Medical Biophysics: Units, Physical Quantities, and Anatomical Coordinates

Vocabulary flashcards covering the definitions of biophysics, SI units, base and derived quantities, measurement errors, scalar and vector mechanics, and anatomical coordinate systems.

Medical Physics

The science of applying physics concepts, theories, and techniques to healthcare, with a focus on developing medical imaging technologies, therapeutic methods, and ensuring radiation safety in diagnostic and treatment processes.

Medical Biophysics

An interdisciplinary field that applies the principles and laws of physical sciences to describe and investigate biological processes for medical diagnosis and treatment, combining physics, biology, and medicine.

Physical Quantity

A measurable attribute that characterizes a physical phenomenon amenable to numerical specification, expressed mathematically as the product of a numerical value and a unit.

Unit

A selected reference sample of a quantity against which measurements are evaluated (e.g., $\text{m}$, $\text{kg}$, $\text{m}\,\text{s}^{-1}$).

Basic Quantities

The seven dimensionally independent physical quantities defined arbitrarily in the SI system: length (meter), mass (kilogram), time (second), electric current (Ampere), temperature (Kelvin), amount of substance (mole), and luminous intensity (candela).

Second ($\text{s}$)

The SI base unit of time, defined as the duration of $9{,}192{,}631{,}770$ oscillations of the radio waves absorbed by a vapor of cesium-133 atoms.

Meter ($\text{m}$)

The SI base unit of length, defined as the distance traveled by light in a vacuum during a time interval of $\frac{1}{299{,}792{,}458}$ of a second.

Kilogram ($\text{kg}$)

The SI base unit of mass, historically defined by the mass of an international standard platinum-iridium cylinder kept in Sèvres, France, serving as an artifact standard.

Supplementary Quantities

Dimensionless geometric quantities in the SI system, consisting of plane angle (measured in radians) and solid angle (measured in steradians).

Radian ($\text{rad}$)

The unit of plane angle, defined as the ratio of subtended arc length on a circle to its radius ($\theta = \frac{l}{r}$), where a complete circle contains $2\pi\,\text{radians}$.

Solid Angle ($\Omega$)

A dimensionless geometric quantity defined as the ratio of subtended area on a sphere to the radius squared ($\Omega = \frac{A}{r^2}$), measured in steradians, where a full sphere encompasses $4\pi\,\text{steradians}$.

Derived Quantities

Physical quantities defined as algebraic combinations (products or quotients) of two or more basic or supplementary quantities, such as velocity ($\text{m}\,\text{s}^{-1}$), acceleration ($\text{m}\,\text{s}^{-2}$), or energy ($\text{J} = \text{kg}\,\text{m}^2\,\text{s}^{-2}$).

Special Quantities

Quantities recognized by official authorities that are restricted to specific fields of physics despite sharing identical base units, such as activity measured in Becquerel ($1\,\text{Bq} = 1\,\text{s}^{-1}$) for radioactivity versus frequency measured in Hertz ($1\,\text{Hz} = 1\,\text{s}^{-1}$) for electrical circuits.

Systematic Errors

Inherent errors originating from apparatus or experimental methodology that consistently produce a constant deviation in measurements; categorized into constructional, determination, instrument, and environmental errors.

Random Errors

Statistical fluctuations in measured data in either direction caused by precision limitations of the measuring instrument or human inconsistency, which are minimized by averaging a large number of readings.

Scalar Quantity

A physical quantity described entirely by magnitude alone without spatial direction (e.g., distance, speed, mass, time, pressure, energy, volume, density).

Vector Quantity

A physical quantity that possesses both magnitude and direction in space (e.g., displacement, velocity, weight, acceleration, force, momentum).

Unit Vector

A dimensionless vector with a magnitude of exactly $1$ ($\hat{\mathbf{i}}$, $\hat{\mathbf{j}}$, $\hat{\mathbf{k}}$) that serves exclusively to specify direction along orthogonal coordinate axes without physical units.

Anatomical Planes

Hypothetical geometric planes used to section the human body in the standard anatomical position, consisting of the coronal (frontal), sagittal (median), and axial (transverse) planes.

Coronal (Frontal) Plane

An anatomical reference plane that divides the body into front (anterior/ventral) and back (posterior/dorsal) sections.

Sagittal Plane

An anatomical plane that divides the body vertically into right and left sections; when dividing the body into equal halves along the midline, it is termed the median or midsagittal plane.

Axial (Transverse) Plane

A horizontal anatomical plane that divides the body into upper (superior/cranial) and lower (inferior/caudal) segments.

Dextral vs. Sinistral

Anatomical directional terms defining orientation toward the subject's right side (dextral) versus left side (sinistral).

Superior (Cranial) vs. Inferior (Caudal)

Directional coordinates along the vertical axis; superior (cranial) refers to orientation toward the head or above (larger $z$), whereas inferior (caudal) indicates direction away from the head (smaller $z-$).

Anterior (Ventral) vs. Posterior (Dorsal)

Directional coordinates along the front-back axis; anterior (ventral) denotes toward or from the front of the body (larger $x$), whereas posterior (dorsal) denotes toward or from the back.

Medial vs. Lateral

Anatomical relative positions referring to distance from the center line; medial indicates closer to the midline, while lateral indicates farther from the midline.

Proximal vs. Distal

Positional terms relative to a point of attachment; proximal indicates closer to the point of attachment (smaller $r$), while distal indicates further away from the point of attachment (larger $r$).