Review: Prediction of Respiratory Motion - Prediction and Classification of Respiratory Motion - page 7

2.1.1 Radiographs
Radiographs (referred to as plain X-rays) are photographic images produced by the
activity of X-ray or nuclear radiation to view a non-uniformed physical object. The
rays may penetrate the human body through the different density and structure of
the object. The rays that pass through are recorded behind the object with a
detector which can display the different density and structure of the body. Gen-
erally, radiographies are generated by X-ray beams, whereas in nuclear medicine
gamma rays are involved [ 27 ]. Radiographs are unceasingly used and employed as
a major tool to detect and measure the target position [ 28 ].
2.1.2 Fiducial Markers
Fiducial markers located around the tumor position are often employed to act as
surrogates for optical signal tracking, to synchronize the internal and external
breathing motion signals, and to provide real-time information during beam
delivery [ 26 , 29 - 34 ]. In real-time tumor tracking, multiple implanted fiducial
markers are detected as surrogate on the images of fluoroscopy systems for
accurate tumor location, but their use can be limited due to the risk of pneumo-
thorax during marker implantation [ 30 , 33 , 34 ]. External fiducial markers are also
attached on the patient's chest for respiratory gated radiotherapy, where they can
be used to correlate internal breathing motion with external optical signal based on
the infrared tracking system [ 2 , 26 , 35 ].
2.1.3 Fluoroscopy
Fluoroscopy is a method for obtaining real-time moving images of deep body
structures using fluoroscope [ 26 ]. A patient is placed between an X-ray tube and
fluorescent screen during fluoroscopic procedures. Modern fluoroscopes are
associated with an image intensifier and video camera so that they can display a
continuous series of images with maximum 25-30 images per second [ 36 ].
Fluoroscopy is often used not only to watch the digestive track but also to track
moving organs during therapeutic procedures [ 28 , 31 , 37 ].
2.1.4 Computed Tomography
Computed tomography (CT) [ 4 , 23 , 28 , 29 ] is a specialized X-ray imaging method
employing a series of individual small X-ray sensors with computer processing.