The Evolution of Medical Imaging: Spectral Computed Tomography (CT)
Conventional Computed Tomography (CT) has long been the backbone of diagnostic radiology, providing detailed cross-sectional views of the human body. However, standard CT operates on a significant limitation: it integrates all X-ray photons into a single "grayscale" value (Hounsfield Units). This can lead to ambiguity when different materials, such as iodine and calcium, exhibit similar attenuation at a single energy level. Spectral CT overcomes this by utilizing the energy-dependent nature of X-ray attenuation to differentiate and quantify tissue composition with unprecedented precision.
How It Works: Beyond the Grayscale
The fundamental principle of Spectral CT lies in the fact that materials absorb X-rays differently depending on the energy of the photons. While conventional CT uses a polychromatic beam and treats it as a single average, Spectral CT acquires data at multiple energy levels. This is typically achieved through two primary methods:
Source-based: Using two X-ray tubes at different voltages (Dual-Source) or rapidly switching the voltage of a single tube (kV-switching).
Detector-based: Utilizing specialized "sandwich" detectors that separate high and low-energy photons or advanced Photon-Counting Detectors (PCDs) that measure the energy of every individual photon.
By analyzing these energy-specific datasets, the system can perform material decomposition. This allows clinicians to "see through" certain substances or highlight others, essentially adding a dimension of chemical color to a traditionally black-and-white medium.