thyroid cancer imaging. Iodine is imported into the thyroid as it is required for thyroid hormone production. (It’s imported by a sodium/iodine transporter). In thyroid cancer cases, the rate of uptake of iodine will change.
