Before the 1890s, the only way to see a broken bone or a tumour inside a living person was to cut them open. Today a doctor can watch a fetus's heart beat, find a tiny bleed in the brain, or see a torn ligament in a knee without a single incision. Each imaging technology uses a different kind of wave or field, so each sees certain tissues well and others poorly. Knowing how they work explains which one is chosen for which job. This lesson also looks at how knowledge of tissues and organs is used to protect whole populations, and at the hard ethical questions some technologies raise.
Seeing inside the body
| Technology | How it works | Best for | Drawbacks |
|---|---|---|---|
| X-ray | High-energy electromagnetic waves pass through soft tissue but are absorbed by dense tissue such as bone; a detector behind the body records the shadow | Broken bones, teeth, some chest problems such as pneumonia | Uses ionizing radiation (a small dose); soft tissues show poorly; flat image, so structures overlap |
| CT (computed tomography, or CAT) scan | An X-ray source and detector rotate around the body, taking many images; a computer combines them into cross-section slices and 3-D views | Internal bleeding, head injuries and strokes, tumours, complex fractures; very fast in emergencies | A much larger X-ray dose than a single X-ray image |
| MRI (magnetic resonance imaging) | A very strong magnet lines up hydrogen nuclei (mostly in water and fat); radio-wave pulses knock them out of line, and the signals they give off as they realign are turned into detailed images | Soft tissues: brain, spinal cord, ligaments, cartilage, many tumours | No ionizing radiation, but slow, loud, expensive, often has long wait times, and unsafe with some metal implants |
| Ultrasound | High-frequency sound waves, far above human hearing, are sent into the body; echoes from boundaries between tissues are timed to build a live image | Pregnancy, the heart (echocardiogram), abdominal organs, blood flow | No ionizing radiation and portable, but cannot see through bone or air-filled organs such as the lungs |
| Light microscopy and biophotonics | Light and lasers examine tissue samples or the body directly, for example through an endoscope camera | Examining biopsy samples for cancer cells; laser eye surgery; looking inside the digestive tract | Microscopy needs a tissue sample; light does not travel far through tissue |
- Has enough energy to damage DNA, so each scan adds a very small cancer risk
- A chest X-ray gives roughly the same dose as a few weeks of natural background radiation; an abdominal CT is closer to a few years' worth
- Used when the benefit of the information clearly outweighs the small risk
- Lead aprons shield parts of the body not being imaged
- Do not damage DNA, so they are preferred for pregnancy and repeated scans where they can do the job
- MRI's strong magnet can pull on some metal objects and implants, so patients are screened first
- Ultrasound is cheap, portable and gives live, moving images
- Each still has limits on what it can see
Public health: protecting whole populations
Public health works on the health of a whole community rather than one patient at a time. Its strategies are built on biology: cancer screening programs find tumours while they are small and local; vaccines train the immune system before a person meets a virus; education programs (for example, about tobacco, sun safety, or how HIV spreads and how to prevent it) lower the risk of disease before it starts.
| Vaccine | What it protects against | How it is given in Ontario |
|---|---|---|
| HPV vaccine | Infection with the types of human papillomavirus that cause most cervical cancers, as well as some throat, mouth and genital cancers and genital warts | Offered free to all students through a school-based program, starting in Grade 7 |
| MMR vaccine | Measles, mumps and rubella, three viral diseases that can cause brain swelling, deafness and (for rubella in pregnancy) serious birth defects | Two doses in early childhood; Ontario requires students to be immunized unless a valid exemption is filed |
Vaccines protect more than the person vaccinated. When enough of a community is immune, a virus cannot find enough new hosts to keep spreading, which protects babies too young to be vaccinated and people whose immune systems are weak. This is community (herd) immunity. Measles is so contagious that about 95% of people need to be immune to stop it. Canada had eliminated measles in 1998, but as vaccination rates fell, a large outbreak beginning in 2024 spread for more than a year, and in November 2025 Canada lost its measles elimination status.
Ethical questions in systems biology
| Issue | Possible benefits | Concerns people raise |
|---|---|---|
| Organ transplants from deceased or living donors | Save or greatly improve lives (kidney, liver, heart, lungs, corneas); one donor can help several people | Not enough donors; recipients need anti-rejection drugs for life; living donors take on surgical risk; fairness in who gets organs |
| Opt-out (presumed consent) donation | More registered donors; Nova Scotia adopted this system in 2021 | Some worry people are counted as donors without a real, informed choice |
| Transgenic animal organs (xenotransplants) | Pigs genetically modified so their organs are less likely to be rejected could ease the shortage | Risk of passing animal viruses to humans; animal welfare; long-term safety still unknown |
| Reproductive cloning | Could preserve endangered animals or copy valuable livestock (Dolly the sheep, 1996) | High failure rates and health problems in cloned animals; human reproductive cloning is banned in Canada |
| Stem cell therapies | Could repair tissues such as the heart, spinal cord or insulin-making cells | Use of embryos; risk of tumours; unproven treatments sold before testing |
- State the issue as a clear question (for example: should Ontario switch to opt-out organ donation?).
- Identify the stakeholders: patients, donors and their families, health workers, taxpayers.
- Gather reliable evidence about the benefits and the risks.
- Identify the values in conflict, such as saving lives, personal choice and fairness.
- Reach a reasoned position, and acknowledge the strongest point on the other side.