The transformation of medical imaging and diagnosis

Like the transition from film-based to digital cameras, X-rays have advanced from a film imaging process to one based on digital technologies. Digital radiography greatly benefits the healthcare industry, but it also places high demands on medical equipment manufacturers. Here Neil Oliver, Technical Marketing Manager of Accutronics, explores how smart batteries are designed to meet these challenges.

Diagnostic imaging remains an important tool for the detection and treatment of many disorders. In various clinical settings, an X-ray is often the starting point for diagnosis. 

During the process, a beam of X-rays is transmitted through the part of the patient's body which needs further investigation. The X-rays are absorbed by the body in differing amounts, resulting in the familiar contrast seen in X-ray images. 

Film versus digital

Thanks to digital radiography (DR), medical imaging is being transformed by better detectors, more powerful computers, sharper displays, faster processing and more efficient archiving. 

The benefits are great and wide ranging - an image can be acquired in seconds and viewed on any computer monitor; it can be accepted or deleted at the click of a button - it can be easily shared with other medical professionals and archived in an online database.

It also allows for greater precision, and the balance between image quality and radiation dose can be controlled more accurately, making it a safer process for the patient.

Traditionally, the images were exposed onto photographic film, but with the advent of digital radiography an electronic detector is used instead. The image is then processed by a computer, rather than being chemically developed.

The initial cost of a DR system, compared to the conventional film-based system, is high. However, hospitals save money by eliminating film costs and reducing the storage space required to archive the images. Because it is a faster and more efficient process, perhaps the biggest saving is time. Fewer operators are required to man the service and patients can be seen more quickly.

The basic principle is very similar to that of a digital camera. Both the conventional camera and its digital counterpart work by using a series of lenses that focus light to create an image. In the digital camera, instead of focusing the light onto a piece of film, it focuses it onto a semiconductor device that records light electronically. A computer then breaks this electronic information down into digital data. 

In digital radiology, amorphous silicon detectors are combined with a caesium iodine or gadolinium oxysulfide scintillator to convert X-rays into light. The light is channelled through the amorphous silicon photodiode layer where it is converted to a digital output signal. The signal is then read by thin film transistors or fibre coupled CCDs before being sent to a computer for processing and display. 

Introduced in the mid-1980s, DR has steadily gained in popularity. Like the digital camera, it rapidly began to compete with the more conventional film-based process and today is moving towards replacing it altogether.

The portable detector

In digital radiography, the X-ray source will often be built into a medical trolley. The battery allows the detector to be completely portable, so that if the patient is in a hospital bed, the trolley can be wheeled to them and the detector can be slipped underneath the patient to take the X-ray. Portable X-ray detectors need to be light weight and slim but extremely robust.

The comparison with the digital camera ends when it comes to the size of the detector required for each device. For example, the detector on your smart phone camera is about 3mm across, whereas a DR detector can be the size of a briefcase.

Furthermore, the batteries within smart phones usually consist of a single Lithium ion cell whereas the large portable detector panels require a far more complicated multi-cell battery pack.

Although the batteries for detectors need to be larger, they must still maintain a slender profile if they are to fit into the rear of the detector – the need for thinness in such a large footprint creates a number of challenges for the battery designer.

The lithium ion cells used within such batteries are more commonly of the ‘pouch’ type which cannot tolerate bending or twisting. The battery case must provide enough torsional rigidity to prevent damage to the cells which may cause internal short circuit leading to overheating or fire. The use of modern plastics technology can aid in the design of such cases but clever mechanical design can also ensure that rigidity is built into the structure and still maintain the thinness that the market requires.

Removable and rechargeable

Some digital radiography detectors contain an embedded battery similar to that used in handheld tablet devices, but the consequence is that, once the battery reaches its end of life, the hospital has to send the detector back to the manufacturer for the power source to be replaced. This is a costly exercise which puts a vital piece of medical equipment out of service. The solution is a removable, rechargeable battery, enabling the hospital to achieve continuous use.

However, batteries used in critical environments in this way must provide genuinely accurate fuel gauging to ensure that the remaining battery life indicators are reliable. This provides the user with predictive run time of the device, giving them the ability to know how many images they can take.

For clinical environments, Accutronics has developed multi-bay smart charger technology which means that multiple batteries can be charged at a time, resulting in a quick changeover and a device that can remain in continuous use.

Smart features

These innovative power products contain the latest smart battery technology, including active and passive protection circuits that prevent over-temperature, over and under-voltage, overload and short circuit. They are capable of accurate fuel gauging and are built to international regulatory standards, all features especially useful in the increasingly dynamic nature of modern hospital care.

Digital radiography's future

Because of the initial cost of a DR system, it mostly being adopted in countries with a tier-one health system, however, digital technology is evolving at a rapid rate and becoming more flexible and affordable. More than two billion people in the world now have access to the internet and five billion of have mobile phones. Like the transition from film-based to digital cameras, it's conceivable that digital radiography will also, one day soon, have a global appeal.