Dynamic Contrast-Enhanced Imaging — MCQs
Volume of distribution of a drug is 500 ml and target concentration of drug in blood is 5 g/L. 20% of administered drug is reached to systemic circulation. What will be the loading dose of that drug -
Gadolinium is a contrast agent used for:
In the evaluation of a suspected hepatic hemangioma, what is the expected behavior of Tc-99m labeled RBCs during scintigraphy?
Best investigation to detect rupture of silicone breast implants is-
Most common benign tumor of the liver is:
A man comes to the emergency department with stab injury to left flank. He has stable vitals. What would be the next step in management?
A 48-year-old woman presents with suspected myocardial ischemia. Pharmacologic stress myocardial perfusion SPECT with Tc-99m sestamibi shows reversible perfusion defect in the inferior wall. Evaluate the optimal management approach based on this functional imaging finding.
A 70-year-old male with recurrent prostate cancer post-prostatectomy has rising PSA (4.2 ng/mL) but negative conventional imaging. Which functional imaging modality would provide the highest detection rate for disease localization in this clinical scenario?
A 58-year-old presents with progressive cognitive decline. MRI brain is unremarkable. FDG-PET shows bilateral temporoparietal and posterior cingulate hypometabolism with relative sparing of sensorimotor cortex. Analyze these findings to determine the most likely diagnosis.
A 62-year-old male with lung cancer undergoes baseline PET-CT showing a 4 cm right upper lobe mass with SUVmax of 8.5. After 2 cycles of chemotherapy, repeat PET-CT shows the mass measures 3.5 cm with SUVmax of 3.2. Analyze the metabolic response according to PERCIST criteria.
Dynamic Contrast-Enhanced Imaging Indian Medical PG Practice Questions and MCQs
Question 1: Volume of distribution of a drug is 500 ml and target concentration of drug in blood is 5 g/L. 20% of administered drug is reached to systemic circulation. What will be the loading dose of that drug -
- A. 1 gm
- B. 5 gm
- C. 25 gm
- D. 12.5 gm (Correct Answer)
Explanation: ***12.5 gm*** - The formula for loading dose (LD) is: LD = (Target Concentration × Volume of Distribution) / Bioavailability. - Given: Target Concentration = 5 g/L, Volume of Distribution = 500 mL = 0.5 L, Bioavailability = 20% = 0.2. - So, LD = (5 g/L × 0.5 L) / 0.2 = 2.5 g / 0.2 = **12.5 g**. *1 gm* - This value would be obtained if the target concentration was 2 g/L with 100% bioavailability, or if the calculation incorrectly handled the volume or bioavailability factor. - It does not account for the specified **bioavailability of 20%** or the given target concentration and volume of distribution. *5 gm* - This result would be obtained if the bioavailability was assumed to be 50% (LD = 2.5 g / 0.5 = 5 g), or if the volume of distribution was incorrectly used in the calculation. - This option does not correctly factor in the **20% bioavailability** of the administered drug. *25 gm* - This value would result from mistakes such as dividing by bioavailability of 10% instead of 20% (LD = 2.5 g / 0.1 = 25 g), or by multiplying bioavailability instead of dividing by it. - This answer significantly **overestimates** the required dose, which could lead to drug toxicity.
Question 2: Gadolinium is a contrast agent used for:
- A. CT - angiography
- B. Bronchography
- C. MRI - Imaging (Correct Answer)
- D. Contrast Sonography
Explanation: ***MRI - Imaging*** - **Gadolinium** is a paramagnetic substance commonly used as a contrast agent in **Magnetic Resonance Imaging (MRI)**. - It works by altering the **T1 relaxation times** of protons in tissues, enhancing the signal and improving the visibility of certain structures or pathologies like **tumors** or **inflammation**. *CT - angiography* - **CT angiography** typically uses **iodine-based contrast agents**, not gadolinium, to visualize blood vessels. - Iodine contrast agents work by absorbing X-rays, making blood vessels appear bright on CT images. *Bronchography* - **Bronchography** is an older imaging technique that involved introducing an **iodinated contrast medium** directly into the bronchial tree. - It has largely been replaced by **high-resolution CT scans** for evaluating airways. *Contrast Sonography* - **Contrast-enhanced ultrasound (CEUS)**, or contrast sonography, primarily uses **microbubble contrast agents** made of inert gas. - These microbubbles enhance the reflectivity of blood, improving visualization of blood flow and organ perfusion.
Question 3: In the evaluation of a suspected hepatic hemangioma, what is the expected behavior of Tc-99m labeled RBCs during scintigraphy?
- A. Increased uptake on delayed images (Correct Answer)
- B. Decreased uptake on delayed images
- C. No uptake
- D. Diffuse uptake
Explanation: ***Increased uptake on delayed images*** - Hepatic hemangiomas are vascular malformations with **slow blood flow** within their extensive sinusoidal spaces. - This slow flow causes the **Tc-99m labeled RBCs** to accumulate gradually and remain trapped within the lesion, leading to characteristic increased uptake on delayed images (typically 1-2 hours after injection). *Decreased uptake on delayed images* - This pattern would suggest **washout** of the tracer, which is not characteristic of hemangiomas where the tracer is retained due to sluggish flow. - It could be seen in highly vascular but non-hemangioma lesions where tracer clearance is rapid. *No uptake* - Lack of uptake would indicate a **non-vascular lesion** or a lesion with very poor perfusion, which is not consistent with a hemangioma's highly vascular nature. - While initial images might show less uptake than surrounding liver due to slow flow, delayed images will show accumulation. *Diffuse uptake* - **Diffuse uptake** throughout the liver would indicate normal liver parenchyma or a condition affecting the entire organ, not a localized benign tumor like a hemangioma. - Hemangiomas are typically discrete lesions that show focal uptake.
Question 4: Best investigation to detect rupture of silicone breast implants is-
- A. Mammography
- B. X-ray
- C. MRI (Correct Answer)
- D. USG
Explanation: ***MRI*** - **Magnetic Resonance Imaging (MRI)** is considered the **gold standard** for detecting silicone breast implant ruptures due to its superior soft tissue contrast and ability to differentiate silicone from other tissues. - It can accurately identify both **intracapsular** (linguine sign) and **extracapsular** ruptures, as well as associated silicone granulomas. *Mammography* - While useful for breast cancer screening, **mammography** has limited sensitivity for detecting silicone implant ruptures, especially subtle ones. - It can show indirect signs like implant contour abnormalities or increased implant density but is often inconclusive for rupture diagnosis. *X-ray* - **X-rays** provide very little information regarding the integrity of silicone breast implants because silicone is radiolucent and does not show up clearly on standard radiographs. - Its utility is primarily for detecting calcifications or foreign bodies, not implant rupture. *USG* - **Ultrasound (USG)** can be a useful initial screening tool for detecting implant ruptures, showing signs like the **"stepladder sign"** for intracapsular rupture or anechoic collections (silicone outside the capsule). - However, its accuracy is highly operator-dependent, and it may miss subtle ruptures or be limited by poor visualization due to scar tissue, making MRI a more definitive choice.
Question 5: Most common benign tumor of the liver is:
- A. Focal nodular hyperplasia (FNH)
- B. Hepatic adenoma
- C. Hepatic hemangioma (Correct Answer)
- D. Angiomyolipoma of the liver
Explanation: ***Hepatic hemangioma*** - **Hepatic hemangiomas** are the **most common benign solid tumors of the liver**, often discovered incidentally [1]. - They are composed of a tangled mass of **blood vessels** and are generally asymptomatic [1]. *Focal nodular hyperplasia (FNH)* - FNH is the **second most common benign liver tumor**, characterized by a central scar on imaging [1]. - While benign, it is less common than hepatic hemangioma [1]. *Hepatic adenoma* - Hepatic adenomas are benign tumors with a higher risk of **hemorrhage** and **malignant transformation** compared to hemangiomas [1], [2]. - Their incidence is linked to oral contraceptive use or anabolic steroid use. *Angiolipoma of the liver* - **Angiomyolipomas** are rare benign tumors, more commonly found in the kidney, and are not the most frequent benign liver tumor. - They are composed of varying amounts of **fat**, **smooth muscle**, and **blood vessels**. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Liver And Biliary System Disease, pp. 398-399. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Liver and Gallbladder, pp. 874-875.
Question 6: A man comes to the emergency department with stab injury to left flank. He has stable vitals. What would be the next step in management?
- A. Diagnostic peritoneal lavage
- B. Laparotomy
- C. CECT (Correct Answer)
- D. Laparoscopy
Explanation: ***CECT*** - A **Contrast-Enhanced Computed Tomography (CECT)** scan is the preferred initial diagnostic step for a hemodynamically stable patient with a stab wound to the flank. - It effectively assesses the **depth of penetration** and identifies potential internal organ injuries in the abdomen or retroperitoneum, guiding further management. *Diagnostic peritoneal lavage* - **Diagnostic peritoneal lavage (DPL)** is less commonly used for stab wounds in hemodynamically stable patients due to its **invasiveness** and lower specificity compared to CT scans. - While it can detect peritoneal penetration or significant hemorrhage, it often leads to **unnecessary laparotomies** and is not as precise in identifying specific organ injuries. *Laparotomy* - **Laparotomy** (surgical exploration) is indicated for **hemodynamically unstable** patients or those with definitive signs of peritonitis or evisceration. - Since the patient has **stable vitals**, immediate laparotomy is not the next step, as diagnostic imaging is needed first. *Laparoscopy* - **Laparoscopy** is a minimally invasive surgical procedure that can be used diagnostically or therapeutically in stable patients. - However, in the initial assessment of a flank stab wound, a **CECT scan** is typically performed first to get a comprehensive view of potential organ damage before considering a more invasive procedure like laparoscopy.
Question 7: A 48-year-old woman presents with suspected myocardial ischemia. Pharmacologic stress myocardial perfusion SPECT with Tc-99m sestamibi shows reversible perfusion defect in the inferior wall. Evaluate the optimal management approach based on this functional imaging finding.
- A. Reassure patient as findings represent artifact
- B. Start medical management without further investigation
- C. Recommend coronary angiography for further evaluation and potential revascularization (Correct Answer)
- D. Proceed directly to coronary artery bypass grafting
Explanation: ***Recommend coronary angiography for further evaluation and potential revascularization*** - A **reversible perfusion defect** on SPECT denotes **stress-induced ischemia** with viable myocardium, characterized by reduced tracer uptake during stress that normalizes at rest. - This finding indicates significant **coronary artery stenosis** (often >70%) and requires **coronary angiography** to define the anatomy and plan possible **percutaneous coronary intervention (PCI)**. *Reassure patient as findings represent artifact* - While **diaphragmatic attenuation** can cause inferior wall artifacts, a truly **reversible defect** (normal rest scan) is diagnostic of ischemia rather than a permanent artifact. - Attenuation artifacts typically present as **fixed defects** or are clarified using **ECG-gated SPECT** to check for normal wall motion. *Start medical management without further investigation* - Although medical therapy is a pillar of CAD treatment, a documented **reversible defect** in a symptomatic patient warrants anatomical assessment to evaluate the risk of **major adverse cardiovascular events (MACE)**. - Management solely with drugs is insufficient for patients with high-risk ischemia patterns on **functional imaging** who may benefit from revascularization. *Proceed directly to coronary artery bypass grafting* - **Coronary artery bypass grafting (CABG)** is a surgical intervention that requires prior visualization of coronary anatomy via angiography to determine the extent of disease (e.g., **triple-vessel** or **left main disease**). - It is premature to provide surgical referral before confirming the **syntax score** or the suitability of the lesions for less invasive procedures like **angioplasty**.
Question 8: A 70-year-old male with recurrent prostate cancer post-prostatectomy has rising PSA (4.2 ng/mL) but negative conventional imaging. Which functional imaging modality would provide the highest detection rate for disease localization in this clinical scenario?
- A. 68Ga-PSMA PET-CT (Correct Answer)
- B. In-111 Capromab pendetide scan
- C. 18F-FDG PET-CT
- D. Tc-99m MDP bone scan
Explanation: ***68Ga-PSMA PET-CT*** - **68Ga-PSMA PET-CT** is currently the gold standard for detecting **biochemical recurrence** of prostate cancer, showing a detection rate of over 90% when PSA levels are >2 ng/mL. - It targets the **Prostate-Specific Membrane Antigen**, which is significantly overexpressed in prostate cancer cells, allowing for precise localization of both local recurrence and **distant metastases**. *In-111 Capromab pendetide scan* - This older imaging modality (ProstaScint) targets an **intracellular epitope** of PSMA, which is less accessible in viable, non-necrotic cells compared to the extracellular targets of modern tracers. - It has a much lower **sensitivity and specificity** compared to 68Ga-PSMA PET-CT and is rarely used in contemporary clinical practice. *18F-FDG PET-CT* - **18F-FDG** is generally not useful for prostate cancer because these tumors are typically slow-growing and have **low glucose metabolism** (low glycolytic rate). - It is primarily reserved for **aggressive, high-grade**, or neuroendocrine-differentiated prostate cancers that have lost the ability to express PSMA. *Tc-99m MDP bone scan* - This is a conventional imaging modality that detects **osteoblastic activity** rather than the cancer cells themselves, often resulting in low sensitivity at low PSA levels. - It is specifically limited to detecting **bone metastases** and cannot identify soft tissue recurrence or lymph node involvement in the pelvis.
Question 9: A 58-year-old presents with progressive cognitive decline. MRI brain is unremarkable. FDG-PET shows bilateral temporoparietal and posterior cingulate hypometabolism with relative sparing of sensorimotor cortex. Analyze these findings to determine the most likely diagnosis.
- A. Normal pressure hydrocephalus
- B. Frontotemporal dementia
- C. Alzheimer's disease (Correct Answer)
- D. Vascular dementia
Explanation: ***Alzheimer's disease*** - The classic FDG-PET findings for this condition involve bilateral **temporoparietal** and **posterior cingulate** hypometabolism while typically sparing the **sensorimotor cortex**. - This metabolic signature often appears during the **prodromal phase**, frequently preceding the structural **atrophy** seen on traditional MRI scans. *Normal pressure hydrocephalus* - On imaging, this condition is characterized by **ventriculomegaly** disproportionate to the degree of cortical atrophy, which is not described here. - Clinically, it presents with the classic triad of **gait disturbance**, **urinary incontinence**, and **dementia**, rather than isolated metabolic patterns on PET. *Frontotemporal dementia* - FDG-PET would typically demonstrate hypometabolism localized to the **frontal** and **anterior temporal lobes**, which differs from the posterior pattern seen in this case. - Early symptoms usually include significant **personality changes** or **behavioral disturbances** rather than generalized progressive cognitive decline alone. *Vascular dementia* - PET scanning usually shows a **focal or multifocal** "patchy" pattern of hypometabolism corresponding to areas of prior **infarction** or chronic ischemia. - Diagnosis is generally supported by MRI evidence of **lacunar infarcts**, **extensive white matter disease**, or territorial strokes.
Question 10: A 62-year-old male with lung cancer undergoes baseline PET-CT showing a 4 cm right upper lobe mass with SUVmax of 8.5. After 2 cycles of chemotherapy, repeat PET-CT shows the mass measures 3.5 cm with SUVmax of 3.2. Analyze the metabolic response according to PERCIST criteria.
- A. Progressive metabolic disease
- B. Stable metabolic disease
- C. Partial metabolic response (Correct Answer)
- D. Complete metabolic response
Explanation: ***Partial metabolic response*** - According to **PERCIST** criteria, a reduction in **SULpeak** or **SUVmax** of **≥30%** is classified as a partial metabolic response. - In this case, the SUVmax decreased from **8.5 to 3.2**, which is a **62% reduction**, far exceeding the 30% threshold for response. *Progressive metabolic disease* - Defined by a **>30% increase** in SUVmax or the appearance of **new metabolic lesions**. - This patient showed a significant decrease in metabolic activity, contradicting a diagnosis of progression. *Stable metabolic disease* - This category applies when the change in SUVmax falls between a **30% decrease and a 30% increase**. - Since the metabolic activity dropped by 62%, the response is too significant to be labeled as stable. *Complete metabolic response* - Requires a total **disappearance of metabolic uptake** in all lesions, ideally dropping below the level of **background liver activity**. - While the uptake decreased significantly, a residual **SUVmax of 3.2** indicates persistent metabolic activity, preventing a classification of complete response.
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