Radiology Physics Flashcards
Imaging principle of CT, ultrasound, MRI, and nuclear medicine
Contrast agents in CT, ultrasound, MRI, nuclear medicine
Microbubbles in ultrasound
Contrast for US that is not FDA approved in the US, but is used commonly abroad
Unit of radiation in medical imaging
mSv
Millisieverts
Latency period from irradiation event to carcinogenesis
Depends on the dose, but generally ~20-30 years
Largest source of background radiation
Radon
Five levels of density on a conventional radiograph
- Air
- Fat
- Fluid OR Soft tissue
- Calcium/Bone
- Metal
Hounsfield units
The density value assigned to pixels in a CT scan
ranges from -1000 to 1000
-1000 HU is defined as the density of air on a CT scan. With this definition, bone is 400-600 HU, fat is -40 to -100 HU, water is 0 HU, and soft tissue is 20-100 HU.
Degree of visualization on CT scan
Attenuation
Common HU windows used to visualize different areas on CT
- Lung window
- Mediastinal window
- Bone window
Best way to differentiate a solid vs cystic structure
Ultrasound
Remember that on CT and conventional radiographs soft tissue and fluid have the same attenuation!
Which chemicals to isotopically label in order to image which tissues
Iodine - Thyroid
Brain - Glucose
Bone - Phosphate
Lung - Particles of a particular size
SPECT imaging
Single photon emission computed tomography
Nuclear medicine study that is performed with a gamma camera to acquire many 2D images from multiple angles, which are then reconstructed by computer into a 3D data set that can be manipulated to demonstrate thin slices in any projection.
Think of this as the love child of CT and nuclear imaging
Most commonly utilized PET substrate
Fluorodeoxyglucose
Tumors are often “FDG avid”
Average annual background radiation
~3 mSv
