Computerized Axial Tomography tomography Computeri (CAT), zed ing tomographic images, major axial
method for obtainis a advance in diagnostic radiology. Unlike conventional tomographic systems that use film both for the storage and display of transmitted x\x=req-\ rays, CAT makes use of sensitive scintillation detectors to detect x-rays that pass through a body section, and a digital computer is used to process this information. Tomographic images of selected planes through a subject are mathematically derived from a series of transmitted x-ray scan profiles, recorded from an x-ray tube head/detector assembly rotating about the subject. Alterations in tissue density in individual transverse cross sections are displayed on intensity modulated displays. Conventional tomography can contribute valuable diagnostic information and is an important radiological method.1 Depending on techniques and the structures to be examined, however, blurring of object elements outside of the focal plane can detract from the overall image quality of a tomogram. The digital image processing techniques employed by the new¬ ly developed CAT minimize some of the problems resulting from superimposition of structures lying outside the plane of interest and provide to¬ mographic images with improved res¬ olution. The initial commercially available CAT unit, the EMI Scanner, was de¬ veloped in England by G. N. Hounsfield.2 This unit was developed specifi¬ cally for the study of the skull and required that the patient's head be im¬ mobilized and surrounded by a water bath. Subsequent units have been de¬ veloped for the whole body and do not require the use of the water absorber. The first commercial system of the latter type was the Automatic Com¬ puterized Transverse Axial Scanner a new
(ACTA-Scanner).3 Sharing several common characteristics, each of the different systems makes use of an xray tube mounted opposite a scintilla-
tion detector tector is
so
on a
uously monitor rays from a
manner
a
gantry. The de¬
positioned
as
to contin¬
the transmitted
x-
collimated x-ray beam in
analogous
to
roentgen¬
ographic film used in routine proce¬ dures. Unlike roentgenographic film recording, however, the collimated beam of x-rays is tracked or moni¬ tored by a scintillation detector for a series of linear scans taken at various projections about the subject. Each scan profile is stored digitally under computer control on magnetic disk or other type of high-speed storage. Single scans are converted to a digi¬ tal profile of the transmitted x-rays consisting of 160 or more data points. Rotating the tube/detector assembly through 180° around the subject, lin¬ ear scan profiles are recorded at pro¬ jections spaced as fine as every 1°. Scan times for a complete rotation generally require a few minutes; how¬ ever, it is anticipated that as new in¬ struments are developed, these times will be considerably shortened. Using split x-ray beam technique, two con¬ tiguous slices can be obtained per ro¬ tation with currently available units. Typically, six to eight slices are ob¬ tained in a tomographic study of the brain. Final
graphs
image displays or CAT tomo¬ derived by the computer
are
from the linear scan data recorded at the selected projections. Images are made up of a detailed plot of the rela¬ tive x-ray absorption coefficients de¬ rived from the scan data by using image reconstruction techniques. Ab¬ sorption coefficients are calculated for volume elements of the order of 1 mm square by 5 to 10 mm thick. Final im¬ ages are displayed on intensity modu¬ lated cathode ray tubes or color tele¬ vision, as well as in other optional display formats. With complete digi¬ tal control of contrast in these im¬ ages, a fine enhancement control in all units allows small changes (of the order of a few percent) of tissue ab¬ sorption coefficient to be displayed over the entire gray range or color
Downloaded From: http://archpedi.jamanetwork.com/ by a New York University User on 06/14/2015
range of the display. The pictures may be looked at much in the same way as a structures
roentgenogram; however, can
be identified and small
changes in absorption coefficients can
be evaluated. Lesions are seen as changes or alterations of the normal density and are interpreted in a sim¬ ilar manner as are conventional
roentgenograms.
This new technique appears to have considerable potential in the study of the brain and other parts of the body. Early reports suggest that this proce¬ dure is a valuable addition to the ra¬ diology armamentarium and may well be the preferred diagnostic procedure in selected diseases that had previ¬ ously undergone contrast or nuclear medicine procedures. Collin S. MacCarty, MD, in the 1974 Caldwell Lec¬ ture to the American Roentgen Ray Society said that the CAT procedure "surely will become the most nearly accurate
single neuroradiographic ex¬
amination."4 Already shown to be of unique assistance in the study of orbi¬ tal abnormalities,5 intracerebral and intraventricular hemorrhage,6 as well as other brain abnormalities,4 it is ex¬ pected that CAT will play a dominant role in many other diagnostic areas as exoerience is rained. DAVID A. WEBER, PHD
Department of Radiology University of Rochester Medical Center
Rochester, NY 14642 1. Littleton JT:
Tomography:
A current
as-
Probl Radiol 4:1-42, 1974. 2. Hounsfield GN: Computerized transverse axial scanning (tomography): I. Description of system. Br J Radiol 46:1016-1022, 1973. 3. Ledley RS, Di Chiro G, Luessenhop AJ, et al: Computerized transaxial x-ray tomography of the human body: A new tomographic instrument is able to distinguish between soft tissues everywhere in the whole body. Science 186:207-212, sessment. Curr
1974. 4. MacCarty CS: A significant symbiotic relationship: Caldwell Lecture, 1974. Am J Roentgenol Radium Ther Nucl Med 122:455-468,1974. 5. Lampert VL, Zelch JV, Cohen DN: Computed tomography of the orbits. Radiology 113:351-354, 1974. 6. Scott WR, New PFJ, Davis KR, et al: Computerized axial tomography of intracerebral and intraventricular hemorrhage. Radiology 112:73\x=req-\ 80, 1974.
method for obtainis a advance in diagnostic radiology. Unlike conventional tomographic systems that use film both for the storage and display of transmitted x\x=req-\ rays, CAT makes use of sensitive scintillation detectors to detect x-rays that pass through a body section, and a digital computer is used to process this information. Tomographic images of selected planes through a subject are mathematically derived from a series of transmitted x-ray scan profiles, recorded from an x-ray tube head/detector assembly rotating about the subject. Alterations in tissue density in individual transverse cross sections are displayed on intensity modulated displays. Conventional tomography can contribute valuable diagnostic information and is an important radiological method.1 Depending on techniques and the structures to be examined, however, blurring of object elements outside of the focal plane can detract from the overall image quality of a tomogram. The digital image processing techniques employed by the new¬ ly developed CAT minimize some of the problems resulting from superimposition of structures lying outside the plane of interest and provide to¬ mographic images with improved res¬ olution. The initial commercially available CAT unit, the EMI Scanner, was de¬ veloped in England by G. N. Hounsfield.2 This unit was developed specifi¬ cally for the study of the skull and required that the patient's head be im¬ mobilized and surrounded by a water bath. Subsequent units have been de¬ veloped for the whole body and do not require the use of the water absorber. The first commercial system of the latter type was the Automatic Com¬ puterized Transverse Axial Scanner a new
(ACTA-Scanner).3 Sharing several common characteristics, each of the different systems makes use of an xray tube mounted opposite a scintilla-
tion detector tector is
so
on a
uously monitor rays from a
manner
a
gantry. The de¬
positioned
as
to contin¬
the transmitted
x-
collimated x-ray beam in
analogous
to
roentgen¬
ographic film used in routine proce¬ dures. Unlike roentgenographic film recording, however, the collimated beam of x-rays is tracked or moni¬ tored by a scintillation detector for a series of linear scans taken at various projections about the subject. Each scan profile is stored digitally under computer control on magnetic disk or other type of high-speed storage. Single scans are converted to a digi¬ tal profile of the transmitted x-rays consisting of 160 or more data points. Rotating the tube/detector assembly through 180° around the subject, lin¬ ear scan profiles are recorded at pro¬ jections spaced as fine as every 1°. Scan times for a complete rotation generally require a few minutes; how¬ ever, it is anticipated that as new in¬ struments are developed, these times will be considerably shortened. Using split x-ray beam technique, two con¬ tiguous slices can be obtained per ro¬ tation with currently available units. Typically, six to eight slices are ob¬ tained in a tomographic study of the brain. Final
graphs
image displays or CAT tomo¬ derived by the computer
are
from the linear scan data recorded at the selected projections. Images are made up of a detailed plot of the rela¬ tive x-ray absorption coefficients de¬ rived from the scan data by using image reconstruction techniques. Ab¬ sorption coefficients are calculated for volume elements of the order of 1 mm square by 5 to 10 mm thick. Final im¬ ages are displayed on intensity modu¬ lated cathode ray tubes or color tele¬ vision, as well as in other optional display formats. With complete digi¬ tal control of contrast in these im¬ ages, a fine enhancement control in all units allows small changes (of the order of a few percent) of tissue ab¬ sorption coefficient to be displayed over the entire gray range or color
Downloaded From: http://archpedi.jamanetwork.com/ by a New York University User on 06/14/2015
range of the display. The pictures may be looked at much in the same way as a structures
roentgenogram; however, can
be identified and small
changes in absorption coefficients can
be evaluated. Lesions are seen as changes or alterations of the normal density and are interpreted in a sim¬ ilar manner as are conventional
roentgenograms.
This new technique appears to have considerable potential in the study of the brain and other parts of the body. Early reports suggest that this proce¬ dure is a valuable addition to the ra¬ diology armamentarium and may well be the preferred diagnostic procedure in selected diseases that had previ¬ ously undergone contrast or nuclear medicine procedures. Collin S. MacCarty, MD, in the 1974 Caldwell Lec¬ ture to the American Roentgen Ray Society said that the CAT procedure "surely will become the most nearly accurate
single neuroradiographic ex¬
amination."4 Already shown to be of unique assistance in the study of orbi¬ tal abnormalities,5 intracerebral and intraventricular hemorrhage,6 as well as other brain abnormalities,4 it is ex¬ pected that CAT will play a dominant role in many other diagnostic areas as exoerience is rained. DAVID A. WEBER, PHD
Department of Radiology University of Rochester Medical Center
Rochester, NY 14642 1. Littleton JT:
Tomography:
A current
as-
Probl Radiol 4:1-42, 1974. 2. Hounsfield GN: Computerized transverse axial scanning (tomography): I. Description of system. Br J Radiol 46:1016-1022, 1973. 3. Ledley RS, Di Chiro G, Luessenhop AJ, et al: Computerized transaxial x-ray tomography of the human body: A new tomographic instrument is able to distinguish between soft tissues everywhere in the whole body. Science 186:207-212, sessment. Curr
1974. 4. MacCarty CS: A significant symbiotic relationship: Caldwell Lecture, 1974. Am J Roentgenol Radium Ther Nucl Med 122:455-468,1974. 5. Lampert VL, Zelch JV, Cohen DN: Computed tomography of the orbits. Radiology 113:351-354, 1974. 6. Scott WR, New PFJ, Davis KR, et al: Computerized axial tomography of intracerebral and intraventricular hemorrhage. Radiology 112:73\x=req-\ 80, 1974.
