- mathematical theory of tomographic image reconstructions (Johann Radon). ○ - conventional tomography (A. Vallebona). ○ - theoretical . My special thanks to the CT Scan Technicians More Rahul. – Hariqbal Singh The advent of multiple modalities for Cross Sectional Imaging over last four decades has revolutionized the field of medicine leading to mystifying ways to image the patient. viii Cross Sectional Imaging. PDF | Since its introduction in , X-ray computed tomography (CT) has evolved into an essential diagnostic imaging tool for a continually increasing variety of.
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CT Basics. From Single-Slice to Cone-Beam Spiral CT. • Technology. – Basic parameters Phase-correlated CT (e.g. cardiac CT) . Easy to understand. Summary of review: In the unconscious and acutely ill patient a head CT is often artifacts) common acute cerebral disorders can be easily assessed by the. Pocket Guide for Emergent Head CT Interpretation. 1. Become familiar with normal neuroanatomy at key levels of the head. A. Figure 1 Posterior Fossa. B.
Further information: Radiobiology The radiation used in CT scans can damage body cells, including DNA molecules, which can lead to radiation-induced cancer. Compared to the lowest dose x-ray techniques, CT scans can have to 1, times higher dose than conventional X-rays.
In general, the radiation dose associated with a routine abdominal CT has a radiation dose similar to 3 years average background radiation from cosmic radiation. In this group one in every CT scans was followed by an excess cancer. People with mild kidney impairment are usually advised to ensure full hydration for several hours before and after the injection.
For moderate kidney failure, the use of iodinated contrast should be avoided; this may mean using an alternative technique instead of CT. Those with severe renal failure requiring dialysis require less strict precautions, as their kidneys have so little function remaining that any further damage would not be noticeable and the dialysis will remove the contrast agent; it is normally recommended, however, to arrange dialysis as soon as possible following contrast administration to minimize any adverse effects of the contrast.
In addition to the use of intravenous contrast, orally administered contrast agents are frequently used when examining the abdomen.
However, oral alternatives to iodinated contrast exist, such as very dilute 0. Many soft-tissue structures would be displayed with the same gray level as their surroundings and thus would be invisible. The solution, which is taken for granted today, is windowing, illustrated in supplemental Figure 3.
A viewer may interactively decide how gray levels are to be allocated by specifying a window width the range of CT numbers to display, e. Adjustable window settings may then be altered to view other CT number ranges. Universally today, windowing can be interactively performed with a mouse or trackball.
The results obtained with this first clinical EMI scanner installed in September were presented at a British radiologic society meeting in April The results left no doubt as to the revolutionary clinical value of the process. The historic success of the scanner created enormous interest and led to an explosion of research and development by many groups and corporations. One such development was FBP reconstruction, described earlier. However, a technology race to improve and expand the CT process was also under way.
Of course, one important application was body scanning, but the water-filled box had to be eliminated. However, a discussion of why it was used in the first place is worthwhile.
It served 2 purposes, both of which allowed Hounsfield to maximize the accuracy of attenuation coefficient measurements. These 2 reasons were as follows.
Limitation of Dynamic Range The water-filled box greatly reduced the range of intensities over which the detector needed to accurately respond, thus allowing optimization of the detector sensitivity. Beam-Hardening Correction x-Rays produced in x-ray tubes are mostly bremsstrahlung x-rays which, unlike the discrete photon energies emitted by radioactive isotopes, cover a broad continuum of energies up to a maximum numerically equal to the x-ray tube kilovoltage.
Such beams are referred to as polychromatic.
Beam hardening refers to a gradual increase in the effective energy of polychromatic x-ray beams as they penetrate deeper into attenuating materials.
It is caused by preferential attenuation of the lower-energy and thus less penetrating photons in the beam by each successive layer of attenuating material 1.
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Abdominal CT scan made easy 1. Abdominal CT Scan Crossing the barrier in bedside interpretation 2.
Can a Clinician interpret CT scan like a Radiologist? Read the information on the CT scan Do not get disoriented Hold the film in the proper orientation Follow the IV contrast filled Aorta as we descend caudally. Branches and points of interest will be noted.
Azygous Vein. Hemiazygous Vein This is an excellent image of the right, middle and left hepatic veins draining into the Inferior Vena Cava. The outline of the Inferior Vena Cava is more distinct in this image. More portal vein branching into the liver lobes Splenic Artery.