Principles of Molecular Imaging — MCQs
99m Technetium labeled RBC scintigraphy is PRIMARILY used in the diagnosis of
What is the investigation of choice for whole body imaging in metastatic breast cancer?
In radionuclide imaging, the most useful radiopharmaceutical for skeletal imaging is:
Which imaging modality is most sensitive for detecting early ischemic stroke?
Gold standard investigation for breast carcinoma screening in a patient with silicone breast implants
Substance used for PET scan is
Which of the following is used in the treatment of well-differentiated thyroid carcinoma?
Radiation-induced necrosis can be diagnosed by:
Tc-labeled RBCs are used for all except:
Which one of the following conditions is diagnosed by Tc99m Pertechnetate Scintigraphy?
Principles of Molecular Imaging Indian Medical PG Practice Questions and MCQs
Question 1: 99m Technetium labeled RBC scintigraphy is PRIMARILY used in the diagnosis of
- A. Hepatoma
- B. Left ventricular function wall motion
- C. Hepatic hemangioma
- D. GI Bleeding (Correct Answer)
Explanation: ***GI Bleeding*** - Technetium-99m labeled RBC scintigraphy (**<sup>99m</sup>Tc-RBC scan**) is highly sensitive for detecting **active gastrointestinal bleeding**, especially slow or intermittent bleeding. - The labeled red blood cells extravasate at the site of bleeding, accumulating and outlining the bleeding focus over time. *Hepatoma* - **Hepatoma** (hepatocellular carcinoma) is primarily diagnosed using imaging modalities like **CT, MRI**, and **ultrasound**, often with contrast enhancement. - While nuclear medicine scans like **FDG-PET** can be used in some cases for staging or assessing viability, <sup>99m</sup>Tc-RBC scans are not a primary diagnostic tool for hepatoma. *Left ventricular function wall motion* - **Left ventricular function** and **wall motion abnormalities** are typically assessed using **echocardiography**, cardiac **MRI**, or **nuclear cardiology studies** like **SPECT** or **PET** using tracers that localize in the myocardium (e.g., <sup>99m</sup>Tc-Sestamibi or Thallium-201). - <sup>99m</sup>Tc-RBC scans are sometimes used for **gated blood pool scans** to assess global ejection fraction, but not directly for wall motion analysis in the same way as other dedicated cardiac modalities. *Hepatic hemangioma* - **Hepatic hemangiomas** can be characterized by **<sup>99m</sup>Tc-RBC scintigraphy**, which shows **early photopenia** followed by **delayed fill-in and retention** of the tracer due to the characteristic slow blood flow within these benign vascular tumors. - While it can be used for confirmation, it's not the most commonly used primary diagnostic tool (which is often **ultrasound** or **MRI** with specific contrast patterns), and GI bleeding is a more direct application where the scan detects extravasation rather than vascular pooling.
Question 2: What is the investigation of choice for whole body imaging in metastatic breast cancer?
- A. Angiography
- B. Venography
- C. Magnetic Resonance Imaging
- D. CT Scan (Correct Answer)
Explanation: ***CT Scan (Correct answer for NEET 2013)*** - **Contrast-enhanced CT scan** was the standard imaging modality for **whole-body staging** in metastatic breast cancer at the time of this exam (2013). - CT offers **excellent spatial resolution** for detecting metastases in **bone, lung, liver, and lymph nodes**. - It is widely available, relatively quick, and provides comprehensive anatomical information. - **Modern Update:** While CT was the standard in 2013, **PET-CT (FDG-PET/CT) is now considered the gold standard** for whole-body staging in metastatic breast cancer due to its combined metabolic and anatomical imaging capabilities. However, PET-CT was not among the options in this historical question. *Magnetic Resonance Imaging* - **MRI** is highly sensitive for specific sites, particularly for **brain metastases** and **bone metastases (especially spine and bone marrow)**. - **Whole-body MRI** protocols are emerging but require longer acquisition times and specialized equipment. - Not ideal as a single first-line modality for comprehensive whole-body staging compared to CT (or modern PET-CT). *Angiography* - **Angiography** is an invasive vascular imaging procedure used to visualize **arterial blood flow**. - It has **no role in routine metastatic screening or staging** of breast cancer. - Reserved for specific indications like preoperative vascular mapping or interventional procedures. *Venography* - **Venography** specifically visualizes **venous structures** and is used to detect venous thrombosis or venous obstructions. - It is **not applicable** for detecting solid organ metastases, bone lesions, or lymph node involvement in cancer staging.
Question 3: In radionuclide imaging, the most useful radiopharmaceutical for skeletal imaging is:
- A. Technetium-99m linked to Methylene diphosphonate (Correct Answer)
- B. Gallium 67
- C. Technetium-99m
- D. Technetium-sulfur-colloid
Explanation: ***Technetium-99m linked to Methylene diphosphonate*** - **Technetium-99m MDP** is the most widely used radiopharmaceutical for skeletal imaging due to its **high affinity for hydroxyapatite crystals** in bone and favorable physical properties. - It readily incorporates into areas of **increased bone turnover**, making it excellent for detecting fractures, infections, and metastatic lesions. *Gallium 67* - **Gallium 67** is primarily used for **oncology, infection, and inflammation imaging** and has limited utility for general skeletal imaging. - It accumulates in areas of infection and inflammation, but its **biodistribution is not specific for bone metabolism**. *Technetium-sulfur-colloid* - **Technetium-sulfur-colloid** is mainly used for **liver and spleen imaging** (reticuloendothelial system), not for bone scans. - Its particle size and chemical properties prevent its significant uptake in bone tissue. *Technetium-99m* - **Technetium-99m** is a **radioisotope generator** for many different radiopharmaceuticals, but by itself, it's not directly used for skeletal imaging. - It serves as the **radionuclide scaffold** that is chelated to specific bone-seeking ligands like MDP.
Question 4: Which imaging modality is most sensitive for detecting early ischemic stroke?
- A. Ultrasound
- B. PET scan
- C. CT
- D. MRI with DWI (Correct Answer)
Explanation: ***MRI with DWI*** - **Diffusion-weighted imaging (DWI)** within an MRI scan is highly sensitive in detecting **cytotoxic edema** within minutes of **ischemic stroke** onset. This makes it crucial for early diagnosis and treatment decisions. - DWI can identify areas of restricted water diffusion, which is a hallmark of acute cellular injury due to **ischemia**, even before changes are visible on conventional T1 or T2-weighted MRI sequences. *CT* - While frequently used in acute stroke settings, **non-contrast CT** is primarily used to **rule out hemorrhagic stroke** and may only show subtle or no signs of acute ischemia in the first few hours. - Early ischemic changes on CT, often referred to as the **"ischemic penumbra"**, may appear hours after stroke onset, making it less sensitive for very early detection compared to DWI. *Ultrasound* - **Transcranial Doppler (TCD) ultrasound** can evaluate blood flow velocities in intracranial arteries and detect stenoses or occlusions but is not a primary imaging modality for directly visualizing brain parenchymal ischemia. - Cervical ultrasound (e.g., **carotid duplex**) assesses extracranial vessels but cannot directly detect **ischemic changes** within the brain tissue itself. *PET scan* - **PET (Positron Emission Tomography)** can assess brain metabolism and blood flow but is typically not the preferred or most sensitive modality for **early detection of acute ischemic stroke** due to its complexity, cost, and limited availability in emergency settings. - PET is more commonly used in research or for assessing chronic conditions and **metabolic abnormalities**, rather than acute stroke diagnosis.
Question 5: Gold standard investigation for breast carcinoma screening in a patient with silicone breast implants
- A. Mammography
- B. CT scan
- C. USG
- D. MRI (Correct Answer)
Explanation: ***MRI*** - **MRI** is considered the **gold standard** for breast cancer screening in patients with silicone breast implants due to its superior ability to visualize breast tissue through the implant and detect subtle lesions. - It offers **high sensitivity** in detecting both implant rupture and early malignancies, often providing better clarity than mammography in augmented breasts where implants can obscure tissue. *Mammography* - While a standard screening tool, **mammography** can be limited in patients with silicone implants because the implants can **obscure adjacent breast tissue**, making detection of small masses challenging. - Special views (e.g., **Eklund views**) can be used, but sensitivity is still reduced compared to MRI in augmented breasts. *CT scan* - **CT scans** are not routinely used for primary breast cancer screening due to their use of **ionizing radiation** and lower sensitivity for detecting early breast lesions compared to MRI. - CT is more commonly used for **staging** advanced cancers or evaluating complex masses detected by other modalities. *USG* - **Ultrasound (USG)** is a valuable complementary tool, especially for evaluating palpable lumps or clarifying findings from mammography, but it is **operator-dependent** and has a lower overall sensitivity for general screening compared to MRI. - It is particularly useful for differentiating between **cystic and solid masses** and detecting implant ruptures but is not the gold standard for comprehensive screening in augmented breasts.
Question 6: Substance used for PET scan is
- A. Gadolinium
- B. Gastrografin
- C. Iodine
- D. 18F-FDG (Correct Answer)
Explanation: ***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.
Question 7: Which of the following is used in the treatment of well-differentiated thyroid carcinoma?
- A. I131 (Correct Answer)
- B. 99m Tc
- C. 32p
- D. MIBG
Explanation: ***I131*** - **Radioactive iodine (I131)** is specifically absorbed by **well-differentiated thyroid cancer cells** because these cells retain the ability to uptake iodine, unlike other types of cancer cells. - Used for **ablating residual thyroid tissue** after surgery and for treating **metastatic well-differentiated thyroid carcinoma** [1]. *99m Tc* - **Technetium-99m (99m Tc)** is primarily used for **diagnostic imaging** (e.g., thyroid scans, bone scans), not for therapeutic treatment of thyroid cancer. - It has a short half-life and emits gamma rays, making it suitable for imaging but generally not for delivering sustained radiation for therapeutic effect. *32p* - **Phosphorus-32 (32p)** is a beta-emitting radionuclide used in the treatment of certain hematological malignancies, such as **polycythemia vera**, and for palliative treatment of bone metastases. - It is not selectively taken up by thyroid cancer cells and therefore is not used in the treatment of thyroid carcinoma. *MIBG* - **Metaiodobenzylguanidine (MIBG)**, often labeled with I123 (diagnostic) or I131 (therapeutic), is used in the diagnosis and treatment of **neuroendocrine tumors** like **pheochromocytoma** and **neuroblastoma**. - Its uptake mechanism targets cells of neuroectodermal origin, which is distinct from the iodine uptake mechanism of thyroid cells.
Question 8: Radiation-induced necrosis can be diagnosed by:
- A. MRI
- B. CT
- C. PET
- D. Biopsy (Correct Answer)
Explanation: ***Biopsy*** - A **biopsy** is the definitive diagnostic method for radiation-induced necrosis, allowing for histological examination of tissue to confirm necrosis and rule out residual or recurrent tumor. [1], [2] - It provides a direct view of cellular changes, identifying **necrosis, atypical cells**, and ruling out **malignancy**. *MRI* - While **MRI** can show structural changes indicative of necrosis (e.g., mass effect, edema), it often cannot definitively differentiate between **radiation necrosis** and **tumor recurrence.** [2] - It often shows **T1 hypointensity** and **T2 hyperintensity**, but these findings are not specific. *CT* - **CT scans** are useful for detecting gross changes like **mass effect** and **edema** but have limited sensitivity for distinguishing necrosis from tumor recurrence. - It may show **low-density lesions** but lacks the resolution and specificity for precise diagnosis. *PET* - **PET scans** measure metabolic activity and can help distinguish between **tumor recurrence** (high uptake) and **radiation necrosis** (low uptake) in some cases. - However, false positives can occur, as some inflammatory processes in necrosis can also show increased uptake, making it **less definitive** than a biopsy. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Central Nervous System, pp. 1307-1308. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Neoplasia, pp. 340-341.
Question 9: Tc-labeled RBCs are used for all except:
- A. Liver adenoma (Correct Answer)
- B. LV function
- C. GI bleeding
- D. Liver hemangioma
Explanation: ***Liver adenoma*** - Tc-labeled RBCs are primarily used to highlight a specific type of tissue or process. **Liver adenomas** do not typically show an affinity for **Tc-labeled RBCs**, as they are benign epithelial tumors with a different vascular composition. - While adenomas can be vascular, they do not inherently contain the **vascular pooling** or blood volume characteristics that would be specifically targeted by **Tc-labeled RBCs** for diagnostic imaging. *LV function* - **Tc-labeled RBCs** (or Tc-99m-pertechnetate) are commonly used in **gated blood pool imaging** (MUGA scan) to assess **left ventricular (LV) function**, including **ejection fraction** and wall motion abnormalities. - This technique directly visualizes the blood pool within the cardiac chambers, making it suitable for assessing functional parameters of the heart. *GI bleeding* - **Tc-labeled RBCs** are a standard imaging agent for detecting and localizing **active gastrointestinal (GI) bleeding**, especially when the bleeding rate is intermittent or slow. - The labeled RBCs extravasate at the site of hemorrhage, creating a 'hot spot' that can be identified over time. *Liver hemangioma* - **Tc-labeled RBCs** are highly effective in diagnosing **liver hemangiomas**, which are benign vascular tumors composed of large, dilated blood vessels. - These lesions show characteristic uptake and retention of **labeled RBCs** due to their slow blood flow and large intravascular space, appearing as early peripheral enhancement with subsequent centripetal filling.
Question 10: Which one of the following conditions is diagnosed by Tc99m Pertechnetate Scintigraphy?
- A. Meckel's diverticulum (Correct Answer)
- B. Pharyngeal diverticulum
- C. Duodenal diverticulum
- D. Colonic diverticulum
Explanation: ***Meckel's diverticulum*** - **Meckel's diverticulum** often contains **ectopic gastric mucosa**, which has parietal cells that secrete acid. - **Tc99m Pertechnetate** is taken up by these gastric parietal cells, allowing visualization of the diverticulum on scintigraphy. *Pharyngeal diverticulum* - A **pharyngeal diverticulum**, such as **Zenker's diverticulum**, is a pouch-like herniation of the pharyngeal mucosa; it does not contain ectopic gastric mucosa. - Diagnosis is typically made through **barium swallow studies** or **endoscopy**, not scintigraphy. *Duodenal diverticulum* - A **duodenal diverticulum** is a common pouch-like protrusion in the duodenum and usually lacks ectopic gastric mucosa. - It is often asymptomatic and diagnosed incidentally on **upper endoscopy** or **cross-sectional imaging** (CT, MRI). *Colonic diverticulum* - **Colonic diverticula** are small, bulging pouches common in the large intestine that do not contain gastric tissue. - They are typically diagnosed with **colonoscopy** or **CT colonography**, particularly in cases of diverticulitis.
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