Medical physcis part 2 Flashcards
What is sharpness in X-ray imaging?
Sharpness is how easily the edge of a structure can be determined in an image.
How can X-ray sharpness be improved?
Reduce target anode size, reduce aperture size, and place lead grid in front of film.
What is contrast in X-ray imaging?
Contrast is the visual difference between black and light areas in an X-ray image.
How can X-ray contrast be improved?
Increase exposure time, use harder X-rays, reduce scattering, and use fluorescent contrast medium.
How does X-ray intensity decrease in a medium?
Intensity decreases exponentially as X-rays pass through a medium: I = I₀e⁻ᵏˣ.
What is the linear absorption coefficient (μ)?
μ is a medium-specific value that determines how much X-rays are absorbed per unit distance.
What is Half-value thickness (x₁/₂)?
It is the thickness of the medium needed to reduce X-ray intensity to half its initial value.
What is the relationship between x₁/₂ and μ?
x₁/₂ × μ = ln 2.
What is the purpose of tomography in CT scans?
Tomography creates 3D images by compiling multiple 2D X-ray planes.
What are the advantages of CT scans?
CT scans show 3D relationships and can distinguish tissues with similar densities.
What is the ultrasound imaging procedure?
A transducer with gel is placed on the skin, and ultrasound pulses are sent to the body. The reflected waves are used to create an image.
What are the two techniques used in ultrasound imaging?
A-scan (measures distance) and B-scan (creates 2D image from multiple angles).
What are the advantages of X-ray?
Sharp images, improved contrast, and ability to form images where air is trapped.
What are the disadvantages of X-ray?
Equipment is heavy, and it can cause tissue damage.
What are the advantages of ultrasound?
Portable, less harmful, and useful for treating sprained joints.
What are the disadvantages of ultrasound?
Not suitable for air-trapped areas like lungs and can be less sharp due to refraction.
What are the advantages of CT scans?
Show 3D relationships and detect cancer.
What are the disadvantages of CT scans?
Heavy equipment and not portable.
What is Positron Emission Tomography (PET)?
A diagnostic tool for cancers, heart diseases, and brain function using radiotracers.
What is a radiotracer in PET?
A molecule like fluorodeoxyglucose that emits positrons, used for imaging.
What happens during annihilation in PET?
A positron meets an electron, annihilates, and emits two gamma rays.
How are gamma rays detected in PET?
Gamma rays excite a crystal, which emits light detected by photomultiplier tubes and processed by a computer.
What is the role of a cyclotron in PET?
It accelerates particles to create isotopes like fluorine-18 for use in radiotracers.
Why is fluorine-18 safe for PET scans?
It has a short half-life of 2 hours, making it safe for patients.
