Cell Tracking and Imaging — MCQs
Which radiopharmaceutical is commonly used in positron emission tomography (PET) imaging?
Which common tracer in PET is usually administered in the form of a glucose sugar?
Radiation-induced necrosis can be diagnosed by:
Tc-labeled RBCs are used for all except:
Which of the following methods is commonly used to study oncogenes?
A young male presents with a testicular mass on the right side. The AFP is elevated while the HCG is normal. The most appropriate next step is
What type of laser is primarily used in confocal scanning laser ophthalmoscopy?
Which one of the following imaging modalities is most sensitive for localizing extra-adrenal pheochromocytoma?
What type of uterine anomaly is shown in this X-ray HSG image?
Which of the following are enantiomers?
Cell Tracking and Imaging Indian Medical PG Practice Questions and MCQs
Question 1: Which radiopharmaceutical is commonly used in positron emission tomography (PET) imaging?
- A. 18F-FDG (Fluorodeoxyglucose) (Correct Answer)
- B. Oxygen-15 (used in specific PET scans)
- C. Carbon-11 acetate
- D. Nitrogen-13 ammonia
Explanation: ***18F-FDG (Fluorodeoxyglucose)*** - **18F-FDG** is the most widely used radiopharmaceutical in PET imaging, particularly for **oncology**, as it's a glucose analog that accumulates in metabolically active cells. - Its widespread use is due to its favorable physical properties for PET and its ability to reflect **tumor metabolism**. *Carbon-11 acetate* - **Carbon-11 acetate** is used in specific PET applications, primarily for **cardiac imaging** to assess myocardial oxidative metabolism. - It has a very short half-life (around 20 minutes) which limits its availability to centers with on-site cyclotrons. *Oxygen-15 (used in specific PET scans)* - **Oxygen-15** (e.g., O-15 water) is used in highly specialized PET scans for measuring **blood flow** and oxygen metabolism, especially in brain studies. - Its extremely short half-life (approximately 2 minutes) necessitates an on-site cyclotron and immediate use. *Nitrogen-13 ammonia* - **Nitrogen-13 ammonia** is a common radiopharmaceutical for **myocardial perfusion imaging** with PET, reflecting regional blood flow to the heart. - Like other C-11 and O-15 tracers, its short half-life (about 10 minutes) requires proximity to a cyclotron facility.
Question 2: Which common tracer in PET is usually administered in the form of a glucose sugar?
- A. Aluminum - 12
- B. Fluorine 18 (Correct Answer)
- C. Carbon 11
- D. Oxygen 15
Explanation: ***Fluorine 18*** - **18F-FDG** (Fluorodeoxyglucose) is the most common PET tracer, utilizing **Fluorine-18** as its radioactive component. - FDG is a glucose analog, meaning it mimics glucose and is taken up by metabolically active cells, allowing for imaging of **glucose metabolism**. *Aluminum - 12* - **Aluminum-12** is not a common radionuclide used in PET imaging. - The most common tracers in PET are **positron emitters** like Fluorine-18, Carbon-11, Nitrogen-13, and Oxygen-15. *Carbon 11* - **Carbon-11** can be used in PET tracers (e.g., 11C-methionine), but it is **less common** than 18F-FDG due to its shorter half-life. - Its short half-life (20 minutes) requires an **on-site cyclotron** for production, limiting its widespread use. *Oxygen 15* - **Oxygen-15** is employed in PET tracers (e.g., 15O-water for cerebral blood flow), but it has an **even shorter half-life** (2 minutes) than Carbon-11. - Its extremely short half-life makes it **impractical** for routine clinical use in the form of a glucose sugar.
Question 3: 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 4: 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 5: Which of the following methods is commonly used to study oncogenes?
- A. Transformation (Correct Answer)
- B. Transduction
- C. Conjugation
- D. Gene editing (e.g., CRISPR)
Explanation: ***Transformation*** - **Transformation** is the classical and most commonly used method to study oncogenes in the laboratory. - In this technique, **oncogenes are introduced into normal cells** (often NIH 3T3 fibroblasts) to observe whether they can induce **malignant transformation** [1]. - Transformed cells exhibit characteristic changes including **loss of contact inhibition**, **anchorage-independent growth** (colony formation in soft agar), **immortalization**, and ability to form tumors in nude mice. - This method has been fundamental in **identifying and characterizing oncogenes** since the 1970s and remains a gold standard for functional oncogene studies [1]. *Transduction* - **Transduction** involves introducing oncogenes into cells using **viral vectors** (especially retroviruses) [1]. - While this is indeed a common method for delivering oncogenes in research, it is a **technique for gene delivery** rather than the broader experimental approach. - Often used in conjunction with transformation assays. *Conjugation* - **Conjugation** is a mechanism of horizontal gene transfer in **bacteria** involving direct cell-to-cell contact. - This is **not relevant** for studying oncogenes in mammalian/eukaryotic cells where cancer biology is studied. *Gene editing (e.g., CRISPR)* - **CRISPR** and other gene editing technologies are modern tools that allow precise manipulation of endogenous genes. - While increasingly used in oncogene research, CRISPR is a **newer technique** and not the **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 228-230.
Question 6: A young male presents with a testicular mass on the right side. The AFP is elevated while the HCG is normal. The most appropriate next step is
- A. Biopsy
- B. Orchidectomy (Correct Answer)
- C. USG
- D. Wait and Watch
Explanation: ***Radical Inguinal Orchidectomy*** - In a patient who already presents with a **testicular mass** and **elevated AFP** (suggesting non-seminomatous germ cell tumor), the most appropriate next step is **radical inguinal orchidectomy**. - This procedure is both **diagnostic and therapeutic**, providing tissue for histopathological confirmation while removing the primary tumor. - The standard management sequence is: clinical examination → scrotal USG → tumor markers → **orchidectomy** → staging imaging → further treatment based on histology and stage. - Since the mass is already identified and tumor markers are done, proceeding directly to orchidectomy is appropriate. *USG* - Scrotal **ultrasound** is typically the **first imaging modality** when a testicular mass is suspected or palpated. - However, in this scenario, the mass is already clinically identified and tumor markers (AFP) have been measured, suggesting that initial workup including USG has likely been completed. - USG would have been the appropriate answer if the question asked for the "first investigation" before tumor markers were done. *Biopsy* - Direct **biopsy** of a testicular mass is **contraindicated** due to the high risk of tumor cell spillage along the needle tract, which can alter staging and worsen prognosis. - Testicular cancer is diagnosed via **radical inguinal orchidectomy**, not biopsy. *Wait and Watch* - A **wait and watch** approach is inappropriate and dangerous in the presence of a **testicular mass with elevated AFP**, which strongly suggests malignancy (non-seminomatous germ cell tumor). - Delayed treatment can lead to disease progression, metastasis, and poorer outcomes.
Question 7: What type of laser is primarily used in confocal scanning laser ophthalmoscopy?
- A. Infrared laser (Correct Answer)
- B. Diode laser
- C. YAG laser
- D. Excimer laser
Explanation: ***Infrared laser*** - **Confocal scanning laser ophthalmoscopy (CSLO)** primarily uses **near-infrared diode lasers** with wavelengths typically between **670-830 nm**. - Infrared wavelengths provide **optimal tissue penetration** with minimal light scatter, allowing high-resolution, three-dimensional imaging of the retina and optic nerve head. - The **Heidelberg Retina Tomograph (HRT)**, a widely used CSLO device, operates at **670 nm** (near-infrared range), making infrared laser the standard for this imaging modality. - The infrared spectrum is particularly useful for imaging through **media opacities** and provides excellent **contrast** for structural analysis. *Diode laser* - While CSLO does use **diode laser technology**, the distinguishing characteristic is the **wavelength** (infrared spectrum), not just the laser type. - Diode lasers can emit light across various wavelengths; the specific use of **infrared wavelengths** is what makes them suitable for CSLO. - In ophthalmology literature, CSLO is characterized by its use of **infrared** light rather than just being described as "diode laser" imaging. *Excimer laser* - **Excimer lasers** emit ultraviolet (UV) light and are used in **refractive surgery** such as **LASIK** for precise corneal ablation. - The high-energy UV spectrum is **not suitable for diagnostic imaging** such as CSLO, as it would cause tissue damage rather than provide safe, non-invasive imaging. *YAG laser* - **Nd:YAG lasers** (neodymium-doped yttrium aluminum garnet) are used for **photodisruptive procedures** such as **posterior capsulotomy** and **peripheral iridotomy**. - They produce **high-energy, short-duration pulses** at 1064 nm to create tissue disruption, not the continuous low-power scanning required for CSLO imaging.
Question 8: Which one of the following imaging modalities is most sensitive for localizing extra-adrenal pheochromocytoma?
- A. USG
- B. MRI
- C. MIBG scan
- D. 68Ga-DOTATATE PET/CT (Correct Answer)
Explanation: ***68Ga-DOTATATE PET/CT*** - **68Ga-DOTATATE PET/CT** is highly sensitive for detecting **neuroendocrine tumors**, including pheochromocytomas and paragangliomas, due to its affinity for **somatostatin receptors** which are overexpressed on these cells. - This modality offers superior sensitivity in localizing both adrenal and **extra-adrenal pheochromocytomas**, particularly in cases of metastatic disease or multifocal lesions. *USG* - **Ultrasound (USG)** has limited utility for localizing **extra-adrenal pheochromocytomas**, especially if they are small, located in less accessible anatomical sites, or obscured by bowel gas. - While useful for initial screening of adrenal masses, its sensitivity for **extra-adrenal disease** is low. *MRI* - **MRI** is a valuable imaging modality for pheochromocytoma localization, offering good soft tissue contrast, but its overall sensitivity for detecting **extra-adrenal lesions** may be surpassed by more specific functional imaging techniques like 68Ga-DOTATATE PET/CT. - It is particularly useful for assessing the extent of disease and anatomical proximity to vital structures once a lesion is identified, but less sensitive for identifying occult **extra-adrenal tumors**. *MIBG scan* - **MIBG scintigraphy** relies on the uptake of a chemical analog of norepinephrine by **sympathetic neurosecretory cells**, making it useful for detecting pheochromocytomas. - However, its sensitivity in detecting **extra-adrenal pheochromocytomas** and metastatic disease is generally lower compared to 68Ga-DOTATATE PET/CT, particularly for certain genetic subtypes.
Question 9: What type of uterine anomaly is shown in this X-ray HSG image?
- A. Septate uterus
- B. Uterus didelphys
- C. Unicornuate uterus (Correct Answer)
- D. Bicornuate uterus
Explanation: ***Unicornuate uterus*** - The image shows a single, elongated uterine horn with a single fallopian tube arising from it, consistent with a **unicornuate uterus**. - This congenital anomaly results from the **failure of one Müllerian duct to develop**, leading to an abnormally shaped uterus. *Septate uterus* - A **septate uterus** would show a normal uterine fundus with an internal septum dividing the uterine cavity. - This image clearly depicts only **one rudimentary horn** and no visible septum. *Uterus didelphys* - **Uterus didelphys** involves two completely separate uteri, each with its own cervix and vagina. - The image does not show evidence of a **second, separate uterine structure**. *Bicornuate uterus* - A **bicornuate uterus** is characterized by two distinct uterine horns, which fuse at the cervix or lower uterine segment, creating a heart-shaped appearance of the fundus. - The image shows a **single, long horn** rather than two distinct horns.
Question 10: Which of the following are enantiomers?
- A. D-glucose and D-mannose
- B. D-glucose and D-galactose
- C. D-glucose and D-fructose
- D. D-glucose and L-glucose (Correct Answer)
Explanation: ***D-glucose and L-glucose*** - **Enantiomers** are stereoisomers that are **non-superimposable mirror images** of each other. - **D-glucose** and **L-glucose** fit this definition perfectly; they have the same chemical formula and connectivity but differ in the spatial arrangement of all their chiral centers, resulting in mirror images. - Any pair of D- and L- forms of the same sugar are enantiomers. *D-glucose and D-mannose* - These are **epimers**, specifically C-2 epimers, meaning they differ in the configuration at **only one chiral carbon atom** (the second carbon from the carbonyl group in their open-chain forms). - They are not mirror images of each other because the configurations at the other chiral centers are the same. *D-glucose and D-galactose* - These carbohydrates are **epimers**, specifically C-4 epimers, meaning their difference lies in the configuration around the **fourth carbon atom**. - As they differ at only one chiral center and have the same "D-" configuration for their penultimate carbon, they are not mirror images of each other. *D-glucose and D-fructose* - These are **constitutional isomers** (structural isomers), not stereoisomers. - D-glucose is an aldohexose (aldose sugar) while D-fructose is a ketohexose (ketose sugar). - They differ in the position of the carbonyl group, so they cannot be enantiomers.
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