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CAT Scan/CT ScanComputed Axial TomographyComputed Tomography

DR. JAMES M. ALO, RN, MAN,MAP,PHD

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Basic principlesMathematical principles of CT were first developed in 1917 by Radon

Proved that an image of an unknown object could be produced if one had an infinite number of projections through the objectdrjAlo2

X-Raysphotons produced by an electron beamsimilar to visible light, but higher energy!

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X-Rays - PhysicsAssociated with inner shell electronsAs the electrons decelerate in the target through interaction, they emit electromagnetic radiation in the form of x-rays.patient between an x-ray source and a film -> radiographcheap and relatively easy to usepotentially damaging to biological tissuedrjAlo4

Basic principlesPlain film imaging reduces the 3D patient anatomy to a 2D projection imageDensity at a given point on an image represents the x-ray attenuation properties within the patient along a line between the x-ray focal spot and the point on the detector corresponding to the point on the imagedrjAlo5

Basic principles (cont.)With a conventional radiograph, information with respect to the dimension parallel to the x-ray beam is lostLimitation can be overcome, to some degree, by acquiring two images at an angle of 90 degrees to one anotherFor objects that can be identified in both images, the two films provide location informationdrjAlo6

CT - basicsCT's primary benefit is the ability to separate anatomical structures at different depths within the body.

A form of tomography can be performed by moving the X-ray source and detector during an exposure.

Anatomy at the target level remains sharp, while structures at different levels are blurred.

By varying the extent and path of motion, a variety of effects can be obtained, with variable depth of fieldand different degrees of blurring of 'out of plane' structures.drjAlo7

CT Basics

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CAT stands for Computerized Axial Tomography which was later changer to just CT or rather Computerized Tomography.

The scanners originally only did axial images (referring to the plane of the image) but later became able to do other planes such as coronal or saggital imaging and can now do anything with the block of information it collects.

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Godfrey Newbold Hounsfield introduced the system to the public in 1972Nobel Prize in 1979It looks like a donut Made up of a series of X-ray sources and sensorsTomogram

Computed Axial TomographydrjAlo11

Process and ProcedureX-ray + Axial view + Computer Imaging = CAT ScanX-ray + (digital) Computer Imaging = CT scanProvides cross-sectional views and images of body organs and structures Pixel, Radiodensity, Voxel, WindowingContrast Material

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Computed Axial TomographyAlso called CAT scanning or CTImage formed using a rotating thin beam(s) of ionizing radiationImage slices reconstructed by computationThe image formed is related to the subjects densityImage display on computer or multiple filmsNew technology is multislice helical scannerdrjAlo13

CT - principleBecause contemporary CT scanners offer isotropic, or near isotropic, resolution, display of images does not need to be restricted to the conventional axial images.

Instead, it is possible for a software program to build a volume by 'stacking' the individual slices one on top of the other. The program may then display the volume in an alternative manner.

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Tomographic imagesThe tomographic image is a picture of a slab of the patients anatomyThe 2D CT image corresponds to a 3D section of the patientCT slice thickness is very thin (1 to 10 mm) and is approximately uniformThe 2D array of pixels in the CT image corresponds to an equal number of 3D voxels (volume elements) in the patientEach pixel on the CT image displays the average x-ray attenuation properties of the tissue in the corrsponding voxeldrjAlo15

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Tomographic acquisitionSingle transmission measurement through the patient made by a single detector at a given moment in time is called a rayA series of rays that pass through the patient at the same orientation is called a projection or viewTwo projection geometries have been used in CT imaging:Parallel beam geometry with all rays in a projection parallel to one anotherFan beam geometry, in which the rays at a given projection angle divergedrjAlo17

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diagnostic UsesThe HeadHemorrhaging, cerebrovascular accidents, traumaThe Abdomen, Pelvis, and ChestCancers, pneumonia, infectionBarium SulfateThe Spine and BonesVertebrae, disc, spinal cord definition, and bone densityIndicator of Osteoporosis Cardiac CT angiography.

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CT - diagnostic use

Cranial diagnosis of cerebrovascular accidents and intracranial hemorrhage CT generally does not exclude infarct in the acute stage of a stroke. For detection of tumors, CT scanning with IV contrast is occasionally used but is less sensitive than magnetic resonance imaging (MRI).

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CT - diagnostic useChestCT is excellent for detecting both acute and chronic changes in the lung parenchyma.

For evaluation of chronic interstitial processes (emphysema, fibrosis, and so forth), thin sections with high spatial frequency reconstructions are used - often scans are performed both in inspiration and expiration. This special technique is called High resolution CT (HRCT).

For detection of airspace disease (such as pneumonia) or cancer, relatively thick sections and general Purpose image reconstruction techniques may be adequate.

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CT - diagnostic useAbdominal and pelvic

CT is a sensitive method for diagnosis of abdominal diseases. It is used frequently to determine stage of cancer and to follow progress. It is also a useful test to investigate acute abdominal pain.

Renal/urinary stones, appendicitis, pancreatitis, diverticulitis, and bowel obstruction are conditions that are readily diagnosed and assessed with CT.

CT is also the first line for detecting solid organ injury after trauma.drjAlo27

CT step by step

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CT step by step

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CT step by step

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CT step by step

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Benefits:Painless procedureother than needing great deal of patienceAlternative to catheters and other guide camera optionsA good option for those weary of enclosed spacesUsually preferred over MRI, and costs less!!!Improved technology has lead to Spiral and Helical Scansfaster processesdrjAlo32

Spiral and Helical ScannersSpiralCircular PathConstant gantry rotation and readingsLess exposure to radiationFaster scan = better accuracy when patient must hold their breathdrjAlo33

Potential RisksExposure to RadiationReduced with Spiral ScanReaction to contrast materialDiabeticsIsovuePregnant and nursing women should not be exposeddrjAlo34

Investigating Emotionality and PsychopathologyDementiaAnorexia NervosaNeurological AbnormalitiesSchizophreniadrjAlo35

hedTESTPURPOSEPREPARATIONPOST-TEST NURSING CAREComputed TomographyDetects hemorrhage, infarction, abscesses, tumorsWritten consentExplain procedurePainlessImmobile during examIf contrast dye used, may experienced flushed, warm faced, & metallic taste during injectionNo specific intervention Assess for allergic responses to contrast dye, eg., rash, pruritus, urticariaEncourage PO fluids

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THANK YoudrjAloLearners are learning from experiences they have experienced which cannot be taught by teachers except themselves.- Dr. James M. Alo

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