PET and SPECT Functional Imaging — MCQs
Gamma camera in Nuclear Medicine is used for –
Investigation of choice for leptomeningeal carcinomatosis:
Which radioisotope is PRIMARILY used for detecting acute myocardial infarction rather than assessing myocardial perfusion?
A patient is suspected to have vestibular schwannoma. The investigation of choice for its diagnosis is:
In a child, non-functioning kidney is best diagnosed by:
Tc-labeled RBCs are used for all except:
Which of the following liver metastases appear hypoechoic on ultrasound?
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.
PET and SPECT Functional Imaging Indian Medical PG Practice Questions and MCQs
Question 1: Gamma camera in Nuclear Medicine is used for –
- A. Organ imaging (Correct Answer)
- B. Measuring the radioactivity
- C. RIA
- D. Monitoring the surface contamination
Explanation: ***Organ imaging*** - A **gamma camera** is primarily used to detect gamma rays emitted from **radiopharmaceuticals** introduced into the body. - This detection allows for the creation of 2D images or 3D tomographic images (SPECT) of organ function and structure. *Measuring the radioactivity* - While radioactivity is measured by the gamma camera, its primary purpose is not just to quantify dps/Bq, but to create a **spatial distribution** of this radioactivity. - Dedicated **dosimeters** or **activity meters** are used for precise measurement of radioactivity. *RIA* - **Radioimmunoassay (RIA)** is a laboratory technique used to measure the concentration of substances (e.g., hormones, drugs) in a sample, not a function of the gamma camera. - RIA utilizes **radioactively labeled antibodies** and antigens but does not involve imaging the body. *Monitoring the surface contamination* - **Geiger counters** or specific contamination meters are used for monitoring surface contamination. - A gamma camera is designed for internal imaging and is not practical or optimized for detecting external surface contamination.
Question 2: Investigation of choice for leptomeningeal carcinomatosis:
- A. Gd enhanced MRI (Correct Answer)
- B. CT scan
- C. SPECT
- D. PET
Explanation: ***Gd enhanced MRI*** - **Gadolinium-enhanced MRI** is the investigation of choice for **leptomeningeal carcinomatosis** as it can visualize the subtle nodular or linear enhancement along the leptomeninges, indicating tumor dissemination. - It offers superior **soft tissue contrast** and spatial resolution compared to CT, enabling detection of small lesions and accurate mapping of disease extent. *CT scan* - A **CT scan** has limited sensitivity for detecting leptomeningeal involvement due to poor contrast resolution of soft tissues and the dura/arachnoid spaces. - It might show hydrocephalus or large tumor deposits, but subtle leptomeningeal enhancement is often missed. *SPECT* - **Single photon emission computed tomography (SPECT)** is primarily used for functional imaging and is not the investigation of choice for anatomical visualization of leptomeningeal carcinomatosis. - Its resolution is too low to detect the fine structural changes associated with leptomeningeal spread. *PET* - **Positron emission tomography (PET)**, often combined with CT, identifies metabolically active tumor cells and can detect diffuse metastatic disease. - While useful for overall cancer staging and identifying primary lesions, it is less effective than gadolinium-enhanced MRI for directly visualizing the morphology and enhancement patterns of leptomeningeal carcinomatosis due to limited spatial resolution in the CSF spaces.
Question 3: Which radioisotope is PRIMARILY used for detecting acute myocardial infarction rather than assessing myocardial perfusion?
- A. Thallium 201
- B. Tc-99m Sestamibi
- C. Tc-99m Pyrophosphate (Correct Answer)
- D. 18-FDG PET
Explanation: ***Tc-99m Pyrophosphate*** - This radioisotope binds to **calcium deposits** in infarcted myocardial tissue, which accumulate 12-24 hours after injury. - It is particularly useful for detecting **acute myocardial infarction** (hot spot imaging) when cardiac biomarkers may be unreliable or in cases of delayed presentation. - Shows positive uptake in necrotic tissue, making it a "positive" or "hot spot" agent for acute MI. *Thallium 201* - **Thallium 201** is a potassium analog that is actively transported into viable myocardial cells. - It is primarily used for assessing **myocardial perfusion** and viability, showing areas of reduced blood flow or scar tissue. - Acts as a "cold spot" agent - infarcted areas show reduced uptake. *Tc-99m Sestamibi* - **Tc-99m Sestamibi** is a commonly used tracer for **myocardial perfusion imaging (SPECT)**, indicating blood flow to the heart muscle. - It accumulates in viable myocardial cells in proportion to blood flow and is not specific for acute myocardial necrosis. - Used primarily for stress testing and perfusion assessment, not acute infarct detection. *18-FDG PET* - **18-FDG PET** (Fluorodeoxyglucose Positron Emission Tomography) primarily measures **glucose metabolism** in the myocardium. - It is predominantly used to assess **myocardial viability** in areas of hibernating myocardium rather than acute infarction. - Helps distinguish viable but ischemic tissue from scar tissue.
Question 4: A patient is suspected to have vestibular schwannoma. The investigation of choice for its diagnosis is:
- A. SPECT
- B. Gadolinium enhanced MRI (Correct Answer)
- C. PET scan
- D. Contrast enhanced CT scan
Explanation: ***Gadolinium enhanced MRI*** - **Gadolinium-enhanced MRI** is the **gold standard** for diagnosing vestibular schwannomas due to its superior soft tissue contrast and ability to visualize the fine structures of the **cerebellopontine angle** and internal auditory canal. - Vestibular schwannomas enhance brightly with gadolinium, allowing for clear delineation of the tumor from surrounding brain tissue and nerves, even when small. *SPECT* - **SPECT** (Single-Photon Emission Computed Tomography) is primarily used for assessing **brain perfusion**, **metabolism**, or receptor activity, not for detailed anatomical imaging of tumors like schwannomas. - It has **limited spatial resolution** compared to MRI and would not accurately visualize a vestibular schwannoma, especially when small. *PET scan* - **PET scans** (Positron Emission Tomography) are mainly used to detect **metabolically active tumors** or differentiate benign from malignant lesions, as well as for staging cancer and assessing treatment response. - While it can detect some tumors, PET is **not the primary imaging modality** for initial diagnosis of vestibular schwannoma, as MRI provides superior anatomical detail. *Contrast enhanced CT scan* - A **contrast-enhanced CT scan** can identify larger vestibular schwannomas, especially if they cause **bone erosion** of the internal auditory canal. - However, CT has **inferior soft tissue resolution** compared to MRI, making it less sensitive for detecting small tumors or differentiating them from adjacent structures in the posterior fossa.
Question 5: In a child, non-functioning kidney is best diagnosed by:
- A. Ultrasonography
- B. IVU
- C. Creatinine clearance
- D. DTPA renogram (Correct Answer)
Explanation: ***DTPA renogram*** - A **DTPA (diethylenetriamine pentaacetic acid) renogram** is a nuclear medicine study that assesses **renal blood flow**, **glomerular filtration**, and urinary drainage. It directly measures the function of each kidney by quantifying tracer uptake and excretion, making it ideal for diagnosing a non-functioning kidney in a child. - The test provides information on the **relative function** of each kidney and outflow obstruction, which is crucial for determining if a kidney is truly non-functioning rather than just poorly visualized. *Ultrasonography* - While ultrasound can visualize the **anatomy** of the kidney (size, shape, presence of hydronephrosis), it does not directly assess renal function. - It may show a small, atrophic, or poorly developed kidney, but cannot definitively determine if it is non-functioning without functional studies. *IVU (Intravenous Urogram)* - An **IVU** relies on the kidneys' ability to excrete contrast material, which is visualized by X-ray. If a kidney is non-functioning, it will not excrete the contrast, leading to non-visualization. - However, IVU exposes the child to **radiation** and **iodinated contrast**, and newer, safer, and more precise functional studies like renograms are preferred, especially in pediatric cases where radiation exposure should be minimized. *Creatinine clearance* - **Creatinine clearance** is a measure of overall **glomerular filtration rate (GFR)** for both kidneys combined. - It does not provide information on the individual function of each kidney, so it cannot diagnose a non-functioning unilateral kidney.
Question 6: 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 7: Which of the following liver metastases appear hypoechoic on ultrasound?
- A. RCC
- B. Colon cancer
- C. Breast cancer (Correct Answer)
- D. Mucinous adenocarcinoma
Explanation: **Breast cancer** - Liver metastases from **breast cancer** frequently present as **hypoechoic lesions** on ultrasound, due to the tumor's cellular composition and vascularity. - This appearance helps differentiate them from other more commonly echogenic or mixed metastatic patterns. *RCC* - **Renal cell carcinoma (RCC)** metastases to the liver often appear **hyperechoic** or **mixed echogenicity** on ultrasound due to their rich vascularity. - This is a distinct characteristic, different from the predominantly hypoechoic nature seen with breast cancer metastases. *Colon cancer* - Liver metastases from **colon cancer** are typically **echogenic** or **mixed echogenicity** on ultrasound, sometimes with a hypoechoic rim ("target sign"). - Their presentation is generally not purely hypoechoic, making them distinguishable from breast cancer metastases. *Mucinous adenocarcinoma* - Liver metastases from **mucinous adenocarcinoma** can be quite variable, but they often appear **complex**, possibly with **cystic components** or mixed echogenicity, rather than uniformly hypoechoic. - The mucin content can create a distinct internal architecture on ultrasound that differs from solid hypoechoic lesions.
Question 8: 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 9: 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 10: 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.
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