Nuclear Medicine — MCQs

Nuclear Medicine Indian Medical PG Practice Questions and MCQs

Question 211: Half life of tritium is?

A. 10.2 years
B. 12.3 years (Correct Answer)
C. 15.5 years
D. 20.7 years

Explanation: ***12.3 years*** - The **half-life of tritium** is a well-established physical constant, representing the time it takes for half of a given sample of the radioactive isotope to decay. - This value is crucial in fields such as **radiometric dating**, **nuclear medicine**, and assessing the environmental impact of tritium. *10.2 years* - This value is **incorrect** for the half-life of tritium. - While within a similar range, it does not match the empirically determined and widely accepted value. *15.5 years* - This value is also **incorrect** for the half-life of tritium. - It is significantly longer than the known decay constant for this isotope. *20.7 years* - This value is substantially **incorrect** and much longer than the true half-life of tritium. - This duration would imply a much slower radioactive decay rate than observed.

Question 212: What is the appropriate dose range for MIBG in the treatment of neuroblastoma?

A. 7.4-11.1 GBq (200-300 mCi)
B. 11.1-14.8 GBq (300-400 mCi) (Correct Answer)
C. 3.7-5.5 GBq (100-150 mCi)
D. 5.5-7.4 GBq (150-200 mCi)

Explanation: ***11.1-14.8 GBq (300-400 mCi)*** - This range represents the **standard high-dose MIBG therapy** commonly used for treating neuroblastoma in recurrent or refractory cases. - The precise dose is often adjusted based on patient factors like **body surface area** and tolerance, but this range is widely accepted for therapeutic efficacy. *3.7-5.5 GBq (100-150 mCi)* - This dose range is typically considered for **diagnostic MIBG scans** or for **lower-dose therapies**, not the higher therapeutic doses needed for effective neuroblastoma treatment. - Doses in this range are **insufficient** to achieve the desired cytotoxic effect on neuroblastoma cells. *7.4-11.1 GBq (200-300 mCi)* - While higher than diagnostic doses, this range is generally considered **suboptimal** for achieving significant tumor regression in advanced neuroblastoma when compared to the higher established therapeutic doses. - It may be used in specific situations, but the **maximal effective dose** is generally preferred. *5.5-7.4 GBq (150-200 mCi)* - Similar to the 7.4-11.1 GBq range, this is usually **below optimal therapeutic doses** for neuroblastoma. - This range might be explored in patients with **compromised organ function** or as a bridge therapy, but it is not the standard full therapeutic dose.

Question 213: Which of the following primarily governs the uptake of Tc-99m MDP in body?

A. Amount of osteogenic activity (Correct Answer)
B. Amount of iodine uptake
C. Amount of calcium uptake
D. Amount of catecholamine activity

Explanation: ***Amount of osteogenic activity*** - The **uptake of Tc-99m MDP** (Technetium-99m Methylene Diphosphonate) is directly proportional to the rate of **bone turnover** and **osteoblastic activity**. - MDP is a **phosphate analog** that adsorbs onto the hydroxyapatite crystals at sites of new bone formation. *Amount of iodine uptake* - **Iodine uptake** is primarily associated with the **thyroid gland** and its function in hormone synthesis, not bone metabolism. - Radioactive iodine isotopes like **I-131** or **I-123** are used for thyroid imaging and treatment, not bone scans. *Amount of calcium uptake* - While calcium is a major component of bone, the uptake of **Tc-99m MDP** is not directly governed by the amount of **calcium being deposited**. - Instead, it reflects the *rate* of crystal formation and bone matrix production, which involves osteoblastic activity. *Amount of catecholamine activity* - **Catecholamine activity** refers to the production and release of neurotransmitters like **epinephrine** and **norepinephrine**, typically associated with the **adrenal glands** and nervous system. - This has no direct relevance to the uptake mechanism of **Tc-99m MDP** in bone.

Question 214: Technetium-99m methylene diphosphonate is structurally similar to

A. Calcium phosphate (Correct Answer)
B. Phosphorus
C. Sodium bicarbonate
D. Magnesium sulfate

Explanation: ***Calcium phosphate*** - **Technetium-99m methylene diphosphonate (Tc-99m MDP)** is a **radiopharmaceutical** used in **bone scans** because it mimics **calcium phosphate**, the main mineral component of bone. - This structural similarity allows it to incorporate into the **hydroxyapatite crystals** in bone, localizing to areas of active bone turnover. *Phosphorus* - While phosphorus is a component of MDP and bone, it is not structurally similar to **elemental phosphorus** alone. - **Elemental phosphorus** is highly reactive and not used as a clinical imaging agent. *Sodium bicarbonate* - **Sodium bicarbonate** is a salt used as an antacid or for metabolic acidosis, with no structural or physiological resemblance to bone mineral. - Its chemical structure is entirely different, involving sodium, hydrogen, carbon, and oxygen. *Magnesium sulfate* - **Magnesium sulfate** is a salt used for conditions like eclampsia or constipation, with no structural or physiological similarity to bone mineral. - Its primary role involves magnesium and sulfate ions, not the phosphate backbone critical for bone imaging.

Question 215: A PET scan uses which of the following tracer materials?

A. FDG (Correct Answer)
B. CDF
C. ADP
D. MIBG

Explanation: ***FDG*** - **FDG (18F-Fluorodeoxyglucose)** is a glucose analog labeled with fluorine-18 that is the most commonly used radiotracer in PET scans. - Tissues, especially **cancer cells**, with high metabolic activity avidly take up FDG, making them visible on PET imaging. - FDG-PET is widely used in **oncology, neurology, and cardiology**. *CDF* - **CDF** is not a standard or recognized radiotracer material used in PET scans. - This option is a distracter and does not correspond to any known medical imaging agent. *ADP* - **ADP (Adenosine Diphosphate)** is a molecule involved in cellular energy transfer but is not used as a tracer material for PET scans. - PET tracers are typically radioisotopes attached to biologically active molecules, not ADP itself. *MIBG* - **MIBG (Metaiodobenzylguanidine)** is a radioactive pharmaceutical used in **scintigraphy** (a type of nuclear medicine scan), primarily for imaging neuroendocrine tumors like **pheochromocytoma** and **neuroblastoma**. - While it is a radioactive tracer, it is used with **SPECT or planar imaging**, not typically with PET scans.

Question 216: What is the best investigation for detecting bone metastases?

A. MRI
B. CT Scan
C. Bone Scintigraphy (Correct Answer)
D. X-Ray

Explanation: ***Bone Scintigraphy*** - This imaging technique, also known as a **bone scan**, demonstrates high sensitivity for detecting increased **osteoblastic activity**, which is characteristic of most bone metastases. - It involves injecting a **radioactive tracer** (usually technetium-99m-labeled bisphosphonates) that uptakes in areas of increased bone turnover, making it excellent for surveying the entire skeleton. *MRI* - While very sensitive for soft tissue and certain types of bone lesions, **MRI** is typically used to evaluate specific sites of concern or for **spinal cord compression**, rather than as a primary screening tool for widespread metastases due to its limited field of view and high cost for whole-body imaging. - Tumors that primarily cause **osteolytic lesions** or have significant soft tissue components often show well on MRI but it can miss subtle osteoblastic activity spread across the skeleton. *CT Scan* - **CT scans** are excellent for demonstrating **cortical bone destruction**, matrix patterns, and soft tissue masses related to bone lesions, offering superior anatomical detail compared to X-rays or bone scans at a specific site. - However, CT is less sensitive for detecting subtle or early **medullary involvement** and its role in screening the entire skeleton for metastases is limited due to higher radiation exposure and limited field of view compared to bone scintigraphy. *X-Ray* - **X-rays** are typically the initial imaging modality for evaluating focal bone pain, but they are **insensitive** for detecting early bone metastases, requiring significant bone destruction (typically >30-50%) before a lesion becomes visible. - They also have **poor sensitivity** for detecting lesions in areas with complex anatomy or superimposed structures, making them inadequate for comprehensive screening for metastatic disease.

Question 217: Which common tracer in PET is administered in the form of fluorodeoxyglucose (FDG)?

A. Oxygen 15
B. Fluorine 18 (Correct Answer)
C. Saccharide - 12
D. Aluminum - 12

Explanation: ***Fluorine 18*** - **Fluorine-18 (¹⁸F)** is the most widely used radionuclide in Positron Emission Tomography (PET) scanning, primarily in the form of **fluorodeoxyglucose (FDG)**. - FDG-PET is extensively used in oncology to detect cancer, stage diseases, and monitor treatment response, as cancer cells often exhibit increased **glucose metabolism**. *Oxygen 15* - **Oxygen-15 (¹⁵O)** is a PET tracer primarily used to measure **cerebral blood flow** and oxygen metabolism, typically as H₂¹⁵O. - Its very short half-life (approximately 2 minutes) makes it challenging for routine clinical use outside of specialized research centers. *Saccharide - 12* - **Saccharide-12** is not a recognized or common radionuclide used in PET imaging. - PET tracers generally involve **radioisotopes** of elements that can be incorporated into biologically active molecules. *Aluminum - 12* - **Aluminum-12** is not a radioisotope used in PET imaging. - Common PET radionuclides such as **¹⁸F**, ¹¹C, ¹³N, and ¹⁵O are **positron emitters** with suitable decay characteristics.

Question 218: Substance used for PET scan is

A. Gadolinium
B. Gastrografin
C. Iodine
D. 18F-FDG (Correct Answer)

Explanation: ***18F-FDG*** - **18F-FDG (Fluorodeoxyglucose)** is a glucose analog labeled with a **positron-emitting radioisotope**, fluorine-18 (18F). - It is the most commonly used radiotracer in PET scans, as it accumulates in cells with high metabolic activity, particularly **cancer cells** and activated brain cells. *Gadolinium* - **Gadolinium** is a paramagnetic contrast agent primarily used in **MRI scans** to enhance the visualization of blood vessels and abnormal tissues. - It does not emit positrons and is therefore not suitable for PET imaging. *Gastrografin* - **Gastrografin** is an oral, water-soluble contrast agent containing **iodine**, typically used in **X-rays** and **CT scans** of the gastrointestinal tract. - It is not a radioactive tracer and has no application in PET imaging. *Iodine* - **Iodine** in various forms can be used as a contrast agent in **X-rays** and **CT scans**, or as a radioactive isotope (e.g., **I-131**) for **thyroid imaging** and treatment. - While some isotopes of iodine are radioactive, they are not typically used for PET imaging, which relies on positron emission.

Question 219: Investigation with least radiation dose in the diagnosis of Meckel's diverticulum is -

A. MRI
B. CT
C. Contrast radiography
D. Technetium -99m scanning (Correct Answer)

Explanation: ***Technetium-99m scanning*** - **Technetium-99m pertechnetate scan** (Meckel's scan) is the **gold standard investigation** for diagnosing Meckel's diverticulum with ectopic gastric mucosa - Among the investigations that can actually **diagnose Meckel's diverticulum**, it has the **lowest radiation dose** (approximately 1-2 mSv) - The radioisotope is specifically taken up by ectopic gastric mucosa, providing both diagnostic utility and relatively low radiation exposure - **Sensitivity: 85-95%** for detecting ectopic gastric mucosa in Meckel's diverticulum - The radiation dose is comparable to a few months of natural background radiation and significantly lower than CT or contrast studies *MRI* - While **MRI uses no ionizing radiation**, it is **not a standard or practical investigation** for diagnosing Meckel's diverticulum - MRI cannot identify ectopic gastric mucosa specifically - It is rarely used in clinical practice for this indication - The question asks about investigation "in the diagnosis" of Meckel's diverticulum, implying a test that is actually used diagnostically *CT* - **Computed Tomography (CT)** delivers a **high radiation dose** (typically 5-10 mSv or more) - While it can identify structural abnormalities, it is not specific for Meckel's diverticulum - Not the first-line investigation for this condition *Contrast radiography* - **Contrast studies** (barium studies) use **moderate ionizing radiation** (3-5 mSv) - Limited utility in diagnosing Meckel's diverticulum as it primarily assesses luminal patency - Cannot identify ectopic gastric mucosa - Lower sensitivity compared to Tc-99m scanning

Question 220: Which of the following is used in the treatment of well differentiated thyroid carcinoma?

A. I-131 (Correct Answer)
B. Technetium-99m
C. Phosphorus-32
D. MIBG

Explanation: ***I-131*** - **Iodine-131** is used in the treatment of **well-differentiated thyroid carcinoma** due to the thyroid gland's unique ability to uptake and concentrate iodine. - The emitted **beta particles** from I-131 destroy residual thyroid tissue and metastatic thyroid cancer cells after surgery. *Technetium-99m* - **Technetium-99m** is primarily used for **diagnostic imaging** (e.g., bone scans, SPECT scans), not for therapeutic purposes in thyroid cancer. - While it can be taken up by thyroid tissue, its **short half-life** and emissions are not suitable for ablative therapy. *Phosphorus-32* - **Phosphorus-32** is a beta-emitter used in the treatment of **polycythemia vera** and other myeloproliferative disorders. - It has no role in the **diagnosis or treatment of thyroid carcinoma**. *MIBG* - **Metaiodobenzylguanidine (MIBG)**, labeled with iodine isotopes (e.g., I-123 for imaging, I-131 for therapy), is used for **neuroendocrine tumors** like **pheochromocytoma** and **neuroblastoma**. - It is not used for **well-differentiated thyroid carcinoma**.

Practice by Chapter

Physics of Nuclear Medicine

Practice Questions

Radiopharmaceuticals

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Radiation Detection in Nuclear Medicine

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Thyroid Scintigraphy

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Bone Scintigraphy

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Renal Nuclear Medicine

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Cardiac Nuclear Medicine

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Pulmonary Nuclear Medicine

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Neurological Nuclear Medicine

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PET/CT Principles and Applications

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Radionuclide Therapy

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Radiation Safety in Nuclear Medicine

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