d03a.jpg (16247 bytes)Finding the right technology for your hospital requires some good technical knowledge. There’s no way around it.

If it’s CCD-based digital radiography that you’re evaluating, then you may be in for some pleasant surprises. CCD technology is growing and changing rapidly much to the benefit of those considering the purchase of a CCD-based DR system in the future.

The main technology driving CCD-based digital radiography (DR) systems is the CCD (charged coupled device) cameras themselves. CCD technology is not medical-specific and is used in a variety of industries including aerospace imaging and consumer products. Currently, there are several CCD-based digital X-ray systems available in the U.S. with prices ranging from $90,000 to $450,000. Most experts say the primary technological difference between the CCD-based systems is the number of CCD cameras that each system uses.

Among those companies opting for the multiple CCD configuration are Swissray International Inc. (New York), which uses four CCD cameras, and Wuestec Medical Inc. (Mobile, Ala.), which uses two CCD cameras in its current system. Yet, at press time, Wuestec said it is in the process of finalizing a single-CCD system due for release in April.

Companies that use a single CCD configuration include Nucletron B.V. (Veenendaal, The Netherlands), Oy Imix (Tampere, Finland) and its Imix digital radiography system which is distributed in the U.S. by Advanced Instrument Development (AID of Melrose Park, Ill.) and Trex Medical Corp. (Danbury, Conn.). Newcomer to the market Imaging Dynamics Corp. (Calgary, Alberta, Canada) experimented with using as many as 12 CCDs in its early days, but has decided on a single-CCD configuration for its product.

Cost
The advantages and disadvantages to the different configurations vary depending on the source, but there are definitely some effects.

According to Steve McArthur, CEO of SpectraSource Instruments (Westlake Village, Calif.), a CCD camera maker, the number of CCDs used will vary depending on the marketing objectives of the company and the type of product it’s looking to market.

“One company may want to target the high end and get the highest resolution possible,” says McArthur, adding that those companies would be more likely to use multiple CCDs. “Another company may want to make low-cost systems and deal with performance compromises to keep the cost down.”

Cost is an issue that can’t be ignored in any review of DR technologies. Logic would follow that a multiple CCD configuration would mean a higher list price due to the technology involved, but not always.

Ueli Laupper, CEO of Swissray America Inc. (New York), agrees with that assessment, but offers a justification of the increase in system cost. He feels that using multiple CCDs allows the customer to use the system for a variety of applications and, in doing so, reduces the cost of purchasing additional systems for those applications.

“Obviously, if you use more CCDs, you increase the cost,” says Laupper. “But if you have a single CCD, you cannot provide a multi-functional direct digital radiography unit because you cannot provide enough spatial resolution for general radiography.”

Imaging Dynamics is a newcomer to the CCD market and looks to maximize the single-CCD’s ability to reduce costs. Company officials say its Xplorer 1000 is listing for $90,000, yet produces comparable images to $400,000 systems.

“While we may have had to build a much fancier lens to bring the whole image into our one CCD, the fact of the matter is we’ve only got one CCD,” explains Robin Winsor, CTO at Imaging Dynamics. “So we can build it more cheaply and our raw material costs are less. And you can see that by the relative selling prices of our units.”

CCD Sensors and Image Capture: How It Works

Below is a step-by-step explanation of the CCD sensor and its role in the digital image capture process.
1.??? Mechanical shutter opens, exposing the
??? CCD sensor to light.
2.??? Light is converted to charge in the CCD.
3.??? The shutter closes, blocking the light.
4.??? The charge is transferred to the CCD ????????
??? output and converted to a signal.
5.??? The signal is digitized, and the digital
??? data is captured in memory.
6.??? The captured image is processed and
??? displayed on the camera LCD or computer.

CCD imaging is performed in a three-step process:
1.??? Exposure, which converts light into an
??? electronic charge at discrete sites called
??? pixels.
2.??? Charge transfer, which moves the packets
??? of charge within the silicon substrate.
3.??? Charge-to-voltage conversion and output
??? amplification.

Source: Eastman Kodak Co. Web Site

Image quality
When it comes to acquiring images, the resolution of one CCD vs. multiple depends on who you ask. The recent introduction of a 4K by 4K pixel CCD chip has changed a lot of theories though. Ron Averitt, director of sales at Wuestec Medical, says his company is in the process of moving to a single-CCD system which is scheduled for release in April. The move comes as Wuestec incorporates a 4K by 4K chip into its system – instead of using two 2K by 2K chips to get the same resolution.

Swissray’s Laupper contends that with single-CCD imaging, the highest spatial resolution is 2.5 line pairs per millimeter, which limits the system’s applications.

“That’s good enough for chest imaging but if you want to do extremities and bone work and skull work and imaging where you have bone and soft tissue tied together, you need at least three line pairs per millimeter,” Laupper says. “You can only get that with multiple CCDs.”

The Imix chest system from AID and the 4000M from Trex are both supplied by Oy Imix as chest-only systems because of the system’s resolution limitations. They utilize a single 2K by 2K CCD.

Using multiple CCDs requires that software algorithms be used to “sew” the multiple images together and compensate for the boundaries where the images meet. Therein lies a topic of hot debate among the CCD technology experts – can those separate images be combined without losing information in the process?

Wayne Hibbs, a healthcare technology consultant and president of C. Wayne Hibbs and Associates (Dallas), feels that the software used to combine the multiple images from a multiple CCD-based DR system is working nicely in the current systems.

“You’re taking multiple images and lacing them into one image,” says Hibbs. “That to me is not a problem because our computer software is so good and so fast now that it doesn’t concern me.”

The manufacturers of single-CCD systems feel that stitching the images together lends itself to too many problems. Imaging Dynamics’ Winsor points out that he’s experimented with a variety of different multiple CCD configurations in the past.

“Actually I have a U.S. patent covering the use of multiple cameras for this purpose,” Winsor says. Eventually, though, he decided that the accurate combining of the images is nearly impossible.

“[Stitching the images together] has to be done exactly because at the boundary where the two lenses converge and have a little overlap, you have to decide how to put that image together. If you have a small feature right on that boundary, can you guarantee that it will be treated properly?”

Averitt says that was one of the primary factors in Wuestec’s decision to move to a single-CCD system from its current two CCD configuration. Early on, Wuestec was considering using a five-CCD system but that product never came to market and was replaced by the two-camera system, the DX-1480, which is now being marketed by the company.

“If [the combining of the images] is done correctly – and we did it correctly – you can’t see it,” Averitt says. “To the human eye, you can’t see it. But if you magnify that image to the point where you can see the interpolation of the pixels, then you can see it.”

Winsor also points out that using multiple CCDs may lead to producing images with higher resolution areas on one part of the image and lower resolution on others as the individual CCDs degrade.

“Each one will move and vibrate and have electronic wear a little differently,” he says. “How do you compensate for that? You can constantly recalibrate and try to bring things into sync with one another, but it’s still not going to be perfect.”

Both Wuestec and Imaging Dynamics are using the new 4K by 4K chips in their single CCD configuration, but according to John Macko, associate vice president for Rad/R&F at Trex Medical, his company’s 4000M, which is designed by Oy Imix, uses a 2K by 2K chip. Macko says the typical radiologist will not notice the difference between the 2K chip and the 4K chip. AID’s Imix chest unit also utilizes the 2K by 2K chip configuration.

“When you put multiple CCDs together you have some physical separation that has to be electronically interpreted,” he says. “Since we have a single device, we don’t run into that. The limitation is that if you took four 2Ks by 2Ks you could have 4K by 4K and obviously we don’t have that. A lot of people would say you need the additional resolution, but on the other hand, practicality indicates the doctors can diagnose quite well off 2K by 2K images.”

Manufacturers of CCD-based DR Systems

Manufacturer

Product Name

CCD Configuration

List Price

Swissray

DDR MultiSystem?

Multiple CCDs

$450,000

AID (Oy Imix)

Imix DR system

Single CCD

Not available

Trex Medical (Oy Imix)???

4000M

Single CCD

$250,000 to $400,000

Wuestec

DX-1480

Multiple CCDs

$197,500

Nucletron

Digidelca-M

Single CCD

$200,000 to $300,0000

Imaging Dynamics

Xplorer 1000

Single CCD

$90,000

*Wuestec is moving to a single CCD system, which is expected in April of this year

Reliability
The issue of CCD technology’s reliability and maintenance seems to be a unifying factor among CCD-based DR companies. The argument can be made that a multiple CCD configuration involves more technology and, therefore, more chance of failure, but compared to imaging tube life and flat-panel DR systems’ early reviews, the CCD-based systems offer a more reliable option.

“CCD is so stable and reliable because it was designed for space surveillance industries by the military,” Laupper points out. “These industries have the highest quality requirements on the planet. CCD is such a mature and reliable technology it doesn’t matter how many you have.”

Swissray uses a configuration that takes its four CCD cameras out of the X-ray exposure field to minimize the wear on the cameras. Macko says the 4000M digital chest system that Trex distributes also uses mirror optics to place the CCDs out of the X-ray field and minimize the radiation exposure to the CCDs. Both companies feel that will increase the life expectancy of the average CCD chip, although the average life expectancy of the chips is difficult to predict. Despite the technology’s use in other industries, the life cycle of a CCD chip in a medical imaging application remains to be seen.

“With CCD cameras, I feel real comfortable they’re going to be working at the end of five years,” says Hibbs, who can’t resist comparing the reliability of CCD technology with that of the flat-panel technology used in other DR systems. “With the amorphous silicon plate, I can’t guess what the expense of maintaining or exchanging those might be.” (Editor’s Note: Medical Imaging will examine amorphous silicon and amorphous selenium plate technology as well as service requirements in an upcoming issue this spring.)

The strength and reliability of a CCD-based DR system relies much on the supplier of the CCD technology itself. With a wide variety of applications for CCD technology outside medical imaging, there are a wide variety of CCD suppliers. Some of the suppliers are large, well-known companies like Eastman Kodak Co. (Rochester, N.Y.), which supplies Swissray with its CCDs, while smaller suppliers like SpectraSource also hold a place in the market.

Cooling Down
Cooling systems are important when dealing with CCD cameras and another area where manufacturers differ in their approach to the products. If a system is not properly cooled, the signal-to-noise ratio can be adversely affected.

“I think without exception when you’re talking about a radiography application like this, you’re talking about cooling the CCDs,” says SpectraSource’s McArthur. “Cooling them requires that the camera be in a hermetically sealed environment. So the maintenance on that, where the design is complicated, will be higher. The risk is if the housing on the CCD gets cold, moisture will condense upon it and destroy the device. Those are very expensive commodities not to mention the down time and the headaches.”

Macko says the design of the Trex 4000M utilizes nitrogen, which is a ready gas that is available in the hospital, passed over the CCD chip which serves two purposes. First, it cools the chip down to reduce the inherent noise and improve the image. Also, since nitrogen is dry, it makes sure there is no moisture that accumulates on the chip.

Swissray uses a cooling unit housed in the system with a closed loop cooling line passing through the cameras. Fischer Imaging Corp. (Denver) has designed a CCD-based digital mammography system that doesn’t require the use of an outside coolant.

“Most of the heat in the detector is generated by the electronics surrounding the chip,” explains Mike Tesic, vice president of R&D at Fischer. “Thermal management and basically putting the system into the idle mode when it’s not being used allows us to manage the temperature of the detector at a level that is acceptable.”

CCD History 101

The charge-coupled device (CCD) was invented in the late 1960s by researchers at Bell Labs. Originally conceived as a new type of computer memory circuit, it soon became apparent that the CCD had many other potential applications, including signal processing and imaging – the latter because of silicon’s light sensitivity.

CCDs begin on thin wafers of silicon processed with a series of steps that define the various functions within the circuit. On each wafer lie several identical devices, or die, each capable of yielding a functional device. Selected die are then cut from the wafer and packaged in a carrier for use in a system.

Like the engine of a car, the CCD sensor in a digital camera acts as the primary tool to capture an image. In its most elementary form, the CCD sensor is like the camera’s “electronic eye” – collecting light and converting it to charge, and subsequently emitting the signal that results in a digital image.

The Real-world Test
Reviewing the technologies involved in these products is helpful, but most manufacturers realize it may be too much information for the average facility team buying a DR system. While purchasing facilities are concerned with issues like cost, image quality and reliability, they are less concerned with the factors that contribute to those issues.

“I don’t mean to sound facetious, but a lot of people in the hospital don’t understand the technology,” says Wuestec’s Averitt. “They understand the image they see, but they don’t always know how that image is acquired.”

Winsor realizes that as well. The end product – the image – is what matters most to the end user – the radiologist.

“All of us techies may be in love with what we’re doing and think it’s all wonderful and interesting, but when you get right down to it, the radiologist doesn’t even work with the machine – a technologist usually does,” Winsor says. “Within the lab, you test and make sure you meet the specs, but when it comes right down to it, you need to put radiologists in front of it and say, ‘How does this look?'” And you hope the answer is “good.” end.gif (810 bytes)