logging in or signing up Computed Tomography - Harshavardhan bg_harsha Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINT lite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 674 Category: Education License: All Rights Reserved Like it (2) Dislike it (0) Added: November 04, 2010 This Presentation is Public Favorites: 1 Presentation Description No description available. Comments Posting comment... By: majidbme (7 month(s) ago) Dear sir, i wonder if you mail it this wonderful ppt. Best regards. Majid Majidbme@yahoo.com Saving..... Post Reply Close Saving..... Edit Comment Close By: kean3010 (14 month(s) ago) I like this presentation. Can I get permission to download! Saving..... Post Reply Close Saving..... Edit Comment Close Premium member Presentation Transcript Slide 1: Basic Principles of CT Scanning Dr. Harshavardhan.B 1st year PG in radiology TSMU The basics of CT : The basics of CT CT imaging chain System components Acquisition methods Image quality Applications X-ray: The beginning : X-ray: The beginning X-Rays founded in 1895 by Wilhelm Conrad Roentgen CT: The beginning : CT: The beginning CT founded in 1970 by Sir Godfrey Hounsfield Engineer with EMI, LTD. first applications were in neuroradiology CT Scanner : CT Scanner X-Ray modality used to the body in cross section Used to determine extent of trauma location and type of tumors status of blood vessels pre surgical planning CT or CAT - Principles : CT or CAT - Principles Computerized (Axial) Tomography introduced in 1972 by Hounsfield and Cormack natural progression from X-rays based on the principle that a three-dimensional object can be reconstructed from its two dimensional projections based on the Radon transform (a map from an n-dimensional space to an (n-1)-dimensional space) CT or CAT - Methods : CT or CAT - Methods measures the attenuation of X-rays from many different angles a computer reconstructs the organ under study in a series of cross sections or planes combine X-ray pictures from various angles to reconstruct 3D structures CT - Reconstruction: FBP : CT - Reconstruction: FBP Filtered Back Projection common method uses Radon transform and Fourier Slice Theorem f(x,y) f y x s gf(s) Gf(r) u F(u,v) Spatial Domain Frequency Domain CT - Reconstruction: ART : CT - Reconstruction: ART Algebraic Reconstruction Technique iterative technique attributed to Gordon Reconstructedmodel Actual DataSlices Projection Back-Projection Initial Guess CT - FBP vs. ART : CT - FBP vs. ART Computationally cheap Clinically usually 500 projections per slice problematic for noisy projections Still slow better quality for fewer projections better quality for non-uniform project. “guided” reconstruct. (initial guess!) FBP ART CT - 2D vs. 3D : CT - 2D vs. 3D Linear advancement (slice by slice) typical method tumor might fall between ‘cracks’ takes long time helical movement 5-8 times faster A whole set of trade-offs CT or CAT - Advantages : CT or CAT - Advantages significantly more data is collected superior to single X-ray scans far easier to separate soft tissues from one another (e.g. liver, kidney) data exist in digital form -> can be analyzed quantitatively adds enormously to the diagnostic information used in many large hospitals and medical centers throughout the world CT or CAT - Disadvantages : CT or CAT - Disadvantages significantly more data is collected soft tissue X-ray absorption still relatively similar still a health risk Basic CT scanner components : Basic CT scanner components Gantry X-Ray Tube Detector Control Console Gantry : Gantry CT X-ray tube High voltage generator Detector array Data acquistion system Slip ring The CT X-ray Tube : The CT X-ray Tube Anode heat capacity 3.5 MHU up to 6.5 MHU Determines maximum mAs Determines volume length Dictates generator size Detector Elements : Detector Elements Capture energy that has not been attenuated by the patient Control console : Control console Set scan parameters kVp, mA, scan time, reconstruction filter, etc. Set scan mode Digital radiograph, axial or volume Houses reconstructor Review and archive images Post-processing CT : CT CT - Computed Tomography CAT Scan - Computerized Axial Tomography Scanning methods : Scanning methods Digital projection AP, PA, Lat or Oblique projection Surview, Scanogram Conventional CT Axial Start/stop Volumetric CT Helical or spiral CT Continuous acquisition Digital Projection : Digital Projection X-ray tube and detector remain stationary Patient table moves continuously With X-rays “on” Produces an image covering a range of anatomy Similar to a conventional X-ray image, e.g. flat plate of the abdomen Image used to determine scan location Axial CT : Axial CT X-ray tube and detector rotate 360° Patient table is stationary With X-ray’s “on” Produces one cross-sectional image Once this is complete patient is moved to next position Process starts again at the beginning Volume CT : Volume CT X-ray tube and detector rotate 360° Patient table moves continuously With X-ray’s “on” Produces a helix of image information This is reconstructed into 30 to 1000 images Volume Scanning: Pitch : Volume Scanning: Pitch Advantages of Volume CT : Advantages of Volume CT More coverage in a breath-hold Chest, Vascular studies, trauma Reduced misregistration of slices Improved MPR, 3D and MIP images Potentially less IV contrast required Gapless coverage Arbitrary slice positioning Fundamentals of Multislice CT : Fundamentals of Multislice CT Multislice Fundamentals : Multislice Fundamentals Everything is better (R)esolution Z-axis, spatial, low contrast (S)peed Temporal - bolus capture, stopped motion (V)olume Thin slice - organ-specific coverage (P)ower Enough photons - uncompromising image quality Multislice Effectiveness : Single Slice = One 10mm slice per rotation Dual Slice = Two 5mm slices per rotation Quad Slice = Four 2.5mm slices per rotation Multislice Effectiveness Everything is better Resolution 2x 4x-8x Speed same same Volume same same Power same same Dual Quad Attenuation : Attenuation X-ray beam passes through patient Each structure attenuates X-ray beam differently According to individual densities Radiation received by detector varies according to these densities Density information : Density information Transferred from detector to CT computer(A to D converter) Reconstructed by computer into a cross-sectional image Displayed on screen Each pixel displayed on monitor has varying brightness The greater the attenuation, the brighter the pixel The less attenuation, the darker the pixel Density information : Density information Density values correspond to a range of numbers Hounsfield scale Window settings : Window settings Window width Determines range of CT numbers displayed on an image Values above this range = white Values below this range = black Window level Sets the center CT number displayed on the monitor Determines the location on the Hounsfield scale about which the window width will be centered CT image quality : CT image quality Spatial resolution Ability to resolve small objects in an image Measured in lp/cm Isotropic Imaging : Isotropic Imaging True 0.5mm Isotropic imaging CT image quality : CT image quality Contrast resolution Ability to differentiate small density differences in an image Post Processing Options : Post Processing Options Visualization ofvasculature in relation to pathology Show course of vessels Show stent placement Define vascular stricture You do not have the permission to view this presentation. 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Computed Tomography - Harshavardhan bg_harsha Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINT lite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 674 Category: Education License: All Rights Reserved Like it (2) Dislike it (0) Added: November 04, 2010 This Presentation is Public Favorites: 1 Presentation Description No description available. Comments Posting comment... By: majidbme (7 month(s) ago) Dear sir, i wonder if you mail it this wonderful ppt. Best regards. Majid Majidbme@yahoo.com Saving..... Post Reply Close Saving..... Edit Comment Close By: kean3010 (14 month(s) ago) I like this presentation. Can I get permission to download! Saving..... Post Reply Close Saving..... Edit Comment Close Premium member Presentation Transcript Slide 1: Basic Principles of CT Scanning Dr. Harshavardhan.B 1st year PG in radiology TSMU The basics of CT : The basics of CT CT imaging chain System components Acquisition methods Image quality Applications X-ray: The beginning : X-ray: The beginning X-Rays founded in 1895 by Wilhelm Conrad Roentgen CT: The beginning : CT: The beginning CT founded in 1970 by Sir Godfrey Hounsfield Engineer with EMI, LTD. first applications were in neuroradiology CT Scanner : CT Scanner X-Ray modality used to the body in cross section Used to determine extent of trauma location and type of tumors status of blood vessels pre surgical planning CT or CAT - Principles : CT or CAT - Principles Computerized (Axial) Tomography introduced in 1972 by Hounsfield and Cormack natural progression from X-rays based on the principle that a three-dimensional object can be reconstructed from its two dimensional projections based on the Radon transform (a map from an n-dimensional space to an (n-1)-dimensional space) CT or CAT - Methods : CT or CAT - Methods measures the attenuation of X-rays from many different angles a computer reconstructs the organ under study in a series of cross sections or planes combine X-ray pictures from various angles to reconstruct 3D structures CT - Reconstruction: FBP : CT - Reconstruction: FBP Filtered Back Projection common method uses Radon transform and Fourier Slice Theorem f(x,y) f y x s gf(s) Gf(r) u F(u,v) Spatial Domain Frequency Domain CT - Reconstruction: ART : CT - Reconstruction: ART Algebraic Reconstruction Technique iterative technique attributed to Gordon Reconstructedmodel Actual DataSlices Projection Back-Projection Initial Guess CT - FBP vs. ART : CT - FBP vs. ART Computationally cheap Clinically usually 500 projections per slice problematic for noisy projections Still slow better quality for fewer projections better quality for non-uniform project. “guided” reconstruct. (initial guess!) FBP ART CT - 2D vs. 3D : CT - 2D vs. 3D Linear advancement (slice by slice) typical method tumor might fall between ‘cracks’ takes long time helical movement 5-8 times faster A whole set of trade-offs CT or CAT - Advantages : CT or CAT - Advantages significantly more data is collected superior to single X-ray scans far easier to separate soft tissues from one another (e.g. liver, kidney) data exist in digital form -> can be analyzed quantitatively adds enormously to the diagnostic information used in many large hospitals and medical centers throughout the world CT or CAT - Disadvantages : CT or CAT - Disadvantages significantly more data is collected soft tissue X-ray absorption still relatively similar still a health risk Basic CT scanner components : Basic CT scanner components Gantry X-Ray Tube Detector Control Console Gantry : Gantry CT X-ray tube High voltage generator Detector array Data acquistion system Slip ring The CT X-ray Tube : The CT X-ray Tube Anode heat capacity 3.5 MHU up to 6.5 MHU Determines maximum mAs Determines volume length Dictates generator size Detector Elements : Detector Elements Capture energy that has not been attenuated by the patient Control console : Control console Set scan parameters kVp, mA, scan time, reconstruction filter, etc. Set scan mode Digital radiograph, axial or volume Houses reconstructor Review and archive images Post-processing CT : CT CT - Computed Tomography CAT Scan - Computerized Axial Tomography Scanning methods : Scanning methods Digital projection AP, PA, Lat or Oblique projection Surview, Scanogram Conventional CT Axial Start/stop Volumetric CT Helical or spiral CT Continuous acquisition Digital Projection : Digital Projection X-ray tube and detector remain stationary Patient table moves continuously With X-rays “on” Produces an image covering a range of anatomy Similar to a conventional X-ray image, e.g. flat plate of the abdomen Image used to determine scan location Axial CT : Axial CT X-ray tube and detector rotate 360° Patient table is stationary With X-ray’s “on” Produces one cross-sectional image Once this is complete patient is moved to next position Process starts again at the beginning Volume CT : Volume CT X-ray tube and detector rotate 360° Patient table moves continuously With X-ray’s “on” Produces a helix of image information This is reconstructed into 30 to 1000 images Volume Scanning: Pitch : Volume Scanning: Pitch Advantages of Volume CT : Advantages of Volume CT More coverage in a breath-hold Chest, Vascular studies, trauma Reduced misregistration of slices Improved MPR, 3D and MIP images Potentially less IV contrast required Gapless coverage Arbitrary slice positioning Fundamentals of Multislice CT : Fundamentals of Multislice CT Multislice Fundamentals : Multislice Fundamentals Everything is better (R)esolution Z-axis, spatial, low contrast (S)peed Temporal - bolus capture, stopped motion (V)olume Thin slice - organ-specific coverage (P)ower Enough photons - uncompromising image quality Multislice Effectiveness : Single Slice = One 10mm slice per rotation Dual Slice = Two 5mm slices per rotation Quad Slice = Four 2.5mm slices per rotation Multislice Effectiveness Everything is better Resolution 2x 4x-8x Speed same same Volume same same Power same same Dual Quad Attenuation : Attenuation X-ray beam passes through patient Each structure attenuates X-ray beam differently According to individual densities Radiation received by detector varies according to these densities Density information : Density information Transferred from detector to CT computer(A to D converter) Reconstructed by computer into a cross-sectional image Displayed on screen Each pixel displayed on monitor has varying brightness The greater the attenuation, the brighter the pixel The less attenuation, the darker the pixel Density information : Density information Density values correspond to a range of numbers Hounsfield scale Window settings : Window settings Window width Determines range of CT numbers displayed on an image Values above this range = white Values below this range = black Window level Sets the center CT number displayed on the monitor Determines the location on the Hounsfield scale about which the window width will be centered CT image quality : CT image quality Spatial resolution Ability to resolve small objects in an image Measured in lp/cm Isotropic Imaging : Isotropic Imaging True 0.5mm Isotropic imaging CT image quality : CT image quality Contrast resolution Ability to differentiate small density differences in an image Post Processing Options : Post Processing Options Visualization ofvasculature in relation to pathology Show course of vessels Show stent placement Define vascular stricture