Nuclear Medicine Practice Questions

Q: What diagnosis is implied by the results of this gallium scan?

Sarcoidosis. ***Sarcoidosis*** - **Gallium-67 scan** shows characteristic **panda sign** (parotid and lacrimal gland uptake) and **lambda sign** (bilateral hilar and right paratracheal lymph node uptake), which are pathognomonic for sarcoidosis. - These specific uptake patterns on gallium scan are highly diagnostic and distinguish sarcoidosis from other inflammatory conditions. *Mumps* - Involves **parotid gland swelling** but lacks the characteristic **bilateral hilar lymphadenopathy** seen on gallium scan. - **Viral parotitis** would not show the **lambda sign** or **systemic inflammatory uptake** pattern typical of sarcoidosis. *Paget's disease* - Primarily affects **bone metabolism** and would show increased uptake in **affected bones** rather than parotid glands or hilar lymph nodes. - **Gallium scan** is not typically used for Paget's disease diagnosis; **bone scan** with technetium-99m is preferred. *Septic emboli* - Would show **multiple scattered hot spots** in lungs corresponding to **infected embolic foci**, not the organized bilateral hilar pattern. - Lacks the characteristic **panda sign** and **lambda sign** that are specific for sarcoidosis on gallium imaging.

Q: Which of the following statements about isotope scanning of the thyroid is FALSE?

Isotope scanning is useful in hypothyroid patients.. **Explanation** The primary objective of thyroid isotope scanning is to assess the **functional status** of a thyroid nodule (categorizing it as hot, warm, or cold). **1. Why Option D is the Correct (False) Statement:** Isotope scanning relies on the thyroid gland's ability to trap and organify iodine under the influence of **TSH**. In hypothyroid patients, the gland is underactive or destroyed, and the scan typically shows poor or absent uptake, providing no diagnostic utility. The first-line investigation for hypothyroidism is a biochemical profile (TSH, Free T4), while the first-line investigation for a thyroid nodule is **USG-guided FNAC**, not a scan. **2. Analysis of Other Options:** * **Option A:** **I-123** is the isotope of choice for thyroid imaging because it has a short half-life (13 hours) and emits pure gamma radiation, resulting in a lower radiation dose than I-131. * **Option B:** While "cold" nodules (non-functioning) have a higher risk of malignancy than "hot" nodules, the vast majority (**~80-85%**) are still **benign** (e.g., cysts, adenomas, or thyroiditis). * **Option C:** "Warm" or "Hot" nodules (functioning) are rarely malignant, but the risk is not zero; approximately **5%** or less may harbor malignancy. **Clinical Pearls for NEET-PG:** * **Cold Nodule:** High risk of malignancy (~15-20%). * **Hot Nodule:** Low risk of malignancy (<1-5%); usually represents a toxic adenoma. * **Technetium-99m pertechnetate:** Often used in clinical practice due to low cost and ready availability, though it is only trapped and not organified. * **I-131:** Primarily used for **therapeutic** purposes (ablation) rather than routine imaging due to high-energy beta emission.

Q: Which one of the following conditions is diagnosed by Tc-99m Pertechnetate Scintigraphy?

Meckel's diverticulum. **Explanation:** **Meckel’s diverticulum** is the correct answer because it frequently contains **ectopic gastric mucosa** (present in approximately 50% of symptomatic cases). The radiopharmaceutical **Technetium-99m (Tc-99m) Pertechnetate** has a natural affinity for the mucoid cells of the gastric mucosa. When injected intravenously, it is taken up and secreted by these cells, allowing for the visualization of the diverticulum as a "hot spot" (area of increased tracer uptake) usually located in the right lower quadrant. This procedure is clinically known as a **Meckel’s Scan**. **Why other options are incorrect:** * **Pharyngeal (Zenker’s), Duodenal, and Colonic diverticula** do not typically contain ectopic gastric mucosa. Therefore, they do not concentrate Tc-99m Pertechnetate. These conditions are better diagnosed using anatomical imaging like Barium studies or CT scans. **High-Yield Clinical Pearls for NEET-PG:** * **Rule of 2s:** Meckel’s diverticulum occurs in 2% of the population, is 2 inches long, located 2 feet from the ileocecal valve, and often presents by age 2. * **Pharmacological Augmentation:** To increase the sensitivity of the scan, the following may be used: * **Pentagastrin:** Stimulates uptake by gastric mucosa. * **H2 Blockers (e.g., Cimetidine):** Inhibits the release of the pertechnetate from the mucosal cells into the lumen. * **Glucagon:** Decreases peristalsis, preventing the "washout" of the tracer. * **False Negatives:** Can occur if there is no ectopic gastric mucosa or if there is brisk bleeding washing away the tracer.

Q: What is the modality of choice for screening of bony metastases?

Bone scan. **Explanation:** The modality of choice for **screening** bony metastases is a **Bone Scan (Technetium-99m MDP scintigraphy)**. This is due to its high sensitivity and ability to perform a whole-body survey in a single session. **Why Bone Scan is correct:** Bone scans detect **osteoblastic activity** (bone remodeling). Metastatic cells disrupt normal bone metabolism, leading to increased uptake of the radiopharmaceutical ("hot spots"). Its primary advantage is that it can detect functional changes **weeks to months before** structural changes become visible on conventional imaging. **Why other options are incorrect:** * **Plain Radiograph:** It has very low sensitivity. A bone lesion only becomes visible on an X-ray after **30-50% of bone mineral density** is lost. It is used for confirming a site at risk of pathological fracture, not for screening. * **CT Scan:** While excellent for evaluating cortical bone and detailed anatomy, it is not used for screening because it is difficult to scan the entire skeleton at once and involves high radiation doses. * **MRI:** This is the **most sensitive** modality for detecting early marrow involvement (even before a bone scan). However, it is not the "screening modality of choice" due to high costs, long scan times, and limited availability for whole-body imaging. **High-Yield Clinical Pearls for NEET-PG:** 1. **"Cold" Lesions:** Highly aggressive tumors (e.g., Multiple Myeloma, Renal Cell Carcinoma) may show no uptake on a bone scan because they are purely osteolytic and do not trigger a bone-forming response. 2. **Flare Phenomenon:** An apparent increase in uptake/number of lesions on a bone scan shortly after starting chemotherapy, which actually represents healing, not progression. 3. **Superscan:** A bone scan showing intense, symmetrical skeletal uptake with **absent renal activity**, typically seen in widespread metastases (Prostate CA) or metabolic bone disease.

Q: What is the gold standard method for detecting renal scarring in a patient with recurrent urinary tract infection?

99mTc-DMSA scan. **Explanation:** **99mTc-DMSA (Dimercaptosuccinic Acid)** is the gold standard for detecting renal cortical scarring and assessing differential renal function. DMSA is a **static renal imaging agent** that binds to the sulfhydryl groups in the proximal convoluted tubules of the renal cortex. Because it remains fixed in the cortex for a prolonged period, it provides high-resolution images of the renal parenchyma. Areas of scarring appear as "cold spots" (photopenic areas) or wedge-shaped defects with associated volume loss. **Analysis of Incorrect Options:** * **99mTc-DTPA (Diethylene Triamine Pentaacetic Acid):** This is a **dynamic renal imaging agent** primarily filtered by the glomerulus. It is the investigation of choice for measuring the Glomerular Filtration Rate (GFR) and evaluating obstructive uropathy, but it lacks the cortical resolution required to detect scars. * **99mTc-MIBG Scan:** Used primarily for imaging neuroendocrine tumors, such as pheochromocytoma and neuroblastoma. It is an analog of norepinephrine and has no role in renal cortical imaging. * **99mTc-MDP (Methylene Diphosphonate):** This is the standard agent for **skeletal scintigraphy (bone scan)**. While it is excreted by the kidneys, it is used to detect osteoblastic activity, not renal pathology. **High-Yield Clinical Pearls for NEET-PG:** * **DMSA Scan Timing:** In acute pyelonephritis, a DMSA scan can show temporary defects. To confirm permanent **scarring**, the scan should be performed at least 4–6 months after the acute infection. * **VUR Link:** Recurrent UTIs and Vesicoureteral Reflux (VUR) are the most common causes of DMSA-detected scars (Reflux Nephropathy). * **MAG3 (Mercaptoacetyltriglycine):** Another dynamic agent (secreted by tubules) used for renal scans, especially in patients with impaired renal function, but DMSA remains superior for cortical morphology.

Q: Whole-body iodine scan after total thyroidectomy is not recommended for which type of thyroid cancer?

Medullary thyroid cancer. **Explanation:** The fundamental concept behind iodine scanning is the ability of thyroid follicular cells to concentrate iodine via the **Sodium-Iodide Symporter (NIS)**. **Why Medullary Thyroid Cancer (MTC) is the correct answer:** MTC originates from the **Parafollicular C-cells** (neuroendocrine cells), which produce calcitonin. Unlike follicular cells, C-cells do not express the NIS and do not have the physiological machinery to trap or organify iodine. Therefore, MTC is **non-iodine avid**. A whole-body iodine scan (WBS) would be negative even in the presence of metastatic disease, making it clinically useless for this subtype. **Why the other options are incorrect:** * **Papillary (PTC) and Follicular (FTC) Thyroid Cancer:** These are "Differentiated Thyroid Cancers" (DTC) arising from follicular epithelium. They retain the expression of the NIS (though often at lower levels than normal tissue). Post-thyroidectomy WBS is a standard procedure in these cases to detect residual thyroid tissue or distant metastases (e.g., lungs, bone). * **Anaplastic Thyroid Cancer:** While anaplastic cancer is also non-iodine avid, it is typically excluded from this specific question's logic because it is undifferentiated. However, in the context of standard management protocols, MTC is the classic "high-yield" answer because it arises from a completely different cell lineage (C-cells). **NEET-PG High-Yield Pearls:** * **Tumor Marker for MTC:** Calcitonin and CEA (used for follow-up instead of Thyroglobulin). * **Imaging for MTC:** Since iodine scans don't work, **Ga-68 DOTATATE PET/CT** or FDG-PET/CT are preferred for localization. * **Genetics:** MTC is associated with **RET proto-oncogene** mutations (MEN 2A and 2B). * **Stunning Effect:** Diagnostic doses of I-131 can "stun" cells, reducing the efficacy of subsequent therapeutic doses; hence, I-123 is often preferred for diagnostic WBS.

Q: What is the investigation of choice for detecting renal scarring defects?

DMSA scan. **Explanation:** The investigation of choice for detecting renal scarring is the **DMSA (Dimercaptosuccinic Acid) scan**. **1. Why DMSA is the Correct Answer:** DMSA is a **static renal scintigraphy** agent. It is taken up by the proximal convoluted tubules of the renal cortex and remains fixed there for several hours. This allows for high-resolution imaging of the renal parenchyma. Areas of scarring appear as "cold spots" (photopenic areas) with associated contour loss or thinning. It is the gold standard for diagnosing acute pyelonephritis and permanent cortical scarring, especially in pediatric patients with Vesicoureteral Reflux (VUR). **2. Why Other Options are Incorrect:** * **DTPA (Diethylenetriaminepentaacetic acid) scan:** This is a **dynamic scan** primarily used to assess the Glomerular Filtration Rate (GFR) and renal perfusion. It is the investigation of choice for evaluating obstructive uropathy (e.g., PUJ obstruction). * **DEXA scan:** This is used to measure Bone Mineral Density (BMD) for diagnosing osteoporosis; it has no role in renal imaging. * **MCU (Micturating Cystourethrogram):** This is the gold standard for diagnosing **Vesicoureteral Reflux (VUR)** and Posterior Urethral Valves (PUV). While VUR causes scarring, the MCU identifies the *cause*, whereas the DMSA identifies the *scar* itself. **High-Yield Clinical Pearls for NEET-PG:** * **Best time for DMSA:** To confirm permanent scarring, the scan should be performed **4–6 months** after an acute Urinary Tract Infection (UTI). * **MAG-3 Scan:** The most accurate dynamic scan for renal function in neonates/infants due to better secretion by immature kidneys. * **Investigation of choice for Renovascular Hypertension:** DTPA scan with Captopril challenge.

Q: Which bone scan is used to detect bone metastasis?

Tc99 MDP. **Explanation:** **Tc99m-MDP (Methylene Diphosphonate)** is the gold standard radiopharmaceutical for skeletal scintigraphy (bone scan). It works on the principle of **chemisorption**, where the phosphate groups bind to the hydroxyapatite crystals in the bone matrix. Areas with increased osteoblastic activity (bone formation) and increased blood flow—common in metastatic deposits—show high uptake ("hot spots"). It is highly sensitive for detecting early bone metastases, often identifying lesions 6–18 months before they appear on conventional X-rays. **Analysis of Incorrect Options:** * **Thallium-201 (Tl-201):** A potassium analog primarily used for **myocardial perfusion imaging** (stress tests) and occasionally for tumor viability or parathyroid imaging. * **Tc99m-DMSA:** Used for **renal cortical imaging**. It is the investigation of choice for detecting renal scarring and evaluating differential renal function. * **Tc99m-Sulphur Colloid:** Used for **reticuloendothelial system (RES) imaging**, specifically for liver-spleen scans and bone marrow imaging. It is also used in gastric emptying studies and lymphoscintigraphy. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of Uptake:** Chemisorption onto hydroxyapatite crystals. * **Flare Phenomenon:** A temporary increase in tracer uptake seen 1–3 months after successful chemotherapy, which should not be confused with disease progression. * **Superscan:** A bone scan showing intense, symmetrical skeletal uptake with **absent or faint renal activity**, typically seen in diffuse metastatic disease (e.g., prostate cancer) or metabolic bone disease. * **Cold Spots:** Some aggressive or purely lytic lesions (e.g., Multiple Myeloma, Renal Cell Carcinoma) may appear as "cold spots" due to a lack of osteoblastic response.

Question 1

What diagnosis is implied by the results of this gallium scan?

Accepted Answer

Sarcoidosis

Answer

Mumps

Answer

Paget's disease

Answer

Septic emboli

Question 2

Which of the following statements about isotope scanning of the thyroid is FALSE?

Accepted Answer

Isotope scanning is useful in hypothyroid patients.

Answer

Radiolabeled iodine (123I) can be used.

Answer

The majority (80%) of 'cold' swellings are benign.

Answer

Approximately 5% of functioning or 'warm' swellings will be malignant.

Question 3

Which one of the following conditions is diagnosed by Tc-99m Pertechnetate Scintigraphy?

Accepted Answer

Meckel's diverticulum

Answer

Pharyngeal diverticulum

Answer

Duodenal diverticulum

Answer

Colonic diverticulum

Question 4

What is the modality of choice for screening of bony metastases?

Accepted Answer

Bone scan

Answer

Plain radiograph

Answer

CT

Answer

MRI

Question 5

What is the gold standard method for detecting renal scarring in a patient with recurrent urinary tract infection?

Accepted Answer

99mTc-DMSA scan

Answer

99mTc-DTPA scan

Answer

99mTc-MIBG Scan

Answer

99mTc-MDP scan

Question 6

Whole-body iodine scan after total thyroidectomy is not recommended for which type of thyroid cancer?

Accepted Answer

Medullary thyroid cancer

Answer

Papillary thyroid cancer

Answer

Anaplastic thyroid cancer

Answer

Follicular thyroid cancer

Question 7

What is the investigation of choice for detecting renal scarring defects?

Accepted Answer

DMSA scan

Answer

DTPA scan

Answer

Dexa scan

Answer

MCU

Question 8

What is true about PET scan?

Accepted Answer

Coincident photons detected at 511 keV

Answer

Single photon detected at 511 keV

Answer

X-rays are used

Answer

Lead collimators are used

Question 9

All are true about 18 FDG PET scanning except?

Accepted Answer

Half-life of 18F is 110 minutes.

Answer

Brown adipose tissue shows normal symmetrical uptake.

Answer

Detects pairs of gamma rays produced.

Answer

Provides good functional detail but poorer anatomical detail than CT.

Question 10

Which bone scan is used to detect bone metastasis?

Accepted Answer

Tc99 MDP

Answer

Th201

Answer

Tc99 DMSA

Answer

Tc99 sulphur colloid

Nuclear Medicine — MCQs

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