Module 8 - Week 12 Flashcards
How does mA affect the x-ray beam?
mA influences the number (quantity) of x-ray photons in a directly proportional way (e.g., doubling mA doubles the number of photons).
How does kV influence x-ray beam quality and quantity?
kV affects both quantity and quality. A 15% increase in kV results in twice the photon quantity and increased photon energy, improving penetrability.
Why is differential absorption important in digital image formation?
Digital images rely on differential absorption, where tissues absorb x-rays differently, creating contrast essential for image quality.
What is exponential attenuation?
X-rays lose 50% of photons for every 5 cm of tissue thickness, requiring adjustments in mA or kV to compensate.
What are the two main types of photon interactions with matter in medical imaging?
The photoelectric effect (PE) and Compton scatter.
How does increasing kVp affect PE and Compton scatter?
Increasing kVp decreases PE interactions significantly while Compton interactions remain relatively constant but slightly decrease.
How does tissue density affect x-ray interactions?
Higher density tissues (e.g., bone) have more tightly packed atoms, increasing the probability of PE interactions.
How does atomic number affect PE interactions?
Higher atomic numbers significantly increase PE interactions (e.g., bone has 6.5x more PE interactions than soft tissue).
What is the purpose of an exposure index (EI)?
It provides feedback on receptor exposure to help technologists optimize techniques and prevent over- or underexposure.
What is Dose Creep?
The tendency to use higher exposures than necessary because digital systems correct images automatically, leading to unnecessary patient dose.
How do Fuji and Siemens exposure indices differ?
Fuji uses the S-number, which is inversely proportional to exposure, while Siemens’ EXI increases linearly with exposure.
What is a correct S-number range in Fuji systems?
Between 100-250 for proper exposure.
What are key methods for technique optimization?
Adjusting kV and mA based on tissue thickness, using exposure indices for feedback, and following manufacturer-recommended kV ranges.
How do grids affect exposure settings?
Using a grid requires increasing mAs or kVp to compensate for absorbed scatter radiation (e.g., a 5:1 grid requires 2x mAs).
