Nuclear Medicine Practice Questions

Q: Radioisotope used in PET-CT scan?

18F-FDG. ***18F-FDG*** - It is a **glucose analogue** labeled with the positron-emitting isotope **Fluorine-18**, making it the ideal tracer for measuring metabolic activity in tissues. - It is widely used in PET-CT because highly metabolic cells (like cancer cells and active neurons) accumulate it, allowing visualization of **hypermetabolic activity**. *Iodine* - Refers typically to **Iodine-131** or **Iodine-123**, which are primarily used in **thyroid imaging** and therapy. - These isotopes are **gamma emitters** detected by SPECT, not positron emitters required for PET. *Radium* - **Radium-223** (Radium chloride) is an **alpha emitter** used therapeutically for **metastatic prostate cancer** affecting the bone. - It is not a positron emitter and is not designed for diagnostic functional imaging scans like PET. *Cesium-131* - **Cesium-131** is a low-energy **gamma emitter** primarily used in **brachytherapy seeds** for localized radiation treatment. - It does not undergo positron decay and is therefore unsuitable for generating the specific annihilation photons required for PET scanning.

Q: Ga-68 PSMA PET scan is used to diagnose which of the following conditions?

Prostate cancer. ***Prostate cancer***- **Ga-68 PSMA PET** scan targets **Prostate-Specific Membrane Antigen** (**PSMA**), a protein highly overexpressed on the surface of prostate cancer cells.- This scan is crucial for staging, restaging (e.g., in case of **biochemical recurrence** with rising **PSA**), and detecting metastatic foci of prostate carcinoma.*Lung cancer*- Diagnosis and staging of lung cancer primarily use **F-18 FDG PET/CT**, which identifies tumors based on high glucose uptake (the **Warburg effect**).- Lung malignancies do not typically overexpress **PSMA** to a clinically significant degree for diagnostic imaging.*Colon cancer*- Colon cancer (colorectal carcinoma) staging relies primarily on **CT** scans; **F-18 FDG PET** is used mostly for high-risk, recurrent, or metastatic disease.- **PSMA** expression is not a reliable or standard biomarker for routine clinical imaging of colon cancer.*Liver cancer*- Standard imaging for liver cancer (**Hepatocellular carcinoma**) involves dynamic contrast-enhanced **CT** or **MRI**.- While some advanced PSPCs (Prostate-Specific PET probes) might show incidental uptake, **PSMA** is not the target for diagnosing or staging primary liver malignancies.

Q: A patient presented to OPD with complaints of fatigue, loss of appetite, constipation, urinary symptoms of kidney stone, and increased urination. The patient has a history of psychiatric disorder; you suspect a case of hyperparathyroidism. Which of the following investigations is useful in this condition?

Sestamibi scan. ***Sestamibi scan*** - This is the standard **nuclear medicine study** used for localizing hyperfunctioning **parathyroid adenomas** prior to surgery (parathyroidectomy), essential for confirming the source of hypercalcemia [1]. - The scan is highly sensitive because the tracer (**Technetium-99m Sestamibi**) is retained longer in the hyperactive parathyroid tissue than in the surrounding thyroid tissue [1]. *USG neck* - **Ultrasonography** is an anatomical study that is often used as a basic initial imaging step due to its non-invasiveness, but it has lower overall sensitivity (50-80%) in localization. - It is poor at locating **ectopic or deep-seated adenomas** and cannot confirm if the lesion is truly hyperfunctioning, which is critical for diagnosis. *CT neck* - **Computed Tomography** is generally reserved for situations where non-invasive methods fail, especially when trying to localize **ectopic glands** deep in the **mediastinum** or neck. - It is not preferred as a first-line investigation due to the associated **radiation exposure** and lack of functional information regarding the glandular activity. *PET scan* - Standard **FDG-PET scans** are mostly ineffective for localizing benign parathyroid adenomas because they rarely exhibit the high metabolic activity required for tracer uptake. - Specialized PET tracers, such as **11C-methionine**, may be used in complicated cases of persistent or recurrent hyperparathyroidism, but are not routine for initial diagnosis. Note: The patient's presentation of kidney stones, psychiatric symptoms, and polyuria is consistent with primary hyperparathyroidism secondary to hypercalcemia [2, 3].

Q: A 30-year-old woman presented with complaints of bone pain and abdominal cramps. Her family says she has a history of abnormal behavior. The consultant doctor arrived at a provisional diagnosis based on the clinical features. Which of the following would be the best investigation to arrive at a definitive diagnosis?

Sestamibi scan. ***Sestamibi scan*** - The clinical features (bone pain, abdominal cramps, abnormal behavior being "bones, groans, and psychic moans") strongly suggest **primary hyperparathyroidism** due to hypercalcemia, which requires definitive localization of the culprit adenoma. - The **Technetium-99m Sestamibi scan** is the best definitive investigation because it is a functional imaging study that specifically identifies hyperactive parathyroid tissue, showing increased, persistent uptake relative to the thyroid gland. *MRI* - MRI is primarily a **structural imaging** modality and is usually reserved for cases where initial localization studies (like Sestamibi and Ultrasound) are equivocal or to assess for **ectopic parathyroid tissue** located deep in the neck or mediastinum. - It lacks the high **functional specificity** of the Sestamibi scan required to definitively confirm that the identified mass is the hyperfunctioning parathyroid adenoma. *Ultrasonogram* - Ultrasound is often the **initial screening tool** for identifying parathyroid adenomas in the neck, being easily accessible and inexpensive, but it is **operator-dependent**. - It is not considered the single best definitive test because it often fails to localize small, posterior, or **ectopic adenomas** and provides only structural, not functional, information about the gland. *CT scan* - CT scans provide excellent **anatomical detail** and are helpful in complex cases or for locating mediastinal/ectopic glands, especially when planning highly focused surgery. - Like MRI, CT is a structural study that identifies masses but does not definitively prove the **hyperfunctionality** specific to parathyroid adenomas, making Sestamibi superior for definitive diagnosis.

Q: Which of the following is the best imaging modality to diagnose neuroendocrine tumors (NETs)?

PET. ***PET***- **PET** imaging, particularly using tracers like **Gallium-68 DOTATATE** or **DOTATOC**, is the best modality because it targets the **somatostatin receptors (SSTr)** highly expressed on most well-differentiated neuroendocrine tumors (NETs).- This molecular imaging technique offers the highest **sensitivity and specificity** for identifying the primary tumor, effectively staging the disease, detecting occult metastases, and assessing therapeutic response.*USG*- **Ultrasound (USG)** is often limited to screening the abdominal organs (like the liver or pancreas) but lacks the anatomical comprehensiveness and sensitivity required for definitive staging of systemic NET disease.- Its performance is highly **operator-dependent**, and it is generally poor for evaluating deeply located tumors or detecting **pulmonary** or **osseous** involvement.*CT*- **CT scans** provide excellent anatomical information, are essential for tumor size measurement (using **RECIST criteria**), and are often used as the anatomical backbone to complement functional imaging like PET/CT.- However, CT relies on structural changes (size and density) and is significantly **less sensitive** than somatostatin receptor PET for finding small primary tumors or widespread, metabolically active metastases.*MRI*- **MRI** offers superior soft tissue contrast compared to CT, making it highly valuable, especially for evaluating complex areas like the **liver parenchyma** for metastatic disease or specific NETs (e.g., pancreatic NETs).- Like CT, MRI is a structural modality and fails to provide the **functional information** that PET offers regarding the presence and density of **somatostatin receptors**, limiting its use for overall tumor burden assessment and staging compared to PET.

Q: A patient who was diagnosed with prostate cancer is being investigated. The bone scan is reported as a super scan with increased uptake in the bones and reduced activity in the spleen. What is the reason for this super scan appearance?

Increased uptake due to diffuse metastasis. ***Increased uptake due to diffuse metastasis***- The **super scan** appearance is pathognomonic for **widespread skeletal metastasis**, particularly common in advanced prostate cancer, where nearly all the tracer is utilized by diffuse bony lesions.- The reduced or absent visualization of soft tissues (like the **spleen**, **kidneys**, and **bladder**) results from the extremely high proportion of the radiotracer being extracted by the vast surface area of the metastatic bone lesions.*Increased uptake by carcinoma prostate*- Bone scans (using Tc-99m MDP) primarily reflect **osteoblastic activity** in bone, not the direct uptake by the primary non-osseous tumor tissue in the prostate.- While uptake might occasionally be seen in the primary tumor due to adjacent bony involvement or calcification, this is not the cause of the diffuse **super scan** pattern across the entire skeleton.*Increased uptake by the bone*- While the super scan is characterized by increased uptake in the bone, this statement fails to detail the underlying pathological *reason*, which is the widespread **diffuse skeletal metastasis**.- Normal physiological uptake by bone would not lead to the non-visualization of the **kidneys** and **spleen**, which is a crucial defining feature of the super scan.*Decreased uptake by adrenal glands and kidney*- The non-visualization (or decreased uptake) in soft tissue organs, including the **kidneys**, is a *consequence* of the super scan pattern, not the underlying cause of the appearance.- The primary mechanism is the massive tracer uptake in the skeleton due to **diffuse pathological activity**, leaving insufficient free tracer for normal soft tissue background and excretion.

Q: What is the most useful investigation for localization of a parathyroid adenoma?

Sestamibi scan. ***Sestamibi scan*** - **Sestamibi scan (Tc-99m MIBI)** is the **gold standard** for preoperative localization of parathyroid adenomas, with a sensitivity of 80-95% when combined with SPECT. - The radiotracer is taken up by both thyroid and parathyroid tissue, but is **retained longer in the hyperfunctioning parathyroid adenoma**, allowing for differential washout imaging. - Can be enhanced with **SPECT/CT** for better anatomical localization, especially for ectopic glands. *USG* - **Ultrasound (USG)** is a useful anatomical localization tool, particularly for glands in typical locations, but its sensitivity (70-80%) is operator-dependent and limited by gland size/location. - Often used as a **complementary first-line investigation** alongside Sestamibi, especially for guiding needle aspiration or confirming location. - Less sensitive for ectopic or small adenomas compared to Sestamibi. *FDG PET* - **Fluorodeoxyglucose (FDG) PET** is generally not the primary investigation for typical parathyroid adenomas as they do not show intense FDG avidity. - Its use is reserved primarily for **parathyroid carcinoma** localization or in cases where other modalities have failed. - **C-11 Methionine PET** or **F-18 Choline PET** are specialized functional scans with better utility for adenomas than FDG PET, but are less commonly available than Sestamibi. *SPECT* - **SPECT (Single-Photon Emission Computed Tomography)** is an imaging technique that **enhances Sestamibi scan** anatomical resolution (Sestamibi-SPECT or SPECT/CT), especially for small or ectopic adenomas. - SPECT alone without a radiotracer like Sestamibi is not useful; it is the **combination of Sestamibi tracer with SPECT imaging** that provides superior localization. - The option likely refers to this combined modality, but Sestamibi scan (with or without SPECT) remains the most useful overall investigation.

Q: The image shows a characteristic "Christmas tree" appearance. Identify the organ/structure depicted.

Thyroid. ***Thyroid*** - The **"Christmas tree" appearance** on scintigraphy is pathognomonic for **multinodular goiter**, where multiple hot and cold nodules create a characteristic branching pattern - The thyroid's anatomical structure with **bilateral lobes** connected by an **isthmus** naturally resembles a tree shape, enhanced by nodular changes *Liver* - Liver scintigraphy would show **uniform hepatic parenchyma** with portal and hepatic vein patterns, not the nodular branching appearance - The liver lacks the **bilateral symmetrical structure** with central isthmus that creates the tree-like morphology *Parotid gland* - Parotid gland imaging shows a **more uniform lobular pattern** without the distinctive isthmus connection - Would not demonstrate the **characteristic bilateral lobe configuration** that creates the Christmas tree silhouette *Lymph node* - Lymph nodes show **cortical and medullary architecture** with follicular patterns on imaging - Lack the **thyroid's distinctive anatomical structure** of two lobes connected by an isthmus that creates the tree appearance

Q: All of the following agents are used in the imaging technique shown below except:

Gadolinium. ***Gadolinium*** - The image shown is a **PET scan**, which utilizes radiotracers that emit positrons, typically labeled with isotopes like 18F, 11C, 15O, or 13N. - **Gadolinium** is used as a contrast agent in **Magnetic Resonance Imaging (MRI)**, enhancing signal intensity by shortening T1 relaxation times, which is a different imaging modality. *18 Fluoride* - **18 Fluoride (18F-FDG)** is the most commonly used radiotracer in PET scans. - It is a glucose analog that accumulates in metabolically active cells, such as cancer cells, making it useful for **oncologic imaging**. *FLT* - **FLT (3'-deoxy-3'-[18F]fluorothymidine)** is another PET radiotracer. - It measures **cellular proliferation** by reflecting DNA synthesis, making it useful for assessing tumor growth rate. *FMISO* - **FMISO ([18F]fluoromisonidazole)** is a PET radiotracer used to detect **hypoxia** (low oxygen levels) in tissues. - It is often used in oncology to identify hypoxic regions within tumors, which can be resistant to radiation therapy.

Q: The following image shows:

Bone scintigraphy. ***Bone scintigraphy*** - This image displays a typical **bone scan** appearance, characterized by diffuse uptake throughout the skeletal system, with focal areas of increased tracer accumulation (hot spots) indicating increased bone turnover. - The visualization of the entire skeleton with this characteristic intensity and distribution of radioactive tracer is unique to **bone scintigraphy**. *Whole body MRI* - Whole body MRI images would exhibit detailed **anatomical structures** with varying signal intensities depending on tissue composition and MRI sequence, and would not show this uniform skeletal uptake pattern. - MRI is excellent for **soft tissue contrast** and bone marrow evaluation but does not produce the diffuse, radionuclide-based signal seen here. *Whole body CT scan* - A whole body CT scan provides highly detailed **cross-sectional anatomical images** based on X-ray attenuation, showing bone density and soft tissue. - It would not show the diffuse radionuclide uptake pattern characteristic of a bone scan but rather precise **structural details**. *Projectional radiography* - Projectional radiography (X-rays) would provide a 2D image of bone structures by showing differential absorption of X-rays, resulting in a distinct, shadow-like representation of bones. - It does not involve radioactive tracer uptake and therefore would not present this **diffuse uptake pattern** of the entire skeleton.

Question 1

Radioisotope used in PET-CT scan?

Accepted Answer

18F-FDG

Answer

Iodine

Answer

Radium

Answer

Cesium-131

Question 2

Ga-68 PSMA PET scan is used to diagnose which of the following conditions?

Accepted Answer

Prostate cancer

Answer

Lung cancer

Answer

Liver cancer

Answer

Colon cancer

Question 3

A patient presented to OPD with complaints of fatigue, loss of appetite, constipation, urinary symptoms of kidney stone, and increased urination. The patient has a history of psychiatric disorder; you suspect a case of hyperparathyroidism. Which of the following investigations is useful in this condition?

Accepted Answer

Sestamibi scan

Answer

USG neck

Answer

CT neck

Answer

PET scan

Question 4

A 30-year-old woman presented with complaints of bone pain and abdominal cramps. Her family says she has a history of abnormal behavior. The consultant doctor arrived at a provisional diagnosis based on the clinical features. Which of the following would be the best investigation to arrive at a definitive diagnosis?

Accepted Answer

Sestamibi scan

Answer

MRI

Answer

Ultrasonogram

Answer

CT scan

Question 5

Which of the following is the best imaging modality to diagnose neuroendocrine tumors (NETs)?

Accepted Answer

PET

Answer

MRI

Answer

CT

Answer

USG

Question 6

A patient who was diagnosed with prostate cancer is being investigated. The bone scan is reported as a super scan with increased uptake in the bones and reduced activity in the spleen. What is the reason for this super scan appearance?

Accepted Answer

Increased uptake due to diffuse metastasis

Answer

Increased uptake by carcinoma prostate

Answer

Decreased uptake by adrenal glands and kidney

Answer

Increased uptake by the bone

Question 7

What is the most useful investigation for localization of a parathyroid adenoma?

Accepted Answer

Sestamibi scan

Answer

USG

Answer

FDG PET

Answer

SPECT

Question 8

The image shows a characteristic "Christmas tree" appearance. Identify the organ/structure depicted.

Accepted Answer

Thyroid

Answer

Liver

Answer

Parotid gland

Answer

Lymph node

Question 9

All of the following agents are used in the imaging technique shown below except:

Accepted Answer

Gadolinium

Answer

18 Fluoride

Answer

FLT

Answer

FMISO

Question 10

The following image shows:

Accepted Answer

Bone scintigraphy

Answer

Whole body MRI

Answer

Whole body CT scan

Answer

Projectional radiography

Nuclear Medicine — MCQs

Nuclear Medicine — MCQs

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