Image quality (along with radiation dose) is probably one of the most important aspects that providers consider in their purchase decision about the C-arm. A C-arm can serve many clinical applications and providers wish to get an assurance that they can visualize the anatomy as clearly as possible for the kind of the procedures they expertise in. Image quality is paramount because the imaging is in real-time and provides a great deal of information to the providers during their live cases. However, what factors determine the image quality in a C-arm is a less understood subject because there are many factors in play at the same time.
To make it simple to understand, we bucket these factors in 4 broad categories as follows: 1) X-ray dose 2) Detector capability 3) Image processing algorithms and 4) Display screen
- X-ray dose
Providers are increasingly concerned about x-ray exposure to the patients and staff, and wish to reduce the radiation to the lowest possible levels. They use C-arms for many hours in a day, and understand radiation hazards. They expect to have a fine balance between the image quality and x-ray dose. Also, with the advent of more sophisticated and efficient x-ray generators and tubes, the focus is not so much about the x-ray generator power itself, but rather if there will be enough dose to get clinically purposeful images. Skanray leads the way with its C-arm, Skan-C, as it manufactures its own X-rays tubes and generators that tightly configure and couple them to provide excellent generator performance and dose management capability.
Below are the main factors that you should consider in a C-arm to determine dose
Generator specification: X-ray generator plays an important role in determining dose and image quality. When you are reviewing the generator specs, it is worth noting what is the max kW, kV and mA on the systems, and what you may require from the clinical standpoint. Many applications are well served with a lower power generator itself and do not need a high amount of dose. Also, if you are looking to do long duration procedures, please consider noting the heat capacity of the tube to ensure that you can expose for a longer period of time.
Auto technique algorithms - Most C-arms today intelligently analyze the anatomy and automatically adjust kV and mA to provide best image quality. This reduced the dependency of the radiographic tech to manual adjust techniques to get good image quality
Pulse Mode - Pulsing X-ray radiation cuts down the dose without significantly compromising the image quality. Some C-arms can go as low as 2 pulses / sec, which can be significantly helpful for providers who are very radiation conscious.
- Detector capability
There are two types of detectors offered in C-arms; 1) Image Intensifier (II) 2) Flat Panel Detector (FPD). Though, we can go to great depth to compare both, we will limit this article to mode fundamental concepts
Resolution - The resolution offered by the detectors plays a very important role. Higher the resolution, more information is captured. You can always think about the resolution as you do in your photography camera. In general, 1k x 1k is a good resolution and is available on most of the new C-arms. However, if you are looking for a refurbished system, the resolution may be lesser. Lower resolution will mean that if you zoom the image to visualize more information, you will have a pixelation effect - i.e. the image will show checkered.
Frame Rate - C-arm is literally a video of an X-ray and many times the customer wishes to visualize a movement as they are doing a procedure. For example, in cases such as catheterization or peripheral angiography, the doctor wishes to view the exact position of the catheter in the real time or wants to see the contrast flow as it is injected. In these situations, the detector’s capability to capture higher frame rate is very helpful. Gold standard is 30 frames per second which provides a fluid visualization of moving objects. At these frame rates, the human visual system cannot distinguish frame-to-frame variation and motion appears to be continuous, without visible flicker.
Skanray’s Skan-C has a capability to acquire images as 30 frames per second. Different modes allow the user to select the frame rates at which the images have to be displayed. This is helpful because in procedures such as those in pain management, the provider is taking just single shots. Hence, a lower frame rate will allow the system more time to process the frames and display a superior quality image. However, when high frame rate is needed, the user can just select the high frame rate mode and get 30 frames per second.
Size of the detector - Most of the IIs come in standard size of 9”. Its FPD equivalent is 21 cm x 21 cm size. Some applications such as hip replacement or vascular procedures demand a higher field of view which is achieved by having a bigger size of a detector i.e. 12” in II or 31 cm x 31 cm in FPD. It is important to note the application requirement and then select the size of the detector accordingly.
- Image processing algorithms
In today’s digital C-arms, the frames are processed by imaging algorithms that have considerable impact on the overall image quality.
Auto brightness and contrast - Along with the auto-technique for X-ray parameters, advanced algorithms can auto adjust brightness and contrast to provide a good image. That reduced the requirement to manually adjust brightness and contrast
Edge detection - Algorithms can be used to identify the edges in the images. This may be utilized when trying to visualize a crack in a bone as the edge detection can enhance the edges along the crack
Region of interest (ROI) selection - In orthopedic cases, there may be a metal implant which may create difficulty for the algorithm to provide a good contract image. Manual ROI selection can help to select anatomy and balance the contrast in the image in context to the selected ROI
Noise reduction - Images acquired with lower dose may show a lot of noise. Image processing algorithms may average the frames to reduce the noise in the displayed image.
- Display screen
Display screen or monitor is the last main component that determines the image quality in a C-arm.
Resolution - If the display screen is low resolution then it doesn’t really matter how much is the dose or the detector output or the effects by image processing algorithms. Drawing an analogy with a TV screen won’t be incorrect. Assume that you stream a 4K content but your TV has a capability to just display regular high resolution images i.e. 1K. Hence, the remaining data will be lost and won’t be utilized to provide you great image quality that you anticipated.This factor is particularly important in refurbished C-arms as the display screens are generally old and may not provide a good image quality.
Screen size and visualization angle - Last but not the least, display size and visualization angle of the screen matters a lot. A bigger display provides a larger viewing area and hence a lot easier to visualize anatomy during procedures. Skanray’s Skan-C provides a wired or wireless HDMI connection to add a bigger screen that can be wall mounted. This helps providers as well as techs to view images better.
Larger viewing angle on the monitors adds value. Generally, the procedure rooms are cramped for space with RTs, MAs, Anesthesiologists, and many other equipment. So, it may not be possible to arrange the monitor screen in a way where it is equally well visible to both the provider and the RT operating the C-arm. In such situations, it is helpful to have monitors that can provide viewing from a larger angle.