Magnetic Resonance and Medical Imaging

What occurs to nuclei with an odd number of protons when placed in a magnetic field?

They precess around the direction of the magnetic field.

What happens when an external RF pulse matches the Larmor frequency of nuclei?

The nuclei absorb energy and move to a higher energy state.

What is T1 relaxation in magnetic resonance?

Energy transfer to surrounding tissues after the RF pulse is switched off.

What is T2 relaxation in magnetic resonance?

Dephasing due to interactions between spins after the RF pulse is switched off.

What does Larmor frequency depend on?

It is determined by the magnetic field strength.

What is a key diagnostic use of MRI?

Producing detailed images of soft tissues.

What type of radiation exposure does MRI use?

No ionizing radiation exposure.

What is an advantage of using ultrasound for imaging?

It is non-ionizing and safe for pregnancy.

What is a disadvantage of ultrasound imaging?

Limited penetration depth and poor imaging of bones.

What are the advantages of X-ray imaging?

Good for bone imaging, fast, and widely available.

What is a major disadvantage of X-ray imaging?

It exposes patients to ionizing radiation.

What is an advantage of MRI compared to other imaging techniques?

It provides excellent soft tissue contrast.

What is a disadvantage of MRI?

It is expensive and time-consuming.

What is α-radiation?

Highly ionizing and low penetrating; dangerous if ingested or inhaled.

What potential harm does β-radiation cause?

Skin burns due to moderate penetration.

What is γ-radiation known for?

Highly penetrating but weakly ionizing, can damage internal organs and DNA.

What unit measures absorbed dose?

Gray (Gy), defined as energy absorbed per kilogram.

What is the equivalent dose unit?

Sievert (Sv), accounting for radiation type and biological effect.

What formula defines the equivalent dose?

H = DWg (absorbed dose × radiation weighting factor).

What is Technetium-99m (Tc-99m)?

A radionuclide used for imaging bones, heart, and kidneys.

What is the half-life of Technetium-99m?

About 6 hours, reducing radiation exposure.

What are the main components of a gamma camera?

Collimator, scintillation counter, photomultiplier tubes.

What is the role of the collimator in a gamma camera?

It allows only photons traveling in a specific direction to enter.

What does the scintillation counter do in a gamma camera?

It converts gamma rays into light flashes.

What technology is used in PET scans?

Positron-emitting radionuclides, such as fluorine-18.

What happens when positrons emitted in PET scans annihilate with electrons?

They produce gamma rays which are detected to create images.

Why are PET scans important in healthcare?

They are used for cancer detection and monitoring metabolic activity.

What type of images does a CCD provide in a gamma camera?

Digital images from converted electrical signals.

What describes the effective dose in radiation measurements?

E = HW_T (equivalent dose × tissue weighting factor).

How does MRI provide high contrast?

It differentiates between different types of soft tissue well.

How can MRI be unsuitable for some patients?

Due to the presence of metallic implants.