Radioisotope Techniques — MCQs
Which of the following techniques uses radioisotopes?
Gamma camera in Nuclear Medicine is used for –
Radiation exposure can lead to which type of thyroid carcinoma?
Which radioisotope is commonly used in teletherapy?
Which of the following is most radioresistant?
A 26-year-old male presents to the outpatient department with a discrete thyroid swelling. On neck ultrasound, an isolated cystic swelling of the gland is seen. What is the risk of malignancy associated with this finding?
Hot spot in heart is seen in which scan
Radiation causes cell death by:
Expression and release of a repressed emotion is called as
What is Edman's reagent?
Radioisotope Techniques Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following techniques uses radioisotopes?
- A. Sequencing of nucleic acid
- B. Mass spectroscopy
- C. ELISA
- D. RIA (Correct Answer)
Explanation: ***RIA*** - **Radioimmunoassay (RIA)** is a highly sensitive immunoassay that uses **radioisotopes** to label antigens or antibodies. - The detection of the labeled component allows for the quantification of substances in very low concentrations, often in biological fluids. *Sequencing of nucleic acid* - **Nucleic acid sequencing** determines the order of nucleotides in DNA or RNA, historically using methods like Sanger sequencing which employed **dideoxynucleotides** labeled with fluorescent dyes, not radioisotopes for routine detection. Modern methods often use next-generation sequencing technologies without radioisotopes. - While early methods for DNA sequencing, such as the original Maxam-Gilbert method, did utilize radioisotopes for labeling DNA fragments, this is not the technique primarily associated with general nucleic acid sequencing today, which has largely moved to fluorescent or semiconductor-based detection. *Mass spectroscopy* - **Mass spectroscopy** works by ionizing samples and measuring the **mass-to-charge ratio** of the ions to identify compounds, not by incorporating radioisotopes. - It is used for identifying unknown compounds, quantifying known compounds, and elucidating the structure and chemical properties of molecules. *ELISA* - **Enzyme-linked immunosorbent assay (ELISA)** uses an **enzyme** conjugated to an antibody or antigen, which then catalyzes a colorimetric or chemiluminescent reaction for detection. - It does not involve the use of radioisotopes for labeling or detection.
Question 2: Gamma camera in Nuclear Medicine is used for –
- A. Organ imaging (Correct Answer)
- B. Measuring the radioactivity
- C. RIA
- D. Monitoring the surface contamination
Explanation: ***Organ imaging*** - A **gamma camera** is primarily used to detect gamma rays emitted from **radiopharmaceuticals** introduced into the body. - This detection allows for the creation of 2D images or 3D tomographic images (SPECT) of organ function and structure. *Measuring the radioactivity* - While radioactivity is measured by the gamma camera, its primary purpose is not just to quantify dps/Bq, but to create a **spatial distribution** of this radioactivity. - Dedicated **dosimeters** or **activity meters** are used for precise measurement of radioactivity. *RIA* - **Radioimmunoassay (RIA)** is a laboratory technique used to measure the concentration of substances (e.g., hormones, drugs) in a sample, not a function of the gamma camera. - RIA utilizes **radioactively labeled antibodies** and antigens but does not involve imaging the body. *Monitoring the surface contamination* - **Geiger counters** or specific contamination meters are used for monitoring surface contamination. - A gamma camera is designed for internal imaging and is not practical or optimized for detecting external surface contamination.
Question 3: Radiation exposure can lead to which type of thyroid carcinoma?
- A. Lymphoma
- B. Papillary carcinoma (Correct Answer)
- C. Medullary carcinoma
- D. Follicular carcinoma
Explanation: ***Papillary carcinoma*** - Papillary thyroid carcinoma is strongly associated with **radiation exposure**, particularly during childhood [1]. - It is the most prevalent type of thyroid cancer and typically has a **good prognosis** [1]. *Lymphoma* - Thyroid lymphoma is rare and generally not linked to **radiation exposure**; it often presents as a **rapidly enlarging goiter**. - It is more commonly associated with **autoimmune thyroiditis**, not primary radiation effects. *Follicular carcinoma* - Follicular carcinoma shows a correlation with **iodine deficiency** rather than radiation exposure [1]. - Its presentation is more subtle, compared to the classical association of **radiation with papillary carcinoma**. *Medullary carcinoma* - Medullary thyroid carcinoma is primarily linked to **familial syndromes** like MEN 2 and not radiation exposure. - It arises from **parafollicular C cells**, making it clinically distinct from radiation-related types. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1098-1099.
Question 4: Which radioisotope is commonly used in teletherapy?
- A. Ra-226
- B. Cs-137
- C. Co-60 (Correct Answer)
- D. Ir-192
Explanation: ***Co-60*** - **Cobalt-60** is a widely used radioisotope in teletherapy (external beam radiotherapy) due to its high-energy gamma emissions (1.17 and 1.33 MeV). - Its relatively long half-life of **5.27 years** makes it practical for sustained clinical use in **teletherapy units**. *Ra-226* - **Radium-226** was historically used in brachytherapy but has largely been replaced due to its alpha emissions, which are difficult to shield, and its long-lived radioactive decay products. - Its use for teletherapy is **not common** because of these safety concerns and the availability of more suitable isotopes. *Cs-137* - **Cesium-137** is primarily used in **brachytherapy** and some low-dose rate teletherapy machines for specific applications, but not as commonly as Co-60 for general teletherapy. - Its lower gamma energy (0.662 MeV) and shorter half-life than Co-60 (30.17 years) make it less ideal for the widespread **deep penetration** required in many teletherapy treatments. *Ir-192* - **Iridium-192** is predominantly used in **high-dose-rate (HDR) brachytherapy** for temporary implants, delivering radiation over short periods. - Its relatively short half-life of **73.8 days** and lower average gamma energy make it unsuitable for typical long-term teletherapy external beam applications.
Question 5: Which of the following is most radioresistant?
- A. Cartilage (Correct Answer)
- B. Ewing's sarcoma
- C. GIT epithelium
- D. Gonadal tumours
Explanation: ***Cartilage*** - **Cartilage** is a connective tissue with a relatively **low metabolic rate** and **avascular nature**, making its cells (chondrocytes) less susceptible to rapid turnover and DNA damage from radiation. - Its **dense extracellular matrix** and limited cellular division contribute to its inherent resistance to ionizing radiation, requiring higher doses to induce significant damage. *Ewing's sarcoma* - **Ewing's sarcoma** is a highly **malignant bone tumor** that is generally considered **radiosensitive** and often treated with radiation therapy. - Its cells are rapidly dividing, making them more vulnerable to the DNA-damaging effects of radiation. *GIT epithelium* - The **gastrointestinal tract (GIT) epithelium** is characterized by **rapid cell turnover** and high mitotic activity to constantly replace damaged cells and absorb nutrients. - This high proliferative rate makes the GIT epithelium highly **radiosensitive**, leading to common side effects like mucositis and diarrhea during radiation therapy. *Gonadal tumours* - Tumors of the **gonads** (e.g., testicular seminoma, ovarian dysgerminoma) are often highly **radiosensitive** and respond well to radiation therapy due to the germ cell origin and rapid proliferation of tumor cells. - The germ cells themselves are very sensitive to radiation, leading to concerns about **fertility preservation** in patients undergoing treatment.
Question 6: A 26-year-old male presents to the outpatient department with a discrete thyroid swelling. On neck ultrasound, an isolated cystic swelling of the gland is seen. What is the risk of malignancy associated with this finding?
- A. 48%
- B. 12%
- C. 24%
- D. 3% (Correct Answer)
Explanation: ***3%*** - **Purely cystic thyroid nodules** (as described in this case with "isolated cystic swelling") have a **very low risk of malignancy**, typically **2-3%** or less. - According to **ATA guidelines** and **TIRADS classification**, purely cystic nodules are considered **low suspicion** lesions. - The cystic nature suggests a **benign process** such as a degenerated adenoma, colloid cyst, or simple cyst. - **Fine needle aspiration (FNA)** may still be considered if the nodule is >2 cm or has any suspicious solid components, but is often not required for purely cystic lesions. *48%* - This percentage is **significantly higher** than the actual malignancy risk for a purely cystic thyroid swelling. - Such a **high risk** would typically be associated with **solid nodules** exhibiting highly suspicious ultrasound features such as: - Microcalcifications - Irregular or spiculated margins - Taller-than-wide shape - Marked hypoechogenicity - Extrathyroidal extension *24%* - This percentage represents a **moderate to high risk** of malignancy, which is **not characteristic** of an isolated purely cystic thyroid swelling. - A risk in this range might be seen with: - **Mixed solid-cystic nodules** with predominantly solid components - Solid nodules with **intermediate suspicious features** on ultrasound *12%* - While lower than 24% or 48%, 12% is still **considerably higher** than the generally accepted malignancy risk for purely cystic thyroid nodules. - This risk level could be plausible for: - **Predominantly cystic nodules** with some eccentric solid components - Solid nodules with **mildly suspicious** features on ultrasound
Question 7: Hot spot in heart is seen in which scan
- A. Thallium
- B. Gallium
- C. Albumin labelled
- D. Tc pyrophosphate scan (Correct Answer)
Explanation: ***Tc pyrophosphate scan*** - A **technetium-99m pyrophosphate (Tc-PYP) scan** demonstrates a "hot spot" in the heart in cases of **acute myocardial infarction** due to the tracer binding to calcium deposits in necrotic cardiomyocytes. - This hot spot indicates recent myocardial damage and is particularly useful in diagnosing **amyloidosis** (specifically transthyretin cardiac amyloidosis) where the tracer binds to amyloid fibrils. *Thallium* - **Thallium-201** is used in myocardial perfusion imaging to assess areas of reduced blood flow or infarction, creating a "cold spot" (decreased uptake). - It acts as a potassium analog and is taken up by viable myocardial cells, thus areas of ischemia or necrosis appear as defects rather than hot spots. *Gallium* - **Gallium-67** scans are primarily used to detect infection and inflammation, as well as certain tumors. - While it can accumulate in areas of inflammation in the heart (e.g., myocarditis), it does not create a characteristic "hot spot" associated with acute myocardial infarction. *Albumin labelled* - **Technetium-99m labeled albumin** (e.g., Technetium-99m macroaggregated albumin, MAA) is typically used for lung perfusion scans to diagnose pulmonary embolism or for gastrointestinal bleeding studies. - It is not used for direct assessment of myocardial damage or to create a "hot spot" in the heart for ischemic events.
Question 8: Radiation causes cell death by:
- A. Charring of nucleoproteins
- B. Ionization (Correct Answer)
- C. Disruption of cytosol
- D. Destroying their mitochondria
Explanation: ***Ionization*** - Radiation, particularly **ionizing radiation**, causes cell death by directly or indirectly damaging cellular components through the process of **ionization**. [1] - This involves the removal of electrons from atoms or molecules, leading to the formation of highly reactive **free radicals** (especially hydroxyl radicals from water radiolysis) that can damage DNA, proteins, and lipids. [1] - The most critical lethal lesion is **DNA double-strand breaks**, which are difficult to repair and trigger apoptosis or mitotic catastrophe. [1] *Charring of nucleoproteins* - **Charring** typically refers to the combustion or burning of organic matter, which is not the mechanism of cell death caused by therapeutic radiation doses. - While radiation can cause protein denaturation, it does not lead to the macroscopic charring of nucleoproteins within cells. *Disruption of cytosol* - While severe radiation damage can impact the entire cell, direct and selective **disruption of the cytosol** is not the primary or most impactful mechanism of radiation-induced cell death. - The critical targets for radiation-induced cell death are primarily the **nucleus** and its DNA, not the cytoplasm. [2] *Destroying their mitochondria* - Although radiation can induce **mitochondrial dysfunction** and contribute to cell death through apoptosis, it is not the initial or primary mechanism of cell destruction. - The most critical and direct damage leading to cell death is inflicted upon the **DNA** in the nucleus, particularly causing double-strand breaks. [1] **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 100-102. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Central Nervous System Synapse, pp. 438-439.
Question 9: Expression and release of a repressed emotion is called as
- A. Dissociation
- B. Confabulation
- C. Abreaction (Correct Answer)
- D. Regression
Explanation: **Abreaction** - This term refers to the **expression and release of a repressed emotion**, often in a therapeutic context, providing psychological relief. - It involves re-experiencing a traumatic event or repressed emotions to alleviate their negative impact. - Also known as **catharsis** in psychoanalytic therapy. *Dissociation* - **Dissociation** involves a disruption in the normal integration of consciousness, memory, identity, emotion, perception, body representation, motor control, and behavior. - It describes a mental process that causes a lack of connection in a person's thoughts, memories, feelings, actions, or sense of identity, rather than an active release of emotion. *Confabulation* - **Confabulation** is the creation of false memories in the absence of an intention to deceive. - It is often seen in individuals with specific neurological or psychiatric conditions, where they unconsciously fill in gaps in their memory with fabricated details. *Regression* - **Regression** is a defense mechanism in which an individual faced with anxiety or stress retreats to an earlier developmental stage. - It involves reverting to immature patterns of behavior, rather than the release of a specific, repressed emotion.
Question 10: What is Edman's reagent?
- A. 2,4-dinitrophenol
- B. 1-fluoro-2,4-dinitrobenzene
- C. Phenyl-isocyanate (Correct Answer)
- D. Cyanogen bromide
Explanation: ### Explanation **Correct Answer: C. Phenyl-isothiocyanate (Phenyl-isocyanate)** *Note: While the standard chemical name is Phenyl-isothiocyanate (PITC), it is frequently referred to in medical exams as Phenyl-isocyanate.* **Edman’s Degradation** is the gold standard method for **sequencing amino acids** in a peptide chain. The reagent reacts with the uncharged **N-terminal amino group** of the peptide to form a Phenylthiocarbamoyl (PTC) derivative. Under mild acidic conditions, this terminal amino acid is cleaved as a cyclic Phenylthiohydantoin (PTH)-amino acid, which can then be identified via chromatography. The process is repeated sequentially to determine the entire primary structure of the protein without hydrolyzing the rest of the peptide bonds. **Analysis of Incorrect Options:** * **A. 2,4-dinitrophenol (DNP):** This is a metabolic uncoupler of oxidative phosphorylation. It is not used for protein sequencing. * **B. 1-fluoro-2,4-dinitrobenzene (Sanger’s Reagent):** Used by Frederick Sanger to sequence insulin. Like Edman’s reagent, it labels the N-terminal, but it requires total acid hydrolysis of the protein, meaning the rest of the peptide chain is destroyed and cannot be sequenced sequentially. * **D. Cyanogen bromide (CNBr):** This is a chemical cleavage agent that specifically hydrolyzes peptide bonds at the **carboxyl side of Methionine** residues. It is used to break large proteins into smaller fragments before sequencing. **High-Yield Clinical Pearls for NEET-PG:** * **Edman’s Reagent:** Best for sequencing small peptides (up to 50–60 amino acids). * **Sanger’s Reagent:** Historical significance; labels N-terminal but is "destructive." * **Ninhydrin Reaction:** Used to detect amino acids (gives a **purple/Ruhemann's purple** color, except for Proline, which gives a **yellow** color). * **Biuret Test:** Minimum of **two peptide bonds** (tripeptide) are required for a positive result.
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