276
Biomedical Signal and Image Processing
X-ray source
Source
rotation
only
Stationary ring
of detectors
Biological
medium
FIGURE 14.14 Diagram of fourth-generation tomography scanners, representing the presentday most commonly used outline. A large array of detectors form a closed circle around the
patient, only the source moves in a circular motion. (Courtesy of Dr. Bob Jones, Lancaster
University, Lancaster, United Kingdom. http://www.lancs.ac.uk/depts/physics/physics.htm)
14.8 DIAGNOSTIC APPLICATIONS OF X-RAY IMAGING
X-ray imaging is used for various diagnostic applications. For instance, a highdensity tumor in an air-filled lung will look like a gray mass on black background.
Low-density cyst in radiopaque bone will look like a gray mass on white background
on film. Currently, undetectable by x-ray imaging are most soft tissues: liver
metastasis, colon cancer, and infections.
Some of the main applications of x-ray imaging in coronary obstruction visualization
and the classic x-ray image of the broken bone are briefly described in the following.
A typical usage of the x-ray imaging is the detection of coronary obstruction. During
or as a precursor to a heart attack, coronary blood vessels will become occluded. Only
with the aid of contrast fluid injected in the coronary arteries can these arteries be
visualized under fluoroscopy while a catheter is positioned in a feeder artery to the
suspected area of the heart. Blood flow can be seen to either completely avoid a certain
perfusion area of the heart, or it will expose a narrowing of a vessel by contrast.
When a bone is broken, it produces a distinctive look under x-ray imaging.
Conventional x-ray imaging of the extremity or whole body will reveal discontinuities in the standard anatomic geometry of bone structures at places where the bone
is broken or even dislocated. Based on the known geometry of the bone structure,
discontinuities will show up irrespective of prior anatomical knowledge. Anatomical
knowledge will however confirm any other bone structures that may be in a different
plane of the body, and thus may appear as discontinuity in a compressed 3-D display
and only show a 2-D outline of all information in between the camera or photographic
plate and the x-ray source.
A major application of CT is detection of brain and other types of tumors. Due
to high resolution of the CT, these images are significantly more informative than
the conventional x-ray and provide the physicians with accurate geometric information such as the volumetric measurements of the tumor. During the last couple of
decades, MRI technology has replaced CT for such applications, primarily due to
its higher resolution as well as the fact that MRI is not harmful to biological tissues.
Biomedical Signal and Image Processing
X-ray source
Source
rotation
only
Stationary ring
of detectors
Biological
medium
FIGURE 14.14 Diagram of fourth-generation tomography scanners, representing the presentday most commonly used outline. A large array of detectors form a closed circle around the
patient, only the source moves in a circular motion. (Courtesy of Dr. Bob Jones, Lancaster
University, Lancaster, United Kingdom. http://www.lancs.ac.uk/depts/physics/physics.htm)
14.8 DIAGNOSTIC APPLICATIONS OF X-RAY IMAGING
X-ray imaging is used for various diagnostic applications. For instance, a highdensity tumor in an air-filled lung will look like a gray mass on black background.
Low-density cyst in radiopaque bone will look like a gray mass on white background
on film. Currently, undetectable by x-ray imaging are most soft tissues: liver
metastasis, colon cancer, and infections.
Some of the main applications of x-ray imaging in coronary obstruction visualization
and the classic x-ray image of the broken bone are briefly described in the following.
A typical usage of the x-ray imaging is the detection of coronary obstruction. During
or as a precursor to a heart attack, coronary blood vessels will become occluded. Only
with the aid of contrast fluid injected in the coronary arteries can these arteries be
visualized under fluoroscopy while a catheter is positioned in a feeder artery to the
suspected area of the heart. Blood flow can be seen to either completely avoid a certain
perfusion area of the heart, or it will expose a narrowing of a vessel by contrast.
When a bone is broken, it produces a distinctive look under x-ray imaging.
Conventional x-ray imaging of the extremity or whole body will reveal discontinuities in the standard anatomic geometry of bone structures at places where the bone
is broken or even dislocated. Based on the known geometry of the bone structure,
discontinuities will show up irrespective of prior anatomical knowledge. Anatomical
knowledge will however confirm any other bone structures that may be in a different
plane of the body, and thus may appear as discontinuity in a compressed 3-D display
and only show a 2-D outline of all information in between the camera or photographic
plate and the x-ray source.
A major application of CT is detection of brain and other types of tumors. Due
to high resolution of the CT, these images are significantly more informative than
the conventional x-ray and provide the physicians with accurate geometric information such as the volumetric measurements of the tumor. During the last couple of
decades, MRI technology has replaced CT for such applications, primarily due to
its higher resolution as well as the fact that MRI is not harmful to biological tissues.