Advantages and Disadvantages of Computed Tomography in Cranial Gunshot Injuries: Experimental Animal Study

Cranial gunshot injuries (GSIs) are severe traumas associated with high mortality and morbidity. Computed tomography (CT) is the gold standard imaging modality for these cases (1-3). Cranial imaging is recommended as soon as possible after arrival at the hospital. Brain damage depends on the type of firearm, the distance of the shot, and the entry angle, mass, and velocity of the bullet. While the majority GSI cases die at the scene, mortality can be reduced in those who reach the hospital with rapid, appropriate and aggressive treatment (3, 4). Tomography provides critical information about the location and size of entry and exit wounds, determination of brain damage, bullet trajectory, cranial bone fractures, detection of foreign bodies, and bullet residues (bullet core or jacket fragments). It plays a pivotal role in surgical decision-making and in determining the surgical strategy. Given the high mortality rate associated with GSIs, physicians must make rapid decisions. At this stage, CT provides rapid information among all radiological imaging methods (1, 3, 5, 6).

The first postmortem CT scan was reported in the late 1970s in a fatal cranial GSI. The VIRTOPSY project, presented in 2003, described minimally invasive imaging methods to complement traditional autopsies. Medical imaging methods, particularly CT, are increasingly used for forensic purposes (7-9). Images obtained using this non-invasive method can be re-examined, stored, shared, presented in courts, and used to create 2D and 3D images (10-12). CT has proven particularly effective in detecting fractures, foreign bodies, and gases (13-16). Forensic physicians detect entry-exit wounds and trajectory, determine the type of weapon, and ascertain the cause of death (17-21). Rapid and accurate identification of victims is essential after disasters. Interpol has deemed CT-based data suitable and useful. The interpretation of reconstructed images, independent documentation from observers, the ability to reconstruct various images long after the event, the sharing of workload through digital transmission of CT data, and the reduction in time and expertise required in the disaster area have demonstrated that it is a valuable tool for disaster victim identification. Age determination and identification through comparison of antemortem and postmortem CT images have become possible with CT (22, 23).

Limited literature exists on the use of CT for crime-scene and shooting reconstruction. CT scans detect bullet fragments in decomposed, skeletal, mummified, or charred corpses. Limited data regarding ammunition and caliber support the usefulness of CT. CT findings are valuable in cases with minimal skin findings or intraoral GSIs. While limited number of publications report that shooting distance with CT, these studies are generally based on animal experiments and the detection of gunshot residue (24-26). Shooting reconstruction is the study conducted to identify the person who pulled the trigger and the shooting location (27). Azimuth (horizontal) and vertical angles are the necessary for shooting reconstruction (28). Existing literature provides insufficient information on the contribution of CT to shooting reconstruction by determining azimuth and vertical angles. This study aimed to fill this gap. We aimed to examine the findings required for shooting reconstruction and discuss the advantages and disadvantages of CT in GSIs.

Study Population

Although no ideal subject species has been defined in the literature for use in GSIs, organ models, pigs, and sheep have been used most frequently in ballistic studies (29-32). Sheep were preferred for the study because pigs were unavailable after the regional earthquake. Moreover, sheep were more accessible and required fewer anaesthetic agents for control purposes. The study utilized the heads of 12 Adana breed sheep. The heads were obtained at no cost from a slaughterhouse that processes sheep daily, and the animals were automatically slaughtered at the distal part of the C1 vertebra (Atlas). External examination revealed no differences among the heads used. The heads were stored at +4 °C in sterile conditions and transported to the experimental area.

Ammunition used were 9×19 mm calibre M822 type (Full Metal Jacket) rounds (340 m/s), fired from a Canik Mete TP9 semi-auto handgun; this calibre is the most common in civilian injuries. Experienced tests were performed by the staff of the xxxSpecial Operations Directorate, Special Operations Department, General Directorate of Security, Ministry of Internal Affairs, at the same department shooting range.

Test Shots Plan

Test shots were performed from distances of 0.5, 1, 5, and 10 meters, targeting the frontal, temporal and occipital regions (Table 1).

Cranial Imaging

Heads were positioned with the nape and chin aligned, keeping the heads in the midline. Axial images were obtained using a Vimago GT30 (Epica Animal Health, USA) high-resolution CT scanner. Tomography parameters were as follows: 120 kVp, 80 mAs, gantry rotation time =0.6 s, slice thickness =0.35 mm. The time required for imaging was recorded, and a veterinarian appropriately disposed of the imaged heads.

CT images were evaluated by two authors. The axial images and the sagittal and coronal reformats, recorded in DICOM format, were transferred to digital storage and analysed by researchers on personal computers. During the evaluation, factors such as the location, diameter, and angle of the entry wound, the presence of bullet core residue, the bullet trajectory, brain tissue damage, bone fractures, the distribution of bone fragments, Hounsfield unit (HU) values, and the location and diameter of the exit wounds were examined.

Ethical approval for the study was received from the Çukurova University Experimental Animals Local Ethics Committee on 30.04.2024 (meeting number: 4, decision number: 6).

Statistical Analyses

For this descriptive study, HU values were performed using SPSS 20.0 (Chicago, IL), findings are presented as mean ± standard deviation (minimum-maximum).

The time required to obtain images for all 12 heads was less than 1 minute. Findings of entry and exit wounds were obtained from axial and sagittal images for frontal and occipital shots and from axial and coronal images for temporal shots. Bullet trajectory and brain damage were examined on axial and sagittal images for frontal and occipital shots, on axial and coronal images for temporal shots; HU values were measured on axial images for all shots. HU values -808±164 (from -530 to -1024) in cavitation area, +2512±200 (from +2332 to +3071) in pathological tissues, +831±85 (from +707 to +966) in brain tissue, and +2683±359 (from +2128 to +3071) in bone were found (Tables 2 and 3).

In recent years, advancements in tomography and computer technology have created new opportunities for radiologists, clinicians, surgeons, and forensic physicians to evaluate GSI cases. Research on the advantages and disadvantages of CT in forensic cases, particularly in cranial GSIs, has demonstrated that CT is a suitable and beneficial method (Table 4) (33, 34).

Multi-slice CT scanners equipped with 64 detectors rotate around the patient at three revolutions per second. At this speed, whole-body screening takes less than 10 minutes, offering significant dose-time advantages (14, 35). In our study, the time to obtain images with the multi-slice CT device designed for veterinary use was less than 1 minute in all cases, highlighting CT’s efficiency.

During the evaluation, the diameters of skin and/or bone defects were measured after their locations were determined. In frontal and occipital shots, the skin entry wounds were smaller than the bullet diameter, while the bone entry wounds were equal to or larger than the bullet diameter. Millimetric entry wounds were observed on the skin in shots to the temporal region. The skin elastic structure resists penetration, causing the tissue to pit and stretch until the elasticity limit is exceeded, after which the bullet pierces the skin (36, 37). This explains why the observed skin entry wound was smaller than the bullet diameter in this study.

The azimuth angle was determined by measuring the angle formed between the entry wound and the midline in axial images. In contrast, the vertical angle was measured as the angle between the entry wound and the midline on sagittal and coronal images. The vertical angle represents the upward (+) or downward (-) component of the bullet’s trajectory, while the azimuth angle reflects the lateral direction as seen from above. For forensic shooting analysis and reconstruction, knowing the impact angles and entry wound characteristics is crucial (28). Our most important findings suggest that CT provides essential data for forensic shooting analysis (shooting reconstruction studies).

Our evaluations also revealed that bullets create varying defects in the skin and bone. Two factors contribute to the variable sizes of exit wounds in GSIs. First is the bullet tumbling and exiting the body at different angles, and the second is the fragmentation and deformation of the bullet (36, 38). The CT findings in our study aligned with established principles of wound ballistics.

Cranial CT HU values help differentiate tissues: -1000 represents air, negative values near zero (-10, -20) indicate fatty tissues, positive values near zero (+10, +30) indicate fluid structures, +300 to +350 indicate calcified tissues, and +1000 represents bone, the densest structure (15). Advanced reconstruction algorithms enable more detailed measurement of tissue attenuation and provide a wider HU range. The application used in this study had an HU range of -1024 to +3071. Air was represented by -1024 and bone by +3071. Bullet core residue, depending on its copper, lead, aluminium, or zinc content, can appear with extremely high HU values, such as +10,000 (39, 40). In this study, HU measurements showed that air largely replaced brain tissue in the cavitation area, while bone fragments were detected as pathological tissue in the brain. No bullet core residue was found in brain tissue. The absence of bleeding from the vessels was attributed to insufficient blood flow in the cranial region following decapitation.

The entry wound, bullet trajectory, exit wound, and HU values of subject 10 (impacting the frontal region from a distance of 10 meters) are presented as examples in Figures 1 and 2.

While the need for infrastructure such as hospital information management system, digital imaging and communications in medicine and picture archiving and communication system can be seen as a disadvantage, the “Regulation on Health Information Management Systems (HIMS)” dated August 22, 2022, indicates that the current health system in our country has the necessary infrastructure to support the evaluation of cranial GSI cases using CT (41). During the study, the ability to share, export, and use DICOM-formatted data on personal computers enabled physicians to interpret images independently. Similarly, the HIMS regulation enables physicians to access and report data in certain situations, and telemedicine-integrated systems allow remote physicians to report data rapidly and without interruption. Another disadvantage is the presence of artifacts, including linear and ring artifacts, partial-volume effects, noise and motion artifacts, windmill effects, and beam hardening. However, these artifacts can be mitigated through various techniques and imaging adjustments (42).

Study Limitations

The limitations of this study include its animal-based design and the small sample size. The anatomy of the sheep head is similar to that of humans, and the small number of subjects does not alter the findings. The study demonstrated that, regardless of shooting distance and location, CT provides the necessary information for shooting reconstruction. The second limitation was that we could not observe intracranial haemorrhage because of insufficient blood volume resulting from post-decapitation bleeding. However, since CT has been shown in previous studies to be a suitable method for demonstrating intracranial haemorrhage, this will not negatively affect the study’s value.

Cranial CT has numerous advantages, including speed and efficiency. Tomography provides critical information on the location and size of entry and exit wounds, the azimuth and vertical angles of entry, HU values in different tissues, the trajectory of the bullet core, cavitation, and bone fragmentation, and the distribution of bone fragments. The most important result of this study is that we have demonstrated that CT is a fast, non-invasive, and valuable method for forensic ballistic examination and forensic shooting analysis