FMGE 2024 — Radiology
6 Previous Year Questions with Answers & Explanations
A patient with a history of trauma presents with hearing loss. A High-Resolution Computed Tomography (HRCT) scan was performed. Which of the following structures is not typically visualized on HRCT?
Ga-68 PSMA PET scan is used to diagnose which of the following conditions?
Which among the following is the least radiosensitive cell?
Which among the following is most radiosensitive?
Radioisotope used in PET-CT scan?
Ideal thickness of lead aprons to be worn by workers in radiology department?
FMGE 2024 - Radiology FMGE Practice Questions and MCQs
Question 1: A patient with a history of trauma presents with hearing loss. A High-Resolution Computed Tomography (HRCT) scan was performed. Which of the following structures is not typically visualized on HRCT?
- A. Cochlea
- B. Organ of Corti (Correct Answer)
- C. Semicircular canal
- D. Vestibule
Explanation: ***Organ of Corti***- The **Organ of Corti** is a delicate, purely **soft-tissue structure** located within the cochlear duct (scala media).- **HRCT** primarily excels at visualizing **bone and air interfaces**; the soft-tissue resolution is insufficient to distinctly delineate this microscopic sensorineural structure.*Cochlea*- The bony shell of the **cochlea**, forming the **bony labyrinth** wall, is clearly visible on HRCT due to its high **density and calcification**.- HRCT is essential for evaluating the internal auditory canal and **cochlear anatomy**, especially for surgical planning or trauma assessment.*Vestibule*- The **vestibule** is part of the **bony labyrinth** housing the utricle and saccule, and its dense bony walls are clearly depicted by HRCT.- Visualization of the vestibule is crucial for assessing **temporal bone fractures** and identifying developmental anomalies.*Semicircular canal*- The three **semicircular canals** (anterior, posterior, lateral) are osseous structures easily resolved by the fine spatial detail of **HRCT**.- HRCT accurately assesses pathology such as **semicircular canal dehiscence** or traumatic disruption of these structures.
Question 2: Ga-68 PSMA PET scan is used to diagnose which of the following conditions?
- A. Lung cancer
- B. Prostate cancer (Correct Answer)
- C. Liver cancer
- D. Colon cancer
Explanation: ***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.
Question 3: Which among the following is the least radiosensitive cell?
- A. Lymphocytes
- B. Neutrophils
- C. Monocytes
- D. Platelets (Correct Answer)
Explanation: ***Platelets*** - Platelets are **anuclear cell fragments** derived from megakaryocytes, lacking a nucleus and DNA, which makes them highly resistant to the direct cytotoxic effects of radiation. - They are one of the **least radiosensitive** circulating components; platelet counts typically require very high radiation doses to fall significantly. *Monocytes* - Monocytes are generally considered **moderately radiosensitive**, more susceptible to radiation-induced death than mature neutrophils or platelets. - They exhibit susceptibility to **interphase death** upon irradiation, although less sensitive than lymphocytes. *Lymphocytes* - Lymphocytes are the **most radiosensitive** mature circulating blood cells, undergoing rapid apoptosis (programmed cell death) even at low radiation doses (sub-2 Gy). - Their high sensitivity relates to their dependence on DNA integrity for survival and their prompt initiation of the **apoptotic pathway** following damage. *Neutrophils* - Mature neutrophils are considered relatively radiosensitive, but significantly **less sensitive than lymphocytes** and moderately less sensitive than monocytes. - Their numbers drop less rapidly than lymphocytes primarily because of a large pre-formed **reserve pool** in the bone marrow, providing temporary protection.
Question 4: Which among the following is most radiosensitive?
- A. D. Muscle
- B. A. Testis (Correct Answer)
- C. B. Bone
- D. C. Nerve
Explanation: ***Testis*** - The testes contain actively proliferating **spermatogonial stem cells**, making them one of the most radiosensitive organs in the body after the lymphoid tissue and bone marrow. - According to the **Law of Bergonié and Tribondeau**, tissues with high mitotic activity and low differentiation are highly radiosensitive. *Bone* - Mature bone tissue is relatively radioresistant, particularly when compared to highly proliferative organs like the gonads or hematopoietic tissue. - While the red bone marrow within the bone is highly sensitive, the osteocytes and bone matrix are much more resistant to immediate radiation effects. *Nerve* - Nerve tissue is composed of highly specialized, terminally differentiated cells (neurons) that are non-proliferative. - Due to the lack of mitotic activity, the central nervous system and peripheral nerves exhibit very high radioresistance. *Muscle* - Muscle tissue (skeletal, cardiac, and smooth) is differentiated and consists of terminally post-mitotic cells. - Like nerve tissue, muscle is highly radioresistant, requiring large doses of radiation to induce functional or structural damage.
Question 5: Radioisotope used in PET-CT scan?
- A. Iodine
- B. Radium
- C. Cesium-131
- D. 18F-FDG (Correct Answer)
Explanation: ***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.
Question 6: Ideal thickness of lead aprons to be worn by workers in radiology department?
- A. 0.75mm
- B. 0.5mm (Correct Answer)
- C. 2mm
- D. 1mm
Explanation: ***0.5mm***- This thickness is considered the standard and ideal lead equivalent for the front of protective aprons worn by radiology personnel, providing adequate shielding against **scatter radiation**.- A **0.5 mm** lead equivalent attenuates approximately 97% of the scatter radiation generated during standard fluoroscopic procedures (at 100 kVp), offering optimal protection balanced against manageable weight.*1mm*- A **1mm** lead equivalent apron provides marginally greater attenuation but is significantly heavier, leading to high risk of **musculoskeletal injury** due to the excessive load.- This high thickness is generally unnecessary, as the additional protection gained does not outweigh the ergonomic burden imposed by the increased **weight and stiffness**.*0.75mm*- While offering adequate protection, **0.75mm** is heavier than the standardized 0.5mm minimum requirement for routine fluoroscopy and general radiography protection.- The current standards and practice focus on using **0.5mm** lead equivalent to minimize staff injury and fatigue while ensuring sufficient protection against diagnostic X-rays.*2mm*- A **2mm** lead equivalent apron is extremely heavy and completely impractical for daily operational use due to the severe restrictions on mobility and the significant **physical strain**.- Protection levels that high are typically unnecessary because departmental personnel are protected primarily against low-energy **scatter radiation**, not the high-intensity primary X-ray beam.