Physics of Nuclear Medicine — MCQs
Which technetium is most commonly used in bone pathology?
Gamma camera in Nuclear Medicine is used for –
Ionizing radiation acts on tissue leading to
Which of the following statements about the half-life of radioisotopes is false?
A dense nephrogram is obtained by
The T1/2 of Iodine-131 is:
Which of the following agents is used to measure Glomerular Filtration Rate (GFR)?
A thyroid FNA shows 'bubble gum' colloid. Which nuclear feature would best support papillary thyroid carcinoma?
Which artificial radioisotopes are used in nuclear medicine?
Increased radio-isotope uptake is seen in which of the following conditions?
Physics of Nuclear Medicine Indian Medical PG Practice Questions and MCQs
Question 1: Which technetium is most commonly used in bone pathology?
- A. 99mTc-MDP (Correct Answer)
- B. 99mTc-Sestamibi
- C. 99mTc-Pyrophosphate
- D. 99mTc-Exametazime
Explanation: ***99mTc-MDP*** - **Technetium-99m Methylene Diphosphonate (99mTc-MDP)** is the agent of choice for routine **bone scintigraphy** due to its optimal pharmacokinetics and high affinity for bone. - It readily binds to the **hydroxyapatite crystals** of bone, especially in areas of increased osteoblastic activity, making it excellent for detecting bone metastases, fractures, and infections. *99mTc-Sestamibi* - **Technetium-99m Sestamibi (99mTc-Sestamibi)** is primarily used for **myocardial perfusion imaging** to assess cardiac function. - It also has applications in parathyroid imaging for detecting **parathyroid adenomas**, but not for general bone pathology. *99mTc-Pyrophosphate* - **Technetium-99m Pyrophosphate (99mTc-Pyrophosphate)** was an older bone-seeking agent but has largely been replaced by MDP due to MDP's superior imaging characteristics. - Its main current use is in diagnosing **cardiac amyloidosis**, not for routine bone scans. *99mTc-Exametazime* - **Technetium-99m Exametazime (99mTc-Exametazime)**, also known as HMPAO, is specifically used for **leukocyte imaging** to detect infection and inflammation. - It is also used for **brain perfusion imaging** to assess cerebral blood flow, not for direct visualization of bone pathology.
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: Ionizing radiation acts on tissue leading to
- A. Ionization of electrons from orbit (Correct Answer)
- B. Thermal injury
- C. Linear acceleration injury
- D. Formation of pyrimidine dimer
Explanation: ***Ionization of electrons from orbit*** - **Ionizing radiation** is defined by its ability to eject electrons from atoms, creating **ions** and free radicals. - This process directly damages cellular components, including **DNA**, leading to biological effects. *Thermal injury* - **Thermal injury** is caused by heat and is not the primary mechanism of damage from ionizing radiation. - While high doses of radiation can cause local heating, the characteristic damage of ionizing radiation is through **ionization**, not heat. *Linear acceleration injury* - **Linear acceleration injury** refers to trauma caused by rapid changes in speed, often associated with motor vehicle accidents. - This is a form of **mechanical trauma** and is unrelated to the effects of ionizing radiation. *Formation of pyrimidine dimer* - **Pyrimidine dimers** are formed primarily by **ultraviolet (UV) radiation**, not ionizing radiation. - UV light causes **covalent bonds** between adjacent pyrimidine bases in DNA, leading to mutations.
Question 4: Which of the following statements about the half-life of radioisotopes is false?
- A. Co-60: 5.26 years
- B. I-131: 60 years (Correct Answer)
- C. Ra-226: 1626 years
- D. Ir-192 : 74 days
Explanation: ***I-131: 60 years*** - The half-life of **Iodine-131 (I-131)** is approximately **8 days**, not 60 years. This makes the statement false. - I-131 is commonly used in nuclear medicine for thyroid imaging and treatment, and its relatively short half-life is advantageous for patient safety. *Co-60: 5.26 years* - The half-life of **Cobalt-60 (Co-60)** is indeed approximately **5.26 years**. - Co-60 is a significant radioisotope used in **radiotherapy** and for sterilization of medical equipment. *Ra-226: 1626 years* - The half-life of **Radium-226 (Ra-226)** is approximately **1626 years**, making this statement correct. - Ra-226 is a naturally occurring radioisotope with a very long half-life, historically used in medicine and still present in some environmental contexts. *Ir-192 : 74 days* - The half-life of **Iridium-192 (Ir-192)** is approximately **73.8 days (often rounded to 74 days)**, making this statement correct. - Ir-192 is commonly used in **brachytherapy** for cancer treatment and **industrial radiography**.
Question 5: A dense nephrogram is obtained by
- A. Dehydrating the patient
- B. Rapid (Bolus) injection of dye (Correct Answer)
- C. Using non ionic media
- D. Increasing the dose of contrast media
Explanation: ***Rapid (Bolus) injection of dye*** - A **rapid bolus injection** of contrast material ensures a high concentration reaches the kidneys simultaneously, leading to optimal opacification and a **dense nephrogram**. - This method allows for the collection of a **large bolus of undiluted contrast** in the renal vessels and parenchyma, improving visualization of the renal parenchyma during the nephrographic phase. - The dense nephrogram phase occurs when contrast is within the renal tubules and interstitium, producing uniform opacification. *Dehydrating the patient* - **Dehydration** would concentrate the urine in the collecting system, but it does not directly contribute to the **dense nephrogram** appearance of the renal parenchyma. - While dehydration may improve visualization of the pelvicalyceal system on delayed images, it can increase the risk of **contrast-induced nephropathy**. *Using non ionic media* - **Non-ionic contrast media** are associated with fewer adverse reactions and greater patient safety compared to ionic media due to their lower osmolality. - However, the type of contrast media (ionic vs. non-ionic) does not primarily determine the **density of the nephrogram** itself, but rather patient tolerability and safety profile. *Increasing the dose of contrast media* - While increasing the dose might provide more contrast overall, it does not guarantee a **dense nephrogram**, which requires a high concentration of contrast to be present acutely in the renal parenchyma. - A dense nephrogram is better achieved by **rapid bolus injection technique** rather than simply increasing the total dose. - Excessive contrast increases the risk of **adverse reactions** and contrast-induced nephropathy without necessarily improving nephrographic density proportionally.
Question 6: The T1/2 of Iodine-131 is:
- A. 8 days (Correct Answer)
- B. 12 hours
- C. 13 days
- D. 2 days
Explanation: ***8 days*** - Iodine-131 (¹³¹I) has a relatively short half-life of **8.02 days**, making it suitable for diagnostic and therapeutic uses with a controlled radiation exposure window. - This **half-life** allows for effective patient monitoring and targeted treatment while minimizing long-term radiation risks. *12 hours* - This is an incorrect value; 12 hours is a significantly shorter half-life than that of **Iodine-131**. - Other isotopes, such as **Iodine-123**, have a half-life of 13.2 hours, which is closer to this value but still distinct from **Iodine-131**. *13 days* - This value is close but incorrect; the correct half-life for **Iodine-131** is approximately **8 days**. - A 13-day half-life would imply a longer period of radioactivity, altering its clinical applications. *2 days* - This is an incorrect half-life for **Iodine-131**, which has a significantly longer half-life of approximately 8 days. - A 2-day half-life would mean the isotope decays much faster than it actually does.
Question 7: Which of the following agents is used to measure Glomerular Filtration Rate (GFR)?
- A. Iodohippurate
- B. Tc99m-DTPA (Correct Answer)
- C. Tc99m-MAG3
- D. Tc99m-DMSA
Explanation: ***Tc99m-DTPA*** - Technetium-99m-Diethylenetriaminepentaacetic acid (**Tc99m-DTPA**) is a radiopharmaceutical that is cleared almost exclusively by **glomerular filtration** (~98%), making it the ideal agent for measuring GFR. - Its **renal clearance rate** directly correlates with the GFR, providing an accurate, non-invasive assessment of kidney function. - Used for dynamic renal scintigraphy to calculate GFR quantitatively. *Iodohippurate* - **Iodohippurate (OIH)** is primarily cleared by **tubular secretion** (~80%), similar to Para-aminohippuric acid (PAH). - It is used to measure **renal plasma flow (RPF)** or **effective renal plasma flow (ERPF)**, not GFR. - Not suitable for GFR measurement due to its tubular handling mechanism. *Tc99m-MAG3* - Technetium-99m-Mercaptoacetyltriglycine (**Tc99m-MAG3**) is predominantly handled by **tubular secretion** (~90%). - Used to assess **effective renal plasma flow (ERPF)** and is preferred in patients with impaired renal function due to its high extraction efficiency. - Has largely replaced OIH in clinical practice but does not measure GFR. *Tc99m-DMSA* - Technetium-99m-Dimercaptosuccinic acid (**Tc99m-DMSA**) binds to the **proximal tubular cells** in the renal cortex (~40-50% accumulation). - Used for **static renal cortical scintigraphy** to evaluate renal morphology, differential renal function, and detect cortical scarring. - Not cleared by glomerular filtration and unsuitable for GFR measurement.
Question 8: A thyroid FNA shows 'bubble gum' colloid. Which nuclear feature would best support papillary thyroid carcinoma?
- A. Nuclear grooves
- B. Ground glass nuclei (Correct Answer)
- C. Prominent nucleoli
- D. Salt and pepper chromatin
Explanation: ***Ground glass nuclei*** - **Ground glass nuclei**, also known as **Orphan Annie eye nuclei** [1][2], are the most **characteristic and recognized nuclear feature** of **papillary thyroid carcinoma (PTC)** on FNA cytology. [1] - This appearance results from **fine, evenly dispersed chromatin** that gives the nucleus a clear, empty, or translucent appearance with a prominent nuclear membrane. [1] - Among the given options, this is the **single best feature** that would support a PTC diagnosis when 'bubble gum' colloid is present. *Nuclear grooves* - **Nuclear grooves** are a common and highly supportive feature of PTC, particularly when **prominent and numerous**. - However, as a **single finding**, they are less definitive than ground glass nuclei, as grooves can occasionally be seen in benign conditions (though usually less prominent). - In combination with other features, nuclear grooves are highly specific for PTC. *Prominent nucleoli* - **Prominent nucleoli** are more frequently associated with **follicular neoplasms**, **medullary thyroid carcinoma**, or anaplastic thyroid carcinoma. - Classical PTC typically has **inconspicuous nucleoli**, so prominent nucleoli would suggest an alternative diagnosis or a tall cell variant of PTC. *Salt and pepper chromatin* - **Salt and pepper chromatin** (finely stippled chromatin) is a classic cytological feature of **medullary thyroid carcinoma** (MTC). - This chromatin pattern reflects neuroendocrine differentiation and is distinct from the nuclear characteristics of PTC. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Endocrine System, pp. 1098-1100. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Liver And Biliary System Disease, pp. 429-430.
Question 9: Which artificial radioisotopes are used in nuclear medicine?
- A. Radium
- B. Uranium
- C. Plutonium (Correct Answer)
- D. Iridium
Explanation: ### Explanation **Correct Answer: C. Plutonium** In nuclear medicine, radioisotopes are categorized as either **natural** (found in nature) or **artificial** (man-made via nuclear reactors or cyclotrons). **Plutonium (specifically Pu-238)** is an artificial radioisotope produced in nuclear reactors. While not used as a diagnostic tracer or therapeutic agent for internal administration, it has a significant historical and niche clinical application as a power source for **Radioisotope Thermoelectric Generators (RTGs)** in long-lived **cardiac pacemakers**. Its high energy density and long half-life made it ideal for devices requiring decades of operation without battery replacement. **Analysis of Incorrect Options:** * **A. Radium:** This is a **naturally occurring** radioactive metal found in uranium ores. While Radium-223 is used in treating bone metastases (Xofigo), the element itself is classified as natural. * **B. Uranium:** This is a **naturally occurring** heavy metal. It is the raw material used to produce artificial isotopes but is not used directly in clinical nuclear medicine. * **C. Iridium:** While Iridium-192 is used in Brachytherapy, it is generally classified as a transition metal used in "sealed sources" for radiotherapy rather than being the classic example of an "artificial radioisotope" in the context of general nuclear medicine tracers (like Technetium-99m). However, in the context of this specific question, Plutonium is the most distinct "artificial/man-made" element. **High-Yield Clinical Pearls for NEET-PG:** * **Technetium-99m (Tc-99m):** The most commonly used artificial radioisotope in diagnostic nuclear medicine (produced in a Mo-99/Tc-99m generator). * **Cyclotron-produced isotopes:** Include F-18 (used in PET scans), I-123, and Thallium-201. * **Reactor-produced isotopes:** Include I-131, Mo-99, and Xenon-133. * **Therapeutic Alpha Emitter:** Radium-223 is the first alpha-emitting radiopharmaceutical approved to improve survival in castration-resistant prostate cancer with bone metastases.
Question 10: Increased radio-isotope uptake is seen in which of the following conditions?
- A. Osteoclastoma
- B. Enchondroma
- C. Pseudoarthrosis (Correct Answer)
- D. Ewing's sarcoma
Explanation: **Explanation:** In nuclear medicine, bone scintigraphy (Bone Scan) using **99mTc-MDP** (Methylene Diphosphonate) is the gold standard for assessing bone turnover. The uptake of the radiopharmaceutical depends on two primary factors: **blood flow** and **osteoblastic activity** (bone formation). **Why Pseudoarthrosis is the Correct Answer:** Pseudoarthrosis (a "false joint" resulting from non-union of a fracture) is characterized by persistent mechanical stress and abnormal motion at the fracture site. This leads to continuous, localized **reactive osteoblastic activity** and increased vascularity as the body attempts to heal the bone. On a bone scan, this manifests as a focal area of **increased radio-isotope uptake** (a "hot spot"). **Analysis of Incorrect Options:** * **Osteoclastoma (Giant Cell Tumor):** While GCT can show uptake, it typically presents with a "cold" center (photopenia) due to extensive bone destruction and hemorrhage, surrounded by a rim of increased uptake. * **Enchondroma:** These are benign cartilaginous tumors. They are typically **"cold"** or show very minimal uptake unless they are complicated by a pathological fracture or undergo malignant transformation. * **Ewing’s Sarcoma:** While Ewing’s sarcoma generally shows increased uptake due to its aggressive nature, in the context of this specific question (often derived from standard textbooks like *Bailey & Love* or *Maheshwari*), **Pseudoarthrosis** is the classic teaching example for identifying active bone remodeling in non-malignant conditions. **NEET-PG High-Yield Pearls:** * **Hot Spots (Increased Uptake):** Osteoblastic metastases (Prostate CA), Osteoid Osteoma (Double density sign), Paget’s Disease, and Fractures. * **Cold Spots (Decreased Uptake):** Multiple Myeloma (often missed on bone scans), Renal Cell Carcinoma metastases, and early Avascular Necrosis (AVN). * **Three-Phase Bone Scan:** Used to differentiate Cellulitis (increased uptake in first two phases) from Osteomyelitis (increased uptake in all three phases).
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