Nuclear Medicine Practice Questions

Q: In which condition is salivary scintigraphy particularly useful?

Sjogren syndrome. ***Sjogren syndrome*** - Salivary scintigraphy is highly useful in diagnosing **Sjogren syndrome** by assessing **salivary gland function**, specifically the uptake and excretion of the radiotracer. - In Sjogren syndrome, there is **reduced uptake** and **delayed excretion** of the tracer, reflecting the **exocrine gland dysfunction** characteristic of the autoimmune disease [1]. *Salivary gland tumors* - While salivary scintigraphy can sometimes show **"cold" or "hot" spots** corresponding to tumors, its primary role in tumor diagnosis is **limited**. - **MRI** and **CT scans**, along with **fine-needle aspiration biopsy**, are generally **more definitive** for characterizing salivary gland tumors. *Sialolithiasis* - **Sialolithiasis**, or salivary gland stones, is best diagnosed with **plain radiographs**, **ultrasound**, or **CT scans** which can directly visualize the calcifications within the ducts. - Salivary scintigraphy may show **obstruction** but does not directly identify the stone, making it **less specific** for this condition. *Acute sialadenitis* - **Acute sialadenitis** is typically diagnosed clinically based on **pain**, **swelling**, and **tenderness** of the salivary gland, often with purulent discharge from the duct. - Imaging like **ultrasound** or **CT** can help demonstrate inflammation or abscess formation, but scintigraphy is **not a primary diagnostic tool** for acute infection.

Q: What is the best investigation for detecting bone metastases?

Bone Scintigraphy. ***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.

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

FDG. ***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.

Q: In which condition is the Lambda-Panda sign typically observed?

Sarcoidosis. ***Sarcoidosis*** - The **Lambda-Panda sign** is a characteristic finding in sarcoidosis on **gallium-67 scintigraphy**. - **Lambda sign**: Bilateral hilar and right paratracheal lymph node uptake forming a pattern resembling the Greek letter lambda (λ). - **Panda sign**: Symmetric uptake in the **lacrimal and parotid glands**, creating a facial pattern resembling a panda. - These signs are highly specific for sarcoidosis and reflect the **non-caseating granulomatous** inflammation characteristic of the disease. *Tuberculosis* - While tuberculosis can cause lymphadenopathy, it typically does not present with the specific **Lambda-Panda sign** on gallium-67 scintigraphy. - **Granulomas** in tuberculosis are caseating, differentiating it from the non-caseating granulomas of sarcoidosis. *Histoplasmosis* - Histoplasmosis is a fungal infection that can cause pulmonary and disseminated lesions, but the **Lambda-Panda sign** is not characteristic of its presentation. - Diagnosis relies on fungal cultures, **antigen detection**, or serology. *Leishmaniasis* - Leishmaniasis is a parasitic disease that manifests as cutaneous, mucocutaneous, or visceral forms, which do not typically involve the specific sites to produce the **Lambda-Panda sign**. - Diagnosis is primarily by **microscopic identification** of amastigotes in tissue samples.

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

Fluorine 18. ***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.

Q: Substance used for PET scan is

18F-FDG. ***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.

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

Technetium -99m scanning. ***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

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

I-131. ***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**.

Q: Investigation of choice for studying Renal Cortical mass

99mTc DMSA. ***99mTc DMSA*** - **99mTc DMSA** (Technetium-99m dimercaptosuccinic acid) is the radiopharmaceutical of choice for imaging the **renal cortex** and assessing **renal cortical mass** and scarring. - It binds preferentially to the cells of the **renal tubules**, allowing for excellent visualization of cortical tissue. *99mTc DTPA* - **99mTc DTPA** (Technetium-99m Diethylenetriaminepentaacetic acid) is primarily used to assess **glomerular filtration rate (GFR)** and renal blood flow. - It is filtered by the **glomeruli** but not reabsorbed or secreted by the tubules, making it suitable for functional studies rather than morphological assessment of cortical mass. *53Cr Study* - **53Cr** (Chromium-51) is used in studies to measure **red blood cell mass**, survival, or gastrointestinal protein loss. - It has no role in the direct assessment of **renal cortical mass** or function. *99mTc Pyrophosphate* - **99mTc Pyrophosphate** is primarily used to evaluate **myocardial infarction** (hot spots) or detect bone lesions. - It is not indicated for, nor does it provide useful information about, **renal cortical mass**.

Q: Half-life of iodine-131 is

8 days. ***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 1

In which condition is salivary scintigraphy particularly useful?

Accepted Answer

Sjogren syndrome

Answer

Salivary gland tumors

Answer

Sialolithiasis

Answer

Acute sialadenitis

Question 2

What is the best investigation for detecting bone metastases?

Accepted Answer

Bone Scintigraphy

Answer

MRI

Answer

CT Scan

Answer

X-Ray

Question 3

A PET scan uses which of the following tracer materials?

Accepted Answer

FDG

Answer

CDF

Answer

ADP

Answer

MIBG

Question 4

In which condition is the Lambda-Panda sign typically observed?

Accepted Answer

Sarcoidosis

Answer

Tuberculosis

Answer

Histoplasmosis

Answer

Leishmaniasis

Question 5

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

Accepted Answer

Fluorine 18

Answer

Oxygen 15

Answer

Saccharide - 12

Answer

Aluminum - 12

Question 6

Substance used for PET scan is

Accepted Answer

18F-FDG

Answer

Gadolinium

Answer

Gastrografin

Answer

Iodine

Question 7

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

Accepted Answer

Technetium -99m scanning

Answer

MRI

Answer

CT

Answer

Contrast radiography

Question 8

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

Accepted Answer

I-131

Answer

Technetium-99m

Answer

Phosphorus-32

Answer

MIBG

Question 9

Investigation of choice for studying Renal Cortical mass

Accepted Answer

99mTc DMSA

Answer

99mTc DTPA

Answer

53Cr Study

Answer

99mTc Pyrophosphate

Question 10

Half-life of iodine-131 is

Accepted Answer

8 days

Answer

8 hours

Answer

8 weeks

Answer

8 months

Nuclear Medicine — MCQs

Nuclear Medicine — MCQs

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