Medical Technology: X-ray, CT Scan and Ultrasound
Medical technology is a recurring subject in the 'Science in Daily Life' section of the REET Level 2 Maths-Science syllabus, where questions are built around the principles, discoverers and uses of X-ray, CT scan and ultrasound. This page explains all three technologies in terms of how they work, how they differ, and how best to teach them in class.
- No direct REET 2024 question, syllabus-based
- Class 6-8 level
- 8 min read
How this topic is asked in REET
We currently have no verified direct question on medical technology from the REET 2024 paper on record, so we are not showing any fabricated past question here — this note is based entirely on the wording of the official REET Level 2 Science syllabus ('Application of Science in Daily Life') and NCERT-level understanding. Since this topic is clearly included in the syllabus, there is a strong chance that a direct question on the principle, discoverer, or use of X-ray/CT/ultrasound will appear in upcoming papers.
X-ray: the first ray to peek inside the body
X-ray is a high-energy electromagnetic radiation, discovered by the German scientist Wilhelm Röntgen in 1895 — for this discovery, he was awarded the very first Nobel Prize in Physics in 1901.
X-rays have a very short wavelength and very high energy, so they pass straight through soft tissue (skin, muscle) but get stopped/absorbed by dense parts like bone. This difference is what creates a clear shadow of the bone on a photographic plate or detector — which is why the most common use of X-ray is checking for a bone fracture, examining teeth, and checking the lungs with a chest X-ray.
X-ray is an ionising radiation — repeated or excessive exposure to it can be harmful to the body's cells, which is why the rest of the body is covered with a lead apron while taking an X-ray.
CT scan: a layered picture taken from many angles
CT stands for Computed Tomography. It also uses X-rays, but not from a single direction — the machine rotates around the body and takes hundreds of X-ray images from different angles, and a computer combines all of them to create a 'slice'-like cross-sectional image of an organ in the body.
This technology is built on the work of Godfrey Hounsfield (an engineer, England) and Allan Cormack (a physicist), for which both jointly received the Nobel Prize in Medicine in 1979.
In an ordinary X-ray, all the organs overlap in a single flat image, whereas a CT scan can show soft organs like the brain, lungs and liver layer by layer, with much greater clarity — this is why CT scans are preferred for checking serious injuries, internal bleeding, or tumours. Since it too is based on X-rays, the radiation dose in a CT scan is also higher than in a regular X-ray.
Ultrasound (sonography): a picture built from sound waves
An ultrasound machine uses no radiation at all — instead, it uses high-frequency sound waves (above about 20,000 hertz) that the human ear cannot hear. A transducer (probe) sends these waves into the body; the echo bouncing back off different tissues is captured, and a computer screen builds a moving picture from it.
Because it involves no ionising radiation at all, it is considered relatively safe — this is why ultrasound is the standard technique for checking the foetus during pregnancy (sonography). It is also used to examine abdominal organs, the heart (echocardiography), and the kidneys.
Worth noting: in India, using ultrasound to check the sex of a foetus is legally prohibited under the PC-PNDT Act, 1994 — the purpose of sonography is meant to be health-related examination only.
Comparing the three technologies
| Technology | Basis | Radiation? | Main use |
|---|---|---|---|
| X-ray | Electromagnetic waves (ionising) | Yes | Bone fracture, teeth, chest examination |
| CT scan | X-rays from many angles + computer | Yes (higher dose) | Brain, internal injury, tumours |
| Ultrasound | High-frequency sound waves | No | Pregnancy check, abdomen and heart examination |
All three technologies work on a different principle, so their safety level and use also differ.
Related terms that may appear in the syllabus
- Radiography
- The process/technique of creating internal images of the body using X-rays.
- Radiologist
- A specialist doctor who reads imaging reports such as X-ray, CT and ultrasound to diagnose disease.
- MRI (Magnetic Resonance Imaging)
- A technology different from X-ray or CT — it uses a magnetic field and radio waves, and involves no ionising radiation; it gives a very clear picture of soft tissues (brain, nerves).
- Use of a lead apron
- During an X-ray/CT, a lead apron is worn to protect the rest of the body from unnecessary radiation.
How to teach this to students
Activity
Shine a torch on a hand to show the shadow of the bones on a wall, and explain that the dense part (bone) blocks the light/ray, while it passes straight through the thin skin — this is the basic principle of an X-ray. This can also be done as a group 'shadow box' activity.
Teaching aids
Showing a real X-ray film, a printed CT scan image, and a sonography report (if available) in class makes it easier for children to understand the difference between the technologies. Bringing an old, name-redacted report from a nearby hospital/diagnostic centre is a practical option.
Common misconception
Children often think all three technologies are 'the same kind of machine'. Make it clear that only X-ray and CT are based on radiation, while ultrasound is based on sound — which is why only ultrasound is considered safe during pregnancy. Also clarify that having radiation does not mean 'dangerous' but rather 'safe in a limited, controlled amount'.
Assessment
Have students classify all three technologies in a table based on principle, radiation, and use — this checks both understanding and recall. Then ask verbally which technology would be suitable in a given situation (like a broken bone or a pregnancy check).
A trick to remember this
'S for Sound, Safe' — remember that in ultrasound, S stands for both Sound and Safe; the other two — X-ray and CT — both involve Radiation, remember 'X and C both have Ray'. In the exam, the question is often which technology is 'radiation-free' — the answer is always ultrasound.
Practice questions
Question 1
Which scientist discovered X-rays?
- Aविल्हेम रॉन्टजन
- Bमैरी क्यूरी
- Cआइज़क न्यूटन
- Dजगदीश चंद्र बोस
Explanation
German scientist Wilhelm Röntgen discovered X-ray in 1895 and was awarded the first Nobel Prize (in Physics) in 1901 for this discovery.
Question 2
Why does bone appear white/clear in an X-ray image?
- Aहड्डी में पानी अधिक होता है
- Bहड्डी X-ray किरणों को अवशोषित कर लेती है
- Cहड्डी प्रकाश उत्सर्जित करती है
- Dहड्डी चुम्बकीय होती है
Explanation
Bone is dense tissue, so it absorbs most of the X-rays and fewer rays reach the detector, which creates a clear shadow/image of that part.
Question 3
What is the full form of CT scan?
- AComplete Tomography
- BCellular Tomography
- CComputed Tomography
- DContrast Technique
Explanation
CT stands for Computed Tomography — a layered image built with the help of a computer.
Question 4
Why is a CT scan able to give a clearer image than a normal X-ray?
- Aयह ध्वनि तरंगों का उपयोग करता है
- Bयह चुम्बकीय क्षेत्र का उपयोग करता है
- Cयह लेज़र किरण का उपयोग करता है
- Dयह कई कोणों से लिए गए चित्रों को जोड़कर क्रॉस-सेक्शन बनाता है
Explanation
A CT scan machine rotates around the body and takes X-ray images from many angles, which a computer combines to build a layer-by-layer picture of the organ — this is why it is clearer than a regular X-ray.
Question 5
On which principle does an ultrasound machine work?
- Aउच्च-आवृत्ति ध्वनि तरंगों की प्रतिध्वनि
- Bआयनकारी विकिरण
- Cचुम्बकीय अनुनाद
- Dप्रकाश के अपवर्तन
Explanation
An ultrasound machine sends out high-frequency sound waves and builds a picture from the echo bouncing back off tissues; it does not involve radiation.
Question 6
Which technique is generally preferred for examining the foetus during pregnancy?
- ACT स्कैन
- Bअल्ट्रासाउंड (सोनोग्राफी)
- Cसाधारण X-ray
- Dइनमें से कोई नहीं
Explanation
Ultrasound involves no ionising radiation, which is why it is considered relatively safe for checking the foetus during pregnancy.
Question 7
Godfrey Hounsfield and Allan Cormack received the 1979 Nobel Prize for which achievement?
- Aअल्ट्रासाउंड के विकास के लिए
- BX-ray की खोज के लिए
- CCT (कम्प्यूटेड टोमोग्राफी) तकनीक के विकास के लिए
- DMRI तकनीक के विकास के लिए
Explanation
Godfrey Hounsfield and Allan Cormack jointly received the 1979 Nobel Prize in Medicine for developing CT (Computed Tomography) technology, which was based on their work.
Question 8
Which simple activity is most suitable for a science teacher to demonstrate the principle of X-rays in class?
- Aपानी में नमक घोलना
- Bचुम्बक से लोहे की कील उठाना
- Cपौधे में जड़ का प्रयोग दिखाना
- Dटॉर्च की रोशनी में हाथ की हड्डी की छाया दिखाना
Explanation
Showing the shadow of a hand's bones in torchlight simply demonstrates that a dense part blocks the ray/light while a thin part lets it pass through — this is the basic idea behind X-ray imaging.
Question 9
Which of the following techniques does NOT use ionizing radiation?
- Aअल्ट्रासाउंड
- BX-ray
- CCT स्कैन
- DA और B दोनों
Explanation
Ultrasound is based on sound waves, so unlike X-ray and CT scan, it does not involve ionising radiation.
Question 10
Which is the most suitable assessment method to check understanding of all three medical technologies in class?
- Aकेवल परिभाषा रटवाना
- Bसिद्धांत, विकिरण और उपयोग के आधार पर तुलनात्मक तालिका बनवाना
- Cकोई मूल्यांकन न करना
- Dकेवल चित्र बनवाना
Explanation
Having students build a comparative table based on principle, radiation, and use checks both their understanding and their ability to classify, which is a better proof of learning than rote memorisation alone.
Frequently asked questions
Who discovered X-ray and when?+
German scientist Wilhelm Röntgen discovered X-ray in 1895, for which he received the very first Nobel Prize in Physics in 1901. Since it was an 'unknown ray' at the time of discovery, it was named X-ray, and it is still known by that name today.
What is the main difference between a CT scan and a regular X-ray?+
A regular X-ray is a flat image taken from a single direction, while a CT scan combines X-ray images taken from many angles using a computer to build a layer-by-layer (cross-sectional) image of an organ, which is much clearer. This is also why a CT scan costs more than a regular X-ray.
Why is ultrasound considered safe during pregnancy?+
Ultrasound is based on sound waves and does not involve the ionising radiation of an X-ray or CT scan, which is why it is considered relatively safe for checking the foetus.
What is the difference between MRI, CT and X-ray?+
Both X-ray and CT are based on X-rays (ionising radiation), while MRI is based on a magnetic field and radio waves and involves no ionising radiation. MRI gives the clearest picture of soft tissues (such as the brain and nerves), but it is more expensive and time-consuming than the other two.
How many questions come from medical technology in REET?+
This topic is part of the 'Science in Daily Life' section of the REET Level 2 Science syllabus, but no verified direct question came from it in REET 2024 — since it is in the syllabus, a question could still appear in a future paper.
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Official Sources
Change Log
- 17 September 2026 — English page published — mirrors the fact-checked Hindi page, independently bilingual-accuracy checked