Multislice CT Basics

Multislice CT Basics This web-based training will introduce the learner to the technology of Multislice Computed Tomography (MSCT).  All clinical imaging professionals will benefit from a review and comparison of basic MSCT terminology.  The evolution of the CT detector will be chronicled, from the first single-slice systems to today’s highest-end scanners.  Additionally, adaptive array detectors, fixed array detectors, interleaved reconstruction (IVR), and Siemens’ proprietary Z-sharp technology will be discussed.  Describe scanner collimation versus scanner slice thickness Explain cone beam and relay the importance of isocenter to CT image quality Explain the concept of Z-sharp technology Identify various multislice detector configurations Upon completion of this course, you will be able to: Basic components of all CT scanning systems:  X-ray source - tube X-Ray receiver - detector Gantry houses tube and detector as they rotate around patient gathering information Table to move patient through gantry Slice Collimation Thickness of physical detector element Selected prior to the actual scan Equals detector size Combined to make thicker images Slice Thickness The size - thickness - of reconstructed image Thicker images made from combining detector elements Thinnest image can only be as thin as smallest detector size used Single Slice   Earliest scanners were single-detector Entire detector used to create the thickest possible slice Only one image per rotation Collimators limited x-ray to make thinner images Z-axis coverage was limited and scans were long   Multislice  Scanners have evolved exponentially 2, 4, 6, 8, 10, 16, 20, 32, 40, 64, 128, 256, 320 slice systems Hundreds of images per rotation More coverage = faster scans On a two slice scanner, the single detector is divided into two equal parts.  When the collimated X-ray beam hits the detector, two equal slices are created The size of the resulting slice is dependant on how much of the detector is exposed to the X-ray beam Slice Collimation Available Slice Widths 2 x 1.0 mm 1.25,1.5, 2.0 mm 2 x 1.5 mm 2, 3, 4, 5, 6, 8, 10 mm 2 x 2.5 mm 2.5, 3, 4, 5, 6, 8, 10 mm 2 x 4 mm 5, 6, 8, 10 mm 2 x 5 mm 6, 8, 10 mm Advanced Multidetector Technologies Fixed Array Detectors Adaptive Array Detectors Z-Sharp Technology Interleaved Volume Reconstruction (IVR) Four Slice - Adaptive Array Four-slice scanners evolved from two-slice systems Two-slice detector divided again into four equal parts Using collimation could result in unequal sizes Siemens took a different approach Using collimation could result in unequal sizes of four-slice detector Siemens divided detector into unequal parts Thinner elements in center, thicker elements at periphery Adaptive Array Detector Adaptive Array Detector  Most flexibility at the time Detectors were still small, so Z-axis coverage was limited Three or four different sized elements in a detector array were common For Siemens, this includes the Emotion and Sensation products Z-Sharp  Siemens introduced first 64-slice scanner at RSNA 2004 Further improvements to image quality, detail and speed Greater spatial resolution Better temporal resolution Reduction of spiral artifacts Conventional approach to improve resolution: detector < 0.6mm Smaller detectors = need for more dose Siemens solution: STRATON tube and z-Sharp Technology Video 1 Video 1   Video 2 Video 2   Video 3 Video 3   Fixed Array Z-Sharp Technology enabled larger Z-axis coverage with better IQ Easier, more efficient acquisition of thin slices Now, less need/desire for thick slices As such, Siemens recent products have moved away from Adaptive Array and now utilize detectors with a Fixed Matrix Array In a Fixed Matrix Detector Array, all detector elements are the same size The detector elements can be combined to create thicker slices, if desired For Siemens, this includes: Definition AS 20, AS 40, AS 64, AS 128, Edge, Flash SOMATOM Perspective Interleaved Volume Reoncstruction Double the reconstructed number of images Overlapped image reconstruction Cone Beam  Larger detectors = more Z-axis coverage Larger detectors = changes in scanning geometry Introduction of Cone Beam Artifact Cone Beam   Larger detectors = wider x-ray required to cover "Pencil beams" are now fan-shaped beams Smaller detectors have a fan-shaped beam width Larger detectors have a cone-shaped beam width The cone beam intersects as a volume as the tube and gantry rotate around the patient.  More apparent at the periphery of the detector More pronounced as detector arrays get larger Cone beam results in artifacts similar to partial volume averaging This is addressed by vendors though various cone beam reconstruction methods Cone beam exaggerated by patient positioning Off-center positioning means that the beam “sees” the anatomy from slightly different points at opposite tube positions.  Isocenter positioning means that the beam “sees” the anatomy at similar points at opposite tube positions. System/ Technolgies Matrix The Most Popular CT in the World Adaptive Array Detector systems Emotion 6, Emotion 16   Adaptive Array Detector Systems STRATON Tube and Z-sharp Technology Fixed Array Detector systems STRATON Tube and Z-sharp Technology Definition AS20, AS40, AS64, AS+ Definition Edge Definition Flash     New addition to portfolio SAFIRE eMode Fixed Array Detector systems Interleaved Volume Reconstruction (IVR) Perspective 64, Perspective 128   jQuery(document).ready(function () { if (jQuery("object").length) { var obj = jQuery('#jwplayer', parent.document)[0]; if (obj != null && !obj.Playing) { obj.sendEvent('PLAY'); }; } }); jQuery(document).ready(function () { if (jQuery("object").length) { var obj = jQuery('#jwplayer', parent.document)[0]; if (obj != null && !obj.Playing) { obj.sendEvent('PLAY'); }; } }); jQuery(document).ready(function () { if (jQuery("object").length) { var obj = jQuery('#jwplayer', parent.document)[0]; if (obj != null && !obj.Playing) { obj.sendEvent('PLAY'); }; } }); jQuery(document).ready(function () { if (jQuery("object").length) { var obj = jQuery('#jwplayer', parent.document)[0]; if (obj != null && !obj.Playing) { obj.sendEvent('PLAY'); }; } }); You should now be able to: Identify various multislice detector configurations Describe scanner collimation versus scanner slice thickness Explain the concept of Z-sharp technology Explain cone beam and relay the importance of isocenter to CT image quality Adaptive Array Examples Take a closer look at examples of Adaptive Arrays. Checklist TitleChecklist TypeChecklist Content6 x 0.5 mmHTML 6 x 1.0 mmHTML 6 x 2.0 mmHTML 6 x 3.0 mmHTML