Last revised 5/21/2026

Physithon - Biophysics & Medical Physics

Secondary

Molecular and cellular biophysics, medical imaging (CT, MRI, ultrasound, PET), radiation therapy, biomechanics, and optical methods — the physics applied inside life sciences and medicine.

Explore the intersection of physics and life sciences. This collection covers molecular and cellular biophysics (protein folding, membrane physics, molecular motors), medical imaging (X-ray, CT, MRI, ultrasound, PET/SPECT), radiation therapy physics (dose planning, proton therapy, brachytherapy), biomechanics (fluid dynamics of blood flow, musculoskeletal mechanics), and optical methods (fluorescence microscopy, spectroscopy, laser-tissue interaction). Perfect for physics competition students interested in biomedical applications.

Academic primerPhysics olympiad prep

Earn2CreditsinPhysics

5Modules16Sessions209Cards67Quizzes

Modules in this Collection’s System

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Molecular and Cellular Biophysics

Protein folding (Anfinsen's principle), membrane physics, ion channels, and molecular motors — the cellular machinery taught as physics.

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4Sessions

Medical Imaging Physics

X-ray, CT, MRI, ultrasound, PET, and SPECT — the physics behind every major medical imaging modality and the clinical questions each answers best.

5Sessions

Radiation Therapy Physics

MV photon beams, proton therapy (Bragg peak), brachytherapy, dose planning, and the radiobiology behind effective cancer treatment.

3Sessions

Biomechanics

Pulsatile blood flow, Womersley number, musculoskeletal mechanics, and the fluid dynamics underlying cardiovascular disease.

2Sessions

Optical and Spectroscopic Methods

Fluorescence microscopy, super-resolution techniques (STED, PALM, STORM), spectroscopy, and laser-tissue interactions across thermal to ablative regimes.

2Sessions

What You'll Walk Away With

1medical imaging modality comparison — X-ray, CT, MRI, ultrasound, PET, SPECT — on physical principle, spatial/temporal resolution, contrast mechanism, and clinical use cases
1radiation therapy planning primer covering MV photon beams, proton Bragg peak, brachytherapy sources, dose units (Gy), and the radiobiology behind fractionation schedules
1molecular motor reference mapping myosin, kinesin, dynein, and F-ATPase to their cellular roles and the ATP-to-mechanical-work conversion mechanism
1fluorescence microscopy toolkit covering basic fluorescence, confocal, multi-photon, and the super-resolution methods (STED, PALM, STORM) that broke the diffraction limit
1biomechanics quick-reference on blood flow (Womersley number, pulsatility), musculoskeletal mechanics, and the fluid dynamics behind cardiovascular disease

You'll Have Answers To

?Why does Anfinsen's principle (sequence determines fold) make protein misfolding the mechanism behind Alzheimer's, Parkinson's, and prion diseases?
?How do molecular motors (myosin, kinesin, F-ATPase) convert ATP chemistry into mechanical work — one stochastic step at a time?
?Why does each medical imaging modality (X-ray, MRI, ultrasound, PET) exploit different physics — and how do clinicians match modality to question?
?What makes the proton Bragg peak superior to photon beams for treating pediatric tumors and cancers near critical structures?
?How did fluorescence microscopy and the super-resolution techniques (STED, PALM, STORM) break the diffraction limit and revolutionize cell biology?

Critical Concepts Explored

Anfinsen's principle and protein foldingLipid bilayers and ion channelsMolecular motors (myosin, kinesin, F-ATPase)X-ray, CT, MRI, ultrasound, PET, SPECTLinear accelerators and MV photon beamsProton therapy and the Bragg peakBrachytherapy and dose units (Gy)Womersley number and pulsatile blood flowFluorescence microscopy and GFPSuper-resolution techniques (STED, PALM, STORM)

Editor's Note

“Biophysics and medical physics taught as physics — for students who want both”

This collection covers a remarkably wide range — protein folding, ion channels, every major medical imaging modality, radiation therapy, biomechanics, and fluorescence microscopy — without ever losing the physics through-line. Each topic earns its place by the physical principle it exploits, and the medical applications never substitute for the mechanism. A genuinely Physithon-grade biophysics primer.

Editor's Brief

Who it's for: Physithon competitors preparing for biophysics and medical physics rounds, pre-medical and biomedical-engineering students who want the physics treated rigorously, and physics students looking to bridge into life-science applications.
What stands out: The collection treats the medical applications as physics, not biology — every imaging modality, every therapy, every cellular machine is introduced through the physical principle that makes it work.
Read if: You want to understand how MRI, proton therapy, and super-resolution microscopy actually work — at the level of the physical principles, not the marketing brochures.

Gold Quotes

Anfinsen's principle (1961) showed that a protein's native structure is the global free-energy minimum — the sequence determines the fold. The corollary: misfolding is what produces Alzheimer's amyloid, prion diseases, and most neurodegenerative conditions.

A folded protein achieves its functional shape because evolution selected sequences whose lowest-energy configuration matches the required function. Misfolding can produce stable aggregates (amyloid plaques) that resist clearance and accumulate. Alpha-synuclein in Parkinson's, beta-amyloid in Alzheimer's, PrPSc in prion diseases — all share the structural-misfolding signature. Modern drug development increasingly targets the misfolding process itself.

Each medical imaging modality exploits different physics, and that difference determines what tissue and what pathology it can see. There is no universal best modality — there are right modalities for specific clinical questions.

X-ray and CT image electron density (great for bone, calcified plaque, lung air spaces). MRI images proton spin precession in magnetic fields (great for soft tissue, brain, spinal cord). Ultrasound images acoustic impedance differences (great for fluid-filled structures, real-time imaging). PET images positron annihilation from radiolabeled tracers (great for metabolic activity, tumor staging). Choosing the wrong modality produces no diagnostic value at substantial cost.

The Bragg peak — a sharp dose maximum at the end of a charged particle's range — is why proton therapy can deliver high doses to tumors while sparing surrounding tissue.

Photons (conventional radiation therapy) deposit energy along the entire beam path, exposing healthy tissue both before and after the tumor. Protons slow as they travel, depositing maximum energy at a depth determined by initial energy, then stopping. Tumor depth can be matched to the Bragg peak; tissue beyond the tumor receives essentially zero dose. This is why proton therapy is preferred for pediatric cancers and tumors near critical structures, despite the much higher facility cost.

About the Curator

AAcademic Marathon

Academic Marathon is the editorial voice behind LearningFirst's Physithon and Biothon competition-prep collections — producing rigorous, mathematically grounded primers across the cutting-edge sub-disciplines of physics and biology that competition-track high-school students need to know.