[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Radiology](https://durgical.com/en/radiology/) › Principles and safety

# Principles and safety

How each image is made, the densities, radiation, contrast and how to request a study.

10 pages

## Choosing a study

- [**Choosing the right study: appropriateness and incidental findings** The best scan answers the clinical question with the least risk](https://durgical.com/en/radiology/choosing-the-right-study-appropriateness-and-incidental-findings/)
- [**Requesting a study and reading the report** A good request asks a clear question and gives the facts the radiologist needs; a good reader…](https://durgical.com/en/radiology/requesting-a-study-and-reading-the-report/)

## Modality

- [**CT: windows, Hounsfield units and contrast phases** A CT scanner spins an X-ray tube around the body and a computer builds thin slices, giving every…](https://durgical.com/en/radiology/ct-windows-hounsfield-units-and-contrast-phases/)
- [**Gadolinium and the kidney** MRI contrast is removed by the kidneys](https://durgical.com/en/radiology/gadolinium-and-the-kidney/)
- [**How each imaging study makes a picture: X-ray, CT, ultrasound, MRI and nuclear medicine** Each scan builds its picture from something different: X-rays passing through, sound echoes, a…](https://durgical.com/en/radiology/how-each-imaging-study-makes-a-picture-x-ray-ct-ultrasound-mri-and-nuclear-medic/)
- [**Iodinated contrast: reactions and the kidney** The iodine dye used in CT makes vessels and organs show up](https://durgical.com/en/radiology/iodinated-contrast-reactions-and-the-kidney/)
- [**MRI safety: implants, metal and gadolinium** The MRI magnet is always on and pulls on iron-containing metal](https://durgical.com/en/radiology/mri-safety-implants-metal-and-gadolinium/)
- [**MRI: T1, T2, FLAIR and diffusion** MRI uses a strong magnet and radio waves, not X-rays](https://durgical.com/en/radiology/mri-t1-t2-flair-and-diffusion/)
- [**Radiation in medical imaging: risk, ALARA and pregnancy** X-rays and CT carry a small radiation risk, so each study should be needed and done with the…](https://durgical.com/en/radiology/radiation-in-medical-imaging-risk-alara-and-pregnancy/)

## Sign

- [**The five densities on an X-ray** An X-ray shows only five shades: air black, fat dark grey, water and soft tissue grey, bone…](https://durgical.com/en/radiology/the-five-densities-on-an-x-ray/)

## A to Z

- [A](https://durgical.com/en/radiology/a-z/a/)
- [B](https://durgical.com/en/radiology/a-z/b/)
- [C](https://durgical.com/en/radiology/a-z/c/)
- [D](https://durgical.com/en/radiology/a-z/d/)
- [F](https://durgical.com/en/radiology/a-z/f/)
- [G](https://durgical.com/en/radiology/a-z/g/)
- [H](https://durgical.com/en/radiology/a-z/h/)
- [I](https://durgical.com/en/radiology/a-z/i/)
- [K](https://durgical.com/en/radiology/a-z/k/)
- [L](https://durgical.com/en/radiology/a-z/l/)
- [M](https://durgical.com/en/radiology/a-z/m/)
- [N](https://durgical.com/en/radiology/a-z/n/)
- [P](https://durgical.com/en/radiology/a-z/p/)
- [R](https://durgical.com/en/radiology/a-z/r/)
- [S](https://durgical.com/en/radiology/a-z/s/)
- [T](https://durgical.com/en/radiology/a-z/t/)
- [U](https://durgical.com/en/radiology/a-z/u/)
- [V](https://durgical.com/en/radiology/a-z/v/)
- [W](https://durgical.com/en/radiology/a-z/w/)

[← Radiology and diagnostic imaging](https://durgical.com/en/radiology/)

Educational content; it does not replace a radiologist's report and is not a clinical instruction. Each study is ordered on the patient's assessment and your institution's protocols.

Representative model, for educational purposes only.

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Source: https://durgical.com/en/radiology/areas/principles/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/radiology/areas/principles/