Advanced CT Concepts for Hybrid Imaging Technologists

Advanced CT Concepts for Hybrid Imaging Technologists   By the end of this course you should be able to: • Describe the fundamentals of CT imaging which include CT instrumentation, CT scanning methods, acquisition, reconstruction and post processing techniques. • List the Siemens' features that reduce patient dose and describe their use • List the Siemens' features that optimize workflow and describe their use                              Review of CT Basics                                  CT Instrumentation                                    CT Scanning Methods     Produces the X-ray Beam • Vacuum glass housing • Anode • Cathode StratonTM CT Tube Available on all Biograph mCT and mCT Flow scanners   • Direct Anode Cooling • 5 MHU/min Cooling Rate (20 seconds) • Conventional tubes cool at 30 MHU/min (120 seconds) • Compact • Enables as low as 0.28 second rotation speed*       *Biograph mCT Flow Edge DURATM High Performance CT Tube Available on the Symbia Intevo, Intevo Exel and Bold SPECT/CT, and Biograph Horizon   • 5 MHU/min Cooling Rate (20 seconds) • Conventional tubes cool at 30 MHU/min (120 seconds) • Compact • Enables .5 second rotation speed on the Intevo 16*       *Symbia Intevo 6 and Biograph Horizon have a minimum 0.6 rotation speed. *Symbia Intevo 2 has a minimum 0.8 rotation speed. Allows production of the photons in the X-ray tube:   • Passes low voltage through a series of wire coils to produce a very large voltage   • High voltage is in the hundreds of thousands of volts (hundred kilovolts or kV)     Components on the CT scanner which restrict the path of the x-ray potons, keeping the x-rays within the area of interest, thereby reducing patient dose and increasing image quality.   • Reduces scatter • X-ray opaque materials • Pre-patient collimation     X-ray Tube Pre-Patient Collimation The task of the slip-ring assembly is to transmit data from the rotating gantry to the stationary gantry. Edge Technology for high 0.30 mm spatial resolution TrueSignal Technology for optimized low-signal imaging HiDynamics for improved functional imaging Topogram  Localizer scan in a single projection. Used for positioning and FOV placement. Stationary tube and moving table. Dynamic Sequence Scanning  Small ISD, but delayed display due to reconstruction delay. Spiral Scanning  Corkscrew path around the patient. The path is determined by the thickness of the x-ray beam and the speed of the patient table. Tube and detectors rotate around the patient at the same time the patient moves into the gantry. Creates a volume of data. Sequence Scanning   Cross sectional image that provides the ability for retrospective reconstruction. Patient table moves as an increment after each x-ray tube rotation. Includes an Inter Scan Delay • Since raw data is acquired in a volume in “corkscrew” pattern, the data does not correspond to any particular slice position • Mathematical calculation is applied to the data prior to reconstruction   - Attenuation information has to come from single slice planes in the raw data   - Divides the spiral raw data into individual, planar slices                                Image Quality & Aquisition Parameters         Images Courtesy of Siemens Training and Development Center   mAs (milliamps per second)  Tube current per second. This controls the number of photons produced by the x-ray tube times the rotation time of the x-ray tube. Determines the number of photons the patient is exposed to. 25 mAs 200 mAs Images Courtesy of Siemens Training and Development Center kVp (kilovoltage peak) The maximum energy of the x-ray photons that are leaving the tube. The higher the kVp, the more penetration of the beam.  The lower the kVp, the less beam penetration 140 kV 80 kV Thicker Slices Soft Tissue - Less noise and better contrast detectability 3 mm slice 10 mm slice Thinner Slices Boney Tissue - Better spatial resolution 5 mm slice 1 mm slice Slice Thickness  The number of millimeters of anatomy, intersected by the thickness of the x-ray beam, which is represented by the CT image.   Images Courtesy of Siemens Training and Development Center Table Increment is the advancement, in millimeters, of the patient table between consecutive sequence slices.  It determines the gap or overlap between slices • If the increment is equal to the slice thickness = no overlap or gaps • If the increment is less than the slice thickness = overlap • If the increment is more than the slice thickness = gaps Increment equals slice thickness Increment less than slice thickness Increment more than slice thickness Pitch is the extent of how much the x-ray spiral is stretched during the scan.   Pitch = Table Feed/Rotation Collimator Size  x  # of collimators used   20 Seconds   10 Seconds Pitch 2 Pitch 2           20 Seconds   20 Seconds Pitch 1 Pitch 1 Isocentering To center the area of interest vertically and horizotally in the FoV. • Isocenter positioning means that the beam displays the anatomy at  similar points at opposite tube positions • FoV not isocenter can result in image artifacts Not Isocenter Isocenter                                Image Quality & Reconstruction Parameters                   Images Courtesy of Siemens Training and Development Center   Reconstruction Increment work the same way as table increment by determining the gap or overlap of the reconstructed slices. • If the increment is equal to the slice thickness = no overlap or gaps • If the increment is less than the slice thickness = overlap • If the increment is more than the slice thickness = gaps Increment equals slice thickness Increment less than slice thickness Increment more than slice thickness Scan FoV - Number of millimeters of anatomy over which projection data is collected. • A cross section of the patient's anatomy should be completely contained in the FoV Reconstruction FoV - Number of millimeters of information reconstructed and displayed in the final image. • Equal to or smaller than the scan FoV Images Courtesy of Siemens Training and Development Center Image Matrix - Grid of rows and columns of pixels that form the digital image. Increasing the Image Matrix will: • Yield smaller pixels • Increase the image resolution Kernel is the filter applied to the data upon reconstruction.   Kernels play a part in determining resolution and appraent noise of the image. • Sharper Kernel   -  Improves resolution   -  Increases apparent noise • Smoother Kernel   -  Minimizes noise to improve contrast   -  Decreases ability to distinguish fine details   H70 H50 H30 Images Courtesy of Siemens Training and Development Center                                Post Processing Parameters that Affect Image Quality                  Images Courtesy of Siemens Training and Development Center   Windowing is the adjustment of the brightness and contrast of the shades of gray assigned to represent the tissues in the pixels of a CT image.   Window Width – the range of CT values that occupy the full gray scale on an image monitor.   Window Width Window Width Images Courtesy of Siemens Training and Development Center Window Center - The center CT value around which the window width is positioned • Low window - used to evaluate less dense structures • High window - used to evaluate more dense structures   Low Window Center High Window Center Images Courtesy of Siemens Training and Development Center Magnification – Allows a small region of the image to be displayed larger.  This can be used in reconstruction (defined by X/Y coordinates) as well as post-reconstruction.   Images Courtesy of Siemens Training and Development Center                                3D Post Processing Techniques             Images Courtesy of Siemens Training and Development Center   Multi-Planar Reconstruction (MPR) reformats the images in one orientatin to produce images in other orientations.   • Allows for reconstruction of images in planes that would otherwise be difficult or impossible to acquire • Created from the transverse reconstructed CT data   Images Courtesy of Siemens Training and Development Center Maximum Intensity Projection (MIP) is a post-processed image that is based on the hgihest densities withing the image.   • Blood vessels using contrast are shown clearly • Differentiation between contrast and calcium is visible • Used most commonly for vascular structures in 3D views Images Courtesy of Siemens Training and Development Center Shaded Surface Display (SSD) - A 3-dimensional representation of an object using a defined HU threshold range to generate the surface of body structures.   • Primarily shows surfaces of objects within a threshold • Density information is lost   Images Courtesy of Siemens Training and Development Center Volume Rendering Technique (VRT) is the technique that renders the entire volume of data rather than just the surfaces or minimum/maximum densities.   • A number of anatomical structures can be displayed simultaneously • Different levels of brightness, opacity or colors   Images Courtesy of Siemens Training and Development Center                              Advanced CT Features                                  CT Dose Reduction     Effective Dose   • Takes into account the specific organs and areas of the that are exposed to radiation • Not all body parts and organs equally sensitive to adverse effects Effective Dose (Gy) = Absorbed Dose (Gy) x wT        Penumbra  The radiation profile of a single slice is rounded and the radiation actually extends outside the intended slice thickness. •   Caused by imperfect collimation   Penumbra Penumbra CTDI - CT Dose Index   • Indicator of radiation dose which includes the radiation located within the intended slice thickness as well as that from the penumbra   -  Takes into account radiation from direct beam and scatter                                                                                                                                       DLP - Dose Length Product   • Measure of the total radiation exposure for the whole series of images • Product of CTDI value and the length of the body scanned                                                                                                                                         Estimates of Patient Dose:   Study Skin Dose Head Scan 1-5 rads Body Scan 2-6 rads Topogram .05-.1 rad Approximate doses quoted from MIC "CT Cross Trainer" Physical factors that have an effect on dose: •   Geometric features of the scanner •   Patient size •   Anatomy composition Scan parameters that can reduce patient dose include:   mAs • Reducing the mAs reduces the total number of photons     kVp • Reducing kVp reduces highest energy level of the photon beam • Not usually used for reducing dose because of maintenance of tissue contrast     Anatomical Coverage • By scanning a smaller region of anatomy, dose is reduced • If slice thickness is unchanged, there are few slices scanned Scan parameters that can reduce patient dose include:   Slice Thickness • Only affects those patients being scanned on a single row scanner   Reduced number of slices reduce the number of penumbra     Table Increment (Sequence Mode) • Increasing the table increment, for a given slice thickness, will result in less overlap or more space between adjacent slices • Results in fewer slices     Pitch (Spiral Mode) • Increasing the pitch will result in each loop of the spiral scan being increased • Fewer loops or rotations are required to cover the same anatomy                                Siemens' Technologies that Help Reduce Dose & Optimize CT Workflow     Adaptive Dose Shield                         • •   Additional collimation that dynamically opens and closes with every spiral scan Blocks the irrelevant dose to the patient                                                CARE Combined Applications to Reduce Exposure               Images Courtesy of Siemens Training and Development Center What is CARE Dose 4D? Image Courtesy of Siemens Training and Development Center • Automatic exposure control • Varies the mAs over X, Y, and Z axis     What are the benefits of CARE Dose 4D? • Can use the same scan protocols for all patients slim/average/obese or adult/pediatric • Optimal diagnostic quality in every slice • Image quality achieved at lowest dose levels How Does It Work? 1. Topogram acquired and evaluated.   a.  Attenuation is measured for the acquisition projection of the topogram, usually the AP   b.  AP and lateral projection attenuation is calculated analyzing extension and structure 2. Appropriate mA settings are calculated based on the user defined protocol.   a.  Optimal mA is calculated for each axial position   b.  Tube load and systems limits are checked 3. On-line attenuation mA modulation is applied during the scan. 4. mAs is caqlculated for every single image and saved as image text. 5. Average mAs, CTDI volume and DLP calculated and recorded. 140mAs 55mAs 110mAs 130mAs       Courtesy of Elangen University, Germany CARE kV enables automatic kVp adaptation to optimize dose while providing optimized image quality based on patient size and the desired examination type. Benefits Include: • Optimized exposure • Optimized image quality • Optimized contrast to noise ration • No calculations to get the right mAs value Mode Parameter Results In OFF CARE Dose4D -  fixed kV -  Quality ref. mAs -  Fixed kV -  Eff. mAs SEMI CARE Dose4D -  fixed kV -  Quality ref. mAs -  Fixed kV -  Optimized Eff. mAs ON CARE Dose4D & CARE kV -  fixed kV -  Quality ref. mAs -  Actual kV -  Optimized Eff. mAs Dose will be optimized for:   • Non-contrast scans • Soft tissue with contrast scans • Vascular scans  By selecting ON, the    window will open for    quality reference       mAs & kV     Dose Optimization slider used to adjust contrast to noise ratio of a specific examination  The Semi mode provides the freedom to select the kV you want and the effective mAs will then be calculated accordingly.   • Fixed kV is desired in combination with the appropriate mAs value • Demonstrate which CTDI/eff. mAs values are taken when different kV settings are chosen When the Off mode is selected the system behaves with CARE Dose4D modulation only.   • Select the kV you want and the quality reference mAs desired • Eff. mAs will not be adjusted accordingly for changes to kV Display of areas where mAs values have been reduced and the maximum mAs has been reached. It points out areas of conflict when system limits have been reached.                  Image Courtesy of Siemens Training and Development Center •  •    Effective mAs that is needed for the scan can be applied by the scanner Load is possible   Image Courtesy of Siemens Training and Development Center • •  •    Eff. mAs (in combination with other parameters) needed for the scan exceeds the limit of the system Scan is invalid and action is required Load is not possible   Image Courtesy of Siemens Training and Development Center • •    The system cannot deliver the eff. mAs  that is needed for the whole scan range Load is possible   Image Courtesy of Siemens Training and Development Center • •  •  •  •  Striped area exceeds the system limit but image quality will be sufficient The peak (striped part) exceeds the system limit and will be removed The peak mAs will be cut to the max mAs The length and the strength of the striped range will affect the decision Load is possible     Image Courtesy of Siemens Training and Development Center To turn off the CARE Profile feature, navigate to the Options pull down menu and then select: Configuration → Examination → Dose tab.  Click the check box to de-select CARE Profile. The CARE Dashboard provides a quick overview of dose optimization features and technologies. Pediatric scanning with CARE Child offers a low dose 70 kV scan mode with the new STRATON tube • Optimized Parameter Settings • Specific Modulation Curves • Dedicated Pediatric Protocols CARE Contrast aids in reducing iodine exposure in contrast enhanced CT studies • Synchronization of scan with contrast media • Transfers the contrast protocol to the Patient Protocol, MPPS, etc • Manage contrast protocols on the scanner console • Export protocols to other scanners                                FAST Fully Assisted Scanner Technologies                          Direct scan adjustment at the push of a button. FAST Scan Assistant   •   Precise value indication (a) •   Direct parameter setting (b) •   Instant preview of applied dose (c)                                                                                                          FAST Scan Adjust                                                                                            •  Direct adjustment of all parameters with a single click FoV range selection with a single click • Uses landmarks to set the ranges • Fast reproducible results with any operator 1. From the Recon task card/Recon Region, select the desired region from the drop list menu. 2. Select Wide for soft tissue or Narrow to exclude soft tissue. 3. There is one width available for Head, Neck, Heart, Vasuclar, and Spine.        Automatic segmentation of the spine anatomy •   Defines vertebra (ex: L3) •   Defines disc spaces (ex: L5/S1) •   Defines spine ranges (ex: T3-T6) Image Courtesy of Siemens Training and Development Center     • kV changes can alter image impression • FAST Window automatically calculates the new window settings (WW & WC) to maintain quality image impression with the new kV • Choice is to switch ON or OFF Step-by-Step guides that assist with scanning and reconstruction parameters for CT Cardiac studies.                                Siemens' Technologies that Help Reduce Dose & Optimize CT Workflow   Image Courtesy of Siemens Training and Development Center   • On CT tube / Two successive spiral scans • One automated procedure • Two scans performed at different kV and mA levels • High temporal and spatial resolution • Both spirals are performed at half the dose • Auto-range of two spiral scans • Cannot split auto-range and insert addiitonal scans • Only parameters of the first entry can be modified • Changes will be inherited into the second entry • New kernels available: D10s, D20s, D30s, D40s, D45s • Image evaluation is performed on syngo.via using Dual Energy Applications Protocols Available:   • DE_Abdomen_KidneyStones • DE_Abdomen_Monoenergetic • DE_Foot_Gout • kV are set to 80 and 130 • Delay can be set for the first entry but not the second • Effective mAs and Quality Reference mAs can be set for the first entry but not the second • SNR will automatically be corrected   syngo.CT Dual Energy – basic viewer including Optimum Contrast, syngo.CT DE Rho/Z and Monoenergetic imaging syngo.CT DE Calculi Characterization syngo.CT DE Gout syngo.CT DE Monoenergetic Plus  syngo.CT DE Bone Marrow syngo.CT DE Virtual Unenhanced - Liver VNC syngo.CT DE Brain Hemorrhage Accurate and non-invasive diagnosis of gout • Acute cases where aspiration cannot be performed • Uric acid concentration in the blood not reliable indicator • Visualization of uric acid crystals Characterization of kidney stones • Kidney stones contain varying amounts of heavy atoms (uric acid vs calcified stones) • Differentiation of these material • Visualization of chemical differences • Visualization of the contrast agent concentration in the liver • Based on material decomposition into iodine contrast agent, fat, and liver tissue • Allows creation of non-contrast information from DE fat and liver materials • No need for a non-contrast scan Differentiating hemorrhage from iodine-uptake in bleeds and lesions • Assists in visualization of iodine concentration and distribution in the brain • Lesions and bleeds may show significant iodine uptake • Inactive hemorrhages are not enhanced Images Courtesy of Siemens Training and Development Center                                Siemens' Technologies that Help Reduce Dose & Optimize CT Workflow     Back Projection •  Basic algorithm •  Projections are gathered at angles around the object •  Star pattern •  Blurred images Filtered Back Projection •  Uses back projection basics •  Various filters applied to improve image quality •  Can impart different impressions based on diagnostic purpose •  Smooth ⇒ Soft tissue •  Sharp ⇒ High resolution ImPACT (2005, October). Filtered back projection (3). Retrieved from http://www.impactscan.org/slides/impactcourse/basic_principles_of_ct/img1 Iterative Reconstruction (IR) •  Decouple spatial resolution and image noise •  Correction loop •  Impractical in computational time and power •  Change in Hounsfield units   In clinical practice, the use of IRIS may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. • Utilizes raw (measured) data in a master volume reconstruction • Master volume reconstruction provides all detail information, but with much image noise • Image reconstruction loop moves into the image domain   -  Avoiding time consuming forward projections • Advanced image enhancement is applied to reduce noise and enhance contrast • Occurs fast enough for routine clinical use • Image similar to standard kernels 70% dose H41 kernel (left image), 70% dose with IRIS (.140 kernel - right image) Images Copyright 2010, Mayo Foundation for Medical Education & Research   Example of IRIS used in an abdominal exam.  The image on the left is at 50% dose (reconstructed from only 1 tube of a dual source exam). The image on the right is after applying IRIS. Images Copyright 2010, Mayo Foundation for Medical Education & Research   The statements by Siemens customers described herein are based on results that were achieved in the customer's unique setting. Since there is no “typical” hospital and many variables exists (e.g., hospital size, case mix, level of IT adoption) there can be no guarantee that other customers will achieve the same results. The statements by Siemens customers described herein are based on results that were achieved in the customer's unique setting. Since there is no “typical” hospital and many variables exists (e.g., hospital size, case mix, level of IT adoption) there can be no guarantee that other customers will achieve the same results. • Raw data based iterative reconstruction • More powerful dose reduction than image based methods • Well established image impression • Fast • Improved workflow with variable settings CT enterography at 80 kV.  Images were reconstructed at 2-mm slices using the B40 kernel for the full-dose and half-dose exam.  The corresponding 140 kernel was utilized for reconstructing the half-dose SAFIRE images. Images Copyright 2011, Mayo Foundation for Medical Education & Research   Pediatric Congenital Heart Disease: RVOT conduit at 80 kV, DLP 12.  Left: standard weighted FBP reconstruction (B36 kernel). Right: SAFIRE reconstruction (136 kernel). Images Copyright 2011 Minneapolis Heart Institute Foundation   In clinical practice, the use of SAFIRE may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. The following test method was used to determine a 54 to 60% dose reduction when using the SAFIRE reconstruction software. Noise, CT numbers, homogeneity, low-contast resolution, and high contrast resolution were assessed in a Gammex 438 phantom. Low dose data reconstructed with SAFIRE showed the same image quality compared to full dose data based on this test. Data on file. The statements by Siemens customers described herein are based on results that were achieved in the customer's unique setting. Since there is no “typical” hospital and many variables exists (e.g., hospital size, case mix, level of IT adoption) there can be no guarantee that other customers will achieve the same results. The statements by Siemens customers described herein are based on results that were achieved in the customer's unique setting. Since there is no “typical” hospital and many variables exists (e.g., hospital size, case mix, level of IT adoption) there can be no guarantee that other customers will achieve the same results. Other IR Techniques   Distortion of image texture   •  Over smoothed, plastic, blotchy appearance •  Speed not comparable     ADMIRE • Statistical IR method • Statistical weighting and back projection • Regularization function and smoothness constraint and statistical model • Forward projection for "pseudo raw data" comparison to "measured raw data" Example of routine non-enhanced head CT using a 5-mm slice reconstruction. (A) Routine WFBP, and (B) ADMIRE with strength 5. In the example, the calculation of the mean and standard deviation of CT numbers in selected locations (Hounsfield Unites HU) showed that ADMIRE led to reduced image noise and improved CNR (2.9 vs 1.9) relative to standard WFBP reconstruction. Images reconstructed with ADMIRE also exhibited anatomical edges and borders, which were better defined when compared with WFBP. The patient was scanned with 120 kV and 340 mAs, with recorded radiation exposure parameters of CTDIvol - 59.8 mGy and Dlp - 1039 mGy•cm.  Courtesy of the Medical University of South Carolina, USA   ADMIRE used with an ultra-high resolution temporal bone protocol for imaging of the inner ear, with an effective slice thickness of 0.4 mm. (A) Coronal and (B) oblique plane reconstructions. Data acquisition used 120 kV, CTDIvol = 55 mGy and DLP = mGy•cm. Images Copyright 2015 Mayo Foundation for Medical Education and Research, Rochester MN, USA   See ADMIRE data sheet for further information. In clinical practice, the use of ADMIRE may reduce CT patient dose depending on the clinical task, patient size, anatomical location, and clinical practice. A consultation with a radiologist and a physicist should be made to determine the appropriate dose to obtain diagnostic image quality for the particular clinical task. The statements by Siemens customers described herein are based on results that were achieved in the customer's unique setting. Since there is no “typical” hospital and many variables exists (e.g., hospital size, case mix, level of IT adoption) there can be no guarantee that other customers will achieve the same results. The statements by Siemens customers described herein are based on results that were achieved in the customer's unique setting. Since there is no “typical” hospital and many variables exists (e.g., hospital size, case mix, level of IT adoption) there can be no guarantee that other customers will achieve the same results.                                Metal Artifact Reduction     Image Courtesy of Siemens Training and Development Center   Causes for Metal Artifacts • Beam hardening • Scatter • Partial volume effect • Photon starvation                                Images Courtesy of Siemens Training and Development Center • New metal artifact reduction algorithm • Combines 3 successful approaches to reduction of artifacts   -  Beam hardening correction   -  Sinogram inpainting   -  Frequency split Without iMAR With iMAR Without iMAR With iMAR Images Courtesy of Siemens Training and Development Center You have now completed the course, Advanced CT Concepts for Hybrid Imaging Technologists.  You should now be able to: • Describe the fundamentals of CT imaging which include CT instrumentation, CT scanning methods, acquisition, reconstruction and post processing techniques. • List the Siemens' features that reduce patient dose and describe their use • List the Siemens' features that optimize workflow and describe their use