Written By:

Rock Mackie, PhD, Chief Innovative Officer

David Ergun, PhD, CEO

Sabrina Brounts DVM, MS, PhD, DACVS/ECVS, DACVSMR, Scientific Advisor

Introduction

Advancements in imaging technology have made computed tomography (CT) more accessible to veterinarians, particularly for scanning horses' distal limbs (Ref 1), and head and neck (Ref 2). With this increased accessibility comes an important decision: should you choose a fan-beam or cone-beam CT scanner? While both technologies serve the purpose of producing three-dimensional images, they do so in very different ways, impacting image quality, diagnostic accuracy, and ease of use in a clinical setting. Let’s explore these differences and determine which option is best for equine veterinary applications.

CT training session at Wisconsin Equine Clinic and Hospital

How CT Imaging Works

Before diving into the differences between fan-beam and cone-beam CT, let’s quickly review how CT imaging functions.

A CT scanner takes multiple X-ray images from different angles around a subject, then combines them using computer algorithms to create a detailed cross-sectional view of the internal structures. This allows veterinarians to see bones, soft tissues, and abnormalities that might be missed with traditional X-rays. However, how the scanner acquires these images varies depending on the type of CT technology used.

Fan-Beam vs. Cone-Beam CT: What’s the Difference?

The key distinction between these two technologies lies in how the X-rays are emitted and detected:

Fan-Beam CT: Uses a narrow, fan-shaped X-ray beam that moves around the patient in a full rotation. The detector, which collects the X-rays after they pass through the patient, is curved to match the beam’s path.

Cone-Beam CT: Uses a wider, cone-shaped X-ray beam and a flat detector similar to the type used for conventional planar x-rays. The system may rotate only partially around the patient to collect the image data.

These differences in X-ray beam shape and motion affect image quality, scan time, and the ability to detect certain conditions.

Illustration of the geometry and typical scanner setup for cone-beam and fan-beam CT.

Speed and Efficiency

When scanning horses, speed is a crucial factor. Horses are large animals that may not always stand perfectly still, making rapid image acquisition essential for reducing motion blur and obtaining clear images.

Fan-Beam CT is significantly faster because it collects data in a continuous, full-circle rotation. The speed of acquisition can be 60 rotations per min or higher, generating around 1000 views or more per second. This allows for quick scans with minimal disruption to the horse.
Cone-Beam CT requires more time to capture a full image since it uses a partial rotation and slower acquisition rates (<5 rotations per min and <100 views per second). This lower rate of views increases the risk of motion artifacts (blurry images caused by movement).

For veterinarians looking to minimize scan time while maximizing image clarity, fan-beam CT is the better choice.

Image Quality: Resolution and Noise

High-quality images are vital for detecting subtle injuries, such as small bone fractures or early-stage joint disease.

Fan-Beam CT produces high-quality images with less noise, meaning clearer images free from motion artifacts. This is because its curved detector array captures X-ray data with more efficient image sensors, operating at higher speeds, thereby reducing inconsistencies.

An additional benefit of the high-efficiency fan-beam detector array and high scan speeds is that the system can be set to operate at significantly lower x-ray power levels, thereby reducing the level of radiation to the patient and moreover the amount of scatter radiation from the patient. For example, the Asto CT Equina system operates at a very low power level of 1.28 kW, allowing equine patient handlers wearing standard personal protective equipment to be in the CT room during a patient scan, and not exceed the recommended safe thresholds of occupational radiation exposure (Ref 3).

Cone-Beam CT, while capable of high pixel resolution, as measured by a modulation transfer function (MTF), neighboring image sensors are ganged together to improve their reduced sensitivity and speed compared to fan-beam detectors. It suffers from increased noise and lower signal strength. This can lead to grainy or unclear images, making it harder to identify minor abnormalities.

Human head axial and head and neck sagittal CT image comparison.
Adapted from Lechuga and Weidlich (Ref 4)

Artifacts: Distortions That Affect Diagnosis

Artifacts are distortions or errors in a CT scan that can make it harder to interpret the images accurately.

Fan-Beam CT is designed to minimize scatter artifacts, producing cleaner, more reliable images
Cone-Beam CT is more susceptible to artifacts caused by scattered radiation, which can result in blurry or distorted images.

This is especially important for equine imaging, where small anatomical details can make a big difference in diagnosis.

Field of View: Capturing the Whole Picture

The size of the area that a CT scanner can capture in one scan, known as the field of view or FOV, is another important factor.

Fan-Beam CT can allow veterinarians to scan larger areas of the horse’s anatomy in a single pass, reducing the need for multiple scans. The Asto CT Equina, for example can scan a full 75-cm FOV (the entire CT bore opening) allowing all anatomy within the CT bore opening to be acquired . Scout scans are unnecessary for the Equina fan-beam CT scanner because it scans everything within its gantry bore, eliminating the need for orthogonal scout views to determine anatomy placement in the field. Not doing scout scans reduces the diagnostic scan time by more than a factor of two.
- In vertical scan mode (fore- or hind-limb studies), the Equina CT gantry can travel up to 75 cm to seamlessly acquire a limb pair from the mid-tibia/mid-radius to the hoof in a single setup.
- In horizontal scan mode (Head studies), the Equina CT gantry can travel up to 100 cm to seamlessly acquire the head & neck from nostril to C4/C5 standing or C7/TI in dorsal recumbency in a single setup.
Cone-Beam CT has a more limited field of view, often requiring multiple stitched-together scans to cover the same area. This can lead to inconsistencies, multiple setups and longer scanning times.

For scanning long structures like a horse’s limbs, fan-beam CT provides a more seamless and efficient experience. The following table, along with the example images of the human head and the human head and neck, nicely summarize the comparison of cone-beam and fan-beam CT cone beam scanner systems.

Image quality metric comparison of cone-beam and fan-beam CT scanners.

Weight-Bearing Fan-Beam CT: A Game-Changer for Equine Imaging

The Equina is not a repurposed human fan-beam CT scanner but was designed specifically for scanning horses. A critical advantage of fan-beam CT, particularly with the Equina by Asto CT, is the ability to perform weight-bearing scans. Unlike traditional non-weight-bearing imaging, Asto CT’s weight-bearing 24-row helical fan-beam CT allows veterinarians to assess the limb in its natural, load-bearing position. This provides a more accurate representation of anatomical structures under physiological stress, revealing subtle abnormalities that might not be visible in non-weight-bearing scans.

Additionally, the ability to scan limb pairs offers a clear advantage. By comparing the left and right limbs under identical weight-bearing conditions and veterinarians can detect asymmetries. This is an advantage that is not present with a single-limb scan. This comparative approach enhances diagnostic accuracy and provides more comprehensive data for treatment planning.

Conclusion: Which CT Scanner is Best for Equine Veterinary Use?

When choosing between fan-beam and cone-beam CT for equine imaging, fan-beam CT—especially the weight-bearing Equina by Asto CT—emerges as the superior choice due to its:

Better image quality
Head and neck in horizontal mode and fore- or hind-limb pairs in vertical mode
Faster scan times – no need for scout views.
Reduced noise and better contrast
Fewer motion artifacts
Lower x-ray power levels, allowing patient handlers to care for the standing sedated patient during the scan
Larger field of view (FOV) – the bore diameter is equal to FOV
Weight-bearing capability for more accurate diagnostics
Ability to scan limb pairs for enhanced comparative analysis

For equine practitioners looking to improve disease diagnosis, a weight-bearing fan-beam CT scanner is the optimal solution. The ability to quickly and clearly detect issues—such as stress fractures, joint problems, or other orthopedic conditions—can make a significant difference in treatment outcomes.

As CT technology continues to evolve, it’s important to choose a system that aligns with the needs of equine practitioners and ensures the best possible care for their patients. Fan-beam CT, particularly with the Equina by Asto CT, stands out as the clear winner in this comparison, making it an invaluable tool for any veterinary clinic specializing in equine imaging.

References

1. Brounts SH, Lund JR, Whitton RC, Ergun DL, Muir P. Use of a novel helical fan beam imaging system for computed tomography of the distal limb in sedated standing horses: 167 cases (2019-2020). J Am Vet Med Assoc. 2022;260(11):1351-1360. doi:10.2460/javma.21.10.0439

2. Brounts SH, Henry T, Lund JR, Whitton RC, Ergun DL, Muir P. Use of a novel helical fan beam imaging system for computed tomography of the head and neck in sedated standing horses: 120 cases (2019-2020). J Am Vet Med Assoc. 2022;260(11):1361-1368. doi:10.2460/javma.21.10.0471

3. Veitch KE, Szczykutowicz TP, Brounts SH, Ergun DL, Muir P, Loeber SJ. Radiation exposure during simulated head and limb fan beam standing computed tomography appears safe for personnel using lead shielding. J Am Vet Med Assoc. 2024;263(1):63-70. doi:

https://doi.org/10.2460/javma.24.06.0424

4. Lechuga L, Weidlich G. Cone beam CT vs. fan beam CT: A comparison of image quality and dose delivered between two differing CT imaging modalities. Cureus 8(9) (September 12, 2016): e778. doi:10.7759/cureus.778)

Fan-Beam CT vs. Cone-Beam CT: Choosing the Right Technology for Equine Imaging