Biophysics & Medical Physics — 60 Terms Defined

Fick's Laws of Diffusion Biophysics & Medical Physics mol/(m²·s) (Flux J) & m²/s (Diffusion Coefficient D) Physical laws describing solute diffusion mass transport across biological concentration gradients. 1st: J = -D (dC / dx); 2nd: ∂C / ∂t = D (∂²C / ∂x²)

Fluorescence Microscopy Biophysics & Medical Physics nm (Spatial Resolution) An optical microscopy technique utilizing fluorophores excited by specific light wavelengths to image cellular structures with high contrast. Abbe Diffraction Limit: d_min = λ / (2 NA) ≈ 200 nm

Fluoroscopy Biophysics & Medical Physics Frames per Second (fps) & Dose Rate (mGy/min) 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

Goldman-Hodgkin-Katz Equation Biophysics & Medical Physics mV (Membrane Potential) An equation calculating resting membrane potential considering relative membrane permeabilities (P_Na, P_K, P_Cl) and concentrations of multiple key ion species. 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))

Hemodynamics Biophysics & Medical Physics L/min (Cardiac Output) & mmHg (Pressure) 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)

Ion Channels Biophysics & Medical Physics pS (Picosiemens Conductance) & pA (Current) Pore-forming transmembrane proteins that allow selective passive passage of specific ions down their electrochemical gradient. I_channel = g_channel (V_m - E_ion)

Linear Energy Transfer (LET) Biophysics & Medical Physics keV/μm (Kiloelectronvolts per micrometer) A measure of the rate at which an ionizing radiation particle deposits ionization energy along its path length through biological tissue. LET = dE / dx

Magnetic Resonance Imaging (MRI) Biophysics & Medical Physics Tesla B₀ (~1.5–3.0 T) & MHz A non-invasive medical imaging modality utilizing powerful magnetic fields, radiofrequency (RF) pulses, and nuclear magnetic resonance (NMR) of hydrogen protons to image soft tissue. Larmor Frequency ν₀ = (γ / 2π) B₀ (γ_proton ≈ 42.58 MHz/T)

Magnetoencephalography (MEG) Biophysics & Medical Physics fT (Femtoteslas = 10⁻¹⁵ T) A non-invasive functional neuroimaging technique mapping brain activity by measuring weak magnetic fields produced by neuronal electric currents using SQUID sensors. Magnetic Field B ~ 10–100 fT (10⁻¹⁵ Tesla)

Medical Lasers Biophysics & Medical Physics W or J/cm² (Fluence) Laser devices engineered for surgical cutting, tissue coagulation, and photomedical treatments exploiting specific light-tissue absorption interactions. Selective Photothermolysis: Laser Pulse Duration ≤ Thermal Relaxation Time τ_r

Medical Linear Accelerator (LINAC) Biophysics & Medical Physics MV (Megavoltage Photon Beams 6–18 MV) 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

Medical Ultrasound Biophysics & Medical Physics MHz (Frequency 2–15 MHz) & MRayl (Acoustic Impedance) 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)

Membrane Potential Biophysics & Medical Physics mV (Millivolts) 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)

Molecular Motors Biophysics & Medical Physics pN (Piconewtons) & nm (Step Length) 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)

Nanomedicine Biophysics & Medical Physics nm (Nanoparticle Diameter ~10–100 nm) The medical application of nanotechnology utilizing engineered nanoparticles for disease diagnosis, targeted drug delivery, and therapy. EPR Effect: Enhanced Permeability and Retention in Tumors

Nernst Equation in Biophysics Biophysics & Medical Physics mV (Equilibrium Potential) 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)

Neurophysics Biophysics & Medical Physics Biophysical Neural Network Model 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)

Optical Tweezers Biophysics & Medical Physics pN (Piconewton Forces ~0.1–100 pN) A biophysical instrument using a strongly focused laser beam to trap, manipulate, and exert piconewton forces on microscopic dielectric particles or biological molecules. F_gradient = ½ α ∇(E²), Hooke's Law F = -k_trap x

Osmosis Biophysics & Medical Physics Pa or kPa (Osmotic Pressure) The net passive diffusion of solvent molecules (water) across a selectively permeable membrane from lower solute concentration toward higher solute concentration. Π = i C R T (van 't Hoff Equation)

Patch Clamp Technique Biophysics & Medical Physics pA (Picoamperes) & GΩ (Gigaohm Resistance) An electrophysiological laboratory technique used to record ion currents flowing through single individual ion channel proteins in cell membranes. I_single_channel ~ 1–10 pA (Gigaohm Seal Measurement)

Poiseuille's Law of Blood Flow Biophysics & Medical Physics m³/s or L/min (Volumetric Flow Rate) A fluid dynamics equation governing laminar viscous fluid flow through a cylindrical vascular pipe. Q = (π r⁴ ΔP) / (8 η L)

Positron Emission Tomography (PET Scan) Biophysics & Medical Physics MBq (Activity) & Standardized Uptake Value (SUV) A 3D nuclear medicine imaging technique detecting pairs of 511 keV gamma photons emitted during positron annihilation to map metabolic activity. Coincidence Detection of 180° Back-to-Back 511 keV Gamma Photons

Protein Folding Biophysics & Medical Physics kJ/mol (Conformational Stability) 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

Proton Therapy Biophysics & Medical Physics MeV (Proton Beam Energy ~70–250 MeV) 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