Week Two - Medical Data Sampling & Acquisition Flashcards
What is a pathological process?
Process occurring as a consequence of disease.
Name three methods of detecting external signals.
- Physical exam.
- Thermal imaging.
- Transillumination imaging.
Name the three planes of the human body.
Transverse, sagittal, coronal.
What are the two types of x-ray imaging? What is the difference between them?
Conventional and digital. Conventional uses film or heavy metal target, digital uses detector to pick up x-rays.
What is x-ray absorption proportional to?
Tissue density. Thicker bone = more electrons x-ray encounters = more likely x-ray gets scattered or absorbed.
What are 3 issues related to x-ray imaging?
- Single 2D projection, no depth perception.
- All organs appear to sit on top of each other, hard to distinguish between.
- Repeated high levels of radiation can be an issue.
What are some uses of X-ray imaging?
Mammography, angiography, bone fractures, pneumonia.
What is a CT scan?
Rotating x-ray source allows for the construction of a 3D digital volume from a series of stacked 2D slices.
What is an issue with CT?
Radiation doses typically 100x normal x-ray - risk of inducing DNA damage that could lead to cancer.
What are some uses of CT scans?
Chest, abdomen and pelvic scans.
Location and size of tumours.
Diagnosis of trauma or injury.
How does an MRI work?
Powerful magnets produce radio waves - hydrogen nuclei (protons) absorb radio wave and flip their spins (excitation) - proton relaxes and releases radio wave - picked up by scanner.
What is the main principle behind an MRI image having different contrasts?
Different parts of the brain (white matter, grey matter, CSF) have different densities of water - and therefore different H+ densities; meaning that they take different amounts of time to return to their resting positions. Relaxation time differences = difference in contrasts.
What is MRI used for?
Brain structure and function.
Soft tissues - ligaments, tendons etc.
Spinal cord injuries.
What are two issues with MRI?
Powerful magnetic field - risk with metal implants.
Constant flipping of magnetic field is very loud.
How does ultrasound work?
A probe sends pulses of ultrasonic frequencies into tissue; sound echoes off the tissue with different tissues reflecting varying degrees of sound.
What are two issues with ultrasound imaging?
Various limits in field of view - very dependent on skilled operator.
Difficulty imaging structures behind bone.
What does PET stand for?
Positron emission tomography.
How does PET work?
Radioactive tracer injected into patient (molecule such as glucose with a radioisotope attached). Blood carries tracer to tumour. Radioisotope decays by releasing positrons, which collide with surrounding electrons and annihilate each other - releasing photons at 180 degrees. Photons are detected and the size, shape, and position of the tumour is calculated.
What is PET used for?
Tumours
Pre and post cancer treatment.
What is an issue related to PET?
Ionising radiation.
What does SPECT stand for?
Single photon emission computer tomography.
How does SPECT work?
As radioisotope decays, gamma rays are produced and collected by detector.
What are the main differences between PET and SPECT?
Different radioisotopes and different detectors.
What are two uses of SPECT?
Myocardial perfusion imaging. Functional brain imaging.
What are some advantages of SPECT?
Low cost and wide spread. Large number of tracers available that track different things.
What are some disadvantages of SPECT?
Low resolution, high noise.
Why would you combine PET and CT?
Functional PET images can be interpreted by comparing to high quality anatomical CT scans.
What does the formula L = 2^k refer to?
Grey level resolution = 2^(bits per pixel)
