Dual-Source CT: What is it and How Do I Test it? Cynthia H. McCollough, Ph.D. CT Clinical Innovation Center Department of Radiology Mayo Clinic College of Medicine Rochester, MN Research Support National Institute of Health EB04898, CA75333, AR27065, HR46158 Flight Attendant Medical Research Institute Siemens Medical Solutions Bayer Healthcare RTI Electronics Tube A: 50 cm FOV Tube B: 26 cm FOV Each tube/detector pair has: 80 kw generator 32 x 0.6 mm detector array Double z sampling with Z-FFS No gantry tilt Tube A: 50 cm FOV Tube B: 26 cm FOV
I. Single Tube Operation - Performs Same as a Sensation 64 Temporal Resolution = Rotation Time 2 = 330 ms 2 = 165 ms II. Dual Tube Operation - x 2 Improved Temporal Resolution Temporal Resolution = Rotation Time 4 = 330 ms 4 = 83 ms 83 ms vs. 165 ms (same raw data, same phase) Dual tube recon Single tube recon RCA LAD RCA Mean HR=90 bpm LAD
125 ms 82 ms 165 ms Dose Continuous irradiation (spiral acquisition) with two x-ray tubes would double the radiation dose Four dose reduction strategies: Cardiac beam shaping filter (bowtie filter) 3-D adaptive noise filtration Variable pitch values (based on heart rate) ECG-pulsing with arrhythmia detection and adjustable temporal windows 70 60 50 40 30 20 10 0 McCollough et al., Radiology 243(3):775-784 (2007) MDCT DSCT MDCT pulsed DSCT 310 ms DSCT 210 ms DSCT 110 ms 0.2 0.2 0.2 0.2 No ECG pulsing 0.2 0.265 0.36 0.46 No ECG No ECG No ECG Pulsing pulsing Pulsing pulsing Pulsing pulsing Pulsing <55 55-70 70-90 >90 Heart Rate (bpm) III. Dual Source (Obese) Mode Use both tubes at same kv to double the available power to 160 kw Reconstructed images are the SUMMATION of Tube A and B Avoids need to trade off exam speed (pitch) or narrow slices (collimation) for photon flux Allows much higher mas for Obese patients 80 kvp imaging
IV. Material Specific Imaging Use each tube at a different kv to exploit the kv-dependent nature of CT # 80kV Bone 670 HU Iodine 296 HU Applications of Dual-Energy CT Iodine imaging Automated bone removal in CT angiography Plaque removal Blood pool imaging (Perfused blood volume) Soft tissue imaging Enhanced visualization of tendons & ligaments Virtual non-contrast (Iodine removal) Bone 450 HU Iodine 144 HU 140kV Dose reduction Material characterization TR Johnson et al. Eur Radiology 17(6):1510-1517 (2007)
Applications of Dual-Energy CT Iodine imaging Automated bone removal in CT angiography Plaque removal Blood pool imaging (Perfused blood volume) Soft tissue imaging Enhanced visualization of tendons & ligaments Virtual non-contrast (Iodine removal) Dose reduction Material characterization Direct subtraction of bone in complicated anatomical regions Courtesy of University Hospital of Munich - Grosshadern / Munich, Germany Applications of Dual-Energy CT Iodine imaging Automated bone removal in CT angiography Plaque removal Blood pool imaging (Perfused blood volume) Soft tissue imaging Enhanced visualization of tendons & ligaments Virtual non-contrast (Iodine removal) Dose reduction Material characterization Contrast enhanced - Nephrographic phase DE image from same scan Virtual non-contrast O. Dzyubak, Tuesday 2:42 pm, Rm L100J
Implications for Performance Testing Image Quality Single source mode: No change from any MDCT Dual source cardiac mode: optional Use demo ECG mode Coronary CTA: 120 kvp, 240 mas/rot, 0.33 sec, 32x0.6, pitch auto selected, 3 mm, B26f, retrospectively-gated spiral mode ACR phantom: CT number accuracy Large (> 30 cm diameter) water or uniform acrylic phantom Uniformity and noise in axial and coronal images mas/rot represents mas sum from both tubes (not effective mas = mas/pitch) Implications for Performance Testing Image Quality Dual source non-cardiac (obese) mode: Optional Average image (0.5 Tube A + 0.5 Tube B) Obese XXL: 120 kvp, 300 eff. mas, 0.5 s, 24x1.2 mm, pitch < 1.0, 5 mm, B20f, spiral ACR phantom: CT number accuracy Large (> 30 cm) water or uniform acrylic phantom Uniformity and noise in axial and coronal images Implications for Performance Testing Image Quality Dual energy mode: Suggested Mixed image (0.3 80 kv + 0.7 140 kv) DE abdomen: 140/80 kvp, 95/400 eff. mas, 0.5 s, 14x1.2 mm, pitch < 0.7, 5 mm, D30f, spiral ACR CT phantom: CT number accuracy Fat (polyethylene) and bone (Teflon) expected to have different CT numbers relative to 120 kvp Check accuracy of water and air CT numbers Large (> 30 cm) water or uniform acrylic phantom Uniformity and noise in axial and coronal images Implications for Performance Testing Dose Must test both tubes, recommend to do separately Tube A: No change from any MDCT CTDIw in head and body phantoms for routine head and body CTDIair for all collimations at routine kvp CTDIair for all kvp settings at routine collimation IEC 61223-2-6-Ed2 (Constancy Testing) Tube B: Fewer collimations available HVL for both tubes at acceptance testing (required after any tube chance in some states) Change of one tube does NOT affect other tube Doses are additive
Body Dose Measurement (Body CTDI phantom, Body filter) 80kVp 100kVp 120kVp 140kVp 2x1 1x5 1x10 14x1.2 24x1.2 32x0.6 CTDIw 32x0.6(UHR) AT (A,B) UHR =Ultra highresolution focalspot. AT = acceptance test only. QC = AT + scheduled QC or after tube change Cardiac Dose Measurement (Body CTDI phantom, Head filter) 80kVp 100kVp 120kVp 140kVp 2x1 1x5 1x10 24x1.2 32x0.6 CTDIw 32x0.6(UHR) AT (A,B) UHR =Ultra highresolution focalspot. AT = acceptance test only. QC = AT + scheduled QC or after tube change Head Dose Measurement (Head CTDI phantom, Head filter) 80kVp 100kVp 120kVp 140kVp 2x1 1x5 1x10 14x1.2 24x1.2 32x0.6 CTDIw 32x0.6(UHR) AT (A,B) UHR =Ultra highresolution focalspot. AT = acceptance test only. QC = AT + scheduled QC or after tube change
Mayo CT Clinic Innovation Center and Dept. of Radiology L Yu, MR Bruesewitz, JM Kofler, AN Primak, AP Dzyubak, X Liu JG Fletcher, TJ Vrtiska, EE Williamson, JF Breen, DM Hough Additional Reference: Flohr, TG et al., European Radiology 16:256-268 (2006)