Since the first brain scanner was constructed several years ago，computed tomography or computed medical imagery, has become fairly widely used.Its rapid acceptance is due to the fact that it has overcome several of the drawbacks of conventional X-ray technology.
To begin with， Conventional two-dimensional X-ray pictures cannot show all of the information contained in a three-dimensional object.Things at different depths aresuper
Imposed，causing confusion to the viewer，computed tomography can give three-dimensional information.The computer is able to reconstruct pictures of the body’s interior by measuring the varying intensities of X-ray beams passing through sections of the body from hundreds of different angles.Such pictures are based on series of thin “slices”.
In addition, conventional X-ray generally differentiates only between bone and air，as in the chest and lungs.They cannot distinguish soft tissues or variation in tissues.The liver and pancreas are not discernible at all，and certain other organs max only be rendered visible through the use of ratio paque dye.Since computed tomography is much more sensitive，the soft tissues of the kidneys or the liver can be seen and clearly differentiated.This technique can also accurately measure different degrees of X-ray absorption, facilitating the study of the nature of tissue.
A third problem with conventional X-ray methods is their inability to measure quantitatively the separate densities of the individual substances through which the X-ray has passed.Only the mean absorption of all the tissues is recorded.This is not a tumor and subsequently monitor the progress of radiation treatment，so that in addition to its diagnostic capabilities, it can play a significant role in
therapy.
55.Conventional C-rays mainly show the difference between
A.bone and air B.liver and pancreas C.muscle and other body issues D.heart and lungs
56.It can be inferred from the passage that compared to conventional X-ray techniques，computed tomography is more
A.compact B.rapid C.economical D.informative
57.What is the author’s attitude toward this new technique？
A.Cautious B.Tolerant C.Enthusiastic D.Critical
58.According to the passage，computed tomography can be used for all of the following except
A.monitoring a patient’s disease
B.diagnosing disorders
C.locating tumors
D.reconstructing damaged issues