Q.Write notes on EEG.
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🔒 Start your 14-day free trial to unlock the full solution →Concept understanding — Diagnostic Imaging and Monitoring — X-rays, MRI, ECG, EEG and ELISA
Several imaging and monitoring techniques let clinicians look inside the body or track an organ's activity without surgery.
Radiographs (X-rays) are obtained by passing a controlled beam of X-rays — a high-energy form of electromagnetic radiation — through the body onto a photographic film or digital detector on the far side. Dense tissue such as bone absorbs more of the beam and so appears light/white on the resulting image, while soft tissue absorbs less and appears darker, producing a single two-dimensional picture useful for viewing bones, detecting fractures, and examining the chest.
A tomogram is a single cross-sectional image of the body produced by tomography (as in a CT/CAT scan): X-ray images are taken from many different angles around the body and combined by computer into a detailed slice-by-slice picture, unlike a plain radiograph, which flattens the whole thickness of the body into one two-dimensional projection.
MRI (Magnetic Resonance Imaging) uses a strong magnetic field and radio waves, not ionising radiation, to build detailed cross-sectional images of soft tissue. In the procedure, the patient lies inside the scanner's large magnet, which aligns the hydrogen nuclei present throughout the body's water and fat molecules; brief pulses of radio-frequency energy are then applied, which knock these nuclei briefly out of alignment; as the nuclei realign afterward, they emit detectable radio signals, which the scanner's computer processes into detailed images. MRI is considered a harmless diagnostic technique specifically because it uses no ionising radiation at all — unlike X-ray or CT imaging, the magnetic fields and radio waves involved do not damage tissue or DNA.
The ECG (electrocardiogram) records the heart's electrical activity over time as a characteristic trace of waves and intervals: the P wave (depolarisation, i.e. electrical activation, of the atria), the QRS complex (depolarisation of the ventricles), and the T wave (repolarisation, or electrical recovery, of the ventricles). Between these waves, clinically important intervals are measured, including the P-R interval (the time from the start of atrial activation to the start of ventricular activation, reflecting how long the signal takes to pass through the conducting tissue between the atria and the ventricles) and the Q-T interval (spanning ventricular depolarisation together with its subsequent repolarisation). A prolonged P-R interval indicates a delay in the electrical signal passing from the atria to the ventricles along the conducting pathway — a finding associated with a conduction disturbance often referred to as heart block. …
EEG records the brain's electrical activity as brainwave patterns via scalp electrodes. …
An EEG (electroencephalogram) records the electrical activity of the brain, picked up through electrodes placed on the scalp as characteristic patterns of brainwave activity. Different patterns and frequencies of brainwaves are associated with different states, such as being awake, relaxed, or in different stages of sleep, and abnormal patterns can point to an underlying neurological condition. …
- Confusing an EEG (brain's electrical activity) with an ECG (heart's electrical activity) — the names and traces are e …
- CBSE 2026Set ANNUAL2 marksQ.What is tomogram?
›Reveal solutionSolution
A tomogram is the sectional image produced by a tomography/CT scan.
Tomography is an imaging technique that produces detailed pictures of internal structures of the body by taking images in sections/slices, typically using X-rays combined with computer processing (as in Computed Tomography, CT scan).
During a CT scan, an X-ray source rotates around the patient, and detectors record the amount of radiation passing through the body at many different angles. A computer then reconstructs this data into a two-dimensional cross-sectional image representing a "slice" through the body at a particular level.
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- CBSE 2026Set ANNUAL2 marksQ.'MRI scan is harmless.' Justify.
›Reveal solutionSolution
MRI avoids ionising radiation entirely, using magnetism and radio waves instead, which is why it is considered a safe, non-invasive imaging technique.
Magnetic Resonance Imaging (MRI) works by placing the patient in a strong magnetic field, which aligns the hydrogen nuclei (protons) present abundantly in the body's water and fat molecules. A pulse of radio-frequency waves is then applied, temporarily disturbing this alignment; as the protons relax back to their original state, they emit weak radio signals which are detected and processed by a computer to construct detailed images of soft tissues.
Why MRI is considered harmless:
- It does not use ionising radiation (unlike X-rays or CT scans), so there is no risk of the radiation damaging DNA or causing cancer from cumulative radiation exposure.
- The magnetic fields and radio waves used have not been shown to cause any tissue damage at the intensities used clinically.
- It is a non-invasive procedure — no surgical incision, injection (usually), or exposure to harmful rays is required. …
- CBSE 2026Set ANNUAL2 marksQ.MRI scan is harmless - Justify.
›Reveal solutionSolution
MRI is harmless because it images the body using a magnetic field and non-ionising radio waves, avoiding the tissue-damaging ionising radiation used in X-ray/CT scans.
Magnetic Resonance Imaging (MRI) works by placing the body in a strong magnetic field and applying radio-frequency waves. These make the hydrogen (proton) nuclei in the body's water and tissues emit signals, which are processed by a computer into detailed images of internal organs.
The radiation used (radio waves) is non-ionising. It does not carry enough energy to knock electrons out of atoms, so it does not ionise or damage cells, tissues or DNA.
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- CBSE 2025Set ANNUAL2 marksQ.MRI scan is harmless - justify.
›Reveal solutionSolution
MRI uses magnetism and radio waves, not ionising radiation, so it does not damage living tissue the way X-rays can.
Magnetic Resonance Imaging (MRI) is a diagnostic imaging technique used to visualise internal body structures, especially soft tissues (brain, spinal cord, muscles, joints, internal organs), in great detail.
Why it is considered harmless:
- No ionising radiation: Unlike X-rays or CT scans, which use ionising radiation capable of damaging DNA and increasing cancer risk with repeated exposure, MRI uses a powerful magnetic field combined with radiofrequency (radio) waves to align and then detect the resonance signals of hydrogen nuclei (protons) in the body's water/fat molecules.
- Non-ionising energy: Radio waves carry far too little energy to knock electrons out of atoms or break chemical bonds in tissue — they simply cause the aligned protons to briefly resonate and then relax, emitting a detectable signal that a computer reconstructs into an image. This process causes no known tissue damage. …
- CBSE 2023Set ANNUAL2 marksQ.MRI scan is harmless - Justify.
›Reveal solutionSolution
Unlike X-rays or CT scans, MRI does not use ionising radiation, so it does not cause the cellular or genetic damage associated with ionising radiation, and is considered a safe imaging technique.
Magnetic Resonance Imaging (MRI) is a diagnostic imaging technique that uses a strong magnetic field together with radio-frequency (radio) waves to align and then detect signals from hydrogen nuclei in the body's water and fat molecules, producing detailed images of soft tissues.
Justification that MRI is harmless:
- MRI does not employ ionising radiation (such as X-rays or gamma rays), unlike CT scans or conventional radiography, which use ionising radiation capable of damaging DNA and increasing cancer risk with repeated exposure.
- The magnetic field and radio waves used in MRI are non-ionising - they do not have enough energy to remove electrons from atoms or break chemical bonds in tissue. …
- CBSE 2018Set ANNUAL2 marksQ.MRI scan is harmless. Justify.
›Reveal solutionSolution
Unlike X-ray/CT imaging, MRI does not use ionising radiation — it uses magnetic fields and radio waves, which do not damage biological tissue, making it a safe, non-invasive diagnostic technique.
Magnetic Resonance Imaging (MRI) works by placing the body in a strong magnetic field and applying radio-frequency pulses. Hydrogen protons (abundant in the water/fat of body tissues) align with the magnetic field and, when disturbed by the RF pulse, emit signals as they realign; these signals are computer-processed into detailed cross-sectional images of soft tissues (brain, muscles, ligaments, organs), usually without needing any contrast dye.
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- CBSE 2018Set ANNUAL2 marksQ.MRI scan is harmless. Justify.
›Reveal solutionSolution
MRI uses magnetic fields and radio waves, not ionising radiation, so it does not damage tissue and is considered harmless.
MRI (Magnetic Resonance Imaging) is a diagnostic imaging technique (Applied Biology / modern diagnostic tools) that produces detailed pictures of internal soft tissues and organs. Its safety is explained as follows:
- It works by placing the body in a strong magnetic field and applying radio-frequency waves; these make the hydrogen protons of body water emit signals that are computer-processed into images.
- Unlike X-rays and CT scans, MRI uses NO ionising radiation. Ionising radiation is what damages DNA and cells, and MRI simply does not produce it.
- The magnetic field and radio waves used are not known to harm living cells, so the scan causes no radiation burns or genetic damage and can be repeated without cumulative risk. …
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