Radiopharmaceuticals — MCQs
99m Technetium labeled RBC scintigraphy is PRIMARILY used in the diagnosis of
In radionuclide imaging, the most useful radiopharmaceutical for skeletal imaging is:
Half-life of iodine-131 is
Which test is used for detecting gunshot residue?
Tc-labeled RBCs are used for all except:
Which of the following statements about the half-life of radioisotopes is false?
Which artificial radioisotopes are used in nuclear medicine?
Which radiopharmaceutical is used for a liver scan?
What is the investigation of choice for whole-body imaging in metastasis?
Increased radio-isotope uptake is seen in which of the following conditions?
Radiopharmaceuticals Indian Medical PG Practice Questions and MCQs
Question 1: 99m Technetium labeled RBC scintigraphy is PRIMARILY used in the diagnosis of
- A. Hepatoma
- B. Left ventricular function wall motion
- C. Hepatic hemangioma
- D. GI Bleeding (Correct Answer)
Explanation: ***GI Bleeding*** - Technetium-99m labeled RBC scintigraphy (**<sup>99m</sup>Tc-RBC scan**) is highly sensitive for detecting **active gastrointestinal bleeding**, especially slow or intermittent bleeding. - The labeled red blood cells extravasate at the site of bleeding, accumulating and outlining the bleeding focus over time. *Hepatoma* - **Hepatoma** (hepatocellular carcinoma) is primarily diagnosed using imaging modalities like **CT, MRI**, and **ultrasound**, often with contrast enhancement. - While nuclear medicine scans like **FDG-PET** can be used in some cases for staging or assessing viability, <sup>99m</sup>Tc-RBC scans are not a primary diagnostic tool for hepatoma. *Left ventricular function wall motion* - **Left ventricular function** and **wall motion abnormalities** are typically assessed using **echocardiography**, cardiac **MRI**, or **nuclear cardiology studies** like **SPECT** or **PET** using tracers that localize in the myocardium (e.g., <sup>99m</sup>Tc-Sestamibi or Thallium-201). - <sup>99m</sup>Tc-RBC scans are sometimes used for **gated blood pool scans** to assess global ejection fraction, but not directly for wall motion analysis in the same way as other dedicated cardiac modalities. *Hepatic hemangioma* - **Hepatic hemangiomas** can be characterized by **<sup>99m</sup>Tc-RBC scintigraphy**, which shows **early photopenia** followed by **delayed fill-in and retention** of the tracer due to the characteristic slow blood flow within these benign vascular tumors. - While it can be used for confirmation, it's not the most commonly used primary diagnostic tool (which is often **ultrasound** or **MRI** with specific contrast patterns), and GI bleeding is a more direct application where the scan detects extravasation rather than vascular pooling.
Question 2: In radionuclide imaging, the most useful radiopharmaceutical for skeletal imaging is:
- A. Technetium-99m linked to Methylene diphosphonate (Correct Answer)
- B. Gallium 67
- C. Technetium-99m
- D. Technetium-sulfur-colloid
Explanation: ***Technetium-99m linked to Methylene diphosphonate*** - **Technetium-99m MDP** is the most widely used radiopharmaceutical for skeletal imaging due to its **high affinity for hydroxyapatite crystals** in bone and favorable physical properties. - It readily incorporates into areas of **increased bone turnover**, making it excellent for detecting fractures, infections, and metastatic lesions. *Gallium 67* - **Gallium 67** is primarily used for **oncology, infection, and inflammation imaging** and has limited utility for general skeletal imaging. - It accumulates in areas of infection and inflammation, but its **biodistribution is not specific for bone metabolism**. *Technetium-sulfur-colloid* - **Technetium-sulfur-colloid** is mainly used for **liver and spleen imaging** (reticuloendothelial system), not for bone scans. - Its particle size and chemical properties prevent its significant uptake in bone tissue. *Technetium-99m* - **Technetium-99m** is a **radioisotope generator** for many different radiopharmaceuticals, but by itself, it's not directly used for skeletal imaging. - It serves as the **radionuclide scaffold** that is chelated to specific bone-seeking ligands like MDP.
Question 3: Half-life of iodine-131 is
- A. 8 days (Correct Answer)
- B. 8 hours
- C. 8 weeks
- D. 8 months
Explanation: ***8 days*** - The half-life of **iodine-131** is approximately 8.02 days, which makes it suitable for both diagnostic imaging and therapeutic applications in thyroid conditions. - This specific half-life allows sufficient time for the isotope to localize in the thyroid gland and deliver a therapeutic dose, while also ensuring it clears from the body relatively quickly to minimize long-term radiation exposure. *8 hours* - A half-life of 8 hours would be too short for many therapeutic applications of iodine-131, as it would decay too rapidly to deliver an effective dose to the thyroid. - Isotopes with such short half-lives are typically used for diagnostic imaging where rapid clearance and minimal patient exposure are paramount, such as **technetium-99m**. *8 weeks* - A half-life of 8 weeks would be excessively long for clinical use of iodine-131, leading to prolonged radiation exposure for the patient. - Such long half-lives increase the risk of adverse effects from cumulative radiation, making it unsuitable for routine diagnostic or therapeutic procedures. *8 months* - A half-life of 8 months is impractically long for any medical application requiring regular administration, as it would lead to very high and persistent radiation doses. - This duration would result in significant and unacceptable long-term radiation hazards, making its use unfeasible for imaging or therapy.
Question 4: Which test is used for detecting gunshot residue?
- A. Lie test for Firearm injury
- B. Neutron activation analysis for firearm use (Correct Answer)
- C. Toluidine blue test
- D. Benzidine test for blood stain
Explanation: ***Neutron activation analysis for firearm use*** - **Neutron activation analysis (NAA)** is a highly sensitive and reliable method for detecting specific elements characteristic of **gunshot residue (GSR)**, such as **barium**, **antimony**, and **lead**. - This technique works by irradiating samples with neutrons, causing them to emit gamma rays that are unique to each element, allowing for precise identification and quantification of GSR particles. *Lie test for Firearm injury* - A "lie test" typically refers to a **polygraph test**, which assesses physiological responses to detect deception, not physical evidence like gunshot residue. - Polygraph tests are not used for identifying **firearm injury** or the presence of actual physical traces. *Toluidine blue test* - The **Toluidine blue test** is primarily used in dentistry to detect and delineate **dysplastic or malignant lesions** in the oral mucosa. - It has no application in the forensic analysis of gunshot residue or firearm use. *Benzidine test for blood stain* - The **Benzidine test** was historically used as a preliminary test for the presence of **blood stains**, as it reacts with the heme component of hemoglobin. - It is not used for detecting **gunshot residue** and has largely been replaced by safer and more specific tests due to its carcinogenic properties.
Question 5: Tc-labeled RBCs are used for all except:
- A. Liver adenoma (Correct Answer)
- B. LV function
- C. GI bleeding
- D. Liver hemangioma
Explanation: ***Liver adenoma*** - Tc-labeled RBCs are primarily used to highlight a specific type of tissue or process. **Liver adenomas** do not typically show an affinity for **Tc-labeled RBCs**, as they are benign epithelial tumors with a different vascular composition. - While adenomas can be vascular, they do not inherently contain the **vascular pooling** or blood volume characteristics that would be specifically targeted by **Tc-labeled RBCs** for diagnostic imaging. *LV function* - **Tc-labeled RBCs** (or Tc-99m-pertechnetate) are commonly used in **gated blood pool imaging** (MUGA scan) to assess **left ventricular (LV) function**, including **ejection fraction** and wall motion abnormalities. - This technique directly visualizes the blood pool within the cardiac chambers, making it suitable for assessing functional parameters of the heart. *GI bleeding* - **Tc-labeled RBCs** are a standard imaging agent for detecting and localizing **active gastrointestinal (GI) bleeding**, especially when the bleeding rate is intermittent or slow. - The labeled RBCs extravasate at the site of hemorrhage, creating a 'hot spot' that can be identified over time. *Liver hemangioma* - **Tc-labeled RBCs** are highly effective in diagnosing **liver hemangiomas**, which are benign vascular tumors composed of large, dilated blood vessels. - These lesions show characteristic uptake and retention of **labeled RBCs** due to their slow blood flow and large intravascular space, appearing as early peripheral enhancement with subsequent centripetal filling.
Question 6: 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 7: 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 8: Which radiopharmaceutical is used for a liver scan?
- A. Tc-99m sulphur colloid (Correct Answer)
- B. Tc-99m mebrofenin
- C. Tc-99m MIBI
- D. Tc-99m DTPA
Explanation: **Explanation:** The correct answer is **Tc-99m sulphur colloid**. The underlying principle for a liver-spleen scan is the **phagocytic activity of the Reticuloendothelial System (RES)**. When Tc-99m sulphur colloid is injected intravenously, the particles (sized 0.1–1.0 μm) are cleared from the blood by Kupffer cells in the liver (80–90%), splenic macrophages (5–10%), and bone marrow. This scan is primarily used to evaluate functional liver anatomy and detect "cold nodules" (e.g., abscesses or tumors) or "hot spots" (e.g., Focal Nodular Hyperplasia). **Analysis of Incorrect Options:** * **Tc-99m Mebrofenin:** This is an IDA (Iminodiacetic acid) derivative used for **HIDA scans**. It evaluates the **hepatobiliary system** (hepatocyte uptake and biliary excretion) and is the gold standard for diagnosing Acute Cholecystitis. * **Tc-99m MIBI:** Primarily used for **Myocardial Perfusion Imaging** and Parathyroid imaging. It is taken up by mitochondria. * **Tc-99m DTPA:** A chelating agent cleared by glomerular filtration, used for **Renal Dynamic Scans** to assess GFR and obstructive uropathy. **High-Yield Clinical Pearls for NEET-PG:** 1. **Colloid Shift:** In portal hypertension or cirrhosis, there is decreased liver uptake and increased uptake in the spleen and bone marrow. 2. **Focal Nodular Hyperplasia (FNH):** This is the only liver lesion that typically appears "hot" or "isointense" on a sulphur colloid scan due to the presence of Kupffer cells. 3. **Hot Spot on Liver Scan:** Classically seen in **Superior Vena Cava (SVC) Obstruction** (due to collateral flow via the vein of Sappey).
Question 9: What is the investigation of choice for whole-body imaging in metastasis?
- A. Magnetic Resonance Imaging
- B. Radiography
- C. Bone scan (Correct Answer)
- D. CT Scan
Explanation: **Explanation:** **Bone Scan (Technetium-99m MDP)** is the investigation of choice for screening whole-body skeletal metastases because of its high sensitivity and ability to image the entire skeleton in a single session. It works on the principle of detecting increased osteoblastic activity (bone remodeling) at sites of tumor infiltration. Its primary advantage is the ability to detect "hot spots" weeks or months before structural changes become visible on conventional X-rays. **Why other options are incorrect:** * **Radiography (X-ray):** It has low sensitivity for early metastasis. A bone lesion only becomes visible on an X-ray after **30-50% of bone mineral density is lost**. It is, however, the best modality to confirm a finding seen on a bone scan. * **CT Scan:** While excellent for evaluating cortical bone and detailed anatomy, it is not practical for whole-body screening due to high radiation doses and lower sensitivity for early marrow-based lesions compared to nuclear imaging. * **MRI:** MRI is the most sensitive modality for detecting **bone marrow infiltration**. However, it is not typically the first-line "investigation of choice" for whole-body screening due to high costs, long scan times, and limited availability of whole-body MRI protocols. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Tc-99m MDP (Methylene Diphosphonate) adsorbs onto the **hydroxyapatite crystals** of the bone. * **The "Cold Scan" Exception:** Highly aggressive or purely osteolytic tumors (e.g., Multiple Myeloma, Renal Cell Carcinoma, or Thyroid Cancer) may show as "cold" or false-negative on a bone scan because they do not trigger an osteoblastic response. * **Flare Phenomenon:** An apparent increase in tracer uptake seen shortly after starting chemotherapy, which actually represents healing bone rather than disease progression. * **Superscan:** A bone scan showing intense, uniform skeletal uptake with **absent renal/bladder activity**, typically seen in diffuse metastatic prostate cancer or hyperparathyroidism.
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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