C.T. Scancomputed tomography

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Ayat Yaseen AlaniPharmacy student at Al-anbar uni.

Iraq

Introduction

A radiographic examination that produces a 3-d cross sectional view of an area of the body, displayed in slices. Can demonstrate bones, organs, soft tissues and blood vessels. May be performed with or without contrast medium.

Terminology

Hounsfield Unit (HU) :- mean attenuation of x-rays by different tissues. Data Acquisition :- method by which the patient is scanned to obtain enough data for image reconstruction.Beam Geometry :- the size, shape, and motion of the x-ray beam and its path.Ray :- part of the beam that falls on the detector.Scan plane :- region where the x-ray tube and detectors rotate.

Basic Principle

1. Count # of X-Rays which pass through patient2. Calculate and map out cross sectional image.

Advantages

Relatively inexpensive compared with MRI and PET scanning. Accurate, 3-dimensional data including attenuation information. Rapid acquisition of data and no need for patients to remain for planning process. 4-dimensional data acquisition is possible using gating technology.

Disadvantages

Relatively high amount of ionising radiation per scan (increased for 4-D imaging).Subject to artefacts due to patient movement.Contrast required for certain structures, particularly vessels. Some people may have an anaphylactic response to intravenous contrast, which may occasionally be fatal.

When CT scans are used

CT scans can be used to diagnose and monitor a variety of different health conditions including brain tumours, certain bone conditons and injuries to internal organs such as the kidneys, liver or spleen.They are also often used to look inside the body before another procedure takes place, such as radiotherapy treatment or a biopsy (where a small tissue sample is taken so that it can be examined under a microscope).

CT Scan of the Brain

SafetyCT scans are safe procedures and, in most cases, the benefits of having a scan outweigh any potential risks.

A CT scan does expose you to radiation. The amount is small and will not cause you any harm. However, CT scans are not recommended for pregnant women because there is a small risk that the X-rays that are used could harm the unborn baby.

Children are also more at risk than adults are from developing a build-up of radiation. Therefore, a CT scan will only be recommended if a child has a serious condition that puts them at greater risk.

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