**Core Concept**
High-resolution computed tomography (HRCT) of the chest is the investigation of choice for detecting and characterizing interstitial lung disease (ILD), providing detailed images of lung morphology and parenchymal abnormalities. This imaging modality is particularly useful for visualizing the extent and distribution of ILD, guiding diagnosis, and assessing disease progression. HRCT's superior resolution allows for the identification of subtle changes in lung architecture.

**Why the Correct Answer is Right**
HRCT's ability to detect and characterize ILD lies in its capacity to resolve small details in lung morphology, including ground-glass opacifications, honeycombing, and reticulations. The images obtained from HRCT can be used to differentiate between various types of ILD, such as idiopathic pulmonary fibrosis, sarcoidosis, and hypersensitivity pneumonitis. This differentiation is crucial for determining the underlying cause of ILD and guiding treatment decisions.

**Why Each Wrong Option is Incorrect**
**Option A:** Chest X-ray is not the investigation of choice for ILD as it lacks the sensitivity and specificity to detect and characterize the disease, often showing non-specific findings such as bilateral reticular markings.
**Option B:** Positron emission tomography (PET) is not suitable for ILD diagnosis as it is primarily used for assessing metabolic activity and is not capable of providing detailed images of lung morphology.
**Option C:** Magnetic resonance imaging (MRI) is not typically used for ILD diagnosis due to its limited ability to resolve lung parenchymal details and the presence of artifacts from respiratory motion.

**Clinical Pearl / High-Yield Fact**
When interpreting HRCT images for ILD, it's essential to recognize that honeycombing, a characteristic feature of advanced pulmonary fibrosis, represents a poor prognostic sign and is associated with a higher risk of mortality.

**Correct Answer: C. High-resolution computed tomography (HRCT) of the chest.**