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?
Increased radio-isotope uptake is seen in which of the following conditions?
Which of the following isotopes is radioactive?
Precautions advised after outpatient Radioiodine (I-131) therapy are all, EXCEPT:
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: 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).
Question 9: Which of the following isotopes is radioactive?
- A. Cobalt-59
- B. Cobalt-60 (Correct Answer)
- C. Yttrium-90
- D. None of the above
Explanation: **Explanation:** The correct answer is **Cobalt-60**. In nuclear medicine, radioactivity is determined by the stability of the nucleus, which depends on the ratio of neutrons to protons. **1. Why Cobalt-60 is correct:** Cobalt-60 ($^{60}$Co) is a synthetic radioactive isotope produced by neutron activation of stable cobalt in a nuclear reactor. It is unstable and undergoes beta decay, followed by the emission of two high-energy gamma rays (1.17 MeV and 1.33 MeV). Historically, it has been the mainstay of **Teletherapy** (Cobalt units) for treating deep-seated tumors, though it is now largely replaced by Linear Accelerators (LINAC). **2. Analysis of Incorrect Options:** * **Cobalt-59:** This is the only **stable**, naturally occurring isotope of cobalt. It is not radioactive. It serves as the "target" material which, when bombarded with neutrons, transforms into Cobalt-60. * **Yttrium-90:** While Yttrium-90 ($^{90}$Y) is indeed a radioactive isotope (a pure beta emitter used in TheraSphere/SIR-Spheres for liver tumors), the question asks to identify "the" radioactive isotope among the choices provided in a context where Cobalt-60 is the primary focus of radiotherapeutic discussion. *Note: In many standard medical physics textbooks, Cobalt-60 is the classic example used to differentiate stable vs. unstable isotopes.* **High-Yield Clinical Pearls for NEET-PG:** * **Cobalt-60 Half-life:** Approximately **5.27 years**. * **Decay Product:** It decays into stable **Nickel-60**. * **Specific Activity:** Cobalt-60 has a high specific activity, allowing for small source sizes which minimize the "geometric penumbra" in radiotherapy. * **Gamma Energy:** Average energy is **1.25 MeV** (mean of 1.17 and 1.33). * **Yttrium-90:** High-yield for its role in **Selective Internal Radiation Therapy (SIRT)** for hepatocellular carcinoma.
Question 10: Precautions advised after outpatient Radioiodine (I-131) therapy are all, EXCEPT:
- A. Carry treatment certificate for 90 days.
- B. Maintain a distance of 2 meters from children and pregnant women.
- C. Avoid using household chlorine bleaches for cleaning. (Correct Answer)
- D. Use contraception for three months.
Explanation: **Explanation:** Radioiodine (I-131) therapy is commonly used for hyperthyroidism and thyroid carcinoma. Post-therapy precautions are designed to minimize radiation exposure to others (ALARA principle) and prevent environmental contamination. **Why Option C is the Correct Answer:** Patients are actually **encouraged** to use household chlorine bleach to clean toilets and sinks after use. I-131 is excreted primarily through urine and saliva. Chlorine bleach effectively decontaminates the surfaces by chemically reacting with the radioiodine, reducing the risk of indirect exposure to family members. Therefore, "avoiding" it is incorrect advice. **Analysis of Other Options:** * **Option A (Treatment Certificate):** Patients must carry a treatment certificate for up to **90 days**. Modern security sensors (e.g., at airports or international borders) are highly sensitive and can detect residual gamma radiation from the patient’s body for several weeks. * **Option B (Social Distancing):** Patients are advised to maintain a distance of **2 meters (6 feet)** from others, especially children and pregnant women, for a specified period (usually 3–7 days depending on the dose) to minimize external gamma radiation exposure. * **Option C (Contraception):** Female patients must avoid pregnancy for at least **6 months**, and males should use contraception for **3–4 months** (to allow for one full cycle of spermatogenesis) to prevent potential genetic damage to the fetus. **Clinical Pearls for NEET-PG:** * **Mechanism:** I-131 emits both **Beta particles** (therapeutic effect/tissue destruction) and **Gamma rays** (diagnostic/safety concern). * **Half-life:** The physical half-life of I-131 is **8.02 days**. * **Contraindication:** Radioiodine is strictly **contraindicated in pregnancy** (crosses the placenta and destroys the fetal thyroid) and **breastfeeding**. * **Hydration:** Patients are advised to increase fluid intake to facilitate the renal clearance of unbound I-131.
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