Nuclear Medicine Practice Questions

Q: Which is the most sensitive test for metastatic deposits?

Isotope scan. **Explanation:** The **Isotope scan** (specifically the **Technetium-99m MDP bone scan**) is the most sensitive screening test for detecting skeletal metastatic deposits. **1. Why Isotope Scan is Correct:** The sensitivity of a bone scan lies in its ability to detect **functional/metabolic changes** in the bone. It identifies increased osteoblastic activity and increased vascularity at the site of a lesion long before structural changes occur. A bone scan can detect a lesion when there is only a **3–5% change** in bone metabolism. **2. Why Other Options are Incorrect:** * **Skeletal Survey (X-ray):** This is relatively insensitive. A lesion becomes visible on a plain radiograph only after **30–50% of the bone mineral content** is lost. It is often used for specific conditions like Multiple Myeloma (where bone scans may be "cold"). * **CT Scan:** While excellent for evaluating cortical bone and providing anatomical detail, it is less sensitive than an isotope scan for early marrow involvement and is not practical for whole-body screening. * **Tomography:** Conventional tomography is an outdated technique that provides sectional images but lacks the metabolic sensitivity required for early metastasis detection. **Clinical Pearls for NEET-PG:** * **Most Sensitive Overall:** PET-CT (especially for many solid tumors), but among the given options, Isotope scan is the standard answer. * **"Cold" Scan:** Metastatic lesions from **Multiple Myeloma**, thyroid cancer, or highly aggressive anaplastic tumors may appear "cold" (negative) on a bone scan because they are purely osteolytic. * **Flare Phenomenon:** An apparent increase in uptake on a bone scan shortly after starting chemotherapy, which actually represents healing rather than progression. * **Hot Spots:** Common in prostate, breast, and lung cancers.

Q: Which radiopharmaceutical is used to estimate renal GFR?

Tc99m DTPA. **Explanation:** The estimation of the **Glomerular Filtration Rate (GFR)** requires a radiopharmaceutical that is handled exclusively by glomerular filtration, with neither tubular secretion nor reabsorption. **1. Why Tc99m DTPA is correct:** **Tc99m DTPA (Diethylene Triamine Penta-acetic Acid)** is the gold standard for dynamic renal imaging to estimate GFR. It is a small chelate that is filtered solely by the glomeruli. Because it is not secreted or reabsorbed by the renal tubules, its clearance rate directly reflects the GFR. **2. Why other options are incorrect:** * **Tc99m MAG3 (Mercaptoacetyltriglycine):** This agent is primarily cleared by **tubular secretion** (approx. 95%). It is the agent of choice for estimating **Effective Renal Plasma Flow (ERPF)** and is preferred over DTPA in patients with impaired renal function or suspected obstruction due to its higher extraction fraction. * **Tc99m DMSA (Dimercaptosuccinic Acid):** This is a **static** renal imaging agent. It binds to the proximal convoluted tubules and remains in the renal cortex for a long duration. It is used to evaluate **renal morphology**, cortical scarring (e.g., in pyelonephritis), and differential renal function, but not GFR. **High-Yield Clinical Pearls for NEET-PG:** * **GFR Estimation:** Tc99m DTPA. * **ERPF Estimation:** Tc99m MAG3 (replaced the older I-131 Hippuran). * **Renal Cortical Imaging/Scarring:** Tc99m DMSA. * **Diuretic Renography (Lasix Scan):** Uses DTPA or MAG3 to differentiate between obstructive and non-obstructive hydronephrosis. * **Captopril Scan:** Used for diagnosing **Renovascular Hypertension** (Renal Artery Stenosis).

Q: Which radioisotope study is preferred for the detection of parathyroid adenoma?

Sestamibi scan. **Explanation:** The **Tc-99m Sestamibi scan** (also known as the MIBI scan) is the gold standard nuclear imaging modality for localizing parathyroid adenomas. **Why Sestamibi is the Correct Choice:** The principle relies on **differential washout**. Sestamibi is a lipophilic cation that accumulates in mitochondria-rich cells. Both the thyroid and the hyperfunctioning parathyroid tissue (adenoma) take up the tracer initially. However, the tracer washes out rapidly from normal thyroid tissue but is **retained much longer** in the oxyphil cells of a parathyroid adenoma. Delayed imaging (usually at 2 hours) allows the adenoma to be visualized as a "hot spot" against a faded thyroid background. **Analysis of Incorrect Options:** * **A. I-131:** This is used for imaging and treating **thyroid** pathologies (like Graves' disease or thyroid cancer) because the thyroid gland actively traps and organifies iodine. It has no role in parathyroid imaging. * **C. Thallium-201 scan:** Historically used in a "Subtraction Scan" (Thallium minus Technetium), it is now obsolete. Thallium is taken up by both thyroid and parathyroid, but it has poorer image quality and higher radiation compared to Sestamibi. * **D. Tc 99m-MDP:** This is a phosphonate used for **Bone Scans**. It detects osteoblastic activity and is used for metastases or fractures, not endocrine adenomas. **High-Yield Clinical Pearls for NEET-PG:** * **SPECT/CT:** Combining Sestamibi with CT provides anatomical localization, which is crucial for ectopic parathyroid adenomas (commonly found in the **mediastinum**). * **Dual-Tracer Imaging:** If Sestamibi is unavailable, **Tc-99m Pertechnetate** (thyroid only) can be subtracted from **Tl-201** (thyroid + parathyroid) to isolate the adenoma. * **Intraoperative MIBI:** Can be used with a gamma probe to guide the surgeon during minimally invasive parathyroidectomy.

Q: Radioactive phosphorus is used in the treatment of which condition?

Polycythemia. **Explanation:** **Radioactive Phosphorus-32 (P-32)** is a pure beta-emitter with a physical half-life of 14.3 days. It is used in the treatment of **Polycythemia Vera (PV)** because phosphorus is a key component of nucleic acids. Since hematopoietic cells in the bone marrow have a high turnover rate and rapid DNA synthesis, they preferentially concentrate P-32. The emitted beta particles cause local ionization, leading to the suppression of hyperactive bone marrow and a reduction in red blood cell production. **Analysis of Options:** * **A. Polycythemia (Correct):** P-32 was historically the treatment of choice for PV. While hydroxyurea and phlebotomy are now preferred due to the long-term risk of leukemic transformation associated with radiation, P-32 remains an option for elderly patients or those refractory to other therapies. * **B. Thyroid metastasis:** These are treated with **Radioactive Iodine-131 (I-131)**, which is sequestered by thyroid tissue via the sodium-iodide symporter. * **C. Multiple myeloma:** Treatment typically involves chemotherapy, proteasome inhibitors, and autologous stem cell transplant. While P-32 was once explored for bone pain, it is not a standard treatment. * **D. Embryonal cell carcinoma:** This is a germ cell tumor treated primarily with surgical resection and platinum-based chemotherapy (BEP regimen). **High-Yield Clinical Pearls for NEET-PG:** * **P-32 Properties:** Pure beta emitter; maximum tissue penetration is approximately 8 mm. * **Other uses of P-32:** It is also used for the **palliative treatment of painful bone metastases** (though Strontium-89 and Samarium-153 are more common) and via intra-articular injection for **radiosynovectomy** in chronic synovitis. * **Diagnostic use:** The "P-32 uptake test" was formerly used to differentiate benign from malignant intraocular melanomas.

Q: What does a "cold nodule" represent on a thyroid scintiscan?

A nonfunctioning nodule that is potentially malignant. ### Explanation **Underlying Medical Concept** Thyroid scintigraphy (using **Technetium-99m pertechnetate** or **Iodine-123**) assesses the functional activity of thyroid tissue based on its ability to trap and organify radionuclides. A **"cold nodule"** is a region of the thyroid gland that fails to take up the radioactive tracer. This lack of uptake indicates that the tissue is **non-functioning** (hypofunctional). While most cold nodules are benign (e.g., cysts, adenomas, or focal thyroiditis), they are clinically significant because approximately **10–15%** of them represent thyroid malignancy. In contrast, "hot" (hyperfunctioning) nodules are almost never malignant. **Analysis of Options** * **Option A (Incorrect):** "Cold" refers to the lack of tracer uptake on the scan image, not the physical temperature of the nodule upon palpation. * **Option B (Incorrect):** A hyperactive nodule is termed a **"hot nodule."** These appear darker/more intense than the surrounding thyroid tissue and typically suppress the rest of the gland. * **Option D (Incorrect):** While inflammation can affect tracer uptake, the term "cold" specifically describes the functional imaging appearance, not the presence or absence of clinical inflammatory signs like rubor or calor. **High-Yield Clinical Pearls for NEET-PG** * **Incidence:** Cold nodules are the most common finding on thyroid scans (approx. 80-85% of nodules). * **Next Step in Management:** If a cold nodule is identified, the gold standard for definitive diagnosis is **Fine Needle Aspiration Cytology (FNAC)**. * **Warm Nodule:** Has uptake similar to normal thyroid tissue; the risk of malignancy is low (approx. 5%). * **Tracer of Choice:** Tc-99m is preferred for routine scans due to its short half-life (6 hours) and lower radiation dose compared to Iodine-131.

Q: Which of the following conditions is NOT evaluated using 99mTc-DMSA scintigraphy?

Renal artery stenosis. **Explanation:** **99mTc-DMSA (Dimercaptosuccinic Acid)** is a **static renal imaging agent** that binds to the proximal convoluted tubules in the renal cortex. Because it remains fixed in the cortex for a prolonged period, it is the gold standard for visualizing **functional renal anatomy** rather than physiological drainage. 1. **Why Renal Artery Stenosis (RAS) is the correct answer:** RAS is a vascular and functional perfusion abnormality. It is evaluated using **99mTc-MAG3 or 99mTc-DTPA** (dynamic renography), often combined with an **ACE inhibitor (Captopril) challenge**. DMSA is a static cortical agent and cannot assess real-time blood flow or glomerular filtration changes required to diagnose RAS. 2. **Analysis of Incorrect Options:** * **Renal Scarring:** DMSA is the **investigation of choice** for detecting cortical scarring (e.g., from chronic pyelonephritis) as scars appear as "cold" defects (areas of photopenia). * **Renal Pseudomass:** It helps differentiate a true tumor from a "pseudotumor" (like a prominent Column of Bertin). A pseudomass will show normal DMSA uptake (functioning tissue), whereas a malignant tumor will appear as a void. * **Renal Anomalies:** It is excellent for identifying ectopic kidneys, horseshoe kidneys, or assessing the functional contribution of a multicystic dysplastic kidney. **High-Yield Clinical Pearls for NEET-PG:** * **Static Agents:** 99mTc-DMSA (Cortex imaging), 99mTc-Glucoheptonate (Both cortex and excretion). * **Dynamic Agents:** 99mTc-DTPA (GFR measurement), 99mTc-MAG3 (ERPF; best for neonates/renal failure). * **Acute Pyelonephritis:** DMSA is the most sensitive test to detect early cortical inflammation. * **Wait Time:** Imaging is typically performed **2–4 hours** after injection to allow for optimal cortical fixation.

Q: Which of the following isotopes of Iodine is used for thyroid scan?

I-123. ### Explanation **1. Why I-123 is the Correct Answer:** Iodine-123 (I-123) is the isotope of choice for **diagnostic thyroid scanning** because it emits pure **gamma radiation (159 keV)**, which is ideal for detection by a gamma camera. It has a short half-life of approximately **13.2 hours**, resulting in a significantly lower radiation dose to the patient compared to I-131. It provides superior image quality for assessing thyroid morphology and function. **2. Analysis of Incorrect Options:** * **I-125:** This isotope has a long half-life (60 days) and emits low-energy photons. It is primarily used in **radioimmunoassays (RIA)** and **brachytherapy** (e.g., prostate cancer seeds), but not for routine thyroid imaging. * **I-127:** This is the only **stable, non-radioactive** isotope of iodine. It is the form found in iodized salt and does not emit radiation, making it useless for imaging. * **I-131:** While used for thyroid uptake studies, its primary role is **therapeutic** (treatment of Graves' disease or thyroid cancer). It emits **beta particles**, which cause tissue destruction, and has a long half-life (8 days), leading to high radiation exposure. It is generally avoided for routine diagnostic scans unless looking for metastatic thyroid cancer. **3. NEET-PG High-Yield Pearls:** * **Technetium-99m pertechnetate (Tc-99m):** Often used as an alternative for thyroid scans because it is cheaper and more readily available than I-123. However, it is only "trapped" by the thyroid and not "organified." * **Cold Nodule:** A region of decreased uptake on a scan; carries a ~15-20% risk of malignancy. * **Hot Nodule:** Increased uptake; usually benign (e.g., Toxic Adenoma). * **Stun Phenomenon:** Large diagnostic doses of I-131 can "stun" thyroid tissue, reducing the effectiveness of subsequent therapeutic doses; this is why I-123 is preferred for pre-treatment scanning.

Q: Vesicoureteric reflux is demonstrated by using which imaging modality?

MAG3 - Tc 99 (Mercaptoacetyltriglycine scan). **Explanation:** The correct answer is **MAG3 - Tc 99 (Mercaptoacetyltriglycine scan)**. Vesicoureteric reflux (VUR) is typically evaluated using a **Radionuclide Cystogram (RNC)**. In this procedure, the radiopharmaceutical (most commonly **Tc-99m MAG3** or Tc-99m Sulfur Colloid) is introduced into the bladder to detect the retrograde flow of urine into the ureters or kidneys. MAG3 is preferred for indirect cystography because it is cleared rapidly by the kidneys via tubular secretion, providing high-contrast images of the urinary tract. **Analysis of Options:** * **A. DMSA Scan:** This is a "static" renal scan. DMSA binds to the proximal convoluted tubules. It is the gold standard for detecting **renal cortical scarring** (often a consequence of VUR) and acute pyelonephritis, but it cannot demonstrate active reflux. * **B. DTPA Scan:** This is a "dynamic" scan used primarily to estimate the **Glomerular Filtration Rate (GFR)** and evaluate obstructive uropathy. While it can be used for indirect cystography, MAG3 is superior due to better target-to-background ratios. * **D. I123 Iodocholesterol Scan:** This is used for **adrenal cortical imaging** (e.g., diagnosing Cushing’s syndrome or Conn’s syndrome), not the urinary tract. **High-Yield Clinical Pearls for NEET-PG:** * **Direct Radionuclide Cystography (DRC):** More sensitive than MCU (Micturating Cystourethrogram) for detecting VUR and involves lower radiation. However, it provides poor anatomical detail compared to MCU. * **DMSA = "D" for Detail/Damage:** Used for cortical scars. * **DTPA = "G" for GFR:** Filtered by the glomerulus. * **MAG3 = "T" for Tubular secretion:** Best for neonates and patients with impaired renal function.

Question 1

What is the best diagnostic method for ectopic gastric mucosa in a Meckel's diverticulum?

Accepted Answer

Radionuclide scan

Answer

Fluoroscopy

Answer

Occult blood test in stool

Answer

Ultrasound abdomen

Question 2

Myocardial uptake gated acquisition (MUGA) scan is done for what purpose?

Accepted Answer

Assessing ventricular function and anthracycline-induced cardiotoxicity

Answer

Testing drug toxicity

Answer

Evaluating myocardial perfusion

Answer

None of the above

Question 3

Which is the most sensitive test for metastatic deposits?

Accepted Answer

Isotope scan

Answer

CT scan

Answer

Skeletal survey

Answer

Tomography

Question 4

Which radiopharmaceutical is used to estimate renal GFR?

Accepted Answer

Tc99m DTPA

Answer

TC99m MAG3

Answer

TC99m DMSA

Answer

All of the above

Question 5

Which radioisotope study is preferred for the detection of parathyroid adenoma?

Accepted Answer

Sestamibi scan

Answer

I-131

Answer

Thallium-201 scan

Answer

Tc 99m-MDP

Question 6

Radioactive phosphorus is used in the treatment of which condition?

Accepted Answer

Polycythemia

Answer

Thyroid metastasis

Answer

Multiple myeloma

Answer

Embryonal cell carcinoma

Question 7

What does a "cold nodule" represent on a thyroid scintiscan?

Accepted Answer

A nonfunctioning nodule that is potentially malignant

Answer

A nodule that is cool to the touch

Answer

A hyperactive nodule

Answer

A nodule without signs of inflammation

Question 8

Which of the following conditions is NOT evaluated using 99mTc-DMSA scintigraphy?

Accepted Answer

Renal artery stenosis

Answer

Renal anomalies

Answer

Renal pseudomass

Answer

Renal scarring

Question 9

Which of the following isotopes of Iodine is used for thyroid scan?

Accepted Answer

I-123

Answer

I-125

Answer

I-127

Answer

I-131

Question 10

Vesicoureteric reflux is demonstrated by using which imaging modality?

Accepted Answer

MAG3 - Tc 99 (Mercaptoacetyltriglycine scan)

Answer

DMSA (Dimercaptosuccinic acid) scan

Answer

DTPA (Diethylenetriaminepentaacetic acid) scan

Answer

I123 iodocholesterol scan

Nuclear Medicine — MCQs

Nuclear Medicine — MCQs

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