Although the radiation from a CT scan is unlikely to injure your baby, your doctor may recommend another type of exam, such as ultrasound or MRI, to avoid exposing your baby to radiation. At the low doses of radiation used in CT imaging, no negative effects have been observed in humans. In certain cases, your doctor may recommend that you receive a special dye called contrast material. This can be something that you are asked to drink before your CT scan, or something that is given through a vein in your arm or inserted into your rectum. Although rare, the contrast material can cause medical problems or allergic reactions.
Most reactions are mild and result in a rash or itchiness. In rare instances, an allergic reaction can be serious, even life-threatening. Tell your doctor if you've ever had a reaction to contrast material. A special dye called contrast material is needed for some CT scans to help highlight the areas of your body being examined.
The contrast material blocks X-rays and appears white on images, which can help emphasize blood vessels, intestines or other structures. If your infant or toddler is having a CT scan, the doctor may recommend a sedative to keep your child calm and still. Movement blurs the images and may lead to inaccurate results.
Ask your doctor how to prepare your child. You can have a CT scan done in a hospital or an outpatient facility. CT scans are painless and, with newer machines, take only a few minutes. The whole procedure typically takes about 30 minutes. CT scanners are shaped like a large doughnut standing on its side. You lie on a narrow, motorized table that slides through the opening into a tunnel. Straps and pillows may be used to help you stay in position. During a head scan, the table may be fitted with a special cradle that holds your head still.
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While the table moves you into the scanner, detectors and the X-ray tube rotate around you. Each rotation yields several images of thin slices of your body. Using the computer, it presents the elementary surfaces of the reconstructed image from a projection of the data matrix reconstruction, the tone depending on the attenuation coefficients.
The image by the CT scanner is a digital image and consists of a square matrix of elements pixel , each of which represents a voxel volume element of the tissue of the patient. In conclusion, a measurement made by a detector CT is proportional to the sum of the attenuation coefficients. The typical CT image is composed of rows, each of pixels, i. In the process of the image, the value of the attenuated coefficient for each voxel corresponding to these pixel needs to be calculated. Each image point is surrounded by a halo-shaped star that degrades the contrast and blurs the boundary of the object.
To avoid this, the method of filtered back projection is used.
The action of the filter function is such that the negative value created is the filtered projection, when projected backwards, is removed, and an image is produced, which is the accurate representation of the original object. The CT scan deals with the attenuation of the x-rays during the passage through the body segment.
However, several features distinguish it from conventional radiology: the image is reconstructed from a large number of measurements of attenuation coefficient. Before the data are presented on the screen, the conventional rescaling was made into CT numbers, expressed in Hounsfield Units HU , as mentioned before.
So, the signal transmitted by the detector is processed by the PC in the form of the digital information, the CT image reconstruction. Please Note: You can also scroll through stacks with your mouse wheel or the keyboard arrow keys.
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Emerging clinical applications of computed tomography
Readers will thus be informed how to use a CT system to an optimum depending on the different diagnostic requirements. This includes a detailed discussion about the dose required and about dose measurements as well as how to reduce dose in CT. All considerations pay special attention to spiral CT and to new developments towards advanced multi-slice and cone-beam CT. For the third edition most of the contents have been updated and latest topics like dual source CT, dual energy CT, flat detector CT and interventional CT have been added.
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The enclosed CD-ROM again offers copies of all figures in the book and attractive case studies, including many examples from the most recent slice acquisitions, and interactive exercises for image viewing and manipulation. This book is intended for all those who work daily, regularly or even only occasionally with CT: physicians, radiographers, engineers, technicians and physicists. A glossary describes all the important technical terms in alphabetical order.
The enclosed DVD again offers attractive case studies, including many examples from the most recent slice acquisitions, and interactive exercises for image viewing and manipulation.
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