Digital Variance Angiography: A Revolutionary New Angiography Imaging Technology

Digital Subtraction Angiography (DSA) is the traditional imaging method used for interventional radiology to visualise blood vessels in cardiovascular and oncological disorders. However, the large amount of iodinated contrast media (ICM) and high X-ray dose radiation applied during this process causes complications and occasionally leads to contrast-induced nephropathy and radiation-induced tissue damage. There is also a growing need to improve present DSA image quality, especially in CO2 angiography interventions, and in the meantime, a need to reduce both contrast medium and radiation doses. A novel image processing method called Digital Variance Angiography (DVA) provides a potential solution for these limitations in the angiography field.

As of 2021, five peer-reviewed publications from the clinical research team at Semmelweis University’s Heart and Vascular Centre, Hungary, have appeared in leading radiology journals with promising results. Digital Variance Angiography (DVA) is a state-of-the-art technology, focusing on lower extremity and endovascular carotid angiographic interventions. In these articles, the diagnostic value of DVA images was compared to traditional Digital Subtraction Angiography (DSA) images in a group of patients who were undergoing this kind of angiographic examination.

 

In the first study, Gyánó, M, et al (2019) compared the quality of DVA and DSA images in a retrospective observational crossover study. This study analysed 232 image pairs from 42 patients who underwent lower limb x-ray angiography by using iodinated contrast media (ICM) between February and June 2017. Methods included the measurement of signal-to-noise ratio (SNR) and visual quality comparison by experienced specialists.

 

Although other factors like spatial resolution, sharpness, and object size may contribute to image quality and object perceptibility, noise places a fundamental limitation on the ability to recognize structures on low-contrast images. This limitation was the main reason why the SNR measurement method was chosen; higher SNR values indicates lower noise levels, and therefore improved images. The results from the study showed two to three times higher SNR values in the case of DVA images compared to traditionally used DSA images, which indicates that DVA has the potential to improve the ability to view blood vessels,

 

Qualitative comparison was performed by three vascular surgeons and three interventional radiologists, who have approximately 17 years of experience on average. In an online visual questionnaire,  the participants in the study were shown DVA and DSA image pairs of the same anatomical regions, and then were asked to choose the image which they found to be more useful for making a diagnosis. Overall, the participants judged the kinetic images better in 69 % of all images. Regarding different anatomical regions, the participants agreed that the DVA was significantly better for talocrural (ankle) and popliteal (back of the knee) regions.

 

The authors concluded that the higher SNR values indicate that the DVA method has the ability to generate angiographic images of the same quality as the currently used DSA, but with a reduced dose of the administered radiation and/or ICM and still maintaining the same vessel visibility for ease in diagnostics.

 

In 2019 Óriás, V, et al published the results of a clinical study which investigated the feasibility of DVA in lower extremity carbon-dioxide angiography. It also compared the quantitative and qualitative performance of the new image processing technique to that of the current reference standard DSA.

 

The study comprised 24 patients who underwent lower limb carbon-dioxide angiography between December 2017 and April 2018 at two clinical centres. For comparative purposes, the SNR of DSA and DVA images was calculated, and the visual quality of DSA and DVA images was also compared by independent clinical specialists. During the visual evaluation, 120 DSA and DVA image pairs were compared and it was judged that the DVA provided higher quality images in both of the clinical centres, in 78% and 90% of comparisons. DVA images also received consistently higher individual rating than DSA images, regardless of the research site or the anatomical region.

 

These results have shown that in lower limb carbon-dioxide angiography, DVA produces higher SNR and significantly better image quality than DSA, regardless of the image acquisition instruments and protocols. Therefore, this new image processing method might help the widespread use of carbon-dioxide as a safer contrast agent in clinical practice.

 

The aim of the next retrospective study by Gyano et al (2019), was to verify the clinical usefulness and benefits of DVA in carbon dioxide (CO2)-assisted lower limb interventions. In this study, the DSA and DVA images of 46 CO2-assisted runs were visually evaluated by five experts in single-image evaluation using a 5-grade rating scale, and also in paired comparisons. DVA images received significantly higher scores than DSA images. DVA images were preferred in terms of diagnostic value and usefulness for therapeutic decisions in 85.2% and 83.9% of all comparisons. Furthermore, these benefits were achieved at lower frame rates (1-3 FPS) than usually recommended for CO2 angiography (4-6 FPS).

 

Bastian et al(2020), further examined this promising technique in 12 patients with metal implants. The aim of Bastian’s study was to evaluate whether DVA could counterbalance the image quality impairment of lower-limb angiographies with metal implants. 85 raw lower-limb iodine contrast angiograms from patients with metal implants were processed retrospectively with DVA analyses. This pilot study shows that DVA provides significantly improved image quality in lower-limb angiography with metal implants when compared to DSA imaging. The improved SNR suggests that this approach could reduce radiation exposure for lower-limb angiography with metal implants as well.

 

This proof-of-concept study shows that DVA could facilitate correct diagnostic and therapeutic decisions, as well as potentially helping to reduce radiation exposure in lower limb CO2 angiography, contributing to the safety and efficacy of CO2-enhanced endovascular interventions.

 

The research team also extended the reach of this innovative technology beyond the lower limb angiographic region, and started studying its usage in endovascular carotid interventions.  The prospective study by Óriás (2020) included 26 patients undergoing carotid percutaneous transluminal angioplasty. The SNR of DSA and DVA image pairs obtained by a standard (100% with 6ml iodinated contrast) or a low-dose (50% with 3 ml iodinated contrast) protocol were compared. Visual evaluation of all images was performed by five specialists using a 5-grade rating scale.

 

The aim was to investigate whether the quality reserve of DVA images, which had been proven in previous publications, would provide an opportunity for the reduction of ICM in carotid X-ray angiography. The result did not show statistical difference between the DSA with 6 ml contrast and DVA with 3 ml contrast images’ scores. This prospective study showed that DVA allows for a substantial ICM reduction (50 %) in carotid X-ray angiography, without affecting the quality or diagnostic value of angiograms.

 

To summarise, the published articles have successfully presented the promising advantages of new DVA technology against traditional DSA to reserve image quality, together with the possibility of concrete and substantial reduction of X-ray radiation and contrast medium dose. In conclusion, this new image processing method enables safer and faster treatment for the intervention of cardiovascular and oncological diseases.

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