Have a go at answering the questions below. Don’t worry if you get any wrong – after clicking ‘Check Answers’ the correct answer will be highlighted in green!
1. What is the correct order of tissue densities?
2. What is the contrast medium used in MRI?
3. How many times more radiation do you get from an abdominal X-ray, compared to a chest X-ray?
4. Is air bright or dark on ultrasound?
1. What is the correct order of tissue densities?
Air < Fat < Fluid < Soft tissue < Bone < Metal
Remember: Fat floats on water, so is less dense than fluid. Soft tissue is connective tissue + intracellular fluid, so is more dense than fluid alone.
2. What is the contrast medium used in MRI?
In MRI scans requiring contrast, a metal-based IV contrast called gadolinium is used. Iodine is used in X-rays and CT. Gastrografin is used in contrast studies; it is similar to barium but is water soluble.
3. How many times more radiation do you get from an abdominal X-ray, compared to a chest X-ray?
An abdominal X-ray exposes you to approximately 0.7 mSV of radiation, compared to a chest X-ray with only 0.02 mSv. For comparison, we each get 2.7 mSv in background radiation every year from environmental sources in the UK.
4. Is air bright or dark on ultrasound?
Air is bright on ultrasound, unlike other imaging modalities.
