X-Ray Optics For Minimal Radiation Exposure

From Discovered To Optimized

x-ray imaging is crucial to today's medical professionals for diagnoses and prognosesIn 1895, German physics professor Wilhelm Roentgen discovered a new form of electromagnetic radiation, which we know today as X-rays. While the potential effects were initially unknown, he suspected that this kind of radiation was not good for human health and routinely used protective lead shields. His suspicions were eventually confirmed in the early 1900's. Despite their potential danger, X-rays are one of the most powerful instruments and resources utilized in medical diagnostics to help medical professionals restore health by identifying the correct prognosis. When it comes to achieving the best imaging with the lowest X-ray exposure, lenses made by Optec are almost inevitably involved. Their aperture, focus, filters and zoom are moved by FAULHABER motors.

X-rays are a form of electronmagnetic radiation, with a wavelength ranging from 0.01 to 10 nanometers, which is shorter than UV rays but longer than gamma rays. Since X-rays are different from visible light, it stands to reason that X-ray optics are unlike the optics of visible light as well; the first difference being that X-rays are generated by an X-ray tube.

An X-ray tube uses high voltage to make electrons collide with a metal target, which in turn releases high-energy, low-wavelength radiation. X-rays can penetrate most materials, but the denser the material, the more they are attenuated. This difference in penetration intensity is what we see on an X-ray image. Before the image can appear to the eye, the invisible X-rays have to be “converted” or transferred into the visible spectrum. Today, this is mostly done by flat panel detectors which produce digital images, similar to the optical sensors of common digital cameras.

A Bulky Past

Standard optical lenses, however, cannot be used to direct rays to the detector. As the refraction index of X-rays is very close to 1, optical glass barely changes their direction. This is why X-ray lenses were traditionally very bulky and difficult to handle, remembers Giuseppe Cilia, General Manager of Optec: “When our company was founded in 1985, two big lenses were necessary to transfer the X-ray image to the camera. They had a very long focal length, and the focus had to be adapted manually. They needed a clumsy lead aperture and a high level of radiation energy to produce acceptable pictures. And the patient, of course, was exposed to this radiation.” That year, Optec devised an optic relay, doubling radiation transmission through the lens and improving image quality while significantly reducing radiation levels at the same time. Now only one lens was needed instead of two.Each lens can be developed and manufactured in accordance with individual customer requirements.

Getting Smaller and More Powerful

This breakthrough formed the basis for Optec’s success in X-ray optics. About 70% of the lenses now used in medical radiography are manufactured by the company based in Parabiago, in the north-west of Milan's metropolitan area. Today, these lenses are even smaller and optically more powerful. "The latest digital image processing techniques have markedly improved the perception of anatomical details, but, at the same time, impose new requirements on the performance of the X-ray imaging system as a whole," says Giuseppe Cilia. "The dynamic range of the lens plays a crucial role here." Depending on a client's needs, Optec can even develop and produce one-off pieces.

xrays are generated by an x-ray tube, using high voltage to make electrons collide with a metal target

Compact Flexibility

by combining aperture, focus and filters, we get a very high transmission, thus resulting in the lowest possible radiation exposureIn photography, the dynamic range describes the limits on the amount of luminance that can be captured, or otherwise referred to as a spectrum of exposure. The greater this range, the more details doctors are able to see on X-ray images. The technology developed by Optec has allowed the dynamic range of the lenses to be extended tenfold, from 300:1 to 3000:1. Thanks to this optical flexibility, Optec’s compact lenses can be used for both high and low sensitivity capture. Fluoroscopy is an example of the latter and is used for real-time imaging during surgical interventions, e.g. during critical operations close to the spinal cord or on the heart. Since exposure to X-rays can last for many seconds or even some minutes here, the radiation exposure dose must reduced as much as possible.

"You can open the aperture of our lenses very wide to get a clear picture of the procedure," explains Giuseppe Cilia. "When you need a static picture, of a knee joint exposition, for example, this takes just a few milliseconds. However, the radiation dose can and must be higher to obtain a more detailed image. By combining aperture, focus and filters, we get a very high transmission and therefore expose patients to as little radiation as is technically possible. The resolution is also very high, close to the diffraction limit. With the FAULHABER motors moving the parts no manual handling or adjustment is necessary."

Powerful For Medicine and Space

One of the biggest advantages of the lenses is their compact size which requires the motors to be very small, too. Optec uses FAULHABER 0816 SR series micro dc motors for its X-ray lenses; the 0816 SR series features precious metal commutation, and a diameter of just 8 mm and a length of 15.9 mm. A planetary gearhead from the 08/1 Series, also only 8 mm in diameter, transmits power to the optical mechanics. This combination delivers the power, speed and accuracy required for Optec's X-ray optics. "We produce lenses of the highest quality for the most sophisticated applications. FAULHABER motors are the best fit for our products because they have the same levels of quality and engineering," says the General Manager.

Apart from the motors, Optec purchases very little other than glass from external suppliers. From polishing and coating the optical lenses to assembling the units, all manufacturing steps are performed in Parabiago. There is no mass fabrication: depending on a client’s needs, Optec can even develop and produce one-off pieces. The product range includes short-wave infrared lenses, micro-lenses for endoscopes and lenses for optical applications in space. Giuseppe Cilia is especially proud that Optec will be the first company to supply a zoom lens to be mounted on a satellite. "The lens and the zoom's motor need to work reliably for many years under the extreme conditions in space. At the same time, every gram counts and the equipment needs to be as light as possible. Our product was the one to meet all requirements." As with all Optec lenses, the first zoom lens in space will also be powered by none other than a FAULHABER motor.

You can learn more about Optec and their products by visiting their website, here.