Introduction

Imaging technologies have become increasingly integrated into forensic sciences due to their ability to identify, visualize, and preserve two- and three-dimensional structures in a non-destructive manner [1–3]. Among these modalities, computed tomography (CT) has gained relevance by enabling volumetric reconstruction and supporting both qualitative and quantitative analyses while minimizing physical intervention on the specimen [4–8]. These attributes have positioned CT as a valuable adjunct to conventional forensic examinations. Nevertheless, its spatial resolution remains insufficient for the investigation of structures at the micrometric scales, thereby limiting its applicability to the analysis of microtraces [9].

Micro-computed tomography (micro-CT) has emerged as a high-resolution extension of conventional CT, operating on the same physical principles while providing substantially enhanced spatial resolution [10–12]. This advancement enables detailed three-dimensional reconstructions and precise volumetric and density measurements at the microscale. As a result, micro-CT offers a comprehensive spatial assessment of microtraces [9, 13], defined as minute traces that are not discernible without magnification or advanced imaging techniques [14, 15].

Within the spectrum of forensic microtraces, ballistic-related evidence warrants particular attention, given the persistently high global burden of firearm-related violence and homicide [16]. Among such evidence, gunshot residue (GSR) represents one of the most frequently examined trace materials. GSR consists of metallic and non-metallic microparticles generated during cartridge deflagration and firearm discharge, which may be deposited on the shooter, the victim, or surrounding surfaces [17, 18]. Currently, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDS) is widely regarded as the gold standard for GSR analysis due to its high sensitivity and elemental specificity [19]. However, complementary analytical techniques, including colorimetric assays, Raman spectroscopy, time-of-flight secondary ion mass spectrometry [20, 21], and micro-CT [22] have been increasingly explored to overcome methodological limitations and expand interpretative frameworks.

The application of micro-CT to GSR analysis provides distinct advantages, particularly through non-destructive visualization of the three-dimensional spatial distribution of residue particles, as well as micrometric measurements of particle size, morphology, and density. These capabilities support a more refined understanding of the ballistic behavior of GSR across different substrates and contribute to inferential approaches related to shooting distance estimation [22]. Despite its theoretical and practical potential, the literature addressing the use of micro-CT in GSR analysis remains limited and methodologically heterogeneous.

Considering the current evidence, the present study aimed to systematically synthesize and critically appraise the available evidence regarding the application of micro-CT for the visualization, analysis, and characterization of gunshot residues. Additionally, it aimed to quantitatively evaluate the relationship between micro-CT–detectable residues and shooting distance, thereby clarifying the current evidentiary value of this technique within forensic ballistic investigations.