**Core Concept**
Liver cancer, specifically hepatocellular carcinoma (HCC), is a major cause of cancer-related mortality worldwide. Early detection of HCC is crucial for improving survival rates in high-risk populations, such as those with chronic liver disease, cirrhosis, or liver dysfunction.

**Why the Correct Answer is Right**
In high-risk populations, HCC is best detected by surveillance using **Alpha-Fetoprotein (AFP) levels**. Elevated AFP levels are a sensitive indicator of HCC, particularly in the early stages of the disease. However, it's essential to note that AFP levels can be elevated in other conditions, such as cirrhosis and liver regeneration, which may lead to false positives. Therefore, a combination of clinical evaluation, imaging studies, and laboratory tests, including AFP levels, is necessary for accurate detection.

**Why Each Wrong Option is Incorrect**
* **Option A:** Imaging studies, such as ultrasound, CT scans, or MRI, are useful for detecting HCC but are not sufficient for surveillance in high-risk populations. They may not detect early-stage tumors, and the risk of false negatives is high.
* **Option B:** Liver biopsy is an invasive procedure and not suitable for routine surveillance in high-risk populations. It is typically used to confirm the diagnosis of HCC after a suspicious lesion has been detected on imaging studies.
* **Option C:** Other tumor markers, such as CA 19-9 or CEA, are not specific for HCC and may be elevated in other cancers or conditions.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that **elevated AFP levels are not specific for HCC**, and a combination of clinical evaluation, imaging studies, and laboratory tests is necessary for accurate detection. Additionally, the American Association for the Study of Liver Diseases (AASLD) recommends surveillance with AFP levels and imaging studies every 6 months for high-risk populations.

**Correct Answer: A. Alpha-Fetoprotein (AFP) levels**