Anesthesia for MRI and CT — MCQs
Anaesthetic agent causing analgesia?
What is the best imaging modality for detecting early osteomyelitis?
Anesthetic agent contraindicated in raised ICT is?
Gold standard investigation for breast carcinoma screening in a patient with silicone breast implants
Enhancement in CT contrast is due to -
Radiation exposure occurs in all of the following except:
Which one of the following imaging techniques gives the maximum radiation exposure to the patient?
A 50-year-old smoker presents with hoarseness, dysphagia, and weight loss. Flexible laryngoscopy shows a mass on the vocal cords. What is the next best step?
A patient comes to ER with headache describing it as worst headache in his life. What is the next step?
Which one of the following imaging modalities is most sensitive for the evaluation of extra-adrenal pheochromocytoma?
Anesthesia for MRI and CT Indian Medical PG Practice Questions and MCQs
Question 1: Anaesthetic agent causing analgesia?
- A. Thiopentone
- B. Ketamine (Correct Answer)
- C. Propofol
- D. Etomidate
Explanation: ***Ketamine*** - Ketamine provides excellent **analgesia** by acting as an **NMDA receptor antagonist**, making it unique among commonly used intravenous anesthetics [1]. - It induces a state of **dissociative anesthesia**, where the patient is conscious but detached from painful stimuli, maintaining cardiovascular stability [1]. *Thiopentone* - Thiopentone is a **barbiturate** that causes rapid **induction of anesthesia** and profound **sedation** but has no analgesic properties. - Its primary action is through potentiation of GABA-A receptor activity, leading to central nervous system depression. *Propofol* - Propofol is a widely used intravenous anesthetic known for its rapid onset and short duration of action, but it lacks significant **analgesic effects** [3]. - It primarily works by enhancing GABA-A receptor function, leading to **sedation** and hypnosis. *Etomidate* - Etomidate is an intravenous anesthetic characterized by its minimal cardiovascular depression, making it suitable for patients with **hemodynamic instability**, but it provides **no analgesia** [1], [2]. - Its anesthetic effect is mediated through GABA-A receptor potentiation, resulting in rapid loss of consciousness.
Question 2: What is the best imaging modality for detecting early osteomyelitis?
- A. CT scan
- B. X-ray
- C. MRI (Correct Answer)
- D. Bone scintigraphy
Explanation: ***MRI*** - **Magnetic Resonance Imaging (MRI)** is considered the **gold standard** for detecting early osteomyelitis due to its excellent soft tissue contrast and ability to visualize **bone marrow edema**, which is an early sign of infection. - It can identify changes within **3-5 days** of infection onset, much earlier than other modalities. *CT scan* - While useful for showing **bone destruction**, cortical integrity, and sequestra, **CT scans** are less sensitive than MRI for detecting early marrow edema. - Its ability to diagnose osteomyelitis is usually delayed until significant **bony changes** have occurred, typically around 1-2 weeks. *X-ray* - **Plain radiographs** are often the initial imaging study but are **insensitive** for early osteomyelitis, showing changes only after 10-14 days or more. - Early findings on X-rays can be subtle, such as **periosteal elevation** or **soft tissue swelling**, but frank bone destruction is a late finding. *Bone scintigraphy* - **Bone scintigraphy** (e.g., technetium-99m) is sensitive for detecting increased bone turnover associated with infection but lacks **specificity**, as it can be positive in other conditions like trauma or tumors. - While it can detect changes earlier than X-rays, typically within 2-3 days, it cannot clearly differentiate infection from other processes, and its spatial resolution is poor compared to MRI.
Question 3: Anesthetic agent contraindicated in raised ICT is?
- A. Thiopentone
- B. Etomidate
- C. Ketamine (Correct Answer)
- D. Sevoflurane
Explanation: ***Ketamine*** - **Ketamine** is known to increase **cerebral blood flow** and metabolic rate, which can lead to a significant increase in **intracranial pressure (ICP)**. - This effect makes **ketamine** contraindicated in situations of elevated ICP, as it can worsen neurological outcomes. *Thiopentone* - **Thiopentone** is a barbiturate that typically causes a dose-dependent **decrease in cerebral blood flow** and **metabolic rate**, leading to a *reduction* in ICP. - It is often used to *lower* ICP in neurosurgical settings rather than being contraindicated. *Etomidate* - **Etomidate** also causes a **reduction in cerebral blood flow** and **cerebral metabolic rate**, leading to a *decrease* in ICP. - It is considered a relatively **hemodynamically stable** induction agent, making it suitable in many cases with neurological concerns. *Sevoflurane* - **Sevoflurane**, an inhaled anesthetic, can cause **cerebral vasodilation** at higher concentrations, potentially *increasing* ICP. - However, this effect is often *attenuated* by concurrent hyperventilation, and its overall impact on ICP is less pronounced than **ketamine's** and often manageable.
Question 4: 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 5: Enhancement in CT contrast is due to -
- A. Iodine (Correct Answer)
- B. Gadolinium
- C. Mercury
- D. Silver
Explanation: ***Iodine*** - **Iodine-based contrast agents** are commonly used in CT scans to enhance the visualization of blood vessels, organs, and certain lesions due to their **high atomic number** and ability to absorb X-rays. - The degree of enhancement observed on a CT image is directly proportional to the concentration of **iodine** in the tissue or blood. *Gadolinium* - **Gadolinium-based contrast agents** are predominantly used in **Magnetic Resonance Imaging (MRI)**, not CT scans. - Gadolinium works by altering the **magnetic properties** of water molecules in tissues, thereby improving MRI signal intensity. *Mercury* - **Mercury** is a highly toxic heavy metal and is **not used as a contrast agent** in any imaging modality due to its severe health risks. - While historically used in some medical applications, it has been replaced by safer alternatives. *Silver* - **Silver** is not used as a contrast agent in medical imaging; it has no suitable properties for enhancing images in CT or other common modalities. - It is known for its **antimicrobial properties** and is sometimes used in wound dressings.
Question 6: Radiation exposure occurs in all of the following except:
- A. Plain X-ray
- B. CT scan
- C. Fluoroscopy
- D. MRI (Correct Answer)
Explanation: ***MRI*** - **Magnetic Resonance Imaging (MRI)** uses strong **magnetic fields** and **radio waves** to produce detailed images of organs and soft tissues. - It does not involve **ionizing radiation**, making it a safe choice for patients requiring multiple imaging studies. *CT scan* - **Computed Tomography (CT) scans** utilize **X-rays** taken from multiple angles to create cross-sectional images of the body. - This process involves exposure to **ionizing radiation**, which should be considered when ordering the scan. *Fluoroscopy* - **Fluoroscopy** is an imaging technique that uses a continuous **X-ray beam** to obtain real-time moving images of the body's internal structures. - Due to the continuous nature of the X-ray exposure, it can result in a higher **radiation dose** compared to a single plain X-ray. *Plain X-ray* - A **plain X-ray** uses a small dose of **ionizing radiation** to create images of bones and some soft tissues. - While the dose is generally low, it still constitutes **radiation exposure**, and repeated exposure should be carefully considered.
Question 7: Which one of the following imaging techniques gives the maximum radiation exposure to the patient?
- A. Chest X-ray
- B. MRI
- C. CT scan (Correct Answer)
- D. Bone scan
Explanation: ***CT scan*** - **CT scans** involve multiple X-ray projections and computer processing, resulting in a significantly higher radiation dose compared to conventional X-rays. - The effective dose from a single chest or abdominal CT scan can be equivalent to hundreds of standard chest X-rays, making it the highest radiation contributor among the options listed. *Chest X-ray* - A **chest X-ray** uses a very small amount of ionizing radiation, typically one of the lowest doses among diagnostic imaging techniques that involve radiation. - While it uses radiation, its contribution to overall exposure is minimal, especially compared to CT scans. *MRI* - **MRI (Magnetic Resonance Imaging)** uses strong magnetic fields and radio waves to create detailed images of organs and soft tissues, not ionizing radiation. - Therefore, it involves **no radiation exposure** to the patient. *Bone scan* - A **bone scan** uses a small amount of **radioactive tracer** (radionuclide) injected into the bloodstream, which is then detected by a special camera. - While it involves radiation, the dose is generally lower than that of a CT scan and is comparable to or slightly higher than a series of X-rays.
Question 8: A 50-year-old smoker presents with hoarseness, dysphagia, and weight loss. Flexible laryngoscopy shows a mass on the vocal cords. What is the next best step?
- A. Direct laryngoscopy with biopsy (Correct Answer)
- B. MRI of neck
- C. CT scan of neck
- D. Radiotherapy
Explanation: ***Direct laryngoscopy with biopsy*** - A definitive diagnosis of a vocal cord mass requires **histological examination** to rule out malignancy, especially given the patient's risk factors (age, smoking) and symptoms (hoarseness, dysphagia, weight loss). - **Direct laryngoscopy** allows for a thorough, magnified view of the mass and precise biopsy collection, which is superior to flexible laryngoscopy alone for definitive diagnosis and staging. *MRI of neck* - While MRI can provide excellent soft tissue detail for **staging** a known malignancy, it cannot provide a **histological diagnosis**. - It would typically be performed after a biopsy confirms malignancy to assess the extent of the tumor and potential spread. *CT scan of neck* - A CT scan is useful for evaluating **bony involvement**, lymph node status, and tumor extension for **staging purposes**, but it is not a diagnostic tool for identifying the specific type of tissue or cell pathology. - Like MRI, a CT scan would generally follow a biopsy confirming malignancy. *Radiotherapy* - **Radiotherapy** is a treatment modality for laryngeal cancer, not a diagnostic step. - Initiating treatment without a definitive histological diagnosis of malignancy would be inappropriate and potentially harmful.
Question 9: A patient comes to ER with headache describing it as worst headache in his life. What is the next step?
- A. MRI brain
- B. Observation and analgesics
- C. CT brain (Correct Answer)
- D. Lumbar puncture
Explanation: ***CT brain*** - A patient presenting with the "worst headache of his life" is a classic presentation of a **subarachnoid hemorrhage (SAH)** [1], [2]. - An **urgent non-contrast CT scan of the brain** is the initial and most appropriate diagnostic step to rule out SAH as it is rapid, readily available, and highly sensitive for acute blood [1], [2]. *MRI brain* - While MRI can provide more detailed imaging of the brain, it is generally **less accessible** and takes longer to perform than a CT scan in an emergency setting [1]. - CT is superior for detecting **acute hemorrhage**, which is the primary concern in this acute presentation [1]. *Observation and analgesics* - This approach would be **inappropriate and dangerous** as it delays diagnosis and potential treatment for a life-threatening condition like SAH. - SAH can lead to severe complications, including **permanent neurological damage or death**, if not promptly identified and managed. *Lumbar puncture* - A lumbar puncture is performed if the **CT scan is negative but suspicion of SAH remains high** [1], [2]. - It is used to look for **xanthochromia** (yellowish discoloration of CSF due to bilirubin degradation from red blood cells), which indicates prior hemorrhage, but it is not the initial diagnostic test [1].
Question 10: Which one of the following imaging modalities is most sensitive for the evaluation of extra-adrenal pheochromocytoma?
- A. CT
- B. MRI
- C. MIBG scan (Correct Answer)
- D. Ultrasound
Explanation: ***MIBG scan*** - **Iodine-123 metaiodobenzylguanidine (MIBG) scintigraphy** is highly sensitive for **extra-adrenal pheochromocytomas** and metastases due to its specific uptake by cells that synthesize and store catecholamines. - MIBG is structurally similar to **norepinephrine** and is concentrated in adrenergic tissues, making it ideal for detecting these neuroendocrine tumors, including those outside the adrenal glands. *CT* - While useful for localizing adrenal pheochromocytomas and larger extra-adrenal tumors, **CT scans** have lower sensitivity for small or multifocal extra-adrenal lesions compared to MIBG. - CT imaging primarily depends on anatomical visualization and density differences, which may not be specific enough for all pheochromocytoma presentations. *MRI* - **MRI** offers good soft tissue contrast and is valuable for evaluating pheochromocytomas, especially in the adrenal glands and for delineating their relationship to surrounding structures. - However, for detecting widely dispersed or **extra-adrenal pheochromocytomas**, particularly in the abdomen and pelvis, its overall sensitivity might be surpassed by functional imaging methods like MIBG. *Ultrasound* - **Ultrasound** is primarily used for initial screening of adrenal masses or large abdominal tumors, but its sensitivity is highly dependent on the operator and limited by factors like patient body habitus and bowel gas. - It has very **low sensitivity** for detecting small or extra-adrenal pheochromocytomas, particularly those located in less accessible regions of the body.
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