1. What is the main advantage of Fluoroscopy?

Fluoroscopy and angiography are the only ionizing imaging modalities that can provide real-time changes in vasculature with up to 30 frames per second. They are essential imaging modalities in interventional procedures, particularly in cardiac and neurosurgery. These procedures typically require high temporal resolution to accurately visualize fast-moving structures such as the beating heart or cerebral blood flow. However, quality assurance (QA) and quality control (QC) protocols often neglect temporal testing, focusing primarily on dose rates for common protocols and static image quality metrics like spatial resolution and contrast measurements. This oversight can lead to clinicians missing important aspects, due to motion blur, ghosting artifacts, and misregistration errors, impacting surgical precision and patient safety.

On the other hand, high frames per second, which is also high dose rate, is not necessary in all procedures and situations, but without testing the exact relationship between frames and dose, we can’t optimize procedures. In other words, just because a fluoroscopy system is producing X pulses per second, that does not mean it is also capturing X different frames per second. The X-ray system is independent of the imaging system, and as such, should be independently evaluated.

This article highlights the current gaps in fluoroscopy testing, impact of temporal tests on clinical procedures (or lack thereof), reasons why comprehensive tests should be included in routine QA/QC, and the tools and phantoms available to improve system performance. 

In the end, the potential benefits of integrating temporal resolution assessments should be evident, ensuring real-time imaging is optimized for critical interventions.

The article will not deal with ultrasound, which can also provide real time imaging of the heart, but lacks penetration ability, and has a much smaller Field of View (FoV).

2. Current Situation: Gaps in Temporal Resolution Testing

In most medical physics QA/QC protocols, tests focus on static image quality metrics such as contrast-to-noise ratio (CNR), spatial resolution, and detector uniformity. While these are critical for fluoroscopy and angiography, they do not account for motion-related artifacts that can degrade real-time imaging.

Common issues due to the lack of temporal resolution testing include:

• Motion blur in dynamic imaging, reducing vessel and implanted device clarity.
• Frame lag and ghosting artifacts, making it harder to track stents, guidewires, and catheters.
• Misregistration in Digital Subtraction Angiography (DSA), leading to inaccurate vessel visualization.
• Increased radiation dose, as operators compensate for poor imaging by increasing exposure time.

Despite these issues, most QA programs do not include temporal tests, largely due to:

1. Lack of standardized temporal testing protocols compared to spatial resolution tests.
2. Complexity of motion simulation, requiring specialized equipment, which may be expensive and hard to obtain.
3. Reliance on manufacturers’ built-in compensation algorithms, like digital frame averaging, which do not always perform optimally in clinical settings, and often operate like black boxes.
4. Lack of regulations and guidelines necessitating the need for temporal testing, which leaves specific and specialized temporal tests at the discretion of the medical physicist.

3. Clinical Impact: Brain and Cardiac Surgery Risks

Lack of proper temporal resolution assessment can lead to significant risks in high-precision interventional procedures, especially in the heart and brain, where fast-moving structures demand real-time accuracy.

3.1 Cardiac Interventions

Coronary angioplasty and stent placement require real-time imaging to track guidewires and balloon catheters.

Poor temporal resolution can cause motion blur, making it difficult to determine precise device positioning.

Pulsatile coronary artery motion may appear smeared, increasing the risk of misplacing a stent.

3.2 Neurosurgical and Stroke Procedures

DSA is critical for stroke thrombectomy, aneurysm coiling, and AVM embolization.

Frame lag and motion artifacts can lead to misregistration errors, misguiding clot retrieval devices.

In carotid artery stenting, low temporal resolution can make it harder to detect flow abnormalities post-deployment.

Delayed image updates or motion-related blurring can cause surgeons to misinterpret vessel dynamics, leading to procedural complications or increased intervention time.

4. Why Temporal Resolution Tests Should Be Added to Routine QA/QC

To ensure imaging systems function optimally during dynamic procedures, medical physicists should incorporate temporal testing into regular QA/QC protocols.

Key reasons to implement temporal tests:

1. Improves real-time visualization, ensuring accurate device tracking in fast-moving structures.
2. Reduces motion artifacts that may obscure critical anatomical details.
3. Prevents unnecessary radiation exposure by avoiding prolonged fluoroscopy time. Therefore, ionising radiation to both patients and staff in the operating theatre can be effectively reduced. In Europe and the UK, this will make it easier to remain as close as possible to established Diagnostic Reference Levels for specific procedures.
4. Ensures system compliance with manufacturer and/or national specifications for frame rate and pulsed fluoroscopy response time (see NEMA in references).
5. Optimizes DSA image subtraction accuracy, improving diagnostic and procedural confidence.

By integrating motion phantoms, pulsed frame rate tests, and automated motion analysis software, medical physicists can quantify and correct temporal resolution deficiencies.

5. Tools and Phantoms for Temporal Resolution Testing

To evaluate and optimize fluoroscopic and angiographic systems for motion performance, the following tools are recommended:

MOTUS Motion Platform (Leeds Test Objects, UK)

Programmable movement in the Z-axis (0–7.5 cm/s) with optional Y-axis motion.

Enables testing of motion artifacts in real-time imaging.

QUART DSA Phantom (QUART GmbH, Germany)

Assesses DSA misregistration and temporal resolution in vascular imaging.

Model L-629 Rotating Spoke Test Tool (Ludlum Measurements, Inc., TX, USA)