Recent Advances in CT Radiation Dose Reduction Techniques

Kalpana Kanal, PhD, FACR William Shuman, MD, FACR

University of Washington Seattle, WA DISCLOSURE

•Kanal • None

•Shuman • Unrestricted grant from GE to support clinical CT research

2 ACKNOWLEGMENT •Use of slides with permission from: General Electric Healthcare Siemens Healthcare Philips Healthcare

3 Talking points • Detector Technology • Post-Patient Collimation • Dual Energy • Iterative Reconstruction • Automatic kV Selection • Organ Sensitive Dose Reduction • Automatic Tube Current Modulation Range • Dose Monitoring and Dose Registry • Regulations and Protocol Review 4 DETECTOR TECHNOLOGY AND POST-PATIENT COLLIMATION

5 GE Detector Technology

16 cm Wide-Detector

6 Mitigating wide coverage issues (GE) – cone beam

• Focally aligned detector • Focally modules designed for cone aligned detector beam geometry minimizes artifacts • VHD reconstruction reduces Hounsfield unit uniformity variation across 160 mm • Hounsfield z-axis coverage unit uniformity

6 GE Post-Patient Collimation

8 post-patient collimator

9 GE Gemstone detector plus post-pt. collimator

• 160 mm coverage • 0.23 mm spatial resolution • Fast scintillator speed • Reduced electronic noise by 25% • Reduced scatter by more than 50% • Overcome cone beam artifacts, scatter, beam hardening and HU uniformity

10 SIEMENS SOMATOM Force Stellar Infinity Detector

New key components:

. Stellar Infinity detector . 2 x 6 cm . 2 x 920 channels

. Integrated PD and AD-converters in one ASIC . Virtually no connection distance . Significantly reduced elec. noise

11 Siemens - Innovative Z-coverage

• Dynamic imaging with the exceptional StellarInfinity detector

• 50% more detector coverage at ultra-low dose

• Honey Comb Filter: 3D scatter

Up to 50% dose reduction in 4D imaging compared to other state-of-the-art CTs

11 Siemens - Dose increases with larger detectors

Unnecessary dose in all current Unnecessary dose increases with MSCT‘s larger detectors

13 Siemens - Adaptive Dose Shield

Scan Scan range range

Conventional technology without SOMATOM Definition AS+ with Dose Shield Adaptive Dose Shield

14 Siemens - Adaptive Dose Shield

Dose reduction with new Adaptive Dose Shield * Deak, van Straten, Shrimpton, Zankl, Kalender. European Radiology 2008 AS+ -25%* -20% -18% -15% -10%

Procedures performed in Spine clinical routine* 4% Cardio 20% Brain 15% Head & Neck 30%Abdomen 16% Chest Range 12 cm 12 cm 16 cm 20 cm 30 cm

Dose increase with no elimination of pre- and post dose

* IMV 2006 CT Market Summary Report, October 2006 15 GE - Dynamic Z-axis Tracking

Dynamic Z-axis tracking provides: Automatic and continuous correction of the X-ray beam shape Block unused X-ray at the beginning and end of a helical scan to reduce unnecessary radiation.

16 / GE Title or job number / 9/7/2015 15 Philips - Managing Dose & Image Quality Throughout the Imaging Chain

16 Philips - Reducing Dose Throughout the Imaging Chain

SmartShape: Increase beam hardness and reduce soft radiation when possible

IntelliBeam Filters: Shapes the beam intensity based on object size

Eclipse DoseRight Collimator: Blocks unnecessary “over- ranging” at the start and end of all helical scans

17 Philips - Reducing Dose Throughout the Imaging Chain

NanoPanel Detector: Reduced electronic noise. 86% improvement over conventional electronics

ClearRay Collimator: Reduces scatter artifact and nonuniformity. 3x improved scatter to primary ratio (SPR)

Spherical Detector: Geometry for true cone-beam focus.

18 Philips - Reducing Dose Throughout the Imaging Chain

ClearRay Reconstruction: Reduces beam hardening and scatter artifacts. Improved homogeneity of HU and sharpness of organs.

19 Dose Management Technologies Adaptive Axial Collimation with Step & Shoot

128x0.625 112x0.625 96x0.625

Walker MJ, Olszewski ME, Desai MY, et al. IJCVI 2009 20 DUAL ENERGY

22 Dual Energy

23 Dual Energy

• Markedly increased HU Density of Iodine at energy levels just above the outer shell electron binding energy (33 keV) • Iodine K-edge

• DECT polychromatic raw data obtained from 80 and 140 kVp scanning can be post-processed to create synthetic monochromatic images at single keV levels between 40 and 140 keV

• Fast kV Switching or Dual Source

24 24 Siemens - Dual Energy quantification

• Dual Energy (DE) imaging with improved energy separation • Vectron tube plus StellarInfinity detector

• New energy pairings, e.g. 90 and 150 kV Sn for imaging of obese patients

• Up to 35 cm DE field of view (FoV)

• Up to 258 mm/s DE scan speed

• Selective Photon Shield II utilization

Increased energy separation for better DE imaging outcomes 25 Siemens - Dual Energy quantification New SPS II – two times thicker • Significantly less dose with the new Selective Photon Shield II (SPS II)

. good dose efficiency because of narrow spectrum

. less artifacts from bone Rel. intensity . at same tube current Sn100kV has • 90% less dose than 100kV • 80% less dose than 80kV

Potential for additional dose reduction Energy / keV

26 Dual Energy

• Low keV images make iodine very bright but also have increased image noise compared to higher keV images

• Some comparabilities:

• 77 keV images look like 120 kVp • 70 keV images look like 100 kVp • 60 keV images look like 80 kVp • 50 keV images may have best CNR for organs • 40 keV images – lowest calculable

28 Dual Energy

Selected “Large” GSI Preset preset to match CTDIvol of SECT

29 Dual Energy Spectral Imaging: HCC

70 keV

30 Dual Energy

40 keV 50 keV 70 keV

Iodine 77 keV only

31 Half Dose of Iodine and GSI

Kev 51 Kev 77 HU 650 HU 271

31 Dual Energy CT: Dose Reduction

• Greatest potential is replacing true non-contrast phase of single energy multi-phase CT exam with virtual non-contrast images. Examples:

• 4 phase liver becomes a 3 phase exam • 3 phase pancreas becomes a 2 phase exam • 2-3-4 phase CT IVP becomes 1-2-3 phase

• Potential dual energy dose reduction is 25 -50% compared

33 ITERATIVE RECONSTRUCTION

34 Spectrum of iterative reconstruction

Noise Object Physics Optics

Photon statistics Anatomical X-ray spectrum Focal spot, beam Electronic noise properties and and attenuation shape, pixel shape, characteristics characteristics detector shape

Reduce image noise, Reduce image noise, Reduce low- enable lower dose, Improve spatial enable lower dose, signal artifacts improve LCD, improve LCD, resolution preserve resolution preserve resolution

35 36 Full Model based iterative Recon vs. ASIR-V (GE)

37 BAC K ASiR-V* - Veo technology flow down (GE)

• Designed to be used for all applications and enable routine use of dynamic acquisitions for perfusion and 4D studies • Next-generation iterative reconstruction to reduce noise levels, low signal artifacts such as streaks, improve low contrast detectability and may enable a reduction in dose for all clinical applications

38 Generations of iterative reconstruction (GE)

1 1 1 ASiR* ASiR-V* Veo*

Physics

Noise Object Noise Object

Optics

Real-time performance (up to 35 ips Reduce dose up to 82% Profound image quality under 1 mSv Over 4,200 systems in use Full model-based IR 2 41,000,000 exams to date Longer reconstruction times

39 GE - ASiR-V*1 – routine low-dose imaging

Veo*

ASiR-V A novel technology allowing you to lower dose and improve image quality, routinely. ASiR* ✓Reduce dose up to 82% ✓Improve LCD up to 135% Reduce image noise up to 91%

Image quality / dose/ quality reduction Image Filtered back projection ✓ ✓Reduce streak artifacts Speed

1. In clinical practice, the use of ASiR, ASiR-V or Veo 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.

40 ASiR-V

41 ASiR-V

42 SIEMENS – ADMIRE (Advanced Modeled Iterative Reconstruction)

Potential to lower radiation

Superb details, delineation and sharpness of organ borders

Positive impact on the image quality of e.g. streak artifacts in the shoulder region

43 SIEMENS – ADMIRE

Five image noise and sharpness levels

Strength 1 Strength 4 Strength 5 Image 3

There is an incremental reduction of noise in each of the images at a natural image impression.

Clinical Target Optimization Function

Incorporate knowledge of desired characteristics Incorporate knowledge of object properties

Enables user control over desired results Targets results with lowest noise

Iterative

Optimization

System Geometry Model Statistical Model

Incorporate knowledge of system geometry Incorporate knowledge of X-ray statistics

Enables pathway between projection & image domains Enables identification of real noise 44 PHILIPS - IMR Simultaneously Low Dose and High Image Quality

60 - 80% 43 - 80% 70 - 83% Lower + Improved + Lower Dose LCD Noise

* In clinical practice, the use of IMR 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. Low-contrast detectability and noise were assessed using 45 Reference Factory Protocol comparing IMR to FBP; measured on 0.8 mm slices, tested on the MITA CT IQ Phantom (CCT183, The Phantom Laboratory), using human observers. PHILIPS Low-Contrast and Low-Noise and High-Detail 71 year old man with hemorrhagic lesions not seen on FBP

1 mm slice thickness 3 mm slice thickness 1 mm slice thickness Standard Reconstruction Standard Reconstruction IMR (FBP) (FBP)

120 kVp, 300 mAs, 14.3 mGy, 1.8 mSv (k=0.0021*) 46 Courtesy: UCL, Belgium * AAPM technical report 96 APPLICATIONS

48 Abdomen/pelvis on a 9-year-old using 70 kV at 0.43 mSv1 • 79 lbs • Axial 2 volumes • 70 kV

• IMAGES COURTESY OF DR. CURY, WEST KENDALL MIAMI BAPTIST HOSPITAL, MIAMI, USA Triple-rule-out showing coronaries with high heart rate of 139 BPM during coronary acquisition group

• Acquisition • 0.28 sec rotation • 120 kV • 139 BPM • 689 mA • Phase 75% • 34 BMI

• IMAGES COURTESY OF DR. CURY, WEST KENDALL MIAMI BAPTIST HOSPITAL, MIAMI, USA High speed and coverage from circle of Willis to mid-aorta including coronaries • Acquisition • Axial 4 volumes • Superior-inferior • 100 kV • 0.28 sec rotation • 220 mGy-cm DLP • 69 BPM

• 3D VR • Endoporosthesis leakage • Curved view of RCA • Internal and vertebral carotids curved views

• IMAGES COURTESY OF DR. J-L SABLAYROLLES, CENTRE CARDIOLOGIQUE DU NORD, SAINT-DENIS, FRANCE One beat, high definition, motion-free coronary imaging at any heart rate

80 kV | 500 mA | 61 BPM | 23 BMI | 0.9 mSv 100 kV | 450 mA | 54 BPM | 28 BMI | 1.6 mSv CAD rule out Stent follow-up

Images courtesy – Dr. Ricardo Cury, West Kendall Baptist Hospital SOMATOM Force Turbo Flash Spiral enables pitch 3.2 for fastest Turbo Flash Spiral mode speed of 737mm/sec without any gaps

Conventional Technology Turbo Flash Spiral 737mm/sec Scan321 Scan123

1: Sommer WH et al. Saving dose in triple-rule-out computed tomography examination using a high- pitch dual spiral technique. Invest Radiol. 2010 Feb;45(2):64-71 “Free-breathing" CT imaging: TAVR

211 lbs Gated Turbo Flash Single Beat Aquisition

• Scan time: 1.44 sec • Pitch: 2.2 • CTDIvol: 4.4mGy • DLP: 344 mGy cm • 5.0 mSv • 80kV

30 mL* of contrast media w/o breath hold

SOMATOM Force Single Beat Cardiac

Turbo Flash Mode (3.2 Pitch) collimation: 2x 192 x 0.6 mm rotation time: 0.25 s 70 kV HR for Turbo Flash ≤ 75 bpm (potential for higher HR Research) 0.18 mSv

47 GE - kV Assist

Scout assisted Clinical indication (patient attenuation)

kV Assist

Recommendation of scan & display parameters

* Trademark of General Electric Company 48 GE kV Assist

58 Siemens – Care KV

70 kV 70 kV 80 kV 80 kV 90 kV 90 kV 100 kV 100 kV 110 kV 110 kV 120 kV 120 kV 130 kV 130 kV 140 kV 140 kV 150 kV 150 kV

59 Care kV – Research

60 ORGAN SENSITIVE DOSE REDUCTION

61 GE - Organ dose modulation (ODM)

ODM provides reduction of radiation dose via X-ray tube current modulation for superficial tissues, such as breasts

* Trademark of General Electric Company 53 SOMATOM Force Organ dose reduction with X-CARE

without X-CARE with X-CARE SOMATOM Force

X-CARE

Low dose

High dose

Organ dose reduction distribution Dose

Vollmar SV, Kalender WA. Reduction of dose to the female breast in thoracic CT: a comparison of standard-protocol, bismuth-shielded, Unrestricted © Siemens AG 2014 All rights reserved. partial and tube-current-modulated CT examinations. Eur Radiol. 2008 Aug;18(8):1674-82. Epub 2008 Apr 15.. Page 63 April 2014 P. Aulbach AUTOMATIC TUBE CURRENT MODULATION AND CENTERING

64 Combined Dose Modulation - can restrict mA range

Dose too low with fixed mA Fixed mA Tube current (mA) current Tube Dose too high with fixed mA fixed with high too Dose

z axis of scan slide courtesy: Dr. Gunn, UW 65 Fully automated dose modulation in x, CARE Dose4D y and z direction in real time

• Adjustments follow the configurable curve to best fit the clinical needs

• Every organ characteristic has a configurable curve

66 Patient Centering: Image Noise in ATCM

SD noise ↑ mA boost Centered 6.47 0 % 0% 4 cm 8.40 30% 68% Dose 6 cm 9.22 43% 100% high!

cf: Mahesh, MDCTFigure From Physics, MDCT Physics: Maheshpg. 58 67 Centering on the GE Revolution

68 Patient Centering: Quality Review on Dose Watch

cf: Mahesh, MDCT Physics, pg. 58 69 DOSE MONITORING AND DOSE REGISTRY

70 Commercial Dose Monitoring Systems

• eXposure™ - Radimetrics

• DoseMonitor - PACSHealth

• DoseTrack™- Sectra Medical Systems

• Dose Index Registry – American College of Radiology

• PEMNET – Clinical Microsystems Inc.

• DoseWatch – GE Medical

71 Commercial Dose Monitoring Systems Dose Watch DoseWatch* is a web-based patient radiation dose monitoring software used to capture, track and report radiation dose directly from any imaging device or PACS. DoseWatch is multi-modality and vendor agnostic.

72 Commercial Dose Monitoring Systems Dose Watch

73 Commercial Dose Monitoring Systems Dose Watch

74 75 Commercial Dose Monitoring Systems Dose Watch

76 Analysis Tools – Dose Comparison

77 ACR – CT DOSE INDEX REGISTRY

78 ACR – CTBackground Dose Index Registry DIR Data Transfer • Registered sites generally route image and/or dose information to the DIR in one of two main ways: 1. Scanner to ACR Triad Server (local install, de-identifies and sends data to DIR Central Server) 2. Radiation Exposure Management System to ACR Triad Server

Site A Site B

Scanner to REMS to TRIAD TRIAD

ACR Dose Index Registry (DIR) Central Server

79 ACR – CT Dose Index Registry

80 81 Regulations and Protocol Review

• Some states now require CT dose reporting and dose monitoring. More will.

• Putting CT dose in the radiology report is now required in California. Likely to expand to other states.

• ACR CT Accreditation now requires CT protocol review on an annual basis by a team of radiologist, technologist and medical physicist

Conclusions

• There have been several CT dose reduction technological advances over the past 3 years.

• It is important to understand these technological advances and implement them appropriately in your daily practice

• Resulting CT Dose reductions are substantial and significant

• An active ongoing CT dose monitoring program is essential

84 THANK YOU!