Nuclear Medicine Practice Questions

Q: What is the best investigation to check for extra thyroid spread of thyroid gland neoplasm ?

MRI. ***MRI*** - **MRI (Magnetic Resonance Imaging)** is the gold standard for evaluating retrosternal extension, airway infiltration, and **extra-thyroidal soft tissue invasion** due to its superior soft tissue contrast resolution. - It provides detailed, cross-sectional anatomy necessary for surgical planning when distinguishing between capsular invasion and surrounding neurovascular bundle involvement. *USG* - **Ultrasonography** is the primary modality for detecting thyroid nodules and regional cervical lymphadenopathy, but it has significant **limitations in evaluating deep structures** or retrosternal extension. - Its field of view is too restricted to assess the full extent of invasive disease beyond the immediate thyroid bed and cervical compartment. *Iodine scan* - **Radioiodine scanning** is primarily used for the functional assessment of differentiated thyroid cancer **metastases** or residual tissue rather than anatomical staging. - It cannot assess structural invasion of contiguous organs or soft tissues like the trachea or larynx. *PET scan* - **PET scanning** (usually with FDG) is highly sensitive for detecting metabolic activity in distant metastases or recurrent disease but lacks the **spatial resolution** of MRI to define local anatomical invasion. - It is generally reserved for de-differentiated tumors or cases where radioiodine scans are negative despite elevated thyroglobulin levels.

Q: A patient with treated breast cancer shows a liver lesion on CT. FDG-PET shows SUVmax of 2.8 in the lesion. Follow-up scan after 3 months shows increase in size but SUVmax decreased to 1.9. What is the most likely explanation?

Treatment-induced necrosis with favorable prognosis. ***Treatment-induced necrosis with favorable prognosis*** - A decrease in **SUVmax** indicates a reduction in **metabolic activity** and viable tumor cells, even if the physical dimensions of the lesion increase. - The increase in size is often due to **necrosis, edema, or inflammation** following successful therapy, representing a favorable response to treatment rather than failure. *Progressive disease requiring treatment escalation* - Progressive disease typically presents with an **increase in both size and SUVmax**, reflecting active metabolic growth of the tumor. - Relying solely on **CT size measurements** (like RECIST criteria) can be misleading when PET shows a significant drop in **glucose metabolism**. *Flare phenomenon indicating treatment response* - The **flare phenomenon** usually refers to a transient *increase* in tracer uptake (SUVmax) shortly after starting treatment (e.g., bone flare in breast cancer patients). - In this scenario, the activity **decreased over 3 months**, which is more consistent with a sustained metabolic response than a metabolic flare. *Infection complicating the metastasis* - An active infection or inflammatory process would typically lead to an **increase in SUVmax** due to high metabolic activity in activated white blood cells. - There is no clinical information provided to suggest systemic **fever or local infection**, and the metabolic trend (decreasing SUV) contradicts an inflammatory spike.

Q: What is the underlying principle behind FDG uptake in malignant cells during PET imaging?

Warburg effect and increased glycolysis. ***Warburg effect and increased glycolysis*** - Malignant cells exhibit the **Warburg effect**, which is characterized by high rates of **glycolysis** and glucose uptake even in the presence of oxygen. - **FDG (Fluorodeoxyglucose)** is a glucose analogue that is transported into cells by **GLUT transporters** and phosphorylated, but it remains trapped as it cannot undergo further metabolism. *Increased fatty acid metabolism* - While some cancers may utilize fatty acids, PET imaging with FDG specifically targets the **glucose metabolic pathway**, not lipid metabolism. - Fatty acid imaging typically requires different radiopharmaceuticals, such as **11C-acetate** or **18F-FCHP**. *Increased DNA synthesis* - Increased DNA synthesis is a hallmark of cellular proliferation but is not the mechanism detected by **FDG-PET scans**. - Radiotracers like **18F-FLT (fluorothymidine)** are used to measure proliferation and DNA synthesis rather than glucose consumption. *Enhanced protein synthesis* - Enhanced protein synthesis reflects the **anabolic state** of a tumor but does not explain the accumulation of glucose analogues. - Amino acid analogues, such as **11C-methionine** or **18F-FET**, are specifically used to image protein synthesis and amino acid transport in oncology.

Question 1

What is the best investigation to check for extra thyroid spread of thyroid gland neoplasm ?

Accepted Answer

MRI

Answer

USG

Answer

Iodine scan

Answer

PET scan

Question 2

In designing a clinical protocol for PSMA PET imaging in prostate cancer, which combination of factors would provide optimal image quality while minimizing radiation exposure?

Accepted Answer

68Ga-PSMA with 1 hour uptake time and furosemide administration

Answer

18F-PSMA with 4 hour delayed imaging

Answer

68Ga-PSMA with 3 hour uptake time without furosemide

Answer

18F-PSMA with 30 minutes uptake time and forced hydration

Question 3

A patient with treated breast cancer shows a liver lesion on CT. FDG-PET shows SUVmax of 2.8 in the lesion. Follow-up scan after 3 months shows increase in size but SUVmax decreased to 1.9. What is the most likely explanation?

Accepted Answer

Treatment-induced necrosis with favorable prognosis

Answer

Progressive disease requiring treatment escalation

Answer

Flare phenomenon indicating treatment response

Answer

Infection complicating the metastasis

Question 4

A 45-year-old diabetic patient presents for FDG-PET scan for lymphoma staging. Blood glucose is 220 mg/dL. What is the most appropriate management before proceeding with imaging?

Accepted Answer

Administer insulin and delay scan until glucose <150 mg/dL

Answer

Double the FDG dose to compensate

Answer

Cancel scan and reschedule after glucose control

Answer

Proceed immediately with scanning

Question 5

What is the underlying principle behind FDG uptake in malignant cells during PET imaging?

Accepted Answer

Warburg effect and increased glycolysis

Answer

Increased fatty acid metabolism

Answer

Increased DNA synthesis

Answer

Enhanced protein synthesis

Nuclear Medicine — MCQs

Nuclear Medicine — MCQs

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