Dual-Energy 101: Principles, Methods and Dose

Transcription

1 Dual-Energy 101: Principles, Methods and Dose Juan Carlos Ramirez-Giraldo, Ph.D Staff Scien2st, Collabora2ons Manager SE Region ISCT San Francisco, 2017 Siemens Medical Solu2ons USA, Inc., 2017 Page 1

2 Summary 1. Principles 2. Acquisi2on Methods 3. Dose 4. DE image types Restricted Siemens Medical Solu2ons USA, Inc., 2016 Page 2

3 Dual Energy CT Principle What is Dual Energy CT? Acquisi2on of CT datasets with two different spectra (eg. using two different kv) What is MulB Energy CT? Acquisi2on of CT datasets with two or more spectra Page 3

4 Dual Energy CT Principle WHY DUAL / MULTI ENERGY CT? Informa2on Beyond Anatomy ü Quan2fica2on (eg iodine, mono+) ü Mass characteriza2on ü Func2on ü Reduc2on of ar2facts ü Improved Visualiza2on More than just color!? Page 4

5 Dual Energy CT Principle Two pictures are taken of the same slice, one at 100 kv and the other at 140 kv so that areas of high atomic numbers can be enhanced. Tests carried out to date have shown that iodine (z = 53) can be readily differenhated from calcium (z = 20) G. Hounsfield, 1973* *Hounsfield G.N. Computarized transverse axial scanning (tomography): Part I. Description of system. British Journal of Radiology, , Page 5

6 Dual Energy CT Principle Different energies allow us to discriminate materials 80kV iodine 100kV 120kV 140kV fat bone plastic higher CT-value at 80kV: iodine, bone, metal... higher CT-value at 140kV: fat, plastic, uric acid... (almost) same CT-value: water, soft tissue, blood... Page 6 bright iodine dark fat

7 Dual Energy CT Principle Bone 80kV CT-value 80 kv Iodine 140kV IDENTITY 0 HU Blood Water HU Fat CT-value 140 kv Air 0 HU LimitaBon: no separa2on for materials at same posi2on in diagram CT and DECT are not sensi2ve to chemical binding Page 7

8 Dual Energy CT Principle How to realize Dual Energy CT? Scan pa2ent at two different spectra Mean X-ray spectrum energy varies with the applied tube voltage (kv). Use two different kilovoltage (kv) or different pre-filters or different detector layers or an energy-resolving detector ( future ) 140 kv 120 kv 100 kv 80 kv Energy / kev Page 8

9 DE Data AcquisiBon Methods: Fast kv Switching Tube potential is switched between successive views Low kvp High kvp Page 9

10 DE Data AcquisiBon Methods : Dual-Energy First Implementa:on Kalender, W. A., Klotz, E., & Suess, C. (1987). Vertebral bone mineral analysis: an integrated approach with CT. Radiology, 164(2), Page 10

11 DE Data AcquisiBon Methods: Dual-Spiral ( Slow kv switch) Two consecu2ve CT scans at two different kv values low kv high kv 4s delay Low kvp High kvp Page 11

12 DE Data AcquisiBon Methods: Dual-Layer ( Sandwich ) Detectors 1 st layer detects low-energy photons, 2 nd layer detects high-energy photons Page 12 Low Energy Spectrum High Energy Spectrum

13 DE Data AcquisiBon Methods : Twin Beam Dual Energy Movable filter Au Creates Low & high Energy Spectra Al Sn Al + Au Low Energy Spectrum High Energy Spectrum Page 13 Low Energy Spectrum High Energy Spectrum

14 DE Data AcquisiBon Methods: Dual Source Two tubes are operated at a different potential to exploit the kvp-dependent nature of attenuation Simultaneous DE acquisition Independent ma for both high and low kv More power for low kv images Better spectral separation due to tin filter Page 14 Low kvp High kvp

15 Dual Energy CT AcquisiBon Methods Spectral Separa2on 15 x 10 4 S 1 : 80 kv S 2 : 140 kv + SPS 80 kv 140 kv 140 kv + SPS 10 5 Page photon energy (kev)

16 Dual-Source CT: 3 GeneraBons SOMATOM DEFINITION DS SOMATOM DEFINITION FLASH SOMATOM FORCE 80/140 kv 80/140Sn kv 100/140Sn kv 80/140 kv 80/150Sn kv 90/150Sn kv 100/150Sn kv 70/150Sn kv* Page *Separate License required

17 Dual Energy CT AcquisiBon Methods Spectral Separa2on Only materials with substan2ally different aeenua2on behavior (effec2ve atomic number Z eff ) can be discriminated using DECT. Quality/accuracy of DE-based material discrimina2on depends on the separa2on between the high and low-kv spectra. Beeer spectral separa2on is desired. Noise in dual-energy material-specific image is inversely propor2onal to the difference in the DE ra2o (difference in slopes in the DE plane) Kelcz et al Med Phys 1979; Primak et al Med Phys 2007 Page 17

18 Dual Energy CT AcquisiBon Methods DE Bone Removal WITHOUT SPS: Separation of iodine and bone Separation line 600 Iodine pixels 500 HU at 80 kv Soft tissue Blood+Iodine Blood Marrow Marrow+bone Bone pixels HU at 140 kv Page 18

19 Dual Energy CT AcquisiBon Methods DE Bone Removal WITHOUT SPS: Separa2on of iodine and bone Separation line 600 Iodine pixels HU at 80 kv Marrow+bone Soft 100 tissue Page 19 Bone pixels Blood+Iodine Blood Marrow HU at 140 SN kv

20 Dual Energy CT AcquisiBon Methods Dual Source Single Source Dual-Source (3 Generations) Fast kv Switching Dual-Spiral Twin Beam Dual-Layer Detector Dual-Rotation Page 20 Low Energy Spectrum High Energy Spectrum

21 Dual Energy CT AcquisiBon Methods Which criteria are relevant for clinical Dual Energy applications? Iodine ratio LOW HIGH Temporal coherence Temporal resolution Dose efficiency Page 21

22 Dual Energy CT AcquisiBon Methods McCollough CH et al. Dual- and Multi-Energy CT: Principles, Technical Approaches and Clinical Applications, Radiology Vol 276(3), 2015 Page 22

23 Dual Energy CT Dose Dual-Source CT Page 23 JC Schenzle et. al. Investigative Radiology Volume 45, Number 6, June 2010

24 Dual Energy CT Dose Page 24 Courtesy of, Clinical Innovation Center, Mayo Clinic Rochester, USA

25 Dual-Source CT Arterial DE mixed SD=19.4 HU patient s weight 180 lb The combined DLP for the DE exam is ~ 22% less than for the SE exam Page 25 Arterial SE 120 kv SD=20.0 HU patient s weight 185 lb Courtesy Cleveland Clinic

26 Dual Energy CT Dose DICOM SR SureView CARE Dashboard Real-time Imaging IRIS Adaptive ECG-Pulsing CARE Dose4D Adaptive Cardio Sequence Dose Alert & Notification SAFIRE Selective Photon Shield Stellar Detectors X-CARE Adaptive Dose Shield ADMIRE Page 26 "In clinical practice, the use of SAFIRE and 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."

27 Dual Energy CT Dose Use in Pediatrics Repaired Pulmonary Atresia 12 year old boy, post surgery Superior and inferior cava to pulmonary artery S I Page 27 Shunt intact Overall good perfusion CTDIvol 1.24 mgy Courtesy Marilyn Siegel, Wash. University St Louis

28 Dual Energy CT Dose Use in Pediatrics AJR, October 2016 Highlights N = 79 patients DECT scans vs CARE kev (Estimates) CTDI and SSDE were comparable (or lower) with DECT N = 16 patients (subset) DECT scans vs CARE kev (actual scans) - Similar contrast, CNR and CTDI - (Small) Noise increase *(Flash scanner) Page 28 Siegel MJ et al. AJR, October 2016

29 Summary 1. Principles 2. Acquisi2on Methods 3. Dose 4. DE Postprocessing and Image Types Page 29

30 Dual Energy Postprocessing and Image Types Mixed Images Single Energy equiv 80kV Sn140kV Mix (M0.5) Page 30

31 Dual Energy Postprocessing and Image Types Energy SelecBve Images (Virtual MonoenergeBc Images) Images at energies ( kev) can be calculated from Dual Energy datasets (low-high-kv images) x kVp spectra 80 kv 140 kv mix (0.3) Mixed image 10 70keV 5 Monoenergetic images 40 kev 70 kev 100 kev 190 kev photon energy (kev) Page 31

32 Dual Energy Postprocessing and Image Types Material Specific Images Iodine HU at 80 kv Iodine content 65 0 Tissue -100 Fat HU at 140 kv Page 32 Removal of iodine from the image: virtual unenhanced image

33 Dual Energy Postprocessing and Image Types Material Specific Images DE Bone Marrow Iodine Overlay Virtual Unenhanced Courtesy of Universitätsspital Basel / Basel, Switzerland. Courtesy of Vancouver General Hospital, Vancouver BC, Canada Page 33

34 Dual Energy Postprocessing and Image Types Material DifferenBaBon Modified 2-material decomposition: Characterization of kidney stones à Urine + calcified stones / uric acid stones HU at 80 kv high Z low Z HU at 140 kv Page 34

35 Dual Energy Postprocessing and Image Types syngo.ct DE Gout Optimum Contrast syngo.ct DE Calculi Characterization syngo.ct DE Direct Angio syngo.ct DE Lung Analysis syngo.ct DE Virtual Unenhanced syngo.ct DE Rho/Z Monoenergetic syngo.ct DE Brain Hemorrhage syngo.ct DE Lung Nodules syngo.ct DE Monoenergetic Plus syngo.ct DE Hardplaque Display syngo.ct DE Heart PBV syngo DE Xenon: not FDA USA syngo DE Musculoskeletal syngo.ct DE Bone Marrow Virtual Unenhanced contains Liver VNC Lung Analysis contains Lung PBV Page 35

36 Summary 1. Principles 2. Acquisi2on Methods 3. Dose 4. DE image types Restricted Siemens Medical Solu2ons USA, Inc., 2016 Page 36

37 Juan Carlos Ramirez Giraldo, Ph.D Thank You! Siemens Medical Solu2ons USA, Inc., 2016 Page 37