Direct Conversion - An Interview with Spencer Gunn

Sunday, December 8, 2019


Jacqueline Wheeler


Jacqueline Wheeler from Direct Conversion sits down to interview Spencer Gunn, CEO, about the Varex Imaging acquisition.


How was Direct Conversion formed?

Direct Conversion started to take shape in 2009 when we saw an opportunity to bring together the expertise of both XCounter, a Swedish photon counting technology company, and Ajat, a Finnish company  skilled in hybridization and makers of reliable, high yield sensors for use in charge integrating sensors and now photon counting detectors. Later, we chose the name Direct Conversion because it unites the two companies through our common technology, mission and vision. We convert X-ray and gamma photons directly to electrons instead of to light, this is what “direct conversion” means.


What do you mean by your tag line: “empowered X-ray imaging"?

Photon counting empowers our users because the data gathered from this technology is quantitative and the pixel values reflect the actual number of photons detected. The images generated by our detectors provide our users with the power to extract more information about the object being examined.


What is the advantage of direct conversion X-ray when compared to indirect conversion?

Directly converted X-rays are immediately turned into an electrical signal, whereas indirectly converted X-rays are converted into light first, which causes a blurring effect. The advantage of using direct conversion technology is that we avoid this blurring effect when converting X-rays. Without the light blur directly converted x-ray images can be sharper and have higher MTF (Modulation Transfer Function) than indirectly converted images.


Can you tell us more about your photon counting technology? 

We are the first company to bring affordable photon counting to the mass market so that it can be used in everyday X-ray inspection where high levels of safety are required but a manageable cost is desirable to keep the system price down.

Our ASIC, the CMOS that does the actual counting, is a mature product that has been field proven and commerciaized in a variety of X-ray imaging applications. Its broad range of applications means we manufacture high volumes and can therefore keep our prices affordable.


What applications are the photon counting detectors best suited to and used in? 

Our detectors are especially useful if one is trying to identify and separate different materials in the object being X-rayed. They can detect very small bones in processed meat or pieces of PVC in granola. The high sensitivity and high efficiency of direct conversion detectors also makes them the ideal choice for very high energy imaging, where electronic scatter rejection is essential.


Where will Direct Conversion’s detectors fit into the Varex detector portfolio and what advantages do they offer in comparison to CMOS and a-Si detectors?

Direct Conversion’s detectors are best used in imaging moving objects as well as long length imaging such as full body scanning.

At the moment, our detectors are Time Delay Integration (TDI) detectors, except that they actually sum instead of integrate, so really, they are Time Delay Summation (TDS) detectors. This type of detector is used for slot scanning and Varex did not have an offering for applications of this sort prior to the acquisition.

Our TDI detectors are used in medical and industrial applications and have the advantage of intrinsic scatter rejection and low cost per mm2 imaged because a single line scanner can scan many metres of object. In the industrial markets, we are focused on production lines where conveyors transport products through several stages of manufacture, including X-ray inspection.

Direct Conversion

Our devices are also suitable for helical CT, the largest medical sensor market, and we are developing a 6 bin multi-spectral CT detector so that Varex can enter this market.


What are the advantages of your detectors for medical applications such as mammography and CT?

Efficiency. The thickness of the convertor allows us to stop more X-rays without loss of resolution and this means low dose imaging with high resolution images. This is very important for mammography, of course, as healthy women are irradiated during a scan and the dose needs to be as low as reasonably achievable.

For CT, the same applies; we can capture more of the X-rays, in general, greater efficiency leads to the same signal in a shorter time. Photon counting energy discrimination means CT reconstructions can be improved too, as well as opening up a whole new field of multi spectral CT which we expect to emerge in the next 5 to 10 years. Direct Conversion already has a breast CT customer who has launched a system employing our sensors in a curved array and this validates our technology in a real world, CE marked device.


How do you expect your detectors to fit into Varex’s packaged solutions for CT?

Varex currently supplies many of the parts for X-ray imaging in a CT system, but it doesn’t have a CT detector.  With our technology, our goal is to expand these supplied components by adding a detector sub-system fully assembled and ready for use to plug into the rest of the CT system.


Tell us more about your charge integrating technology product line?

Charge integration (CI) is our legacy technology; it has been very successful in the dental market and was the starting point for the hybridization process that led to Direct Conversion becoming experts in using cadmium telluride (CdTe) as a converter. CI will be phased out as we move to photon counting. We will not create new CI sensors but will continue to support customers who use them in their dental and industrial systems.


You have a long history making detectors for the dental market - what makes your products for this application stand out and have such longevity?

Image quality underpins our success. While CMOS has narrowed the gap in image quality slightly, direct conversion technology and the efficiency of CdTe leads to very high-quality sensors and detectors.


Do you have any new products planned for the dental market?

We are launching a photon counting version of our dental range later this year and we are already working with new customers to implement this technology. We plan to have panoramic and cephalometric sensors as well as a dental CT small area flat panel on the market by 2021. We are supporting our existing customers so they can progress to this platform as seamlessly as possible.


There is a real opportunity for growth in the Industrial NDT / quality control market as they adopt digital technology. What do the Direct Conversion products offer for this opportunity?

Direct Conversion products offer fast inspection speeds in addition to completely new inspection methods to detect things that were previously undetectable. These speeds are a result of our efficiency in detection and fast speeds translate to the possibility of more products inspected per hour which in turn would reduce costs for the end user and increase value for the OEM system manufacturers.

We can improve food safety inspection by enabling applications that were not possible before, like finding PVC in products that have a complex background in absorption X-ray images. We can also improve weld inspection in the oil and gas industries and create value for our partners in faster, more thorough process control.

Direct Conversion


You have recently opened the Application Innovation Centre in Munich. Can you tell us more about the Centre and what it will offer to customers?

The Centre provides customers with an opportunity to see our detectors working in real applications. Our goal is to shorten the time for evaluation and therefore allow us to progress sales more rapidly. We can give customers demonstrations of imaging so they gain confidence in the solution we are offering, and the Centre can act as a hub for internal and external learning.

I can see real advantages for Varex from adding Direct Conversion products to our portfolio. What advantages do you think Direct Conversion will gain by joining the Varex team?

Direct Conversion will benefit from Varex’s global presence and a team of experts who understand X-ray and how we can help improve safety and patient care. Direct Conversion will be able to access this pool of talent and build on its success to push photon counting into the mainstream and help Varex to continue as a leader in X-ray imaging technologies.