Medical physics

About this lab: Medical physics

Interactive simulation for Cambridge A Level Physics 9702 topic 24 Medical physics: an ultrasound pulse reflecting at tissue boundaries with the reflected fraction from the acoustic impedances, echo timing and an A-scan, attenuation with depth and frequency, the X-ray tube with its continuous and characteristic spectrum, the eV cut-off and attenuation I = I₀e^(−μx) for lung, soft tissue, bone, contrast medium and lead with half-value thickness, and a PET scanner ring with positron annihilation into two 0.511 MeV photons detected in coincidence.

Ultrasound echoes and acoustic impedance, the X-ray tube spectrum and attenuation, and positron emission tomography

Medical physics is a free, browser-based simulation for Cambridge International AS & A Level Physics 9702 (topic 24 Medical physics). The course is assessed in Paper 1 (multiple choice), Paper 2 (AS structured), Paper 3 (advanced practical), Paper 4 (A Level structured) and Paper 5 (planning, analysis and evaluation). There are 3 tabs, each a self-contained experiment with its own controls and live readings, and nothing to install: it runs on a laptop, tablet or classroom projector.

Syllabus coverage

• 24.1 Production and use of ultrasound: Piezoelectric crystals: changing shape and generating e.m.f.; Ultrasound generation and detection (piezoelectric transducer); Pulse reflection at tissue boundaries; Specific acoustic impedance: Z = ρc; Intensity reflection coefficient: I_R/I₀ = (Z₁ − Z₂)²/(Z₁ + Z₂)²; Attenuation: I = I₀ e^(−μx). Lessons: Production and use of ultrasound.
• 24.2 Production and use of X-rays: X-ray production by electron bombardment; X-ray imaging and contrast; X-ray attenuation: I = I₀ e^(−μx); CT scanning: 2D sections combined into 3D images. Lessons: Production and use of X-rays.
• 24.3 PET scanning: Radioactive tracers in the body; β⁺ decay tracers and positron annihilation; Gamma-ray pair detection and image construction. Lessons: PET scanning.

Full syllabus map: A Level Physics 9702 topic 24.

How to use this simulation

1. 1. Ultrasound.
2. 2. X-rays.
3. 3. PET scanning.
4. The buttons at the end of the tab strip give the scene the whole window (Full screen, Hide controls) and, on a dark stage, a projector-friendly palette (Light scene). Many scenes also have drag handles: drag them to change the set-up directly.

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