Introduction to Radiology Lecture Notes

A collection of vocabulary terms covering the fundamentals of radiology, including X-ray, CT, MRI, and ultrasound imaging principles and safety, and history.

Radiology

A branch of medicine that uses imaging technology to diagnose and treat disease, derived from the Latin word Radius meaning ray.

Wilhelm Roentgen

A German physicist who discovered X-rays in 1895 while experimenting with electron beams in a gas discharge tube.

X-ray Tube Efficiency

An energy converter that transforms electrical energy into x-radiation ($1\%$) and heat ($99\%$).

Thermionic Emission

The process by which a filament, acting as a cathode, is heated to release electrons within an x-ray tube.

Radiodense

Materials such as bone, calcium, barium, and metal that appear white on radiographs because they absorb more X-rays.

Radiolucent

Substances such as air and fat that allow X-rays to pass through more easily, appearing dark or black on radiographs.

ALARA

A radiation safety guiding principle that stands for "as low as reasonably achievable."

Contrast Agent

A substance, such as Iodine or Barium, used to increase the contrast of structures or fluids within the body during medical imaging.

Barium Sulphate ($BaSO_4$)

An insoluble, chalky powder mixed with water to create a liquid used during swallowing tests to improve X-ray visibility.

Breast Tomosynthesis

Advanced 3D mammography that reconstructs multiple images from different angles into a three-dimensional image set.

Godfrey Hounsfield and Allan M. Cormack

The creators of the first Computed Tomography scanner who shared the Nobel Prize in Medicine in 1979.

Gantry

The circular tube in a CT scanner that houses the X-ray generator and the detector, which are located $180$ degrees apart.

Axial Plane

Also known as the transverse plane; a horizontal plane that divides the body into superior (upper) and inferior (lower) sections.

Coronal Plane

Also known as the frontal plane; a vertical plane that divides the body into anterior (front) and posterior (back) sections.

Sagittal Plane

Also known as the median plane; a vertical plane that divides the body into right and left parts.

Hounsfield Unit (HU)

A scale for describing radiodensity in CT scans, where $-1000$ is air, $0$ is water, and $1000$ is cortical bone.

Xenon CT

A rare CT technique involving inhaled gas contrast used for special lung and brain imaging.

Echogenicity

The characteristic ability of a tissue or substance to reflect sound waves and produce echoes in ultrasound imaging.

Hyperechoic

A term used in ultrasound to describe structures that appear bright, such as bone, gas, or stones.

Hypoechoic

A term used in ultrasound to describe structures that appear dark, such as fluid, urine, or bile.

Doppler Ultrasound

A type of ultrasound using sound waves to measure the flow of blood through vessels, often used for fetuses with intrauterine growth restriction (IUGR).

Gadolinium

The contrast material specifically used for Magnetic Resonance Imaging (MRI).

MRI Signal Basis

Hydrogen atoms found in water and fat, which emit signals when placed in a magnetic field.

MRI Contraindications

Medical items that prohibit the use of MRI, including Heart Pacemakers, Aneurismal Clips, and Cochlear Implants.

T1 Weighted Sequence

An MRI sequence where fluid appears as low signal intensity (black) and fat appears as high signal intensity (white).

T2 Weighted Sequence

An MRI sequence where fluid, CSF, and the bladder appear as high signal intensity (white).

Fiber Tractography

A 3D reconstruction technique used in medical imaging to assess neural tracts.