CT成像原理介绍.pptVIP

CT 成像原理介紹 History of Computed Tomography Early 1970s Concept of X-ray Attenuation An X-ray beam passing through the body is attenuated (loses its energy) by : Absorption Scattering CT Generations Design “Generation” is used to label CT tube-detector designs Slip-ring Technology Power is transmitted through parallel sets of conductive rings instead of electrical cables ? Continuous Gantry Rotation ? Prerequisite for Spiral CT What is Spiral Scan? -- just 4“C” Continuously rotating tube/detector system Continuously generating X-ray Continuously table feed Continuously data acquisition Scan Parameters X-ray Tube Voltage (kVp) X-ray Tube Current (mA) Scan Time (s) Slice thickness or Collimation (mm) Table Speed Pitch Table Speed is defined as distance traveled in mm per 360o rotation Slice Profile (SP) Effective slice thickness of an image Slice Profile Comparison Smallest Possible Effective Slice Thickness Peripheral vein eg. antecubital vein 19-20 gauge needle or IV catheter Tailoring Scan Injection Protocols Test Bolus Procedure Dynamic Evaluation Time-density curve Scan Delay ? Peak Enhancement Time CT Angiography 3D Post-processing Slice Profile Resolution Factors influencing Slice Profile Collimation Pitch Interpolation algorithm (360° or 180°) Factors influencing SSP Collimator width collimation = SSP Spiral CT Table speed or Pitch Interpolation Algorithm = mathematical process required to reconstruct axial images from the spiral volume data set Pitch Slice Profile Slim vs Wide – SSP Comparison Slice Profile Slim %Broaden Wide %Braden Pitch One 5.0 mm 0 6.3 mm 26 Pitch Two 6.5 mm 30 10.8 mm 116 WIDE 720 degree More photons SLIM 464 degree Less photons SSP Spatial resolution SSP Spatial resolution Smoother image Noisier image Slim - Advantages Improved Z – Resolution Reduced partial volume artifacts Slim + extended Pitch Longer coverage Same