Electromagnetic Waves and Magnetic Resonance Imaging (MRI)

Comprehensive vocabulary flashcards covering the properties, divisions, and medical uses of the electromagnetic spectrum, as well as the fundamental physics, hardware components, clinical types, and safety contraindications of Magnetic Resonance Imaging (MRI).

Electromagnetic (EM) Waves

Waves produced solely by accelerating charges, composed of mutually sustaining oscillating electric and magnetic fields that propagate through matter or a vacuum at $3.00 \times 10^8\,\text{m/s}$.

Electromagnetic Spectrum

The entire continuous range of electromagnetic radiation frequencies and wavelengths, categorized into seven standard regions from gamma rays to radio waves.

Gamma Rays

The highest-energy electromagnetic waves with wavelengths shorter than $0.01\,\text{nm}$, originating in space from pulsars, neutron stars, black holes, and supernovae, and naturally absorbed by Earth's atmosphere.

Computed Tomography (CT)

A medical imaging technique that records transmitted X-ray radiation across multiple projections to generate detailed cross-sectional slices of internal bodily structures.

Linear Accelerator

A radiotherapy machine that rotates around a patient to deliver therapeutic X-ray beams from multiple angles, selectively destroying rapidly dividing cancer cells while minimizing exposure to healthy tissue.

Ultraviolet (UV) Radiation

Electromagnetic radiation spanning from approximately $400\,\text{nm}$ down to $10\,\text{nm}$, capable of triggering cutaneous vitamin D synthesis and clinically applied to treat conditions like psoriasis, vitiligo, and cutaneous T-cell lymphoma.

Visible Light

The narrow segment of the electromagnetic spectrum detectable by human vision, spanning frequencies from $430\,\text{THz}$ to $750\,\text{THz}$ and vacuum wavelengths from $700\,\text{nm}$ (red) to $400\,\text{nm}$ (violet).

Blue Light Phototherapy

A medical treatment utilizing visible blue light to degrade excess bilirubin in infants suffering from neonatal jaundice.

Scanning Laser Ophthalmoscope

An ophthalmic imaging instrument that utilizes a collimated beam of laser light to visualize and examine detailed ocular structures, especially the retina and optic nerve head.

Photodynamic Therapy (PDT)

A clinical treatment combining visible light irradiation with photosensitizing medications to generate reactive oxygen species that destroy cancer cells, psoriasis, acne, and localized infections.

Endoscopy

A diagnostic procedure using an endoscope—a long, slender tube integrated with illumination and a camera—introduced via natural orifices to inspect internal organs.

Infrared (IR) Radiation

Electromagnetic radiation with wavelengths between $700\,\text{nm}$ and $1\,\text{mm}$, emitted naturally by room-temperature objects as thermal radiation peaking at approximately $0.01\,\text{mm}$ ($10\,\mu\text{m}$).

Medical Thermography

The clinical use of infrared imaging to map skin surface temperatures as an objective evaluation of physiological and vascular abnormalities.

Pulse Oximetry

A non-invasive clinical monitoring method utilizing dual-wavelength spectrophotometry to determine the percentage of hemoglobin saturated with oxygen in circulating blood.

Near Infrared Spectroscopy (NIRS)

A continuous non-invasive optical technique that monitors hemodynamics and oxygenation status within deep tissues such as the brain and skeletal muscles.

Microwaves

Electromagnetic waves with wavelengths from roughly $1\,\text{mm}$ to $30\,\text{cm}$, situated between infrared and radio waves, employed in communications, radar, and therapeutic hyperthermia (microwave thermotherapy).

Radio Waves

The lowest-frequency (up to approximately $1\,\text{GHz}$) and longest-wavelength (greater than $0.3\,\text{m}$) region of the electromagnetic spectrum, used widely in telecommunications and diagnostic MRI.

Radiofrequency (RF) Ablation

A minimally invasive intervention using radio waves to produce localized thermal coagulation, used in cardiology and oncology to ablate abnormal electrical pathways or tumors.

Shortwave Diathermy

A physical therapy modality that utilizes localized dielectric heating generated by radiofrequency waves to treat deep musculoskeletal pain and inflammation.

Magnetic Resonance Imaging (MRI)

A non-invasive diagnostic modality that produces high-resolution anatomic images through the interaction of transmitted radiofrequency pulses with hydrogen nuclei ($H^+$) inside a powerful static magnetic field.

Nuclear Magnetic Resonance (NMR)

The underlying physical and spectroscopic phenomenon discovered independently in 1946 by Felix Bloch and Edward Purcell, which laid the theoretical foundation for clinical MRI.

Proton Spin

The intrinsic rotational motion of a positively charged proton that creates an electrical current and an associated microscopic magnetic dipole moment.

Superconducting Magnet (MRI)

The primary component of an MRI unit that produces a high magnetic field ($1.5\text{--}3\,\text{T}$) using electrical currents running without resistance through coils cooled by liquid helium at $-269^\circ\text{C}$.

Gradient Coils

Electromagnetic coils arranged in three orthogonal planes ($x, y, z$) within an MRI scanner that alter the primary magnetic field for spatial encoding, which also generate the scanner's characteristic loud tapping noises.

Radiofrequency (RF) Coil

A transceiver coil within an MRI system that transmits RF excitation pulses to displace hydrogen protons from alignment and subsequently detects the weak returning signals emitted as the protons relax.

Functional MRI (fMRI)

An MRI protocol that maps localized brain function by detecting blood-oxygen-level-dependent (BOLD) hemodynamic changes during neural activity.

Magnetic Resonance Angiography (MRA)

A tailored MRI application designed specifically to image arteries and veins to detect vascular anomalies, blockages, or aneurysms.

Diffusion MRI

An MRI sequence that maps the microscopic Brownian diffusion of water molecules within biological tissues, widely used in evaluating cerebral ischemia and white-matter tracts.

Projectile Effect (MRI)

The severe physical hazard in MRI environments where loose ferromagnetic items (such as scissors, tools, gas cylinders, and chairs) are violently drawn into the scanner bore by the magnetic field.

Absolute Contraindications to MRI

Medical conditions or devices—namely cardiac pacemakers, cochlear implants, and ferromagnetic surgical clips—that completely prohibit a patient from undergoing MRI due to lethal safety risks.