Your hospital’s instructions come first. This is an educational guide, not individual medical advice, MRI safety clearance or a diagnosis. Confirm the MRI body region, hospital and appointment details with the treating team.
Physics laboratory
Change a setting. See the science respond.
Conceptual models · no real scanner control
How MRI works
Start with the simple explanation. Open a topic to go deeper.
MRI means magnetic resonance imaging. A strong magnetic field, radiofrequency pulses and position-encoding gradients let a computer form images from hydrogen signals. It uses no ionising radiation. The scanner repeats measurements using different timings to reveal different tissue features. Sources and further reading
A fixed dental bridge and MRI
A fixed bridge replaces missing teeth and is attached to teeth or implants. It stays in place during everyday use.
Usually manageable — still declare it
Many fixed dental restorations can be scanned after screening. The team needs to know what is present, whether it is firmly attached, and which scanner and sequence will be used. A fixed bridge is different from removable dentures or a magnet-retained dental appliance.
Bridges may contain ceramics, zirconia, gold-based alloys, cobalt–chromium, nickel–chromium or other materials. Their magnetic behaviour depends on composition, processing and structure; a material name alone cannot establish safety.
Diamagnetic materials respond weakly against an applied field; paramagnetic materials respond weakly along it. Ferromagnetic materials can respond strongly and retain magnetisation. Explore these differences in experiment 6 of the physics laboratory.
Ask your dentist for available material or manufacturer information. Tell the MRI team if the bridge is loose or damaged. Do not try to remove a fixed bridge yourself.
Four separate effects
Force
A non-uniform magnetic field can pull on a magnetically responsive object.
Torque
A magnetic moment can try to turn into alignment: τ = μ × B. Here τ is turning force, μ is magnetic moment, and B is field. This is a physical model, not a bridge risk calculation.
RF heating
Conducting structures can couple to radiofrequency fields. Heating depends on geometry, material, position and scanner settings, including electric fields.
Image artefacts
Susceptibility differences can cause signal loss and distortion nearby. Dental metal may affect facial or upper cervical pictures; the extent depends on the restoration and technique.
The MRI safety team makes the individual decision. Declare your bridge before entering the scanner room. Report pain, warmth, pulling or any unusual sensation immediately using the call bell.
The upper neck supports the head and protects the spinal cord.
C1, the atlas, is the ring beneath the skull. C2, the axis, sits below it. Its upward peg, the odontoid process (dens), helps the head rotate around C2.
The spinal cord passes through the canal behind the dens. Ligaments connect and restrain the bones. Stability depends on the fracture pattern, alignment and ligament integrity; it cannot be judged from this guide.
CT is particularly useful for fine bony detail and fractures. MRI provides complementary information about the spinal cord, ligaments, discs, marrow and other soft tissues. It may be requested after trauma to answer a specific clinical question.
Simplified side/structural schematic, not an anatomical scan. Not to scale.
Keep prescribed collar and movement precautions. Do not remove or adjust a collar for the scan yourself. Contact the team in advance about safe transfers, positioning and MRI compatibility of the collar. The MRI region is unconfirmed: do not assume it will examine C2.
Tell staff about rib pain, trouble lying flat and kidney injury or current kidney problems. If contrast is being considered, the team may need kidney function information. New weakness, numbness or breathing difficulty requires urgent medical assessment; do not wait for a planned scan.
A map of tracer distribution, combined with a map of anatomy.
What the tracer does
PET means positron emission tomography. CT means computed tomography: X-rays produce anatomical images. Gallium-68 is a radioactive isotope attached to DOTATATE, a molecule that binds somatostatin receptors, particularly subtype 2.
Many neuroendocrine tumours express these receptors. The scan can help locate receptor-positive tissue and inform investigation or treatment planning. Normal organs, some benign processes and inflammation can also show uptake; some tumours show little uptake. Uptake alone cannot decide whether a mass is benign or malignant. The specialist interprets it with other imaging, clinical findings and sometimes biopsy.
Gallium-68 decays mainly by emitting a positron, the electron’s positively charged antiparticle, as it becomes zinc-68. The positron slows in tissue before annihilating with an electron.
Gallium-68 has a physical half-life of about 68 minutes: A(t) = A₀ × 2^(−t/68 min). Biological clearance also affects the amount in the body. This is not a personalised radiation precaution timer.
See coincidence detection
Two photons, each 511 keV, travel in nearly opposite directions. Detectors register a timed pair along a line of response. Many such lines form an image. Position and paths here are illustrative, not to scale.
MRI and PET-CT answer different questions
Feature
MRI
DOTATATE PET-CT
Signal
Hydrogen response to magnetic and radiofrequency fields
Injected radioactive tracer plus CT X-rays
Main information
Detailed tissue structure, depending on sequence
Somatostatin receptor tracer distribution located on anatomy
Ionising radiation
No
Yes, from tracer and CT
Preparation
Metal screening and scan-specific instructions
Tracer-specific medicine, food, drink and radiation instructions
Use the letter from your own department for exact timings and preparation.
MRI · what to expect
Before arrival: check the body region and preparation. Discuss the bridge, implants, neck precautions, pain, anxiety and any need for support.
Screening: complete the safety questionnaire honestly. Staff check metal, implants and clothing and may provide a gown.
Positioning: the team helps you onto the table with appropriate support and a receiver coil. Agree safe collar management and transfers first.
During the scan: wear the hearing protection provided. Expect loud bursts of knocking. Use the intercom or call bell if uncomfortable. Keep still as instructed.
Timing: many scans take roughly 15–60 minutes; some take longer. Ask about the planned examination.
Afterwards: follow instructions about contrast or sedation if used. A radiologist reports to the referrer; ask how and when results will be explained.
Gallium PET-CT · what to expect
Preparation: verify the hospital and written fasting, hydration and medicine instructions. Check somatostatin analogue timing with nuclear medicine; do not stop medication yourself.
Arrival: staff check relevant history, medicines and any pregnancy or breastfeeding considerations. Discuss neck support and fluid restrictions.
Injection: a cannula is placed in a vein and a measured tracer dose is given.
Uptake: wait while the tracer distributes, often around an hour. The department confirms its schedule.
Scan: lie supported on the moving bed for the PET and CT images. The team confirms duration and whether any additional CT contrast is planned.
Going home: follow the exact written contact precautions, including around children and pregnant people. Ask about drinking and passing urine within any fluid limits.
Results: the specialist reviews the report with the wider evidence. Results are usually explained later by the referring team.
Confirm the venue. A Coventry appointment has not been verified. This guide does not establish which hospital you will attend. Fasting, medicine and radiation instructions vary: your own department’s written guidance takes precedence.
The general PET pathway is informed by CUH patient information; its local instructions must not be substituted for your appointment letter.
One step at a time
Six practical checklists. Saved in this browser on this device.
No names, appointments or notes are collected. Checklist ticks and appearance preferences stay on this device.
Private browsing, clearing website data or changing device/browser can remove progress. Offline copies may contain older guidance: always check your current hospital letter.
The discoveries behind the scanner
Open a milestone to explore its contribution. MRI grew from many people’s work.
Prepared 30 October 2026. Links below provide patient information and scientific background. This guide has not received an independent clinical review. Local appointment instructions and individual assessment always take precedence.
Use on an iPhone, offline access and privacy
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