Medical Physics

Chapter Overview

Medical Physics bridges fundamental physical theories with modern clinical healthcare and biomedical engineering. The chapter opens with Ultrasound and the Piezoelectric Effect, explaining how piezoelectric transducer crystals (such as quartz or lead zirconate titanate) mechanically oscillate when driven by high-frequency alternating voltages to emit ultrasound beams into human tissue. Returning echoes reflected at acoustic impedance boundaries deform the crystal in reverse, generating electrical waveforms. Factors influencing ultrasound image quality-including acoustic impedance mismatch (Z = ρc), acoustic attenuation, transducer operating frequency, pulse duration, and resolution limits-are examined alongside diagnostic applications in obstetrics, cardiology, and soft-tissue scanning.

The chapter subsequently explores diagnostic radiology through X-Rays, elucidating how high-velocity thermionic electrons accelerated through kilovolt potentials bombard high-melting-point metallic targets (such as tungsten or molybdenum) inside vacuum tubes. The physical origin of the Continuous X-ray Spectrum (Bremsstrahlung or braking radiation) is established, showing that rapid electron deceleration converts kinetic energy directly into photons with minimum wavelength cutoff λ_min = hc/(eV). Planar X-ray radiography principles and differential tissue absorption (attenuation by bone versus soft tissue) lead directly into advanced Computed Tomography (CT-Scan) systems, which rotate thin X-ray beams through multiple projection angles to digitally reconstruct cross-sectional slices and eliminate 3D structural overlap.

The curriculum culminates in nuclear medicine imaging and oncology via Positron Emission Tomography (PET). PET uses biologically targeted radiopharmaceuticals (such as fluorodeoxyglucose, FDG) labeled with positron-emitting isotopes that accumulate in hyper-metabolic neoplastic cells. Emitted positrons rapidly encounter tissue electrons, undergoing matter-antimatter annihilation to generate two collinear 511 keV gamma photons captured by coincidence detector rings. Finally, the chapter details the role of medical physics in cancer treatment, comparing radiotherapy delivery methods (linear accelerators for external beam radiation and brachytherapy implants) and the biophysical principles of radiation protection and dose optimization.