Biophysics & Medical Physics

Absorbed Dose

The physical quantity measuring the amount of energy deposited by ionizing radiation per unit mass of matter.

D = dE / dm, 1 Gy = 1 J / kg = 100 rad Gy (Gray = J/kg)

Action Potential

A rapid, self-propagating electrical voltage impulse along the membrane of excitable cells (neurons and muscle cells).

v_conduction ∝ √(d) (Unmyelinated), v_conduction ∝ d (Saltatory Myelinated) mV (Amplitude ~100 mV) & m/s (Conduction Speed)

Biophysics & Medical Physics

Active Transport

The energy-requiring transport of ions or molecules across a biological cell membrane against their concentration gradient.

3 Na⁺_out + 2 K⁺_in per ATP Hydrolyzed (Sodium-Potassium Pump) Ions/sec or μmol/min

Biophysics & Medical Physics

ALARA Principle

A fundamental radiation protection safety principle stating that all radiation exposures must be kept 'As Low As Reasonably Achievable'…

Dose Optimization: Minimize Time, Maximize Distance, Optimize Shielding Radiation Safety Protocol

Biophysics & Medical Physics

Audiometry

The clinical evaluation and quantitative measurement of human hearing sensitivity across pure tone sound frequencies.

Hearing Level dB HL = 20 log₁₀(P_measured / P_reference) dB HL (Decibels Hearing Level) & Hz

Biophysics & Medical Physics

Bio-optics

The study of light interaction with biological tissues and the development of optical diagnostic and therapeutic instruments.

Radiative Transport Equation (RTE) in Turbid Tissues Scattering Coefficient μ_s (cm⁻¹) & Absorption μ_a (cm⁻¹)

Biophysics & Medical Physics

Bioenergetics

The branch of biophysics and biochemistry studying energy transformation, transfer, and coupling mechanisms in living organisms.

ΔG = ΔH - T ΔS, ΔG'° = -R T ln K_eq kJ/mol (Gibbs Free Energy)

Biophysics & Medical Physics

Bioimpedance

The measure of a biological tissue's opposition to the flow of electric alternating current.

Z = R + i X_c = √(R² + X_c²) Ω (Ohms)

Biophysics & Medical Physics

Biological Transducers

Specialized sensory receptor cells that convert external physical or chemical stimuli into graded bioelectrical signals.

Transduction: Physical Stimulus Energy → Receptor Potential (mV) mV / pA (Receptor Signal Output)

Biophysics & Medical Physics

Bioluminescence

The enzymatic production and emission of light by living organisms through chemical reactions converting ATP into photon energy.

Luciferin + O₂ + ATP → Oxyluciferin + AMP + PPi + h ν (Light) Photons/s (Bioluminescent Flux)

Biophysics & Medical Physics

Biomechanics of Gait

The quantitative analysis of human locomotion mechanics, muscle force coordination, and ground reaction forces during walking or running.

Center of Mass Inverted Pendulum Energy Exchange (T ↔ V) m/s (Walking Speed) & Ground Reaction Force (N)

Biophysics & Medical Physics

Bone Mechanics

The study of mechanical structural behavior, anisotropy, and remodeling of bone tissue under physical loads.

Stress σ = F / A, Young's Modulus E_cortical ≈ 18 GPa MPa / GPa (Tensile & Compressive Strength)

Biophysics & Medical Physics

Brachytherapy

An internal radiation therapy technique where sealed radioactive sources are placed directly inside or adjacent to a tumor.

Inverse Square Dose Falloff: D(r) ∝ 1 / r² Gy/h (High or Low Dose Rate)

Biophysics & Medical Physics

Cardiac Biomechanics

The application of solid and fluid mechanics principles to model heart chamber contraction, blood flow dynamics, and myocardial wall stress.

Wall Stress σ = (P × r) / (2 h) (Law of Laplace for Spheres) kPa (Myocardial Wall Stress) & mmHg (Pressure)

Biophysics & Medical Physics

Computed Tomography (CT Scan)

A diagnostic medical imaging modality combining rotating X-ray tubes and digital detectors with filtered back-projection algorithms to…

Hounsfield Unit HU = 1000 × (μ_tissue - μ_water) / (μ_water - μ_air) Hounsfield Units (HU, Water = 0, Air = -1000, Bone = +1000)

Biophysics & Medical Physics

Cytoskeleton Mechanics

The study of the mechanical properties, viscoelasticity, and force generation of the intracellular filament network (actin, microtubules…

Flexural Rigidity EI = E_young × I_area_moment pN·μm² (Bending Stiffness)

Biophysics & Medical Physics

DNA Biophysics

The physical study of mechanical stiffness, elasticity, topology, and base-pairing thermodynamics of double-stranded DNA.

Persistence Length A_p ≈ 50 nm, Contour Length L nm (Persistence Length) & pN (Stretching Force)

Biophysics & Medical Physics

Effective Dose

A radiation protection quantity representing the overall stochastic health risk to the whole body by weighting organ equivalent doses by…

E = ∑ H_T × w_T = ∑ D_T × w_R × w_T mSv (Millisieverts)

Biophysics & Medical Physics

Electro-osmosis

The motion of a liquid containing mobile ions through a porous biological membrane or microchannel driven by an applied electric field.

v_eo = (ε_r ε₀ ζ / η) E (Smoluchowski Equation) m/s (Electro-osmotic Velocity)

Biophysics & Medical Physics

Electrocardiography (ECG)

A non-invasive diagnostic technique recording the spatial bioelectric potential changes produced by heart muscle depolarization and…

Cardiac Dipole Vector P(t), Einthoven's Triangle Lead Vectors mV (Amplitude ~1 mV) & bpm (Heart Rate)

Biophysics & Medical Physics

Electroencephalography (EEG)

A non-invasive neurophysiological technique measuring electrical brain activity using surface scalp electrodes.

Frequency Bands: Delta (1–4Hz), Theta (4–8Hz), Alpha (8–12Hz), Beta (12–30Hz) μV (Microvolts ~10–100 μV) & Hz

Biophysics & Medical Physics

Electroporation

A biophysical technique applying short, high-voltage electric field pulses to cells to temporarily increase cell membrane permeability by…

Critical Transmembrane Breakdown Voltage V_c ≈ 0.5–1.0 V kV/cm (Electric Field Strength)

Biophysics & Medical Physics

Entropy in Biological Systems

The thermodynamic concept describing how open biological systems maintain high internal structural order by expelling heat and entropy to…

dS_system + dS_environment ≥ 0 (Schrödinger: 'Living on Negative Entropy') J/K (Entropy)

Biophysics & Medical Physics

Equivalent Dose

A radiation protection dose quantity weighing absorbed dose by the specific biological effectiveness factor w_R of the radiation type.

H = D × w_R (Radiation Weighting Factor w_R) Sv (Sievert = J/kg) or rem