LESSON 3
COMPUTED TOMOGRAPHY
MAGNETIC RESONANCE TOMOGRAPHY
COMPUTED TOMOGRAPHY
Computed tomography (CT) is an imaging procedure that uses special x-
ray equipment to create detailed pictures, or scans, of areas inside the body. It is
also called computerized tomography and computerized axial tomography
(CAT).
CT relies on X ray transmitted through the body. It differs from radiography
in that a more sensitive X ray detection system is used the date is manipulated by a
computer. The outstanding feature of CT is that very small differences in X ray
absorption values can be visualized. It is the gold standard in the diagnosis of a
large number of different diseases of internal organs.
Tomography had been one of the pillars of radiological diagnostics until the
late 1970s, when the availability of minicomputers and of the transverse axial
scanning method, this last due to the work of Godfrey Newbold Hounsfield and
Allan McLeod Cormack.
CT scan gives radiographic information about a single axial cross area of the
body. In CT the patient is placed supine on a table within a cylindrical gantry ,
which houses a rotating X ray source and electronic X ray detectors. During
examination for each image a highly of X rays passes through a thin section of the
patients body and reaches to the sensitive detectors on the other side. In just a few
seconds the X ray source revolves 360 degree around the patient. A sophisticated
computer then analyses the detection from each angle and reconstructs an image.
The table, on which patient lies is then moves slightly so that a new area of the
body is in the path of the beam and the next image is obtained. The operator selects
the level and thickness ti be imaged. The usual thickness is between 1-10 mm.
CT scanning of the body usually lasts between 5-30 minutes.
The attenuation values are expressed on arbitrary scale (Hounsfield scale),
ewith water density being zero, air density being with minus 1000 units and bone
density being with plus 1000 units. The range of densities visualized on a
particular image is known as the window width.
CT is used in medicine as a diagnostic tool and as a guide for interventional
procedures. Sometimes contrast materials such as intravenous iodinated contrast
are used. This is useful to highlight structures such as blood vessels that otherwise
COMPUTED TOMOGRAPHY
MAGNETIC RESONANCE TOMOGRAPHY
COMPUTED TOMOGRAPHY
Computed tomography (CT) is an imaging procedure that uses special x-
ray equipment to create detailed pictures, or scans, of areas inside the body. It is
also called computerized tomography and computerized axial tomography
(CAT).
CT relies on X ray transmitted through the body. It differs from radiography
in that a more sensitive X ray detection system is used the date is manipulated by a
computer. The outstanding feature of CT is that very small differences in X ray
absorption values can be visualized. It is the gold standard in the diagnosis of a
large number of different diseases of internal organs.
Tomography had been one of the pillars of radiological diagnostics until the
late 1970s, when the availability of minicomputers and of the transverse axial
scanning method, this last due to the work of Godfrey Newbold Hounsfield and
Allan McLeod Cormack.
CT scan gives radiographic information about a single axial cross area of the
body. In CT the patient is placed supine on a table within a cylindrical gantry ,
which houses a rotating X ray source and electronic X ray detectors. During
examination for each image a highly of X rays passes through a thin section of the
patients body and reaches to the sensitive detectors on the other side. In just a few
seconds the X ray source revolves 360 degree around the patient. A sophisticated
computer then analyses the detection from each angle and reconstructs an image.
The table, on which patient lies is then moves slightly so that a new area of the
body is in the path of the beam and the next image is obtained. The operator selects
the level and thickness ti be imaged. The usual thickness is between 1-10 mm.
CT scanning of the body usually lasts between 5-30 minutes.
The attenuation values are expressed on arbitrary scale (Hounsfield scale),
ewith water density being zero, air density being with minus 1000 units and bone
density being with plus 1000 units. The range of densities visualized on a
particular image is known as the window width.
CT is used in medicine as a diagnostic tool and as a guide for interventional
procedures. Sometimes contrast materials such as intravenous iodinated contrast
are used. This is useful to highlight structures such as blood vessels that otherwise
