*4.1.2. Mobile C arm*

*4.1.1. General purpose fluoroscopy X-ray machine*

38 Medical Imaging and Image-Guided Interventions

**Figure 4.** Modern C arm X-ray machine (large).

The first type is a general purpose fluoroscopy X-ray machine (permanently fixed fluoroscopic unit) which is usually installed at radiology departments or other interventional radiology departments such as orthopedic. There are two configurations of permanent units: fluoroscopic unit with under couch X-ray tube and over couch image intensifier or vice versa. Over couch X-ray unit has some advantages including better flexibility in patient positioning, possibility to use the same X-ray tube for radiography imaging with stand Bucky, and possibility to adjust source-skin distance. However, over couch X-ray units are not recommended for interventional procedures because staff exposure increases five to six times compared with under couch X-ray tube and over couch image intensifier configuration [5]. The minimum source (X-ray tube) to skin distance must be at least 30.5 cm away from the surface of skin. Modern C arm machine has mobile spacer cones to maintain the correct distance. Operator can remove the cone temporarily if it interferes with the procedure in under couch position. The other configuration is C arm unit. C arm is an X-ray unit where the image intensifier (flat-panel detector (FPD)) and X-ray tube are at two ends of the letter C as illustrated in **Figures 4** and **5**. C arm equipped with FPD, which costs three times, has the capability to produce better image quality compared with image intensifier. C arm is utilized to provide more wherever greater flexibility in image acquisition at different projections (views). The machine is used to perform minimally invasive procedures such as cardiac catheterization, angiography, orthopedic, gastroenterology and therapeutic interventional procedures. Recent development in imaging technology enables C arm system to obtain fluoroscopy images and 3D cone-beam CT (CBCT) images. Vascular studies are usually performed in fixed fluoroscopy unit. A C-arm X-ray machine is preferable because it can be rotated rather than the patient during the procedure. Some fluoroscopic X-ray systems are equipped with two radiation sources, which enable reduction of the number of injections of contrast required.

> The second type is mobile C arm, which is more convenient and can be moved from one place to another according to the need of the operator, and image can be transferred via Bluetooth in modern equipment to the printer. Thus, C arm is commonly used in operation rooms.

C arm has two types:


Mini C arms are small fluoroscopes used mainly in orthopedic procedures (extremities) and pediatric procedures. Operators can control the fluoroscopic unit from the control panel and inside the room with a foot pedal. The image quality is lower in fluoroscopy compared with radiography due to low tube current used in the first one. The dose is lowered by 45–60% during fluoroscopy image acquisition compared with radiography [6]. Auto fluoroscopy is an option that provides an optimum tube current (mA) to provide sufficient image quality. Acceding to the international recommendations, pulsed fluoroscopy intermittent pulses (from 2 to 30 times per second) are used to reduce patient doses during the procedures by 50% of its initial value while maintaining image quality. Digital fluoroscopic units are capable to store images from the detector (fluorography) and last image hold (the last frame acquired is left on the monitor after the X-ray beam is switched off).
