# An MRI's Skeleton (DD-290)

> The machine in the footage is almost certainly a CT (computed tomography) scanner with its covers off, not an MRI. In a CT scanner, an X-ray tube and detector array are mounted on a ring-shaped gantry that spins rapidly around the patient, and a computer turns the measurements into cross-sectional images. An MRI works differently and has no spinning parts. A strong static magnet lines up hydrogen nuclei in the body, radio-frequency pulses tip them, and stationary gradient coils briefly vary the magnetic field so the signals can be located in space. The nuclei give off radio signals as they relax, and a computer builds images in which tissues differ by how fast they relax. The Reel's description of magnets, radio waves and gradient fields fits MRI; only the 'spinning' parts and the footage belong to CT.

- Department: Science (also Tech)
- First published: 2024-08-05
- Last updated: 2024-08-05
- Permalink: https://detailenjoyer.com/case/an-mris-skeleton/
- Author: Marcus Easterling (DetailEnjoyer), The Detail Department

## Quick facts

- **DD-290-F01**: MRI uses magnets and radio waves and has no spinning parts. _(Write-up · Exhibit A (Magnets and radio))_
- **DD-290-F02**: A CT scanner's X-ray tube spins on a ring gantry. _(Write-up · Exhibit D (CT spins))_

## Write-up

Strip the covers off a scanner and the ring starts spinning. An MRI has no spinning parts; the whirling ring belongs to a CT scanner.

1. **Magnets and radio**: MRI uses a strong magnet and radio-frequency pulses to get signals from hydrogen nuclei.
2. **Gradient coils**: Stationary gradient coils vary the field so signals can be located.
3. **Tissue contrast**: Tissues differ by how fast their nuclei relax after each pulse.
4. **CT spins**: A CT scanner's X-ray tube and detectors spin on a ring around the patient.
5. **The footage**: The spinning ring in the footage matches an uncovered CT gantry.

## Related case files

- [Berlin Heart (DD-577)](https://detailenjoyer.com/case/berlin-heart/): I linked more hospital machinery

## Reel vs. record

- **Note**: 'Spinning gradient coil assembly': I'd correct this. MRI gradient coils are stationary; they vary the field electrically. The spinning ring in the footage looks like a CT scanner's gantry with its covers off.
- **Note**: 'The spinning component aids in differentiating tissues': in MRI, contrast comes from how tissues' nuclei relax, not from rotation. In CT, the rotation lets the computer build cross-sections from X-ray measurements.
- **Note**: Footage vs. record: I'm treating the footage as a CT scanner shown in place of an MRI, so I covered both machines.

## Video: An MRI's Skeleton: Strip the Covers off a Scanner and the Ring Starts Spinning

- Duration: 23.6 s · Published: 2024-08-05
- File: https://detailenjoyer.com/assets/videos/C-UC5NptJX_.mp4

### Transcript

DID YOU KNOW? An MRI or magnetic resonance imaging machine works by using powerful magnets and radio waves to generate detailed images of the body's internal structures. The machine's spinning gradient coil assembly creates varying magnetic fields allowing for precise spatial encoding. This process manipulates the resonance frequency of hydrogen protons in the body, which emits signals that are converted into detailed images by a computer. The spinning component aids in differentiating tissues. NOW YOU KNOW!

## Questions & answers

**Q: What does MRI use to image the body?**  
A: The signals come from hydrogen nuclei. _(Source: Write-up · Exhibit A (Magnets and radio) · NIBIB (NIH): Magnetic Resonance Imaging (MRI))_

**Q: Do MRI gradient coils spin?**  
A: They vary the field electrically. _(Source: Write-up · Exhibit B (Gradient coils) · NIBIB (NIH): Magnetic Resonance Imaging (MRI))_

**Q: What creates contrast between tissues in MRI?**  
A: Different tissues relax at different rates. _(Source: Write-up · Exhibit C (Tissue contrast) · NIBIB (NIH): Magnetic Resonance Imaging (MRI))_

**Q: Which scanner has a spinning ring?**  
A: The X-ray tube and detectors rotate. _(Source: Write-up · Exhibit D (CT spins) · NIBIB (NIH): Computed Tomography (CT); US FDA: Computed Tomography (CT); Wikipedia: CT scan)_

**Q: What does the footage most likely show?**  
A: That's why the ring spins. _(Source: Write-up · Exhibit E (The footage) · NIBIB (NIH): Computed Tomography (CT); Wikipedia: CT scan)_

## Sources

- [NIBIB (NIH): Magnetic Resonance Imaging (MRI)](https://www.nibib.nih.gov/science-education/science-topics/magnetic-resonance-imaging-mri)
- [NIBIB (NIH): Computed Tomography (CT)](https://www.nibib.nih.gov/science-education/science-topics/computed-tomography-ct)
- [US FDA: Computed Tomography (CT)](https://www.fda.gov/radiation-emitting-products/medical-x-ray-imaging/computed-tomography-ct)
- [Wikipedia: CT scan](https://en.wikipedia.org/wiki/CT_scan)

## Cite this case file

Easterling, Marcus. "An MRI's Skeleton." The Detail Department (DetailEnjoyer), case file DD-290, last updated Aug 5, 2024. https://detailenjoyer.com/case/an-mris-skeleton/