**Core Concept**
High-resolution computed tomography (HRCT) is a crucial diagnostic tool in pulmonology, providing detailed images of lung parenchyma and interstitial spaces. It enables the detection and characterization of various interstitial lung diseases (ILDs), such as idiopathic pulmonary fibrosis, sarcoidosis, and pneumoconiosis.

**Why the Correct Answer is Right**
HRCT is the investigation of choice for ILD due to its ability to visualize the lung's microstructure, particularly the interstitial spaces. This is achieved through its high spatial resolution, which allows for the detection of subtle abnormalities, such as ground-glass opacification, reticular patterns, and honeycombing. HRCT can also assess the extent and distribution of lung involvement, guiding further management and treatment decisions.

**Why Each Wrong Option is Incorrect**
* **Option A:** Chest X-ray is not suitable for ILD diagnosis due to its low spatial resolution, which may not detect subtle interstitial changes.
* **Option B:** Lung function tests, such as spirometry and diffusion capacity, provide functional information but do not directly visualize ILD.
* **Option D:** Positron emission tomography (PET) is not typically used for ILD characterization, although it may be useful in assessing disease activity or response to treatment.

**Clinical Pearl / High-Yield Fact**
When interpreting HRCT images, remember that ILD can be classified into three main patterns: ground-glass opacification (GGO), reticular patterns, and honeycombing. GGO is often associated with early or mild disease, while honeycombing is a hallmark of advanced fibrosis.

**Correct Answer: C. High-resolution computed tomography (HRCT) is the investigation of choice for detection and characterization of interstitial lung disease.**