Biophysics & Medical Physics

Fick's Laws of Diffusion

Physical laws describing solute diffusion mass transport across biological concentration gradients.

1st: J = -D (dC / dx); 2nd: ∂C / ∂t = D (∂²C / ∂x²) mol/(m²·s) (Flux J) & m²/s (Diffusion Coefficient D)

Fluorescence Microscopy

An optical microscopy technique utilizing fluorophores excited by specific light wavelengths to image cellular structures with high…

Abbe Diffraction Limit: d_min = λ / (2 NA) ≈ 200 nm nm (Spatial Resolution)

Biophysics & Medical Physics

Fluoroscopy

A dynamic X-ray imaging technique obtaining real-time moving video images of interior anatomical structures and contrast agents.

Real-time continuous low-dose X-ray video acquisition Frames per Second (fps) & Dose Rate (mGy/min)

Biophysics & Medical Physics

Goldman-Hodgkin-Katz Equation

An equation calculating resting membrane potential considering relative membrane permeabilities (P_Na, P_K, P_Cl) and concentrations of…

V_m = (R T / F) ln((P_Na[Na]_out + P_K[K]_out + P_Cl[Cl]_in) / (P_Na[Na]_in + P_K[K]_in + P_Cl[Cl]_out)) mV (Membrane Potential)

Biophysics & Medical Physics

Hemodynamics

The physical study of blood flow dynamics, vascular resistance, and pressure relations within the circulatory system.

Q = ΔP / R_v, R_v = (8 η L) / (π r⁴) (Poiseuille Flow) L/min (Cardiac Output) & mmHg (Pressure)

Biophysics & Medical Physics

Ion Channels

Pore-forming transmembrane proteins that allow selective passive passage of specific ions down their electrochemical gradient.

I_channel = g_channel (V_m - E_ion) pS (Picosiemens Conductance) & pA (Current)

Biophysics & Medical Physics

Linear Energy Transfer (LET)

A measure of the rate at which an ionizing radiation particle deposits ionization energy along its path length through biological tissue.

LET = dE / dx keV/μm (Kiloelectronvolts per micrometer)

Biophysics & Medical Physics

Magnetic Resonance Imaging (MRI)

A non-invasive medical imaging modality utilizing powerful magnetic fields, radiofrequency (RF) pulses, and nuclear magnetic resonance…

Larmor Frequency ν₀ = (γ / 2π) B₀ (γ_proton ≈ 42.58 MHz/T) Tesla B₀ (~1.5–3.0 T) & MHz

Biophysics & Medical Physics

Magnetoencephalography (MEG)

A non-invasive functional neuroimaging technique mapping brain activity by measuring weak magnetic fields produced by neuronal electric…

Magnetic Field B ~ 10–100 fT (10⁻¹⁵ Tesla) fT (Femtoteslas = 10⁻¹⁵ T)

Biophysics & Medical Physics

Medical Lasers

Laser devices engineered for surgical cutting, tissue coagulation, and photomedical treatments exploiting specific light-tissue absorption…

Selective Photothermolysis: Laser Pulse Duration ≤ Thermal Relaxation Time τ_r W or J/cm² (Fluence)

Biophysics & Medical Physics

Medical Linear Accelerator (LINAC)

A high-energy medical accelerator generating megavoltage X-ray photon or electron beams for external beam radiation cancer therapy.

RF Cavity Electron Acceleration to 6–18 MeV → Bremsstrahlung X-Rays MV (Megavoltage Photon Beams 6–18 MV)

Biophysics & Medical Physics

Medical Ultrasound

A non-invasive diagnostic imaging modality using high-frequency acoustic waves (2–15 MHz) to image soft tissue reflection interfaces.

R = ((Z₂ - Z₁) / (Z₂ + Z₁))², Z = ρ c (Acoustic Impedance) MHz (Frequency 2–15 MHz) & MRayl (Acoustic Impedance)

Biophysics & Medical Physics

Membrane Potential

The electrical potential difference across a biological cell membrane produced by asymmetric ion concentration gradients.

V_m = V_in - V_out (Resting Potential ≈ -70 mV) mV (Millivolts)

Biophysics & Medical Physics

Molecular Motors

Protein-based molecular machines that convert chemical energy from ATP hydrolysis into mechanical work and linear movement.

F_step ≈ 6 pN, Step Size d ≈ 8 nm (Kinesin on Microtubule) pN (Piconewtons) & nm (Step Length)

Biophysics & Medical Physics

Nanomedicine

The medical application of nanotechnology utilizing engineered nanoparticles for disease diagnosis, targeted drug delivery, and therapy.

EPR Effect: Enhanced Permeability and Retention in Tumors nm (Nanoparticle Diameter ~10–100 nm)

Biophysics & Medical Physics

Nernst Equation in Biophysics

An equation calculating the exact electrical equilibrium potential across a membrane permeable to a single ion species.

E_ion = (R T / (z F)) ln([Ion]_out / [Ion]_in) mV (Equilibrium Potential)

Biophysics & Medical Physics

Neurophysics

The interdisciplinary field applying physical principles and non-linear mathematical modeling to study nervous system function.

Hodgkin-Huxley Model: C_m (dV/dt) = I_ext - g_Na m³ h (V-E_Na) - g_K n⁴ (V-E_K) - g_L (V-E_L) Biophysical Neural Network Model

Biophysics & Medical Physics

Optical Tweezers

A biophysical instrument using a strongly focused laser beam to trap, manipulate, and exert piconewton forces on microscopic dielectric…

F_gradient = ½ α ∇(E²), Hooke's Law F = -k_trap x pN (Piconewton Forces ~0.1–100 pN)

Biophysics & Medical Physics

Osmosis

The net passive diffusion of solvent molecules (water) across a selectively permeable membrane from lower solute concentration toward…

Π = i C R T (van 't Hoff Equation) Pa or kPa (Osmotic Pressure)

Biophysics & Medical Physics

Patch Clamp Technique

An electrophysiological laboratory technique used to record ion currents flowing through single individual ion channel proteins in cell…

I_single_channel ~ 1–10 pA (Gigaohm Seal Measurement) pA (Picoamperes) & GΩ (Gigaohm Resistance)

Biophysics & Medical Physics

Poiseuille's Law of Blood Flow

A fluid dynamics equation governing laminar viscous fluid flow through a cylindrical vascular pipe.

Q = (π r⁴ ΔP) / (8 η L) m³/s or L/min (Volumetric Flow Rate)

Biophysics & Medical Physics

Positron Emission Tomography (PET Scan)

A 3D nuclear medicine imaging technique detecting pairs of 511 keV gamma photons emitted during positron annihilation to map metabolic…

Coincidence Detection of 180° Back-to-Back 511 keV Gamma Photons MBq (Activity) & Standardized Uptake Value (SUV)

Biophysics & Medical Physics

Protein Folding

The physical process by which a polypeptide chain folds spontaneously into a characteristic 3D functional native structure.

Energy Funnel Concept: Minimizing Native State Free Energy G kJ/mol (Conformational Stability)

Biophysics & Medical Physics

Proton Therapy

An advanced form of external beam radiation therapy utilizing accelerated proton beams to destroy cancerous tumors.

Bragg Peak Energy Deposition Curve: (-dE/dx) ∝ 1 / v² MeV (Proton Beam Energy ~70–250 MeV)