MIT211 Lec Comp Final

Fleming's right-hand rule

It shows the relationship between motion, magnetic field, and induced current in a conductor.

Faraday's Law

A current is induced in a conductor when it experiences a changing magnetic field or relative motion with a magnet.

Relative motion in electromagnetic induction

Without motion between the magnetic field and conductor, no current is induced.

Type of magnet used in MRI machines

Superconducting magnets.

Ferromagnet

A material that can be magnetized, like iron, and is strongly attracted to magnets.

Difference between AC and DC power

AC alternates direction; DC flows in one direction.

Common device that uses AC power

Household appliances.

Common device that uses DC power

Flashlights or battery-operated devices.

Ohm's Law

V = IR, where V is voltage, I is current, and R is resistance.

Function of motors in imaging systems

Convert electrical energy into mechanical energy to rotate the anode.

Function of generators in imaging systems

Convert mechanical energy into electrical energy.

Main parts of an x-ray tube

Anode, cathode, filament, rotor, target.

Function of the glass envelope

Maintains a vacuum inside the tube for electron travel.

Purpose of the tube housing

Shields radiation leakage and provides mechanical support.

Function of the tube window

Allows x-rays to exit the tube with minimal absorption.

Difference between rotating and stationary anodes

Rotating anodes spread heat over a larger area; stationary anodes do not.

Components internal to the x-ray tube

Anode, cathode, filament, target, glass envelope.

Components external to the x-ray tube

Rotor, stator, housing.

Who discovered x-rays and when

Wilhelm Roentgen in 1895.

How x-rays are produced

Electrons strike the anode target, releasing x-ray photons.

Two types of x-ray production interactions

Bremsstrahlung and Characteristic.

How x-ray energy is measured

Kilovoltage peak (kVp).

What kVp affects

Beam quality and penetration.

Ionization

Removal of an electron from an atom.

Coherent interaction

Low-energy interaction with no ionization; contributes little to imaging.

Compton interaction

Scattering interaction that involves outer-shell electrons and contributes to scatter.

Photoelectric effect

Total absorption of x-ray energy by inner-shell electrons; improves image contrast.

Compton scattering

Interaction that causes scatter.

Pair production

Interaction of high-energy x-rays with the nucleus, producing an electron and positron (occurs at energies >1.02 MeV).

Grid function in radiography

Absorbs scatter radiation to improve image contrast.

Types of grids

Parallel, crossed, and focused.

Grid cutoff

Loss of image density due to improper grid use.

Scatter control methods

Using collimation, proper kVp, smaller patient size, and grids.

Beam restriction devices

Aperture diaphragms, cones, and collimators.

SID effect on magnification

A longer SID reduces magnification.

OID effect on magnification

A larger OID increases magnification.

Object size and image size relationship

Greater distance or misalignment increases image size (magnification).

Factors increasing magnification

Large OID, short SID, tube angling.

Minimizing magnification

Use long SID and small OID.

Factors affecting radiographic contrast

Primarily kVp and scatter radiation.

Cardinal rules of radiation protection

Time, Distance, Shielding.

Direct vs indirect digital capture

Direct uses photoconductors; indirect uses scintillators and photodiodes.

Common image artifacts

Motion blur, distortion, noise.

Computed Radiography (CR) operation

Uses photostimulable phosphors that emit light when stimulated by a laser.

Role of a PACS Administrator

Manages digital image storage, retrieval, and system performance.

ALARA

As Low As Reasonably Achievable.

Image receptor exposure factor

mAs (milliampere-seconds).

Subject contrast factor

kVp.

CT contribution to radiation

CT (Computed Tomography) contributes the most man-made ionizing radiation to the public.

First law of electrostatics

Like charges repel; unlike charges attract.

Inverse Square Law

Intensity decreases by the square of the distance from the source.

Beta emission

A neutron is converted into a proton, and a beta particle (electron) is emitted.

Parts of an induction motor

Rotor (inside) and stator (outside).

Tungsten use for anode target

High atomic number, high melting point, efficient x-ray production.

Inventor of the first radiographic grid

Gustav Bucky.